T DEPARTMENT OF THE INTERIOR

Hubert Work, Secretary

U. S. GEOLOGICAL SURVEY 

George Otis Smith, Director

Bulletin 776

THE 

MESOZOIG STRATIGRAPHY OF ALASKA

BY

GEORGE C. MARTIN

WASHINGTON

GOVERNMENT PRINTING OFFICE 

1926
ADDITIONAL COPIES

OF THIS PUBLICATION MAY BE PROCURED FROM

THE SUPERINTENDENT OF DOCUMENTS

GOVERNMENT PRINTING OFFICE

WASHINGTON, D. C.

AT

75 CENTS PER COPY

^

y;

^ 

,**>

 *?

 -*> 

^»
CONTENTS

Pag*

Preface, by A. H. Brooks - XI

Scope and purpose - 1

Triassic system 3

Occurrence and general character . 3

Character of the pre-Triassic basement 5

Permian (?) strata 5

Pre-Triassic (?) slate of undetermined age 5

Early Triassic (?) volcanic rocks . 6

Local sections 6

.^Chitina Valley____. 6

General features. '- 6

Nikolai greenstone (Permian or Triassic) 7

Chitistone limestone - 10

Nizina. limestone__ 18

Chert of Fohlin Creek_______-_ 25

McCarthy formation__________ . 26

Nabesna-White River district-______ . 32

General features- 32

Shale and volcanic rocks _ . . 33

Limestone and shale of Cooper Pass . 36

Upper Susitna Valley____ _____ _ . 37

General features _ . 37

Basic lavas and tuffs _ 38

Limestone _ _ 39

Slate, tuff, arkose, and calcareous beds . 40

Chulitna Valley_________1__________________. 42

General features__________________________. 42

Tuff, limestone, shale, and lava of West Fork_________. 43

Limestone and shale of East Fork_______________. 44

Kenai Peninsula ___.J_______________________ 45

General features ________________________. 45

Ellipsoidal lava___________________________, 45

Chert _____________________________ 47

v Limestone and tuff_________________________ 49

^West coast of Cook Inlet_________________±_____. 51

General features_._________________________. 51

Greenstone ______________________.______ 51

Limestone______________________________. 52

Kamishak chert__________________________ 55

Hiamna Lake ___________________________ 57

Greenstone _____________________________ 57

Limestone_____________________________ 57

Alaska Peninsula___________________________ 60

Greenstone _____________________________ 61

Chert ____________________________ 61

Shale and limestone of Cold and Alinchak Bays______ 61

ni
\,

CONTENTS

Triassic system Continued.

Local sections Continued. Page

Kodiak Island______________,_______________ 64

Chert and lava___________________________ 64

x Southeastern Alaska__________^______________ 65

General features ___________________ 65 

Conglomerate, limestone, sandstone, and slate of Gravina

Island_______ ___________________ 67

Triassic (?) rocks of Prince of Wales, Annette, and Revillagigedo Islands_________________________ 73

Triassic (?) limestone of Screen Islands___________ 76

Triassic rocks of Keku Strait and vicinity___________ 78

Triassic limestone of Admiralty Island_____________ 89

Gastineau volcanic group of the Juneau district., _____ 92

Yukon Valley_____ __________ 95

Limestone near Nation River ____________ ____ 95

Triassic (?) limestone of the Kantishna district_______ 99

^Arctic slope ________ ____________________ 100

General features_ 100

Shale and limestone of Firth River______________ 100

Shublik formation___________________.__.__ 103

Noatak Valley______________________________ 106

Cherty limestone float__:____________________ 106

Northwestern Alaska____________:_____________ 106

General features__ _ __________ __ 106

Shale, chert, and limestone near Cape Lisburne_ 1_ 108

Chert and limestone near Cape Thompson..__________ 112

St. Lawrence Island__________________________: __ 115

Triassic (?) float____________ ________:_____ 115

Seward Peninsula ______-_ ___-_'________ _ _ 116

Middle Triassic rocks of Brooks Mountain__________ 116

General character and correlation____:_______________ 117

Middle Triassic__________________________ 117

Upper Triassic ______ _ __________ ____ 119

General distribution_________________________ 119

D'awsonites zone__ _______\ _ _____________ 119

Zone of HaloMa, cf. H. superta_________________ 120

Coral-reef horizon. _ _____________. ___ ]22

Chert horizon ___________________________ 123

Zone of Pseudomonotis subcircularis______________ 123

Geologic history of Alaska in Triassic time_____________ 128

Jurassic system ____ _____ __ _ 130

General features_______________________________ 130

Local sections__________________________________ 133

Cook Inlet_______________.___________________ 133

General features______________:___________ 133

Lower Jurassic____________:________________ 134

Tuff of Kenai Peninsula___________________ 134

Porphyry and tuff of the west coast of Cook Inlet___ 137

Middle Jurassic_____________________L ______ 140

Tuxedni sandstone___ _________________ 140
CONTENTS

Jurassic system Continued. 

1 Local sections Continued. 

Cook Inlet Continued.

Upper Jurassic 158

Chinitna shale _ 158

Naknek formation. 168-

< Alaska Peninsula ^ 181

General features- 181

Lower Jurassic (?) 182

Middle Jurassic - 186

Kialagvik formation- 186

Tuxedni sandstone (?) - 191

Upper Jurassic 192

Shelikof formation_ _ 192

Naknek formation___ 203

»\ Matanuska Valley and Talkeetna Mountains 218

General features 218

 '° Lower Jurassic_ _ 219

Talkeetna formation _ 219

Middle Jurassic. __________ _ 223

Tuxedni sandstone_ _ 223

Upper Jurassic_______ 227-

^ Chinitna formation________________ 227

Naknek formation______________ _____ 229

Alaska Range (Yentna and Skwentna Valleys) __ 232

General features- _____ _ _ ___ ___ - 232

Lower Jurassic (?)________________ _____ 233

Skwentna group__ _______-____________ 233

Middle Jtirassic ___ ____ _ _______ 235

Tordrillo formation_______________________ 235

Upper Susitna Valley-________________________ 236

^ General features- _____ __________________ 236

Upper Jurassic (?) _ ____ ______________ 236

Conglomerate near Eoosevelt Lakes ...__________ 236

/Chitina Valley_____________________________ 237

r / General features _______,________________ 237

| Lower (?) Jurassic________________________ 238

* . ) Tuffaceous conglomerate near Taral___________ 238

! Middle Jurassic__________________________ 239

, Tuffaceous slate near the mouth of Chitina River___ 239

\Nutzotin Mountains____________________________ 240

V General features__________________________ 240

* Upper Jurassic___________________________ 242

Aucella-beSirins beds of Nutzotin Mountains_______ 242

*- Southeastern Alaska__________________________ 245

General sequence_________________________ 245

Lower or middle (?) Jurassic___________________ 249

Breccia, tuff, and lava of Gravina Island________ 249

Melaphyre breccia of the Wrangell district_______ 251

^ Thane volcanic group____________________ 251

Upper Jurassic (?) slate, limestone, and tuff of Gravina

v Island______________________________..__ 252
VI CONTENTS

Jurassic system Continued. 

Local sections Continued.

Southeastern Alaska Continued.

Upper Jurassic (?) rocks of Prince of Wales Island 254

Sandstone and volcanic rocks of Windfall Harbor 254 

Treadwell slate and Douglas Island volcanic group of the

Juneau district _ 255

" Berners formation "___ _ 256

Graywacke of Chichagof and Baranof Islands_ _ _ . 260

\ Arctic slope _______-___ 262

General features_________ 262

Middle or Lower Jurassic _ 262

Kingak shale_________-____ _ _ 262

Crinoid bed of Firth River __ _ _ 264

Jurassic (?)___________ _ - _ 265

Ignek formation.. _ 265

Summary___________ 268

Stratigraphy - 268

Lower Jurassic____________ _ _ 268

Middle Jurassic 270

Upper Jurassic 271

Correlation_______ __ ______. 274

Lower Jurassic__________-___ ___ ____. 274

Middle Jurassic_______________ ____ ___ 277

Upper Jurassic _ __. 279

Chronologic record____________________________. 283

Cretaceous system__ _____ _ . 286

Occurrence and general character _ ____ ___. 286

Local sections________ _ __ __ __ 289

Alaska Peninsula__________ _ ____________. 289

General features __________________________. 289

Lower Cretaceous__________________________. 291

Staniukovich shale______________________ 291

Herendeen limestone____________________. 292

Upper Cretaceous _______________________. 295

Chignik formation______________________. 295

Cook Inlet and Susitna Valley____________________. 308

General features__________________________. 308

Upper Cretaceous (?) _ ______________. 308

Slate and grayvvacke of Cache Creek__________. 308

 ^ Matanuska Valley _ _______________._______. 310

General features._ __ ______________/__. 330

Lower Cretaceous .-______________________. 310

Conglomeratic tuff and arkose ___________. 310

Nelchina limestone______________________ 313

Limestone north of Castle Mountain___________. 315

Upper Cretaceous _______________________. 317

Matanuska formation ____________________. 317

Chitina Valley______________________l______. 327

General features__________________________ 327

Lower Cretaceous_________________________ 330

Kennicott formation ____________________. 330
CONTENTS VII

Cretaceous system Continued. 

Local sections Continued.

Chitina Valley Continued. 17 - Page

Lower (?) Cretaceous_____ . 349

Kotsina conglomerate and overlying strata . 349

Upper (?) Cretaceous _ . 355

Sandstone and conglomerate of Nikolai Creek 355

Grit and sandstone of Dan Creek____ . 358

Upper Cretaceous- _ 360

Shale of Chititu and Young Creeks __ . 360

Upper Cretaceous (?)__________ __ 369

Conglomerate of ridge south of Young Creek _ 369

Conglomerate and overlying volcanic rocks of McCarthy

Creek____________________________ 371

3,^ Nutzotiu Mountains__________________ 372

General features_____ - 372

Lower Cretaceous___________ -_ 373

AttceZZa-bearing beds of Chisana and White Rivers . 373

Southeastern Alaska__________________ _ 375

General sequence 375

Lower Cretaceous ___ _ 376

Aucella-bea.Ti.ng beds of Pybus Bay __ 376

AttceZZa-bearing beds of Kupreanof Island _ 379

AttceZZa-bearing beds of Etolin Island_ _ 380

Conglomerate, graywacke, and slate of Gravina Island 381

Graywacke, slate, and conglomerate of Prince of Wales

Island__________._________________ 382

Upper Yukon region___ __ ___ ___ _ 383

General features____________._____________ 383

Lower Cretaceous_ __ ___ _ 383

Slate and quartzite-__ _____ __ _____ 383

Upper Cretaceous_ ______ ___ ____ 387

Shale, sandstone, and conglomerate near Seventymile

River _____________________________ 387

Rampart-Tanana district ______________________ 390

General features___-______________________ 390

Lower Cretaceous_________________________ 390

Quartzite and slate near Quail Creek____________ 390

Upper Cretaceous ____ __ __________ 392

Shale near Wolverine Mountain______________ 392

Lower Yukon region__________________________ 395

General features__________________________ 395

Upper Cretaceous ___ ________________ 395

Innoko and Iditarod Valleys_____________________ 429

General features ____________________ 429

Upper Cretaceous_________________________ 429

) Shale and sandstone______________,______ 429

"^Kuskokwim region_____________________ _____ 432

General features_________________________ 432

Lower Cretaceous_________________________ 433

Upper Cretaceous- -______________________ 435

Koyukuk Valley .____________________ 441

General features__________________________ 441
VHI CONTENTS

Cretaceous system Continued. 

Local sections Continued.

Koyukuk Valley Continued. Page

Lower Cretaceous 442

Koyukuk group__ 442

Upper Cretaceous___ 444

Shale and sandstone on the lower Koyukuk 444

Upper Cretaceous (?) 446

Bergman group 446

^ 'Kobuk Valley___________ _ 448

General features 448

Upper Cretaceous (?) _ 449

Bergman group _ _ _ 449

>/ f - Colville Valley______ _____ _ 451

' General features 451

Lower Cretaceous___________ _ __ 451

Anaktuvuk group. 451

Upper Cretaceous _ 453

Nanushuk formation_ _______ _ ___ __ 453

Northwestern Alaska __ _ _ _ __ 455

General features__________________________ 455

Cretaceous or Jurassic _________ _____ 456

Corwin formation______________________^_ 456

Lower Cretaceous (?)__ ______ _ _______ 466

Sandstone and shale near Cape Lisburne________ 466

Summary.. _ _ _ ________ 467

Stratigraphy. __ __ _ __________________ 467

Lower Cretaceous _____________________ 467

Upper Cretaceous _ __ ______________ 470

Correlation ^_____________________________ 474

Chronologic record___________________________ 476

Bocks of undetermined age, Mesozoic or older______________._ 480

Slate, graywacke, and greenstone of the Pacific coast________ 480

General features ________________________ 480

Local descriptions__________________________.._ 481

Slate and graywacke of Kodiak Island____________ 481

Sunrise group______________________________ 482

Valdez and Orca groups_____________________ 484

Slate and graywacke of Susitna Valley____________ 484

Slate of Controller Bay___________,_________, 485

Yakutat group _________________________ 485

Age _ ________^_________ 486

Index ______________________________ 489
ILLUSTRATIONS

FIGURE 1. Map of Alaska showing principal Triassic localities -_ 

2. Ground plan of outcrops adjoining the probable fault contact 

between the Triassic and Cretaceous (?) formations 3 miles 

east of Cape Lisburne__ __ _-_ - 110

3. Sketch showing stratigraphic relations of the Triassic and

Carboniferous formations south of Cape Lewis _ _____ 111

4. Sketch of the section exposed in the cliffs at Cape Thompson 113

5. Map of Alaska showing principal Jurassic localities. ___ 131

6. Generalized geologic sections of the Cold Bay district __ 182

7. Map of Alaska showing principal Cretaceous localities____ 287

8. Columnar section of beds exposed on Nikolai Creek, formerly 

erroneously identified as the basal part of the Kennicott 

formation______________________________ 356

9. Generalized columnar section of the post-Triassic sediments in

the Nizina district__________-__-__-_____ 363

10. Section of Upper Cretaceous rocks on Yukon River near Melozi_ 401

11. Section of Upper Cretaceous rocks on Yukon River near Fossil Bluff________________________________ 402

12. Sketch showing position of fossiliferous beds near Fossil Bluff- 403

13. Sketch showing general relations of Upper Cretaceous rocks

between Pickart coal mine and Nulato. ___________ 404 

49448 26 2 ix

PREFACE

By ALFRED H. BROOKS

Before the middle of the nineteenth century Eussian explorers 

found Mesozoic fossils on the Alaska Peninsula, and these were 

indeed the first features of geologic interest definitely recognized 

in the Territory. With the progress of areal geologic surveys during the last 25 years it has gradually come to be realized that the 

Mesozoic rocks, because of their widespread distribution and the 

great range in the periods of their deformation and intrusion, afford 

the most important clues to the geologic history of Alaska. The 

deciphering of the Mesozoic history is not only all-important to an 

understanding of the geology but it has a direct bearing on the 

mineral resources of the Territory. The intrusions of Jurassic and 

Cretaceous time were accompanied by the most intense metallization 

that has occurred in Alaska; the best known oil-bearing formation 

is of Mesozoic age; and valuable coal deposits occur in Mesozoic 

strata. Therefore, although this volume deals not at all with economic geology, the results here set forth have a very important 

bearing on that su'bject.

George C. Martin began his work on Alaska Mesozoic geology on 

his first trip to the Territory, in 1903, when his purpose was a 

preliminary study of the coal and petroleum resources of its Pacific 

seaboard. In the. succeeding years he has done field work in Alaska 

during 17 seasons, most of it in Mesozoic areas, and has therefore 

acquired an intimate personal knowledge of the field occurrences of 

the rocks of this era. His field studies of the Mesozoic rocks have 

taken him through southeastern Alaska, the Chitina Valley of the 

Copper River Basin, Kenai and Alaska Peninsulas, the Iliamna Lake 

region, Matanuska Valley, Yukon Valley, and parts of the upper 

Kuskokwim River Basin. The wide distribution of the Mesozoic 

rocks of course makes it impossible for any one individual to study 

personally all the occurrences; moreover, Mr. Martin's field work on 

his chosen problem was much interrupted by incursions into other 

geologic fields, notably the subject of mineral fuels, and by important administrative duties. Therefore, in spite of the fact that he 

has established the present standard section of the Mesozoic formaXI
XII PREFACE

tions in the regions which he has investigated, were he summarizing 

only his own observations this volume would be very incomplete. 

As is shown in the following pages, however, he has drawn very 

extensively on the work of others. Since Mr. Martin's work was 

started, more than 20 years ago, two score geologists have mapped 

and investigated areas of Mesozoic rocks in Alaska. Their results 

are summarized in this volume.

Necessarily, the results here set forth are in a large measure based 

on the work of paleontologists largely on that of T. W. Stanton, 

who himself devoted a season to Alaska field work. Mesozoic fossil 

studies by F. H. Knowlton and J. B. Reeside, jr., are also cited.

This volume was first planned about 15 years ago, and Mr. Martin 

has given such time to its preparation as other important duties 

permitted. It is part of a large plan to prepare a summary volume 

on the geology of Alaska, the facts about which are now widely 

scattered through many publications. This summary will be more 

serviceable when the geologic map of Alaska, now in preparation, 

becomes available.
THE MESOZOIC STRATIGRAPHY OF ALASKA

By GEORGE C. MARTIN

SCOPE AND PURPOSE

One of the most valuable results' of the investigations made by theGeological Survey in Alaska has been the discovery of thick sections of marine Mesozoic strata in many parts of the Territory. 

These strata are of extreme interest, not only because they occupy 

so large a part both of the area and of the stratigraphic section of 

Alaska that an intimate knowledge of them is essential for a full 

understanding of the local geologic features, but because they show 

significant relations with the known sections in other regions and! 

because they will, when thoroughly studied, undoubtedly be foundto constitute one of the most extensive and complete sections of 

much of the Mesozoic, especially of the Jurassic and Upper Triassic 

rocks, in North America, if not in the world. They will fill out the 

American stratigraphic column at points' where it is very deficient 

in many other parts of the continent.

It has become evident that the rocks of Alaska offer very valuable 

.contributions not only to mineral wealth but to pure science. In 

the acquisitidn of Alaska we received a European and Asiatic inheritance, both historically and geologically, for much of Alaska is 

essentially Russian in its geologic as well as in its human history. 

It is not a mere accident that the most elaborate publication on 

Alaskan fossils deals with faunas from the shores of both the Caspian Sea and the Alaska Peninsula. It is1 .perhaps a fortunate circumstance that the best of the early collections of Alaskan Jurassic 

ammonites are in Europe, where they are accessible for comparison 

with the closely related European and Asiatic forms. The lately 

terminated Russian dominion on the eastern shore of the North 

Pacific followed most fittingly the often-repeated submergence of 

parts of both Alaska and Russia beneath a common sea in Permian, 

Triassic, Jurassic, and Cretaceous time.

Although no intensive stratigraphic and paleontologic studies of 

Alaskan Mesozoic rocks have yet been undertaken, except for Hoilick's monograph of the Upper Cretaceous floras, for the description by J. P. Smith of some of the Upper Triassic fossils, and for

l
2 MESOZOIC STRATIGRAPHY OF ALASKA

preliminary studies by W. R. Smith on some of the Upper Cretaceous invertebrates, nevertheless a large number of important stratigraphic data have already been accumulated. These data are partly 

unpublished and partly scattered through a large number of reports 

on regional and economic geology, where they are not so accessible 

as they should be, nor is their volume and significance fully appreciated.

There is need for a general preliminary discussion of these rocks 

in order to call attention to the available information and thus render 

it more accessible, and also, so far as possible, to coordinate the 

known facts, present some important conclusions, and set forth some 

of the problems which further studies of the Alaskan rocks may help 

to solve or for the solution of which additional facts from other 

regions are necessary. With this purpose the writer presented to the 

Geological Society of America in December, 1911, the outline x of a 

paper entitled "The Mesozoic stratigraphy of Alaska." The work 

begun at that time has developed into a rather extensive and elaborate treatise on the Mesozoic rocks of Alaska, which, although primarily a summary of existing knowledge, is to a large degree based 

on special field investigations the results of which have not hitherto 

been published except for general descriptions of the Triassic rocks 2 

and for various conclusions cited in regional reports that have been 

written while these studies were under way. The Upper Cretaceous 

plant-bearing beds are described in a monograph that has not yet 

been sent to press.3

The general scheme of the work includes a division of the volume 

into three sections on -the Triassic, Jurassic, and Cretaceous. 

Each section includes general discussions of the areal occurrence, 

stratigraphic sequence, correlation, and geologic history and detailed 

descriptions of local sections by regions arranged approximately in 

geographic sequence, beginning with the region in which the rocks 

of the particular system are best developed or best known. In each 

detailed regional description there is a general discussion followed 

by an account of each formation. The description of each formation 

includes a historical review in which all previous descriptions are 

cited and briefly summarized; a stratigraphic description, which may 

include a summary or quotation of some previous description or a 

new description based on the writer's field observations; and a discussion of age and correlation, which includes lists of fossils, many 

of them not hitherto published, abstracts or quotations of published

> Geol. Soc. America Bull., vol. 23, pp. 724-725, 1912.

2 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 685-718, 

1916.

3 Martin, G. C., The Upper Cretaceous plant-bearing beds of Alaska (in Hollick, Arthur, 

The Upper Cretaceous floras of Alaska) : U. S. Geol. Survey Mon. (in preparation).
TEIASSIC SYSTEM 3

or unpublished discussions by paleontologists, and the writer's own 

conclusions concerning the stratigraphic position and correlation of 

the formation. Some rocks of possible Mesozoic age which can not 

be referred definitely to- the Triassic, Jurassic, or Cretaceous are described briefly in a final section.

Acknowledgments should be made to the many geologists, cited 

below, who made the field observations that are the basis of the 

descriptions here given, and also to the paleontologists whose determinations of the fossils are the substantial basis of the conclusions 

here presented. It should be remembered that these field observations have been ^gathered, for the most part, in the course of pioneer 

reconnaissance investigations and necessarily are scanty and generalized. It should be remembered also that the fossils have not yet 

been exhaustively studied. The determinations of genera and species 

can be accepted as definite, except where a doubt is expressed; but 

no attempt has yet been made to list all the species, many of which 

are undescribed, or to determine the precise relations of the faunas 

to those of other regions. The writer has based his interregional 

correlations of the Triassic rocks largely on the published results of 

Prof. J. P. Smith's elaborate studies and correlations of the Triassic 

rocks of California, Nevada, and Oregon. Professor Smith should 

not, however, be held responsible for the correlations of the Alaska 

and British Columbia rocks except where he is directly cited.

TRIASSIC SYSTEM

OCCURRENCE AND GENERAL CHARACTER

Triassic rocks are widely distributed in Alaska, being now known 

at many localities (see fig. 1) in nearly all parts of the three major 

mountain regions, though absolutely restricted to those regions. 

The most striking fact regarding the distribution of Triassic rocks 

in Alaska is this remarkable agreement between the areas of present 

Triassic outcrops and the areas of the major mountain regions.j In 

this respect conditions in Alaska are in accord with those in many 

other parts of the world. The marine Triassic is, with good reason, 

called the alpine Trias, for in Alaska, as in the Alps, in the Himalayas, and in the western part of the United States and of Canada 

it is generally if not invariably restricted to mountain regions of 

the almne (structural) type. The general world-wide geographic 

accordance of the present areas of marine Triassic rocks with mountains of alpine'form, structure, and date has previously been recognized and has been stated by Frech 4 as follows:

4 Frech, Fritz, Riickblick auf die Trias: Lethaea geognostica, Teil II, Band 1, Lief. 4, 

pp. 510, 518, 1908. .
4 MESOZOIC STRATIGRAPHY OF ALASKA

Scarcely in any period of the earth's history is the connection between the 

distribution of mountain zones and later sedimentation so clearly expressed as 

in the Trias.

1. The provinces of the late Paleozoic folding correspond to the continental 

development of the Trias.

2. The great Mediterranean Sea of Eurasia and the margin of the Pacific 

Trias-ocean coincide with the zones of the Tertiary high mountains. Only the 

eastern margin of the Cordilleras (that is, the Eocky Mountains of North 

America, in a strict sense) contain a continental development of the Trias.

3. The flat-lying Arctic Trias (Spitzbergen, North Siberia, Arctic (extraPacific) North America), where neither late Paleozoic nor Tertiary mountain
PRE-TBIASSIC BASEMENT 5

building is encountered, can not be regarded as an exception to the above rule 

but belongs, in a tectonic sense, to an indifferent province.

The dependence of the distribution of the oceanic Trias on the later Alpine 

that is to say, Eurasian and circum-Pacific folding has been repeatedly emphasized and means essentially that the accumulation of thick masses of sediments in the geosynclines determines the later folding. From northern Spain, 

the Balearics, Sicily, the Alps, and Binaries to the Himalayas and Sumatra 

the same uniform law holds that also governs on the circumference of the 

Pacific Ocean. Here we see also from Alaska, Kamchatka, and Japan to New 

Caledonia, New Zealand, California, Mexico, Colombia, and Peru the oceanic 

Trias constantly appearing in the provinces of Tertiary mountain building, 

which, without exception, are coincident with a great thickness of sediments.

The Alaskan Triassic is noteworthy not only because it affords an 

additional example of the law stated by Frech but because the law 

holds there in such remarkable detail.

All the Triassic rocks of Alaska that are now known belong in the 

Upper Triassic, except for a single area of Middle Triassic rocks 

on Seward Peninsula. It is probable that the Lower Triassic and 

much of the Middle Triassic are not represented in the Alaska rooks, 

except possibly by terrestrial volcanic rocks or by some metamorphosed strata of very doubtful age.

CHARACTER OF THE PRE-TRIASSIC BASEMENT

Permian (?) strata. The youngest rocks of known age that 

underlie the Triassic beds of Alaska are early Permian (?) limestones. These limestones carry a fauna closely related to that of the 

Artinskian of Russia, which is regarded by some as pre-Permian 

but which is more generally considered as the lowest division of the 

Permian. These limestones are very widely distributed in Alaska, 

occurring in nearly all the larger geographic regions, and show that 

toward the end of the Paleozoic era (at about the beginning of 

Permian time) limestone-forming seas extended over the larger part 

if not all of the area that is now Alaska. Marine Permian deposits 

younger than the Artinskian are not known and probably are not 

present in Alaska.

Pre-Triassic (?) slate of undetermined age. Throughout most of 

the mountains on the Pacific coast of Alaska are large areas of slaty 

rocks of very uncertain age. The evidence on the age of these rocks 

is scanty and conflicting, and all that can be safely said concerning 

it is that they may be as old as early Paleozoic or as young as Upper 

Cretaceous. It is practically certain that these rocks are, at least 

in part, older than Upper Triassic, and the Writer believes that they 

are, at least for the most part, Paleozoic. They clearly underlie the 

lavas that are beneath the Upper Triassic limestones and tuffs of 

the Kenai Peninsula. (See pp. 45, 481-487.)
6 MESOZOIC STRATIGRAPHY OF ALASKA

Eafrly Triassic (?) volcanic woks. The Upper Triassic sedimentary rocks described below are underlain in many places 

throughout the Pacific Mountain belt by volcanic rocks that include 

both lavas and tuffs and that have in some places been described as 

greenstones. These rocks include the Nikolai greenstone of the 

Chitina Valley, the basic lavas and tuffs of the upper Susitna 

Valley, the ellipsoidal lavas of Kenai Penensula and Kodiak Island, 

s,ome of the greenstones of the Iliamna-Clark Lake district, and the ellipsoidal lavas of Hamilton Bay, in southeastern Alaska. In all 

these districts they clearly underlie the marine Upper Triassic 

strata without recognizable unconformity. It is only in the Chitina 

Valley that the basal contact of these rocks with underlying beds 

of known age has been observed. Here they rest on Carboniferous 

tuffs, cherts, and slates. In the Kenai Peninsula, on Kodiak Island, 

and probably on the west shore of Cook Inlet they overlie the slaty 

rocks of unknown age that are described above. On Hamilton Bay 

they are probably underlain by lower Permian (?) limestones. 

These volcanic rocks may include also the greenstone associated with 

the Orca group of Prince William Sound, as well as part of the 

greenstones of southeastern Alaska. They may possibly be correlated with the lavas and tuffs beneath the Permian (?) limestone 

of White River, but it is more probable that they are either Permian 

or early Triass.ic.

LOCAL SECTIONS

CHITINA VALLEY 

GENERAL FEATURES

The most complete known section of Triassic rocks in Alaska is 

in the Chitina Valley, where there are several thousand feet of 

marine Upper Triassic strata, mostly shale and limestone, resting 

with apparent conformity on a thick series of lava beds (Nikolai 

greenstone) whose precise age has not been determined but which 

are probably either Triassic or late Paleozoic (Permian?). The 

Triassic strata are overlain unconformably by Jurassic and Cretaceous rocks, which are described farther on.

There are notable differences between the sections exposed in different parts of the Chitina Valley, as is shown by the two following 

sections, which are characteristic of the east and west ends :

General section of Triassic rocks in the Nizina Valley

Upper Triassic: Feet 

McCarthy formation: Black shale, with a few 

thin beds of limestone and with much thinbedded black chert at the base. Contains 

Pseudomonotis sulcircularis _______________ 1, 500-2, 500
TRIASSIC, CHITINA VALLEY 7

Upper Triassic Continued. Feet

Conformity (?).

Nizina limestone: Thin-bedded limestone, becoming shaly toward the top. No fossils yet 

found________________________ 1,000-1, 200

Conformity.

Chitistone limestone: Massive bluish-gray 

limestone, with HaloWa cf. H. superla, Terebratula, Spiriferina,, Tropites, Juvavites (f), 

Arcestes, and Atractites ____ _ 1, 800-2,000

Conformity (?). 

Triassic or Permian:

Nikolai greenstone: Basaltic lava flows___ 4,000-5,000

Basal contact and underlying rocks not exposed.

Ueneral section of Triassic rocks m the Kotsina and Kuskulana valleys

Upper Triassic: Feet

Kuskulana formation: Black shales, with a 

few thin beds of limestone. Contains Pseudomonotis subcircularis ________ 2,000 ?

Unconformity (?).

Thin-bedded limestone, with some intercalated 

shale, including Nizina limestone. Contains 

Orbiculoideaf, HaloMa cf. H. superla, Myophoriaf, Pecten, Tropites, Juvavites?, Ceratitesf, and Arcestes f _____________ 500-3,000 ?

Conformity (?).

Chitistone limestone: Massive gray limestone, 

with Terebratula, Spiriferina, Avicula, HaloMa cf, H. superba, OrypJiaea?, Myophoria, 

Pecten, Hinnitesf, Pleuromya, Tropites?, and 

Arcestes__________:____________ 75-700 +

Conformity (?). 

Triassic or Permian:

Nikolai greenstone: Basaltic lava flows____ 6, 500

Underlain conformably (?) by early Carboniferous beds.

NIKOLAI GREENSTONE (PERMIAN OR TRIASSIC)

. Historical review: The Nikolai greenstone was named and first 

described by Oscar Rohn,5 who made an exploratory journey through 

the Chitina Valley in 1899. Rohn recognized the fact that the Nikolai greenstone is older than the Chitistone limestone, which was 

then considered Devonian or Carboniferous, and consequently assigned it to the Silurian. The "bedded volcanics" at the head of 

Kotsina River, which Rohn described 6 as distinct from the Nikolai 

greenstone, were considered by some later writers part of it, but they

6 Rohn, Oscar, A reconnaissance of the Chitina River and the Skolai Mountains, 

Alaska : U. S. Geol. Survey Twenty-first Ann. Rept., pt. 2, pp. 425, 426, 431, 433, 1900. 

 Idem, pp. 420-421.
8 MESOZOIC STRATIGRAPHY OF ALASKA

have recently been separated as the Strelna formation, which is now 

known to be early Carboniferous.

The Nikolai greenstone was described in considerable detail by 

Schrader and Spencer,7 who made a geologic reconnaissance of the 

Chitina Valley in 1900. They referred this formation to the Devonian and described it as including not only the original Nikolai 

greenstone of Kohn but also the underlying tuffaceous beds that were 

not included in the original description and that are now known to 

be Carboniferous. It was described by Mendenhall and Schrader 8 

on the basis of a brief examination of the ore deposits of the Kotsina 

Valley by Mendenhall in 1902. They regarded it as of Carboniferous 

age and assigned to it the same limits as Schrader and Spencer. A 

later description, based on the same field work, was given by Mendenhall,9 who discussed at length the problem of age, concluding that 

it is either Carboniferous or else " early Triassic or late Permian."

The account of the Nikolai greenstone by Moffit and Maddren 10 

includes a general description, mostly quoted from Schrader and 

Spencer, and a large amount of local detail scattered through the 

" description of properties." The investigations upon which this 

account were based had as their primary object the study of the 

copper deposits, and no attempt was made to revise either the geologic map or the geologic descriptions of Schrader and Spencer, except 

as such work could be done incidentally to the examination of the 

ore deposits. The most important contribution by Moffit and Maddren to our knowledge of these rocks is their description 11 of the 

tuff, chert, and slate and their suggestion that these beds should be 

separated from the rest of the formation. This would be practically 

a return to Kohn's original usage. It should be noted that this 

suggestion has subsequently been carried out (see p. 9) and that 

these beds have been found to contain early Carboniferous (Mississippian) fossils.

The character of the Nikolai greenstone in the Nizina Valley has 

been described in detail by Moffit and Capps.12 The area covered 

in their report includes the type locality of the formation, and in 

this area the tuffaceous beds that underlie the lavas of the original 

Nikolai greenstone are not exposed. Consequently the use of the for-'

7 Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special pub.). PP. 33, 40-43, 

1901.

8 Mendenhall, W. C., and Schrader, F. C., The mineral resources of the Mount Wrangell district, Alaska: U. S. Geol. Survey Prof. Paper 15, p. 14, 1903.

9 Mendenhall, W. C., Geology of the central Copper Riv.er region, Alaska: U. S. Geol. 

Survey Prof. Paper 41, pp. 26, 39, 50-51, 1905.

10 Mofflt, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Kuskulana region, 

Alaska: U. S. Geol. Survey Bull. 374, pp. 21, 23-25, 54-92, 1909.

"Idem, p. 24.

12 Moffit, F. H., and Capps, S. E., Geology and mineral resources of the Nizina district, 

Alaska : U. S. Geol. Survey Bull. 448, pp. 60-63, 1911.
TRIASSIC, CHITINA Vi LLEY 9

mation name by Moffit and Capps is identical with the original usage 

by Kohn.

The Nikolai greenstone and the underlying tuffaceous rocks of 

the upper Chitina Valley have been described briefly by Moffit 13 

as "Triassic (?) and Carboniferous greenstones" and in greater 

derail by Overbeck 14 as "tuffs and flows of Carboniferous and 

Triassic (?) age." The lavas that were correlated with the typical 

Nikolai greenstone were not mapped separately from the underlying and presumably early Carboniferous tuffs, but the distinction 

was recognized in the description.

A detailed account of the character and occurrence of the Nikolai 

greenstone in the Kotsina and Kuskulana Valleys has been given by 

Moffit and Mertie,15 who have restricted the term Nikolai greenstone to the lavas that overlie the early Carboniferous tuff, lava, 

chert, limestone, and shale described as the Strelna formation. This 

is practically a return to the original usage of Rohn and also of 

Moffit and Capps. A detailed description of the petrographic character and a discussion of the age of the Nikolai greenstone were 

given by Mertie.16

Character. The Nikolai greenstone is made up of a succession of 

well-bedded lava flows aggregating at least 4,000 feet, and possibly 

5,000 feet, in thickness in the Nizina Valley and about 6,500 feet in 

the Kotsina and Kuskulana Valleys. The rock is a typical diabase, 

in a well-advanced and general degree of alteration. Interbedded 

tuffaceous or sedimentary strata have not been observed in the 

Nikolai greenstone proper, although they occur in the underlying 

beds that some authors have included in it.

In the Chitina Valley it occurs on the southern slope of the 

Wrangell Mountains, or in that part of the valley lying north of 

the river. It is believed to be generally present throughout this area, 

although buried by younger rocks over considerable tracts. Its areal 

distribution at the surface is indicated on several published maps 

accompanying the reports cited above.

Age. The basal contact of the Nikolai greenstone is not known, 

and there is consequently no evidence of its relations to any Paleozoic 

rocks, except in the Kotsina and Kuskulana Valleys, where it rests 

upon early Carboniferous tuff, chert, and slate. It is overlain by 

the Chitistone limestone, described below, without evidence of unconformity. It has hitherto been correlated with lava and tuff beds

13 Mofflt, P. I-I., The upper Chitina Valley, Alaska: TJ. S. Geol. Survey, Bull. 675, pp. 

17, 18, 68-69, pi. 3, 1918.

14 Overbeck, R. M., Igneous rocks [of the upper Chitina Valley] : II. S. Geol. Survey 

Bull. 675, pp. 62-64 1918.

18 Mofflt, F. EL, and Mertie, J. B., jr., The Kotsina-Kuskulana district, Alaska: U. S. 

Geol. Survey Bull. 745, pp. 18, 19, pi. 3, 1923.

16 Mertie, J. B., jr., Igneous rocks [of the Kotsina-Kuskulana district]: U. S. Geol. 

Survey Bull. 745, pp. 58-67, 1923.
10 MESOZOIC STRATIGRAPHY OF ALAS.KA

which are exposed in the valley of Skolai Creek and at the head 

of White Eiver and which appear to rest conformably upon an upper 

Carboniferous limestone, but as shown on page 35 this correlation must be rejected. It is possible, however, that the Nikolai 

greenstone represents the lava and tuff below the upper Carboniferous limestone of White River. The most definite conclusion that 

can be made at present is that the Nikolai greenstone is probably 

either Permian or early Triassic.

CHITISTONE LIMESTONE

Historical review. The Chitistone limestone was named by 

Bohn,17 who sometimes called it the " Nizina limestone," but the use 

of the latter name was evidently unintentional. The original description is very general, the formation being defined as " a massive 

bed of limestone 500 or more feet thick." No section or stratigraphic 

details were given, and the limits of the formation were not defined, 

except by the statements that it overlies the Nikolai greenstone and 

is overlain by " a series of soft black, highly fissile shales and slates." 

Eohn referred the limestone tentatively to the Carboniferous or 

Devonian.

The Chitistone limestone was mapped and described in greater 

detail by Schrader and Spencer,18 who assigned it to the Carboniferous on the basis of a correlation with the Carboniferous limestone 

of Skolai Pass and White River. They described it as " composed of 

very massive limestones without any important intercalations of 

shale " and as having a thickness, in the type area, of about 2,000 

feet. It is shown below (p. 13) that this estimate of the thickness 

is approximately correct. The position of the boundary between 

the Chitistone limestone and the overlying formation was discussed 

as follows: .

Studies * * * have not been sufficiently detailed to afford evidence as 

to where the line between these two formations should be drawn. Above the 

massive basal series of limestones there is a series of thin-bedded limestones 

with shaly partings, which is apparently in perfect conformity with the underlying beds and which passes by gradation into the black shale's above. These 

black shales contain the fossils by means of which the Triassic age of the 

formation has been determined. The provisional and arbitrary line between 

the two formations has been placed at the top of the massive limestone series.

Schrader and Spencer were consistent in their attitude on this 

point and defined the overlying formation as including a basal member, 1,000 feet thick, which rests conformably upon the Chitistone lime17 Rohn, Oscar, A reconnaissance of the Chitina River and the Skolai Mountains, 

Alaska: U. S. Geol. Survey Twenty-first Ann. Rept., pt. 2, pp. 425, 426, 427, 431, 433. 

434-435, 1900.

18 Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), pp. 32, 33, 

44-46, 1901.
TRIASSIC, CHITINA/GALLEY 11

stone and which consists of " a series of thin-bedded limestones, in 

strata from a few inches to a foot or more in thickness, separated 

by thin partings of black shale." These beds were included by 

Moffit and Capps in the Chitistone limestone. (See p. 12.)

The description of the Chitistone limestone by Mendenhall and 

Schrader 19 is very brief and contains no new data, except in the 

descriptions of the mineral deposits, with which their report is 

chiefly concerned.

The account by Mendenhall,20 who correlated the Chitistone limestone provisionally with the upper Carboniferous (Pennsylvanian 

and Permian) Mankomen limestone of the Alaska Range and described and mapped it under the name Mankomen, contains very 

little new descriptive matter relative to the Chitistone limestone. 

Mendenhall discussed the age and correlation of this formation in 

great detail, pointing out that there were strong reasons in favor 

of its assignment to the Triassic.

The Chitistone limestone was first referred definitely to its proper 

position in the Triassic by Moffit and Maddren.21 Their general description of the formation is quoted from the account by Schrader 

and Spencer, but the discussion of its age, with the accompanying 

lists of fossils, is new, as is also considerable information given 

under the " description of properties."

The Chitistone limestone of the Nizina Valley has been mapped 

and described in detail by Moffit and Capps,22 who extended its 

upper limit to include the thin-bedded limestone which Schrader 

and Spencer regarded as the lower member of the overlying formation.

A general account of the Chitistone limestone, based chiefly on the 

descriptions by previous observers, but presenting some new information, including lists of fossils, has been given by Martin,28 who 

restricted the formation to the massive limestone.

The Chitistone limestone of the upper Chitina Valley was described briefly by Moffit.24

A detailed account of the occurrence of the Chitistone limestone 

in the Kuskulana and Kotsina Valleys has been given by Moffit

19 Mendenhall, W. C., and Schrader, F. C., The mineral resources of the Mount 

Wrangell district, Alaska: U. S. Geol. Survey Prof. Paper 15, pp. 14-15, 18-23, 1903.

20 Mendenhall, W. C., Geology of the central Copper River region, Alaska: U. S. GeoL 

Survey Prof. Paper 41, pp. 26, 47, 48-51, 1905.

21 Moffit, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Chitina region, 

Alaska: U. S. Geol. Survey Bull. 374, pp. 25-28, 54-92, 1909.

22 Moffit, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska: U. S. Geol. Survey Bull. 448, pp. 21-28, 1911.

23 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 69(M>93, 

1916.

24 Mofflt, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 25- 

26, pi. 3, 1918.
12 MESOZOIC STRATIGRAPHY OF ALASKA

and Mertie,28 who restricted the formation to the massive limestone, 

which is 75 to TOO feet thick in that district. They, thus brought 

the limits of the formation back to approximately the position assigned by Schrader and Spencer and the other early observers. 

The description by Moffit and Mertie includes detailed information 

concerning the distribution, character, thickness, structure, age, and 

correlation, with a table showing the occurrence of fossils.

Stratigraphic description. The Chitistone limestone crops out in 

many discontinous areas throughout the south front of the Wrangell 

Mountains from Chitistone River to Cheshnina Biver or throughout 

the part of the Chitina Valley that lies north of Chitina River. It 

has not been recognized south of the river.

The stratigraphic position of this limestone relative to the other 

formations of this district is clearly defined, for it rests everywhere 

with apparent conformity upon the Nikolai greenstone and is overlain at most places by the Nizina limestone and the supposedly 

equivalent thin-bedded limestones in the lower part of the Kuskulana formation. The contact of the Chitistone limestone with the 

Nizina limestone and its supposed equivalents is everywhere apparently conformable. In many places the rocks overlying the 

Chitistone limestone are Jurassic or Cretaceous and rest with a very 

pronounced unconformity upon not only the Chitistone limestone 

but also upon the other Triassic formations.

The Chitistone limestone of the type area was described by Moffit 

and Capps 26 as being about 3,000 feet thick, but this thickness and 

their description quoted below include the thin-bedded Nizina limestone.

In the Nizina district the lower part of the Chitistone formation is made up 

of thick, massive beds of a dark-gray or bluish-gray color, but weathering to a 

lighter gray on the surface. The upper part, on the other hand, is made up of 

thinner beds, and this thinness increases toward the top. A slight difference 

in chemical composition between the upper and the lower parts of the Chitistone limestone is indicated by the brownish-yellow weathering of the upper 

part. Changing conditions of sedimentation are indicated, too, in a more 

noticeable way by the appearance of thin shale beds at the top of the formation. This limestone is the oldest of the sedimentary formations exposed 

within the mapped area and lies on the Nikolai greenstone conformably, ex- . 

actly as if both were sedimentary formations deposited in the same sea and 

the limestone had been laid down on the greenstone before any movement or 

disturbance had taken place In the greenstone. This conformable relation 

holds true wherever the contact has been examined, although in many places it 

is found that there has been movement of the two formations along this contact surface. In several places a bed of red and green shale with a maximum 

thickness of about 5 feet was found to intervene between the limestone and the -

85 Mofflt, F. H., and Mertie, J. B. jr., The Kotsina-Kuskulana district, Alaska: U. S. 

Geol. Survey Bull. 745, pp. 29-34, 1923.

26 Moffit, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska : U. S. Geol. Survey Bull. 448, pp. 21-23, 1911.
TRIASSIC, CHIT1NA VALLEY 13

greenstone, but it is not known whether the shale is widely distributed or not, 

since the limestone-greenstone contact is nearly everywhere covered with talus. 

The shale is present in the vicinity of Bonanza mine and on Kennicott Glacier. 

Excellent sections of the Chitistone limestone are seen on the west side of 

Nizina River, opposite the mouth of Chitistone River, and on McCarthy Creek. 

On McCarthy Creek the lower part of the formation, which dips about 30° NE., 

consists of massive" beds of bluish-gray limestone, making up approximately 

three-fifths of the total thickness. Above this lower massive portion is a succession of more thinly bedded limestone strata weathering a rusty-yellow color 

and making up the remaining two-fifths of the formation. The thickness of 

individual beds decreases from the base toward the top, as has been stated, and 

near the top thin beds of black shale make their appearance. Then comes an 

indefinite thickness, approximately 300 feet, of thin-bedded limestone and 

shale,27 overlain in turn by a great thickness of black shale, which Rohn called 

the McCarthy Creek shale. It is thus seen that there is a transition from the 

bedded limestones below through interbedded thin limestones and shales to 

shale above, and it is readily understood that difficulty arises in choosing a 

definite dividing plane between these two formations.

The thickness of the Chitistone limestone as restricted above is 

approximately 2,000 feet on Nikolai Creek. The thickness on McCarthy Creek was estimated by Moffit and Capps at about 1,800 feet. 

In the hills between Kennicott Glacier and Fohlin Creek the thickness is at least 1,500 feet and may be 2,000 feet or more. On the 

tributaries of Kuskulana and Kotsina Rivers, in the western part 

of the Chitina Valley, the Chitistone limestone seems to be reduced 

to a single massive plate which is, in general, not more than 75 to 

TOO feet thick. The Chitistone limestone thus apparently thins 

toward the west, whereas the overlying Nizina limestone grows 

thicker. The exposures in the intervening district have not been 

studied in detail, so it is unfortunately not known whether there 

is a gradual change from the one section to the other. It is possible 

that the apparent westward thinning of the Chitistone limestone 

may be due to the cutting out of parts of the formation, in some 

places by faults and in other places by unconformity, and the apparent westward thickening of the overlying Nizina limestone may 

be caused by structural repetition of the beds. If the apparent westward thinning of the Chitistone limestone exists as a purely stratigraphic feature, it may be due to the variation in the volume of the 

original sediments, the limestone having been deposited in the form 

of a wedge-shaped plate thinning westward; or it may be due to 

variation in the character of the original sediments, the massive limestone beds of the eastern area grading westward into thin-bedded 

limestone and shale; or may be due to subsequent erosion.

Age and correlatwn. The fauna of the Chitistone limestone, as 

shown in the following table, consists wholly of marine invertebrates.

27 Moffit and Capps did not intend to include these beds in the Chitistone limestone 

and mapped themi as part of the overlying McCarthy shale.--G. C. M.
Fossils from the Chitistone limestone d

Halobia (small with fine ribs). __ __________ ..

Qryphaea ____________ . __________ _

Pleuromya ________ __ --.. __________ ...

Pleuromya? ____ .--.. _ _ -- ___ __ _______

Pleurotomaria (Sisenna) ------- ___ . ____ ..- ..-

Pseudomelania?.-.- ____ .-- _________ .-.

Fusus-like gastropod ____ . ........................

2 

S3

CO

1 

o

a

CO

1

ft

o»-^ 

00

 <»<

a

e-j

S

1C

oc

OO 

GO

a

o

88

a

IM

a

S8 

S?

--

8CO 

CO

O)

CO 

CO 1

ft

1

-na

CO

SCO 1CO

a

 ^

1

h

h

h

b

Sct

b

b

h

b

b

b

b

b

b

b

SCC

h

c

CC

oc

a

a

1

n

a

1

<M

a

a

I

b

oCO 

§ 
a

a

a

h

b

b

b

b

b b

b

b

0 a, Identified by T. W. Stanton; b, identified by J. B. Reeside, jr.; c, identified by F. A. Bather. 

6 This species was probably obtained in float material derived from the overlying beds.
16 MESOZOIC STRATIGRAPHY OF ALASKA

6319. South side of Chitistone River, east side of lowest large tributary, 

about 4 miles above Nizina River. Near base of Chitiston-e limestone. F. H. 

Moffit, 1909.

6320. South side of Chitistone River, west side of lowest large tributary, 

about 4 miles above Nizina River. Near base of Chitistone limestone. F. H. 

Moffit, 1909.

6333. South side of Chitistone River, at Potter's mine, about 4% miles above 

Nizina River. Near base of.Chitistone limestone. S. R. Capps, 1909.

4810. South side of Chitistone River. Talus slide near Houghton-Alaska Co.'s 

prospect. F. H. Moffit, 1907.

6321. Mountain north of Texas Creek, Copper Creek valley. Probably well 

up in the formation. F. H. Moffit, 1909.

8885. Valley of Nikolai Creek, about a quarter of a mile east of Nikolai 

mine. About 500 feet above base of Chitistone limestone. G. C. Martin, 1914.

8884. Valley of Nikolai Creek, about 0.3 mile N. 70° E. of Nikolai mine. 

About 800 feet above base of Chitistone limestone. G. C. Martin, 1914.

8882. Valley of Nikolai Creek, about two-thirds mile east of Nikolai mine. 

About 1,000 feet above base of Chitistone limestone. G. C. Martin, 1914.

8883. Valley of Nikolai Creek, about two-thirds mile east of Nikolai mino, 

200 or 300 yards northwest of 8882. From about 1,200 feet above base of Chitistone limestone. G. C. Martin, 1914.

6306. Valley of Nikolai Creek, about two-thirds mile northeast of Nikolai 

mine. About 2,000 feet above base of Chitistone limestone. F. H. Moffit, 1909.

6312. Valley of Nikolai Creek, northeast of Nikolai mine. F. H. Moffit, 1909. 

This lot was apparently obtained either from approximately the same locality 

as 6306 or from a locality about a quarter of a mile north of it. The writer 

believes that the material in this lot is probably mixed, the cephalopods coming 

from the Chitistone limestone at or near locality 6306 and the Pseudomonotis 

coming from the McCarthy shale at a locality about a quarter of a mile 

farther north.

8886. Valley of Nikolai Creek, small gulch 0.56 mile N. 50° E. from Nikolai 

mine. Boulder probably near the horizon of lot 6306. G. C. Martin, 1914.

8887. Valley of Nikolai Creek, about 0.6 mile N. 48° E. from Nikolai mine. 

Boulder probably from about the same horizon as 6306. G. C. Martin, 1914.

6303. Nikolai Creek. Boulder in bed of creek. F. H. Moffit, 1909.

6330. McCarthy Creek. Said to be 10 feet above base of Chitistone limestone. 

Given to F. H. Moffit, 1909.

11384(23). Upper part of Chitistone limestone on ridge between McCarthy 

Creek and East Fork. Elevation 5,000 feet. F. H. Moffit, 1922.

11385(24). Ridge between McCarthy Creek and East Fork. Elevation 5,100 

feet. F. H. Moffit, 1922.

11386 (24a). Same locality as 11385, in float that could not have traveled 

more than 50 feet. F. H. Moffit, 1922.

6300. Jurnbo Creek, on spur 0.4 mile southwest of Bonanza Peak. Base of 

Chitistone limestone. F. H. Moffit, 1909.

4808. Near the Bonanza mine and Bonanza Creek. Talus material probably 

from the lower 1,000 or 1,500 feet of the Chitistone limestone. F. H. Moffit, 

1907.

4809. Jumbo Creek near the Bonanza mine. Talus material, probably from 

lower 1,000 or 1,500 feet of the Chitistone limestone. F. H. Moffit, 1907.

2209. East side of Lakina Glacier. Limestone mapped as Chitistone. A. C. 

Spencer, 1900.

11366 (3). Top of ridge between west headwater branch of Gilahena River 

and west fork of Lakina River. F. H. Moffit, 1922.
TRIASSIC, CHITIFA VALLEY 17

9960 (F42). Chokosna River. Chitistone limestone bluff, three-quarters of a 

mile southeast by east from mouth of creek flowing from Kuskulana Pass. 

Massive limestone. F. H. Moffit, 1916.

10251-10254. Berg Creek. F. H. Moffit, 1919.

9946 (F28). Gulch tributary to Dry Creek from'east at elevation 3,400 feet. 

Chitistone limestone in gulch at elevation about 3,700 feet. F. H. Moffit, 1916.

9948 (F 30). Locality 33. North fork of creek between Squaw and Clear 

.Creeks; elevation, 2,900 feet. Float near base of cliffs of massive limestone. 

F. H. Moffit, 1916.

9919 (Fl). At bench mark 3664, on north fork of Strelna Creek. Thin, 

vertical limestone beds, in places shaly, 150 feet north of base of Chitistone 

limestone. F. H. Moffit, 1916.

9927 (F9). East branch of east fork of Strelna Creek, 300 feet north of F 8, 

100 feet higher on hill. Black thin-bedded limestone. F. H. Moffit, 1916.

9929 (F 11). North branch of east fork of Strelna Creek, 1,300 feet eastnortheast of locality 10 (on north branch of east fork of Strelna Creek, at 

elevation of 4,250 feet, about 4,700 feet southwest of bench mark 6270). F. H. 

Moffit, 1916.

8925. 8,200 feet S. 67° W. from forks of east fork of Strelna Creek; elevation, 4,500 feet. F. H. Moffit, 1914.

8148. North fork of Strelna Creek on east side of first large creek near its 

mouth. Upper part of Chitistone limestone (?). F. H. Moffit, 1912.

8946. South fork of Rock .Creek, on trail leading to west fork of Strelna 

Creek; elevation, 4,800 feet. Probably thin plate of Chitistone limestone. G. C. 

Martin, 1914.

2194. Near pass between head of Pass Creek and Rock Creek. Talus just 

under reef of heavy-bedded limestone. F. C. Schrader, 1900.

8938. About 11,800 feet S. 80%° E. from Alice Peak; elevation, 4,800 feet. 

F. H. Moffit, 1914.

 4805 (3-6). Talus from lower 200 feet of Chitistone limestone on Copper 

Creek. Moffit and Maddren, 1907.

4805(2,23). Hoodoo or Mullen claim on Copper Creek. About 200 feet 

above base of Chitistone limestone. Moffit and Maddren, 1907.

8152. Clear Creek. Blue limestone above roadhouse. Theodore Chapin, 1912.

8164. Clear Creek. Theodore Chapin, 1912.

8159. Clear Creek. Talus slope below the Chitistone and the overlying thinbedded limestone. Theodore Chapin, 1912.

i 8931. About 6,600 feet N. 44° E. of Dixie Pass; elevation, 5,500 feet. F. H. 

Moffit, 1914.

8923. West side of Lime Creek valley; elevation, 4,900 feet. Moffit and 

Mertie, 1914.

8932. About 5,850 feet N. 31° W. from Ammann's cabin on Kluvesna River. 

F. H. Moffit, 1914.

8165. Nugget Creek near forks. Fault block of Chitistone limestone. Theodore Chapin, 1912.

8167. Divide between Nugget and Roaring creeks. Theodore Chapin, 1912.

8166. Divide between Nugget and Roaring creeks. Theodore Chapin, 1912. 

. 4806. Crawford's Skyscraper claim on Roaring Creek. Lower 100 feet of 

Chitistone limestone. Moffit and Maddren, 1907.

The table represents provisional identifications of 50 small collections from as many localities, distributed through practically the 

entire thickness of the formation. This list does not adequately
18 MESOZOIC STBATIGEAPHY OF. ALASKA

represent the complete fauna, for the collecting has been very far 

from exhaustive, and no attempt has been made to enumerate all the 

species, many of which are probably undescribed.

The list is sufficient to show the general aspect of the fauna, that 

it is certainly Upper Triassic, and that it probably belongs in the 

middle or Karnic stage of the Upper Triassic, being the equivalent 

of at least part of the Hosselkus limestone of California. Although 

most of the identified genera of brachiopods and pelecypods have a 

long range, yet both the character of many of the individual forms 

and the general aspect of the assemblage are unmistakably Triassic. 

The ammonites are all highly characteristic Upper Triassic genera 

and point strongly toward a horizon in the Karnic, as does also the 

pelecypod identified as Hcdobia cf. H. superba Mojsisovics, which 

is identical with the Californian species known by that name and is 

very closely related to Hcdobia superba of Europe, even though it 

may not be the same species. The Chitistone fauna belongs to the 

Mediterranean type of Triassic faunas and is indicative of warmwater conditions.

NIZINA LIMESTONE

Historical review. The Nizina limestone comprises the rocks that 

were described by Schrader and Spencer 28 as the lower unnamed 

member of the " Triassic series " or " Triassic shales and limestones." 

Schrader and Spencer clearly recognized the fact that the rocks 

which they grouped as " Triassic shales and limestones" do not 

form a lithologic unit when they said 29 that "the Triassic series 

has not been called by the name proposed by Rohn, because it seems 

so complex that it will be eventually divided into several formations." They also indicated the proper basis for the main* subdivision in the following statement:80

In the lower part, and resting conformably upon the " Carboniferous" 

[Chitistone] limestone, is a series of thin-bedded limestones, in strata from 

a few inches to a foot or more in thickness, separated by thin partings of black 

shale. The thickness of this member is approximately 1,000 feet, and the 

limestone, so far as observed, did not contain fossil remains. .

The Nizina limestone is part of the "Triassic shales and limestones" described by Mendenhall and Schrader.31 Their account 

is very brief and general, the Nizina limestone being covered by the

28 Schrader, F. C., and Spencer, A. C., Tbe geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), pp. 32, 33, 

46-47, 1901.

28 Idem, p. 32. '

80 Idem, p. 46.

81 Mendenhall, W. C., and Schrader, F. C., The mineral resources of the Mount Wrangell district, Alaska: U. S. Geol. Survey Prof. Paper 15, p. 15, 1903.
TRIASSIC, CHITINA VALLEY 1&

statement that "the thin limestone beds are abundant near the 

base of the section, but toward the top they die out."

These beds were also included under the general designation 

" Triassic shales and limestones " by Mendenhall,82 who gave a very 

brief description in which he indicated a twofold division of therocks identical with that suggested by Schrader and Spencer.

A description of these rocks is also to be found under the heading 

"Triassic limestones and shales" in the account of the mineral1 

resources of the Chitina Valley by Moffit and Maddren.33 This account was quoted in full from the description by Schrader and Spencer, the reexamination of the ore deposits by Moffit and Maddrennot having included a detailed examination of this formation, in 

which no prospects had been discovered.

The Nizina limestone, as the term is here used, includes part .of 

the rocks described as the Chitistone limestone by Moffit and Capps.8* 

It has already been shown on pages 11-12 that Moffit and Capps in 

describing the rocks of the Nizina district extended the Chitistone 

limestone to include thin-bedded limestone that was regarded by 

Schrader and Spencer as the lower member of the overlying formation. These beds were described by Moffit and Capps as follows:

The upper part [of the Chitistone limestone], on the other hand, is madeup of thinner beds, and this thinness increases toward the top. A slight 

difference in chemical composition between the upper and the lower parts of 

the Chitistone limestone is indicated by the brownish-yellow weathering of theupper part. Changing conditions of sedimentation are indicated, too, in a 

more noticeable way by the appearance of thin shale beds at the top of theformation. * * *

Above this lower massive portion [of the Chitistone limestone] is a succession of more thinly bedded limestone strata weathering a rusty-yellow color 

and making up the remaining two-fifths of the formation. The thickness of 

individual beds decreases from the base toward the top, as has been stated,, 

and near the top thin beds of black shale make their appearance. Then 

comes an indefinite thickness, approximately 300 feet, of thin-bedded limestoneand shale,88 overlain in turn by a great thickness of black shale, which 

Eohn called the McCarthy Creek shale. It is thus seen that there is a transition from the bedded limestones below through interbedded thin limestones 

and shales to shale above, and it is readily understood that difficulty arises 

in choosing a definite dividing plane between these two formations.

The Nizina limestone was first described under that name by 

Martin,36 who included in it the rocks described by Schrader and!

82 Mendenhall, W. C., Geology of the central Copper River region, Alaska: U. S. Geol.. 

Survey Prof. Paper 41, pp. 26, 52, 1905.

83 Moffit, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Chitina region,. 

Alaska: U. S. Geol. Survey Bull. 374, pp. 28-29, 1909.

84 Moffit, F. H., and Capps. S. R., Geology and mineral resources of the Nizina district,. 

Alaska: U. S. Geol. Survey Bull. 448, pp. 21-27, 1911.

86 It was the intention of the authors to refer these beds to the overlying formation. 

G. C. M.

88 Martin, G. C., The Triassic rocks of Alaska: Geol. Soc. America-Bull., vol. 37, pp. 690,. 

692-694,
20 MESOZOIC STRATIGRAPHY OF ALASKA

Spencer as the unnamed lower member of the "Triassic series" or 

"Triassic shales and limestones," and the rocks were described by 

Moffit and Capps as the upper part of the Chitistone limestone. 

The name Nizina limestone had previously been used a few times in 

Rohn's account of the geology of the Chitina Valley, being applied 

to the same beds that Eohn formally described as the Chitistone 

limestone. This previous use of Nizina limestone, however, appears 

only incidentally in the descriptions of other formations and of the 

structure and obviously was unintentional. The writer's account of 

the Nizina limestone includes a brief definition and description of 

the formation based chiefly on the work of earlier observers.

The description of the Chitistone limestone of the upper Chitina 

Valley by Moffit 37 contains a brief discussion of the Nizina limestone, which was included in the rocks represented as the Chitistone 

limestone on the map.

The western extension of the Nizina limestone in the Kotsina and 

Kuskulana Valleys is presumably represented by part of the rocks 

mapped by Rohn 38 . as the Kuskulana shales and also part of the 

rocks represented on the same map as "unclassified sediments." 

Most of the rocks included under Rohn's description 39 of the Kuskulana shales carry the fauna of the McCarthy shale (see pp. 26, 29) 

and belong above the Nizina limestone.

The equivalent of the Nizina limestone in the Kotsina and Kuskulana Valleys is also believed to be represented in the rocks that 

Moffit and Mertie 40 described as the Kuskulana formation. The 

Kuskulana formation probably contains the lateral equivalent not 

only of the Nizina limestone but of part or all of the overlying McCarthy shale and possibly of some of the underlying Chitistone limestone. The description of the Kuskulana formation contains detailed accounts of the distribution, character, thickness, structure, 

age, and correlation of the rocks, with tables showing the occurrence 

of fossils. The relation of the Nizina limestone to the Kuskulana 

'formation is discussed.

Stratigraphic description. The Nizina limestc/ne consists of a succession of thin-bedded limestones with a minor amount of interstratified shale. Massive limestone beds occur rarely throughout the 

formation, and a few thick beds of shale may be seen. There is a 

more or less gradual progressive change in the character of the formation from the base toward the top, the number and thickness of

'"'Moffit, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 

25-26, pi. 3, 1918.

38 Rohn, Oscar, A reconnaissance of the Chitina River and the Skolai Mountains, 

Alaska: U. S. Geol. Survey Twenty-first Ann. Rept., pt. 2, pi. 52, 1900.

38 Idem, pp. 423, 424, 425, 431-432, 433.

40 Mofflt, F. H., and Mertie, J. B., Jr., The Kotsina-Kuskulana district, Alaska : U. S. 

Geol. Survey Bull. 745 pp. 18, 19-20, 35-44, pi. 3, 1923.
TRIASSIC, CHITINA VALLEY 21

the limestone beds decreasing upward. The lower part of the formation consists at many places of practically all limestone, broken 

only by very thin shaly partings. The greater part of the formation 

consists of a fairly regular alternation of limestone and shale beds in 

about the proportion of 5 or 10 parts of limestone to 1 of shale; the 

limestone beds are from 4 to 18 inches thick and the shale beds from 

1 to 3 inches thick. Toward the top of the formation the proportion 

of shale increases still more, there being a more or less gradual 

transition into the shales and thin limestones of the overlying McCarthy formation. The thickness of the beds here described as the 

Nizina limestone was estimated by Schrader and Spencer as approximately 1,000 feet, and by Moffit and Capps as about 1,200 feet. The 

latter estimate is approximately correct. The type section is in the 

cliffs on the west side of Nizina Kiver opposite the mouth of Chitistone River. At this place the Chitistone limestone forms the lower 

vertical cliffs, which are about 2,000 feet high; the Nizina limestone 

forms the upper more sloping and uneven cliffs, which are partly 

covered by talus slopes, and the McCarthy formation forms the 

smooth slopes above the highest cliffs. The Nizina limestone rests on 

the Chitistone limestone with apparent conformity and is overlain by 

the McCarthy formation. The contact with the McCarthy also is 

apparently conformable in the type section, although there is evidence (see p. 124) of a marked unconformity at other localities. No 

determinate fossils have yet been obtained from the type section of 

the Nizina limestone.

In parts of the Kotsina-Kuskulana district, notably in the valley 

of Elliott Creek and in the hills between Rock and Copper Creek?, 

the strata occupying the normal position of the Nizina limestone 

consist of shale that has both the lithologic and the faunal character of the McCarthy shale. This circumstance apparently indicates abrupt variations in the thickness or character of the formation and may be explained either by undetected faults, by rapid 

changes along the bedding in both lithologic and faunal character, 

or by a surface of unconformity separating the Nizina limestone 

from the overlying McCarthy shale. Moffit considers that there is 

a lateral gradation in the character of the sediments, and that some 

of these shale beds are the equivalent of the Nizina limestone. The 

writer believes that so sharp a change from calcareous to argillaceous 

sediments, affecting a thickness of at least many hundred and possibly several thousand feet of strata and taking place within a horizontal distance of not more than 3 or 4 miles without any evidence 

of progressive lateral change, is inherently improbable. He finds 

it easier to believe that these shale beds are the McCarthy shale 

49448 26 3
22 MESQZOIC STBAT1GRAPHY OF ALASKA

brought down into the position of the Nizina limestone by either a 

fault or an unconformity.

Age and correlation. The only fossils that have been obtained 

in the Nizina limestone of the type area consist of one small lot concerning which J. B. Keeside, jr., has submitted the following statement :

11387 (22 F 25). Ridge between McCarthy.Creek and East Fork, elevation 

about 5,900 feet. Near top of Nizina limestone. F. H. Mofflt, 1922. Undetermined gastropod.

Inasmuch as these fossils are not characteristic, the determination 

of the age of the Nizina limestone must be based on its relation to 

the underlying and overlying formations and on its relations to the 

rocks of neighboring districts. The Nizina limestone is underlain 

with apparent conformity by the Chitistone limestone, which is certainly Upper Triassic and probably belongs in the middle or Karnic 

stage of the Upper Triassic. It is overlain with apparent conformity, but possibly with an actual unconformity, by the McCarthy 

shale, which is also Upper Triassic and probably belongs in the 

Upper Noric, near the top of the Upper Triassic.

The Nizina limestone is believed to be represented in the Kotsina 

and Kuskulana valleys by at least part of the thin-bedded fossiliferous limestone in the lower part of the Kuskulana formation. The 

known fauna of the lower calcareous portion of the Kuskulana 

formation, as represented in the following table, was identified from 

31 small collections of fossils from localities mostly in the Kuskulana and Kotsina valleys. The complex structure of the KotsinaKuskulana district makes it impossible to identify the exact horizons represented by these collections. The fauna appears to be essentially the same as that of the Chitistone limestone. The writer is by 

no means convinced that some of these collections were not obtained 

from the Chitistone limestone. A striking difference between this 

fauna and that of the Chitistone limestone consists in the presence 

of Ceratitesf in three collections from the Kuskulana formation. 

This is probably not a true Ceratites, for that genus is supposed to 

be characteristic of the Middle Triassic.
Fossils from lower part of Kuskulana formati

Pteria?. _ ... ____ -_.-.._...- 

Halobia cf. H. superba Mojsisovics.. ...

Halobiacf. H. superba (small fine-ribbed

Tropites cf. T. subbullatus Hauer. . __

Juvavites (Anatomites) subintermitUndetermined ammonites.. _ ..........

9956

h

b

b

8169 8153 8154 8157 8158 892S 8150 8151 8929 8147 9921

b

b

9922

b

9923

b

9924

b

' a, Identified by T. W. Stanton; b, identified by J. B. Reeside, jr.
24 MESOZOIC STRATIGRAPHY OF ALASKA

9956 (F 38). Chokosna River. On ridge northeast of F 37; elevation about 

5,200 feet. Dark bluish-gray or black thin-bedded limestone, Triassic. F. H. 

Mofflt, 1916.

8169. Divide between Nugget and Roaring Creeks. Thin-bedded shale. 

Theodore Chapin, 1912.

8153. Clear Creek. Theodore Chapin, 1912.

8154. Ridge south of Clear Creek. Theodore Chapin, 1912.

8157. First creek south of Clear Creek. Gray limestone. Theodore Chapin, 

1912.

8158. Clear Creek. Thin-bedded limestone and shale. Theodore Chapin, 

1912.

8928. North fork of Strelna Creek, elevation 3,000 feet. F. H. Moffit, 1914.

8149. North fork of Strelna Creek. Shale area 600 feet south of first large 

branch on east. F. H. Moffit, 1912.

8930. Left branch of north fork of Strelna Creek, mouth of gulch about 1,400 

feet above forks. F. H. Moffit, 1914.

8150. North fork of Strelna Creek, 2,000 feet north of first large branch on 

east. F. H. Moffit, 1912.

8151. First branch of north fork of Strelna Creek near its mouth. Float. 

F. H. Moffit, 1912.

8929. 4,700 feet N. 57° E. from forks of north fork of Strelna Creek, elevation 4,000 feet. F. H. Moffit, 1914.

8147. 300 feet above canyon of upper Strelna Creek. F. H. Moffit, 1912.

9921 (F 3). North fork of Strelna Creek, 235 feet upstream from F 2 

(where trail to Rock Creek leaves Strelna Creek). Thin-bedded black limestone, dipping about 25° W. About 50 feet stratigraphically below F 2. 

F. H. Moffit, 1916.

9922 (F 4). North fork of Strelna Creek, 400 feet upstream from F 2. Thin 

limestone beds, dipping under beds at F 2. F. H. Moffit, 1916.

9923 (F 5). Locality 8, east branch of east fork of Strelna Creek at elevation 4,200 feet. Black shale, argillite, impure limestone, folded and faulted, 

about 100 feet stratigraphically above exposure of Chitistone limestone. F. H. 

Moffit, 1916.

9924 (F 6). East branch of east fork of Strelna Creek, upstream from 

F 5, at elevation 4,300 feet. Calcareous argillite with shale beds. F. H. 

Moffit, 1916.

9925 (F 7). East branch of east fork of Strelna Creek. Talus between F 8 

and F 9. F. H. Moffit, 1916.

9928 (F 10). North branch of east fork of Strelna Creek, elevation 4,250 

feet; 4,700 feet southwest of bench mark 6270. Alternating beds of shale and 

calcareous shale. F. H. Moffit, 1916.

9930 (F 12). On ridge between Dixie Pass branch of Strelna Creek and Clear 

Creek, 1,500 feet south-southwest of bench mark 6270. Thin shaly limestone. 

F. H. Moffit, 1916.

9932 (F 14). South brow of round-topped hill on ridge between the east 

branch of the east fork of Strelna Creek and the small creek between Squaw 

and Clear Creeks; elevation, 5,500 feet. Black shale and limestone, Triassic. 

F. H. Moffit, 1916.

9945 (F 27). Dixie Pass branch of Strelna Creek, elevation 4,000 feet. Thin 

dark limestone. F. H. Moffit, 1916.

9934 (F 16). Locality 566 (1914). West branch of Rock Creek, 2,500 feet. 

East-northeast of hill 5,350 (map) ; elevation 4,700 feet. Massive gray shaly 

limestone 100 feet above exposure of Chitistone; Triassic. F. H. Moffit, 1916.
TBIASSIC, CHITINA VALLEY 25

9935 (F 17). Locality 14. On top of ridge between forks of Rock Creek, 1,500 

feet southeast of northwest end of ridge. Limestone beds with shaly partings; 

Triassic. F. H. Moffit, 1916.

9941 (F 23). Float at base of limestone (Chitistone cliffs) above F 22, which 

is 3,000 feet northwest by north of Dixie Pass, elevation 4,600 feet. F. H. 

Moffit, 1916.

9943 (F 25). Locality 22. Gulch tributary to Rock Creek (east fork) from 

north side, 7,000 feet above forks; elevation 4,500 feet. Thin-bedded limestone 

and shale. F. H. Moffit, 1916.

8933. Creek entering Kotsina ,River from north at junction of Kotsina and 

Kluvesna Rivers, elevation 3,400 feet. F. H. Moffit, 1914.

8943. Outcrop by side of trail at gulch on north side of Kotsina River about 

1% miles below Kluvesna Bridge. G. C. Martin, 1914.

8942. About 10 feet above trail at same locality as 8943. Limestone a few feet 

above 8943. G. C. Martin, 1914.

8941. About 100 feet above trail at same locality as 8943. Limestone above 

8943 and 8942. G. C. Martin, 1914.

8944. Float from same locality as 8943. G. C. Martin, 1914.

CHERT OF FOHLIN CREEK

Chert beds, which have not been described in any of the earlier 

accounts of this region except for brief mention by Martin 41 and by 

Moffit and Mertie,42 are well exposed in the canyon of Fohlin Creek 

a little over a mile above the mouth of Bear Creek. The outcrops at 

this point consist of a highly folded and apparently conformable 

series of beds of chert, limestone, and shale, occurring immediately 

north of and apparently just below some Upper Jurassic strata. The 

chert, which is the predominating rock, occurs in the beds 4 to 8 

inches thick, separated by very thin strata of shale and by minute 

partings of indeterminate lithologic character which are probably 

also shale. The limestone was seen only in a few thin, irregularly 

distributed strata.

The rocks exposed on the north fork of Fourth of July Creek, 

from the fork leading to Fourth of July Pass to the greenstone area 

near the head of the creek, are mostly cherty beds similar to those 

seen on Fohlin Creek.

No fossils have been found in these chert beds, nor has their relation to the other rocks of the district been determined. They bear a 

close resemblance to the chert beds in the lower part of the McCarthy formation on Nikolai Creek, as described on page 28, and the 

writer believes that they are the approximate equivalent of those 

beds. Beds of shaly limestone containing (see lot 8881, p. 30) 

Pseudomonotis subcircularis (Gabb), the characteristic fossil of the 

McCarthy shale, crop out on the mountain north of Fourth of July 

Pass and seem to be in contact with if not interbedded with the

°- Martin, G. C., Triassic rocks of Alastea: Geol. Soc. America Bull., vol. 27, p. 690, 1916. 

42 Moffit,. F. H., and Mertie, J. B., jr.. The Kotsina-Kuskulana district, Alaska: U. S. 

Geol. Survey Bull. 745, p. 35, 1923.
26 MESOZOIC STRATIGRAPHY OF ALASKA

chert. The same fossil was found (lot 8874, p. 30) in float material 

on the bank of Fohlin Creek a short distance below the chert outcrops. There is little doubt that the chert beds belong approximately 

at the horizon of Pseudomonotis subcircularis. They bear a striking 

resemblance to the Kamishak chert of Cook Inlet, described on pages 

55-57", the upper part of which is characterized by this same fossil.

In regard to the precise position and relation of these chert beds 

in the local stratigraphic column there seems to be three plausible 

interpretations. They may be a distinct local formation occurring 

between the Nizina limestone and the McCarthy shale, they may be 

a local sedimentary facies of the lower beds of the McCarthy shale, 

or they may be the local alteration product of limestone beds. 

Under either of the first two interpretations their stratigraphic position is clear. Under the third they probably represent thin-bedded 

limestones which are likely to belong at various horizons in both the 

McCarthy shale and the Nizina limestone, and probably in the latter 

formation to a greater extent than in the former, for limestones were 

originally more abundant there.

The writer believes that beds of chert will probably be found to 

have a wide distribution in the Chitina Valley. Those here described have hitherto not merely remained unvisited they have" 

been overlooked, and this may also have occurred at other places. 

The photographs 43 of crumpled, "thin-bedded limestone" in the 

Gilahina Valley show a type of folding which is characteristic of the 

Triassic cherts of Cook Inlet.

MCCARTHY FORMATION

Historical review. The formation named the "McCarthy Creek 

shales " by Kohn 44 was described as " a series of soft black, highly 

fissile shales and slates, typically exposed on McCarthy Creek." 

Most of the rocks which Rohn described 45 as the Kuskulana shales 

and part of those which he mapped as "unclassified sediments" 

west of Gilahina Kiver (not those east of it) also belong in this 

formation.

The McCarthy formation constitutes part of the unnamed upper 

member of the " Triassic series " or " Triassic shales and limestones " 

as described by Shrader and Spencer.46 The rocks thus described

43 Schrader, F. C., and Spencer, A. C-, The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), pi. 7, 1901. 

Moffit, F. H., and Maddren, A. G-, Mineral resouces of the Kotsina-Chitina region, 

Alaska: U. S. Geol. Survey Bull. 374, pi. 4, A, 1909.

44 Rohn, Oscar, A reconnaissance of the Chitina River and the Skolai Mountains, 

Alaska: U. S. Geol. Survey Twenty-first Ann. Kept, pt. 2, pp. 426-427, 431-433, 439-440, 

pi. 52, 1900.

45 Idem, pp. 423, 424, 425, 431-432.

46 Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), pp. 33, 46, 

47, 1901.
TEIASSIC, CHITINA VALLEY 27

include, however, a great thickness of strata which have recently 

been determined (see pp. 360-369) as of Upper Cretaceous age. The 

rocks here referred to the McCarthy formation were described by 

Schrader and Spencer as follows:

Above the thin-bedded limestones and sharply defined from them are black 

shales containing occasional bands of impure limestone, locally affording 

fossils from which the age of the formation has been determined. The thickness of the upper member, of the Triassic is very great, possibly more than 3,000 

feet, but no opportunity was afforded for its direct measurement, since its 

occurrence as the surface formation beneath strata lying unconformably upon 

it, together with the attitude which it has assumed as the result of folding and 

faulting, renders its relations complicated and obscure. A few thin flows of 

greenstone, similar to that of the Nikolai series, were observed here and there 

interbedded with the black Shales of the Triassic. The Triassic series may be 

easily recognized from its general homogeneous nature and the fine-grained 

character of its black carbonaceous shales.

Brief mention of these beds under the designation " Triassic shales 

and limestones " was made by Mendenhall and Schrader 4r and also 

by Mendenhall.48 These authors did not attempt to describe this 

formation in detail, because of the lack of valuable mineral deposits 

in it.

These rocks were included by Moffit and Maddren 49 as an undifferentiated part of the " Triassic limestones and shales," and as 

their investigations yielded no new information concerning these 

beds they quoted in full the description by Schrader and Spencer.

The beds of this formation in the Nizina Valley were mapped and 

described in detail by Moffit and Capps,50 who called it the McCarthy 

shale, restricting the term approximately to Rohn's original usage.

A brief description of the McCarthy formation, chiefly summarized from descriptions by previous observers, was given by Martin.51

The occurrence of the McCarthy shale in the upper Chitina Valley has bean described briefly by Moffit.52

The McCarthy shale is undoubtedly represented in the upper part 

of the Kuskulana formation of the Kotsina and Kuskulana valleys. 

The Kuskulana formation was described in detail by Moffit and

*7 Mendenhall, W. C., and Schrader, F. C., The mineral resources of the Mount Wrangell 

district, Alaska : U. S. Geol. Survey Prof. Paper 15, p. 15, 1903.

48 Mendenhall, W. C., Geology of the central Copper River region, Alaska: U. S. Geol. 

Survey Prof. Paper 41, pp. 26, 52, 1905.

^Moffit, F. H., and Maddren, A. G.,, Mineral resources of the Kotsina-Chitina region, 

Alaska: U. S. Geol. Survey Bull. 374, pp. 28-29, 1909.

50 Moffit, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska: U. S. Geol. Survey Bull. 448, pp. 28-30, 1911.

' 6l Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 690, 

695-696, 712, 1916.

52 Moffit, F, H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 

26-27, pi. 3, 1918.
28 MESOZOIC STRATIGRAPHY OF ALASKA

Mertie,53 who did not differentiate the McCarthy shale from the 

underlying thin-bedded limestone.

Stratigraphic description. The McCarthy formation consists of 

a. conformable succession of shale, chert, and limestone, which overlie the Nizina limestone. It was described by Moffit and Capps as 

follows:

The formation as it is exposed in the Nizina district is essentially a shale 

formation, although at its base are numerous thin limestone beds forming 

part of the transition zone at the top of the Chitistone limestone or the base 

of the shale. Thin beds of limestone are found interstratifled with the shales 

wherever they are exposed within the mapped area but are not abundant and 

form only a small proportion of the whole. The top of the McCarthy shale 

has not been recognized. Bedding is easily distinguished in most places, either 

by the presence of the thin limestones or of thin limy shale beds with surfaces 

highly colored by weathering. Some of the smooth bare hilltops about the 

eastern tributaries of East Fork are marked with exceedingly intricate patterns produced by the colored beds, for the McCarthy shale is found to be 

intensely folded wherever it has been examined, and if the folds are cut by 

planes or curved surfaces making slight angles with their axes the patterns 

appear.

A thickness of about 1,500 feet of Triassic shale overlies the limestone on 

the west side of Nizina River. The shales near the center1 of the broad 

syncline in this locality have' a horizontal position and are probably less distorted by folding than they are to the northwest. This measurement is considered the minimum and probably much less than the true thickness, for 

some of the shale has certainly been removed by erosion.

The mountains about the head of the East Fork of McCarthy Creek are 

made up of the black Triassic shales. They reach an altitude of 6^960 feet 

above sea level or 3,000 feet above the limestone-shale boundary at the creek 

on the southwest. The shales are much folded about the upper part of the 

East Fork valley, and measurements are consequently uncertain, but it is 

probable that the thickness of the formation is at least 2,500 feet in this 

vicinity. No measurements of value were obtained in the Copper Creek 

section, for, as previously stated, only a part of the formation is present there.

Although the McCarthy formation has hitherto been* described 

as consisting of shales and limestone, it contains a very considerable 

amount of black chert, which was not mentioned in most of the 

earlier descriptions. The position of the chert beds and the general 

character of the formation on the headwaters of Nikolai Creek are 

shown in the following section:

Section of part of McCarthy formation on Nikolai Creek

Feet 

Black shale with some chert beds (the fossils of lot 8889 were

obtained near the top)-__ _ . _ ________ 500 

Thin-bedded black chert______________________ 800 

Shale and thin-bedded shaly limestone, with PseudomonotiS 200 

Concealed to contact with Nizina limestone.

53 Moffit, F. H., and Mertie, J. B., jr., The Kotsina-Kuskulana district, Alaska : U. S. 

Geol. Survey Bull. 745, pp. 35-44, pi. 3, 1923.
TRIASSIC, CHITINA VALLEY 29

Age and congelation. The fauna of the McCarthy formation is 

small in species but large in numhers. It consists chiefly of Pseudomonotis subcircularis (Gabb), which occurs in vast multitudes, 

making up practically the whole of many beds. Almost no other 

fossils occur in association with the Pseudomonotis, and great thicknesses of strata appear to contain no fossils. Pseudomonotis subcircularis is characteristic of the highest beds in the Triassic of 

California and Nevada. It is very closely related to if not identical with Pseudomonotis ocJiotica, which is the characteristic fossil 

of the boreal f acies of the Noric of Europe and Asia.

The ammonite provisionally identified as Arniotites? which was 

found at three localities high up in the McCarthy formation, does 

not yield any conclusive evidence on the position of the strata. It 

may not be an Arniotites, and the stratigraphic and biologic position of that genus are none too well established. The genus as 

originally described was based on forms from British Columbia 

now believed to be of Upper Triassic (Noric) age, but it possibly 

includes also a species from the supposed Noric of Japan.

Fossils from the McCarty formation °

Pseudomonotis subcircularis (Gabb)~ 

Pseudomonotis subPecten? ..........

Undetermined ammonites ...........

Pseudomonotis subcircularis (Gabb)... 

Pseudomonotis .......

Hinnites?. ...........

Undetermined ammonites ______

9482

a

996S

b

6323

a

997

b

i

Coral?. __ . __ .... ___ .

Pseudomonotis subcircularis 

(Gabb)....................

Pecten ____ _______ .

Lima (Plagiostoma) . ____ .

Undetermined small pelecypods... _________ .

Halorites cf. H. americanus 

Hyatt. _ ... _ ........... .

Juvavites? ______ _ .. .

6335 

a

1887

a

202 f

a

6317

1681

947 f

b .

13

3997

. b

51561

...

8885

a

889C

a

9 11367

b

889

a

113685

b

1631

a

2072

a

2206

a

3160

a

3162

a

9931

b

1631

!199£

a

9926

b

1 11379

. b

1961

b

b

b

9920

h

b

11381

b

b

9962

b

9936

b

9964

b

993

b

b

11382

b

11365

b

79938

b

11388 

b

9953

b

9939

b

2200

a

9958

b

9940

b

7

9959

b

9944

b

b

b

8

a

8881

1 "

i

1

a

8945

a

2

a

4804

a

1 a, Identified by T. W. Stanton; b, identified by J. B. Reeside, jr.; c, identified by F. H. Knowlton. 

49448 26 4
30 MESOZOIC STRATIGRAPHY OF ALASKA

9482. Streams entering Chitina River at camp 12, about 3 miles above mouth 

of Canyon Creek, elevation 2,365 feet. Thin-bedded shale and limestone. 

F. H. Mofflt, 1915.

6323. Idaho Gulch near junction with Copper Creek. F. H. Moffit, 1909.

6335. Idaho Gulch about one-third mile above mouth. S. R. Capps, 1909.

6317. Dan Creek about 1% miles below mouth of Copper Creek. F. H. 

Moffit, 1909.

13. Boulder on flood plain of Nizina R.ver. Oscar Rohn, 1899.

8889. About 100 feet southwest of summit of 6,550-foot peak north of headwaters of Nikolai Creek. Probably 1,500 or 2,000 feet above base of McCarthy formation. G. C. Martin, 1914.

8890. About 0.3 mile southeast of summit of 6,550-foot peak north of headwaters of Nikolai Creek. Nearly the same horizon as 8889. G. C. Martin, 

1914.

8891. About 0.2 mile south-southwest of summit of 6,550-foot peak north of 

headwaters of Nikolai Creek. From nearly the same horizon as 8889. G. C. 

Martin, 1914.

6311. Mountain north of headwaters of Nikolai Creek, about 1% miles N, 

20° E. of Nikolai mine, elevation 6,000 feet. Near the locality and horizon 

of 8889. F. H. Moffit, 1909.

6314. McCarthy Creek, forks N. 33° E. of Bonanza Peak, elevation 3,850 feet, 

F. H. Moffit, 1909.

11379 (22 F 18). McCarthy Creek, mouth of third tributary below glacier, 

on east side. F. H. Moffit, 1922.

11381 (22 F 20). McCarthy Creek, eastern tributary 6 miles north of mouth 

of East Fork, or 2 miles above Diamond Creek, near mouth of creek. F. H. 

Moffit, 1922.

11382 (22 F 21). McCarthy Creek, eastern tributary 6 miles north of mouth 

of East Fork, or about 1% miles north of Mother Lode camp, south of and 

500 feet higher than 22 F 20. F. H. Moffit, 1922.

11388 (22 F 26). Ridge between McCarthy Creek and East Fork, 100 yards 

north of 22 F 25 and only a short distance above it stratigraphically. F. H. 

Moffit, 1922.

2200. Float along edge of Kennicott Glacier, 7 miles above Pot Hole. 

Schrader and Spencer, 1900.

7. West lateral moraine of Kennicott Glacier. Oscar Rohn, 1899.

8. Kennicott Glacier. Oscar Rohn, 1899.

8881. Mountain north of Fourth of July Pass, elevation 4,300 feet, on southeast side. Thin-bedded shaly limestone. G. C. Martin, 1914.

9968 (F 51). Falls of Bear Creek tributary to FohKn Creek, elevation 3,200* 

feet. (Float.) F. H. Moffit, 1916.

9974 (F 57). Bear Creek, a quarter of a mile west of Fourth of July Passand 200 feet higher. Thin-bedded limestone. F. H. Moffit, 1916.

8874. Fohlin Creek about 1 mile above mouth of Bear Creek. Float from 

east bank of creek. G. C. Martin, 1914.

6813. Fohlin Creek about 1 mile above mouth of Bear Creek. Float from 

same locality as 8874. G. C. Martin, 1914.

9979 (F 62). Fohlin Creek 12,200 feet north of mouth of Bear Creek. Talus 

below cliff of thin shale and limy argillite. F. H. Moffit, 1916.

11367 (22 F 4). South side of Lakina River S. 50° W. from mouth of Fohlin 

Creek, 1,000 feet above Lakina River. F. H. Moffit, 1922.

11368 (22 F 5). South side of Lakina River S. 50° W. from mouth of Fohlin 

Creek, 1,600 feet above Lakina River. F. H. Moffit, 1922.
TRIASSIC, CHITINA VALLEY 31

2207. West slope of ridge oi> west side of north fork of Lachina River. 

Schrader and Spencer, 1900.

2199. Ridge west of north branch of Lachina River, north of triangulation 

station 75. Schrader and Spencer, 1900.

9961 (F 43). Float in gulch below cliff on Mill Creek at locality F 44. F. H. 

Moffit, 1916.

9962(F 44). Mill Creek, tributary to Lakina River on west side. Shale and 

thin limestone near forks of creek, 2% miles from Lakina River. F. H. Mofflt, 

1916.

9964(F 46). Mill Creek, north fork, 1 mile north of mouth. F. H. Moffit, 1916.

11365(22 F 2). Ridge south of west branch of Lakina River, 800 feet higher 

than little lake south of trail. F. H. Moffit, 1922.

9953(F 36). One mile south of mouth of creek that comes down from Kuskulana Pass into Chokosna River. Thin shale and limestone. F. H. Moffit, 1916.

9958(F 40). Chokosna River, 1 mile southeast of mouth of creek flowing from 

Kuskulana Pass. Shale and thin limestone. F. H. Moffit, 1916.

9959(F41). Chokosna River, about iy2 miles southeast of mouth of creek 

flowing from Kuskulana Pass. Thin-bedded shale and limestone. F. H. Moffit, 

1916.

1. West side of Kuskulana River. Oscar Rohn, 1899.

2. West side of Kuskulana River, a short distance north of No. 1. Oscar 

Rohn, 1899.

2202. Creek on north side of Kuskulana River, near camp 16. A. C. Spencer, 

1900.

9947(F 29). Squaw Creek, elevation 3,100 feet. Dark limestone in beds as 

much as 2 feet thick. F. H. Moffit, 1916.

8156. First creek south of Clear Creek. Black calcareous shale. Theodore 

Chapin, 1912.

2206. Head of Rock Creek. Black slaty limestone in thin-bedded limestone 

and slate series. F. C. Schrader, 1900.

8160. Divide between Clear Creek and Rock Creek, ridge east of Dixie Pass, 

elevation 6,100 feet. Theodore Chapin, 1912.

8162. Divide between Clear Creek and Rock Creek, trail on ridge south of 

6,270-foot peak, elevation 6,100 feet. Theodore Chapin, 1912.

9931 (F 13). Ridge 200 feet north of F 12 (on ridge between Dixie Pass 

branch of Strelna Creek and Clear Creek, 1,500 feet south-southwest of bench 

mark 3270). F. H. Moffit, 1916.

9926(F8). Locality 9. East branch of east fork of Strelna Creek; elevation 

5,200 feet; 5,000 feet south of bench mark 6270. Alternating beds of soft shale 

and calcareous limestone. F. H. Moffit, 1916.

9920(F 2). North fork of Strelna Creek where trail to Rock Creek leaves 

Strelna Creek. Thin shale and limestone dipping about 20° W. F. H. Moffit, 

1916.

9936 (F 18). Gulch leading from west branch of Rock Creek to saddle 

between Rock Creek and East Fork 5 of Copper Creek. Pseudomonotis common 

in float of this gulch up to elevation 5,200 feet, above which talus is all very 

fine. F. H. Moffit, 1916.

9937 (F 19). Highest point of ridge between East Fork of Copper Creek, 

Pass Creek, and Rock Creek. Zone of shaly limestone, 8 to 10 feet thick, 

with abundant Pseudomonotis. F. H. Moffit, 1916.

9938 (F 20). Locality 18, on west branch of Rock Creek, 2,200 feet from 

forks, 150 feet northeast of exposure of Chitistone limestone. Alternating 

shale and calcareous shale or argillite. F. H. Moffit, 1916.
32 MESOZOIC STRATIGRAPHY OF ALASKA

9939 (F 21). West branch of Rock Creek, 400 feet from mouth. Alternating 

shale and hard argillite beds. F. H. Moffit, 1916.

9940 (F 22). Locality 19, 3,000 feet northwest by north of Dixie Pass, elevation 4,600 feet; 200 feet below outcrops of Chitistone limestone. Hard 

brown-weathering limestone or calcareous shale. F. H. Moffit, 1916.

9944 (F 26). Gulch tributary to east branch of Rock Creek from north 

side, 200 feet from east branch. Thin shale and limestone or calcareous 

shale. F. H. Moffit, 1916.

8945. Rock Creek, elevation 3,475 feet. G. C. Martin, 1914.

4804. Magpie Creek, 1 mile above junction with Elliott Creek. F. H. Moffit, 

1907.

NABESNA-WHITE RIVER DISTRICT 

GENERAL FEATURES

A well-defined although probably discontinuous belt of Triassic 

rocks extends through the southern foothills of the Nutzotin and 

Alaska ranges from the vicinity of the Canadian boundary to the 

headwaters of Susitna River. The eastern part of this belt, which 

is known as the Nabesna-White River district, lies north of the 

Chitina Valley and is separated from it by the Wrangell Mountains, 

in which the Quaternary and late Tertiary lavas and the existing 

glaciers conceal the underlying Mesozoic strata. Because of this 

lack of continuity and because of differences in the character of 

the sediments, the rocks in the two districts are somewhat difficult 

of correlation. The probable sequence of strata in the NabesnaWhite River district has been indicated by Moffit and Knopf 54 in the 

following table:

_ . f Gravels, till, and other unconsoli- Quaternary_ _ _______\ * <. * * -^

dated deposits.

Volcanic rocks.

 ,. Lignite-bearing formation, includ-

^ shales, sandstones, lignite 

beds, etc.

Shales of Jacksina Creek. 

Jurassic __ ____. Shales, slates, and graywackes of

the Nutzotin Mountains.

Triassic __ __ __ _ ___ _ __ I Tnin'Dedded limestone of Cooper

Creek. 

Lava's and pyroclastic beds tuffs,

Carboniferous or later. volcanic breccias, etc. 

Shales of Skolai Pass. 

Massive limestone. 

Shales with some tuffs and lava

 , .* flows. Carboniferous __________________ . .__ . , , . ,. . , Basic lavas and pyroclastic beds,

with some shale and limestone 

beds.

54 Mofflt, F. H., and Knopf, Adolpli, Mineral resources of the Nabesna-White River district, Alaska: U. S. Geol. Survey Bull. 417, p. 16, 1910.
TKIASSIC; NABESNA-WHITE RIVER DISTRICT 33 

SHALE AND VOLCANIC BOCKS

Historical review. The "shales of Skolai Pass" and the "lavas 

and pyroclastic beds," both of which are classed in the above table 

as "Carboniferous or later," are at least in part of Triassic age. 

They include part of the rocks seen by Hayes 55 at Skolai Pass and 

described by him as including "red sandstone and jasper and a 

great thickness of black shale." They include part of the rocks 

mapped by Brooks 56 as the "Nutzotin series" and as the "effusive 

series," but the parts of these aggregates that are now known to be 

of Triassic age were not described specifically. These rocks also 

include a portion of the rocks described and mapped by Rohn 57 as 

the " Skolai volcanics." They comprise an apparently large part 

of the "Diabasic series" described by Mendenhall and Schrader 58 

from the field observations of Schrader.

These rocks were described by Moffit and Knopf 59 under the heading "Carboniferous," with the qualification that this assignment 

was provisional, and they were represented on the geologic map,60 

together with the shales and volcanic beds beneath the Carboniferous 

limestone, as " undifferentiated Carboniferous rocks, possibly also 

including some rocks of Mesozoic age." The failure to separate the 

Triassic and Carboniferous rocks was due partly to the lithologic 

similarity of the Triassic shale, lava, and tuff to the sedimentary 

and volcanic beds beneath the Carboniferous limestone, partly to the 

scarcity of fossils, and partly to the complex structure.

These rocks are also an undifferentiated part of those which 

Capps 61 described and mapped as " mainly Carboniferous lava flows, 

tuffs, and agglomerates." Capps did not specifically describe any 

rocks that are known to be Triassic, but he stated that " within the 

areas composed predominantly of Carboniferous rocks there are 

minor amounts of beds of both older and younger formations." He 

also mentioned 62 the occurrence on the Middle Fork of White River 

(see p: 35) of Triassic fossils which he erroneously referred to as 

" Jurassic."

65 Hayes, C. W., An expedition through the Yukon district: Nat. Geog. Mag., vol. 4, 

p. 140, 1892.

68 Brooks, A. H.f A reconnaissance from Pyramid Harbor to Eagle City, Alaska, including a description of the copper deposits of the upper White and Tanana rivers : U. S. 

Geol. Survey Twenty-first Ann. Kept., pt. 2, pp. 359-360, 362-363, pi. 47, 1900.

67 Rohn, Oscar, A reconnaissance of the Chitina River and the Skolai Mountains, 

Alaska: U. S. Geol. Survey Twenty-first Ann. Rept., pt. 2, pp. 429-430, pi. 52, 1900.

58 Mendenhall, W. C., and Schrader, F. C., The mineral resources of the Mount Wrangell 

district, Alaska: U. S. Geol. Survey Prof. Paper 15, pp. 35-36, 1903.

68 Moffit, F. H., and Knopf, Adolph, Mineral resources of the Nabesna-White River 

district, Alaska: U. S. Geol. Survey Bull. 417, pp. 17-27, 1910.

00 Idem, pi. 2.

81 Capps, S. R., The Chisana-White River district, Alaska: U. S. Geol. Survey Bull. 630, 

pp. 30, 33-47, pi. 2, 1916.

62 Idem, p. 34.
34

The writer believes that the "lavas and pyroclastic beds with 

some shales" which constitute the upper member of the Carbon- 

'iferous section of Capps 63 may prove to be post-Carboniferous, as 

was suggested by Moffit and Knopf.64 Evidence in favor of the 

assignment of these rocks to the Triassic is given by the Triassic 

fossils from the volcanic breccia on the Middle Fork of White 

Eiver. The "distorted argillites and cherts" which Capps 65 mentions as occurring near the mouth of Beaver Creek, and which he 

" provisionally included with the Carboniferous," are suggestive of 

some of the Triassic rocks of other regions.

Stratigraphic description. The massive Carboniferous limestone 

of Skolai Pass and vicinity is overlain by shale, above which is a 

great thickness of lava, tuff, and breccia. These beds, because of 

their association and apparent conformity with the Carboniferous 

limestone, were provisionally assigned to the Carboniferous by 

Moffit and Knopf. The shales which immediately overlie the limestone in Skolai Pass were described by Moffit and Knopf 66 as being 

nearly 300 feet thick, as containing interbedded tuffs in their upper, 

part, and as being barren of fossils. Characteristic Upper Triassic 

fossils were, however, found at this locality by Hayes,67 who described the occurrence as follows:

In the walls of Skolai Pass, by which the range is crossed, its stratigraphy 

and structure are magnificently displayed. The rocks are comparatively recent, for the most part Carboniferous, Triassic, and Cretaceous. A bed of 

limestone about 500 feet thick contains many crinoids and corals, probably 

of Carboniferous age. Above it are red sandstone and jasper and a great 

thickness of black shale. Collections of fossils from the limestone and the 

black shale were made, but before reaching the coast they unfortunately were 

lost, with the exception of a single small piece of shale; this, however, contained several tolerably perfect impressions and was submitted to Prof. 

Alpheus Hyatt for identification. He says: " The fossils in the shale are 

clearly the remains of a Monotis [Pseudomonotis] of a Triassic type, allied to 

M. subcircularis, Gabb, a characteristic Triassic form in California. This one 

seems to be distinct specifically, but is evidently of the same age.

Age and correlation. The presence of Pseudomonotis subcircularis in the shales of Skolai Pass indicates that these rocks are to be 

assigned to the same general position as the McCarthy formation 

of the Chitina Valley. The pyroclastic beds of the north front of

63 Capps, S. R., The Chlsana- White River district, Alaska: U. S. Geol. Survey Bull. 

630, p. 39, 1916.

°*Mofflt, P. H.f and Knopf, Adolph, op. cit., p. 16.

65 Capps, S. R., op. cit., pp. 35-36.

« Mofflt, F. H., and Knopf, Adolph, op. cit., p. 17.

OT Hayes, C. W., An expedition through the Yukon district: Nat. Geog. Mag., vol. 4, p. 

140, 1892.
TRIASSIC, NABESNA-WHITE RIVER DISTRICT 35

the Wrangell Mountains, which probably overlie the shale of Skolai 

Pass, have also yielded Upper Triassic fossils as listed below. These 

fossils were collected by A. Neustaedter and are said to have been 

obtained from a volcanic breccia, but the locality has never been 

visited by a geologist, so it is impossible to describe the occurrence 

in detail. They were identified as follows by T. W. Stanton, according to whom the Clionites " is a characteristic Upper Triassic type 

of ammonite."

8479. About 3 miles from foot of glacier on Middle Fork of White Elver, in 

a southerly direction and about 800 feet above the river: 

Pseudomonotis subcircularis (Gabb) 1 

Clionites (Shastites) sp.

The correlation of the Upper Triassic shale, tuff, and lava of the 

Nabesna-White River district with the rocks of other districts involves serious difficulties. These rocks carry the fauna of the 

McCarthy formation of the Chitina Valley,, but that formation contains no volcanic material. A correlation of these beds with the 

Nikolai greenstone of the Chitina Valley has been suggested by 

Moffit and Maddren,68 by Moffit and Knopf,69 and by Moffit and 

Capps.70 This correlation seemed highly probable as long as there 

were grounds for believing that both formations belong in the interval between the Carboniferous limestone of White River and the 

Chitistone limestone of the Chitina Valley. The Nikolai greenstone 

is, however, certainly older than the Chitistone limestone, which It 

clearly underlies, and is'probably older than Upper Triassic, possibly being upper Carboniferous, whereas the Triassic shale, tuff, 

and lava of White River and Skolai Pass include beds that carry 

a fauna younger than that of the Chitistone limestone. It is consequently clear that these volcanic rocks can not be correlated with the 

Nikolai greenstone.

The apparent absence of any Triassic rocks in the Nabesna-White 

River district that can be correlated with either the Nikolai greenstone or the Chitistone limestone indicates that there is profound 

unconformity between the Carboniferous limestone and the overlying Upper Triassic Pseudomonotis-\>§2xmg beds. No physical evidence of this unconformity has yet been found, but the absence of 

detailed stratigraphic data and the known complexity of the structure make it impossible to say that because the unconformity has

68 Mofflt, F. H., and Maddren, A. G. Mineral resources of the Kotsina-Chitina region, 

Alaska: U. S. Geol. Survey Bull. 374, p. 24, 1909..

69 Mofflt, F. H., and Knopf, Adolph, Mineral resources of the Nabesna-White River district, Alaska: U. S. Geol. Survey Bull. 417, p.' 26, 1910.

70 Mofflt, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska : U. S. Geol. Survey Bull. 448, p. 03, 1911.
36 MESOZOIC STRATIGRAPHY OF ALASKA

not been seen it probably does not exist. The irregular distribution 

of the upper Carboniferous limestone beds is in itself a possible 

indication of a post-Carboniferous unconformity. The writer 

believes that extreme lenticularity in a limestone bed is inherently a 

highly improbable original feature, and he is consequently inclined 

to assert that the irregular distribution of the upper Carboniferous 

limestone is almost certain proof that the original continuity of the 

limestone has been destroyed either by erosion or by structural 

disturbances.

There is evidence that an unconformity may be present (see p. 

124) at the base of the McCarthy formation in the western part of 

the Chitina Valley. This unconformity agrees in stratigraphic position with the hypothetical unconformity now being considered.

LIMESTONE AND SHALE OF COOPER PASS

Historical review. The Triassic rocks in the vicinity of Cooper 

Pass, on the south front of the Nutzotin Mountains between Chisana 

and Nabesna Rivers, were first recognized by Schrader and were 

mentioned briefly by Mendenhall and Schrader.,71 in a report on the 

mineral resources of this district, as part of the "Mesozoic series." 

Mendenhall 72 also made brief mention of these rocks in a discussion 

of the age of the Chitistone limestone. A brief account of the 

occurrence and character of the Triassic limestone of Cooper Pass 

was given by Moffit and Knopf . 78 The occurrence and correlation of 

this limestone have been discussed briefly by Capps 74 and by 

Martin.75

Stratigraphic description. The Triassic rocks of Cooper Pass 

were described by Moffit and Knopf 76 as consisting of a single limestone formation that occurs in close geographic and structural association with a massive Carboniferous limestone. The Triassic and 

Carboniferous limestones are not easily distinguished, except by 

their faunas. The Triassic limestone is more thinly bedded than the 

Carboniferous limestone. It has been so much faulted and cut by 

dikes that neither it.s thickness nor its relations to the associated 

formations have been determined, but its thickness is apparently

71 Mendenhall, W. C., and Schrader, F. O., The mineral resources of the Mount Wrangell district, Alaska: U. S. Geol. Survey Prof. Paper 15, pp. 36-37, 1903.

7a (Mendenhall, W. C., Geology of the central Copper River region, Alaska: U. S. Geol. 

Survey Prof. Paper 41, pp. 49-50, 1905.

73 Mofflt, F. H., and Knopf, Adolph, Mineral resources of the Nabesna-White River district, Alaska: U. S. Geol. Survey Bull. 417, pp. 27-32, 1910.

7*Capps, S. R., The Chisana-White River district, Alaska: U. S. Geol. Survey Bull. 

630, pp. 29, 30, 47-53, 1916.

75 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, p. 696, 

1916.

76 Mofflt, F. H., and Knopf, Adolph, op. cit., pp. 27-28.
TRIASSIC, UPPEE SUSITFA VALLEY 37

much less than that of the Carboniferous limestone. Mendenhall" 

described the Triassic rocks of Cooper Pass, from Schrader's observations, as "consisting of black shales and dark limestones closely 

resembling the thin-bedded dark limestones that are above the 

Chitistone limestone in the Chitina Valley."'

Age and correlation. The fauna of the Triassic rocks of Cooper 

Pass, as now known, is represented by the fossils from the localities 

listed below, identified by T. W. Stanton. Fossils were seen also at 

the mouth of Wilson Creek, but no collections were made at that 

locality, for the fossils show only on the weathered surface of the 

rocks and it is difficult to procure good specimens. The age of the 

limestone on Wilson Creek, consequently, is more or less doubtful.

1454.1 Round Mountain, northeast of Cooper Pass. Triangulation station1 

No. 27. F. C. Schrader, 1902. Pseudomonotis.

5721. Limestone between the forks of Cooper Creek. Moffit and Knopf, 

1910. Pseudomonotis subcircularis (Gabb).

5724. Cooper Pass. Moffit and Knopf, 1910. Pseudomonotis subdrcularis 

(Gabb).

The Upper Triassic limestone of Cooper Pass bears some resemblance to the Chitistone limestone, with which Moffit and Knopf suggested a correlation. It differs from the Chitistone limestone in 

being far thinner, in being more thinly bedded, and in carrying a 

younger fauna. In its lithologic character it bears closer resemblance to the limestone at the base of the McCarthy formation, and as 

it carries the fauna of the McCarthy formation it may be assigned to 

that horizon.

UPPER SUSITNA VALLEY 

GENERAL FEATURES

A belt of Triassic rocks extends through the foothills south of the 

Alaska Range from the headwaters of Gulkana River to a point west 

of Susitna River. This belt lies in a geographic and structural position similar to that of the Triassic rocks south of the Nutzotin Mountains and should probably be regarded as their western discontinuous extension. The Triassic rocks south of the Alaska Range include 

fossiliferous Upper Triassic limestone and a group of slate, tuff, 

arkose, calcareous sandstone, and limestone that are closely associated with and probably overlie the fossiliferous limestone. The 

latter is underlain by basic lava and tuff that seem to rest on a 

Carboniferous (?) limestone and that consequently correspond in

77 Mendenhall, W. C., op. cit., p. 50.
38 MESOZOIC STRATIGRAPHY OF ALASKA

stratigraphic position, as well as in lithologic character, to the 

Nikolai greenstone of the Chitina Valley and should probably be 

assigned to the Permian or early Triassic.

The Triassic beds and the rocks most intimately associated with 

them in the belt between Gulkana and Susitna Kivers were described by Moffit 78 as including (a) Carboniferous or Triassic lavas; 

(5) fossiliferous Upper Triassic limestone; (c) slate, tuff, arkose, 

calcareous sandstone, and limestone, all closely associated with and 

probably overlying the fossiliferous Upper Triassic limestone; and 

(d) highly metamorphosed schist that may be the altered representative of the Triassic rocks. The extension of this belt west of 

the Susitna Kiver was described by Moffit 79 as including "Triassic 

or Carboniferous (?) basic lava flows with tuff beds [the extension 

of a above]; Upper Triassic (?) slate, with intercalated beds of 

graywacke, arkose, etc. [the extension of c and part of d] ; and 

undifferentiated Mesozoic (?) slates, argillites, graywacke, and thinbedded limestone [the extension of d in part]." A further southwest extension of this belt was mapped by Chapin,80 who described 

" Triassic (?) lavas and tuffs " and " Upper Triassic (?) slate, graywacke, limestone, and schist," and by Capps,81 who described some 

" possibly Triassic " limestone, marble, shale, slate, and quartzite in 

the western Talkeetna Mountains. The possible northeast extension of this belt into the Chistochina district is suggested by an ammonite which is said to have been found on Slate Creek.

BASIC LAVAS AND TUFFS

Historical review. The Upper Triassic limestone of the upper 

Susitna Valley, described below, is apparently underlain by Triassic 

or Carboniferous volcanic rocks that cover large areas in the southern foothills of the Alaska Range.

These rocks were first observed on the headwaters of Gulkana 

River, in the vicinity of Tangle Lakes, by W. C. Mendenhall in 

1898. Mendenhall was making a rapid exploratory journey and 

had no opportunity to study or describe the rocks in detail. These 

rocks apparently constitute the " acid effusives and associated 

rocks" and possibly also part of the ci greenstone series" as described by Mendenhall.82

78 Moffit, F. H., Headwater regions of Gulkana and Susitna rivers, Alaska: U. S. Geol. 

Survey Bull. 498, pp. 22, 29-33, pi. 2, 1912.

79 Moffit, F. H., The Broad Pass region, Alaska: U. S. Geol. Survey Bull. 608, 1915, 

pp. 24, 26-31, pi. 2.

80 Chapin, Theodore, The Nelchina-Susitna region, Alaska : U. S. Geol. Survey Bull. 

668, pp. 21, 26-28, pi. 2, 1918.

81 Capps, S. R., Mineral resources of the western Talkeetna Mountains: U. S. Geol. 

Survey Bull. 692, p. 195, 1919.

82 Mendenhall, W. C., A reconnaissance from Resurrection Bay to the Tanana River, 

Alaska, in 1898: U. S. Geol. Survey Twentieth Ann. Rept., pt. 7, pp. 311-313, 1900.
TRIASSIC, UPPER ST7SITNA VALLEY 39

The occurrence of these volcanic beds in the area between Gulkana 

and Susitna rivers has been noted by Moffit, these rocks constituting 

the "basic lavas and tuffs" as described in the text 83 and the 

" amygdaloidal lava flows with intercalated tuffaceous and shaly 

beds " as represented on the map.84 Moffit considered these beds probably either late Carboniferous or early or Middle Triassic, and 

probably approximately synchronous with the Nikolai greenstone. 

The western extensions of these rocks in the hills west of Susitna 

River were described by Moffit 85 as "Triassic (?) lavas" and by 

Chapin 80 as " Triassic (?) lavas and tuffs."

Character and age. The lava and tuff of the area between Gulkana and Susitna Rivers were described by Moffit as follows:

These rocks consist largely of diabase and locally are amygdaloidal, showing 

that in part, at least, they are surface lava flows. They are associated with 

argillites, tuffs, and tuffaceous conglomerates in a number-of places and are 

intruded by diabases and by dikes of less basic, light-colored porphyritic rock.

The extension of these rocks west of Susitna River was described 

by Moffit as consisting principally of basaltic lava flows with associated andesitic flows and water-laid tuffaceous beds. The estimated 

thickness is 3,500 feet.

The volcanic rocks of the upper Susitna Valley apparently underlie the Upper Triassic limestone and are believed to rest upon an 

upper Carboniferous limestone. They thus correspond approximately in stratigraphic position, as well as in lithologic character, 

with some of the late Carboniferous volcanic rocks of the NabesnaWhite River district, or with the Nikolai greenstone.

LIMESTONE

Fossiliferous Triassic limestone occurs in several small areas in 

the foothills of the Alaska Range between Maclaren and Susitna 

Rivers. This limestone constitutes an undifferentiated part of the 

" Triassic rocks " as described by Moffit,87 and is the " Triassic limestone " as represented on his geologic map.88

This limestone crops out in a series of small detached areas lying 

in a belt between Maclaren and Susitna Rivers but mostly in the val83 Moffit, F. H., Headwater regions of Gulkana and Susitna rivers, Alaska: U. S., Geol. 

Survey Bull. 498, pp. 22, 29-30, 1912.

M Idem, pi. 2.

85 Moffit, F. H., The Broad Pass region, Alaska: U. S. Geol. Survey Bull. 608, pp. 24, 

26-28, 1915.

88 Chapin, Theodore, The Nelchina-Susitna region, Alaska: TJ. S. Geol. Survey Bull. 

668, pp. 21, 26-27, 1918.

87 Moffit, F. H., Headwater regions of Gulkana and Susitna rivers, Alaska: U. S. Geol. 

Survey Bull. 498, pp. 22, 31, 33, 1912.

88 Idem, pi. 2.
40 MESOZOIC STRATIGRAPHY OF ALASKA

ley of Clearwater Creek. The discontinuity of the outcrops is probably due to structural disturbances rather than to original lenticularity. Several of these limestone masses rest directly upon the 

amygdaloidal lava flows described on pages 38-39, and all of them 

are not far from the main area of the volcanic rocks. The limestone, which apparently can not be more than a few hundred feet 

thick, is overlain by the Upper Triassic slate, tuff, arkose, and calcareous beds described on pages 40-42.

The fauna of this limestone, as at present known, is represented 

by the fossils enumerated in the following list, which were identified 

by T. W. Stanton. These fossils were obtained from bluish-gray 

limestone beds that rest upon the volcanic rocks.

6570. Limestone area on a small western tributary of Clearwater Creek: 

Halobia sp. related to H. superba Mojsisovics. 

Tropites sp. 

Discotropites ? sp. 

Arcestes sp.

This fauna appears to be essentially identical with that of the 

Chitistone limestone of the Chitina Valley. The equivalence of this 

limestone with part of the Chitistone limestone is also indicated by 

the facts that it rests directly upon the volcanic rocks and that, like 

the Chitistone limestone, it is apparently overlain by beds carrying 

Pseudomonotis subcircularis (Gabb). It consequently is presumably 

low in the local Upper Triassic sequence.

SLATE, TUFF, ARKOSE, AND CALCAREOUS BEDS

Historical .review. The Triassic slate, tuff, arkose, and calcareous beds of the upper Susitna Valley occur in a belt that extends 

through the southern foothills of the Alaska Range from Maclaren 

Glacier into the hills west of Susitna River. The limestone described 

on pages 39-40 occurs along the southern border of these rocks and 

presumably underlies them.

The rocks of the eastern part of this belt, from Maclaren Glacier 

to Susitna River, were mapped by Moffit 89 as " Upper Triassic slates, 

tuffs, arkose, calcareous sandstones, and limestones, with some diorite 

and diabase intrusives," and were described in his text 90 as " Triassic 

rocks"; that heading included also the Upper Triassic limestone 

that is discussed on pages 39-40 and some highly metamorphosed 

schist that may be the altered representative of the Triassic rocks, 

but was mapped as distinct from them.

80 Moffit, F. H., Headwater regions of Gulkana and Susitna Rivers, Alaska: TJ. S. Geol. 

Survey Bull. 498, pi. 2, 1912. 

»o Idem, pp. 22, 31-33.
TRIASSIC, UPPER SUSITNA VALLEY 41

The rocks of that part of the belt lying west of Susitna River were 

discussed by Moffit 91 under the heading " Triassic sediments." They 

apparently include only the rocks here under consideration, the limestone being absent, and the metamorphic rocks being mapped and 

described separately.

There is a possible extension of these rocks farther southwest, 

on the west side of Tsisi Creek between Susitna and Talkeetna 

Rivers, where Chapin S2 noted some " Upper Triassic (?) slate, 

argillite, and graywacke with some thin beds of limestone," and in 

the valleys of Iron Creek and Sheep River in the western Talkeetna 

Mountains, where Capps 93 noted same "limestone, marble, shale, 

slate, and quartzite " that are possibly Triassic.

Stratigraphic description. The Upper Triassic slate, tuff, arkose, 

and calcareous, beds of the belt that extends northeastward from 

Susitna River between Valdez and Windy Creeks to Maclaren 

Glacier were described by Moffit as being but little metamorphosed 

and as including banded slate, black slate, red-weathering slate or 

shale, graywacke or fin tuff, tuffaceous conglomerates, diabase flows 

or intrusions, shaly limestone, and calcareous sandstone. The thickness has not been determined but is probably many hundred if not 

several thousand feet.

The rocks of the extension of this belt to the west of Susitna 

River were described by Moffit as including dark-blue and black 

slate, with interstratified beds of arkose and graywacke, probably 

several thousand feet thick. These rocks are closely folded and show 

a varying degree of metamorphism that has locally changed the 

argillite and arkose to phyllite and schist.

The " undifferentiated Mesozoic (?)" slate, argillite, graywacke, 

and thin-bedded limestone on the headwaters of Susitna River may 

or may not include Triassic rocks. They were described by Moffit 

as comprising " a complex of beds that could not be differentiated 

in the time available." Moffit said of them:

.The age of these sediments is unknown. It is perhaps possible but does 

not appear probable that they may correspond in part with some of the 

Devonian formations. On the other hand it seems much more likely that 

they are of Mesozoic age and are to be correlated with the Triassic slates 

and limestones of the Valdez Creek district or with the Jurassic (?) sediments of Jack Eiver. It may even be that they include beds belonging to 

both of these groups.

The supposed Triassic rocks between Susitna and Talkeetna rivers 

were described by Chapin as consisting of limestone, slate, argil81 Moffit, Fi H., The Broad Pass region, Alaska : U. S. Geol. Survey Bull. 608, pp. 24, 

29-31, 1915.

92 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U. S. Geol. Survey Bull. 

668, pp. 27-28, pi. 2, 1918.

83 Capps, S. R., Mineral resources of the western Talkeetna Mountains: U. S. Geol. 

Survey Bull. 692, p. 195, 1919.
42

lite, and related coarser sediments as well as dioritic and other intrusive rocks. .The most prominent members are dark-blue and black 

slate and argillite and greenish-gray graywacke. Thin beds of 

crystalline limestone are intercalated with the other sediments. A 

section on a tributary of Tsisi Creek indicates that the thickness is at 

least 2,000 feet and may be much greater, for neither top or bottom 

was seen. These rocks have yielded no fossils. Chapin referred 

them tentatively to the Triassic because they lie on the strike of the 

Triassic rocks southeast of Valdez Creek and bear some resemblance 

to those rocks.

The supposed Triassic rocks of the western Talkeetna Mountains 

were described by Capps as including a massive limestone at least 

600 feet thick, in some places overlain by a considerable thickness of 

shale slate, and quartzite. These rocks have yielded no fossils. They 

are apparently overlain by volcanic rocks that are believed to be 

Lower Jurassic.

Age and correlation. The slate, tuff, arkose, and calcareous beds 

of the upper Susitna Valley apparently overlie the limestone just 

described. They contain Pseudomonotis subcircularis (Gabb) ? 

which, together with the position of the rocks relative to the underlying limestone, indicates that they belong in the same general position as the McCarthy formation. The rocks associated with the f ossilferous beds, however, are strikingly unlike those of the McCarthy 

formation, which consist of shale, chert, and limestone, withono beds 

of tuff or arkose. The formation as a whole, both in its lithologic 

and in its faunal character, bears a strong resemblance to the Upper 

Triassic limestones and tuffs of Port Graham, described on pages 

49-51, and to the Triassic volcanic beds of Skolai Pass, described on 

pages 33-36, both of which contain this same fossil.

The fossils obtained at the localities listed below were identified! 

by T. W. Stanton.

6571. Coal Creek, a tributary of Clearwater Creek, 15 miles east of Susitna 

River. Exposure showing several hundred feet of thin-bedded shaly limestone 

and calcareous sandstone. Their position within the formation has not been 

determined but is probably considerably above the base. F. H. Moffit, 1910. 

Pseudomonotis subcircularis (Gabb).

6572. West of Clearwater Creek, about 2 miles northwest of the locality from 

which No. 5670 was taken. Limestone bed of indeterminate position. F. EL 

Mofflt, 1910. Serpula.

CHULITNA VALLEY 

GENERAL FEATURES

Upper Triassic rocks are known in two areas in the Chulitna 

Valley. One of these areas lies in the foothills of the Alaska Range 

on several of the western tributaries of the West Fork of the Chu-
TRIASSIC, CHULITNA VALLEY 43

litna. The other area lies on eastern tributaries of the East Fork of 

the Chulitna. The two areas are not parts of the same structural 

belt but occur in two distinct and apparently parallel belts that are 

10 miles or more apart at the nearest place and are separated by 

areas of pre-Triassic igneous and metamorphic rocks and by the 

alluvial filling of the main Chulitna Valley.

The Triassic rocks west of Chulitna River consist chiefly of tuff, 

limestone, shale, and lava. They rest unconformably on greenstones 

and metamorphic sedimentary rocks that are believed to be preTriassic. They are apparently overlain by argillite, slate, and graywacke that may be Jurassic or Cretaceous. They contain a fauna 

that certainly is Triassic but is different from most of the Upper 

Triassic faunas of Alaska, though it has some resemblance to the 

Triassic fauna of Gravina Island.

The Triassic rocks east of Chulitna River consist chiefly of thinbedded limestone and shale. The character and relations of the 

underlying and overlying rocks are not known. They carry the 

well-known Pseudomonotis fauna.

TTTFF, LIMESTONE, SHALE, AND LAVA OF WEST FOEK

Stratigraphic description. The Triassic tuff, limestone, shale, and 

lava of the West Fork of Chulitna River were described by Capps 9* 

substantially as follows:

Triassic tuff, limestone, shale, and basic lava flows, with minor 

amounts of conglomerate and graywacke, apparently lie unconformably upon the underlying greenstone, tuff, slate, and chert. On 

Ohio Creek an excellent section is exhibited. There the older group 

of tuff, slate, and chert appears to lie unconformably beneath a heavy 

bed of conspicuous red tuff and agglomerate. This red tuff is the 

basal member of a group of rocks that has an aggregate thickness of 

several thousand feet and includes tuff, agglomerate, conglomerate, 

amygdaloidal greenstone flows, and massive limestone beds. The 

tuffs range in texture from fine-grained rocks that resemble red 

sandstone to coarse agglomerates containing fragments of volcanic 

debris several inches across. They range in color from vivid red, 

in which the composing fragments are chiefly jaspilite, through 

green and purple shades. In some of the tuffs the fragments all 

appear to be sharply angular; in others partly rounded. These tuffs 

grade into conglomerates. On upper Ohio Creek there are five massive limestones. One of these yielded fossils of Triassic age, and 

other fossils from boulders in Copeland Creek appear to be of the 

same age. The tuff beds so abundant in the lower rocks give place

04 Capps, S. R., Mineral resources of the upper Chulitna region : U. S. Geol. Survey 

Bull. 692, pp. 216-217, 1919.
44 MESOZOIC STRATIGRAPHY OF ALASKA

higher up to amygdaloidal lava flows, and on Ohio Creek a considerable thickness of lava appears above the uppermost limestone.

The section on West Fork of Chulitna River, though presenting 

certain features in common with that on Ohio Creek, is greatly 

different in detail. The red and green tuffs are present at the base. 

The abundant intrusive dikes and sills have altered the surrounding rocks, and as a result the limestone, here inconspicuous, is generally changed to marble, and white, cream-colored, and bluish cherts 

appear. The amygdaloidal greenstone so abundant on Ohio Creek is 

relatively scarce on West Fork of Chulitna River, where the group 

is overlain by a heavy body of black argillite, slate, and graywacke.

Age and correlation. The Triassic rocks of the West Fork of 

Chulitna River differ both in their stratigraphic sequence and in 

their fauna from most of the other Triassic rocks of Alaska. The 

fauna does not include any of the common fossils such as Halobia, 

Pseudomonotis, or the ammonites which are characteristic of the 

well-known horizons in the Upper Triassic of Alaska. T. W. Stanton, who determined the fossils listed in the following table, stated 

that the presence of Cassiwnella, in these collections suggests the 

Triassic fauna of Gravina Island, in southeastern Alaska."

Fossils from West Fork of Chulitna River a

A.viculiD6ctGH^

PsctGD * -

Pecten?.... _____ ......... __ ... ________ . ..........

Lima ___ __ ........... ... ____ ___ . .....

Lima? _______ .... __ ... ........ _ ... .....

Astarte?..... . .- - - . -.

10090

X

X

10091

X

X

X

10092

X

X

........

10093

y

X

10094

Identified by T. W. Stanton.

10090-10093 (Nos. 1-4). Stream bar of Copeland Creek.. S. R. Capps, 1917. 

10094 (No. 5). Talus below limestone outcrop on Ohio Creek 1% miles 

above mouth of Christy Creek. S. R. Capps, 1917.

LIMESTONE AND SHALE OF EAST FOHK

The Upper Triassic limestone and shale of the East Fork of Chulitna River were discovered by R. M. Overbeck in 1919 but have 

not yet been described. They consist, according to Overbeck's 

field notes, of rather thin bedded, much crushed and folded bluish 

slate and limestone. He mentions the presence of graywacke and 

chert near the localities that vielded the Triassic fossils but does
TBIASSIC, KENAI PENINSULA 45

not state their relation to the fossiliferous beds. No information is 

available concerning the thickness of the Triassic rocks or the 

character and relations of the underlying and overlying beds.

The fossils that have been found in the Upper Triassic limestone 

and shale of the East Fork of Chulitna River were identified by 

T. W. Stanton and are listed below. The presence of Pseudomonotis 

subdrcularis as well as the character of the rocks indicates a correlation with the McCarthy shale and with the Pseudomonotis-beaiTmg 

beds of other Alaskan districts. Concerning the coral Heterostridium, which has been found elsewhere in Alaska only in the limestone of Iliamna Lake (see p. 60), Stanton said: "This genus of 

hydroid coral is characteristic of the Upper Triassic in the Alps 

and in India."

10241 (F 4). East Fork of Chulitna River, south side, 1% miles below 

camp 9. R. M. Overbeck, 1919. Heterastridium.

10242 (F 2). Creek entering East Fork below camp 9, upper Chulitna 

Valley. R. M. Overbeck, 1919. Pseudomonotis subcircularis (Gabb).

10243 (F 3). Same locality as F 2. R. M. Overbeck, 1919. Heterastridium.

KENAI PENINSULA

GENERAL FEATURES

The Triassic rocks of the east coast of Cook Inlet occur at the 

southwest end of Kenai Peninsula, in a belt that extends northeastward from Porto Graham parallel to the south shore of Kachemak 

Bay. They include limestone and tuff with Upper Triassic fossils, 

apparently underlain by contorted chert which has yielded no characteristic fossils but which the writer believes to be Upper Triassic. 

Beneath the chert is ellipsoidal lava, which is underlain by slate 

and graywacke. The Upper Triassic limestone and tuff are overlain, probably unconformably, by Lower Jurassic tuff and agglomerate. The probable sequence of formations is indicated in the following table:

General section of Mesozoic rocks in Kenai Peninsula

Lower Jurassic.: Tuff and agglomerate with Lower Jurassic fossils. 

Upper Triassic:

Limestone and tuff with Upper Triassic fossils.

Contorted chert.

Triassic or Carboniferous: Ellipsoidal lava. 

Paleozoic (?) : Slate and graywacke.

ELLIPSOIDAL LAVA

Historical review. The first published description of the ellipsoidal lava of the Kenai Peninsula was a brief note on the spheroidal
46 MESOZOIC STRATIGRAPHY OF ALASKA

diabase oi Halibut Cove by Emerson.95 A more complete description of the lava observed at different places along the coast from 

Seldovia Bay to Aurora was given by Moffit,96 who described the 

rocks as pre-Jurassic diabase. Brief mention of the occurrence of 

ellipsoidal greenstone was made by Grant and Higgins 97 in their 

preliminary report on the ore deposits of this district, but they did 

not attempt to describe the rocks in detail. The lava of the entire 

belt has been described and mapped by Martin 98 as "Triassic (?) 

ellipsoidal lavas."

Character, stratigraphic position, and age. Ellipsoidal lava is 

widely distributed in the parts of Kenai Peninsula that border on 

the south shore of Kachemak Bay and on the extreme southern part 

of Cook Inlet. Exposures are abundant along a probably discontinuous series of belts extending from Port Graham at least as far 

northeastward as Aurora, but the best exposures are on Port Graham, 

Seldovia Bay, Hesketh and Yukon Islands, and Halibut Cove.

The ellipsoidal lava of Kenai Peninsula consists predominantly of 

green scoriaceous and ellipsoidal lava, interbedded with a small 

amount of tuff. At a few places, notably on Hesketh and Yukon 

Islands, the color is dark red rather than green. The lava is well 

displayed in the cliffs on the east shore of Seldovia Bay, where the 

exposures begin at a point almost 2 miles below the head of the bay 

and extend as far north as the end of the cape just above the cannery. These exposures consist of greenish ellipsoidal and scoriaceous basalt containing veins and irregular masses of epidote. A 

little chert is interbedded with the lava. The thickness of these 

rocks, as computed from the width of the belt and the average dip 

on the shores of Seldovia Bay, on the assumption that there is no 

repetition by faulting, is about 3,000 feet.

The stratigraphic relations of the lava to the underlying and 

overlying rocks are shown most clearly on Seldovia Bay. The excellent exposures on the east shore of the bay show that the lava is underlain by slate, graywacke, crumpled chert, and some volcanic rocks, 

aggregating over 5,000 feet in thickness. The dip of the slate and 

other rocks places them beneath the lava, but there is no conclusive 

evidence as to whether or not the contact is conformable. The lava 

is, however, considerably less altered than the volcanic members of 

the slate and graywacke series, and it is consequently assumed to be 

considerably younger.

85 Emerson, B. K., General geology: Alaska, vol. 4, p. 26, Harriman Alaska Expedition, 1904.

86 Mofflt, F. H., Gold fields of the Turnagain Arm region : U. S. Geol. Survey Bull. 

277, p. 23, 1906.

97 Grant, U. S., and Higgins, D. P., Preliminary report on the'mineral resources of the 

southern part of Kenai Peninsula: TJ. S. Geol. Survey Bull. 442, p. 167, 1910.

98 Martin, G. C., The western part of Kenai Peninsula : U. S. Geol. Survey Bull. 587, 

pp. 52-55, pi. 3, 1915.
TRIASSIC, KENAI PENINSULA 47

The ellipsoidal lava is overlain by the Triassic chert described on 

pages 4T-49, lout there is no evidence as to the presence or absence 

of a stratigraphic break between them. Most of the contacts are not 

 exposed in detail or are faults. The lava is comparatively unaltered and appears to be not very much older than the chert. It 

may reasonably be assigned either to the Triassic or to the latest 

Paleozoic. It appears to correspond closely in stratigraphic position and in litholo,gic character to the Nikolai greenstone of the 

Chitina Valley.

CHERT

Historical.review. The chert of Kenai Peninsula was first described by Emerson," who briefly noted the occurrence at Halibut Cove 

of " an interesting section of green and red radiolarian cherts " which 

he tentatively correlated, on the basis of lithologic similarity, with 

the Jurassic or Cretaceous radiolarian chert of the Franciscan formation of California. The occurrence of similar chert at Seldovia 

was noted by Stanton and Martin,1 who correlated it with the Upper 

Triassic chert of the west coast of Cook Inl:t on the basis of lithologic similarity and assigned it to the Upper Triassic on the ba.sis 

of this correlation and of its relation to the Lower Jurassic tuff of 

Seldovia Bay. A more complete discussion of this chert has been 

.given by Moffit,2 who concluded that it is certainly pre-Jurassic and 

probably Triassic. The chert was discussed briefly by Grant and 

"Higgins,3 whose description includes also an account of the underlying ellipsoidal lava, together with a description of the chert associated with th: presumably older slate and graywacke. The writer 

believes that at least part of the last-mentioned chert is not the same 

as the contorted chert of Seldovia Bay. A rather full discussion of 

this chert has been given by Martin,4 who assigned it tentatively to 

the Upper Triassic and from whose description the following account 

is taken. The age and correlation of the chert of Kenai Peninsula 

"have also been discussed by Martin. 5 ,

Stratigraphic description. Contorted chert occurs in the southwestern part of Kenai Peninsula, along the south shore of Kachemak 

.Bay. The best exposures are on Bear Cove, Halibut Cove, Chinaput 

Bay, Eldred Passage, Seldovia Bay, and Port Graham.^

99 Emerson, B. K., General geology : Alaska, vol. 4, pp. 26-27, Harriman Alaska Expedition, 1904.

1 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, p. 393, 1905.

3 Moffit, F. H., Gold fields of the Turnagain Arm region, Alaska: U. S. Geol. Survey 

Bull. 277, pp. 16, 17, 19-20, 1906.

8 Grant, U. S., and Higgins, D. F., Preliminary report on the mineral resources of the 

southern part of Kenai Peninsula: U. S. Geol. Survey Bull. 442, pp. 167-168, 1910.

4 -Martin, G. C., The western part of Kenai Peninsula: U. S. Geol. Survey Bull. 587, 

pp. 60-63, pi. 3, 1915.

6 Martin, G. C., Triassic rocks of Alaska : Geol. Soc. America Bull., vol. 27, p. 699, 1916.
48 MESOZOIC STRATIGRAPHY OF ALASKA

The chert consists of thinly and evenly bedded rocks made up of 

hard siliceous layers, from half an inch to 2 inches thick, separated 

by thin films of softer material. The siliceous layers are of fairly 

uniform appearance except in color. They are of very fine grainr 

being uniformly of almost glassy texture, and do not contain any 

recognizable detrital fragments. The material between the hard 

beds was not definitely determined, but it is probably argillaceous. 

The color of the chert at most places is green, gray, or black, but a. 

few occurrences of brown or red chert were noted.

The chert is intensely deformed, minute crumpling being general 

and faulting being common, so that no estimate of the thickness of 

the formation can be made nor can the top and bottom of a local section be determined with certainty. On the east shore of Seldovia, 

Bay, just above the cannery, the chert apparently rests upon ellipsoidal lava. This is assumed to be the base of the formation, but. 

there may be a fault or an overturn at this point. Within the area, 

of the chert at several places are masses of ellipsoidal lava, which 

may be either interbedded or structurally included. There is apparent interbedding of thin strata of lava and chert at some localities, but at others there are wider alternate bands of chert and lava, 

that suggest structural repetition. Probably each main mass of 

chert or lava contains thin interbedded strata of the other rock, and 

masses of each kind of rock have been included by folding and 

faulting within the main areas of the other. The-only fossils that 

have been recognized in these rocks are poorly preserved Radiolaria.

Age and correlation. The contorted chert of Kenai Peninsula has. 

yielded no characteristic fossils, and its age is somewhat doubtful. 

The local field relations indicate that the chert lies immediately 

above the ellipsoidal lava and beneath the limestone and tuff, which 

seem to occur directly beneath the Lower Jurassic beds and to be the 

youngest Triassic rocks in the local section. This sequence accordswell with the relations of similar beds in other regions, provided that 

the Halobia, belongs to a species whose range is such that the limestone and tuff can be correlated with the McCarthy formation and 

with the upper part of the Kamishak chert, and that the chert can be 

correlated with the chert at the base of the McCarthy and Kamishak 

formations. But if the Halobia is a strictly Karnic species which isrestricted to the horizon of the Chitistone limestone and of the lower 

part of the Hosselkus limestone, the lower part of the limestone and 

tuff must be correlated with rocks occurring beneath the chert at the 

base of the McCarthy and Kamishak formations, and the chert can 

not be considered as occurring beneath the limestone and tuff of Port 

Graham and be correlated with any of the Triassic cherts known in 

other Alaskan districts. The writer believes that this Halobia is-
TRIASSIC, KENAI PENINSULA 49

probably not an exclusively Karnic (lower Hosselkus) species, and 

that the chert of Kenai Peninsula should be regarded as occurring 

beneath the limestone and tuff and above the ellipsoidal lava and 

should be correlated with the chert at the base of the McCarthy 

formation and with the lower part of the Kamishak chert.

LIMESTONE AND TUFF

Historical review. The occurrence of Upper Triassic limestone 

and tuff in the Kenai Peninsula was first noted by Grant and Higgins,6 who described them briefly as "a series of cherts and black 

limestones near the base of this [Lower Jurassic] tuff formation." 

The exposures on Port Graham were subsequently discussed more 

fully by Martin,7 who described and mapped these rocks as Upper 

Triassic limestone and tuff. The southern extension of the belt from 

Port Graham to Koyuktolik Bay has been mapped and briefly 

described by Grant.8 The character, position, and age of the Upper 

Triassic limestone and tuff of Kenai Peninsula were discussed by 

Martin.9

Stratigraphic description. The Upper Triassic limestone and 

tuff of Kenai Peninsula are known only in the vicinity of Port 

Graham and Koyuktolik Bay. The exposures in- these two localities are parts of one continuous belt that extends northward from 

Koyuktolik Bay, forming the shores of Port Graham for 2^ to 

3 miles on each side of the bay, and terminates in the hills between 

Port Graham and Seldovia Bay.

These rocks consist of limestone with considerable amounts of 

chert and fine-grained volcanic material, which is mostly tuffaceous. 

Their thickness is not known, and their stratigraphic relations to 

the beds that underlie and overlie them have not yet been determined with certainty.

The exposures on the north shore of Port Graham consist of 

limestone, both cherty and noncherty; rather massive black chert; 

and volcanic rocks that include tuff, tuffaceous conglomerate, and 

breccia. The exposures are fairly continuous, but folding and faulting and concealed intervals at critical points make it impossible to 

measure a complete stratigraphic section or to estimate the total 

thickness of the beds.

The beds exposed on the south shore of Port Graham seem to 

correspond to part of those seen on the north shore and include also

6 Grant, U. S., and Higgins, D. P., Preliminary report on the mineral resources of the 

southern part of Kenai Peninsula: U. S. Geol. Surrey Bull. 442, p. 168, 1910.

7 Martin, G. C., The western part of Kenai Peninsula:' U. S. Geol. Survey Bull. 587, pp. 

55-59, pi. 3, 1915.

8 Grant, U. S., The southeastern coast of Kenai Peninsula: U. S. Geol. Survey Bull. 

587, pp. 210-211, 227, 1915.

0 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 698-699, 

1916.
50 MESOZOIC STBATIGRAPHY OF ALASKA

beds that were not recognized across the bay, notably those that carry 

Pseudomonotis subcircularis (Gabb). The thickness of the beds 

exposed on the south shore exceeds 1,000 feet.

Age and correlation. The fossiliferous Upper Triassic rocks of 

the Kenai Peninsula, as exposed on Port Graham, are composed of 

limestone, chert, and tuff at least 1,000 feet thick. Pseudomonotis 

subcircularis (Gabb) occurs near the top of the sequence, and lower 

down a species of Halobia has been found. The former species 

indicates that at least part of the succession is of Upper Noric age 

and is to be correlated approximately with the McCarthy formation 

and with the banded chert and calcareous shale in the upper part 

of the Kamishak chert. If the Halobia is identical with the Alaskan 

and Californian species usually referred to Halobia superba Mojsisovics, it possibly indicates that the lower part of the sequence is of 

Karnic age and is to be correlated approximately with at least part 

of the Chitistone limestone of the Chitina Valley and of the Hosselkus limestone of California. The writer would suggest, however, 

that this Halobia and possibly also the one that has been obtained 

from the west coast of Cook Inlet may belong to the species which 

Stanton 10 has noted in the lower part, of the Brock shale of California or possibly to one of the species 11 that occur in the Lower 

Noric beds of Oregon. If this is the case, the occurrence of Halobia 

in these beds does hot necessarily indicate that they are the equivalent of the Chitistone limestone or that they are older than the supposed Noric strata of California.

Fossils from, limner Triassic limestone of Kenai Peninsula °

Astrocoenia? _ ___________

Nucula? _____________ _ ___ ...

Pseudomonotis subcircularis (Oabb) ____

6380 6381 6383

X

6382 6573

y

7452

X

7235

X

7234

X

10546

X

' Identified by T. W. Stanton.

6380. North side of Port Graham, latitude 59° 21' 8", longitude 151° 48'. 

U. S. Grant, 1909.

6381. South side of Port Graham, latitude 59° 20' 42", longitude 151° 49' 

45". U. S. Grant, 1909.

6383. South side of Port Graham, latitude 59° 20' 46," longitude 151°' 49' 

57". U. S. Grant, 1909.

6382. South side of Port Graham, latitude 59°' 21' 2", longitude 151° 50' 24". 

U. S. Grant, 1909.

10 Stanton, T. W., cited by Diller, J. S., U. S. Geol. Survey Geol. Atlas, Redding folio 

(No. 138), p. 5, 1906.

11 Smith, J. P., The occurrence of coral reefs in the Triassic of North America: Am. 

Jour. Sci., 4th ser., vol. 33, p. 95, 1912.
TBIASSIC, WEST COAST OF COOK INLET 51

6573. South, shore of Port Graham about a quarter of a mile northwest of 

the wharf (same locality as 6382). G. C. Martin, 1910.

7452. South shore of Port Graham 1 mile below the wharf. G. C. Martin, 

1911. v

7235. South shore of Port Graham iy2 miles below wharf. G. C. Martin, 

1911.

7234. South shore of Port Graham 1% miles below wharf. G. C. Martin, 

1911.

10546. North shore of Port Graham near mouth of small stream northeast of 

cannery. A. C. Gill, 1918.

WEST COAST OF COOK INLET 

GENERAL FEATURES

The undoubted Triassic rocks of the west coast of Cook Inlet 

include two fossiliferous Upper Triassic formations, the Kamishak 

chert and an older unnamed limestone. The local section also includes greenstone which is older than the fossiliferous Triassic rocks 

and which probably belongs in the Triassic. Beneath the greenstone is slate which is probably Paleozoic, and above the Triassic 

rocks are porphyry and tuff that are probably Lower Jurassic. The 

local sequence is indicated in the following table:

General section of Triassic and associated rocks on west coast of Cook Inlet

Lower Jurassic (?) : Porphyry and tuff. 

Upper Triassic:

Kamishak chert.

Limestone.

Triassic (?) : Greenstone. 

. Paleozoic (?) : Slate.

GREENSTONE

The greenstone of the west coast of Cook Inlet, as described by 

Martin and Katz,12 includes basic igneous rocks, chiefly of volcanic 

origin, that are considerably altered at most places. These rocks 

are probably of general occurrence in association with the Triassic 

sedimentary formations of the west coast of Cook Inlet, but only 

those in the vicinity of Iliamna Bay and Ursus Cove have been 

described in detail.

The greenstone on Cottonwood Bay is in contact with slate, which 

apparently rests upon the greenstone. The slate is nevertheless 

believed to be older than the greenstone, as it is more metamorphosed, and the local attitude of the rocks is probably due to a 

fault or an overturned fold.

12 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 38-41, 1912.
52 MESOZ01C STRATIGRAPHY OF ALASKA

The contacts of greenstone and granite were seen at many places 

on Iliamna and Cottonwood Bays, where it is clearly evident that 

the contacts are intrusive, the granite being the younger. The 

granite is probably of Lower Jurassic age, so the greenstone is 

probably Triassic or older.

The sedimentary Upper Triassic rocks of Ursus Cove, which are 

described on pages 52-54, contain much associated igneous material, 

some of which closely resembles the greenstone on Cottonwood Bay. 

This igneous material is most abundant in the lower part of the 

Ursus Cove section, the relations suggesting that the Upper Triassic 

sediments grade downward into the greenstone and that the latter 

possibly belongs within the Triassic.

The greenstone of the west coast of Cook Inlet seems to correspond in position, at least approximately, with the Nikolai greenstone of the Chitina Valley. The local section differs, however, 

from the section in the Chitina Valley, in that the greenstone of 

Cook Inlet is apparently overlain by chert beds, whereas the Nikolai 

greenstone is directly overlain by a massive limestone. This apparent difference may, however, be due to structural disturbances. 

The greenstone of this district resembles the ellipsoidal lava or 

greenstone of Seldovia Bay, which is described on pages 45-47, and 

which, like the greenstone of this district, is underlain by slaty 

rocks and apparently overlain by contorted chert.

LIMESTONE

Historical review. The Upper Triassic limestone of the west 

coast of Cook Inlet forms part of the Upper Triassic rocks of 

Cook Inlet as described by Stanton and Martin.13 It includes 

the Upper Triassic limestone of Iliamna Bay, described by Martin 

and Katz,14 and also probably includes at least part of the limestone 

tentatively referred to the Kamishak chert by the same authors.15 

A brief description and discussion of the age and correlation of this 

limestone has been published.16

Stratigraphic description. The Upper Triassic limestone of the 

west coast of Cook Inlet is best exposed on the south shore of Iliamna Bay and probably occurs also on Bruin Bay and Ursus Cove. 

The limestone on Iliamna Bay occurs in a belt about a mile wide 

but is so complexly folded that no estimate of its thickness can be

13 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska 

Peninsula: Geol. Soc. America Bull., vol. 16, p. 396, 1905.

14 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska : U. S. Geol. Survey Bull. 485, pp. 41, 43, 44, 45, 46, pi. 2, 1912.

18 Idem, pp. 47-48.

16 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 697- 

698, 1&16.
TRIASSIC, WEST COAST OP COOK INLET 53

made. The associated rocks consist of amygdaloidal basaltic tuff, 

probably of Lower Jurassic age, on the west side and granitic intrusives, younger than the limestone, on the east. The structural 

relations of the tuff to the limestone have not been determined. The 

granitic rocks are believed to be late Lower Jurassic or Middle 

Jurassic and are intrusive into the limestone.

The limestone beds on the north shore of Ursus Cove and on the 

south shore of Bruin Bay are intimately associated with the Kamishak chert and have previously been tentatively assigned 17 to that 

formation. They are discussed here because of their lithologic character and because their fauna apparently indicates a lower horizon 

than that of the Pseudomonotis-bea,i:'mg beds in the upper part of 

the Kamishak chert.

The Upper Triassic rocks of Bruin Bay are described in T. W. 

Stanton's unpublished field notes as follows:

About a mile within the entrance to the bay a peninsula on the south shore 

projects half a mile or more into the bay. On the west side of this peninsula 

there are exposures of a considerable thickness of contorted light-gray and 

banded chert, cherty limestone, and shale cut by several dikes of greenish 

igneous rock. In the cherty limestone a few fossils were found that seem to 

be a small slender Gryphaea (3094). This cherty limestone is identical in appearance with that which occurs on the left at the entrance to Seldovia Bay. 

I think it is Triassic and probably underlies the HaloMa and Pseudomonotis 

bearing shale. The limestone of 3094 is essentially a part of the banded cherty 

series and is not separable from it.

Farther around at the northeast angle of the peninsula there are beautiful 

exposures of folded and faulted cherty and slaty beds banded in black and 

white so that the structure is very prominent. The most striking feature is 

& steeply dipping sharp anticline with small faults and many narrow dikes of 

greenish igneous rock. A short distance south of these contorted beds and in 

the same continuous exposure the highly inclined black slaty beds yielded a 

few distorted specimens of a small HaloMa, (3091). These dark and banded 

Triassic beds in various portions are continuously exposed along the east side 

of the peninsula to the Indian hut about a quarter of a mile north of the south 

end of the narrow neck of the peninsula.

It is by no means certain that the limestone beds here described all 

represent the same horizon. The doubt concerning their identity and 

position is well shown b}^ the various assignments that have been 

given to them in the previous descriptions. This doubt probably 

 can not be removed without further field evidence.

The limestone of Iliamna Bay constitutes a formation that is obviously distinct from the Kamishak chert, although the two formations have not been seen in contact. The limestone of Bruin Bay is 

described above, in Stanton's field notes, as probably underlying the

17 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska : U. S. Geol. Survey Bull. 485, pp. 41, 47-48, 1912.

49448 26 5
54 MESOZOIC STRATIGRAPHY OF ALASKA

Halobia and Pseudomonotis bearing shale, but it is not certain 

whether the statement that they are " not separable " implied a belief 

in close stratigraphic relationship or a doubt concerning the feasibility of deciphering the structure. It is doubtful whether the fossils 

of lot 3091 should be referred to this limestone, for they are described as having been obtained from "black slaty beds." These 

beds are, however, obviously older than the Pseudomonotis-loe&Ting 

beds that are described on pages 55-56 as the upper member of the 

Kamishak chert. It is possible that these specimens of Halobia 

were obtained from the typical lower member of the Kamishak 

chert, which otherwise has possibly not yielded any fossils. The 

limestone bed on Ursus Cove, from which the fossils of lot 3 were 

obtained, has previously been regarded as a member of the Kamishak 

chert and may belong in that formation.

Age and correlation. The Upper Triassic limestone of the west 

coast of Cook Inlet has been observed only at places of complex 

structure and generally in close association with the Kamishak chert. 

Its exact relations to that formation are somewhat doubtful, but it 

is believed to underlie the chert. It probably contains a species of 

Halobia which resembles the Alaskan species that is usually compared with Halobia superba Mojsisovics, and which may indicate 

that the limestone corresponds in general position with the Chitistone 

limestone and is of Karnic age. The following fossils have been 

collected:

Fossils from Upper Triassic limestone of west coast of Cook Inlet °

Halobia?.. ... .- . .... ... ___ .. _ ...................

Pecten?. ..................... ............. ....... ...... ........................

Cardium?.... __ ................................... ___ ....................

2 3 3091

h

3094

b

b

o a, Identified by George H. Girty; b, identified by T. W. Stanton.

2. South shore of Iliamna Bay, 1.1 miles S. 75° W. of west end of White 

Gull Island. G. C. Martin, 1909.

3. North shore of Ursus Cove, at mouth of creek that heads near Cottonwood Bay. G. C. Martin, 1909.

3091. South shore of Bruin Bay, on east side of peninsula 1 mile inside 

entrance to bay. Black slaty beds. T. W. Stanton, 1904.

3094. South shore of Bruin Bay, on west side of peninsula 1 mile inside 

entrance to bay. Altered limestone. T. W. Stanton, 1904.
TRIASSIC, WEST COAST OF COOK INLET 55 

KAMISHAK CHERT

Historical review. The Kamishak chert constitutes part of the 

Upper Triassic rocks of the west coast of Cook Inlet as described 

by Stanton and Martin.18 This description, although nominally 

including all the Upper Triassic rocks of Cook Inlet and Alaska 

Peninsula, was based chiefly upon the occurrence of the Kamishak 

chert on Ursus Cove and Bruin Bay.

The Kamishak chert was named by Martin and Katz,19 who described all the observed occurrences on Cook Inlet and mapped its 

known distribution. Their description includes some of-the limestone beds which are believed by the writer probably to belong in 

an older formation. (See pp. 52-54.) The reference of these limestone beds to the Kamishak chert was stated,20 however, to be purely

tentative. A description and discussion of the age and correlation 

of the Kamishak chert 21 has been published.

Stratigraphic description. The Kamishak chert, which is typically 

exposed on the west shore of Kamishak Bay, crops out in a more or 

less continuous belt parallel to the west shore of Cook Inlet from 

Iliamna Bay to the vicinity of Bruin Bay.' The most characteristic exposures of the formation are on the north shore of 

Ursus Cove, where the section includes 2,000 feet or more of dark 

chert occurring in fairly massive strata interbedded with thinner 

layers of shale, sandstone, and limestone. In the lower part of the 

section there is considerable igneous material, probably partly intrusive, and also some limestone. The limestone has hitherto 22 

been tentatively included in this formation but is now assigned to the 

limestone described on pages 52-54. The following description, 

which was taken from Stanton's unpublished field notes, applies to 

the upper part of the section exposed on Ursus Cove:

These beds are much disturbed and in some places highly contorted, consisting of dark-colored, somewhat calcareous shale, banded chert, more dark 

shale, thin beds of altered limestone, and several hundred feet of greenish 

and brownish rocks that appear to be intrusive, as along the contact they include masses of the altered shale, chert, etc. There are also small dikes cutting the sediments.

Pseudomonotis was collected in the highest shale exposed near the beach 

at the entrance to the cove (locality 3086), though there are apparently stratigraphically higher beds exposed near the top of the high hill.

The total thickness of Triassic rocks exposed is probably not less than 1,000 

feet, including the intrusive masses. Of the sediments less than half may

18 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, pp. 393-396, 1905.

19 Martin, G. C., and Katz, P. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 47-50, pi. 2, 1912.

20 Idem, pp. 47-48.

21 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 697- 

698, 1916.

22 Martin, G. C., and Katz, F. J., op. cit., p. 48.
56 MESOZOIC STRATIGRAPHY OF ALASKA

be described as calcareous shale containing Pseudomonotis subcircularis (Gabb) 

and the rest are light-colored chert. Some of the banded chert and associated 

igneous rocks and limestone are very suggestive of the older series at Seldovia, 

though not quite so much altered.

The exposures on Bruin Bay also consist largely of chert, much 

of which is thin bedded and crumpled. Lime.stone is present at this 

locality also, but it possibly belongs to the older formation described 

on pages 52-54, rather than to' the Kamishak chert.

The Kamishak chert consists of banded chert, calcareous shale, and 

thin limestone in the upper part, grading downward into more massive beds of dark chert. The total thickness is at least 1,000 feet 

and probably exceeds 2,000 feet. The upper shaly and calcareous 

part of the formation contains Pseudomonotis siibcircula/ris (Gabb), 

 but the lower, more massive chert has thus far yielded no fossils.

Age and correlation.. The fossils represented in the accompanying table were obtained from beds included in the uppermost 1,000 

feet of the Kamishak chert as exposed on Ursus Cove. The fossiliferous beds, according to Stanton's description, as given on page 

55, consist largely of calcareous shale. The shale is interstratified 

with chert beds and is underlain, with apparent conformity, by 

many hundred feet of massive beds of chert that constitute, lithologically, the most characteristic part of the formation. These, chert 

beds have not thus far yielded any fossils, and consequently it is 

not safe to assume, as the writer has previously done,23 that the 

Kamishak chert is characterized by Pseudomonotis subcircularis 

(Gabb). This species is characteristic of the uppermost shaly and 

calcareous members of the Kamishak chert as that formation was 

originally defined and shows that these beds are the equivalent of 

at least part of the McCarthy formation of the Chitina Valley and 

are probably of Noric age. There is still considerable doubt, however, concerning the exact age and correlation of the lower and 

more cherty members of the Kamishak chert. There is a strong 

presumption in favor of correlating them with the chert of the 

Chitina Valley, which is described on pages 25-26. That chert, however, is likewise of somewhat doubtful age and position, although 

it apparently belongs near the base of the McCarthy formation and 

is closely associated with, even though it may not include, beds 

carrying Pseudomonotis. Chert similar to these occurs on the east 

coast of Cook Inlet (see pp. 47-49) where it has yielded no characteristic fossils and has very doubtful relations to the associated 

Triassic rocks. Similar chert occurs also on the Alaska Peninsula 

(see pp. 60-61) where it has yielded no fossils but underlies shale 

and limestone containing Pseudomonotis subcircularis (Gabb).

23 Martin, G. C., The western part of Kenai Peninsula: U. S. Geol. Survey Bull. 587, 

pp. 59, 62, 1915.
TRIASSIC, ILIAMNA LAKE . 57

Each of the localities listed below yielded Pseudomonotis subcircularis (Gabb), and 3089 also Area. These fossils were identified 

by T. W. Stanton.

3086. North shore of Ursus Cove near entrance. T. W. Stanton, 1904.

3088. North shore of Ursus Cove l3^ miles west of entrance. T. W. Stanton, 

.1904.

3089. North shore of Ursus Cove 2 miles west of entrance. T. W. Stanton, 

1904.

ILIAMNA LAKE

The Triassic rocks of Iliamna Lake and its tributaries include 

Upper Triassic limestone on the north shore of the lake, limestone of 

presumably the same age in the mountains east of the lake, and 

greenstone at several localities on the shores of both Iliamna and 

Clark Lakes, at least part of which is probably Triassic.

GEEENSTONE

The greenstone of Iliamna and Clark Lakes, as described by Martin and Katz,24 occurs in six areas of more or less altered and partly 

schistose ferromagnesian rocks, chiefly of volcanic origin but probably including intrusive masses as well as lava and tuff. The evidence concerning the age of these rocks is not strong, and there is 

considerable uncertainty both in their assignment to the Triassic and 

in the assumption that they are all of the same age. The reasons for 

referring them to the Triassic are their general similarity to' the supposed Triassic greenstones of other areas, their intrusion by granite 

rocks that, are presumably Middle or Lower Jurassic, and the local 

absence of the Paleozoic sedimentary formations that are associated 

with the Paleozoic greenstones elsewhere in Alaska.

LIMESTONE

Historical review. Fossiliferous Upper Triassic limestone is 

known in a small area on the north shore of Iliamna Lake, and limestone of probably the same age is present in the hills east of the lake. 

These occurrences have been described in detail by Martin and Katz,25 

who referred the limestone on the shore of the lake to the Upper 

Triassic on the basis of statements regarding the character of the 

fossils, furnished by G. H. Girty and J. P. Smith, which were 

quoted in the description cited. A brief account of this fauna, with

24 Martin, G. O., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 38-41, 1912. 

28 Idem, pp. 41-47.
58 MESOZOIC STRATIGRAPHY OF ALASKA

a discussion of its age and significance, has been given by Smith.26 

Martin 27 has discussed the age and correlation of this limestone.

StratigrapJiio description*. The limestone on the north shore of 

Iliamna Lake is exposed in the cliffs about 3 miles west of the mouth 

of Chekok Eiver, or just east of Millet's copper prospects, which are 

on the western edge of the limestone. The limestone belt is about 

two-thirds of a mile wide and extends from the lake shore northward over the first ridge and down to the edge of the alluviumfloored valley beyond. The thickness of the limestone has not been 

measured, but is at least several hundred feet.

The stratigraphic relations of the limestone to the neighboring 

rocks are obscure and offer little aid in determining its position. 

The adjacent rocks south of the limestone are tuffs, which have at 

their base, resting discordantly across the beveled edges of the limestone, a bed of volcanic breccia consisting of angular fragments of 

limestone in a matrix of volcanic glass. This is regarded as the local 

base of a series of volcanic beds of Tertiary age. The rocks in contact with the limestone on the east and west sides are basic igneous 

masses, which have been tentatively correlated on lithologic evidence with other volcanic rocks that are believed to be Lower 

Jurassic. The relations of the limestone to these supposed Jurassic 

volcanic rocks have not been determined.

The limestone east of Iliamna La'ke, which has yielded no fossils, 

is in contact with schist of unknown age and with basic igneous 

masses, in part tuffaceous, now altered to greenstone. This greenstone is certainly older than the Lower or Middle Jurassic granite, 

which is intrusive into it, and consequently is probably Triassic or 

older. '(See p. 57.) The greenstone appears to be younger than 

the limestone, although the exact relations have not been positively 

established. The doubtful point is whether certain rocks that are 

known to be intrusive into the limestone are an integral part of the 

main greenstone mass or are younger. Upon this point depends the 

determination of the age of the limestone. If the greenstone as a 

whole is younger than the limestone, then .the limestone is preTriassic. If, however, the basic rocks that cut the limestone are not 

part of the main greenstone mass, then there is no local proof as to 

the relative age of the limestone and greenstone, and they can be 

correlated, as the lithologic evidence seems to warrant, with the similar rocks on Iliamna Lake. This interpretation is accordingly 

adopted, even though it can not be regarded as positively established.

28 Smith., J. P., The occurrence of coral reefs in. the Triassic of North America: Am. 

Jour. Sd., 4th ser., vol. 33, pp. 92-96, 1912.

27 Martin, G. C., Triassic rocks of Alaska : Geol. Soc. America Bull., vol. 27, pp. 700, 

709, 1916.
TB-IASSIC, ILIAMNA LAKE 59

Age and correlation. The limestone is of interest because it has 

yielded a fauna of different type from any found elsewhere in 

Alaska. The only fossils obtained from this limestone were collected at a single locality on the north shore of Iliamna Lake, 3 

miles west of the mouth of Chekok River. This collection was referred to George H. Girty, who determined the fossils to be of 

Triassic age and described them 2S as follows:

The dominant types of this fauna are the corals, to which I shall refer 

later. There are in addition an echinoid spine, a large number of fragmentary and ill-preserved pelecypods, a smaller number of gastropods, which are 

likewise and for the same reason undeterminable, and two species of brachiopods. There are evidently several types among the gastropods and also among 

the pelecypods. One of the latter is marked by radiating ribs and has the general appearance of Pecten, Lima, Pseudomonotis, etc. There may be two species 

of this sort. One of the brachiopods, represented by several fragments, is 

probably a terebratuloid, but its generic affinities are doubtful. The other 

species is fairly abundant, and it is provisionally referred to Bittnerula. This 

is a rather small plicated shell with ribs also on the fold and sinus. The 

ventral valve is high and conical, with a high; area marked by longitudinal 

striae, which give the hinge a crenulated appearance. The shell substance 

is punctate. Fragments of the spiral arms can be seen on the inside. There 

are also short dental plates which converge and unite with the septum, as in

Cyrtina 

*******

and Bittnerula. All the Cyrtinas have a simple fold and sinus. 

A comparison of the corals with those described by Frech*9 from the 

Alpine Trias reveals a striking resemblance between the Alaskan forms and 

those from the Alps. This is true of the astraeid corals and is especially 

significant in the case of the spongiomorphine and tubularian forms. In 

view, therefore, of the fact that this fauna is completely unlike not only any 

Paleozoic faunas known from Alaska but any known from North America, 

and that the corals are in the main of types unknown in the Paleozoic and 

show on the contrary marked affinities with Triassic corals, I am strongly of 

the opinion that the geologic age of this fauna is Triassic, in spite of the fact 

that it is unlike any of the known Triassic faunas of Alaska. If this opinion 

is correct, the occurrence in Alaska of this coral fauna of the Alpine Trias, 

and especially the development there of the singular group of spongiomorphine 

corals, is new and important.

This collection was subsequently referred to J. P. Smith, who 

submitted the following preliminary discussion: 30

The coral fauna is certainly Upper Triassic, of the lower Noric horizon. 

The species are closely allied to the Zlambach coral fauna of the Fischerwiese locality in the Alps, which is the best Noric coral fauna known. Some 

of the species are probably identical with forms I have collected in the Upper 

Triassic, Noric horizon, of Shasta County, Calif., and are represented by 

kindred forms in the Blue Mountains of Oregon.

88 Girty, G. H., cited1 by Martin, G. C., and Kate, F. J.,, op. cit, p. 45., 

28 Frecli, Fritz, Die Korallenfauna der Trias: Palaeontographica, vol. 37, pp. 1-116, 

pla. 1-21, 1890. 

30 Smith, J. P., cited by Martin, G. C., and Katz, F, J., op. cit., pp. 45-46.
60 MESOZOIC STRATIGRAPHY OF ALASKA

These forms will have to be sectioned and studied with the microscope 

before positive identifications can be made, but the forms capable of more 

definite determination, and their probable affinities, are listed below:

Preliminary list of fossils from the limestone on Iliamna Lake

Thecosmilia cf. fenestrata Reuss (also in Shasta County, Calif.).

Isastraea cf. profunda Reuss (also in Shasta County, Calif.).

Phyllocoenia cf, incrassata Frech.

Phyllocoenia cf. decussata Reuss.

Stylophyllopsis cf. mojsvari Frech (also in Shasta County).

Astrocoenia cf. waltheri Frech (probably same as in the Noric of

Nevada).

Stylophyllopsis cf. zitteli Frech.

Heterastridium sp.? (probably the same as in Oregon). 

Spongiomorpha sp.? (probably the same as in Oregon).

A slightly different list of fossils from this locality has been 

published by Smith,31 who pointed out that these corals are reef 

builders and are related to forms that now live only in warm water.

Professor Smith correlated this fauna with that of' the coral reef 

zone in the Upper Triassic of Shasta County, Calif., and of Baker 

County, Oreg. In Shasta County this fauna occurs at the base of 

the beds that have been correlated with the Noric of Europe.32 Its 

position, relative to that of the other Triassic faunas that have been 

recognized in Alaska is below the beds containing Pseudomonotis 

subcircularis^ which belong at the top of the Noric, and above the 

beds containing Halobiai cf. H. superba, which belong in the Karnic. 

This fauna may be present, although it has not been recognized, in 

the upper part of the Chitistone limestone or in the Nizina limestone 

of the Chitina Valley, or possibly it occurs in beds that have been 

cut out by an unconformity (see p. 124) at the base of the McCarthy 

formation. The fauna may also be present on Gravina Island 

(p. TO), in the Chulitna Valley (p. 45), and on the west coast of 

Cook Inlet (p. 54).

ALASKA PENINSULA

The Upper Triassic rocks of the Alaska Peninsula, which are 

known only on Cold and Alinchak bays, include limestone and shale, 

700 feet or more in thickness, containing Pseudomonotis subcircularis (Gabb), underlain by contorted chert in which no fossils have 

been obtained. The chert is underlain by basic igneous rocks, and 

the Pseudomonotis-besiTmg beds are overlain by shale that may be 

either Triassic or Jurassic.

81 Smith, J. P.,, The occurrence of coral reefs in the Triassic of North America: Am. 

Jour. Sci., 4th sen, vol. 33, pp. 92-96, 1912.

82 Idem, p. 93.
TEIASSIC, ALASKA PENINSULA 61 

GREENSTONE

The presence of Triassic (?) greenstone beneath the Upper Triassic sedimentary rocks of the Alaska Peninsula is suggested by the 

presence on Alinchak Bay 33 of basic igneous rocks that apparently 

underlie the contorted chert beneath the shale and limestone that 

contain Pseudomonotis.

CHERT

Contorted chert that resembles the Triassic chert of Cook Inlet 

is exposed on Alinchak Bay 34 and on some of the islands in its 

mouth. The chert yielded no fossils, but its Upper Triassic age is 

indicated by the fact that it is apparently underlain by the basic 

igneous rocks described above and overlain by shale and limestone 

carrying Pseudomonotis subcirculmis. (See pp. 61-64.)

SHALE AND LIMESTONE OF COLD AND ALINCHAK BAYS

Historical review. Triassic rocks crop out in the Alaska Peninsula, as far as is now known, only in an area extending along the 

south coast from Cold Bay to Alinchak Bay. The Triassic rocks of 

this area were discovered by Pinart,35 who collected fossils at Cape 

Kekurnoi (" Nounakalkhak"), which is at the southeast entrance to 

Cold Bay. A brief account 86 of the fossils collected by Pinart was 

given by Fischer, who afterward republished the same description 

with illustrations.37 The Triassic fossils from this locality, according to Fischer, consist of a single species, which he described as 

Monotis salmario) Bronn but which has more recently been considered as being Pseudomonotis subcircularis (Gabb) or Pseudomonotis 

ochotica (Keyserling). The occurrence of Triassic fossils at this 

locality has been referred to briefly by Teller,38 who pointed out that 

they represented a species of Pseudomonotis related to Pseudomonotis ochotica (Keyserling). Mojsisovics 39 enumerated this as one of 

the known occurrences in what he described as the "Arctic-Pacific 

Trias province." The occurrence of Triassic rocks at this locality was

33 Martin, G. C., Preliminary report on petroleum in Alaska: U, S. Geol. Survey Bull. 

719, p. -38, 1921.

34 Idem, p. 58.

35 Pinart, A. L., Voyage & la c6te nord-ouest d'Amerique d'Ounalashka a Eadiak: Soc. 

geog. (Paris) Bull., 6th ser., vol. 6, pp. 561-580, 1873.

86 Fischer, P., Sur quelques fossil.es de 1'Alaska,. rapportSs par. M., A. Pinart: Compt. 

Rend., vol. 75, pp. 1784-1786, 1872,

87 Fischer, P., Sur quelques fossiles de 1'Alaska: Voyages a la c6te nord-ouest de 

I'Amgrique, pt. 1, pp. 33-36, pi. A, 1875.

38 Teller, Friedrich, Die Pelecypod-Fauna von Werchojansk in Ostsiberien: ^ Acad. imp. 

sci. St.-Petersbourg Mem., 7th ser., vol. 33, No. 6, pp. 110, 113, 115, 1886.

88 Mojsisovics, Edmund von, Arktische Triasfaunen: Acad. imp. sci. St Petersbourg 

M6m., 7th ser., vol. 33, No. 6, p. 147, 1886.

49448 26 6
62 MESOZOIC STBATTGRAPHY OF ALASKA

mentioned briefly by Dall 40 and by Martin.41 The Triassic fauna of 

Cold Bay has been discussed by Frech,42 who reexamined the fossils 

collected by Pinart and identified them as including both the typical 

form of Pseudomonotis ocKotic® (Keyserling) and also Pseudomonotis ocJwtica var. spaxricostata Teller, the latter being figured. All 

the accounts mentioned above were based upon the field observations 

and the collections of Pinart.

The Triassic outcrops on Cold and Alinchak Bays were examined 

in 1904 by Stanton and Martin, who briefly described them.48 Their 

description, however, applies to this occurrence only in a general 

way, being based chiefly upon the Cook Inlet exposures. This description was repeated by Atwood 44 in his summary of the geology 

of the Alaska Peninsula. A more complete description, based chiefly 

on unpublished information obtained by Stanton and Martin in 1904, 

has recently been published.45 Additional information, obtained by 

investigations made in 1921 and 1922, has been given by Capps 46 and 

by Smith and Baker.47

Stratigraphic description. Triassic rocks form the northeast 

shore of Cold Bay for at least half a mile inside Cape Kekurnoi and 

probably extend continuously northeastward along the shore of 

Shelikof Strait to Alinchak Bay, where they crop out for at least 

a quarter of a mile along the southwest shore of the bay and on some 

of the islands in its mouth.

The exposures at Cape Kekurnoi consist of crumpled limestone 

and calcareous shale cut by dikes and sills of basalt. Within the bay 

the dip becomes uniformly westward at angles of about 20°, the cliffs 

exposing a thickness of about TOO feet of limestone and shale similar to those at the cape. Fossils consisting exclusively of Pseudomonotis subcircularis (Gabb) are distributed through the upper half 

of the strata and were collected at several localities (3107) from a 

quarter to half a mile northwest of the cape. Similar calcareous beds 

about 100 feet above the highest noted occurrence of Pseudomonotis 

yielded a small collection (3108) of ammonites. A gradual change

40 Dall, W. H., Report on coal and lignite of Alaska: U. S., Geol. Survey Seventeenth 

Ann. Kept, pt 1, pp. 865-866, 870, 1896.

41 Martin,, G. C., The petroleum, fields of Alaska, with an account of the Bering River 

coal deposits: U. S. Geol. Survey Bull. 250, p. 51, 1905.

42 Frech, Fritz, Die zircumpacifische Trias: I/e'thaea geognostica, Teil 2, Das Mesozoicum; Band 1, Trias, p. 489, pi., 68, figs. 3a, 3b, 1908.

43 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, pp. 393-396, 1905.

** Atwood,, W. W., Geology and mineral resources of parts1 of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 46,7, pp., 30-31, 1911.

46 Martin, G. C., Preliminary report on petroleum in Alaska: U. S. Geol. Survey Bull. 

719, pp. -57-58, 1921.

"Capps, S. R., The Cold Bay district: U. S. Geol. Survey Bull, 739, pp. 91, 92-93, 

1923.

47 Smith, W. R., and Baker, A. A., The Cold Bay-Chignik district: U. S. Geol. Survey 

Bull. 755, pp. 171-172, 1924.
TRIASSIC, ALASKA PENINSULA 63

in the lithologic .character of the beds, the rocks becoming less calcareous, begins a short distance northwest of and stratigraphically 

above this locality. The beginning of this change is regarded as 

marking the top of the undoubted Triassic rocks. The overlying 

beds may also belong partly or wholly in the Triassic, but as there 

are reasons for believing that they may be at-least in part Jurassic, 

and as there is no evidence of a break within them, they will be discussed with the Jurassic rocks on page 183.

The rocks exposed on Alinchak Bay, named in order of age, are 

basic igneous rocks, contorted chert, and shale and limestone that 

contain Pseudomonotis (3129). The beds that yield Pseudomonotis 

crop out for about 500 feet along the shore. They differ in dip from 

place to place, but they are nearly everywhere steeply inclined and 

at some places reach an angle of 45°. The next exposures are a 

quarter of a mile farther up the shore and consist of Jurassic or 

possibly Triassic rocks. (See p. 184.)

Some additional information was given by Capps 48 in the following description:.

This formation includes a thickness estimated as well over 1,000 feet of 

hard, dense thin-bedded limestone and limy shale, cut by dikes and sills of 

basalt. There is evidence that some of the bodies of basalt are lava flows interbedded with the sediments, but this was not proved conclusively. Near Cape 

Kekurnoi the beds are locally much distorted and folded in several directions, 

and the included basaltic intrusives are metamorphosed and reticulated with 

a network of calcite veinlets. Farther northwest, along the shores of Cold 

Bay, the structure is less intricate, and the beds have a general northeasterly 

strike and dip 10°-20° NW. Calcite veinlets are abundant in the limestone.

Many layers of the limestone abound in fossil shells which consist almost ' 

exclusively of the single form Pseudomonotis. * * *

In proceeding northwestward along the shore of Cold Bay, and so "getting 

higher in the stratigraphic section and above the Pseudomonotis-bearing beds, 

the observer notes that the zone of limestone and calcareous shale gradually 

gives place to less calcareous and more sandy beds, and some distance farther 

northwest the sandy beds contain fossils of Jurassic age. The Upper Triassic 

beds are therefore considered to end at the point where the sandy phase begins 

to appear, but there is apparently perfect conformity -between the Triassic 

and Jurassic beds, the transition having been marked by continuous deposition but a gradual change in the character of the material deposited.

Age (md correlation. The known fauna of the Upper Triassic 

rocks of Alaska Peninsula consists practically of a single species, 

Pseudomonotis subcircularis (Gabb), which may be the same as 

Pseudomonotis ochotica (Keyserling), of the Triassic rocks of 

Europe and Asia. This species is characteristic of at least part of 

the McCarthy formation of the Chitina Valley and has been recognized at many other localities in Alaska. It indicates a horizon

48 Capps, S. E., op. cit.,, pp. 92-93. 
64 MESOZOIC STRATIGRAPHY OF ALASKA

corresponding to the uppermost Triassic of California and to the 

Noric of Europe.

This species has been found on the Alaska Peninsula only in limestone and shale, which are underlain, on Alinchak Bay, by contorted 

chert in which no fossils have thus far been found. The stratigraphic conditions are possibly similar to those on the west coast of 

Cook Inlet, where this same species is abundant in the uppermost 

shaly and calcareous members of the beds that have been referred 

to the Kamishak chert, but not in the more massive chert beds below.

Upper Triassic fossils from Alaska Peninsula °

Ammonites (undetermined).. _ . __ . .....--.-...-...... __ ........ _ ....

3107

X

3108

X

3129 10821

X

v

o Identified by T. W. Stanton.

3107. Northeast shore of Cold Bay, one-fourth to one-half mile northwest of 

Cape Kekurnoi. Upper half of 700 feet of limestone and calcareous shale. 

T. W. Stanton, 1904.

3108. Northeast shore of Cold Bay, about half a mile northwest of Cape 

Kekurnoi. Calcareous beds about 100 feet above 3107. T. W. Stanton, 1904.

3129. West shore of Alinchak Bay. Shale and limestone overlying contorted 

chert. Lawrence Martin, 1904.

10821(1-128). North shore of Cold Bay, half a mile northwest of mouth of 

bay. S. R. Capps, 1921.

KODIAK ISLAND 

CHERT AND LAVA

Some chert and lava that are probably Triassic crop out on the 

southwest coast of Kodiak Island just west of Uyak. They have 

never been described, except for brief mention in descriptions of the 

associated schist by Martin 49 and by Maddren.50

The supposed Triassic rocks of Kodiak Island include contorted 

chert and ellipsoidal lava, which are identical in character with 

the chert and lava of Seldovia, described on pages 45-49. They 

resemble the rocks at Seldovia in that the chert and lava are intimately but obscurely associated with each other, and also in occurring 

between a belt of quartzitic schist, crystalline limestone, and chloritic schist and a belt of slate and graywacke.51 The chert at Uyak 

has yielded no fossils but can nevertheless be confidently correlated

49 Martin, G. C., Mineral deposits of Kodiak and the neighboring islands: U. S. Geol. 

Survey Bull. 542, p. 128, 1913.

. M Maddren, A. G., The beach placers of the west coast of Kodiak Island: TJ. S. Geol. 

Survey Bull. 692, p. 301, 1919.

61 Martin, G., C., The .western part of Kenai Peninsula: U. S. Geol. Survey Bull. 587- 

pp. 44, 60-63, pi. 3, 1915.
TRIASSIC, SOUTHEASTERN ALASKA 65

with that at Seldovia on the basis of the striking similarity in 

lithologic character and sequence.

SOUTHEASTERN ALASKA 

GENERAL FEATUEES

Upper Triassic rocks occ'ur in several small widely distributed 

areas in southeastern Alaska. They have been recognized at the 

south end of Gravina Island; possibly on Prince of Wales, Annette, 

and Revillagigedo Islands; on the Screen Islands; at Hamilton Bay 

and other neighboring localities on Kupreanof and Kuiu Islands 

and Keku Islets, near the north end of Keku Strait; at several localities on the southeast shore at Admiralty Island; and near Juneau. 

At most of these localities the Triassic rocks consist largely of limestone that occurs in close geographic and structural association with 

Carboniferous and Devonian limestones. As these Paleozoic limestones are widely distributed in southeastern Alaska, as most of their 

known occurrences are at localities where the structure is complex 

and the available information is scanty, and as none of the known 

occurrences of Triassic rocks were recognized in the earlier reconnaissance surveys, it is possible that additional Triassic localities will 

be found.

The Triassic rocks of southeastern Alaska consist chiefly of limestone having a thickness of apparently only a few hundred feet. A 

basal conglomerate has been recognized at several localities. The 

underlying rocks are Permian, except on Gravina Island and at some 

places on Keku Strait, where they are Devonian, and at Juneau, 

where they are of unknown age. On Keku Strait the Triassic limestone is underlain locally by ellipsoidal lava, which bears a close 

resemblance to the lava that underlies the Upper Triassic limestone 

at many other Alaskan localities. This lava probably overlies Permian limestone. It is possible that much of the greenstone of southeastern Alaska belongs in this position.

The Triassic limestone of southeastern Alaska in general yields 

faunas containing Halobia cf. H. superba Mojsisovics, and consequently seems to correspond, at least approximately, in position to 

the Chitistone limestone, although these faunas contain elements 

which are not known in the Ghitistone fauna and which may indicate 

either a slightly different horizon or another f acies of deposits of the 

same age. For example, the fossils from Hamilton Bay, near the 

north end of Keku Strait, include species related to Spiriferma 

borealis Whiteaves and Trachyceras (Dawsonites) canadense 

Whiteaves, which are elsewhere known only in the Triassic rocks of 

Liard Kiver, British Columbia, and of Bear Island, between Norway and Spitzbergen, and which are believed to be slightly older
66

than the Hcdobia-be&Tnig beds. Some of the limestone on Keku 

Strait also contains ammonites that are suggestive of the Middle 

Triassic. . The Triassic rocks of the Juneau district contain HaloMa cf. H. 

superba, but differ from most of the other Halobia-bearing beds of 

Alaska in consisting chiefly of volcanic material.

The Triassic rocks of Gravina Island, which contain only a small 

proportion of limestone, consisting chiefly of conglomerate and shale, 

carry a fauna that, although including a species of Halobia resembling Halobia superba Mojsisovics, is of a somewhat different type 

from the other recognized Alaskan Triassic faunas. The abundant 

corals in some of the limestone beds on Gravina Island suggest the 

Lower Noric coral fauna of Iliamna Lake.

It is only at Hamilton Bay and on Admiralty Island that Pseudomonotis subeircularis (Gabb), indicative of the boreal Upper Noric, 

has been found. At Hamilton Bay, where the strata are overturned, 

the Pseudomonotis zone is separated from the Halobia zone by a 

conglomerate that suggests an unconformity corresponding to the 

one for which the writer believes there is strong evidence at the base 

of the Pseudomonotis zone in the western part of the Chitina Valley 

and at Skolai Pass. The beds containing Pseudomonotis near Hamilton Bay, according to Buddington, are intercalated with ellipsoidal 

lava.

Other volcanic rocks at localities on Keku Strait near Hamilton 

Bay are interbedded with limestone and calcareous sandstone that 

contain a Triassic fauna of a very different type from any that has 

been found elsewhere in America. The beds that contain this fauna 

have not been found in contact with either the \5ToiZ0 frwr-bearing or 

the Pseudomonotis-be&rmg rocks. They might be correlated either 

with the volcanic rocks that lie beneath the .fifofo&m-bearing beds or 

with the lava which Buddington believes is interstratified with the 

Pseudomonotis-besiYnig beds. The evidence from the fossils is not 

conclusive but is suggestive of a horizon near the top of the Triassic.

On Admiralty Island there is a contorted chert that is somewhat 

similar to the Upper Triassic chert of Cook Inlet. It apparently 

overlies the Triassic limestone, but has yielded no fossils and may 

not be Triassic.

The top of the Triassic beds of southeastern Alaska has not been 

recognized except on Gravina Island, where the Triassic rocks are 

overlain by volcanic beds that are believed to be Lower or Middle 

Jurassic, and at Juneau, where they are overlain by volcanic beds 

that may also be Jurassic, but it is probably marked by a great unconformity, for the next younger sedimentary rocks known at most 

places are Upper Jurassic or Lower Cretaceous.
TRIASSIC, SOUTHEASTERN ALASKA 67 

CONGLOMERATE, LIMESTONE, SANDSTONE, AND SLATE OF GRAVINA ISLAND

Historical review. The rocks of Gravina Island that are now 

known to be of Upper Triassic age were first described by Brooks,52 

who named them the " Gravina series " and at first referred them to 

the Cretaceous, on the basis of a correlation with the somewhat similar rocks of the Queen Charlotte Islands. His later conclusion M 

was that " on reviewing the evidence its identity with the Vancouver 

series (Triassic) seems equally probable."

These rocks were mapped by F. E. and C. W. Wright 5 * as " undifferentiated Paleozoic " but were not described except in the statement 55 that fossils, which were provisionally referred to the early 

Carboniferous but which "may represent a Triassic horizon," were 

found in beds of calcareous schist. These authors also quoted a 

statement prepared by G. H. Girty giving a list and discussion of 

these fossils. Brief mention of the fossiliferous beds 3 miles north 

of Ball Head has been made also by C. W. Wright,56 who mapped 

these rocks as undifferentiated Paleozoic.

These rocks were first referred definitely to the Triassic by Smith, 

who collected fossils of undoubted Upper Triassic age and who described the fossiliferous and associated beds in considerable detail.57 

His account of these rocks includes detailed descriptions of the 

exposures and lists of fossils determined by Stanton. The rocks on 

the east coast of Gravina Island, described by Smith as Triassic, 

include the conglomerate, graywacke, and slate that were subsequently referred to the Upper Jurassic or Lower Cretaceous.

A description of the Triassic rocks of Gravina Island by Martin 5S 

includes brief mention of the lithology, fauna, and stratigraphic 

relations of the beds, based in part on his own field observations and 

in part on the description by Smith.

Some Triassic crinoids from the west coast of Gravina Island, 

collected by the writer and Theodore Chapin, have been described 

and figured" by F. A. Bather.59

M Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska,, with 

an introductory sketch of the geology of southeastern Alaska: U. S. Qeol. Surrey Prof. 

Paper 1, pp. 25, 40, 45, 52, 69, pi. 2, 1902.

M Brooks, A. H., The geography and geology of Alaska: TJ. S. Geol. Survey Prof., Paper 

45, p. 226, 1906.

"Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pis. 1, 2,; 1908.

K Idem, pp., 52-53.

88 Wright, C. W., Geology and ore deposits of Copper Mountain; and Kasaan Peninsula, 

Alaska: U. S. Geol. Survey Prof. Paper 87, p. 18, pi. 1, 1915,

67 Smith, P. S., Notea on the geology of Gravina Island, Alaska: U. S. Geol. Survey, 

Prof. Paper 95, pp. 100-104, 1915.

68 Martin, G, C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 

700-701, tables opp. pp. 687, 716, 1916.

68 Bather, F. A., The Triassic crinoids from New Zealand collected by Dr. C. T. 

Trechmann: Geol. Soc. London Quart. Jour., vol. 73, pp. 247-256, 1917.
68 MESOZOIC STRATIGRAPHY OF ALASKA

The description of the Triassic rocks of Gravina Island by 

Chapin 60 includes discussions of the distribution and character, 

structure, stratigraphic relations, origin, and age and correlation of 

the rocks of Gravina Island that are here referred to the Triassic 

and also of some more metamorphosed unfossiliferous rocks on 

Eevillagigedo Island which Chapin correlated with them on the basis 

of lithologic similarity and structural relations. The account contains lists of fossils identified by T. W. Stanton and J. B. Reeside.

/Stratigraphic description. The Mesozoic rocks of Gravina Island 

include the Upper Triassic and Jurassic or Cretaceous beds represented in the following section:

Section of Mesozoic rocks on Gravina Island

Feet 

Lower Cretaceous (?) : Conglomerate, graywacke, and

black slate with Belemnites____________________ 800±

Upper Jurassic (?) : Slate and limestone interbedded with

tuff and containing Aucella. 1,200±

Lower or Middle Jurassic (?) : Breccia, tuff, and lava____ 

Upper Triassic:

Black slate with thin beds of limestone and sandstone 

and some conglomerate ______________

Massive limestone __________________

Black slate interbedded with some graywacke and '

limestone __ 

 Massive conglomerate with limestone lenses_____ 

Unconformity (Devonian limestone beneath).

The Upper Triassic rocks of Gravina Island are underlain unconformably by Devonian limestone. They are overlain, with apparent conformity according to Chapin,61 but with probable unconformity according to Smith,62 by the breccias, lava, and tuff which 

the writer refers tentatively to the Lower or Middle Jurassic. The 

breccia, lava, and tuff were referred by Smith 63 to the Jurassic or 

Cretaceous because of their lithologic resemblance to the supposed 

Upper Jurassic or Lower Cretaceous augite melaphyre in the region 

north of Juneau. They were referred by Chapin 64 to the Upper 

Triassic and Jurassic because they grade upward with apparent 

conformity into tuff interbedded with slate and limestone which 

have yielded specimens of Aucella that are " probably Upper Jurassic or possibly Lower Cretaceous " and because he regarded them as

80 Chapin, Theodore, The structure and stratigraphy of Gravina Island, Alaska: U. S. 

Geol., Survey Prof. Paper 120, pp. 89-95, 1918. a

61 Chapin, Theodore, The structure and stratigraphy of Gravina and Revillagigedo 

Islands, Alaska: U. S. Geol. Survey Prof. Paper 120, pp. 95, 96, 1918.

62 Smith, P. S., Notes on the geology of Gravina Island, Alaska: U. S. Geol. Survey 

Prof. Paper 95, pp. 104-105, 1915. 

<»Idem, pp. 104-105. 

64 Chapin, Theodore, op. cit., pp. 95-97.
TRIASSIC, SOUTHEASTER ALASKA 69

equivalent to the black slate and schistone tuff at Ketchikan, which 

he correlated with the Upper Triassic slate and greenstone at Juneau. 

The following description of the Upper Triassic rocks of Gravina 

Island is chiefly quoted from the description by Chapin.65

The Upper Triassic rocks on Gravina Island comprise a conformable series 

of conglomerates, limestones, sandstones, and slates about 1,600 feet thick. 

They are most typically exposed on the southwest coast of the island, where 

they occupy a narrow belt that extends from a small cove opposite Dall Bay 

northwestward for about 7 miles.

The Upper Triassic rocks fall naturally into three main divisions one 

composed essentially of conglomerate, one essentially of limestone, and one 

of interbedded black slate, sandstone, conglomerate, and limestone. These 

three conformable terranes are shown by fossils to be probably Upper Triassic. 

Overlying the Upper Triassic sediments, with apparent conformity, are volcanic agglomerates, breccias, and lavas which are overlain by tuffs, slates, 

and limestones containing fossils of Upper Jurassic or Lower Cretaceous age.

The exposed basal member of the series on Gravina Island is a coarse conglomerate that extends along the southwest coast of the island from Conglomerate Point northwestward to Open Bay and occupies three narrow strips 

whose continuity is broken by Fivemile Cove, Thompson Cove, and Threemile 

Cove. The conglomerate is a heavily bedded, massive rock. The boulders are 

essentially of angular coarse-grained granite resembling the granite of Annette 

Island, and the matrix is quartz-feldspar sand presumably derived from the 

same source as the boulders. Intercalated with the coarse conglomerate are 

thin beds of sandstone, which are composed of the same material as the matrix 

of the conglomerate, and gradation al beds of grits. Thin beds of fossiliferous 

limestone and black slate with pronounced cleavage occur sparingly. The 

conglomerate and intercalated sandstone beds are strongly indurated and 

break with prominent fractures across the boulders.

On a small cove south of Threemile Cove 66 the conglomerate is finer grained 

toward the top and passes upward into grits, sandstone, and slate which are 

overlain by a large block of fossiliferous massive limestone. There has been 

some movement along this contact, so that the relations are confused, but the 

limestone is apparently above the conglomerate and sandstone. On Thompson 

Cove the conformable relations of the limestones to the conglomerate, sandstone, and slate are more evident, although here also there has been some 

faulting.

In the upper part of the conglomerate the beds are thinner and the material 

is much finer grained and contains more sandstone, slate, and thin beds of 

limestone, which are conformably overlain by the massive limestone.

The limestone varies in appearance from place to place. On Thompson Cove 

and Open Bay it is a soft gray fossiliferous rock, corals being especially 

abundant. On Threemile Cove it is more closely folded, is considerably 

silicified, and weathers out brick red. The limestone here is less fossiliferous, 

and the fossils are poorly preserved. The greater amount of deformation of 

the limestones on Threemile Cove is probably the result of contact metamorphism induced by the intrusive rocks of Dall Head.

The massive limestone is conformably overlain by a great thickness of 

black slate with intercalated beds of conglomerate, sandstone, and limestone.

CB Chapin, Theodore, op. cit, p. 90.

08 Threemile cove has appeared in the literature as "cove 3 miles north of Dall Head."
70 MESOZOIC STBATIGBAPHY OF ALASKA

These beds crop out along the coast of Gravina Island for a distance of about 

3 miles north of the limestone area and extend to the high hills of Dall Ridge 

north of Dall Head. Similar rocks are exposed on Bostwick Inlet and Seal 

Cove and extend northwestward in a belt from 2 to 3 miles wide to Vallenar 

Bay and North Vallenar Point.

The dominant rocks of this series are black clay slates having a pronounced 

cleavage. Intercalated with the slate are thin beds of quartz sandstone, 

quartzite, and conglomerate sandstone. The limestone beds are not numerous 

but are usually fossiliferous. The interbedded limestone layers are about 20 

to 30 feet in thickness but appear to be lenticular.

The black slate and associated sediments are closely folded, especially on 

Threemile Cove, where the beds are thrown into sharp contorted folds. The 

beds on Vallenar Bay are much more regular and show none of the close 

folding.

Age and correlation. The Upper Triassic rocks of Gravina Island 

have yielded the fossils listed in the following table. The complex 

structure and the discontinuity of exposures make it impossible to 

determine the precise sequence of all the fossil localities, but it is 

believed that the localities are arranged in the table approximately 

in stratigraphic sequence, the oldest at the left. The fossils- of lot 

9899 were obtained from narrow bands of limestone interbedded 

with the basal conglomerate. The massive limestone and the beds 

between it and the basal conglomerate are believed to have yielded 

lots 9535, 8832, 8831, 8830, 9531, and 9536. The thin-bedded limestone and intercalated slate overlying the massive limestone probably yielded lots 8835, 8834, 8829, 9900, 10097, 112, 9537, 9538, 9534, 

121, and 8836. The slate and limestone in the upper part of the 

sequence are believed to have yielded lots 9532, 9533, 8704, 8705, 

and 124.

The fossils are not well preserved and most of the collections, except those containing Halobiai cf. H. superba, are not characteristic 

even of the Triassic. The fossils suggest, however, that two distinct 

faunas may be present. The limestone members contain abundant 

corals with a variety of other fossils, including crinoids, brachiopods, 

and mollusks, among which are no species, except the corals, that 

have been recognized in any of the other Alaskan Triassic faunas. 

The corals apparently belong to the Lower Noric fauna that is found 

in the Triassic limestone of Iliamna Lake. (See pp. 59-60.) Concerning the fossils in lot 9900 Reeside 67 said: "These forms are 

apparently of the Upper Triassic coral fauna referred by J. P. 

Smith to the Noric." Another collection which contains fossils that 

are different from those in most of the Triassic rocks of Alaska, 

although it includes some characteristic Triassic genera, is lot 8836, 

concerning which Stanton 68 said: " This assemblage suggests the

67 Reeslde, J. B., cited by Chapln, Theodore, The structure and stratigraphy of Gravina 

and Revdllagigedo islands: U. S. Geol. Survey Prof, Paper 120, p. &3, 1918. 

88 Stanton, T. W., cited by Chapin, Theodore, idemi, p. 94.
TRIASSIC, SOUTHEASTERN ALASKA 71

fauna of the lower part of the Modin formation in California, which 

was tentatively assigned to the Jurassic."

The slate that apparently overlies the coral-bearing limestone contains Halobia cf. H. superba Mojsisovics, which suggests an approximate correlation with the Chitistone limestone and indicates a lower 

horizon than the coral fauna. It is possible that the Triassic rocks 

of Gravina Island are inverted or that some of the species have a 

different range in Alaska from that which has been recognized in 

other regions.

Upper Tri&ssic fosstts from Qravina Islwnd a

Isastraea cf. I. proThamnastraea cf. T. 

rectilamellosa Winkler. .... .... .

Undetermined corals _ Hydrozoan _____

Isocrinus gravinae 

Bather-. ... .

Cidaris? . ... 

Rhynchonella? .......

Undetermined braHalobia cf. H. suHalobia _____ . ...

Halobia? . .

Myophoiia _ .... ....

Myophoria? .... .

Myophoria or Trigonia _______ .

Pecten?... ___ .....

Plicatula? ..... ...

Astarte?........ ......

Undetermined peleMurchisonia? . .......

Turbo?......... __ ..

Pseudomelania? ......

Purpurina?? _ ......

Natica?. .............

Turritella?. ... ...

Cerithium?... _ . ...

Undetermined gasTrachyceras? (small

Arcestes? .............

Arcestes?? (fragment)

Undetermined amI

...

b

iO5

...

N

CO°S

oo

a

rH

...

g

COCO

a

a

a

H 

1

a

CO

CO§

a

a

a

IQ

a

a

a

a

I

a

a

a

8 

g

a

I

b

b

b

b"

b

b

I

a

a

(EMK)

a

cJ

*H

...

a

N

S?

o>

a

a

£ §

...

 *

CO'S

a

>HM

a

c,

<o

CO%

...

a

a

a

a

N

CO 1Oo>

...

CO 

CO

g

...

a

a

I

...

1 £5

...

a

%?}

i

 a, Identified by T. W. Stanton; b, identified by J. B. Reeslde; c, identified by F. A. Bather.
72 MESOZOIC STRATIGRAPHY OP ALASKA

9899 (16 ACh 136). Threemile Cove, north shore, just west of low gap leading northward to Thompson Cove. Limestone lenses in massive conglomerate. 

Theodore Chapin, 1916.

9535 (15 ACh 123). Thompson Cove, north shore. Black slate interbedded 

with graywacke and limestone and overlying the massive conglomerate exposed 

at the mouth of the cove. Theodore Chapin, 1915.

8832 (4). Near south foreland on south arm of Threemile Cove. Near contact with conglomerate. G. C. Martin, 1914.

8831 (3). South arm of Threemile Cove, on shore east of wooded island. 

Large limestone nodule in conglomerate. G. C. Martin, 1914.

8830 (2). South arm of Threemile Cove. Massive limestone outcrop near 

anchorage behind wooded island, apparently at least 100 or 200 feet above 

8834. G. C. Martin, 1914.

9531 (15 ACh 111). Inlet 2% miles north of Dall Head. Massive gray limestone beds near the head of the inlet. At the mouth of the inlet is massive 

conglomerate, which passes up into sandstone and slate. The limestone overlies the slate apparently conformably, although the slate is crumpled, and the 

relations are not evident. Theodore Chapin, 1915.

9536 (15 ACh 129). Open Bay, 5 miles north of Dall Head. Thin bedded 

limestone apparently overlying the massive conglomerate exposed along the 

west coast of Gravina Island. The limestone is blue and weathers brown. 

Interbedded with it is black slate. Theodore Chapin, 1915.

8835 (7). Reef west of cabin on north arm of Threemile Cove. Thin-bedded 

limestone interstratifled with shale, about 20 or 30 feet below 8834. G. C. 

Martin, 1914.

8834 (6). North arm of Threemile Cove. Massive limestone in reef west of 

cabin, 20 or 30 feet above 8835. G. C. Martin, 1914.

8829 (1). North arm of Threemile Cove. Float on outcrop of shale and thin 

limestone beds of localities 8834 and 8835. G. C. Martin, 1914.

9900 (16 ACh 137). Threemile Cove, east shore, 200 yards north of low pass 

leading to east coast of island. Lenses of limestone interbedded with black 

slates. Theodore Chapin, 1916.

10097. Threemile Cove. Lenticular limestone interbedded with slate. Edwin

Kirk, 1917.

(EMK). "Cove 3 miles north of Dall Head." Exact locality not known. 

E. M. Kindle (?), 1906.

 (15 ACh 112). Threemile Cove, 300 yards north of 15 ACh 111. Thin 

beds of limestone interbedded with conglomeratic sandstone and slate. These 

beds are believed to overlie the massive gray limestone (15 ACh 111). Their 

relations, however, are concealed. Theodore Chapin, 1915.

9537 (15 ACh 130). Open Bay, 5 miles north of Dall Head. From same 

locality but from beds overlying those of 9536 conformably. Theodore Chapin, 

1915.

9538 (15 ACh 132). Open Bay, 5 miles north of Dall Head, immediately north 

of 15 ACh 130. Overlying the beds at 15 ACh 130 a conglomerate occurs 

which grades into an impure gritty limestone with quartz and limestone pebbles 

and many fossils at 15 ACh 132. These conglomeratic beds pass upward into 

black slate. Theodore Chapin, 1915.

9534 (15 ACh 122). Northeast shore of Thompson Cove. Small fault block 

adjoining that of 15 ACh 121. Theodore Chapin, 1915.

 (15 ACh 121). Northeast shore of Thompson Cove. Small fault block 

of limestone. Theodore Chapin, 1915.

8836 (8). West shore of Bostwick Inlet near entrance. Angular nodules in 

a brecciated (?) nodular limestone. G. C. Martin, 1914.
TRIASSIC, SOUTHEASTERN ALASKA- 73

9532 (15 ACh 113). Threemile Cove, 300 yards southeast of north end of cove 

and about 700'yards north of 15 ACh 112. Black slate and limestone, apparently overlying the rocks of 15 ACh 111 and 112 and the red-weathering gritty 

limestone. Theodore Chapin, 1915.

9533 (15 ACh 115). Thompson Cove. HaloUa, slate similar to that at 15 

ACh 113. At this locality it occupies a fault block on the south arm of the 

 cove and lies between conglomerate and nodular limestone. Theodore Chapin, 

1915.

8704. Threemile Cove, " north of the center of the small bay on the northern 

limb of the appressed pitching syncline." Probably about 100 feet above 8834. 

P. S. Smith, 1913.

8705. Open Bay. P. S. Smith, 1913.

 (15 ACh 124). Dall Ridge, one-fourth mile northeast of Thompson Cove. 

Thin beds of limestone apparently interbedded with sandstone and slate. 

Theodore Chapin, 1915.

TB.IASSIC (?) ROCKS OF PRINCE OF WALES, ANNETTE, AND REVILLAGIGEDO

ISLANDS

The presence of Triassic rocks is suspected but not definitely established at various localities in the Ketchikan district, notably on 

Prince of Wales, Annette, and Revillagigedo Islands. The following information concerning these localities is taken from a manuscript report by Chapin: 69

Conglomerate, sandstone, and slate on Annette Island are probably the 

equivalent of the Gravina Island sedimentary formations and may include both 

Triassic and Upper Jurassic or Cretaceous.

Small areas of conglomerate, sandstone, and black slate that occur on Hotspur Island are believed to be Upper Triassic. They unconformably overlie 

the Middle Devonian limestone and greenstone and occupy the flanks of a 

.very closely compressed anticline with the Middle Devonian beds exposed along 

the crest of the fold. The only fossils which these sediments yielded are 

some Favosites in the limestone boulders included in the conglomerate. On 

lithologic similarity, these sediments are regarded as Upper Triassic and correlated with similar rocks on Gravina Island.

A small area of conglomerate, sandstone, and black slate that occurs on 

Hunter Bay resembles the Triassic rocks of Gravina Island. These sediments 

unconformably overlie the Middle Devonian greenstone but are very closely 

folded with Paleozoic rocks, from which they were not differentiated in the 

.mapping. The only fossils found in these beds were boulders of Devonian limestone, found in the conglomerate. Other rocks regarded as possibly Triassic 

are some shales infolded with Middle Devonian limestone .on Clover Bay on 

Prince of Wales Island. These beds contain fossils determined as "possibly 

Triassic or later."

Clover Bay is a small indentation 4 or 5 miles north of the mouth of Cholmondeley Sound on Prince of Wales Island. A small mass of fossiliferous 

limestone and other sediments too small to map occurs near the head of the 

bay inclosed within a mass of intrusive quartz diorite. These rocks comprise 

beds of conglomerate, graywacke, argillite, and limestone, which strike N. 60° 

W. and stand at a steep angle. The following sequence of rocks is exposed:

88 Chapin, Theodore, The Ketchikan district: U. S. Geol. Survey Bull. (in preparation).
74 MESOZOIG STRATIGRAPHY OF ALASKA

Apparent section on Clover Bay, Prince of Wales Island

Quartz diorite. . Feet 

. Limestone with Middle Devonian fossils_______ _ 15 

Conglomerate graywacke with fossils, probably Triassic?

(lot 152)_______________________.______ 12 

Concealed _______________________________ .. 25

Argillite ________________________________ 20 

Limestone with Middle Devonian fossils_______________ 10

Argillite __________________________________ 10 

Graywacke _______ _____________________ 30

Concealed __________________________..__ 43

Graywacke with fossils, probably Triassic (lot 9539)____ 10 

Limestone with Middle Devonian fossils.,____________ 22 

Graywacke ___ ________________ _______ 17

Argillites with dikes of quartz diorite________ _..______ 43

Quartz diorite.

In the field this section was regarded as consisting of intcrbedded limestone 

and graywacke, but upon the fossil evidence it appears that the limestone is 

Middle Devonian and that the graywacke is probably Mesozoic and therefore 

younger. * * * The beds are closely folded and overturned. The Middle 

Devonian limestone comes to the surface along the crests of the anticlines and 

is overlain by the younger sediments which occupy the synclines.

On the east side of the mouth of Klakas Inlet extending from Klinkwan 

"Village to Tab Bay is an unmapped area of conglomerate and black slate with 

a little sandstone, which unconformably overlie the Middle Devonian greenstone and tuff. The base of the formation is conglomerate carrying limestone 

boulders that contain Middle Devonian fossils, and overlying the conglomerate 

are black slate and sandstone. The age of these rocks is not clear. They may 

possibly be correlated with sediments that occur in the upper part of the Middle Devonian, or they may be younger rocks. If Middle Devonian they mark 

an unconformity which was not recognized elsewhere. In general appearance 

they resemble "the Triassic rocks of Gravina Island more than they do any 

known Middle Devonian rocks, and they may be Triassic. On the map these 

rocks were not differentiated from the Devonian sediments which they overlie.

Greenstone which Chapin described as " schistose green tuff " and 

referred to the " Upper Triassic or Jurassic " is present on Revillagigedo Island near Ketchikan and on the opposite shores of Tongass 

Narrows. This schistose green tuff was called " greenstone schist" 

by Brooks 70 and the " green schist near Ketchikan " by Smith 71 and 

was regarded by both as Paleozoic. According to Chapin's interpretation of the structure of Gravina and Revillagigedo islands the 

tuff stratigraphically overlies the massive igneous rocks that carry 

Jurassic fossils and occupies a position near the top of the formation. 

Its schistose nature he believed to be due to contact metamorphism 

induced by the intrusive masses of Revillagigedo Island, as indi-

*° Brooks, A. H., Preliminary report on the Ketchikan mining district. Alaska: U. S. 

Geol. Survey Prof., Paper 1, p. 48, 1902.

71 Smith, P. S., Notes on the geology of Gravina Island, Alaska: U. S. Geol. Survey 

Prof. Paper 95, p. 100, 1915.
TRIASSIC, SOUTHEASTERN ALASKA 75

cated by the increase of schistosity toward the igneous rocks on the 

northeast. Chapin 72 described these rocks as follows:

The black slates and green bedded tuffs are best developed along the north 

shore of Tongass Narrows from Ketchikan to Mountain Point. The black 

slates are in places considerably metamorphosed and schistose and might more 

correctly be called phyllites. They are closely interbedded with and grade into 

fissile green tuffs, both of which are interbedded with more massive tuffs. 

The green tuffs are also schistose and in places completely recrystallized. The 

greater part of the town of Ketchikan stands on rocks of this character, and 

excavations for street building show both the blocky and fissile types. The 

most schistose types are completely recrystallized and consist of secondary 

quartz, feldspar, calcite, epidote, and chloritic material. The massive types 

consist essentially of secondary epidote, hornblende, chlorite, sericite, and 

calcite, with pyroxene and plagioclase feldspar crystals almost entirely replaced 

by secondary minerals.

The greenstone of Tongass Narrows was referred to the Mesozoic 

by Chapin on the basis of an assumption concerning its structural 

relations to the Mesozoic rocks of the west and south coasts of 

Gravina Island and on the basis of a correlation witli the Mesozoic 

greenstones near Juneau. The evidence for its assignment to the 

Mesozoic, in the writer's opinion, is weak, and it may with equal 

confidence be referred to the Carboniferous or Devonian.

The supposed Mesozoic rocks of Annette and Hotspur islands 

have yielded no conclusive evidence as to their age, but there is no 

special reason to doubt that they are Mesozoic.

The supposed Triassic rocks of Prince of Wales Island have 

yielded a few fossils concerning which T. W. Stanton has submitted 

the following statement: .

9539 (15 ACh 154). Head of 'Clover Bay, Prince of Wales Island. Small 

block of limestone inclosed in granite: 

Rhynchonella? sp. 

Pelecypod fragments. 

. Possibly Triassic or later. Fossils not diagnostic.

9540 (15 ACh 199). Klakas Inlet, west coast of Prince of Wales Island, opposite Max Cove:

No determinable fossils.

9541 (15 ACh 202). Max Cove, Klakas Inlet, west coast of Prince of Wales 

Island:

Several obscure undetermined corals. 

Triassic or older.

9542 (15 ACh 206). East shore of Keete Inlet, west coast of Prince of Wales 

Island, 1% miles from head of inlet. Limestone interbedded with green slate 

and andesite:

Fragments and obscure imprints of pelecypods, mostly Aviculidae. 

Triassic or older. .

73 Chapin, Theodore,, The structure and stratigraphy of Gravina and Revillagigedo 

islands, Alaska: U. S. Geol. Survey Prof. Paper 120, pp. 95-96, 1918.
76 MESOZOIG STRATIGRAPHY OF ALASKA

TRIASSIC (?) LIMESTONE OF SCREEN ISLANDS

Historical review. The occurrence of Triassic limestone on the 

Screen Islands, which are situated in Clarence Strait near the west 

coast of Etolin Island, was first suggested by F. E. and C. W. 

Wright,73 who enumerated this as one of the localities of Triassic 

" gray argillaceous limestone, fossiliferous calcareous sandstone, conglomerate." A brief description of the rocks at this locality has 

been given by A. F. Buddington.74

StratigmpMc description. Thick-bedded limestone and conglomerate, in a highly disturbed condition, form the Screen Islands, off 

the west coast of Etolin Island, in Clarence Strait. These beds 

comprise two limestone formations separated by a thick and massive conglomerate; the upper limestone and the conglomerate are 

probably Triassic, and the lower limestone may be Carboniferous. 

On the northernmost island, according to Buddington, beds about 

900 feet thick are exposed, comprising limestone with intercalated 

beds of coarse conglomerate and conglomeratic and sandy limestone about 200 feet thick. The cobbles and pebbles in the conglomerate are predominantly chert and limestone, with some rhyolite porphyry and greenstone.

The section exposed on the Screen Islands, according to the unpublished field notes of E. M. Kindle, is as follows:

Section of Triassic (f) and Carboniferous (?) roclcs on Screen Islands

Feet

1. Conglomerate bands in much wider bands of blue-gray 

limestone__________ ________________ 50

2. Dark-gray hard limestone. Fossils (lot 22G) from lower 

35 feet____________________________ 400

3. Covered ______________________________ 50

4. Black, rather soft shale _ 50

5. Dark-gray to blackish limestone; few small pebbles

(partly covered) ____ 110

6. Conglomerate, containing large limestone pebbles full of 

Carboniferous fossils (lot 22C) and other pebbles, interbedded with bands of hard blue limestone 1 to 3 

feet thick____'_______________________ 140

7. Dark-gray to buff limestone, with large Spirifer at base-_ 50

8. Black argillaceous limestone, with fossils (lot 22A)____ 160

Age and correlation. The lower limestone, which is exposed .on 

the more northerly islands, yielded the Carboniferous (?) fossils 

collected by the writer in 1914, of which G. H. Girty says:

73 Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska : 

U. S. Geol. Survey Bull. 347, p. 34, 1908.

74 Buddington, A. F., Mineral deposits of the Wrangell district, southeastern Alaska: 

U. S. Geol. Survey Bull. 739, p. -33, 1922.
TRIASSIC, SOUTHEASTERN ALASKA 77

Intrinsically they might be Carboniferous, but they are so unlike the usual 

run of Alaskan Carboniferous faunas that I am disposed to think that they 

may be Triassic. I have provisionally identified the following species: 

Lot 12. Next to the northernmost of Screen Islands: 

Pseudomonotis sp. 

Aviculopecten ? aft'. A. fasciculatus. 

Pleurotomaria? sp.

Kindle also obtained from the lower limestone (bed 8 of the section on p. 76) some fossils concerning which Girty submitted the 

following statement:

Lot 22A. Screen Islands:

Tegulifera? sp.

Pseudomonotis? sp.

These [lots 22A and 22G] differ from any other Alaskan Carboniferous fauna 

known to me. Intrinsically, while they contain types that are unusual and 

interesting, they seem to be without anything which is diagnostic. I am at 

present unable to say either that they are Carboniferous or that they are not, 

and as there seems to be a certain amount of extrinsic evidence for supposing 

that they do represent that period, I have accepted them, though only very 

provisionally.

The conglomerate that forms bed 6 of the section on page 76 contains fossiliferous pebbles from which several collections have been 

made. The fossils of lot 22C, which were collected by Kindle, have 

been determined by Girty as upper Carboniferous. As these fossils 

were obtained, according to Kindle's notes, from "large limestone 

pebbles" in a conglomerate, they prove the age of the rock from 

which the pebbles were derived, rather than the age of the conglomerate that now contains them. The fossils in the pebbles are not only 

upper Carboniferous but represent the youngest Carboniferous fauna 

known in Alaska. They consequently indicate that the conglomerate 

in which they are now contained is probably post-Carboniferous. 

Fossils obtained by Buddington from limestone cobbles in conglomerate on the largest island were identified as of Carboniferous 

age, from which Buddington concluded that the conglomerate probably overlies the lower limestone unconformably.

The upper limestone, which crops out only on the southernmost 

island, yielded the Triassic (?) fossils represented in the following 

table:
78 MESOZOIC STRATIGRAPHY OF ALASKA 

Fossils from upper limestone on Screen Islands'1

Terebratula? _____ ...............................

.A, vicul OD6Ct/6n SD

8839 8838 (22Q)

h

b

b

h

b

b

b

b

b

11075 11076 (3)

b

(3)

b

(4)

h

h

 a, Identified by T. W. Stanton; b, identified by G. H. Girty.

8839. Near, south end of the southernmost of Screen Islands, 100 or 200 feet 

below 8838. G. 0. Martin, 1914.

8838. South end of the southernmost of Screen Islands. Nearly the highest 

beds exposed on this island. G. C. Martin, 1914.

(22G). Screen Islands. Bed 2 in section on p. 76. E. M. Kindle, 1905.

11075. South tip of southernmost of Screen Islands. A. F. Buddington, 1921.

11076. Southwest side of longest of Screen Islands. A. F. Buddington, 1921.

(2). Screen Islands. G. H. Girty, 1918.

(3). Near north end of northernmost of Screen Islands. G. H. Girty, 1918.

(4). Screen Islands. G. H. Girty, 1918.

TBIASSIO BOCKS OF KEKU STRAIT AND VICINITY

Historical review. The Upper Triassic rocks at Hamilton Bay, 

which were the first Triassic rocks to be recognized in southeastern 

Alaska, became known through the discovery by E. M. Kindle, in 

1905, of a loose fragment of fossiliferous limestone at the head of the 

bay. Kindle did not describe his discovery, but the occurrence was 

mentioned briefly by F. E. and C. W. Wright 75 in a general account 

of the geology of southeastern Alaska. The locality was revisited in 

1907 by Atwood,76 who found the Triassic rocks in place and who 

has given a brief account of the occurrence, to which Stanton contributed lists of the fossils and a discussion of their age and significance. Additional collections from the north shore of Hamilton Bay 

were made in 1914 by Martin," who has briefly discussed the rocks 

and their faunas. More detailed investigations of these rocks were 

made in 1922 and 1923 by A. F. Buddington, who has contributed, 

from his field notes and manuscript report, much of the information 

presented below.

75 Wright, F. B. and C. W., The Ketcbikan and Wrangell mining districts, Alaska: 

U. S. Geol, Survey Bull. 347, pp. 34,, 57, 1908.

78 Atwood, W. W., Some Trlasslc fossils from southeastern Alaska: Jour. Geology, vol. 

20, pp. 653-655, 1912.

77 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 700-701, 

706, 1910.
TRIASSIC, SOUTHEASTERN ALASKA 79

 t i

jStratigraphic description. The Triassic rocks exposed on Hamilton Bay and elsewhere on the shores and islands at the north end 

of Keku Strait comprise both sedimentary and volcanic beds. The 

sedimentary rocks include conglomeratic limestone or calcareous 

conglomerate, calcareous sandstone or sandy limestone, black shale, 

and limestone. Most of the limestones are fine-grained gray rocks 

with some black slaty layers. The conglomerate and sandstone are 

restricted to the basal sedimentary beds. The volcanic rocks include 

green andesitic lava, breccia, and tuff, with local intercalated sedimentary beds. The lava predominantly shows a pillow structure 

and is in part amygdaloidal. Some of the breccia has a limestone 

matrix.

No complete section of the Triassic rocks on Keku Strait has been 

found, because the continuity of the exposures is interrupted in so 

many places by structural disturbances or by areas of water. The 

evidence on the stratigraphic relations of the rocks, obtained by the 

several observers at different localities, is conflicting.

The Triassic rocks observed by Atwood are on the north shore and 

adjacent islands of Hamilton Bay about halfway between Kake and 

the head of the bay. They include a bed of limestone conglomerate, 

which Atwood 78 described as

& peculiar formation in that there are huge angular blocks of limestone in it 

associated with boulders ranging from 1 to 3 feet in diameter. The conglomerate formation is at least 100 feet thick and may represent an important 

structural division line in the Mesozoic section.

According to Atwood's field notes, this conglomerate is underlain 

by "dark-red brittle, much jointed argillite" containing Pseudomonotis subcircularis (Gabb) (lot 4819) and is overlain by the beds 

containing Halobia superb a Mo jsiso vies? (lot 4823). It has been suggested by Stanton 79 that, as the limestone conglomerate occurs between 

the horizons of lots 4819 and 4823, both of which are definitely determined to be Triassic, " Nos. 4821 and 4822 may have come from concretions rather than boulders." It should be noted that the beds at 

this locality are apparently not in their normal sequence, the Pseudomonotis indicating a higher horizon than the Halobia. It is possible, therefore, that the beds are locally overturned. In that case 

the conglomerate may mark an unconformity corresponding to the 

one that possibly occurs in the Chitina Valley (see p. 124) between .the beds containing Halobia and those containing Pseudomonotis. It is also possible that the " limestone conglomerate " that 

Atwood described as containing "angular blocks of limestone" is 

in reality a coarse fault breccia, the fault having produced the local 

inversion of the strata.

78 Atwood, W. W., op. cit, p. 654.

79 Stanton, T. W., cited by Atwood, W. W., idem,, pp. 654-655.
80 MESOZOIC STRATIGRAPHY OF ALASKA

The writer, in studying the section on the north shore of Hamilton Bay east of the localities visited by Atwood, found that ellipsoidal lava is exposed from the head of the bay to the islands that 

fringe the lower part of the northern shore, except for an interval 

of about half a mjle about 2 miles below the head of the bay. The 

lava dips southeast and thus apparently overlies the Permian limestone exposed on the creek entering the head of the bay, although 

the contact was not seen. It is apparently overlain by Upper 

Triassic dark cherty limestone, which is exposed on the north shore 

from a point 2 miles below the head of the bay to the mouth of the 

creek half a mile farther down the shore. This limestone was 

observed practically in contact with the underlying ellipsoidal lava, 

As there is a considerable discordance in strike and dip between 

the limestone and the lava, the contact is either an unconformity or 

a fault. The thickness of the limestone exposed along this part of 

the shore does not exceed a few hundred feet and may be less than 

100 feet. Halobia was obtained near the base of the limestone (lot 

8843) and Pseudomonotis from somewhat higher beds (lot 8844). 

The writer believes that the exposures at this locality are not complete, the presence of Upper Triassic beds older than the Halobia^ 

bearing beds being indicated by fossils found in float collected along 

the shore (lots 8842 and 8845).80

The Triassic rocks of the localities at the north end of Keku Strait 

are regarded by A. F. Buddington as probably including three formations a formation, exposed chiefly on Kuiu Island, that lies unconformably on Permian and Devonian rocks and is made up chiefly 

01 basaltic and andesitic lavas, breccia, and tuff interbedded with 

some sedimentary rocks including a basal conglomerate and some 

limestone containing fossils that are believed to be Upper Triassic; 

a formation that lies, in most places, unconformably on Permian and 

Devonian rocks, is composed wholly of sedimentary rocks, mostly 

conglomerate, limestone, and sandstone, and contains fossils that 

are chiefly characteristic Upper Triassic forms such as Halobia cf. H. 

superba and its customarily associated ammonites; and a formation 

that is believed to lie unconformably on the sedimentary formation 

just described and is composed chiefly of lava and tuff with some 

intercalated slate, quartzite, and limestone containing Pseudomonotis.

The following notes on the undoubted Upper Triassic sedimentary 

rocks seen at various localities at the north end of Keku Strait were 

submitted by Mr. Buddington:

On the north side of the Cornwallis Peninsula about a mile southeast of 

Point Cornwallis the contact between the Upper Triassic and the Permian beds 

is exposed. The Upper Triassic limestone is very gently folded and extends

80 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 700, 

706, 1916.
TRIASSIC, SOUTHEASTERN ALASKA 81

along the shore, with local interruptions, for 2y2 miles. At the northern contact the Triassic beds are gently folded and rest on Permian limestone with 

white chert layers. The basal beds of the Triassic limestone contain pebbles 

of white chert. At the southern contact the Triassic limestone lies unconformably on volcanic rocks that are probably Permian. The limestones are 

locally fossiliferous (11931 and 11932).

About 4 miles from the head of Hamilton Bay is a small elongate island 

north of which the following section was measured:

Section of Upper Triassic rocks behind island 4 miles below head of Hamilton

Bay

Volcanic rocks. Feet 

Quartzite and limestone with Pseudomonotis (lot 11437)_ 25± 

Bluish-gray and black limestone with fossils (lots 11243,

11241, 11242, 11240)________________________ 100 

Calcareous sandstone and limestone_.___________ 125 

Calcareous sandstone and sandy limestone__________ 50 

Coarse conglomerate with calcareous matrix________ 100 

Unconformity (Permian limestone beneath).

Several hundred feet of limestone, black calcareous shale, and chert is exposed on the west side of the narrow neck joining the two portions of the large 

island several miles south of Kake. Conglomerate, sandstone, and black slate 

about 125 feet thick apparently overlie these beds. The conglomerate is overlain by volcanic rocks with intercalated fossiliferous slate beds containing 

P&eudomonotis (11246).

At the northwest end of the large island south of Kake the basal Upper 

Triassic conglomerate rests directly on Devonian chert and tuff. The pebbles 

in the conglomerate are mostly chert, with some green tuff like that in the 

underlying Devonian beds. The conglomerate contains fossiliferous limestone 

nodules (11237). The Upper Triassic rocks here consists of about 100 feet of 

conglomerate, thin-bedded limestone, calcareous sandstone, and slate, overlain 

by limestone of unknown thickness, above which is a most extraordinary appearing volcanic agglomerate.

Mr. Buddington has submitted the following statement concerning the supposed uppermost volcanic formation:

The Pseudomonotis-besiTmg volcanic rocks of Hamilton Bay lie, probably 

unconformably, upon the calcareous sedimentary Upper Triassic rocks.

Along the southwest limb and at the southeast nose of the Kake anticline 

a conglomerate bed, in part of volcanic origin and 150 to 200 feet or more thick, 

lies at the base of the volcanic rocks. This bed was not found elsewhere. On 

the west side of the narrow neck in the long island south of Kake several hundred feet of the limestone, black calcareous shale, and somewhat crumpled 

chert, which belong in the older beds described above, are overlain by about 

125 feet of conglomerate, sandstone, and black slate. These beds are believed 

to represent the base of the volcanic series. The conglomerate has a greenish 

hue on the fresh surface but weathers with a reddish glazed appearance. It 

is composed of fragments of chert, in part carrying Permian fossils, andesite, 

and black slate. Many of the fragments are angular, and those of sedimentary 

rock are from Paleozoic formations, but the volcanic fragments are. similar to 

the Upper Triassic lava. The beds are overlain by andesitic lava with associated thin beds of black slate, calcareous quartzite, and limestone. Fossils 

were obtained (11246) from layers between pillow lava.
82 MESOZOIC STKATIGRAPHY OF ALASKA

Northwest of the large island south of Kake are two small islands formed 

in part of volcanic breccia and in part of beds that may be either breccia or 

conglomerate. The rocks are much sintered and consequently weather with 

a glazed surface. There are about 200 feet of these beds consisting of very 

coarse conglomerate at the base and medium-grained conglomerate above. 

The fragments comprise black slate, andesite, andesite 'porphyry, chert, green 

tuff, calcareous quartzite, and limestone. Some of the chert is fossilliferous 

and is presumably upper Carboniferous, whereas the green tuff is doubtless 

Upper Devonian. Many of the fragments are sharply angular; others are 

rounded. One 2-foot boulder of andesite porphyry had a 2-inch chill zone surrounding it. In thin section fragments of andesite show similar chill zones 

completely surrounding them. Fragments of unmistakable perlite were seen; 

vesicular and amygdaloidal volcanic rocks are abundant, and feldspar fragments very common. These phenomena suggest that volcanic material and 

perhaps fragments of underlying sedimentary beds were showered by volcanic 

explosions into waters where normal conglomerate was accumulating. Hence 

the beds are correlated with the volcanic series.

The volcanic rocks are exposed along the southwest limb of the Kake anticline, as on the southwest side of the long island south of Kake. They here 

comprise pillow lava from 5 to 20 feet thick, massive and polygonal jointed 

flows from 10 to 30 feet thick, and sedimentary beds from 1 inch to 10 feet 

thick. The sedimentary beds consist of black slate, quartzite, and limestone. 

On the extreme northwest headland of this island the sedimentary beds are 

broken to fragments and included in a glassy andesitic matrix. Each individual fragment is usually inclosed in a ball of glass, so that on weathering 

the appearance is that of a very coarse agglomerate. The diameter of most 

of the fragments is about 9 inches, but blocks as large as 18 by 300 feet were 

seen. The upper beds are finer, the fragments ranging from the size of a 

hickory not to that of an apple. The breccia beds stand about vertical and are 

about 150 feet across the strike. At the south end the contact between the 

breccia and the sedimentary beds is at an angle to the strike of the sediments.

The volcanic rocks are again exposed within the Cape Bendel syncline, along 

the north side of Hamilton Bay, where they consist of amygdular and pillow

lava, in part variolitic, with intercalated sedimentary beds. The interstices 

between the pillows are filled with limestone and the pillows show a radial 

jointing and an outer vesicular crust. A peculiar feature of some of the more 

massive flows is a pseudo-breccia structure in which the fragments have not 

been displaced more than an inch at the maximum but still maintain their 

relative positions and are separated by a limestone filling. The intercalated 

sedimentary beds consist of black calcareous slate, gray quartzite, and thin 

limestone bands. Many of the layers are highly fossiliferous (11245).

The following notes on the supposed Upper Triassic volcanic 

rocks of Kuiu Island and on some beds that are their possible equivalents were submitted by Mr. Buddington:

Near the point west of Hound Island, where the shore turns southward, the 

Permian beds are overlain by sandstone with conglomeratic layers followed by 

interbedded limestone and green andesitic tuff with a few layers of conglomerate. About three-fifths of a mile south of the point the limestone is fossiliferous 

(11406). These beds are overlain by basaltic and andesitic lava, breccia, and 

tuff with interbedded limestone containing a few andesite pebbles.

The entire peninsula between Six and a Quarter Fathom Cove and the cove 

south of it is composed of coarse agglomerate and pillow lava. The agglomer-
TKIASSIC, SOUTHEASTERN ALASKA 83

ate predominates in the western half of the peninsula, and the flows with interbedded agglomerate in the eastern half. Here also the pillow lava with interstitial limestone is seen to grade upward into breccia with a limestone matrix. 

At a point on the east side of the peninsula, west of Pup Island, there is a 

conspicuous pillow lava with layers of limestone 12 inches or less thick molded 

to the surfaces of the ellipsoids. The limestone is baked to a pinkish-brown 

hornstone at the contact with the lava. Some of the limestone pockets are extraordinarily rich in well-preserved fossils (11407 and 11962). Hound Island 

and several islets northwest of it consist of green andesitic breccia with a 

limestone matrix, which is interbedded with a little dense buff-weathering or 

agglomeratic limestone.

Turnabout Island, off the northwest end of Kupreanof Island, consists of 

andesite and andesite porphyry lava and breccia with intercalated tuff and a 

50-foot bed of gray sandstone. The flows are in part amygdular and in part 

have pillow structure. The sandstone lies on the east side of a bight on the 

south side of the island and contains thin layers of calcareous sandstone and 

conglomerate, some of which are richly fossiliferous (11405). Traces of carbonized plant stems are also common.

In the northern part of the cove just south of Cape Bendel the basal Upper 

Triassic beds consist of interbedded conglomerate and lava having a thickness 

of 100 feet or more. Green Devonian tuff lies west of the Triassic rocks. The 

cobbles of the conglomerate consist of limestone, chert, and green Devonian 

tuff. Some beds are composed almost wholly of fragments of red shale. On 

the east side of the syncline the base of the formation consists of about 100 

feet of conglomerate interbedded with lava and sandy fossiliferous limestone 

(11933). The beds here overlie the Permian. Overlying these basal beds 

comes a series of volcanic rocks which comprise predominantly green andesitic 

lava, chiefly with pillow structure but in part amygdaloidal. The lava, including the conglomerate at the base, was estimated to be approximately 1,400 feet 

thick. About 1% miles northeast of Cape Bendel, on the east headland of a 

cove due south of Pinta Rocks, a zone of sedimentary beds about 225 feet thick 

is intercalated within the andesitic lava. These beds consist of about 50 feet 

of conglomerate which grades upward into sandstone and is overlain by 

isoclinally folded thin-bedded limestone. Many of the limestone layers are 

highly fossiliferous (11934). These beds are overlain and underlain by pillow 

lava.

Age and correlation. The apparent stratigraphic succession and 

the character of the Triassic faunas on Keku Strait are somewhat 

different from anything that has been found elsewhere in Alaska. 

The fossils from the limestone and associated sedimentary rocks that 

are regarded by Buddington as forming the basal portion of the 

Triassic rocks of this locality and the fossils from sedimentary 

beds that he regards as intercalated in the overlying volcanic formation are listed in the following table. Most of these collections include well-known Upper Triassic species that are characteristic of 

the Triassic rocks of other Alaskan localities, such as Pseudomonotis 

subcircularis (Gabb) and Hdlobia, cf. H. superba Mojsisovics, as 

well as some of the ammonites that are customarily associated with 

the Halobia.
Upper Triassic fossils from north end of Keku 

Ootrofl?

rVrfltitac?

1

X

X

X

X

X

N

o>

~~

X

X

X

CO

I

X

X

o*

s <(<

X

X

X

X

X

X

CM

9

X

X

N

X

"O

 <£ 

00

oo

X

X

X

X

X

CO

3,

CO

X

X

S00

v

X

 *»«

s

X

X

X

v

b-

§3

X

X

X

X

1

X

X

X

X

§

X

X

X

I

X

X

X

X

X

X

i

X

X

X

X

c<

3

X

X

1 Identified by T. W. Stanton.
TRIASSIC, SOUTHEASTERN ALASKA 85

11931 (No. 910). Kuiu Island, about 3 miles southeast of Point Cornwallis, 

on Keku Strait side. Gently folded limestones. A. F. Buddington, 1923.

11932 (No. 961). Kuiu Island, opposite round island about 4 miles southeast 

of Point Cornwallis. Limestone apparently overlying felsite breccia and tuff. 

A. F. Buddington, 1923.

11933 (No. 980). Kupreanof Island, about 2 miles northeast of Cape Bendel. 

Brown sandy limestone between the white Permian limestone and the conglomerate. May be either basal portion of Upper Triassic or upper part of 

Permian. A. F. Buddington, 1923.

4822 (7). North side of Hamilton Bay near south end of large island southeast of Kake. Boulder in limestone conglomerate. W. W. Atwood, 1907.

4821 (6). North side of Hamilton Bay near south end of large island southeast of Kake. Another boulder in the limestone conglomerate. W. W. 

Atwood, 1907.

8842 (16). North shore of Hamilton Bay, about 2 miles below head of bay. 

Float. G. C. Martin, 1914.

8845 (19). North shore of Hamilton Bay, about 3 miles below head of bay. 

Float. G. C. Martin, 1914.

8846 (20). North shore of Hamilton Bay, about 3 m'les below head of bay. 

Float. G. C. Martin, 1914.

8841 (15). Hamilton Bay, about three-fourths of a mile up the northernmost 

creek entering the head of the bay. Gray limestone that appears to underlie 

the white Carboniferous limestone at the falls near the mouth of the creek. 

R. M. Overbeck, 1914.

11934 (No. 979). 1*4 miles northeast of Cape Bendel, Kupreanof Island, on 

east headland of cove due south of Pinta Rocks. Near top of limestone. 

A. F. Buddington, 1923.

11237 (39). About 2 miles south of Kake, on northwest point of large island. 

Limestone nodules in calcareous conglomerate beds intercalated in limestone 

at top of conglomerate series (basal conglomerates). A. F. Buddington, 1923.

11238 (92). Extreme southeast tip of large island south of Kake. Limestone 

overlying basal (?) conglomerate series. A. F. Buddington, 1923.

11239 (91). Limestone overlying that of 92; many interlayers of slate. 

A. F. Buddington, 1923.

11240 (62). 7 miles southeast of Kake, on Kupreanof Island. Limestone 

overlying conglomerate and sandstone. A. F. Buddington, 1923.

11241 (67). Limestone beds a trifle above those of 11240 and about 350 feet 

above base of conglomerate series. The underlying buff-weathering Carboniferous (?) limestone with chert layers is exposed beneath the conglomerate. 

A. F. Buddington, 1923.

11242 (66). Limestone beds at about same horizon as 11241, on islet just 

south of 11241. ' On nose of anticline pitching southeast. A. F. Buddington, 

1923.

11243 (68). Same locality as 11240, about 275 feet above base of conglomerate 

series. Limestone. A. F. Buddington, 1923.

8843 (17). North shore of Hamilton Bay, 2 miles below head of bay. Near 

base of cherty limestone that overlies ellipsoidal lava. G. C. Martin, 1914.

4823- (8). North side of Hamilton Bay, near south end of large island southeast of Kake. Beds that seem to overlie the limestone conglomerate that 

yielded lots 4821 and 4822. W. W. Atwood, 1907.

9543. Islet in Frederick Sound, one-fourth mile southwest of Kake. Mrs. 

Theodore Chapin, 1915.

10196. South end of northernmost large island of Keku Islets. G. H. Girty, 

1918.

49448 26 7
86 MESOZOIC STEATIGEAPHY OF ALASKA

10197. Near middle of north shore of small island southeast of northernmost 

large island of Keku group. G. H. Girty, 1918.

11408 (211 Bu). Northeast end of large island southeast of northernmost 

large island of Keku group. Black calcareous shale adjacent to limestone 

with white chert beds. Shale probably same formation as 215 and 205. A. F. 

Buddington, 1922.

11436 (205 Bu). Southwest side of northernmost large Keku Islet. Same 

formation (?) as 215 but more sheared. A. F. Budd.'ngton, 1922.

11245 (56 Bu). North shore of Hamilton Bay, about 2 miles below head of 

bay. From thin-bedded slate, quartzite, and limestone intercalated with 

pillow lava. These beds overlie the limestone beds of 66 and 67. A. F. Buddington, 1922.

11246 (68). West shore of large island southeast of Kake. From similar 

beds to 56 intercalated in pillow lava overlying limestone of 91. A. F. Buddington, 1922.

11437 (65 Bu). Kupreanof Island, southwest of Kake. From interbedded 

quartzite and limestone overlying the limestone of 67. A. F. Buddington, 1922.

4820 (2). North side of Hamilton Bay near south end of large island southeast of Kake, Beds that seem to underlie the limestone conglomerate that 

yielded lots 4821 and 4822. W. W. Atwood, 1907.

4819 (1). North side of Hamilton Bay near south end of large island southeast of Kake. Same series of beds that yielded lot 4820, apparently a few 

feet lower. W. W. Atwood, 1907.

8844 (18). North shore of Hamilton Bay, 2 miles below head of bay. About 

40 or 50 feet above lot 8843. G. C. Martin, 1914.

(16 B). Near head of Hamilton Bay. Float. E. M. Kindle, 1905.

The fossils of lots 11245 to 16B are indicative of the Upper 

Noric Pseudomonotis-be&Tmg beds that constitute the upper 

most known Triassic rocks of other Alaskan regions. The fossils of 

lots 11934 to 11436, all of which contain Halobia, most of which 

contain Halobia cf. H. superba, and some of which contain several 

of the ammonites that are generally associated with Halobia cf. 

H. superba, are indicative of the Middle or Upper Karnic Halobiabearing beds that generally underlie the Pseudomonotis-bea,r'mg 

beds of other regions.

The fossils of lots 11931 to 8841, in which both Pseudomonotis and 

Halobia are absent, call for special consideration. The fossils of 

lot 11931 include, an ammonite which Stanton has identified as 

Ceratites. This ammonite, if correctly identified, is suggestive of the 

Middle Triassic. Lots 11932 and 11933 contain only a few fossils 

that are not of any special significance. Lots 4822 to 8841, from 

boulders in the Upper Triassic conglomerate, from float of unknown 

origin, and from beds that apparently underlie the Permian rocks at 

an isolated locality on the creek that enters the head of Hamilton Bay, 

differ from the faunas at the other localities not only in the absence 

of Pseudomonotis, of Halobia, and of the ammonites that are generally associated with Halobia, but in the presence of Trachyceras 

and of abundant brachiopods. The float material of lots 8842, 8845, 

and 8846 was noted in the field as having come "from beds that
TUIASSIC, SOUTHEASTERN ALASKA 87

were not recognized in the observed outcrops." The fossils at 

localities 8842 and 8845 include species related to Spiriferina 

borealis Whiteaves and Trachyceras (Dawsonites) canadense Whiteaves, which have not been found elsewhere in Alaska or at any 

American localities except in the Triassic rocks of Liard River, in 

the eastern foothills of the Rocky Mountains of British Columbia. 

. The Triassic rocks of Liard River, according to McConnell,81 " consist of dark shales, usually rather coarsely laminated, and passing 

into calcareous shales interstratified with sandstones and shaty and 

massive limestones." The fossils, which have been described by 

Whiteaves,82 include 11 species, among which are /Spiriferina Itorealis 

Whiteaves and Daiosonites canadense Whiteaves, which have beeit 

doubtfully identified from Hamilton Bay. Mojsisovics 83 has pointed 

out that some of these fossils are indicative of Karnic age. Threeof the Liard River species (Dawsonites canadense, N atJiorstitesmcconnetti, and NatKorstites lenticularis} , one of which occurs ak 

Hamilton Bay, have been found, according to Bohm,84 in the Upper 

Triassic rocks of Bear Island, between Norway and Spitzbergen. 

The Triassic rocks of 'Bear Island are generally regarded as of 

Karnic (possibly Lower Karnic) age, and an assignment of thebeds on Liard River to the same position has been made by Frech 85 

on the basis of the presence of the above-mentioned species, which 

are common to the two regions.

The Hamilton Bay fauna may also be tentatively correlated with 

that from Bear Island and referred to the Karnic. This fauna 

possibly represents a boreal facies of the Karnic which has not beeia 

recognized farther south in North America.

The fauna of the limestone and calcareous sandstone interbedded 

with the lava and tuff of Kuiu Island is very different from any of 

the previously known Triassic faunas of America. Concerning this 

fauna, which is represented in the table given below, T. W. Stanton 

has furnished the following statement:

Although this small collection [lot 11407] contains an unusually largenumber of species of fairly well preserved fossils which are apparently of" 

Mesozoic types, there seems to be nothing in it strictly comparable with any 

known Mesozoic fauna in Alaska or indeed in America. Several of the speciesdo not show important characters that are necessary for positive generic as81 McConnell, R. G., Report on an exploration in the Yukon and Mackenzie basins,. 

Northwest Territory: Canada Geol. Survey Ann. Rept., new ser., voL 4, pp. 19D, 4'JD.,, 

1890.

82 Whiteaves, J. F., On some fossils from the Triassic rocks of British Columbia: 

Contr. Canadian Paleontology, vol. 1, pt. 2, No. 3, pp. 127-149, pis. 17, IS, 1889.

83 Mojsisovics, Edmund von, Beitrage zur Kenntniss der obertriadischen, Cephalopo^euFaunen des Himalaya: K. Akad. Wiss. Wien.Denkschr., Band 63, p. 697, 1896.

84 Bohm, Johannes, Ueber die obertriadische Fauna der Biireninsel: K. svenska VeteoBkaps-Akad. Handlingar, Band 37, No., 3, pp. 56-58, 61-64, 73-76, 1903.

85 Frech, Fritz, Die zircumpaciflsche Trias: Lethaea geognostica, Teil 2, Das Mesozoicum, Band 1, Trias, pp. 488-491, 508, 1908.
88 MESOZOIC STKATTGRAPHY OF ALASKA

signment, and this fact weakens the determination of the age of the fauna. 

It is reasonably certain, however, that this fauna belongs to the Triassic and 

probably to the Upper Triassic, as determined by comparison with European 

Triassic faunas.

Fcxsils from Upper Triassic (?) limestone and calcareous sandstone associated 

with lava and tuff on Keku Strait °

Gervillia'' ... _ ...........

Pteria'

Pecten

Cardita?. . -- ............................................

Pleurotomaria...... ....... ..................................................

11407

X

X

X

X

v

v

X

X

X

X

X

X

y

y

X

X

X

X

X

X

X

X

11962

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

11406

X

X

X

X

X

X

X

11405

T

X

X

X

 Identified by T. W. Stanton.

11407 (256 Bu). Kuiu Island, 3 miles a little north of west of Point Camden, 

on west side of 9%-fathorn cove about halfway between 9% mark and north 

point. Conspicuous pillow lava involved, with thick layers of limestone molded 

to the pillows. One pocket of limestone extraordinarily rich in well-preserved 

fossils. The limestone for several inches adjacent to pillow is baked to a 

pinkish-brown hornstone. Fossils are all from this pocket. A. F. Buddington, 

1922.
TRIASSIC, SOUTHEASTERN ALASKA 89

11962- (256 Bu). Same locality as 11407, but on different pocket. Kuiu 

Island, 3 miles a little north of west of Point Camden, on west side of 

9%-fathom cove. A. F. Buddington, 1923.

11406 (244 Bu). Kuiu Island, west side of Keku Strait, 7 miles northwest 

of Pup Island, just north of first creek shown on chart south of point where 

shore line changes from east-west to north-south. Interbedded argillaceous 

limestone and andesitic tuff, with rare thin conglomerate beds and intercalated sandstone. Many layers of the limestone are richly fossiliferous. 

Traces of leaf impressions poorly preserved are present in same layers with 

shells; and carbonized plant stems are common in the limestone and abundant 

in the sandstone. A. F. Buddington, 1922.

11405 (145 Bu). Turnabout Island, Frederick Sound. East side of the bight, 

on the south side of the island, where the house stands. Basalt and basalt 

porphyry flows and breccia with intercalated tuff and a 50-foot bed of gray 

sandstone. The sandstone contains intercalated layers of calcareous sandstone and conglomerate 1 inch to several inches thick, some of which are' 

richly fossiliferous. Traces of carbonized plant stems also noted in the 

sandstone. A. F. Buddington, 1922.

An assignment of the volcanic beds containing these fossils to a 

position beneath Zfafo&m-bearing limestone would accord with the 

occurrence of volcanic rocks immediately beneath the Halobiabearing limestone in other parts of Alaska, notably in the Chitina 

' Valley (pp. 6-10) and on Cook Inlet (pp. 45-49). There are difficulties, however, in the assignment of the rocks to this position. 

The ZTaZo&m-bearing beds at near-by localities rest unconformably 

upon Devonian and Permian rocks. If the beds that contain the 

fauna in question belong under the ZTaZo&m-bearing beds they are 

separated from the .Efafofo'a-bearing beds by an unconformity and 

consequently are considerably older. The fossils themselves, according to an oral statement by T. W. Stanton, are suggestive of a 

horizon above that of Halobia or even above that of Pseudomoiiotis 

rather than of a horizon below that of Halobia, cf. &. superba. The 

writer believes, therefore, that the volcanic rocks containing this 

fauna are to be correlated with the lava and tuff which Buddington 

regards as interbedded with the rocks that contain Pseudomonotis, 

or may even be assigned to some horizon even higher in the Noric 

or in the Khaetic. The volcanic beds that overlie the Triassic rocks 

of Graviiia Island, which the writer has referred tentatively to the 

Lower or Middle Jurassic, may possibly belong at the same horizon.

TRIASSIC LIMESTONE OF ADMIRALTY ISLAND

Historical review. Upper Triassic rocks are exposed at several 

localities near the south end of Admiralty Island. The rocks at 

these localities were considered Carboniferous by C. W. Wright,86 

who obtained upper Carboniferous fossils near by, and have never

88 Wright, C. W., A reconnaissance of Admiralty Island : U. S. Geol. Survey Bull. 287, 

pp. 142-143, pi. 33, 1906.
yO MESOZOIC STRATIGRAPHY OF ALASKA

been described as Triassic, except for a brief mention 87 of the rocks 

near Herring Bay. Edwin Kirk has contributed additional information concerning some of these localities but has not published any 

description of them.

StratigrapMc description. The Triassic rocks of Admiralty 

Island consist chiefly of limestone. The section at Herring Bay 

includes 273 feet of limestone and shale, which are faulted upon 

Lower Cretaceous shale and are overlain by unfossiliferous chert, 

shale, and conglomerate that may also be Triassic. The Triassic 

fossils from Pybus Bay were obtained from limestone, possibly only 

40 or 50 feet thick, which rests upon Permian (?) conglomerate and 

is overlain by Lower Cretaceous shale. The Triassic fossils near 

Carroll Island were obtained from argillite and sandstone. No 

information is available concerning the character of the Triassic 

rocks on Mole Harbor and between Gambier Bay and Point Pybus.

The following section was measured by the writer on the south 

side nxjar the extremity of the cape between Chapin and Herring 

Bays. Most of the outcrops are low reefs, covered by the highest 

tides and consisting of steeply dipping rocks, which do not furnish 

conclusive evidence as to which are the lower and which the upper 

beds. The sequence indicated in the following section is based on an 

assumption that the strata are not overturned and that the contact 

with the apparently underlying Lower Cretaceous shale is a bedding 

fault rather than an unconformity.

Sectwn of Upper Triassic rocks on point at north entrance to Herring Bay,

Admiralty Island

Feet

1. Green shale and chert________________________ 20

2. Conglomerate ___________________________ 38

3. Thin-bedded limestone________:_______________ 18

4. Fossiliferous thin-bedded limestone (lot 8849)________ 2

5. Thin-bedded contorted limestone_________________ 40

6. Limestone and gray shale_ _______________ 40

7. Massive limestone________________________ 47

8. Limestone and gray shale_ _________ 24

9. Fossiliferous limestone (lot 8848)_______________ 3

10. Limestone and gray shale____________________ 28

11. Fossiliferous limestone (lot 8847)_______________ 1

12. Gray shale and limestone __ 70 

Fault (Lower Cretaceous shales beneath).

North of these exposures, or just around the cape toward Chapin 

Bay, are outcrops of black contorted chert and shale. These beds 

are apparently higher than those of the section just described and 

were regarded in the field as probably Triassic. It is possible, how-

"Martin, G. C., Triassic rocka of Alaska: Geol. Soc. America Bull., vol.. 27, p. 701, 

inset opp. p. 687, 1916.
TEIASSIC, SOUTHEASTERN ALASKA 91

ever, that the entire section is overturned. In that case the conglomerate that constitutes bed No. 2 of the preceding section should 

probably be regarded as the basal member of the Triassic rocks, arid 

the shale and chert are probably the source of the upper Carboniferous fossils that were collected at or near this locality by Wright.88 

The following section was measured by E. M. Kindle at or near 

the same locality as the section given above. The writer believes 

that bed No. 2 of Kindle's section is probably the same as bed No. 

2 of the preceding section.

Section on point off Chapin Bay

Feet

1. Grayish-white massive chert conglomerate_ ______ 250

2. Coarse conglomerate with large and small pebbles of 

green and gray chert. Thin fossiliferous calcareous 

bands at top (lot 9917)__________ ______ 20-25

3. Hard black slate with occasional thin bands of dark

limestone____________________-______ 150

Triassic rocks were discovered by Kirk near Carroll Island, on 

Pybus Bay, between Gambier Bay and the small cove south of False 

Point Pybus, and on Mole Harbor. Fossils from these localities 

are listed in the table below, and the available information concerning their occurrence is given in the accompanying description of 

localities.

Age and correlation. The Triassic rocks of Admiralty Island 

have yielded the fossils listed in the following table:

Trias'Sic fossils from Admiralty Island a

Pseudomonotis subcircularis(Gabb).... .........

Halobia cf. H. superba

Atractites ?................

Undetermined ammonites.

Undetermined spherical

10195 8847 8848

X

X

X

8849

v

9117

y

X

X

X

10180

X

X

X

X

X

10172

X

X

X

10194

X

10171

X

X

X

10196

X

10168

X

< Identified by T. W. Stanton.

10195. South of Carroll Island. Argillite and sandstone. Edwin Kirk, 

1918.

8847. Point at north entrance to Herring Bay, Admiralty Island. Bed No. 

11 of section on page 90. Martin and Overbeck, 1914.

88 Wriglit, C. W., op. cit., p. 143.
92 MESOZOIC STRATIGRAPHY OF ALASKA

8848. Point at north entrance to Herring Bay, Admiralty Island. Bed No. 9 

of section on page 90. Martin and Overbeck, 1914.

8849. Point at north entrance to Herring Bay, Admiralty Island. Bed No. 4 

of section on page 90. Martin and Overbeck, 1914. '

9117. 1 mile east of Herring Bay, Admiralty Island. "Thin fossiliferoua 

calcareous bands at top of a coarse conglomerate." E. M. Kindle, 1905.

10180. Point between Chapin Bay and Herring Bay. Edwin Kirk, 1918.

10172. South point of V-shaped bay just south of False Point Pybus. Edwin 

Kirk, 1918.

10194. About half a mile north of False Point Pybus. Edwin Kirk, 1918.

10171. East side of Church Point south of Gambier Bay. Edwin Kirk, 1918.

10196. North shore of east arm of Pybus Bay. Limestone overlying Carboniferous (?) conglomerate. Edwin Kirk, 1918.

10168. West side of Mole Harbor. Edwin Kirk, 1918.

These fossils indicate, for most of the localities, the well-known 

Karnic fauna with Halobia cf. H. superba and its characteristic 

ammonites. The younger Pseudomonotis horizon of the Noric is 

indicated at two localities. It is noteworthy that one of these (No. 

10196, on Pybus Bay) is very close to the base of the local Triassic 

section, which may be a further indication of an unconformity at 

the base of the Pseudomonotis-besirmg beds. No information concerning the occurrence of Pseudowwnatis at Mole Harbor is available.

GASTINEAU VOLCANIC GROUP OF THE JUNEAU DISTRICT

Historical review. The andesitic Gastineau volcanic group of 

Eakin and Spencer 89 is the lower volcanic part of the " slate-greenstone band" earlier described and mapped by Spencer 90 and part 

of the rocks which he mapped as "greenstone." 91 Spencer's early 

description of these rocks includes a brief general account of the 

character and occurrence of the "slate-greenstone band" with more 

specific description of some of the constituent rock types. He referred the "slate-greenstone band" to the Carboniferous on the 

basis of a correlation of some of its limestone with the fossiliferous 

Carboniferous limestone of Taku Harbor. The Gastineau volcanic group forms part of the rocks within the Juneau district 

which Rnopf 92 mapped as "greenstones" but which he did not 

differentiate from the other volcanic rocks of the region and which 

he did not describe. It may possibly be represented in the "altered amygdaloidal basalts," near Berners Bay, which Knopf 93 described.

89 Eakin, H. M., and Spencer, A. C., Geology and ore deposits of Juneau, Alaska: 

II. S. Geol. Survey Bull. (in. preparation).

90 Spencer, A. C., The Juneau gold belt, Alaska : U. S. Geol. Survey Bull. 287,, pp. 16-18, 

pi. 37, 1906.

91 Idem, pi. 4.

9a Knopf, Adolph, The Eagle River region, southeastern Alaska.: U. S. Geol. Survey 

Bull. 502, pi. 5, 1912.

98 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, pp., 13, 19-21, pi. 2, 1911.
TRIASSIC, SOUTHEASTERN ALASKA 93

Eakin and Spencer's description of the Gastineau volcanic group 94 

includes a general account of the character of the rocks and a discussion of their age, with lists of Triassic fossils identified by Reeside from material collected by Eakin and Spencer. The geologic 

map shows the distribution of the beds represented in the section 

below, but these beds are not described individually in the text.

Stratigraphic description. The general sequence of rocks in the 

Juneau district, according to Eakin and Spencer, is represented in 

the following table, in which the age assignments are those of the 

writer:

StratigrapMc section near Juneau

Upper Jurassic (?) :

Douglas Island volcanic group (melaphyre flows, tuff, and agglomerate).

Treadwell slate (black clay slate with some conglomerate and considerable graywacke). 

Lower or Middle Jurassic (?) : 

Thane volcanic group: 

Melaphyre tuff. 

Limestone. 

Tuff and slate. 

Upper Triassic:

Gastineau volcanic group: 

Slate.

Andesitic tuff.

Calcareous slate with Upper Triassic fossils. 

Andesitic lava, with local lenses of slate. 

Triassic or older:

Perseverance slate (clay slate). 

Paleozoic, with possibly some infolded Triassic:

Clark Peak schist (schistose rocks derived from slate, sandstone, 

limestone, and conglomerate).

This section represents the present sequence of rocks from a 

point near the crest of Douglas Island (top of section) to the western margin of the granite mass of the Coast Kange east of Juneau 

(base of section). It has been assumed that the present sequence of 

the rocks from west to east is their normal stratigraphic sequence 

from top to base that is, the rocks now lie in their original stratigraphic sequence with no structural disturbance except for minor 

crumpling and faulting, which have not affected the sequence of 

the beds, and for a general overturn of the entire section. It is 

entirely possible, in the writer's opinion, that there may be undetected faults and close folds which have caused gaps, repetitions, 

and local overturns within this section. No indication of any such

M Eakin, H. M., and Spencer, A. C., op. cit. 

49448 26 8
94 MESOZOIC STRATIGRAPHY OF ALASKA

disturbances has been found, but if such disturbances were present 

they would be very difficult to detect.

There is no conclusive evidence on the age of any of the rocks at 

Juneau, except for the slate in the Gastineau volcanic group, which 

has yielded characteristic Upper Triassic fossils. The other beds 

have yielded no fossils, and there is only indirect and inconclusive 

evidence on their age.

The Gastineau volcanic group is composed of andesitic lava and 

tuff interbedded with calcareous slate that contains Upper Triassic 

fossils. It is overlain by the Thane volcanic group, which is composed largely of melaphyre tuff interbedded with' slate and limestone. The Thane group has yielded no fossils, but in its lithologic 

character and stratigraphic relations it seems to correspond to some 

of the early Jurassic rocks of other regions. It will accordingly be 

described (pp. 251-252) as probably Lower or Middle Jurassic.

The Gastineau volcanic group consists of andesitic lava at the 

base with local lenses of slate, overlain by calcareous slate containing marine Upper Triassic fossils, above which is andesitic tuff 

overlain by slate. The thickness of this group is possibly about 

5,000 feet.

Beneath the Gastineau volcanic group is the Perseverance slate, 

consisting of unfossiliferous clay slate, possibly 3,000 feet thick. 

The Perseverance slate may perhaps be Triassic and was regarded 

by Eakin and Spencer as probably Triassic because it is apparently 

conformable with the overlying Gastineau volcanic group. As it 

does not appear to correspond in character and position with any of 

the known Triassic rocks of other parts of Alaska, however, the 

writer doubts its Triassic age. The Clark Peak schist, which underlies the Perseverance slate was also regarded by Eakin and Spencer 

as probably Triassic, but as it does not bear a notable resemblance 

to any known Triassic rocks and as it lies on the strike of the Carboniferous rocks of Taku Harbor and other localities south of Taku 

Inlet, the writer believes that it belongs in the Paleozoic, where it 

was formerly placed by Spencer.95 It may, however, include some 

infolded Triassic beds.

Age and correlation. The Upper Triassic age of the Gastineau 

volcanic group is shown by the fossils listed on page 95. The presence 

of Halobia cf. H. -superba indicates a position approximately equivalent to that of most of the other Triassic rocks of southeastern 

Alaska.

86 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, 1906.
TRIASSIC, YUKON VALLEY 95 

Fossils from the Qastineau volwnic group a

Undetermined ammonite ___ . ____________ . _________ . .........

9844

v

v

9845

X

X

9846

X

a Identified by J. B. Eeeside, jr.

9844. Middle. Peak on Sheep Creek-Grindstone divide. H. M. Eakin, 1916.

9845. Head of Sheep Creek near Goldstein divide. A. C. Spencer, 1916.

9846. Sheep Creek basin, head of west tributary. A. C. Spencer, 1916.

YUKON VALLEY

The only known Triassic rocks in the Yukon Valley are near the 

mouth of Nation River, not far below the Canadian boundary, and 

possibly in the Kantishna district.

LIMESTONE NBAS NATION BIVER

Historical review. The presence of Triassic rocks on Yukon 

River was first noted by Brooks and Kindle,96 who gave a brief description of the occurrence of fossiliferous Triassic beds near the 

mouth of Nation River, together with a general discussion of the 

other Triassic occurrences in Alaska and Yukon Territory. This 

description of the Nation River occurrence was in part quoted by 

Prindle,97 who added no new data, the occurrence being outside of 

the area that he described. The Triassic localities near Nation 

River were visited in 1914 and 1919 by the writer, who has given 

a brief description of the rocks with a stratigraphic section and a 

discussion of the faunas.98

Stratigraphic description. The Upper Triassic rocks near Nation 

River consist of thin-bedded limestone and calcareous shale at least 

400 feet thick, resting with probable unconformity though without 

marked discordance of bedding upon upper Carboniferous limestone. 

The top of the Triassic rocks has not been observed, but as the next 

younger rocks known in -this region are Lower Cretaceous the upper 

contact is probably marked by a profound unconformity. The 

Cretaceous and the Triassic rocks, so far as known, however, do not 

crop out in contact.

These Triassic rocks are exposed on the south or left bank of the 

Y ukon about a mile above the mouth of Nation River-. The Triassic

98 Brooks, A., H., and Kindle, E. M. Paleozoic and associated rocks on the upper Yukon, 

Alaska: Geol. Soc. America Bull., vol. 19, pp. 262, 297, a04-305, 313, 1908.

97 Prindle, L. M., A geologic reconnaissance of the Circle quadrangle, Alaska: TJ. S. 

Geol. Survey Bull. 538, p. 30, 1913.

9S Martin, G. C., Triassic rocks of Alaska: Geol. Soc, America- Bull., vol. 27, pp. 701- 

702, 708, 1916.
96 MESOZOIC STRATIGRAPHY OF ALASKA

exposures consist of small discontinuous outcrops on the river bank 

just north of a series of cliffs containing upper Carboniferous limestone. Both the Triassic and the Carboniferous rocks dip northward, or downstream, with approximately parallel bedding. The 

highest of the recognized Carboniferous strata is a bed of yellowish 

subcrystalline limestone with Productus and other brachiopods and 

corals, indicating a very high Carboniferous fauna corresponding to 

the Artinskian of Europe.

Section of Upper Triassic strata on south bank of Yukon River 

1 mile above Nation River

Feet

Calcareous shale and shaly limestone with Pseudomonotis subcircularis (Gabb), Rhynchonellaf sp., and Terebratula sp__ 20+

Calcareous shale and shaly limestone with Halobia cf. H. superba Mojsisovics, Pleurotomaria? sp., and Clionites? sp_ 320

Limestone with Rhynchonella sp., Terebratula sp., Spiriferina 

sp., Halobia sp., Aviculipecten sp., Pecten sp., Pleurophorus? 

sp., Nat-leaf sp., Orthoceras sp., Nautilus sp., Popanoceras 

(Parapopanoceras) f sp., Monophyllites? sp., Placites? sp., 

and Trachyceras (Protrachyceras) f cf. T. lecontei Hyatt 

and Smith ________________________________ 60

Underlain unconformably (?) by lower Permian (?) limestone 

with an Artinskian fauna.

About 50 feet above the uppermost exposed bed of Carboniferous 

limestone and separated from it by a concealed interval is a 10-foot 

bed of dark noncrystalline limestone which is probably Triassic. 

The bedding of this stratum is approximately parallel to that of the 

underlying Carboniferous limestone. The difference in degree of 

crystallinity is a possible indication of an unconformity, although 

this difference may be due to a difference in composition or to local 

deformation or local water channels. This bed of limestone yielded 

the fossils contained in lot 8895. These fossils have been examined 

by T. W. Stanton, who decided that they are "probably Triassic" 

and identified the genera listed in the table on page 98.

The succeeding section, exposed farther down the river bank, is 

incomplete but apparently consists chiefly of calcareous shale and 

shaly limestone. These beds contain characteristic Upper Triassic 

fossils, of which lot 8896 was obtained about 30 feet above the somewhat doubtful bed that yielded lot 8895, and lot 8897 was olftained 

about 10 feet still higher. These two lots contain Halobia cf. H. 

superba Mojsisovics and consequently indicate a horizon corresponding approximately to that of part of the Chitistone limestone. The 

northernmost of the observed Triassic exposures, which is about 300 

feet still higher, or about 400 feet above the highest recognized 

Carboniferous bed, yielded lot 8899, which contains Pseudomonotis 

subcircularis (Gabb). It consequently indicates a horizon corresponding approximately to that of the McCarthy formation, which
TEIASSIC, YUKON VALLEY 97

is the equivalent of the highest recognized marine Triassic horizon 

of America.

The Triassic rocks described by Brooks and Kindle are exposed 

on the hill slope about a quarter of a mile northeast of Nation River, 

on the north or right side of the Yukon. They consist, according 

to Kindle's field notes, of .

heavy and thin bedded dark-gray limestone, shaly at the top, of which 15 

or 20 feet is exposed. Sandy shale is seen at the top of the limestone, and 

the interval between this limestone and locality No. 15 [upper Carboniferous] 

is covered but is probably mostly shale. The interval is about 500 or 600 feet.

According to the published description,"

This fauna occurs in a limestone exposing about 15 feet at the outcrop. 

The limestone apparently belongs in a shale and sandstone series immediately following the upper Carboniferous limestone, which is but slightly exposed where the collection was made. Our very limited knowledge of this 

terrain makes it impossible to offer any estimate of the thickness of the 

beds which should be assigned to it

The fossils from this locality are included in lot 4054, which, according to Stanton,

contains many specimens of Halobia cf. H. superba Mojsisovics, and on the 

evidence of this species it was referred to the Triassic. The lot also contains, in limestone of somewhat different texture, many other small fossils 

among which Girty made the following tentative generic reference. [See lot 

4054a, p. 99.] This fauna is practically duplicated in 8895, which was collected by Martin in the same neighborhood. The natural inference from 

Kindle's collection is that this fauna occurs in a bed intercalated among those 

containing HaloMa, while Martin's collection indicates that it comes from 

beds, lower than the HaloHa, horizon. The question of age must still be left 

open.

The Rhynchonella, [of lot 8895] is the same as Puynax of Girty's tentative 

list based on Kindle's collection (4054), and the Terebratula is the same as 

the Dielasma? of the same list. Leffingwell got similar, possibly identical 

brachiopods at his locality 17 on Canning River.

Upper Triassic rocks were seen also on Trout Creek, which enters 

the Yukon about 2 miles below .the old Montauk roadhouse, or about 

6 miles above Nation River. The Triassic rocks are exposed about 3 

miles above the mouth of the creek. They consist of thin-bedded 

shaly limestone, possibly several hundred feet thick, which is apparently underlain by Carboniferous limestone and is apparently 

overlain by gravel that is believed to be derived from decayed Upper 

Cretaceous or Tertiary conglomerate.

Age and correlation. Three more or less distinct f aunal zones are 

indicated by the fossils from the Triassic rocks near Nation River. 

The fauna of the lower limestone differs strikingly from any of the 

Triassic faunas recognized in the southern part of Alaska. Its 

Upper Triassic age is indicated by the ammonites doubtfully identi89 Brooks, A. H., and Kindle, E. M., op. cit, p. 304.
98 MESOZOIC STRATIGRAPHY OF ALASKA.

fied as Monophyllites, Platites, and Trachyceras (Protrachyceras) 

lecontei. The ammonite doubtfully identified as Popanoceras (Parapopanoceras) sp. is suggestive of the Middle Triassic, but as it is 

an immature specimen its evidence is inconclusive and is overbalanced by that of the other fossils. The fauna differs strikingly from 

that of the Chitistone limestone and supposedly equivalent beds of 

the southern part of Alaska in the absence of such characteristic 

fossils as Trapites, Juvavites, Arcestes, and Halobia> cf. H. superba 

and in the abundance of brachiopods and nautiloids. Its nearest relations among known Alaskan faunas are a fauna found on Canning 

River, with which it has several species in common, and possibly some 

of the collections from Hamilton Bay on Kupreanof Island.

The calcareous shale and shaly limestone, with Halobia cf. H. 

superba, Pleurotomariaf', and Clionitesf, which overlie the limestone just discussed and make up the greater part of the section 

exposed at this locality,' are to be correlated approximately with 

the Chitistone limestone, although their fauna also differs( from 

those of southern Alaska and resembles that of Canning River in the 

absence of the common ammonites of the southern region and in the 

probable presence of Glionites. The beds at the top of the section, 

containing Pseudomonotis subcircularis (Gabb), represent the boreal 

Upper Noric horizon of the McCarthy formation.

Fossils from, Triassic limestone near Nation River a

Coral? (doubtfully organic). ___ .. __ . ...

Rhynchonella- - - ____ ." ____ . ...........

Rhynchonella?- -.............-.... .... ....

Terebratula. __ . ___ ....... _ .... _ . ...

Pseudomonotis (apparently distinct from subSalobia?--..,. . ....... -.. . . 

Natica?........ . . ...........

Popanoceras (Parapopanoceras) ? (immature

Placites? --._.- _ ............................

Clionites? -.... .. ... .... .............

Trachyceras (Protrachyceras) ? cf. T. lecontei

i

oo

a

1

a

a

£ 

§

a

1

a

<S

So

Tt<

h

b

b

b

b

b

b

b

b

J3 

S

9

! »

00& 1 s

§8

r106

S3

S

o o>%

IN

a

1

h.

e*

2

a, Identified by T. W. Stanton; b, identified by Q. H. Girty.
TRIASSIC, YUKON VALLEY 99

8895. South bank of Yukon River, about 1 mile above Nation River. Tenfoot bed of dark noncrystalline limestone which is probably not more..than 

50 feet (unconformably?) above the crystalline Carboniferous limestone. 

Martin and Overbeck, 1914.

9384. South bank of Yukon River, about 1 mile above Nation River. Same 

locality and bed as 8895. Eliot Blackwelder, 1915.

9385. Hillside about one-third of a mile northeast of the mouth of Nation 

River. Probably same bed as 9384 and apparently near the same locality and 

bed as 5054. Eliot Blackwelder, 1915.

9386. Hillside about one-third of a mile northeast of the mouth of Nation 

River. Same locality as 9385, but top of 25-foot limestone (upper part of same 

bed). Eliot Blackwelder, 1915.

4054a. Mountain north of Yukon River, about a quarter of a mile northeast 

of the mouth of Nation River. Fifteen-foot bed of limestone in a shale and 

sandstone series. E. M. Kindle, 1906.

4054b. Same locality as 4054a, but limestone of somewhat different texture. 

E. 'M. Kindle, 1906.

9387. Hillside about one-third of a mile northeast of the mouth of Nation 

River. Shale about 25 feet above 9385. Eliot Blackwelder, 1915.

9388. Hillside about one-third of a mile northeast of the mouth of Nation 

River. Black shaly limestone about 15 feet above 9387. Eliot Blackwelder, 

1915.

8896. South bank of Yukon River, about 1 mile above Nation River, a short 

distance downstream from 8895. About 30 feet above 8895, in' a series of 

calcareous shale and shaly limestone. Martin and Overbeck, 1914.

8897. South bank of Yukon River, about 1 mile above Nation River. About 

10 feet above 8896. Martin and Overbeck, 1914.

8898. South bank of Yukon River, about 1 mile above Nation River. Float 

from river bank between 8897 and 8899. Martin and Overbeck, 1914.

9383. South bank of Yukon River, about 1 mile above Nation River. Calcareous shale and shaly limestone about 260 feet above 9384. Eliot Blackwelder, 1915.

8899. South bank of Yukon River, about 1 mile above Nation River, downstream from 8897. About 300 feet (stratigraphically) above 8897. Martin 

and Overbeck, 1914.

9382. South bank of Yukon River, about 1 mile above Nation River. Calcareous shale and shaly limestone about 350 feet above 9384. Eliot Blackwelder, 1915.

10266. Trout Creek, tributary to Yukon River from the south about 2 miles 

below old Montauk roadhouse, about 3 miles above mouth of creek. Shaly 

limestone. G. C. Martin, 1919.

10267. Same locality as 10266. G. C. Martin, 1919.

9321. Trout Creek, about 4 miles from mouth. Probably same locality as 

10266. Preston J. Billiard, 1915.

TRIASSIC (?) LIMESTONE OF THE KANTISHNA DISTRICT

The supposed Triassic rocks of the Kantishna district were described by Capps l as consisting of black siliceous limestone that 

contains imperfectly preserved corals. The limestone occurs near 

the headwaters of Sushana River in close association with the slates

1 Capps, S. R., The Kantishna region, Alaska: U. S. Geol. Survey Bull., 687, pp. 32, 33, 

37, 1919.
100 MESOZOIC STRATIGRAPHY OF ALASKA

and phyllites of the Tonzona group which were considered by both 

Capps and by Brooks 2 as probably Silurian or Devonian. Capps 

believes that the limestone is not a member of the Tonzona group 

but that it has been folded or faulted into its present position. It is 

possible, however, that the Tonzona group may itself be Mesozoic. 

No other Mesozoic rocks have been found in or near the Kantishna 

district. The following statement was made by Stanton 3 concerning the fossils collected by Capps in 1916:

10031 (No. 2). At extreme head of Sushana River. This lot contains a 

few imperfectly preserved corals which seem to be of Mesozoic types, though 

it has not been possible to identify them even generically. They are similar 

to corals obtained in Triassic limestones in other Alaskan areas, and it is 

most probable that these are of that age. Messrs. Kirk and Girty, who have 

examined the corals, both are of the opinion that they are not Paleozoic 

forms.

ARCTIC SLOPE 

GENERAL FEATURES

The Upper Triassic rocks of the Arctic slope of Alaska are known 

in two districts in the Firth Valley, near the international boundary, and in the vicinity of Canning Kiver, about 130 miles west of 

the boundary. The Triassic rocks of these two districts are very 

much alike in lithologic character, consisting mostly of limestone 

and shale, and are probably alike also in their relation to the underlying and overlying formations. The Triassic beds of Firth Kiver 

are underlain by upper Carboniferous limestone. The Triassic beds 

of Canning River are clearly underlain by upper Carboniferous sandstone and overlain by lower Jurassic shale. In the Firth Valley the 

top of the Triassic rocks has not been recognized because of complex 

structure. The presence of a lower Jurassic fauna similar to that 

of Canning River is indicated by fossils that have been found in 

this district, and consequently there is little doubt that the Upper 

Triassic rocks of Firth River resemble those of Canning River in 

being overlain by Middle or Lower Jurassic strata. It is also highly 

probable that the Triassic rocks of these two districts occur in the 

same structural belt, and it is possible that the Triassic rocks are 

exposed continuously from one section to the other.

SHALE AND LIMESTONE OF FIRTH' RIVER

Historical review. Upper Triassic rocks were discovered by A. G. 

Maddren in the Firth Valley near the international boundary. These

s Brooks, A. H.,, The Mount McKinley region, Alaska: TJ. S. Geol. Survey Prof. Paper 

70, pp. 73-76, 1911.

8 Stanton, T. W., cited by Capps, S. R,, op. cit, p. 33.
TEIASSIC, ARCTIC SLOPE 101

occurrences have been briefly described by Maddren.4 A brief account of these rocks has also been given by Martin.6

Stratigmphic description. The Upper Triassic rocks of the Firth 

Valley consist of impure limestone and sandy shale having a thickness of at least several hundred and possibly a thousand feet or more. 

They are closely associated with upper Carboniferous limestone, 

which is in places folded or faulted over them. On account of the 

structural conditions the character of the basal contact of the Triassic beds is not known, nor has the thickness been determined with 

certainty. The top of the Triassic rocks has also, for the same reason, not been recognized. It is probable, however, that the succeeding formation is a Middle or Lower Jurassic limestone, which is 

now complexly infolded with the Triassic beds so that it has not been 

differentiated, although its presence (see pp. 264r-265) has been recognized from fossils.

The Triassic shale and limestone of Firth River have been described by Maddren 6 as follows:

Several miles south of the northern border of the Carboniferous rocks just 

described and about 8 miles west of the 141st meridian marine fossils of Upper 

Triassic age occur in a formation that is made up largely of black shales and 

impure thin-bedded shaly limestones but possibly contains some massive limestones. This formation appears to be involved by profound folding and possibly faulting with the intimately associated Carboniferous limestones in such 

a manner that its position is now apparently beneath the older formations. At 

least, this is the tentative view now held as a result of the preliminary examination made in 1911.

Similar Upper Triassic rocks are situated approximately 1 mile west of the 

141st meridian about 5 miles south of the upper Firth River basin or Valley 

of Three Rivers. These are likewise associated with the massive Carboniferous 

limestone series and in the field examination of 1911 were considered possibly 

to underlie them. The outcrops from which the Triassic fossils were obtained 

are poorly exposed beds of impure flaggy limestone interbedded with sandy 

shales, which have not been observed in contact with the older series. They 

lie in the wide valley head of one of the extreme northern headwaters of Old 

Crow River. These rocks were not recognized elsewhere in this basin by fossils, but some black limy shales of somewhat similar appearance occur along 

the foot of the eastern slopes of the basin several miles to the southwest.

Age and correlation. Two faunal zones are indicated by the fossils that have been collected 'from these rocks. The older zone contains Halobia cf. H. superba, Mojsisovics and other pelecypods, 

which have been found in beds of flaggy limestone interbedded with 

sandy shale on the international boundary about 80 miles north

4 Maddren, A. G., Geologic investigations along the Canada-Alaska boundary: U. S. 

Geol. Survey Bull. 520, pp. 300, 312-313, 1912.

5 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp., 702-703, 

1916.

8 Madden, A. G., op. cit, pp. 312-313.
102 MESOZOIC STRATIGRAPHY OF ALASKA

of Porcupine Kiver (lots 7380 and 7381, below). A younger zone 

is indicated ; by the presence (lot 7382)' of Pseudomonotis subcirculafris (Gabb) in limestone beds west of the boundary and about 

28 miles farther north. The relation of the beds at these two localities to each other is not known. The Pseudomonotis-be&Tmg 

beds occur on the contact with upper Carboniferous rocks which are 

apparently folded or faulted over them. Another collection (lot 

8207) contains both Halobi® and Pseudomonotis. As this lot, 

when received, included some crinoids that are probably Lower 

Jurassic (see p. 265), as well as some upper Carboniferous fossils 

contained in limestone which, according to Stanton, "differs in 

color and other characters from the limestone containing the Triassic fossils," and as according to Maddren's field notes, "about 1,000 

feet of Triassic beds appear to be involved in the exposure, but much 

of this is composed of dark shale too much crumpled to be deciphered with satisfaction at this locality," it is obvious that this collection does not prove that the HaloMa and the Pseudomontis lived 

in the same sea.

It may be that in parts of the Alaskan Triassic seas Halobia 

superba and Pseudomonotis subcircularis had a different range and 

distribution from that which their kindred species are supposed to 

have had in the European and Californian Triassic, where the HaloMa is supposed to be a warm-water Karnic species and the Pseudomonotis a cold-water Noric species, but this occurrence does not 

prove that such is the case. It is possible that here, as at some of the 

other Alaskan localities where these forms seem to be in the same 

beds, the apparent facts may be explained by mixed collections, by 

structural conditions, or by unrecognized specific differences.

Upper Triassic fossils from Firth River °

Avicula. ___ _' _ . ________________ ..-_.-_.--_ ....................

Pecten. __ .. _______ . __ . _____________ .... _________

Pecten?. .......................................................................

7380 7381

X

X

7382 8207

 Identified by T. W. Stanton.

7380. About a mile west of heliograph station T, on international boundary 

80 miles north of Porcupine River. Impure flaggy limestone interbedded with 

the sandy shale that yielded lot 7381. A. G. Maddren, 1911.

7381. Same locality as 7380. Sandy beds: A. G. Maddren, 1911.

7382. About 1% miles up a gulch southwest of west camp on West Fork 

of Firth River, about 6% miles west of international boundary and 108 miles 

north of Porcupine River. Ferruginous limestones apparently near base of the
TRIASSIC, AECTIC SLOPE 103

limestone that forms the ridge along the south side of the West Fork. The 

Carboniferous is apparently folded over the Triassic at this point.. A. G. 

Maddren, 1911.' .

8207. About 100 to 500 feet above mouth of a south-side gulch, tributary to 

Overthrust Creek, 1% miles above its mouth. About 8 miles west of the international boundary, in latitude 68° 56' 10" N. Thin dark brittle limestone 

alternating with crumpled dark calcareous and ferruginous sandy shale. A. G. 

Maddren, 1912.

SHUBLIK FORMATION

Historical review. Upper Triassic rocks are well exposed in the 

vicinity of Canning River on the Arctic slope about 130 miles west 

of the international boundary. This occurrence was discovered and 

has been investigated in detail by E. de K. Leffingwell in the course 

of his extensive explorations of the north coast and Arctic slope of 

Alaska. These Triassic rocks were described by Leffingwell 7 as 

the Shublik formation,, and .his. account, included a detailed description of the formation with lists of fossils as determined by T. W. 

Stanton. The fauna of the Shublik formation has been discussed 

by Martin.8

Stratigraphic description. The Shublik formation, as described 

by Leffingwell, is exposed along the northern front of the Franklin 

Mountains on the tributaries of Canning and the neighboring rivers. 

The type locality is at Shublik Island, in Canning River. This formation consists of dark limestone, shale, and sandstone and is probably about 500 feet thick. It includes at least three characteristic 

members a lower member, about 30 feet thick, composed of calcareous 

sandstone; a middle member, about 100 feet thick, composed of limestone with some interbedded shale; and an upper member, about 100 

feet thick, composed of black shale. Between these recognized 

members are concealed intervals of unknown character and extent. 

The Shublik formation overlies the upper Carboniferous (Pennsylvanian) rocks of the Sadlerochit formation, and is overlain by the 

Middle or Lower Jurassic Kingak shale, which is described on 

page 263. Neither the lower nor the upper contact has1 been observed 

in detail, but both contacts are apparently conformable.

Age and correlation. The fauna of the Shublik formation, as 

represented in the following table, includes fossils from all three of 

the characteristic members described above. The lower sandstone 

member is represented by 10294; the middle limestone member by 

10297. 10300, 10302, 10303, 10305, and 10310; and the upper shale 

member by 10299 and 10301. The remaining collections came from 

unknown beds. The brachiopods of 10297, according to T. W. Stan7 Leffingwell, B. de K., The Canning River region, northern Alaska: U. S. Geol. Survey 

Prof. Paper 109, pp. 103, 115-118, pi. 2, 1919.

8 Marian, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, p. 

703, 1916.
104 MESOZOIC STRATIGRAPHY OF ALASKA

ton, "suggest a fauna closely related to the somewhat doubtful 

Triassic fauna collected near the mouth of Nation River on the 

Yukon." (See lots 4054 and 8895, p. 98.)

Fossils from the ShubUk formation a

Halobia. ........ ......... ..... 

Clionites?... -..--.-.---......-....-.-----

i

X

o

X

X

X

X

X

X

X

X

o

,

X

X

X

N

o

8

X

X

o

X

1

X

X

X

X

X

X

1o

X

o

8

X

X

X

X

v

X

10

X

X

X

o

X

00

so

X

X

X

X

CO

CO

o

X

X

X

X

X

X

X

 *

1 1

s

X

v

U)

CO

o

X

to

8

X

S

X

X

X

X

I

X

X

0

o

X

X

X

v

0 Identified by T. W. Stanton.

10294 (6). Canning River, near top of Red Hill at camp 146. Isolated outcrop of dark sandstone, of which 10 feet is exposed. Lower sandstone member of formation. E. de K. Leffingwell, 1908.

10297 (17). Canning River, cut half a mile above camp 152, on north side 

of Ikiakpaurak Creek. Top of anticline, within 1 or 2 feet of a single bed, 

in hard dark limestone, of which 50 feet is exposed. E. de K. Leffingwell, 

1908.

10300 (22A). Canning River, half a mile east of No. 21, on the south side 

of the river. Top of a 35-foot bed of dark limestone which is overlain by 

100 feet of soft black shale. E. de K. Leffingwell, 1908.

10302 (30). Canning River. Cut on creek about half a mile above camp 

149. About 100 feet of dark limestone exposed. E. de K. Leffingwell, 1908.

10303 (30A). Canning River, same locality as No. 30 but top of exposure. 

E. de K. Leffingwell, 1908.

10304 (SOB). Canning River, talus below 30A. E. de K. Leffingwell, 1908.

10305 (30C). Canning River, same locality as No. 30 but bottom of exposure. 

E. de K. Leffingwell, 1908.

10310 (115B). Sadlerochit River, Camp 263 Creek, near the mountains. Outcrop of 12 feet of dark limestone, probably about 80 feet below the top of the 

limestone member of the formation. E. de K. Leffingwell, 1910-1912.
TRIASSIC, ARCTIC SLOPE 105

10295 (13). Canning River. Float from creek near camp 149. E. de K. 

Leffingwell, 1908.

10296 (15). Canning River. Outcrop across creek from camp 150. B. de K. 

Leffingwell, 1908.

10298 (18). Canning River. Isolated outcrop at base of hogback 2 miles 

 east of camp 152, on north side of creek. E. de K. Leffingwell, 1908.

10313. Hulahula River, fishing place at edge of mountains. Collected in 

winter from scattered outcrops along the river. E. de K. Leffingwell, 1910-1912.

10314. Shublik Falls, Canning River. Collected in winter from scattered outcrops along the river. E. de K. Leffingwell, 1910-1912.

10315. Sagavanirktok River. Slab collected by natives. E. de K. Leffingwell, 1910-1912.

10316. Black Island, Canning River, near Shublik Falls. E. de K. Leffingwell, 1910-1912.

10299 (21). Canning River, cut on south side of Ikiakpaurak Valley 1 mile 

above camp 152. Bottom of exposure of 100 feet of fissile black shale.

E. de K. Leffingwell, 1908.

10301 (22C). Canning River, same locality as 22A, but from 1 to 3 feet of 

black shale 30 feet above 22A. About the same horizon as No. 21. E. de K. 

Leffingwell, 1908.

10301' (22C'). Canning River, same locality as 22C, but from a talus block 

immediately below 22C. E. de K. Leffingwell, 1908.

The fauna of these rocks is certainly Upper Triassic, as is shown 

by the presence of Glionites and Ealobia cf. H. superba Mojsisovics. 

The presence of the Halobia suggests a position in the middle or 

Karnic stage of the Upper Triassic, corresponding approximately to 

the horizon of the Chitistone limestone. The association of such 

genera as Megalodon? and Aviculipecten, which are not known from 

rocks younger than the Triassic, with such genera as Gervillia, 

Gryphaea, Cardium, Natica, and Atractites, which are not known 

from rocks older than the Triassic, would in itself indicate the 

Triassic age of this fauna. This fauna differs from the betterknown Triassic faunas of the southern part of Alaska in the entire 

absence of the corals and of such pelecypods as Myophoria and 

Pleuromya and in the practical absence of the ammonites, especially 

such ammonite genera as Tropites, Juvavites, and Arcestes, which 

are very abundant in most of the Triassic areas of southern Alaska. 

It differs also from the other known Alaskan Triassic faunas in the 

preponderance of the brachiopods and in the presence of Gervillia 

and Megalodon?, and it differs from most of the others in the presence of Clionites. The Alaskan fauna most closely related to this 

occurs in the lowest bed of the Triassic limestone near Nation River.

The presence of Pseudomonotis subcirculwris (Gabb) in talus and 

float material at several localities in the Canning River district indicates the presence of beds corresponding to those of the McCarthy 

formation. The Pseudomonotis zone from which this material was 

derived may occur either in the uppermost part of this formation or 

in a thin overlying formation that has not been recognized.
106 MESOZOIC STRATIGRAPHY OF ALASKA

NOATAK VALLEY 

CHERTY LIMESTONE FLOAT

The presence of Upper Triassic rocks in the Noatak Valley is 

indicated by a boulder containing well-preserved specimens of Pseudomonotis subcircularis (Gabb) in the gravel of Noatak Elver. 

The fossils, according to Philip S. Smith,9 who found them, occur in 

masses of black chert contained in dark thin-bedded limestone. The 

rocks that crop out in the vicinity consist of dark limestone that is 

practically indistinguishable in lithologic character from the Triassic boulders but has been considered a member of the Noatak sandstone, of lower Carboniferous (Mississippian) age. It was the 

opinion of Smith that the Triassic boulders had probably not been 

transported far, but that they might possibly have come from a considerable distance. The river gravel contains boulders with Carboniferous fossils and also some that are possibly Devonian. It 

seems possible that there may be a large area of Triassic rocks where 

the fossils were found, the neighboring outcrops consisting of Triassic limestone rather than being members of the Noatak sandstone, 

as Smith considered them, and the Carboniferous float being brought 

down from the hills to the north. It is also possible that all the 

neighboring rocks are Carboniferous and that the Triassic float was 

brought in from a distance. A third possibility is that the Carboniferous and the Triassic rocks are both present near this locality, 

but that they occur in such intimate stratigraphic or obscure structural relations that they have not been differentiated.

The age of the fossiliferous cherty limestone was determined by 

T. W. Stanton, who states:

7244. No. 11 AS 44; Noatak River at first stream from south, west of the 

camp of August 8, approximately latitude 68° N., longitude 159° W.: 

Pseudomonotis subcircul'aris (Gabb).

Upper Triassic. The collection contains only a single species, but it is represented by a number of well-preserved specimens and is a widely distributed 

and very characteristic form found thus far only in the Upper Triassic.

NORTHWESTERN ALASKA 

GENERAL FEATURES

The known Triassic rocks of the extreme northwestern part of 

Alaska include chert, shale, and thin-bedded limestone exposed in 

several areas near Cape Lisburne and in an area about 55 miles 

farther south, near Cape Thompson. The Triassic rocks of Cape 

Lisburne and Cape Thompson not only are practically identical in

8 Smith, P. S., The Noatak-Kobuk region, Alaska: U. S., Geol. Survey Bull. 536, pp. 

79-80, 1913.
TRIASSIC, NORTHWESTERN ALASKA 107

lithologic and faunal character but apparently occur in very similar 

stratigraphic relations to the associated formations.

The general character, sequence, and relations of the rocks in the 

vicinity of Cape Lisburne were represented by Collier 10 as follows:

Tabular statement of stratigraphy, Cape Lisburne region, Alaska

Age

Recent.

Pleistocene.

Lower Cretaceous (?).

Upper Jurassic.

Lower Carboniferous 

(Mississippian) .

Devonian (?).

Formation

Corwin.

Lisburne.

Contact 

relations

Unconformity.

Unconformity.

Conformity.

Unconformity.

Conformity.

Conformity.

Conformity (?) .

Thickness 

(feet)

50+

50+

10,000+

15,000+

3, 000+

1, 000+

.500+

Lithologic character

Sands, gravels, etc.

.Gravels, silts, talus, and'ground 

1 ice. '

Sandstones interbedded with 

shales. Nonfossiliferous.

Calcareous and carbonaceous 

shales with sandstones and 

conglomerates at infrequent 

intervals. Many coal beds. 

Jurassic plants. No marine 

fauna.

(a) Massive limestones interstratified with white cherts. 

Extensive coral and bryozoan 

fauna.

(b) Thinly bedded shales, slates, 

cherts, and limestones. Fauna 

includes brachiopods, trilobites, cephalopods, and lamellibranchs. °

(c) Thinly bedded black shales, 

slates, and limestones. Several coal beds. Lower Carboniferous flora. Brachiopod and 

coral fauna. ">

9 nnn-L Calcareous sandstones and 

AUUU+ slates. No fossils found.

0 The brachiopods, trilobites, and cephalopods were obtained at only two localities (4 AC 15 and 4 AC 

17, which possibly do not belong in this formation. 

* In one possible instance.

The preceding table shows that the rocks south and southeast of 

Cape Lisburne were divided by Collier into three supposed lower 

Carboniferous formations. The fossils of the upper and lower formations prove beyond doubt that they are of lower Carboniferous 

age. Collier considered that the three formations were in conformable sequence, and as the fossils of the "middle formation" were 

regarded as of rather indefinite character, the Carboniferous age of 

the entire sequence was not doubted. It should be pointed out that 

the structure in this district is very complex, overturned folds and 

thrust faults being numerous and all the less rigid beds being 

minutely crumpled. It should also be remembered that Collier, in 

addition to measuring stratigraphic sections and collecting fossils, 

obtained sections and samples from a large number of coal beds and 

carried topographic and geologic mapping along 100 miles of un10 Collier, A. J., Geology and coal resources of the Cape Lisburne region, Alaska: 

U. S. Geol. Survey Bull. 278, p. 16, 1906.
108 MESOZOIC STRATIGRAPHY OF ALASKA

sheltered ocean coast, doing all this traveling in an open boat during 

a single month in which "there were not more than 10 calm days." 

It is consequently not surprising that the sequence as given above 

is not altogether correct, a reexamination of the fossils having shown 

that the fauna at some of the localities referred to the " middle formation " is Upper Triassic.11 This conclusion makes it necessary to 

reconsider the evidence concerning the age of this formation and its 

stratigraphic and structural relations to the Lisburne limestone and 

to the lower coal-bearing formation. On reconsidering the evidence 

in full (see pp. 109-112) the writer concludes that the entire " middle 

formation " is Upper Triassic, its contacts with the lower Carboniferous rocks of the Lisburne limestone being thrust faults. The general 

sequence near Cape Lisburne is probably about the same as at Cape 

Thompson, where the section described by Kindle" may be represented as follows:

General section of Mesozoic and Paleozoic rocks near Cape Thompson

Feet

Jurassic or Cretaceous (?) : Soft black shale_______ 5004- 

Upper Triassic: Chert, shale, and thin-bedded limestone- 625 

Carboniferous (?) : Light-gray cherty limestone______ 2,000± 

Lower Carboniferous:

Light-gray limestone with abundant lower Carboniferous fossils, chiefly corals and brachiopods_____ 3,000+ 

, Shale and sandstone, with lower Carboniferous fossil

plants____________________________ 400

SHALE, CHERT, AND LIMESTONE NEAR CAFE LISBURNE

Historical review. The Upper Triassic rocks near Cape Lisburne

were first described by Collier 13 as the " middle formation " of the 

local Carboniferous section, and were assigned to the lower Carboniferous because of their apparent position beneath the Lisburne 

limestone and above the "lower formation," both of which contain 

lower Carboniferous fossils.

The same publication includes a short general discussion of the 

fauna of these beds by G. H. Girty,14 with lists of the fossils that 

Collier collected. The fossils from the beds that are now regarded 

as Triassic were discussed briefly, with a statement that they are 

different from the characteristic lower Carboniferous faunas of the 

other formations and seem to include no diagnostic forms, and were 

assigned tentatively to the lower Carboniferous on the basis of an

11 Kindle, E. M., The section at Cape Thompson, Alaska: Am. Jour. Sci., 4th ser., 

vol. 28, pp. 527-528, 1909.

13 Idem, pp. -520-52S.

19 Collier, A. J., Geology and coal resources of the Cape Lisburue region, Alaska: 

U. S. Geol. Survey Bull. 287, pp. 16, 18, 19-21, pi., 1, 1906.

"Idem, pp. 22-26.
TRIASSIC, NORTHWESTERN ALASKA 109

assumption that the strata from which they were obtained are interbedded with the known Carboniferous rocks.

The presence of Upper Triassic rocks near Cape Lisburne was 

first pointed out by Kindle 15 on the basis of the following statement 

by Stanton:

Among the collections obtained by Mr. Collier in the Cape Lisburne region 

some years ago there are several small lots consisting mainly of a form that 

seems to be identical with Pseudomonotis subcircularis and probably comes 

from about the same horizon as this Cape Thompson locality. These fossils 

were at that time identified as Aviculopecten and referred to the Carboniferous, chiefly because of the stratigraphic relations they were supposed to hold 

with well-characterized Carboniferous faunas.

Kindle added a brief statement indicating which of the collections 

previously regarded as Carboniferous were to be considered probably Triassic.

The Triassic rocks at Cape Lisburne were described briefly, on the 

basis of Collier's description, by Martin,16 who pointed out that the 

entire " middle formation " of Collier is probably Triassic.

Stratigraphic description. The Triassic rocks near Cape Lisburne, which have a thickness of over 1,000 feet and contain Pseudomonotis subcircularis (Gabb), constitute the "middle formation" 

of the Carboniferous as described by Collier. Neither base nor top 

of these beds has been recognized, all the observed contacts being 

faults. The next older rocks known in the vicinity are the lower 

Carboniferous (Mississippian) beds of the Lisburne limestone, and 

the next younger are the Corwin formation, of Cretaceous or Jurassic age. Collier's description 17 of the "middle formation" is as 

follows:

The middle formation of the Carboniferous series has also been identified 

at three localities along the coast. It consists of thinly bedded black slates, 

shales, cherts, and cherty limestones and is distinguished from the lower formation, which it resembles in general appearance, by the absence of coal beds or 

fossil flora of any kind, and from the upper formation of the series, first by 

its lithologic character and second by its fauna, which consists principally of 

brachiopods and mollusks, while that of the upper consists principally of corals. 

In general the formation is harder than the coal-bearing formation, and for 

this reason the topography produced by it is more rugged. Like the coalbearing formation it is rather intensely folded, and faulting has usually occurred along its contacts with the massive limestones which overlie it.

The "middle formation" has been recognized in three or four 

areas in the Lisburne region. The area that yielded most of the 

Triassic fossils (lots 4 AC 15, 4 AC 18, 4 AC 21, 4 AC 81, 4 AW 33,

16 Kindle,, B. M., The section at Cape Thompson, Alaska: Am. Jour. Sci., 4th ser., vol. 

28, pp. 527-528, 1909.

18 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 

703-704, 1916.

17 Collier, A. J., op. cit, pp. 19-20.
110 MESOZOIC STBATIGBAPHY OF ALASKA

4 AW 34) is a belt about 2 miles wide which extends southeastward 

from a point on the coast near Wevok, about 8 miles east of Cape 

Lisburne, between an area of supposed Cretaceous rocks on the northeast and an area of the Lisburne limestone on the southwest. The 

contact of the " middle formation" with the supposed Cretaceous 

rocks, as indicated in Figure 2, was regarded by Collier as probably 

an overthrust fault.

The relation between the " middle formation " and the Lisburne 

limestone is not so clear, it being stated that the Lisburne limestone

Miles

Cretaceous (?) sandstone 

and shale

Triassic shales, slates, limestones, and cherts. Solid 

lines represent beds whose 

outcrops have been actually 

traced on the ground

FIGUBB 2. Ground plan of outcrops adjoining the probable fault contact between the 

Triassic and Cretaceousi (?) formations 3 miles east of Cape Lisburne. (After A. J. 

Collier)

seems to overlie the cherty rocks of the "middle formation" but 

that 

along the poorly exposed contact there is brecciation and other evidences of 

faulting. The slate and chert area here is marked by low hills and valleys, 

above which the massive limestone mountains rise abruptly to an elevation of 

about 1,000 feet. The base of this mountain extends in a nearly straight 

line, which suggests a fault escarpment. In this area the sinuous outcrops of 

the cherty beds (see fig. 2), which can be traced for considerable distances, 

indicate that the formation is intensely crumpled and probably closely folded.

In view of this suggestion of faulting, together with the testimony 

of the fossils to the effect that the apparently underlying beds are 

the younger, an overthrust fault may reasonably be assumed along 

the southwestern as well as the northeastern boundary of the cherty. 

rocks of this area.

The same Triassic fauna has been collected about 3 miles north of 

Cape Lewis (4 AW 38), from chert beds 450 or 500 feet thick. These
TRIASSIC, NORTHWESTERN ALASKA 111

cherts seem to be both overlain and underlain conformably by limeftone. The underlying limestone contains Carboniferous fossils 

(4 AW 39), but no fossils were collected from the overlying beds.

Chert beds which are similar to those containing the Triassic 

fauna but from which no fossils have been obtained occur also about 

a mile south of Cape Lewis. Collier says of the " middle formation " 

of this locality: "It seems to rest conformably on the coal-bearing 

formation and to be overlain conformably by the massive limestone 

[Lisburne], as shown in Figure 3. Its thickness here is estimated at 

about 1,000 feet." The notes taken by Chester Washburne at this 

locality read:

In the sketch [fig. 3] the underlying limestone on the right is thin bedded, 

black, and in places somewhat sandy. It contains many brachiopods and corals, 

of which 4 AW 35 is a sample collection. This limestone is about 200 feet

500ft.

Lisburne limestone Shales, slates, cherts.and limestones Coal-bearing shales,clays.and 

(coral fauna) (brachiopods,pectenoids.and corals) limestones (Paleozoic plants)

FIGDRB 3. Sketch showing stratigraphic relations of the Triassic and Carboniferous formations south; of Cape Lewis. (After A. J. Collier)

thick. Overlying it is a thin-bedded varicolored chert, mostly black, about 

250 feet thick and somewhat contorted. Overlying the chert, probably conformably, is another thin-bedded limestone, purer than the first and with an 

exposed thickness in the next hill north (Cape Dyer) of [several] thousand 

feet. The basal 500 feet of this limestone contains considerable interstratified 

nodular and broken chert and numerous fossils (4 AW 36). Above 500 feet 

from the base, chert fragments are comparatively rare.

As the fossils in lots 4 AW 35 and 4 AW 36 are clearly Carboniferous, it is evident either that the cherty beds at this locality are 

not Triassic or that there is a fault between the cherty rocks and the 

apparently overlying limestone. The latter alternative is the more 

probable, for the basal contact of the upper limestone as represented 

in Figure 3 and more especially as drawn in the original field sketch 

is not parallel to the bedding of the underlying cherty beds and 

might be either an unconformity or a thrust fault.

The " middle formation " is also represented on the map as occurring at a locality 4 miles south of Cape Lisburne. No fossils have 

been collected at this locality, nor have the local relations been 

described.

Age and correlation. The Triassic shale, chert, and limestone near 

Cape Lisburne have yielded the fossils listed in the following table.
112 MESOZOIC STRATIGRAPHY OF ALASKA

The presence of Pseudomonotis subcircularis indicates a correlation 

with the Pseudomonotis-be&r'mg beds at the tip of the Upper Triassic. No trace of the older Triassic faunas has been found near 

Cape Lisburne.

Fossils from Upper Triassic shale, chert, and limestone near Cape Lisburne °

Pseudomonotis subcircularis

(Oabb). ...... . .........

^H

O<$ *

b

00

O

O

"*

b

O

 at.

 *

b

O

 <J

 *

b

S3'

^

 <!

 « 

a

b

S

& ^

 HI

W

p

<!

^

a

b

S

^

<1

 *

b

^,

^

b

0 a, Identified by George H. Girty; b, identified by T. W. Stanton.

4 AC 15. 1% miles southeast of Wevok. Chert, cherty limestone, and shale. 

A. J. Collier, 1904.

4 AC 18. 3% miles southeast of Wevok. A. J. Collier, 1904.

4 AC 21. 3 miles east-southeast of Wevok. A. J. Collier, 1904.

4 AC 81. 4 miles southeast of Wevok. A. J. Collier, 1904.

4 AW 33. About 2 to 3V2 miles southeast of Wevok. Chert. C. W. Washburne, 1904.

4 AW 34. About half a mile southeast of camp near Wevok. Chert. C. W. 

Washburne, 1904.

4 AW 38. 3% miles north of Cape Lewis. Chert 450 or 500 feet thick, which 

is conformably underlain and overlain by fossiliferous limestone. From the 

underlying limestone the fossils of lot 4 AW 39 were obtained. C. W. Washburne, 1904.

4 AW 45. Cobblestone on beach at south side of Point Hope. C. W. Washburne, 1904.

(?) Southeast of Wevok. Collier and Washburne, 1904.

CHERT AND LIMESTONE NEAB CAFE THOMPSON

Historical review. The presence of Upper Triassic rocks near 

Cape 'Thompson was first indicated by Hyatt 18 in the following 

statement: "A slab from Cape Thompson, Arctic coast, has numerous 

specimens of Halobia, or Daonella, and is probably Triassic."

Cape Thompson was not actually visited by Collier, but he made a 

sketch showing the geologic section exposed in the cliffs as seen from 

the deck of the steamship Corwin at a distance of about 3 miles. 19 

This sketch is shown in Figure 4. The arch in the center, which is 

called "Agate Rock," is shown in greater detail in a photograph 20

18 Hyatt, Alpheus, Report on the Mesozoic fossils: U. S. Geol. Survey Seventeenth Ann. 

Rept., pt, 1, p. 907, 1896'.

19 Collier, A. J., G-eology and coal resources of the Cape Lisburne regrion, Alaska: U. S. 

Geol. Survey Bull. 278, p. 21,, fig. 7, 1906.

20 Idem, pi. 4, A.
TRIASSIC, NORTHWESTERN ALASKA 113

which Collier obtained from Doctor Call, surgeon of the United 

States revenue cutter Thetis.

The fossils from Cape Thompson that were identified by Hyatt 

as probably Triassic were discussed briefly by G. H. Girty,21 who 

stated that they resemble and occur in a matrix similar to that containing the doubtful fossils from Cape Lisburne that are now regarded (see p. 108) as Triassic.

The occurrence of Upper Triassic rocks near Cape Thompson was 

described by Kindle,22 who gave a stratigraphic section showing the 

position of the fossiliferous Triassic beds and discussed their relation to the underlying and overlying rocks in some detail.

The Triassic rocks near Cape Thompson have been briefly doscribed by Martin.23

Stratigraphic description. The Triassic rocks near Cape Thompson consist of chert, argillite, and thin-bedded limestone aggregating 

625 feet in thickness. They rest with apparent conformity on unfossiliferous limestone which overlies a Mississippian (lower CarFIGUHE 4. Sketch of the section exposed in the cliffs at Cape Thompson. (After A. J.

Collier)

boniferous) limestone and which is supposed to be of Carboniferous 

age. They are overlain with apparent conformity by shale that is 

possibly Jurassic or Cretaceous. Pseudomonotis subcircularis 

(Gabb) has been obtained near the top of the strata referred to the 

Triassic.

The Triassic rocks, according to Kindle, are exposed in a belt 1% 

to 2 miles wide, bounded on both sides by Carboniferous limestone. 

The Triassic rocks lie in a syncline whose axis trends north of northwest and reaches the coast about 2 miles southeast of the northwesterly outcrops near Cape Thompson. The Triassic and overlying 

beds are apparently included in No. 4 in the accompanying sketch 

by Collier.24 (See fig. 4.) It should be noted, however, that, according to Kindle, the structure is not altogether correctly represented 

in this sketch. The character and occurrence of the Triassic and 

associated rocks near Cape Thompson were described by Kindle 2d 

as follows:

21 Collier, A. J., op. cit.,-p. 25.

22 Kindle, E. M., The section at Cape Thompson, Alaska: Am. .Tour., Sci., 4th ser., vol. 

28, pp. 521-522, 526-528, 1909.

28 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 703- 

704, 1916.

24 Collier, A. J.f Geology and coal resources of the Cape Lisburne region, Alaska: U. S. 

Geol., Survey Bull. 278, p. 21, 1906.

» Kindle, B. M., op. cit., 526.
114 MESOZOIC STKATIGBAPHY OF ALASKA

i

The higher beds of the Cape Thompson section are brought in contact with 

the beds already described in the midst of a zone of rather local but complicated 

folding and possibly of faulting, which renders it impossible to give even an 

approximate estimate of their thickness as seen from the top of the southeastern portion of the Cape Thompson cliffs; but between the second and the 

fourth deep ravines separating the high ridges just southeast of the cape along 

the coast the exposures are continuous for 2 miles, exposing a section of 

northerly dipping beds in which the dip .decreases from 35° to 0 near the 

middle of the synclinal. We find in the series of cliffs which face the sea to the 

southeast of the second ravine below Cape Thompson a section which passes 

without structural complications from the fossiliferous Carboniferous limestones to the top of the highest beds exposed in this vicinity. This section is 

as follows:

Section 15, 2 miles southeast of Cape Thompson

Feet

e. Soft black shales________ _ - 500+ 

d. Dark cherts and thin-bedded cherty limestones with some

greenish bands _ _ ___ 25 

c. Argillites with bands of black, green, and dull red cherts- 600 

b. Light-gray limestone weathering buff, with some bands of

dark chert. Apparently barren of fossils _ 2, 000+ 

a. Light-gray limestone similar to the above but with less

chert and containing numerous fossils, in which corals

are conspicuous _ 3, 000+

The lowest member (a) of this section contains a characteristic 

lower Carboniferous fauna. No fossils were obtained from the next 

higher member (b), which consequently may be either Carboniferous or Triassic. According to Kindle,26 however,

The close physical resemblance of the second division (b) of the limestone 

series to the lower leaves little doubt that it is also of Carboniferous age. 

It may represent the upper Carboniferous, which has not been recognized 

anywhere on the northwestern coast of Alaska, though known on the Yukon 

and in southeastern Alaska.

The contact between the Triassic and the Carboniferous rocks, 

according to Kindle, is probably at the base of bed c, and the highest' 

black shale (e) was believed to be possibly the equivalent of the 

Cretaceous or Jurassic Corwin formation. (See p. 457.) Kindle 

described the supposed Triassic members of this section as follows:

The lithologic change at the top of this limestone series is abrupt. The 

beds included in c and d are essentially similar and represent the same 

formation, although there is less of the calcareous element in the lower beds. 

Fossils were found, however, only in the upper beds marked d in the section. 

They occur in great abundance in certain strata in this portion of the section. 

About 7 feet near the top are composed almost exclusively of shells which 

have been largely altered to chert.

Age and correlation. The only fossils that have been obtained 

from the Triassic rocks near Cape Thompson are the collection de28 Kindle, E. M.( op. cit., p. 527.
TRIASSIC, ST. LAWRENCE ISLAND 115

scribed by Hyatt and the collection obtained by Kindle, described 

on pages 113-114 and listed below. Concerning the fossils collected 

by Kindle (lot 15d) Stanton 27 said:

This collection consists of limestone fragments with numerous specimens of 

aviculoid shells referable to Pseudomonotis subcircularis (Gabb) or to a 

closely related species. No other recognizable species are associated with it. 

This species occurs in an Upper Triass'c horizon in California, and it has 

been accepted as sufficient evidence for the Triassic age of rocks containing 

it at Cold Bay and in the Copper River region of Alaska. In my opinion 

the horizon which yielded it at Cape Thompson is also Upper Triassic.

The localities are as follows:

15d. Mouth of creek 2 miles southeast of Cape Thompson. Uppermost 7 

feet of bed d in section on page 114. E. M. Kindle, 1908. Pseudomonotis cf. 

P. subcircularis (Gabb).

( ). Near Cape Thompson. Exact bed and collector not known. Halobia 

or Daonella. (identified by Alpheus Hyatt.)

ST. LAWRENCE ISLAND 

TRIASSIC (1) FLOAT

It is possible that Upper Triassic rocks are present on St. Lawrence Island, where Collier 28 found a boulder of uncertain derivation 

which he described as follows:

On St. Lawrence Island Carboniferous rocks of the formation immediately 

below the Lisburne are probably represented, since drift material containing 

fossils of this horizon has been obtained by the writer on the island at some 

distance from the sea, though the rocks in place have not yet been located.

The fossils in this boulder were referred by Girty 20 to the Carboniferous on account of their identity with the supposed Carboniferous (Triassic) fossils of the " middle formation " at Cape Lisburne, 

described on pages 109-112, it being stated that

* * * and a specimen from St. Lawrence Island (4 AC 53), though rather 

scanty evidence, as they show what apparently is the same species in the same 

sort of matrix, can with a good degree of probability be correlated with the 

beds about Cape Lisburne.

If these fossils are identical with the supposed "Aviculopecten" 

from the "middle formation" near Cape Lisburne, described on 

pages 109-112, they are obviously of Triassic age. This does not, 

however, prove that Triassic rocks crop out on this island, for there is 

a possibility that the fossiliferous boulder was transported by ice 

from the mainland. It may have been derived from outcrops on the 

shore near Cape Lisburne.

27 Stanton, T. W., cited by Kindle, E. M., op. cit., p. 527.

28 Collier, A. J., Geology and coal resources of the Cape Lisburne region, Alaska: 

U. S. Geol., Survey Bull. 278, p. 26, 1906. 

»Idem, pp. 23, 25.
116 MESOZOIC STRATIGRAPHY OP ALASKA

4 AC 53. 15 miles southeast of Cape Chibukak, St. Lawrence Island. Drift 

pebble. Aviculopecten sp. (same as at 4 AC l8)=Pseuctomonotis siibcvrcularis 

(Gabb)? A. J. Collier, 1904.

SEWAKD PENINSULA 

MIDDLE THIASSIC BOCKS OF BEOOKS MOUNTAIN

The presence of Triassic rocks on Seward Peninsula is indicated 

by a small collection of fossils of Middle Triassic age, which are reported by Kindle 80 to have been collected from black slate, between 

1,000 and 2,000 feet above sea level, on the southeast slope of Brooks 

Mountain, in the western part of Seward Peninsula. The occurrence and age of these fossils have been discussed by Martin.31

As the field occurrence of these fossils has never been studied by 

a geologist it is impossible to affirm positively just what beds contain them. They were probably, however, derived from the area of 

slate that forms a large part of Brooks Mountain. This slate was 

described by Collier 32 as probably part of the Kuzitrin " series " and 

as probably unconformably 'underlying the supposed Ordovician 

beds of the Port Clarence limestone. In a later account by Collier 33 

they were described as " slates in the York region " and were mapped 

as " chiefly dark phyllites and slates " of " undetermined Paleozoic " 

age. They were described by Knopf 34 as "slates near York" and 

were considered as underlying the Port Clarence limestone conformably. It was pointed out by Kindle 35 that the slates of the Brooks 

Mountain area " have been correlated without any conclusive evidence of their identity " with the slates of the main area west of the 

York Mountains. Kindle did not state any conclusion regarding the 

relation of these slates to the Port Clarence limestone, but showed 

that the Port Clarence includes rocks " ranging in age from Upper 

Cambrian to Devonian or Carboniferous " and that " the determination of the thickness and relationships of the several terranes 

* * * must await the completion of much detailed work on the 

stratigraphy and faunas of the region."

The geology of Brooks Mountain has been studied by Steidtmann 

and Cathcart, who were unable to find any rocks that they regarded 

as of Triassic age. They described the rocks on Brooks Mountain 

as follows 36 :

80 Kindle, E. M., The faunal succession in the Port Clarence limestone, Alaska: Am. 

Jour. Sci.,, 4th. ser., vol. 32, p. 339, 1911.

31 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull., vol. 27, pp. 690, 

704-705, 1916.

82 Collier, A. J., A reconnaissance of the northwestern portion of Seward Peninsula, 

Alaska: U. S. Geol. Survey Prof. Paper 2, pp. 17, 19, 21, pi. 3, 1902.

83 Collier, A. J., Geography and geology,, in the gold placers of parts of Seward Peninsula, Alaska: U. S. Geol. Survey Bull. 328, pp.. 79-80, pi. 11, 1908.

34 Knopf, Adolph, Geology of the Seward Peninsula tin deposits, Alaska : U. S. Geol. 

Survey Bull. 358, pp. 10-12, 13, 1908.

83 Kindle, E. M., op. cit, p. 339.

38 Steidtmann, Edward, and Cathcart, S. H., Geology of the York tin deposits: U. S. 

Geol. Survey Bull. 733,. p. 83, 1922.
TRIASSIC, GENERAL CHARACTER AND CORRELATION 117

The rocks at Brooks Mountain include an unknown thickness of black slate 

overlain by at least 1,000 feet of limestone. The contact between the slate and 

limestone is not exposed, hence it is not certain whether the slate was eroded 

before the limestone was laid down upon it. The lower 100 feet of the limestone consists of black slaty layers a fraction of an inch in thickness, interbedded with thin layers of gray fine-grained limestone. From this fact it 

would appear that there is a gradation from slate to limestone. The slates, 

however, are more intensely folded than the basal limestone beds. In position 

and character they are like the slates of other parts of the York region. Outside of the Brooks Mountain area the evidence is strong that the slates lie 

unconformably below the limestones, hence it is probable that they bear the 

same relation here.

The limestone was assigned by Steidtmann and Cathcart to the 

Ordovician and Silurian and the slate to the Cambrian or preCambrian. A statement by Kirk 3T on the fossils is quoted, in which 

the presence of Carboniferous corals from the north side of Brooks 

Mountain is mentioned.

The failure of any of the geologists, especially of Steidtmann and 

Cathcart, to find Triassic fossils on Brooks Mountain casts serious 

doubt on the supposed occurrence of Triassic rocks at that locality. 

It is possible that the fossils given to Kindle were brought from 

some other region, but the writer does not believe that this was done. 

It is entirely possible, in the writer's opinion, that unrecognized 

masses of Triassic rocks may be structurally included in the early 

Paleozoic limestone or that the slate which apparently underlies the 

limestone may be Triassic slate on which the limestone has been 

overthrust.

The following statement regarding the Triassic fossils that are 

supposed to have come from Brooks Mountain was made by T. W. 

Stanton:

5654. Southeast slope of Brooks Mountain, between 1,000 and 2,000 feet 

above sea level. From black slates. Collected by Peter Esch, of Nome, 1908: 

Daonella cf. D. lommeli Wissmann. 

Ceratites (Gymuotoceras) sp.

These are characteristic Triassic fossils and probably caine from the Middle 

Triassic. The collection is interesting from the fact that it affords the first 

evidence of the existence of Triassic rocks in that part of Alaska.

It .should be noted also that these are the only Middle Triassic 

fossils known from Alaska.

GENERAL CHARACTER AND CORRELATION 

MIDDLE TRIASSIC

The only known Middle Triassic rocks in Alaska are the slates of 

Brooks Mountain, Seward Peninsula. It has already been shown 

that these rocks occur in a region where no other Triassic rocks are

37 Steidtmann, Edward, and Cathcart, S. H., op. cit,, pp. 27-28. 

49448 26 9
118 MESOZOIC STKATIGRAPHY OP ALASKA

known, and that Middle Triassic rocks that can be correlated with 

them do not occur in other Alaskan regions.

The fossils in this locality include a species of Daonella that is 

closely related to though probably not identical with the species 

from Nevada and California which has been referred to Daonella 

lommeli Wissman, and an undetermined species of Ceratites (Gymnotoceras}. Daonella lommeli Wissman is a European species which 

is considered characteristic of beds that are generally referred to 

the Ladinic and, according to most writers, are regarded as representing the uppermost division of the Muschelkalk, or Middle Triassic, although they are sometimes regarded as constituting the lowest 

division of the Upper Triassic. The fossils from Nevada that have 

sometimes been considered identical with Daonella lommeli are regarded by J. P. Smith 38 as constituting a distinct species, Daonella 

dubia Gabb, and as belonging near the middle of the Middle Triassic. Gymnotoceras is an ammonite which is supposed to be highly 

characteristic of the Arctic type of Middle Triassic faunas. All 

known American species of Gymnotoceras are characteristic of the 

Daonella dubia zone of the Middle Triassic of Nevada. The Alaskan 

fossils are presumably to be regarded as belonging in approximately 

the same position.

The same horizon is probably represented by part of the Nicola, 

series of the Interior Plateau region of British Columbia. The 

Nicola series 39 is a thick succession of volcanic rocks with some 

interbedded limestone and argillite containing Pentacrinus asteriscus, Terebratula humboldtensis, Spiriferina or Cyrtina, Myacites 

cf. M. humboldtensis, Daonella cf. D. lommeli, Trigonodus, Cardita^ 

and Panopea cf. remondi.^ The Nicola series has been supposed to 

contain Pseudomonotis subcircularis, but this fossil does not occur 

in association with the others, having been obtained from an outlying area of argillite resting on volcanic beds that were correlated 

with those of the Nicola series.41

It should be noted that Daonella lommeli has been reported from 

many other localities in British Columbia. As in most of these 

reports more or less doubt has been expressed concerning the identification; as the Canadian fossil doubtfully referred to this species

88 Smith, J. P., The Middle Triassic marine invertebrate faunas of North America: 

U. S. Geol. Survey Prof. Paper 83, pp. 143-144, 1914.

30 Dawson, G. M., Report on the area of the Kamloops map-sheet, British Columbia: 

Canada Geol., Survey Ann. Kept, new ser., vol. 7, pp. 49B-62B, 112B-146B, 1896.

40 Idem, pp. 50B-51B. (The crinoid and brachiopods were identified by Whiteaves, 

the pelecypods by Hyatt.)

41 Dawson, G. M., Preliminary report on the physical and geological features of the 

southern portion of the interior of British Columbia: Canada Geol. Survey Kept. Progress 

for 1877-78, pp. 66B-67B.
TRIASSIC, GENERAL CHARACTER AND CORRELATION 119

has never been described or figured; and as in nearly all the reports 

the fossil has been listed as occurring in close association with characteristic Upper Triassic forms, the writer believes that the species 

may have been incorrectly identified and that it is probably an 

Upper Triassic species of Halobm. There is as yet no proof that 

Middle Triassic rocks are present in British Columbia, except in the 

Kamloops district. (See p. 126.)

UPPER TRIASSIC

General distribution. Upper Triassic rocks are widely distributed throughout those parts of Alaska occupied by the Pacific, 

Kocky, and Arctic Mountain systems, which are the three major 

mountain regions of the Territory. The Triassic deposits in each of

these regions constitute a section which, in its general stratigraphic 

and faunal character, is more or less typical of that entire region 

but which differs in greater or less degree from the sections in the 

other regions. These resemblances and differences possibly mean 

that the present major mountain areas occupy the sites of Triassic 

basins of deposition. The most complete local representation of 

these rocks is in the Chitina Valley, which must now and probably 

will always be regarded as containing the typical and standard 

section of the Upper Triassic rocks of Alaska and more especially 

of the Pacific Mountain region. The Chitina Valley section is 

typical in all its more essential features, both stratigraphic and 

faunal, of the Upper Triassic deposits of southern Alaska, although representatives of several horizons known in other Alaskan 

districts have not yet been recognized here. The Upper Triassic 

rocks of the region south of the Alaska Range are underlain in 

most places by volcanic beds that include the Nikolai greenstone of 

the Chitina Valley and the similar and probably corresponding 

lava or tuff and lava of other districts. Volcanic rocks are not 

present in this stratigraphic position north of the Alaska Range, 

where the Upper Triassic rocks rest directly on late Paleozoic limestone.

Dawsonites zone. The occurrence in southeastern Alaska of an 

Upper Triassic limestone that is probably older than any Upper 

Triassic beds known elseAvhere in Alaska is indicated by the presence, on the shores of Hamilton Bay, Kupreanof Island, of float 

containing fossils related to Spiriferina borealis Whiteaves and 

Dawsonites canadense Whiteaves. Neither of these species has been 

fouEid elsewhere in Alaska or at any American localities except 

in the Triassic rocks of Liard River, in the eastern foothills of the 

Rocky Mountains of British Columbia.
120 MESOZOIC STRATIGRAPHY OF ALASKA

The Triassic rocks of Liard Kiver, according to McConnell,42 

" consist of dark shales, usually rather coarsely laminated, and passing into calcareous shales interstratified with sandstones and shaly 

and massive limestones." The fossils, which have been described 

by Whiteaves,43 include 11 species, among which are Spiriferina 

borealis Whiteaves and Dawsonites canadense Whiteaves, which 

have been doubtfully identified from Hamilton Bay. Mojsisovics 44 

has pointed out that some of these fossils are indicative of Karnic 

age. Three of the Liard River species (Dawsonites canadense, 

Nathorstites McOonnelli, and Nathorstites lenticularis] , one of 

which occurs at Hamilton Bay, have been found, according to 

Bohm,45 in the Upper Triassic rocks of Bear Island, between Norway and Spitzbergen. The Triassic rocks of Bear Island, are 

generally regarded as of Karnic (possibly Lower Karnic) age, and 

an assignment of the beds on Liard River to the same position has 

been made by Frech 46 on the basis of the presence of the abovementioned species, which are common to the two regions.

The Hamilton Bay fauna may also be tentatively correlated with 

that from Bear Island and referred to the Karnic. This fauna 

possibly represents a boreal facies of the Karnic which has not been 

recognized farther south in North America.

Zone of Halobia of. H. superb®. The Chitistone limestone, which 

is the basal formation of the Upper Triassic section in Chitina Valley, is represented in other parts of the Pacific Mountain system by 

limestones which, although thinner, are similar to the Chitistone 

limestone in their general lithologic character, in their stratigraphic 

position between underlying volcanic rocks and overlying shale or

chert with Pseudomonotis, and in the general character of their 

fauna. The limestones which should be correlated with the Chitistone limestone include those of the upper Susitna Valley, of Herring 

Bay on Admiralty Island, and part of the Triassic limestone of 

Hamilton Bay on Kupreanof Island.

The fauna of these limestones includes unidentified species of. 

Tropites, Juvavitesf, and Arcestes, a species of Halobia closely related to Halobia superba Mojsisovics, and many other fossils of 

lesser significance. These fossils show that the fauna is certainly 

LTpper Triassic and that it probably belongs in the middle or Karnic

*2 McConnell, R. G., Report, on an exploration In the Yukon and Mackenzie basins, 

Northwest Territory: Canada Geol. Survey Ann. Rept, new ser., vol. 4, pp. 19D, 49D, 

1890.,

43 Whiteaves, J. F., On some fossils from th© Triassic rocks of British, Columbia: Contr. 

Canadian, Paleontology, vol. 1, pt 2, No. 3, pp. 127-149, pis. 17, 18, 18S9.

u Mojsisovics, Edmund von, Beitrage zur Kenntniss der obertriadischen CephalopodenFaunen des Himalaya: K. Akad. Wissenschaften Wien Denkschr., Band 63, p. 697, 1896.

43 Bohm, Johannes, Ueber die obertriadische Fauna der'Bareninsel: K. svenska Vetenskaps-Akad. Handlingar, Bandet 37, No. 3, pp. 56-58, 61-64, 73-76, 1903.

48 Frech, Fritz, Die zirkumpacifische Trias: Lethaea geognostica, Tell 2, Das Mesozoicum, Band 1, Trias, pp. 488-491, 508, 1908.
Tentative correlation of the Triassic rocks in various parts of Alaska

Age

Triassic. Tipper 

Noric. Upper 

Lower Noric.

Noric. Karnic or

Karnic.

Middle Triassic.

Permian orTriassic.

Nizina Valley

McCarthy formation 

(shale and thin limestone with Pseudomonotis subcircularis; 

much chert in lower 

1,000 feet). 1,500 to 

2,000 feet.

Nizina limes tone(thinbedded limestone). 

No fossils. 1,000 to 

1.200 feet.

Chitistone limestone, 

(massive bluish-gray 

limestone). Contains HaloUa cf. H. 

superba, Tropites, 

Juvamtes, Arcestes, 

etc. 1,800 to 2,000 

feet.

Nikolai greenstone 

(basaltlava). 4,000 

to 5,000 feet. Base 

not exposed.

Kotsina and Kuskulana 

valleys

Kuskulana formation.

(Black shale with 

thin limestone) . 

Contains Pseudomonotis subcircularis. 2,000 (?) 

feet.

Thin -bedded limestone with some 

shale. Fauna 

similar to that of 

Chitistone limestone. 500 to 3,000 

feet.

Chitistone limestone 

(massive limestone). 

300 to 1,200 (?) feet.

Nikolai greenstone (basalt lava). 6,500(?)feet. 

Underlain by Carboniferous beds.

White River

Lava, tuff, and breccia 

with Pseudomonotis. 

Shale with Pseudomonotis. Underlain 

unconformably by 

Permian (?) limestone.

Cooper Pass

Thin-bedded limestone with Pseudomonotis subcir cularis. Thickness and 

relations not known.

i

Upper Susitna Valley

Slate, tuff, arkose, and 

calcareous beds with 

Pseudomonotis subcircularis. Many 

hundred feet.

Limestone with Halobia cf. H. superba, 

jTropites, etc. A few 

hundred feet.

Basic lava and tuff. 

3,500 feet. Probably underlain by 

Carboniferous (?) 

limestone.

East Fork of Chulitna River

Thin-bedded 

limestone and 

shale with Pseudomonotis subcir cularis and 

Heterastridium.

West Fork of 

Chulitna River

Tuff, limestone, 

shale, and lava 

with Cassianetta 

(underlain unconformably by 

greenstone).

Kenai Peninsula

Limestone with Pseudomonotis subcircularis near top and 

Halobia below. 

1,000+ feet.

Contorted chert. 

Thickness unknown.

Ellipsoidal lava. 

3,000 feet. Underlain by slate and 

eraywacke of unknown age.

West coast of Cook Inlet

Calcareous shale and 

some chert. Con- 

's tains PseudomonJ3 otis subcir cularis. 

" 1,000 (?) feet.

 CM 

03 a

a03

W Massive chert with 

no fossils. 1,000 (?) 

feet.

Limestone with Halobia. Thickness and 

relations not known.

Greenstone. Thickness 

and relations not 

known. Probably 

underlain by slate.

Hiamna Lake

Limestone with 

corals. Thickness several 

hundred feet.

Greenstone (?)

Alaska Peninsula

Limestone and shale 

with Pseudomonotis 

subcircularis. 700+ 

feet.

Contorted chert with 

no fossils. Thickness not known.

Greenstone.

Kodiak Island

Contorted chert 

with no fossils. 

Thickness not 

known.

Ellipsoidal lava. 

Thickness unknown. Probably underlain by 

slate and graywacke.

Gravina Island

Shales with Halobia cf. 

H. superba. Limestone with corals. 

(Position and relations uncertain). 

Probably underlain 

by Devonian limestone.

Screen Islands

Limestone of unknown position 

(underlain by 

Permian limestone).

Keku Strait

Basaltic and andesitic 

lava, breccia, and 

tuff interbedded 

with cherty limestone with Pseudomonotis subcircularis. 

Basal conglomerate.

Conglomerate limestone and sandstone 

with Halobia cf. H. 

superba, etc. Relation to Dawsonitesbearing beds not 

known.

Limestone float with 

. Spiriferina borealis (?) andDawsonites 

canadense (?).

Ellipsoidal lava. Relations to Dawsonto-bearing beds 

not known. Underlain by Permian (?) 

limestone.

Herring Bay, Admiralty Island

Limestone with Pseudomonotis subcircularis.

Chert and shale with 

no fossils. Position 

doubtful.

Limestone with Halobia cf. H. superba, 

Juvavites, Arcestes, 

etc. 273 feet. Basal 

contact not seen.

Juneau district

1 

w^

° £ 

3 g Slate containing 

§ g Halobia cf. H. su3 S perba interbed- 

;* £ ed with ande3 te siticlava and tuff. 

g~

2 ° 

as 

O

Yukon River near 

Nation River

Calcareous shale and 

shaly limestone 

with Pseudomonotis 

subcircularis.

Conformity (?)

Limestone and shale 

with Halobia cf. H. 

superba and Clionitis(1). Basal limestone bed with many 

brachiopods, nautiloids, and TracJiyceras cf. T. leconti. 

300+ feet. Underlain by Permian (?) 

limestone.

Kantishna district

Limestone of unknown position 

(con tains corals).

Firth River

Limestone with Pseudomonotis subcircularis. Thickness 

and relations unknown.

Flaggy limestone with 

Halobia cf. superba. 

Thickness not 

known. Underlain 

by Permian (?) limestone.

Canning River

Float with Pseudomonotis subcircularis. 

Derivation uncertain.

Black shale with 

Halobia cf. H. suri perba; Limestone 

2 and some shale 

to with Halobia cf. 

8 H. superba, brachg ipods as at Nation 

tj River, Gervillia, 

a MegalodonCl),&ad 

 g Clionites (?) 

a Calcareous sand03 stone without 

characteristic fossils.

Permian (?) limestone.

Noatak Valley

Float of cherty 

limestone with 

Pseudomonotis 

subcircularis. 

Derivation not 

known.

Cape Lisburne

Shale, chert, and limestone with Pseudomonotis subcircularis. 

1,000+ feet. Probably underlain by 

Carboniferous limestone.

Cape Thompson

Chert and limestone 

with Pseudomonotis 

subcircularis. 625 

feet. Underlain by 

Carboniferous (?) 

limestone.

St. Lawrence Island

Float with Pseudomonotis subcircularis. Derivation uncertain.

Brooks Mountain, 

Seward Peninsula

Slate with Ceratites (Qymnotoeeras) and Daonella. Thickness 

and relations not 

known.

49448 26. (Face p. 120.)
TRIASSIC, GENERAL CHARACTER AND CORRELATION" 121

stage of the Upper Triassic. Although most of the identified genera 

of brachiopods and pelecypods have a long range, yet both the 

character of many of the individual forms and the general aspect of 

the assemblage are unmistakably Triassic. The ammonites all belong to highly characteristic Upper Triassic genera and point 

strongly toward a horizon in the Karnic, as does also the pelecypod 

identified as Halobia cf. H. superba Mojsisovics. The latter, according to Stanton, is identical with the species known by that name in 

the Triassic rocks of California and is very closely related to Halobia 

superba of the Triassic rocks of Europe, even though it may not be 

the same. The Chitistone limestone may be regarded as certainly 

the equivalent of at least part of the Hosselkus limestone of California and as probably representing in general the lower part of the 

Hosselkus limestone. The Chitistone fauna belongs to the Mediterranean type of Triassic faunas and is believed to be indicative of 

warm-water conditions.

On Yukon Kiver and in the eastern part of the Arctic Mountains 

(Firth and Canning Valleys) are limestones which seem to correspond in general position to the Chitistone limestone. The fauna of 

these limestones is connected with that of the Chitistone limestone 

by the presence of Halobia cf. H. superba, although it differs from 

it in the absence of the characteristic ammonite genera Tropites, 

Juvavites, and Arcestes, of the corals, and of such pelecypods as 

Myophoria and Pleuromya. It differs also in the abundance of the 

brachiopods and in the presence of Glionites and several other genera 

that have not been found in the Chitistone limestone. This fauna 

may represent the boreal f acies of the Karnic, which is elsewhere not 

well developed in America. The writer regards these beds as probably being approximately synchronous with the Chitistone limestone but as having been deposited in a different basin.

It is highly probable that the equivalent of the Chitistone limestone is present in the Queen Charlotte Islands, British Columbia, 

where, according to Dawson,47 a massive limestone at least 400 feet 

thick rests on volcanic rocks and is overlain by thin-bedded limestone 

and flaggy calcareous argillite containing Pseudomonotis subcircularis. The similarity of this section to that of the Chitina Valley is 

striking and suggestive. It is not possible, however, to establish 

this correlation definitely on paleontologic evidence, for the published lists of fossils 48 unfortunately do not indicate which of the 

species described by Whiteaves 49 were obtained from the massive 

limestone. A suggestion that these fossils include Karnic forms

47 Dawson, G. M., Report on. the Queen Charlotte Islands: Canada Geol. Survey Kept. 

Progress for 1878-79, pp. 48B, 5'5B,, 61B-62B, 63B, 1880.

48 Idem; pp. 49B, 53B.

48 Whiteaves, J. F., On some fossils from the Triassic rocks: of British, Columbia: Contr. 

Canadian Paleontology, vol. 1, pt. 2, No. 3, pp. 133-134, 141-142, 148-14&, 1889.
122 MESOZOIC STRATIGRAPHY OF ALASKA

has been made by Mojsisovics,50 who said: "The same conclusion 

[of Karnic age] holds for Aulacoceras &a-rlottense, since the genus 

Aulacoceras until now has been known only in the Karnic. The 

fragment of a coil figured as Acrochordioceras? carlottense may 

belong to a Jiwavites."

The same horizon is possibly present at the north end of Vancouver 

Island, where, according to Dawson,51 the section is very similar to 

that in the Queen Charlotte Islands and includes a massive limestone, possibly 1,000 feet thick, underlain by volcanic rocks and 

overlain by "flaggy limestones interbedded with calcareous argillites, black flinty argillites, and felsites." This limestone and also 

the supposedly equivalent limestone of the Queen Charlotte Islands 

is part of the thick and heterogeneous aggregate of rocks that has 

been described as the Vancouver series.

Coral-reef horizon. An Upper Triassic limestone occurring on 

Iliamna Lake has yielded a fauna composed chiefly of corals, which 

has not been recognized with certainty elsewhere in Alaska and 

which, according to J. P. Smith,52 is of Lower Nbric age and is to 

be correlated with the coral-reef zone in the upper part of the Hosselkus limestone of California and in the Blue Mountains of Oregon 

and with the Zlambach fauna of the Alps. The position of this limestone in the Chitina Valley section is above the Halobia zone of the 

Chitistone limestone and below the Pseudomonotis zone of the 

McCarthy formation. It may be represented by the thin-bedded 

Nizina limestone or by beds that have been cut out by an unconformity at the base of the McCarthy formation.

This limestone' may be present also on the west coast of Cook 

Inlet and on Gravina Island, in southeastern Alaska, but at neither 

of these localities has it been recognized with certainty.

The Lower Noric coral-reef horizon is possibly represented in 

British Columbia by the Sutton limestone 53 of Cowichan Lake, 

Vancouver Island. The fauna of the Sutton limestone has been described by Clapp and Shinier,54 who referred it to the lower part of 

the Lower Jurassic on the ground that its species are more primitive than certain species from the Middle and Upper Jurassic of 

England and India, and are less primitive than certain species

60 Mojsisovics' Edmund von, Beitriige zur Kenntniss der obertriadischen CephalopodenFaunen des Himalaya : K. Akad., Wiss. Wien Denkschr., Band 63, p. 697, 1896.

51 Dawson, G. M., Report on a geological examination of the northern part of Vancouver Island and adjacent coasts: Canada Geol. Survey Ann. Kept., new ser., vol. 2, pp. 

9B, 60B, 76B, S9B, 91B. 1886.

62 Smith, J. P., The occurrence of coral reefs in the Triassic of North America: Am. 

Jour. Sci., 4th ser.. vol. 33, pp. 92-96, 1912.

63 Clapp, C. H., Southern Vancouver Island: Canada Geol. Survey Mem, 13 (1121), pp. 

36, 61-69, 1912.

54 Clapp, C. H., and Shimer, H. W., The Sutton. Jurassic of the Vancouver group, Vancouver Island : Boston Soc. Nat. Hist. Proc., vol. 34, No.. 12, pp. 425-438, pis. 40-42. 

1911.
TRIASSIC, GENERAL CHARACTER AND CORRELATION 123

from the Rhaetic of Europe, and that it does not contain Daonella 

lommeli, Halobia superba, or Pseudomonotis subcircularis. They 

regarded it as representing a Eurasian type of Liassic fauna which 

is rather closely related to certain unspecified Liassic faunas of 

Europe and India.

The writer believes that the reasons stated for the reference of 

this fauna to the Lower Jurassic are, to say the least, by no 

means conclusive. The absence of Daonella lommeli, Halobia 

superba, and Pseudomonotis subcircularis does not make its 

assignment to the Triassic impossible or even improbable. On 

the other hand, the fact that all the five recognized genera 

occur abundantly in the Triassic, while two of them (Ghoristoceras and Myophoria) are highly characteristic of the Triassic, 

being authentically known, so far as the writer is aware, only in 

rocks of that system, makes it appear highly probable that this 

fauna is of Triassic age. The superficial resemblance of the corals, 

moreover, to those of the Lower Noric reefs of California, Oregon, 

Alaska, and the Alps suggests that the Sutton fauna may also be 

of Lower Noric age. In this connection it should be pointed out 

that the only recognized ammonoid genus, Choristoceras, in the 

Sutton fauna occurs also in association with the Zlambach corals of 

the Alps.

Chert horizon. The chert that forms the lower part of the McCarthy formation of the Chitina Valley is apparently the equivalent 

of the more massive lower part of the Kamishak chert of the west 

coast of Cook Inlet and of the chert that occurs in a corresponding 

stratigraphic position beneath the Pseudomonotis zone of the Alaska 

Peninsula. The contorted chert of Kenai Peninsula, of Kodiak 

Island, and of Herring Bay on Admiralty Island is probably also to 

be assigned to the same position, though on more slender evidence. 

The occurrence of these cherts below the Pseudomonotis zone and 

above the Halobia zone in the Chitina Valley indicates their general 

position, but as they contain no fossils they can not be assigned to a 

definite horizon or be correlated with any rocks of other regions.

Zone of Pseudomonotis subcircularis. The highest Upper Triassic 

rocks known in Alaska are the Upper Noric Pse.udomonotis-be&rmg 

beds, which are widely distributed throughout the three major 

mountain regions. This horizon is represented in the Pacific 

Mountain belt by the McCarthy formation of the Chitina Valley 

and by strata carrying a similar fauna at the head of White River, 

at Cooper Pass, in the upper Susitna Valley, on both shores of Cook 

Inlet, on the Alaska Peninsula, and on Kupreanof Island in southeastern Alaska. In the Rocky Mountain area Pseudomonotis-be>a,Ting beds form the upper part of the Triassic section near Nation
124 MESOZOIC STRATIGRAPHY OF ALASKA

Kiver. Kocks belonging at the same horizon occur at many places 

throughout the Arctic Mountains, being known on Firth, Canning, 

and Noatak rivers and at Cape Lisburne and Cape Thompson.

These rocks consist in general of shale and flaggy limestone. They 

contain chert beds in the Chitina Valley, on both shores of Cook 

Inlet, at Cape Lisburne, at Cape Thompson, and in the Noatak Valley. Volcanic material is present at the head of White River, in the 

upper Susitna Valley, and on Kenai Peninsula.

The writer believes that there is a marked unconformity at the 

base of the Pseudomonotis-be&rmg beds of Alaska and British 

Columbia. The evidence for this unconformity is as follows:

In the western part of the Chitina Valley, notably in the valley 

of Elliot Creek and in the hills between Eock and Copper Creeks, 

shale having the lithologic and faunal character of that of the McCarthy formation occurs not far above the top of the Chitistone 

limestone, thus apparently occupying the normal stratigraphic position of the Nizina limestone, over 1,000 feet thick, which elsewhere 

separates these two formations. In the vicinity of Skolai Pass, near 

the head of White River, the Pseudomonotis zone immediately overlies a Permian (?) limestone. There is consequently a hiatus here 

that is represented in the Nizina Valley, about 20 miles distant, by 

the Nikolai greenstone, the Chitistone limestone, and the Nizina 

limestone, which have an aggregate thickness of at least 7,000 or 

8,000 feet. At Hamilton Bay, Kupreanof Island, in southeastern 

Alaska, the Pseudomonotis zone is separated from the older Halobia 

zone (the strata being inverted) by a conglomerate containing fossiliferous boulders of the older limestone. It is evident that the 

same unconformity is present on Cumshewa Inlet, Queen Charlotte 

Islands, where, according to Dawson,55 the relations are as follows:

On the southeast side of the South Ann flaggy argillites occur. They were 

observed to become conglomeratic in one place with fragments of the underlying 

[Triassic] limestone, which might be supposed to show that they belong to 

the coal-bearing [Cretaceous] series. They hold, however, the characteristic 

Triassic Monotis.

Further evidence of an unconformity at the base of the Pseudomonotis zone is indicated by the apparent absence at most places of 

the coral-bearing strata that belong below the Pseudomonotis zone 

and above the Halofiia zone. The fact that in both Alaska and 

British Columbia the Pseudomonotis-be&rmg beds have a far wider 

distribution than the older Halobia-bea.T'mg beds and that the intervening coral-reef limestone is even more restricted, occurring only 

near the present continental margin, also suggests an Upper Noric 

transgression following a Lower Noric recession of the sea. The

M Dawson, G. M., Report on the Queen Charlotte Islands: Canada Geol. Survey Kept 

Progress for 1878-79, p. 82B, 1880.
TEIASSIC, GENEBAL CHAEACTEB AND CORRELATION 125

abrupt change in faunal character from the supposedly warm-water 

Halobia zone to the boreal Pseudomonotis zone also suggests a withdrawal of the Karnic Sea, followed by an Upper Noric transgression, presumably from the Arctic regions.

The fauna of the McCarthy formation as now known includes 

P seudomonotis subcircularis (Gabb), Halofoia sp., Pecten sp., and 

Arniotites? sp. The Pseudomonotis-bB&T'mg beds of the other Alaskan districts are correlated with the McCarthy formation on the 

basis of general lithologic similarity and sequence and also on the 

basis of the presence of Pseudomonotis subcircularis. This is the 

only fossil recognized in these beds at most localities, although a few 

fossils have been found associated with the Pseudomonotis at some 

places. These include Clionites (Shastites] sp. at the head of White 

River, Area? sp. on the west coast of Cook Inlet, RhyncJionellaf sp. 

and 1"erebratula, sp. near the mouth of Nation River^ and some undetermined pelecypods near Cape Lisburne.

The presence of Pseudomonotis subcircularis in these beds is sufficient evidence for their approximate correlation with the Brock 

shale of Shasta County, Calif., with the Swearinger slate of Plumas 

County, Calif., and with the Pseudomonotis-\)Qa,rmg slate and slaty 

limestone of the West Humboldt Range, Ney.

In British Columbia and Yukon there is an extensive development 

of Pseudomonotis-bQwrng beds that can be correlated on the basis 

of faunal content, as well as of stratigraphic sequence, with those of 

Alaska. They occcur in two well-defined belts a western or coastal 

belt that includes Triassic areas in the Queen Charlotte Islands, on 

Vancouver and the adjacent islands, and at the north end of the 

Cascade Range; and an eastern or interior belt that is situated on 

the eastern front of the Rocky Mountains and that includes known 

Triassic areas on Pine, Peace, and Stewart Rivers.

The Pseudomonotis-bearing beds of the Queen Charlotte Islands, 

according to Dawson,56 consist of flaggy calcareous argillite and thin 

limestone more than 1,000 feet thick. These beds are underlain by 

massive limestone and are overlain 5r by feldspathic sandstone, coarse 

conglomerate, and agglomeratic rocks which Dawson considered Cretaceous but which are now known to be Lower and Middle Jurassic.58 

These rocks have all been included in the Vancouver series. The 

contact of the argillite with the underlying limestone, although supposed to be in general conformable, is apparently unconformable in 

at least one locality, according to Dawson's description.59 The fossils

68 Dawson, G. M., Report oa the Queen Charlotte Islands: Canada Geol. Survey Rept. 

Progress for 1878-79, pp. 48B, -35B, 58B, 59'B, 61B, 62B, 63B, 82B, 1880.

87 Idem, pp. 48B, 59B, 62B.

^McKenzie, J. D., South-central Graham Island, British Columbia: Canada Gcol. 

Survey Summary Rept. for 1913, pp. 4O-42.

58 Dawson, G. M., op. cit, p. 82B.

49448 26 10
126 MESOZOIC STRATIGRAPHY OF ALASKA

listed from these beds include Pseudomonotis subcircularis (Gabb) 

an " extreme local variety " of " Halobia lommeli?" and Arniotites 

vancouverensis Whiteaves.

It is probable that the same horizon is present in the Vancouver 

series at the north end of Vancouver Island, where, according to 

Dawson,60 flaggy limestone, calcareous argillite, black flinty argillite, 

etc., overlie a massive limestone and are overlain by sandstone, above 

which are volcanic beds. The section is closely similar to that of the 

Queen Charlotte Islands. The fossils from the flaggy limestones and 

argillites were described by Whiteaves 61 as including the following 

species :

Halobia (Daonella) lommeli? (extreme local variety).

Arcestes gabbi Meek.

Amiotites vancouverensis Whiteaves.

Arniotites sp.

Amiotites or Celtites sp.

It has been generally assumed that these fossils are Middle Triassic which they would undoubtedly be, at least the Daonella and the 

Arcestes,'if the species have been correctly determined. It was the 

opinion of Frech 62 that the ammonites described as Arniotites are 

also indicative of Middle Triassic age, "'Amiotites vancouverensis " 

probably being a Celtites^ "Arniotites or Gelites sp." being a Celtites 

related to G. epolense Mojsisovics, and "Arniotites sp." being a Geratites related to G. japonicus Mojsisovics.

The writer doubts whether any of these fossils from Vancouver 

Island are Middle Triassic and believes that it is highly probable 

that they are all Upper Triassic. The reasons for this belief are as 

follows: Whiteaves expressed considerable doubt;concerning the 

identification of Halobia (Daonella) lommeli and considered that 

the Vancouver Island specimens "may possibly represent an extreme local variety of this species." 63 He recognized the same " extreme local variety " as occurring in association with Pseudomonotis 

subcircularis in the flaggy limestone and argillite of the Queen 

Charlotte Islands. This form is probably identical with neither 

Daonella lommeli Wissman, of Europe, nor Daonella dubia Gabb, 

of Nevada, but is more likely an Upper Triassic species of Halobia. 

The fossils identified by Whiteaves as Arcestes gabbi Meek have been 

neither described nor figured and may possibly belong to some of 

the Upper Triassic species of Arcestes which had not been recognized

60 Dawson, G. M., Report on a geological examination of the northern part of Vancouver Island and adjacent coasts: Canada Geol. Survey Ann. Kept., new ser., vol. 2, 

pp. 9B, 26B, 73B, 76B, 83B, S9B, 1886.

01 Whiteaves, J., F., On some fossils from the Triassic rocks of British Columbia: Oontr. 

Canadian Paleontology, vol. 1, pt. 2, No. 3, pp. 134, 141, 146-147,, pi. 19, figs. 3, 4, 1889.

"SFreca, Fritz, Die zircumpaciflsche Trias: Lethaea geognostica, Tell 2, Band 1, pp.

490-491, 1908. 

63 Whiteaves, J. F., op. cit., p. 134.
127

'in America at the time Whiteaves made his studies. Amiotites vaxncouverensis was described by Whiteaves from specimens found in 

the argillite of Queen Charlotte Islands that contains Pseudomonotis 

sulciroularis. This species has been reported 64 also as occurring together with Pseudomonotis subcircularis, in the Parson Bay group 

of Harbledown Island. It probably occurs also in the argillite of 

the Cultus formation 85 on the west slope of the Cascades, where 

it is associated with Aulacocerasf cf. A. carlottense Whiteaves. The 

genus Aulacoceras, according to Mojsisovics, is known only in the 

Upper Triassic. The fossil from Kobson Island, described by Whiteaves 60 as Arniotites sp., is closely related, according to Frech,67 to 

Geratites japonicus Mojsisovics of the Triassic of Japan. Although 

that species has been referred to the Ladinic,68 it occurs in beds that

apparently overlie those containing Pseudomonotis ochotica. It 

should also be noted that Arniotites probably occurs in Alaska (see 

p. 30) in the upper part of the McCarthy formation.

The Pseudomonotis horizon of Alaska is probably represented on 

the islands east of Vancouver Island by the Parson Bay group/0 

which consists of "shales, argillites, impure limestones, calcareous 

sandstones and quartzites," which contain Pseudomonotis subcirc-ularis, Halobia, Natica?, and Arniotites vancouverensis, and which 

rest on the lava, breccia, and tuff described as the Valdez group.

These rocks may be correlated also with the argillites of the Cultus 

formation,71 which is exposed near the western base of the Cascade 

Kange and which contains Arniotites vmcouverensis Whiteaves? 

and Aulacocerasf cf. A. carlottense Whiteaves.

The argillite of Whipsaw Creek, near the headwaters of the 

Similkameen, on the crest of t^e Cascade Range, which was described by Dawson 72 as occurring in a syncline and as underlain 

by volcanic rocks that were correlated with those of the Nicola

84 Bancroft, J. A., Geology of the coasts and islands between the Strait of Georgia and 

Queen Charlotte Sound, British Columbia: Canada Geol. Survey Mem. 23 (No. 1188), 

pp. 75-76, pi. 9 (b), 1913.

Oli Daly, R. A., Geology of the North American Cordillera at the Forty-ninth parallel: 

Canada Geol. Survey Mem. 38, pt. 1, pp. 516-517, 1912.

09 Whiteaves, J. F., op. cit, p. 147, pi. 19, fig. 3.

07 Frech, Fritz, Die zircumpacifische Trias: Lethaea geognostica, Teil 2, Band 1, p. 

490, 1908.

88 Noetling, Fritz, Die asiatische Trias : Lethaea geognostica, Teil 2, Band 1, Lief. 2, 

pp. 195-196, 220, 1905.

08 Mojsisovics, Edmund von, Ueber einige japanische Triasfossilien: Beitr. Palaeontologie Osterreich-Ungarns, Band 7, pp. 163-178, 1889.

70 Bancroft, J. A., op. cit., pp. 75-77.

71 Daly, R. A., op. cit., pp. 516-517.

72 Dawson, G. M., Preliminary report on. the physical and geological features of the 

southern portion of the interior of British Columbia: Canada Geol. Survey Rept. 

Progress for 1877-78, pp. 66B, 67B, 1879.
128 MESOZOIC STRATIGRAPHY OF ALASKA

series and which contain's fossils that Whiteaves 73 doubtfully re-* 

ferred to Pseudomonotis subcircularis, possibly also belongs at this 

horizon. It should, however, not be confused with the Middle 

Triassic beds (see p. 118) of Thompson Kiver and of Nicola Lake 

(?), with which Dawson 74 correlated it.

Beds containing Pseudomonotis subcircula/ris occur in a more or 

less continuous belt along the eastern front of the Kocky Mountains 

of British Columbia and Yukon. The known localities are on upper Pine Kiver;75 on Peace River, about 27 miles below the junction 

of Finlay and Parsnip Rivers, where the rocks have been described 

by Selwyn 76 and by McConnell 77 as consisting of calcareous shale 

and impure limestone; and near the headwaters of Stewart River, 

where, according to Keele,78 the beds include impure limestone, 

argillite, and quartzite, with Pseudomonotis subcircularis, " Halobia 

lommeli" and Arpaditesf.

The generally accepted assignment of the Pseudomonotis-bB&riug 

beds of Alaska to the horizon of the Upper Nojic of Europe and 

Asia is based on the close relationship of the Alaskan fossil identified as Pseudomonotis subcircularis (Gabb), with Pseudomonotis 

ochotica (Keyserling), which is the characteristic fossil of the boreal 

Upper Noric beds of Asia. This relationship was long ago shown 

by Teller 79 and by Mojsisovics.80 Specimens from Cold Bay, on 

the Alaska Peninsula, have more recently been examined by Frech,81 

who has identified them as including both the typical form of 

Pseudomonotis ochotica (Keyserling) and also Pseudomonotis 

ochotica var. sparicostata Teller. Further confirmation of this correlation is found in the general similarity of the Alaskan Upper 

Triassic section as a whole to that^of California and other regions.

GEOLOGIC HISTORY OF ALASKA IN. TRIASSIC TIME

The youngest known Paleozoic rocks of Alaska consist of the 

Permian (?) limestone, which carries a fauna closely allied to that

73 Whiteaves, J. P., op. cit., pp. 127-132.

74 Dawson, G. M., Report on the area of the Kamloops map-sheet, British Columbia: 

Canada Geol. Survey Ann. Kept., new ser., vol. 2, pp. 50B-137B, 1896.

76 Whiteaves, J. F., Notes on some Jurassic fossils collected by G. M. Dawson in the 

Coast Range of British Columbia: Canada Geol. Survey Rept. Progress for 1876-77, 

p. 158.

78 Selwyn, A. R. C., Report on exploration in British Columbia: .Canada Geol. Survey 

Rept. Progress for 1875-76, pp. 75, 80, 97, 1877.

77 McConnell, R. G., Report on an exploration of the Finlay and Omenica Rivers: 

Canada Geol. Survey Ann. Rept. for 1894, pp. 32C, 35C, 1896.

78 Keele, J., Report on the upper Stewart River region, Yukon: Canada Geol. Survey 

Ann. Rept, new ser., vol. 16, pp. 14C, 15C, 17C, 1906.

78 Teller, Friedrich, Die Pelecypod-Fauna von Werchojansk in Ostsiberien : Acad. imp. 

sci. St-P6tersbourg M4m., 7th ser., vol. 33, No. 6, pp. 110, 113, 115, 1886.

80 Mojsisovics, Edmund von, Arktische Triasfaunen: Acad. imp. sci. St.-P6tersbourg 

M<5m., 7th ser., vol. 33, No. 6, p. 147, 1886.

81 Frech, Fritz, Die zircumpacifische Trias: Lethaea geoguostica, Teil 2, Band 1, p. 

489, pi. 68, fig. 3a, 1908.
Interregional correlation of the Triassic 

[After J. P. Smith, except for Alaska]

O

S

1

i

gCD 

§

Triassic. Lower 

Series"

Bajuvaric.

Tirolic.

Upper 

Muschelkalk.

Middle 

Muschelkalk.

Lower 

Muschelkalk.

Dinaric.

Scythic.

Stage0

'Rhaetlc.

Noric.

Karnic.

Ladinic.

Anisic.

Hydaspic.

Jakutic.

Brahmanic.

Substage0

Tuvalic.

Julic.

Oordevolic.

Longobardian.

Fassanic.

Bosnian.

Balatonic.

Gangetic.

Gandaric.

Interregional 

zone

Pseudomonotis ochotica.

Tropites 

subbullatus.

Daonella 

lommeli.

Ceratites 

trinodosus.

Columbites 

fauna.

Tirolites 

cassianus in 

Mediterranean region 

and Idaho.

Meelioceras 

fauna in Siberia, India, 

California, 

and Idaho.

Mediterranean region

German

Rhaetic.

KeuperUpper Muschelkalk.

Middle Muschelkalk.

Lower Muschelkalk with 

Hungarites 

strombecki.

Buntsandstein.

Alpine

Noric limestone 

of Hallstatt.

Pseudomonotis 

ochotica 

in the 

Crimea.

Sandling beds with Tropites 

subbullatus.

Raibl beds with Trachyceras 

aonoides.

Cassian beds with Trachyceras aon.

Wengen beds with Trachyceras archelaus.

Buchenstein beds with 

Trachyceras reitzii.

Rei fling limestone. Limestones of Han 

Bulo& Bakony, and 

the Schrey Alps, 

with Ceratites trinodosus.

Ceratites binodosus beds in 

the South Alps.

Beds on Gulf of Ismid, in 

Asia Minor.

Warfen beds.

Columbites beds in 

Albania.

Campil beds with 

Tirolites cassianus.

Seis beds with Pseudomonotis clarai.

Arctic-Pacific region

Pseudomonotis ochotica slate of 

northern Siberia, Japan, and 

Indian Ocean.

Halobia slate of Eureka Sound 

and Spitzbergen.

f

i 

Dawsonites slate of Bear 

Island)

Ceratite slate of 

Analtites and

Beds Ussuri ofBay in eastern 

Siberia withMonophyllites 

sichoticus.... 

Japan with 

Danubites.

Mengilftch beds. (?)

Daonella 

limestone 

of Spitzbergen.

Olenek beds of northern 

Siberia.

Proptyc 

of USE 

in sou 

eria.

rites beds 

uri Bay, 

hern SibPosidonomya limestone of 

Spitzbergen.

Oriental region

Himalaya

Monoyis beds.

Limestone with Halorite.

O

 S"g Tropites limestone. &I-0

Beds with Trachyceras tibeticum.

4m

.2 Beds with Trachy- 

"3 ceras archelaus and 

§ Daonella lommeli.

Q

Beds with Trachyceras cautleyi.

Upper Muschelkalk with 

Ptychites rugifer and 

Ceratiles trinodosus.

Lower Muschelkalk.

Stephanites beds.

Hcdenslroemia and Flemingites beds.

Meekocoras beds.

"tcccr= bci.

Salt Range

Upper 

Ceratite 

limestone.

Ceratite 

<A sandstone. a

<O

"g Ceratite 

g marl.

Lower 

Ceratite 

limestone.

American region

California

§'3

4? -a pq to

Hosselkus limestone.

Pit shale.

P5 

o

a

IS

8 

a o

J3

bt.

£>

"3

S3 

0

Slate carrying Pseudomonotis subcircularis, Jthabdoceras and Haloriles.

Spiriferina beds.

Coral zone.

OJ3J3 Juvavites beds.

Trachyceras 

beds.

Halobia superba zone.

Slate with Halobia 

cf. H. rugosa.

Shale and tuffs without 

determinable fossils.

Clay and siliceous shale 

with Nevadites cf. N. whitneyi and Ceratites cf. C. 

humboldtensis.

Black limestone with Parapopanoceras, Xenodiscus, 

Acrochordiceras, and 

Hungarites.

Calcareous slate without 

fossils.

Meekoceras zone of Inyo 

County, Calif., with 

Meekoceras gracilitatis, 

Ussuria, Pseudosageceras, 

Inyoites, Owenites, Nannites.

Nevada

Star Pek formation.

Pseudomonotis bearing slate, with F>habdoceras and Placites.

Limestone without 

characteristic fossils.

^0

S-g Daonella dubia 

o .a zone with 

"3 S Ceratites 

| 3 trinodosus.

q

Idaho

Beds ofAspen Mountains.

Columbites 

zone.

Tirolites 

zone.

Meekoceras 

zone.

British 

Columbia

Pseudomonotisbearing slate.

Dawsonites zone.

Daonella zone.

Alaska

Chitina Valley

McCarthy formation 

(shale with chert in 

lower part) . Contains Pseudomonotis 

subcircularis.

Nizina limestone? 

(in part?)

Nizina limestone (in 

part?) 

Chitistone limestone 

(with Halobia cf. H. 

superba, Tropites, 

Juvavites, Arcestes, 

etc.) .

Southwestern 

Alaska

Calcareous shale with 

Pseudomonotis subcircularis.

Chert (fossils not 

known) .

Coral limestone of 

Iliamna Lake.

Southeastern 

Alaska

Upper limestone at 

Hamilton Bay with 

Pseudomonotis.

? Limestone of Gravina Island (corals).

Limestone of Herring 

and Hamilton bays, 

with Halobia cf. H. 

superba, etc.

Limestone near Hamilton Bay with Dawsonites (not found in 

place).

Yukon Valley and 

northern Alaska

Pseudomonotis zone of 

Yukon River and 

Arctic Mountains.

Limestone of Yukon, 

Firth, and Canning 

rivers, with Halobia 

cf. H. superba, 

Clionites, brachiopods, etc.

Slate of Brooks 

Mountain with 

Daonella and Ceratites (Oymnotoceras) .

49448 2G. (Face p. 11'8. i

'These series, stage, and substage terms have not been adopted by the United States Geological Survey
TRIASSIC, GENERAL CHARACTER AND CORRELATION 129

of the Artinskian of Russia. The wide distribution of this limestone indicates that there was a period of profound submergence in 

late Paleozoic time, and that the sea probably extended over the 

larger part if not all of Alaska.

As Lower Triassic rocks have not been recognized in Alaska, it is 

believed that the end of Paleozoic time was marked by a, widespre'ad emergence, which continued until the beginning of the Upper 

Triassic.

The Permian or early Triassic lavas of the Pacific coastal belt, 

which are represented by the Nikolai greenstone of the Chitina Valley, the basic lava and tuff of the upper Susitna Valley, the ellipsoidal lava of Kenai Peninsula and Kodiak Island, the greenstone 

of the Iliamna-Clark Lake district, and the ellipsoidal lava of 

Hamilton Bay (and which may be represented by the greenstone 

associated with the Orca group of Prince William Sound and by 

some of the greenstones of southeastern Alaska), indicate a period 

of intense, widespread, and probably long-continued volcanic activity that probably occurred in early Triassic time. These volcanic 

deposits, so far as known, are not intercalated with marine sediments 

and presumably were poured out on land during the Permian or 

early Triassic period of emergence. The nonfossiliferous sedimentary rocks of the Orca group that are intercalated with the greenstone are, in the writer's opinion, not marine. The volcanic activity 

of this period apparently extended throughout the region south of 

the Alaska Eange, from the Alaska Peninsula eastward and southward into British Columbia. Volcanic rocks of this date are not 

known north of the Alaska Eange and probably were never present 

there, although their absence may be due to post-Triassic erosion. 

This sharp limitation of the distribution of these rocks along the 

present line of the major mountain axis of Alaska is very significant and, in the writer's opinion, clearly indicates that this line 

marked the northern limit of the supposed early Triassic volcanic 

activity.

Middle Triassic time was probably a period of emergence in 

Alaska, for Middle Triassic rocks are known only in Seward 

Peninsula.

The upper Triassic was a time of submergence, when limestoneforming seas swept over large Alaskan areas. The initial Upper 

Triassic submergence was probably in Karnic time, when limestone 

was deposited throughout the greater part if not all of the present 

Pacific Mountain region, being known along the Pacific coast from 

southeastern Alaska to Cook Inlet and in the Copper and Susitna 

Valleys. This limestone locally attains a thickness of at least 3,000 

feet and, in general, is not interbedded with strata of other kinds. 

The fauna of these supposed Karnic beds of southern Alaska is of
130 MESOZOIC STRATIGRAPHY OF ALASKA

the Mediterranean type and probably indicates warm-water conditions. The Karnic Sea probably advanced from the south. Limestones that were presumably synchronous with these but possibly 

were laid down in different basins that may have maintained a 

connection with the boreal sea are known in the present sites of the 

Rocky and Arctic Mountains or on the upper Yukon and the eastern 

part of the Arctic slope.

The sea probably receded in Lower Noric time from the greater 

part of Alaska, for rocks of supposed Lower Noric age are definitely 

knoWn only in the vicinity of Iliamna Lake, where they are represented by limestone containing a warm-water coral-reef fauna.

The Upper Noric was the time of a great transgression of the sea, 

when the greater part if not all of Alaska was submerged. The 

supposed Upper Noric rocks consist of shale, impure limestone, and 

chert, with some local volcanic beds. They contain a boreal fauna 

that is allied to that of northern Asia and that possibly indicates a 

 cold-water sea, in contrast with the preceding warm-water seas of 

Karnic and Lower Noric time. This marked difference in faunal 

conditions, together with the general absence of Lower Noric beds 

between the Upper Noric and the underlying Karnic strata and 

with the strong suggestions of an unconformity at the base of the 

Upper Noric beds (see pp. 21, 36, 124), indicates that there was 

an important recession of the sea at the end of Karnic time. The 

invading Upper Noric sea probably came from the northwest.

There was a general emergence of the land at the end of Noric 

time, when the sea probably retired beyond the present continental 

limits. Rhaetic and early Lias deposits are not known in Alaska, 

and it is believed that the continent stood above sea level from the 

end of Noric time until late Lias (Toarcian) time. Marked folding 

followed the deposition of the local Upper Triassic strata, but the 

date of this folding has not been determined more closely than postTfiassic and prioi to Upper Jurassic. The beginning of the local 

record in Jurassic (probably Upper Lias or Toarcian) time was 

marked by a moderate submergence, accompanied or followed by 

intense volcanic activity along the present Pacific seaboard.

JURASSIC SYSTEM 

GENERAL FEATURES

The Jurassic rocks of Alaska are for the most part restricted to 

the south-central and southwestern parts of the Territory (fig. 5), 

being best developed in a belt extending through the Alaska Peninsula, the Cook Island drainage basin, and. the Chitina Valley. 

Within this region there is a great thickness of marine fossiliferous 

beds ranging in age from the Liassic to uppermost Jurassic and
JURASSIC SYSTEM 131

constituting the most complete development of the Jurassic known in 

North America. The faunas are abundant and well developed and 

indicate the presence of many well known world-wide horizons. 

Fossil plants also occur in association with the marine fossils at several horizons in the Lower, Middle, and Upper Jurassic.

The broad extent and great thickness of the Jurassic strata in 

south-central and southwestern Alaska are in striking contrast with 

the poor development of the Jurassic in other parts of the Territory. 

Marine Jurassic beds apparently are entirely absent north of the
132 MESOZOIO STRATIGRAPHY OF ALASKA

Alaska Kange, except for the Lower or Middle Jurassic rocks of the 

eastern part of the Arctic slope. No undoubted Jurassic rocks have 

been found anywhere in the Kuskokwim and Yukon Basins, except 

on tributaries heading south of the Alaska Kange. The only Jurassic rocks that have been reported from northern Alaska are the 

marine Lower or Middle Jurassic beds of the eastern part of the 

Arctic slope and the nonmarine plant-bearing beds of the Corwin 

formation near Cape Lisburne, which are now believed to be probably Cretaceous. (See p. 467.) In southeastern Alaska there are 

also some plant-bearing and other nonmarine deposits that may be of 

Jurassic age. At other localities in various parts of Alaska, but 

chiefly in the central and southern parts, there are metamorphic 

rocks of possible Jurassic age whose fossils are such that they can 

not be positively affirmed to be Jurassic or even Mesozoic. For most 

of these metamorphic rocks the probabilities are more strongly in 

favor of other than Jurassic age, and the rocks have been here 

described accordingly.

The known or supposed Lower Jurassic rocks of Alaska include 

fossiliferous marine tuff exposed at Seldovia Bay and Port Graham 

on Kenai Peninsula, possibly some porphyry and tuff on the west 

coast of Cook Inlet, shale and sandstone that overlie the Upper 

Triassic rocks of Cold and Alinchak bays on Alaska Peninsula, the 

marine tuff of the Matanuska Valley and Talkeetna Mountains, possibly the volcanic rocks of the Skweiitna gro'up of the Alaska Range, 

possibly the tuffaceous conglomerate near Taral in the Chitina Valley, and perhaps some of the melaphyre breccia and tuff of southeastern Alaska. The Kialagvik formation of the Alaska Peninsula 

and the Kingak shale of the Arctic slope may also be partly or 

wholly Lower Jurassic.

The oldest of the Middle Jurassic rocks of Alaska may include the 

Kialagvik formation of the Alaska Peninsula and the Kingak shale 

of the Arctic slope. A slightly higher horizon in the Middle Jurassic is represented by the Tuxedni sandstone of Cook Inlet, the sandstone that carries the Tuxedni fauna in the Matanuska. Valley, the 

Tordrillo formation of the Alaska Kange, and the fossiliferous 

tuffaceous slate near the mouth of Chitina River. There are alsosuggestions that the Tuxedni fauna may be present on the Alaska 

Peninsula. It is also possible that some of the volcanic rocks of 

southeastern Alaska may be Middle Jurassic.

The oldest of the Upper Jurassic formations of Alaska is the Chinitna shale of Cook Inlet. The fauna of the Chinitna shale has been 

recognized in the Shelikof formation of the Alaska Peninsula and 

in shale underlying the Naknek formation in the Matanuska Valley. 

A younger horizon in the Upper Jurassic is represented by the Naknek formation of the Alaska Peninsula and Cook Inlet. The fauna
JURASSIC, COOK INLET 133

of the Naknek formation has been clearly recognized in some shale 

and sandstone of the Matanuska Valley, and it is believed to be also 

represented by some of the Aucella-be&Ymg beds of the Nutzotin 

Mountains and of southeastern Alaska. The Kennicott formation 

of the Chitina Valley was formerly referred to the Upper Jurassic, 

but the writer believes that its fauna is entirely different from that 

of the Naknek formation and that it is Lower Cretaceous. (See p. 

335.) The Corwin formation of the Cape Lisburne district carries a 

flora somewhat similar to that of the Kennicott formation and was 

formerly regarded as Upper Jurassic, but the writer believes that it 

also is probably Lower Cretaceous.

LOCAL SECTIONS

COOK INLET 

GENERAL FEATURES

The most complete known section of Jurassic rocks in Alaska, or 

in fact in North America, is on Cook Inlet, where most of the recognized Alaskan horizons are represented by beds that attain great 

thickness, contain abundant and well-preserved faunas and floras, 

and for the most part show clearly their stratigraphic relations. 

The Cook Inlet section will therefore be described in detail, as the 

standard and typical section for the Alaskan Jurassic, and the other 

local sections will subsequently be described and interpreted in terms 

of their relation to it.

Jurassic rocks occur upon both shores of Cook Inlet, but the sections exposed on the opposite sides are strikingly unlike. The 

known Jurassic of the east shore of Cook Inlet includes only Lower 

Jurassic marine-laid tuff, the Middle and Upper Jurassic not being 

represented, except possibly by part of the slate and graywacke of 

the Kenai Mountains (pp. 482-483). The section on the west shore 

includes lava and tuff that may represent the Lower Jurassic, overlain by Middle and Upper Jurassic formations, aggregating many 

thousand feet of fossiliferous marine strata.

The sequence of Jurassic rocks on the west coast of Cook Inlet, as 

represented in the peninsula between Chinitna and Iniskin Bays,, 

was given by Moffit 82 as follows:

82 Moffit, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, p. 120, 1922.
134 MESOZOIC STRATIGRAPHY OF ALASKA 

Jurassic rocks on west coast of Cook Inlet

Age

Upper Jurassic.

Middle Jurassic.

Lower Jurassic.

Formation

Naknek formation.

Chisik conglomerate."

Chinitna shale.

Tuxedni sandstone.

<_ 

Lithologic character

Massive light-colored sandstone, arkose, and tuff.

Gray shale with sandstone beds.

Massive conglomerate with boulders, possibly represented 

in many places by grit and arkose.

Fairly homogeneous argillaceous gray, black, and reddish 

shales with subordinate calcareous and arenaceous beds.

Arenaceous gray shale with subordinate sandstone beds.

Sandstone, shale, arkosic sandstone, and conglomerate.

Volcanic rocks; porphyry and tuff (basaltic and andesitic 

lavas and tuffs) .

Thickness 

(feet)

3,000

1,500

290

2,300

8,000

1,000?

1 Now classified as basal member of Naknek formation.

The rocks of this section overlie or are faulted against Upper 

Triassic strata that crop out west of them and are overlain unconformably at one or two localities by Tertiary beds. Cretaceous rocks 

a're not present on Cook Inlet.

LOWER JURASSIC 

TUFF OF KENAI PENINSULA

Historical review. The oldest Jurassic horizon known on Cook 

Inlet is represented by the Lower Jurassic tuff that is well developed 

on the shore of Kenai Peninsula from Point Bede to Seldovia Bay. 

It probably includes the " compact Neocomian limestone " that Eichwald 83 mentioned as occurring near English Bay and as containing 

Arcomya crassissima and Janira. These rocks were first referred to 

the Lower Jurassic by Stanton and Martin,84 who discussed briefly 

the occurrence and probable age of the fossiliferous beds. The lithologic character of the rocks was described in somewhat greater detail 

by Moffit,85 whose account includes the previously unpublished lists 

of the fossils collected by Stanton and Martin, together with a discussion of their age contributed by Stanton. Brief mention of the 

occurrence of these rocks has been made by Grant and Higgins,86 

and also by Grant.87 They comprise the Lower Jurassic tuff of

83 Eichwald, Eduard von, Geognostlsch-palaeontologische Bemerkungen fiber die Halbinsel 

Mangischlak und die aleutischen Inseln, pp. 91-92, St. Petersburg, 1871.

84 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, pp. 396-397, 1905.

86 Moffit, P. H., Gold fields of the Turnagain Arm region : U. S. Geol. Survey Bull. 277, 

pp. 20-22, 1906.

88 Grant, U. S., and Higgins, D. F., Preliminary report on the mineral resources of the 

southern part of Kenai Peninsula : D. S. Geol. Survey Bull. 442, p. 168, 1910.

87 Grant, U. S., The southeastern part of Kenai Peninsula: U. S. Geol. Survey Bull. 

587, pp. 211, 228, 1915.
JUBASSIC, COOK INLET 135

Kenai Peninsula as described and mapped by Martin,88 whose account includes a long description of the lithologic character of the 

formation, full lists of the fossils collected by Stanton, Martin, and 

Grant, and a discussion of age and correlation in which there is a 

short statement by Stanton regarding the probable relations of the 

fauna.

Stratigraphic description. The Lower Jurassic rocks of Kenai 

Peninsula consist of tuff and volcanic agglomerate which are interbedded with thinner and less numerous strata of sandstone, shale, 

and limestone. The presence of marine shells indicates the marine 

deposition of at least part of the series. The absence of any sharp 

break in the sequence or of anything that indicates a considerable 

change in the character of the sedimentation suggests that the entire 

series may have been laid down in marine waters.

Volcanic beds are distributed through all parts of the formation, 

there being repeated alternations between well-stratified sedimentary 

detritus and the coarser and rudely stratified tuff and agglomerate. 

Some of the agglomerate is very coarse, fragments 5 feet in diameter 

having been observed. The tuff shows considerable variation in 

composition, rhyolite, andesite, and quartz ceratophyre tuff having 

been noted.

No stratigraphic section has been measured, and the thickness of 

the beds can therefore be stated only approximately. The available data on which an estimate of thickness can be based are the 

general width of the outcrop and the amount of dip. The dip is 

apparently monoclinal and is northwestward, ranging from 10° to 

80°. With an average dip of 30°, the thickness of the strata would 

be about 8,000 feet. This is probably much in excess of the true 

thickness, for the beds are broken by normal faults. As the amount 

of movement on these faults has not been determined, it is impossible 

to surmise the aggregate amount of repetition by faulting. It is 

safe, however, to assume a thickness of at least 1,000 feet, and the 

beds are probably 2,000 or 3,000 feet thick.

The base and top of this formation have not been recognized. 

Upper Triassic rocks, which probably immediately underlie these 

Lower Jurassic beds, lie east of them on the shores of Port Graham, 

but the observed contacts appear to be faults, and therefore the 

nature of the initial deposition is not known. The next younger 

rocks locally present are Tertiary and overlie the Lower Jurassic 

rocks with a profound unconformity.

Age and correlation. The Lower Jurassic tuffs of Kenai Peninsula have yielded the fossils listed below:

88 Martin, G. C., The western part of Kenai Peninsula: U. S. Geol. Survey Bull. 587, 

pp. 63-67, pi. 3. 1915.
136 MESOZOIC STBATIGRAPHY OF ALASKA

Fossils from Lower Jurassic tuffs of Kenai Peninsula a

Montlivaultia?... ................

Astrocoenia?- ____ . ...........

Undetermined coral--.. _ _ ....

Pentacrinus... ...................

Perna??-. ........................

Ostrea.. _____________ .

Ostrea or Gryphaea.-- __ . .....

Grypnaea __________ . .....

Cardiniasp. a. __________

Cardinia? sp. b ...................

Cardinia ..........................

Myophoria?- ___________

Trigoniasp. a.. ..................

Trigoniasp. b._ ___ . ____ ..

Trigonia?. .......................

Pecten sp. a.. ____ . ___ ...

Pecten sp. b ___ ....... ___ ..

Pecten (small ribbed form) -...-..

Pecten (large smooth form) .......

Pecten _______ . .............

Anomia?.. .......................

Pleuromya. ...... .,.. __ ..

Pleurotomaria? __ . ...........

Pseudomelania?. .................

Natica?.. ........................

Arietites?.... .....................

2977 2978

X

X

X

X

X

X

2979

?

X

X

6385

X

X

6384

X

X

X

2980

X

X

2981

X

X

?

X

X

7237

X

7236

X

X

X

X

2982

X

2983

X

X

X

"Identified by T. W. Stanton.

2977 (904). West side of Seldovia Bay, opposite village, one-fourth mile 

southeast of 2978. T. W. Stanton, 1904.

2978 (905). Point Naskowhak, at entrance to Seld'ovia Bay. T. W. Stanton, 

1904.

2979 (906). Three-fourths of a mile west of 2978. T. W. Stanton, 1904.

6385 (G684). East shore of Cook Inlet, 1 mile southwest of Point Naskowhak. U. S. Grant, 1909.

6384 (G682). East shore of Cook Inlet, about one-third of the way from 

Point Naskowhak (which is at the south entrance to Seldovia Bay) to Dangerous Cape. TJ. S. Grant, 1909.

2980 (907A). Shore of Cook Inlet, 2 miles west of Seldovia Bay. T. W. 

Stanton, 1904.

2981 (907B). Same locality as 2980, but 200 feet higher. T. W. Stanton, 

1904.

7237. About 2% miles southwest of Point Naskowhak. G. C. Martin, 1911. 

7236 (113). Three miles' southwest of Point Naskowhak. G. C. Martin, 1911.

2982 (908). Shore of Cook Inlet, 3 miles west of Seldovia Bay. Lawrence 

Martin, 1904.

2983 (909). Port Graham, iy2 miles southeast of coal' mine. T. W. Stanton, 

1904.

The evidence of the fossils on the age of these rocks has been discussed by Stanton as follows:

The evidence can not be considered final on account of the imperfect state 

of preservation, the small number of species, and the lack of definitely characteristic forms, but so far as I can judge from the present collections and 

from the field relations of the beds containing them it seems most probable
JURASSIC, COOK INLET 137

that all these small lots belong to one general fauna and that the age of the 

beds ig Lower Jurassic. The fossils are certainly Mesozoic, and the collections 

include no species in common with the Middle1 and Upper Jurassic faunas, 

which are so well developed in thick formations on the west side of Cook 

Inlet and on the Alaska Peninsula, and' contain several types that are apparently older than any found in those faunas. On the other hand, the only 

evidence suggesting the Triassic age is the presence1 of shells doubtfully 

referred to Myophoria from superficial characters, and this evidence is overbalanced by the Jurassic affinities of the other species'.

The exact position of these rocks relative to that of the other 

Jurassic formations of Alaska .has not been definitely established. 

The absence of other Jurassic strata above or below them on Kenai 

Peninsula of course removes the possibility of the most satisfactory 

determination of their relative position. It is also unfortunate that 

in none of the other and more complete Alaskan Jurassic sections 

have rocks been found that can be positively correlated with this formation. The Lower Jurassic of Alaska is probably best represented 

on the Alaska Peninsula (pp. 181-186), but our knowledge of that 

section is very incomplete, and the fauna of these beds has not yet been 

found there. The Matanuska Valley section (pp. 219-223) contains 

strata very similar to these, both in lithology and in faunal character, 

but the correlation has not yet been established beyond all doubt. 

The Lower Jurassic tuff of the Matanuska Valley, which the writer 

believes will yet prove to be the equivalent of these beds, also contains 

a rather sparse fauna of none too well established age. It is, however, overlain by Middle Jurassic strata. The section on the west 

coast of Cook Inlet includes nonfossiliferous volcanic rocks (pp. 

137-139), which have been correlated with these beds on the basis of 

lithologic resemblance, and those rocks are also overlain by fossiliferous Middle Jurassic strata identical with those of the Matanuska 

Valley. It is consequently evident that the available stratigraphic 

evidence points strongly toward the Lower Jurassic age of this 

formation but does not help in determining its position within the 

Lower Jurassic.

PORPHYRY AND TUFF OF THE WEST COAST OF COOK INLET

Historical review. Volcanic rocks that are somewhat similar to 

the Lower Jurassic tuff of Kenai Peninsula crop out in a more or 

less continuous belt parallel to the west coast of Cook Inlet from 

Tuxedni Bay to Bear Cove. These rocks form the volcanic part of 

the " pre-Jurassic crystallines and intrusives" as mapped and very 

briefly described by Martin 89 and were described and mapped in

89 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey 

Bull. 250, p. 38, pi. 4, 1905.
138 MESOZOIC STRAT1GKAPHY OF ALASKA

much greater detail by Martin and Katz 90 as " Lower Jurassic (?) 

porphyries and tuffs." The stratigraphy and structure of these rocks 

at various localities between Tuxedni and Kamishak Bays have been 

discussed by Martin.91

The distribution, field occurrence, lithologic character, structure* 

age, and interrelations of the supposed equivalents of these lavas in 

the Chulitna and Mulchatna Valleys west of Clark Lake have been 

discussed by Smith.92

The occurrence of these rocks in the vicinity of Tuxedni Bay 9 * 

and in the vicinity of Iniskin and Chinitna Bays °4 was indicated by 

Moffit in columnar sections and on geologic maps, but no description was given.

A brief general account of the occurrence of these porphyries and 

tuffs in the area west of Kamishak Bay has been given by Mather,9& 

who also described some basic lavas that underlie and overlie shale,, 

sandstone, grit, and tuff that carry the fauna of the Tuxedni sandstone.

Lithologic character and stratigraphic relations, The supposed 

Lower Jurassic tuff of the west coast of Cook Inlet is well exposed 

on the south shore of Cottonwood Bay, where there are outcrops 

revealing a thick series of volcanic beds, including both flows and 

tuffs, which overlie the Upper Triassic Kamishak chert with apparent conformity. Amygdaloidal basalt and volcanic agglomerate are among the more characteristic rocks seen at this locality. 

Similar rocks are exposed on the north shore of Iliamna Bay, where 

they include fine-grained green and gray felsitic rocks and tuffs^ 

in part cherty, invaded by large dikes of quartz-feldspar porphyry; 

and also on the south shore of Ursus Cove, where quartz porphyry 

tuff, andesite, and andesitic and rhyolitic agglomerates are present. 

The belt also extends northward from Iliamna Bay, being exposed 

on the west and north shores of Iniskin Bay, where basalt, gabbro,. 

and tuff are present; near the head of Chinitna Bay, where it includes olivine basalt and tuff; and on the upper arm of Tuxedni 

Bay, where quartz porphyry, augite andesite tuff, and quartz porphyry tuff were seen.

00 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 50-59, pi. 2, 1912.

91 Martin, G. C., Preliminary report on petroleum in Alaska: U. S. Geol. Survey Bull. 

719, pp. 43-49, 1921.

82 Smith, P. S., The Lake Clark-central Kuskokwim region, Alaska : U. S. Geol. Survey 

Bull. 655, pp. 46, 104-112, pi. 5, 1917.

83 Mofflt, F. H., Geology of the vicinity of Tuxedni Bay, Cook Inlet: U. S. Geol. Survey 

Bull. 722, p. 142, pi. 2, 1922.

94 Mofflt, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, p. 120, pi. 3, 

1922.

86 Mather, K. F., Mineral resources of the Kamishak Bay region : U. S. Geol. Survey 

Bull. 773, pp. 164-165, 1925.
JURASSIC, COOK INLET 139

Volcanic rocks of the same general character occur north of 

Iliamna Lake from the valley of Chekok River northward through 

the valleys of Lower Tazimina and Kontrashibuna Lakes to Lake 

Clark, possibly extending thence westward; and at several detached 

areas on the south shore and on some of the islands of Iliamna Lake 

below Pile Bay. These rocks may or may not be of the same age.

The volcanic rocks as seen on the south shore of Cottonwood Bay 

overlie the Triassic Kamishak chert. The relations are apparently 

those of conformable stratigraphic succession, for not only was no 

erosional break observed, but there is a more or less gradual change 

in lithologic character from the fine-grained homogeneous cherty 

beds below to the coarser heterogeneous volcanic accumulation above. 

The exposures on the east shore of Iniskin Bay show that these rocks 

lie unconformably beneath the Middle Jurassic Tuxedni sandstone. 

The local relations thus indicate that these rocks are either very higli 

in the Triassic or low in the Jurassic.

No Lower Jurassic faunas have been found west of Cook Inlet, 

either in the beds here described or in any others, but the volcanic 

beds on the west shore of Cook Inlet and possibly also those on 

Iliamna and Clark Lakes may be correlated with the tuff at Seldovia 

and assigned to the Lower Jurassic, on the basis of similar lithology 

and sequence. This correlation is regarded as probable for the rocks 

on Cottonwood and Iliamna Bays. The assignment of the rocks 

west of the mountains to the Lower Jurassic is dependent on a correlation through the rocks on Iliamna Bay and is subject to more 

or less doubt.

The apparent absence of fossils in these rocks may be explained 

by more intense volcanic activity than in the vicinity of Seldovia, or 

by terrestrial rather than marine deposition west of Cook Inlet. It 

should be noted that these rocks differ from their supposed equivalents on Kenai Peninsula in containing a larger proportion of lava.

The basic lava on the west shore of Kamishak Bay which Mather 90 

described as underlying shale, sandstone, grit, and tuff that contain 

fossils indicative of the Middle Jurassic fauna of the Tuxedni sandstone, and possibly the tuff that is interbedded with the fossiliferous 

strata, as well as the basic lava that overlies them, may belong with 

the rocks here under discussion. Part or all of the supposed Lower 

Jurassic porphyry and tuff of the west coast of Cook Inlet may therefore be Middle Jurassic. The writer believes, however, that the general absence of volcanic material at the horizon of the Tuxedni sandstone indicates that the volcanic beds west of Kamishak Bay either 

underlie the Middle Jurassic rocks or are involved with them in 

structural disturbances.

88 Mather, K. F., op. cit., pp. 165-166.
140 MESOZOIC STRATIGRAPHY OF ALASKA

MIDDLE JURASSIC " 

TUXEDNI SANDSTONE

Historical review. The Tuxedni sandstone is the lowest of the 

apparently conformable Middle and Upper Jurassic formations that 

are exposed in the cliffs on the west coast of Cook Inlet. It was first 

described under this name by Martin and Katz,97 although rocks 

belonging in it had previously been described by several geologists. 

The first mention of rocks belonging to this formation was apparently made by Eichwald,98 who described " hard black sandstones 

with ammonites" as occurring on Chisik ("Chasik") Island. The 

fossils described by Eichwald 99 as occurring in the " Neocomian or 

Gault" of " Chasik Island " and " Tukusitnu " [Tuxedni] Bay and 

probably at least part of those from undescribed localities on Cook 

Inlet and "Alaska" or Alaska Peninsula belong in this formation. 

The rocks on Tuxedni Bay that constitute the type section of this 

formation have been briefly described by Dall,1 and the fossils that 

Ball collected from these beds in 1895 were examined by Hyatt,2 who 

without enumerating the species in detail discussed the relations of 

some of the more characteristic forms and referred the fauna to the 

"Inferior Oolite." The Tuxedni sandstone constitutes the lower 

part (zones A, B, and C) of the " Enochkin formation " as described 

by Martin 3 and also by Stanton and Martin.4 Both of these descriptions contain detailed stratigraphic sections and lists of fossils, 

and the latter includes also a disc'ussion of the probable position of 

these rocks in the European section. The flora of these rocks was 

considered briefly by Knowlton 5 in a discussion of the JurassicCretaceous problem of Oregon and California. The description of

this formation by Martin and Katz 6 is largely a summary of the 

earlier descriptions by Stanton and Martin and by Martin, but 

adopts a new classification of the beds, and includes some details not 

presented before, among which is a previously unpublished discussion of the fossil plants contributed by Knowlton.

97 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 59-64, pi. 2, 1912.

98 Eichwald, Bduard von.,, Geognostisch-palaeontologische Bemerkungen fiber die Halbinsel Mangischlak und die ateutischen, Inseln, p. 91, St. Petersburg, 1871. 

09 Idem, pp. 138-200.

1 Dall, W. H., Report on coal and lignite of Alaska: U. S. Geol. Survey Seventeenth 

Ann. Kept, pt. 1, pp. 8G9-870, 1896.

2 Hyatt, Alpheus, Report on the Mesozolc fossils (appendix to Ball's Report on coal and 

lignite of Alaska) : U. S. Geol. Survey Seventeenth Ann. Rept., pt. 1, pp. 907-908, 1896.

3 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey 

Bull. 250, pp. 38-44, 1905.

4 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc.' America Bull., vol. 16, pp. 397-402, 1905.

5 Knowlton, F. H., The Jurassic age of the "Jurassic flora of Oregon " : Am. Jour. Sci., 

4th ser., vol. 30, pp. 49-50, 1910.

0 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 59^64, pi. 2, 1912.
JURASSIC, COOK INLET 141

The description of the Tuxedni sandstone given by Martin 7 in a 

discussion of the oil fields of Cook Inlet includes a brief general 

description of the formation, followed by detailed'statements concerning the ^tratigraphic relations and structure on Tuxedni, Chinitna, and Iniskin Bays. It is chiefly compiled from information 

contained in the report by Martin and Katz.

A geologic reconnaissance in the vicinity of Tuxedni Bay was 

made in 1920 by Moffit,8 who has given a brief general description of 

the Tuxedni sandstone. A detailed geologic investigation of the 

peninsula between Chinitna and Iniskin Bays was made by Moffit 

in 1921. A preliminary report on this investigation contains a description of the Tuxedni sandstone, with a generalized stratigraphic 

section of the formation which indicates that its thickness is more 

than 8,000 feet.9

Rocks that are supposedly equivalent to the Tuxedni sandstone, 

though of different composition and apparently interbedded with 

volcanic strata, were described by Mather 10 as occurring on the west 

shore of Kamishak Bay near Amakdedori. The description included a brief account of the character and the stratigraphic and 

structural relations of the rocks, with a list and discussion of some 

fossils by Stanton.

Stratigraphic description. The Tuxedni sandstone, which rests 

unconformably upon the lava and tuff of probable Lower Jurassic 

age as described on page 138, consists predominantly of sandy beds 

but contains many thin strata of shale and limestone and at least 

one bed of coarse conglomerate. Its thickness at the type locality 

on Tuxedni Bay, according to the writer's estimate, is at least 1,500 

feet and may be 2,000 feet or more. Moffit states that the thickness 

is possibly 3,000 feet on Tuxedni Bay and may be 8,000 feet in the 

Iniskin-Chinitna Peninsula. Fossils) are abundant, a large and 

highly characteristic marine molluscan fauna ranging throughout 

the formation and terrestrial plants having been found in the marine 

deposits at several horizons.

The following section is exposed on the south shore of the western 

arm of Tuxedni Bay. The base of the section is about 2 miles west 

of Fossil Point, near an obscure contact with older volcanic rocks 

that are probably Lower Jurassic. This contact is possibly a fault; 

consequently it is not certain that the section includes the lowest 

beds of the Tuxedni sandstone.

7 Martin, G. C., Preliminary report on petroleum in Alaska : U. S. Geol. Survey Bull. 

719, pp. 43-48, pi. 8, 1921.

8 Moffit, F. H., Geology of the vicinity of Tuxedni Bay, Cook Inlet: U. S. Geol. Survey 

Bull. 722, pp. 143-144, pi. 2, 1922.

8 Moffit, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, pp. 120-122, pi. 

3, 1922.

10 Mather, K. F., Mineral resources of the Kamishak Bay region: U. S. Geol. Survey 

Bull. 773, pp. 165-166, 1925.
142 MESOZOIC STRATIGRAPHY OF ALASKA

Section of part of Tuxedni sandstone on south shore of Tuxedni Bay

Feet

1. Shaly sandstone with scattered fossils, Inoceramus,

Trigonia, Sphaeroceras, Phylloceras, etc. (lot 2993)- 55

2. Black sandstone with small white angular grains__" 8

3. Hard gray sandstone 1

4. Black sandstone with Inoceramus ambiguus, Stephanoceras cf. 8. humphriesianum, Sphaeroceras oblatum, 

etc. (lot 3995) ______________________ 3

5. Dark shale_________ 8

6. Soft coarse black sandstone with white grains (lot

10519) ____________________ _- 39

7. Fine-grained gray shale with Sphaeroceras oblatum,

Belemnites, etc. (lot 2996 at base and lot 10517)_ 18

8. Fine-grained gray shale 35

9. Bands of sandstone and shale______________ 3^-6

10. Dark soft shaly rock with coarse grains__________ 10

11. Dark limestone with abundant fossils, Sphaeroceras

cepoides, Pleuromya, etc. (lots 2997 and 10516) ____ 2-4

12. Dark shale__________________________ 3

13. Dark conglomerate rock (arkose)_____-______ 7%

14. Dark shale with conglomerate bands and with fossils

(lot 2998)_________________________ 26.

15. Sandstone__________________________ 1

16. Gray shale__________________________ 15

17. Sandstone________ _____-^__________ __ 2

18. Shale with scattered fossils (lot 10520)________ 12V2

19. Sandstone and shale with Stephanoceras carlottense, 8. 

richardsoni, Sphaeroceras cepoides, Lytoceras, Phylr 

. loceras, and many other fossils (lot 3000)_____ 3-3^

20. Shale"with concretionary bands_____________ 10

21. Concealed by a fault__________________' 100±

22. Gray shale with numerous sandstone and concretionary bands and a few fossils, including Stephanoceras cf. 8. humphriesianum (lot 3013, near top)_ 100

23. Gray shale with sandstone and concretionary bands 150

24. Gray sandstone with Inoceramus ambiguus and a few

other bivalves at base (lot 3001)___________ 1

25. Limestone conglomerate with clavellate and undulate

Trigonias, etc. (lots 3002 and 10521)_________ 1

26. Gray sandstone ___ _________________ 3*4

27. Dark-gray fossiliferous sandstone___________ 1

28. Gray sandstone with many small fossils (lot 3303) at

base____________________________ 11

29. Fossiliferous conglomerate with Belemnites__________ 2

30. Shaly sandstone with Inoceramus lucifer and Lima cf.

L. gigantea (lot 3005)_________________ 52

31. Sandy shale with a few thin fossiliferous sandstone

bands (lot 3006)_____________________ 35

32. Indurated ledges of argillaceous sandstone 1 to 4 feet 

thick, alternating with somewhat thicker beds of 

fossiliferous clay (lot 3008, upper part)_______ 25

33. Shale with abundant ammonites, Stephanoceras, Harpoceras, etc. (lot 3009)________________ 20
JURASSIC, COOK INLET 143

Feet

34. Indurated bauds of sandstone in ledges 1 to 1% feet

thick, alternating with thicker beds of shale___ 14

35. More or less sandy shale weathering yellowish. Fossils (lot 3011) in lower 10 feet ;__________ 100

36. Sandstone with clay partings with abundant Lima cf. 

L. gigantea and other fossils (lot 3012 from 3%-foot 

band of grit at top)__ _______________ 36

37. Softer sandstone and shale to base of exposure, partly

covered by shale talus_________________ 100

1,128

The top of this section is at Fossil Point, south of which the 

rocks are concealed in the low ground on the west shore of the bay. 

Higher beds belonging in the Tuxedni sandstone are exposed at the 

northwest end of Chisik Island. The concealed interval, beneath the 

waters of the bay, is of unknown magnitude but probably does not 

exceed a few hundred feet and may be so small as to be negligible. 

The absence on the mainland of a characteristic bed of conglomerate 

that crops out on Chisik Island indicates that the sections on the 

mainland and on the island do not overlap, although they carry essentially the same fauna.

The lowest rocks exposed at the northwest end of Chisik Island 

consist of concretionary shale that yielded the fossils of lot 3014. 

These rocks are overlain by coarse massive conglomerate, at least 200 

feet thick, that includes lenses of sandy shale with fossiliferous 

concretions near its base. This conglomerate and the associated 

shale were erroneously referred to the Chinitna shale by Martin and 

Katz.11 The conglomerate is overlain by fossiliferous concretionary 

shale from which the fossils of lots 3015 and 2992 were collected. 

This shale was not measured but is possibly several hundred feet 

thick. It is overlain by the Chinitna shale, which will be described 

below. The total thickness of the formation as exposed on Tuxedni 

Bay is probably at least 1,500 or 1,600 feet and may be as much as 

2,000 feet, according to the writer's estimate, or 3,000 feet according 

to Moffit, if there is no duplication of beds in the concealed intervals.

The Tuxedni sandstone of the peninsula between Chinitna and 

Iniskin bays was described by Moffit 12 as follows:

The Tuxedni sandstone is not a homogeneous sandstone formation. It 

consists principally of sandstone and sandy shale but includes also conglomerate, grit, arkose, and, in the type locality, limestone. In general the 

lower part of the formation shows all the rocks mentioned, but the upper 

part is made up of sandy shale with which thin beds of sandstone in sub11 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, p. 66, pi. 2, 1912.

^Moffit, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, pp. 120-121, 

1922.
144 MESOZOIC STEATIGEAPHY OF ALASKA

ordinate amount and rare conglomerate beds are interstratifled. A generalized 

section based on observations of the formation in different parts of the district follows.

Generalized section of the Tuxedni sandstone in the Iniskm-Chinitna Peninsula

Feet

Shale_1______________._______________ 1,075 

Coarse gray sandstone ___-_________ __ 75 

Shale_______________._________________ 1,000 

Coarse conglomerate.

Shale_________________________________ 300 

Gray sandstone.

Shale __________._________________ 1,000 

Coarse conglomerate -: _____._________ 20

Thin shale. 

Heavy sandstone.

Dark shale_______________._____________ 1,200 

Fine-grained gray sandstone with small beds of shale and 

sandy shale____________________________ 1,500

Conglomerate____________ ________-___ 30 

Sandy beds, including sandstone, sandy shale, and conglomerate. 

Dark shale, sandy shale, and thin Sandstones-

,800

8,000+

Study of the Tuxedni sandstone during the Summer of 1921 shows that the 

formation is much thicker than earlier work in Cook Inlet seemed to indicate. No single section is known where the thickness of all the beds can be 

measured consecutively. The evidence of the thickness is therefore obtained 

from a number of incomplete sections in different localities and is subject 

to errors arising from incorrect correlation of beds in these sections and also' 

from possible duplication of beds through faulting or folding. Furthermore, 

the base of the Tuxedni sandstone has never been unmistakably recognized in 

this district, although the top, determined solely on paleontologic evidence, 

was seen in a few places. The combined sections from all of the localities 

indicate a maximum thickness of 8,000+ feet for the formation. These figures 

are large and represent a thickness muoh greater than the formation attains 

elsewhere on Cook Inlet, so that some doubt is felt as to their correctness, 

although they are comparable with the thickness of the overlying Upper 

Jurassic rocks in that region.

The following section on the east shore of Iniskin Bay probably 

includes the basal beds of the formation, but the concealed intervals 

are very large, less than half of the total thickness of the formation 

being represented, and the contact with the overlying formation is 

probably cut off by a fault.
JURASSIC, COOK INLET 145

Section of Tuxedni sandstone on east shore of TnisMn Bay

" Zone C ": Feet 

Sandy shale with many Belemnites and other fossils__ 50 

Concealed ___________________________ 20

Soft shale____________________________ 20 

Dark-drab shale with scattered fossils___________ 33 

Hard calcareous shale full of fossils, principally Inoceramus, Pleuromya, and other pelecypods________ 2 

Black sandstone________________________ 1 

Dark shale___________________________ 5 

Black sandstone -__ ________ 1 

Dark shale with many fossils________________ 12 

Reddish limestone - - ___ ____ ^ 

Dark shale with many fossils ____________:__ 14 

Dark shale with scattered fossils____________ 62 

Dark soft sandstone with streaks of conglomerate___ 10 

Concealed. 

" Zone B " :

Shale with several fossil bands containing Trigonia

doroschini, etc ___ ______ ______ 50 

Concealed. 

" Zone A": '

Shale with several fossil beds each 10 to 25 inches thick

and packed with fossils; Trigonia doroschini, T.

devexa, etc __ __ __ __________ 30 

Concealed.

Shale _______________________________ 12 

Coarse conglomerate ______________ 20 

Unconformity.

Beds equivalent to the Tuxedni sandstone in age may be present 

on the west shore of Kamishak Bay near Amakdedori, where Mather 

found a series of sediments about 500 feet thick comprising dark 

carbonaceous shale, sandstone, grit, and volcanic tuff, which are 

underlain and overlain by dense basic lava overthrust upon the rocks 

of the Naknek formation. Some of the more calcareous beds are 

crowded with fragments of shells, chiefly pelecypods but with a few 

Belemnites. The fossils of lot 12101 were obtained from one of 

these beds.

Age and correlation. The fossils of the Tuxedni sandstone, as 

represented in the following table, include a large number of marine 

mollusks, most of which belong to undescribed species, and a few 

fossil plants.
Fossils from Tuxedni sandstone of Cook Inle

Fieldenia? ___ . ___________ _ . ...

Stems ...

Cucullaea?? _..-.__. _ __ __ ..--.-....--..-...

Pinna (more slender than P. expansa and with

Pteria.. .....--.- _ -...-...-.---.-..-..-..-.--

o

n

»

IM

i

a

i i

a

1

h

i

|

a

o 1 i 1 g «05

8

a

1

h

S 

I i

a

i

h

h

1

CO

to

o

00

o

CD

t^

i

ca

i . g

a

a

i

h

h

h
Pteria?. ..................... ..................

Eumicrotis cf. E. curta Hall _ ............. _

Ostrea? _____ ........ _ .............. __

Trigonia doroschini Eichwald ___ _ --------

Trigonia sp. d, (clavellatae resembling sp. c

Pecten (small smooth form)..... ___ __ ......

Pecten (large form with coarse complex strucPecten (small ribbed form)... _____ ____

Pleuromyasp. b _ ............... _ ... _ ...

Pleuromya (different from sp. a and b). ____

Pleuromya.. __ _ _ .-.-...... _ ------- _

Pleuromya? _____________________

Pholadomya _ __ ..----..----. _ .. _ .. ....

Ooniomya _ _ . __ . _ ......... _ -.--.. ....

Thracia __ - __ .. __ . ___________

Thracia? _____________________

Aretica ____________ ... _ . __ . __

Arctica? (large form )..... ___ .. ____ . ......

'

1

I

-'

a 

1 a, Identified by T. W. Stanton; b, identified by F. H. Knowlton.
Fossils from Tuxedni sandstone of Cook Inlet Co

Cyprina? (large shell with anterior and posAstarte sp. a (large, nearly smooth, crenulated

Undetermined Solenidae? _____ . _____ ..

Turbo? ______________________

Natica.. . . - 

Turritella? _______________ ____

Alaria?. _____ ...... _ .--.... _ ...... ....

Phylloceras _________ . _____ ........

Oppelia? __ .. ____ . ______ . _ -. ---...

c

§

a

8

a

a

a

a

p;

E §i

I

§0}

IT,

[

1 1

a

IM 

|

.

SCO

1

1

1 

CO

a

a

a

CO

5CO CO

a

a

a

! §3

i

c§

§

a

V

,

a

a

a

1

«: 

1

oc

1

to

1

CO

i

"5

I

a

S 

S

"

O

a
Sonninia? (smaller form with strong sculpture) .

Sonninia? (small form with strong sculpture) . .

Sonninia? __ ... ._--. . ... .

Harpoceras.... _ _-. .... ........ _

Harpoceras? ________ .... _______ ...

Stephanoceras richardsoni Whiteaves?... ......

Stephanoceras ______ .. _ . ________ .

Stephanoceras? .cf. Ammonites asterianus 

D'Orbigny and A. loganianus Whiteaves ....

Stephanoceras? (robust form with small umbilicus) _______ .... __ .. _ ..... _ ....

Stephanoceras? (more compressed form with 

larger um bilicns) ...'... __ .... ..... ........

Stephanoceras? cf. Perisphinctes carlottensis

Sphaeroceras cf. Olcostephanus oblatum

Sphaeroceras cf. Olcostephanus cepoides 

Whiteaves.................................

""

"

~~

"

""

~"

"

a

a

1

a

R

1

a

a

a
Fossils from Tuxedni sandstone of Cook Inlet 

Fieldenia? ___ .. __ ....... _ . __ .. __ ..

Pagiophyllum? ................................

Fossil wood _________________ .. ....

Serpula ____ __ ------ _ .. _ -------------

Terebratula ____ . ____ . ...............

Orammatodon? sp. b. _____ __ .. ........

CuculJaea..-. _ ;. ------------------------ _ -

Oiicullaea?..--- ...... ......____. ...-.-..--.-

Area? -.... __ -. __ .-----...------..----.-.

Pinna (more slender than P. expansa and with 

longitudinal striae). _______ _______

Pinna.. __ . _ . _ ... _ ............. ___ .

Inoceramus ambiguus Eichwald -. .............

Inoceramus eximius Eichwald...--. _ ..- __ .

Inoceramus cf. I. lucifer Eichwald.. __ .......

Inoceramus porrectus Eichwald? -... ..........

Inoceramus .. __ ._--.--.-__-_____

Avicula ___ . _ .. _____ .. _ . .........

Pteria (large, strongly sculptured) ......... __

Pteria.....-.. -.-....-.. ...-,..... ......

, 8 i

a

t»

h

8 S i

a

o 

3 1

c»

o 1 *

CO

8

a

t--

8

it*

1

b

 h

a>

3

a

S

b

8 §!

a

fh

,

i! §3

b

g

o

3
Pteria?... _ . _ ..............................

Eumicrotis cf. E. curta Hall ____ .. .........

Eumicrotis . . __ __ . . __ .

Ostrea ___ ...

Ostrea?.. ____ .. __ ____ ......

Exogyra _____ ________ . ____ ....

Trigonia devexa Eichwald. __ .. ____ . __ .

Trigoniasp. 3. _________ .. ___ . .......

Trigonia sp. d (clavellatae resembling sp. c

Trigonia .......................................

Pecten (large form with coarse complex strucThracia?... ........ __ .......................

Arctica? (large form) _ ... _ .*......*..... ...

.

"

^

i

i

i

^
Fossils from Tuxedni sandstone of Cook Inlet C

Cyprina? (large shell with anterior and posCyprina? __________ . _____ ....... ...

Astarte sp. a (large, nearly smooth, crenulated

Astarte (small). _____ . _______ .......

Tancredia?. _______ ____ . __ ___ ..

Sphaeriola? ________________ .

Isocardia?.... ______ . __ .. ____ 1... _

Undetermined Solenidae?. _ . _____ .... ...

Dentalium?... _____________ ..

Turbo?............. __ ......................

Amberleya.-.. ______ ___ _____ . ...

Amberleya?..- ____________ ___ . _

TurriteUa?. ........ _ ..........................

Cerithium ___________ . __ ___ .....

Alaria?... .....................................

Actaeon?.. ____ _________ _ ... ....

Gastropod...... __ ..... . .............

Phylloceras. _ .. _ ...........................

Phylloceras? (large, with coarse sculpture) .....

Phylloceras? (young specimen) ............

HaplOceras? ............................. ...

Lytoceras.. ................................ ...

Oppelia?.....^..... ..........................

.

^

81-1

i

1-1

|

3

a

i.

*

1023-11029

1

a

§ I I

a

i

a

CO

8

"

1.

t>-

3

1

i

1038,7521

a

a1

1

a

a

§

o

i

a

|

i

« 

3 i § j

JO

S

a

i
Sonninia? (large, smooth form).......__.....

Sonninia? (smaller form with strong sculpture).

Sonninia? (small form with strong sculpture)..

Sonninia? (another sculptured form)..--...-...

Sonninia?_....._...........................

Harpoceras......................_...........

Harpoceras? (Sonninia) (small keeled form 

with coarse ribs).............................

Harpoceras?---..--.....-.---..................

Stephanoceras cf. S. humphresianum (Sowerby)

Stephanoceras richardsoni Whiteaves..........

Stephanoceras richardsoni Whiteaves?_......

Stephanoceras sp. a.._...._._____....

Stephanoceras sp.b _ .........................

Stephanoceras-__..____.__......_..

Stephanoceras? cf. Ammonites asterianus 

D'Orbigny and A. loganianus Whiteaves-.-.

Stephanoceras? (robust form with small umbilicus)......................................

Stephanoceras? (robust form with small umbilicus) ._-_.._________..__.._____-__--__..-_-

Stephanoceras? (more compressed form with 

larger umbilicus)............................

Stephanoceras ?................................

Stephanoceras? cf. Perisphinctes carlottensis 

Whiteaves_....___.__.________

Stephanoceras? (or Perisphinctes).....__....

Sphaeroceras cf. Olcostephanus oblatum 

Whiteaves..-.----._.._ ..................

Sphaeroceras cf. Olcostephanus cepoides 

Whiteaves. .---..---.------...---..-..-------

Sphaeroceras? sp. a..___..........___....

Sphaeroceras sp. b..--..-----------------------

Sphaeroceras ---.--.--..-------------.--..--..-

Sphaeroceras?----..--.-..-.-.----.--.--.--. ...

Macrocephalites.........-...-..._--.....-.-...

Macrocephalites?..__......._....... .

Perisphinctes cf. P. carlottensis (Whiteaves)...

Perisphinctes--__._._...__........ ...

Perisphinctes (small form with bifurcating ribs))

Parkinsonia? cf. P. parkinsoni Sowerby .

Ammonite....-.------.--.--------..- -.

Belemnites sp. a_........-...-.-..---.....

Belemnites sp. b........._................

Belemnites sp.c............... _..........

Belemnites (slender form)--.......-..-....-

Belemnites (hastate form)..................

Belomnites-..----..--..-----------..-------

.!..!.
154 MESOZOIC STRATIGRAPHY OF ALASKA

3010. South shore of Tuxedni Bay. Talus at base of bed 37 of section on >^ 

p. 143. These probably came from either bed 36 or bed 37 and could not have 

come from higher than bed 35. T. W. Stanton, 1904.

3012. South shore of Tuxedni Bay. Band of grit 3V2 feet thick at top of 

bed 36. T. W. Stanton, 1904.

3011. South shore of Tuxedni Bay. Lower 10 feet of bed 35. T. W. Stanton, 

1904.

3009. South shore of Tuxedni Bay. Bed 33. T. W. Stanton, 1904. v,

3008. South shore of Tuxedni Bay. Upper part of bed 32. T. W. Stanton, 

1904.

3006. South shore of Tuxedni Bay. Bed 31. T. W. Stanton, 1904.

3007. South shore of Tuxedni Bay. Talus from same locality as 3006. 

T. W. Stanton, 1904.

3005. South shore of Tuxedni Bay. Bed 30. T. W. Stanton, 1904. r

3003. South shore of Tuxedni Bay. Base of bed 28. T. W. Stanton, 1904. '

3002. South shore of Tuxedni Bay. Bed 25. T. W. Stanton, 1904.

10521 (20 F 11). South shore of Tuxedni Bay. Bed 25. F. H. Mofflt, 1920.

3001. South shore of Tuxedni Bay, 3 miles west of Chisik Island. Base of 

bed 24. T. W. Stanton, 1904.

3004. South shore of Tuxedni Bay. Talus just east of the outcrop of bed 

29, probably from a higher horizon than 3001. T. W. Stanton, 1904. /

3013. South shore of Tuxedni Bay. Upper member (clay shale) of bed 

22. T. W. Stanton, 1904. "*

3000. South shore of Tuxedni Bay. Concretions in bed 19. T. W. Stanton, 

1904.

1052Q, (20 F 10). South shore of Tuxedni Bay. Bed 18. F. H. Moffit, 1920.

2998. South shore of Tuxedni Bay. Bed 14. T. W. Stanton, 1904.

2999. South shore of Tuxedni Bay. Talus, probably mostly from beds 11 

to 14. T. W. Stanton, 1904.

2997. South shore of Tuxedni Bay. Bed 11. T. W. Stanton, 1904.

10516 (20 AI 5). South shore of Tuxedni Bay. Bed 11. Herbert Insley. 1920. '*

10518 (20 F 6). South shore of Tuxedni Bay. Bed 7 or 8. F. H. Moffit, 1920.

2996. South shore of Tuxedni Bay. Base of bed 7. T. W. Stanton, 1904.

10517 (20 F 5). South shore of Tuxedni Bay. Bed 7. F. H. Moffit, 1920. ,,-

10519 (20 F 7, 8, 9). South shore of Tuxedni Bay. Bed 6. F. H. Moffit, 

1920.

2995. South shore of Tuxedni Bay. Bed 4. T. W. Stanton, 1904.

2993. South shore of Tuxedni Bay 2 miles west of cabin on Chisik Island. ^ 

Bed 1. T. W. Stanton, 1904.

2994. South shore of Tuxedni Bay, small gulch about half a mile south of 

2993. Probably about same horizon as 2993. T. W. Stanton, 1904.

10515 (20 F 4). South shore of Tuxedni Bay one-fourth mile west of Fossil 

Point. F. H. Moffit, 1920.

10514, 10523 (20 AI 3, 20 F 3). South shore of Tuxedni Bay 200 feet west of 

Fossil Point. Moffit and Insley, 1920. *

10513, 7466 (20 AI 2, 20 F 2). South shore of Tuxedni Bay just west of 

extreme end of Fossil Point. Moffit and Insley, 1920.

7467 (20 F 2). South shore of Tuxedni Bay at Fossil Point. F. H. Moffit, 

1920. 1

10511 (20 AI 1). South shore of Tuxedni Bay just southeast of end of Fossil 

Point. Herbert Insley, 1920.

10512 (20 F 1). South shore of Tuxedni Bay on south side of Fossil Point. « 

F. H. Moffit, 1920.
JURASSIC, COOK INLET 155

7465 (20 AI 1, 20 F 1). South shore of Tuxedni Bay just southeast of end 

of Fossil Point. Mofflt and Insley, 1920.

10245 (B). South-.shore of Tuxedni Bay near Fossil Point. C. N. Fenner, 

1919.

7467 (20 F 12 a). South shore of Tuxedni Bay 200 yards south of Fossil 

Point. F. H. Moffit, 1920.

7468 (20 F 12 b). South shore of Tuxedni Bay 200 yards south of Fossil 

Point. F. H. Moffit, 1920.

7469 (20 F 12 c). South shore of Tuxedni Bay 200 yards south of Fossil 

Point. F. H. Moffit, 1920.

7440 (20 F 13 a). West shore of Snug Harbor 5 miles squth of Fossil Point. 

F. H. Moffit, 1920.

10522 (20 F 13 b). West shore of Snug Harbor 5 miles south of Fossil Point. 

Limy concretions in creek. F. H. Moffit, 1920.

12074 (A) Chisik Island, 5 miles north of cannery. W. R. Smith, 1923.

3014. West shore of Chisik Island 1 mile north of cabin. Concretions in 

shale beds below a massive conglomerate. T. W. Stanton, 1904.

3015. North end of Chisik Island, about one-fourth mile northeast of 3014; 

from higher beds. T. W. Stanton, 1904.

2992. West shore of Chisik Island 4,000 to 4,200 feet north of cabin. Shale 

and calcareous concretions overlying a massive conglomerate. T. W. Stanton, 1904. 

3050. South shore of Chinitna Bay 1 mile below head of bay. G. C. Martin, 

1904.

3049. South shore of Chinitua Bay 3 miles below head of bay. G.. C. Martin, 1904.

11014 (AB F 5). South shore of Chinitna Bay about a mile northwest of 

mouth of Fitz Creek. Arthur A. Baker, 1921.

11020 (AB F 27). South shore of Chinitna Bay 300 feet north of 11019. 

Arthur A. Baker, 1921.

10980 (F 3). South shore of Chinitna Bay 800 feet west of 10979. Fred H. 

Moffit, 1921.

11019 (AB F 26). South shore of Chiuitna Bay about 700 feet north of 

emergence of Tuxedni sandstone from under alluvium. Arthur A. Baker, 1921.

11021 (AB F 28). 100'feet southeast of .11019. Arthur A. Baker, 1921.

10979 (F 2). South shore of Chinitna Bay, most easterly exposure of Tuxedni 

sandstone on west side of Fitz Creek. Fred H. Moffit, 1921.

10998 (AB F 6). South shore of Chinitna Bay about two-thirds of a mile 

northwest of Fitz Creek. Arthur A. Baker, 1921.

10999 (AB F 7). Cliffs south of head of Chinitua Bay. Arthur A. Baker, 

1921.

11000 (AB F 8). At elevation 250 feet, up creek that drains from topographic 

station " Sharp " into head of Chinitna Bay. Arthur A. Baker, 1921.

11063 (AB F 80). 3,500 feet up tributary of Fitz Creek from north about 

1% miles from Chinitna Bay. Arthur A. Baker, 1921.

11033 (AB F 40). Mountain top 3 miles southwest of mouth of Fitz Creek. 

Arthur A. Baker, 1921.

7520 (AB F 41). Same locality as 11033. Arthur A. Bakec, 1921.

10981 (F 4). East side of Fitz Creek, 3 miles south of Chinitna Bay. Fred 

H. Moffit, 1921.

11022 (AB F 29). Fitz Creek about 3 miles from Chinitna Bay. Arthur A. 

Baker, 1921.

11023-11029 (AB F 30-36). Same locality as 11022. Arthur A. Baker, 1921.
156 MESOZOIC STRATIGRAPHY OF ALASKA

11030 (AB F 37). Short distance up tributary to Fitz Creek that drains 

divide northeast of Tonnie Peak. Arthur A. Baker, 1921.

11031 (AB F 38). About 1,000 feet up same tributary as 11030. Arthur A. 

Baker, 1921.

11032 (AB F 39). About 1,500 feet up same tributary as 11030. Arthur A. 

Baker, 1921..

11034 (AB F 42). About 7,200 feet up small creek coming from south into 

Fitz Creek about 1% miles from Chinitna Bay. Arthur A. Baker, 1921.

11035 (AB F 44). About 9,000 feet up same creek as 11034. Arthur A. Baker, 

1921.

11036 (AB F 43). About 8,000 feet up same creek as 11034. Arthur A. 

Baker, 1921.

11037 (AB F 45). About 3,000 feet up creek that drains into headwaters of 

Bowser Creek from the south. Arthur A. Baker, 1921.

11038 (AB F 46). About 1,000 feet up creek from 11037. Arthur A. Baker, 

1921.

7521 (AB F 46). About 1 mile south from divide between Fitz Creek, 

Brown Creek, and Bowser Creek; same locality as 11038. Arthur A. Baker, 

1921.

11039 (AB F 47). 2,000 feet farther up creek than 11038. Arthur A. Baker, 

1921.

7522 (AB F 48). About 8,300 feet up creek from 7521. Arthur A. Baker, 

1921.

11040 (AB F 49). 1,120 feet from 11039, on first right fork of left fork. 

Arthur A. Baker, 1921.

11041 (AB F 50). Crossing over hill to next creek to west at altitude 875 feet. 

Arthur A. Baker, 1921.

10983 (F 5). Head of Bowser Creek, south side of valley at about elevation 

800 feet. Fred H. Mofflt, 1921.

7527 (F 5). Bowser Creek, same locality as 10983. Fred H. Mofflt, 1921.

10984 (F 6). Head of Bowser Creek, near 10983. Fred H. Moffit, 1921.

11042 (AB F 51). On tributary to Bowser Creek from south about 1,900 feet 

up creek from trail crossing. Arthur A. Baker, 1921.

11043 (AB F 52). On same tributary as 11042, about 2,300 feet up creek 

from trail crossing. Arthur A. Baker, 1921.

7523 (AB F 52). About 2% miles from divide described under 7521. Arthur 

A. Baker, 1921.

11044 (AB F 53). 3,300 feet up creek from trail crossing at altitude 360 

feet (taking east fork at 2,500). Arthur A. Baker, 1921.

11045 (AB F 54). 3,900 feet up creek described under 11042 (taking east 

fork at 2500), at B 370. Arthur A. Baker, 1921.

10985 (F 7 a and b). Tributary to Bowser Creek from south next below head 

of stream; 3,800 feet from point where tributary enters Bowser Creek valley. 

Fred H. Moffit, 1921.

11046 (AB F 55). 4,400 feet up same creek as 11042. Arthur A. Baker, 1921.

11047 (AB F 56). 4,800 feet up same creek as 11042. Arthur A. Baker, 1921.

7524 (AB F 56). About 7,200 feet up same creek as 11042. Arthur A. Baker, 

1921.

11048 (AB F 57). 6,540 feet up same creek as 11042, taking west fork at 

5550. Arthur A. Baker, 1921.

11051 (AB F 62). 5,400 feet up same creek as 11042. Arthur A. Baker, 1921.

10987 (F 9). Tributary to Bowser Creek from south, next below head branch 

of stream, three-fourths mile below forks, a little less than 50 feet south of and 

stratigraphkally below F 8. Fred H. Moffit, 1921.
JURASSIC, COOK INLET 157

11053 (AB F 64). A short distance above assumed Tuxedni-Chinitna contact 

along same creek as 11042. Arthur A. Baker, 1921.

10993 (F 15). Northwest side Right Arm of Iniskin Bay, at head of arm. 

Fred H. Moffit, 1921.

7528 (F 16). Right Arm of Imskin Bay. Fred H. Moffit, 1921.

7526 (AB F 79). Sandstone on east shore of west arm of Right Arm of 

Iniskin Bay. Arthur A. Baker, 1921.

3040. East shore of Iniskin Bay iy2 miles above Brown's upper cabin, 

which is 4 miles above the entrance to the bay. T. W. Stanton, 1904.

3038. East shore of Iniskin Bay about 1 mile above upper cabin, or near 

point at entrance to east arm of bay. Zone A. T. W. Stanton, 1904.

3037. East shore of Iniskin Bay about half a mile above upper cabin. 

T. W. Stanton, 1904.

3039. East shore of Iniskin Bay 100 to 400 yards above upper cabin. T. W. 

Stanton, 1904.

3036. East shore' of Iniskin Bay 1% miles above lower cabin.

2919. East shore of Iniskin Bay. " Zones. A and B." Mixed specimens from 

beds represented by lots 3038 and 3035. G. C. Martin, 1903.

3035. East shore of Iniskin Bay 1^ miles above lower cabin. "Zone B." 

T. W. Stanton, 1904.

11062 (AB F 78). East shore of Iniskin Bay 6,500 feet north from end of 

trail at lower cabin. Arthur A. Baker, 1921.

11061 (AB F 77). East shore of Iniskin Bay 5,400 feet north from end of 

trail at lower cabin. Arthur A. Baker, 1921.

3034. East shore of Iniskin Bay 1 mile above lower cabin. T. W. Stanton, 

1904.

3033. East shore of Iniskin Bay one-fourth to 1 mile above lower cabin. 

Sixty-five feet of strata above fault. T. W. Stanton, 1904.

3032. East shore of Iniskin Bay 300 yards above lower cabin. About 300 feet 

of strata. T. W. Stanton, 1904.

2920. East shore of Iniskin Bay near lower cabin. From " Zone C." G. C. 

Martin, 1903.

11057 (AB F 70). East shore of Iniskin Bay about 250 feet south from end of 

trail at lower cabin. Arthur A. Baker, 1921.

3027. East shore of Iniskin Bay between lower cabin and next creek below it. 

Upper part of '.' Zone C." T. W. Stanton, 1904.

12101. About 2 miles north of Amakdedori, on west shore of Kamishak Bay. 

K. F. Mather, 1923.

Stanton's opinion 13 regarding the marine fossils is that

The fauna, except possibly a few species of Belemnites and pelecypods, is 

entirely distinct.

No closely similar fauna has been found elsewhere in Alaska or on the 

American continent, except on the Queen Charlotte Islands, where certain 

localities in the " Lower Shales" have yielded ammonites and a few other 

forms that evidently belong to this fauna and have no connection with the 

Cretaceous fauna from other localities on Queen Charlotte Islands, supposed 

to be in the same formation. Its exact correlation with European Jurassic 

faunas must await the exhaustive study and description of the collections, but 

it certainly includes at least a part of the Lower Oolite or Middle Jurassic.

18 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, p. 402, 1905.

49448 26 12
158 MESOZOIC STRATIGRAPHY OF ALASKA

The opinion stated by Hyatt 14 regarding the fossils from Tuxedni 

Bay is as follows:

The fossils from Tuxedni Harbor, Chasik Island (No. 1495), are Inferior 

Oolite. A characteristic species of Trigonia is identical with one found in the 

Mormon sandstone at Taylorville, Calif., which is characteristic in that formation. There is also a well-preserved specimen of Ammonitinae, sufficient in 

itself to settle the age of this rock. It is a species of Sphaeroceras, closely 

allied if not identical with the Mormon sandstone species and a very close 

ally of the Sphaeroceras (Stephanoceras) ffietelii Gottsche, found in the Inferior Oolite west of Mendoza in Chile. The aperture is well preserved in 

one specimen, and successful cleaning has exposed the inner whorls, so that no 

doubt can reasonably be held that this is a representative of the common fossils 

of this genus in the Inferior Oolite or Europe.

The fossil plants from the Tuxedni sandstone have been discussed 

by Knowlton,15 as follows:

The forms that have been specifically named are determined with a great 

degree of certainty, the most abundant being the Sagenopteris, which occurs 

at five localities. * * * The named species, not to go further afield, are 

found in the so-called " Jurassic " at Oroville, Calif., but apparently have not 

been found in the Cape Lisburne region of Alaska, although the Sagenopteris 

is not greatly different from a species that is.

UPPER JURASSIC 

CHINITNA SHALE

Historical review. The rocks now included in the Chinitna shale 

Avere first described by Martin 16 as the uppermost member (zone 

D) of the "Enochkin formation," and the description included detailed stratigraphic sections and lists of fossils identified by T. W. 

Stanton. The " Enochkin formation " was described in greater detail 

by Stanton and Martin,17 who discussed at length its age and correlation and gave stratigraphic sections and lists of fossils. They 

recognized the possible desirability of subdividing it into two formations, as was subsequently done, when they said: 18

The Enochkin formation, as defined and described in the preceding pages, 

might well be divided into two formations, differing somewhat lithologically, 

and each characterized by a distinct fauna. In the upper two-thirds shales 

predominate, and the most characteristic fossils are several species of Cadoceras. This portion, which we have mentioned as " zone D " or the " Cado14 Hyatt, Alpheus, Report on the Mesozoic fossils (appendix to Ball's Report on coal 

and lignite of Alaska) : U. S. Geol. Survey Seventeenth Ann. Kept., pt. 1, pp. 907-908, 

1896.

15 Knowlton, F. H., cited by Martin, G. C., and Katz, F. J., A geologic reconnaissance 

of the Iliamna region, Alaska : U. S. Geol. Survey Bull. 485, p. 64, 1912.

18 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey 

Bull. 250, pp. 38-44, 1905.

17 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Bull. Geol. Soc. America, vol. 16, pp. 397-402, 1905.

18 Idem, p. 401.
JURASSIC, COOK INLET 159

ceras zone," has been recognized by its fossils from Snug Harbor (Tuxedni 

Bay) to Cold Bay.

Brief mention of the fauna of the "upper part of the Enochkin 

formation," which is now known as the Chinitna shale, was made 

by Stanton19 in discussing the position of the Jurassic rocks of the 

Rocky Mountain region. The flora of these beds was also discussed briefly by Knowlton 20 in a consideration of the JurassicCretaceous problem of Oregon and California.

The Chinitna shale was first described as a separate formation 

by Martin and Katz,21 who defined it as including the strata formerely referred to " zone D " or the ^Cadoceras zone " of the " Enochkin formation," the type exposures being on the north shore of 

Chinitna Bay. This account consists of a compilation of the earlier 

descriptions and includes detailed stratigraphic sections and lists 

of fossils identified by Stanton and by Knowlton.

A brief description of the Chinitna shale, summarized from previous descriptions, was given by Martin 22 in an account of the oil 

fields of Cook Inlet. The occurrence of the Chinitna shale on Tuxedni Bay has been briefly described by Moffit.23 The exposures of 

the Chinitna shale and other Jurassic rocks in the peninsula between 

Chinitna and Iniskin bays were studied in considerable detail by 

Moffit, and his preliminary report on these studies 24 contains a 

discussion of the character, distribution, thickness, structure, and 

age of the formation.

A possible occurrence of the Chinitna shale on the west shore of 

Kamishak Bay has been described briefly by Mather. 25 

 /Stratigraphic description. The Tuxedni sandstone is overlain, 

probably conformably, by the basal Upper Jurassic formation of 

the Cook Inlet section, which has been named the Chinitna shale. 

This formation has a thickness of at least 1,300 feet, and probably 

2,400 feet, and consists of a conformable and fairly uniform succession of fine-grained marine sediments, mostly shale.

The limits of the formation are somewhat in doubt. The contact with the underlying formation has nowhere been clearly ob-

 ;

39 Stanton, T. W., Succession and distribution of later Mesozoic invertebrate faunas in 

North America: Jour. Geology,' vol. 17, pp. 411-412, 1909.

20 Knowlton, F. H., The Jurassic age of the "Jurassic flora of Oregon " : Am. Jour. 

Sci., 4th ser., vol. 30, pp. 49-50, 1910.

21 Martin, G. *C., and Katz, F. J., A. geologic reconnaissance of the Iliamna region, 

Alaska: U. 'S. Geol. Survey Bull. 485, pp. 65-68, pi. 2, 1912.

32 Martin, G. C., Preliminary report on petroleum in Alaska: U. S. Geol. Survey Bull. 

719, pp. 43-48, pi. 8, 1921.

33 Moffit, F. H., Geology of the vicinity of Tuxedni Bay, Cook Inlet: U. S. Geol. Survey 

. Bull. 722, pp. 142, 144, pi. 2, 1922.

34 Moffit, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, pp. 122-123 

pi. 3, 1922.

26 Mather, K. F., Mineral resources of the Kamishak Bay region : U. S. Geol. Survey 

Bull. 773, p. 168, 1925.
160 MESOZ01C STRATIGRAPHY OF ALASKA

served. The base of the formation is not exposed in the type section in Chinitna Bay, and the contact with the underlying formation of Iniskin Bay is possibly along a fault. The exposures at the 

type locality on the north shore of Chinitna Bay include, above the 

characteristic fossiliferous beds of this formation, other apparently 

nonfossiliferous beds of somewhat similar lithologic character, 

which aggregate at least 1,200 feet in thickness. These in turn are 

overlain by the characteristic Upper Jurassic strata of the Naknek 

formation. These nonfossiliferous strata have been tentatively assigned to the Chinitna shale but should not be regarded as constituting an essential part of its type section. The Chinitna shale, as 

originally defined and as now regarded by the writer, is the exact 

equivalent of " zone D " or the " Cadoceras zone " of the " Enochkin 

formation." It should include the strata characterized by Gadoceras 

and its associates and should exclude the higher Aucella and Cardioceras-bear'mg beds. The apparently barren zone between the Gcudocenw-bearing beds and the Aucella, and Cardioceras-beariiig beds at 

Chinitna Bay can not be assigned to a, definite position on the basis 

of the facts now available. If in the future fossils are found in 

that zone, the contained strata may be referred to the Chinitna shale, 

the Naknek formation, or a new intermediate formation, according 

as the relationships of the fauna indicate.

Section of part of Chinitrta shale on creek half a mile ivest of high cliffs on 

north shore of Chinitna Bay

Feet

1. Dark shale with a few bands of more indurated argillaceous sandstone __ __ __ _ ____ 425

2. Dark shale with beds of argillaceous sandstone forming

many cascades. Cadoceras seen near the middle___ 650

3. Indurated bands of argillaceous sandstone with abundant

specimens of Cadoceras and Belemnites (lot 3018)__ 10

4. Dark shale and argillaceous sandstone ____ 115

5. Similar beds not well exposed - 200

6. Dark shale weathering to brownish slopes, with bauds of 

small concretions containing Cadoceras doroschini, etc. 

(lot 3019), near top___________ _________ 330

7. Similar shale, mostly covered- _ __ __ 75

8. Dark clay shale, weathering brownish, with concretions

containing Cadoceras, etc., near middle_________ 110

* 1,915

The exposures recorded in this section, which were measured by 

T. W. Stanton, extend upward into inaccessible cliffs whose rocks, 

dipping northeastward, descend into the cliffs on the shore of the 

bay, where the following section was measured by Stanton. The 

uppermost beds of the preceding section consist of dark shale like 

that of No. 2 in the following section, and beds resembling No. 1 of
JURASSIC, COOK INLET 161

the following section were seen at an estimated distance of 100 feet 

above. The exposures as viewed from a point across the bay appear, 

however, to include a considerable thickness of light-colored banded 

sandstone that was not recognized as such in the preceding section 

and that may represent a few hundred feet of strata that should be 

interpolated between the two sections. The following section, which 

was also measured by T. W. Stanton, immediately underlies the 

section of strata referred to the Naknek formation as given on 

pages 172-173.

Section 'Of part of Chmitna shale (?) at west end of cliffs on north shore of

Chinitna Bay

Feet

 1. Dark argillaceous sandstone, passing downward into indurated dark shale with conspicuous thin bands and 

elongated lenses of yellowish impure limestone 475 

2. Dark indurated shale______________________ 37

It should be noted that no fossils have been found in the upper 

750 feet of strata in the creek section given on page 160, or in the 

lower 690 feet of the cliff sections given on pages 161 and 172-173. 

This apparently barren interval includes a total of 1,200 feet or more 

of beds that have been included in the Chinitna shale, as well as the 

lower 175 feet of the section referred to the Naknek formation. (See 

p. 173.) The present assignment of these apparently nonfossiliferous 

strata is based wholly upon the lithologic character of the rocks and 

is purely tentative.

The following section, measured by the writer in 1903, was the 

type section 26 for the upper member (zone D) of the "Enochkin 

formation." It is immediately overlain by the Chisik conglomerate 

member of the Naknek formation, as described on page 170.

Section of Chinitna shale on east shore of In-iskin Bay

Feet

1. Dark-drab shale with numerous bands of calcareous concretions filled with well-preserved specimens of Cadoceras, Belemnites, etc., and with a few sticks of 

fossilized wood______________ 146

2. Shale as above, partly concealed by talus at Mushroom

Rocks; thickness computed______ 77

3. Dark shale as above, with same concretions, wood, and

fossils ____________________ _ 190

4. Shale as above, with Cadoceras_______ 6

5. Limestone ___ _ 1

6. Shale as above (large cephalopod collected at base) 68

7. Shale as above. _ 295

8. Shale, partly concealed by talus; thickness computed 300

9. Shale as above________-___-_ 200

10. Concealed_________________________ - 25±

1,308±

28 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey 

Bull. 250, pp. 41-42, 1905.
162 MESOZOIO STRATIGRAPHY OF ALASKA

The lowest strata in this section are in close proximity to the 

highest bed of the Tuxedni sandstone, as given in the section on page 

145, and appear to overlie that bed. It is possible, however, that a 

fault is present in the concealed interval.

The fossils of lot 2921 were collected from the positions indicated 

in beds 1, 3, 4, and 6, and from talus at the base of the cliffs. They 

were not kept separate, as they seemed to represent a single fauna, 

and as lack of time prevented the making of exhaustive collections 

from the individual beds.

This section was reexamined in 1904 by Stanton, who collected 

Cadoceras and other fossils from a bed near the base of the section 

(3028), from higher beds about three-fourths of a mile farther 

south (3029), and from the upper 100 feet of bed 1 (3030). Stanton 

noted, a short distance above the lower Cadoceras zone, rocks that resembled the "dark shale with yellowish indurated bands" of the 

Chinitna Bay section, but states that " the conspicuously banded 

light-colored sandstones higher up in the section at Chinitna Bay 

have apparently disappeared or changed their lithologic character." 

Cadoceras occurs most abundantly at Iniskin Bay in the shale and 

sandstone overlying the " dark shale with yellowish indurated 

bands " and extending 200 or 300 feet higher (3029). This circumstance points strongly toward the probability of Cadoceras occurring 

considerably higher at Chinitna Bay than it has been recorded and 

tends to justify the tentative reference of the apparently nonfossiliferous shale of the Chinitna Bay section to this formation.

The following section was measured by the writer in the cliffs on 

the northeast shore of Oil Bay. The rocks at the base of the section 

are concealed, the Tuxedni sandstone not being exposed on Oil Bay, 

and there is considerable doubt as to just what part of the Chinitna 

shale is represented. The upper bed of the section is directly overlain, apparently conformably, by the rocks referred to the Naknek 

formation in the section given on page 173.

Section of upper part of Chinitna shale on east shore of Oil Bay

. Feet

1. Dark shale with concretions and with fossils (lot

3041) 46 feet above base_______________,. 690

2. Hard dark sandstone___________________ %

3. Dark-drab shale with numerous concretions______ 530

4. Calcareous shale with Cadoceras schmidti Pompeckj, 

Cadoceras sp. cf. C. stenololoide Pompeckj, and 

Phylloceras (lot 2941)__________________ 1

5. Dark shale with Cadoceras doroschini, etc. (lot 3042)_ 60

6. Soft green sandstone____________________ %

7. Dark-drab shale _______________________ 12

1, 294
JURASSIC, COOK INLET 163

The typical Chinitna fauna, with Cadoceras, has been found in 

only the lower 72 feet of the Oil Bay exposures. Above these beds 

is a great thickness of strata, including the remainder of this section 

and the lower 150 feet of the beds referred to the Naknek formation 

in the section on page 173, in which only a few fossils have lj>een 

found, and these few do not furnish conclusive evidence as to their 

age. These beds accordingly, like the nonfossiliferous strata on 

Chinitna Bay, have been divided between the Chinitna shale and 

the Naknek formation on the basis of their lithologic character.

The exposures on Chisik Island, which have not been studied in 

detail, seem to show a section similar to that on Iniskin Bay. A 

few fossils were found (lot 2990) not far below the base of the Chisik 

conglomerate, and Gadoceras was collected (lot 2991) several hundred feet lower.

The following description by Moffit 27 was based on a detailed 

study of exposures in the peninsula between Chinitna and Iniskin 

bays.

The Chinitna shale consists of gray, black, and reddish argillaceous shale, in 

which are interstratifled some sandy and calcareous beds and rare beds of 

grit. This formation is of fairly homogeneous character and differs from the 

prevailing shales of the upper part of the Tuxedni sandstone in that it is 

argillaceous rather than arenaceous, yet the shales of both formations at their 

contact are similar in appearance and composition and are distinguished from 

each other on paleontologic and not on lithologic evidence. Lines of fossiliferous concretions indicating the bedding planes are numerous in the lower part 

of the formation, and in most places where exposures are good they make it 

possible to determine within narrow limits the boundary line between this and 

the underlying formation. The upper part of the Chinitna shale, on the other 

hand, yields few fossils, yet it is characterized by discontinuous thin calcareous beds which are shaped like much elongated lenses and have a conspicuous yellowish color where weathered. These yellowish bands, although 

present throughout the upper 500 feet of the shale, give much assistance in 

determining the position of the formation boundary.

The Chinitna shale occupies the intermediate slopes of the landward side of 

the coast mountains, overlying the Tuxedni sandstone of the foothills and 

lower slopes and underlying the Chisik conglomerate and Naknek formation, 

which form the brow and crest of the ridge. It thus appears on the map as 

a narrow band nowhere more than a mile wide.

The thickness of the Chinitna shale in its type locality, as measured by 

Stanton, is 2,315 feet, and that of the partial sections on Iniskin and Oil bays 

is 1,308 feet and 1,294 feet, respectively. The base of the shale is not included 

in either of these partial sectiens, yet the thickness represented by them is 

nearer the thickness of some other sections between Iniskin and Chinitna bays 

than that of the type section. A section at the head of Bowser Creek gives 

1,425 feet as the thickness of the Chinitna shale at this locality.. | .

Age and correlation. The fossils obtained from the j Chinitna 

shale are listed in the accompanying table. |

"Moffit, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, p. 123, 1922.
Fossils from Chinitna shale of Cook Inlet 

Cladophlebis denticulata 

(Brongniart) Seward _

Dictyophyllum cf. D. 

obtusilobum..-. .......

Hausmannia sp.? (mere 

fragment). __ .. __ .

Ctenis grandifolia Fontaine _ -. ... . .... .......

Nilsonia cf. N. orientalis 

Heer. _ . _ ... ___ .

Phoenicopsis speciosa 

Heer. .... _ ....

Plant fragments _ _ .

Fossil wood _______

Serpula?. --------- _ . ...

Bryozoa? . _ .-.-

Rhynchonella. ... __ __

Leda?.... ........ .-...

Qrammatodon.. __ ....

Inoceramus --.-... _ ....

Avicula..-. _ .-. __ ...

Pteria ___________

Trigonia ---.-. . _ -.-.

Pecten (small smooth 

form). -. _ __ -.

Pecten (smooth form) ....

Lima _ .-. _ .-.. __ .

Modiola? . . _ ...

Pleuromya? ... . ......

Pholadomya-.--. .......

Ooniomya.-.. ......

Thracia.... _ .... 

Astarte _ . ______ -.

Lucina? . .. .

Venerid? .-..-. _ ......

Tellina? . ...........

Pelecypod burrows. _ ..

Dentalium. ___ . ......

Amberleya _ -._. ......

Cerithium.... .......

3>

s

ft

1

o

N

CO

O

CO

1 < I

<»

3

00

D 

CO

o'

1

1

o

0

3

§

CO

i 1 5

a

m

i

a

a

a

1 S

I

o

<N

0

a

a

a

a

0>

b

S

§

1-

i

i

1

1

1-

I

i

i

1

!

i

)

i

CD

a

i

O
Gastropod--..: . _- 

_

Phylloceras subobtusiforme Pompeckj ?.. ...

Phylloceras.- __ ___

Phylloceras?.. _____

Oxynotoceras?.. .........

Oxynotoceras? (smooth, 

sharp-centered form)..

Harpoceras?. __ . .....

Stephanoceras cf. Ammonites asterianus 

(Eichwald)- _ ......

Kepplerites? cf. K. loganianus (Whiteaves) ... 

.

Sphaeroceras? _______

Macrocephalites _____

Macrocephalites? __ .

Cadoceras catostoma 

Pompeckj? _____ ..

Cadoceras doroschini 

(Eichwald)-.--.----.

Cadoceras doroschini 

(Eichwald)?.- - _ -

Cadoceras g r e w i n g k i 

Pompeckj.--- __ ....

Cadoceras s c h m i d t i

Cadoceras stenoloboide

Cadoceras stenoloboide 

Pompeckj?- _______

Cadoceras wosnessenCadoceras (less convex

Cadoceras (compressed

Cadoceras. ___ . .......

Cadoceras?? (smooth,

Cadoceras? (globose with

Belemnites (very large

a I i

- ! 

1 a, Identified by T. W. Stanton; b, identified by F. H Knowlton.
166 MBSOZOIC STRATIGRAPHY OF ALASKA

2991. West shore of Chisik Island, several hundred feet below top of 

Chinitna shale. T. W. Stanton, 1904.

2990. West shore of Chisik Island, near top of Chinitna shale. T. W. 

Stanton, 1904.

3016. Northeast shore of Chisik Island, near top of Chinitna shale. T. W. 

Stanton, 1904.

12050 (G). Chisik Island. "Limestone above heavy conglomerate." C. N. 

Fenner, 1919.

3020. North shore of Chinitna Bay about 125 feet above sea level, on first 

small creek west of the high cliffs. T. W. Stanton, 1904.

3019. North shore of Chinitna Bay about 270 feet above sea level, on first 

small creek west of the high cliffs. Near top of bed 6 of section on p. 160. 

T. W. Stantou, 1904.

3018. North shore of Chinitna Bay about 410 feet above sea level, on first 

small creek west of the high cliffs. Bed 3. T. W. Stanton, 1904.

10978 (Fl). South side of entrance to Chinitna Bay, 700 feet west of point 

2y2 miles east of Camp Point. F. H. Moflftt, 1921.

11010 (ABF18). South shore of Chinitna Bay. Upper middle part of 

Chinitna shale. A. A. Baker, 1921.

10994 (ABF1). South shore of Chinitna Bay. Upper member of Chinitna 

shale. A. A. Baker, 1921.

10996 (ABF3). South shore of Chinitna Bay. Upper member of Chinitna 

shale. A. A. Baker, 1921.

10997 (ABF4). South shore of Chinitna Bay. Top member of Chinitna 

shale. A. A. Baker, 1921.

11003 (ABF 10). South shore of Chinitna Bay. Top member of Chinitna 

shale. A. A. Baker, 1921.

11004 (ABF 12). South shore of Chinitna Bay. Talus probably near top 

of Chinitna shale. A. A. Baker, 1921.

11005 (ABF 13). South shore of Chinitna Bay. A. A. Baker, 1921.

11007 (ABF 15). South shore of Chinitna Bay. Talus probably near top 

of Chinitna shale. A. A. Baker, 1921.

11008 (ABF 16). South shore of Chinitna Bay. Upper part of Chinitna 

shale. A. A. Baker, 1921.

11009 (AB F 17). South Shore of Chinita Bay. A. A. Baker, 1921.

11011 (AB F 19). South shore of Chinitna Bay. Upper part of Chinitna 

shale. A. A. Baker, 1921.

11012 (AB F 20). South shore of Chinitna Bay. Upper part of Chinitna 

shale. A. A. Baker, 1921.

7519 (AB F 2). South shore of Chiuitna Bay. A. A. Baker, 1921.

10982 (F 4 a) Head of Bowser Creek, south side of valley, at about eleva- 

'tion 1,000 feet above sea level. F. H. Moflit, 1921.

11041 (AB F 50). Crossing over hill to next creek to west, at altitude 875 

feet. A. A. Baker, 1921.

10986 (F 8). Tributary to Bowser Creek from south, next below head branch 

of stream; three-fourths mile below forks of stream at locality 507. F. H. 

Moffit, 1921.

11049 (AB F 58). Chinitna shale, 8,080 feet up same creek as 10986. A. A. 

Baker, 1921.

11050 (AB F 59 and 60). 8,400 feet up creek leading to peak east of C Y 

Peak. A. A. Baker, 1921.

11052 (AB F 63). Chinitna shale about 9,000 fe,et up creek. A. A. Baker, 

1921.
\

JURASSIC, COOK INLET 167

11052a (AB F 68). East shore of Oil Bay at northeast corner. A. A. Baker, 

1921.

3042. Northeast shore of Oil Bay. Lower 50 feet of section. T. W. Stanton, 

1904.

2941. Northeast shore of Oil Bay. Bed 4 of section on p. 162. G. C. Martin, 

1903.

3041. Northeast shore of Oil Bay near large waterfall. Forty-six feet above 

base of bed 1 of section. T. W.' Stanton, 1904.

11054 (AB F 65). West shore of Oil Bay about 600 feet from Bowser Greek. 

A. A. Baker, 1921.

3028. East shore of Iniskin B;iy one-fourth mile below lower cabin. "Zone 

D." T. W. Stanton, 1904.

3029. East shore of Iniskin Bay 1 mile below lower cabin. Three hundred 

feet or more above 3028. T. W. Stanton, 1904.

3030. East shore of Iniskin Bay 1% miles below lower cabin. Upper 100 

feet of Chinitna shale. T. W. Stanton, 1904.

2921. East shore of Iniskin Bay. Upper 1,200 feet of Chinitna shale. G. C. 

Martin, 1903.

10989 (F 11). East shore of Iniskin Bay south of trail to Oil Bay. F. H. 

Moffit, 1921.

10990. East shore of Iniskin Bay 1 mile south of trail to Oil Bay. F. H. 

Moffit, 1921.

10991. East shore of Iniskin Bay 1 mile south of trail to Oil Bay. Float. 

F. H. Moffit, 1921.

10992 (F 14). East shore of Iniskin Bay 1 mile south of trail to Oil Bay. 

F. H. Mofflt, 1921.

11058 (AB F 72). East shore of Iniskin Bay 4,700 feet below end of trail at 

lower cabin. A. A. Baker, 1921.

11059 (AB F 73 and 75). East shore of Iniskin Bay 6,100 feet south from 

end of trail at lower cabin. A. A. Baker, 1921.

7525 (AB F 74). East shore of Iniskin Bay about 6,050 feet south from end 

of trail at lower cabin. A. A. Baker, 1921.

11060 (AB F 76). East shore of Iniskin Bay 8,200 feet down shore from 

lower cabin, or. about 750 feet below Toadstool Islands. Just below contact 

with Chisik conglomerate. A. A. Baker, 1921.

The fauna includes abundant cephalopods and a few other marine 

mollusks. The most abundant and characteristic members of the 

fauna are ammonites, especially the several species of CadocGrais, 

which are characteristic of the Callovian of Europe and of other 

northern regions. A meager fossil flora is associated with the 

marine mollusks at several localities.

The following discussion 28 of the fauna of the Chinitna shale 

was written by Stanton:

Its -characteristic ammonites have been assigned to the Callovian by Neumayr, Hyatt, and Pompeckj, all of whom recognized the character of the 

fauna, which is represented by closely similar forms in Russia, Franz Josef 

Land, and elsewhere in northern regions, as well as in other parts of Europe. 

This Callovian fauna is placed by many geologists in the lower part of the

V

28 Stanton, T. W., and Martin-, G. C., Mesozolc section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 17, p. 401, 1905.
168 MESOZOIC STRATIGRAPHY OF ALASKA

Upper Jurassic, but it seems to accord better with the local development in 

Alaska to follow the custom of some German geologists and assign it to the 

top of the Middle Jurassic. Seven species of Cadoceras have been named 

from Alaska, some of which will evidently become synonyms when the large 

collections now on hand are fully studied, and possibly one or two additional 

names will be necessary. With these are associated Sphaeroceras, Phylloceras, 

and one or two other genera of ammonites, belemnites, and a very few pelecypods and gastropods.

The flora of the Chinitna shale was described by Knowlton,29 as 

follows:

The forms that have been specifically named are determined with a great 

degree of certainty. * * * The two remaining forms are mere fragments 

that will not admit of specific identification, though there can be absolutely no 

doubt as to the correctness of the generic reference, especially that of the 

Dictyophyllum, which seems to be in fruit. As to the distribution of the named 

species, the Cladophlebis occurs in the Jurassic of England and France as well 

as other parts of the Old World and, moreover, is very close to what has been 

called "Asplemum " whitbiense, which occurs abundantly in the Jurassic of 

eastern Siberia and California. The other named species, not to go farther 

afield, are found in the " so-called " Jurassic at Oroville, Calif., but apparently 

have not been found in the Cape Lisburne region of Alaska.

NAKNEK FORMATION

Historical review. The Naknek formation, the typical occurrence 

of which is on the Alaska Peninsula and is described on pages 203- 

218, is also well developed on the west coast of Cook Inlet. The occurrence of the Naknek formation in this district was first indicated 

by Martin,30 who gave only a brief and general description. The 

Naknek formation of Cook Inlet was described in detail by Stanton 

and Martin.31 This account includes stratigraphic sections and a 

general discussion of the character and relations of the fauna. The 

fauna of the Naknek formation of Cook Inlet was discussed briefly by 

Stanton 32 in an account of the Jurassic beds of the Rocky Mountain 

region. The occurrence, character, and relations of the Naknek 

formation on that part of the west coast of Cook Inlet lying north 

of Iniskin Bay were described by Martin and Katz,33 whose account 

comprises the detailed stratigraphic sections and the discussion of 

age and correlation substantially as given by Stanton and Martin 

but includes some additional data on the petrographic character 

of the tuffaceous beds and a more complete discussion of the correla29 Knowlton, F. H., cited by Martin, G. C., and Katz, F. J., A geologic reconnaissance 

of the Iliamna region, Alaska: U. S. Geol. Survey Bull. 485, p. 64, 1912.

30 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey 

Bull. 250, pp. 43-45, 1905.

81 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, pp. 402-407, 1905.

32 Stanton, T. W., Succession and distribution of later Mesozoic invertebrate faunas in 

North America: Jour. Geology, vol. 17, pp. 411-412, 414, 1909.

33 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: £J. S. Geol. Survey Bull. 485, pp. 69-74, pi. 2, 1912.
JURASSIC, COOK INLET 169

tion of these beds with the Jurassic rocks of other Alaskan districts. 

The occurrence of these rocks is also represented on a geologic map 

and in structure sections.

'An account of the oil fields of Cook Inlet by Martin contains a 

description of the Naknek formation 34 that includes a general discussion and local details of the exposures north of Iniskin Bay 

compiled from the publication just mentioned, together with descriptions of the exposures south of Iniskin Bay not previously published.

The specimens of Cardioceras collected by Stanton from the lower 

part of the Naknek formation on the east shore of Oil Bay have been 

 described by Reeside,35 who gave systematic descriptions of the 

species, most of which were new, together with a discussion of the 

age of the beds, which he correlated with the Sundance formation of 

Wyoming and with the Argovian or Lower Oxfordian of most 

European stratigraphers.

The Naknek formation of the vicinity of Tuxedni Bay was described briefly by Moffit,36 who stated that the formation includes a 

lower part composed chiefly of shale, with some sandstone, arkose, 

tuff, and conglomerate, and an upper part composed of massive lightcolored sandstone. These two divisions are mapped separately.

The Naknek formation of the peninsula between Chinitna and 

Iniskin Bays was described by Moffit 37 as including a lower division, 

1,500 feet thick, composed of gray shale with sandstone beds, and 

an upper division, 3,000 feet thick, composed of massive light-colored 

sandstone, arkose, and tuff. These divisions are mapped separately.

The exposures of the Naknek formation on the west shore of 

Kamishak Bay have been described briefly by Mather. 38

The Chisik conglomerate was first described by Martin 39 as 

Upper Jurassic "agglomerate." It was described by Stanton and 

Martin 40 as a local lens of coarse agglomerate constituting the basal 

part of the Naknek formation. The Chisik conglomerate was first 

given a name by Martin and Katz,41 who described it briefly as a distinct formation, and discussed its probable relations to the rocks of

34 Martin, G. C., Preliminary report on petroleum in Alaska : U. S. Geol. Survey Bull. 

719, pp. 43-50, pi. 8, 1921.

35 Reeside, J. B., jr., Some American Jurassic ammonites of the genera Quenstediceras, 

Cardioceras, and Amoeboceras, family Cardioceratidae: U. S. Geol. Survey Prof. Paper 

118, 64 pp., 1919.

30 Mofflt, F. H., Geology of the vicinity of Tuxedni Bay, Cook Inlet: U. S. Geol. Survey 

Bull. 722, pp. 142, 145, pi. 2, 1922.

37 Mofflt, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, pp. 119-120, 

125-126, pi. 3, 1922.

38 Mather, K. F., Mineral resources of the Kamishak Bay region: U. S. Geol. Survey 

Bull. 773, pp. 169-171, 1925.

39 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey 

Bull. 250, p. 44, 1905.

40 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, p. 406, 1905.

41 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 68-69, pi. 2, 1912.
170 MESOZOIC STRATIGRAPHY OF ALASKA

this and other Alaskan districts. Martin 42 also gave a brief general 

description, compiled from the above-mentioned' accounts, in a discussion of the oil fields of Cook Inlet.

The type section was studied in 1920 by Moffit,43 who gave a brief 

description of the conglomerate. Moffit has also made a detailed 

study of the exposures in the peninsula between Chinitna and 

Tuxedni bays, on which a preliminary report 44 has been issued.

The occurrence of a conglomerate on the west shore of Kamishak 

Bay, which is believed to represent Chisik conglomerate, has been 

described by Mather.45

SfrratigrapJdc description, The Naknek formation of the west 

coast of Cook Inlet consists of sandstone, shale, arkose, conglomerate, andesitic tuff, and probably some interbedded ande.sitic lava, aggregating a thickness of more than 5,000 feet, conformably underlain 

by a massive conglomerate 300 to 400 feet thick. In previous reports this massive conglomerate has been treated as a distinct formation, but it has recently been considered best by the United States 

Geological Survey to classify it as a local basal member of the Naknek formation.

The Chisik conglomerate is a massive plate of coarse conglomerate 

that consists of boulders of granite or diorite and other igneous rocks 

embedded in a tuffaceous andesitic matrix. It occurs locally in the 

Upper Jurassic strata of Cook Inlet. At the type locality, on Chisik 

Island, its maximum observed thickness is 300 to 400 feet; on the 

east shore of Iniskin Bay its thickness is about 290 feet. The Chisik 

conglomerate lies with structural conformity on the C'adoceras-be&i'- 

ing beds of the Chinitna shale and is overlain conformably by the 

coarse sandy Aucella-bQar'mg beds of the Naknek formation.

On Moffit's geologic map of the peninsuja between Chinitna and 

Iniskin Bays the Chisik conglomerate is represented as a narrow band 

extending only part way betAveen Iniskin and Oil Bays, for the beds 

resting on the Chinitna shale on both sides of Oil Bay are made up 

of grit or fine conglomerate and arkosic sandstone and bear no resemblance to the beds occupying this position on Iniskin Bay. In all 

other places from Oil Bay to Chinitna Bay, where the base of the 

Naknek formation was examined by Moffit, the beds in this position 

consist of coarse arkose and fine grit. It therefore appears that the 

Chisik conglomerate of Iniskin Bay is probably a local phase of the 

basal Naknek if its local development and variation in thickness are

42 Martin, G. C., Preliminary report on petroleum in Alaska: U. S. Geol. Survey Bull. 

719, pp. 43-48, pi. 8, 1921.

43 Mofflt, F. H., Geology of the vicinity of Tuxedni Bay, Cook Inlet: U. S. Geol. Survey 

Bull. 722, pp. 144-145, pi. 2, 1922.

"Mofflt, F. H., The Iniskin Bay district: TJ. S. Geol. Survey Bull. 739, pp. 124-125, 

pi. 3, 1922.

45 Matber, K. F., Mineral resources of the Kamishak Bay region : U. S. Geol. Survey 

Bull. 773, pp. 168-169, 1925.
JURASSIC, COOK INLET 171

due to original conditions of deposition, but these irregularities may 

possibly be due to an unrecognized overlying unconformity. No 

fossils have been seen in the Chisik conglomerate except possibly 

uncharacteristic species of Belemnites. Its exact age is consequently 

somewhat in doubt, but its approximate age is clearly shown by its 

position between the Chinitna shale and the Gardioceras zone of the 

Naknek formation, both of which are Upper Jurassic.

Where the Chisik conglomerate is absent the overlying beds of the 

Naknek rest, with apparent conformity, upon the nonfossiliferous 

shale referred tentatively on pages 160-161 to the upper part of the 

Chinitna shale. The original top of the Naknek formation has not 

been observed on Cook Inlet, the Cretaceous being lacking and the 

next younger beds being Tertiary and overlying the Naknek formation unconformably.

The following account by Moffit 40 was based on exposures in the 

peninsula between Chinitna and Iniskin Bays, but it is descriptive of 

the formation as exposed all along the west coast of Cook Inlet.

In the area between Chinitna and Iniskin Bays the lower part of the 

formation, ranging from about 1,500 to 1,645 feet in thickness, consists of 

gray shale with dark arkosic beds and fine conglomerate or grit at the base 

and thin sandy beds scattered through it. The overlying sediments are 

white or light-colored sandstones containing an abundance of igneous ma: 

terial, in part tuff, in part clastic material derived from granite or granitelike rocks, and in part intrusive sills. This jipper part includes the remainder 

'of the formation as exposed in the district. These rocks are confined to a 

curving belt from 2 to 4 miles in width and extend along the whole seaward side of the peninsula from Iniskin Bay to Chinitna Bay.

The basal arkosic beds are also made up of material from a land mass 

where granite or granitic rocks supplied an abundance of waste for the 

formation of new sediments and are believed to be the time equivalent 

of the Chisik conglomerate of Iniskin Bay, for no conglomerate comparable 

to the Chisik conglomerate of Iniskin Bay was seen elsewhere in the district. 

The thickness of the coarse-grained basal beds is 147 feet on the east shore 

of Oil Bay and is approximately the same in other places where the beds 

were examined. Sandy shales with beds of sandstone succeed the basal beds 

and together with them make up the lower part of the Naknek formation 

below the light-colored cliff-forming beds. This part of the Naknek reaches 

a thickness of 1,645 feet in the section measured by Martin at Oil Bay.

, The upper part of the Naknek formation is conspicuous wherever it crops 

out because of its light color and because it resists erosion better than the 

underlying beds. It forms the dip slope on the seaward face of the mountains along the coast. Its scarp makes the white cliffs along most of the 

crest of the mountains as seen from the landward side. This part of the 

Naknek formation reaches a thickness of at least 3,000 feet. The beds are 

prevailingly hard and massive but in large exposures show distinctly the 

bedding lines. They include hard arkosic sandstone, andesitic tuff, coarse 

and fine sandstone, shale, and conglomerate. Thin sills of quartz diorite are 

intruded into the sedimentary beds and are distinguished from them only 

on close examination.

* Moffit, F. H., The Iniskin Bay district: U. S. Geol. Survey Bull. 739, pp. 125-126,1922.
172 MESOZOIC STRATIGRAPHY OF ALASKA

The Naknek beds above the Chisik conglomerate as exposed on 

Chisik Island include several hundred feet of sparsely fossiliferous 

calcareous shale that yielded the fossils of lot 3017 (p. 177). This 

shale is overlain by massive sandstone and tuff that are regarded 

as also constituting part of the Naknek formation.

The rocks of the Naknek formation exposed on Chinitna Bay 

are very thick, as shown in the folloAving section, which was measured in the cliffs that border the north shore of the bay for a distance of about 4 miles west from the mouth of East Glacier Creek.

Section of Naknek formation on north shore of Chmitna Bay 4T

Feet

1 (1-19). Conglomerate and tuff, with some shale and sandstone ; Beleminites 18 feet above base. _ 113

2 (20-21). Shale with Aucella (lot 3022) at top______ 18

3 (22-37). Conglomerate and tuff with some shale and

sandstone ______________ ___ ___ 84

4 (38). Shale___________________________ 25

5 (39). Concealed_________________________ 462

6 (40-46). Lava and tuff with large concealed intervals_ 160

7 (47-52). Tuff or lava with some interbedded agglomerate and shale__________________________ 192

8 (53). Concealed__________________________ 182

9 (54-60). Tuff and agglomerate with some shale_____ 473

10 (61). Concealed___________..____________ 24

11 (62-64). Shale and sandstone with some interbedded

tuff or lava ; a few Betemnites -_______________ 123

12(65). Concealed__________________________ 338

13 (66-75). Coarse gray sandstone with some shale and

fine conglomerate____ ___ _ ___ 344

14 (76). Fault (displacement probably small).

15 (77-82). Coarse gray sandstone with bands of fine conconglomerate and some shale_________ 120

16 (83). Dark shale with Belemnites______________ 40 

17(84-87). Sandstone and shale________________ 310 

18 (88). Concealed except two or three small outcrops of

shaly sandstone -______________________ 425

19(89). Dark shale with Belemnites______________ 160

20 (90). Coarse cross-bedded sandstone____________ 30

21 (91). Dark shale and shaly sandstone with Aucella,

etc. (lot 3026)________________________ 290

22 (92). Alternating bands of coarse gray and argillaceous

fossiliferous sandstone (lot 3025)_____________ 100 

. 23 (93-95). Thin-bedded argillaceous sandstone in irregularly alternating light and dark bands, with coarser 

gray sandstone at top and bottom_____________ 388

24 (96-97). Banded sandstone with Belemnites__________ 340

25 (98-99). Sandstone and conglomerate____________ 9.1

47 Condensed from more detailed section given in Geol. Soc. America Bull., vol. 16, 

pp. 403-405, 1905, and in U. S. Geol. Survey Bull. 485, pp. 69-71, 1912. The numbers in 

parentheses are those designating the beds in the detailed section.
JURASSIC, COOK INLET 173

26 (100). Banded argillaceous sandstone with fossil if erous

beds 30 feet (lot 3024) and 25 (75?) feet (lot 3023) Feet

above base__________________________ 156

27 (101). Somewhat massive dark-gray argillaceous sandstone with a few thin yellowish bands__________ 150

5,138

The section on the east shore of Oil Bay, which is given below, 

was measured by T. W. Stanton and differs somewhat from the more 

roughly measured and less carefully studied section measured by 

Martin. 48 This section is of importance in showing the relative 

positions of the Aueella and Oardiocercus zones. The light-colored 

sandstone of No. 8 bears a strong lithologic resemblance to the 

banded beds of the cliffs on Chinitna Bay. The conglomeratic beds 

(9 to 16) have been interpreted by Martin 48 as possibly a phase of 

the Chisik conglomerate, which is otherwise not present on Oil Bay.

Section of Naknek formation on east shore of Oil Bay

Feet

1. Andesite, interbedded with shale and other sediments- 1,400±

2. Dark shale and shaly sandstone with a few thin beds

of dark volcanic ash; Aucella- near base (lot 3047)_ 600

3. Dark shale and shaly sandstone, as above, with crustacean remains 160 feet above base__________ 480

4. Coarse grit__________________________ 3

5. Shale and sandstone _____________________ 25

6. Coarse grit __________________________ 3

7. Dark shale and shaly sandstone, as above, with 

Cardioceras, etc., 80 feet (lot 3045) and 150 feet 

(lot 3046) above base_________.._______ 190

8. Irregularly bedded and banded, light-colored, more or 

less shaly sandstone with fossils 15 feet (lot 3043) 

and (in talus) 170 feet (lot 8044) above base. __ 362

9. Fine conglomerate, like No. 4___.____________ 7

10. Thin-bedded shaly sandstone_______________ 37

11. Coarse gray grit_ ___ _ _ ____,_____ 1

12. Gray shaly sandstone ___________________ 34

13. Conglomerate, like No. 4_________________ 3

14. Shaly sandstone with Pleuromya, Ammonites, etc__ 1

15. Gray conglomerate, somewhat coarser than the underlying bed_________________________ 8

16. Coarse gray grit or fine conglomerate with many small 

angular white pebbles one-eighth inch in dianjeter 

and some shaly bands toward the top________ 34

17. Fine gray sandstone with fragmentary bivalves___ 12

3,200

^Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey 

j Bull. 250, p. 43, 1905. 

V
174 MESOZOIC STRATIGRAPHY OF ALASKA ,.

On the east shore of Iniskin Bay the Chisik conglomerate member 

is overlain by 300 feet or more of sandy shale with Aucella and 

Belevynites (lot 3031), above which is light-colored thin-bedded 

sandstone which resembles those of the section in the cliffs on Chinitna Bay and which apparently does not contain fossils. The shale 

and sandstone aggregate about 580 feet in thickness. These strata 

are overlain near the mouth of the bay by massive beds of coarse 

conglomerate and lava or tuff, of which a thickness of 270 feet is 

exposed on the shore of Iniskin Bay. Higher beds of the same general character form the cliffs outside the entrance to the bay.

A small area of Upper Jurassic rocks forms the bold headland at 

the north entrance to Ursus Cove. These rocks consist of an undetermined thickness of sandstone with Aucella and other fossils (lot 

3087). Neither the top nor the bottom of the formation is here exposed, the Jurassic strata being in contact with Triassic rocks that 

are overthrust upon them.

The Naknek formation is exposed on the foreland south of Ursus 

Cove. The outcrops on a small indentation of the coast known as 

Eocky Bay consist of about 75 feet of dark-gray shaly sandstone and 

sandy shale, resembling those of beds 2 to 7 of the Oil Bay section 

(p. 173) and containing Aucella and other fossils (lot 3090). Higher 

strata are exposed along the coast farther south, there being an estimated thickness of possibly 800 feet of strata overlying these beds 

between Eocky Bay and the fault contact with the Triassic rocks 

just north of Bruin Bay.

The exposures on the cape at the south entrance to Bruin Bay and 

in the cliffs for about 5 miles south of this point consist of nearly 

horizontal dark-gray sandstones and sandy shale having a thickness 

of at least 500 feet. Neither the top nor the bottom of the formation is exposed, the contact with the adjacent Triassic rocks being a 

fault. Aucella and other fossils (lot 9032) were collected near the 

entrance to Bruin Bay.

The Naknek formation crops out almost continuously in the cliffs 

on the south shore of Kamishak Bay for about 10 mile's west of the 

mouth of Douglas Eiver. The exposures consist of nearly horizontal beds of buff and gray sandstone, and some of the beds carry 

numerous fossils, Aucella being especially abundant. A very striking but apparently not stratigraphically significant unconformity 

was observed near the mouth of Douglas Eiver. The character and 

relations of the beds at this unconformity are shown in the following section, which was measured by T. W. Stanton:
JURASSIC, COOK INLET 175

Section of part of Naknek formation on south shore of Kamishak Bay, near 

mouth of Dougla-s River

Feet

1. Gray sandstone; many fossils (lot 3096) in lower part__ 50

2. Unconformity.

3. Brownish-yellow cross-bedded sandstone, mostly very friable and barren of fossils. Lignitized wood, Tancredia, 

etc. (lot 3097), near top, and Modiola, etc. (lot 3098), 

25 f.eet above base_______________- 100

4. Gray sandstone, with some masses weathered yellowish 

brown. Aucella, etc. (lot 3099), 70 feet above base, 

and Tancredia, etc. (lot 3100), 50 feet above base___ 75

The total thickness of the Naknek formation along this part of 

the coast was not determined. The top and bottom of the formation 

and its contacts with other formations were not observed. The beds 

are in most places nearly horizontal and undulate gently, so that 

only a slight thickness is exposed at the base of the cliffs. Similar 

horizontal beds appear to extend inland up to an altitude of 800 or 

1,000 feet, there forming the hilltops.

Age and correlation. The fauna of the post-Chisik beds of the 

Naknek,formation of the west coast of Cook Inlet, as now known, is 

represented in the following table. It includes 60 or more species 

of marine mollusks, most of which are undetermined and many of 

which are probably undescribed. The most significant members of 

this fauna are the species of Aucella, Lytoceras, Phylloceras, and 

Cardiooeras, of which those belonging to the first three genera are 

characteristic of the formation. According to Stanton,40

The fauna of the Naknek formation is especially characterized by the presence of Aucella belonging to species very closely related if not identical with 

A. pallasi and A. bronni of the Russian Volga beds. These fossils are at some 

localities very abundant, completely filling thick beds. At other places they 

are so rare that they may be easily overlooked, but a careful search will find 

them in almost every section. Associated with the Aucella there are usually 

two or three species of Belemnites, frequently a large Lytoceras and a Phylloceras, and occasionally a few gastropods, Trigonia, and other pelecypods.

Aucella has been found about 1,100 feet above the base and 100 feet 

below the top of the thick section on Chinitna Bay (pp. 172-173), in 

the upper 2,500 feet of the section on Oil Bay, at many localities in 

the beds exposed on Kamishak Bay that seem to represent the upper 

part of the formation, and apparently in the lowermost 300 or 400 

feet of the sections on Chisik Island and Iniskin Bay.

Cardioeeras has been found only in the beds exposed on Oil Bay 

and is there apparently restricted to the lower 700 feet of the section 

described on page 173. Regarding this genus Stanton 49 said:

49 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, p. 407, 1905.
176 MESOZOIC STRATIGRAPHY OF ALASKA

At Oil Bay the lower part of the formation yielded two species of Cardioceras 

related to C. alternans and C. cordatus, which aid greatly in making more definite correlations with both American and European horizons.

The relation of the beds containing Cardioceras to those containing Aucella at Oil Bay is so clear, and the absence of Cardioceras in 

the Aucella-loearmg beds, not only at this locality but at all the other 

localities, is so striking, that it is practically certain that Cardioceras 

can not be regarded as characteristic of the whole formation. In 

this connection it should be noted that Cardioceras has been found 

at only one locality in the type area of the Naknek formation on the 

Alaska Peninsula (see pp. 211-212) and has not been found in any 

of the other Alaskan areas where the supposed equivalents of the 

Naknek formation are believed to occur, except at a single locality in 

the Matanuska Valley, described on page 232.

The following is Stanton's opinion 50 regarding the equivalence 

of the Naknek fauna:

It is clear that the Naknek formation is of about the same age as the Mariposa beds of California with Aucella erringtoni and Cardioceras cf. 0. alternans, and it also includes the horizon of the marine Jurassic with Cardioceras 

cordiforme in the Black Hills, where, however, the Aucella element is lacking from the fauna, and probably only the horizon of the basal portion of the 

Naknek is represented. A similar fauna occurs in Russia in the Volgian beds, 

and it is widespread in the boreal region, occurring on Spitzbergen, Nova 

Zembla, and elsewhere.

The following statement was made by Reeside: 51

The four species of Cardioceras and one variety from the lower part of the 

Naknek formation warrant the correlation of the zone containing them with 

the Sundance and with the Cardioceras zone of British Columbia. As the 

overlying part of the Naknek formation contains Aucella, it probably is equivalent, at least in part, to the Mariposa slate and the Aucelld zone of British 

Columbia.

Concerning the stratigraphic position of the Sundance formation,. 

Reeside 52 said:

The close relationship between the cardioceratids of the Sundauce and those 

of the zone of Cardioceras cordatum Sowerby, of the European Jurassic, indicates their equivalence. It is true that some of the American species seem 

to have no close relatives in the European faunas, so far as one may judge 

from the literature of the subject, but the remaining species are sufficient to 

establish the correlation. Many European stratigraphers refer the cordatum 

zone to the Lower Oxfordian, others to the Upper Oxfordian or to the Lower 

Corallian, and still others drop the terms Oxfordian and Corallian and 

substitute Argovian or Sequaninn.

50 Stanton, T. W., and Martin, G. C., op. cit., p. 407.

51 Reeside, J. B., jr., Some American Jurassic' ammonites of the genera Q'lienstedticeras, 

Cardioceras, and Amoeboceraa, family Cardioceratidae: U. S. Geol. Survey Prof. Paper 

118, p. 11, 1919.

62 Idem, p. 10. /
Fossils from post-Chisik beds of the Naknek formation 

Plant fragments -------------

Leda.-... ______ , ___ ......

Grammatodon. ___ . _ . .........

Area ___ . ______ ---.....

Pinna.. __ ------- ........

Avicula---. __ ...

Pteria.-.. __ .. _ ................

Eumicrotis?--.. _ .. _ ......

Eumicrotis? (large, coarsely striated)............................

Aucella (striated) _____ ..... ...

Aucella-. _ .. __ .- _ .....

Trigonia cf. T. doroschini Eichwald 

Pecten.... ___ .. ...............

Pecten (small smooth form) . .

Pecten?... ___ .. ____ ........

Modiola (small form) . ______ .

Pleuromya?.. __ _______ . ...

Qoniomya.--..--.-. ... ...

Thracia.... ______ . __ .. ...

Thracia?--.... ....

Arctica?.. ____ .............

Cyprina? _____ _____ .. ....

Praeconia?.... ________ . _ ...

Astarte distans ( Whitfleld) .......

Tancredia? (more compressed form) 

Tancredia.- _ .....

Corbula?... ...... ............

Panopaea?

i

00

i ,

a

a

,

a

a

a

a

/

8

a

o

i ,

§S

j

1

1

3

« S

CO

o o

CC

o

a

a

a

o

a

a

a

oo

o

a

i 9

,

SCO

CO

a

a

i

lO

I

" a, Identified by T. W. Stanton; b, identified by J. B. Reeside.
Fossils from post-Chisik beds of the Naknek formation of Coo

Turbo? ____ ------ _ . ____ . _

Indeterminate gastropods (very

Phylloceras? (young) ....

Cardioceras aff. C. distans (Whitfield - - --------

Cardioceras distans var. depressum

i

0

CO

£J

co

S

co SCO CO CO CO

S

8

a

0

I

0

CO

o

«

o

<o

o

t~

o

00

o 0

CM

S

CO

h

S

CO

0

CO

h

*

CO

b

b
JURASSIC, COOK INLET 179

3017. West shore of Chisik Island, 1 mile north of south end of island. 

Shale overlying Chisik conglomerate member and beneath higher lava beds. 

T. W. Stanton, 1904.

3048. North shore of Chinitna Bay, near head of small creek. T. W. 

Stanton, 1904.

3021. North shore of Chinitna Bay, at west end of cliffs. Talus. T. W. 

Stanton, 1904.

3024. North shore of Chinitna Bay. 30 feet above base of bed 26 in section on p. 173. T. W. Stanton, 1904.

3023. North shore of Chinitna Bay. 25 (75?) feet above base of bed 26. 

T. W. Stanton, 1904.

3025. North shore of Chinitna Bay. Bed 92. T. W. Stanton, 1904.

3026. North shore of Chinitna Bay. Bed 91: T. W. Stanton, 1904.

3022. North shore of Chinitna Bay one-fourth mile west of mouth of East 

Glacier Creek. Bed 20. T. W. Stanton, 1904.

10995 (AB F 2). South shore of Chinitna Bay. Lower part of Naknek 

about 200 feet above assumed base. Arthur A. Baker, 1921.

11001 (AB F 9). South shore of Chinitna Bay. Talus, probably in lower 

part of Naknek. Arthur A. Baker, 1921.

11002 (AB F 11). South shore of Chinitna Bay. Talus, probably in lower 

part of Naknek. Arthur A. Baker, 1921.

11006 (AB F 14). South shore of Chinitna Bay. Talus, probably in lower 

part of Naknek. Arthur A. Baker, 1921.

11013 (AB F 21). South shore of Chinitna Bay. Lower part of Naknek. 

Arthur A. Baker,' 1921.

11015 (AB F 22). South shore of Chinitna Bay. Lower part of Nakuek. 

Arthur A. Baker, 1921.

11016 (AB F 23). South shore of Chinitna Bay. Lower part of Naknek. 

Arthur A. Baker, 1921.

11017 (AB F 24). South shore of Chinitna Bay. Lower part of Naknek. 

Arthur A. Baker, 1921.

11018 (AB F 25). South shore of Chinitna Bay. Lower part of Naknek. 

Arthur A. Baker, 1921.

11050a (AB F 61). Near headwaters of tributary entering Bowser Creek from 

east 2 miles above its mouth. Talus below Chinitna-Naknek contact at same 

locality as AB F 60. Arthur A. Baker, 1921.

2942. East shore of Oil Bay. Shale near base of Naknek formation (?). 

(See U. S. Geol. Survey Bull. 485, p. 72, 1912.) G. C. Martin, 1903.

3041. Northeast shore of Oil Bay. Sandstone fragments found at foot of 

cliff near large waterfall, but derived from a much higher bed. T. W. Stanton, 

1904.

3043. Northeast shore of Oil Bay. Stratum 15 feet above base of bed 8 of 

section on p. 173. T. W. Stanton, 1904.

3044. Northeast shore of Oil Bay. Talus at outcrop of strata 170 feet above 

base of bed 8. T. W. Stanton, 1904.

3045. Northeast shore of Oil Bay. SO feet above base of bed 7. T. W. 

Stanton, 1904.
180 MESOZOIC STBATIGRAPHY OF ALASKA

3046. Northeast shore of Oil Bay. 350 feet above base of bed 7. T. W. 

Stanton, 1904.

3047. Northeast shore of Oil Bay. Near base of bed 2. T. W. Stanton, 1904.

11056 (AB F 69). East coast of Oil Bay N. 61° E. of Mount Pomeroy. Arthur 

A. Baker, 1921.

10988 (F 10). West side of Oil Bay, about half a mile from head. Fred H. 

Mofflt, 1921.

11055 (AB F 66 and 67). At second point down Oil Bay from gravel pit near 

Bowser Creek. Near contact of Chinitna shale and Chisik conglomerate member. Arthur A. Baker, 1921.

3031. East shore of Iniskin.Bay, in first cove near entrance to bay. Shales 

overlying Chisik conglomerate. T. W. Stanton, 1904.

3087. Point at north entrance to Ursus Cove. Sandstone resembling part of 

beds 2 to 7 of the Oil Bay section. T. W. Stanton, 1904.

3090. Rocky Bay, 8 miles southwest of Ursus Cove. Shaly sandstone and 

sandy shale, about 75 feet thick, resembling those of beds 2 to 7 of the Oil Bay 

section. T. W. Stanton, 1904.

3092. South shore of Bruin Bay, bluffs near entrance. Dark-gray sandstone 

and sandy shale. T. W. Stanton, 1904.

3093. South shore of Kamishak Bay 1 mile east of entrance to " Lower Bear 

Bay." Gray sandstone. T. W. Stanton, 1904.

3095. South shore of Kamishak Bay 8 or 9 miles southeast of entrance to 

" Lower Bear Bay" and not over 2 miles west of mouth of Douglas River. 

Dark-gray sandstone overlying a massive light-buff sandstone. T. W. Stanton, 

1904.

3100. South shore of Kamishak Bay near mouth of Douglas River. 50 feet 

above base of bed 4 of section on p. 175. T. W. Stftnton, 1904.

3099. South shore of Kamishak Bay near mouth of Douglas River. 70 feet 

above base of bed 4. T. W. Stanton, 1904.

3098. South shore of Kamishak Bay near mouth of Douglas River. 25 feet 

above base of bed 3. T. W. Stanton, 1904.

3097. South shore of Kamishak Bay near mouth of Douglas River. Near 

top of bed 3. T. W. Stanton, 1904.

3096. West bank of Douglas River 1 mile above mouth. Lower part of bed 

1 of section on p. 175, above unconformity. T. W. Stanton, 1904.

The localities in the preceding table are arranged geographically 

from north to south. The lower member of the post-Chisik rocks 

that have been referred to the Naknek formation on Cook Inlet, 

which constitutes the lower Naknek of Moffit and the Gardioceras 

zone as described in this volume, yielded the fossils of lots 3048?, 

3021(?), 3023, 3024, 3025, 10995 to 11050a, 2942, 3041 to 3046, 11056, 

10988, and 11055. The upper member of the Naknek formation of 

Cook Inlet, which constitutes the upper Naknek of Moffit, yielded 

lots 3017, 3026, 3022, 3047, 3031, and 3087 to 3096.
JURASSIC, ALASKA PENINSULA 181

ALASKA PENINSULA 

GENERAL FEATURES

The Jurassic rocks of Alaska Peninsula include the direct southwestward extension of the Jurassic rocks on Cook Inlet and constitute a section which, when fully known, will probably be found to 

rival if not excel the section of Cook Inlet in thickness and completeness. Most of the formations and faunal zones at Cook Inlet are 

now known on Alaska Peninsula, which contains also some Lower 

or Middle Jurassic strata that are but little known and that are 

apparently absent on Cook Inlet. The contact of the Jurassic with 

the Cretaceous rocks is also exposed on the Alaska Peninsula but not 

on Cook Inlet. The general section of the Jurassic rocks on Alaska 

Peninsula is as follows, according to Capps,55 who also represented 

it as in Figure 6.

Generalised section of the sedimentary rocks of the Cold Bay district

Upper Jurassic: Feet 

Naknek formation (conglomerate and arkosic 

sandstone from 1,000 to 3,000 feet thick, overlain by sandy shale)______________ 5,000+

Shelikof formation (700 to 1,000 feet of black 

shale, with some limestone lenses at top, overlying a thick series of sandstone, with minor 

amounts of conglomerate and sandy to calcareous shale; carries the Chinitna fauna) _ 5,000-7,000 

Unconformity. 

Middle Jurassic: Kialagvik formation (sandstone

and sandy shale at Kialagvik Bay)________ 500+ 

Lower Jurassic (calcareous sandstone and sandy

shale, with limestone at Cold and Alinchak bays) _ 2,300± 

Upper Triassic (thin-bedded limestone and calcareous shale with basaltic dikes and sills at Cape 

Kekurnoi) _______________________ 1, 000+

88 Capps, S. R., The Cold Bay district: U. S. Geol. Survey Bull. 739, p. 91, 1922. 

49448 26 13
182 MESOZOIO STRATIGRAPHY OF ALASKA

LOWER JTIHASSIC (?)

Historical review. Overlying the Upper Triassic rocks near 

the entrance to Cold Bay is several thousand feet of shale and 

sandstone that are probably, at least in part, Lower Jurassic.

B

UpPER Shelikof NaVnek formation formation . 

JURASSIC TRIASSIC JURASSIC PROBABLY LOWER JURASSIC UPPER 

 Barabara Cr

"T^ 

T^Er 

A I jpti

Cold Bay |. $$$&

 ,°1 V-'0"- 't!>;

^:'-T-L- -

~''""T5

' ' :^.f /:':' '

':?-&£?

 :&&';;

 ." '; '. ' '.: 

 383$*

 ?''fc? " ' ' 

.- "I-":::-'.-

iiiiflliliv.

 . ; .' ^.'. .:i'

.'..j...:.i.vqgr

ie^§§R?

^

Sandy shafe g $2g&f?

Tparjs (/ray antose z ^^:'|s@ 

and pebbly sandstone; . _ . tt^i^ij^

tion and thickness of ?i£i3i"SS2 

conglomerate beds D^T-.V.'-.'"^ 

varies greatly inshore SsH^s^s 

, distance &V-:-.'i-:i£-

Mainly black shale 

with somesands&ne<^ 

and some limy shale *- ^^

-~.

^ __

MainJy massive bror/n 

sandstone,some beds 

concretionary. Minor 

amounts of shale and 

cony/omaratA

Sandfitne and shale 

cut by basic dikes.

Conglomerate 

 ^/CONFORMITY

Red toblack sandy 

shale x ^

Coarse sandstone^ ^ >v> 

sandy conglomerate, ^ ^ ,^ 

a/?rf thin-bedded shales, X. ^ ^ 

all more or less calcarc- ^^ -. 

oos <3/7rf grading into x,. 

impure limestone >^

Dense blue thin -bedded limestone with 

some limy sandstone 

and shale

Thin -bedded dense 

limestone cut by basaltic 

sills or interbedded 

with basalt flows

zek

Kic

Shale. send* shale, 

and sandstone

c' 

Arkosic sandstone/ g

Massive conglpmer- J 

ate with arkosic. c

Sandstone, pebbly 

sandstone, conQlomer 

gte,and sandy shale

FEET r°

-1,000 c

n

-2,000 |

oi 

in

-3,000 

-4,000

X

\

V N.

X*

C

ilagvik E

^?^S

1^til

IBS

sf§&^>H

&^

.'' . ' .. -^

 ; ;' '; . ^

^B

^tty&j

HI

^ S:^

^ilSSS*

ilii

^aWiSii

77^?.:A-;y

*^^?SI

L iii^il

*y

Conglomerate

Coarse arkosic sandstone with some finf 

conglomerate

Coarse conglomerate

Shale with limy

concretions and 

some sandstone

Brown sandstone with 

small pebbles. 

^ Siliceous tocherty shaleMaasire brown to gray 

sandstone wtthsome 

shale

Conglomerate 

Dark tolight cjray arkosic. sandstone rrith 

thin conglomerate beds' 

fossilf

Impure sandstonewith some shale beds

Conglomerate

Heavy, sandstone 

beds alternating 

with thin shales

Mostly shale, 

poorly exposed

Conglomerate 

ANGULAR UNCOHnHMlTr

Sandstone oral 

sandy shale

FIGURE 6. Generalized geologic sections of the Cold Bay district. (After S. B. Capps)

The occurrence of these rocks was mentioned briefly by Stanton 

and Martin,56 but no detailed description of their character or

68 Stanton, T. W., and Martin, G. C., Mesozolc section on Cook Inlet and the Alaska 

Peninsula: Geol. Soc. America Bull., vol. 16, p. 397, 1905.
JURASSIC, ALASKA PENINSULA 183

discussion of their age was given. A brief statement regarding 

the occurrence was made by Atwood 57 on the basis of the account 

by Stanton and Martin.

Knowlton's discussion of the Lower Jurassic flora of the Matanuska Valley 58 contains a brief mention of fossil plants from Cold 

Bay that may be Lower J'urassic. The species in lot 3109 are listed.

A description of the supposed Lower Jurassic of Cold and Alinchak bays was given by Martin 59 in an account of the oil fields of 

the Alaska Peninsula. The description, which was based on the 

investigation by Stanton and Martin in 1904, contains a discussion 

of the character and sequence of the rocks and fossils and consists 

chiefly of hitherto unpublished information.

An account of the geology of the Cold Bay district by Capps, 

based on reconnaissance surveys in 1921, contains a description 00 

of the character, thickness, and age of the Lower Jurassic rocks 

of Cold Bay that includes a list by Stanton of some fossils (lot 

10820) collected by Capps. The same information was used as the 

basis of a description .of these rocks by Smith and Baker.61

Additional information concerning the Lower Jurassic rocks at 

Cold and Alinchak bays, based on a reconnaissance survey in 1923, 

has been given by Smith,62 whose description includes a brief account of the character, sequence, and age of the rocks, with lists 

of fossils determined by Stanton from material collected by Smith 

in 1923.

Stratigraphic description. The Triassic rocks on the northeast 

shore of Cold Bay (see pp. 61-64) appear to grade upward, with no 

abrupt change, into less calcareous beds, which do not contain the 

characteristic Upper Triassic fauna. The change begins about half 

a mile northwest of Cape Kekurnoi, which is at the eastern entrance 

to Cold Bay, and the first several hundred feet of strata overlying 

the known Triassic beds is barren of fossils. Beds of fissile, somewhat calcareous sandstone containing ammonites, pelecypods, and 

plants (lot 3109; see p. 185) were seen a mile northwest of the cape at 

a horizon about 700 feet above the highest observed occurrence of 

Triassic fossils. The general aspect of the ammonites from this 

locality, according to Stanton, is Jurassic rather than Triassic, but

57 Atwood, W. 'W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, p. 31, 1911.

68 Knowlton, F. H., A Lower Jurassic flora from the upper Matanuska Valley, Alaska: 

U. S. Nat. Mus. Proc., vol. 51, No. 2158, p. 454, 1916.

69 Martin, G. C., Preliminary report on petroleum in Alaska: U. S. Geol. Survey Bull. 

719, pp. 57-60, 1921.

00 Capps, S. R., The Cold Bay district: U. S. Geol. Survey Bull. 739, 1922, pp. 90, 91, 

93-94, pi. 11. . '

61 Smith, W. R., and Baker, A. A., The Cold Bay-Chignik district: U. S. Geol. Survey 

Bull. 755, pp. 169-170, 172-173, pi. 8, 1924.

82 Smith, W. R., The Cold Bay-Katmai district: U. S. Geol. Survey Bull. 773, pp. 

195-196, pi. 4, 1925.
184 MESOZOIC STRATIGRAPHY OF ALASKA

the fossils are unlike any previously known from Alaska. A little 

farther northwest along the shore, 200 or 300 feet higher, a few more 

ammonites were collected (lot 3110) and a few specimens of Rhynchonella were obtained from a boulder (not in place) on the beach. 

These ammonites, according to Stanton, include two or three genera 

of Jurassic aspect and are probably Lower Oolite or older. Another 

small collection of ammonites and pelecypods (lot 3111) was obtained a short distance south of a large waterfall about iy2 miles 

northwest of Cape Kekurnoi, about 1,800 feet stratigraphically above 

the highest beds containing Pseudomonotis. There is a sharp change 

from sandstone to shale at this place, and the dip abruptly changes 

from 18° to 28°. These changes possibly indicate a fault. The next 

rocks exposed on the shore northwest of this locality consist of soft 

brownish shale several hundred feet thick, above which is a heavy 

bed of coarse conglomerate. The overlying rocks are apparently 

Upper Jurassic and will be described on page 198.

These Lower Jurassic (?) rocks probably extend northeastward 

through the hills to Alinchak Bay, where a collection of ammonites 

(lot 3130) similar to those of lot 3109 has been obtained. The beds 

that yielded this collection crop out about a quarter of a mile up the 

shore beyond the Upper Triassic beds containing Pseudomonotis 

(see p. 62) and were not studied in detail. The interval between 

them and the Triassic exposures is concealed, and the beds that overlie them were not observed.

The Lower Jurassic rocks at Cold Bay, according to Capps,63

occur near Cape Kekurnoi in a narrow belt that extends from Cold Bay 

across the narrow peninsula to Alinchak Bay. The Triassic rocks at the 

cape, described above, become more sandy and less calcareous northwestward from the highest Pseudomonotis zone, although without any observed 

structural break. The transition from the Triassic limestone and limy 

shale to impure limestone, calcareous sandstone, and shale is gradual, and 

it is believed that deposition was here continuous. About 1% miles from 

the cape a collection of fossils was made that has been determined by 

T. W. Stanton as probably of Lower Jurassic age.

The sandstone from which this collection was made and some similar 

conglomerates for some distance above and below the fossiliferous zone are 

characteristic in that they contain abundant grains of bright-red jasper and 

brightly colored greenstone particles, with larger fragments of carbonaceous 

shale.

Of the total thickness of about 2,300 feet of beds here included in the 

Lower Jurassic, the lower 1,500 feet is prevailingly limestone and limy sandstone and shale at the bottom and prevailingly sandstone at the top. It 

was in the upper portion that the only fossils were found. Above the portion 

in which sandstone is dominant there is about 800 feet of beds that consist 

mainly of black to rusty weathered sandy shales with some thin beds of 

limestone. It is not certain that these shaly beds belong in the Lower

83 Capps, S. R., op. cit., pp. 93-94.
JURASSIC, ALASKA PENINSULA 185

Jurassic, but as they seem to lie conformably on the sandstone, they are 

here tentatively included with the Lower Jurassic. The shales are overlain 

by a conglomerate 75 feet thick which is believed to mark an unconformity 

between the Lower Jurassic and the overlying Upper Jurassic beds. It is 

possible, however, that these shales are to be correlated with the shales in 

the lower part of the Shelikof formation, as exposed in the Kial'agvik Bay 

section; if so, they are of Upper Jurassic age.

Age and correlation. The supposed Lower Jurassic shale and 

sandstone constitute a formation of somewhat problematic age. 

They apparently overlie the Upper Triassic Pseudomonotis-bearmg 

beds conformably and are either overlain by or separated by a fault 

from strata that carry the Upper Jurassic fauna of the Chinitna 

shale. It is possible that they may, at least in part, represent the 

highest Triassic, which elsewhere in Alaska was either not deposited 

or was removed by subsequent erosion. It is also possible that they 

may include the off-shore representatives of the Lower Jurassic 

volcanic beds of Cook Inlet. There are several horizons known in 

Europe between the Khaetic and the Oolite that may here be 

represented.

Fossils from Lower Jurassic (?) shale and sandstone of Cold and Alinchak

bays a

-

Leda?. - .. .. . . ..

Arietites? . ___ .. ______ . _____ . .....

Stephanoceras? _ .. _________ . .............

Ammonite (another coarse-ribbed discoid genus) ...

Ammonite (nearly smooth discoid specimen).. .....

Ammonites (two or three other genera of Jurassic

8

S

cT 

o

TO

h

b

o

CO

a

s

CO

a

rH

CO

C3

CO

£

a

l-H

O t~

o

a

g

co

ICO

so

h

d

y

> a, Identified by T. W. Stanton; b, identified by F. H. Knowlton.
186 MESOZOIC STRATIGRAPHY OF ALASKA

3109,3520. Northeast shore of Cold Bay about a mile northwest of Cape 

Kekurnoi. T. W. Stanton, 1904.

3110. Northeast shore of Cold Bay a short distance northwest of 3109, and 

200 or 300 feet higher. T. W. Stanton, 1904. 

3110a. Some locality as 3110. Boulder on beach. T. W. Stanton, 1904.

3111. Northeast shore of Cold Bay a short distance south of a large waterfall about 1% miles northwest of Cape Kekurnoi. T. W. Stanton, 1904.

3111a. Same locality as 3111, but in different matrix. T. W. Stanton, 1904.

3111b. Same locality as 3111, but not in place. T. W. Stanton, 1904.

10820(1-127). North shore of Cold Bay 1% miles northwest of mouth of 

bay. S. R. Capps, 1921.

12076(2). South shore of Cape Kekurnoi, Cold Bay. W. E. Smith, 1923.

3130. South shore of Alinchak Bay. Lawrence Martin, 1904.

3130a. South shore of Alinchak Bay, near 3130. Not in place. Lawrence 

Martin, 1904.

12075(1). Southwest shore of Alinchak Bay. W. R. Smith, 1923.

12082(10). West of Alinchak Bay. W. R. Smith, 1923.

Of the fossils included in the earlier collections from these beds, 

neither the marine mollusks nor the plants are sufficiently characteristic for the determination of the exact horizon. The fossils 

obtained by Capps in 1921, according to Stanton,64 include

several genera of ammonites which in form and sculpture resemble Arietites, 

Aegoceras, Amaltheus, etc., but which do not show details of sutures and 

can not be positively identified. This lot is probably from the Lower Jurassic 

and older than the oldest fauna from Kial'agvik Bay.

Concerning the fossils collected by Smith in 1923, Stanton 6S said 

that lot 12075 " is believed to be Jurassic as old as the Tuxedni sandstone or older " and lot 12076 also " is believed to be Jurassic."

MIDDLE JURASSIC 

KIALAGVIK FORMATION

Historical review. An undescribed Jurassic formation has long 

been known to be present on Wide Bay (formerly called Kialagvik 

Bay), where two collections of fossils were made many years ago, 

but no account of the local stratigraphy has been written until recently. The first fossils brought back from this locality were obtained by a private collector and were described by White,08 who 

concluded that "they are certainly of Mesozoic age, and the'types 

to which they belong seem to indicate that they come from a formation of somewhat earlier date than the Cretaceous." After commenting upon the occurrence of Aueella at other Alaskan localities, 

he referred to his previously expressed conclusion 67 that the

«* Stanton, T. W., cited by Capps, S. R., op. cit, p. 94.

68 Stanton, T. W*., cited by Smith, W. R., op. cit., p. 195.

69 White, C. A., Mesozoic Mollusca from the southern coast of the Alaskan Peninsula: 

U. S. Geol. Survey Bull. 51, pp. 64-70, pis. 12-14, 1889.

67 White, C. A., On a small collection of Mesozoic fossils collected in Alaska by Mr. 

W. H. Dall, of the United States Coast Survey : U. S. Geol. Survey Bull. 4, p. 11, 1884
I

JTJBASSIC, ALASKA PENINSULA 187

Aucella-be&T'mg beds of the Alaska Peninsula are of Neocomian 

age and said:

I do not think it impossible that the fossils which form the subject of this 

article belong to the same formation in Alaska which bears Aucella conGentrica, but the two types of Ammonites which are found among these fossils 

are at least suggestive of a lower horizon. Indeed, if we had only the type 

character of the fossils themselves to consider, we should hardly be justified 

in referring them to. a later age than the Jurassic.

White recognized seven species from Wide Bay, as follows:

Cucullaea increbescens, n. sp.

Glycymeris? dalli, n. sp.

Belemnites.

Ammonites (Lillia) howelli n. sp.

Ammonites (Lillia) kialagvikensis, n. sp.

Ammonites (Amaltheus) whiteavesii, n. sp.

White's description of the fossils from Wide Bay has been reviewed by several European geologists, all of whom believe that the 

ammonites have been referred to wrong genera and that their age 

can be much more closely determined. E. Haug,68 in a brief review, 

states that the fossils are " very probably Liassic " and that the 

relationships of the ammonites are as follows:

Lillia howelli=Hammatoceras.

Lillia kialagvikensis=Grammoceras near G. toarceuse (D'Orbigny). 

Amaltheus whiteavesii=Harpoceras extremely near H. lythense 

(Young).

A review by Holzapfel 69 expresses the opinion that Amaltheus 

vihiteavesii is a Harpoceras, and that one of the species referred 

to Lillia is a Perisphinctes. Holzapfel believes that the ammonites 

indicate a horizon corresponding to that of the Volga beds of the 

Upper Jurassic of Russia, an apparently untenable conclusion 

in which he was probably influenced by the erroneous belief that 

these ammonites came from the same beds as the species of 

Aucella from Port Moller that White described in an earlier 

publication. He was also in error in ascribing to White a belief that the ammonites are Cretaceous. It has been shown above 

(p. 186) that White believed in 1884 that the species of Aucella 

from Port Moller were Cretaceous, but that in 1889 he concluded the ammonites from Wide Bay are Jurassic. White's 

further opinion that the Aucellas might possibly belong in the 

same formation with the Wide Bay fossils (which undoubtedly 

is not the case) may mean either that he believed the formation 

to include rocks of both Jurassic and Cretaceous ages, or that 

he then believed the Aucellas to be Jurassic. The latter conclusion, which is apparently identical with that of Holzapfel, is

88 Annuaire g^ologique universal, vol. 8, 1892-93, p. 703. 

« Neues Jahrb., 1892, Band 2, p. 155.
188 MESOZOIO. STRATIGRAPHY OF ALASKA

possibly correct, although the Aucetta-be&r'mg beds belong at a 

far higher horizon (pp. 211-218) in the Jurassic than the beds that 

yielded the ammonites of Wide Bay.

These fossils have also been discussed by Pompeckj,70 who assigned 

them to the Upper Liassic and indicated the identity of the ammonites as follows:

Amaltheus whiteavesii=Harpoceras ex. aff. exarati Young and Bird sp. 

Lillia howelli=Hammatoceras howelli. 

Lillia kialagvikensis=Hammatoceras.

Wide Bay was visited in 1895 by Dall, who collected fossils 71 " at a 

locality northeast of the mouth of the river which drains a valley up 

which the natives go to make a portage over to Ugashik Lake." 

These fossils were studied by Hyatt,72 who discussed them as follows:

The Ammonitinae from this locality are excellent but belong to peculiar 

types, and I have been obliged to make a thorough investigation of the entire 

series of hammatoceran groups in order to get clear ideas of their exact age. I 

can now state provisionally that this fauna is somewhat older than that of the 

lighter-colored limestone of Tuxedni Harbor, Chasik Island. The nearest relatives heretofore found belong to the lowest parts of the Inferior Oolite, in formations placed by many German and French authors in the Upper Lias. There 

is one species of Trigonia identical with a very rare species found at Taylorsville, Calif., in the Mormon sandstone, one of the " costatus " group, and the 

belemnites are also apparently very close allies of those in the same rocks.

The fossils from Wide Bay were briefly referred to by Stanton 

and Martin,73 who concluded that " whatever may be the final decision as to their age, they are evidently older than any part of the 

Enochkin formation."

A brief reference to the occurrence at Wide Bay of the rocks now 

known as the Kialagvik formation was made by Martin.74

The first stratigraphic description of the rocks of the Kialagvik 

formation was given.and the the first use of the formation name 

made by Capps, who studied'the exposures on Wide Bay in 1921. 

His account of the formation includes a brief description of the 

character of the rocks followed by lists and a discussion of the fossils by Stanton.75 The Kialagvik formation was also described by 

Smith and Baker 76 in a paper based on investigations in 1922.

_______________________0________________________________.___________________________________

70 Pompeckj, J. P., Jura-Fossilien aus Alaska: K. russ. min. Gesell. St. Petersburg 

Verb., 2d ser., vol. 38, No. 1, pp. 275-276, 1900.

71 Dall, W. H., Report on coal and lignite of Alaska: U. S. Geol. Survey Seventeenth, 

Ann. Kept., pt. 1, p. 871, 1896.

72 Hyatt, Alpbeus, Report on Mesozolc fossils (appendix to Ball's report on coal and 

lignite of Alaska. U. S. Geol. Survey Seventeenth Ann. Rept., pt. 1, p. 907, 1896.

73 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska 

Peninsula: Geol. Soc. America Bull., vol. 16, p. 397, 1905.

74 Martin, G. C., Preliminary report on petroleum In Alaska. U. S. Geol. Survey Bull. 

719, pp. 59, 60-61, 1921.

7B Capps, S. R., The Cold Bay district: U. S. Geol. Survey Bull. 739, pp. 91, 94-97, 

pi. 2, 1922. . '

76 Smith, W. R., and Baker, A. A., The Cold Bay-Chignik district: U. «. Geol. Survey 

Bull. 755, pp. 169, 173-176, pi. 8, 3925.
JURASSIC, ALASKA PENINSULA 189

Stratigraphic description. The Original description, by Capps, 

of the Kialagvik formation is as follows:'

The rocks here named the Kialagvik formation occupy a narrow belt along 

the northwest shore of Kialagvik [Wide] Bay from a point near the mouth of 

Pass Creek to the southwest end of the bay. Their extent southwest of the 

bay is not known. They consist of a few hundred feet of sandstone, sandy 

shale, and conglomerate that form the bluffs along the beach and extend a 

short distance inland.

Little is known of the character or thickness of this formation, for the outcrops are scanty and are largely limited to rather widely separated exposures 

in the shore cliffs, in which massive sandstone, sandy shale, and conglomerate 

were seen. The exposures are so far from one another that it is not yet 

possible to construct the stratigraphic section. The contact with the overlying Shelikof formation is in most places concealed on the vegetation-covered 

benches between the shore and the mountains, but on the shore a short distance east of the mouth of Lee Creek a conglomerate was seen overlying with 

angular unconformity a series of sandy shales, and this unconformity is believed to mark the contact between the Shelikof formation and the Kialagvik 

beds.

Age and correlation. The fossils of the older collections from the 

Kialagvik formation have been r:ferred by .several paleontologists 

to different horizons in the Lower Jurassic (Lias) and Middle 

Jurassic (Inferior Oolite), but the more general opinion is that the 

fossils are Lias. These opinions have been cited in detail on pages 

186-188. The later collections obtained by Capps and by Smith have 

been studied by Stanton, who believes that they are probably Middle 

Jurassic. In discussing the collections obtained by Capps, Stanton 78 

made the following statements:

Lot No. 1-104 from Kialagvik [Wide] Bay contains the fauna, rich in ammonites, described by C. A. White many years ago from the same locality. 

Lots 1-107, 108, and 110 also have the same or a closely related fauna. The 

ammonites of this fauna are all different from those of the Tuxedni sandstone, which also has a varied ammonite fauna, but some of the other mollusks 

of the Kialagvik Bay fauna are identical with species found in the lower part 

of the Tuxedni sandstone. A fauual zone in No. 33 of the type section of the 

Tuxedni sandstone, 250 feet above the lowest bed of the formation there exposed, seems to be pretty definitely represented in lot 1-113, which I am assuming to be higher than 1-104. I judge therefore that lot 1-104 is not much 

older than the lowest fossiliferous bed of the Tuxedni Bay section and that its 

horizon may well be included in the Tuxedni formation. I would refer it to 

the lower part of the Middle Jurassic rather than to the Lias or Lower 

Jurassic.

The named species in this list were all originally described by White as 

found in a collection from Kialagvik Bay, probably from the same locality as 

the present lot. Pompeckj has referred the fauna to the upper Lias, and Hyatt 

said that the nearest relatives ttf" the fauna are found in the " lowest parts 

of the Inferior Oolite, in formations placed by many German and French 

authors in the upper Lias." It is either basal Tuxedni or slightly lower.

 Capps, S. R., op. cit., pp.- 94-95.

78 Stanton, T. W., cited by Capps, S. R., op. cit, pp. 96, 97.

49448 26 14
190 MESOZOIO STRATIGRAPHY OF ALASKA

This little collection permits pretty definite correlation with the lower 

part of the Tuxedni sandstone. The ammonite Sonninia and the Inoceramus 

are both identical with forms in No. 33 of Martin's Tuxedni Bay section (U. S. 

Geol. Survey Bull. 485, p. 61), which is 250 feet above the base.

Stanton also made the following statement 79 concerning lot 11358:

The fragment of a small ammonite (Stephanoceras?) in this lot is closely 

related to if not identical with a form in the Tuxedni sandstone and thus 

apparently gives another tie between the Tuxedni and the Kialagvik.

Fossils from Kialagvik formation °

Cladophlebis?-...... __ ........... __ . __ ..

GervilHa. .. ................ ...................

Pteria.... ........................................

Ostrea.. .........................................

Trigonia.. ....................................

Pecten ....... ....................................

Anomia?. __________________

Pleuromya dalli (White)....... __ . _ ......... 

Pleuromya _________________

Thracia?. .............. .......................

Cypricardia? ..... _ . _ ................ _ .

Tancredia?... . ................................

Protocardia. .....................................

Venerids? _ . _ . __ . __ ........... __ . __ .

Turbo?.. _ .... _ .... _ ... __ . ........

Natica. ..... ...................................

Cerithium-. .....................................

Phylloceras. .....................................

Hammatoceras howelli (White) . .................

Hammatoceras cf. H. howelli (White) ............

Hammatoceras cf. H. variabile (d'Orbigny). .....

Hammatoceras? kialagvikense (White) ...........

Hammatoceras? cf. H. kialagvikense (White) _ .

Sonninia? ... ..... .........................

Harpoceras whiteavesi (White) __ . ___ .....

Dactylioceras?.. .................................

Stephanoceras? __________________

,

a

I

...

r»

a

.

a

...

1

a

a

s

a

.

a

1

...

S 

S

1

b

a

a

a

...

.

A

a

a

a

a

1

a

a

a

a

a

1

a

a

a

...

a

,

a

...

5

...

«

...

i

...

a a, Identified by T. W. Stanton; b, identified by Arthur Hollick.

10804 (1-104). Wide Bay, about 9 miles northeast of southwest end of bay 

and 1 mile southwest of mouth of Pass Creek. S. R. Capps, 1921.

10806 (1-107). Wide Bay, 3 miles from southwest end. S. E. Capps, 1921.

10807(1-108). Same .as 1-107, but 100 yards farther southwest along the 

shore. S. R. Capps, 1921.

10808 (1-110). Shore cliffs on point 2 miles from southwest end of Kialagvik 

Bay. S. R. Capps, 1921.

78 Staaton, T. W., cited by Smith, W. R., and Baker, A. A., op. clt., p. 176.
JUEASSIC, ALASKA PENINSULA 191

10809 (1-113). On creek that enters Wide Bay from the northwest at southwest end of bay. Lowest collection from this creek. S. R. Capps, 1921.

11064 (E 1). Northwest shore of Wide Bay about 1% miles southwest of 

mouth of Desmoines Creek. Ernest Marquardt, 1921.

11065 (E 2). Northwest shore of Wide Bay, 1 mile southwest of mouth of 

Desmoines Creek. About the same horizon as 11064. Ernest Marquardt, 1921.

11066 (F 1). Northwest shore of Wide Bay near cabin at mouth of Desmoines, 

Creek. Ernest Marquardt, 1921.

11349,7570 (F 13). South shore at southwest end of Wide Bay. W. R. 

Smith, 1922.

11350 (F 14). West shore of Wide Bay south of Short Creek. Stratigraphically 150 feet above F 31. W. R. Smith, 1922.

11351 (F 31). Same locality as 104, Wide Bay. W. R. Smith, 1922.

11352 (F 15). Wide Bay, 1 mile up creek southwest of Short Creek. W. R. 

Smith, 1922.

11353 (F 16). Wide Bay, 1 mile up Short Creek. W. R. Smith, 1922.

11357 (F 30). 1 mile northwest of Lee's cabin, at Wide Bay. W. R. Smith, 

1922.

11358 (F 32). Float found by Ray Russell on point at Wide Bay. W. R. 

Smith, 1922. 

11961. Near Lee's cabin, Wide Bay. Jack Lee, 1923.

TUXEDNI SANDSTONE (?)

The possible presence of the Tuxedni sandstone on the Alaska 

Peninsula has been suggested by Martin.80 The reason for the suspicion that the Tuxedni sandstone may be represented in the Cold 

Bay district is the presence of fossils, identified by Stanton as Eumicrotisf cf. E. curta Hall, in two small collections obtained by James 

Casey and George Jamme, jr., from localities that were said to be 

on the "west shore of Dry Bay" and "near Becharof Lake." No 

other fossils that are indicative of the Tuxedni sandstone have been 

obtained near Dry Bay or Becharof Lake. It is possible, therefore, 

that these fossils actually came from some other region, or from 

another formation, or it may be that small areas of the Tuxedni 

sandstone have been overlooked in the reconnaissance surveys of this 

region. Fossils of this type have a great stratigraphic range in the 

Jurassic elsewhere.

It should be noted that the other fossils indicative of the horizon 

of the lower part of the Tuxedni sandstone were obtained by Capps 

(lot 10809, p. 190) in beds that he believed to be part of the Kialagvik 

formation and by Smith (lot 11358) in float material within the 

area of the Kialagvik formation. Neither of these collections contains any of the ammonites that are characteristic of the Kialagvik 

formation. The presence of Inoceramus cf. /. eximius Eichwald at 

locality 10802, on Wide Bay, within the supposed area of the Shelikof 

formation (p. 200), is also suggestive of the Tuxedni sandstone.

80 Martin, G. C., Preliminary report on petroleum in Alaska. U. S. Geol. Survey Bull. 

719, pp. 59, 61, 1921.
192 MESOZOIC STRATIGRAPHY OF ALASKA ;/

TIPPER JURASSIC ' . 

SHELIKOF FORMATION

Historical review. The Shelikof formation was described by 

Capps 81 in 1922, to include all the Upper Jurassic rocks lying beneath the basal conglomerate of the Naknek formation at Cold Bay 

and neighboring localities on the northwest shore of Shelikof Strait. 

The Shelikof formation as defined by Capps includes an upper shale 

member, which has yielded only fossils that are not characteristic of 

any known horizon, and a lower member composed chiefly of sandstone with minor amounts of conglomerate and shale, which carries 

the fauna of the Chinitna shale. The lower member of the Shelikof 

formation and its fossils were described in several publications prior 

to that of Capps.

The Chinitna fauna of the Alaska Peninsula has been recognized 

in several old collections of fossils from localities the exact geographic position of some of which is more or less in doubt.

Some fossils collected by Ilia Wosnessenski from a locality " near 

Katmai" were referred by Grewingk 82 to the Jurassic and were 

described by him as including the following species:

Ammonites wosnessenskii, n. sp. 

Ammonites biplex Sowerby. 

Belemnites paxillosus? 

Unio liassinus?

The two species of ammonites listed above were discussed briefly 

by Eichwald,83 who regarded Ammonites wosnessenskii as very 

similar to Ammonites dorochini Eichwald, from the supposed Neocomian or Gault of Chisik Island, and Ammonites biplex as identical 

with a form referred by him to Ammonites milletianus D'Orbigny, 

and coming from the supposed Gault of an undescribed locality on 

the Alaska Peninsula.

Neumayr 84 stated that Ammonites biplex Grewingk is without 

doubt an Upper Jurassic Perisphinctes and that Ammonites wosnessenskii is an Olcostephanus.

These fossils were reexamined and described in detail by Pompeckj,85 who has shown that three distinct horizons are represented,

81 Capps, S. R., The Cold Bay district: U. S. Geol. Survey Bull. 739, pp. 90, 91, 92, 

97-101, pi. 2, 1922.

82 Grewingk, C., Beitrag zur Kenntniss der orographischen und geognostischen Beschaffenheit der Nord-West-Kiiste Amerikas mit den anliegenden Inseln: Russ.-k. min. Gesell. 

St. Petersburg Verb., 1848-49, pp. 121, 344-347, pi. 4.

83 Eichwald, Eduard von, Geognostisch-palaeontologische Bemerkungen iiber die Halbinsel Mangischlak und die aleutischen Inseln, pp. 141-142, 145-146, St. Petersburg, 

1871.

81 Neumayr, M., Die geographlsche Verbreitung der Juraformatlon: K. Akad. Wiss. 

Wien Denkschr., 1885, p. 94.

85 Pompeckj, J. F., Jura-Fossilien aus Alaska: K. russ. min. Gesell. St. Petersburg, 

2d ser., Band 38, No. 1, pp. 239-282, 1900.
JURASSIC, ALASKA PENINSULA . 193

the ammonites being Callovian species of Cadoceras, the pelecypod 

(Unio liassinus?) being an Upper Jurassic Aucella, (see p. 203), and 

the belemnite being an Upper Cretaceous Belemmtella (see p. 300).

The precise localities from which these fossils were obtained are 

doubtful. No rocks older than the Naknek formation crop out on the 

shores of Katmai Bay (pp. 208-209) or were recognized by Spurr or 

any subsequent observer along the trail between Katmai and Naknek 

Lake. The locality description "near Katmai" must therefore be 

regarded as probably only a very general designation that may include places as far distant as Cold Bay.

A large number of fossils collected by Peter Doroschin, a mining 

engineer who was in Alaska from 1847 to 1852, were described by 

Eichwald 86 in 18T1 and referred to the Cretaceous (Neocomian or 

Gault). Most other writers have agreed that they are Jurassic, it 

having been shown by Neumayr 87 that they represent several different horizons and include especially Jurassic types of northern 

relationships, the faunas of the Callovian and Volga beds probably 

being represented. These fossils were obtained at several localities, 

mostly unspecified, on the Alaska Peninsula and Cook Inlet. A few 

of these localities were discussed 88 in Eichwald's general description 

of "the Miocene and Cretaceous formations of Alaska [ Alaska 

Peninsula] and the Aleutian Islands," but the statements there 

given as to the species occurring at these localities do not in all 

respects correspond with the localities given under the descriptions 

of the species. There are other contradictions for example, a species is described as occurring in association with other named 

species which are in turn described as occurring only at other places. 

Most of the species were described as coming from "Alaska" or 

Alaska Peninsula ("Halbinsel Alaska"). These terms are probably synonymous, as the name "Alaska" was applied only to the 

Alaska Peninsula by the Russians. It is possible, however, that 

Eichwald was following the newer American usage rather than the 

older Russian usage and intended to use "Alaska " in a broader sense. 

It is certain that he included localities on Cook Inlet, such as Tuxedni Bay, in "Alaska," 80 and it is consequently not certain that 

occurrences designated "Alaska " are on'what we now regard as the 

Alaska Peninsula. The term " Insel Alaska," which he used in a few 

places, must also be regarded as indefinite.

80 EichwaJd, Eduard von, op.' cit., pp. 8S -106, 138-200.

87 Neumayr, M., op. cit., pp. 93-94.

88 Eichwald, Eduard von, op. cit., pp. 90-91. 

80 Idem, pp. 192, 194, 199.
194 MESOZQIO STRATIGRAPHY OF ALASKA

Jurassic fossils from Cook Inlet and Alaska Peninsula described by Eichioald

Ammonites dutempleanus D'Orbigny aff .

Cucullaea insularis Eichwald.. ...........

Cardium imbricatarium Leymerie D'OrCaroium cooperi Qabb afl. ................

Cypricardia (Crassatella) trapezoidalis

A Qfartfl IQA"\HQ "RipTiwfllfl

Locality

Cook Inlet

X

X

Chisik ("Chasik") 

Island

X

X

X

X

X

Tuxedni ("Tukusitnu") Bay

X

0

X

X

X

X

X

i

o

 9«"c 

-O M

 a§

M

-

X

North shoreKat- of

chemak Bav"

-

Alaska Peninsula"

-

X

X

X

X

X

1

1

1

X

X

X

X

X

 Alaska"

"

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Insel Alaska"

-

X

X

X

"North Cape of Unalischaelak"

X

Kodiak Island

X

Age according 

to Eichwald

Neocomian

X

X

X 

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Neocomian Qault or 

X

X

X

O

X

X

X

X

"Black limestone of

undetermined age"

X
JURASSIC, ALASKA PENINSULA 195

The only definite locality on the Alaska Peninsula cited by Eichwald as having yielded a species that is known to belong to the 

fauna of the Chinitna formation is noted as follows: 90

A compact black limestone containing many ammonites and almost no other 

shells except'a small specimen of Cardium imbricatarium and Astarte germani, 

is found on the eastern shore of the Alaska Peninsula north of the island 

[elsewhere Cape] Unalischachtak.

Cape Unalishagvak is the foreland between Portage Bay and Dry 

Bay, and the ammonites from this locality are described by Eichwald 91 as Ammonites ishmae Keyserling, which is stated to occur 

abundantly "at many places on the Alaska Peninsula and on the 

other islands." This ammonite is stated by Hyatt 92 to be the young 

of a species of Gadoceras that he recognized among Dall's fossils 

from Cold Bay. Hyatt stated furthermore that the Alaska ammonites described by Grewingk and Eichwald are, in his opinion, " all 

either Callovian or Inferior Oolite."

It was also pointed out by Pompeckj 93 that Ammonites ishmae 

Eichwald from "north of Cape Unalishaglak" and other Alaska 

localities is distinct from Macrocephalites ishmae Keyserling and is 

a Callovian species allied to Cadoceras tchefkini (D'Orbigny).

A large collection of Jurassic ammonites from Alaska was described by Pompeckj 94 in 1900. These fossils were described as 

coming from the " Sotkin'sches Ufer " of Kodiak Island, but no such 

locality is now known, nor have similar fossils been otherwise 

reported from Kodiak Island, so the position of the locality is more 

or less doubtful. The fossils were received by the museum of the 

Academy in St. Petersburg in 1859 and were collected by Dr. J. S. 

Petelin, junior surgeon of the Russian-American Co., while stationed on Kodiak Island. The labels indicate, according to a letter 

from T. Tolmachef, that Petelin's specimens may have come from 

several localities, some of them reading " Sookhom " or " Sookhom's 

shores." There is nothing on the labels that indicate that the locality is on Kodiak Island, the only connection with that island apparently being that the collector lived there. Copies of the labels, in 

Russian, were sent to Doctor Petelin's son, Rev. A. J. Petelin, of Af ognak, who suggested that the specimens may have come "from the 

shores of the island of Sootkhom, originally named by Aleuts as

, M Eichwald, Eduard von, op. cit., p. 91. .

91 Idem, p. 147.

82 Hyatt, Alpheus, Report on the Mesozoic fossils: U. S. Geol'. Survey Seventeenth 

Ann. Kept., pt. 1, p. 908, 1896.

93 Pompeckj, J. F., The Jurassic fauna of Cape Flora, Franz Josef Land: The Norwegian north polar expedition, 1893-96 (scientific results edited by Fridtjof Nansen), 

vol. 1, No. 2, pp. 112, 138, 143, 1900.

84 Pompeckj, J. F., Jura-Fossilien aua Alaska: Verhandlungen. der Kaiserlichen, Russischen mineralogischen Gesellchaft zu St. Petersburg, Zweite Serie, Band 38, No. 3, 

1900, pp. 239-282.
196 MESOZOIC STRATIGRAPHY OF ALASKA

Sutwik, situated between Wrangell and Chignik," or " from Sootkhom Settlement, as at that time there was a village on the point of 

the mainland west of Sutwik Island which was known as Sootkhom." 

The following species were described by Pompeckj as coming 

from this locality and were referred to the Middle Callovian:

Phylloceras subobtusiforme, n. sp. 

Cadoceras wosnessenski Grewingk? 

Cadoceras grewingki, n. sp. 

Cadoceras schmidti, n. sp. 

. Cadoceras petelini, n. sp. 

Cadoceras sp. indet. 

Cadoceras steneloboide, n. sp.

Buckman 95 made the following statement concerning Cadoceras 

grewingki Pompeckj:

This species is hardly a true Cadoceras, but it belongs to a series which in 

form and appearance is intermediate between Cadoceras and Quenstedtoceras. 

This species and its allies occur in the Kellaways Kock of Kellaways and have 

been placed sometimes as Ammonites marine D'Orbigny. The " Russian variety" which he figures by that name (Terr, jurassique: C6phalopodes, 1842- 

1849, pi. 179, figs. 7 and 8 only) belongs to the grcwingM series, but the other 

examples are quite distinct. (See Q. mariae, p. 164.)

The first account of the rocks that are now included in the Shelikof 

formation was given by Dall,9B who described very briefly the lith-. 

ologic character of the fossiliferous beds which he observed at Cold 

Bay. The fossils collected by Ball were discussed by Hyatt,97 who 

recognized a species of Cadoceras on the basis of which he concluded 

that the beds are of Callovian age. These rocks were described 

briefly by Martin 98 as the "Enochkin formation." They were also, 

discussed briefly by Atwood,99 whose account is based wholly upon 

the earlier descriptions.

In a later account of the oil fields of the Alaska Peninsula by 

Martin, the rocks of the Shelikof formation are described* as " sandstones, shales, and conglomerates carrying the fauna of the Chinitna 

shale" and are mapped 2 as "Middle Jurassic sandstone, shale, and 

conglomerate." This description, was based on the investigations of 

Stanton and Martin in 1904 and includes stratigraphic sections, notes

98 Buckman, S. S., The " Kelloway rock" of Scarborough: Geol. Soc. London Quart. 

Jour., vol. 69, p. 162, 1913.

86 Dall, W. H., Report on- coal and lignite of Alaska: U. S. Geol. Survey Seventeenth 

Ann. Report, pt. 1, pp. 801, 870-871, 1890.

87 Hyatt, Alpheus, Report on the Mesozolc fossils (appendix to Ball's Report on coal 

and lignite of Alaska)': Idem, p. 908.

88 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. 

Survey Bull. 250, pp. 52-53, 1905.

89 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula : 

U. S. Geol. Survey Bull. 467, pp. 32-33, 1911.

1 Martin, G. C., Preliminary report on petroleum in Alaska: U. S. Geol. Survey Bull. 

719, pp. 59, 61-62, 1921.

2 Idem, pi. 10.
JURASSIC, ALASKA PENINSULA 197

on several exposures, and statements concerning the occurrence of 

fossils. Much of it had not been published previously.

The description of the Shelikof formation by Capps 3 was based 

on his own reconnaissance investigations of the area between Cold 

Bay and Wide Bay in 1921. It includes a brief general description 

of the lithologic character and sequence of the beds, accompanied 

by graphic columnar sections and by lists of the fossils collected by 

Capps and determined by Stanton.

The Shelikof formation was also described by Smith and Baker 4 

on the basis of a geologic reconnaissance from Cold Bay to Chignik. 

Their description includes a general account of the character of the 

rocks with lists of fossils determined by Stanton.

A description of the Shelikof formation by Smith,5 which was 

based on a geologic reconnaissance in 1923, includes a brief general 

account of the character of the rocks.

Stratigraphic description. The Shelikof formation was described 

by Capps as including a lower member 1,500 feet thick, composed 

mostly of shale; a middle member 4,000 to 4,700 feet thick, composed 

of sandstone with minor amounts of conglomerate and sandy to 

calcareous shale that carry the Chinitna fauna; and an upper member 700 to 1,000 feet thick, composed of black shale with some limestone lenses in the upper part, carrying a fauna that is not characteristic of any known horizon.

The only localities where the base of the Shelikof formation was 

seen by Capps are at Cold Bay and on the creeks tributary to Wide 

Bay from the northwest. He described the lower member and the 

basal contact as follows:

On Kialagvik [Wide] Bay the lower 1,500 feet of the formation is mostly 

shale, with some limy lenses and concretions. At Cold Bay the lower limit of 

the formation is placed at a conglomerate below which is 800 feet of shale that 

has been tentatively placed in the Lower Jurassic, though it may correspond 

to the basal shale of the Kialagvik Bay section and therefore properly belong in the Shelikof formation.

The part of the Shelikof formation lying between the basal and 

upper shales, according to Capps,

comprises 4,000 to 4,700 feet of beds that consist dominantly of massive brown 

to gray sandstones, with minor amounts of shale and of conglomerate. In 

many places the sandstone is concretionary, the concretions ranging from 

small hard well-rounded spherical bodies a few inches to a foot or more in 

diameter to large irregular, poorly defined masses with indefinite boundaries.

3 Capps, S. R., The Cold Bay district: U.' S. Geol. Surrey Bull. 739, pp. 90, 91, 92, 

97-101, pi. 2, 1922.

* Smith, W. R., and Baker, A. A., The Cold Bay-Chignik district: U. S. Geol. Survey 

Bull. 755, pp. 169, 176-178, pi. 8, 1925.

6 Smith, W. R., The Cold Bay-Katmai district: U. S. Geol. Survey Bull. 773, pp, 

196-197, pi. 4, 1925.
198 MESOZOIO STRATIGRAPHY OF ALASKA

The sandstone and included shale are locally calcareous and are in placea 

so impure that they might well be called sandy shales.

The upper shale member was described by Capps as follows:

Nearly every normal section shows that the uppermost member, lying immediately beneath the basal conglomerate of the Naknek formation, consists 

of a massive black shale from 700 to 1,000 feet thick which contains some 

limestone lenses and nodules. This shale is in places sandy and calcareous 

and is poorly fossiliferous.

The cliffs on the northeast shore of Cold Bay, according to the 

observations of the writer and his associates in 1904, contain a thick 

section of strata carrying the fauna of the Chinitna shale. These 

strata probably belong in the middle sandstone member of the 

Shelikof formation. Neither the bottom nor the top of these beds 

has been clearly recognized, for the contacts with the adjacent 

formations are probably faults. The contact of these beds with the 

underlying Lower Jurassic (?) shale and sandstone, which has been 

described on page 184, is about 1^ miles northwest of Cape Kekurnoi. 

Here the Lower Jurassic (?) rocks are either overlain by or faulted 

against soft brownish shale, several hundred feet thick, that is overlain by a heavy bed of coarse conglomerate. Above this conglomerate are sandstone and thinner interbedded strata of shale and conglomerate, which form the cliffs for about 2 miles and have an estimated thickness of probably 1,000 or 1,200 feet. The fossils contained in lot 3106 were obtained from a fine conglomerate near the 

top of these beds. The overlying rocks consist of massive sandstone, 

possibly 1,400 feet thick, overlain by 200 feet of dark shale. Near 

the top of the shale is a thin band with, abundant fossils, as in lot 

3105. Above the shale is coarse gray sandstone, apparently containing no fossils except Belemnites, probably 1,200 or 1,500 feet thick. 

These beds are separated by a fault from the rocks of the Naknek 

formation northwest of them.

The sandstone member of the Shelikof formation is also -represented in the following section, which was measured by T. W. 

Stanton in the cliffs on the southwest shore of Cold Bay. The 

base of the section is at Cape Aklek and its top is at Lathrop's store. 

Neither the base nor the top of the formation is exposed.

Section of part of Shelikof formation on southwestern shore of Cold Bay.

Shaly sandstone with some beds of shale and with Belem- Feet 

nites__________-____-__ ______ ____________ 800±

Coarse gray sandstone with thinner beds of more shaly 

sandstone and some bands of conglomerate. Cadoceras, 

Phylloceras, and Belemnites found sparingly from base 

to above the middle ___________________ 1,000

Dark shaly sandstone, with some beds of shale and thinner bands and local lenses of conglomerate. Belemnites 

abundant in conglomerate about 100 feet above the base. 400
JURASSIC, ALASKA PENINSULA 199

The following section, which was measured by the writer about 

10 miles southwest of Cold Bay, shows the character of the upper 

beds of this formation and the contact with the overlying rocks:

Section of part of Shelikof formation on hillside east of Rex Creek, 1 mile

above head of Dry Bay

Feet

Shale and sandstone (overlain by 600 feet of arkose, sandstone, and shale belonging to Naknek formation______ 500 

Sandstone___________ ____ ________ 90 

Argillaceous shale __________________________ 400 

Sandstone, shale, and conglomerate _______ 300

Age and correlation. The fossils that have been obtained from 

the Shelikof formation are listed in the following table. The 

lower shale member of the formation is not known to have yielded 

any of these fossils, except possibly lot 10802, the stratigraphic 

position of which is uncertain. The next 32 lots in the tables are 

believed to have come from the middle sandstone member. The 

last 12 lots came from the upper shale member.

The fossils of lot 10802 include Inoceramus cf. /. eosimius Eichwald. This fossil is suggestive of the Tuxedni sandstone.

The fauna of the middle sandstone member is characterized by 

several species of Cadoceras. The presence of Gadoceras indicates 

that the rocks are to be correlated with the Chinitna shale of Cook 

Inlet and that their horizon is at the base of the Upper Jurassic.

The fauna of the upper shale member, as now known, includes 

no fossils that are characteristic of special horizons. The position 

of this shale, immediately above the Cadoceras-\)Q&r'mg beds and 

under the conglomerate that forms the basal member of the Naknek 

formation, indicates that the shale belongs in the lower part of the 

Upper Jurassic. It is probably to be correlated either with the 

unfossiliferous shale in the upper part of the Chinitna shale (pp. 

161, 163), or with the sparsely fossiliferous shale that has been assigned to the lower part of the Naknek formation of Cook Inlet (pp. 

161, 172-173).
Fossils from Shelikof formation

Coniopteris burejensis (Zalessky)

Cidaris? .. 

Inoceramus cf. I.

Pteria.. - . _-

Pecten (smooth form)

Corbis? (or Astarte) . .

Cardium?. _ .-.... 

Protocardia.. .--..

Venerid?... .--

Turbo?.. ...... 

,

«O

o 2

a

a

a

CO

i » s i s

z 

s

a

S 

S

t~

9 

S

s

§

5

Si

m <N cj

§

<M

oq 1

o

i

§8 

fe i

Q

8 I

S

§

1O

i o
Amberleya ...........

Rissoina? ___ .. .....

Tornatellaea? .........

Gastropod ............

Cadoceras catostoma

Cadoceras doroschini 

(Eichwald)... ......

Cadoceras doroschini 

(Eichwald)?........

Cadoceras grewingki

Cadoceras schmidti

Cadoceras cf. C.

Cadoceras stenoloCadoceras wosnessenCadoceras? (with nara

tv a !

B

1 a. Identified by T. W. Stanton; b, identified by F. H. Knowlton; c, identified by Arthur Hollick.
202 MESOZOIC STRATIGRAPHY OF ALASKA

10802 (1-98). North shore of Wide Bay 1 mile south of mouth of Big 

Creek. S. R. Capps, 1921.

3106. Northeast shore of Cold Bay about 3 miles northwest of Cape 

Kekurnoi. Fine conglomerate. T. W. Stanton, 1904.

3105. Northeast shore of Cold Bay about 4 miles northwest of Cape 

Kekurnoi, or N. 16° W. of Lathrop's store. Thin fossiliferous bed at top of 

200 feet of dark shale. T. W. Stanton, 1904.

10818(1-126). North shore of Cold Bay 4 miles northwest of mouth of 

bay. S. R. Capps, 1921.

2944. Base of cliffs 2 miles southwest of Cape Yaklog. G. C. Martin, 1903.

3104. Southwest shore of Cold Bay near Cape Yaklog. Conglomerate 100 

feet above base of bed 3 in section on p. 198. T. W. Stanton, 1904.

3104a. Southwest shore of Cold Bay near Cape Yaklog. From bed 2 of section on p. 198. T. W. Stanton, 1904.

3103. Southwest shore of Cold Bay 1 mile east of Lathrop's store or half a 

mile inside entrance to bay. Thin bed of conglomerate intercalated in sandstone and shale. T. W. Stanton, 1904.

10824 (C). Southwest shore of Cold Bay. S. R. Capps, 1921.

10826 (E). Creek that enters Cold Bay at store. S. R. Capps, 1921.

3117. Near head of- small creek that enters Cold Bay at Lathrop's store. 

T. W. Stanton, 1904.

2945. Southwest shore of Cold Bay 1 mile above Lathrop's store. G. C. 

Martin, 1903.

10822 (3). Head of creek above store, Cold Bay. S. R. Capps, 1921.

2943. Near mouth of Oil Creek, Dry Bay. G. C. Martin, 1903.

3113. West side of Oil Creek, 500 feet above creek and half a mile above 

its mouth, or 4 miles west of Cold Bay. Calcareous nodules in sandy shale. 

T. W. Stanton, 1904.

3112. Oil Creek about 2 miles above its mouth, or 5 miles west of Cold Bay. 

Sandy shale. T. W. Stanton, 1904.

(952). Oil Creek about 250 yards below residue deposit. T. W. Stanton, 

1904.

3122. Near head of Oil Creek. T. W. Stanton, 1904.

10787 (1). Dry Bay, three-fourths of a mile north of the mouth of Rex 

Creek, at an elevation of 1,150 feet. S. R. Capps, 1921.

10790 (1-57). About 3% miles above mouth of Rex Creek. S. R. Capps, 1921.

10788 (2). East shore of Jute Bay half a mile south of head of bay. S. R. 

Capps, 1921.

11071 (L 10). East shore of Portage Bay. Ernest Marquardt, 1921.

10800 (1-95). About iy2 miles northeast of mouth of Big Creek, a tributary 

of Wide Bay at its northeast end. S. R. Capps, 1921.

10801 (1-96). Same as 1-95, but about 1,200 feet higher in section. S. R. 

Capps, 1921.

10803 (1-101). Wide Bay near barabara on point IVz miles south of mouth 

of Big Creek. S. R. Capps, 1921.

10815 (1-119). Lee Creek, a tributary of Wide Bay; 3 miles above mouth of 

creek. S. R. Capps, 1921.

10805 (1-105). Wide Bay, stratigraphically 1,000 feet, more or less, above 

1-104. S. R. Capps, 1921.

10814 (1-118). North shore of Wide Bay 4 miles from its southwest end. 

Loose boulder. S. R. Capps, 1921.
JURASSIC, ALASKA PENINSULA 203

11072 (M 5). About 3 miles northwest of shore of Wide Bay, on creek that 

empties into bay 4 miles southeast of mouth of Lee Creek. Ernest Marquardt, 

1921.

10810 (1-114). On creek that enters Wide Bay from the northwest at 

extreme southwest end of bay. Higher in the section than 1-113. S. R. Capps, 

1921.

10811 (1-115). Same as 1-113 but higher in section. S. R. Capps, 1921.

10812 (1-116). Same as 1-115 but higher in section. S. R. Capps, 1921.

10813 (1-117). Same as 1-116 but higher in section. S. R. Capps, 1921.

3123. Southwest shore of Cold Bay near upper end, one-fourth mile north 

of the fault that cuts the conglomerate cliff. T. W. Stanton, 1904.

10819 (1-125). Head of Cold Bay, on west shore three-fourths mile southwest of mouth of lagoon. S. R. Capps, 1921.

3102. Southwest shore of Cold Bay, half a mile south of northwest end. 

Lower part of beds exposed in cliffs north of fault. T. W. Stanton, 1904.

10791 (1-60). About 300 feet below base of Naknek formation on Bear 

Creek-Porcupine Creek divide, 5 miles east-southeast of mouth of .Bear Creek. 

S. R. Capps, 1921.

10792 (1-65). About 200 feet below base of Naknek formation on Bear 

Creek-Salmon Creek divide, 4% miles east-southeast of mouth of Salmon Creek. 

S. R. Capps, 1921.

10793 (1-79). About 300 feet below base of Naknek formation on shore of 

Portage Bay, half a mile southwest of Kanatak village. S. R. Capps, 1921.

7516 (1-79). Same locality as 10793. S. R. Capps, 1921.

11344 (F 1). Kanatak. Chinitna shale just beneath Naknek, 100 feet 

higher stratigraphically than 10793. W. R. Smith, 1922.

11323 (F 22 B 1). South side of Kanatak Creek valley. A. A. Baker, 1922.

11958 (1). Tributary of Kanatak Creek from the west about half a mile 

above wagon road and about 1% miles north of Kanatak. Upper Jurassic 

(probably Chinitna shale). G. C. Martin, 1923.

11346 (F 8). West bank of head of north branch of Big Creek, Wide Bay. 

Shale just below Naknek formation. W. R. Smith, 1922.

11347 (F 11). Northwest end of Wide Bay. W. R. Smith, 1922.

7571 (P 9). Talus slope at head of Crooked Creek Pass. W. R. Smith, 1922.

NAKNEK FOBMATION

Historical review. Among the fossils collected by Wosnessenski 

near Katmai is a form identified by Grewingk 6 as Unio liassinus? 

and described by Pompeckj 7 as Aucella sp. indet. According to 

Pompeckj, this form is related to Aucella bronni. It was probably 

obtained from beds belonging to the Naknek formation.

Pavlow 8 believes that this specimen is referable to Aucella lota 

Trauschold and that it is Sequanian or Oxfordian. Pavlow believes also that some of the specimens of Aucella figured by Eichwald 

are Lower Portlandian 9 , that possibly one of the specimens from

8 Grewingk, C., Beitrag zur Kenntniss der orographischen und geognostischen Beschaffenheit der nord-west-Ktiste Amerikas mlt den anliegenden Inseln: Russ. k. min. Gesell. 

St. Petersburg Verb., 1848-49, pp. 121, 347.

7 Pompeckj, J. F., Jura-fossllien aus Alaska: K. russ. mln. Gesell. St. Petersburg 

Verh., 2d ser., Band 38, No. 1, pp. 270-271, 273-274, 282, pi. 7, flg. 5, 1900.

8 Pavlow, A. P., Enchainment des aucelles et aucellines du cr6tac6 russe: Soc. imp. 

naturalistes Moscou Nouv. mgm., vol. 17(22), livr. 1, pp. 12, 81, 1907. 

»Idem, pp. 22, 36, 38, 56, 81.
204 MESOZOIO STEATIGRAPHY OF ALASKA

Port Moller figured by C. A. White may be Aquilonian or Upper 

Portlandian,10 and that the specimens collected by Pinart and figured 

by Fischer are Lower or Middle Portlandian.11 The specimens 

figured by Eichwald, White, and Fischer have been generally regarded as Lower Cretaceous. (See pp. 292-293.) If they are Upper 

Jurassic they probably came from the Naknek formation.

The Naknek formation was named and described by Spurr 12 as 

the Naknek " series." Spurr saw the rocks belonging to this formation only in the course of a rapid exploratory journey on which he 

crossed the Alaska Peninsula from Naknek Lake to Katmai, and his 

account of the.se rocks is consequently very general. This account includes descriptions of individual exposures, a general lithologic 

description of the series as a whole, a few short lists of fossils as 

determined by T. W. Stanton, and general discussions of age, correlation, and conditions of deposition.

Brief mention of the occurrence of the Nalmek formation in the 

vicinity of Cold Bay was made by Martin,13 but no detailed description was given.

The account of the Naknek formation by Stanton and Martin 14 

contains no data relating to the Alaska Peninsula except statements 

regarding localities where it occurs, a general description quoted 

from Spurr, and descriptions of some of the exposures on Kamishak 

Bay. _ .

The Naknek formation of the Herendeen Bay district was described very briefly by Paige 15 as the result of a hasty reconnaissance 

of the coal field. No formation name was used, and the rocks were 

described under the heading Upper Jurassic. This description includes merely a statement as to the presence of Upper Jurassic sandstone, with a list of fossils as determined by Stanton.

The account of the Naknek formation by Atwood 16 includes detailed descriptions of the Upper Jurassic rocks of the Chignik Bay 

and Herendeen Bay districts, with lists of fossils identified by T. W. 

Stanton, and a general description of the Upper Jurassic rocks of 

the eastern part of the Alaska Peninsula, based upon the earlier accounts of the investigations by Spurr, Stanton, and Martin.

"Pavlow, A. P., op. cit., pp. 60, 81. 

"Idem, pp. 22, 70, 81.

12 Spurr, J. E., A reconnaissance In southwestern Alaska in 1898: TJ. S. Geol. Survey 

Twentieth Ann. Kept, pt. 7, pp. 145-147, 169-171, 179-180, 1900.

13 Martin, G. C., The petroleum fields of the Pacific coast of Alaska: U. S. Geol. Survey * 

Bull. 250, pp. 52-53, 1905.

14 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska 

Peninsula: Geol. Soc. America Bull., vol. 16, pp. 402-407, 1905.

15 Paige, Sidney, The Herendeen Bay coal field: U. S. Geol. Survey Bull. 284, pp. 102, 

104, 1906.

18 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, pp. 25, 33-38, pis. 6-8, 1911.
JURASSIC, ALASKA PENINSULA 205

The Naknek formation of the Cold Bay district was described 

by Martin 17 in an account of the oil fields of the Alaska Peninsula. This description was based in part on previous publications and in part on unpublished information obtained by Stanton and Martin in 1904. It includes a general discussion of the 

character and fauna of the Naknek formation of Alaska Peninsula and descriptions of some of the exposures near Cold Bay.

A description of the Naknek formation of the Cold Bay district by Capps,18 based on a geologic reconnaissance in 1921, contains a detailed account of the character of the rocks, with columnar 

sections and lists of the fossils collected by Capps and identified by 

Stanton.

A geologic reconnaissance of the area between the headwaters 

of Becharof Lake and Chignik in 1922 was the basis of a further 

description of the Naknek} formation by Smith and Baker.19 

This description includes a general discussion of.the character of 

the formation, statements concerning the stratigraphy and structure at several localities, and lists of fossils collected by the authors and identified by Stanton.

Additional information concerning the Naknek formation of 

the area north of Cold Bay, including the type locality of the 

formation on Naknek Lake, is contained in a description by 

Smith,20 based on a geologic reconnaissance in 1923. A general 

account of the formation is given, with local details and lists 

of fossils identified by Stanton from material collected by Smith.

A geologic reconnaissance along the axis of the Alaska Peninsula from Kamishak Bay to Naknek Lake in 1923 is the basis of 

a description of the Naknek formation by Mather,21 which applies chiefly to the exposures on Kamishak Bay but in which 

brief statements are given concerning the exposures in the valleys draining into Naknek Lake.

A massive conglomerate that lies above the upper shale member 

of the Shelikof formation at Wide Bay and below the Aucellabearing beds of the Naknek formation at several places in the Cold 

Bay district has been tentatively correlated with the Chisik conglomerate of Cook Inlet.

The conglomerate exposed at the base of the Naknek formation in 

the cliffs near the head of Cold Bay was mentioned briefly by

17 Martin, G. C., Preliminary report on petroleum in, Alaska: U. S. Geol. Survey Bull. 

719, pp. 59, 62-63, pi. 10, 1921.

"Capps, S., R., The Cold Bay district: U. S. Geol. Survey Bull. 739, pp. 90, 91, 101- 

105, pi. 2, 1922.

18 Smith, W. R., and Baker, A. A., The Cold Bay-Chignik district: U. S. Geol. Survey 

Bull. 755, pp. 169, 178-184, pis. 8, 9, 1925.

20 Smith, W. R., The Cold Bay-Katmai district: U. S. Geol. Survey Bull. 773, pp. 

198-201, 1925.

21 Mather, K. P., Mineral resources of the Kamishak Bay region: U. S. Geol. Survey 

Bull. 773, pp. 169-171, pi. 3, 1925.
206 MESOZOIO STRATIGRAPHY OF ALASKA

Martin.22 The account of the Naknek formation by Capps 23 contains a detailed description of this conglomerate, which was described as the basal member of the Naknek formation, although a 

correlation with the Chisik conglomerate at that time treated as a 

distinct formation was suggested. This conglomerate was also 

described as part of the Naknek formation by Smith and Baker 2 * 

and by Smith.25 The occurrence of a conglomerate in the valley of 

Naknek Lake, which Mather compared with the Chisik conglomerate, has also been briefly described.26

Stratigraphic description. The youngest Jurassic rocks known 

in the Alaska Peninsula have been grouped in the Naknek formation, which is composed of beds of arkose, conglomerate, sandstone, 

and shale aggregating several thousand feet in thickness and carrying a marine fauna characterized by species of Aucella related to 

Aucella pallasi and Aucella ~browiM,, underlain by a series of conglomeratic beds ranging in thickness from 50 to 2,000 or 3,000 feet. 

The Naknek formation has been recognized at many places on the 

Alaska Peninsula from the shores of Cook Inlet to Herendeen Bay. 

It coyers large areas, probably being the most extensive of the 

surface formations, and may be areally continuous throughout the 

greater part of the length of the peninsula. On the west coast of 

Cook Inlet the formation, as now defined by the Geological Survey, includes at the base the Chisik conglomerate member, 290 to 

400 feet thick, and rests on the Chinitna shale. At other places 

on the peninsula it includes at the base a series of conglomeratic 

beds 2,000 to 3,000 feet thick and rests on the Shelikof formation. 

In previous reports the Chisik conglomerate has been treated as 

a distinct formation, but in view of its probable equivalence to some 

part of the much thicker conglomeratic series forming the lower 

part of the Naknek formation in other areas the Survey has recently decided to treat it as a local basal member of the Naknek.

This conglomerate in the Cold Bay district was described by 

Capps 27 as follows:

The basal member of the Naknek in this district is generally a coarse conglomerate that lies with structural conformity upon the top of the upper shale 

member of the Shelikof formation. The conglomerate shows great variations 

in thickness from place to place. At the head of Cold Bay there is a basal 

conglomerate 70 feet thick overlying the black-shale member of the Shelikof

23 Martin, G. C., Preliminary report on petroleum in Alaska: U. S. Geol. Survey Bull. 

719, p. 62, 1921.

23 Capps, S, R., The Cold Bay District: U. S. Geol. Survey Bull., 739, pp. 90, 101-103, 

115, 1922.

24 Smith, W. R., and Baker, A. A., The Cold Bay-Chingnik district:. U. S. Geol. Survey 

Bull. 773, p. 170, 1925.

25 Smith, W. R., The Cold Bay-Katmai district: U. S. Geol. Survey Bull. 773, pp. 200- 

201, 1925.

28 Mather, K., F.,, Mineral resources of the Kamishak Bay regiom: U. S. Geol. Survey 

Bull, 773, p. 170, 1925.

27 Capps, S. R., op. clt., pp. 101-102.
JURASSIC, ALASKA PENINSULA 207

x formation and succeeded by gray arkosic sandstone containing scattered pebbles 

and some thin beds of fine conglomerate. At the head of Dry Creek the 

conglomerate has thickened to 200 feet, at Bear Creek to about 300 feet, at the 

head of Portage Bay to 500 or 600 feet, and at the head of Lee Creek to about 

900 feet. In most places a massive coarse conglomerate lies directly upon the 

top of the Shelikof shale. Elsewhere coarse arkosic sandstone or alternating 

sandstone and thin conglomerate constitute the base of the formation, with the 

thick conglomerate higher in the section. At the head of Lee Creek a hastily 

studied section seems to show a lower conglomerate 900 feet thick overlain by 

about 1,200 feet of arkosic sandstone and conglomerate, which are in turn 

succeeded by a second conglomerate 800 feet or more in thickness. The Pearl 

 reek dome shows 1,500 feet of beds that include massive conglomerate, thinbedded conglomerate, pebbly sandstone, and some shale, with the bottom of the 

formation not exposed.

The basal conglomerate of the Naknek consists of well-rounded pebbles and 

boulders of igneous rocks, the most conspicuous of which are gray granite and 

greenstone, in a matrix of coarse arkosic sand. In some places the boulders 

are of fairly uniform size. In others large and small boulders are mixed 

together. Granite boulders several feet in diameter are common, and wellrounded boulders 5, 6, and even 9 feet in diameter were seen.

The conglomerate described above has been generally regarded as 

the equivalent of the Chisik conglomerate of Chisik Island and Iniskin Bay, which is described on page 170. It certainly resembles 

and appears to correspond closely in position with the Chisik conglomerate, but its exact equivalence has not been shown beyond 

doubt. The upper shale member of the Shelikof formation, which 

underlies the conglomerate, may be the equivalent of the lower shaly 

beds of the Naknek formation of Cook Inlet, which they resemble 

in lithologic character and fauna at least as closely as they resemble 

the Chinitna shale. This conglomerate may therefore be the equi- 

; valent of some of the conglomeratic beds higher up in the Naknek 

formation of Cook Inlet.

The Naknek formation was first described as the Naknek "series" 

by Spurr.28 The type occurrences are at the head of Naknek Lake 

and near Katmai. The original description is as follows:

About halfway from the mouth of Naknek Lake to the head of Savonoski 

there outcrops at the chief bend an ancient greenish volcanic rock, which is 

included under the general classification of the Naknek series. From this 

point to Savonoski the mountains on the south side of the lake are all of 

horizontal sedimentary rocks. From Savonoski nearly to the pass which 

separates the waters draining into Naknek Lake from those of the Katmai 

River the same sedimentary series occurs. At the pass the series is broken 

by a chain of volcanoes, but on the southeastern side it reappears and 

outcrops almost continuously as far as Katmai Point, which was the last 

place where it was observed. It will thus be seen that the rocks of the 

Nakriek series, as here classified, occupy most of this section across the 

peninsula of Alaska.

As above noted, the westernmost rock of the Naknek series, as above 

t understood, is an augite andesite which outcrops on Naknek Lake. It is

28 Spiirr, J. E., A reconnaissance in. southwestern Alaska in 1898: U., S. Geol. Survey 

Twentieth Ann. Rept, pt. 7, pp. 145-147, 169-171. 179-180, 1900.

uirr, 

ufeth
208 MESOZOIC STBATIGEAPHY OF ALASKA

not absolutely certain that this rock represents a flow contemporaneous with 

the sedimentary rocks of the series, but in the absence of evidence this ha» 

been assumed, especially as the ancient and decomposed appearance of the 

rock suggests a different age from that of the later volcanic material, portions of which occupy the axis of the mountain range. The most of therocks of the Naknek series, however, are arkoses, sometimes fine, sometime* 

coarse, and merging into conglomerates. These arkoses are either green, from 

the decomposition of ferruginous minerals and the production of chlorite,. 

or light colored, from the predominance of fel.dspathic constituents. In nearly 

every case it is possible to tell under the microscope that the arkose hasbeen derived from granite, and in some cases it is plain that the granite was 

a hornblende-biotite granite, all of the component minerals being found in 

very little altered and reasserted condition in the sedimentary rock. In the 

vicinity of Katmai and at Katmai Point the basal rock exposed just abovetidewater is a hard, massive granitic arkose; above this conies a dense 

andesitic rock, which is perhaps a flow contemporaneous with the deposition: 

of the sedimentary rocks; and higher up come arkoses, made up of very 

coarse granitic fragments, and coarse conglomerates, having pebbles of biotite 

granite.

At the coast in the vicinity of Katmai and for some miles inland are green 

arkoses, fine grained and granitic; there are also beds of conglomerate containing granite pebbles. The rocks in general are horizontal, although at 

the point which bounds Katmai Bay to the east they are uptilted on the sea 

side so as to dip very slightly to the northwest. There is also a system of 

nearly vertical fractures, and some slight faulting, but no folding. Along; 

some of the seams are calcite veins. The rocks at this point are at the bottom hard and massive, dark-gray granitic arkose; above this comes massive 

andesite, probably a flow; while higher up are arkoses and conglomerates.. 

About 200 feet above the base of the cliffs the arkose becomes nearly white 

and is found to be made up of coarse granitic fragments. Jurassic fossils are 

found in these rocks at various points, in gray compact limestone, which 

evidently comes from the upper part of the dark-gray grits that underlie the 

white arkoses, and also from the white arkose itself; indistinct plant remains are also frequent. The entire thickness of the horizontally stratified, 

rocks exposed in the mountains near here is at least 1,500 feet. At Katmai 

Point a large dike of volcanic rock has burst through the grits.

The Naknek series consists of a great thickness of granitic arkose and of 

conglomerate, which generally contain pebbles of granite. All of these sedimentary rocks are evidently derived from the destruction of a land mass 

which consisted largely of hornblende-biotite granite. There are probably 

some volcanic flows interstratified with the arkose and conglomerates, although it is not absolutely proved that those examined may not be intrusive. 

The series is cut by andesite-basaltic (aleutitic) lava of later age, especially 

along the axis of the range, where the amount of volcanic rock is very great.

The rocks seen by Spurr include neither the base nor the top and 

possibly only a small part of the formation.

The exposures on the east shore of Katmai Bay described 1' by 

Spurr were studied by Stanton and Martin in 1904 and were found! 

to be composed of banded light and dark (mostly light) sandstone 

or arkose that has a striking resemblance to the banded sandstone 

overlying the Cadoceras-beaTmg beds in the Cook Inlet section.
JURASSIC, ALASKA PENINSULA 209

{See p. 1T3.) The rocks on Katmai Bay were recognized as in general lithologically similar to and faunally identical with the Upper 

Jurassic beds of Cook Inlet and Cold Bay, which were accordingly 

referred 29 to the Naknek formation.

The exposures on the west shore of Katmai Bay are in low bluffs 

composed of dark-gray sandstone with thinner bands of lighter 

color and dark sandy shale; the beds become gradually less sandy 

toward the top and are in general fossiliferous throughout. The 

Naknek formation crops out almost continuously along the shore 

from Katmai River to Alinchak Bay and dips northward at low 

angles. This formation probably extends continuously through the 

hills from Katmai to the head of Cold Bay.

The rocks which Capps 80 referred to the Naknek formation were 

described by him as follows:

Above the basal conglomeratic phase of the Naknek there is a variable 

thickness of light-gray to brownish-gray arkosic sandstone. Observed sections 

of this portion of the Naknek range in thickness from 500 or 600 feet to 1,600 

feet, with an average of perhaps 800 feet. The sandstones generally contain 

pebbly beds and thin conglomerates, but very little shale. As described by 

Martin, the Naknek on the west shore of Cook Inlet contains arkosic sandstone, conglomerate, shale, and a considerable admixture of tuffs and andesite 

flows. In the Cold Bay district no igneous flows or tuffs were noted, and 

arkosic sandstone, derived from the disintegration of a granite mass, predominates in the part of the formation above the basal conglomeratic phase.and 

below, the upper sandy phase, described below. The arkosic sandstone is not 

generally very fossiliferous, but it has yielded enough collections to show that 

it should undoubtedly be included in the Naknek;

The highest part of the Naknek formation that has been recognized in the 

Cold Bay district consists of a heavy series of sandy shales that lie above the 

arkosic sandstone. These shales are well developed between the extreme head 

of Becharof Lake and Mount Lee, where they have an estimated thickness of 

1,200 feet, although their upper part has been removed by erosion. They are 

believed to have a wide development in the basin of upper Becharof Lake and 

to extend northeastward into the Kejulik (Garkulik) Valley, as well as in the 

basin of the Ugashik Lakes. The shales are locally fossiliferous and have 

yielded many forms of shells, the most common and most characteristic of 

which are several species of Aucella.

The Upper Jurassic rocks of the Chignik Bay district were referred by Atwood 31 to the Naknek formation and were described 

as consisting of sandstone, shale, and conglomerate, exposed in the 

main axis of the Aleutian Range. The base of the formation apparently does not crop out in this district, and the thickness of the 

exposed portion was not recorded. It is overlain unconformably 

(p. 297) by the Upper Cretaceous rocks of the Chignik formation.

29 Stanton, T. W., and Martin, G. C., Mesozoic section; on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, pp. 402-407, 1905.

30 Capps, S. R., The Cold Bay district: U. S. Geol. Survey Bull. 739, p. 103, 1922. 

a Atwood, 'W? W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, pp. 34, 36-38, 1911.
210 MESOZOIC STRATIGRAPHY OF ALASKA

The rocks exposed on the north shore of Ivanof Bay, according to 

the unpublished observations of the writer, consist of sedimentary 

beds, probably in part Upper Jurassic, that are separated by broad 

flats from the volcanic rocks that form the shores and islands 

farther down the bay. These sedimentary beds dip gently northward, so that the lowest beds, consisting of sandstone, are exposed at 

the west end of the cliffs. The sandstone is overlain by a massive 

conglomerate, above which is shale that forms the eastern half of 

the cliffs and appears to extend far up the mountain side. Concretions found among the boulders in one or two of the small gulches 

that head in this shale contain specimens (lot 7824) of Aucella related to Aucella pallasi Keyserling. As these gulches apparently 

contain no detritus other than that derived from the shale, this 

fossil indicates that the shale is Upper Jurassic and belongs in the 

Naknek formation. On the other hand, fossil leaves were found in 

sandstone beds that underlie and are intercalated in the massive conglomerate at the west end of the cliffs. These leaves are Upper 

Cretaceous or Tertiary. It is thus evident either that the Aucellabearing concretions were not derived from the shale exposed in the 

cliffs or that the rocks exposed in the cliffs are not in their true sequence. The writer believes that the latter is the case and that there 

may be either an undetected fault between the shale and the apparently underlying conglomerate or an overturn of the entire section.

Upper Jurassic beds occur in several small areas at Herendeen 

Bay, where their presence was first noted by Paige.32 They were 

subsequently described in greater detail as the Naknek formation 

by Atwood.33 The following section, measured by Atwood, shows 

the character of'the formation as exposed on Herendeen Bay:

Section of part of Naknek formation near the base of the east side of Pinnacle

Mountain, near the head of Herendeen Bay

Feet

1. Sandstone, coarse grained and fossiliferous (lot 5579)___ 600

2. Sandstone, medium grained (with a few fossils)______ 100

3. Sandstone, fine grained and fossiliferous (lot 5578)____ 50

4. Grit or coarse gritty sandstone_________________ 30

5. Sandstone, dark colored and very fine grained (lot 5573)_ 300

Conglomerate, which was not noted in this section, was observed 

at other localities. It probably belongs at a lower horizon than 

any of the beds represented in the section.

The base of the Naknek formation is apparently not exposed, and 

older rocks have not been found in this district. The Naknek formation is overlain at some places by the Lower Cretaceous beds of the 

Staniukovich shale, described on pages 291-292, and at other places

32 Paige, Sidney, The Herendeen Bay coal field : U. S. Geol. Survey Bull. 284, pp. 102, 

104, 1906.

88 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, pp. 34-38, 1911.
JURASSIC, ALASKA PENINSULA 211

by beds of unknown character described on page 299, that lie 

immediately beneath the Upper Cretaceous rocks of the Chignik 

formation and that may be either Upper or Lower Cretaceous. The 

contact with the Staniukovich shale is poorly exposed and may be 

either conformable or unconformable.

Age and correlation. The Naknek formation carries abundant 

fossils, chiefly marine invertebrates, which are listed on pages 214r217. The apparent general absence of other than marine fossils is 

noteworthy, especially in view of the characteristic coarseness of the 

sediments. It was stated by Spurr 34 that plant remains are abundant throughout the formation, but apparently none were collected, 

and none were mentioned in his field notes. A few plants have 

been found, however, by later collectors. It should be noted that 

the fauna of the Naknek formation of most places on the Alaska 

Peninsula differs from that of the supposed equivalent beds on Cook 

Inlet in not containing Gardioceras. Specimens of this genus, which 

is characteristic of the lower (post-Chisik) beds that have been referred to the Naknek formation on Cook Inlet, have been found at 

only one locality on the Alaska Peninsula. The localities in the 

table are arranged approximately in geographic order.

(3) Upper end of Naknek Lake. Shingle of green sandstone or arkose on 

' the beach near Savanoski. J. E. Spurr, 1898.

10249 (F). East arm of Naknek Lake, near Savanoski Camp. Sandstone in 

place and in loose slabs on lake shore. C. N. Fenner, 1919.

12081 (9). Float in tributary east of Savanoski River. W. R. Smith, 1923.

10246 (C). Cliffs of canyon a few miles east of Ukak Camp, Valley of Ten 

Thousand Smokes. C. N. Fenner, 1919.

10247 (D). Shaly strata at altitude of 2,500 to 2,900 feet, west spur of Buttress Mountain, Valley of Ten Thousand Smokes. C. N. Fenner, 1919.

10264 (H). Single specimen in sandstone in vicinity of Katmai Camp, south 

side of Mount Katmai. C. N. Fenner, 1919.

10265 (I). Shale with indistinct fossils from contact with one of the andesitic intrusions in vicinity of the " spire," north side of Valley of Ten Thousand 

Smokes. C. N. Fenner, 1919.

12080 (8). Baked Mountain, north side of Valley of Ten Thousand Smokes. 

W. R. Smith, 1923.

11960 (3) Near Valley of Ten Thousand Smokes. Jack Lee, 1923.

(4) Katmai Pass. J. E. Spurr, 1898.

(8) Five miles southeast of Katmai Pass. J. E. Spurr, 1898.

(2) Bluff above Katmai. J. E. Spurr, 1898.

(7) Bluff back of Katmai. J. E. Spurr, 1898.

(10) Katmai Point. J. E. Spurr, 1898.

3101. West side of Katmai Bay, 3 miles southeast of Katmai Village. Darkgray sandstone with thinner bands of lighter color. T. W. Stanton, 1904.

3124. West side of Katmai Bay 2% miles southwest of village, or half a mile 

south of lagoon. Talus of dark sandy shale that is somewhat higher than the 

beds that yielded lot 3101. Lawrence Martin, 1904.

3125. West side of Katmai Bay. Talus 200 feet north of 3124. Lawrence 

Martin, 1904.

M Spurr, J. H., op. cit., pp. 147, 170, 171.
212 MESOZOIC STRATIGRAPHY OF ALASKA

3126. West side of Katmai Bay. Talus at same locality as 3125. Lawrence 

Martin, 1904.

3127. West side of Katmai Bay. Talus half a mile north of 3124 and at 

about the same horizon. Lawrence Martin, 1904.

3128. West side of Katmai Bay. Talus at same locality as 3127. Lawrence 

Martin, 1904.

10244 (A). Cliffs near beach camp, Katmai Bay. C. N. Fenner, 1919.

10248 (E). Highly fossiliferous stratum on Baer Mountain, near Lagoon 

Camp, Katmai Bay, north of camp and about 500 feet above sea level. C. N. 

Fenner, 1919.

12276 (3). Head of central and principal tributary of Bear Creek, flowing 

into north arm of Alinchak Bay, Alaska Peninsula. W. R. Smith, 1923.

10823 (B). Oilwell Creek, Cold Bay. S. R. Capps, 1921.

10825 (D). 5 miles northwest of head of Cold Bay. S. R. Capps, 1921.

11325 (22AB4). 3 miles up Teresa Creek from shore. A. A. Baker, 1922.

11332 (22AB5). 1 mile north of saddle at head of Teresa Creek. A. A. 

Baker, 1922.

3135. Creek entering marshes at head of Cold. Bay, 1 mile from head and 

one-fourth mile up creek. Lawrence Martin, 1904.

3136. Creek entering marshes at head of Cold Bay, about 25 feet east of 

3135. Lawrence Martin, 1904.

3131. Becharof Creek, half a mile above forks and 2% miles east of Becharof 

Lake. Lawrence Martin, 1904.

3132. About 100 yards upstream from 3131, in somewhat lower beds. Lawrence Martin, 1904.

3133. About three-fourths mile above forks of Becharof Creek, in lower bedsthan 3132. Lawrence Martin, 1904.

3134. About 100 yards upstream from 3133. Lawrence Martin, 1904.

11333 (F 22 AB 6). West side of range across from Alinchak Bay. Basal 

Naknek. A. A. Baker, 1922.

11334 (F 22 AB 7). 1,600 feet southwest of junction of Bast Fork and Kejulik River. A. A. Baker, 1922.

11329 (F 22 AB 8). About 1 mile northwest of Kejulik River, about 2 

miles southwest of point where two large tributaries come into river. A. A. 

Baker, 1922.

11330 (F 22 AB 9). 2 miles up from Kejulik River, along eastern tributary 

mentioned in 11329. A. A. Baker, 1922.

11331 (F22AB10). In canyon near head of East Fork of Kejulik River. 

A. A. Baker, 1922.

11360 (F 34). Fossil Creek, north of Lake Becharof. Collected by Doctor 

Laymore for W. R. Smith, 1922.

11363 (F 37). Shale on bank of Kejulik River, northeast of Becharof 

Lake. W. R. Smith, 1922.

 (F 38). Near mouth of Kejulik River. W. R. Smith, 1922.

12077 (4). East side of Kejulik Pass, below Gas Creek. W. R. Smith, 1923.

12078 (5). Upper part of Gas Creek, lowest exposed beds. W. R. Smith, 1923.

12079 (6). Mountain top east of Yori Pass. W. R. Smith, 1923.

10827 (1-130). 2 miles southeast of Bellim Bay, Becharof Lake. S. R. 

Capps, 1921.

10794 (1-80). Shore of creek between Lake Ruth and Becharof Lake 

at upper Indian village. S. R. Capps, 1921.
JURASSIC, ALASKA PENINSULA 213

10817 (1-122). Southeast shore of Becharof Lake between extreme south 

end of lake and the fish village. S. R. Capps, 1921.

10795 (1-^2). About 1,000 feet above base of Naknek shale, 3 miles southeast of Mount Lee and 1 mile west of shore of Becharof Lake. S. R. Capps, 

1921.

10796 (1-83). About 1,000 feet above base of Naknek shale, three-fourths 

of a mile southeast of 1-82. S. R. Capps, 1921.

11324 (F 229 B 3). In gulch, 2,250 feet S. 60° E. from forks in Peulik 

Creek. A. A. Baker, 1922.

10797 (1-87). Basal conglomerate of Naknek formation. On Barabara or 

Little Ugashik Creek, about 1 mile below its head. Float boulder. S. R 

Capps, 1921.

7517 (1-88). Basal conglomerate of Naknek formation. Pearl Creek 

S. R. Capps, 1921.

7620. Top of bluff on south bank of Pearl Creek, N. 7° B. (magnetic) from 

Standard Oil derrick. G. C. Martin, 1923.

10798 (1-89). 5 miles southeast of Mount Peulik. S. R. Capps, 1921.

10799 (1-93). 5 miles south-southwest of Mount Lee. S. R. Capps, 1921. 

10816 (1-121). Base of Naknek formation. Becharof-Crooked Creek divide. 

S. R. Capps, 1921.

11068 (G 3). Half a mile southwest of G 4. Ernest Marquardt, 1921.

11069 (G 4). On summit of Crooked Creek-Becharof Lake divide. Ernest 

Marquardt, 1921.

11070 (G 5). On ridge three-fourths of a mile north of G 4. Ernest Marquardt, 1921.

11345 (F 7). Across divide at head of Ugashik Creek. W. R. Smith, 1922.

3119. Kanata Bay, 12 miles southwest of Cold Bay. Received from Jack 

Lee, 1904.

- 11067 (F 7). Northeast fork of Big Creek, 2 miles above its mouth. Ernest 

Marquardt, 1921.

7572 (P. 10). East wall of canyon of Moore Creek, 3 miles from head. 

Thin-bedded sandstone in thick member of arkose in Naknek formation. W. R. 

Smith, 1922.

11073 (N 2). About 3 miles south-southwest of south end of Ugashik Lakes. 

Ernest Marquardt, 1921.

11354 (F 18). 8 miles southwest of Wide Bay. W. R. Smith, 1922.

11348 (12). Imuya Bay, south of Wide Bay. W. R. Smith, 1922.

11356 (F 26). East bank near head of Lava Creek. W. R. Smith, 1922.

11359 (F 33). Gates of crater at head of Aniakchak River. W. R. Smith, 

1922.

3118. Hook Bay, on north shore of Chignik Bay. Received from C. J. Brun 

by T. W. Stanton, 1904.

5800. Hook Bay Creek near coal mine about 5 miles north of Hook Bay. 

W. W. Atwood, 1908.

5794. North side of Chignik Bay, on mountain top north of Bear Creek. 

W. W. Atwood, 1908.

5798. Chignik Lake. Fine-grained dark-colored sandstone exposed along the 

shore in the southwest arm of the lake. W. W. Atwood, 1908.

5799a. Chignik Lagoon, about opposite Alaska Packers' Association cannery. W. W. Atwood, 1908.

11959(2). Hills between Chiaktuak Creek and Chignik Lake. Ernest Marquardt, 1923.

i[For other localities see p. 218.] 

49448 26 16
Fossils from Naknek formation of Alaska Pe

Cladophlebis cf. C. haiburnensis

(Lindley and Hutton) ...--..

Polypodiumoregonense Fontaine

Zamites megaphyllus (Philips)

Seward.. __.----_..-....

Cidaris? - -___------__...

Serpula..__-___ 

Rhynchonella.-_____------

Terebratula..-------- . ---

Nucula,-.._ ------- 

Leda?-.-_-----__----- 

Qrammatodon. ----- ..-.

Area.... ----- .---

Area?.- " 

Inoceramus.------ ---- 

Avicula.- .--- - - -- 

Pteria..-. .- - 

Eumicrotis__ 

Eumicrotis?_ - - -- 

Aucella cf. A. brqnni Kouillier.. 

Aucellacf. A. erringtoni (Qabb). 

Aucella cf. A. pallasi Keyserling. 

Aucella-------- ----

Ostrea...___-__ .-- 

Pectensp. a.... -. - 

Pectensp. b.,... 

Pecten (large,smooth form) .. 

Pecten (smooth form) .--. 

Pecten____..__ -- 

Pecten? sp. c.- -- 

Lima..... 

Lima?....__...__--------

Anomia? -----------

Pleuromya__ __ .- 

Pleuromya?..- - 

Pholadomya.. 

Cypricardia?.- -.. .- 

Artica_ --- --------

Cyprina_ -..- 

Cyprina?..--. ---...- 

Astarte.... .. 

Astarte (same as in 10796) __
Tancredia? ____________

Dentalium .. ___ . ......

Patella..... ... _ ... __ . .......

Turbo... ................ _ ....

Turbo?.... __________ ...

Rissoina?? ... _ . __ . _____

Phylloceras.. __________ .

Phylloceras? . . __ .. ____ ..

Lytoceras ____________

Cardioceras cf. C. canadense

Belemnites ________ - . ...

Belemnites (slender form) . . __

Plesiosaur ____ . ___ .....

n

1 a. Identified by T. W. Stanton; b, identified by F. H. Knowlton; c, identified by J. W. Oidley; d, identified 
Fossils from Naknek formation of Alaska Peninsula C

Cladophlebis cf. C. haiburnensis

Zamites megaphyllus (Philips)

Cidatis?...... ...................

Leda?. ......... -......... .. 

Pfpria

Astarte (same as in 10796). __ .

i 1

S5

8 1

t»

i

>o

i

a

a

3 

«

tg

tt^

h

h

1

a

i

CO

§ § § § s

a

A

I S

d

g SCO

0

3

a
Patella __ . ..--.-. ..-......

Turbo?..-.... _ . __ . __ -.--

Cardioceras cf. C. canadense

Va

0 a, Identified by T. W. Stanton; b, identified by F. H. Knowlton; c, identified by J. W. Qidley; d, identified by 
218 MESOZOIO STRATIGRAPHY OF ALASKA

7824. Float from north shore of Ivanof Bay and from creek 1 mile east of 

Perry. Probably derived from concretionary shale exposed in cliffs on north 

shore of the bay. G. C. Martin, 1912.

5574. Bold Bluff Point, Herendeen Bay. W. W. Atwood, 1908.

5573. East base of Pinnacle Mountain, Herendeen Bay. Bed 5 of section on 

p. 210. W. W. Atwood, 1908.

5578. Canyon on east face of Pinnacle Mountain, Herendeen Bay. Bed 3 

in section on p. 210. W. W. Atwood, 1908.

5579. Canyon on east face of Pinnacle Mountain. Bed 1 of section on p. 210. 

W. W. Atwood, 1908.

5581-5584. Crow Point, Herendeen Bay. W. W. Atwood, 1908. 

(Paige). Bluff south of Moss Valley, Herendeen Bay. Sidney Paige, 1905.

MATANUSKA VALLEY AND TALKEETNA MOUNTAINS 

GENERAL FEATURES

The Matanuska Valley contains a thick and fairly complete section of Jurassic rocks, as follows:

General section of Jurassic rocks in the Matanuska, Valley

Upper Jurassic (overlain, conformably (?), by Lower 

Cretaceous beds) :

Naknek formation: Feet 

Shale, sandstone, tuff, arkose, and conglomerate,

with the fauna of the Naknek formation___ 1,000+ 

Unconformity. 

Conglomerate (Chisik ?).

Chinitna formation: Shale, conglomerate, and sandstone, with the fauna of the Chinita shale____ 2,000± 

Conformity. 

Middle Jurassic:

Tuxedni sandstone: Sandstone and sandy shale, with

the fauna of the Tuxedni sandstone_________ 1, 000± 

Conformity (?).

Lower Jurassic: Lava, agglomerate, breccia, and tuff, 

interbedded with lesser volumes of sandstone and shale 

and containing .fossil plants and a marine invertebrate 

fauna_____________________________ 3,000± 

Basal contact and underlying rocks not exposed.

The Jurassic section exposed in the Matanuska Valley is unfortunately incomplete in two important features. Neither the 

base of the Lower Jurassic volcanic rocks nor any older formation is 

exposed in this district, and some of the Jurassic faunas of the 

Alaska Peninsula (see pp. 181-191) are apparently absent. Otherwise the section appears to contain representatives of all the marine 

Jurassic faunas known in Alaska. The section is in general very, 

similar, both lithologically and faunally, to the Cook Inlet section, 

of which it may be regarded as the detached northeastern extension.

The Lower Jurassic volcanic rocks of the Matanuska Valley 

resemble the rocks of the same age at Seldovia, on the east coast of
JURASSIC, MATANUSKA VALLEY AND TALKEETNA MOUNTAINS 219

Cook Inlet, both lithologically and faunally, but differ from them by 

including plant beds. The Middle Jurassic beds of this district 

include beds which resemble, in a general way, the Middle Jurassic 

Tuxedni sandstone of the west coast of Cook Inlet and which contain a fauna that is practically identical with that of Cook Inlet. The 

Upper Jurassic rocks also are in general lithologically similar and 

closely related in faunas to the Chinitna shale and Naknek formation of the Alaska Peninsula and Cook Inlet. The Upper Jurassic 

rocks of this district are overlain conformably by Lower Cretaceous 

rocks. In this respect the section resembles that of the Alaska 

Peninsula and differs from that of Cook Inlet, where the Cretaceous 

is absent.

LOWER JURASSIC 

TAI/KEETNA FORMATION

Historical review. The Lower Jurassic rocks of the Matanuska 

Valley and adjacent areas have a wide geographic extent and constitute a very prominent stratigraphic and structural element in the 

geology of the eastern Talkeetna Mountains. For them the name 

Talkeetna formation is here proposed.

These rocks were first recognized by Paige and Knopf,35 who described them as " greenstones and related pyroclastics " constituting 

the lowest member of the Middle Jurassic. Their account includes a 

brief statement concerning the petrographic character and stratigraphic relations of these rocks, together with a list of fossils and a 

statement of probable age contributed by T. W. Stanton, who referred the fauna tentatively to the Middle Jurassic.

The same authors redescribed these rocks in greater detail in a subsequent publication,36 where they used the term " Lower Middle Jurassic rocks," including not only the volcanic members as described 

in the text but the whole of the "Middle Jurassic andesitic greenstones, etc.," as represented on the map. This account includes a 

more complete description of the petrographic character and stratigraphic relations than was given in the earlier account and includes 

also the list of fossils and discussion of age by Stanton, in which 

there is a suggestion of the subsequently confirmed correlation of 

these beds with the Lower Jurassic tuff of Seldovia.

These rocks were tentatively correlated by Brooks 37 with the 

Skwentna group of the Alaska Kange, which he classified as " Lower 

Middle Jurassic " on the basis of Paige and Knopf's assignment of

85 Paige, Sidney, and Knopf, Adolph, Stratigraphic succession In the region northeast 

of Cook Inlet, Alaska: Geol. Soc. America Bull., vol. 18, pp. 327-328, 1907.

38 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna basins, Alaska: U. S. Geol. Survey Bull. 327, pp. lft-19, pi. 2, 1907.

87 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, pp. 85-87. 1911.
220

their Matanuska Valley rocks. This account of the Skwentna 

group includes a brief abstract of the above-mentioned description 

of the Lower Jurassic tuff of the Matanuska Valley, with the list 

and discussion of the fossils quoted in full.

These rocks were described by Martin and Katz as Lower Jurassic 

" volcanic breccias, agglomerates, and tuffs." Their account includes 

a general description 38 of the occurrence throughout the Matanuska 

Valley, consisting of a series of slightly modified quotations from 

Paige and Knopf, also a detailed description 39 of the occurrence 

in the lower part of the Matanuska Valley, which is entirely new. 

The detailed account comprises a description of the occurrence and 

petrographic character, lists of marine invertebrate fossils as determined by T. W. Stanton, and a discussion of the age and correlation 

in which there is a hitherto unpublished statement contributed by 

Stanton, who concludes that the fauna should probably be referred 

to the Lower Jurassic and be correlated with the supposed Lower 

Jurassic tuff at Seldovia.

Some Lower Jurassic plants from the Matanuska Valley, collected by Martin and his associates in 1913 were described in detail 

by Knowlton,40 who included in his paper a brief account of the 

stratigraphic occurrence contributed by Martin.

The character and distribution of the Lower Jurassic rocks in the 

northeastern part of the Talkeetna Mountains were described by 

Chapin,41 who discussed the distribution, character, structure, thickness, age, and correlation of the rocks and quoted lists of fossils from 

previous descriptions.

The probable extension of these rocks in the western part of the 

Talkeetna Mountains has been described by Capps 42 as "andesite 

greenstones."

Stratigraphic description. The Talkeetna formation of the Matanuska Valley includes lava, agglomerate, breccia, and tuff, interbedded with lesser volumes of sandstone and shale. It is composed 

chiefly of water-laid volcanic detritus. Its thickness is probably 

several thousand feet but can not be accurately estimated on account 

of the complex structure and the lack of recognizable horizons. 

These beds were deposited largely if not wholly in marine waters, 

although the fossil plants are possibly indicative of temporary terrestrial conditions. Neither the basal contact of these beds nor the 

rocks that underlie them have been observed. They are overlain

^/Martin, G. C., and Katz, P. J., Geology and coal fields of the lower Matanuska 

Valley: U. S. Geol. Survey Bull. 500, pp. 17-19, pi. 3, 1912.

89 Idem, pp. 29-32, pi. 5.

*° Knowlton, F. H., A Lower Jurassic flora from the upper Matanuska Valley, Alaska: 

U. S. Nat. Mus. Proc., vol. 51, No. 2158, pp. 451-460, pis. 79-82, 1916.

41 Chapin, Theodore, The Nelchlna-Susitna region, Alaska: U. S. Geol. Survey Bull. 

668, pp. 21, 29-32, pi. 2, 1918.

42 Capps, S. E., Mineral resources of the western Talkeetna Mountains: U. S. Geol. 

Survey Bull. 692, pp. 195-196, pi. 4, 1919.
JUKASSIC, MATANUSKA VALLEY AND TALKEETNA MOUNTAINS 221

by the marine Middle Jurassic beds of the Tuxedni sandstone described on pages 223-226.

Age and correlation. The fossils of the Talkeetna formation of 

the Matanuska Valley include the plants and marine invertebrates 

listed in the accompanying table. It is impossible, from the data at 

hand, to determine the exact position of the fossiliferous beds within 

the formation. The fossils all came from one lithologic unit or complex, which has not thus far proved to be stratigraphically divisible. 

It is possible, however, that this formation may contain more than 

one stratigraphic unit and that the plants and the marine shells are 

not of the same age.

The following statement regarding the age of the fossil plants has 

been contributed by F. H. Knowlton:

Practically the whole of this flora is new to North America, the Dictyophyllum particularly being of interest, as this is the first time, so far as I know, 

that even the genus has been obtained here. The forms representing the genus 

Otozamites are also noteworthy.

This flora is almost all identical with that at Bornholm, near the coast of 

Sweden, in beds regarded as of Liassic age, and for this reason the Matanuska 

material is considered to be of the same age. This is the oldest Jurassic flora 

known to me in North America.

Knowlton 43 has also made the following statements concerning 

the age of these plants:

The Matanuska material undoubtedly finds its closest affinity with the material described by Nathorst, Bartolin, Moller, and others from the island of 

Bornholm, off the southern coast of Sweden, since all but two of the forms 

(Pterophyllum rajmahalense and Ctenophyllum angustifolium) are common to 

the two places.

In the works of Moller, Nathorst, and others the Bornholm locality is 

referred to as Rhaetic or Liassic, there apparently being the same difficulty 

there as in many other parts of Europe in drawing the line between the 

Triassic and Jurassic. Taking everything into account in the present connection, such as the Jurassic affinity of certain of the forms, the absence 

of known plant-bearing Triassic rocks in Alaska, the apparently Lower 

Jurassic indication of the associated invertebrates, etc., all give weight to 

the reference of these rocks to the higher of the two alternatives. The 

material under consideration from the Matanuska Valley is therefore regarded as of Lower Jurassic (Liassic) age. This is the oldest well-defined 

Jurassic flora known to the writer in North America.

The following statement was submitted by Stanton 44 concerning the marine invertebrates collected in the lower Matanuska 

Valley in 1910:

The lots numbered 6693, 6697, 6706^6709 are referred to the Jurassic, and 

are probably Lower Jurassic, though the paleontologic evidence for the latter

43 Knowlton, F. H., A Lower Jurassic flora from the upper Matanuska Valley, Alaska: 

U. S. Nat. Mus. Proc., vol. 51, No. 2158, pp. 453-454, 1916.

** Sfanton, T. W., cited by Martin, G. C., and Katz. F. J., Geology and coal fields of 

the lower Matanuska Valley, Alaska: U. S. Geol. Survey Bull. 500, p. 31, 1912. 

49448 26 16
222

reference is not so full as is desirable. The fossils are almost certainly 

from the same beds from which Mr. Knopf collected his lot No. 201, on the 

head of Matanuska River, in 1906. Mr. Knopf's collection was at that time 

doubtfully referred to the "Enochkin formation," but I am now inclined 

.to consider the beds from which he collected equivalent to the supposed 

Lower Jurassic near Seldovia and to regard them as Lower Jurassic. It 

is true that not more than two or three species have been found c6mmon to 

the different localities from which these fossils have been collected, but the 

general character of the fauna in each case is suggestive of Lower Jurassic, 

and it is probable that more systematic collecting would prove that the different lots really belong to a single fauna.

The Lower Jurassic volcanic rocks of the Matanuska Valley bear 

some resemblance, both lithologic and faunal, to the supposed 

Lower Jurassic tuff near Seldovia, on the east coast of Cook Inlet, 

which is described on pages 134-137, but the tuff near Seldovia is not 

known to contain plant beds. The available evidence, as suggested 

by Stanton, is strongly suggestive of this correlation, but it can 

not yet be regarded as definitely established.

Lower Jurassic fossils from Talkeetna formation of Matanuska Valley a

Cladophlebis hirta? Holler... ....... ........

Gervilla?...... _ ................................

Car dinia? -- -- -. .........................

Thracia?.-- _ ............ .. ....... ........

t»

to

h

b

b

b

b

b

b

b

1 to

b

b

CO

b

b

b

b

001

I

b

b

1

CO

b

1

b

b

b

b

o>CO

3

b

h

b

b

b

h

b

b

b

b

b

g 

%

b

b

b

1

CO

a

a

oo

a

a

a

1

I

a

/..

1

b

i

b

§«J

CO

b

h

b

b

b

b

h

O)

b

h

b

b

h

b

b

° a, Identified by F. H. Knowlton; b, identified by T. W. Stanton.

6697. Doone Creek, at mouth of gulch, 3,950-foot point on traverse of August 

30. Float. G. C. Martin, 1910.
JURASSIC, MATANTJSKA VALLEY AND TALKEETHA MQTJNTAINS

\

6706. Creek entering Chickaloon River from west 1 mile above Government

Bridge, altitude 2,000 feet. G. C. Martin, 1910. ( \

6707. Creek entering Chickaloon River from west 1 mile above Government 

Bridge. Float from base of falls. G. C. Martin, 1910. ;

6708. Creek entering Chickaloon River from west 1 mile,above Government 

Bridge. Float above falls. G. C. Martin, 1910.

6709. Creek entering Chickaloon River from west 1 mild, above Government' 

Bridge. Talus at altitude 2,200 feet. G. C. Martin, 1910. ( \

6693. Creek entering Chickaloon River from west 1 mile' above Government 

Bridge, altitude 2,200 feet. G. C. Martin, 1910. '

8569. West side of Chickaloon River at mouth of creek, 3,. miles above Government Bridge. Black limestone float. G. C. Martin, 1913. "V^

8570. Same as 8569. Breccia float. G. C. Martin, 1913.

6700. Crest of spur between first and second tributaries entering East Fork 

of Boulder Creek above its mouth, altitude 4,780 feet. Shaly and cherty beds 

interstratified with tuff. R. M. Overbeck, 1913.

6698. About three-fourths mile up the next to the lowest creek entering the 

East Fork of Boulder Creek from the south. Sandstone and shale interbedded 

with tuff. J. B. Mertie, 1913.

6701. Float from same locality as 6698. G. C. Martin, 1913.

6699. Talus from cliff about one-third mile upstream from 6698. J. B. 

Mertie, 1913.

8565. Same creek as 6698, about 1% miles above mouth. J". B. Mertie, 1913.

8561. Near head of Boulder Creek. Collected by a prospector.

6AK201. Tributary to Squaw Creek heading under 6,375-foot peak at east 

end of Sheep Mountain. Fossiliferous tuff associated with lava and coarse 

pyroclastic rocks. Adolph Knopf, 1906.

8589. Sheep Mountain, altitude 3,400 feet, on creek flowing southeast from 

6,375-foot peak. G. C. Martin, 1913.

MIDDLE JURASSIC

TUXEDNI SANDSTONE

Historical review. Overlying the Lower Jurassic volcanic rocks 

just described as the Talkeetna formation-is a thick series of sandstone and sandy shale that carrythe fauna of the Tuxedni sandstone of Cook Inlet. These rocks were first recognized by Paige 

and Khopf * 5 and were described very briefly as a "series of graywackes, sandstones, shales, and subordinate conglomerates," which 

constitute the second-mentioned member of the rocks referred to the 

Middle Jurassic. A list of marine invertebrate fossils, as determined by T. W. Stanton, was given.

In a later and more complete description of the geology of this 

region, by the same authors,46 the rocks now referred to the Tuxedni 

sandstone constitute the " sandstones and shales " described under the 

heading "Lower Middle Jurassic rocks" and an undifferentiated 

part of the " Upper Jurassic and upper Middle Jurassic " rocks rep-

** Paige, Sidney, and Knopf, Adolph, Stratlgraphlc succession, in, the region northeast of 

Cook Inlet, Alaska: Geol. Soc. America Bull., vol. 18, p. 328, 1907.

46 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna basins, Alaska: U. S. Geol. Survey Bull. 327, pp. 10, 16, 17-18, 19, 1907.
>, MESOZOIC STRATIGRAPHY OF ALASKA

sented on the'.map.47 This account includes a brief description of 

thejithologic character and stratigraphic relations of the rocks and 

lists of fossils, \with a statement of their age as determined by T. W. 

Stanton. \.

These rocks were described by Brooks,48 as the upper member of 

' the rocks which lie correlated with the Skwentna group of the Alaska 

Jjange. This acpount of the Matanuska extension of the Skwentna 

group consists of\ an abstract of the description by Paige and Knopf, 

but the accompanying lists of fossils were given in full. Brooks also 

represented--these rocks on his geologic map 49 as part of the "Upper 

Jura&sdc and upper Middle Jurassic " rocks and not as the Skwentna 

group, thus following the mapping by Paige and Knopf.

Another general description of these rocks, which includes practically all of the account by Paige and Knopf, has been given by Martin and Katz.50

The exposures of Middle Jurassic rocks in the hills between 

Caribou Creek and Nelchina River were reexamined in 1914 by 

Chapin,51 who described them as the Tuxedni sandstone. The description includes a brief statement concerning the distribution 

and character* of the rocks and a discussion of their age and correlation, with 'a list of some fossils collected by Chapin and identified by Stanton.

Stratigraphic description. The Tuxedni sandstone of the 

Matanuska Valley is composed of sandstone and sandy shale. 

The thickness has not been accurately determined but is known 

to be at least several hundred feet and may be a thousand feet 

or more. The formation contains abundant marine fossils and 

was probably deposited wholly in marine waters, although some 

of the sandstone beds contain abundant poorly preserved vegetable remains, mostly water worn_.stieks and stems. The Tuxedni 

sandstone rests upon the Lower Jurassic volcanic rocks, described 

above, but the scarcity of well-marked bedding planes in, those 

rocks makes it difficult to determine whether the contact is conformable or unconformable. The Tuxedni is overlain by the 

Chinitna formation, described below, with apparent conformity.

Age and correlation. The fossils of the Tuxedni sandstone of the 

Matanuska Valley, as now known and as listed in the table (p. 226), 

consist chiefly of marine invertebrates. Some beds contain numer-

«Idem, pi. 2.

48 Brooks, A. H., The Mount McKinley region, Alaska : U. S. Geol. Survey Prof. Paper 

70, pp. 86-87, 1911.

»Idem, pi. 9.

50 Martin, G. C., and Katz, P. J., Geology and coal fields of the lower Matanuska 

Valley, Alaska: U. S. Geol. Survey Bull. 500, pp. 15, 20, 1912.

81 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U. S. Geol. Survey Bull 

668, pp. 21, 32-33, pi. 2, 1918.
JUEASSIC, MATANUSKA VALLEY AND TALKEETNA MOUNTAINS 225

ous fossil sticks and stems of indeterminate character, but only one 

determinable leaf has been collected.

The Tuxedni sandstone of the Matanuska Valley corresponds 

very closely in lithologic and faunal character, as well as in its 

relations to the overlying and underlying rocks, to the Tuxedni 

sandstone of the type district, on the west shore of Cook Inlet.52 

It differs from the Tuxedni sandstone of Cook Inlet in being apparently somewhat thinner and in containing a larger proportion of 

shaly beds than is shown in the type section on Tuxedni Bay. Its 

fauna, especially as represented in the large collection of lot 8567, 

shows no essential difference from that of the Tuxedni sandstone of 

Cook Inlet.

The other Alaskan rocks which carry this fauna and with which 

these beds may be correlated include at least part of the Tordrillo 

formation of the Alaska Range,53 possibly part of the Middle 

Jurassic rocks of the Alaska Peninsula, and the tuffaceous slate of 

the lower Chitina Valley.5 *

The relative position of the Tuxedni sandstone among the'Jurassic 

rocks in other parts of the world has not yet been definitely established. The fossils have not yet been fully studied, but they appear 

to indicate that the Tuxedni sandstone corresponds approximately 

to part of the Middle Jurassic or Lower Oolite of the European classification, possibly being Inferior Oolite or Bajocian.

8567. Second creek entering Boulder Creek from the north above the canyon 

(creek north of extreme west end of Anthracite Ridge), 3% miles up creek. 

G. C. Martin, 1913.

6AK42. North face of Anthracite Ridge near west end, altitude 3,900 feet. 

Adolph Knopf, 1906.

8564. Tributary entering Boulder Creek from the southeast next below East 

Fork. Float, possibly in part Lower Jurassic. G. C. Martin, 1913.

8571. Creek entering Boulder Creek from the north 3 miles above East Fork, 

G. C. Martin, 1913.

8572. Altitude 4,200 feet on ridge west of creek that enters Boulder Creek 

from the north 3 miles above East Fork. G. C. Martin, 1913.

6AK157. Nelchina River 12 miles N. 17° E. of mouth of Billy Creek, 1 mile 

above trail. Adolph Knopf, 1906.

6AK98. Canyon entering Billy Creek from the east 2 miles above its mouth. 

Adolph Knopf, 1906.

6AK88A. Tributary of Caribou Creek from the west one-fourth mile above 

Billy Creek, altitude 4,050 feet. Adolph Knopf, 1906.

6AK88B. Same as 6AK88A. Boulder in stream bed. Adolph Knopf, 1906.

8548. North bank of Caribou Creek half a mile below Billy Creek. G. C. 

Martin, 1913.

52 Martin, G. C., and Katz, F. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 59-64, 1912.

68 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, pp. 87-90, 1911.

"Mofflt, F. H., Geology of the Hanagita-Brenner .region, Alaska: U. S. Geol. Survey 

Bull. 576, pp. 25-27, 1914.
226 MESOZOIC STRATIGRAPHY OF ALASKA

8585. North bank of Caribou Creek three-fourths mile below Billy Creek. 

G. C. Martin, 1913.

6AK196. Alfred Creek 7 miles above its mouth. Adolph Knopf, 1906.

8951. Small gulch tributary to Crooked Creek just north of Albert Creek. 

Theodore Chapin, 1914.

8949. South end of knob northeast of east end of Sheep Mountain. Theodore Chapin, 1914.

8950. North end of knob northeast of east end of Sheep Mountain. Theodore 

Chapin, 1914.

8588. Sheep Mountain at altitude of 3,400 feet on creek flowing southeastward from 6,375-foot peak. G. C. Martin, 1913.

Fossils from Tuxedni sandstone of the MatanusJca Valley °

Rhynchonella..-. __ .. .....

Terebratula.. .. . 

Inoceramus cf. I. ambiguus

Inoceramus cf.I. lucifer Eichwald.

Trigonia cf. T. dawsoni Whiteaves

Camptonectes? . _ ....

Lima cf. L. gigantea Sowerby .

Lima?.-. _ ... ..............

Pleuromya carlottensis WhitThracia cf. T. semiplanata WhitCyprina?. ...... ... . _ . ...

Astarte?-- . .

Pleurotomaria- - . _ . ...

Natica.. ____ ... c_. ........

Phylloceras. ____ .......

Oppelia?. ........ ................

Sonninia?. _ .. __ _ ....

Sonninia? ____________

Stephanoceras cf. S. humphriesiaSphaeroceras cf. S. oblatum

Belemnites _ . ___ ........

t^

X

X

X

X

X

X

X

y

X

X

X

X

X

X

X

X

X

X

6AK22

X

1

X

X

t *

E5

oo

X

X

N

55co

X

6AK157

V

6AK98

X

6AK88A

X

v

X

y

X

6AK88B

X

X

X

X

CO

X

X

X

1

6AK196

y

m 

o

00

X

X

X

v

y

X

y

»

X

X

8 §

X

co

y

»Identified by T. W. Stanton except the plant. 

»Identified by F. H. Knowlton.
JURASSIC, MATANUSKA VALLEY AND TALKEETNA MOUNTAINS 227

UPPER JURASSIC

c OHINITNA FOBMATION

« Historical review. A thick series of shale, accompanied by beds 

of sandstone and conglomerate, overlies the Tuxedni sandstone. 

This shale carries a characteristic fauna similar to that of the Chinitna shale of Cook Inlet.

The presence of this fauna was recognized by Paige and Knopf,58 

who described it as occurring in an undifferentiated lower member oi 

"a continuous stratigraphic succession of younger Middle Jurassic 

and of Upper Jurassic rocks." The rocks containing this fauna were 

not specifically described, nor were the species belonging to this 

fauna listed separately from the Upper Jurassic fossils of the over-* 

lying beds.

A later and more detailed account of the same investigations 57 includes lists of fossils from these beds as identified by T. W. Stanton. 

These fossils were recognized as indicating a fauna of " late Middle 

Jurassic age " occurring in rocks that were briefly described in general terms under the heading " Upper Jurassic." The rocks carrying this fauna were not specifically described.

An abstract of the above-mentioned account, including a quotation 

in full of Stanton's report on the fossils, was given by Brooks 58 

under the heading "Upper Jurassic and upper Middle Jurassic 

rocks of Matanuska basin."

The list of the fossils from these beds, collected by Paige and 

Knopf and identified by Stanton, was quoted by Martin and Katz,59 

but without any description of the strata.

The Chinitna formation of the Matanuska Valley was first described as a distinct formation by Chapin.60 This account includes a 

brief description of the distribution, character, structure, age, and 

correlation of the strata.

Stratigraphic description. The Chinitna formation as exposed 

on Boulder Creek consists of shale and shaly sandstone with lesser 

amounts of conglomerate and massive sandstone. Calcareous concretions are abundant in the shale. This formation apparently 

occurs in a synclinal area in which it overlies the Tuxedni sandstone with apparent conformity and is overlain unconformably by

68 Paige, Sidney, and Knopf, Adolph, Stratigraphic succession in the region northeast 

of Cook Inlet, Alaska: Geol. Soc. America Bull., vol. 18, p. 329, 1907.

57 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska: U. S. Geol. Survey Bull. 327, p. 22, '1907.

68 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper

 70, p. 91, 1911.

68 Martin, G. C., and Katz, F. J., Geology and coal fields of the lower Matanuska Valley, 

Alaska: U. S. Geol. Survey Bull. 500, p. 22, 1912.

80 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U. S. Geol. Survey Bull.

-668, pp. 21, 33-34, pi. 2, 1918.
228 MESOZQIO STRATIGBAPHY OF ALASKA

the Upper Jurassic Naknek formation. The thickness has not been 

accurately measured but is probably several thousand feet.

The occurrence of the Chinitna formation on the headwaters of 

Nelchina River, in the eastern part of the Talkeetna Mountains, has 

not been studied in detail. The rocks at one locality in this area 

were described in Knopf's field notes as blue shale, striking N. 15° 

W., dipping 10° NE., and containing numerous limestone nodules. 

The nodules are similar in lithologic character to float found at the 

same place and containing the fossils of lot 156 (below). The rocks 

at another locality on Nelchina River were described by Knopf as 

fossiliferous sandstone with a gentle eastward dip. The fossils of 

lot 185 (below) were obtained at this place. The formation appar- 

 ently overlies the Tuxedni sandstone and is overlain by the Naknek 

formation in this area, but there is no available information as to 

whether the contacts are conformable or unconformable or as to 

the thickness.

Age and correlation. The Chinitna formation of the Matanuska 

Valley, although containing a fauna very similar to that of the 

Chinitna shale of Cook Inlet and resembling that formation in its 

stratigraphic relations to the underlying and overlying beds, differs 

somewhat from it in containing a larger proportion of sandstone 

and conglomerate. In this respect it bears a closer resemblance to 

the CWoceras-bearing beds of the Shelikof formation of the Alaska 

Peninsula than it does to the CWoceras-bearing beds of the Chinitna 

shale of Cook Inlet.

The occurrence of Cadoceras in these beds shows that they are 

to be correlated approximately with the Callovian of Europe.

Fossils from, Chinitna formation of Matanuska Valley a

Pecten ___ .. _ . .. _ . ___ . _ . ___ ..

Isocardia __ . _ ... __________ . ___ ~

Cadoceras doroschini (Eichwald) _____ _____

8573

X

X

X

X

X

X

8571

X

8576

X

y

X

X

X

X

X

6AK156

X

X

6AK185

v

v

 Identified by T. W. Stanton.

8573. Altitude 3,400 feet on north side of knob 1 mile north of Boulder Creek 

and about 3 miles above mouth of East Fork. G. C. Martin, 1913.

8571. Float from tributary to Boulder Creek from north 3 miles above East 

Fork. G. C. Martin, 1913.
JURASSIC, MATANUSKA VALLEY AND TALKBETFA MOUNTAIN'S 229

8576. Tributary to Boulder Creek from the north 5% miles above East Fork, 

about 3,000 feet up creek, altitude 3,300 feet. R. M. Overbeck, 1913.

6AK156. Near headwaters of Nelchina River, about 10 miles N. 10° E. of 

mouth of Billy Creek, altitude 5,000 feet. Limestone nodules, not in place. 

Adolph Knopf, 1906.

6AK185. Nelchina River 1% miles east of trail crossing, or about 13 miles 

N. 27° E. of mouth of Billy Creek. Sandstone. Adolph Knopf, 1906.

NAKNEK FORMATION

Historical review: The Upper Jurassic rocks of the Matanuska 

Valley include shale, sandstone, and conglomerate that carry the 

fauna'of the Naknek formation of the Alaska Peninsula.

The rocks here referred to the Naknek formation were observed 

in 1898 by Mendenhall,61 who included them in the "Matanuska 

series." This " series," which was referred to the Lower Cretaceous, 

is now known to include a great variety and thickness of rocks ranging in age from Lower Jurassic to late Tertiary. The only Upper 

Jurassic rocks specifically mentioned in Mendenhall's description are 

the1 conglomeratic beds on Nelchina Kiver ("Bubb Creek").

The occurrence of Upper Jurassic strata in the Talkeetna Mountains was indicated by Martin 62 on the basis of fossils of unknown 

derivation found in a sandstone boulder in the bed of Chickaloon 

Kiver.

Upper Jurassic strata were first recognized in this district by 

Paige and Knopf,63 who described very briefly the AuceUa-bearing 

Upper Jurassic sandstone of the upper Matanuska and Nelchina 

valleys.

In a subsequent account of the same investigations,64 Paige and 

Knopf described the Upper Jurassic strata in considerably greater 

detail. This account includes descriptions of the strata, a report by 

T. W. Stanton upon a collection of fossils, and a discussion of the 

stratigraphic relations. These authors did not attempt to separate 

on their map the Upper Jurassic Aucella-be&rmg beds from the Middle Jurassic formations and erroneously included in the Jurassic, both 

on the map and in the description,65 an " andesite-quartz-monzonite 

conglomerate" that is apparently of late Tertiary age.66 They 

also described as Upper Jurassic the conglomeratic tuff and arkose 67

61 Mendenhall, W. C., A reconnaissance from Resurrection Bay to the Tanana River, 

Alaska, in 1898: U. S. Geol. Survey Twentieth Ann. Kept., pt. 7, pp. 307-308, 1900.

02 Martin, G. C., A reconnaissance of the Matanuska coal field, Alaska, in 1905: U. S. 

Geol. Survey Bull. 289, p. 11, 1906.

63 Paige, Sidney, and Knopf, Adolph, Stratigraphic succession in the region northeast 

of Cook Inlet, Alaska: Geol. Soc. America Bull., vol. 18, p. 329, 1907.

04 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna basins, Alaska: U. S. Geol. Survey Bull. 327, pp. 20-23, pi. 2, 1907.

05 Idem, pp. 21, 23.

B6 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U. S. Geol. Survey Bull. 

668, p. 38, 1918.

07 Paige, Sidney, and Knopf, Adolph, op. cit. (Bull. 327), p. 21.
230 MESOZOIO STRATIGRAPHY OP ALASKA

of the Billy Creek-Nelchina divide, which is here referred (p. 310) 

to the Lower Cretaceous.

A description of these rocks, consisting of an abstract of the account by Paige and Knopf but including the statement regarding 

the fossils in full, was given by Brooks 68 under the heading " Upper 

Jurassic and upper Middle Jurassic rocks of the Matanuska basin."

The account by Paige and Knopf was also quoted, with little modification, by Martin and Katz.09

A later account of these rocks, based upon additional field work on 

their northeastern extension in the adjacent part of the Nelchina 

Valley, has been given by Chapin.70 In this account the Naknek 

formation was differentiated from the underlying strata. The account contains a general description of the character and occurrence 

of the rocks, lists of fossils as identified by T. W. Stanton, and a 

discussion of age and correlation.

Some ammonites collected by Martin from the Naknek formation 

on Boulder Creek in 1913 have been described by Reeside.71

Stratigraphic description. The Upper Jurassic rocks of the Naknek formation as exposed on Boulder Creek consist of green sandy 

shale, several hundred feet thick, which rests unconformably upon 

the shale and sandstone of the Chinitna formation and is overlain 

unconformably by Upper Cretaceous and Tertiary rocks. A large 

part of the original thickness of the Upper Jurassic strata was 

probably removed during the erosion interval represented by the 

upper unconformity.

The rocks of the Naknek formation on the headwaters of Nelchina 

River and Billy Creek lie nearly horizontal and cover a large area. 

As exposed in this area, they include beds of shale, sandstone, and 

conglomerate. No details concerning the stratigraphic sequence are 

at hand, but it is known that the conglomerates, although some of 

them may be several hundred feet thick, occur for the most part as 

thin local lenses. The thickness of the formation is certainly more 

than 1,000 feet and is probably several thousand feet. It rests upon 

the Chinitna formation without known unconformity and is overlain, probably conformably, by the Lower Cretaceous rocks described on pages 310-315.

It is possible but by no means certain that the Chisik conglomerate 

of Cook Inlet is represented by a thick massive conglomerate in the

88 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, p. 91, 1911.

69 Martin, G. C., and Katz, F. J., Geology and coal fields of the lower Matanuska Va) 

ley, Alaska: U. S. Geol. Survey Bull. 500, pp. 20-22, 1912.

70 Chapin, Theodore, The Nelchlna-Susitna region, Alaska: TJ. S. Geol. Survey Bull. 

668, pp. 21, 36-38, pi. 2, 1918.

71 Reeside, J. B., jr., Some American Jurassic ammonites of the genera Quenstedticeras, 

Oardioceras, and Amoeboceras, family Cardioceratidae: U. S. Geol. Survey Prof. Paper 

118, pp. 9, 27-28, pi. 9, 1919.
JURASSIC, MATANUSKA VALLEY AND TALKEETNA MOUNTAINS 231

eastern part of the Talkeetna Mountains adjacent to the upper 

Matanuska Valley. An exposure of this conglomerate on Little Nelchina Kiver (" Bubb Creek ") was mentioned briefly by Mendenhall 72 

in a description of the " Matanuska series." The conglomerate was 

also described by Paige and Knopf ,73 who suggested a correlation 

with the Chisik conglomerate in the statement that its position is 

" probably near the base of the Upper Jurassic, like its analogue on 

the west coast of Cook Inlet."

'this conglomerate was described and mapped by Chapin 74 as a 

distinct unnamed formation which he regarded as the probable 

equivalent of the Chisik conglomerate. It was described by Chapin 

as occurring in two belts. In one belt it lies unconformably on 

Lower Jurassic volcanic rocks and is overlain conformably by sandstone and sandy shale of the Nalmek formation. The conglomerate 

of this belt was believed by Chapin to be " with little doubt the 

Chisik conglomerate." The conglomerate of the other belt he discussed as follows: 

The conglomerate on Little Nelchina River and Idaho Creek is with less 

confidence also regarded as Chisik. Its lower contact is concealed, but it is 

believed to lie next above the Chinitna formation, which is of Middle Jurassic 

age. It is known by its fossils to be Upper Jurassic. It is overlain with apparent conformity by Upper Jurassic shales and sandstone of the Naknek 

formation. This conglomerate may be a member of the Naknek formation 

nnd may thus occupy a higher position among the Upper Jurassic rocks than 

the Chisik conglomerate, but probably not, for to assume that it occupies such 

a position is to assume also that the beds were brought to their present position by faulting, no evidences of which were seen at this place. By reason 

of their similar stratigraphic relation to the known Naknek rocks, their 

lithologic similarity, and absence of proof to the contrary the conglomerate on 

Little Nelchina River and the Chisik conglomerate that extends from Tyone 

Creek to Little Oshetna River are believed to be the same.

Age and correlation. The rocks here described are referred to the 

Upper Jurassic and are correlated with the Naknek formation of the 

Alaska Peninsula and of Cook Inlet on the basis of similarity of 

fauna, of lithologic character, and of stratigraphic sequence. The 

presence of the two species of Aucella related to Aucella pallasi 

Keyserling and Aucella bronni Kouillier and of Cardioceras martini 

Keeside is the paleontologic basis of this age assignment and correlation.

72 Mendenhall, W. C., A reconnaissance from Resurrection Bay to the Tanana River, 

Alaska, in 1898: U. S. Geol. Survey Twentieth Ann. Rept., pt. 7, p. 308, 1900.

73 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska: U. S. Geol. Survey Bull. 327, pp. 22, 23, 1907.

74 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U, S. Geol. Survey Bull. 

668, pp. 21, 35-36, pi. 2, 1918.

75 Idem, p. 35.
232

Fossils from Naknek formation of the Matanuska Valley a

Serpula? _________________________

Astarte ____________________ . .........

Tancredia?... .. .....................................

Turbo.......... ........................ .............

I

B

S3

h

B

% CO

sCO

a

6AK136

1

CO CO

a

1

00 1CO

a

a

i^r-4

8

° &, Identified by T. W. Stanton; b, identified by J. B. Beeside, jr.

8574. Lowest outcrop on creek entering Boulder Creek from the northwest 

5% miles above East Fork. Green sandy shale. G. C. Martin, 1913.

8575. Concretions on talus across creek from 8574, probably from about the 

same beds. G. C. Martin, 1913.

8579. Limestone Gulch, tributary to Billy Creek from the east. 300 feet 

below base of Lower Cretaceous limestone. G. C. Martin, 1913.

8583. Limestone hills east of Billy Creek. About 200 or 300 feet below base 

of limestone. G. C. Martin, 1913.

8581. Near Limestone Gap, east of Billy Creek. About 100 or 200 feet below 

base of limestone. G. C. Martin, 1913.

6AK136. One-quarter mile up creek entering Billy Creek from the west, 8 

miles above its mouth. Adolph Knopf, 1906.

8952. North bank of Nelchina River just above Idaho Creek. Sandstone 

embedded with conglomerate. Theodore Chapin, 1914.

8953. Idaho Creek 1% miles above its mouth. Theodore Chapin, 1914.

8954. Ridge between Little Nelchina River and Little Tyone Creek, 2 miles

north of Idaho Creek. Theodore Chapin, 1914.

8955. Yacko Creek on claim " No. 10 above." Near base of Upper Jurassic, 

overlying conglomerate. Theodore Chapin, 1914. 

3317. Boulder in Chickaloon River. G. C. Martin, 1905.

ALASKA RANGE (TENTNA AND SKWENTNA VALLEYS) 

GENERAL FEATURES

The rocks of the Alaska Range, as exposed on Skwentna and 

Kichatna Rivers in the Yentna basin, consist chiefly of Lower (?) 

and Middle Jurassic strata. The Middle Jurassic sediments and the 

intrusive rocks that cut them occur in the synclinal axis of the mountains ; the Lower Jurassic (?) volcanic beds form the eastern foothills. The Middle Jurassic beds are underlain, along the western 

front of the range, by Silurian or Devonian argillite, chert, and 

graywacke. Slaty rocks that are somewhat similar to these Paleozoic 

beds probably underlie the Middle Jurassic and possibly underlie
JURASSIC, ALASKA RANGE 233

the Lower Jurassic (?) beds in the eastern foothills of the range on 

Kichatna Kiver.

The general sequence in this district is shown in the following 

table:

General section of rocks in the Alaska Range on Yentna and Skwentna Rivers

Middle Jurassic: Tordrillo formation (grit, sandstone, and argillite, with some conglomerate and Feet 

limestone) ________-____-_-______ 2, 000-^3,000+

Lower Jurassic (?) : Skwentna group (dacitic and 

basaltic lava and tuff, interbedded with arkose 

and some chert and limestone)__________ 1,000-4,000+

Paleozoic (,?) : Slate and phyllite, with some graywacke and grit, exposed in the Yentna Valley 2,000-3,000

LOWER JTTBASSIC (?) 

SKWENTNA GROUP

Historical review, The Skwentna group, which is possibly of 

Lower Jurassic age, occurs in the eastern foothills of the Alaska 

E,ange on Skwentna and Yentn,a Rivers. These rocks were first described as the Skwentna " series " by Spurr,76 who assigned them to 

the Jurassic on the basis of a correlation with the rocks of the 

Naknek " series " and their geographic position in the general trend 

 of the belt of known Jurassic rocks of southwestern Alaska. They 

were described as the Skwentna group by Brooks,77 who assigned 

them to the " lower Middle Jurassic " on the basis of their stratigraphic position beneath the Tordrillo formation, which is known to 

be of Middle Jurassic age (p. 235), and on the basis of a correlation 

with Mesozoic lava and tuff of the Matanuska Valley, which were 

iormerly considered as belonging in the Middle Jurassic but are 

now regarded (p. 219) as Lower Jurassic and herein named Talkeetna formation.

Stratigraphic description. These rocks were described by Spurr 

as " a series of ancient and somewhat altered volcanics interstratified 

with tuffs. Besides these volcanic rocks there is sometimes carbonaceous chert and beds of arkose whose minerals show an evident 

derivation from granite."

The Skwentna group, according to Brooks,

consists chiefly of a complex of igneous rocks which are largely volcanic. 

Dacites predominate among these volcanic rocks, which include both lavas 

and tuffs. Some basalts were, however, also noted. With the volcanic rocks

78 Spurr, J. E., A reconnaissance in southwestern Alaska in 1898 : U. S. Geol. Survey 

Twentieth Ann. Kept., pt. 7, pp. 149-152, 180, 1900.

77 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Taper 

70, pp. 85-87, 1911.
234 MESOZOIC STRATIGRAPHY OF ALASKA

are associated some arkoses, but these were not studied in detail in the field, 

for they were identified only after microscopic investigation. A few cherts 

and one small belt of black limestone were also found intermingled with the 

volcanic rocks. The whole series is cut by many intrusions.

The thickness of these rooks has not been measured, and there are 

but few data upon which to base an estimate. Brooks 78 believed it 

to be from 1,000 to 4,000 feet or moreAge and correlation. The Skwentna group has yielded no fossils; consequently the only available evidence on its age consists in 

its stratigraphic relation to the associated rocks and its lithologic 

resemblance to other rocks of known age. The basal contact of 

the Skwentna group has never been observed, but, according to 

Brooks,79 "it seems likely that the Skwentna group rests unconformably on the Paleozoic rocks of the Kichatna Valley," which he 

regarded as possibly Silurian or Devonian. The Skwentna group is 

overlain by the Tordrillo formation (p. 235), which includes beds 

that carry a Middle Jurassic fauna. The information at hand indicates that this contact is probably unconformable.

It has been shown by Brooks that these rocks resemble the Lower 

Jurassic lava and tuff of the Matanuska Valley (Talkeetna formation of this report), with which he provisionally correlated them. 

There is a considerable degree of probability in this correlation, but 

it should be pointed out that the Talkeetna formation contains a 

considerable volume of marine deposits and some plant beds, neither 

of which have been recognized in the Skwentna group, and that there 

are notable differences in the lithologic character of the rocks. The 

rocks of the Skwentna group bear a much closer resemblance to the 

porphyry and tuff 80 of the west coast of Cook Inlet and of Iliamna

and Clark lakes, which do not include any known marine deposits 

but which are probably of Lower Jurassic age. The presence of 

chert and limestone suggests that the Skwentna group may possibly 

include Upper Triassic beds life those at Port Graham. (See pp. 

49-50.) Martin 81 has suggested a correlation of the Skwentna group 

with the Triassic or Carboniferous volcanic rocks that include the 

ellipsoidal lava beneath the known Triassic beds of Kenai Peninsula, 

the Nikolai greenstone of the Chitina Valley, and the volcanic rocks 

occurring in this same general position in other parts of Alaska.

78 Brooks, A. H., op. clt, pp. 55, 86. 

78 Idem, p. 87.

80 Martin, G. C., and Katz., P. J., A geologic reconnaissance of the Iliamna region, 

Alaska: U. S. Geol. Survey Bull. 485, pp. 50-59, 1912.

81 Martin, G. C., General features of Kenai Peninsula: U. S. Geol. Survey Bull. 587, 

table opp. p. 32, 1915.
JURASSIC, ALASKA RANGE

MIDDLE JURASSIC 

TORDRILLO FORMATION

235

Historical review. The Tordrillo formation occupies the heart of 

the Alaska Kange along the valleys of Skwentna and Kichatna 

Rivers. It was described originally as the Tordrillo "series" by 

Spurr,82 who referred it tentatively to the Cretaceous, and was subsequently reexamined and redescribed by Brooks,83 who discovered 

the fossils that establish its age as Middle Jurassic.

Stratigraphic description. The Tordrillo formation, according to 

Brooks, consists of a series of grit, sandstone, and fine conglomerate, 

together with argillite and a few layers of limestone. The thickness is between 2,000 and 3,000 feet.

The lower third of the formation includes massive grit and sandstone, with some conglomerate and argillite, the latter mostly in the 

form of slate but locally altered to phyllite. The conglomerate includes pebbles that are apparently derived from the underlying 

Paleozoic rocks. The upper two-thirds of the formation is made 

up chiefly of argillite with some sandstone and a few beds of 

limestone.

On the west side of the Alaska Range the Tordrillo formation 

rests unconformably on the argillite, chert, and graywacke of the 

Tonzona group, which is believed to be of Devonian or Silurian age. 

On the east side of the range, in the Kichatna Valley, it appears to 

overlie unconformably some slate and phyllite that are probably 

Paleozoic and are possibly the equivalent of the Tonzona group. In 

the Skwentna Valley, according to Spurr, it overlies the rocks of the 

Skwentna group.

Age and correlation. The fossils represented in the following 

table show that the Tordrillo formation includes beds that are the 

equivalent of at least part of the Tuxedni sandstone.

Fossils from Tordrillo formation of Alaska Range °

Inoceramus (fragment of large form) _____ . __ .... _

2

X

4 6 7

«Identified by T. W. Stanton.

2. Kichatna River, opposite camp of July 9. A. H. Brooks, 1902. 

4. About 3 miles southeast of Simpson Pass, near camp of July 10. A. H. 

Brooks, 1902. 

6,7. Near Rainy Pass, camp of July 14. A. H. Brooks, 1902.

82 Spurr, J. B., A reconnaissance In southwestern Alaska in 1898: U. S. Geol. Survey 

Twentieth Ann. Kept., pt. 7, pp. 153-155, 183, 1900.

88 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, pp. 87-90, 1911.
236 MESOZOIC STRATIGRAPHY OF ALASKA 

UPPER SUSITNA VALLEY 

GENEBAL FEATURES

In many parts of the upper Susitna Valley there are large areas 

of unfossiliferous, somewhat metamorphic rocks of undetermined 

age that comprise slate, graywacke, and conglomerate, some or all 

of which may possibly be Jurassic. These rocks inclnde the 

"Sushitna slates" described by Eldridge,84 the "slates and schists 

of the Susitna and Talkeetna Valleys " 85 and the " undifferentiated 

Paleozoic rock in the headwater region of the Susitna " 8e described 

by Brooks, the "Jurassic (?) rocks" 87 and the "undifferentiated 

Mesozoic (?) rocks" 88 of the Broad Pass region described by 

Moffit, and the " argillites, slates, and graywackes " of the Chulitna 

Valley described by Capps.89

Although some of these rocks have been tentatively assigned to 

the Mesozoic and even to the Jurassic, no conclusive evidence of 

their age has yet been obtained. In the writer's opinion, there 

is no special reason for assigning them to the Jurassic rather than 

to the Triassic or Cretaceous, and they may even be Paleozoic. Consequently no further reference will be made to them here, and they 

will be discussed in a later chapter with other Mesozoic or' older 

rocks of undetermined age.

The Upper Jurassic (?) conglomerate near the Roosevelt Lakes 

bears a closer resemblance to some of the known Jurassic rocks of 

Alaska than any of the aforementioned slaty rocks and consequently 

will be described below.

UPPER JURASSIC (?)

CONGLOMERATE NEAR ROOSEVELT LAKES

Jurassic rocks are possibly represented by a massive conglomerate 

which crops out a short distance southeast of the Roosevelt Lakes, 

in the southern foothills of the Alaska Range, near the headwaters of Susitna River. This conglomerate was described by 

Moffit 90 under the heading "Triassic rocks" and was mapped as 

an undifferentiated member of the Upper Triassic "slates, tuffs,

84 Eldridge, G. H., A reconnaissance in the Susitna basin and adjacent territory, 

Alaska, in, 1898 : U. S. Geol. Survey Twentieth Ann. Kept., pt. 7, pp. 15-16, 1900.

85 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, p. 65, 1911. 

88 Idem, pp. 68-69.

87 Moffit, F. H., The Broad Pass region, Alaska: U. S. Geol. Survey Bull. 608, pp. 

32-38, 1915.

88 Idem, pp. 39-40.

88 Capps, S. R., Mineral resources of the upper Chulitna region : U. S. Geol. Survey 

Bull. 692, pp. 217-218, 1919.

90 Moffit, F. H., Headwater regions of Gulkana and Susitna Rivers, Alaska, including 

accounts of the Valdez Creek and Chistochina placer districts : U. S. Geol. Survey Bull. 

498, pp. 31-32, °pls. 2, 4A, 1912.
JURASSIC, CHITINA VALLEY 237

arkose, calcareous sandstones, and limestones," although the fact 

that he considered this reference to the Triassic as purely tentative is clearly shown by the statement that the conglomerate " suggests the presence of younger Mesozoic or possibly Tertiary sediments." Mbffit's description follows:

The heterogeneous character of the rocks associated with the Triassic 

limestones and the rocks immediately north of the limestones and apparently overlying them, especially a massive conglomerate a mile or more 

southeast of the Roosevelt Lakes, suggests the presence of younger Mesozoic or possibly Tertiary sediments in this region, but no fossils were found 

to support this possibility. The best exposure of this conglomerate is in 

the mountain between the branch of the tributary of Clearwater Creek 

heading against Windy Creek and the branch heading toward Roosevelt 

Creek. The western face of this mountain is a massive conglomerate made 

up almost entirely of igneous rocks, chiefly dark basic volcanics but with 

a considerable amount of granitic rock in a groundmass of tuffaceous material. The pebbles and cobbles are well rounded, and many of them are 

a foot or more in diameter. This conglomerate, although it forms a large 

part of the mountain, is restricted to a small area, probably less than 2 

square miles. No similar conglomerate was seen at any other locality during the summer.

This conglomerate is at least 400 or 500 feet thick and may 

be 1,000 feet or more. It appears to overlie the Upper Triassic 

strata, but the nature of the contact is not known, and there is 

no other evidence of its age.

Comparison of the conglomerate near the Eoosevelt Lakes with 

the possible equivalents in other districts shows that it bears' a 

strong resemblance to the Upper Jurassic Chisik conglomerate of 

Cook Inlet, described on pages 170-171, and to the similar and presumably equivalent conglomerate described on pages 218, 230-231 as 

occurring at the base of the Upper Jurassic rocks of the Matanuska 

Valley. It also resembles the Lower or Middle Jurassic tuffaceous 

conglomerate near Taral, in the Chitina Valley, described on 

page 238.

CHITINA VALLEY 

GENERAL FEATURES

The rocks of undoubted Jurassic age in the Chitina Valley include 

Middle and possibly Lower Jurassic rocks on the south side of the 

river near its mouth. The Jurassic rocks of the Chitina Valley 

were formerly described as including the Kennicott formation and 

other supposed Upper Jurassic rocks that occur in discontinuous 

areas scattered throughout various parts of the valley. These rocks, 

which are believed by the writer to be chiefly if not wholly Cretaceous, are described on pages 330-349.
238

LOWEE (?) JURASSIC 

TUFFACEOUS CONGLOMERATE NEAR TABAL

A belt of massive conglomerate extends parallel to and from 100 

to 300 feet above the east bank of Copper Eiver from Chitina Kiver 

nearly to Taral. This conglomerate has been described by Moffit 91 

as the lower member of the " Middle Jurassic rocks " afrd mapped 

as "tuffaceous conglomerate." 92 The account by Mofjfit includes 

a brief general description of the occurrence, character, and relations 

of these rocks. According to this description, it is a " massive conglomerate containing well-rounded pebbles and cobbles of argillite, 

diorite, greenstone, and quartz in a tuffaceous matrix." The conglomerate apparently rests unconformably upon Palebzoic (Carboniferous?) schist, although some of the contacts seem to be faults. 

It is at least 500 or 600 feet thick. The overlying beds consist of 

the Middle Jurassic fossiliferous tuff described on pages £39-240.

There is no available evidence as to the age of this conglomerate, 

except that it is younger than the Paleozoic (Carboniferous?) schist, 

which lies unconformably beneath it, and older than the Middle 

Jurassic tuff, which lies conformably (?) above it. Thd tuff carries 

the fauna of the Tuxedni sandstone and consequently belongs in the 

lower part of the Middle Jurassic. Moffit has assumed, in the absence of evidence to the contrary, that the conglomerate, being 

closely associated with the Middle Jurassic tuff and being somewhat 

akin to it in lithologic character, should presumably be regarded as 

its basal member and assigned with it to the Middle Jurassic. This 

reasoning is valid, and this assignment, if the local evidence alone is 

considered, should undoubtedly be accepted. But comparison of the 

local rocks with the Jurassic sections in other parts of Alaska shows 

that this tuffaceous conglomerate is entirely unlike,1 the Middle 

Jurassic rocks of most other Alaskan districts and thiat it bears a 

closer resemblance to some of the Lower Jurassic rocks of Cook 

Inlet and other districts. (See pp. 134, 220.) There is ,an important 

difference in that the Lower Jurassic beds of the Cook Inlet and 

Matanuska districts are composed mainly of volcanic, detritus and 

contain only very subordinate amounts of conglomerate. Such a 

difference may, however, be merely the expression o| purely local 

conditions. The fact of general significance is that vplcanic conditions were dominant along the Alaskan coast in Lower Jurassic 

rather than in Middle Jurassic time. There is consequently a presumption in favor of assigning volcanic beds of probable early 

Jurassic age to the Lower rather than to the Middle Jurassic. The

81 Mofflt, F. H., Geology of the Hanagita-Bremner region, Alaska: U. S. Geol. Survey 

Bull. 576, pp. 17, 18, 25-27, 1914. 

81 Idem, pi. 2.
JURASSIC, CHITINA VALLEY 239

argument is weakened, however, in this particular case by the fact 

that the undoubted Middle Jurassic rocks that overlie the conglomerate (see below) are also composed largely of volcanic detritus; 

but it may possibly be assumed that the volcanic detritus in the overlying undoubted Middle Jurassic rocks is of secondary rather than 

primary origin and is derived from Lower Jurassic volcanic rocks.

The only conclusion that can be reached at present regarding the 

age of the tuffaceous conglomerate is that it is probably early Jurassic 

and may be either Middle Jurassic or Lower Jurassic.

MIDDLE JURASSIC

TUFFACEOUS SLATE NEAR THE MOUTH OF CHITINA BIVEB

The fossiliferous tuffaceous beds described by Moffit 93 as occurring on the south bank of Chitina Eiver near its mouth and on the 

mountain south of Taral Creek include the upper fossiliferous member of the " Middle Jurassic rocks " as described in the text and the 

"tuffaceous slate" as represented on the map. The account by 

Moffit includes a brief general description of the occurrence, character, and relations of these beds; lists and statements regarding the 

age of the fossils, contributed by T. W. Stanton; and a general discussion of the possible relations of these rocks to the Mesozoic rocks 

of other Alaskan localities. The description is quoted below:

The fossiliferous tuffaceous beds here grouped with the conglomerate are 

exposed on the south side of Chitina River near its mouth and form prominent 

cliffs along the river. They lie immediately east of the conglomerate and are 

thought to overlie it. The beds are composed of a dark fine-grained sandstonelike rock, slightly calcareous and showing numerous small flakes of mica on 

the cleavage surface. The rock is much jointed, slightly altered, and breaks 

down readily under the influence of the weather, forming talus slopes of angular platy fragments. A considerable amount of this rock is exposed along 

Chitina River, but it was not recognized farther south along Copper River, 

although its presence there was expected. Several small areas of unaltered 

brownish-gray sandstone found east of Taral, however, may represent a phase 

of the tuffaceous beds, now largely removed by erosion. On the ridge south of 

Taral Creek this sandstone contains much quartz, numerous grains of clear 

unaltered feldspar, and flakes of biotite in a calcareous cement, and also some 

small black spots which are thought to be organic remains but which are too 

imperfect for identification.

These rocks rest with apparent conformity upon the tuffaceous 

 conglomerate described above. (See pp. 238-239.) The thickness 

lias not been measured but is probably at least several hundred feet. 

"No overlying beds have been observed.

83 Moffit, F. H., Geology of the Hanagita-Bremner region, Alaska: U. S. Geol. Survey 

Bull. 567, pp. 17, 18, 25-27, pi. 2, 1914.
240 MESOZOIO STRATIGRAPHY OF ALASKA

Several small collections of marine invertebrate fossils have been 

obtained from a locality of indeterminate stratigraphic position, 

but probably in the lower part of the formation. The faunay 

though small, is characteristic and shows that the rocks are of Middle Jurassic age and are the general equivalent of the Tuxedni 

sandstone of Cook Inlet, described on pages 140-158.

Middle Jurassic fossils from Chitina Valley °

Leda?._ ....-. ................................ .......................

7231

X

x.

X

7232

X

7233

X

X

0 Identified by T. W. Stanton.

7231. South bank of Chitina River about miles above its mouth. Theodore Chapin, 1911.

7232. 7233. Same locality as 7231. F. H. Moffit, 1911.

NUTZOTIN MOUNTAINS 

GENERAL FEATURES

The presence of Upper Jurassic rocks in the Nutzotin Mountains 

is indicated'by the fossils, notably by the occurrence of a supposed 

Upper Jurassic species of Aucella. It is probable that a great thickness of Jurassic rocks exists in this district, but complex structure, 

metamorphism, and the lack of detailed stratigraphic studies make 

it impossible to determine just what part of the Jurassic is locally 

represented, or how much of the known section is of Jurassic 

age. The uncertain features include not only the position of the 

boundary between the Upper Jurassic Aucetta-bQ&Ting becls and the 

lithologically similar Lower Cretaceous Aucella-bea,Tmg beds, but 

the differentiation of the Jurassic and Cretaceous Aucella-loQSiTmg 

beds from an apparently unfossiliferous metamorphic complex that 

possibly includes older rocks of similar lithologic character.

The general sequence of the Mesozoic and associated rocks west of 

Chisana River, in the Nutzotin Mountains and the valleys southwest 

of them, was represented by Moffit and Knopf 94 as follows :

Quaternary _______ Gravels, till, and other unconsolidated deposits.

I Volcanic rocks. 

Lignite-bearing formation, including shales, 

sandstones, lignite beds, etc.

M Moffit, F. H., and Knopf, Adolph, Mineral resources of the Nabesna- White River 

district, Alaska : U. S. Geol. Survey Bull. 417, p. 16, 1910.
JURASSIC, NUTZOTIN MOUNTAINS 241

JurassicShales of Jacksina Creek.

Shales, slates, and graywackes of the Nutzotiu

Mountains. 

Triassic_______..___." Thin-bedded limestone of Cooper Creek.

Lavas and pyroclastic beds tuffs, volcanic

breccias, etc. 

Shales of Skolai Pass. 

Massive limestone.

Shales with some tuffs and lava flows. 

Basic lavas and pyroclastic beds, with some

shale and limestone beds.

The same authors indicated the correlation of these rocks with 

those of the'Chitina Valley as in the following table: 95

Correlation of the formations on the east and south sides Of the Wrmgell

Hiountains

Carboniferous or later__

Carboniferous.

Era System

[Tertiary (Eocene) ..... 

Cretaceous(?)..__ _

Upper Jurassic _ ....

East side of Wrangell 

Mountains

Volcanics, shales, sandstones, 

lignite. Unconformity.

region. 

Slates, graywackes, and conglomerates of the Nutzotin 

Mountains.

canics.

South side of Wrangell 

Mountains

Volcanics, lignite-bearing beds. 

Unconformity.

Kennicott formation. Unconformity.

Chitistone limestone.

The general sequence of the rocks in the Nutzotin Mountains 

between Chisana River and the international boundary was indicated by Capps 96 as below.

Quaternary:

Glacial deposits, gravels, volcanic ash, peat, and other unconsolidated materials.

Glacial morainal deposits, with associated lava flows. 

Tertiary:

Conglomerates and unconsolidated gravels.

Sandstones, shales, conglomerates, and tuffs, locally containing

lignite. 

Cretaceous:

Shales, slates, and graywackes. 

Jurassic:

Shales, slates, graywackes, and conglomerates. 

Triassic:

Thin-bedded limestone of Cooper Pass. Possibly includes also part 

of the slates and graywackes of the Nutzotin Mountains.

"o Moffit, F. H., and Knopf, Adolph, op. cit., p. 31.

98 Capps, S. R., The Chisana-White River district, Alaska : U. S. Geol. Survey Bull. 630, 

pp. 29-30, 1916.
242 MESOZOIC STRATIGRAPHY OF ALASKA

Carboniferous:

Lava flows.

Massive limestone.

Lava flows and pyroclastic rocks.

Massive limestones and shales.

Basic lavas and pyroclastic beds, with minor amounts of sediments. 

Devonian:

Lavas and pyroclastic beds, with considerable black shale.

In the following description only the Aucella-be&r'mg shale on 

the border of the Nutzotin Mountains will be considered. It is 

highly probable that a large part of the apparently unfossiliferous 

slate and graywacke that constitute the main mass of the Nutzotin 

Mountains is also Upper Jurassic. As these rocks probably include 

Lower Cretaceous strata, however, and may also include some Jurassic beds older than the Upper Jurassic, as well as rocks that are even 

pre-Jurassic, and as the Upper Jurassic members of this aggregate 

have not been differentiated, the doubtful rocks will be classed with 

similar rocks of more or less uncertain age described on pages 

480-487.

UPPER JURASSIC

AUCELLA-BEAR1NG BEDS OF NUTZOTIN MOUNTAINS

Historical review. The Upper Jurassic Aucella-bea,Ying beds of 

the Nutzotin Mountains were first described by Brooks 97 as a part 

of the "Nutzotin series." The "Nutzotin series" as described by 

Brooks was a large aggregate which included the Carboniferous 

limestone of the upper White River and other pre-Jurassic rocks. 

It was assigned to the Carboniferous and Devonian. The Jurassic 

part of the original "Nutzotin series" includes part of the slate, 

graywacke, and associated beds exposed on Nabesna River, which 

Brooks considered as representing some of the older members of the 

"series," although they are now known to include some of the 

younger members. These rocks were described only briefly and in 

general terms.

The next account of these rocks was given by Mendenhall and 

Schrader 08 and was based upon the observations of Schrader. In 

this account these Jurassic rocks were included in what was described 

very briefly as the "Mesozoic series," which comprised rocks supposed to range from Triassic to Lower Cretaceous. Although the 

presence of Jurassic fossils was recognized by Stanton in the collections, no lists or account of the occurrence of the fossils and no 

specific description of the Jurassic strata were given.

87 Brooks, A. H., A reconnaissance from Pyramid Harbor to Eagle City, Alaska, including a description of the copper deposits of the upper White and Tanana Rivers: U. S. 

Geol. Survey Twenty-first Ann. Rept., pt. 2, pp. 359-360, 369, pi. 47, 1900.

88 Mendenjiall, W. C., and Schrader, F. C., The mineral resources of the Mount Wrangell 

district, Alaska: U. S. Geol. Survey Prof. Paper 15, pp. 36-37, 1903.
JURASSIC, NUTZOTIN MOUNTAINS 243

Further mention of these rocks was made by Brooks in his summary of the geology of Alaska," where he pointed out that Schrader 

had shown that most of the rocks of the Nutzotin Mountains are of 

Mesozoic age and formally abandoned the name "Nutzotin series" 

as a stratigraphic term.

The Jurassic Aucella-bea,Ymg beds of this district constitute part 

of the aggregate described as "Mesozoic rocks" and mapped as 

" Mesozoic sediments " by Moffit and Knopf.1 This account contains 

descriptions of the supposed Jurassic strata, lists of fossils as 

determined by T. W. Stanton, and a discussion of the correlation of 

these rocks with those of neighboring districts.

These beds have been described also by Capps,2 who did not 

differentiate them from the closely associated Lower Cretaceous 

strata. The area described by Capps adjoins and is the southeastern 

extension of the area described by Mendenhall and Schrader and by 

Moffit and Knopf. The account by Capps, like the earlier descriptions, was based on reconnaissance investigations and consequently 

includes only a general description. It is accompanied, however, by 

lists of fossils as determined by T. W. Stanton.

Stratigraphic description. The Upper Jurassic rocks of the Nutzotin Mountain district west of Chisana Kiver were described by 

Moffit and Knopf 3 as follows:

The Jurassic system is represented in the Nabesna-White district by banded 

shales or slates, graywacke, and conglomerate. With these are associated 

sandstone and limestone in minor amount. This group of rocks is not well delimited and, as will be seen later, probably includes some Triassic sediments 

and possibly some of Cretaceous age. 

Jurassic fossils were collected from thin-banded gray and black shales on 

the east side of Notch Creek opposite the mouth of Wilson Creek and from 

dark shales on the west side of Jacksina Creek 4 miles above its mouth. 

Schrader found a few imperfect Jurassic fossils on the east side of Nabesna 

River almost directly opposite the locality last named.

The Upper Jurassic rocks of the Nutzotin Mountains east of Chisana Kiver have not been differentiated from the closely associated 

and somewhat similar Lower Cretaceous strata. The following descriptions, given by Capps,4 consequently apply in general to both 

the Jurassic and the Cretaceous beds:

"Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 

45, pp. 230, 231, jl906.

1 Moffit, F. H., and Knopf, Adolph, Mineral resources of the Nabesna-White River district, Alaska: U. S. Geol. Survey Bull. 417, pp. 16, 27-32, pi. 2, 1910.

2 Capps, S. R., The Chisana-White River district, Alaska : U. S. Geol. Sur.vey Bull. G'M, 

pp. 47-53, pi. 2, 1916.

3 Mofflt, F. H., and Knopf, Adolph, op. cit., p. 28. 

* Capps, S. R., op. cit, pp. 31, 50, 51, 52.
244 MESOZOIC STRATIGRAPHY OF ALASKA

Shales and graywackes of Jurassic age have been recognized on Bonanza 

Creek, but their upper and lower limits were not determined. The fossiliferous 

rocks of Jurassic age lie stratigraphically above the thick section of unfossiliferous sediments which forms the Nutzotin Mountains, and the lower beds may 

be either Triassic or Jurassic, or they may be in part Jurassic and in part older.

The rocks that have yielded Jurassic and Cretaceous fossils on upper Bonanza Creek are dominantly shales and argillites, with much less interbedded 

graywacke than is present in the sediments which form the main mountain 

mass. Some fine conglomerates are present, and a little impure limestone was 

seen, but the shales preponderate greatly. The proportion of graywacke is 

greatest in the lowest part of the section exposed and decreases upward.

So many uncertain factors enter into such estimates as can be made of the 

thickness of the Mesozoic beds that only round numbers can be used. Where 

they are most extensive, in the Nutzotin Mountains, the unfossiliferous argillite and graywacke beds are so intricately folded and faulted that the beds 

may be many times reduplicated in any section examined across the range. 

They are continuously exposed, however, for a distance of 13 miles along 

Chisana Canyon and form mountains on both sides of the river which reach 

heights of 5,000 to 7,500 feet above the stream. It seems certain that the beds 

must be many thousand feet thick to form this mountain range. The younger, 

fossiliferous slates of known Jurassic and Cretaceous age, as exposed on Bonanza and Chathenda creeks, are of less intricate structure, for they have rather 

uniform monoclinal dips to the southwest. They may also be reduplicated by 

faulting, but if the series is not reduplicated the beds have a minimum thickness of 3,000 feet and may exceed that figure.

Structurally above the typical slates and graywackes of the Nutzotin Mountains, in the vicinity of the Chisana placer mines, is a series of shales and 

graywackes, with some conglomerate, which has yielded fossils that are possibly of Upper Jurassic age. Its lower limit is not known, but its upper part 

merges, without any observed stratigraphic break, into rocks that are similar 

in lithology but bear Lower Cretaceous fossils.

Age md correlation. The supposed Upper Jurassic Aucella-bearing beds bf the Nutzotin Mountains have yielded the fossils listed 

in the following table. These fossils have been referred to the 

Upper Jurassic because they include a species of Aucella that is 

related to the supposed Upper Jurassic species Aucella brormi 

Rouillier. The other fossils listed in the table are not characteristic 

of any horizon more definite than Jurassic or Cretaceous. The 

presence of Aucella cf. A. bronni is suggestive of a correlation with 

the Naknek formation of the Alaska Peninsula.

Fossils from Upper Jurassic Aucella-bearing beds of Nutzotin Mountains °

Astarte? .....................................

Tancredia?... ..-..-.--..-......-..--.........

Undetermined pelecypods __________

(1443)

X

(1449)

v

(1454)

X

(1456)

X

X

»

5722

X

5723

X

8809

< Identified by T. W. Stanton.
JURASSIC, SOUTHEASTERN' ALASKA 245

(1443). Head of Nabesna River, locality 26 O. State talus apparently derived from a series composed of limestone or massive slate. F. C. Schrader, 

1902.

(1449). Nabesna River east of camp of August 1, vicinity of Knob Point. 

Dark slaty limestone. F. C. Schrader, 1902.

(1454). Nabesna River 27 E. "From the same locality as 1449 but at a 

little higher geologic horizon." F. C. Schrader, 1902.

(1456). Nabesna River, mountain east of camp of August 1. Dark impure 

slaty limestone, associated with graywacke, shale or slate, sandstone, and 

conglomerate " at a still higher horizon than 1454." F. C. Schrader, 1902.

5722. Trail of Notch Creek. F. H. Mofflt, 1908.

5723. Bluff near mouth of Jacksina Creek. From hard shale, much crushed 

and slickensided. Adolph Knopf, 1908. 

8809. Claim No. 14 on Bonanza Creek. Black shale. S. R. Capps, 1914.

The fossils represented by the following list 5 are possibly also 

Upper Jurassic. They are obtained, however, from shale that occurs in close association with supposed Paleozoic rocks and that has 

unknown relations to the other Mesozoic rocks of the district. The 

fossils themselves contain no intrinsic evidence of their age, other 

than that it is Mesozoic and post-Triassic.

9109. Bryan Creek. From sandy shales apparently interbedded with supposed Carboniferous lavas. S. R. Capps, 1914: 

\ Terebratula sp. 

^ Inoceramus sp. 

Pecteh sp. 

Pecten? sp. 

Alaria? sp.

Ammonite (fragmentary imprint of an undetermined genus). 

This lot is certainly Mesozoic and not older than Jurassic. The collection 

is too small and fragmentary for closer determination.

SOUTHEASTERN ALASKA 

. GENERAL SEQUENCE

Although Jurassic rocks cover considerable areas in southeastern 

Alaska, the Jurassic sequence is by no means complete, several of 

the characteristic Jurassic formations and faunas that are so well 

developed elsewhere in the southern part of Alaska apparently being 

absent here. The next younger marine sedimentary beds above the 

Triassic are the supposed Upper Jurassic AuceUa-be&ring beds. The 

interval between the Upper Triassic and the Upper Jurassic probably includes some volcanic rocks that may be Lower or Middle 

Jurassic and may be represented by some of the unfossiliferous 

metamorphic rocks, chiefly slate, graywacke, and greenstone. The 

age and relations of these metamorphic rocks are in general highly 

problematic. Some of these rocks have been regarded as the metamorphic equivalent of the Lower Cretaceous AuceUa-bQ&rmg beds,

5 Stanton, T. W., cited by Capps, S. R., op. cit, p. 53. 

49448 26 17
246 MESOZOIC STRATIGRAPHY OF ALASKA

and this interpretation undoubtedly is in part correct. (See pp. 

375-383.) Others have been assigned to the Carboniferous, for which 

there apparently is strong evidence. See pp. 93-94.) Another part 

of these rocks contain Aucellas of the Jurassic type. Still others, 

which have been included in the " Berners formation," contain poorly 

preserved fossil plants which indicate a Jurassic or Lower Cretaceous age, the evidence, though by no means conclusive, favoring an 

assignment to the Jurassic. The evidence from these plants and 

from the supposed Jurassic Aucellas is the only paleontologic evidence that Jurassic rocks are present in southeastern Alaska.

In assigning the unfossiliferous or poorly fossiliferous rocks of 

southeastern Alaska to the Jurassic, to the Cretaceous, or to the preJurassic the writer has used a combination of paleontologic and 

physical evidence. The Aucellas of the Jurassic type occur in or 

associated with beds that contain volcanic deposits and do not contain granitic boulders. The Aucellas of the Cretaceous type occur 

in beds that contain only reworked volcanic material and are interbedded with conglomerate containing granitic boulders. This occurrence is in harmony with the facts known in other parts of Alaska, 

where volcanic beds are not known in the Cretaceous rocks and 

where the larger masses of granitic rocks are believed to have been 

intruded in early Jurassic time. It has been assumed, therefore, 

that if the beds contain unreworked volcanic material they are 

probably pre-Cretaceous or post-Cretaceous; if they are intruded by 

granitic rocks they are probably early Jurassic or pre-Jurassic; and 

if they contain boulders of granitic rocks they are probably late 

Jurassic or, more likely, post-Jurassic. Additional evidence on the 

age of the rocks may be obtained from the apparent continuity or 

discontinuity of the succession. For example, it is believed that 

beds which directly overlie the known Triassic rocks, with no evidence or with slight evidence of unconformity, like some of the 

interbedded sedimentary and volcanic strata of Gravina Island and 

near Juneau, are probably Jurassic rather than Cretaceous, whereas 

beds which overlie the Triassic or older rocks with a more evident 

unconformity and without the intervention of rocks of transitional 

character, or beds which are separated from the Triassic rocks by a 

considerable thickness of intervening strata, are more likely to be 

Cretaceous than Jurassic. All these criteria ought to be used with 

caution, and little confidence can be placed in one kind of evidence 

alone; but when several kinds of evidence agree, the age assignments 

may be made with considerable confidence.

The supposed Lower or Middle (?) Jurassic rocks of southeastern 

Alaska include breccia, tuff, and lava on Gravina Island, the Thane 

volcanic group of the Juneau district, and possibly the melaphyre
JUEASSIC, SOUTHEASTERN ALASKA 247

breccia of the Wrangell district. The Jurassic rocks of Gravina 

Island and the Juneau district are included in the following sections:

Section of Mesozoic rocks on Gravina Island 6

Feet 

Lower Cretaceous (?) : Conglomerate, graywacke, and

black slate with Belemnites_ ____ 800± 

Unconformity. 

Upper Jurassic: Slate and limestone interbedded with tuff

and containing Aucelld- 1,200±

Lower or Middle Jurassic (?) : Breccia, tuff, and lava 

Unconformity (?). \ 

Upper Triassic: Limestone, slate, and conglomerate 1, 600±

StratigrapUic section near Juneau 1

Upper Jurassic (?) :

Douglas Island volcanic group (melaphyre flows, tuff, and agglomerates).

Treadwell slate (black clay slate, with some conglomerate and considerable graywacke). 

Concealed (Gastineau Channel). 

Lower or Middle Jurassic (?) : 

Thane volcanic group: 

Melaphyre tuff. 

Limestone. 

Tuff and slate. 

Upper Triassic:

Gastineau volcanic group: 

Slate.

Andesitic tuff.

Calcareous slate with Upper Triassic fossils. 

Andesitic lava with local lenses of slate. 

Triassic or older:

Perseverance slate (clay slate). 

Paleozoic, with perhaps some infolded Triassic:

Clark Peak schist (schistose rocks derived from slate, sandstone, 

limestone, and conglomerate).

The breccia, tuff, and lava of Gravina Island overlie the Upper 

Triassic rocks unconformably (?) and grade upward into finergrained tuff which is interbedded with slate and limestone containing fossils that are probably Upper Jurassic. The Thane volcanic 

group rests with apparent conformity on the andesitic tuff, lava, and 

interbedded fossiliferous Upper Triassic sediments that make up 

the Gastineau volcanic group. The melaphyre breccias of the 

Wrangell district are known only in contact with metamorphic rocks 

of undetermined age and with granitic intrusive rocks.

9 Complied by the writer from Information given by Chapin (U. S. Geol. Survey Prof. 

Paper 120, pp. 83-100, 1918).

7 After Eakin, H. M., and Spencer, A. C., Geology and ore deposits of Juneau, Alaska: 

U. S. Geol. Survey Bull. (in preparation), with age assignments by the writer.
248 MESOZOIG STRATIGRAPHY OF ALASKA

None of these supposed early Jurassic rocks have yielded any 

fossils. They are assigned to the Lower or Middle Jurassic because 

of their position relative to the Upper Triassic rocks of Gravina 

Island and near Juneau and relative to the Upper Jurassic rocks 

of Gravina Island and because of their general similarity to the 

Lower Jurassic volcanic rocks of Cook Inlet, the Matanuska Valley, and Graham Island, B. C., and to the Middle Jurassic volcanic 

rocks of Graham Island and the lower Chitina Valley.

The supposed Upper Jurassic rocks of southeastern Alaska in- 

. elude slate, limestone, and tuff on Gravina Island; some graywacke, 

slate, argillite, conglomerate, and greenstone on Chichagof and 

Baranof islands; the Treadwell slate and Douglas Island volcanic 

group of the Juneau district; a part of the "Berners formation" 

of Berners Bay; some sandstone and volcanic rocks at Windfall 

Harbor, on Admiralty Island; and perhaps some andesitic lava 

interstratified with tuff, conglomerate, and graywacke on Prince of 

Wales Island.

The slate, limestone, and tuff of Gravina Island (see section 

on page' 247) rest unconformably (?) on the supposed Lower or 

Middle (?) Jurassic breccia, tuff, and lava; are overlain unconformably by supposed Lower Cretaceous conglomerate, slate, and 

graywacke; and contain Aucella of the Jurassic type. The graywacke, slate argillite, conglomerate, and greenstone of Chichagof 

and Baranof islands are underlain conformably (?) by undifferentiated metamorphic rocks, part of which may be Upper Triassic, and contain Aucella of the Jurassic type. The Treadwell 

slate and the overlying Douglas Island volcanic group have 

yielded no fossils and have been assigned tentatively to the Upper 

Jurassic, because, as is shown in the section on page 247, they appear to overlie the supposed Lower or Middle (?) Jurassic rocks 

composing the Thane volcanic group, because they lie in the 

southern extension of the supposed Upper Jurassic rocks included 

in the "Berners formation," and because they contain volcanic 

beds. The "Berners formation" consists of slate and graywacke, 

with some interbedded greenstone, and contains in its upper part 

fossil plants which Knowlton believes to be probably Upper 

Jurassic. It is now separated into several mapped units of different ages. The supposed Upper Jurassic rocks of Windfall Harbor consist of sandstone interstratified with volcanic sediments 

which occur in close but undetermined relations with Permian 

rocks and which have yielded a species of Pecten that is " probably 

Jurassic." The rocks of Prince of Wales Island that are possibly 

Upper Jurassic include lava, tuff, conglomerate, and graywacke 

which have yielded no fossils but which are assigned tentatively
JUBASSIC, SOUTHEASTERN ALASKA 249

to the Upper Jurassic because they contain volcanic members and 

rest unconformably on granite intrusive rocks,

LOWER OB MIDDLE (?) JURASSIC

BRECCIA, TUFF, AND LAVA OF GRAVINA ISLAND

Historical review. The supposed early Jurassic volcanic rocks 

of Gravina Island were mapped by Brooks 8 as part of the Vallenar 

"series," which includes Devonian limestone, schist, and slate and 

associated greenstone. Brooks gave no specific description of the 

rocks that are now believed to be Jurassic. These rocks were also 

mapped by F. E. and C. W. Wright,9 without specific description, 

as part of the "Upper Carboniferous greenstone lava flows interstratified with volcanic tuffs and black slate" and as part of the 

" undifferentiated Paleozoic rocks." They were described by 

Smith 10 as "andesitic effusive rocks" of supposed Jurassic or 

Cretaceous age. They are the "lower series of purely igneous material" in the "Upper Triassic or Jurassic rocks" described by 

Chapin,11 whose description includes an account of the distribution, 

character, stratigraphic relations, structure, origin, age, and correlation of not only these supposed early Jurassic volcanic rocks but 

of the overlying beds, which are described on pages 252-254 as probably Upper Jurassic, and of the slate and schistose greenstone of 

Tongass Narrows, which the writer believes may be Paleozoic.

Stratigrapkic description. The supposed Lower or Middle Jurassic breccia, tuff, and lava of Gravina Island (see section on p. 24T) 

are part of the rocks which Chapin mapped as "greenstone and 

slate " and which are made up of an interbedded series of altered tuff, 

flows, and black slate, with some intrusive rocks, occurring on Gravina and Revillagigedo islands. These rocks, according to Chapin, 

consist essentially of volcanic breccia and tuff with interbedded black 

slate and water-laid fine-grained tuffaceous sediments. The detailed 

sequence of the volcanic rocks of Gravina Island has not been worked 

out. In general they may be divided into two parts a lower series 

of purely igneous material, mainly coarse pyroclastic rocks and 

breccia, which are here referred tentatively to the. Lower or Middle 

Jurassic, and an upper series of mixed water-laid tuff, black slate, 

and limestone, with porphyritic basic rocks of similar composition, 

evidently partly intrusive and partly explosive, which are described

6 Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska: U. S. 

Geol. Survey Prof. Paper 1, pp. 42-43, pi. 2, 1902.

 Wright, F. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pis. 1, 2, 1908.

10 Smith, P. S., Notes on the geology of Gravina Island, Alaska: U. S. Geol. Survey 

Prof. Paper 95, pp. 104-105, fig. 35, 1915.

11 Cbapin, Theodore, The structure and stratigraphy of Gravina and Revillagigedo 

Islands, Alaska: U. S. Geol. Survey Prof. Paper 120, pp. 95-97, fig., 11, 1918.
250 * MESOZOIC STRATIGRAPHY OF ALASKA

(pp. 252-254) as probably Upper Jurassic. No sharp line separates 

the two parts, which Chapin did not differentiate on his geologic 

map. The black slate passes into green fissile tuff and this into more 

massive varieties, so that as a rule a sharp line of contact can not 

be drawn between them. By more detailed work the lower purely 

volcanic material might be separated from the upper mixed sedimentary and igneous material. The limestone bodies are too small 

to be shown on a map.

The base of the volcanic rocks is evidently the coarse breccia that 

overlies the Upper Triassic sediments of the west coast of Gravina 

Island. This breccia occupies the southern part of Dall Ridge and 

portions of California Ridge. It is a fine-grained green rock with 

large angular fragments set in a dense matrix of the same composition. It overlies the Upper Triassic rocks with apparent conformity according to Chapin but with probable unconformity according to Smith.

The volcanic breccia at the base of the series is evidently the 

product of volcanic explosions. The stratification of much of this 

igneous material and the conformable intercalations of slate and 

limestone show that at least portions of it were deposited in water. 

The pillow-like structure of some of the flows that occur with the 

fragmental rocks indicates that they also were subaqueous.

Age and correlation. No fossils have been found in the supposed Lower or Middle Jurassic breccia, tuff, and lava of Gravina 

Island. The only local evidence on their age is that they overlie 

Upper Triassic rocks, with apparent conformity, according to 

Chapin, but with probable unconformity, according to Smith, and 

grade upward into finer-grained tuff interbedded with slate and 

limestone containing probable Upper Jurassic fossils. The local 

evidence therefore indicates that these rocks are either Lower or 

Middle Jurassic.

On Graham Island, one of the Queen Charlotte group, according 

to MacKenzie,12 are the Maude formation, which is Lower Jurassic, 

and the Yakoun formation, which is Middle Jurassic. The Maude 

formation is composed of a lower part, made/up of banded slaty 

and flaggy argillite, in places carbonaceous, and an upper part, consisting of feldspathic sandstone. Partly crystalline bituminous 

massive limestone is provisionally classed with the Maude formation. 

Near the top of the formation, where it begins to grade into the 

overlying Yakoun formation, the sandstone contains igneous material. The Maude formation, according to Stanton,13 contains characteristic Jurassic (probably Lower Jurassic) fossils. Some Upper

12 MacKenzie, J. D., Geology of Graham Island, B. C.: Canada Geol. Survey Mem. 88, 

pp. 39-51, 1916. 

18 Idem, pp. 46-47.
JURASSIC, SOUTHEASTERN ALASKA 251

Triassic fossils were' found in detached areas of rocks which were 

questionably referred to the Maude formation but which are more 

than 50 miles from any rocks of undoubted Maude age. The conformably overlying Yakoun formation consists chiefly of andesitic 

and basaltic pyroclastic rocks including water-laid agglomerate and 

and tuff, conglomerate, and lava, with possibly some intrusive rocks. 

Fossils contained in the tuff and tuffaceous sandstone, according to 

Stanton,14 indicate a Jurassic age, the ammonites in two lots suggesting a correlation with the Middle Jurassic Tuxedni sandstone 

of Cook Inlet.

The character and position of these rocks suggest a correlation* 

also with the Lower Jurassic agglomerate and tuff of Seldovia and 

of the Matanuska Valley or with the Middle Jurassic tuffaceous slate 

of the lower Chitina Valley.

MELAPHYRE. BRECCIA OF THE WRANGELL DISTRICT

The supposed Jurassic rocks of the Wrangell district consist of 

schistose melaphyre breccia (greenstone) with intercalated tuff 

and flows and beds of slate and graywacke. These rocks were described by Buddington 15 as follows:

The rocks assigned tentatively to the Jurassic system consist predominantly 

of schistose and altered porphyritic basic volcanic breccias, with a minor 

amount of interbedded tuff, slate, and graywacke, and flows. The most conspicuous feature of the rocks consists of the abundant black hornblende 

crystals that occur as phenocrysts in the fragments of the breccias. In the 

more massive phases plagioclase feldspars, in all stages of alteration to 

epidote, chlorite, sericite, and other secondary products, form the groundmass. In the more altered phases actinolite is an abundant constituent and 

the feldspars may be entirely altered to secondary products. In other districts 

less altered phases of what is possibly the same formation have been determined as augite melaphyre and andesite porphyry. The rocks are similar 

to the greenstones of the Juneau gold belt and of Gravina Island, in the 

Ketchikan district. For those in the Gravina area a Jurassic age has been 

suggested by Chapin, and the greenstone or schistose melaphyre agglomerate 

of this district may be of similar age, though no fossils were found to corroborate this conjecture, and the structural evidence is indeterminate.

THANE VOLCANIC GROUP

Historical review. The melaphyre tuff, limestone, and slate which 

constitute the Thane volcanic group of Eakin and Spencer 16 are 

part of the rocks that Spencer earlier described as the " slate-greenstoixe band " 17 and part of the rocks that he mapped as " greenstone

14 MacKenzle, J. D., op. cit., pp. 50-51.

18 Buddington, A. F., Mineral deposits of the Wrangell district: U. S. Geol. Survey 

Bull. 739, 1922, pp. 53-54.

18 Eakin, H. M., and Spencer, A. C., Geology and ore deposits of Juneau, Alaska: U. S. 

Geol. Survey Bull. (in preparation).

17 Spencer, A. C.,.The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, pp. 

16-18, 1906.
252 MESOZOIC STRATIGRAPHY OF ALASKA

(volcanic)" 18 and as the "slate-greenstone band." 19 They are also an 

undifferentiated part of the rocks that Knopf 20 mapped, in an area 

that includes both the Juneau district and the adjacent region on 

the north, as " greenstone " and are presumably represented in some 

of the rocks in the neighboring Eagle River 21 and Berners Bay 22 

districts which Knopf described as augite melaphyre.

Stratigraphic description, The Thane volcanic group (see section 

on p. 247) consists of melaphyre tuff underlain by limestone, beneath 

which there are interbedded tuff and slate. The total thickness of 

the group is probably about 5,000 feet. These rocks are underlain 

 with apparent conformity by the andesitic tuff, lava, and interbedded 

Upper Triassic sediments that make up the Gastineau volcanic group. 

(See pp. 92-95.) They are believed to be directly overlain, though 

the waters of Gastineau Channel intervene, by the supposed Upper 

Jurassic Treadwell slate, which is described on pages 255-256.

Age and correlation, No fossils have been found in the Thane 

volcanic group. The only evidence on its age is its position, apparently conformably above the Upper Triassic rocks that form the 

Gastineau volcanic group. As it resembles in composition and seems 

to hold the position of some of the Lower or Middle Jurassic volcanic 

rocks of other regions it is referred tentatively to the Lower or 

Middle Jurassic.

UPPER JUEASSIC (?) SLATE, LIMESTONE, AND TUFF OF GEAVINA ISLAND

Historical review. The supposed Upper Jurassic rocks of Gravina Island were mapped by Brooks 23 as part of the Vallenar 

" series," but he gave no description of these Jurassic rocks, and the 

beds which he did describe are now known to be Devonian. The 

Wrights 24 mapped these Jurassic rocks in part as " Upper Carboniferous greenstone " and in part as " undifferentiated Paleozoic rocks," 

but gave no description of any of the rocks that are now believed to 

be Jurassic. These rocks are part of the "Jurassic or Cretaceous 

andesitic effusive rocks " described by Smith.25 They are also part of 

the "Upper Triassic or Jurassic greenstones and slates" described

18 Spencer, A. C., op. cit, pi. 4.

18 Idem, pi. 37.

20 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey 

Bull. 502, pi. 5, 1912.

** Idem, pp. 13-14, 18-20, pi. 2.

28 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, p. 15, 1911.

23 Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska : U. S. 

Geol. Survey Prof. Paper 1, pi. 2, 1902.

^Wright, F. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pis. 1, 2, 1908.

25 Smith, P. S., Notes on the geology of Gravina Island, Alaska: U. S. Geol. Survey 

Prof. Paper 95, pp. 104-105, fig. 35, 1915.
JURASSIC, SOUTHEASTERN ALASKA 253

by Chapin,28 whose description includes a rather full account of the 

distribution, character, stratigraphic relations, structure, origin, age, 

and correlation not only of the rocks that are here referred to the 

Upper Jurassic but of the underlying coarse volcanic beds which 

have been described (pp. 249-251) as probably "Lower or Middle Jurassic (?)" and of slate and schistose greenstone on Tongass Narrows 

which the writer believes are Paleozoic or possibly Triassic.

Stratigraphic description. The base of the greenstone and slate 

series of Gravina Island is evidently the coarse breccia found along 

the west coast, which has been described (pp. 249-251) as probably 

Lower or Middle Jurassic. The breccia was believed by Chapin 

to overlie the Upper Triassic sediments with apparent conformity 

and grades upward into a more dominantly sedimentary series of 

green tuff and black slate (see section on p. 247), which are tinconformably overlain by the conglomerate, slate, and graywacke 

described on pages 381-382 as probably Lower Cretaceous.

The finer-grained tuff; that overlies the breccia) is .composed, 

at least in part, of water-laid material, with which are intercalated 

black slate and thin beds of crystalline limestone. The black slate 

is a typical clay slate having a well-developed cleavage, with bedding planes discernible, in places. The slate is plainly conformable 

with the green tuff.

Age and correlation. The age determination of the greenstone 

and slate rests upon rather slender paleontologic foundation. The 

collections from Bostwick Inlet were submitted to T. W. Stanton, 

who stated that lots 9528 and 9529 are "probably Upper Jurassic 

or possibly Lower Cretaceous" and that lot 9530 is "not sufficient 

for determining age, but probably from the same formation as 9528 

and 9529."

These fossils were collected from the west coast of Bostwick 

Inlet about half a mile south of the localities at which the Triassic 

and doubtful collections were made. They were found in sedimentary beds apparently interbedded with the volcanic breccia and 

overlying the Triassic sediments, but the relations are somewhat 

obscured by the gravel covering. The localities are listed below.

9528 (15 ACh 104). West coast of Bostwick Inlet iy2 miles south of head 

of inlet. Thin limestone beds which, together with slate and graywacke, 

are interbedded with andesitic greenstone. Theodore Chapin, 1915. Aucella.

9529 (15 ACh 105). West coast of Bostwick Inlet 500 feet south of 9528. 

Between the two localities the beds are closely folded and partly concealed, 

but the beds containing 9529 appear to underlie those containing 9528. Both 

are interbedded with andesitic greenstone. Theodore Chapin, 1915. Aucella.

28 Chapin, Theodore, The structure and stratigraphy of Gravina and Revillagigedo 

Islands, Alaska; U. S., Geol. Survey Prof. Paper 120, pp. 95-97, fig. 11, 1918.

49448 26 18
254 MESOZOIC STRATIGRAPHY OF ALASKA

9530 (15 ACh 106). West coast of Bostwick Inlet 1,500 feet south of 9529. 

Andesite flows apparently lower than 9529. Theodore Chapin, 1915. Pecten.

9532 (15 ACh 113). Cove 2 miles north of Ball Head, 300 yards southeast 

of north end of cove. Fossils contained in limestone which was regarded in 

the field as interbedded with black slate that contains Upper Triassic fossils. 

(See U. S. Geol. Survey Prof. Paper 120, p. 93, 1918.) Theodore Chapin, 

1915. Aucella?

UPPER JURASSIC (?) BOCKS OF PRINCE OF WALES ISLAND

The Upper Jurassic may be represented by some andesitic lava 

flows interstratified with volcanic tuff, conglomerate, and graywacke, 

having an aggregate thickness of probably about 1,000 feet, which 

F. E. and C. W. Wright 2T observed at several localities in the 

southern part of Prince of Wales Island and assigned to the " JuraCretaceous (?)." These rocks were described as follows, and a very 

similar description was repeated by C. W. Wright 28 in a later 

publication.

On the southern end of Prince of Wales Island is a succession of andesitic 

flows, conglomerates, and tuffs, which grade into a series [possibly Lower 

Cretaceous; see p. 382] of graywackes or indurated sandstones. These have 

been considered Mesozoic because of their structural and petrographic relations to the older rocks. In this complex, basaltic and andesitic flows are 

intercalated with the tuffaceous beds, and both flows and tuffs alternate with 

the sedimentary slates, graywackes, and conglomerates. They are readily 

distinguished from the greenstones by the wide difference in composition 

and texture of the interstratified beds and by their predominant reddish color. 

A fine, compact green tuff is usually overlain by an andesitic lava with 

numerous large phenocrysts, which in turn is overlain by a basaltic lava or a 

red lava conglomerate. The greenstone beds, on the other hand, vary little in 

composition and where massive, augite crystals form the phenocrysts.

On the south end of Prince of Wales Island the andesitic flows and conglomerates overlie at several points the eroded surfaces of granitic intrusive 

masses, and numerous dikes of the andesite intrude these older granites. 

Pebbles and fragmentary masses of the granite were observed in the tuffaceous 

conglomerates, showing clearly that the andesites are younger than these 

masses of granitic rock. The granites at this point were more altered and 

contained more shearing planes than are usual in the Coast Range intrusives, 

and they may represent a batholith intruded before or during the earliest 

stages of the period of the Coast Range granitic invasion.

SANDSTONE AND VOLCANIC ROCKS OF WINDFALL HARBOR

The rocks on Windfall Harbor, which is on the west shore of 

Seymour Canal, on Admiralty Island, were mapped by Wright 29 

as " Paleozoic, probably chiefly Carboniferous. limestones and

27 Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pp. 34, 58, pi. 1, 1908.

28 Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

.Alaska: U. S. Geol. Survey Prof. Paper 87, pp. 19-20, pi. 1, 1915.

29 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287. 

pi. 33, 1906.
JURASSIC, SOUTHEASTERN ALASKA 255

schists," but no description was given. The limestone on the east 

coast of Admiralty Island includes both Permian and Upper Triassic 

beds. The only evidence of Jurassic rocks on Admiralty Island was 

yielded by some fossils which Edwin Kirk obtained in 1918 from 

sandstone interstratified with volcanic sediments on the north shore 

of Windfall Harbor. The following statement concerning these 

fossils was submitted by T. W..Stanton:

10170. North shore of Windfall Harbor, east side of Admiralty Island 

Sandstone interstratified with volcanic sediments. Fragments of a large 

coarsely ribbed Pecten. Probably Jurassic.

TREADWELL SLATE AND DOUGLAS ISLAND VOLCANIC GROUP OF THE 

JUNEAU DISTRICT

Historical review. The supposed Upper Jurassic rocks of the 

Juneau district, which have been called by Eakin and Spencer 30 

the Treadwell slate and the Douglas Island volcanic group, are the 

upper part of the rocks which Spencer 31 earlier described and represented on his general geologic map as the "slate-greenstone band." 

On his detailed geologic map 32 they were represented as the " black 

slate," " alternating slates and greenstones," and "greenstones" of 

Douglas Island. A belt of rocks which occurs throughout Glass 

Peninsula, on Admiralty Island, and which seems to be the southern 

extension of the Treadwell slate and the Douglas Island volcanic 

group was described by Wright 33 as "Paleozoic, probably chiefly 

Carboniferous slates and greenstones." The Treadwell slate and the 

Douglas Island volcanic group are also part of the rocks which 

Knopf 84 grouped in a southern extension of the "Berners formation " and greenstone of the Eagle River district.

Stratigmphic description. The Treadwell slate (see section on 

p. 247) consists of black clay slate with some conglomerate and considerable graywacke. Its thickness is probably about 7,000 feet. 

Apparently it comprises the oldest rocks on Treadwell Island, and 

it is supposed to overlie the Thane volcanic group, but it has not 

been observed in direct superposition, as Gastineau Channel separates the formations.

The Douglas Island volcanic group which overlies the Treadwell 

slate with apparent conformity (see section on p. 247), consists of 

melaphyre flows, tuff, and agglomerate having a thickness of possibly 

15,000 feet.

80 Eakin, H. M., and Spencer, A. C., Geology and ore deposits of Juneau, Alaska: 

U. S. Geol. Survey Bull. (in preparation).

31 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, pp. 

16-18, pi. 37, 1906.

82 Idem, pi. 4.

83 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

pp. 141-142, pi. 33, 1906.

84 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey 

Bull. 502, pi. 5, 1912.
256 MESOZOIC STRATIGRAPHY OP ALASKA

Age and correlation. No fossils have been found in the Treadwell 

slate or in the Douglas Island volcanic group. Their apparent position above the Thane volcanic group indicates that they are younger 

than Triassic and probably younger than Lower or Middle Jurassic. 

Their general position along the southern extension of the supposed 

Upper Jurassic rocks that have been included in "Berners formation " is suggestive of Upper Jurassic.age. Their volcanic character, 

together with the fact that volcanic rocks are not known in the Cretaceous of Alaska, indicates that at least the Douglas Island volcanic 

group is either pre-Cretaceous or post-Cretaceous. The Treadwell 

slate and the Douglas Island volcanic group are therefore referred 

tentatively to the Upper Jurassic, but it must be admitted that the 

evidence for this age assignment is very far from conclusive.

" BEENEHS FORMATION "

Historical review. The "Berners formation" was named and 

defined by Knopf as including " an interstratified series of slates 

and graywackes well exposed on both shores of Berners Bay." The 

original description 85 includes an account of the general character 

and distribution of the formation, a rather detailed petrographic 

description, and a discussion of the age and correlation, in which 

there is a statement furnished by Knowlton concerning the character and probable age of the fossil plants. The occurrence of the 

formation was mapped in detail within the small area covered by 

Knopf's report. Knopf assigned the formation, on the basis of 

Knowlton's determination of some fossil plants found within it, to 

the Jurassic or Lower Cretaceous and suggested, on his own authority, an approximate correlation with the Lower Cretaceous Aucellabearing rocks of Admiralty Island.

The supposed southern extension of the "Berners formation" 

from Berners Bay to the north end of Gastineau Channel has also 

been described and mapped in detail by Knopf.36 This account 

includes a description of the rocks, a detailed petrographic description, and a discussion of age and correlation. The determination 

of age was based wholly upon the collection of fossil plants from 

Berners Bay, described in the report cited above. The discussion 

of correlation has been misinterpreted as containing a definite statement to the effect that there is no doubt concerning the identity of 

the " Berners formation " with the Lower Cretaceous AuceUa-bQ&Ting beds of Pybus Bay. This statement was intended,37 however,

86 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey 

Bull. 446, pp. 12-13, 14-17, pi. 2, 19.11.

88 Knopf, Adolpb, The Eagle River region, southeastern Alaska: U. S. Geol. Survey 

Bull. 502, pp. 13-14, 15-18, pis. 2, 5, 1912.

37 Oral statement by Adolph Knopf.
JURASSIC, SOUTHEASTERN ALASKA 257

to mean only that in Knopf's opinion the " Berners formation " is 

identical with the slate, graywacke, and conglomerate at Point 

Young, which Wright 38 correlated with the Lower Cretaceous rocks 

at Pybus Bay. In the writer's opinion the latter correlation is 

based upon very scanty evidence (see p. 377) and probably is altogether incorrect.

The " Berners formation " as described and mapped by Knopf 

included part of the rocks which had previously been described and 

mapped by Spencer 39 as the " slate-greenstone band" and which 

had been considered Carboniferous because they were supposed to be 

the northern extension of the fossiliferous Carboniferous rocks of 

Taku Harbor.

Knopf included also in the " Berners formation " some of the rocks 

at the north end of Admiralty Island which Wright 40 described as 

" slates and greenstones *' and considered " Paleozoic, probably chiefly 

Carboniferous."

The rocks that were described by Knopf 41 in the report on the 

Eagle Kiver district under the heading " Volcanic rocks " and were 

mapped as " augite melaphyre " 42 and " greenstone " 43 were regarded 

as approximately of the same age as the " Berners formation."

The schist that occurs in a belt east of the " Berners formation," 

between it and the main belt of the Coast Range granitic rocks, was 

described and mapped by Knopf 44 as a metamorphic phase of the 

" Berners formation." These rocks were previously described by 

Spencer 45 as the " schist band." The writer believes that they are 

probably chiefly Paleozoic, though they may include some infolded 

Triassic beds (see section on p. 247).

Knopf 40 has also suggested that the graywacke, slate, and conglomerate of the western shores of Chichagof and Baranof Islands 

may possibly be correlated with the " Berners formation."

StratigrapMc description. The " Berners formation" consists 

chiefly of slate and graywacke but includes some interbedded lava 

and tuff. Part of the graywacke beds are slightly conglomeratic.

88 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 

287, p. 143, pi. 33, 1906.

88 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, pp. 

16-18, pis. 4, 37, 1906.

*° Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

pp. 141-142, pi. 33, 1906.

41 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey 

Bull. 502, pp. 13-14, 18-20, 1912.

42 Idem, pi. 2.

*a Idem, pi. 5.

«* Idem, pp. 14, 20-23, pis. 2, 5.

« Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, p. 16, 

pis. 4, 37, 1906.

«Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey BulL 504, 

pp. 13-14, pi. 1, 1912.
258 MESOZOIC STRATIGRAPHY OF ALASKA

The original definition of the formation by Knopf 47 includes the 

following general description:

A sedimentary formation consisting predominantly of slates and graywackes 

occupies the largest part of the Berners Bay area. Some basaltic greenstones 

and quartz porphyry schists are associated with it but are of small importance. 

The slates comprise in the main highly cleaved black clay slates but include 

some of green and to a less extent some of red color. The graywackes are 

intimately interstratified with the slates in beds ranging from a few inches 

to 8 feet or more in thickness and are commonly of a gray or greenish-gray 

color. They are roughly schistose and in the thicker beds nearly massive.

In places the graywackes constitute the bulk of the formation and comprise 

a thick succession of heavy beds separated only by thin beds of slate. This 

massive development of graywacke is particularly well shown toward the south 

end of the peninsula.

The southern extension of the " Berners formation " was described 

by Knopf 48 as follows:

The most important rocks in the region are an interstratified series of clay 

slates and graywackes which have been named the Berners formation because 

they are typically exposed at Berners Bay. Rocks of volcanic origin, usually 

known as greenstones, are also included in the formation, but the larger areas 

underlain essentially by the greenstones, are separately shown on the geologic 

map under an appropriate symbol. Toward the northeast the slates and graywackes grade into schists, which are also shown under a separate symbol. The 

Berners formation forms a long belt trending northwest and southeast, which 

contains nearly all the mineral deposits of the region.

At Berners Bay the graywackes are intimately interstratified with the spates. 

The beds of graywacke are not persistent along the strike but are lenticular 

and interdigitate with the slates. Cross-bedding is finely developed at some 

places, and some beds are slightly conglomeratic, containing small well-rounded 

pebbles. The graywackes are massive and do not show the cleavage characteristic of the associated argillite strata.

Toward the south the graywackes become less abundant, and in the territory 

south of Eagle River they are comparatively scarce. At Auke Bay they are 

practically absent and the rocks consist almost wholly of fissile black clay 

slates, which are of roofing-slate quality, unlike those at any other locality 

in the gold belt. The maximum thickness of individual strata of graywacke, 

so far as observed, is 80 feet.

The thickness of the "Berners formation" has never been measured, and it is probable that no accurate estimate can be made, 

because of the intense deformation that the rocks have undergone. 

The slaty rocks of Douglas Island, which Knopf correlated with the 

" Berners formation," were considered by the Wrights 49 as possibly 

having a thickness of 3,000 or 4,000 feet.

Age and correlation. Some fossil plants were collected from the 

" Berners formation " by Adolph Knopf on the east side of Berners

a Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, pp. 14-16, 1911.

48 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey 

Bull. 502, pp. 15-16, 1912.

*" Wright, F. B. and C. W., The Ketchlkan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, p. 35, 1908.
JURASSIC, SOUTHEASTERN ALASKA 259

Bay just north of Sawmill Cove. The rocks at the fossil locality, 

according to Knopf ,50

consist of an interdigitating series of thick lenses of graywacke and argillite 

standing on edge. The graywackes show crossbedding, and the argillites are 

ripple marked. The argillaceous rocks are, as a rule, too highly cleaved 

to have retained the imprints of leaves, which are now commonly represented 

by graphitized flakes. Leaf-bearing beds seem to be scarce, and the best fossils collected were obtained from a roughly schistose argillite which was gashed 

by quartz veinlets.

These fossil plants were examined by F. H. Knpwlton,51 who discussed them as follows:

This material is very difficult to study, for practically all traces of nervation are absent, and dependence must be placed on outline, which has obviously been more or less modified by pressure. With these limitations in 

mind, I think I., have been able to demonstrate the presence of Taeniopteris, 

Asplenium or Dicksonia, Thinnfeldiaf, and possibly another fern something 

like Dryopteris.

The choice appears to lie between Jurassic and Lower Cretaceous, and if 

what has been supposed to be Taeniopteris is really such the odds favor the 

former. I have not found anything that can be identified as a dicotyledon, 

which also is favorable to the probability of its being Jurassic. Although the 

evidence as adduced is not very strong and the identifications are tentative, 

it seems most probable that they are of Jurassic age.

The following statement on the same material has also been submitted by Knowlton: (

The specimens are very small, almost devoid of nervation, and obviously 

more or less distorted by pressure. The specimens I said might be Taeniopteris have nothing but the midrib preserved or possible faint traces of 

lateral nerves. Without some positive notion of the lateral nerves it is impossible to distinguish this genus from Pterophyllum, Nilssonia, etc. It is 

not of much value as it stands.

Another specimen, identified in the first report :xs possibly Asplenium or 

Dicksonia, with wider experience I should now incline to call OnycMopsis, 

close to and perhaps identical with 0. mantelli, but it is obscure as to outline and without a trace of nervation. I therefore hesitate to say it is 

Onychiopsis, though it certainly does look like it.

The scrap referred to as Thinnfeldia? looks also like some forms of Thyrsopieris, but it is without nervation and hence very uncertain.

There are some fragments that suggest Cladophlebis, but I can't be certain 

about them.

So much for the things themselves: What can be said with reasonable safety 

regarding their age indications? Obviously, if we can not determine the 

genera, we are not in position to interpret their stratigraphic value with 

accuracy. However, I will go so far as to say that they are, in my opinion, 

undoubtedly Mesozoic. There is not a thing that could be as old as the 

Paleozoic. If I have been anywhere near correct in identifying them, the 

choice must still lie between Lower Cretaceous and Upper Jurassic. They

50 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, p. 17, 1911.

81 Idem, p. 17. . .
260 MESOZOIO STRATIGRAPHY OF ALASKA

might well enough be Upper Jurassic, but I do not think they can be older 

than Jurassic.

Some fossils were also collected by Theodore Chapin, concerning 

which the following statement was made by G. H. Girty:

15 ACh 310. Locality, Jualin wharf, Berners Bay. Graywacke float. It is 

not believed that this rock traveled far, for it is similar to the rock in place 

along the coast the graywacke of the " Berners formation." This collection 

contains a few fossils in a fragmentary condition, as follows:

Some impressions that suggest either graptolites or fenestelloid Bryozoa. 

Mr. Kirk showed these fossils to Mr. Ulrich, who states that they belong to 

the genus Pinnatopora (one of the Fenestellidae). If the fossils are graptolites the age of this lot would be Cambrian or-=0rdovician. If they belong 

to the genus Pmnatopora the age would be Devonian or Carboniferous.

Besides these there are impressions that might be external molds of the 

dorsal valve of a Derbya or Schuchertella, another impression that suggests 

some species of Aviculipecten, and part of a spirally ribbed 'coiled shell that 

might be either a cephalopod or a gastropod, according to the character of the 

missing parts of the fossil.

So far as I can see you have a free hand in making this lot anything in the 

Paleozoic except Cambrian, with the probabilities, however, in favor of 

Carboniferous (Mississippian?).

The rocks heretofore mapped as the " Berners formation " are now 

divided by Eakin and Spencer 52 into several mapped units, of widely 

different ages, so that the name has ceased to be a useful stratigraphic term.

GRAYWACKE OF CHIOHAGOF AND BARANOF ISLANDS

Historical review. A. belt of graywacke, slate, and conglomerate 

that extends along the west coast of Chicagof and Baranof islands 

includes some rocks which are probably Jurassic. The first description of any of these rocks, according to Becker,53 was given by 

Hoffman,54 who stated that the rocks in the vicinity of Sitka consist 

of graywacke and slate. Becker 55 gave a description of the petrographic character and a discussion of the origin and age of some of 

these rocks, which he called "pyroclastic diorite" but which all 

other observers have regarded as graywacke. These rocks have been 

described briefly by Brooks, who tentatively assigned them first to 

the Tertiary 66 and afterward to the Mesozoic.57 Emerson 58 gave a

83 Eakin, H. M., and Spencer, A. C., Geology and ore deposits of Juneau, Alaska: 

U. S.. Geol. Survey Bull. (in preparation).

88 Becker, G. F., Reconnaissance of the gold fields of southern Alaska, with some notes 

on general geology: U. S. Geol. Survey Eighteenth Ann. Kept., pt. 3, p. 43, 1898.

M Hoffman, P., Geognostic observations collected on a journey around th<; world in 1829.

58 Becker, G. F., op. cit, pp. 44-47.

66 Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska, with an 

introductory sketch of the geology of southeastern Alaska: U. S. Geol. Survey Prof. 

Paper 1, p. 26, 1902.

6T Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 

45, p. 227, 1906.

68 Emerson, B. K., General geology: Alaska, vol. 4, pp. 47-48, Harrlman Alaska expedition, 1904.
JURASSIC, SOUTHEASTERN ALASKA 261

brief description of tuffaceous graywacke near Sitka, which he referred to the Vancouver series. These rocks were mentioned briefly 

by the Wrights,59 who referred them to the "Permian or Upper 

Carboniferous" and who casually spoke of them, apparently unintentionally, as the " Sitka series." 60 These rocks were described at 

greater length by Knopf ,61 who suggested that they may lie unconformably on the supposed Carboniferous greenstone and may perhaps be correlated with the "Berners formation.". A much more 

detailed description of these rocks has been given by Overbeck,62 

who found fossils that are probably Upper Jurassic.

Stmtigraphic description. The Upper Jurassic rocks of the west 

coast of Chichagof Island include graywacke, slate, argillite, conglomerate, and greenstone. Graywacke is the prevailing rock type, 

the other rocks occurring in relatively small amounts. The pebbles 

in the conglomerate consist of graywacke, sandstone, chert, lightcolored fine-grained igneous rock, and limestone. The series is apparently very thick, possibly many thousand feet, but no estimate of 

the thickness was made by Overbeck. The Wrights estimated its 

thickness at 3,000 feet, more or less. The graywacke °is underlain 

by undifferentiated metamorphic rocks, which include sheared conglomerate, limestone, argillite, tuff, lava, and schist. These metamorphic rocks, according to Overbeck, are probably of different 

ages and may perhaps be correlated with the Upper Triassic or early 

Jurassic of Gravina Island. The graywacke appears to be structurally conformable with the underlying rocks, but as it has not been 

so much metamorphosed, an unconformity may be present.

Age and correlation. The best evidence on the age of the graywacke of Chichagof Island was obtained from two small lots of 

invertebrates collected by R. M. Overbeck in 1917, concerning which 

T. W. Stanton made the following statement: 6S

10147 (17AOF7). First prominent bight on southwest side of Slocum Arm, 3 

miles southwest of Falcon Arm. Aucella sp. related to A. fischeriana (D'Orbigny) ; Belemnites sp., fragments of a small slender form.

10148 (17AOF8). Second prominent bight on southwest side of Slocum Arm, 

5 miles southwest of Falcon Arm. Aucella sp., small distorted specimens possibly belonging to two species, one of which may be same as species in 10147.

The form of Aucella, in these two lots appears to be distinct from those 

identified as A. piochi Gabb and A. crassicollis Keyserling in previous collec69 Wright, P. B. and C. W., The Ketcliikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pp. 35, 5&-51, 1908.

80 Idem, p. 58.

81 Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, pp. 

13-14, 1912.

82 Overbeck, R. M., Geology and mineral resources of the west coast of Chichagof 

Island: U. S. Geol. Survey Bnll. 692, pp. 100-109, 1&19. 

68 Stanton, T. W., cited by Overbeck, R. M., idem, p. 108.
262

tions from Pybus Bay, Admiralty Island. The present collections are believed 

to be of Upper Jurassic age. It should be remembered, however, that the distinction between Jurassic and Lower Cretaceous on the basis of Aucella alone 

is not always safe. It is possible that all the AweZto-bearing rocks of southeast Alaska may belong in the same series.

Additional evidence that the graywacke of Chichagof Island is 

Jurassic rather than Cretaceous is found in the presence of interbedded volcanic strata and in the absence of pebbles of granite in the 

conglomerate.

ARCTIC SLOPE 

GENERAL FEATURES

The Jurassic rocks of the Arctic slope of Alaska include a marine 

shale, which is well developed in the valleys of Canning and Sadlerochit Rivers, where it has, been described as the Kingak shale, and 

which probably occurs also near the Canadian boundary, where fossils have been obtained that apparently represent part of the fauna 

of the Kingak shale. The Jurassic rocks of the Arctic slope are noteworthy as being the only marine Jurassic rocks known north of the 

Alaska Range and as containing a, Jurassic fauna of a type that is 

known elsewhere in Alaska only in the Kialagvik formation of the 

Alaska Peninsula.

The Kingak shale of the Canning River district is probably overlain by other marine and coal-bearing strata, described as the Ignek 

formation, which may be of Jurassic age but the exact horizon of 

which is much in doubt. This formation is here described as possibly Jurassic, although it may be either Jurassic or Cretaceous.

It should be noted that these Jurassic beds of the eastern part, of 

the Arctic slope, like the Triassic beds of the same region, are apparently absent farther west in the Colville Valley, where Lower 

Cretaceous AwceZ&z-bearing rocks, which are absent in the Canning 

River and international boundary districts, have transgressed upon 

or have been faulted against the lower Carboniferous limestone.

MIDDLE OR LOWER JURASSIC

KINGAK SHALE

Historical review. An interesting occurrence of supposed Middle 

or Lower Jurassic rocks has been found by E. de K. Leffingwell in 

the valleys of Sadlerochit and Canning Rivers, 90 and 120 miles west 

of the international boundary. These rocks have been described 64 

as the Kingak shale by Leffingwell, whose account of the formation 

includes a description of its occurrence, character, and thickness and

M Leffingwell, E. de K., The Canning River region, northern Alaska: U. S. Geol. Survey 

Prof. Paper 109, pp. 103, 119-120, pi. 2, 1919.
263

a discussion of its age and correlation. Statements by T. W. Stanton 

and Frank Springer concerning fossils collected by Leffingwell are 

quoted.

Stratigraphic description. The Kingak shale was named by Leffingwell from its type occurrence at Kingak Cliff on Sadlerochit 

Kiver, and was described 85 as follows:

The Kingak shale, which consists of about 4,000 feet of black shales, overlies the Shublik formation of Triassic age and probably underlies the Ignek 

formation of Jurassic (?) age. It is apparently conformable in bedding with 

the Shublik formation, but nothing is known of the upper contact. The formation named is confined to the shales which contain the fauna that is listed 

below. The Kingak shale has been identified at only one locality, Kingak 

Cliff, near camp 263, at the southeast end of Sadlerochit MountainsAge and correlation. The faima of the Kingak shale, as now 

known, is restricted to the five species represented in the table on 

page 264. These fossils apparently occur generally and abundantly 

distributed throughout the lower 1,500 feet of the formation. The 

higher shale has not thus far yielded any fossils, but no exhaustive 

search was made for them.

The most significent members of this fauna are the ammonites, 

which are referred to characteristic Liassic and Lower Oolitic genera 

and which include forms that are very closely related to if not 

identical with, species that have hitherto been found only in the 

Middle (?) Jurassic rocks of the Alaska Peninsula, described on 

pages 186-191 as the Kialagvik formation, which several European 

paleontologists" have classified as Upper Liassic (Toarcian) but 

which Stanton considers (p. 189) Middle Jurassic. Stanton's statement regarding the ammonites from the Kingak shale is as follows:

The collections from localities 110 and 114 all belong to a single fauna, 

and the ammonites in them indicate that the horizon' represented is probably 

about the same as the exposures on Kialagvik [Wide] Bay, Alaska Peninsula, 

which have yielded an ammonite fauna described' by White and referred to 

the Lower Jurassic (upper Lias) by Hyatt and Pompeckj.

The pelecypod identified by Stanton as Inoceramus cf. /. lucifer 

Eichwald is closely related to if not identical with a species that has 

been regarded as characteristic of the Tuxedni sandstone of Cook 

Inlet. The Tuxedni sandstone, which is described on pages 140-158, 

is Middle Jurassic and, according to Stanton, "certainly included 

at least part of the Lower Oolite."

The crinoid, which was not associated with the other fossils, was 

identified by Frank Springer, who said of it (and of the similar 

crinoids from Firth River, described on p. 265):

While this material is not sufficient for any accurate specific determination 

or description, there is enough to show that it clearly belongs to the true

88 LefflngweJl, E. de K., op. cit., p. 119.
264 MESOZOIG STRATIGRAPHY OF ALASKA

Pentacrmus (= Extracrmus Austin of DeLoriol, P. H. Carpenter, and other 

authors), of the Lower Jurassic of England and continental Europe, and of 

the type of P. subangularis Miller, from the Middle Liassic of Lyme-Regis, 

England, and Boll, Holzmaden, and other localities in Wurtemburg, Germany. 

In default of more perfect specimens it may be referred to that species.

The specimens No. 12 Md. 82 (from a tributary to Overthrust Creek, 1% 

miles above the mouth and about 8 miles west of the 141st meridian) consist 

of column and arm fragments of very large size. The matrix is highly ferruginous, with much oxidation on the surface, so -that the preservation of the 

specimens is poor. The material from Black Island, Canning River, brought 

in by Mr. Leffingwell, is of very different character and is of great interest. 

It consists of part of a set of arms belonging to a very large individual, in 

exquisite preservation. The matrix and mode of deposition are very similar 

to those of the Pentacrinus beds at Lyme-Regis1 , and the condition of the 

specimen indicates that it was part of a considerable colony, of which a large 

number of individuals were embedded together.

The specimens from the two localities, which I understand are upward' of 

100 miles apart, agree in their uniformly large1 size, which is greater than 

that of those usually found at Lyme-Regis, but not than that of specimens 

from the Wurtemburg localities, which are sometimes even larger.

So far as I know this is the first discovery of remains of Pentacrinus, with 

the exception of isolated1 stem joints, yet found in American rocks, and it is 

interesting to note that a specimen of the same genus and type has recently 

been found in the Dutch East Indies, thus showing the great geographical 

range of this genus.

Fossils from the Kingalc shale a

110

a

HOE 114a 1Mb Bl, 1.

b

 a, Identified by T. W. Stanton; b, identified by Frank Springer.

110. Sadlerochit River, cut on north side running northeast from camp 

258, about 2,400 feet northeast (magnetic) from camp at edge of bank. 

Friable black shale with pyrite concretions. E. de K. Leffingwell, 1910-1912.

HOE. Talus and wash, Sadlerochit River. E. de K. Leffingwell.

114a. Sadlerochit River, half a mile up the creek from camp 263. Fossils 

mostly from concretions in black shale at foot of exposure. E. de K. Leffingwell, 1910-1912.

114b. Sadlerochit River, about 200 to 300 yards below camp on north 

side of river or about half a mile down the creek from 114a. About 1,500 

feet above 114a. E. de K. Leffingwell, 1910-1912.

Bl. I. Black Island, Canning River, opposite Mount Coplestone. Collected 

by an Eskimo, supposedly from a small exposure of black shale. E. de K. 

Leffingwell, 1910-1912.

CBINOID BED OF FIRTH RIVER

Lower Jurassic rocks are probably present in the Firth Valley 

near the international boundary. This horizon has been recognized
JUBASSIC, ARCTIC SLOPE , 265

from some fossils collected by A. G. Maddren, but the rocks containing this supposed Lower Jurassic fauna have not been differentiated from the Upper Triassic rocks,66 which they closely 

resemble and with which they are intimately associated both 

stratigraphically and structurally. These supposed Lower Jurassic 

rocks were not described by Maddren, but a brief reference to their" 

occurrence was made by Leffingwell.07

The supposed Lower Jurassic rocks of Firth River have been 

recognized only in a thin ferruginous stratum occurring in the 

midst of an area of Upper Triassic shale and limestone on a tributary of Overthrust Creek about 8 miles west of the international 

boundary, in latitude 68° 56' 10". The exposure of Triassic and 

Jurassic beds, according to Maddren, apparently includes about 

1,000 feet of strata composed chiefly of dark shale that is too much 

crumpled to permit a deciphering of the stratigraphy and structure. 

The supposed Lower Jurassic fauna consists wholly of crinoids, 

which were recognized only in a highly ferruginous calcareous 

bed, 3 to 5 inches thick, apparently interstratified with beds of dark 

limestone containing the Upper Triassic fossils described on 

page 100-103.

These crinoids have been studied by Frank Springer, whose statement concerning them is quoted on pages 263-264. In commenting 

upon the fossils supposed to have been obtained at or near this 

locality, Stanton said:

While the crinoids suggest Lower Jurassic age, all the other invertebrates 

above listed [see p. 102] indicate Upper Triassic. . The crinoids were not actually 

intermingled with the other fossils, and this fact suggests the possibility that 

they came from a different formation. A few fragments of fossiliferous Carboniferous limestone differing in color and other characters from the limestone containing the Triassic fossils were in this lot when it was received.

A crinoid which, according to Springer, probably belongs to the 

same species was obtained by Leffingwell on Canning Eiver, about 

120 miles west of this locality. This occurrence is described on pages 

263-264. The crinoid from Canning River apparently occurs in a 

formation that has yielded Lower or Middle Jurassic ammonites.

JURASSIC (?) 

IGNEK FORMATION

Historical review. Some rocks of probable Jurassic age but of 

indeterminate position within the Jurassic were discovered by E. 

de K. Leffingwell on Canning and Marsh Rivers about 90 to 120 miles 

west of the international boundary. These rocks have been deM Maddren, A. G., Geologic investigations along the Canada-Alaska boundary : U. S. 

Geol. Survey Bull. 520, pp. 312-313, 1912. 

OT Leffingwell, B. de K., op. clt., p. 120.
266 MESOZOIC STRATIGRAPHY OF ALASKA

scribed as the Ignek formation by Leffingwell,68 whose account includes detailed descriptions of the rocks exposed at various places 

and a discussion of their age in which statements by Stanton and 

Knowlton concerning the fossils are quoted.

Stratigraphic description. The Ignek formation as described by 

Leffingwell 69 was named from its typical occurrence on Ignek Creek, 

on the south side of Red Hill, at the west end of the Sadlerochit 

Mountains. This formation occurs at both ends and probably along 

the north front of these mountains. It " consists of about 2,500 feet 

of black shale with coal or ' red beds' and subordinate sandstone 

members." These rocks probably overlie the Lower (?) Jurassic 

Kingak shale, although there is some doubt about this, as the two 

formations have not been observed in the same district. The top of 

the Ignek formation has not been recognized, and younger rocks are 

not known in this region. The section at the type locality was recorded by Leffingwell as follows:

Section of Ignek formation on the south side of Red Hill

Feet

1. Blue-gray fine-grained sandstone______________ 200

2. Black shale, with red bed near the top. The fossils of

lot 3 were obtained near the middle___________ 1, 500

3. Unexposed ____________________________ 400

4. Gray sandstone, weathering yellow_____________ 100

5. Unexposed ___________________________ 400

The red beds near the top of this section are considered by Leffingwell to " mark the former existence of coal" that has been burned.

Near the head of Marsh Creek, at the east end of the Sadlerochit 

Mountains, is a poorly exposed and complexly folded section containing sandstone and shale that overlie some red beds like those at 

Red Hill. The sandstone yielded the fossils of lots 117A and 118A.

On the west side of Canning River, opposite Mount Coplestone, is 

sandstone from which the fossils of lot 100 were obtained. This 

sandstone is probably the same as that at the head of Marsh Creek.

Age and correlation. The known fossils of the Ignek formation 

as represented in the following table include 24 or more undetermined species of marine invertebrates, mostly mollusks, from four 

localities, and some fossil wood. The fauna of three of these localities (100, 117a, and 118a) is connected by a common species of 

Astarte. The fourth locality (No. 3) has no species and only one 

or two genera in common with any of the other three localities. 

It is possible, therefore, that two entirely distinct faunas are repre68 Leffingwell, E. de K., The Canning River region, northern Alaska: U. S. Geol. Survey 

Prof. Paper 109, pp. 103, 120-125, pi. 2, 1919.

69 The description here given consists of an abstract prepared with Mr Leffingwell's 

assistance from the manuscript of the detailed report cited above.
JURASSIC, ARCTIC SLOPE 267

sented. The fossils of lot 3, which came from the black shale below 

the coal beds, are regarded by Leffingwell as the typical fauna of 

the Ignek formation. The fossils from the other three localities, 

which came from the sandstone above the coal beds, should possibly 

be regarded as a distinct fauna representative of a higher formation. 

However, as the fossils from all these localities are of doubtful 

relationships, and as no striking and essential differences have been 

recognized, they will be tentatively considered as constituting a 

single fauna.

These rocks are shown to be post-Triassic, both by their stratigraphic position and by the occurrence of such genera as Yoldia, 

Inoceranwsf, Pholadomyaf', Goniomyaf, Cyprinaf, Astarte, and 

Belemnites?. The occurrence of Spiriferinaf, Inoceramusf, Pleuromya, Goniom/ya?, Homomya,) and Belemnites? shows that they 

are not younger than Cretaceous. The presence of Spiriferina 

would seem to indicate that they are pre-Cretaceous, and the presence of Yoldia would seem to indicate that they are post-Jurassic. 

It consequently is impossible, on the basis of the data now available, 

to determine their age more closely than Jurassic or Cretaceous.

In regard to the fossils from locality 3, 'Stanton 70 said:

This rather poorly preserved collection is puzzling because of its lack of 

relationship to any other Alaskan fauna known to me and because of the 

absence of characteristic types. It is probably Mesozoic and may be Jurassic.

Concerning locality 100, he said: "This puzzling collection of 

fairly well preserved Mollusca is presumably of Jurassic age, but 

it seems to have no species in common with any of the known 

Jurassic or other Mesozoic faunas of Alaska." The Astarte in lots 

117a and 118a is the same species as that in lot 100, according to 

Stanton, who said: " Nos. H7a and 118a are probably Jurassic, from 

about the same horizon as No. 100."

The fossil wood from locality No. 3 has been examined by F. H. 

Knowlton,71 who said of it:

I have examined the thin sections of this material and find it to be coniferous 

wood with unusually small wood cells or tracheids. In the radial section the 

pits on the tracheids are found to be nearly circular in outline and disposed 

in a single vertical row. The pores or slits in the pits could not be made out 

with certainty, nor could markings or pits of any kind be noted on the lateral 

walls of the medullary rays.

In the tangential section the medullary rays are seen to be arranged in a 

single series of usually two to four cells, though occasionally there is only 

one and rarely there may be six or seven.

I do not find any characters which would mark this wood as unmistakably 

of Paleozoic age, and to the best of my knowledge and belief it is Mesozoic. 

It is probably to be best regarded as a species of Araucarioxylon.

70 Stanton, T. W., cited by Leffingwell, E. de K., op. clt., p. 124.

71 Knowlton, F. H., cited by Leffingwell, E. de K., op. cit., p. 125.
268 MESOZOIC STRATIGRAPHY OF ALASKA 

Fossils from the Ignek formation a

Terebratula? ___ .... __________________ . _________ ...

Yoldla. 

Astarte.- _ .. ____ .. ________ . __ . ........... ...... .......

Astarte (asin lot 100)... ... .. _ ._ _ ..............

Belemnites? (phragmacones?) ......... ___ . ____ ..... __ .. _ . _ . .....

3

X

X

X

X

X

X

X

100

s/

X

X

v

' X

X

X

117a

X

118a

X

 Identified by T. W. Stanton, except as indicated. 

»Identified by F. H. Knowlton.

3. Canning River, cut on south side of Red Hill, Ignek Valley, about halt 

a mile east of red beds. Very friable black shale, as indicated in section on 

p. 266. E. de K. Leffingwell, 1908.

100. Canning River, cut on west side of river opposite Shublik Island. 

Second outcrop of sandstone going north. The fossils are very abundant in 

a rusty band a few inches thick and are not found elsewhere. Two lots 

(A and B) were collected from the same bed at two places 50 or 100 feet 

apart. This sandstone is considered the same as 118a, on Marsh River. E. 

de K. Leffingwell, 1910-1912.

117a. Marsh River, exposure 50 yards above camp 266, on east side of 

river. E. de K. Leffingwell, 1910-1912.

118a. Marsh River, cut on northeast side of the river a mile above camp 266, 

at the first good exposure of sandstone. Fossils from a rusty band. B. de K. 

Leffingwell, 1910-1912.

SUMMARY

STRATIGRAPHY 

LOWER JURASSIC

General sequence. The Lower Jurassic rocks of Alaska are believed to include a lower sedimentary division, a middle dominantly 

volcanic division, and an upper sedimentary division. The supposed lowest division comprises the Lower Jurassic calcareous sandstone, shale, and limestone of the Alaska Peninsula. The supposed 

intermediate volcanic division comprises the Talkeetna formation 

of the Talkeetna Mountains and Matanuska Valley, the Skwentna 

group of the Alaska Range, some unnamed lavas and tun's on 

Kenai Peninsula and the west coast of Cook Inlet, and possibly
JURASSIC, SUMMARY 269

the Thane volcanic group and other breccias, tuffs, and lavas of 

' southeastern Alaska. The supposed upper division of the Lower 

. Jurassic comprises the Kialagvik formation of the Alaska Peninsula c 

and the Kingak shale of the Arctic coast. The assignment of all 

these rocks to the Lower Jurassic has not, however, been positively 

established. The Kialagvik formation, the Kingak shale, some of 

' the volcanic rocks of Cook Inlet, and the Thane volcanic group of 

/ southeastern Alaska are possibly Middle Jurassic.

The sequence of these rocks within the Lower Jurassic has not

been clearly proved either by observed succession or by paleontologic

. evidence. The sequence that is indicated above and that is shown

in the table opposite page 270 represents the writer's opinion, which

is based on incomplete and indirect evidence that will be discussed

,' below.

! Lower Lias (?) horizon. The oldest Jurassic rocks of Alaska 

are believed to be the 2,300 feet of calcareous sandstone, sandy shale, 

and limestone of the Alaska Peninsula, which lie with apparent 

conformity on Upper Triassic beds and are overlain by or faulted 

against Upper Jurassic beds. These rocks have been found only in 

a small area near Cold Bay. Their equivalent has not been recognized elsewhere in Alaska, but it may possibly be represented by 

unrecognized beds in or associated with the Lower Jurassic volcanic 

rocks of Cook Inlet and the Talkeetna Mountains. These rocks have 

. been assigned to the lowest position in the Alaskan Jurassic sequence, 

\ because of their apparently conformable position on the Upper Trias- 

\ sic rocks and because the few fossils which they have yielded include 

ammonites that are suggestive of the Lower Lias.

Talkeetna horizon (Middle Lias?). The Talkeetna formation of 

the Talkeetna Mountains and Matanuska Valley is believed to occupy 

a position in the Lower Jurassic somewhat above the horizon of the 

bi*sal Jurassic (Lower Lias?) calcareous sandstone, shale, and limestone of Alaska Peninsula. It is composed of lava, agglomerate, 

and tuff interbedded with sandstone and shale. Its thickness is probably at least 3,000 feet. It contains fossil plants and marine shells. 

It is probably represented by the tuff, agglomerate, and interbedded 

marine fossiliferous strata of Seldovia and Port Graham, on Kenai 

Peninsula, by the basaltic and andesitic lava and tuff of the west 

coast of Cook Inlet, by the lava, tuff, arkose, chert, and limestone 

of the Skwentna group of the Alaska Range, possibly by the sup- 

' posed Lower Jurassic tuffaceous conglomerate near Taral, in the 

Chitina Valley, possibly by part or all of the Thane volcanic group 

near Juneau, and possibly by part or all of the lower or Middle Jurassic breccia, tuff, and lava of the Wrangell district and of Gravina 

\ Island.
270 MESOZOIC STRATIGRAPHY OF ALASKA

The rocks of the Talkeetna horizon have not been observed in 

contact with those of the supposed older (Lower Lias?) beds of 

' Alaska Peninsula or with those of the supposed younger Kialagvik 

formation, Paleontologic evidence of their relation to these formations is also lacking. The Talkeetna formation is tentatively assigned 

to a position next above the basal Jurassic (Lower Lias?) of Alaska 

Peninsula, because its fossils include genera that are suggestive of a 

position fairly low in the Lias, and because neither the fossils nor 

any known superposition of the rocks on Triassic beds offers any 

suggestion that these rocks are at the base of the Alaskan Jurassic 

sequence.

Kialagvik horizon (Upper Lias ?}. The writer believes that the 

youngest Lower Jurassic rocks of Alaska are those of the Kialagvik 

formation of the Alaska Peninsula and the Kingak shale of the 

Arctic slope. The rocks of the Kialagvik horizon have not been seen 

in contact with the supposedly next older rocks of the Talkeetna 

horizon. The Kialagvik fauna is clearly younger than any fossils 

that have been found in the Talkeetna formation or in its supposed 

equivalent on Kenai Peninsula.

The exact relation of the Kialagvik formation to the next younger 

rocks of the Tuxedni. horizon, which are Middle Jurassic, has not 

been determined. Fossils that are supposed to be representative of 

the Tuxedni fauna have been found in close geographic association 

with the rocks of the Kialagvik formation, but there* is some doubt 

as to whether this association implies a transition from the Kialagvik 

to the Tuxedni beds or the presence of unrecognized areas of the 

Tuxedni sandstone within the supposed area of the Kialagvik formation. The writer believes that the rocks and faunas of the Tuxedni 

and Kialagvik horizons will probably prove to be sharply defined 

and that they may be separated by an unconformity.

MIDDLE JURASSIC

Tuxedni horizon (Bajocian and Bathoniari). The undoubted 

Middle Jurassic rocks of Alaska include the Tuxedni sandstone of 

the west coast of Cook Inlet and the Matanuska Valley; the Tordrillo 

formation, which carries the Tuxedni fauna, in the Yentna and 

Skwentna Valleys; and a tuffaceous slate with the Tuxedni fauna 

near the mouth of Chitina River. Fossils that occur in the Tuxedni 

fauna have also been found on the Alaska Peninsula, and it is possible that part of the rocks that have been mapped as belonging in 

the Kialagvik (Middle? Jurassic) and Shelikof (Upper Jurassic) 

formations may actually represent unrecognized areas of the Tuxedni 

sandstone. It is also possible that the Tuxedni horizon may be represented in some of the volcanic rocks of southeastern Alaska, not-
Correlation of Jurassic rocks of AtasJca

Age

Jurassic. Upper 

Jurassic. Middle 

1

Jurassla Lower 

European 

classification

Purbecklan.

Portlandian.

Kimmeridgian.

Sequanian or Upper Oxfordian.

Argovian or 

Lower Oxfordian.

Callovian.

Bathonian or 

Great oolite.

Bajocian or 

Inferior oolite.

Torcian or 

Upper Lias.

Charm on thian. 

or Middle Lias.

Lower Lias.

Alaska Peninsula

Naknek formation

Shale, sandy shale, 

and sandstone; 

1,200 feet. 

Arkosic sandstone; 

800 feet.

Conglomerate 

(Chisik?); 2,000- 

3,000 feet.

Shelikof formation: 

Black shale; 700- 

1,000 feet. 

Sandstone with 

some shale and 

conglomerate; 

4,000-4,700 feet. 

Shale; 1,500 feet.

Kialagvlk formation; 

sandstone and sandy 

shale; 500-f feet. 

(May be partly or 

wholly Middle Jurassic.)

'.Calcareous sandstone, 

sandy shale, and 

limestone; 2,300 feet.

West coast of Cook 

Inlet

formation Naknek 

Massive sandstone, 

arkose, and tuff; 

3,000 feet.

Gray shale with 

some sandstone; 

Cardioceras in 

lower part; 1,500 

feet,

Chisik conglomerate member; 290- 

400 feet.

Chinitna shale; dark 

shale with Cadoceras 

2Jm lower part; 2,300 

feet.

Tuxedni sandstone; 

A sandstone and sandy 

4 shale, with some 

ff conglomerate and 

 , limestone; 1,500 to 

'-. 3,000 or possibly 

j. 8,000 feet.

Basaltic and andesitic 

lava and tuff; 1,000 

feet.

Kenai Peninsula

Tuff and conglomerate with interbedded 

marine fossilifcrous 

strata; 1,000 to 3,000 

feet.

Alaska Range 

(Yenta and Skwentna 

valleys)

Tordrillo formation; 

grit, sandstone, and 

argillite, with some 

conglomerate and 

limestone; includes 

beds with Tuxedni 

fauna; 2,000 to 3,000 

feet.

Skwentna group; lava, 

tuff, arkose, chert, 

and limestone; 1,000 

to 4,000 feet. Probably Lower Jurassic.

Matanuska Valley 

and 

Talkeetna Mountains

Naknek formation

Shale, sandstone, 

and conglomerate 

with Aucella and 

Cardioceras; 1,000 -t-feet.

Conglomerate 

(Chisik?).

Chinitna formation; 

shale, conglomerate, 

and sandstone with 

Chinitna fauna; 

2,000dbfeet.

Tuxedni sandstone; 

sandstone, sandy 

shale with Tuxedni 

fauna; l.OOOzfc feet.

Talkeetna formation; 

lava, agglomerates, 

and tuff interbedded 

with sandstone and 

shale; 3,000 ± feet. 

Largely or wholly 

marine.

Chitina Valley

Tuffaceous slate 

near mouth of 

Chitina River 

with Tuxedni 

fauna.

Tuffaceous conglomerate near 

Taral; 500+ 

feet.

Nutzotin 

Mountains

Slate, graywacke, 

and conglomerate with Aucella.

Chichagof and 

Baranof islands Juneau district

Graywacke, slate, 

and conglomerate with Aucella.

-

Douglas Island volcanic group; melaphyre flows, tuff, 

and agglomerate. 

May be post- Jurassic. 

Treadwell slate; black 

clay slate with some 

conglomerate and 

considerable graywacke. May be 

post-Jurassic.

Thane volcanic group; 

melaphyre tuff, 

limestone, tuff, and 

slate (possibly 

Lower or Middle 

Jurassic) .

Gravina Island

Slate and limestone interbedded with tuff 

and containing 

Aucella.

Breccia, tuff, and 

lava (possibly 

Lower or Middle 

Jurassic) .

Canning River 

and vicinity

Ignek formation; black 

shale with coal beds 

and some sandstone; 

contains marine 

"Jurassic or Cretaceous" fossils; position uncertain; 

2,500 feet.

Kingak shale; black 

shale with fauna of 

Kialagvik formation 

and crinoids; several 

thousand feet. (May 

be Middle Jurassic) .

Firth River

Dark shale with crinoids; rocks associated with Triassic 

beds; thickness not 

known.

49448 26. (Face p. ?7C.)
JURASSIC, SUMMARY 271

ably in the Thane volcanic group and in the "Lower or Middle 

Jurassic breccias, tuffs, and lavas " of Gravina Island.

The Tuxedni sandstone of Cook Inlet includes sandstone and 

sandy shale with some conglomerate and limestone. It has a thickness of probably 1,500 to 3,000 feet and possibly 8,000 feet. It is 

believed to lie unconformably on Lower Jurassic lava and tuffs of the 

Talkeetna horizon and is overlain with apparent conformity by the 

Upper Jurassic Chinitna shale. It contains many marine invertebrate fossils and some fossil plants.

The Tuxedni sandstone of the Matanuska Valley includes'.sandstone and sandy shale that seem to be about 1,000 feet thick, underlain by the Talkeetna formation and overlain by beds that carry the 

, fauna of the Chinitna shale.

The Tordrillo formation of the Alaska Range (Yentna and 

Skwentna Valleys) is composed of grit, sandstone, and argillite with 

some conglomerate and limestone. It is 2,000 to 3,000 feet thick. It 

contains beds that carry the Tuxedni fauna. The Tordrillo formation is believed to lie unconformably on the rocks of the Skwentna 

group, which is believed to belong at the Talkeetna horizon. Its top 

and the overlying beds have not been recognized.

The tuffaceous slate near the mouth of Chitina River which contains the Tuxedni fauna is underlain by tuffaceous conglomerate 

that may be Lower Jurassic. No overlying beds have been seen.

The Thane volcanic group, which is perhaps of Tuxedni age, consists of melaphyre tuff, limestone, and tuff and slate. Melaphyre 

tuff that may be of the same age has been found in the Wrangell district. Some breccia, tuff, and lava on Gravina Island may also belong at the Tuxedni horizon.

UPPER JURASSIC

General sequence. The Upper Jurassic rocks of Alaska include 

beds assigned to three generally recognizable horizons. At the base 

of the Upper Jurassic is the Gadoceras zone of the Chinitna shale 

and its equivalent, which corresponds to the Callovian of the European classification. Next above the Chinitna is the Gardioceras 

zone, which occurs in the lower part of the rocks that have been 

described as the Naknek formation of Cook Inlet and which corresponds to the Oxfordian of Europe. At the top of the Upper 

Jurassic is the upper part of the Naknek formation of the Alaska 

Peninsula and its probable equivalents, which are characterized by 

Aucella cf. A. pallasi Keyserling, Aucella cf. A. bronni Rouillier, and 

Aueella cf. A. erringtoni Gobi) and which are believed to correspond 

to the Kimmeridgian and Portlandian of the European sequence.

Gadoceras zone (Oallovian). The oldest Upper Jurassic rocks of 

Alaska the Cadoceras zone include the typical Chinitna shale of
272 MESOZOIC STEATIGEAPHY OF ALASKA

the west coast of Cook Inlet; some shale, conglomerate, and sandstone with the fauna of the Chinitna shale in the Matanuska Valley; 

and the middle member of the Shelikof formation of the Alaska 

Peninsula, which consists of sandstone, shale, and conglomerate 

carrying the Chinitna fauna.

The Chinitna shale of the west coast of Cook Inlet consists of 

dark shale about 2,300 feet thick. It overlies the Tuxedni sandstone 

with apparent conformity and is overlain, without known conformity, 

in some places by unfossiliferous conglomeratic beds (Chisik conglomerate member of Naknek formation) and in others by the shale 

of the higher Gardioceras zone of the Naknek formation. The 

Chinitna shale contains several species of Cadoceras, which are 

regarded as. characteristic of its horizon.

The Chinitna formation of the Matanuska Valley is composed of 

shale, conglomerate, and sandstone about 2,000 feet thick. It rests 

conformably on the Tuxedni sandstone and is believed to be overlain conformably by shale of the Gardioceras zone and perhaps locally 

by the equivalent of the Chisik conglomerate member.

The Shelikof formation of the Alaska Peninsula includes three 

members shale about 1,500 feet thick at the base; sandstone interbedded with some shale and conglomerate, having a thickness of 

4,000 to 4,700 feet, in the middle; and black shale 700 to 1,000 feet 

thick at the top. The middle member contains the fauna of the 

Chinitna shale. The lower and upper members have yielded only 

fossils that are not characteristic of definite horizons. The base 

of the Shelikof formation has not been clearly recognized. There 

are some indications that it may rest unconf ormably on the Kialagvik 

and basal Jurassic formations, but these supposed basal contacts 

may be faults. The Shelikof formation is overlain, with apparent 

conformity, by conglomerate that is supposed to be the approximate 

equivalent of the Chisik conglomerate member of the Naknek formation of Cook Inlet.

Cardioceras zone (Oxfordian). The next fossiliferous strata 

above the Cadoceras-be&rmg beds of the Chinitna shade on the west 

ooast of Cook Inlet consist of shale that contain several species of 

Gardioceras. This shale has heretofore been included in the Naknek 

formation, but inasmuch as Gardioceras has been found at only one 

locality on the Alaska Peninsula, there is some doubt as to whether 

the shale is represented in the type section of the Naknek formation 

and as to whether it should be considered part of the Naknek formation. The writer believes that the Cardioceras-beaTmg beds should 

be excluded from the Naknek formation. Cardioceras has also been 

found at one locality in the Matanuska Valley, in beds which have 

been referred to the Naknek formation but whose precise position
JURASSIC, SUMMARY 273

\

relative to the other horizon has not been determined. Cardioceras 

has not been found in other Alaskan regions.

The position of the Cardioceras-be&r'uig beds on Cook Inlet is 

perhaps occupied locally by the massive, lenticular, unfossiliferous 

beds of the Chisik conglomerate member of the Naknek formation, 

which directly succeeds the Chinitna shale at some localities and is 

absent or reduced to pebbly sandstone at other localities, notably 

at the localities near which Cardioceras has been found. The Chisik 

conglomerate is supposed to be represented by conglomerate in the 

Matanuska Valley and Alaska Peninsula, but the writer suspects 

that in one or both of these localities the conglomerate may occur 

at a higher horizon than that of the Chisik conglomerate.

Aucella zone (Kimmeridgian and Portlcmdian). The rocks of 

the Aucella zone include the major part of the Naknek formation 

of the Alaska Peninsula; the upper part of the Naknek formation 

as heretofore described on the west coast of Cook Inlet; the upper 

part of the rocks in the Matanuska. Valley that have been described 

as the Naknek formation; the slate, graywacke, and conglomerate 

with Aucella cf. A. browni in the Nutzotin Mountains; the graywacke, slate, and conglomerate with Aucella cf. A. flscheriana 

(D'Orbigny) of Chichagof and Baranof islands; possibly the 

Treadwell slate and the Douglas Island volcanic group of the Juneau 

district; a; part of the "Berners formation" of Berners Bay; and 

possibly the slate, limestone, and tuff containing Aucella on Gravina 

Island.

The Naknek formation of the Alaska Peninsula has been described as including at its base the probable representative of the 

Chisik conglomerate member of the Naknek formation of the west 

coast of Cook Inlet, above which is 800 feet of arkosic sandstone, 

overlain by 1,200 feet of shale, sandy shale, and sandstone. The 

fauna of the typical Naknek formation, which is characterized 

especially by several species of Aucella related to A. pallasi Keyserling, A. bronm Kouillier, and A. erringtoni Gabb, occurs chiefly if 

not wholly in the upper shale member.

The rocks on the west coast of Cook Inlet that have heretofore 

been described as the Naknek formation include 3,000 feet of massive sandstone, arkose, and tuff, underlain by 1,500 feet of gray shale 

with some sandstone. The lower beds, which contain Cardioceras 

in their lower part, have already been described as the Cardioceras 

zone. The upper beds, which overlie the lower beds conformably, 

and possibly part but probably not all of the lower beds are believed by the writer to represent the Naknek formation of the Alaska 

Peninsula.
274 MESOZOIC STRATIGRAPHY OF ALASKA

The Naknek formation of the Matanuska Valley comprises at 

least 1,000 feet of shale, sandstone, and conglomerate. An undetermined part of these rocks belong in the Gardioceras zone. The 

Naknek rocks of the Matanuska Valley include some beds of conglomerate, which may either represent the Chisik conglomerate or 

may belong at some higher horizon in the Naknek, probably at the 

top of the Gardioceras zone.

The Naknek is represented in the Nutzotin Mountains by slate, 

graywacke, and conglomerate containing Aucella bronni Rouillier. 

These beds are believed to be underlain unconformably by Upper 

Triassic rocks and to be overlain by Lower Cretaceous beds.

The Naknek is probably represented on Chichagof and Baranof 

Islands by graywacke, slate, and conglomerate containing Aucella 

cf. A. fischeriana (D'Orbigny).

In the Juneau district the Naknek may possibly be represented by 

part or all of the Treadwell slate, which is composed of black clay 

slate with some conglomerate and considerable graywacke, and of 

the Douglas Island volcanic group, which is composed of melaphyre 

lava, tuff, and agglomerate. Neither the Treadwell slate nor the 

Douglas Island volcanic group has yielded any fossils.

The " Berners formation " of Berners Bay also includes some 

Upper Jurassic rocks, which probably represent the Naknek formation.

The Aucella-be&r'mg slate, limestone, and tuff of Gravina Island, 

which are underlain by supposed Lower or Middle Jurassic volcanic rocks and overlain by supposed Lower Cretaceous conglomerate, graywacke, and slate, may also belong at the Naknek horizon.

CORRELATION 

LOWER JURASSIC

The evidence for the correlation of the Lower Jurassic rocks of 

Alaska, together with that concerning the other Jurassic rocks of 

the territory, has already been presented in detail in the description of local sections on pages 133-268. A summary of the correlation of the Jurassic formations of the several Alaskan districts with 

each other has been given in the table facing page 270. A similar 

summary of the correlation of the Alaska Jurassic formations with 

those of other North American regions is given in the table facing 

this page. .

It has been shown on page 268 that the supposed Lower Jurassic 

rocks of Alaska probably include three formations of different ages, 

which the writer has designated, in ascending order, basal calcareous 

sandstone, sandy shale, and limestone of Lower Liassic (?) age; the
Correlation of Jurassic rocks of North America

Age

 * »

1

Middle Jurassic

Jurasslo Lower 

European 

classification

PurbecHan.

Portlandtan.

Kunmeridgian.

8«quanian or 

'Upper Oxford* 

ten.

Argovian or Lower Oxfordian.

Callovian.

Bathonian or 

Great oolite.

Bajodan or Inferior oolite.

Upper Lias or 

Toarcian.

Middle . Lias or 

Charmouthian:

Lower Lias.

Alaska

Naknek formation

Aucetta-bearhrgBeds.

Cardiocerag 

cone.

Chisik conglomerate; 

member.

Chinitna shale.

Tuxedni sandstone.

Kialagvik formation. (Maylbe 

partly or wholly 

Middle Jurassic.)

Talkeetna formation.

Calcareous sandstone, sandy, 

shale, and limestone of Cape 

K e k u r n o i 

region.

Graham Island, 

B.C."

Yakoun formation; basaltic agglomerate, lava, 

and tuff and 

tuftaceous sandstone with Tuxedni fauna.

Maude formation; 

argillite, sandstone, and tuff.

Skeena River, 

B.C.*

Hazelton group; 

andesitic porphyry and tuff, 

interbedded 

with fossiliferous sandstone 

and shale; probably contains 

Upper Jurassic 

(Naknek) and 

Middle Jurassic 

(Tuxedni) faunas.

Dtasyoucou (Dean) 

River, B. C.«

"Porphyrite 

series"; porphyry and tuff 

interbedded 

with sediments 

containing Tuxedni fauna.

)

Kamloops district, 

B. C.*

Nicola series; upper part comprising limestone with Lower or Middle 

Jurassic fossils, 

underlain by 

Triassic volcanic rocks.

Alberta 

Fernie shale; 

dark shale 

with Cardioceres.

Montana f

Bills formation; 

calcareous 

shale, sandstone 

and limestone 

with Quenstedticeras in ..upper 

part;?CallovJan 

-genera in lower 

part.

WyomingjColorado, and Utah /

0

guidance formation; sandstone 

and shale with 

Cardiocerat.

Humboldt Range, 

Nevada 

Slate with some 

limestone containing Arietites 

( Caloceras) cf . 

A. nodotianus 

D'Orbigny.

Cascade Mountains, Washington*

Sandstone, slate, 

and conglomerate, with Aucella 

. emngtoni.

**

Blue Mountains, 

Oregon <

Red sandstone 

with fauna of 

Hardgrave 

sandstone.

Western Oregon 

and northern California'

Knoxville group 

(?) Qower part 

?) and Myrtle 

formation (?) 

Gower part ?); 

may be Jurassic 

or Cretaceous. 

Dothan formation; -f sandstone/ 

and shale with 

Aucella erring' 

toni. Qalice formation; slate 

with some sandstone and con* 

glomerate; contains AttceUa 

errtnfftoni.

Redding quadrangle, California *

 if.

Fotem formation; 

shale, sandstone, and tuffaceous conglomerate.

Bagley andesite; 

flows and tuff. 

Modin formation; 

sandstone and 

shale underlain 

by volcanic conglomerate.

Tayloravffle region, California '

Foreman - forma-, 

tion (exact position doubtful).

TTinniiTmm sandstone.

Bicknell sandstone.

Mormon sand° 

stone. Thompson limestone.

Fant meta-andesite. Hardgrave 

sandstone.

Trail formation.

Sierra Nevada, 

California*"

 Vi*

Marlposa slate; 

slate, sandstone, 

conglomerate, 

and tuff, with 

Amoeboeerat 

and Aucella er~ 

riitfftoni.

Texas 

Malone formation; (limestone 

with some conglomerate, sandstone, and gypstun.

Mexico*

Marly and phosphatiic limestone in Sierra de Mazapll 

and Santa Rosa.

Shale^and limestone" near 

Mazapil, with Aucella and 

ammonites.

Limestone with Nerinea 

near MazapU; marly limestone in Oaxaca.

Marly beds with Stephanaceras in Oaxaca.

Micaceous clay slate with 

Arietites in Puebla and 

Vera Cruz; plant beds in 

Vera Cruz, Puebla, and 

Oaxaca.

Cuba » .

Limestone near 

Vinales, in Pinar del Rio.

 McKenzie, J. D., Canada Qeol. Survey Mem. 88, No. 1622, pp. 40-61,1916.

* Leach, W. W., Canada Qeol. Survey Summ. Rept. for 1911, pp. 93-94. McConnell, R. Q., Canada Qeol. Survey Summ. Rept. for 1912, pp. 58-59. O'Neill, J. J., Canada Qeol. 

Survey Mem. 110, pp. 4-5,1919.

 Dawson, Q. M., Canada Qeol. Survey Rept. Progress for 1876-77, pp. 58-66. Whiteaves, J. F., idem, pp. 150-159.

-> Dawson, Q. M., Canada Qeol. Survey Ann. Rept., new ser. vol. 7, pp. 51B, 113B, 115B, 1896.

-Dowling, D. B., Canada Qeol. Survey Pub. 949, pp. 8-9, 36-37,1907.

/Reeside, J. B., jr., U. S. Qeol. Survey Prof. Paper 118, 1920.

« Louderback, Q. D., Qeol. Soc. America Bull., vol. 15, p. 295,1904. Smith, J. P., California Acad. Sci. Proc., 3d ser., vol. 1, p. 364,1904.

» Smith, Q. O., and Calkins, F. C.. U. S. Qeol. Survey Bull. 235, p. 27, 1904.

i Hyatt, Alpheus, Qeol. Soc. America Bull., vol. 5, p. 401,1894.

i Stanton, T. W.. U. S. Oeol. Survey Bull. 133, pp. 30-31, 1895. Diller, J. 8., Am. Jour. Sci., 4th ser., vol. 23, pp. 401-421,1907. Smith, J. P., Science, new ser., vol. 30, pp. 

347-348,1909. Knowlton, F. H., Am. Jour. Sci., 4th ser.. vol. 30, pp. 33-64,1910.

* Dffler, J. S., U. S. Qeol. Survey Qeol. Atlas, Redding folio (No. 138), 1908. 

«Diller, J. S., U. S. Qeol. Survey Bull. 353,1908.

» Smith, J. P., Qeol. Soc. America Bull., vol. 5, pp. 243-248,1894. Hyatt, Alpheus, idem, pp. 403-413. Turner, H. W., and Ransome, F. L., U. S. Qeol. Survey, Qeol. Atlas, 

Sonora folio (No. 41), 1897. Lindgren, Waldemar, U. S. Qeol. Survey, Qeol. Atlas, Colfax folio (No. 66), 1900. Reeside, J. B., jr., U. S. Qeol. Survey Prof. Paper 118,1920. 

« Cragin, F. W., U. S. Qeol. Survey Bull. 266,1905.

 Various authors dted by Willis, Bailey, U. S. Qeol. Survey Prof. Paper 71, 1912; De Lapparent, A., traitfi de gfiologie, 1893, and Stanton, T. W., Qeol. Soc. America Bull., 

vol. 29, pp. 604-605, 1918.

» O'Connell, Marjorie, Qeol. Soc. America Bull., vol. 31, p. 136,1920; Am. Mus. Nat. Hist. Bull., vol. 42, pp. 643-692,1920.

49448^-26. (Face p. 274.)
JURASSIC, SUMMAEY 275

Talkeetna formation, of Middle (?) Liassic age; and the Kialagvik 

formation, of Upper Liassic (?) age. The writer believes that these 

formations possibly represent, in a general way, the subdivisions of 

the Liassic mentioned, but it should be frankly admitted that there 

is very little evidence on which definite correlation of these rocks can 

be based. The evidence on the age and correlation of the rocks of 

the several districts has been given on the preceding pages in some 

detail. The general character of the Lower Jurassic faunas and 

floras is also indicated in the following table.

Lower Jurassic floras and faunas

Ptoria

Pleuromya dalli (White)... __ - ____ ......... ___ ...

Arcomya crassissima Eichwald.... ___ . 

1

X

X

X

X

y

X

X

X

?

X

?

2

X

X

?

X

X

X

X

X

X

X

X

X

?

?

?

X

X

X

X

X

3

X

X

X

X

X

X

X

X

X

X

4

X

X

5

X

X

X

X

X

X

X

X

X

X

6

X

7

X

,
276 MESOZOIC STRATIGRAPHY OF ALASKA 

Lower Jurassic floras and faunas Continued

Thracia? _ ............. ....................................

Tancredia?.........-.-.--........-...........-.-...........

Venerids? . ...............................................

Pseudomelam'a?...---. ___ ...... _ . ___ _. _ .... .....

Aegoceras? _______ . _ . __ ...----.... ___ . _ .. ...

Amaltheus? _____________ ... _ . _ ......... __ .

Hammatoceras? kialag vikense (White) .... ...... __ . _

Harpoceras. _______ .... _ . ___ ............... .....

Stephanoceras?.... __ ... __ . ___ ... __ __ _ ... __ ...

1

X

X

?

X

2

X

y

y

X

V

3

X

X

X

?

X

4 5

X

X

X

X

X

?

X

X

X

X

X

X

?

X

X

X

X

6

X

X

X

7

1. Basal (unnamed) Jurassic formation of Alaska Peninsula.

2. Talkeetna formation of Matanuska Valley.

3. Tuffs of Kenai Peninsula.

4. " English Bay."

5. Kialagvik formation (Lower or Middle Jurassic).

6. Kingak shale (Lower or Middle Jurassic).

7. Crinoid bed of Firth River.

The basal Jurassic rocks of Alaska Peninsula are assigned to the 

base of the Alaskan Jurassic sequence and are correlated with the 

Lower Lias because they lie with apparent conformity on Upper 

Triassic rocks and contain ammonites that have been questionably 

identified as Aegoceras, Arietites, and Amalthem, which are indicative of the Lower or Middle Lias. Collections made in 1924 by 

W. R. Smith on the shores of Cold and Alinchak bays indicate that 

the Kialagvik fauna may also be present in this area.

The Talkeetna horizon is assigned to the next higher position in 

the Alaskan Jurassic sequence and is tentatively correlated with the 

Middle Lias because there is no evidence that it immediately succeeds the Upper Triassic rocks, except in Kenai Peninsula, where it 

may lie unconformably upon them, and because it contains ammonites, such as Aegoceras and Deroc&ras, which are indicative of the 

Lower or Middle Lias. The fossil plants, according to Knowlton, 

suggest a correlation with the Ehaetic or Lias flora of the Island of 

Bornholm, off the coast of Sweden, but are seemingly not indicative 

of any special position within the Lias. The. equivalent of the 

Talkeetna formation may possibly be found in the argillite, sandstone, and tuff of the Maude formation 72 of Graham Island, B. C.,

 McKenzle, J. D., Canada Geol. Survey Mem. 88, No. 1622, pp. 40-61, 1916.
JURASSIC, SUMMARY 277

and in the upper but not the very highest part of the Nicola series 73 

of the Kamlops district, B. C. The Bagley andesite 74 of California 

may also belong at the same horizon.

The Kialagvik formation, which has been referred to the Middle 

Jurassic by Hyatt and by Stanton and to the Upper Lias by several 

European paleontologists, is here referred tentatively to the Upper 

. Lias, chiefly because its characteristic ammonites, Hammatoceras, 

' Harpoceras, and Dactylioceras, have been regarded as indicative of 

the Upper Lias (Toarcian), and because the writer believes that 

there is no connection between its fauna and that of the Tuxedni 

sandstone except in the presence of Inoceramus lucifer Eichwald. 

Its American equivalents, outside of Alaska, may perhaps be found 

in the upper part of the Nicola series 75 of British Columbia and in 

the Hardgrave sandstone or the Mormon sandstone of California.76

MIDDLE JURASSIC

The Middle Jurassic rocks of Alaska include only the Tuxedni 

sandstone and its equivalents, unless the rocks of the Kialagvik 

horizon are Middle Jurassic. The Tuxedni sandstone contains a 

large marine fauna, which has not yet been exhaustively studied 

and whose precise position has therefore not yet been determined. 

The general character of the fauna and the presence of ammonites 

related to Stephanoceras humphriesianum (Sowerby) and Parkinsonia parkinsoni Sowerby indicate a correlation with the Bajocian 

or Inferior oolite of Europe. The great thickness of the Tuxedni 

sandstone and its position conformably beneath the Chinitna shale, 

which is of Callovian age, suggest that it may also represent part 

or all of the Bathonian or Great oolite. In this connection it should 

be noted that Parkinsonia parkinsoni occurs in some of the Bathonian beds of Europe. The presence in the Tuxedni fauna of 

Harpoceras and of Lima cf. L. gigantea Sowerby suggest that it 

may also include part of the Upper Lias. The writer believes that 

the Tuxedni horizon certainly represents the Bajocian, that it probably represents part or all of the Bathonian, and that it possibly 

represents part of the Upper Lias of Europe.

The equivalents of the Tuxedni in British Columbia include the 

basaltic agglomerate, lava, and tuff and tuffaceous sandstone of 

the Yakoun formation 77 of Graham Island; the lower part of the 

andesitic porphry and tuff and fossiliferous sandstone and shale

73 Dawson, G. M., Canada Geol. Survey Ann. Kept., new ser., vol. 7, pp. 51B, 113B, 

115B, 1896.

 "Diller, J. S., U. S. Geol. Survey Geol. Atlas, Redding folio (No. 138), 1906.

75 Dawson, G. M., op. cit., pp. 51B, 113B, 115B.

 Diller, J. S.. U.«. Geol. Survey Bull. 353, 1908.

" McKenzie, J. D., Canada Geol. Survey Mem. 88, No. 1622, pp. 40-51, 1916.

49448 26 19
278 MESOZOIC STRATIGRAPHY OF ALASKA

of the Hazelton group 78 of Skeena River; at least part of the porphyry, tuff, and sedimentary rocks of the Porphyrite series 79 of 

Iltasyoucou (Dean) River; and possibly the uppermost part of the 

Nicola series 80 of the Kamloops district. It is probably represented 

in California by the Mormon sandstone and Thompson limestone 

of the Taylorsville region 81 and by the upper part of the Potem 

formation of the Redding quadrangle.82

The fauna and flora of the Tuxedni sandstone as found in several Alaskan districts are listed in the following table:

Middle Jurassic (Tuxedni) fauna and flora

Cladophlebis. _ . ___ . ____ . ___ . ___ . ___ . ___ ..........

Marattiopsis or Danaeopsis ___ . _______ . _ . _ . ___ ..........

Sagenopteris goppertiana Zigno _____ ......... ____ ..............

Macrotaeniopteris californica Fontaine.. ................................

NilsoniaorientalisHeer... ___ .... __ . __________ . __ . ....

Nilsonia.. __________________ . __ . _____ ... __ . ....

Pterophyllum rajmahalense Morris ___ . _ . _______ .. ........

Pterophyllum or Zamites.. _______ . _ .. __________ . _ ...

Fieldenia nordenskioldi Nathorst? .. ___________ . __ . ........

Fieldenia?................................ ...... ...... ........ ........

Phoenicopsis?.. _ __ ...... _ ..... _ ........... _ .................

Stems... __ . _ . _ . _ .. ___ ...... _ . ____________ .

Fossil wood. _____ . ________________ .. ____ .... ...

Rhynchonella... ___ .. _ ..... . . . .... __ ... ......

Terebratula. - _ . ____ . ____ ....... _____ . ___ . __ . ....

Leda?................... ...... .......... ...... .. ...............

Nemodon?... _ ..... . . . . ..,. _ . ......

Cucullaea.. __ . ____ . __ . _ ..... __________ . _ . ....

Area. ______ . __ .... .... _ .... .... ........................

Pinna....... __ .......... .........................................

Gervillia.. ......... _ .. _ ..................................... .

InoceramusambiguusEichwalcL.. ..__..__.___.____.__ ... .

Inoceramus porrectus Eichwald? __ . _ .. ______ _ . ............

Pteria.. ......... .......-...... ................... ....................

Eumicrotis. _____________ . ________________ ...

Trigonia devexa Eichwald ______ . __ . .............................

1

X

X

X

X

X

X

X

X

X

X

x

X

X

y

2

?"

?

?

?

3

y

X

X

X

?

4 5

V

?

78 Leach, W. W., Canada Geol. Survey Summ. Rept. for 1911, pp. 93-94. McConnell, 

R. G., Canada Geol. Survey Summ. Rept. for 1912, pp. 58-59. O'Neill, J. J., Canada 

Geol. Survey Mem. 110, pp. 4-5, 1920.

79 Dawson, G. M., Canada Geol. Survey Rept. Progress for 1876-77, pp. 58-66,. 

Whlteaves, J. F., idem, pp. 150-159.

80 Dawson, G. M.f Canada Geol. Survey Ann. Rept., new ser., vol. 7, -pp. 51B, 113B, 

115B, 1896.

a Diller, J. S., U. S. Geol. Survey Bull. 353, 1908. 

82 Diller, J. S., U. S. Geol. Survey Geol. Atlas, Redding folio (No. 138), 1906.
JURASSIC, SUMMARY 

Middle Jurassic (Tuxedni) fauna and flora Continued

279

Pec ten _______ ____ .................... __ . ___ . ___ --...

Lftna ___ .. _ .... ____ ... _ ........... __ .. __ .-.- _ . ...

Modiola __ . ___ .-. _ . _ .......... _ ...... _ ... ___ .....

Pleuromya carlottensis Whiteaves?. .............. _ ........... __ .....

Anatina? _________ . __ ........ ___ . _ ..................

Thracia.. ____________ ... _____ ... _____ ............. _ .

Arctica. __ . _ . ___ .... ___ . __ ............... _ ......... ....

Cyprma?...-----------.-------...----... -----._._...._.._.--._-.-....._.

Praeconia?...... __ . _ . ___ ............... ___ ... ___ . ......

Tancredia?.- _ .. _ . _ -... _ .... _ ...... ___ . ___ _ ...

Sphaeriola?.. _____________ ..... _ . _________ ... ...

Undetermined Solenidae? _ ..... __ .... ____ . _ . _____ . ......

Natica ____________ . ______ . ______________

Turritella?. ...........................................................

Nerinea.. _ . ___ ... _ _ ................... ___ .. _ . .......

Alaria? _ __ . ____ . __ . ___ ... _ ..... _________ . ___ ..

Aporrhais?. ...... ___ .. __ ..... __ .... ______ .. __ ......

Oppelia? __ .... _____ .... __ .. _______ . __________ .

Stephanoceras cf. S. humphriesianum (Sowerby) _____ . __ . __ ..

Stephanoceras richardsoni Whiteaves ____ .. _ .... __ . ___ .......

Stephanoceras? cf. S. loganianus (Whiteaves) __ .. _ ________ . ...

Stephanoceras? cf. S. carlottensis (Whiteaves)...................... _ .

Macrocephalites. ______________ .......... __ . ____ ... ...

Perisphinctes. ........ __ .. ______ .... _ . ______ . ___ _ ...

Parkmsonia? cf. P. parkinsoni Sowerby __ .. _ ..... __ _ .. _ ...

Belemnites (slender form) __ ____ . ___ ... __________ . ......

Belemnites (hastate form) . ..............................................

Belemnites ______________ . ...... .. .......................

1

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

?

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

--X

X

X

X

2

?

?

?

?

3

X

X

?

X

?

X

X

X

?

?

X

X

X

X

X

X

X

X

X

4 5

?

?

1. Cook Inlet

2. Alaska Peninsula (Tuxednl sandstone).

3. Matanuska Valley (Tuxedni sandstone).

4. Alaska Range (Tordrillo formation).

5. Chitlna Valley (tuffaceous slate).

UPPER JURASSIC '

The Upper Jurassic rocks of Alaska embrace three faunal divisions the Cadoceras zone at the base (represented in the Chinitna 

and Shelikof formations), the CoKrdioceras zone next above (represented in the lower part of the Naknek formation), and the Aucella 

zone at the top (represented in the upper part of the Naknek formation.)
280 MESOZOIC STRATIGRAPHY OF ALASKA

The Chinitna fauna is characterized by the genus Cadoceras, 

which is indicative of a position in the Callovian at the base of the 

Upper Jurassic of Europe. This fauna has not been found in North 

America outside of Alaska, but the possible equivalent of the Chinitna horizon may be found in the Bicknell sandstone 83 of the 

Taylorsville region of California and possibly in the lower part of 

the Ellis formation84 of Montana.

The fauna and flora of the Chinitna horizon as found in the 

several Alaskan districts are listed in the following table:

 Fauna and flora of the Upper Jurassic Cadoceras zone of Alaska

Coniopteris burejensis (Zalessky) Seward _____ ...-......_.-.--..._.

Fossil wood ___ . ____ ...... _ . _ ........ .............. .....

Serpula.. __ .... ___ .--.-..--..... __ .....--.. .. ...... __ .

Pinna... ...... -.--.--.--.---------------.-.-------------------------.---

Pf-oria

Gryphaea.-. . I...- -- 

Gardium?. .............. ............................... .............

Venerid?.... 

Tellina?.. ........ ...................... ........ .....^... ...............

*

X

X

X

X

X

X

X

?

?

X

X

X

y

X

X

y

X

X

X

X

X

X

X

X

X

X

2

X

X

X

y

X

3

?

4

?

X

X

X

?

X

X

X

X

Xf

X

5

X

X

X

X

0

X

y

X

X

y

?

X

X

X

X

X

X

X

?

X

88 Diller, J. S., U. S. Geol. Survey Bull. 353, 1908.

* Reeside, J. B., jr., U. S. Geol. Survey Prof. Paper 118, 1920.
JURASSIC, SUMMARY 281 

Fauna and flora of the Upper Jurassic Cadoceras zone of Alaska Continued

Phylloceras subobtusiforme Pompeckj... ........... _ ....... _ ........

Phylloceras _______ - ___ - __ ......................... _ .......

Macrocephalites __ ____ ........ ^. ................... ... ... ....

Cadoceras catostoma Pompeckj. .................. _ . _ _. ..._..__ ...

Cadoceras grewingki Pompeckj. ...................... __ ..............

Cadoceras petelim Pompeckj- _..:...__. _ ................... _ ........

Cadoceras schmidti Pompeckj. ......... _ .............. ....^.. ... ......

Cadoceras stenoloboide Pompeckj................... _ . _ .............

Cadoceras cf. C.tchefkini (D'Orbigny). _ .................. ___ ......

Cadoceras wosnessenskiGrewingk.. ..__-__......__._._. _ . _ .........

Cosmoceras?.... .-,...---.-. ... .... ...... ........ ..,.. .........

Ammonite ____ ... _ .. _ .................. _ . _ ... _ .......

1

X

V

V

v

V

v

v

X

?

?

X

X

2

X

3 4

?

X

X

X

?

X

X

?

X

X

y

5

X

X

1. Chinitna shale of Cook Inlet.

2. Chinitna formation of the Matanuska Valley.

3. Shelikof formation, Alaska Peninsula, lower member.

4. Shelikof formation, Alaska Peninsula, middle member.

5. Shelikof formation, Alaska Peninsula, upper member.

The Cardioceras zone of Alaska contains a characteristic marine 

fauna, listed below, in which the most significant members are several species of Cardioceras. This genus is indicative of a correlation 

with the Argovian or Lower Oxfordian and perhaps with part of the 

Sequanian or Upper Oxfordian of the European section.

The North American equivalents of the Alaskan Cardioceras zone 

include the Fernie shale of Alberta,85 the upper part of the Ellis 

formation of Montana,86 and the Sundance formation of Wyoming, 

Colorado, and Utah.86

Fauna and flora of the Upper Jurassic Cardioceras xone of Alaska

Pteria..........................

Pecten...... ...................

Cyprina? __ .. __ -........-

1

X

X

X

X

X

X

X

X

X

X

X

X

X

X

v

2 3

v

Gastropods................ _ ..

Phylloceras.. _ .......... ....

Lytoceras ________ .......

(Whiteaves).. ___.-_.. _ ....

Cardioceras distans (Whitfield)

Cardioceras spiniferum Ree1

X

V

2

?

3

X

X

X

1. Lower part of Naknek formation of Cook Inlet.

2. Naknek formation of Alaska Peninsula.

3. Naknek formation of Matanuska Valley.

83 Bowling, D. B., Canada Geol. Survey Pub. 949, pp. 8-0. 36-37, 1907. 

^Reeside, J. B., jr., U. S. Geol. Survey Prof. Paper 118, 1020.
282 MESOZOIC STEATIGEAPHY OF ALASKA

The upper part of the Naknek formation and equivalent rocks in 

Alaska is characterized especially by several species of Aucella related to Aucella bronni Rouillier, A. erringtoni (Gabb), A. fischeriana 

(D'Orbigny), and A. pallasi Keyserling. The position of these 

rocks and the presence in them of the Jurassic type of Aucella indicate that they are to be correlated with the Kimmeridgian and Portlandian of Europe. They represent the boreal type of the Upper 

Jurassic. The North American equivalents of these rocks include 

the upper part of the Hazelton group of Skeena River, in British 

Columbia;87 the sandstone, slate, and conglomerate containing Aucella erringtoni in the Cascade Mountains of Washington;88 the 

Galice and Dothan formations and possibly the lower part of the 

Myrtle formation and of the Knoxville formation of western Oregon 

and northern California ; 89 the Mariposa slate of the Sierra Nevada, 

Calif. ; 90 and the Aucella-be&rmg beds near Mazapil, Mexico.91 The 

probable equivalents of the Aucella zone as represented by strata 

that carry faunas of different type may be found in the Hinchman 

sandstone and possibly in the Foreman formation of the Taylorsville 

region, Calif.,92 in various Upper Jurassic rocks of Mexico,91 probably in some of the Upper Jurassic limestones of Cuba,93 and possibly 

in the Malone formation of Texas.94

The fauna and flora of the Aucella zone of Alaska are represented 

in the following table:

87 Leach, W. W., Canada Geol. Survey Summ. Rept. for 1911, pp. 93-94. McConnell, 

R. G., Canada Geol. Survey Summ. Rept. for 1912, pp. 58-59. O'Neill, J. J., Canada 

Geol. Survey Mem. 110, pp. 4-5, 1920.

88 Smith, G. 0., and Calkins, F. C., U. S. Geol. Survey Bull. 235, p. 27, 1904.

89 Stanton, T. W., U. S. Geol. Survey Bull. 133, pp. 30-31, 1895. Diller, J. S., Am. 

Jour. Sci., 4th ser., vol. 23, pp. 401-421, 1907. Smith, J. P., Am. Jour. Sci., 4th ser., 

vol. 30, 1910, pp. 33-64, 1910.

Ol> Smith, J. P., Geol. Soc. America Bull., vol. 5, pp. 243-248, 1894. Hyatt, Alpheus, 

idem, pp. 403-413. Turner, H. W., and Ransome, F. L., U. S. Geol. Survey Geol. Atlas, 

Sonora folio (No. 41), 1897. Lindgren, Waldemar, U. S. Geol. Survey Geol. Atlas, 

Colfax folio (No. 66), 1900. Reeside, J. B., jr., U. S. Geol. Survey Prof. Paper 118, 1920.

01 Various authors cited by Willis, Bailey, U. S, Geol. Survey Prof. Paper 71,. 1912; 

De Lapparent, A., Traite" de geologic, 1893; and Stanton, T. W., Geol. Soc. America Bull., 

vol. 29, pp. 604-605, 1918.

93 Diller, J. S., U. S. Geol. Survey Bull. 353, 1908.

93 O'Connell, Marjorie, Geol. Soc. America Bull., vol. 31, p. 136, 1920; Am». Mus. Nat. 

Hist. Bull., vol. 42, pp. 643-692, 1920.

84 Cragin, F. W., U. S. Geol. Survey Bull. 266, 1905.
JURASSIC, SUMMARY . .. 283 

Fauna and flora of the Upper Jurassic Aucella zone of Alaska

Cladophlebis cf. C. haiburnensis (Lindley and Button) ___ . ....

Zamites megaphyllus (Philips) Seward. ______________

Cidaris?.......................................... __ .............

Serpula. __ .-. ____ . ___ . _ . ............................

Rhynchonella _ ........ __ . _ . _ . ... .......

Terebratula ________ ..... _______________ . ....

Nucula... __ . ________ . __ . _______________

Leda _ __ ........ _ _ .... _ ..... _ .. _ ____ .. ........

Grammatodon.. _ ... _ ..... _ . _ ..... _________ . ......

Area...... _ .... ______ ... ___ . __ . __ . ............

Avicula ____________ .... __ . _ .'.... ......... . ..... ...

Eumicrotis...... ________ . _ .... __ . ____ ... ..........

Aucella cf. A. bronni Rouillier ___ . ______ . _ . ___ . ...

Aucella cf. A. erringtoni (Gabb) __ . _______________ .

Aucella cf. A. flscheriana (D'Orbigny)..... ........... ............

Aucella cf. A. pallasi Keyserling. _ . __ ... ......................

Ostrea. ____________ ....... ............................

Trigonia cf. T. doroschini Eichwald __ .. ____ . ______ .

Pecten ____ ... _ . _____ . _ ....... _____ .......

Lima - _____ . _____ ..... _ . __ . ......................

Anemia?... .----.___..._. ... . . .

Modiola (small form)... _ . ___ . _ ... _________ . ....

Pholadomya..-.. _ ..... _ . .... _ ....

Thracia? ..........................................................

Arctica.... _ .... __ .. . _ _ . _ . .. ...

Cyprina...... _ ........ , _ . . _ . ....

Praeconia?. ---... ___ .. . _ . _ . ...

Astarte..... ___ . _____ . ___ ... _ . ___ .. . _ . ....

Panoflaea?. _________ . ____ _______ . ....

Pelecypods.--.-. ___ ..... ____ . _____________ ...

DentaJium __ ..___ ___ __ . _ ... ................................

PateUa - -« . .....

Turbo----.---.---..---.-.....,....... ...... ........ ......

Amberleya _ . ___ .... _ .... ___ . ___________ ......

Natica.. _ . __ . _ ........... __ .... ____ . __ ..........

Rissoina?... ___ . ___ .... _ . ...............................

Alaria?... _.....-....__.._.___...____._. ............... . . ....

Gastropods (undetermined) ___________ . _________

Phylloceras. _ . _ ... ____ . ___ . ______ ..... ___ ...

Lytoceras.. ......... ___ . ___ . _ .... _____ . _ . ........

Cardioceras cf. C. canadense Whiteaves. __ ... ..................

Belemnites _ ............ _ .................. __ ..

Crustacean. _____ . ___ ..... ____ . ___ . ___ . ........

Plesiosaur _ . ____ .... ___ . ____ . .......................

1

X

X

X

X

X

X

X

X

?

X

X

X

X

X

X

X

x

X

X

X

X

X

X

X

X

X

X

X

X?

y

X

X

X

X

2

X

X

?

yY

X

y

y

V

?

y

X

3

?

X

X

y

......

X

4

?

?

X

X

?

?

?

X

?

?

5

y

X

6

?

. 1. Naknek formation of Alaska Peninsula.

2. Upper part of Naknek formation of Cook Inlet.

3. Naknek formation of Matanuska Valley.

4. Slate, graywacke, and conglomerate of Nutzotin Mountains.

5. Graywacke of Chichagof Island.

6. Slate, limestone, and tuff of Gravina Island.

CHRONOLOGIC RECORD

There was a general emergence of the land at the end of Triassic 

time, when the sea probably retired beyond the present continental 

limits. The evidence for this emergence is found in the fact that 

the latest Triassic (Rhaetic) is not represented in Alaska and that 

the ea.rliest Jurassic, if present, occurs only in very narrow areas 

close to the present shore.
284 MESOZOIC STRATIGRAPHY OF ALASKA

The beginning of the local record in Jurassic time in Alaska was 

marked by a moderate submergence accompanied or followed by intense volcanic activity along the present Pacific seaboard. The 

oldest known Jurassic sediments in Alaska are probably the shale 

and calcareous sandstone which overlie the Upper Triassic beds at 

Cold and Alinchak Bays, on the Alaska Peninsula.

The lava, agglomerate, breccia, and tuff, with interbedded marine 

fossiliferous strata, of ,the Talkeetna formation of the Talkeetna 

Mountains and the Matanuska Valley and their probable equivalent 

at Seldovia mark a broader and probably somewhat later transgression of the Lower Jurassic sea. The volcanic activity of this period 

has probably left a record also in the porphyry and tuff of the west 

coast of Cook Inlet, in the Skwentna group of the Yentna and 

Skwentna valleys, possibly in the conglomeratic rocks of the upper 

Susitna Valley and of the lower Chitina Valley, and probably in 

some of the volcanic rocks of southeastern Alaska. The volcanic 

activity and the marine transgression of this period were apparently 

limited to the region south of the Alaska Eange and were best developed in the site of the present Cook Inlet basin.

A still later period of deposition, which was.either late Lower 

Jurassic or early Middle Jurassic, is indicated by the sandstone and 

shale of the Kialagvik formation of the Alaska Peninsula, and by 

the Kingak shale of the Arctic coast, which carries a closely related 

fauna. This period of marine transgression was apparently the 

only one that brought any part of Alaska north of the Alaska Range 

beneath the sea in Jurassic time. '

It is highly probable that the intrusion of the granitic masses of 

the Pacific coast began during the period of Lower Jurassic volcanic

activity. It did not culminate, however, till Middle Jurassic time, 

and it continued, probably on a rapidly declining scale, till an unknown date in the Cretaceous.

The earliest known deposits of Middle Jurassic age in Alaska are 

those of the Tuxedni sandstone, which is typically developed on the 

west coast of Cook Inlet. The fauna of the Tuxedni sandstone has 

been recognized on the Alaska Peninsula, in the Matanuska Valley, 

in the Tordrillo formation of the Yentna and Skwentna Valleys, and 

in the lower part of the Chitina Valley. The Tuxedni sea probably 

covered all of south-central Alaska south of the Alaska Range. Its 

deposits were dominantly sandy, although they include, in the Chitina Valley, beds of tuffaceous slate. These slate beds may indicate 

either local volcanism or the local reworking of older volcanic detritus. The second alternative is believed to be the more probable. 

Volcanic deposits of Tuxedni age are known in British Columbia 

and may be present in southeastern Alaska.
« / * 
JONES TOWER

NAME

ROOM # TIME

MESSAGE

Wfr&0&4® J&&J<71:.

DATE I

/

37 / STAFF

P
JURASSIC, SUMMARY 285

The Tuxedni sandstone and its synchronous deposits were laid 

down in an encroaching sea. It rests unconformably upon the nonmarine and supposed Lower Jurassic porphyry and tuff of the 

west coast of Cook Inlet. Its relations to the marine Lower Jurassic 

beds are not definitely known, although there are reasons for suspecting that in the Matanuska Valley, at least, the contact is unconformable.

The deposition of the Tuxedni sandstone was followed without 

any known interruption, by that of the oldest of the Upper Jurassic beds. These include the Chinitna shale of Cook Inlet and beds 

carrying the same fauna on the Alaska Peninsula and in the Matanuska Valley. These beds contain a fauna of Callovian age characterized by the boreal ammonite Cadoceras. Their known distribution in Alaska is somewhat more restricted than that of the underlying Tuxedni beds, and hence it seems probable that the sea receded 

somewhat at the end of Tuxedni time, or else that erosion sometime 

during the Upper Jurassic removed all the marginal deposits of 

the Chinitna sea. Deposition was probably continuous from Tuxedni to Chinitna time, no evidence of an intervening unconformity 

having been found. The beginning of Chinitna time was marked 

by the change from the deposition of sandstone to that of shale and 

by the invasion of a boreal fauna.

The deposition of the beds of the Cardioceras zone was restricted 

to nearly the same limits as those of the Cadoceras zone (Chinitna 

horizon), the deposits of the Cardioceras zone being found on Cook 

Inlet, in the Matanuska Valley, and on the Alaska Peninsula. The 

transition from Chinitna time to the date of the Cardioceras-bQ&rmg 

beds was apparently marked by continuous sedimentation in a 

gradually shoaling sea. The fine shale of the Chinitna was succeeded by sandy shale, sandstone, and conglomerate of the Cardioceras zone within an apparently gradually contracting area, and 

the change was accompanied by the normal faunal succession.

The local deposition of very coarse conglomerate at about the 

date of the Cardioceras-bQ&ring beds is further evidence of a shoaling 

of the Upper Jurassic sea, which probably was caused and certainly 

was accompanied by vigorous mountain growth. The coarse granitic 

detritus in the conglomerate of that date indicates that the granitic 

batholiths of the Pacific coastal region had probably then for the 

first time been unroofed over large areas. The immense size of 

many of the granite bowlders, some of which are too large to have 

been moved by ordinary rivers or by any other known agency except 

ice, indicates that the neighboring mountains, probably like the 

higher mountains of all geologic time, contained glaciers. There is,

49448 26 20
286 MESOZOIC STBATIGRAPHY OF ALASKA

 however, no indication in the Jurassic of Alaska of a " glacial 

period " as the term is ordinarily used.

The Jurassic expansion of the sea reached its culmination in late 

Upper Jurassic time, when marine sediments were laid down in 

great thickness throughout the region south of the Alaska Eange. 

The late Upper Jurassic was a period of intense crustal movements 

and of vigorous erosion, when a large quantity of fresh and only 

partly sorted detritus was delivered to the sea. The character and 

thickness of the deposits indicate that subsidence of the sea floor kept 

pace approximately with marine deposition, or that the deposition 

of the marine sediments in general kept pace with the subsidence 

of the sea floor, while any excess of detritus that cam© to rest on 

flood plains, deltas, and coastal plains was soon thereafter swept 

into the ocean. The area of the late Upper Jurassic marine sedimentation probably included all of south-central Alaska and was 

sharply bounded on the north by the present line of the Alaska 

Range.

Volcanic activities were manifest in the Cook Inlet and southwestern Alaska regions during part of the Upper Jurassic time. 

They were probably the surface expression of the later and presumably the smaller of the Coast Range batholiths.

The late Upper Jurassic sea probably was directly connected with 

the cold-water Upper Jurassic sea of northern Europe and Asia.

The character of the events that terminated Jurassic time in 

Alaska is not well known. It seems probably that at the end of the 

Jurassic the Alaskan lands were worn down and the Alaskan seas 

were largely filled with sediments. The latest Jurassic deposits, 

corresponding to the Purbeckian of Europe, and the earliest Cretaceous deposits have not been recognized in Alaska. The absence 

of these deposits indicates that the transition from Jurassic to 

Cretaceous time was marked in Alaska by a break in the sedimentary 

record.

CRETACEOUS SYSTEM

OCCURRENCE AND GENERAL CHARACTER

Cretaceous rocks are widely distributed through all the major 

geographic provinces of Alaska (see fig. 7) and are the present 

surface rocks in several large areas, notably in the lower Yukon 

region and southwestern Alaska. A widespread marine transgression in early Cretaceous time carried the sea over most if not all 

of the area which is now Alaska. There doubtless were several 

recessions of the sea during the Cretaceous period for the equivalents 

of some of the characteristic major divisions of the Cretaceous have 

not been recognized in Alaska, but the sea must have readvanced
CRETACEOUS SYSTEM 287

again from time to time, for horizons well distributed throughout 

the Cretaceous are widely represented in the Territory. In general 

it is believed that Lower Cretaceous deposits were laid down in all 

the larger geographic provinces, but probably not over the entire

area of the Territory. The extent of the Lower Cretaceous seas, 

so far as known, was not limited along the lines of any of the 

existing geographic features. Upper Cretaceous deposits are also 

widely distributed and crop out at present over large areas, but 

there are several districts in which Upper Cretaceous rocks are not
288 MESOZOIO STEATIGRAPHY OF ALASKA

known and, it is believed, were never deposited. The writer believes 

that the Upper Cretaceous marine transgressions were of less 

extent than those of the Lower Cretaceous sea and were excluded 

from most of the areas of the present mountain axes as well as from 

the upper parts of the present major valleys. In other words, the 

major geographic features seem to have been well outlined in Upper 

Cretaceous time, and the highest Cretaceous beds were restricted to 

coastal belts and to the present major valleys and included river 

deposits and possible lake and land deposits laid down in estuaries, 

valleys, and plains that were the direct predecessors of the existing 

lowlands.

The rocks that have been referred to the Lower Cretaceous include the Staniukovich shale and the Herendeen limestone of the 

Alaska Peninsula; 96 conglomerate tuff and arkose and the overlying Nelchina limestone of the Upper Matanuska Valley; 9T the 

shale, sandstone, and conglomerate of the Kennicott formation of 

the Chitina Valley; *8 some of the AuceUa-loear'mg shale and graywacke of Chisana and White rivers;99 some of the Aucella-be&mrig 

slate and associated rocks of southeastern Alaska;* the Aucellabearing shale and sandstone of the upper Yukon 2 and EampartTanana district; 8 the limestone,, chert, and arkose of the " Oklune 

series " of the region north of Bristol Bay; 4 the limestone, shale, and 

sandstone of the Koyukuk group of the Koyukuk Valley; 5 and the 

sandstone and conglomerate of the Anaktuvuk group of northern 

Alaska.8

The rocks that have been referred to the Upper Cretaceous include 

the marine and terrestrial (coal-bearing) shale, sandstone, and conglomerate of the Chignik formation of the Alaska Peninsula,7 which

98 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, pp. 25, 38-41, pi. 8, 1911.

07 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska: U. S. Geol. Survey Bull. 327, p. 10, pi. 2, 1907.

88 Mofflt, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska: U. S. Geol. Survey Bull. 448, pp. 31-43, 1911. Mofflt, P. H., The upper Chitina 

Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 27-45, 1918.

88 Capps, S. R., The Chisana-White River district, Alaska: U. S. Geol. Survey Bull. 

630, pp. 29, 47-53, pi. 2, 1916.

1 Wright, C. W., A reconnaissance of-Admiralty Island: U. S. Geol. Survey Bull. 287, 

pp. 143-144, 1906.

2 Brooks, A. H., and Kindle, B. M., Paleozoic and associated rocks of the upper Yukon, 

Alaska: Geol. Soc. America Bull., vol. 19, pp. 305-307, 1908.

3 Eakin, H. M., A geologic reconnaissance of a part of the Rampart quadrangle, 

Alaska: U. S. Geol. Survey Bull. 535, pp. 20-21, 1913.

4 Spurr, J. E., A reconnaissance in southwestern Alaska in 1898 : U. S. Geol. Survey 

Twentieth Ann. Rept., pt. 7, pp. 133-134, 163-169, 181-182, 1900.

B Schrader, F. C., A reconnaissance in northern Alaska: U. S. Geol. Survey Prof. 

Paper 20, pp. 53, 77, 97, pi. 3, 1904.

0 Schrader, F. C., op. cit., pp. 53, 74-76, pi. 3.

7 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula : 

D. S. Geol. Survey Bull. 467, pp. 24, 41-48, 97-98, 100-103, 109-114, pis. 7, 8, 1911.
CRETACEOUS, ALASKA PENINSULA 289

contain fossil plants; the marine shale and sandstone composing the 

Matanuska formation of the Matanuska Valley; 8 the marine shale, 

sandstone, arkose, and conglomerate of the Chitina Valley; 9 the nonmarine shale and sandstone exposed in the banks of the Yukon near 

Seventymile,10 which were previously regarded as Tertiary and which 

contain fossil plants; a marine sandstone near Wolverine Mountain, 

in the Rampart district; 11 the marine and terrestrial (coal-bearing) 

shale, sandstone, and conglomerate of the lower Yukon 12 and Norton 

Bay-Nulato district,13 which contain fossil plants; some of the shale 

and sandstone of the Innoko Valley; 14 the sandstone, limestone, and 

shale of the " Holiknuk series " 15 and some of the rocks of the " Kolmakof series " 18 of the Kuskokwim Valley; the shale, sandstone, and 

conglomerate of the lower Koyukuk Valley; 17 the shale, sandstone, 

and conglomerate of the Bergman group of the upper Koyukuk Valley ; 18 and the sandstone, limestone, and shale of the Nanushuk formation of the Arctic slope.19

LOCAL SECTIONS 

ALASKA PENINSULA 

GENERAL FEATURES

The best-known and, so far as present information goes, the most 

complete section of Cretaceous rocks in Alaska is on the Alaska 

Peninsula, where both Lower and Upper Cretaceous strata are 

present and where the contacts with the underlying Jurassic and 

the overlying Tertiary beds have been observed. The Lower Cre8 Martin, G. C., and Katz, F. J., Geology and coal fields of the lower Matanuska Valley, Alaska: U. S. Geol. Survey Bull. 500, pp. 15, 23, 34-39, pis. 3, 5, 1912.

8 Mofflt, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 

29-45, 1918.

10 Collier, A. J., The coal resources of the Yukon, Alaska: U. S. Geol. Survey Bull. 218, 

p. 28, 1903.

11 Prindle, L. M., A geologic reconnaissance of the Fairbanks quadrangle, Alaska: U. S. 

Geol. Survey Bull. 525, pp. 33, 34, 47-48, 1913.

12 Collier, A. J., The coal resources of the Yukon, Alaska: U. S. Geol. Survey Bull. 218, 

pp. 15, 17, 19-20, 46-58, 65, 1903.

18 Smith, P. S., and Eakin, H. M., A geologic reconnaissance in southeastern Seward 

Peninsula and the Norton Bay-Nulato region, Alaska: U. S. Geol. Survey Bull. 449, 

'pp. 54-60, 1911.

14 Eakin, H. M., The Iditarod-Ruby region, Alaska: U. S. Geol, Survey Bull. 578. 

pp. 23-24, pi. 3, 1914.

15 Spurr, J. H., A reconnaissance in southwestern Alaska in 1898: U. S. Geol. Survey 

Twentieth Ann. Kept., pt. 7, pp. 125-128, 159-161, 182, 1900. Smith, P. S., The Lake 

Clark-central Kuskokwim region, Alaska: U. S. Geol. Survey Bull. 655^ pp. 57-84, 1917.

* Spurr, J. E., op. cit, pp. 130-131, 161-163, 182-183.

17 Schrader, F. C., Preliminary report on a reconnaissance along the Chandalar and 

Koyukuk Rivers, Alaska, in 1899: U/ S. Geol. Survey Twenty-first Ann. Rept. pt 2, 

p. 478, pi. 60, 1900.

18 Schrader, F. C., A reconnaissance in northern Alaska: U. S. Geol. Survey Prof. 

Paper 20, pp. 53, 77-79, 97, pi. 3, 1904. 

"Idem, pp. 53, 79-81, pi. 3.
290 MESOZOIC STBAT1GBAPHY OP ALASKA

taceous beds carry marine faunas; the Upper Cretaceous beds have 

yielded not only characteristic marine invertebrate fossils but fossil 

plants. The general character and sequence of the Cretaceous rocks 

of the Alaska Peninsula is as follows:

General section of Cretaceous rocks on Alaska Peninsula

Upper Cretaceous (overlain unconformably (?) by 

Eocene strata) :

Chignik formation: Feet 

Upper member (conglomerate, sandstone, 

and shale with marine invertebrates and 

fossil plants)__________________ 300-500 

Middle member (shale with many coal beds

and some sandstone; contains fossil plants) .300+ 

Lower member (shale with marine fossils) 200± 

Lower Cretaceous:

Herendeen limestone (arenaceous limestone with 

Aucella crassicollis) ______ ___ 800

Staniukovich shale (thin-bedded shale, interbedded 

with thin strata of sandstone and with some 

conglomerate; (contains Aucella piochU) ; underlain conformably (?) by Upper Jurassic strata)- 1000+

The Lower Cretaceous strata of the Alaska Peninsula overlie the 

Upper Jurassic rocks, described above (p. 210), with apparent 

conformity. They are known only in the vicinity of Herendeen 

Bay, near the west end of the peninsula. Farther east they are 

certainly absent at some places, as at Chignik, where the Upper 

Cretaceous rocks rest unconformably upon the Upper Jurassic rocks. 

At other places, as along the coast from Cold Bay to Cape Douglas, 

it is highly probable that they are absent, although positive proof

is lacking. At still other places, as along the coast from Chignik 

Bay to Cold Bay and throughout the greater part of the interior 

of the peninsula, information is very scanty, and no definite statement can be made as to what formations are present, although there 

are reasons for believing (see p. 293) that there may be areas of 

Lower Cretaceous rocks. The writer believes that the Lower Cretaceous formations were deposited over broad areas in southwesternAlaska, and that the small size of the areas of their present occurrence is due to subsequent erosion or burial.

Upper Cretaceous beds are known at several localities at both the 

east and the west ends of the Alaska Peninsula. They overlie the 

Lower Cretaceous beds with a possible unconformity, and where the 

Lower Cretaceous rocks are absent they rest unconformably upon 

the Upper Jurassic rocks. They are overlain, unconformably in 

at least some places, by Tertiary beds.
CRETACEOUS, ALASKA PENINSULA 291

LOWER CRETACEOUS

8TANIUKOVICH SHALE

Historical review. The Lower Cretaceous rocks of the Alaska 

Peninsula include two formations, the Staniukovich shale and the 

Herendeen limestone, both of which are now known only in the 

vicinity of Herendeen Bay.

The Staniukovich shale, which is the lower of these formations, 

was named and described by Atwood,20 and the type locality is on 

Staniukovich Mountain, near the entrance to Port Moller. The account of this formation by Atwood consists of a very brief description of the general character and occurrence of the rocks, a short 

discussion of their stratigraphic relations, and lists of fossils as 

identified by T. W. Stanton.

Stratigraphic description. The Staniukovich shale consists of 

thin-bedded shale, interbedded with thin strata of sandstone and 

with some conglomerate. Its thickness is at least 1,000 feet. It 

overlies the Upper Jurassic rocks of the Naknek formation with 

apparent conformity. The a'ctual contacts with the Jurassic rocks 

are in most places along faults, but in one locality the Staniukovich 

formation was observed to overlie the Jurassic rocks with essentially 

parallel bedding, although the actual contact was obscured by loose 

material and vegetation. This formation is overlain conformably 

by the Herendeen limestone.

Age and correlation. The fauna of the Staniukovich shale, as 

far as now known, probably includes only a single species of Aucella, which is related to Aucella piochii Gabb and which has been 

found at three localities, as described below. The material from 

locality 5572 includes also another species of Aucella which is related to Aucella crassicollis Keyserling. There is some doubt as to 

whether any of the specimens from this locality 21 came from the 

Staniukovich shale, and the writer believes it possible that this is 

float material in which two horizons are represented. T. W. Stanton 22 says regarding these collections:

Judging from past experience in California and Oregon and from the 

recorded occurrence of similar forms in Russia and elsewhere, I would expect the various lots containing Aucella to have the following stratigraphic 

sequence:

1. Highest horizon, with forms related to Aucella, crassicollis 5572 (part), 

5575, 5585, 5589, 5586.

2. Somewhat lower horizon, still within the Lower Cretaceous, with form 

related to A. pioc/m 5571, 5572 (part), 5576.

20 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, pp. 25, 38-41, pi. 8, 1911.

21 See discussion of " collection 13 " by Atwood in U. S. Geol. Survey Bull. 467, p. 40, 

1911.

22 Unpublished letter.
MESOZOIC STRATIGRAPHY OF ALASKA

3. Lower horizon referable to Upper Jurassic, with form related to A. 

pallasi.33

4. Lowest horizon but still Upper Jurassic, with form related to A. bronni.23 

The mixture of forms in lot 5572 and the stratigraphic notes of Doctor 

Atwood on some of the others seem to indicate that the distinction between 

horizons 1 and 2 based on forms of Aucella will not hold in the Herendeen 

Bay district. It should be remembered also that Aucellas with 'difficulty 

distinguishable from A. piochii also occur in the Jurassic, so that the three 

lots associated under 2 may not all be from the same horizon.

The localities may be described as follows:

5571. East shore Herendeen Bay, about 1% miles southeast of Crow Point. 

W. W. Atwood, 1908.

5572. West side of the basin of Coal Valley, east of Herendeen Bay, about 

500 feet above sea level. "Coal series near head of Coal Valley. Shales, 

^sandstones, and coal beds." W. W. Atwood, 1908.

5576. Between Shingle and Marble points, east shore of Herendeen Bay. 

" Sandstone and conglomerate horizon." W. W. Atwood, 1908.

HEBENDEEN LIMESTONE

Historical review. The Herendeen .limestone, which is the upper 

of the two Lower Cretaceous formations of the Alaska Peninsula, 

was named and described by Atwood;24 the type locality is on the 

east shore of Herendeen Bay. The rocks composing this formation 

and the fossils contained in them were previously known from the 

writings of several authors.

The first fossils known to have been obtained from the Herendeen 

limestone were collected at Port Moller by Dall in 1874. These fossils were described and figured by White,26 and their occurrence was 

described very briefly by Dall.28

Another collection, obtained from an undescribed locality near 

Herendeen Bay by Ernest G. Locke, has been mentioned by Brooks.27 

This collection is of extreme interest beca'use it includes both marine 

shells and a fossil plant, which, it has always been assumed, were obtained at the same locality. The marine shells collected by Locke, 

according to Stanton,28 consist of Aucella cf. A. crassicollis Keyserling, which is the characteristic fossil of the Herendeen limestone, 

and are "almost certainly of Lower Cretaceous age." The plant 

has been described and figured by Fontaine 29 as Pterophyllum

23 These were obtained from the Naknek formation ; see p. 203. G. C. M.

24 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, pp. 25, 39-41, pi. 8, 1911.

25 White, C. A., On a small collection of Mesozoic fossils collected in Alaska by Mr. 

W. H. Dall, of the United States Coast Survey: U. S. Geol. Survey Bull. 4, pp. 10-15, 

pi. 6, 1884.

28 Dall, W. H., Report on coal and lignite of Alaska: U. S. Geol. Survey Seventeenth 

Ann. Rept., pt. 1, pp. 804, 867, 1896.

27 Brooks, A. H., The coal resources of Alaska: U. S. Geol. Survey Twenty-second Ann. 

Rept, pt. 3, pp. 528-529, 1902.

28 Stanton, T. W., idem, pp. 528-529.

M Fontaine, W. M., Plants from Herendeen Bay, Alaska (in Ward, L. F., Status of the 

Mesozoic floras of the United States, second paper) : U. S. Geol. Survey Mon. 48, p. 152, 

pi. 38, figs. 19-20, 1905.
CRETACEOUS, ALASKA PENINSULA 293

alaskense, a new species, which Fontaine considered related to the 

European Jurassic (Lias or Oolite) species P. rajmahalense Morris 

and which according to Knowlton 30 is " hardly to be separated from 

it."

The presence of Lower Cretaceous rocks containing Aucella crassicollis at Port Moller and Herendeen Bay was mentioned briefly by 

Stanton and Martin,31 but no description of the rocks was given.

Other small collections of fossils from beds at this horizon were 

obtained in 1905 by Paige,32 who gave the first discussion of the 

relations of the several formations occurring at Herendeen Bay. 

The account includes brief statements regarding the occurrence, 

lithologic character, and relations of the rocks, with statements concerning the identity and age of the fossils by T. W. Stanton.

The account of the Herendeen limestone by Atwood,83 who, as 

stated above, was the first to describe these rocks under a formation 

name, includes a fairly detailed description of the occurrence, character, and stratigraphic relations of the Herendeen limestone, with 

lists of fossils as identified by T. W. Stanton.

Neither the Herendeen limestone nor any other rocks containing 

the Aucdla crassicollis fauna are definitely known to occur elsewhere 

on the Alaska Peninsula than at Herendeen Bay and Port Moller. 

They are certainly absent at Chignik Bay (see p. 297), where Upper 

Cretaceous beds rest unconformably upon the Upper Jurassic. It 

is probable, however, that the formation is present at other localities 

farther east. Such occurrences are indicated by the reported presence of AuceUa crassicollis among the fossils collected by Doroshin.34 

The fossils collected by Pinart 85 from " Nakkhalilik Bay, near 

Chigihinagak Volcano" (probably Chiginagak Bay), and from 

Aniakshak Bay, which were described by Fischer,36 are probably 

Lower Cretaceous. Fischer afterward repeated the same description 

with figures.87

80 Knowlton, F. H., The Jurassic age of the " Jurassic flora of Oregon " : Am. Jour. 

Sci., 4th ser., vol. 30, p. 50, 1910.

31 Stanton, T. W., and Martin G. C., Mesozoic section on Cook Inlet and Alaska 

Peninsula: Geol. Soc. America Bull., vol. 16, pp. 407-408, 410, 1905.

Talge, Sidney, The Herendeen Bay coal field: U. S. Geol. Survey Bull. 284, f pp. 102- 

105, 1906. '

83 Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula: 

U. S. Geol. Survey Bull. 467, pp. 25, 38-41, pi. 8, 1911.

84 Eichwald, Eduard von, Geognostisch-palaeontologische Bemerkungen fiber die Halbinsel Margischlak und die aleutischen Inseln, p. 187, St. Petersburg, 1871.

» Pinart, A. L., Voyage fi. la cOte nord-ouest d'Amerique d'Ounalashka a Kadiak : Soc. 

Geog. (Paris) Bull., 6th ser., vol. 6, pp. 561-580, 1873.

80 Fischer, P., Sur quelques fossiles de 1'Alaska, rapport4s par M. A. Pinart: Compt. 

Rend., vol. 75, pp. 1784-1786, 1872.

87 Fischer, P., Sur quelques .fossiles de 1'Alaska, In Voyages & la cote nord-ouest de 

I'Ame'rique, pt. 1, pp. 33-36, pi. A, 1875. 4
294 MESOZQIO STRATIGRAPHY OF ALASKA

StratigrapJiic description. The Herendeen limestone overlies the 

Staniukovich shale, described on pages 291-292, with apparent conformity and is overlain, probably unconformably, by the Upper 

Cretaceous rocks of the Chignik formation described* on pages 

295-308.

The Herendeen limestone was described by Atwood 88 as follows:

The upper portion of the Lower Cretaceous of this region is an arenaceous 

limestone of light-gray color, locally cross-bedded and fossiliferous. The formation is 800 feet thick, and owing to its superior resistance to the agents 

of weathering it has come to form conspicuous ridges in the coal field.

The Herendeen rock is a yellowish, sand-colored fine-grained limestone, with 

numerous minute plates of black mica on the sedimentation planes. Locally 

it contains abundant fragments of shells, and at places where the shell forms 

are lost the comminuted shell material may be recognized. The shells that 

have yielded most of such material were pectens. A microscopic examination 

of this rock shows that it is " mainly composed of dirty carbonate occurring in 

small short rectangular forms, but longer pieces are found, and these show 

curvature indicating a detrital organic origin. Throughout the section are 

scattered subangular fragments of quartz and plagioclase and sporadic flakes 

of biotite; as accessories there occur fragments of pyroxene, of rounded 

microlitic andesite, and grains of magnetite."

The Herendeen limestone, though folded and somewhat faulted, may be 

traced east from Coal Harbor for several miles, thence northwest until it 

outcrops on the shore of Herendeen Bay a little north of Coal Harbor. These 

outcrops are on the sides of a plunging syncline. Farther north the same 

arenaceous limestone outcrops again on the flanks of a neighboring anticline 

and extends east below recent volcanic tuffs and flows until it outcrops on 

the west shore of Port Moller.

Age and correlation. The fossils of the Herendeen limestone, as 

listed in the following table, include a few species of marine mollusks 

and possibly a plant. The mollusks are indicative of Lower Cretaceous age, although the only characteristic fossil among them is 

the species of Aucetta related to Aucella crassicolUs Keyserling.

The Aucella, related to Aucella piochii Gabb indicates a somewhat 

lower horizon (see pp. 291, 378, 474) than that of Aucella crassicollis, 

possibly being Upper Jurassic, and it may not belong in this list. 

Atwood 89 says that this collection " was secured from what was 

believed to be the Herendeen limestone, but the formation could not 

be absolutely identified because much of the region was covered by 

a heavy mantle of snow."

The fossil plant (Pterophyllum alaskense Fontaine) may also not 

belong in this list. It is considered by Knowlton (see pp. 292-293) 

practically identical with a characteristic J'urassic species. It was 

received, together with some specimens of Aucella cf. A. crassicollis, 

labeled as coming from the " coal 'measures " of Herendeen Bay, 

but there is no available information concerning the exact locality

^Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula : 

U. S. Geol. Survey Bull. 467, p. 39, 1911. 

89 Idem, p. 40.
CRETACEOUS, ALASKA PENINSULA 295

or strata from which it was obtained. As the coal-bearing rocks 

of Herendeen Bay are Upper Cretaceous or Tertiary (see pp. 300- 

301), they could have yielded neither this plant nor the specimens of 

Aucella. It is consequently not safe to assume either that the label 

was intended to give other than a very general locality designation, 

or that the fossils all came from the same locality or formation. If 

the specimens of Aucella and the plant did come from the same beds, 

then the problem of the age of those beds is closely related to the 

Knoxville problem.

Fossils from Herendeen limestone of the Alaska Peninsula a

Aucella concentrica Fischer var « ........

Cyprina? dallii White... ................

Desmoceras?. _____ . ___ . ........

Belemnites macri ti tis White. ........ _

Belemnites __ . __ ... ................

W.H. 

D.

E.G. 

L.

b

S.P. 

1

b

S.P. 

2

b

5572

b

b

5575

b

5585

b

5586

b

b

5587

b

b

b

b

5589

b

0 a, Identified by Wm. M. Fontaine; b, identified by T. W. Stanton; c, identified by C. A. White. 

* This plant is regarded by Knowlton as Jurassic and may not have been obtained from the Herendeen 

limestone. (See p. 294.)

« Probably the same as Aucella cf. A. crassicollis. 

d This species possibly came from the Staniukovich shale. (See p. 294.)

W. H. D. Fossil Point, Port Holler. Limestone " at a bluff point at the head 

of the bay, about east by south by compass from the end of the long sand 

spit." W. H. Dall, 1874. Identified by C. A. White (U. S. Geol. Survey Bull. 

4, pp. 10-15, 1884).

E. G. L. Herendeen Bay. Ernest G. Locke, 1901.

S. P. 1. Divide above Johnson tunnel stream. Sidney Paige, 1905.

S. P. 2. Beach one-fourth mile west of mouth of Coal Creek. Sidney Paige, 

1905.

5572. West side of basin of Coal Valley about 500 feet above sea level. W. W. 

Atwood, 1908.

5575. Just south of Shingle Point, east side of Herendeen Bay. W. W. 

Atwood, 1908.

5585. High ridge south of Johnson tunnel in Mine Creek. W. W. Atwood, 

1908.

5586. Sandstone near Hot Springs, Port Moller. W. W. Atwood, 1908.

5587. Southwest shore of Port Moller about half a mile north of Hot Springs. 

Shale above sandstone of 5586. W. W. Atwood, 1908.

5589. 1,100-foot hill about 3 miles northeast of Mine Harbor. W. W. Atwood, 

1908.

UPPER CRETACEOUS

CHIGNIK FORMATION

Historical review. The Upper Cretaceous rocks "of the Alaska 

Peninsula were described by Atwood 40 as the Chignik formation, so 

named from its typical development on Chignik Bay.

"Atwood, W. W., Geology and mineral resources of parts of the Alaska Peninsula: 

U, S. Geol. Survey Bull. 467, pp. 24, 41-48, 97-98, 100-103, 109-114, pis. 7, 8. 1911.
296 MESOZOIC STRATIGRAPHY OF ALASKA

The coal beds and inclosing strata on Chignik River, which belong 

in this formation, had previously been described briefly by Dall,41 

but his account deals chiefly with the coal and includes only a brief 

mention of the rocks, which at that time had not been named and 

were not known to be Cretaceous.

Dall gave a brief description also of the coal beds on Herendeen 

Bay,42 which probably belong in this formation and which may possibly include also the beds that yielded some of the fossil plants 

(see p. 305) collected by Townsend at what is said to be nearly 

the same locality as the coal, but which have been described by 

Knowlton 4S as Tertiary.

The coal beds of the Chignik formation at Chignik Bay were described by Stone,44 who made only brief references to the character 

of the rocks but pointed out that they included marine fossiliferous 

Upper Cretaceous beds.

The Upper Cretaceous rocks at Chignik Bay were described by 

Stanton and Martin,45 who gave, in addition to the brief description 

of the rocks, a list of fossil plants identified by F. H. Knowlton, 

lists of marine mollusks identified by T. W. Stanton, and a discussion of the correlation of these rocks with the Upper Cretaceous 

of other regions. Brief mention was made also of the occurrence 

of marine Upper Cretaceous beds near the east end of the Alaska 

Peninsula.

The Chignik formation includes the- Upper Cretaceous beds of 

Herendeen Bay that were described by Paige,46 who collected the 

first fossils to be recognized as Upper Cretaceous from this locality. 

This account includes a very brief general description of the rocks, 

a discussion of their field relations, and lists and discussions of the 

plant and invertebrate fossils by F. H. Knowlton and T. W. Stanton.

The account of the Chignik formation by Atwood 47 includes 

detailed descriptions, with stratigraphic sections, of the Upper Cretaceous rocks in the Chignik Bay and Herendeen Bay districts, lists 

of the invertebrate and plant fossils with discussions of their age 

and correlation by T. W. Stanton and F. H. Knowlton, a general 

discussion of the stratigraphic relations, and descriptions of the 

occurrence and character of the coal.

41 Dall, W. H., Report on coal and lignite of Alaska: U. S. Geol. Survey Seventeenth 

Ann. Rept., pt. 1, pp. 801-803, 1896.

42 Idem, pp. 805-807.

43 Knowlton, F. H., A review of the fossil flora of Alaska, with descriptions of new 

species: U. S. Nat. Mus. Proc., vol. 17, No. 998, pp. 207-240, 1894.

44 Stone, R. W., Coal resources of southwestern Alaska: U. S. Geol. Survey Bull. 259, 

pp. 163-166, 1905.

46 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska Peninsula : Geol. Soc. America Bull., vol. 16, pp. 408-410, 1905.

48 Paige, Sidney, The Herendeen Bay coal field: TJ. S. Geol. Survey Bull. 284, pp. 

102-106, 1906.

47 Atwood, W. W., op. cit., pp. 24, 41-48, 97-.9S, 100-103, 109-114, pis. 7, 8.
CRETACEOUS, ALASKA PENINSULA 297

A brief general description of the Chignik formation by Smith 

and Baker 48 was based partly on previous descriptions and partly 

on observations in part of the area by Smith in 1922.

Stratigrqphic description. The general character of the Chignik 

formation on Chignik Bay has been described by Atwood 49 as follows :

In the Chignik Bay region the Chignik formation consists of a series of 

sandstones, shales, conglomerates, and some valuable coal seams. The sandstones range from fine, even-grained sediments to grits. Many of the sandstones in this formation, as exposed in Nigger and Chignik heads, have a light 

green color when fresh but weather to black or to shades of brown in the cliffs. 

Ripple marks are not uncommon on the bedding planes, and in some of the 

strata there are large concretions. The conglomerates are conspicuous memibers in the series, for they are firmly cemented and form cliffs or even, in 

some places, overhanging ledges. These conglomerates in Chignik Head contain pebbles of granite, quartz, greenstones, and flint as large as 2 inches in 

 diameter. Near the entrance to Chignik Lagoon there is a coarse conglomerate 

that for convenience in the field was spoken of as the cobble conglomerate. 

The stones in this conglomerate are commonly 3X or 4 inches in diameter, but 

some of the boulders found in it were 2 feet in diameter. This conglomerate is 

poorly bedded and in some places has a volcanic matrix. The stones include 

granites, basalts, quartz, and shale. There are lenses of sandstone and shale 

in the midst of the conglomeratic layer.

According to Atwood's geologic map of Chignik Bay and vicinity 50 the Chignik formation is composed of three unnamed members, the middle one of which contains coal beds. No complete section of the entire formation has been measured, nor have the character and relations of the members been described in detail. The following section, which was measured by Atwood B1 on the south shore 

of Chignik Bay and Chignik Lagoon from a point near Nigger Head 

to a point about 200 yards southwest of the native village, apparently represents the upper member of the formation:

Section of part of Chignik formation near Nigger Head, Chignik Bay

Feet

1. Black shale (yielded collection 5797, invertebrates)_____ 100

2. Cobble conglomerate- __ ______'________ 150

3. Shale with interbedded conglomerate_____________ 60

4. Sandstone and shale at Nigger Head (the shale yielded collection 5295, plants)______________________ 200

510

The Chignik formation of the type area overlies the Upper Jurassic rocks of the Naknek formation unconformably, the Lower Cre18 Smith, W. R., and Baker, A. A., The Cold Bay-Chignlk district: U. S. Geol. Survey 

Bull. 755, pp. 169, 184-185, 1925. 

48 Atwood, W. W., op. clt., p. 41. 

00 Idem, pi. 7. 

81 Idem, p. 42.
298 MESOZOIC STRATIGRAPHY OF ALASKA

taceous rocks being absent. It is overlain by Tertiary rocks, and the 

contact has been described as conformable,52 but the writer believes 

that there is strong evidence of a marked unconformity.

The Chignik formation in the vicinity of Herendeen Bay was 

described by Atwood 53 as having the following general section:

Section of Chignik formation m Mine Creek

 Feet

Conglomerate___________________________ 300+ 

Coal measures __ ___________________ 300+

Shale_________________________________ 200±

The section given below, which was also measured by Atwood 54 at 

nearly the same place, shows the character of the coal-bearing beds 

in detail. It is evident from the thickness as given in these two sections that all of the detailed section below the uppermost conglomerate belongs in the coal-bearing member of the formation, the " coal 

measures " of the general section.

Section of coal-bearing rocks of Chignik formation on the south slope of 

Mine Creek valley, Herendeen Bay

Ft. in.

Conglomerate____________________________ 300

Sandstone, coarse, cross-bedded, with huge sandstone concretions weathering brown from abundance of limonite. 50 

Sandy shale___________________________ 20 

Coal seam, medium grade________________ 3 

Sandstone, firm, cross-bedded, with fossil leaves_____ 3 

Shale________________________________ 5 

Coal____________________________________________ 10

Shale_______________________________ 2 6

Shaly coal ___________________________ 6

Shale, with sandstone concretions______________ 3

Coal________________________________ 1

Shales_______________________________ 4

Coal_________________________ - ______ 1 2

Shaly sandstone, with sandstone concretions_______ 4

Coal________________________________ 10

Shales______________________________ 4

Coaly shales___________________________ 1 6

Shales.________________________________ 3

Carbonaceous shales. _.!__________________ 1

Shales_______________________________ 2

Coal________________________________ 1

Shales_______________________________ 2

Coaly shales, with shale partings______________ 2 3

Coal, with bony partings and shaly bed____.._____ 7

Shales____________________:__________ 1 8

M Atwood, W. W., op. cit., p. 58. 

63 Idem, p. 42. 

"Idem, pp. 100-101.
CRETACEOUS, ALASKA PENINSULA 299

	Ft. in.

Shaly coal__________ _ ^ 1 2

Shale___________________ ___-_ 2 6

Coal_____________________ 1 1

Shales__________-__ 3

Coal______________________________- 2

Shales____________________ ___ __ 3 6

Coal______________-____ .____ 1 2

Shales___________________________ 6

Coal_______________________________ 1 5

Shales, with sandstone concretions_ __ - 4

Coal_______________________________- 1 8

Shales and sandstone interbedded__ : 15

Coal______________________________ 8

Shales______________________________ 5

Shaly sandstone-__ 2

Shales________________________________- 50 

Coal________________________________ 1 2 

Shales_____________________________ 6 

Coaly shale_______________ _________ 4

Shales______________________________ 7 

Coal_______________________________ 1 

Shales_______________________________ 3

Coal_______________________________ 1 

Shales, with sandstone concretions_ _ ___ 40 

Coarse cross-bedded sandstone and conglomerates____ 15

Shales and sandstones. 

The dip of these measures is 30° N., and the strike N. 91° E.

The base of the Chignik formation in the Herendeen Bay district 

is a surface of unconformity, the Chignik formation resting in some 

places on the Upper Jurassic rocks of the Naknek formation and in 

other places on the Lower Cretaceous rocks of the Herendeen limestone. This trangression, which, without making any allowance for 

the Jurassic strata involved, is at least 1,800 feet within a horizontal 

distance of 2 miles, or the equivalent of an average angular unconformity of 10°, is altogether too much to be accounted for as mere 

overlap. The contact of the Chignik formation with the overlying 

Tertiary rocks is stated by Atwood to be conformable.

The north shore of Kaguyak Bay, near Aievak or Douglas village, not far from the east end of the Alaska Peninsula, contains an 

almost unbroken series of outcrops of sedimentary rocks striking 

slightly north of west and dipping 15° N. The westernmost exposures consist of dark shale with marine Upper Cretaceous fossils 

(lot 3121). The rocks in the east end of the cliffs consist of gray 

sandstone with thinner beds of dark shale in which no fossils were 

found, except fragmentary plant stems and two specimens of dicotyledonous leaves that were too imperfect for identification. The 

high cliffs as seen from the water apparently show an unconformity
300 MESOZOIC STRATIGRAPHY OF ALASKA

above the greater part of the section and below the leaf beds, but this 

unconformity was not detected in studying the exposures at the base 

of the cliffs. The total thickness of the strata in the cliffs was estimated at about 2,000 feet, of which the larger part is Cretaceous. 

The beds above the unconformity are probably Tertiary.

Another locality of Upper Cretaceous rocks on the Alaska Peninsula is indicated by the fossil identified by Grewingk 55 as Belemnites paxillosusf, which was collected by Wosnessenski "near 

Katmai." This fossil was regarded by Pompeckj 56 as an Upper 

Cretaceous Belemnitella. The other fossils collected by Wosnessenski are Middle and Upper Jurassic (see pp. 192, 203), and the 

precise locality of all of them is much in doubt.

Age and correlation. The fossils from the Upper Cretaceous 

Chignik formation of the Alaska Peninsula are listed in the accompanying table. The collections from the type area of the 

Chignik formation are arranged approximately in stratigraphic sequence, beginning with the lowest. The first six lots from this area 

(5796, 11362, 5799, 3116, 5795, and 11361) are from the lower member, eight lots (5793, 3525, 3115, 3521, 5295, 3114, 5294, and 5797) 

are from the upper member, and the other two lots (5296 and 5297) 

are probably from the upper member. In this area the lower 

member has yielded only marine invertebrate fossils, the middle 

member has yielded no fossils, and the upper member has yielded 

both plants and marine invertebrates.

The fossils from the Chignik formation of Herendeen Bay can 

not be assigned to a position within the formation with as much 

confidence as the fossils from Chignik Bay. The lots from Mine 

Creek (3485, 3490, 3709, 37.08, S. P. (c), 5184, and 539) all came 

from the general vicinity of the coal beds and probably came from 

the middle member ("coal measures") or possibly from the lower 

part of the upper member. However, the locality descriptions are 

vague, and it is possible that some of these fossils.came from the 

lower member. These collections include both marine invertebrates 

and plants, but the shells and leaves were apparently not obtained 

from the same beds, nor have the relations of the plant beds to 

the strata carrying the shells been determined. The marine shells, 

according to Stanton, are clearly of Upper Cretaceous age. Some 

of the collections of plants have been regarded as Cretaceous and 

others as Tertiary, but most of them have previously been considered doubtful. The middle member yielded also lots 5185 and

56 Grewingk, C., Beitrag zur KenDtniss der orographischen und geognostischen Beschaffenheit der nordwest KUste Amerikas, mlt den anliegenden Inseln: Russ.-k. min. Gesell. 

St. Petersburg Vgrh., 1848-49, pp. 121, 347.

M Pompeckj, J. F., Jura-Possilien aus Alaska: K. russ. mln. Gesell. St. Petersburg 

Verb., 2d ser., Band 38, No. 1, 1900, pp. 245, 268-270, 274, 276, 282.
CRETACEOUS, ALASKA PENINSULA 301

5187, containing fossil leaves. The marine invertebrates in lots 

5580, 5588, and 5577 were obtained not far below the Tertiary 

rocks, presumably from the upper member. They are, according 

to Stanton, undoubtedly Upper Cretaceous.

Lots 3121 and 5189 contain marine invertebrates and plants from 

two outlying localities near the east end of the Alaska Peninsula 

and on Pavlof Bay, respectively. Their position in the Upper 

Cretaceous sequence has not been determined, but they are believed 

to be in the upper member.
Fossils fromfthe Chignik formation °

Sorbus. n. so ---.----------.---------------.-----

Lower member

|

>o

§CO

1

....

1 E5

1

1

""I " - r- _

1

to

CO

g

«O 1

Middle member

U5 

00

 ^ 

CO

§

s

--

I^ 1CO

^

AH 

oi

2

<3> 

S

a

§

>o

a

a

a

a

a
Paliurus, n. sp ___ . ______ . ...............

Zizyphus, n. sp ___ __________ .. ____ ..

Inoceramus undnlato-plicatus var. chignikensis 

Smith.........................................

Unio?.... ... . ....... .. ........ .

Pecten

Thracia?........ ....... ..........................

Mactra (Cymbonhoria) ashburnerii Gabb _ ....

h

h

b

b

b

b

h

....

b

b

b

b

h

b

b

b

b

b

....

_

b

h

b

h

b

b

b

b

h

1

 i

I

....

....

"

....

b

-..-

a

a

1 a, Identified by Arthur Hollick; b, identified by W. R. Smith; c, identified by T W. Stanton.
Fossils from the Chignik formation a C

Fusus kingii (Gabb) Whiteaves var ..-.-....-...

Lower member

§r-

>o

b

b

b

No

b

S 

>»

b

b

o 

co

to 

c»

«0

1

1

c f~~~

i

i

!

Middle member

3 

$

§

3

1

«

8-

CO

2

^

CO

i

 o s §o

a, Identified by Arthur Hollick; b, identified by W. R. Smith; c, identified by T. W. Stanto
CRETACEOUS, ALASKA PENINSULA 305

5796 (52). North side of Chignik Bay 1 mile north of base of sand spit. 

W. W. Atwood, 1908.

11362 (36). Same locality as 5796. W. R. Smith, 1922.

5799 (58). Chignik Lagoon, nearly opposite Alaska Packers Association's 

cannery. W. W. Atwood, 1908.

3116 (959). Whalers Creek, about 1%-or 2 miles from the shore of Chignik 

Lagoon. Sandstone underlying the coal-bearing beds. T. W. Stanton and 

R. W. Stone, 1904.

5795 (51). Whalers Creek, about 2 miles from Chignik Lagoon. Series of 

sandstones about 100 feet below the coal. W. W. Atwood, 1908.

11361 (35). Head of creek that flows into Hook Bay. W. R. Smith, 1922.

3485 (a). Big exposure on left fork of Mine Creek, Herendeen Bay, just 

above coal. Sidney Paige, 1905.

3490 (b). About 200 yards above left fork of Mine Creek, Herendeen Bay. 

Sidney Paige, 1905.

3709. Right branch of Mine Creek, 200 feet above fork. Herendeen Bay. 

Sidney Paige, 1905.

3708 (4). Mine Creek, right branch below first side stream. Herendeen 

Bay. Sidney Paige, 1905.

S. P. (c). Just above Johnson tunnel, Herendeen Bay. Sidney Paige, 1905.

5184 (30). Mine Creek, Herendeen Bay. "Coal series." W. W. Atwood, 

1908.

539. Cut on tramway, about a mile from the head of Mine Harbor, Herendeen Bay, within a few hundred yards of the mine. C. H. Townsend, 1890.

5185 (31). Coal Bluff, east shore of Herendeen Bay. " Coal series." W. W. 

Atwood, 1908.

5187 (35). Canyon 2 miles west of mouth of creek, about the middle of the 

west shore of Mud Bay, Port Moller. Shale bed. W. W. Atwood, 1908.

5296 (54). North shore of Chignik River just below Long Bay. W. W. Atwood, 1908.

5297 (55). North shore of Chignik River just below Long Bay. About 30 

feet above 5296. W. W. Atwood, 1908.

5580 (23). Canyon on east face of Pinnacle Mountain near summit, near 

head of Herendeen Bay. W. W. Atwood, 1908.

5588 (38). West side of Buck Valley, about 1% miles from shore of Herendeen Bay. W. W. Atwood, 1908.

5577 (18). Canyon north of Pyramid Peak, about 4 miles south of Herendeen Bay. W. W. Atwood, 1908.

3121. North shore of Kaguyak Bay, 1 mile east of mouth of river. G. C. 

Martin, 1904.

5189 (44). East side of Favlof Bay. W. W. Atwood, 1908.

5793 (45). South shore of Chignik Bay just west of end ,of Chignik Head. 

W. W. Atwood, 1908.

3525 (963). East shore of Doris Cove, Chignik Bay. T. W. Stanton and 

R. W. Stone, 1904.

3521 (958). South shore of Chignik Bay, 2 miles northeast of Alaska Packers 

Association's cannery, opposite end of sand spit. Talus which evidently came 

from one of the shaly layers not far above the base of the exposure. T. W. 

Stanton and R. W. Stone, 1904.

3115 (958a). Same locality as 3521. Sandstone fragments in talus. T. W. 

Stanton and R. W. Stone, 1904.

5295 (49). South shore of Chignik Lagoon nearly opposite the end of the 

sand spit. Bed 4 of section on p. 297. W. W. Atwood, 1908.
306 MESOZOIC STRATIGRAPHY OF ALASKA

3114 (957). South shore of Chignik Lagoon 200 yards southwest of native 

village, about 1 mile northeast of Alaska Packers Association's cannery. Dark 

shale. T. W. Stanton and E. W. Stone, 1904.

5797 (53). South shore of Chignik Lagoon, about 200 yards southwest of 

native village. Bed 1 of section on p. 297. W. W. Atwood, 1908.

5294 (48). Anchorage Bay, opposite Northwestern Fisheries cannery- W. W. 

Atwood, 1908.

The preceding table shows that the lower member of the Chignik 

formation has yielded only marine invertebrate fossils, the middle 

member has yielded fossil plants and a few marine mollusks 

(Inoceramus) , and the upper member has yielded a considerable 

variety both of plants and marine invertebrates. The faunas and 

floras of the several members are distinctive. Only one species 

among the invertebrates extends over from one member into another. 

Among the fossil plants 68 per cent of all the species in the middle 

member, or 81 per cent of the angiosperms, and 78 per cent of all 

the species in the upper member, or 91 per cent of the angiosperms, 

are characteristic of the members.

Of the fossils from the lower member, the following have been 

found in other formations:

Glyoimeris veatchi, in the Chico and Martinez.

Inoceramus undulato-plicatus, in the Austin and Niobrara.

Trigonia leana, Maetra, (Cymbophoria,) ashburnerii, and Perissolax

brevirostris, in the Chico. 

Meretrix nitida, Fusus kingii var., and Pachydisous newberryanus var.,

in the Chico and Nanaimo. 

Clisocolus cordatus and Tellina nanaimoensis, in the Nanaimo.

The fauna of the lower member, according to Stanton,57 is certainly Upper Cretaceous and is " the Chico fauna of the Pacific 

coast, especially as developed in the Nanaimo formation of Vancouver 

Island." Concerning another collection of fossils from one of the 

same localities in the lower member Stanton 58 said:

These fossils indicate correlation with a horizon in the Chico as developed 

in California and in the Nanaimo of Vancouver Island, which include practically all of the Upper Cretaceous, but the beds at Chignik are probably not 

older than basal Senonian.

Stanton 59 adds in explanation of this statement that he correlates 

the Niobrara formation of the Great Plains and the Austin chalk of 

Texas with the basal Senonian. Both of these formations contain 

Inoceramus undulato-plicatus Koemer, which is probably specifically 

identical with the form usually identified as /. digitdtus.

87 Stauton, T. W., cited by Atwood, W. W., Geology and mineral resources of parts of 

the Alaska Peninsula: U. S. Geol. Survey Bull. 46T, p. 43, 1911.

58 Stanton, T. W., and Martin, G. C., Mesozoic section on Cook Inlet and Alaska 

Peninsula: Geol. Soc. America Bull., vol. 16, p. 408, 1905.

59 Stanton, T. W., personal note.
CEETACEOUS, ALASKA PENINSULA 307

The middle member of the Chignik formation has yielded the 

fossils listed in the table on pages 302-304. The only marine invertebrate species is an unidentified species of Inocercwws, which occurs 

more abundantly in the lower member and may occur also in the. 

upper member. The fossil plants belong for the most part to species 

not yet described and do not furnish conclusive evidence as to the age 

of the member. The species that are known outside of the formation, 

occur in rocks ranging in age from Potomac to Montana, but most 

of them are cycads and conifers from which a close determination of 

age can not be expected. The evidence of the fossil plants is not. 

out of harmony with Stanton's assignment of the fauna of the lower 

member to a horizon in the Chico. Of the fossils listed in the table,, 

the following have been found in other formations :

Nilssonia serotina, in the Gyliakian of Sakhalin.

Nilssonia n. $p. and Gephalotaxopsis n. var., in the Nulato and Kaltag.

Sequoia, rigida, in the Potomac, Kpme, Lower Atane, and Melozi.

Sequoia obovata, in the Montana and Vermejo.

Populus hyperborea and Populus elliptica, in the Dakota.

Dryophyllum bruneri, in the Mesaverde.

The upper member of the Chignik formation has yielded a large 

number of fossils, including both plants and marine invertebrates,, 

which are listed in the table on pages 302-304. The fauna of the 

upper member is quite distinct from that of the lower member, only 

Inocerofmus undulato-pliccutus and an unidentified species of Anomia. 

being possibly in common. Lot 5797, according to Stanton,60 is " certainly Mesozoic and presumably Upper Cretaceous. The fossils indicate a different horizon, or at least a different facies, from the one 

represented at neighboring localities [in the upper member] from 

which Cretaceous collections were obtained." The flora of the upper 

member includes a large number of new species which are of no value 

at present in correlating. About half of the previously described 

species are known elsewhere in rocks of approximately Montana age, 

and the other half in rocks of older Cretaceous formations. The 

evidence of the fossil plants therefore suggests that the upper member 

of the Chignik formation belongs well up in the Upper Cretaceous,, 

an assignment which is quite in harmony with the evidence of the 

marine invertebrates.

The fossils of the upper member known in other formations are. 

listed below.

Nilssonia serotina, in the Gyliakian of Sakhalin. 

Nageiopsis zamioides, in the Potomac. 

Cephalotaxopsis n. sp., in the Melozi. 

Cephalotaxopsis n. var., in the Molozi and Kaltag.

60 Stanton, T. W., cited by Atwood, W. W., op. cit., p. 44.
308 MESOZOIC STRATIGRAPHY OF ALASKA

Sequoia obovata, in the Montana and Vermejo.

Ficus laurophylla and Persea hayana, in the Dakota.

Colutea primordialis and Cornus forchammeri, in the Magothy and lower

part of the Atane.

Trapa? microphylla,, in the Montana and Fort Union. 

Redera macclurii, in the Orokian of Sakhalin. 

Diospyros steenstrupi, in the Patoot. 

Viburnum simile, in the Vermejo.

Inoceramus undulato-plicatus, in the Austin and Niobrara. 

Desmoceras? cf. D. subquadratum, in the tipper part of the Horsetown. 

Pachydiscus cf. P. multisulcatus, In the Nanaimo.

COOK INLET AND SUSITNA VALLEY 

GENERAL FEATURES

The only rocks in the Cook Inlet-Susitna embayment that have 

been assigned to the Cretaceous, except the Cretaceous rocks of the 

Matanuska Valley, which will be described under a separate heading, 

are some supposed Upper Cretaceous slate and graywacke in the 

vicinity of Cache Creek, in the Yentna district. These beds are 

apparently several thousand feet thick, but their base and the underlying rocks have not been recognized. They are overlain unconf ormably by Tertiary lignite-bearing beds.

Cretaceous rocks may be present at other places in the Cook InletSusitna embayment, as in and near Kenai Peninsula,61 especially at 

the head of Crow Creek, on the north side of Turnagain Arm,62 on 

the West Fork of Chulitna Kiver,63 on Susitna Kiver,64 and on 

Kichatna Kiver.65 There is, however, no proof that any of these 

rocks are Cretaceous, and they may not even be Mesozoic.

UPPER CRETACEOUS (!) 

SLATE AND GRAYWACKE OF CACHE CREEK

The supposed Upper Cretaceous slate and graywacke of Cache 

Creek and vicinity were described by Capps 66 as "slate and graywacke series (Paleozoic or Mesozoic)." His account includes discussions of the distribution, character, structure, thickness, age, and correlation of the rocks, which had then yielded no fossils and could 

be only " provisionally assigned to the Paleozoic or Mesozoic."

81 Martin, G. C., General features of Eenai Peninsula: U. S. Geol. Survey Bull. 587, pp. 

33-35, 1915.

82 Johnson, B. L., The central and northern parts of Kenai Peninsula: U. S. Geol. 

Survey Bull. 587, pp. 118-119, 1915.

68 Capps, S. R., Mineral resources of the upper Chulitna region: U. S. Geol. Survey 

Bull. 692, pp. 217-218, 1919.

64 Eldridge, G. H., A reconnaissance 'in Suslta basin and adjacent territory, Alaska: 

U. S. Geol. Survey Twentieth Ann. Rept., pt. 7, pp. 15-16, 1900.

68 Brooks, A. H., The Mount McKlnley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, pp. 67-68, 1911.

88 Capps, S. R., The Yentna district, Alaska : U. S. Geol. Survey Bull. 534, pp. 24-28, 

pi. 3, 1913.
CEETACEOUS, COOK INLET AND SUSITNA VALLEY 309

These rocks were correlated by Capps with similar rocks observed 

by Brooks 67 in the valley of Kichatna Kiver and with the Susitna 

slate described by Eldridge.68

These rocks were reexamined in 1917 by Mertie,69 who described 

them briefly under the heading " slate and graywacke series." His 

account includes a brief general description, which is largely a summary of the description by Capps, references to the previous descriptions, and a brief discussion of the age of the rocks including a statement by Stanton concerning some fossils collected by Mertie.

In regard to the lithologic character of the slate and graywacke 

of the Cache Creek district, particularly in the Dutch and Peters 

hills, Capps 70 wrote as follows:

They consist chiefly of black to gray slates and phyllites, in many places 

carbonaceous, and beds of graywacke, which range from fine-grained to coarse

gritty rocks. In some places the rocks are massive, with argillites instead 

of slates, but the foliated types are much more widespread than the massive 

types. It is difficult to estimate just what proportion of the whole series is 

formed by the graywacke beds. Many sections show great thicknesses of the 

slaty phases, with very little graywacke present. At other localities the graywackes preponderate, occurring in thick, massive beds that show little foliation or schistosity and that are often mistaken by the miners for fine-grained 

dike rocks, which they closely resemble. The whole series is much jointed, 

the graywackes less closely than the slates, which are in many places broken 

into long prismatic pieces by sets of intersecting joints.

On account of the irregularity of structure and the lack of knowledge of these rocks over a large area, no reliable estimate of thickness can be made other than the statement, as given by Capps,71 that 

the series is several thousand feet thick. The rocks beneath the 

slate and graywacke have not been recognized. The overlying rocks, 

 which rest upon the slate and graywacke unconformably are Tertiary lignite-bearing beds.

The following statement was made by Stanton 72 concerning some 

fossils collected by Mertie in 1917:

10124. No. 4. Angular wash, half a mile from head of Long Creek, tributary 

of Tokichitna River. Elevation, 2,500 feet.

, 10125. No. 5. In place, a quarter of a mile from head of same creek. Elevation, 2,600 feet.

These two specimens are fragmentary imprints in slate and probably represent a single species, which in my opinion is referable to a broad form of

07 Brooks, A. H., The Mount McKinley region, Alaska : U. S. Geol. Survey Prof. Paper 

70, pp. 67-68, 1911.

08 Eldridge, G. H., A reconnaissance In the Susitna basin and adjacent territory, 

Alaska, in 1898 : U. S. Geol. Survey Twentieth Ann. Kept., pt. 7, pp. 15-16, 1900.

89 Mertie, J. B., jr., Platinum-bearing gold placers of the Kahiltna Valley: U. S. Geol. 

Survey Bull. 692, pp. 236-237, 1919.

70 Capps, S. R., The Yentna district, Alaska: U. S. Geol. Survey Bull. 534, p. 25, 1913.

71 Idem, p. 27.

72 Stanton, T. W., cited by Mertie, J. B., jr., op. cit., p. 237.

49448 26 21
310 MESOZOIG STRATIGRAPHY OF ALASKA

Inoceramus more like some of the Alaskan Upper Cretaceous types of Inoceramus than those known from the Jurassic. It is probably worthy of mention that the lithology of the matrix suggests the Yakutat rocks of Woody 

Island and that the fossils themselves have some resemblance to Inoceramya 

concentrica Ulrich from that locality, though they do not belong to that species. 

Though other fossils are needed to make the identification positive, I think 

that these fossils are probably of Upper Cretaceous age.

MATANUSKA VALLEY

The Cretaceous rocks of the Matanuska Valley include both Lo.wer 

Cretaceous and Upper Cretaceous marine sedimentary strata. The 

Lower Cretaceous strata are somewhat but not altogether similar, 

both lithologically and faunally, to the Lower Cretaceous rocks of 

the Alaska Peninsula. The Upper Cretaceous beds are especially 

well developed, comprising several thousand feet of strata that crop 

out over a wide area. They contain'a fauna that is similar to that 

of the Upper Cretaceous beds of the Alaska Peninsula, but they differ strikingly from those beds in that they include neither coal beds 

nor the characteristic Upper Cretaceous flora.

The general sequence is as follows:

General section of Cretaceous strata in Matanuska Valley

Upper Cretaceous (overlain unconformably by nonmarine Tertiary deposits) :

Matanuska formation: Feet 

Sandstone and shale, sparsely fossiliferous 2,100 

Shale with some sandstone. Carries an

abundant marine invertebrate fauna___ 2,000± 

Unconformity (?). 

Lower Cretaceous:

Nelchina limestone (massive dark-colored finegrained unaltered limestone with Belemnites)- 300± 

Conglomeratic tuff and arkose, with Aucella

crassiconis_____________________ 100-200 

Conformity (?), with Upper Jurassic strata beneath.

LOWER CRETACEOUS ° 

CONGLOMERATIC TUFF AND ARKOSE

Historical review. The tuff and conglomerate which are seemingly the basal Lower Cretaceous strata of the Matanuska Valley 

were included by Mendenhall in the thick and heterogeneous aggregate of strata described as the " Matanuska series." Mendenhall 

gave no published description of the tuff and conglomerate, although 

they were apparently the source of the fossils on the basis of 

which the "Matanuska series" was referred to the Lower Creta-
CBETACEOUS, MATANUSKA VALLEY 311

ceous. 73 It should be noted that Mendenhall's statement that the 

fossils " were collected at the base of the limestone " does not mean, 

as has been generally assumed, that the fossils were obtained from 

the limestone, for both Mendenhall's field notes and the character 

of the matrix in which the fossils are embedded clearly show that 

the fossils were obtained from the conglomerate tuff or arkose beneath 

the limestone.

The first published statement regarding the character of these 

fossiliferous beds consists of a brief description quoted by Martin 74 

from Mendenhall's field notes.

These beds were included in the Upper Jurassic by Paige and 

Knopf ,75 who described them as the strata on Billy Creek containing 

" interstratified tuff beds" and arkose. This account contains a 

detailed petrographic description of the tuff, with statements as to 

the general stratigraphic relations and the probable origin of the 

sediments.

The description of these beds by Martin and Katz 76 consists of a 

quotation of the account by Paige and Knopf, with the exclusion of 

part of the petrographic description.

These rocks were mapped by Chapin 77 as part of the Naknek 

formation, but no description of them was given.

Strctfigraphic description. The Lower Cretaceous rocks of the 

Matanuska Valley and of the adjacent headwater area of the Nelchina Valley apparently include at their base highly fossiliferous 

tuff or arkose and conglomerate. These 'rocks are well exposed in 

Limestone Gulch and on the neighboring tributaries of Billy Creek 

and of Nelchina River, where their thickness was estimated by the 

writer to be between 100 and 200 feet. These beds overlie the Upper 

Jurassic sandstone and shale described on page 230 with apparent 

conformity, unless their conglomeratic character is in itself evidence 

of unconformity. They are overlain, probably conformably, by the 

Lower Cretaceous limestone described on page 314.

The strata beneath the limestone are well exposed on the eastern 

tributary of Billy Creek that heads in Limestone Gap. At this 

place, according to the writer's observations, the beds 100 feet below 

the limestone are conglomeratic and are highly fossiliferous, the 

fossils of lot 8580 (p. 313) having been obtained at this horizon. No

78 Mendenhall, W. C., A reconnaissance from Resurrection Bay to the Tanana River, 

Alaska, in 1898 : U. S. Geol. Survey Twentieth Ann. Rept, pt. 7, p. 309, 1900.

74 Martin, G. C., A reconnaissance of the Matanuska coal field, Alaska, in 1905: U. S. 

Geol. Survey Bull. 289, p. 11, 1906.

75 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska: U. S. Geol. Survey Bull. 327, p. 21, 1907.

76 Martin, G. C., and Katz, F. J., Geology and coal fields of the lower Matanuska Valley, 

Alaska: U. S. Geol. Survey Bull. 500, p. 21, 1912.

77 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U. S. Geol. Survey Bull. 

668, pi. 2, 1918.
312 MESOZOIC STRATIGRAPHY OF ALASKA

change in lithologic character was noted between this fossil bed and 

the base of the overlying limestone. The next lower bed concerning 

which observations were recorded is a stratum of sandstone, about 

200 or 300 feet below the limestone, which yielded the Upper Jurassic 

fossils of lot 8579 (p.'232). The strata exposed in this gulch were 

described by Paige and Knopf 78 as follows:

On Billy Creek a number of interstratified tuff beds from 1 to 4 feet thick 

occur near the top of the series, a few hundred feet beneath the base of the 

Cretaceous. These tuffs differ greatly in appearance from the older Jurassic 

tuffs. They consist largely of fragments of glassy, striated feldspar, hornblende, and quartz with fine pyramidal terminations, set in an almost black 

matrix. Belemnites and lamellibranchs are embedded in these tuffs. Higher 

in the series arkoses, closely simulating granites in appearance, are interstratified with the sandstones. Coarser phases contain pieces of a fresh granitic 

rock a hornblende-biotite-quartz rnonzonite. The arkose is composed largely 

of rounded and angular fragments of feldspar in a more or less advanced 

state of alteration. Quartz is notably absent. Deep-brown hornblende is 

somewhat common, and a few flakes of strongly pleochroic biotite are found. 

With these are associated fragments of hornblende andesite, highly altered, 

some of which were noted to contain large idiomorphic feldspars similar to those 

forming the bulk of the rock. The arkose thus appears to have been derived 

principally from the destruction of a volcanic land mass, but some of its material was possibly brought from a monzonite area, as indicated by the fragments of monzonite. Under the microscope the feldspars of these arkoses by 

their alteration contrast strongly with the clear, glassy feldspars of the somewhat older crystal tuffs already described.

The exposures of these same strata on the headwaters of Nelchina 

River, 1 or 2 miles east of this gulch, were described by Mendenhall 79 

as follows:

In the head of the stream rising on the east side of Limestone Gap, at the

beginning of the limestone gorge about a mile from the gap, is a curious exposure of mingled conglomerate and fossil-bearing rocks. The shells [lot 2046, 

p. 313] are embedded in a sand matrix and are often only casts. These beds are 

at the base of the limestone as exposed here. The limestone, however, seems 

to be high up in the sedimentary series. The limestone lies in a syncline, at 

the deepest point of which the fossils were gathered. East of this dips are 

westward and rocks mostly soft shale.

Age and correlation. The fauna of the supposed Lower Cretaceous 

tuff and conglomerate of the Matanuska and Nelchina Valleys is very 

meager and does not fix the age of those beds with absolute certainty. 

Stanton 80 made the following statement regarding the fossils collected by Mendenhall:

78 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska amd 

Talkeetna Basins, Alaska: U. S. Geol. Survey Bull. 327, p. 21, 1907.

79 Mendenhall, W. C., field notes quoted by Martin, G. C., A reconnaissance of the 

Matanuska coal field, Alaska, in 1905: U. S. Geol. Survey Bull. 289, p. 11, 1906.

80 Stanton, T. W., cited by Mendenhall, W. C., op. cit. (Twentieth Ann. Kept, pt. 7), 

p. 309.
CBETACEOUS, MATANTJSKA VALLEY 313

The fossils * * * have been examined and found to consist of numerous 

examples of Aucella crassicollis Keyserling and a few fragments of a large 

Belewnites which can not be identified specifically. The species determined is 

sufficient to fix the age of the bed from which they came as Lower Cretaceous.

Concerning the Aucella collected by the writer (lot 8580) at presumably the same horizon, Stanton 81 said:

This is the same large species which was identified as A. crassicollis Keyserling in Mendenhall's collection from Bubb Creek. While this Alaskan species 

may not belong to A. crassicollis as restricted by the Russian paleontologists, 

who recognize a very large number of species of Aucella, it does belong to a 

group of forms which is most abundant in the Lower Cretaceous and is therefore suggestive of Cretaceous age, though the possibility that Aucella may have 

attained the same development locally during late Jurassic time must be kept 

in mind.

The Mendenhall collection of this species was collected at the base of a 200 

to 400 foot bed of white limestone according to the label, but the dark sandy 

matrix attached to the fossils shows that they did not come from the limestone itself.

The fossil localities are listed below. Aucella cf. A. crassicollis 

was found at both, and locality 2046 yielded also Belemnites.

8580. Limestone Gulch, tributary of Billy Creek. Conglomeratic and sandy 

beds 100 feet below base of limestone. G. C. Martin, 1913.

2046. About 1 mile east of Limestone Gap, near headwaters of a tributary 

of Nelchina River. Sandy matrix of a conglomerate at the base of the limestone. W. C. Mendenhall, 1898.

NELCHINA LIMESTONE

Historical revieio. The rocks to which the name Nelchina limestone is herein applied, from their exposure on the hilltops at the 

headwaters of Nelchina River, were first described by Mendenhall82 

as an unnamed member of the " Matanuska series." This description includes only a brief statement concerning the occurrence and 

thickness of the limestone, which was referred to the Lower Cretaceous on the basis of Stanton's determination of the fossils obtained 

just below the base of the limestone in the underlying conglomeratic 

tuff. (See pp. 310-313.)

A description compiled wholly from the above-mentioned account 

by Mendenhall and from Mendenhall's field notes was published in 

1906.83

This limestone was described as " Lower Cretaceous limestone " 

by Paige and Knopf,84 whose account consists of'a brief statement 

of the occurrence, thickness, and lithologic character.

81 Stanton, T. W., quoted by Martin, G. C., unpublished report on the geology of the 

upper Matanuska Valley.

62 Mendenhall, W. C., A reconnaissance from Resurrection Bay to the Tanana River, 

Alaska, in 1898 : U. S. Geol. Survey Twentieth Ann. Kept, pt. 7, pp. 308, 309, 1900.

83 Martin, G. C., A reconnaissance of the Matanuska coal field, Alaska, in 1905 : U. S. 

Geol. Survey Bull. 289, pp. 10, 11, 1906.

84 Paige, Sidney, and Knopf, Adolph, Stra.tigra.phic succession in the region northeast 

of Cook Inlet, Alaska: Geol. Soc. America Bull., vol. 18, p. 330, 1907.
314 MESOZOIC STRATIGRAPHY OF ALASKA

A more detailed description, based upon the same field observations, was afterwards given by the same authors,85 who were the first 

to map the areal distribution of this limestone or to give a definite 

description of its stratigraphic occurrence. This account includes 

a brief statement concerning the stratigraphic relations of the limestone and a fairly detailed description of its lithologic character.

The description of this limestone by Martin and Katz 80 consists 

of a practically unmodified quotation of the detailed account by 

Paige and Knopf.

Martin and Katz also described,87 as the probable equivalent o'f 

this Lower Cretaceous" limestone, a crystalline limestone of doubtful 

age occurring in the lower part of the Matanuska Valley. (See 

pp. 315-316.)

The occurrence of this limestone in the Nelchina Valley has been 

mentioned briefly by Chapin.88

Stratigraphic description. The Nelchina limestone occurs in several isolated areas, mostly small, on the hilltops at the headwaters 

of Nelchina Eiver and of Billy Creek. It consists of massive darkcolored fine-grained unaltered limestone. Some beds are highly 

siliceous and probably ought to be called calcareous sandstone. The 

massive limestone beds are separated by thin laminae of gray shale. 

The thickness is at least 100 feet and may possibly be as much as 

300 or 400 feet. The maximum thickness is difficult to determine 

with certainty, as there are indications of repetition by faulting 

where the limestone appears thickest. At some places there appear 

to be two massive limestones separated by several hundred feet of 

shale, but it is believed that this condition is due to faulting. The 

limestone overlies, with apparent conformity, the Lower Cretaceous 

tuff and conglomerate described on pages 310-313. Most of its observed occurrences are on hilltops where no overjoying rocks are 

present and where part of the original thickness of the limestone has 

been removed by erosion. At some places, notably in the hills west of 

Billy Creek, the limestone is overlain unconformably by a Tertiary 

conglomerate. The Upper Cretaceous strata that crop out on Billy 

Creek, as described on page 321, were not observed in contact with 

this limestone.

The description of this limestone given by Paige and Knopf 89 

is as follows:

55 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska: U. S. Geol. Survey Bull. 327, pp. 10, 24, pi. 2, 1907.

80 Martin, G. C., and Katz, F. .!., Geology and coal fields of the lower Matanuska Valley, Alaska: U. S. Geol. Survey Bull. 500, pp. 15, 22-23, pi. 3, 1912.

87 Idem, pp. 22, 32-33, pi. 5.

88 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U. S. Geol. Survey Bull. 

668, p. 38, pi. 2, 1918.

80 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska :.U. S. Geol. Survey-Bull. 327, p. 24, 1907.
CRETACEOUS, MATANUSKA VALLEY 315

Rocks of Lower Cretaceous age are represented mainly by a single formation a massively bedded limestone, 300 feet thick, which overlies the Upper 

Jurassic strata conformably. The limestone has a limited areal distribution 

and is known only from the headwaters of Billy Creek and Nelchina Eiver, 

where it weathers in prominent gray cliffs encircling the hilltops. The limestone is white and of very finely saccharoidal texture. On fresh fracture 

it emits a strong fetid odor. It is readily soluble in cold hydrochloric acid 

and evolves an abundance of unpleasant hydrocarbon gases. Qualitative tests 

show the presence of not more than a trace of magnesia. Under the microscope the detrital organic origin of this limestone is readily apparent. It is 

largely composed of irregular granules of dirty-looking calcite, but with these 

are associated numerous prismatic sections referable to organic fragments. 

Rhombohedral cleavage is here and there finely developed, but the characteristic calcite twinning is notably absent. Some of the carbonate is still in 

the aragonite form, as is indicated by negative biaxial interference figures. 

Accessory constituents are limpid plagioclase, quartz with hairlike rutile,

hornblende, and, more rarely, augite and apatite. The incomplete conversion 

of the carbonate to the stable modification and the absence of twin lamellation in the calcite indicate the essentially static conditions in which the limestone has remained since its formation.

Age and correlation. The Nelchina limestone seems to be in general remarkably unfossiliferous, although belemnites were seen in 

some of the thin strata of shale between the massive limestone beds. 

A large number of fragmentary belemnites were obtained from the 

residual soil lying on the surface of the limestone in one of the hilltop areas. They apparently could have been derived from no other 

possible source than the limestone or one of the thin shale strata 

interbedded with it.

The following statement concerning these fossils was furnished by 

T. W. Stanton:

8582. Limestone hills east of Billy Creek. Residual soil on the surface of 

the limestone. G. C. Martin, 1913. Belemnites sp., very large, stout form. 

This species suggests Jurassic rather than Cretaceous.

LIMESTONE NORTH OF CASTLE MOUNTAIN

The limestone in the lower Matamiska Valley north of Castle 

Mountain, as described by Martin and Katz,90 occurs in a belt within 

which there is one large area and at least three smaller ones. The 

best exposures are on the ridge north of the west end of Castle 

Mountain, where the limestone is blue and gray to white and of fine 

to medium grain or degree of crystallinity. It is much shattered 

and full of minute calcite veins. Where seen on top of the ridge 

it is well bedded in strata from 6 inches to several feet thick, there 

being no decided change in lithologic character from bed to bed. 

The thickness is probably several hundred feet. The westernmost

00 Martin, G. C., and Katz, F: J., Geology and coal fields of the lower Matanuska Valley, Alaska: U. S. Geol. Survey Bull. 500, pp. 32-33, pi. 5, 1912.
316 MESOZOIC STRATIGRAPHY OF ALASKA

exposure on top of the ridge, a small, isolated outcrop at an altitude of about 4,700 feet, contains beds that are decidedly cherty.

The limestone on the crest of the ridge north of Castle Mountain 

lies in a closely compressed overturned syncline and rests upon 

somewhat altered volcanic rocks that are considered to be the same 

as the Lower J'urassic tuff of Chickaloon River, with which they are 

areally continuous. An exposure on the west end of this ridge 

shows the volcanic rocks in direct contact with the limestone. Small 

pebble-like fragments of the greenstone are embedded in the lower 

2 inches of the limestone. These fragments give evidence that the 

limestone overlies the greenstone unconformably.

As no fossils have been found in the limestone north of Castle 

Mountain, the determination of its age must depend on the local 

stratigraphic evidence and on correlation with the rocks of neighboring regions.

It has been shown above that the limestone rests unconformably 

upon supposed Lower Jurassic rocks. The Middle and .Upper Jurassic rocks of the upper part of the Matanuska Valley show a complete sequence of several thousand feet of strata in which limestone 

is absent. These Upper Jurassic rocks are overlain, on Billy Creek 

and Nelchina River, by Lower Cretaceous rocks, which, as described 

on pages 313-315, include a massively bedded limestone about 300 

feet thick.

Although there are differences in the features of the two limestones 

they are such as might be explained by the fact that the two occurrences are 25 miles apart and in structurally different areas. These 

limestones consequently were provisionally correlated by Martin and 

Katz 91 and were referred to the Lower Cretaceous.

The correlation of the limestone north of Castle Mountain with the 

Lower Cretaceous Nelchina limestone must still be regarded as 

highly probable although not established beyond all doubt. If the 

altered volcanic rocks north of the west end of Castle Mountain, on 

the tributaries of Kings River, are of the same age as the less altered 

Lower Jurassic tuff on Chickaloon River, with which they are areally 

continuous, then the limestone north of Castle Mountain, which overlies these volcanic o-ocks unconformably, is certainly younger than 

Lower Jurassic and is probably Lower Cretaceous. If, however, the 

altered volcanic rocks of Kings River are not the same as the Lower 

Jurassic tuff of Chickaloon River, then there is no evidence that this 

limestone is Lower Cretaceous. In that case the limestone and the 

underlying volcanic rocks may possibly be correlated with the Upper 

Triassic Chitistone limestone and the underlying Nikolai greenstone 

of the Chitina Valley. (See pp. 7-18.) __________

81 Op. cit, p. 33.
CRETACEOUS, MATANUSKA VALLEY 317 

UPPER CRETACEOUS

MATANUSKA FORMATION

Historical review. Upper Cretaceous strata have a broad extent 

and attain a great thickness in the Matanuska Valley, but they apparently constitute only a single formation which, so far as now 

known, is entirely of marine sedimentary origin. To these strata 

the name Matanuska formation is here applied.

The Upper Cretaceous rocks of the Matanuska Valley were first 

observed by Mendenhall in the course of a rapid exploratory journey 

in which the opportunities for stratigraphic observations were very 

scanty. Mendenhall included these Upper Cretaceous rocks in his 

"Matanuska series," which as originally described 92 comprised all 

the sedimentary rocks seen by him in the Matanuska and Nelchina 

Valleys. / The " Matanuska series " was assigned by Mendenhall to 

the Lower Cretaceous because it was supposed to include the fossiliferous Lower Cretaceous conglomerate tuff of the headwaters of 

Nelchina River, which is described on pages 310-313. The "Matanuska series " as originally described is now known to have included 

a thick and heterogeneous aggregate of sedimentary and pyroclastic 

strata ranging in age from Lower Jurassic to late Tertiary. Mendenhall mentioned but did not specifically describe the strata now 

known to be Upper Cretaceous and herein designated the Matanuska 

formation. It happens, however, that the larger part of the area 

which was supposed to be occupied by the original "Matanuska 

series " contains these Upper Cretaceous strata, and that nearly all 

the exposures on the banks of Matanuska River from its source to its 

mouth consist of these Upper Cretaceous rocks. It is consequently 

believed to be appropriate to revive this long-abandoned name as the 

Matanuska formation, although it must be given a very different 

definition and assigned to a different position from that of the 

original "Matanuska series."

The Upper Cretaceous shale and sandstone of Anthracite Ridge 

were described briefly by Martin 93 as the result of a hasty reconnaissance of the coal fields of the lower part of the Matanuska Valley in 

1905. The description is very brief and includes merely a not altogether accurate statement concerning the lithologic character of the 

rocks, which were represented on the geologic map 94 as "Mesozoic 

slate and graywacke," together with a statement by T. W. Stanton 

concerning two small collections of fossils that " so far as can be determined from these specimens the horizon may be as low as Middle

02 Mendenhall, W. C., A reconnaissance from Resurrection Bay-to the Tanana .River, 

Alaska, In 1898: U. S. Geol. Survey Twentieth Ann. Rept., pt. 7, pp. 307-309, 1900.

fls Martin, G. C., A reconnaissance of the Matanuska coal field, Alaska, In 1905: U. S. 

Geol. Survey Bull. 289, p. 11, 1906.

"Idem, pi. 3.

49448 26 22
318 MESOZOIC STRATIGRAPHY OF ALASKA

Jurassic or as high as Upper Cretaceous," but on comparing them 

with the later and more extensive collections (see p. 236) he has assigned them definitely to the Upper Cretaceous. The other Upper 

Cretaceous areas in the lower part of the Matanuska Valley were 

mapped by Martin as part of the "Tertiary shale, sandstone, and 

conglomerate."

The Upper Cretaceous strata of the Matanuska Valley were not 

recognized as such by Paige and Knopf, who did not distinguish 

them from the somewhat similar Tertiary and Jurassic shale and 

sandstone. The geologic map by Paige and Knopf 95 consequently 

represents the areas now known to be occupied by this formation as 

partly Tertiary and partly Jurassic.

The presence of Upper Cretaceous rocks in the Matanuska Valley 

was first recognized by Martin and Katz,96 who described and 

mapped in detail the occurrence of these rocks in the lower part of 

the valley. This account includes a general description of the formation, detailed descriptions of the section exposed on Granite Creek 

and of several other exposures, and lists of the marine invertebrate 

fossils, with a discussion of the age and relationships of the fauna 

by T. W. Stanton. The account includes also a list, by Arthur Hoilick, of some fossil plants from beds which may belong in this formation but which Hollick considered to be probably Tertiary. (See 

p. 323.)

The Upper Cretaceous shale and sandstone at the headwaters of 

Squaw, Alfred, and Billy creeks were mentioned briefly by Chapin.97

Stratigraphic description. The Upper Cretaceous rocks of the 

Matanuska Valley here designated Matanuska formation consist of 

shale and sandstone, having an aggregate thickness, as exposed on 

Granite Creek, of at least 4,000 feet, of which the lower half is practically all shale and the upper half consists of alternating beds of 

sandstone and shale, the sandstone predominating. Conglomerate is 

present but not in thick or numerous beds. The most complete section observed is in the gorge of Granite Creek and is recorded on 

pages 319-320. Other good sections are exposed on Kings River between the main trail and the coal camp and in the cliffs of Matanuska 

River. Many of these cliffs are not accessible for close study except 

at a very low stage of the water.

The base of the Upper Cretaceous shale has nowhere been observed, and there is much uncertainty not only as to the character 

of the basal contact but as to the identity of the underlying rocks.

96 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissance In the Matanuska and 

Talkeetna Basins, Alaska : U. S. Geol. Survey Bull. 327, pi. 2, 1907.

86 Martin, G. C., and Katz, F. J., Geology and coal fields of the lower Matanuska Valley, 

Alaska: U. S. Geol. Survey Bull. 500, pp. 15, 23, 34-39, pis. 3, 5, 1912.

97 Chapin, Theodore, The Nelchina-Susitna region, Alaska: U. S. Geol. Survey Bull. 668, 

p. 38, pi. 2, 1918.
CBETACEOUS, MATAKUSKA VALLEY . 319

The distribution of the formation, relative to that of the older rocks 

of this region, indicates that it probably rests unconformably upon 

a surface of profound erosion cut across rocks ranging in age from 

Lower Jurassic to Lower Cretaceous.

The Upper Cretaceous sandstone is overlain unconformably by 

Tertiary arkose and conglomerate. The strongest evidence of the 

unconformity is found in the mountains west of Kings Kiver, where 

the Tertiary rocks lie horizontally upon the surface of the presumably early Mesozoic granite within a quarter of a mile of a 

place where the Upper Cretaceous sediments are present in full 

development with the granite faulted against them.98 It is therefore evident that as the Tertiary rocks directly overlie the preCretaceous granite, at least the full thickness of the Upper Cretaceous sediments must have been removed at this place during the 

Cretaceous-Eocene erosion interval. At the coal camp on the east 

bank of Kings River the Tertiary coal-bearing rocks apparently 

rest unconformably across the upturned edges of the Upper Cretaceous sandstone, but as the coal-bearing beds exposed at this place 

are believed not to be the basal Tertiary rocks, this contact is considered a thrust fault rather than an unconformity.

The section on Granite Creek was measured in the gorge that 

begins 1% miles above its mouth and extends northward for 2 miles; 

in this distance exposures are almost continuous on one or the other 

bank, and in some places on both banks of the stream. It is assumed, 

in accepting this section and thickness, that there is no repetition of 

the beds by faulting. The exposures are not of such a character as 

to make this an absolutely safe assumption, although the absence of 

observed faults, or of beds that seem to be repeated, and the fact 

that the ridge on the east of the gorge presents an unbroken dip-slope 

suggest that the section is an uninterrupted and unrepeated monoclinal succession of beds.

The rocks exposed in the gorge of Granite Creek consist of southeastward-dipping sandy shale and flaggy sandstone. Inoceramus 

and other Upper Cretaceous fossils were collected from the shale of 

the lower part of the section, in the positions indicated. The sandstone, which predominates higher in the section, yielded no fossils 

except a fragmentary nuculoid form. No plant fossils were seen.

Section of Matanuska formation on Granite Creek, beginning at lower end of 

canyon, 1% miles from the mouth of the creek

Feet

Black shale at base, overlain by thin-bedded gray sandstone, some of which is very tine and has contorted laminae, and gray or drab-gray shale (beds are interleaved 

lenses rarely more than 6 inches thick)_________ 12 

Black sandy shale________________,______ 4-6

88 See U. S. Geol. Survey Bull. 500, pi. 16. section H-H', 1912.
320 . MESOZOIC STRATIGRAPHY OF ALASKA

Feet

Thin-bedded gray sandstone and shale____________ 15

Black nodular shale____._________________ 8

Sandstone, mainly beds about 5 feet thick, with thin interbedded shale__________________________ 30

Interbedded black shale and thin gray sandstone and 

shale ____ ____________________ 50

Massive sandstone, feldspathic and micaceous_______ 20

Interbedded gray shale, gray sandstone, and black shale_ 40

Sandstone.____________L_____________ 12 

! Alternating beds, 1 to 8 feet thick, of gray sandy shale

and black shale________________________ 250 

| ' Similar beds increasingly to dorninantly sandy and light

gray __________________________ 80

Dark-colored sandstone and sandy shale_____ __ 75

Light-gray sandstone, including several thick, massive 

beds and some very thin shale (in east bank; estimated 

thickness) ___________________________ 200

Dark shale in beds alternating with thin sandstone and 

light-colored shale ______________________ 450

Sandstone, heavy bedded at the top but dominantly thin

bedded (beds 1 to 2 feet and less than 1 foot), with

'. many beds of very thin shaly sandstone having contorted

: laminae; also a few thin shale beds and an increasing

number of beds of dark shale in the lower part_ _ 840

Exposures interrupted and inaccessible for 1,500 feet along 

the creek, equivalent to an estimated stratigraphic interval of____________________________ 500

Dark bluish-black sandy shale outcropping for 200 feet in 

a direction about N. 17°' E.; strike, N. 40° E.; dip, 60° 

SE.; computed thickness______________-_ 80±

Exposure interrupted and inaccessible for 800 feet along 

the creek, equivalent to an estimated stratigraphic interval Of__._______-.__._____ _____________________ 300±

Hard dark blue-black shale,98 outcropping for about 200 

feet in a direction N. 17 0| E.; strike, N. 28° E.; dip, 60° 

to 65° SE.; computed thickness______________ 90±

Exposure interrupted and inaccessible for about 200 feet 

along the creek, equivalent to an estimated stratigraphic 

interval of ______________________ 90±

Hard dark blue-black shale,09 outcropping for 400 feet 

along the creek in a direction N. 17° E.; strike, N. 47° 

E.; dip, 50° SE.; computed thickness______ __ 170±

Exposure interrupted and inaccessible for 100 feet along 

the creek, equivalent to an estimated stratigraphic interval of________ ___ __ _ 45±

Hard dark blue-black shale." outcropping for about 1,000 

i feet along the creek; estimated thickness___ 400±

3, 760±

No exposure for 7,500 feet.

Several small outer ops "through 1,200 feet along the east 

bank of the creek in a northerly direction ; strike, N. 23° 

E.; dip, 49° SE.; computed thickness____ _ 350±:

89 Fossils collected from these beds are lot 6689; see p. 324.
CRETACEOUS, MATANUSKA VALLEY 321

The Upper Cretaceous rocks (Matanuska formation) of the upper 

part of the Matanuska Valley are of the same general lithologic 

character as those in the lower part of the valley. In the belts 

that extend along the river the folding is so severe that no stratigraphic sequence can be recognized, the bedding in many places 

being destroyed. The same condition holds in general, though to 

a somewhat less degree, in the Anthracite Ridge and western Boulder 

Creek areas. Much more gentle structure exists on Alfred and 

Billy creeks and on the upper part of Boulder Creek, where the 

Upper Cretaceous rocks dip at low angles and have not been 

.crumpled or crushed.

The exposures on Alfred Creek reveal several hundred feet of 

fissile drab shale that is sparsely fossiliferous. The rocks dip 

5°-15° S. above the mouth of North Fork and 5°-10° N. below 

that place. They thus apparently lie in a shallow syncline in which 

several hundred feet of strata are exposed.

The rocks exposed on Billy Creek consist of blue sandy shale 

with abundant fossils (lot 8578, p. 324). The beds are horizontal, 

and as the observed exposures are restricted to low cliffs bordering 

the creek, a very small section is visible. The total thickness exposed, including the soil-covered beds, probably does not exceed 300 

or 400 feet. The overlying beds are believed to be Tertiary conglomerate, resting unconformably upon the Upper Cretaceous and 

older strata.

The Upper Cretaceous rocks on the upper part of Boulder Creek 

include about 200 feet of shaly sandstone with Inoceramus (lot 

8577, p. 324). A bed of conglomerate about 100 feet thick overlies 

this sandstone and is in turn overlain by at least 400 feet and 

possibly 600 or 800 feet of poorly indurated shale and sandstone 

with coal beds. These carbonaceous beds carry fossil plants, which 

are clearly of Tertiary age. The field relations also indicate that 

the conglomerate is at the base of the local Tertiary sequence.

Age and correlation. Marine molluscan remains are fairly 

abundant in the shale that constitutes the lower half of the Matanuska formation. They show that it is undoubtedly of Upper 

Cretaceous age. Stanton 1 made the following statement regarding the age and relations of the fauna represented by the material 

collected by Martin and Katz in 1910:

Of the lots referred to the Upper Cretaceous those numbered 6689, 6694, 

and 6696 are certainly of that age and belong to the Upper Cretaceous fauna 

which has been recognized at several points on the Alaska Peninsula and is 

part of the general Indo-Paciflc fauna found in. the Chico formation of Cali1 Stanton, T. W., quoted by Martin, G. C., and Katz, F. J., Geology and coal fields of 

the lo-wei Matanuska Valley Alaska: TJ. S. Geol. Survey Bull. 500, pp. 3S-3&, 1912.
322 MESOZOIC STRATIGRAPHY OF ALASKA

fornia, on Vancouver Island, in Japan, and in India. Most of the other lots 

in this collection, referred to the Cretaceous, contain only fragmentary specimens of Inoceramus which are no.t sufficient in themselves for discrimination between Jurassic and Cretaceous, though it is probable that these fragments belong to the same species that occurs at other localities in the neighborhood where the Cretaceous age of the rocks is definitely determined.

The following statements were made by Stanton 2 concerning some 

of the individual lots of fossils:

This collection [6696] is clearly of Upper Cretaceous age and belongs to 

the general Indo-Pacific fauna, which is well developed in India, Japan, 

Sakhalin, Vancouver, and California.

Inoceramus sp. [in lot 6689 is a] very large compressed form which has 

been collected [see 3121, p. 303] on Alaska. Peninsula north of Aievak or 

Douglas village.

An unpublished report contains the following further comments 

by Stanton: 3

The Inoceramus referred to /. digitatus in this list [8596] is the same 

species that has been so identified by Whiteaves from Vancouver Island. 

But according to H. Wood's recent monograph of the Cretaceous Lamellibranchiata of England the type of Sowerby's imperfectly known Inoceramus 

diffitatus is a different species, and forms such as this are referred to /. undulato-plicO'tus Roemer.

A reexamination of lots numbered 3318 and 3319 in earlier collections from 

the Matanuska Valley and comparison with more recent collections was made, 

and they can now be definitely referred to the Upper Cretaceous.

Knopfs collections from the same regions were also reviewed, and his No. 

6AK42 may possibly be Cretaceous, but it is still believed to be more probably 

Middle Jurassic. The matrix is not like that in which the Cretaceous fossils 

from that area are embedded but is a pebbly sandstone.

The higher sandy beds contain only rare and poorly preserved 

mollusks, chiefly Inoceramus and a few uncharacteristic nuculoid 

forms, together with some fossils of more or less problematic character that may be fucoids (Spirophytonf) and worm tracks or burrows, and possibly at one locality (5898) some leaves of rather 

uncertain age.

The problematic fossils (5893, 5894) occur in immediate association with a large form of Inoceramus (6691) and are thus known 

to be Mesozoic, and as they are apparently found above the horizons 

at which the more characteristic Upper Cretaceous fauna occurs, 

they are consequently Upper Cretaceous also. They are not sufficiently characteristic to yield of themselves any important independent evidence on the age of the rocks.

Fossil plants (lot 5898), which consist of species unlike those in 

the local Tertiary formations, were collected from beds that were

8 Stanton, T. W., quoted by Martin, G. C., and Katz, F. J., op. cit., p. 37, 1912. 

3 Stanton, T. W., quoted by Martin, G. C., manuscript report on the geology of the 

upper Matanuska Valley.
CRETACEOUS, MATANTJSKA VALLEY 323

regarded as occurring in the upper sandy part of the Matanuska 

formation but that are stratigraphically above the highest observed 

beds containing the marine Cretaceous fauna. These plant-bearing 

beds apparently are lithologically identical and stratigraphically 

conformable with the highest recognized Cretaceous rocks and are 

lithologically unlike any of the known Tertiary beds of this region. 

These beds are considerably more indurated than any of the local 

Tertiary rocks except those that have been involved in the intense 

deformation in the mountain region north of the Matanuska1 Valley. 

It is possible, however, that this condition is due to the position of 

these rocks near an intrusive contact. The field relations consequently indicate though they do not prove that this flora is older 

than the Tertiary floras described below and suggest that it belongs 

in the Upper Cretaceous. The flora is somewhat different in character from the known Tertiary floras but is, nevertheless, more like 

them than it is like any known Mesozoic floras.

The following report on' this collection was made by Arthur 

Hollick: 4

5898. Locality (34) at south of pond on top of mountain between Kings 

River and Young Creek, 1% miles N. 10° W. from Kings River Bridge:

Equisetum arcticum Heer? Specimens very fragmentary. Some pieces

might equally well be referred to B. robustum Newberry. 

Glyptostrobus ungeri Heer? Fragmentary remains of a heterophyllous 

conifer, some of which might equally well be referred to Juniperus 

tertiaria Heer. 

Nyassa aretica Heer.

Aristolochia sp. This is in great abundance and is very variable in 

form. Some specimens are hardly to be distinguished from certain 

forms of Populus aretica Heer.

This is a meager and more or less unsatisfactory collection. The general 

facies is different, however, from that of any other collection from the Matanuska field. Age, basal Eocene.

*Hollick> Arthur, quoted by Martin, G. C., and Katz, F. J., Geology and coal fields of 

the lower Matanuska Valley, Alaska: U. S. Geol. Survey Bull. 500, p. 38, 1912.
Upper Cretaceous fossils from Matanuska formation of M

Pecten, n. sp.? ____ . ______________

Oaudryceras kavei Forbes var. __________ .

Baculites __ . .. ... ...

g 

S

% 

S

CO

§ 

CD

O>

3

io

S

S

O>

en

S 1 1

a

1

£

Tj< 

O

co 

<o

as 

§

a

T}« 

g>

S

of

1

h

b

o 

13

I

CO

s? 

s

a,

c

0

c

c

00

1CO

a
Anisoccras? _____ ________________

- 

1 a, Identified by T. W. Stanton; b, identified by Arthur Hollick; c, identified by W. R. Smith.
326 ' MESOZOIC STRATIGRAPHY OF ALASKA

6690. North bank of Matanuska River at lower end of canyon about a mile 

above Moose Creek. G. C. Martin, 1910.

6695. North bank of Matanuska River at upper end of canyon at mouth of 

Eska Creek. G. C. Martin, 1910.

6696. Creek entering Granite Creek from west 5 miles above main trail, 

about half a mile west of and 470 feet above Granite Creek. G. C. Martin, 1910.

6689. Granite Creek, west bank, between altitudes of 1,000 and 1,050 feet. 

Position indicated in section on p. 320. . G. C. Martin, 1910.

6705. Young Creek. Float. G. C. Martin, 1910.

6692. Pass between Kings River and Young Creek. G. C. Martin, 1910.

6699. 3,350-foot knob 1 mile north of east end of Chain Lakes. G. C. Martin, 

1910.

6700. East bank of Kings River 0.35 mile above mouth. G. C. Martin, 1910.

6702. East bank of Kings River one-fourth of a mile above mouth. G. C. 

Martin, 1910.

6703. East bank of Kings River 3,850 feet below mouth of Young Creek. 

G. C. Martin, 1910.

6694. East bank of Kings River three-fourths of a mile below U. S. L. M. 

No. 1. G. C. Martin, 1910.

6691, 5893, 5894. East bank of Kings River at Coal Camp. G. C. Martin, 1910.

6701. North bank of Matanuska River 3% miles above Kings River. G. C. 

Martin, 1910.

6704. Carbon Creek 3,875 feet above mouth. G. C. Martin, 1910.

8559. First tributary to Boulder Creek from the west above the canyon. 

Float. G. C. Martin, 1913.

8568. Float from same creek as No. 8559. R. M. Overbeck, 1913.

8560. About half a mile up first tributary to Boulder Creek from the west 

above the canyon. G. C. Martin, 1913.

8562. North slope of Anthracite Ridge near crest, at head of tributary to 

Boulder Creek next below East Fork. G. C. Martin, 1913.

8563. North slope of Anthracite Ridge at altitude 4,600 feet, at head of next 

to lowest tributary to East Fork of Boulder Creek. G. C. Martin, 1913. 

8566. North slope of Anthracite Ridge near head of next to lowest tributary

of East Fork of Boulder Creek. G. C. Martin, 1913.

3318. Crest of Anthracite Ridge near head of Purihton Creek. G. C. Martin, 

1905.

3319. South slope of Anthracite Ridge near Purinton Creek, altitude 3,450 

feet. G. C. Martin, 1905.

8577. North side of Boulder Creek at base of waterfall about 16% miles 

above mouth. Shaly sandstone beneath conglomerate. G. C. Martin, 1913.

8596. South bank of Matanuska River 5 miles above mouth of Chickaloon 

River. G. C. Martin, 1913. *

8595. North bank of Matanuska River 4 to 5 miles below O'Brien's Ford. 

G. C. Martin, 1913.

8592. North bank of Matanuska River 10 miles above Chickaloon River. 

G. C. Martin, 1913.

8593. About 1,000 feet up third tributary to Matanuska River from the 

north below O'Brien's Ford. R. M. Overbeck, 1913.

(48). Small gulch south of lowest tributary to Gravel Creek from the 

southwest, altitude 1,850 feet. R. M. Overbeck, 1913.

8594. Creek at east end of O'Brien Flats (lowermost large tributary of 

Gravel Creek), altitude 1,760 feet. J. B. Mertie, 1913.
CRETACEOUS, CHITINA VALLEY 327

8591. Hicks Creek opposite mouth of next to lowest tributary from the 

west. G. C. Martin and R. M. Overbeck, 1913.

8947. Knob 1 mile north of Matanuska River and 6^ miles northwest 

of Glacier Point. Theodore Chapin, 1914.

8948. Ridge between Hicks and Caribou creeks, 3% miles north of Matanuska River. Theodore Chapin, 1914.

8586. Mouth of Alfred Creek. G. C. Martin, 1913.

8587. Alfred Creek 1,880 feet below main forks. R. M. Overbeck, 1913. 

8590. Alfred Creek, exact position not known. Obtained from prospectors

by G. C. Martin, 1913. 

8578. Billy Creek about 4% miles above mouth, altitude 3,800 feet. G. C.

Martin, 1913.

CHITINA VALLEY 

GENERAL FEATURES

The undoubted Cretaceous rocks of the Chitina Valley include the 

Lower Cretaceous Kennicott formation and an unnamed Upper Cretaceous formation composed mostly of shale that carries a marine 

Upper Cretaceous fauna.

The Lower Cretaceous Kennicott formation and beds which the 

writer believes should be correlated with it consist of sandstone and 

sandy shale, probably at least 1,000 feet thick, which are believed to 

lie unconformably on Upper Triassic rocks and to be overlain, probably unconformably, by Upper Cretaceous shale.

The Upper Cretaceous shale is about 7,000 or 8,000 feet thick. It 

is underlain with apparent conformity by conglomerate and sandstone that may be either basal Upper Cretaceous or Lower Cretaceous. 

It is apparently overlain by conglomeratic rocks that may be tentatively correlated with late Upper Cretaceous or basal Tertiary conglomeratic rocks on McCarthy Creek, which are overlain by volcanic 

rocks that are supposed to be Tertiary. ^

Near both the east and the west ends of the Chitina Valley are some 

conglomerate and sandstone of doubtful position. These beds rest 

unconformably upon the Upper Triassic formations and in the eastern part of the district are overlain with apparent conformity by 

Upper Cretaceous beds. They differ strikingly in lithologic character from any of the other Mesozoic formations of this region and 

also differ among themselves to such an extent that they either may 

or may not be regarded as a lithologic unit. They carry fossils 

which may be either Cretaceous or Jurassic, which may constitute 

one fauna or several faunas, and among which are none of the characteristic fossils of the recognized Cretaceous and Jurassic faunas of 

Alaska. The available evidence from the east end of the valley 

points strongly toward the Upper Cretaceous age of these rocks, and 

the doubtful rocks of that area will accordingly be described on 

pages 355-360 as probably Upper Cretaceous. In the western part of
328 MESOZOIC STRATIGRAPHY OF ALASKA

t

the valley the evidence suggests that at least part of the doubtful 

sequence may be Lower Cretaceous, and the rocks of that area will 

therefore be described on pages 349-355 as possibly Lower Cretaceous, 

although Upper Cretaceous or even Jurassic rocks may perhaps also 

be present there.

The Upper Cretaceous shale of Chititu and Young Creeks is underlain, with apparent conformity, by sandstone and grit exposed 

on the tributaries of Dan Creek. The sandstone and grit rest unconformably upon Upper Triassic rocks and carry a very meager 

marine invertebrate fauna that might be either Cretaceous or Jurassic. The writer believes that the grit and sandstone probably form 

the basal member of a conformable Upper Cretaceous series.

The grit and sandstone of Dan Creek are probably the equivalent 

of the somewhat similar conglomerate, sandstone, and sandy shale 

of the headwaters of Nikolai Creek. These rocks also rest unconformably upon Upper Triassic rocks and grade upward into black 

shale that resembles the Upper Cretaceous shale. They likewise 

carry a sparse marine invertebrate fauna that may be either Cretaceous or Jurassic.

The shale here referred to the Upper Cretaceous has been described as being overlain by a massive conglomerate that crops out 

on the ridge south of Young Creek. It is doubtful whether the 

rocks really occur in this relationship, for not only are there indications of a fault at the base of the conglomerate, but the beds that 

appear to underlie the conglomerate are not known to be Upper 

Cretaceous. They differ in several important features from the 

known Upper Cretaceous rocks, are separated from them by a 

fault, and have not yielded any fossils. They are accordingly described on^pages 369-371 as doubtfully Upper Cretaceous.

The Kotsina conglomerate and the overlying limestone and sandstone of the Kotsina and Kuskulana Valleys are also of do'ubtful 

position. These rocks have previously been referred to the Upper 

Jurassic, but this was done chiefly because of their apparent relationship to the supposed Upper Jurassic rocks of the Kennicott 

formation. The writer believes that the uppermost of these beds 

are certainly Cretaceous. The basal conglomeratic beds, which have 

yielded no fossils, might possibly be Jurassic, but the writer sees 

no reason for assuming that they are of different age from the 

somewhat similar basal Upper Cretaceous or the basal Lower Cretaceous conglomerates of the eastern part of the Chitina Valley.

The sequence and probable relations of the Cretaceous rocks in 

different parts of the Chitina Valley are indicated in the following 

table. In each of these areas except at the mouth of Chitina River 

the Lower Cretaceous rocks are underlain unconformably by Triassic 

rocks.
Probable relations of Cretaceous and Jurassic rocks in pa

Age

Tertiary.

Upper Cretaceous.

Lower Cretaceous.

Upper Jurassic.

Middle Jurassic.

Lower (?) Jurassic.

Mouth of Chitina 

River

Tuffaceous slate.

Tuffaceous conglomerate.

Kotsina-Kuskulana district

Sandstone. 

Limestone. 

Kotsina conglomerate (may be 

Upper Cretaceous of may 

possibly be Jurassic) .

Fohlin Creek and 

Kuskulana Pass

Coal-bearing shale 

and sandstone. 

Black shale.

Kennicott formation (greenish sandy 

shale and sandstone) .

Headwaters of McCarthy Creek

Volcanic rocks. 

Conglomerate, sandstone, and shale, 

with some coal. 

Black shale.

Sandy shale and conglomerate.

H

B

S
330 MESOZOIC STRATIGRAPHY OF ALASKA

LOWER CRETACEOUS 

KENNICOTT FORMATION

Historical review. The Kennicott formation was first described 

by Kohn 5 as the Kennicott " series " and was loosely defined as consisting of " light-colored arkoses, shales, and limestones." The type 

locality is at Kennicott Pass (now known as Fourth of July Pass), 

where the rocks constitute a very definite lithologic unit, containing 

Aucella and other fossils which were then considered Upper Jurassic. 

Rohn correlated these beds with an outlier near the head of McCarthy Creek, which consists of impure fossiliferous sandstone grading downward into a bed of conglomerate which rests unconformably 

upon the McCarthy shale. His map represents the Kennicott " series " as covering also a large area near the head of Kennicott Glacier. The description includes brief and general statements concerning the occurrence and character of these rocks and lists of fossils with a discussion of their age by T. W. Stanton.

The Kennicott formation was redefined by Schrader and Spencer ft 

to include " a variable series of conglomerates, sandstones, limestones^ and shales," which comprises (1) the original Aucella-bea,Tmg 

Kennicott formation of Kennicott Pass (minus a large area of 

Triassic rocks that were included in the Kennicott " series" on 

Holm's generalized and necessarily inaccurate map); (2) an area 

of Aucella-bearmg rocks in Kuskulana Pass that are doubtless identical with the original Kennicott formation; and (3) conglomerate and sandstone resting upon a surface of profound unconformity, occurring in many isolated mountain-top exposures on the watersheds of Kotsina Kiver, Strelna Creek, Nikolai Creek, and Young 

Creek and 'carrying a fauna in which Aucella is strikingly absent. 

The rocks of this third division, in the writer's opinion, do not 

belong in the Kennicott formation, and part of them are probably 

not Lower Cretaceous. They are accordingly described elsewhere 

(pp. 349-358.)

The following description by Schrader and Spencer 7 applies to 

rocks that undoubtedly belong to the Kennicott formation:

To the east of Kuskulana Glacier it [the Kennicott formation] first appears 

in the bed of Trail Gulch, at an elevation of about 2,200 feet, and may be 

traced eastward for a distance of about 3 miles. In this locality the formation affords fossil remains. It does not appear again west of Lakina River,, 

but to the east of that stream in the drainage of Fohlin Creek, it attains considerable development, having a thickness which possibly reaches 1,000 feet or

6 Rohn, Oscar, A reconnaissance of the Chitlna River and the Skolai Mountains,. 

Alaska: U. S. Geol. Survey Twenty-first Ann. Rept., pt. 2, pp. 424, 428, 431-432, 433,. 

439-440, pi. 52, 1900.

6 Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special pub.), pp. 33, 48-50, 

pi. 4, 1901.

7 Idem, p. 49.
CBETACEOUS, CHITINA VALLEY 331

more. In this locality and in the last it seems as if the formation was deposited in a submerged valley, the sides of which had considerable height above 

the level of the water.

This description contains also a list of fossils from all the supposed Kennicott localities. This is a combined list, which unfortunately is not representative of the fauna of this formation, for it includes the species from several localities that belong to Triassic and 

doubtful horizons. The statement to the effect that Stanton believed 

the fauna to correspond to that of the Knoxville formation is also not 

warranted.

In the reexamination of the mineral deposits of the Chitina Valley by Moffit and Maddren in 1907, the Kennicott formation, which 

does not contain ore deposits, was not studied in detail, and little 

new stratigraphic information concerning it was obtained. The account of the Kennicott formation by Moffit and Maddren 8 accordingly consists of a quotation of the full description by Schrader and 

Spencer.

The Kennicott formation was redefined by Moffit and Capps,9 

who extended its limits to include not only the sandstone and conglomerate of Nikolai Creek, which constituted part of the amended 

Kennicott formation as described by Schrader and Spencer, but also 

a large area and immense thickness of shale which had been mapped 

by Rohn as " unclassified sediments " and by Schrader and Spencer 

as "Triassic shales and limestones." Most of the rocks referred 

to the Kennicott formation by Moffit and Capps are now known to 

be Upper Cretaceous (see pp. 360-369), but the sandstone or arkose 

south of the Young Creek fault, in which no fossils have so far been 

found, is very different from the Upper Cretaceous shale north of 

the fault and is not unlike some of the Lower Cretaceous sandstone 

of the Kennicott formation exposed on Fohlin and Bear creeks. 

The writer believes that with this possible exception none of the 

rocks described by Moffit and Capps belong in the Kennicott formation as the term is here used, and it is doubtful (pp. 357, 359) 

whether any of them are Upper Jurassic or Lower Cretaceous. They 

were formerly referred to the Upper Jurassic because it was assumed that they were the same as the Kennicott formation of 

Fourth of July Pass and because this field determination was not 

disproved by the evidence from the small collections of fossils, 

which, as Stanton 10 said,

indicate that one fauna ranges throughout the formation and that its age 

is most probably Jurassic, though the types represented in the collection are

8 Moffit, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Chitina region, 

Alaska: U. S. Geol. Survey Bull. 374, pp. 30-32, 1909.

9 Moffit F. H., and) Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska: U. S. Geol. Survey Bull. 448, pp. 31-43, 1911.

10 Stanton, T. W., cited by Moffit, F. H., and Capps, S. R'., idem, p. 39.
332 MESOZOIC STRATIGRAPHY OF ALASKA

not as definite as could be wished for determining between Jurassic and 

Cretaceous. The entire absence of Aucella is noteworthy in view of the 

fact that that genus has previously been reported from the formation.

It should be pointed out that the collections upon which Stanton 

based the statement above quoted were very small and include no 

characteristic forms. The present assignment of these rocks to the 

Upper Cretaceous is not based upon a redetermination of these old 

collections but upon new collections that contain characteristic 

Upper Cretaceous genera.

In 1914 the writer made comparative studies of the rocks in 

Fourth of July Pass and on Chititu Creek. He recognized that the 

rocks at these two localities are not the same either lithologically or 

faunally. In Fourth of July Pass he obtained collections of marine 

fossils, including species of Aucella related to Aucella pallasi Keyserling, and collections of fossil plants which were obtained not only 

in the same beds but in the same pieces of rocks with the fossil 

shells. The marine shells and the plants were identified, by Stanton and by Knowlton, respectively, as Upper Jurassic. On Chititu 

Creek the writer obtained marine shells which Stanton identified as 

" certainly Upper Cretaceous."

The upper part of the Chitina Valley, including Chititu and 

Young creeks, was studied in 1915 by Moffit, who described the 

Mesozoic section as including sandstone that contains Aucella and 

other fossils which Stanton identified as " probably Upper Jurassic," 

together with fossil plants which Knowlton identified as Upper 

Jurassic, also another sandstone that contains ammonites and other 

marine shells, which Stanton assigned to "the basal part of the 

Upper Cretaceous or near the top of the Lower Cretaceous," together 

with fossil plants which Knowlton regarded as Upper Jurassic. 

These sandstones were not considered in the field as being of different ages and were differentiated in the description solely on the 

supposed evidence of the fossils.

The account of the supposed Upper Jurassic rocks of the upper 

Chitina Valley 11 includes a brief description of the character and 

distribution of the rocks and a discussion of their age and correlation, with lists of marine fossils as identified by Stanton. Lists of 

fossil plants from these localities, identified by Knowlton, are given 

elsewhere.12 Moffit correlated the Aucetta-be&ring beds of the upper 

Chitina Valley with the Kennicott formation as restricted to the 

Aucetta-be&r'mg beds of Fourth of July Pass.

11 Moffit, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 

17, 18, 27-28, pi. 3, 1918.

"Idem, p. 44 (localities 7035 and 7037).
CRETACEOUS, CHITINA VALLEY 333

The account of the sandstone which Moffit recognized as Cretaceous 13 comprises a detailed description of the character and stratigraphic relations of the beds and a discussion of the age and correlation,14 in which both the sandstone and the overlying Upper 

Cretaceous shale are included. Lists of fossils and discussions of 

their age by Stanton and by Knowlton are quoted. The lists include 

marine fossils from both the supposed Lower Cretaceous sandstone 

and from the overlying Upper Cretaceous shale, but the discussions 

by Stanton and Knowlton and the lists of plants apply only to the 

fossils from the sandstone. Stanton 15 states that the fauna includes 

many ammonites and other mollusks of Cretaceous types and that a 

reexamination of one of the older collections (8872) from the supposed Upper Jurassic rocks of the original Kennicott formation of 

Fourth of July Pass has revealed the presence of characteristic 

Cretaceous ammonoids.

The description of the supposed Upper Jurassic rocks of the 

Kotsina-Kuskulana district, by Moffit and Mertie,16 contains a discussion of the character and age of the Kennicott formation.

Additional investigations of the area between Kuskulana Kiver 

and Kennicott Glacier, including 'the type locality of the Kennicott 

formation, were made by Moffit 17 in 1916. The description of the 

Kennicott formation, based on the investigations in 1916 and other 

years, includes a discussion of the fossils by Reeside, who states that 

collections from the original Kennicott formation contain ammonites 

which are generally regarded as characteristic of the Cretaceous 

directly associated with Aucella and that the Aucellas from the 

Kennicott formation which had previously been compared with the 

Upper Jurassic species Aucella pallasi Keyserling belong to a different species from that in the Jurassic rocks of other Alaskan regions. 

Eeeside suggests that the Aucellas of the Kennicott formation may 

belong to the Cretaceous subgenus Aucellina.

In 1922 Moffit studied the rocks on McCarthy Creek that Rohn 

included in the Kennicott formation, and obtained fossils which 

Reeside referred to Lower Cretaceous species of Aucella.^

/Stratigraphic description. The Kennicott formation, as restricted 

to the Aucella-bQ&Ymg beds of Bear and Fohlin creeks and Kuskulana Pass, consists of greenish sandy shale and sandstone with 

numerous calcareous concretions and coarse grit that is partly conglomeratic. No stratigraphic section has been measured, and the 

thickness of the formation can be stated only approximately. The

18 Moffit, F. H., op. cit., pp. 17, 18, 29-30. 

u ldem, pp. 36-45. 

16 Idem, p. 41.

"Mofflt, P. H., and Mertie, J. B., Jr., The Kotsina-Kuskulana district, Alaska: U. S. 

Geol. Survey Bull. 745, pp. 49-51, 1923. 

"Moffit, F. H., Geology of the Chltina quadrangle (in preparation).
334 MESOZOIC STRATIGRAPHY OF ALASKA

thickness is certainly several hundred feet and is probably 1,000 feet 

or more. Neither the basal nor the upper contact was observed, 

but on Fohlin Creek the Kennicott formation and the Triassic chert 

are exposed in close proximity and in such attitudes as to indicate 

that the contact at this locality is either an unconformity or a fault. 

The beds of the Kennicott formation have been involved in structural disturbances of the same general magnitude as those which 

have affected the Triassic rocks. They do not lie in slightly disturbed attitude across the eroded folds and faults of the older rocks, 

like the Upper Cretaceous (?) beds that were referred to the Kennicott formation by Schrader and Spencer and others. The statement by Schrader and Spencer 18 that at Trail Gulch and Fohlin 

Creek "it seems as if the formation was deposited in a submerged 

valley, the sides of which had considerable height above the level 

of the water," is a recognition of the marked difference in attitude 

between the Aucetta-bear'mg beds of the original Kennicott formation and the Upper Cretaceous (?) sandstone and conglomerate 

which Schrader and Spencer regarded as part of the Kennicott 

formation and which were seen only as flat or gently folded hilltop 

cappings. The writer believes that the Kennicott formation rests 

unconformably upon the Triassic rocks and is beneath the great unconformity that has previously been regarded as basal Kennicott.

The sandstone of the upper Chitina Valley that Moffit assigned to 

the Upper Jurassic was described 19 as including soft brownish or 

pinkish sandstone and gray sandstone, both of which contain concretions, the largest 2 feet or more in diameter, some of them abundantly fossiliferous. The sandstone, of which about 500 feet is exposed, is of rather uniform character, so far as known, but contains 

two prominent thick beds, one at the base and the other near the 

middle, that are clearly distinguishable from the rest of the mass.

Moffit 20 stated that the discrimination of the supposed Jurassic 

and Cretaceous sandstones was based on the evidence afforded by 

the fossils and was not made in the field, for the sandstones are 

lithologically so much alike that no suspicion regarding a difference 

in their age was aroused. Both contain the same round concretionary masses and both, within a short distance of each other, rest unconformably on the Upper Triassic rocks.

A section of the supposed Cretaceous sandstone on Young Creek 

was described as including sandstone, possibly 100 or 200 feet thick, 

with massive basal beds grading upward into thin-bedded sandstone 

and sandy shale, above which are banded chert and hard platy-shale.

18 Schrader, F. C., and Spencer, A. C., op. clt., p. 49.

» Moffit, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, p. 

27, 1918.

20 Idem, p. 30.
CRETACEOUS, CHITINA VALLEY 335

Possibly the sandstone and sandy shale replace each other along the 

bedding planes, but this is not probable. The thickness appears to 

be not less than 500 feet.

The Lower Cretaceous rocks on McCarthy Creek were described 

by Moffit 21 as follows:

The base of the Cretaceous shale appears to be a yellowish-weathering bed, 

about 100 feet thick, in some places argillaceous and in some places sandy, 

which is exposed best on the east side of the valley. A massive bed of conglomerate, possibly 500 feet thick, is exposed on the east side of McCarthy 

Creek within the Cretaceous shale area but does not appear west of the creek. 

Its relation to the shale is in doubt. The whole of the ridge west of McCarthy 

Creek is black shale, probably Cretaceous in larger part.

Age and correlation. The Kennicott formation lies unconformably on Upper Triassic rocks and is believed to be overlain unconformably by Upper Cretaceous beds. It contains abundant fossils, 

including both plants and marine invertebrates. The evidence on 

the age of the formation, as yielded by the different kinds of fossils 

and by the collections from different localities and as interpreted by 

the several paleontologists who have studied the fossils, is somewhat 

conflicting. This evidence, which is discussed in detail on pages 

343-349, indicates, in the writer's opinion, that the formation belongs high in the Lower Cretaceous.

The following table shows the occurrence of all the fossils now 

known from the Kennicott formation, including not only the fossils 

from the type area of the formation in Fourth of July Pass but also 

those from the Ai^eZZa-bearing beds of Kuskulana Pass, from the 

Aucella-besirmg sandstone and " Cretaceous sandstone " of the upper 

Chitina Galley, and from the Aucetta-bear'mg sandy shale near the 

headwaters of McCarthy Creek all of which, in the writer's opinion, 

are of the same age as the Kennicott formation.
Fossils-from Kennicott formation 0 

Araucaria? (single scale) ____ . _________

Pagiophyllum peregrinum Schimper _______

Wood. __ . .. __ . ___ .... _ ..........

Stems.. __ _______________ .

Grammatodon? .... __ ......... .........

Aucella "cf. A. pallasi Keyserling"?.. ___ .. ....

Pecten (Syncyclonema?) ___________ .. ....

Pecten (Camptoneetes) _______ _____ ....

Pecten (Camptonectes?). ___ . _____ . _ ....

Tancredia?.. _ __ ...... ___ ... ...

Natica.... ...-.- ................ ...........

Cinulia? .-. - -. -. 

Desmoceras (Puzosia?)..... _ ........ _ . __ ...

Holcodiscus (Spitidiscus?) . __ - ....... __ ..

Lytoceras (Tetragonites) timotheanurn Mayor. ..

1

00

&% g s

C4

a

tI"

h

b

b

ITS 

S

b

b

S3

§

b

en

,

b

b

b

>o

Sc»

b

b

b

b

t~ 8 

§

b

1

a

CO

a

1

of

i

a

3

<M

a

**

a

CO

i 
Lytoceras (Gaudryceras) . . _ ____ ............

Lytoceras ___ L....... ......... ... .... ..... ....

Oppelia (Neumayria)?. ...........................

Oppelia? ________ _ .

Perisphinctes?-. .....I....... _ ... .. ____ .....

Idoceras?. __ __ ____ .. __ _ ....... _ ......

Hoplites?.. .-.--..-... __ . _ ................ ....

Barnade (Lepadidae).. ...........................

Shark teeth.......................... ____ ......

h

h b

h

b

b

b

b

1 a, Identified by T. W. Stanton; b, identified by J. B. Reeside, jr.; c, identified by F. H. Knowlton; d, iden
Fossils from Kennicott formation a Con

Cladophlebis cf. C. moissenti Saporta________ 

Cladophlebis___ _____.___.______ 

Dictyophyllum--....-_______.......__.._

Hausmannia cf. H. forschhammeri or H. dichomata. 

Taeniopteris lindgreni Nathorst. ___________ 

Taeniopterisparvula? Heer....__.__.....__.

Sagenopteris phillipsi (Lindley and Hutton)........

Sagenopteris--__ ._________............

Sagenopteris?----- . -....____ ...

Cycadites____. __._______..-.-_..

Otozamites beani (Lindley and Hutton) Seward....

Otozamites bunburyanus Zigno.__.__-.----....

Podozamites or Zamites..._________-._.

Ginkgo schmidtiana Heer.._.____............

Elatides curvifolia (Dunker) Nathorst__ ..........

Pinus nordenskioldi Heer........_____.__

Pagiophyllum peregrinum Schimper.____........

Pagiophyllum.._ ____...____._......

Stems.

Serpula?..__________________ 

Rhynchonella__ _____.__.-... 

Rhynchonella?_------_.._.__....

Solemya?.________________. 

Nucula___________________ 

Nucula?. ___ __..-.____. 

Leda .._..;_ ___. 

Nemodon?_________________ 

Pinna __.__.................._..

Inoceramus cf. I. concentricus Parkinson. 

Inoceramus sulcatus Parkinson __....

Inoceramus.. . ___. 

Inoceramus?- . .... ___.

Aucella "cf. A. pallasi Keyserling"?__- 

Aucella cf. A. piochji Qabb___._.....

Aucella cf. A. crassicollis Keyserling_.. 

Aucella ...___ __________ 

Aucella? ..... . ............_..

Trigonia.._________________ 

Pecten._____ __________ 

Pecten (smooth). . ........

Pecten (Camptonectes).._.....__....

Pecten (Camptonectes?).. _____. __
Thracia afl. T. semiplanata Whiteaves....__.

Thracia....---_-_--_____-_......-._.-___-___-

Thracia?....-..------------.---.-----------.---

Astarte?________________...____ 

Tancredia?-.__...----.-...___............

Protocardia?..___..__...___.._.__ 

Venerid pelecypod. _____........__....

Corbula__.__..._-...-..__._..---.-- 

Dentalium_____________._...........

Dentalium?________________._

Turbo?_____________________.-.. 

Natica?._______________________ 

Amauropsis tenuistriata Whiteaves?..__.._ 

Anchura or Aporrhais..________.........

Tessarolax?.--.___-_---.-----._._...---

Actaeon?_______________________ 

Cinulia?......_..._....._.._..__.....

Cylichna?.._......_...._..._..__.....

Trichotropis? cf. T. konincki (Muller)..-......

Gastropods. ...-- ..__..__...------.

Phylloceras cf. P. ramosum Meek..............

Phylloceras...__ ....__..._______.

Desmoceras breweri (Oabb)_.__...........

Desmoceras haydeni (Qabb)._..--.---------.

Desmoceras (coarseribbed)....................

Desmoceras-_______.__________ 

Desmoceras?....... .......... ............

Desmoceras (Puzosia)..__.___..........

Holcodiscus cf. H. cumshewaensis Whiteaves.. 

Holcodiscus..._.___________-....

Baculitescf. B. teres Forbes____.-..-.---.. 

Lytoceras (Tetragonites) timotheanum Mayor. 

Lytoceras (Oaudryceras) sacya (Forbes)..-....

Lytpceras...-___----.--.-.-.----..------.--.

Perisphinctes?-..-.-______..___.._. 

Ammonites.-__._...___---_.-._-.-. 

Ammonite (aptychus?)___.-..__-_------

Belemnites_-...._..__--....-.--.__....

1 a, Identified by T. W. Stanton; b, identified by J. B. Eeeside, jr.; c, identified by F. H. Knowlton; d, iden
340 MESOZOIC STRATIGRAPHY OP ALASKA

8939. Ridge between Slatka and Trail Creeks, 1% miles S. 39° E. from 

mouth of Slatka Creek, altitude 4,800 feet. F. H. Mofflt, 1914.

8926. Southwest side of Trail Creek along trail, altitude 3,300 feet. Limestone. F. H. Moffit, 1914.

8927. Southwest side of Trail Creek along trail, altitude 3,500 feet. From 

soft shales. F. H. Moffit, 1914.

2195. Bed of stream near trail east of Kuskulana River, altitude 3,350 feet. 

A. C. Spencer, 1900.

9950, 7279 (F 32). Trail Creek, altitude 3,500 feet, on west side of creek. 

Soft gray sandy shale. F. H. Moffit, 1916.

9951 (F 33). Trail Creek, altitude 4,000 feet, small gulch on north side 

about 100 yards above forks of Trail Creek. Soft gray shale with concretions. F. H. Moffit, 1916.

9952 (F 34). On ridge about half a mile south of Kuskulana Pass. Float. 

F. H. Moffit, 1916.

9949 (F 31). Locality 41, on creek 1% miles southwest of Trail Creek, 

tributary to Kuskulana River, 2,000 feet from creek, on southwest side, on 

point of ridge, altitude 3,900 feet, just below massive conglomerate. Black 

shale and limestone. F. H. Moffit, 1916.

9954 (F 36a). Northern tributary of Chokosna River, about half a mile 

above mouth of creek that flows from Kuskulana Pass, altitude about 4,200 

feet. Conglomerate float near outcrop. F. H. Moffit, 1916.

9955 (F 37). Same creek as F 36a, altitude about 4,300 feet. Dark-gray 

sandy shale and sandstone. Belemnites of large size common. F. H. Moffit, 

1916.

9957 (F 39). Chokosna River, on ridge east of F 37. Gray sandstone containing belemnites. F. H. Moffit, 1916.

9963 (F 45). Mill Creek, north side, half a mile from glacier on west fork. 

Float. F. H. Moffit, 1916.

2201. Old trail between Lachina and Kennicott Rivers. " Black shale series." 

A. C. Spencer, 1900.

(3). Boulder in creek between Lachina River and Fohlin Creek at camp 9. 

Oscar Rohn, 1899.

6812, 8873. East bank of Fohlin Creek, 4,900 feet above mouth of Bear 

Creek. Green sandstone with calcareous concretions. G. C. Martin, 1914.

2191. Creek tributary to Lachina River, half a mile above crossing of old 

trail between Lachina and Kennicott Rivers. " Black shale series." A. C. 

Spencer, 1900.

(4). East side of Fohlin Creek. Oscar Rohn, 1899.

8876. East bank of Fohlin Creek 5,500 feet above Bear Creek. G. C. 

Martin, 1914.

8875. East bank of Fohlin Creek 6,800 feet above Bear Creek. G. C. 

Martin, 1914.

9976 (F59). Fohlin Creek at point 125 feet higher than mouth of Bear 

Creek. Gray and yellow sandstone and shale with nodular masses. F. H. 

Moffit, 1916.

9977 (F 60). Fohlin Creek 300 feet north of F59. Yellowish sandstone 

overlain by gray shale near base of the Cretaceous rocks. F. H. Moffit, 1916.

9978 (F61). Fohlin Creek 700 feet upstream from F60. Yellowish-weathering sandstone. F. H. Moffit, 1916.

8872, 6811. Bear Creek about 2^ miles above its mouth. Float, the same 

piece of rock containing the plants of lot 6811. G. C. Martin, 1914.
CRETACEOUS, CHITINA VALLEY 341

(5). Three miles east of Fohlin Creek, between camps 11 and 12. Oscar 

Rohn, 1899.

8877. Bear Creek about 3 miles above its mouth. G. C. Martin, 1914.

8878. Bear Creek about 3 miles above its mouth, 100 yards above 8877. 

G. C. Martin, 1914.

8879,6814. Bear Creek about 3 miles above its mouth, 100 yards above 

8878. G. C. Martin, 1914.

8880. Bear Creek about 400 yards below summit of Fourth of July Pass. 

Calcareous concretions in gray sandy shale. G. C. Martin, 1914.

9965 (F 48). Bear Creek, tributary to Fohlin Creek. First northern tributary of Bear Creek, half a mile from mouth of Bear Creek. F. H. Mofflt, 1916.

9966 (F 49). Same locality as 9965, but a short distance upstream. Contains a few plants. F. H. Moffit, 1916.

9967 (F50). Same locality as F47, but farther upstream, altitude about 

2,900 feet. Sandstone abundantly fossiliferous. F. H. Moffit, 1916. 

9967a. Loose block, probably from same locality as 9967. F. H. Moffit, 1916.

9969 (F 52). Falls of first northern tributary of Bear Creek, tributary to 

Fohlin Creek, altitude about 3,200 feet. In place. F. H. Moffit, 1916.

9971,9980 (F54). Boulder at same locality as 9969. F. H. Moffit, 1916.

9972, 7281 (F 55). Bear Creek, altitude 2,850 feet, about halfway from 

Fohlin Creek to Fourth of July Pass. Soft gray sandstone' with nodular 

masses containing fossils. Base of the Cretaceous. F. H. Moffit, 1916.

9973 (F 56). Same locality as 9972. Plant remains. F. H. Moffit, 1916.

9975 (F 58). Tributary that joins Bear Creek 575 feet below Fourth of July 

Pass (farther west than F 57), several hundred feet from Bear Creek. Base 

of sandstone. F. H. Moffit, 1916.

9984 (F 67). Bear Creek. F. H. Moffit, 1916.

11369 (22F 6). Fall Creek, first tributary to Lakina River east of Fohlin 

Creek, 1,000 feet above mouth of Fohlin Creek. F. H. Moffit, 1922.

11370 (22F 7). Fall Creek, 1,200 feet above mouth of Fohlin Creek. F. H. 

Moffit, 1922.

8871. Upper end of canyon of Fourth of July Creek. Talus nearly in place. 

G. C. Martin, 1914.

(6). Canyon between camp 13 and Kennicott Glacier. Oscar Rohn, 1899.

11389, 7574 (22F 10). Northern tributary of Fourth of July Creek, 2 miles 

from Kennicott Glacier. F. H. Moffit, 1922.

9981 (F 64). First creek north of Fourth of July Creek, tributary to Kennicott Glacier, 275 feet above mouth of creek on north side. Gray shale, near 

base of Cretaceous. F. H. Moffit, 1916.

9982 (F 65). Near 64, but above it. Float. F. H. Moffit, 1916.

9983 (F 66). First creek north of Fourth of July Creek, tributary to Kennicott Glacier, 525 feet above mouth of creek. Base of the Cretaceous, yellowweathering sandstone and gray shale. Nodules. F. H. Moffit, 1916.

11371 (22F 8). One-quarter mile up first creek north of Fourth of July 

Creek, tributary to Kennicott Glacier. F. H. Moffit, 1922.

2200. Along right edge of Kennicott Glacier, 7 miles above Pot Hole. Float. 

Schrader and Spencer, 1900.

11372 (22F 11). McCarthy Creek, half a mile below glacier. Float F. H. 

Moffit, 1922.

11373 (22F 12b). McCarthy Creek, east side of west glacier, about halfway 

up glacier. F. H. Moffit, 1922.

11374 (22F 13). McCarthy Creek, first tributary below glacier on east side, 

near mouth. F. H. Moffit, 1922.

49448 26 23
342 MESOZOIC STRATIGRAPHY OF ALASKA

11375 (22F 14). McCarthy Creek, ledge on east- side just north of second 

tributary below glacier. F. H. Mofflt, 1922.

11376 (22F 15). McCarthy Creek, north side of second tributary on east 

side below the glacier, near mouth of stream. F. H. Moffit, 1922.

11377 (22F 16). McCarthy Creek, ridge south of second tributary on east 

side below the glacier, 2,200 feet above creek. F. H. Mofflt, 1922.

11378 (22F 17). McCarthy Creek. Float. Boulder 2 miles below glacier. 

F. H. Moffit, 1922.

11380 (22F 19). McCarthy Creek. First tributary below glacier on east side. 

200 yards up tributary. F. H. Moffit, 1922.

(9). Top of high mountain east of camp 20 on McCarthy Creek. Oscar Rohn, 

1899.

(12). Near same place as No. 9. Oscar Rohn, 1899.

9483, 7035 (F 18). Top of ridge between Short River [Barnard] and Chitina 

glaciers, altitude 6,475 feet. Platy sandstone. F. H. Moffit and R. M. Overbeck, 1915.

9484 (F 19). Four miles northwest of lower end of Chitina Glacier, altitude 2,500 feet. Gray sandstone float from top of mountain on the north. 

F. H. Moffit and R. M. Overbeck, 1915.

9489 (F 31). South side of ridge between Young Creek and Chitina River, 

near trail, altitude 1,900 feet. Concretions in sandstone. F. H. Moffit and 

R. M. Overbeck, 1915.

7037 (F 31). Chitina Valley, at fork of stream near Chitina River-Young 

Creek trail; same locality as 9489. Sandstone nodules. F. H. Moffit and 

R. M. Overbeck, 1915.

9481, 7034 (F 15). North side of Chitina River, 1.4 miles N. 15° W. from 

Gibraltar. Round calcareous concretions in gray slaty sandstone. F. H. 

Moffit and R. M. Overbeck, 1915.

9485 (F 27). Creek 2 miles east of Canyon Creek, tributary to Chitina River, 

altitude 2,125 feet. Nodules in pinkish sandstone. F. H. Moffit and R. M. 

Overbeck, 1915.

9486 (F 28). Creek 2 miles east of Canyon Creek, tributary to Chitina River, 

altitude 2,150 feet. F. H. Moffit and R. M. Overbeck, 1915.

7036 (F 28). Chitina Valley, most easterly of three creeks entering lake together 2 miles east of Canyon Creek, altitude 2,150 feet; same locality as 9486. 

F. H. Moffit and R. M. Overbeck, 1915.

9487 (F 29). Mouth of Canyon Creek, altitude 1,460 feet. Nodules in gray 

sandy shale. F. H. Moffit and R. M. Overbeck, 1915.

9488 (F 30). Mouth of Canyon Creek, altitude 1,470 feet. Conglomerate at 

base of sandy beds. F. H. Moffit and R. M. Overbeck, 1915.

9492, 7038 (F 34). Bluffs of Young Creek, west of big bed. Concretions in 

sandstone. F. H. Moffit and R. M. Overbeck, 1915.

9470 (F 4). South side of Young Creek on ridge west of'Young Creek-Chitina River trail, altitude about 5,100 feet. F. H. Moffit and R. M. Overbeck, 

1915.

9477 (F 11). Young-Canyon Creek divide, altitude 5,600 feet. Black and 

gray shale. F. H. Moffit and R. M. Overbeck, 1915.

9479, 9480 (F 13). Head of east branch of Young Creek. Float. F. H. Moffit and R. M. Overbeck, 1915.

9490 (F 32). Southeast of bend of Young Creek, altitude 4,400 feet. Float 

in stream. F. H. Moffit and R. M. Overbeck, 1915.

9491 (F 33). Southeast of bend of Young Creek, in gulch, altitude 4,000 feet. 

F. H. Moffit and R. M. Overbeck, 1915.
CRETACEOUS, CHITINA VALLEY 343

The earlier collections of fossils from the original Kennicott formation of Fourth of July Pass and from the Aucella-bQa,r'mg beds 

of Kuskulana Pass and McCarthy Creek, obtained by Kohn in 1899, 

by Spencer in 1900, and by the writer in 1914, were referred without 

question to the Upper Jurassic, both by Stanton for the marine 

invertebrates and by Knowlton for the plants. The marine fossils - were considered Upper Jurassic because they include a species of 

Aucella related to Aucella pallasi. A reexamination of some of 

these fossils by Stanton revealed the presence of a. Cretaceous ammonoid among them. The plants were considered Upper Jurassic 

because they include four species (Elatides curvifolia, Pagiophyllum 

peregrinum, Zamites megaphyllus, and Taxites zamioides] that occur 

in the supposed Jurassic rocks of Cape Lisburne, of Oregon, and of 

California, as well as in the Jurassic rocks of other parts of the 

world.

The flora of the Kennicott formation of the type locality comprises seven or more species of land plants. It should be noted 

that these fossil plants were not obtained from plant-bearing beds 

forming a distinct member of terrestrial origin but from beds of 

marine origin, all the plants occurring on the same rocks, as the 

marine shells and in immediate contact with them. Knowlton 

made the following statement concerning the plants collected by 

the writer in 1914:

The number of forms present is not large, though it is perhaps larger than 

might ordinarily be expected in a marine deposit. The age indicated by these 

plants is undoubtedly Upper Jurassic.

The fauna at the type locality comprises marine mollusks, most of 

which belong to undetermined species and many of which are probably undescribed. It was formerly supposed to be closely related to 

the fauna of the Naknek formation of the Alaska Peninsula, the most 

characteristic species being a form of Aucella that Stanton compared with Aucella pallasi Keyserling. It should be noted that the 

Kennicott fauna apparently does not contain the ammonite Ccvrdioceras, which is characteristic of strata that have been included in 

the Naknek formation of Cook Inlet (pp. 1757-176) and which has 

been found also in the Upper Jurassic rocks of the Matanuska Valley (pp. 231-232). Cardioceras is supposed to be characteristic of 

a lower horizon in the Upper Jurassic than that of Aucella pallasi. 

The absence of Cardioceras in the rocks of the Chitina Valley is a 

further indication that they are Lower Cretaceous instead of Upper 

Jurassic.

The fossils collected by Moffit in the upper Chitina Valley in 1915 

include collections that contain a species of Aucella related to Aucella 

pallasi which Stanton regarded as Upper Jurassic and also contain
344 MESOZOIC STRATIGRAPHY OF ALASKA

fossil plants which Knowlton regarded as Upper Jurassic. Moffit 

also obtained, from beds that he regarded as the same as those which 

yielded the Aucellas, other collections that contain ammonites, other 

marine fossils, and fossil plants. The ammonites and other marine 

fossils were identified as belonging to species that have been found 

° only in the upper part of the Lower Cretaceous and the lower part 

of the Upper Cretaceous and as including several genera that are not 

known to occur below the Cretaceous. The fossil plants, most of 

which came from the same localities as the marine fossils, were regarded by Knowlton as Upper Jurassic, although some of the species 

range up into the Wealden. The fossil plants were regarded by 

Knowlton as indicating the identity of the flora with that of the 

Kennicott formation of Fourth of July Pass. The sandstones of the 

upper Chitina Valley that Moffit described as Upper Jurassic and 

Cretaceous have yielded fossil plants which Knowlton 22 discussed as 

follows:

This material consists of five lots, all the specimens being small and many 

of them mere scraps. Although this material is very fragmentary, most of it 

permits the easy recognition of generic types, but some of the species have been 

identified with difficulty and doubt. However, the material has been studied 

with great care and much literature has been consulted. The following specimens have been identified with reasonable certainty:

Elatides curvifolia.

Pagiophyllum peregrinum.

Pagiophyllum sp.? 

 Pinus nordenskib'ldi.

Ginkgo schmidtiana.

Podozamites or Zamites sp.

Otozamites beani.

Otozamites bunburyanus.

Taeniopteris lindgreni.

Taeniopteris parvula? Heer.

Sagenopteris phillipsi.

Sagenopteris sp.?

Hausmannia cf. H. forschhammeri or dichotoma.

Dictyophyllum sp.

Cladophlebis cf. C. moissenti.

Cladophlebis sp.

The species first named (Elatides curvifolia), although first described 

(under the name of Lycopodites curvifoUus) from the Wealden of Germany, 

has since been found abundantly in the Upper Jurassic of Spitzbergen. It is 

also found in the Upper Jurassic of Cape Lisburne. Pagiophyllum peregrinum is abundant in the English Jurassic and, so far as I recall, has not 

been found above this horizon. Pinus nordenslcioldi was described from the 

Upper Jurassic of Siberia by Heer and later was reported with some question 

from the Kootenai by Dawson. The Ginkgo is known only from the Upper 

Jurassic of the Amour. The Podozamites is of the type of P. lanceolata 

and may be one of the forms of that variable species, but as it has fewer

^Knowlton, F. H., cited by Moffit, F. H., The upper Chitina Valley, Alaska: U. S. 

Gaol. Survey Bull. 675, pp. 42-44. 19J*.
CRETACEOUSj CHITINA VALLEY 345

nerves than is usual it is not identified specifically and may be new. It also 

resembles small leaflets of Zamites such as Z. megaphyllus. Taeniopteris 

lindffreni is known only from the Upper Jurassic of Advent Bay, Spitzbergen. 

The other species of Taeniopteris is represented by a single fragment and is 

questionable. It is indistinguishable^ so far as this fragment goes, from T. 

parvula, a well-known Upper Jurassic form. Sagenopteris phillipsi is a variable small species described from the Upper Jurassic of Yorkshire, England. The unnamed Sagenopteris may be one of the forms of the first-mentioned species, but as it is fragmentary it has not been positively identified. 

The Otosamites are mostly in the form of detached leaflets, in which, however,, 

the nervation has been beautifully preserved. They may represent only one* 

species, but as they differ very considerably in size they are referred to the 

two species distinguished by Seward, both of which are found in the Upper 

Jurassic of Yorkshire as well as in beds of similar age in France. The 

Hausmannia is represented by a single broken specimen which might with

nearly equal propriety be identified with one of the forms of H. forsclinammeri from the Lias or Rhaetic of Sweden or with H. diclwtoma from the 

Wealden of Auddinburg, Germany, and elsewhere. The genus ranges through 

the Jurassic and Wealden but is not well authenticated in later Cretaceous 

beds. The Dictyophyllutn is a mere fragment that can not be positively determined. It might well enough be D. rugosum, which is found in the Yorkshire 

beds. This genus is mainly confined to the Rhaetic and Lias but is represented 

in the Jurassic and Wealden, and a single species is known from the Kome of 

Greenland. The forms of Cladophlebis are more or less uncertain. They are 

represented by mere fragments of only a* few pinnules with mostly obscure 

nervation and are very difficult to identify. One form may be compared with 

C. moissenti, from the French Jurassic, or with C'. Jieterophylla as known from 

the Kootenai. They could also be compared with species from the Upper 

Jurassic and Wealdeu, but in truth the material is too scanty to permit a positive decision.

With the data available we now come to the point of deciding the probable 

age of these plants. It is obvious that most of the positively identified forms 

are found in the Upper Jurassic, and at least half of them have not been found 

in beds younger than this. Only two of the named species are known to range 

into beds as young as the Wealden or its approximate equivalent. As pointed 

out, however, the more or less fragmentary material by which several of the 

unnamed forms are represented might be assigned to either Upper Jurassic or 

Wealden species; but clearly, if they can not be positively identified as one or 

the other, they can not be allowed to weigh in the balance against those that 

can be and have been identified with reasonable certainty. I therefore express 

my conviction that these plant beds are Upper Jurassic in age, thus confirming 

the determination reached in the field.

According to a statement made by Moffit and accompanying the specimens: 

" These beds were referred to the Upper Jurassic on the basis of an assumption 

that only one known fossil flora occurs in the Chitina Valley and that these 

plants are the same as those that Martin and Overbeck obtained in 1914 from 

the Upper Jurassic Aucella-bearlng beds on Fohlin Creek."

I believe this reasoning is correct, at least so far as it applies to the identity 

between the material here reported on and that from Fohlin Creek. There were 

only four positively named species in Martin's collections of 1914, and two of 

these are abundant and unmistakable in the present collections. I have reexamined the Fohlin Creek material in the light of the present collection and 

find that what I there called Sagenopteris alaskensis? is without much doubt 

the same as Sagenopteris sp. ? in the Moffit material, and one specimen strongly
346 MESOZOIC STRATIGRAPHY OF ALASKA

suggests 8. phillipsi. I am now quite convinced that they are not the same as 

Fontaine's 8. alaskensis. I also find in the Fohlin Creek lots what I failed to 

note before, namely, a single leaf that appears to be the same as what I am 

calling Pinus nordenskioldi in this report; and I find, furthermore, that the 

Zam'ites megaphyllus of the Martin report (1914) is pretty close to, if not the 

same as, the Podozamites or Zamites sp. of the present report. This appears to 

me to afford strong presumption for the identity of the beds of Fohlin Creek 

and the present (1915) collections. The localities are separated by only 35 

miles, I believe, and this is a short distance in Alaska.

I of course have no opinion as to the stratigraphic relations of the beds 

whence came the Sagenopteris alaskensis of Fontaine, my only contention being 

that the species is not the same as those that represent this genus in the collections from the Chitina Valley.

This flora has been carefully compared with the small flora, consisting of 

about fourteen forms, reported by Dawson and Penhallow from the Queen 

Charlotte Islands, and so far as can be made out the two have not a single 

form in common.

The marine fossils from the sandstones of the upper Chitina Valley that Moffit described as Cretaceous were discussed by Stanton 23 

as follows:

These collections have proved of more than usual interest from the fact that 

they present positive evidence of a Cretaceous fauna, not previously recognized 

in Alaska, by means of which the .beds containing it may be correlated with 

those at certain horizons in the Cretaceous of Queen Charlotte Islands, California, and India. * * * Lots 9481 (F 15), 9485' (F 27), 9486 (F 28), 9487 

(F 29), and 9492 (F 34) contain enough distinctive ammonites and other diagnostic forms to leave no doubt that they are of Cretaceous age, and enough species are common to two or more of these lots to show that they all belong to a 

single fauna. The forms most important for correlation in these lists are the 

following:

Inoceramus sp. cf. I. concentricus Parkinson.

Inoceramus sulcatus Parkinson.

Amauropsis tenuistriata Whiteaves.

Baculites sp. cf. B. teres Forbes.

Lytoceras (Tetragonites) timotheanum (Mayor).

Lytoceras (Gaudryceras) sacya (Forbes).

Holcodiscus sp. cf. H. cumshewaensis Whiteaves.

Phylloceras cf. P. ramosum Meek.

Desmoceras haydeni (Gabb).

Desmoceras breweri (Gabb).

All these species except possibly the Baculites and the Phylloceras occur in 

the Haida formation, recently described by Mackenzie 24 as the lowest formation of the Queen Charlotte series, which series name is applied to all of the 

Cretaceous rocks of the Queen Charlotte Islands. Several of the species were 

in the collections which I identified for Mr. Mackenzie last year, and the others 

are listed and described in earlier reports by Whiteaves. The two species of 

Lytoceras and the two species of Desmoceras are also .found in California, 

where they occur in the upper part of the Horsetown formation or the lowest 

part of the Chico. Phylloceras ramosum Meek also comes from the same part 

of the section in California. From these comparisons with the Cretaceous of 

Queen Charlotte Islands and of California I would assign the collections repre23 Stanton, T. W., cited by Moffit, F. H., op. cit., pp. 37, 41-42.

24 Canada Geol. Survey Summary Rept. for 1913, pp. 43-47, 1914.
CRETACEOUS, CHITINA VALLEY 347

sented by the list above given to the basal part of the Upper Cretaceous or to 

near the top of the Lower Cretaceous.

If the comparisons are carried to more distant regions the same general 

results are obtained. Thus the two species of Inoceramus listed are English 

species and are reported from the Gault and upper Greensand of England. 

They are also of types not known anywhere in older rocks than the Gault. 

BacuUtes teres, Lytoceras timotheanum and L. sacya occur in the Ootatoor 

group of India, which is assigned to the lower part of the Upper Cretaceous and 

contains many other species identical with or closely related to those of the 

Haida and upper Horsetown. Fui chermore, these two Lytoceras species belong 

to the groups Tetragonites and Gaudryceras, respectively, by some treated as 

distinct genera, which are characteristically Cretaceous. BacuUtes, also, is 

unknown in pre-Cretaceous rocks. There is a possibility that the little form 

referred to BacuUtes in these collections may belong to Ptychoceras, another 

characteristic Cretaceous genus in which the long straight shell is bent back on 

itself. An example of Ptychoceras has lately been discovered (or rather uncovered) in one of Martin's collections of 1914 from Bear Creek (No. 8872). 

I am therefore changing the assignment of that lot from Upper Jurassic to 

Cretaceous. Some additional genera, such as Anisoceras, Pachydiscus, and 

Thyasira, found in the smaller lots of this collection, are not known from preCretaceous rocks elsewhere.

As I see it, therefore, the invertebrate evidence is all strongly in favor of the 

Cretaceous age of the entire collection. The fauna of the best localities indicates a horizon slightly lower than that of the Cretaceous of the Matanuska 

Valley, but still far above the basal Cretaceous. There is no suggestion of an 

admixture of Jurassic types such as might be expected in the lowest Cretaceous, 

and my judgment is that the fauna is considerably younger than even the latest 

Knoxville. The fossil plants which, as Knowlton reports, belong to a Jurassic 

flora, are intimately associated in the same beds with the ammonites and other 

invertebrates which are referred to a Cretaceous1 fauna, the two localities (F 15 

and F 34) which yielded the best collections of plants having also yielded the 

best collections of invertebrates. I think that the vertical range of the ammonites is better established than that of the plants.

The fossils collected by Moffit from the Kennicott formation of 

Fourth of July Pass in 1916 contain ammonites that Reeside regards 

as belonging to typical Cretaceous genera, together with the species 

of Aucella which Stanton had previously compared with Aucella pallasi but which Reeside regards as distinct from any of the Aucellas 

from other Alaskan Jurassic rocks and as probably belonging to the 

Cretaceous subgenus Aucellina. Among these fossils are several that 

indicate relationship with the fauna of the Lower Cretaceous sandstone of the upper Chitina Valley, though Reeside believes that the 

fauna of Fourth of July Pass may be somewhat older. The following statement was submitted by Reeside 25 concerning the fossils collected in 1916 by Moffit from the type area of the Kennicott to* 

mation:

Lot 9972 is of considerable interest in that it contains a species of Aucella 

usually compared with A. pallasi Keyserling associated with Ptychoceras sp.,

25 Personal communication..
348 MESOZOIC STRATIGRAPHY OF ALASKA

Lytoceras (Gaudryceras) sp., Holcodiscus (Spitidiscusf) sp., and what may be 

a species of Desmoceras (Puzosia). As Aucella pallasi is confined to the Upper 

Jurassic in Russia, California, and Mexico, and as the ammonites are all typically Cretaceous in other areas, some doubt arises as to the relationship of the 

Alaskan Aucella to Aucella pallasi or as to the true ranges of all the fossils in 

question. Lot 9976 contains Aucella and Lytoceras (Tetragonites) sp., and lot 

9975 Aucella and Inoceramus sp. like I. concentricus Parkinson, of the Gault.

A comparison of the Aucellas in these collections of Mofflt's with one lot 

collected in 1915 (9489) and with several extensive collections from the Kennicott formation by Martin and Overbeck in 1914 shows them to be the same 

referable, I should say, to two species, an .elongated form and an orbicular 

form. A further comparison with the other Alaskan Aucellas available indicated that they are all quite different. Aucella sp. like Aucella pallasi from the 

Matanuska country differs from the present forms in sculpture, though it is 

very like the published figures of the Russian A. pallasi in both form and 

sculpture. I find none of the published figures and descriptions to fit the form 

of the Kennicott Aucellas except those of the subgenus Aucellina Pompeckj, 

which is Cretaceous. Pompeckj, in discussing several species of this group, 

says that they are surprisingly like Aucella pallasi. One might even refer the 

more orbicular Kennicott Aucellas to the species A. (Aucellina) gryphaeoides 

Sowerby, as it is described and figured by several writers, though on neither 

this nor the elongate species is there enough of the shell preserved to show the 

diagnostic hinge of the left valve. , . A reexamination of the ammonites with the Aucellas of Martin's collections 

shows complete agreement with those of Moffit by the presence of Lytoceras 

(Gaudryceras) and Holcodiscus (Spitidiscusf), and also, associated with the 

same species of Holcodiscus found with the Aucellas, a specimen of Ptychoceras 

(mentioned by Stariton in a previous report).

It seems to the writer much more likely that the Aucellas of the Kennicott 

are not really A. pallasi Keyserling, but are of other species (probably of the 

subgenus Aucellina) than that the ammonites associated with them range so 

much lower than is true in other areas.

The complete absence of a number of very diagnostic forms found in 1915 

by Moffit and referred by Stanton to the Cretaceous such as Inoceramus sulcatus, Desmoceras haydeni, D. ~breweri, Anisoceras cf: A. armatum, Thyasira 

sp. Pachydiscus sp., Baculites cf. B. teres, and Holcodiscus cf. H. cumshewaensis points to a different, probably older horizon within the Cretaceous for lots 

9966, 9967a, 9972, 9975, 9976, 9978. Whether the other lots containing Aucella 

like A. pallasi and lacking more diagnostic fossils belong with those just listed 

is a matter for the field geologist to determine, though the presumption is 

reasonable that all belong to the one Cretaceous fauna.

The sandy shale exposed along the upper part of McCarthy 

Creek yielded several lots of fossils, collected by Moffit in 1922, 

which Reeside has determined as Lower Cretaceous. The collections 

contain several species of Aucella including forms related to the 

characteristic Lower Cretaceous species Aucella piochii and Auvella 

crassicollis, as well as the common form occurring in the Kennicott 

formation which Stanton compared with Aucella pallasi but which 

Reeside suggests may be a species of Aucellina.
CBETACEOUS, CHITINA VALLEY 349

The writer believes that the Kennicott formation of Fourth of 

July Pass; the Aucella-loe&rmg beds of Kuskulana Pass, McCarthy 

Creek, and the upper Chitina Valley; and the "Lower Cretaceous 

sandstone" of the upper Chitina Valley are approximately of the 

same age and should all be assigned to the Lower Cretaceous. The 

reasons for this age assignment are that several of the invertebrate 

genera are known only in the Cretaceous, whereas none of the genera 

. of either invertebrates or plants are known only in the Jurassic ; 

that the Cretaceous species of invertebrates outnumber the Jurassic 

species of plants ; that almost half of the positively or approximately 

identified species of plants r"ange up into the Cretaceous, whereas 

only one invertebrate species may possibly range down into the 

Jurassic; that only one of the supposed Jurassic species of plants 

(Zomites megaphyllus] has been found in any of the undoubted 

Jurassic floras of southern Alaska, with which this flora, if Jurassic, 

should have its closest affinity ; and that the general aspect of the 

fauna is wholly unlike that of the Upper Jurassic faunas of other 

Alaskan regions. (See pp. 274^283.)

LOWER (?) CRETACEOUS 

KOTSINA CONGLOMERATE AND OVERLYING STRATA

Historical review. The Triassic rocks of the Kotsina and Kuskulana valleys are overlain unconformably by conglomerate, limestone, and sandstone. These rocks carry Mesozoic fossils, but their 

exact age is doubtful. They appear to correspond approximately 

in lithologic and faunal character, as well as in their stratigraphic 

relations, to the Cretaceous conglomerate and sandstone of Nikolai 

and Dan Creeks, described on pages 355-360. These rocks have previously been described, in the reports on the reconnaissance surveys 

of this district, under two headings as indicated below. This separation was, however, not based upon stratigraphic or lithologic differences but was merely a distinction between the known and the 

unknown.

These rocks were described by Kohn 20 in part as the Kotsina 

conglomerate and in part as " unclassified sediments." The Kotsina 

conglomerate was described as a massive bed of conglomerate that 

overlies folded and contorted shale and slate that in turn rest upon 

the Nikolai greenstone. According to Kohn "the rocks above the 

Kotsina conglomerate are thought to be the same as the Kuskulana 

shales," but they were mapped as "unclassified sediments" and are 

now known to include part of the rocks here described, as well as 

several other formations. Rohn made only occasional references 

to the part of the "unclassified sediments" which are now under 

consideration and did not describe them.

, Oscar, A reconnaissance of the Chitina River and the Skolai fountains, 

Alaska : U. S. Geol. Survey Twenty-first Ann. Kept., pt. 2, pp. 422, 431-432, 1900. 

49448 26 24
350 MESOZOIC STRATIGRAPHY OF ALASKA

These rocks were described by Schrader and Spencer in part 27 

as " undetermined rocks on Kotsina River" and in part 28 as the 

Kennicott formation. The former includes all of Rohn's Kotsina 

conglomerate, together with additional areas that he mapped as 

" undifferentiated sediments." The latter includes several areas of 

conglomerate, limestone, and sandstone that cap the hilltops and 

obviously rest unconformably upon the upturned edges of the Triassic beds. This separation apparently has no stratigraphic basis but 

is essentially a distinction between the known and the 'unknown, or 

between the areas in which the stratigraphic relations to the unconformably underlying Triassic beds are'clear and the areas in which 

the conglomerate is exposed at lower levels, where the unconformable relation is not so obvious.

The " undetermined rocks on Kotsina River " were described by 

Schrader and Spencer 29 as

a series of rocks whose relations and age have not been determined. They are 

made up of sediments, including limestones, shales, and coarse conglomerates, 

with intercalated sheets or flows of basalt like the Nikolai greenstone. The 

pebbles of the conglomerate are composed of greenstone material.

According to Schrader's unpublished field notes, "there seems to 

be a marked unconformity between the conglomerate and the [Chitistone] limestone. The limestone is much older than the conglomerate," and has apparently furnished the limestone pebbles in 

the conglomerate."

The so-called Kennicott formation of this district was described 

by Schrader and Spencer 80 as occurring in isolated outliers capping 

many of the high peaks and ridges between Kuskulana River and 

Clear Creek and resting unconformably upon all the formations from

the Nikolai greenstone to the Triassic shale and limestone inclusive. 

Its lithologic characteristics in these areas were not described specifically.

These rocks were mapped by Mendenhall 31 in part as an "unnamed 

conglomerate and in part as the Kennicott formation. The latter 

was described 32 as a "series of massive conglomerate with interbedded shales, the total aggregate thickness here being about 1,600 

feet." The unnamed conglomerate, which is the same as the "undetermined rocks on Kotsina River " of Schrader and Spencer, was 

not described.

57 Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), p. 40, 

pi. 4, 1901.

28 Idem, p. 49.

29 Idem, p. 40, pi. 4.

80 Idem, p. 49.

81 Mendenhall, W. C., Geology of the central Copper River region, Alaska : U. S. Geol. 

Survey Prof. Paper 41, pi. 4, 1905. 

""Idem, p. 52.
CRETACEOUS, CHITINA VALLEY 351

The account of these rocks by Moffit and Maddren 33 consists of 

quotations in full of the descriptions by Schrader and Spencer, together with a very brief additional statement 34 regarding the " undetermined rocks on Kotsina River." They also made many important corrections on the geologic map.

These rocks have been mapped and described in detail by Moffit 

and Mertie 35 who described them as " Upper Jurassic rocks " and 

mapped them as three formations the Kotsina conglomerate, a supposedly younger unnamed formation consisting of " sandstone, con^ 

glomerate, and shale," and a still younger unnamed " light-colored 

limestone." The description comprises a detailed account of the 

character, distribution, structure, and thickness of the beds exposed 

at various places and a discussion of their age and correlation, with 

a table showing the occurrence of the fossils as identified by Stanton.

Stratigraphic description. The Kotsina conglomerate was described by Moffit and Mertie 30 as follows:

Unconformably overlying the Kuskulana and other formations is the Eotsina 

conglomerate probably of Upper Jurassic age. It consists of waterworn 

pebbles and cobbles inclosed in a shaly or arkosic matrix. The component 

pebbles are plainly derived from the formations already mentioned and from 

the intrusive rocks in them. The conglomerate weathers readily, yielding a 

characteristic rugged topography. Measurements of its thickness are of doubtful accuracy, but in the mountains north of Elliott Creek the conglomerate 

probably is from 1,500 to 2,000 feet thick.

The belt of rock just mentioned is made up of massive black conglomerate, 

almost without lines of bedding, yet containing a little black shale. It is composed largely of waterworn pebbles and cobbles, most of which are plainly of 

local origin and are derived from the underlying formations. Pebbles of 

greenstone, limestone, the light-colored granodioritic intrusives, and quartz are 

most common. It was noticed repeatedly that in the vicinity of areas of the 

Chitistone limestone the limestone pebbles in the conglomerate increase greatly 

in number and form a large proportion of the rock. The same is doubtless 

true of other constituents of the conglomerate, but these are not so readily 

seen.

The pebbles are inclosed in a shaly or arkosic matrix which disintegrates 

rather easily and breaks down rapidly under the influence of weathering. In 

consequence the outcrops are rough, and the talus slopes consist largely of 

pebbles freed from their matrix. The conglomerate mountains are rugged, with 

precipitous cliffs and a ragged sky line. Their dark color and rough surface 

give them a forbidding aspect, and in fact many of the ridges are practically 

impassable.

The later Mesozoic rocks of the Kotsina-Kuskulana district, in 

addition to the Kotsina conglomerate, include several detached areas

33 Mofflt, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Chitina region, 

Alaska: U. S. Geol. Survey Bull. 374, pp. 23, 30, 31, pi. 2, 1909.

34 Idem, p. 21.

38 Mofflt, F. H., and Mertie, J. B., Jr., The Kotsina-Kuskulana district, Alaska: U. S. 

Geol. Surrey Bull, 745, pp. 20, 44-51, pi. 3, 1923. 

88 Idem, pp. 20-45.
352 MESOZOIC STRATIGRAPHY OP ALASKA

of conglomerate, sandstone, and limestone that may be partly or 

wholly the lateral equivalent of beds in the Kotsina conglomerate or 

may be younger. These are the rocks which Moffit and Mertie 

mapped 37 as unnamed Upper Jurassic formations and which they 

described 38 as follows:

The Jurassic rocks of this district in addition to the Kotsina conglomerate 

comprise limestone, sandstone, sandy limestone and shale, and fine conglomerate 

or grit. These beds are not widely distributed in the district and have heretofore been considered part of the Kennicott formation (Upper Jurassic). At 

one place the higher beds appear to rest unconformably on fine sandstone or 

grit' that is referred to the Jurassic. The beds are highly fossiliferous. They 

have a thickness of possibly 500 feet east of Kuskulana River and of 880 feet 

west of the river, but in general the thickness is much less, not exceeding 100 

or 200 feet.

The exposures of later Mesozoic rocks on the mountain between 

Clear Creek (tributary to Kotsina River) and Kluvesna River include several hundred feet of fine conglomerate, grit, and sandstone, 

which lie unconformably on the Upper Triassic rocks. These beds, 

which may be the lateral equivalent of part of the Kotsina conglomerate, grade first to a grit made up of tiny flattened pebbles of 

fairly uniform size and then to a soft yellowish-brown fossiliferous 

sandstone. About 50 feet of massive light-gray limestone with a 

slightly sugary texture and surface peppered over with tiny black 

specks rests on the brown sandstone and is overlain in turn by a small 

thickness of gray limy sandstone. Both the limestone and the sandstone are fossiliferous.

The fossils of lots 8935 and 8924 were obtained near the base of 

the sandstone and grit, and lot 8934 (float) probably came from the 

same horizon. Lot 8936 was obtained near the top of this member, 

not far below the base of the overlying limestone. Lot 8937 was 

obtained near the base of the sandstone that overlies the limestone. 

It seems probable that lots 2210 and 2198 were also obtained from 

the upper sandstone member. Lot 8940 is float material of uncertain 

origin that probably came from some member of this section. The 

same is probably true also of lot 2196, which includes only a single 

specimen of Inoceramus that was formerly regarded by Stanton 39 

as possibly identical with Inoceramus eximius Eichwald, a Middle 

Jurassic species from the Tuxedni sandstone of Cook Inlet. . Stanton's later opinion 40 concerning this fossil is that 

It is probably not a Middle Jurassic species, because it is not identical with 

any of the species of that age in the recent large collections from Cook Inlet, 

and there is no other evidence of the presence here of the fauna that accompanies them.

37 Op. cit, pi. 3.

88 Idem, p. 20.

» Stanton, T. W., cited by Schrader, F. C'., and Spencer, A. C., op. eit., p. 50.

40 Personal communication.
CRETACEOUS, CHITINA VALLEY 35$

The most satisfactory disposal of these rocks which can be made 

at present is to regard them as a somewhat unusual facies of the 

Kotsina conglomerate.

Sandstone and conglomerate occur in three small areas in the 

mountains west of Clear Creek in Kuskulana Valley. Approximately 800 feet of interbedded sandstone and conglomerate are 

exposed in the largest of these areas, near the head of Sheep Creek. 

The sandstone and conglomerate rest unconformably on Triassic 

shale and are faulted against the shale on the west. At the base is 

200 feet of conglomerate, and above is sandstone with intercalated 

conglomerate beds. The fossils of lots 8155, 9933, and 2211 were 

obtained from these beds.

° The exposures east of Kuskulana River occur in several small detached areas, some of which consist of grit or conglomerate and 

some of limestone. The exposures on Trail Creek occur within half 

a mile of the outcrops of the Aucella-be&ring shale described on 

page 340, which is considered as belonging to the Kennicott formation. Their stratigraphic relation to' the Aucella-loe&r'mg rocks is 

not definitely known, but the writer believes that they may belong 

to the Kennicott formation.

Age and correlation. The Kotsina conglomerate has yielded no 

fossils, and there is no evidence on its age except that it rests unconformably on Upper Triassic rocks and is believed either to grade 

into or to be overlain by rocks that contain Jurassic or Cretaceous 

fossils.

The grit and overlying sandstone and limestone which are supposed to overlie or grade into the Kotsina conglomerate have yielded 

the fossils listed iif the following table. These fossils may belong 

anywhere in the Jurassic or Cretaceous. They apparently contain 

no species that are characteristic of any definite horizons, but in its 

general character the assemblage is not unlike the fauna of the 

sandstone of Nikolai and Dan Creeks, which is believed to lie either 

at the base of the Lower Cretaceous rocks of the Kennicott formation or at the base of the Upper Cretaceous shale of Chititu and 

Young Creeks.

The writer believes that the Kotsina conglomerate may be tentatively referred to an indefinite position in the Cretaceous. It possibly represents a coarse phase of the Lower Cretaceo'us rocks, but it 

should not be included in the Kennicott formation. The overlying 

limestone is possibly the equivalent of the Lower Cretaceous Nelchina limestone of the Matanuska Valley (pp. 313-315) and of the 

Herendeen limestone of the Alaska Peninsula (pp. 292-295), 

although these correlations are improbable in view of the absence in 

the Kotsina of the characteristic Lower Cretaceo'us species Aucelfa
354 MESOZOIC STRATIGRAPHY OP ALASKA

crassicollis Keyserling. The sandstone that caps the limestone and 

appears to overlap also upon other rocks is possibly the equivalent 

of the presumably basal Upper Cretaceous grit of Nikolai and Dan 

Creeks, described on pages 355-360. These assignments are, however, 

purely tentative and have very slight basis. The entire series may 

belong anywhere in the Cretaceous or may possibly be Jurassic. 

Stanton believes that the whole list in the following table is rather 

more suggestive of Jurassic than of Cretaceous.

Fossils from limestone and sandstone overlying (the Eotsina conglomerate a

Pentacrinus?.. _______________

Terebratula?.... ..........................

Spiriferina?... ____________ . ....

Nucula? _______________ . .....

Pinna? (young). __ . ___ . __ . ........

Inoceramus (large form)... _______ ..

Inoceramus?.. ___________ ......

Pteria?.,.... ..............................

Lima? _ . __________________

Astarte?.. _________________

Lytoceras? ___________ . ..........

Perisphinctes?.. ..........................

Aspidoceras cf. A. cyclotus Steuer? ........

Belemnites (large species) ________

Belemnites ................................

Belemnites? ...............................

8935

a

8934

a

8924

a

8936

a

a

a

a

8937

a

a

a

a

2210 2198 8940 2196 8168

a

8155

a

9933

h

h

h

9942

b

h

b

b

2211

a

0 a, Identified by T. W. Stanton; b, identified by J. B. Reeside, jr.

6 This is the species listed by Schrader and Spencer as Inoceramus eximius, but it is not the same as 

Inoceramus eximius Eichwald.

8939. Mountain north of mouth of Kluvesna River, aboftt 1% miles N. 47° W.

from Ammann's cabin on Kluvesna River. Sandstone beneath a limestone bed. 

F. H. Moffit, 1914.

8934. Mountain north of mouth of Kluvesna River. Float from same 

locality as 8935. F. H. Moffit, 1914.

8924. Mountain north of mouth of Kluvesna River, about 2,000 feet S. 12° 

W. of 6,005-foot peak. Near base of grit. J. B. Mertie, 1914.

8936. Mountain north of mouth of Kluvesna River, about 9,950 feet N. 40%° 

W. from Ammann's cabin, on Kluvesna River, altitude 5,800 feet. Sandstone 

beneath a limestone bed. F. H. Moffit, 1914.

8937. Mountain north of mouth of Kluvesna River; same locality as 8936. 

Base of sandstone overlying the limestone bed. F. H. Moffit, 1914.

2210, 2198. On mountain 1% to 2 miles north-northeast of camp 13c on Clear 

Creek. Sandstone. F. C. Schrader, 1900.

8940. Boulders in Limestone Creek near confluence with Clear Creek. G. C. 

Martin, 1914.

2196. Impure fossiliferous limestone 2% miles above the mouth of Clear 

Creek. " Large bouldery slab." F. C. Schrader, 1900.

8168. Divide between Nugget and Roaring Creeks. Theodore Chapin, 1912.

8155. First creek south of Clear Creek. Buff sandstone. Theodore Chapin, 

1912.
CRETACEOUS, CHITINA VALLEY 355

9933 (F 15). Locality 13, on ridge between east branch of east fork of 

Strelna Creek and Clear Creek, at head of small creek between Squaw and 

Clear Creeks, altitude 5,500 feet. F. H. Mofflt, 1916.

9942 (F 24). Locality 20a, saddle on ridge between Rock and Lime Creeks, 

7,500 feet southeast of forks of Rock Creek, altitude 5,800 feet. Thin-bedded 

limestone 100 feet below saddle, on Rock Creek side. F. H. Moffet, 1916.

2211. North fork of Kuskulana River. F. C. Schrader and A. C. Spencer,

1900.

UPPER (1) CRETACEOUS

SANDSTONE AND CONGLOMERATE OF NIKOLAI CBEEK

Historical review. The Upper (?) Cretaceous sandstone and conglomerate that unconformably overlie the Triassic rocks at the head 

of Nikolai Creek were described and mapped by Schrader and 

Spencer 41 as part of the Kennicott formation, although they were 

not part of the Kennicott formation as originally described and 

probably do not belong in that formation. The part of this description which applies to the rocks in question consists of a very brief 

statement concerning their occurrence, character, and relations to 

the underlying Triassic beds.

These beds, as they are not known to contain valuable mineral 

deposits, were not studied in detail during the reexamination of the 

mineral deposits of the Chitina Valley by Moffit and Maddren, who 

accordingly described them merely by quoting the description by 

Schrader and Spencer in full without modification.42

A fossil leaf that was collected by A. C. Spencer in float material 

in the bed of Nikolai Creek and was probably derived from these 

beds was described and figured as Sagenopteris alaskensis n. sp. by 

Fontaine,48 who considered that " its resemblance to S. goppertiana 

points to a Jurassic age, but a single fossil like this can not be 

decisive."

These beds were described in great detail by MofSt and Capps,44 

who regarded them as comprising the lower members of the Kennicott formation. Their account includes stratigraphic sections, detailed descriptions of the various beds, and lists of fossils as identified by T. W. Stanton.

Stratigraphic description. The Upper (?) Cretaceous conglomerate and sandstone of Nikolai Creek are separated from the underlying Triassic rocks by a profound unconformity, which cuts across 

the beveled edges of the strongly folded subjacent strata. The beds 

above the unconformity are but gently tilted, and their basal con41 Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), p. 49, 

pi. 4, 1901.

42 Moffit, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Chitdna region, 

Alaska: U. S. Geol. Survey Bull. 374, p. 31, pi. 2, 1909.

4" Fontaine, W. M., Plants from, the Copper River region, Alaska: U. S. Geol. Survey 

Mon. 4'8, pp. 152-153, pi. 38, fig. 21, 1905. .

"Mofflt, F. H., and Capps, S. E>., Geology and mineral resources of the Nizina district, Alaska : U. S. Geol. Survey Bull. 448, pp. 31-34, 36, 37, 39-40, pi. 3, 1911.
356 MESOZOIC STRATIGRAPHY OF ALASKA

Black shale with hard 

calcareous beds; fossils.

Gray, .yellow-weathering shales; fossils.

Ye'low-weathering 

sandy shales.

glomerate includes pebbles derived from all the underlying formations. These beds have the general sequence indicated in the accompanying section (fig. 8), and were described by Moffit and Capps 45 

as follows:

The Kennicott formation where it is exposed about the head of Nikolai Creek 

may be subdivided into three members as follows: A basal member made up of 

conglomerate and sandstone; a second member consisting chiefly of light-gray,

yellow-weathering shale; and an upper member 

of dark-gray or black shale interstratified with 

occasional beds of impure limestone or hard calcareous shale.

The basal member * * * has a thickness 

ranging from 25 to 125 feet, the greater part of 

which is graywacke, the remainder conglomerate 

or grit. In a few places the basal member appears to be entirely absent, although because of 

faulting and talus slopes its seeming absence may 

be explained in other ways. Furthermore, its 

persistence as a whole in many other places in 

spite of rapid changes in character and of variation in thickness makes it probable that if it is 

not seen in a particular locality the failure to 

find it is due to one of the causes mentioned.

The middle member of the formation on Nikolai 

Creek shows far less variation in character than 

the lower one, but it does not appear so conspicuously in other parts of the Nizina region. It 

consists of shale and shaly sandstone, but shale 

predominates. The sandy phases are more or less 

local, and the best exposures are on the ridge 

south of Nikolai mine. A freshly broken surface 

of the shale shows a fine-grained rock of light 

color, but both shale and sandstone .weather a 

bright yellow that makes them conspicuous 

wherever they are exposed. Both shale and 

sandstone break down into thin fragments under 

the influence of the weather, and the debris from 

their ledges gives rise to prominent talus slopes. 

Occasionally fossils are found in the sandstone, 

and rarely a shell is seen in the shale, but fossils are not abundant, and it 

requires some search to find any of value. The thickness of the yellowweathering shales is as great as 500 feet in the mountain between Nikolai 

Creek and the East Fork of McCarthy Creek. At the head of Nikolai Creek 

375 feet of yellow-weather.ing shale overlies the conglomerate, but some of the 

shale has been eroded away.

The highest member of the Kennicott in the Nikolai Creek vicinity consists 

of black shale, with interstratified hard, impure limestone and calcareous shale 

beds ranging in thickness from 1 inch to 2 feet. The hard beds form only a 

small proportion of the total thickness, probably less than one-tenth, but although jointed and broken they stand out in relief from the softer, crumbling 

black shales and form a conspicuous part of the whole. This black shale reYel low-weathering 

sandstones; fossils.

Conglomerate (locally 

with large blocks 

and boulders) grading upward into 6ne 

grit. Some beds with 

an abundance of 

broken shells.

Unconformity.

Limestone and greenstone.

FIGURE 8. Columnar section of 

the basal part of the Kennicott 

formation exposed on Nikolai 

Creek

« Moffit, F. H., and Capps, S. R., op. cit, pp. 31, 33.
CRETACEOUS, CHITINA VALLEY 357

sembles closely the black shales of the Triassic. The hard beds assume a rustyyellowish color on weathering, just as in the Triassic shales, and there seems 

to be no way, except by their stratigraphic position and their fossils, to distinguish them from the older shales. Fossils are fairly plentiful in some beds 

of this member, especially those in the hard beds, and are in a better state of 

preservation than those found lower in the formation. From 125 to 150 feet 

of these shales are exposed north of Nikolai Creek, but the figures take no 

account of what has been removed by erosion or what has been caught up into 

the intruded porphyry.

Age and correlation. These rocks bear a very close resemblance, 

both lithologically and in their relations to the underlying rocks, 

to the grit and sandstone of Dan Creek, described on pages 358-360. 

The fossils that have been obtained from these beds, which are 

listed in the table below, are not numerous or characteristic and 

consist of types that may be found in either the Cretaceous or the 

Jurassic, though they are however more strongly suggestive of the 

Cretaceous. They bear a general resemblance to the meager assemblage found in the grit and sandstone of Dan Creek. They 

include none of the species of the Kennicott formation, except 

possibly the plant, Sagenopteris alaskensis Fontaine, which was 

found in float material of uncertain derivation on Nikolai Creek 

and which has been only doubtfully identified (see p. 347) from the 

Kennicott formation. There is no reason to doubt that the conglomerate and sandstone of Nikolai Creek and the grit and sandstone of Dan Creek are equivalent. The latter probably (see p. 359) 

constitute the basal member of a conformable Upper Cretaceous 

sequence. The conglomerate and sandstone of Nikolai Creek consequently should also be regarded as probably Upper Cretaceous.

Fossils from Upper (?) Cretaceous sandstone of Nikolai Creek®

Sagenopteris alaskensis Fontaine. ... _________

Echinoderm or crinoid fragments....................

Worm trails. __ __ __ ..

Khynchonella.. ............

Terebratella?.... ...........

Inoceramus _______ ...

Ostrea.. ....................

Gastropods .................

Phylloceras. ................

Lytoceras __ ___ ........

6302 6307 6304 6305 6310 6313

a

8888 6308 6309 8892 8893 8894 6331 2193 2204

h

2208 11383

» a, Identified by T. W. Stanton; b, identified by W. M. Fontaine; c, identified by J. B. Reeside, jr.

6302. About one-seventh mile south of Nikolai mine. Calcareous sandstone 

overlying the basal conglomerate of beds formerly erroneously assigned to the 

Kennicott formation. F. H. Mofflt, 1909.

6307. About five-eighths mile northeast of Nikolai mine. Talus near base of 

formation. F. H. MoflSt, 1909.
358 MESOZOIC STRATIGRAPHY OF ALASKA

6304. About half a mile N. 22° E. of Nikolai mine. Massive fine-grained 

grit overlying the basal conglomerate of the formation. F. H. Moffit, 1909.

6305. About one-fourth mile N. 25° W. of Nikolai mine. Arkose overlying the 

basal conglomerate of the formation. F. H. Moffit, 1909.

6310. About a mile N. 15° W. of Nikolai mine. Black sandstone and shale 

resting on greenstone. F. H. Moffit, 1909.

6313. Ridge between forks of McCarthy Creek, about 1% miles N. 30° B. of 

mouth of East Fork. F. H. Moffit, 1909.

8888. Three quarters of a mile N. 43° E. of Nikolai mine. Probably less than 

100 feet above the base of the formation. G. C. Martin, 1914.

6308. Nikolai Creek, about five-sixths mile N. 18° E. of Nikolai mine. Sandstone and conglomerate. F. H. Moffit, 1909.

6309. Divide between headwaters of Nikolai Creek and East Fork of McCarthy Creek, three localities along ridge from 1 to 1% miles north of Nikolai 

mine. Shale, sandstone, and conglomerate. F. H. Moffit, 1909.

8892. About 1% miles N. 48° E. of Nikolai mine. Float probably nearly in 

place and yellow calcareous sandstone 250 or 300 feet above base of formation. 

G. C. Martin, 1914.

8893. 'About 1% miles N. 52° E. of Nikolai mine, on crest of ridge. In place 

and probably from the same bed that yielded lot 8892. G. C. Martin, 1914.

8894. About 1 mile east of Nikolai mine, on top of mesa. Yellow sandstone 

float. G. C. Martin, 1914.

6331. South Fork of Nikolai Creek, about 1% miles above mouth. Near base 

of formation. S. B. Capps, 1909.

2193. Arkose gravel from Nikolai Creek. F. C. Schrader and A. C. Spencer, 

1900.

2204. Nikolai Creek. Boulder in stream near Nikolai City. F. C. Schrader 

and A. C. Spencer, 1900.

2208. Head of Nikolai Creek. F. C. Schrader and A. C. Spencer, 1900.

11383 (22 F 22). Ridge between forks of McCarthy Creek and East Fork at 

altitude 4,500 feet. F. H. Moffit, 1922.

GRIT AND SANDSTONE OF DAN CEEEK

Historical review. The Triassic rocks exposed on Dan Creek and 

its tributaries are overlain unconformably by fine conglomerate or 

grit and sandstone, above which, in apparently conformable sequence, 

is black shale that is seemingly continuous with and part of the 

Upper Cretaceous shale of Chititu Creek, which is described on 

page 362. These grit and sandstone beds were regarded by Moffit 

and Capps as the basal member of the Kennicott formation and as 

the equivalent of the sandstone and conglomerate of Nikolai Creek, 

described on pages 355-358. The account of these beds by Moffit 

and Capps 40 includes a detailed description of the exposures on the 

tributaries of Dan Creek, with lists of fossils as identified by T. W. 

Stanton.

StratigrapMc description. The Upper Cretaceous (?) grit and 

sandstone of Dan Creek were described by Moffit and Capps 47 as 

follows:

48 Moffit, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska: U. S. Geol. Survey' Bull. 448, pp. 34, 40, pi. 3, 1911. 

*7 Idem, p. 34.
CRETACEOUS, CHITINA VALLEY 359

An excellent exposure of the base of the Kennicott formation was found 

on Eagle Creek, in the Copper Creek valley. All the upper part of the long 

ridge separating Eagle Creek from Copper Creek is made up of lower Kennicott beds. They rest on the edges of thin limestone and shale beds that 

"belong to the transition zone between Chitistone limestone and McCarthy 

shale. The limestone and shale beds have a dip about 20° greater than the 

overlying Kennicott, and the unconformity is shown in diagrammatic clearness. The basal beds of the Kennicott at this place consist of from 150 to 200 

feet of fine conglomerate or grit overlain by sandstone. Black shale overlies 

the sandstone and forms the top of the ridge extending southeast to the main 

mountain mass. This basal grit was traced northwest in Copper Creek valley 

to the vicinity of the limestone area north of Idaho Gulch. It may be regarded 

as a constant feature of the Kennicott in the Nizina district. In most places 

it is somewhat fossiliferous.

Age and correlation. The stratigraphic relations of these beds, 

which overlie the Triassic formations with a very great unconformity 

and which underlie the Upper Cretaceous shales with apparent conformity, indicate that their age may be either Jurassic or Cretaceous, 

but is more likely to be Cretaceous. The few fossils that have been 

found likewise indicate nothing more definite than this, for they all 

belong to genera that range throughout the Jurassic and Cretaceous.

These beds were referred by Moffit and Capps to the supposed 

Upper Jurassic Kennicott formation on the basis of a comparison, 

not with the original Kennicott formation, but with the conglomerate and sandstone of Nikolai Creek, described on pages 355-358. 

The age of the latter rocks is, however, subject to exactly the same 

doubt as that which attends the age of the rocks now under consideration. If these rocks are Lower Cretaceous they should contain 

some trace of the highly characteristic Kennicott fauna, which is 

so abundant in all the known outcrops of that formation. If they 

are Jurassic they should be separated from the overlying Upper 

Cretaceous shale by an unconformity. The writer believes that, in 

the absence of further evidence, they should be referred to the Upper 

Cretaceous and considered either the basal member of the Upper 

Cretaceous shale of Chititu Creek or a distinct formation in the 

same conformable series.

Fossils from Upper (?) Cretaceous rocks of Dan Creek a

6316

X

6322

X

X

X

X

6334

X

1 Identified by T. W. Stanton.
360

6316. South side of Dan Creek, 1% miles east of mouth of Copper Creek. 

Talus. F. H. Moffit, 1909.

6322. Ridge between Copper and Eagle Creeks, about two-thirds of a mile 

east of the mouth of Eagle Creek. Near base of formation. F. H. Moffit, 1909.

6334. Ridge between Copper and Eagle Creeks, about 1 mile east of the mouth 

of Eagle Creek. Near base of formation. S. R. Capps, 1909.

UPPER CRETACEOUS 

SHALE OF CHITITTJ AND YOUNG CREEKS

Historical review. The Upper Cretaceous shale of Chititu Creek 

and vicinity has been described in several accounts of the geology of 

the Chitina Valley, but its Upper Cretaceous age was not recognized 

until 1914.

These rocks were mapped as " unclassified sediments " by Rohn,4" 

who apparently did not study any of their exposures. They were included by Schrader and Spencer 49 in the " Triassic series " or " Trias.sic shales and limestones," but the Upper Cretaceous part of this 

aggregate was not recognized or described specifically. The account 

by Moffit and Maddren contains a description 50 of the " Triassic limestones and shales," which is quoted from Schrader and Spencer and 

consequently includes a description of the .shale that is now known 

to be Upper Cretaceous. Brief mention of the Upper Cretaceous 

shale is also made in the description of the gold placers.51 It is possible that the coal-bearing rocks near Fourth of July Pass and near 

the head of Chitistone River, described by Moffit and Maddren,52 

may also be Upper Cretaceous. The occurrence of the Upper Cretaceous rocks in the Chitistone Valley is suggested by a specimen of 

Desmoceras (lot 1696, p. 366) said to have been found in or near an 

area of coal-bearing rocks on the upper Chitistone. These rocks have 

never been examined by a geologist, although the occurrence of the 

coal has been briefly referred to by Mendenhall and Schrader,53 

by Mendenhall,54 by Moffit and Maddren,55 and by Moffit and 

Capps.56

48 Eohn, Oscar, A reconnaissance of the Chitina River and the Skolai Mountains, 

Alaska: U. S. Geol. Survey Twenty-first Ann. Kept., pt. 2, pi. 52, 1900.

48 Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), pp. 33, 

46-47, pi. 4, 1901.

50 Moffit, F. H., and Maddren, A. G., Mineral resources; of the Kotsina-Cnitina region, 

Alaska: U. S. Geol. Survey Bull. 374, pp. 28-29, 1909.

61 Idem, p. 93.

B*Idem, pp. 32-33, 100.

53 Mendenhall, W. C., and Schrader, F. C., The mineral resources of the Mount 

Wrangell district, Alaska: U. S. Geol. Survey Prof. Paper 15, pp. 67-68, 1903.

54 Mendenhall, W. C., Geology of the central Copper River region, Alaska : U. S. Geol. 

Survey Prof. Paper 41, pp. 124, 125, 1905.

65 Moffit, F. H., and Maddren, A. G., Mineral resources of the Kotsina-Chitina region, 

Alaska: U. S. Geol. Survey Bull. 374, pp. 32-33, 100, 1909.

66 Moffit, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district. 

Alaska : U. S. Geol. Survey Bull. 448, p. 73, 1911.
CRETACEOUS, CHITIKA. VALLEY 361

The detailed investigation of the geology of the Nizina district 

by Moffit and Capps established the fact that a great thickness of 

shale, lying south of the main fault of this district, regarded by the 

earlier observers as beneath the basal conglomerate of the Keniiicott formation and previously mapped and described as part of the 

" Triassic shales and limestones," belonged in reality above the beds 

that had previously been considered part of the Kennicott formation. 

The limits of the Kennicott formation were accordingly extended 57 

to include these beds. It is now known, however, that these strata 

are not Upper Jurassic and do not belong in the Kennicott formation. They constitute a distinct formation, which belongs above the 

Kennicott formation, and carries a characteristic Upper Cretaceous 

fauna. These Upper Cretaceous beds comprise the "interbedded 

sandstone and shale" and the " black shale with a few limestone 

beds" of the accompanying columnar section (fig. 9, p. 363), which is 

a modification of a section published in the report by Moffit and 

Capps 58 and which represents! the Kennicott formation as mapped 

and described by them. The lower conglomerate and sandy beds 

of this section are the sandstone and conglomerate of Nikolai and 

Dan Creeks, which are described on pages 355-360 and which the 

writer believes are the basal beds of the local Upper Cretaceous 

sequence. The upper conglomerate of this section is the conglomerate of the ridge south of Young Creek, which is described on 

pages 369-371 and which the writer believes to be possibly the same 

as the conglomeratic beds of Nikolai and Dan Creeks.

The account of these Upper Cretaceous beds by Moffit and Capps 59 

includes a detailed description of their occurrence, lithologic character, thickness, and stratigraphic relations. It includes also lists 

of fossils and a discussion of their age by T. W. Stanton.

In the description of the rocks of the upper Chitina Valley by 

Moffit, the Upper Cretaceous shale of Chititu Creek and vicinity 

is described as the "shales of Young Creek." This shale is considered as overlying with apparent conformity the Lower Cretaceous sandstone which the writer has correlated with the Kennicott formation (see pp. 334-335) and is apparently overlain, in the 

ridge south of Young Creek and some of the hills north of Young 

Creek, by conglomerate, arkose, and shale that are presumably Upper Cretaceous (see pp. 369-371). Moffit's account of the " shales of 

Young Creek" 00 includes a detailed description of their occurrence, 

lithologic character, and stratigraphic and structural relations.

67 Moffit, P. H., and Capps, S. R., op. cit, pp. 31-43, pi., 3. 

58 Idem, flg. 3, p. 37. 

B9 Idems pp. 31-43, pi. 3.

60 Moffit, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 17, 

18, 29, 30-34, 44-45, pi. 3, 1918.
362 MESOZOIC STRATIGRAPHY OF ALASKA

Lists of fossils as identified by T. W. Stanton are quoted,61 but 

Stanton gave no general discussion of the fossils from the Upper 

Cretaceous shale, except in the following statement: 62

The entire collection is believed to be Cretaceous, though a few of the 

smaller lots are uncertain because of the poor preservation or the great 

vertical range of the types represented.

A brief statement concerning the Upper Cretaceous age of this 

shale was made by Moffit and Mertie 63 in a discussion of the age 

and correlation of the later Mesozoic rocks of the Kotsina-Kuskulana 

district.

Stratigraphic description. The Upper Cretaceous rocks of the 

Nizina district constitute a formation 7,000 or 8,000 feet thick, consisting chiefly of dark fissile shale. Much of the shale is sandy,, 

and parts of the formation are made up of alternating shale and 

sandy beds. The shale contains numerous calcareous concretions. 

The general character of the formation is shown in the section, 

(fig. 9).

The Upper Cretaceous shale of the Nizina district apparently includes all that portion of the rocks mapped as the Kennicott formation by Moffit and Capps 64 lying south of the fault that extends parallel to Copper Creek and to the east fork of Nikolai Creek and north, 

of the fault on Young Creek, except the basal grit on Dan Creek that 

has been described on pages 358-360. The rocks south of YoungCreek fault (pp. 369-371) are apparently different from those north, 

of the fault and probably do not belong in the same formation. 

The exposures of shale in Sourdough Peak and on McCarthy Creek, 

at least as far north as Nikolai Creek, are probably Upper Cretaceous. The same formation apparently occupies some of the hills 

between Kennicott and Lakina rivers south of Fourth of July Pass.

These rocks rest with apparent conformity upon the grit and 

sandstone described on pages 358-360. At their contact with the 

sandstone ridge between Eagle and Copper Creeks, according to 

Moffit and Capps,65 " black shale overlies the sandstone and forms 

the top of the ridge extending southeast into the main mountain 

mass." Their contact with the Lower Cretaceous sandstone at the 

bend of Young Creek is believed to be a fault.

The character of the rocks in the various parts of the formation is 

described in the following quotations from Moffit and Capps: 66

Pyramid Peak, at the head of Copper Creek, appears to be made up entirely 

of rocks belonging to the Kennicott formation. The lower part is black shale,

"Mofflt, P. H., op..cit, pp. 37, 38, 40. 

82 Idem, p. 41.

88 Moffit, F. H., and Mertie, J. B., jr., The Kotsina-Kuskulana district, Alaska: U. S. 

Geol. Survey Bull. 745, p. 50, 1923.

«* Moffit, F. H., and Capps, S. R., op. cit., pi. 3.

w ldem, p. 34.

«8 Op. cit., pp. 34-35.
CEETACEOUS, CHITINA VALLEY 363

but the top shows bedding lines that are thought to represent sandstones and 

impure limestones. Sandy shales and hard sandstones are interstratified with 

the black shales on Rex Creek, and the tops of the mountains between Bex 

Creek and White Creek contain a large amount of gray sandstone and impure 

limestone. Beds of brown-weathering nodular limestone in the shales high

Conglomerate with in-1 

tcrbedded sand-[Upper Cretaceous (?). 

stone. I

Interbeddcd sandstone 

and shale.

Black shale with a few 

limestone beds.

Cretaceous

'Cretaceous or Jurassic, probably basal Upper Cretaceous.

Yellow- weathering 

shale and sandstone; 

changes to black 

shale in places.

Conglomerate.

Triassic shale-limestone beds.

FIGURE 9. Generalized columnar section of the post-Triassic sediments in the Nizina district.

(After Moffit and Capps)

up on the slopes of these mountains contain ammonite shells 15 or 18 inches 

across. These mountains appear to be at the axis of a broad, shallow syncline 

and give good sections of the formations.

Bedding in the black shales of Blei Gulch, on the south side of Chititu 

Creek, is shown by lines of small limestone concretions and thin discontinuous 

calcareous beds. More than 4,500 feet of black shale dipping low to the
364 MESOZOIC STRATIGRAPHY OF ALASKA

southwest is exposed in Blei Gulch. Young Creek, south of Chititu Creek, 

flows in a shallow canyon, whose walls are composed of black shale of the 

Kennicott formation. This shale forms the lower slopes of the ridge south of 

Young Creek, and it is probable that Kennicott sediments make up most of 

the ridge.07 The ridge was not examined in detail owing to lack of time, but 

a section up the first southern tributary of Young Creek east of Calamity 

Gulch shows rocks of the Kennicott formation. The section extends up the 

east branch of this creek. For a distance of nearly three-fourths of a mile 

from its mouth the creek flows over black shales with occasional limestone 

beds, all dipping southwest at angles of 30° or less. Thence for nearly a fourth 

of a mile are rocks that have been crumpled and much faulted. They consist 

of shales with interbedded calcareous shales and limestone, from which fossils 

were collected. In many places the strata of this disturbed zone stand on 

edge, and it is evident that displacements of importance have taken place. A 

peculiar feature of this locality is seen in the limestone nodules, which occur 

in beds and reach diameters of 2 or 3 feet. They consist of bluish-gray limestone and show parallel bedding lines crossing them.

The following statement concerning the Upper Cretaceous shale 

on Young Creek was made by Moffit: 68

The shales are prevailingly black and red or reddish brown but include 

some that are gray and greenish gray. They contain lime concretions and 

limestone beds, which are not distributed uniformly and which form only a 

small proportion of the total thickness of the sediments but which are highly 

conspicuous because of the contrast in color. Locally they contain also a 

relatively small amount of brownish-weathering sandy shale and sandstone. 

Dikes and sills of light-colored porphyritic rock and numerous thin " dikes " of 

sandstone cut them.

Nearly all the shale exposed in the canyon of Young Creek is black, except 

that toward the western end, which is red. It contains thin, widely separated 

brownish-weathering calcareous beds and limy concretions, which when seen 

in a large exposure give about the only evidence of structure that can be distinguished. The shale itself is broken into small fragments and commonly is 

without lines of bedding.

The thickness of the beds here referred to the Upper Cretaceous 

was discussed by Moffit and Capps,89 as follows :

The black shale member at the heads of Copper and Rex creeks has a minimum thickness of not less than 4,500 feet, yet the black shales of Williams 

Peak, south of Dan Creek, suggest a considerably greater thickness, possibly as 

much as 6,000 feet. This measurement includes all beds from the top of the 

conglomerate and grit to the beginning of the interbedded shale-sandstone 

succession that forms the tops of the high mountains at the heads of Copper 

and Rex creeks and the upper part of the ridge south of Dan Creek. The 

shale-sandstone member has a thickness of about 2,500 feet.

Age and correlation. The fauna of the Upper Cretaceous shale of 

the Nizina district, as represented in the following table, includes the 

marine invertebrates of 36 small collections from localities that are

67 For a later opinion concerning the identity of the rocks in this ridge see p. 370.

68 Moffit, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survpy Bull. 675, p. 31, 

1918.

88 Mofflt. F. H., and Capps, S. B., op. cit, pp. 37-38.
CRETACEOUS, CHITINA VALLEY 365

apparently distributed throughout the lower 4,500 or 5,000 feet of 

the beds exposed on Chititu and Young Creeks and their tributaries. 

The following statement concerning the fossils collected by the 

writer in 1914 was furnished by T. W. Stanton.70

The fossils from Chitina Valley include several lots from Blei Gulch that 

are certainly Upper Cretaceous and others probably of that age. The earlier 

collections from the same beds [collected by Moffit and others] contain nothing, 

so far as I can determine, that would prohibit their assignment to the Cretaceous. These collections are all small. The specimens of Inoceramus from 

sandstone northeast of the Nikolai mine may well belong to the same general 

fauna.

The lots that were determined as certainly Upper Cretaceous are 

Nos. 8857, 8860, 8865, and 8869. The other lots collected by the 

writer certainly came from the same formation as these. The earlier

collections referred to above were obtained from the same or higherbeds and may therefore be referred confidently to the Upper Cretaceous, too, although they had previously been determined by Stanton 71 as "probably Jurassic, though the types represented in the 

collection are not as definite as could be wished for determining 

between Jurassic and Cretaceous."

70 Personal communication.

71 Stanton, T. W., cited by Moffit, F. H., and Capps, S. R., op. cit, p. 39.
Fossils from Upper Cretaceous shale of CMtitu an

Irregular echinoid __ . ...... __ . ..........

Ecbinoid .... ____-._.----..._

Serpula...... __ ___ _ .. ................

Serpula?-- - _ .. ____ . ........

Rhynchonella? _ ... _ . __ -... __ .. __ ... ......

Terebratula...- .. .. ... __ ... __ .. .......

Solemya... . . ... ___ ._. ..

Nucula..... .- __ . _______ 1-

Leda ................

Nemodon n. sp__-_.. __ ..... __ . ____ __ ..

Nemodon?... ______ . _______________

Area. _ _ __ .. ____________

Inoceramus n. sp _ ________ _ .. ___ ___

Inoceramus.---. . __ _ ___ -... ........

Inoceramus Oarge thick-shelled species) . .............

Inoceramus.- ___ . _____ ___________

Avicula. __ . .. ..................

Ostrea __ __________ . _____ __ ___ .

Pecten. .... __ ...... ___ . .......

Anomia?- __ . _ ____________

Cyprina occidentalis Whiteaves?.. _ .. ___ __ ..

Cyprina?. . __ . _ .. __ -.--.--.... __ _ .. _ .

Thyasira. ________________________

Isocardia? ___ __ __ . _ .--.... _ ... __ ... _ ..

Clisocolus? ___________ ____________

Venerid pelecypod. __ _ __ .. __ ... __ . _ _ .

Corbula __ . ______________________

Teredo?.. _____ . ___ . ___________ ..

Pelecypods-.--.. ____ . _______ . ___ ___ .

Dentalium..... __ .... __ _ __ _____ ... .....

Dentalium? ..........................................

Chemnitzia?. __ ___________________

Aporrhais .. .................................

Tessarolax--- ________ . ____ ___ .......

Tessarolax? *

Gastropods.. ....... .................................

Nautilus. ________________________

Phylloceras n. sp _ . ____ .... ___________

Phylloceras... ________ ____________ .

Desmoceras n. sp ________________ .......

Desmoceras?. ___ . ______________ ......

oo »*

s

88

CO

Si

CO

3 

8

a

a

a

a

a

1

CO

a

a

a

a

S

h

S 

§8

h

55

88

h

h

b

h

b

h

h

h

1

h

00 

00

h

h

<M

OO 

OO

h

b

b

h

CO

b

b

S 

S

b

b

m

b

b

b

CO

§OO

b

b

b

§

oo

b

1 
Shark teeth.. _ _ _____ .. __________ .. .....

b

i

i

i

b

i

0 a, Identified by T. W. Stanton; b, identified by W. R. Smith.

h

b

h

b

b

i

1

1

h

b

b

D 
368 MESOZQIC STRATIGBAPHY OF ALASKA

4811. Chititu Creek. Said to have been washed out from shale bedrock in 

hydraulicking on Kernan's claim No. 11. F. H. Moffit, 1907.

8868. Mouth of Rex Creek. S. R. Capps, 1914.

6336. Rex Creek. Shale in ground sluice on Kernan's claim No. 1. S. R. 

Capps. 1909.

6324. Small gulch tributary to Rex Creek, about 1% miles N. 42° E. of 

mouth of Rex Creek, altitude 3,700 feet. Sandy shale. F. H. Moffit, 1909.

6325. Float at mouth of gulch 2 miles N. 33° E. of mouth of Rex Creek. 

F. H. Moffit, 1909.

8859. Blei Gulch, altitude 3,100 feet, on fork east of trail. G. C. Martin, 

1914.

8858. Blei Gulch, altitude 3,200 feet, on fork east of trail. Concretions in 

soft gray shale. G. C. Martin, 1914.

8857. Blei Gulch, altitude 3,200 feet, on fork east of trail. Float from same 

locality as 8858 and probably from same beds. G. C. Martin, 1914.

8860. Float near mouth of Blei Gulch. G. C. Martin, 1914.

8861. Float near mouth of Blei Gulch. Another slab of rock from same 

place as 8860. G. C. Martin, 1914.

8862. Float near mouth of Blei Gulch. Another piece of rock from same 

locality as 8860. G. C. Martin, 1914.

8863. Float near mouth of Blei Gulch. Another piece of rock from same 

locality as 8860. G. C. Martin, 1914.

8864. Float from Blei Gulch. G. C. Martin, 1914.

8865. Float from mouth of Blei Gulch. Another piece of rock from same 

locality as 8860. G. C. Martin, 1914.

8866,8867. Float from Blei Gulch. G. C. Martin, 1914.

8870. Float from White Creek. G. C. Martin, 1914.

8869. Trail on ridge south _of bend of Virginia Creek, altitude 4,160 feet. 

Concretionary shale. G. C. Martin, 1914.

6329. East fork of tributary that enters Young Creek from the south half 

a mile above Calamity Gulch, altitude 3,450 feet. 15-foot limestone associated 

with shale. F. H. Moffit, 1909.

6326. West end of ridge between Rex and White Creeks, 2% miles N. 62°

E. of mouth of Rex Creek, altitude 5,700 feet. F. H. Moffit, 1909.

6327. Mountain at head of Grubstake Gulch, two-thirds of a mile S. 85* 

W. of 8,135-foot peak, altitude 6,250 feet. Black concretionary shale. F. H. 

Moffit, 1909.

6328. Mountain at head of Grubstake Gulch, one-fourth mile S. 55° W. 

of 8,135-foot peak, altitude 7,500 feet. Impure limestone that forms upper 

500 feet of the mountain. F. H. Moffit, 1909.

6315. Sourdough Peak, about three-fifths mile S. 60° E. of summit, altitude 

4,400 feet. Black shale. F. H. Moffit, 1909.

6301. McCarthy Creek, 2% miles above mouth. Soft biack shale. F. H. 

Moffit, 1909.

1696. "Chitina drainage near cannel coal."- Received from Dan Kane by 

F. C. Schrader, 1902.

9467 (Fl). Gulch on south side of Young Creek, three-fourths of a mile above 

mouth of Calamity Gulch. Nodular limestone in reddish shale. F. H. Moffit 

and R. M. Overbeck, 1915.

9468 (F2 and F2a). Creek on south side of Young Creek, about a mile above 

Calamity Gulch. Float in stream. F. H. Moffit and R. M. Overbeck, 1915.

9469KF3). Near head of Sheep Creek, altitude about 5,200 feet. F. H. Moffit 

and R. M. Overbeck, 1915.
CRETACEOUS, CHITIFA VALLEY 369

9471 (F5). West branch of Young Creek, 2 miles above forks, altitude 4,200 

leet. Float. F. H. Mofflt and R. M. Overbeck, 1915.

9472 (F6). West fork of Young Creek, about 2 miles above forks, opposite 

first glacier from west, altitude 4,300 feet. Nodular limestone. F. H. Moffit 

and R. M. Overbeck, 1915.

9473 (F7). West branch of Young Creek above first glacier from west, 

altitude 4,400 feet. Float. F. H. Moffit and R. M. Overbeck, 1915.

9474 (FS). Above F7 (9473), on west branch of Young Creek, altitude 

4,500 feet. Float. F. H. Mofflt and R. M. Overbeck, 1915.

9475 (F9). West branch of Young Creek, just below first glacier from the 

west,, altitude 4,300 feet. Float. F. H. Moffit and R. M. Overbeck, 1915.

9476 (F10). East branch of Young Creek, on stream from the north, altitude 

4,300 feet. Float. F. H. Moffit and R. M. Overbeck, 1915.

947S (F12). Young-Canyon Creek divide, north of Fll (9477), altitude 5,750 

feet. Black and gray shale. F. H. Moffit and R. M. Overbeck, 1915.

9493 (F35). Stream on south side of Young Creek, three-fourths of a mile 

above Calamity Gulch, altitude 3,225 feet. Concretions in black shale. F. H. 

Mofflt and R. M. Overbeck, 1915.

UPPER CRETACEOUS (?)

CONGLOMERATE OF BIDGE SOUTH OF YOUNG CREEK

Historical review. A. conglomerate that occurs in several small 

areas on the crest of the ridge south of Young Creek was mapped by 

Schrader and Spencer 72 and also by Moffit and Maddren 73 as the 

Kennicott formation. These authors gave no specific description 

of this conglomerate.

The first published description of this conglomerate was given by 

Moffit and Capps,74 who regarded it as the uppermost member of the 

Kennicott formation or as possibly representing "a succeeding formation." Their account includes a brief description of the occurrence 

and lithologic character of the conglomerate, with an estimate of its 

thickness, and a discussion of its probable stratigraphic position.

This conglomerate and the associated arkose and shale constitute 

the uppermost division of the Cretaceous rocks of the upper Chitina 

Valley as described by Moffit,75 whose description includes a detailed 

account of the character, sequence, and stratigraphic relations of the 

beds. A statement by Stanton 70 concerning the single fossil which 

has been obtained from these beds is quoted.

73 Scbrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion 

of the Copper River district, Alaska (U. S. Geol. Survey special publication), pi. 4, 1901.

78 Mofflt, F. H., and Maddren, A. G., Mineral resources of the Kotsina-CMtina region, 

Alaska: U. S. Geol. Survey Bull. 374, pi. 2, 1909.

74 Mofflt, F. H., and Capps, S. R., Geology and mineral resources of the Nizina district, 

Alaska: U. S. Geol. Survey Bull. 448, pp. 35-36, 37, 38, pi. 3, 1911.

75 Mofflt, F. H., The upper Chitina Valley, Alaska: U. S. Geol. Survey Bull. 675, pp. 17, 

18, 29, 34-36, 45, pi. 3, 1918. 

7«Idem, p. 41 (lot 9494).
370 MESOZOIG STRATIGRAPHY OF ALASKA

Stratigraphic description. The description by Moffit of the conglomeratic rocks of the ridge south of Young Creek contains the 

following statements:"

The beds consist of conglomerate, sandstone, sandy shale, and arkose; and, 

although the conglomerate is at first sight the most noticeable component of 

the whole mass, the sandstone, shale, and arkose predominate.

Section of Cretaceous conglomerate, arkose, and shale of Young Creek

Feet 

Sandstone, coarse, green and gray, interbedded with dark

shales containing imperfect plant remains ______ 700

Shale, brown and gray, with subordinate dark beds____ 700

Sandstone, greenish or greenish gray_____________ 100

Shale, fine grained, brown, gray, or greenish gray __ 700

Conglomerate and sandstone_________________ 300

2,500

Sandstone and shale, with subordinate conglomerate, correlated with the 

similar beds south of Young Creek, cap Pyramid Mountain and the highest 

peaks west of the upper part of Young Creek. They are particularly well 

seen in Pyramid Mountain, where they rest on black shale and appear to be 

horizontal, although they dip slightly to the southwest. Here also a thickness 

of about 2,500 feet is exposed, but the massive basal conglomerate was not 

observed.

In regard to the stratigraphic position of the sandstones of Pyramid Peak 

and the high mountains to the west there is no doubt. The nearly horizontal 

sandstone beds overlie the shale. The sandstone, shale, and conglomerate on 

top of the ridge south of Young Creek also overlie the shale, but in both 

places the exact nature of the contact is unknown. The contact south of 

Young Creek is, at least in places, a fault contact. In Pyramid Peak the 

sandstones have a slight southward dip, hardly enough to notice, but they 

show practically no folding. The underlying shales, on the other hand, are 

folded. This might seem to indicate depositional unconformity and folding

of the shale before the sandstone was laid down; yet it should be remembered 

that the soft shales are much less able to withstand deforming pressure than 

the sandstone. In the places where the sandstone-shale contact was observed, 

on the west branch of Young Creek, the two formations appear to be conformable.

Age and correlation. The only determinable fossil that has been 

found in the conglomeratic rocks south of Young Creek is a single 

specimen collected by Moffit in 1915 from sandstone within the area 

mapped as conglomerate. Stanton 78 has made the following statement concerning this fossil:

9494 (F. 36). Same stream as F 35 (9493), elevation 4,500 feet; from horizontal sandstone beds: Inoceramus sp., obscure imprint of a single specimen. 

Probably Cretaceous.

If the conglomerate south of Young Creek and the conglomeratic 

beds of Pyramid Peak are identical, as Moffit believes, there would

77 Mofflt, P. H., op. cit., pp. 35, 36.

78 Stanton, T. W., cited by Mofflt, P. H., op. cit., p. 41.
CRETACEOUS, CHITIETA VALLEY 371

seem to be no doubt that they are Upper Cretaceous, for the conglomeratic beds of Pyramid Peak clearly overlie the Upper Cretaceous shale, whereas the conglomerate south of Young Creek appears to contain Inoceramus and therefore to be not post-Cretaceous. 

It is possible, however, that these rocks are not equivalent and that 

the conglomerate south of Young Creek, which is separated from 

the main mass of the Upper Cretaceous shale by a fault, may be 

directly underlain by the Lower Cretaceous sandstone of Young 

Creek or may even underlie the Lower Cretaceous sandstone. The 

conglomerate south of Young Creek may therefore belong either at 

the base of the Kennicott formation, or at the base of the Upper 

Cretaceous, or near the top of the Upper Cretaceous.

CONGLOMERATE AND OVERLYING VOLCANIC ROCKS OF M'CARTHY CHEEK

Some late Cretaceous or post-Cretaceous rocks are exposed near 

the head of McCarthy Creek, concerning which Moffit 70 has submitted the following statement:

The high mountain at the head of McCarthy Creek and the crest of the 

ridges on both sides of the creek near this mountain are made up of horizon 

tally bedded rocks, including sandstone, volcanic rocks, and conglomerate. 

Rhyolitic beds and tuffs are present. On the ridge west of the glacier the following section was seen:

Section near head of McCarthy Creek

Feet 

Cliff-forming volcanic rocks, sandstone, conglomerate, and

shale. 

Black carbonaceous shale, intruded by dikes and sills of

white sandstone. Contain some thin shaly coal near the

top__________ ____ ______________ 350

Conglomerate and shale_____ _______________ 50 

Black shale at an altitude of about 5,000 feet. This is the

thick shale of the Cretaceous.

Some fossil plants that were collected at the base of the cliffs 

which form the upper member of the preceding section may have 

come from any of the beds therein. Arthur Hollick 79 has submitted 

the following statement concerning these fossils:

7575 (22 F 12 a). East side of west McCarthy glacier, about halfway up 

glacier, collected by F. H. Moffit, 1922. Nine pieces of matrix, consisting of 

fine-grained hard black shaly sandstone, containing an abundance of plant 

remains, mostly fragmentary, among which the following species were provisionally identified: Equisetum perlaevigatum Cockerell (-E. laevigatum 

Lesquereux) ?; Juglans rhamnoides Lesquereux (=Rhamnus rossmaesslerl 

Unger, fide Lesquereux) ? Neither of these species, however, can be safely 

taken as an index fossil. Age, extreme Upper Cretaceous or lower Tertiary.

79 Personal communication.
372 MESOZOIO STRATIGRAPHY OF ALASKA

The volcanic rocks in the upper part of the section are probably 

Tertiary. The fossil plants, which may have been derived either 

from these beds or from some of the underlying strata, indicate a 

position either in the uppermost Cretaceous or in the Tertiary, one 

of the species occurring in the Laramie and the other in the Livingston. The strata beneath the volcanic rocks may perhaps be the 

equivalent of the conglomerate that is supposed to lie above the shale 

of Chititu Creek. The occurrence of coaly strata in the lower part 

of the section suggests that this may be the horizon of the coal 

beds of Fourth of July Pass and Chitistone River. (See p. 360.)

NUTZOTIN MOUNTAINS 

GENERAL FEATURES

Lower Cretaceous strata containing Aucella crassicollis Keyserling 

are present in the Nutzotin Mountains east of Chisana River. These 

Lower Cretaceous rocks have not yet been differentiated, either in 

the stratigraphic section or on the map, from the Upper Jurassic 

AuceHa-be&r'mg beds (see pp. 240-245) with which they are closely 

associated and which they apparently resemble in lithologic character, 

or from the great body of metamorphosed and complexly folded slate 

and graywacke of the Nutzotin Mountains. The latter rocks may be 

largely Cretaceous or Jurassic or may include Paleozoic beds. They 

may belong with the somewhat similar rocks of doubtful position in 

other districts described on pages 480-487.

The general sequence of strata in the Nutzotin Mountains east of 

Chisana was described by Capps 81 as follows:

Quaternary:

Glacial deposits, gravels, volcanic ash, peat, and other unconsolidated 

materials.

Glacial morainal deposits, with associated lava flows. 

Tertiary:

Conglomerates and unconsolidated gravels.

Sandstones, shales, conglomerates, and tuffs, locally containing

lignite. 

Cretaceous:

Shales, slates, and graywackes. 

Jurassic:

Shales, slates, graywackes, and conglomerates. 

Triassic:

Thin-bedded limestone of Cooper Pass. Possibly includes also part 

of the slates and graywackes of the Nutzotin Mountains.

81 Capps, S. R., The Chisana-White River district,. Alaska : U. S. Geol. Survey Bull. 630, 

pp. 29-30, 1916.
CKETACEOUS, NUTZOTIN MOUNTAINS 373

Carboniferous:

Lava flows.

Massive limestone.

Lava flows and pyroclastic rocks.

Massive limestones and shales.

Basic lavas and pyroclastic beds, with minor amounts of sediments. 

Devonian:

Lavas and pyroclastic beds, with considerable black shale.

LOWER CRETACEOUS

AUCELLA-BEARING BEDS OF CH1SANA AND WHITE RIVERS

Historical review. The presence of Lower Cretaceous rocks In the 

Nutzotin Mountains was first indicated by Moffit and Knopf 82 on 

the basis of a small collection of fossils obtained by J. D. Irving at 

an unspecified locality "in the vicinity of Beaver Creek." No description of the rocks at this locality was given, and the published 

account consists merely of a statement, contributed by T. W. Stanton, concerning the character and probable age of the fossils.

Lower Cretaceous fossils were collected by S. R. Capps in 1914 

from the shales on Chathenda Creek. The account of these rocks 

by Capps 83 includes only a general description, it not having been 

feasible, in the reconnaissance survey upon which this description 

was based, to differentiate the Lower Cretaceous Aucella-bewmg 

beds from the Upper Jurassic Aucella-be&Ying beds or from the 

main body of the Jurassic or older slate and graywacke of the 

Nutzotin Mountains, with which the known Lower Cretaceous rocks 

are closely and complexly associated and to which they bear a strong 

lithologic resemblance. This account includes lists of fossils as 

identified by T. W. Stanton.

Stratigraphic description. The Lower Cretaceous rocks of the 

Nutzotin Mountains consist of shale and graywacke that presumably 

overlie conformably the Upper Jurassic shale and graywacke described on pages 242-245. These Cretaceous and Jurassic rocks 

together were described by Capps 84 as follows, the reconnaissance 

character of his investigations and the structural complexity of the 

district making it necessary for him to regard them as an indivisible 

complex:

The rocks that have yielded Jurassic and Cretaceous fossils on upper Bonanza 

Creek are dominantly shales and argillites, with much less interbedded graywacke than is present in the sediments which form the main mountain mass.

82 Mofflt, F. H., and Knopf, Adolph, Mineral resources of the Nabesna-White River district, Alaska: U. S. Geol. Survey Bull. 417, p. 29. 1910.

83 Capps, S. R., The Chisana-White River district, Alaska: U. S. Geol. Survey Bull. 630, 

pp. 29, 47-53, pi. 2, 1916. 

"Idem, pp. 50, 51, 52.

49448 26 25
374 MESOZOIC STRATIGRAPHY OF ALASKA

Some fine conglomerates are present, and a little impure limestone was seen, 

but the shales preponderate greatly. The proportion of graywaqke is greatest 

in the lowest part of the section exposed and decreases upward.

The Cretaceous beds of this group lie immediately adjacent to the oldest 

known rocks of the region, the Devonian, and are separated from them by a 

profound fault.

Although the Mesozoic beds that have yielded Jurassic and Cretaceous fossils have been but slightly metamorphosed and are deformed only by a monoclinal tilting, the argillites, slates, and graywackes which form most of the 

Nutzotin Mountains and seem to lie structurally beneath the recognized Jurassic beds have been subjected to deformational stresses that have produced 

intricate folds.

The younger, fossiliferous slates of known Jurassic and Cretaceous age, 

as exposed on Bonanza and Chathenda creeks, are of less intricate structure, 

for they have rather uniform monoclinal dips to the southwest. They may 

also be reduplicated by faulting, but if the series is not reduplicated, the beds 

have a minimum thickness of 3,000 feet and may exceed that figure.

Structurally above the typical slates and graywackes of the Nutzotin 

Mountains, in the vicinity of Chisana placer mines, is a series of shales and 

graywackes, with some conglomerate, which has yielded fossils that are possibly of Upper Jurassic age. Its lower limit is not known, btft its upper part 

merges, without any observed stratigraphic break, into rocks that are similar 

in lithology but bear Lower Cretaceous fossils.

Age and correlation. The fauna of the Lower Cretaceous rocks of 

the Nutzotin Mountains, like those of all the other Lower Cretaceous 

rocks of Alaska, is characterized by one or more species of Aucella, 

other fossils being comparatively insignificant in numbers or in importance. The most numerous of these fossils is a species of Aucella 

that is closely related to if not identical with Aucella crassicollis 

Keyserling and that occurs in most of the other Lower Cretaceous 

areas of Alaska. The fossils from Beaver Creek are not well preserved but probably belong to this same species. The following 

statement concerning the Beaver Creek Collection was made by T. W. 

Stanton.85

The specimens all belong apparently to a single species of Aucella, and 

though they are much compressed and considerably distorted they seem to be 

of the type of Aucella crassicollis Keyserling, which is referred to the Lower 

Cretaceous. The horizon is probably about the same as that of the Aucella 

bed from which Mr. Mendenhall collected on Matanuska River. Whether the 

fossils belong to the species mentioned or not they are certainly Aucella, and 

the age is therefore Lower Cretaceous or Upper Jurassic.

The Aucella in lot 8,811 apparently belongs to a different and older 

species which, according to Stanton,86 is "probably Lower Cretaceous, and in my judgment from a somewhat lower horizon than Nos. 

8,807 and 8,808." ' '

85 Stanton, T. W., cited by Mofflt, F. H., and Knopf, Adolph, Mineral resources of the 

Nabesna-White River district, Alaska : U. S. Geol. Survey Bull. 417, p. 29, 1910.

86 Stanton, T. W., cited by Capps, S. R., The Chisana-White River district, Alaska: 

U. S. Geol. Survey Bull. 630. p. 52, 1916.
CRETACEOUS, SOUTHEASTERN ALASKA 375 

Fossils from Lower Cretaceous shale of Chisana and White rivers a

Aucella crassicollis? _ _ ___ . ... _ .........

Belemnites. ___________ . _________

8811

X

8807

X

8808

X

X

8810

X

X

(J.D.I.)

X

«Identified by T. W. Stanton.

8811. Gold Run Creek near its mouth. Shale and graywacke. S. R. Capps, 

1914. 

8807. Chathenda (Johnson) Creek. Black shale of Nutzotin (?) series. 

S. R. Capps, 1914.

8808. Bonanza Creek, claim No. 9. Black shale. S. R. Capps, 1914. 

8810. Southeast fork of Chathenda (Johnson) Creek, l1^ miles above its 

mouth. Black shale. S. R. Capps, 1914.

(J.D.I.) Vicinity of Beaver Creek. J. D. Irving, 1907.

GENERAL SEQUENCE

The rocks in southeastern Alaska that are believed by the writer 

to be of Cretaceous age include the Aucella-be&Ymg sandstone, shale,, 

and conglomerate of Pybus Bay and other localities in the southern 

part of Admiralty Island; shale and calcareous sandstone at Hamilton Bay, on Kupreanof Island; slate and graywacke on the west 

coast of Etolin Island; the conglomerate, slate, and graywacke ot 

Blank Inlet, on Gravina Island; and possibly some graywacke, slate, 

and conglomerate on Prince of Wales Island. These rocks are distinguished from the somewhat similar slaty rocks that have been, 

described as Jurassic on pages 245-262 by containing the Cretaceous 

rather than the Jurassic type of Aucella (on Admiralty and Etolin 

islands), by containing no volcanic beds, by containing conglomerate with pebbles of granite that are believed to have been derived 

from £he supposed Jurassic granitic intrusive rocks, and by having 

in some localities, as on Pybus Bay, a notably lesser degree of metamorphism than the Jurassic slate and a distribution and attitude 

that is not controlled by the well-marked northwesterly structural, 

intrusive, and outcrop lines which show in most of the older rocks. 

The writer believes that these rocks are of Lower Cretaceous age 

and that they were laid down unconformably upon the Upper 

Jurassic and older beds after those rocks were folded and metamorphosed and after the intrusive rocks of the Coast Eange had been 

partly unroofed. No "Upper Cretaceous rocks have been recognized 

in southeastern Alaska.
376 MESOZOIC STRATIGRAPHY OF ALASKA

LOWER CRETACEOUS 

AUCELLA-BEAEING BEDS OF PYBUS BAY

Historical review. The Lower Cretaceous rocks of Admiralty 

Island were first described by C. W. Wright 87 as "conglomerates, 

graywackes, and slates." Wright gave a brief description of the 

lithologic character of the rocks, a statement that they lie unconf ormably upon more highly metamorphosed " limestones and schists " 

of Carboniferous age, and a discussion, by T. W. Stanton, of fossils 

collected at Pybus Bay. Although the evidence of the age of the 

rocks and much if not all of the information given in the description 

were obtained from Pybus Bay, it is stated that these rocks are mainly 

developed along the shores and on the Islands of Seymour Canal, 

that their northern continuation is found on Point Young, that they 

are also present on Portland Island, northwest of Douglas Island, 

and that rocks of similar appearance, which may belong to the same 

series, are found at Yankee Cove. This correlation of the rocks near 

Pybus Bay with the rocks on Seymour Canal and at the other localities mentioned above has not been established. (See pp. 256-257.)

The Pybus Bay locality was also visited by Kindle,88 who gave a 

brief description of the character of the Lower Cretaceous beds and 

of their relations to the underlying "Upper Carboniferous" (Permian) limestone.

Brief mention of the Lower Cretaceous rocks at Pybus Bay has 

also been made by F. E. and C. W. Wright,89 who stated that some 

of the fossils were obtained from limestone and calcareous shale

Stratigraphic description. The Lower Cretaceous rocks of Pybus 

Bay consist for the most part of shale and conglomerate, with possibly some limestone near the base. They rest unconformably on Permian and Upper Triassic limestones. The section on Pybus Bay, 

according to Kindle,90 is as follows:

Section on west shore of east arm of Py~bus Bay

Feet

Black to dark-gray argillaceous slates____________ 300 

Covered interval __ _ _ _ _ ___ 100 

Massive or heavy-bedded gray limestone, conchoidal fracture_____ __; ____ __ _-_______________________________________ 40

Unconformity.

Limestone and chert (Permian)________________ 1,530

ST Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

pp. 143-144, pi. 33, 1906.

88 Kindle, E. M., Notes on the Paleozoic faunas and stratigraphy of southeastern 

Alaska: Jour. Geology, vol. 15, p. 332, 1907.

89 Wi-ight, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska : 

U. S. Geol. Survey Bull. 347, pp. 34, 37, 40, 58, 1908. 

80 Kindle, E. M., op. cit, p. 332.
CRETACEOUS, SOUTHEASTERN ALASKA 377

Kindle states that other outcrops just outside the bay indicate a 

total thickness of not less than 900 feet for the black slates. The 

section on Pybus Bay, according to the Wrights,91 includes shale, 

conglomerate, and black limestone, more than 500 feet thick, underlain by more than 200 feet of gray limestone.

The exposures on the point between the arms of Pybus Bay, according to the unpublished observations of the writer, consist of 

gray shale with calcareous concretions containing Aucella (lot 8851), 

underlain, along the east shore of the west arm of the bay, by similar 

gray shale with calcareous concretions in which no fossils were 

found, interstratified with thin beds of yellowish sandstone. A few 

carbonized sticks were seen and also some black flint concretions. 

Worm tracks (lot 8852) were seen in some of the lower beds. According to Kindle's field notes,

the outcrops along the point between the east and west arms of Pybus Bay 

are of the same character and horizon as the black shale in the upper part 

of the section on page 376. Small folds and changing dip and strike between 

the two localities prevented determination of the thickness of beds. Not less 

than 400 feet is exposed along the point, consisting of hard black slate with 

an occasional black calcareous band and numerous 3 to 6 inch bands of graywacke (volcanic) of olive-gray color. One or two species of Aubella (lot 9-a) 

occur in considerable numbers in some of the strata.

Kindle's field notes state that on the east side of the east arm of 

Pybus Bay the Carboniferous limestone and chert beds are found 

farther south than on the west shore, apparently as the result of an 

abrupt bend of the strike to the south. The cherty limestone that is 

the uppermost bed beneath the unconformity in the section on page 

376 is represented here by a belt of extremely coarse conglomerate 

made up largely of fragments of fossiliferous Carboniferous limestone. Resting unconformably on it is 45 feet or more of gray limestone with Mesozoic fossils (lot lOa). These Mesozoic limestone beds 

are followed by the black slate. Edwin Kirk obtained Upper Triassic fossils (pp. 91-92) at or near this locality.

The exposures at Point Pybus, according to the observations of 

the writer, consist of conglomerate interbedded with sandstone and 

shale. Ammonites and Aucella (lot 8854) were found in pebbly 

shale just east of Point Pybus. The conglomerate and pebbly shale 

near Point Pybus are overlain, farther east along the coast, by gray 

shale like that on the point between the arms of Pybus Bay. This 

shale yielded several small collections of fossils (lots 8853, 8855, and 

8856).

According to Kindle's field notes, on the point V/2 miles north of 

Point Pybus about 900 feet of interbedded conglomerate and " green91 Wright, P. E. and C. W., op. cit., p. 34.
"378

MESOZOIO STRATIGRAPHY OF ALASKA

stone" are exposed. These rocks apparently pass into the finegrained black shale which crops out exclusively on the west and 

north sides of the small bay.

Age and correlation. The shale and conglomerate of Pybus Bay 

and vicinity are referred to the Lower Cretaceous on the basis of 

the fossils listed in the following table. Stanton 92 has made the 

following statement concerning .some of these collections:

The specimens of Aucclla from Pybus Bay, Admiralty Island, are apparently 

referable to species that in California and adjacent States are characteristic 

of the Lower Cretaceous, Aucella piochvi occurring in a lower zone than Aucella 

crassicollis. The Alaskan specimens probably also come from the Lower 

Cretaceous, although strict correlation is rendered somewhat hazardous by 

the fact that the genus Aucella with similar specific forms ranges down into 

the Upper Jurassic.

Lower Cretaceous fossils from Admiralty Island a

Aucella piochii Gabb...... ___ . __

Ostrea?. ----...__...-_-..-...._. 

8850

X

X

8851

X

8852

X

C. 

W.

152

X

7a

X

9a

X

3310

X

X

X

10095

X

10169

X

8853

X

8854

X

X

8855

X

8856

c. 

w.

149

X

" Identified by T. W. Stanton.

8850 (25). Admiralty Island, point at north entrance to Herring Bay. 

Gray shale which appears to underlie the Triassic limestone of Nos. 22, 23, and 

24, but which is probably separated from the Triassic limestone by a fault. 

G. a Martin, 1914.

8851 (26). Admiralty Island, point between arms of Pybus Bay. G. C. Martin, 1914.

8852 (27). Admiralty Island, 1 mile north of point between arms of Pybus 

Bay (on east shore of west arm). G. C. Martin, 1914.

C. W. 152. West entrance to north arm of Pybus Bay. Shale. C. W. Wright, 

1904.

7a, 9a. Pybus Bay. E. M. Kindle, 1905.

3310 (lOa). Pybus Bay. "45 feet of limestone below 9a and unconforrnable 

on Carboniferous limestone." E. M. Kindle, 1905.

10095. East end of point separating arms of Pybus Bay. Edwin Kirk, 1917.

10169. Point-between east and west arms of Pybus Bay. Edwin Kirk, 1918.

8853 (30). Admiralty Island, 1 mile northeast of Point Pybus. Gray shale 

that appears to overlie the conglomerate of Point Pybus. G. C. Martin, 1914.

92 Stanton, T. W., cited by Wright, C. W., A reconnaissance of Admiralty Island: U. S. 

Geol. Surrey Bull. 287, p. 144, 1908.
CRETACEOUS, SOUTHEASTERN ALASKA 379

8854 (31). Admiralty Island, three-fourths mile northeast of Point Pybus, 

Conglomerate that appears to underlie shale' that yielded lot 30. G. C. Martin, 

1914.

8855 (32). Admiralty Island, point at west entrance to cove 2 miles northeast of Point Pybus. Concretion in same shale formation that yielded lot 30. 

vG. C. Martin, 1914.

8856 (33). Admiralty Island, point at west entrance to cove 2 miles northeast of Point Pybus, about 800 feet southwest of lot 32. G. C. Martin, 1914.

C. W. 149. Square Point; 4 miles southwest of False Point Pybus. Slate inclusions in conglomerate bed. C. W. Wright, 1904.

AUCELLA-BEARING BEDS OF KUPREANOF ISLAND

The only known Lower Cretaceous rocks on Kupreanof Island are 

found on the north end of the peninsula between Hamilton Bay and 

Keku Strait. These rocks, according to'the unpublished observations of A. F. Buddington, consist of about 1,000 feet of thin-bedded 

gray shale arid sandstone, 1 inch to several inches thick, with intercalated layers of fine-grained limestone from 6 to 12 inches thick. 

The beds have a general northwest strike and dip 10°-20° S. A 

few thin beds of tuff are intercalated with the other strata. East 

of Point Hamilton the Cretaceous beds are intruded by a mass of 

Tertiary gabbro. South of Point Hamilton they are overlain by 

Tertiary sandstone carrying fossil plants. At Point Hamilton a 

slightly calcareous sandstone bed 1 foot thick is exposed and has 

yielded abundant weathered blocks on the tidal flats. It is moderately fossiliferous, but the shells are mostly in fragments and poorly 

preserved (11404 and 11935). Traces of carbonized plant remains 

are found.

Similar beds, predominantly shale, are found in the line of islets 

lying south of Hound Island and halfway between it and Kuiu 

Island. A sill of basalt forms the backbone of this string of islets.

On the west headland of the cove about 3 miles southwest of 

Hound Island more than 300 feet of thin-bedded sandstone and 

shale with a few limestone layers are exposed. Beds of sandstone 

as much as 2 feet thick occur in the basal portion. These beds apparently overlie the Upper Triassic volcanic rocks, but the contact 

is covered, and the beds are nonfossiliferous.

The following statements concerning some fossils collected by 

Buddington have been submitted by T. W. Stanton:

11404 (44 Bu.). Kupreanof Island, islet at Point Hamilton. Thin-bedded 

sandstone with calcareous layers. Fossils rare and good specimens found only 

in weathered beds. A. F. Buddington, 1922. 

Aucella? sp. 

Pteria? sp.

The few fossils in this lot are small and imperfect, and the generic 

identification is not positive in either case. The collection is believed 

to be from the AuceUa-bearing beds of Upper Jurassic or Lower Cretaceous age.
380 MESOZOIO STRATIGRAPHY OF ALASKA

11935 (No. 44). Same locality as 11404. A. F. Buddington, 1923: 

Worm trails or burrows. 

Rhynchonella ? sp., fragment. 

Aucella sp.

Upper Jurassic or Lower Cretaceous.

i

AUCELLA-BEARING BEDS OF ETOLIN ISLAND

Historical review. The Lower Cretaceous rocks of Etolin Island were mapped by the Wrights 93 in part as "Upper Carboniferous greenstone lava flows interbedded with volcanic tuffs and 

black slate " and in part as undifferentiated Paleozoic rocks. They 

gave no description of any of the rocks, which are now known to 

be Lower Cretaceous. The age of these rocks was first determined 

by the writer, who collected Lower Cretaceous fossils from them in 

1914. Additional collections have been made by Buddington,94 

who gave a brief account of the lithology, age, and stratigraphic 

relations of these rocks, which he described as "Upper Jurassic or 

Lower Cretaceous."

Stratigraphic description. The Lower Cretaceous rocks of Etolin 

Island were described by Buddington 94 as follows:

Neither the top nor bottom of the next series of rocks [Upper Jurassic 

or Lower Cretaceous] is shown. The lower portion of the series is essentially 

a black argillaceous slate formation, very thin bedded, with layers and partings of graywacke. Thin intercalated layers of rusty-weathering limestone 

are common, and many of the beds contain conspicuous nodules of blue-black 

chert and of limestone. Rarely a thin bed of fine conglomerate is present. 

The upper portion of the series comprises graywacke with intercalated beds 

of slate; the graywacke is in part thick bedded and in part thin bedded 

like the slate. Fossils collected from this formation were identified by T. W. 

Stanton as Aucella, crassicollis Keyserling? and an imprint of Belemnites sp. 

He further stated that the Aucella, occurs in the form of distorted specimens 

of the type crassicollis, which indicates Lower Cretaceous age if the specific 

identification is correct, and that the formation is not older than Upper 

Jurassic. The rocks of this series are the least metamorphosed of all the 

Mesozoic formations of this district.

Age and correlation. The Lower Cretaceous age of the slaty 

rocks on the west coast of Etolin Island is shown by the fossils obtained at the localities listed below. These fossils were identified by 

T. W. Stanton.

8840 (13). Etolin Island, near cabins on small harbor behind island east of 

Screen Islands. G. C. Martin, 1914.

11077 (G-12). Small islet two-fifths of a mile west of Johnson's Cove on west 

side of Etolin Island. A. F. Buddington, 1921.

83 Wright, P. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pis. 1, 3, 1908.

94 Buddington, A. F., Mineral deposits of the Wrangell district: U. S. Geol. Survey 

Bull. 739, p. 54, 1922.
CKETACEOUS, SOUTHEASTERN ALASKA 381

Aucella crassicollis Keyserling? was found at both localities, and 

Belemnites at 11077.

CONGLOMERATE, GBAYWACKE, AND SLATE OF GBAVINA ISLAND

Historical review. The supposed Lower Cretaceous rocks of 

Gravina Island are part of the "Gravina series" as described by 

Brooks.96 In the report on the Ketchikan district by the Wrights 97 

these rocks are not described but are mapped as " undifferentiated 

Paleozoic rocks." These rocks were described by Smith 98 as part of 

the "Triassic rocks of the east coast of Gravina Island" and as 

"undifferentiated Paleozoic schists." They were described by 

Chapin 99 as "Upper Jurassic or Lower Cretaceous conglomerate, 

slate, and graywacke." Chapin's description contains an account 

of the distribution, character, stratigraphic relations, structure, 

origin, age, and correlation of the beds.

Stratigraphic description. The character of the Lower Cretaceous conglomerate, graywacke, and slate of Gravina Island and 

their relations to the underlying Jurassic rocks are indicated in the 

stratigraphic section on page 247. The Cretaceous rocks of Gravina 

Island were described by Chapin 99 as follows:

A formation consisting essentially of interbedded conglomerate, graywacke, 

and black slate exposed along a wedge-sbaped strip. extending from Blank 

Inlet to tbe northeast coast of Gravina Island is determined on fossil evidence 

to be Upper Jurassic or Lower Cretaceous, and similar rocks just northwest 

of Ward Cove are correlated with this formation.

The conglomerate does not appear to be the basal member but occurs at 

intervals throughout the formation interbedded with the graywacke and slate. 

It is composed of rather fine grained pebbles with a few boulders as much 

as a foot in diameter. The matrix is essentially a graywacke but contains 

a considerable amount of igneous rock fragments. The pebbles and cobbles 

are mostly igneous and resemble the volcanic rocks of Gravina Island. 

Pebbles of dioritic rocks resembling the plutonic rocks of the Coast Range also 

occur. No members of this formation are known to be of igneous origin, 

although both matrix and cobbles of some of the conglomerates contain so 

great an amount of igneous material that they resemble agglomerates.

The conglomerate passes by increasing fineness and decrease of igneous material into typical-looking graywacke with angular slate fragments. Microscopic examination of the graywacke shows it to consist essentially of quartz 

and feldspar grains with angular fragments of, slate and decomposed particles 

of dioritic rocks, hornblende, pyroxene, and epidote. Flakes of biotite may be 

secondary, but no marked schistosity has developed.

86 Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska: U. S. 

Geol. Survey Prof. Paper 1, pp. 25, 40, 45, pi. 2, 1902.

B7 Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pis. 1, 2, 1918.

88 Smith, P. S., Notes on the geology of Gravina Island, Alaska: U. S. Geol. Survey 

Prof. Paper 95, pp. 95, 102-104, fig. 35, 1915.

88 Chapin, Theodore, The structure and stratigraphy of Gravina 'and Revlllagigedo 

Islands, Alaska: U. S. Geol. Survey Prof. Paper 120, pp. 97-98, fig. 11, 1918.

49448 26 26
382 MESOZOIO STRAT1GBAPHY OF ALASKA

The slates are very fissile black clay slates and are closely interbedded with 

the graywacke members. The slates have a marked cleavage.

These Upper Jurassic or Lower Cretaceous beds overlie the volcanic rocks 

of Gravina Island described above and regarded as Triassic or Jurassic, but 

in most places the relations are rather obscure. On the northeast shore of 

Bostwick Inlet near the entrance the slates and graywacke overlie the eroded 

surface of the volcanic rocks with marked unconformity. On the northeast 

shore of Gravina Island conglomerates and graywacke overlie the volcanic 

rocks without apparent angular unconformity. The conglomerate and graywacke of Ward Cove are noticeably unconformable upon the black phyllite 

that has been correlated with the Upper Triassic rocks.

The conglomerate, slate, and graywacke beds of Blank Inlet occupy the 

trough of an overturned syncline in which are also involved the volcanic rocks 

of Gravina Island, which actually overlie them on the east shore of Blank 

Inlet.

These Upper Jurassic or Lower Cretaceous conglomerates, graywackes, and 

slates are the products of normal deposition in a shallow sea. The constantly 

changing character of the deposits indicates corresponding changes of conditions during their deposition. The materials of the rocks were apparently 

derived in part from the volcanic rocks of Gravina Island near by and in 

part from the surrounding regions.

Age (md correlation. The paleontologic evidence on the age of 

the slate and graywacke of Blank Inlet rests on a single collection 

of fossils, concerning which Stanton 2 reports as follows:

9527 (15 ACh 99). Blank Inlet, iy2 miles north of Blank Point, Gravina 

Island. Belemnites sp. Jurassic or Lower Cretaceous.

These fossils are insufficient to show whether the beds are Cretaceous 

or Jurassic, but an indication that they are Cretaceous is to be 

found in the absence of volcanic beds and in the presence in the conglomerate of boulders that seem to have been derived from the 

presumably Jurassic plutonic rocks of the Coast Range and of reworked igneous material, part of which was probably derived, according to Chapin, from the older volcanic rocks of Gravina Island.

GRAYWACKE, SI/ATE, AND CONGLOMERATE OF PRINCE OF WALES ISLAND

Lower Cretaceous rocks may be present in the southern part of 

Prince of Wales Island, where, according to the Wrights,3 there 

are Cretaceous? graywacke, slate, and conglomerate, having an aggregate thickness of perhaps about 2,000 feet, which rest conformably on the Upper Jurassic (?) lava, tuff, conglomerate, and graywacke described on page 254. These rocks were described in the 

report cited as follows, and a similar description was repeated by 

C. W. Wright 4 in a later publication.

2 Stanton, T. W., cited by Chapin, Theodore, op. cit., p. 98.

3 Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pp. 34, 58, pi. 1, 1908.

* Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula. 

Alaska: U. S. Geol. Survey Prof. Paper 87, pp. 19-20, pi. 1. 1915.
CRETACEOUS, UPPER YUKON REGION 383

The graywackes overlying the andesites are compact and indurated, but do 

not show a schistose development (see Bull. 347, PL VII, B) ; the numerous 

slate fragments prominent in the rocks of the " Sitka series " to the north are 

absent, and beds of slate are less common. Pebbles of granodiorite, quartz, 

andesite, and graywacke are plentiful in the conglomerates. These beds, as 

a whole, though tilted at steep angles and folded, have not suffered the intricate folding and metamorphism shown in the older rock beds including the 

" Sitka series." No fossil evidence was found in these beds, but from the above 

facts it is reasonable to suppose that they occupy a position in the stratigraphic 

column between Triassic and Upper Cretaceous.

UPPER YUKON REGION 

GENERAL FEATURES

The Cretaceous rocks of the upper Yukon region are known only 

in the banks of the Yukon and its tributaries between Eagle and 

Woodchopper Creek. They include marine Lower Cretaceous rocks, 

chiefly slate and quartzite, and nonmarine plant-bearing Upper Cretaceous shale, sandstone, and conglomerate. The Lower Cretaceous 

rocks are believed to rest unconformably on Triassic and Paleozoic 

formations, are probably several thousand feet thick, and carry a 

marine invertebrate fauna, including Aucella cf. A. crassicollis, 

which indicates a general correlation with the Lower Cretaceous 

Aucella-bearmg beds of southern Alaska. The Upper Cretaceous 

rocks rest unconformably on Carboniferous rocks, are at least several 

hundred feet thick, and carry a terrestrial flora that indicates a 

correlation with the Upper Cretaceous plant-bearing beds of the 

lower Yukon region and with the Dakota sandstone. The Upper 

Cretaceous rocks are believed to be overlain unconformably by Tertiary (Eocene) plant-bearing beds.

LOWER CRETACEOUS 

SLATE AND QUARTZITE

Historical review. The Lower Cretaceous rocks of the upper Yukon district were first mentioned by McConnell,5 who gives a brief 

description of the shale, sandstone, and conglomerate seen by him 

along the Yukon for 35 miles below the mouth of the " Tatonduc." 

Special mention is made of conglomerate overlying the shale 8 miles 

above Charlie Village and of fossils identified as Aucella rnosquensis 

var. concentrica collected from the beds below the conglomerate " some 

miles below the mouth of the Tatonduc." A description is also given 

of similar shale and conglomerate observed by Ogilvie overlying 

Paleozoic limestone on the Tatonduk.6

B McConnell, R. G., Report on an exploration in the Yukon and Mackenzie Basins, 

N. W. T. : Canada Geol. Survey Ann. Rept, new ser., vol. 4, pp. 21D, 137-138D, 1891. 

«Idem, p. 138D.
384 MESOZOIC STRATIGRAPHY OF ALASKA

These Lower Cretaceous rocks were included by Spurr 7 in the 

" Mission Creek series." His description of that " series " includes 

the rocks of several areas which are now known to belong in widely 

different parts of the geologic column. The rocks described under 

the heading " Napoleon and Chicken Creeks " 8 have been described 

and mapped by Prindle 9 as Tertiary clay, sandstone, lignite, shale, 

and conglomerate with fossil plants. The rocks described by Spurr 

under the heading " Below Fortymile Creek" 10 are believed to be 

chiefly if not wholly Paleozoic. The rocks described under the heading " Mission Creek and below," X1 which ought to contain the type 

section of the " Mission Creek series," include Tertiary plant-bearing 

shale, sandstone, conglomerate, and lignite beds,12 and some shale, 

sandstone, and conglomerate that are Devonian or possibly basal 

Carboniferous.13 The rocks described under the heading "Kandik 

River and vicinity " 14 are believed to be wholly Lower Cretaceous and 

are described in greater detail below.

Brief mention of the "Mission Creek series," without specific 

description of the Lower Cretaceous, AuceUa-bea,?mg members, was 

made by Brooks.15

A brief description by Collier 16 was based on field investigations 

that have not been described in complete detail.

The Lower Cretaceous rocks exposed along the Yukon were mentioned briefly by Prindle.17

A more extensive description of these rocks based on additional 

field investigations was given by Brooks and Kindle.18 The same 

statement has been quoted by Prindle.19

The eastern extension of these Lower Cretaceous rocks exposed 

along the international boundary was included by Cairnes in the

7 Spurr, J. E., Geology of the Yukon gold district, Alaska: U. S. Geol. Survey Eighteenth Ann. Kept, pt. 1, pp. 175-184, 257-258, 1897.

8 Idem, pp. 175-176.

9 Prindle, L. M., The Forty-mile quadrangle, Yukon-Tanana region, Alaska: U. S. Geol. 

Survey Bull. 375, pp. 24, 25, 26, pi. 5, 1909.

10 Spurr, J. E. ( op. cit, pp. 176-178.

11 Idem, pp. 178-180.

» Prindle, L. M., op. cit., pp. 23-24, 25-26, pi. 5.

13 Brooks, A. H., and Kindle, E. M., Paleozoic and associated rocks on the upper Yukon, 

Alaska: Geol. Soc. America Bull., vol. 19, pp. 277, 286-288, 1908.

14 Spurr, J. E., op. cit., p. 180.

16 Brooks, A. H., The coal resources of Alaska: U. S. Geol. Survey Twenty-second Ann. 

Kept, pt. 3, table opp. p. 526, pp. 530. 556, 1902.

19 Collier, A. J., The coal resources of the Yukon, Alaska: U. S. Geol. Survey Bull. 218, 

pp. 15, 16-17, 28, 32, 1903.

17 Prindle, L. M., The Yukon-Tanana region, Alaska Description of the Circle quadrangle : U. S. Geol. Survey Bull. 295, pp. 16, 17, 1906. ,

18 Brooks, A. H., and Kindle, E. M., Paleozoic and associated rocks of the upper Yukon, 

Alaska: Geol. Soc. America Bull., vol. 19, pp. 305-307, 1908.

19 Prindle, L. M., A geologic reconnaissance of the Circle quadrangle, Alaska: U. S. 

Geol. Survey Bull. 538, pp. 31-32, 3913.
CRETACEOUS, UPPER YUKON REGION 385-

" Orange group." The original description 20 of the " Orange group "' 

contains an account of the lithologic character of the rocks with a. 

statement by Stanton concerning some fossils. A brief supplemental description based on field work in 1912 has also been given 

by Cairnes.21

A later description by Cairnes 22 states that the " Orange group " 

consists of an undifferentiated assemblage of rocks ranging from 

upper Carboniferous to Lower Cretaceous.

In the latest report by Cairnes on this district 23 the use of the 

name " Orange group " was discontinued, and the Cretaceous rocks 

formerly included in the group are described under the heading 

"Mesozoic beds." The account includes a statement of the areal 

distribution of the rocks, a general description of their lithologic

character, and a discussion of age and correlation in which there are 

statements by Stanton concerning the fossils. Cairnes 24 states that 

"it seems .quite possible that Jurassic or even Triassic members may 

also be included." However, as most of the fossils obtained from 

these "Mesozoic beds" are characteristic of the Lower Cretaceous, 

as the rocks described by Cairnes bear a close resemblance to the 

Lower Cretaceous rocks and do not resemble the Triassic rocks on 

the Yukon, and as Jurassic rocks are not known anywhere in this 

region and are believed never to have been deposited in the Yukon 

Basin, the present writer concludes that "Mesozoic beds" of the 

main area described by Cairnes probably are wholly Lower Cretaceous. Some of the outlying areas may contain rocks that have 

been incorrectly correlated with the Cretaceous rocks of the main 

area.

StratigrapJiic description. The Lower Cretaceous rocks of the 

upper Yukon region lie in a belt 10 miles or more wide, extending 

along both sides of the Yukon from Coal Creek to a place about 4 

miles above Logan Creek, where it passes to the north of the river. 

The northeastern extension of this belt has been recognized along 

the Canada-Alaska boundary, where the main part of its area lies 

between latitudes 65° 22' and 66° 5' north.

The LoWer Cretaceous rocks of the area south of the Yukon were 

described by Brooks and Kindle 25 as follows:

20 Cairnes, D. D., Geology of a portion of the Yukon-Alaska boundary between Porcupine and Yukon Rivers: Canada Geol. Survey Summary Kept, for 1911, No. 1218, pp. 

27, 31-32, 1912.

21 Cairnes, D. D., Geology of a portion of the Yukon-Alaska boundary between Porcupine and Yukon Rivers: Canada Geol. Survey Summary Kept, for 1912, No. 1305, p. 11, 

1914.

22 Cairnes, D. D., Geological section along the Yukon-Alaska boundary line between 

Yukon and Porcupine Rivers : Geol. Soc. America Bull., vol. 25, pp. 201-202, 1913.

23 Cairnes, D. D., The Yukon-Alaska international boundary between Porcupine and 

Yukon, Rivers: Canada Geol. Survey Mem., 67, pp. 103-107, 1914.

24 Idem, p. 106.

28 Brooks, A. H., and Kindle, B. M., Paleozoic and associated rocks of the upper Yukon. 

Alaska: Geol. Soc. America Bull., vol. 19. p. 306, 1908.
386 MESOZOIC STRATIGRAPHY OF ALASKA

The Lower Cretaceous of the upper Yukon comprises a" series of closely 

folded rocks characterized by a large amount of silica. They include primarily 

siliceous slates, slaty sandstones, and quartzites, with . which are associated 

some argillites and pyroclastics. One heavy bed (50-75 feet thick) of massive 

tuffaceous conglomerate was observed within the Mesozoic area about 5 miles 

below Washington Creek, but may be an infolded older or younger terrane. 

The pebbles of this conglomerate, which are chiefly limestone, are well rounded, 

and some are 2 feet in diameter. The dominating rock type of the Lower 

Cretaceous is a siliceous slate or quartz ite, sometimes interbedded with a clay 

slate. These rocks are usually pyritiferous and iron-stained when weathered. 

Three miles below Washington Creek there is a series of beautifully banded 

slates and quartzites. Here the brittle quartzite is broken by a series of fractures at right angles to bedding, while the same movement has in large measure 

been taken up in the cleavage of the slate. A quartz filling, sometimes carrying pyrite, is not uncommon along these fractures. In at least one instance 

it appears to be established that quartz veins cutting these Cretaceous rockrj 

are auriferous. This conclusion is not without importance in its bearing on 

the age of the mineralization which produced the auriferous deposits of the 

Yukon.

These rocks in a general way strike easterly and northeasterly, but there are 

many local variations. They are usually closely folded, and no determination 

of thickness, which probably does not exceed a few thousand feet, could be 

made. On Washington Creek they appear to rest unconformably on the Devonian and in turn are unconformably overlaid by the Tertiary beds. Near 

Coal Creek the Aucella-bearing beds seems to underlie the upper Carboniferous 

limestone, which has apparently been thrust over them.

The thickness of these rocks is apparently several thousand feet, 

but the obliteration of the bedding in many places by slaty cleavage 

and the presence of crumpled zones in which the detailed structure 

is unsolved and of faults on which the amount of movement is not 

determined detract from the value of any estimates of thickness.

The Lower Cretaceous rocks exposed along the boundary, according to Cairnes,20 consist mainly of shales, sandstones, greywackes, 

conglomerates, slates, and quartzites which have an aggregate thickness of at least 4,000 feet." They " overlie the Upper Carboniferous 

or Permian sediments " and " are the most recent consolidated sediments along the portion of the one hundred and forty-first meridian 

here under consideration."

Age and correlation. The known fossils of the Lower Cretaceous 

rocks of the upper Yukon region include a few small lots of marine 

invertebrates and one plant and are represented in the following 

table. Concerning lots 18, 19, and 21, Stanton 27 said:

The reference of these three lots of fossils provisionally to the Lower Cretaceous is made with the same reservation that has so often been expressed 

when similar collections containing Aucello, and only a few associated forms have 

been submitted from this and other areas in Alaska that is, while the Aucella

 Cairnes, D. D., The Yukon-Alaska international boundary between Porcupine and 

Yukon Rivers : Canada Geol. Survey Mem. 67, pp. 103-107, 1914.

27 Stanton, T. W., cited by Brooks, A. H., and Kindle, E. M., Paleozoic and associated 

rocks of the upper Yukon, Alaska: Geol. Soc. America Bull., vol. 19, p. 307, 1908.
CRETACEOUS, UPPEB YUKON EEGION" 387

itself is indicative of probable Cretaceous age, closely related species are known 

in the Jurassic, and it may be that all of the Aucella, beds of Alaska are 

Jurassic.

Fossils from the Lower Cretaceous rocks of the upper Yukon region n

Pinna.... .............. ...... ................... ......

69 18

y

V

19 21

X

1509A

X

1509B

X

« Identified by T. W. Stanton except as Indicated. 

* Identified by F. H. Knowlton.

69. Washington Creek 6 miles above mouth. A. .T. Collier, 1902.

18. South bank of the Yukon 400 yards below Glen Creek. E. M. Kindle, 

1906.

19. North bank of the Yukon 6 miles above Charlie Village. E. M. Kindle, 

1906.

21. South bank of the Yukon iy2 miles below Sam Creek. E. M. Kindle, 

1906.

1509A. Yukon River 8% miles above Washington Creek. Eliot Blackwelder, 

1915. '

1509B. South bank of the Yukon half a mile above mouth of Charlie Creek. 

Eliot Blackwelder, 1915.

UPPER CRETACEOUS

SHALE, SANDSTONE, AN'D CONGLOMERATE NEAK SEVENTYMILE KIVEB

Historical review. The Upper Cretaceous rocks of the upper Yukon region were included by Spurr 28 as part of the rocks which he 

described as the Kenai "series." The part of these beds which is 

now known to be Upper Cretaceous comprises those " about 25 miles 

below Mission Creek." Spurr's description of the rocks at this locality is very brief, consisting merety of a statement that there is conglomerate associated with shale and sandstone containing abundant 

leaf impressions. A list of species determined by F. H. Knowlton 

is given, also a discussion by Knowlton 29 of the plants from this 

and other localities, part of which are Tertiary.

These rocks were included by Brooks 30 in the "Tertiary rocks" 

without specific mention of the beds now known to be Upper Cretaceous, other than a citation of Spurr's description of the basal 

member near the mouth of Mission Creek.

28 Spurr, J. E., Geology of the Yukon gold district, Alaska : U. S. Geol. Survey Eighteenth Ann. Kept, pt. 3, pp. 185, 192, 1898.

29 Knowlton, F. H., Report on a collection of fossil plants from the Yukon River, 

Alaska: U. S. Geol. Survey Eighteenth Ann. Rept., pt. 3, pp. 194-196, 1898.

30 Brooks, A. H., The coal resources of Alaska: U. S. Geol. Survey Twenty-second Ann. 

Kept., pt 3, p. 536, 1902.
388 ' MESOZOIO STRATIGRAPHY OF ALASKA

The Upper Cretaceous locality at the mouth of Seventymile River 

was visited in 1902 by Collier, who collected plants now known to be 

Upper Cretaceous. The rocks at this locality were not then recognized as Cretaceous. and were included by Collier in the general 

description 31 of the Tertiary rocks of the district, with an additional 

statement 32 that " a great thickness of Kenai sandstone, not known 

to be coal bearing, is exposed at the mouth of Seventymile River."

The description of the section on the upper Yukon by Brooks and: 

Kindle contains no specific mention of any < known Upper Cretaceous rocks, but the account of the Tertiary rocks 33 contains a 

suggestion that the rocks described as Tertiary may include some 

Cretaceous beds. It is also stated 34 that " in some instances the 

rocks are well indurated, being made up of hard conglomerate, 

sandstone, and sandy and clayey shales or slates, while in others 

the sandstones are almost unconsolidated and the argillites very little 

indurated." This statement suggests to the writer a possible unrecognized unconformity between more indurated Upper Cretaceous 

and less indurated Tertiary rocks. The writer also believes that 

some of the rocks referred to the Nation River formation by Brooks 

and Kindle, which are said 3 * to resemble the more indurated Tertiary conglomerate, sandstone, and shale, may possibly be Upper 

Cretaceous.

The notes by Prindle 35 on the Tertiary rocks of the Fortymile 

quadrangle, in which the Upper Cretaceous locality near the mouth 

of Seventymile River lies, contain no mention of the rocks at the 

Upper Cretaceous locality but describe the other more indurated 

supposed Tertiary rocks of the quadrangle, part of which, as suggested above, may possibly be Upper Cretaceous. The same belt 

of Tertiary rocks extends westward into the Circle quadrangle and 

has been described by Prindle.36 The rocks of this part of the belt 

may perhaps also contain some undifferentiated Upper Cretaceous 

members, but there is no special reason to suspect their presence, 

except that some of the beds are described as more thoroughly indurated than the others. The same publication contains a description 37 of a few areas of conglomerate and arkosic sandstone near the 

main divide of Charley, Goodpaster, and Salcha rivers, which

31 Collier, A. J., The coal resources of the Yukon, Alaska: U. S. Geol. Survey Bull. 218, 

pp. 15-17, 1903.

82 Idem, p. 28.

33 Brooks, A. H., and Kindle, E. M., Paleozoic and associated rocks of the upper Yukon, 

Alaska: Geol. Soc. America Bull., vol. 19, pp. 307-309, 1908.

M Idem, p. 308.

35 Prindle, L. M., The Forty-mile quadrangle, yukon-Tanana region, Alaska: TJ. S. Geol. 

Survey Bull. 375, pp. 23-26, 1909.

38 Prindle, L. M., A geologic reconnaissance of the Circle quadrangle,, Alaska: U. S. 

Geol. Survey Bull. 538, pp. 33-34, 1913.

87 Idem, p. 32.
CRETACEOUS, UPPER YUKON REGION 389

Prindle believes to be possibly Upper Cretaceous. No conclusive 

evidence of the age of these rocks was obtained. They are not 

known to contain any fossils except " poorly preserved plant remains," which were apparently not collected.

Stratigraphic description. The Upper Cretaceous rocks of the 

upper Yukon region are exposed in the cliffs on the south bank of 

the Yukon just below the mouth of Seventymile River. These 

cliffs are composed of shale, sandstone, and conglomerate striking 

northwest and dipping about 40° S. The rocks consist for the most 

part of an alternation of thin beds of sandy shale and sandstone, 

but there are some beds of conglomerate 10 feet or more thick. The 

shale contains abundant fossil plants, of which collections were 

made at the mouth of the small creek iy2 miles below the mouth 

of Seventymile River and at several neighboring localities on the 

bank "of the Yukon. At the north end of the cliffs there are exposures of supposed Carboniferous limestone, which appears to 

underlie the Cretaceous rocks unconformably. At the south end 

of the cliffs there are also exposures of supposed Carboniferous 

limestone having an attitude discordant with that of the Cretaceous 

rocks, the limestone striking N. 25° E. and dipping 25° SE. There 

is evidently either a fault or an overturning of the rocks at this 

place probably a fault.

A belt of Tertiary clay, sandstone,, shale, and conglomerate that 

are also plant-bearing lies in the valley of Seventymile River not 

far west of these Cretaceous rocks and possibly adjoins them, but 

the intervening area has not been examined, and the relation of 

the Cretaceous to the Tertiary rocks is not known. The Tertiary 

rocks of Seventymile River have been described by Brooks and 

Kindle 39 and also by Prindle 40 as including beds that differ very 

much in degree of induration. Possibly the more indurated of the 

supposed Tertiary rocks of Seventymile River may be the western 

extension of these Upper Cretaceous beds.

Age and coi^relation. The Upper Cretaceous rocks near Seventymile River have yielded no fossils other than the plants which are 

described and discussed by Hollick in a monograph now in preparation and are listed in the following table. These plants indicate a 

correlation with the Kaltag formation, which constitutes the upper 

coal-bearing division of the Upper Cretaceous section on the lower 

Yukon:

38 Brooks, A. H., and Kindle, E. M., Paleozoic and associated rocks of the upper Yukon, 

Alaska: Geol. Soc. America Bull., vol. 19, p. 310, 190'S.

*° Prindle, L. M., The Fortymile quadrangle, Yukon-Tanana region, Alaska: U. S. Geol. 

Survey Bull. 375, p. 25, 1909.
390 MESOZOIC STRATIGRAPHY OF ALASKA

Upper Cretaceous fossils from upper Yukon region a

flinlrcr/\ QT\

1555

X

X

X

2973

v

X

3243

X

X

X

X

X

X

X

X

6815

X

X

X

X

7407

X

X

X

X

7408

X

X

X

X

0 Identified by Arthur Hollick.

1555. Yukon River 25 miles below Mission Creek. .T. E. Spurr, 1896.

2973 (57). Left (south) bank of the Yukon 2 miles below mouth of Seventymile River. A. J. Collier, 1902.

3243 (3 AH 4). Left (south) bank of Yukon River just below Seventymile 

River. Arthur Hollick, 1903.

6815. South bank of Yukon River at mouth of draw 1% miles below Seventymile River. G. C. Martin, 1914.

7407. Same locality as 6815. G. C. Martin, 1919.

7408. South bank of Yukon River half a mile below next gulch below 

Seventymile River. G. C. Martin, 1919.

RAMPART-TANANA DISTRICT 

GENERAL FEATURES

The Cretaceous rocks of the Kampart-Tanana district include

marine Lower Cretaceous quartzite and slate and marine Upper 

Cretaceous sandy shale. The Lower Cretaceous rocks overlie Silurian and Devonian metamorphic rocks, are of undetermined thickness, and have yielded only a few fragmentary fossils, chiefly 

Aucella. The Upper Cretaceous rocks probably rest unconformably 

on the Lower Cretaceous slate and quartzite, consist of black, rather 

massive carbonaceous sandy shale, probably 200 or 300 feet thick, 

and contain marine mollusks and poorly preserved fossil plants. 

Tertiary rocks, although present elsewhere in the district, are absent 

at this locality, and the only beds known to overlie the Upper Cretaceous rocks are recent unconsolidated deposits.

LOWER CRETACEOUS 

QUARTZITE AND SLATE NEAR QUAIL CKEEK

Historical review. The Lower Cretaceous quartzite and. slate of 

the Rampart-Tananadistrict were described byEakin 41 as "slates,

"Eakin, H. M., A geologic reconnaissance of a part of the Rampart quadrangle, 

Alaska : U. S. Geol. Survey Bull. 535, pp. 20-21, 1913.
CRETACEOUS, RAMPART-TAN ANA DISTRICT 391

quartzites, and schists (Cretaceous and older)." The description 

includes a general discussion of the lithologic character of the rocks 

and a statement by T. W. Stanton concerning some fossils which he 

regards as probably Lower Cretaceous or uppermost Jurassic. 

Eakin says that the fossils were obtained from one of the quartzites 

which he believes to be among the lower members of the assemblage. 

The fossils were obtained near the headwaters of the north fork of 

Quail Creek in an area mapped by Prindle 42 as the Tonzona group, 

very near localities where Devonian and Silurian fossils have been 

collected. It had been previously suggested by Brooks 43 that this 

quartzite is possibly Lower Cretaceous. These rocks are possibly 

the source of some fucoids which Brooks 44 listed with Tertiary 

fossil plants but which he obtained near the Cretaceous localities in 

an area that he mapped as undifferentiated Paleozoic rocks.45

The Lower Cretaceous may also be represented by some slate, 

sandstone, and conglomerate lying between Baker Creek and Tolovana Eiver, which were described as the "Nilkoka beds" by Brooks,40 

who originally referred them to the Paleozoic but afterward 47 suggested that "it now seems more likely that they are Cretaceous." 

Brooks still later 48 correlated these rocks with the Tonzona group 

of the Alaska Range, which is considered Devonian or Silurian. 

These rocks were described by Eakin 49 under the heading " slates, 

sandstones, and conglomerates" and considered probably early 

Mesozoic.

Stratigraphic description. The Lower Cretaceous rocks of the 

Rampart-Tanana district have not been described in detail. Lower 

Cretaceous fossils were obtained from a bed of quartzite which was 

regarded by Eakin as among the lowest members of an assemblage 

of slate, quartzite, and schist which he considered largely if not entirely of Mesozoic age. On the other hand, Prindle, on the evidence 

of some fossils from other members of what seems to be the same 

assemblage of rocks, considered them probably Devonian. The writer 

believes that the quartzite and slate that contain the Lower Cretaceous fossils are at the top of the slate, quartzite, and schist, which 

are probably chiefly Paleozoic.

42 Prindle, L. M., A geologic reconnaissance of the Fairbanks quadrangle, Alaska: U. S. 

Geol. Survey Bull. 525, pp. 44-45, pi. 8, 1913.

43 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, p. 93, 1911.

"Idem, p. 101.

«Idem, pi. 9.

40 Brooks, A. H., A reconnaissance in the Tanana and White River basins, Alaska, in 

1898 : U. S. Geol. Survey Twentieth Ann. Kept., pt. 7, p. 472, 1900.

47 Brooks, A. H., The coal resources of Alaska: U. S. Geol. Survey Twenty-second Ann. 

Kept., pt. 3, p. 530, 1902.

48 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

70, p. 75, 1911.

49 Eakin, H. M., op. cit, p. 19.
392 MESOZOIO STBAT1GEAPHY OF ALASKA

Age and correlation. The fossils that have been obtained from 

the Lower Cretaceous quartzite near Quail Creek are listed in the 

table below. Concerning the fossils of lot 7241 Stanton 50 said:

The collection consists of quartzite filled with fragmentary imprints of pelecypods, which were apparently broken up before they were embedded. There 

is only a single specimen in the lot which shows fairly well the form of the 

shell, and this seems to be referable to the. genus Aucella, though it is an 

internal cast of the left valve which does not show the distinctive features of 

the genus. If the provisional identification of this specimen is correct the 

horizon is either Lower Cretaceous or uppermost Jurassic.

Stanton also made the following statement 50 concerning the fossils 

of lot 11390:

The specimens of Aucella are somewhat better than those previously obtained! 

from the same beds in this neighborhood, but they are all immature. They 

suggest Lower Cretaceous rather than Upper Jurassic.

Lower Cretaceous fossils from quartzite near Quail Creek a

27 7241

b

b

18A01 11390

b

b

b

11391

b

 a, Identified by F. H. Knowlton: b, identified by T. W. Stanton.

27. Southeast of camp of August 12, on ridge about 2 miles east of Little 

Minook Creek. A. H. Brooks, 1902.

7241 (11 AE 5.) "Little Minook-Quail Creek divide," half a mile below 

trail crossing. H. M. Eakin, 1911.

18 AO 1. Peak east of Hunter Creek, about 3 miles southeast of the mouth 

of Fortyseven Pup. R. M. Overbeck, 1918.

11390 (22 AMt 113). 3.7 miles S. 78° W. of mouth of Quail Creek. J. B. 

Mertie, 1922.

11391 (22 AMt 85). 5.37 miles N. 79° W. of mouth of Quail Creek. J. B. 

Mertie, 1922.

UPPER CRETACEOUS

SHALE NEAR WOLVERINE MOUNTAIN

Historical review. The Cretaceous rocks in the Rampart district 

were first recognized by Prindle,51 who described the sandstone and 

shale of Wolverine and Lynx mountains. The description states that 

the rocks are " black, rather massive, impure sandstones and shales,'* 

contain " fragments of dicoyledonous leaves and part of an indeterminable bivalve," " rest on the upturned edges of the older Silurian 

or Devonian rocks and have themselves undergone considerable deformation," " resemble the Upper Cretaceous rocks which occur lower 

down the Yukon," and " are entirely different from the Kenai rocks 

near Rampart and are referred provisionally to the Cretaceous."

60 Unpublished notes.

a Prindle, L. M., Geography and geology [of Rampart gold placer region, Alaska] ; 

U. S. Geol. Survey Bull. 280, pp. 17, 22, 1906.
CRETACEOUS, RAMPART-TAN AN A DISTRICT 393

A subsequent description of these rocks, based on additional field 

studies by Prindle,53 contains a brief statement of the lithologic 

character of the rocks accompanied by lists and a discussion by Stanton of marine invertebrate fos.sils from Wolverine Mountain and 

Quail Creek. A brief reference to the occurrence of these rocks was 

made by Brooks and Kindle.54 A later description by Prindle 55 

contains no mention of the rocks on Lynx Mountain, which had previously been erroneously correlated on lithologic grounds with the 

rocks on Wolverine Mountain. A brief description of these rocks, 

based on the. observations of Prindle, has been given by Brooks.56 

and a brief mention of them was made by Eakin,57 who suggested 

that they may extend southwestward from Wolverine Mountain into 

the area of the Rampart quadrangle.

Stratigraphic description. The Upper Cretaceous rocks of Wolverine. Mountain include a basal conglomerate about 10 feet thick, 

containing pebbles of quartzite and black slate, overlain by several 

Jhundred feet of rather massive black sandy shale, fine-grained black 

shale, and sandstone. The underlying rocks are quartzite and shale 

that are regarded by Prindle as Paleozoic and by Eakin as probably 

mainly Lower Cretaceous. These divergent opinions are based on 

the presence, in near-by localities, of both Lower Cretaceous and 

Devonian or Silurian fossils. There is no question that the rocks 

surrounding Wolverine Mountain include both Lower Cretaceous 

and Devonian or Silurian beds. No conclusive evidence is at hand 

as to whether the Lower Cretaceous or the Paleozoic beds immediately underlie the Upper Cretaceous rocks. The only rocks that are 

younger than these Upper Cretaceous beds and are in contact with 

them are igneous intrusives. Tertiary strata are present in the district, but they do not overlie the Upper Cretaceous beds.

Age and correlation,. The fauna and flora of the Upper Cretaceous rocks of Wolverine Mountain, represented in the following 

table, include some marine invertebrates and a few poorly preserved 

plants. Fragments of dicotyledonous leaves and a part of an indeterminable bivalve Avere collected by Prindle from these rocks in 

1904. Partly on that basis and partly on their lithologic character he 

assigned them to the Cretaceous. In 1907 Prindle obtained additional fossils, including both marine invertebrates and plants. No 

report on these fossil plants or on those collected in 1904 has been

53 Prindle, L. M., The Fairbanks and Rampart quadrangles, Yukon-Tanana region, 

.Alaska: U. S. Geol. Survey. Bull. 337, pp. 16, 23-24, 1908.

54 Brooks, A. H., and Kindle, E. M., Paleozoic and associated rocks of the upper Yukon, 

.Alaska: Geol. Soc. America Bull., vol. 19, p. 307, 1908.

55 Prindle, L. M., A geologic reconnaissance of the Fairbanks quadrangle, Alaska: U. S. 

'Geol. Survey Bull. 525, pp. 33, 34, 47-48, 1913.

C8 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof. Paper 

TO, pp. 51, 55, 93, 130, 1911.

67 Eakin, H. M., A geologic reconnaissance of part of the Rampart quadrangle, Alaska : 

 'U. S. Geol. Survey Bull. 535, pp. 21, 24, 1913.
394 MESOZOIC STEATIGRAPHY OF ALASKA

published. The following statement concerning the marine invertebrates collected by Prindle in 1907 was furnished by Stanton: 5 *

While the fossils are fairly well preserved, they have been considerably distorted, so that it is not practicable to make specific determination. The betterpreserved forms appear to be undescribed. The following list will show the 

forms recognized in each lot.

These fossils evidently all belong to practically a single horizon, which is 

confidently referred to the Upper Cretaceous. * * * The species of Inoceramus is very likely one that has been previously found on the Yukon, but 

the specimens in the present collection are too imperfect to serve as the basis 

for a positive identification. The most important forms are ammonites, which 

make up the bulk of the collection and which I have referred, in some cases 

doubtfully, to the genus Pachydisc'iis. These are unquestionably Upper Cretaceous types.

The presence of Sequoia reichenbachi and Inoceramus cf. /. 

Idbiatus indicates that the Upper Cretaceous rocks of Wolverine 

Mountain are to be correlated with the Nulato formation of the 

lower Yukon.

Upper Cretaceous fossils from Rampart-21 anana district a

Fern............... ...............................

£

<j

b

h

AH 

<!

h

t^

(N

' fr,

 < 

t^S"

b

b

b

g

I

t^r

J2

tc? r~

"5

« a, Identified by Arthur Hollick; b, identified by F. H. Knowlton; c, identified by T. W. Stanton.

4AP306. Southeast spur of Wolverine Mountain, 2.92 miles S. 58° W. of 

mouth of Quail Creek. L. M. Prindle, 1904.

7AP263. Near Wolverine Mountain (?). L. M. Prindle, 1907.

4278 (7AP271). Southeast spur of Wolverine Mountain, 2.6 miles S. 53° W. 

of mouth of Quail Creek. L. M. Prindle, 1907.

 (7AP271). Same locality as 4278. L. M. Prindle, 1907.

4279 (7AP278). Ridge on left side of south fork of Quail Creek. L. M.. 

Prindle, 1907.

4280 (7AP279). Right side of south fork of Quail Creek. L. M. Prindle,. 

1907.

68 Stanton, T. W., cited by Prindle, L. M., The Fairbanks and Rampart quadrangles,. 

Yukon-Tanana region, Alaska: U. S. Geol. Survey Bull. 337, p. 24. 1908.
CRETACEOUS, LOWER YUKON REGION 395

8900. South fork of Quail Creek about 1 mile above main forks. G. C. 

Martin, 1914.

7577 (22AMtl05b). About 3y8 miles S. 69° W. of mouth of Quail Creek. 

J..B. Mertie, 1922.

11392 (22AMtl05a). Same locality as 7577. J. B. Mertie, 1922.

7576 (22AMt79). About 7% miles N. 44° E. of Eureka. J. B. Mertie, 1922.

LOWER YUKON REGION 

GENERAL FEATURES

The Cretaceous rocks of the lower Yukon region are exposed at 

many localities in the north bank of the Yukon between Melozi and 

Andreafski. They consist of probably several thousand feet of 

Upper Cretaceous shale, sandstone, and conglomerate, some of which 

are marine and some of which are of brackish or fresh water origin 

and include coal-bearing members. The stratigraphic sequence is 

believed to be as follows:

Generalized section of Upper Cretaceous rocks on lower Yukon River 

Feet

Kaltag formation: Coal - bearing rocks consisting of 

fresh-water sandstone, shale, and coal beds with 

possibly some thin marine members. Contains fossil 

plants, fresh-water invertebrates, and perhaps a few 

marine invertebrates___-_ ________ _ _ 800+

Nulato formation: Marine sandstone and shale. Contains marine invertebrates and a few plants______ 3, 000?

Melozi formation: Fresh-water shale and sandstone. 

Contains fossil plants and fresh-water invertebrates__ 1,000+

Ungalik conglomerate: Conglomerate, sandstone, and 

sandy shale. Contains worm tubes, trails, and vegetable detritus.__________________________ 3,000

In the northern part of the region the Upper Cretaceous rocks 

adjoin and are believed to rest directly upon early Paleozoic metamorphic rocks. In the southern part of the region they overlie 

upper Carboniferous greenstone and associated sediments. The beds 

that have been observed to overlie the Upper Cretaceous rocks are 

unconsolidated Quaternary deposits, but supposed Tertiary volcanic 

rocks occur near some of the Upper Cretaceous rocks and are believed 

to be the next succeeding formation.

UPPER CRETACEOUS

Historical review^. The first mention of the rocks of the lower 

Yukon region now referred to the Upper Cretaceous is contained in 

a short article by Dall,59 in which there are statements of the kinds 

of rock exposed in the river bank, with mention of the presence of 

fossil mollusks and vegetable remains. In a later article 60 Dall

59 ball, W. H., Explorations in Russian America: Am. Jour. Sci., 2d ser., vol. 45, pp. 

9ek99, 1868. . .

65 Dall, W. H.. Note on Alaska Tertiary deposits : Am. Jour. Sci., 3d ser., vol. 24, pp. 

67-68, 1882.
396 MESOZOIC STRATIGRAPHY OF ALASKA

states that the brown sandstone with marine fossils at Nulato and 

the underlying leaf-bearing shale are Miocene. A brief description 

of the rocks exposed in the bank of the Yukon below the mouth of 

Melozi River has been given by Russell. 61 In a subsequent, more 

extensive discussion of these rocks Dall and Harris 62 described them 

as consisting of the Nulato sandstone and the Kenai " group." The 

Nulato sandstone was described as a brownish marine sandstone, 

which extends along the river from Kaltag to Koyukuk Mountain 

and which lies conformably on the bluish sandstone of the Kenai 

"group." This description was also repeated by Dall 63 with little 

change.

Additional observations on the Upper Cretaceous rocks of the 

lower Yukon region were made by Spurr in 1896. Spurr described 

these rocks as the Kenai "series" 04 and the Nulato sandstones,65 

both of which he referred to the Tertiary. The description contains 

a detailed record of local observations by Spurr and is accompanied 

by a statement by Knowlton 66 oh some fossil plants.

The exposures in the bank of the Yukon between Nulato and the 

mouth of the Koyukuk were observed by Schrader in 1899, and 

marine mollusks, which were determined by Stanton as Upper Cretaceous, were collected. Schrader's report makes mere mention 67 of 

the |act that Upper Cretaceous fossils were recognized. The Nulato 

sandstone, from which these fossils were obtained, and some of the 

contained coal beds are briefly mentioned,68 but no reference is made 

to the fact that the fossils show the Nulato sandstone to be Upper 

Cretaceous and not Miocene. In a later report Schrader gave a 

list of these fossils,69 without a description of their precise occurrence, under the heading " Upper Cretaceous on the Koyukuk." He 

subsequently gave the list again,70 with a correct statement of their 

occurrence, in a discussion of the correlation of the Nanushuk 

" series " of the Arctic coast. Further reference to the Upper Cretaceous fossils collected by Schrader near the mouth of the Koyukuk

61 Russell, I. C., Notes on the surface geology of Alaska: Geol. Soc. America Bull., vol. 

1, p. 108, 1890.

02 Dall, W. H., and Harris, G. D., Correlation papers Neocene: U. S. Geol. Survey 

Bull. 84, pp. 233, 246-248, 253-254, 258, 1892.

63 Dall, W. H., Report on coal and lignite of Alaska: U. S. Geol. Survey Seventeenth 

Ann. Rept., pt. 1, pp. 817-818, 838, 844-845, 849, 860, 862, 1896.

64 Spurr, J. E., Geology of the Yukon gold district, Alaska: U. S. Geol. Survey Eighteenth Ann. Rept, pt. 3, pp. 189-191, 193, 194, 1898.

05 Idem, p. 196.

66 Knowlton, F. H., Report on a collection of fossil plants from the Yukon River: Idem, 

pp. 194-196.

67 Schrader, F. C., Preliminary report on a reconnaissancfe along the Chandalar and 

Koyukuk Rivers, Alaska, in 1899: U.. S. Geol. Survey Twenty-first Ann, Rept., pt. 2, p. 

477, 1900.

68 Idem, pp. 478, 485-486.

68 Schrader, F. C., Geological section of the Rocky Mountains in northern Alaska: 

Geol. Soc. America Bull., vol. 13, p. 248, 1902.

70 Schrader, F. C., A reconnaissance in northern Alaska: U. S. Geol. Survey Prof. Paper 

20, p. 81, 1904.
CRETACEOUS, LOWER YUKON REGION 397

was made by Brooks,71 who gave a list of the fossils as determined 

by Stanton, and stated that the Nulato sandstone is "closely associated with Upper Cretaceous beds" and that "the horizon of the 

coals in the vicinity of Nulato has not been definitely determined."

The Upper Cretaceous coal-bearing rocks of the Yukon were 

studied in considerable detail by Collier in 1902. Collier collected 

fossils, including plants" and marine and fresh or brackish water 

invertebrates, at many localities. The marine invertebrates and some 

of the plants were at once recognized as Upper Cretaceous. Some 

of the plants were for a time regarded as Tertiary and others as 

possibly Lower Cretaceous, but they are now all regarded as Upper 

Cretaceous. The fresh or brackish water fossils collected by Collier 

are not distinctive, but they too are doubtless Upper Cretaceous, as 

they occur interbedded with the other forms.

In a preliminary report 72 on his investigations, dealing chiefly with 

the occurrence and character of the coal beds, Collier states that the 

coal-bearing beds of the lower Yukon consist " of sandstones, shales, 

and conglomerates, which probably form an uninterrupted sedimentary series, ranging in age from the Middle Cretaceous to the upper 

Eocene, and hence include both the Nulato and the Kenai series." 

In a later report these rocks are described by Collier 73 as including 

three divisions fresh-water cycad-bearing beds near Nulato, which 

are "probably assignable to the Lower Cretaceous"; Upper Cretaceous marine and fresh-water (coal-bearing) sandstone, conglomerate, and shale with "a marine invertebrate fauna of Upper Cretaceous age " and fossil plants " assigned by Knowlton to the Upper 

Cretaceous "; and a succeeding horizon, " called the Kenai series," 

of upper Eocene age, with abundant plant remains, extensively 

developed near Nulato, where " its relation to the Upper Cretaceous 

seems to be one of conformity." In this report Collier also gave 

detailed descriptions 74 of the strata exposed at and near the known 

coal beds.

As the result of a preliminary study of the fossil plants collected 

by Collier and of additional collections made by Hollick in 1903, 

Knowlton 75 stated that the fossil plants obtained below Eampart 

"indicate that the age is either undoubted Cretaceous or doubtful 

Tertiary. The Cretaceous plants include cycads of several genera, 

conifers, and many dicotyledons, the combination resembling mostly 

the Middle and Upper Cretaceous flora of Bohemia." 'A summary

71 Brooks, A. H., The coal resources of Alaska: U. S. Geol. Survey Twenty-second Ann. 

Kept., pt. 3; pp. 529, 535, 555-556, 1902.

73 Collier, A. J., Coal resources of the Yukon Basin, Alaska: U. S. Geol. Survey Bull. 

213, 1903, pp. 276-283.

78 Collier, A. J., The coal resources of the Yukon, Alaska: U. S. Geol. Survey Bull. 218, 

pp. 15, 17. 1903.

w ldem, pp. 19-20, 46-58, 65.

76 Knowlton, F. H., Fossil floras of the Yukon : Science, new ser., vol. 19, pp. 733-734, 

1904.
398 MESOZOIC STRATIGRAPHY OF ALASKA

of the results of the field investigations of Collier and Hollick and 

of the studies of their collections by Stanton and Knowlton has 

been given by Brooks. 76

Additional field studies and collections of fossils were made by 

W. W. Atwood and H. M. Eakin in 1907, but no complete report 

on the work has been published, although some of the results have 

been used by the writers cited below, notably by Eakin and by Smith 

and Eakin, as well as by the present writer in this volume.

As a result of his earlier laboratory studies of all the fossil plants 

collected from the Cretaceous rocks of this region, Hollick 77 discussed briefly the broa.der aspects of the floras, without local details, and also made a general preliminary statement 78 dealing 

chiefly with age and correlation of the flora. He also referred to 

the Cretaceous plants in a discussion of the Tertiary flora of 

Alaska. 79

A geologic reconnaissance from Nulato to the head of Norton 

Bay was made by P. S. Smith and H. M. Eakin in 1909. Their 

report contains much information concerning the Upper Cretaceous 

rocks,80 not only of the area between Yukon River and the head of 

Norton Bay, which was the special field of the investigation, but of 

the exposures along the Yukon, especially between Nelozi and 

Kaltag. In the description of the latter area the observations of 

previous investigations were largely used. The Cretaceous rocks 

described by Smith and Eakin are divided into two named units 

" a basal conglomerate called * * . * the Ungalik conglomerate 

and an overlying group of sandstones and shales called the Shaktolik group. The Shaktolik group is separated into two divisions, 

the lower, distinguished by a preponderance of sandstones over 

shale, and the upper, in which shales are in excess."

Brief mention of the Cretaceous rocks exposed along the Yukon 

between Melozi and Nulato was made by Eakin,81 who derived his 

information from his own observations in 1907 but gave no details.

In 1913 Eakin made a geologic reconnaissance of the region between Yukon and Koyukuk Rivers. The account of this investigation contains a rather extensive general description of the Cretaceous

70 Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 

45, pp. 236, 241-242, 1906.

77 Hollick, Arthur, Discussion of the Cretaceous and Tertiary floras of Alaska: Washington Acad. Sci. Jour., vol. 1, p. 142, 1911.

78 Hollick, Arthur, Preliminary correlation of the Cretaceous and Tertiary floras of 

Alaska: Geol. Soc. America Bull., vol. 24, p. 116, 1913.

78 Hollick, Arthur, Results of a preliminary study of the so-called Kenai flora of 

Alaska: Am. Jour. Sci., 4th ser., vol. 31, pp. 327-330, 1911.

80 Smith, P. S., and Eakin, H. M., A geologic reconnaissance in southeastern Seward 

Peninsula and the Norton Bay-Nulato region, Alaska: U. S. Geol. Survey Bull. 449, pp. 

54-60, 1911. . .

81 Eakin, H. M., The Iditarod-Ruby region, Alaska: U. S. Geol. Survey Bull. 578, pp. 

23-24, 1914. . .
CRETACEOUS, LOWER YUKON REGION 399

rocks,82 which is based not only on Eakin's field studies in 1913, but 

also, so far as the area lying along the Yukon is concerned, on previous investigations, including his own observations in 190T. Reports by T. W. Stanton and F. H. Knowlton on fossils collected by 

Atwood and Eakin in 1907 between Melozi and the mouth of the 

IKoyukuk are published for the first time.83 It should be noted that 

. although the section exposed along the Yukon is believed to be 

^wholly Upper Cretaceous, the northern part of the area, along the 

Koyukuk, contains some Lower Cretaceous rocks.

The Upper Cretaceous rocks west of the Yukon between Anvik and 

Andreafski have been described by Harrington. The description 8 * 

includes general accounts of the areal distribution, lithology, stratigraphy, structure, age, and correlation of the Cretaceous rocks of 

the whole region, together with detailed statements of their local 

features in each of the separate areas. The account of age and

 correlation includes statements by F. H. Knowlton and J. B. Reeside, 

jr., concerning the fossil plants and mollusks collected by Harrington 

:and a general statement by Arthur Hollick concerning the fossil 

plants from all the localities on the lower Yukon.

The Upper Cretaceous section exposed between Melozi and Anvik 

Tvas critically examined in 1921 by the writer, who also made some 

observations in the vicinity of Holy Cross in 1920. The results of 

these investigations, which have not hitherto been published, are 

incorporated in the following descriptions.

Stratigraphic description. The Upper Cretaceous rocks exposed 

along Yukon River between Melozi and Andreaf ski consist of sandstone, conglomerate, and shale having an aggregate thickness of perhaps 8,000 feet. These beds include both marine and fresh-water 

members, and the latter contain some coal beds. The complete sequence is not exposed in any one section, there being numerous 

broad areas with no exposures, so that the full succession and thickness must be inferred from incomplete evidence. It is believed, 

however, that the rocks may be subdivided into the four formations 

shown in the table on page 395.

The Ungalik conglomerate, which is the basal division of the 

Upper Cretaceous rocks of the lower Yukon region, consists of conglomerate, sandstone, and sandy shale having an aggregate thickness of probably about 3,000 feet. It was described by Smith and 

Eakin 85 from exposures on Ungalik River east of Norton Bay. The

82 Eakin, H. M,, The Yukon-Koyukuk region, Alaska: U. S. Geol. Survey Bull. 631, pp. 

41-50, 1916.

83 Idem, pp. 47-48.

84 Harrington, G. L., The Anvik-Andreafski region, Alaska: U. S. Geol. Survey Bull.

 683, pp. 22-23, 26-35, 51, 1918.

85 Smith, P. S., and Eakin, H. M., A geologic reconnaissance in southeastern Seward 

Peninsula and the Norton Bay-Nulato region, Alaska: U. S. Geol. Survey Bull. 449, pp. 

55-57, 1911.
400 MESOZOIO STRATIGRAPHY OF ALASKA

only fossils found in it are undetermined marine pelecypods, worm 

tubes, trails, and vegetable detritus.

The Melozi formation, here described for the first time from 

exposures on the north bank of the Yukon from 8 to 20 miles below 

Melozi telegraph station, overlies the Ungalik conglomerate with 

apparent conformity. It consists of fresh-water shale and sandstone 

at least 1,000 and possibly several thousand feet thick. It contains 

fossil plants and fresh-water invertebrates.

The Nulato formation, which overlies the Melozi formation with 

apparent conformity, consists of marine sandstone and shale probably about 3,000 feet thick. It is typically exposed in the northwestbank of the Yukon for 2 to 10 miles above Nulato. It includes therocks which Dall 86 described as the Nulato sandstone. The Nulatoformation contains marine invertebrates and a few fossil plants.

The Kaltag formation, here described for the first time from exposures on the northwest bank of the Yukon between Kaltag and theWilliams mine, consists of coal-bearing rocks, including fresh-water 

sandstone, shale, and coal beds, with possibly some thin marine members. It overlies the Nulato formation with apparent conformity 

and is at least 800 feet thick. It contains fossil plants, fresh-water 

invertebrates, and perhaps a feAv marine invertebrates.

The most complete section of the Upper Cretaceous rocks of the 

lower Yukon is in the cliffs on the north bank of the river between 

Melozi and Louden. The section recorded on page 395 represents 

the sequence observed in these exposures, which are practically continuous, although the cliffs are masked in places by landslides and 

talus slopes and cut by faults of undetermined throw. Below Louden the exposures are less continuous, being interrupted by several 

broad concealed intervals, The several sections below Louden havebeen correlated with one another and with the more complete section between Melozi and Louden, on the basis of similarity in lithology and sequence. Descriptions of the exposures at several places 

and the reasons for the correlations are given below.

A fairly continuous section of Upper Cretaceous rocks is exposed 

in the north bank of the Yukon between Melozi River and Louden. 

The exposures begin at the western edge of the delta of Melozi 

River about 4 miles above Melozi telegraph station, but the Upper 

Cretaceous rocks extend about 6 miles farther east, where they rest, 

upon Paleozoic metamorphic rocks. The base of the Upper Cretaceous rocks is not exposed in the river banks, but Eakin, wholias studied the rocks1 in the area north of the river, says 87 that " the

88 Dall, W. H., and Harris, G. D., Correlation papers Neocene: U. S. Geol. Survey 

Bull. 84, pp. 233, 246-248, 253-254, 258, 1892.

87 Eakin, H. M., The Yukon-Koyukuk region, Alaska: U. S. Geol. Survey Bull. 631, pp.. 

41-42, 1916.
CRETACEOUS, LOWER YUKON REGION 401

base of the series, where recognized, is a massive conglomerate of coarse texture" and that " the basal 

conglomerate ranges in thickness in exposed sections 

from a few feet to about 60 feet."

The rocks exposed between the western edge of the 

delta of Melzoi River and the Melzoi telegraph station include fine sandy shale overlain by conglomerate and coarse sandstone. These beds, which have 

an aggregate thickness of perhaps 2,000 feet, are 

folded as shown in Figure 10.

The rocks for about 7^2 miles below Melozi telegraph station consist of conglomerate and sandstone 

with some shale. The exposures in this interval, as 

shown in Figure 10, reveal several repetitions of the 

beds by folds and faults. These beds are probably 

2,000 or 3,000 feet thick and are believed to be a repetition of those above the telegraph station.

The rocks described above are chiefly coarse, the 

sandy beds consisting of coarse grit with many pebbles and beds of conglomerate being numerous. Shale 

beds are few, thin, and for the most part sandy. 

These rocks may be regarded as dominantly conglomeratic, even though the conglomerate may not 

actually constitute the greater part of their thickness. 

These are the rocks which Smith and Eakin 88 correlated with the Ungalik conglomerate of the Norton 

Bay district. The conglomeratic beds on the Yukon 

have yielded no fossils except lot 4781, obtained 1 

mile below Melozi, consisting of indeterminate marine 

pelecypods, and lot 2968 obtained 3 miles below 

Melozi, consisting of undetermined plants. >

The Ungalik conglomerate was described by Smith 

and Eakin 89 as a fairly coarse conglomerate, several 

hundred feet thick, the type locality of which is on 

Ungalik River east of Norton Bay. The conglomerate at the type locality was correlated on the basis 

of lithologic similarity with the conglomerate of a 

large area 40 miles to the northwest, on the hills 

between Kwik and Tubutulik Rivers, which rests unconformably upon Paleozoic limestone and schist and 

late Paleozoic or Mesozoic greenstone. A similar correlation was made with the conglomerate of an area

88 Smith, P. S., and Eakin, H. M., A geologic reconnaissance in southeastern Seward 

Peninsula and the Norton Bay-Nulato region, Alaska: U. S. Geol. Survey Bull. 449, 

p. 57, 1911.

89 Idem, pp. 55-57.
402 MESOZGIG STRATIGRAPHY OF ALASKA

35 miles north of the type locality, on the divide between Koyuk 

and Buckland rivers, and with the conglomeratic beds on the Yukon 

near the mouth of Melozi Kiver, described above, which are about 

140 miles east of the type locality.

The evidence on the age of the conglomerate on Ungalik Kiver 

described by Smith and Eakin is that it underlies Upper Cretaceous 

sandstone without evidence of unconformity, whereas the conglomerate of the Tubutulik-Kwik area rests unconformably upon latePaleozoic or early Mesozoic rocks and contains poorly preserved 

plants that are apparently of Cretaceous age. No local evidence on 

the age of the conglomerate at the head of Koyuk River has been 

published.

The exposures in the river bank from 8 to 20 miles below the 

Melozi telegraph station constitute the second division of the Upper 

Cretaceous rocks of the lower Yukon, for which the name Melozi 

formation is herein proposed. These exposures reveal shale and

Sandstone and Black shale

.-colored C*' ''s'CWk /Sandstone

-About '/ * mile

FIGURE 11. Section of Upper Cretaceous rocks on. Yukon River near Fossil Bluff. 

(By W. W. Atwood)

sandstone striking nearly parallel to the course of the river and dipping 25° or 30° NW. A computation from the average strike and 

dip indicates that tho thickness may possibly be as much as 5,000 

or 6,000 feet but that it is probably not more than 2,000 or 3,000 feet 

and may be not more than 1,000 feet. It was the writer's opinion, 

while studying this section in the field, that the thickness is not very 

great, and he is inclined to accept the smaller estimate. Even this 

may have to be reduced if there has been any duplication of the beds 

by faulting. The shale and sandstone of this formation, so far as 

known, are wholly nonmarine. They contain fossil plants and freshwater invertebrates but have yielded no marine fossils.

At the bend of the river opposite the upper end of a long island 

about 5 miles below Good Island there is an abrupt change in the 

character and attitude of the rocks. The gray sandstone and shale 

exposed up the river are replaced by coarse reddish sandstone or 

arkose, conglomerate, highly indurated cherty shale, and shaly sandstone. These rocks dip at high angles. About 2 miles farther down
CRETACEOUS, LOWER YUKON REGION 403

the river, at Fossil Bluff, are exposures of sandstone and shale containing both fresh-water and marine invertebrates (lots 2924, 2676j 

2925, 4784). These rocks are regarded as belonging in the Nulato 

formation, which is described in greater detail on pages 404-408. 

The section at this place is shown in the accompanying sketches 

(figs. Hand 12).

About a Quarter of a mile down the river from this place and a 

quarter of a mile back from the shore are shale and sandstone with 

two or more thin coal beds.90 Fossil plants were obtained from the 

roof of one of the coal beds (lot 2962) and also in float material between the mine and the river that is believed to have come from beds 

in the vicinity of the mine (lots 3252 and 4635). The coal and plantsw.

Rock fragments containing 

fossil plants found here, at 

foot of slide; not found on 

river bank above slide, which 

came down valley

Fossil shells in rock, scattered 

alongshore at base of bluff

FIGURE 12. Sketch showing position of fossiliferous beds near.Fossil Bluff. (By Arthur

Hollick)

bearing beds are believed to overlie the marine shale and sandstone 

of Fossil Bluff and to belong in the Kaltag formation.

From Louden to the mouth of the Koyukuk there are no exposures 

of consolidated rocks in the banks of the Yukon except at Bishop 

Rock. The exposures at this place consist of shale and sandstone, 

which apparently are conformable throughout. Fossil shells (lots 

2AC244, 2926, 2927, and 4785) and fossil plants (lots 2977, 3257, 

and 4637) were obtained here. These rocks are believed to be 

correctable in a general way with some of the marine sandstones 

above Louden and to belong in the Nulato formation.

From Bishop Rock to the mouth of Koyukuk River there are no 

exposures except terrace gravel. At the mouth of the Koyukuk 

are exposures of basalt that is intrusive into sandstone and conglomerate.

An almost continuous series of outcrops of Upper Cretaceous 

sandstone and shale extends along the north or west bank of the

00 Collier, A. J., The coal resources of the Yukon, Alaska: U. S. Geol. Survey Bull. 218, 

pp. 47-48, 1903.
404 MESOZOIC STRATIGRAPHY OF ALASKA

Yukon from a point about 5 miles below Koyukuk village, or 3 

miles above the Pickart coal mine, to Nulato. The attitude of the 

beds in these exposures, as they appear in the face of the cliffs, is 

shown in Figure 13. This section is drawn along the bank of the 

river at varying angles, amounting in general to about 45°, with the 

strike. It consequently shows only the general relations of the beds 

and not their true thickness.

The rocks from the upper end of the exposures to the creek just 

above the Pickart mine consist of yellowish sandstone and shale 

striking parallel to the river and dipping about 20° W. They 

yielded the fossil plants and marine invertebrates of lots 3253, 2679, 

and 2964. The beds south of the creek, which are believed to underlie immediately those north of the creek, yielded the marine inverteFIGURE 13. Sketch showing general relations of Upper Cretaceous rocks between Pickart

coal mine and Nulato

brates and plants of lots 3254, 4638, 4787, 2AC250, 3255, and 2928. 

These beds include the sandstone, shale, and coal shown in the following section, which was measured by W. W. Atwood. The upper end 

of this section is a quarter of a mile upstream from the Pickart mine, 

where the rocks strike N. 10° E. (magnetic) and dip 26° NW.

Section of Upper Cretaceous rocks near Pickart mine

Ft. in.

Alternating thin beds of sandstone and shale 50 

Yellow sandstone (conspicuous from river), conglomeratic

at base __ 10 

Carbonaceous shale; contains 2-inch parting of coal in

middle ____________________ 8

Sandstone __ _____ 2

Carbonaceous shale__________________________________

Clean bright lignite______________________ _ 

Sandy shale 5

Blue shale containing coal parting.

Blue shale__________ 6

Sandstone, with shale lenses 2 

Blue shale i - 4 

Alternating thin beds of sandstone and shale ________ 8

Blue shale, with coal lenses ___ 5 

Shaly sandstone - _ 2

6

10

5
CRETACEOUS, LOWER YUKON REGION 405

	Ft. in.

Shale______________ _ . 6

Lignite lenses 4-6

Blue shale, interstratified with sandy shale _ _ 25

Sandstone ____ _ 1

Blue shale__________________ ______ 2 6

Sandstone._ - _ _ 1 6

Blue shale___________ 2

Shaly sandstone__ ____ 4

Blue shale___________ _ 1 6 

Sandstone; weathers yellow; carries gastropod and

lamellibranch fauna (lot 4786)____ ___ 1-3

Blue shale___________ 10

Sandstone _ ______ 1

Blue shale, interstratified with sandy shale_______ 17

Sandstone ___________ o

Blue shale, interstratified with sandy shale ___ 15

Sandstone _ _ _ _ 2

Blue shale, interstratified with sandy shale______ 12

Sandstone ______________ , 3

Shale______________________________ 2

Sandstone, cross-bedded____________ 3

Blue shale___________________________ 11

Sandstone, cross-bedded___ _ _ __ 8

Covered______________________-______ 100

Sandstone___________ __ 6

Covered_____________-_____________ 20 

Sandy shale, interstratified with thin beds of sandstone___ ________ ___ 50 

Sandstone, interstratified with thin beds of shale___ 8 

Sandy shale _ ______ 6

Coaly shale __ ___'._____ ____-_____ 6

Blue shale_ __._____ __ 5

Sandstone, thin bedded__________________ 11

Shale_______________________________ 12

Sandstone _____________ _____________ 10

Sandy shale, with thin beds of sandstone_______ 50

Sandstone______________ __ _______ 3

Shale with thin beds of sandstone___________ 100

Sandstone with shale lenses___ ___ ______ 32 

Shale, with thin beds of sandstone; leaves (lot 4638).

Above Pickart coal mine_ ______________ 6

Sandstone _____________ ___ _ _ ______ 4

Sandy shale__________________________ 3

Sandstone, with thin beds of shale____________ 5 

Shales, interstratifled with beds of sandstone, first

above mine _ ______ _ __________ 60

Heavy sandstone bed with shale pebbles (presumably

clay pebbles on beach) and shale lenses _____ 25

Sandy shale__________________________ 5

Sandstone ___________________________ 2

Shale with beds of sandstone (obscure)________ 50

Sandstone_____________________________ 8 

49448 2fi 27
406 MESOZOIC STRATIGRAPHY OF ALASKA

Ft. in. 

Shale and coal at Pickart mine, obscured by talus.

Coal 2 feet, overlain and underlain by sandstone. 20 

Sandstone______ 5 

Shales, interstratified with thin beds of sandstone_ 35 

Sandstone_ ___ 5 

Shales, with thin beds of sandstone. __ 18 

Sandstone, thin bedded 7 

Sandy shale, crushed 10 

Sandstone_ __ 14 

Shale, carbonaceous, with coaly lenses __ _____ 3 

, Sandstone 25 

Sandstone and shale, alternating thin beds_______ 8 

Sandstone, thin bedded above, massive below, marine

fossils (lot 4787)______________________ 50 

Shale ____________________________ 10 

Sandstone_ ___ _ _ ___ 4 

Shale, with coal stringers and ironstone nodules____ 25 

Sandstone, with thin beds of shale _____ 20 

Shale, with beds of sandstone. ____ 25 

Sandstone, thin bedded_____ _ ____ 17 

Sandstone, carrying marine fauna____________ 3 

Sandstone, in part thin bedded, in part massive. Some

strata carrying shells 65

1,166 8

The rocks between the base of this section and Nulato include 

sandstone and shale that are repeated in the river bank by several 

gently undulating folds and possibly by faults. (See fig. 13.) They 

may include rocks somewhat older than any in this section, and they 

also probably include, near Nulato, some beds that are the equivalent of those near the Pickart mine.

The section from the vicinity of the Pickart mine to Nulato 

includes several thousand feet of marine sandstone and shale with 

fresh-water plant and coal-bearing rocks, interbedded with them in 

the upper part of the sequence. The marine sandstone and shale 

form the type section of the Nulato formation, and the overlying 

coal-bearing fresh-water beds belong in the Kaltag formation. The 

section is believed to be the general equivalent of the section from a 

point 5 miles below Good Island to Louden. The coal north of 

Fossil Bluff, above Louden, is believed to be correctable with the 

coal at the Pickart mine and just above Nulato.

The rocks lying west of the Yukon in the hills between Nulato 

and Norton Sound were described by Smith and Eakin 91 as the 

Shaktolik group, in which they included such of the Mesozoic 

sedimentary rocks of the Nulato-Norton Bay district as are strati81 Smith, P. S., and Eakln, H. M., A geologic reconnaissance in southeastern Seward 

Peninsula and the Norton Bay-Nulato region, Alaska: U. S. Geol. Survey Bull. 449. pp. 

57-60, 1911.
CRETACEOUS, LOWER YUKON REGION 407

graphically above the Ungalik conglomerate. The Shaktolik group 

was. described as including two unnamed formations, which were 

differentiated in the description but not in mapping. The lower division of the Shaktolik group was described as5 consisting of sandstone and shale, the shale aggregating only a small part of the 

total thickness. These beds lie with apparent conformity upon the 

Ungalik conglomerate. The Nulato sandstone of previous reports 

and the associated coal-bearing rocks on the Yukon in the vicinity 

of Nulato were regarded as constituting undifferentiated members 

of undetermined position in the lower division of the Shaktolik 

group.

The upper division of the Shaktolik group was described as consisting predominantly of black shale but containing subordinate 

beds of calcareous sandstone and as having a thickness of possibly 

several thousand feet. It contains marine fossils of Upper Cretaceous age, and the general character of the fauna is very similar 

to that of the Upper Cretaceous beds of the lower Yukon.

Fossils from the Shaktolik group of the hills between Nulato and Norton Sound "

6261

X

X

v

6262

X

6263

X

6264

X

6265

X

6266

X

0 Identified by T. W. Stanton.

6261 (9AE2). Gisana-Nulato divide, 10y2 miles north and 14 *£ miles west 

from Nulato. P. S. Smith, 1909.

6262 (9AE3). Same horizon as 6261, 3% miles west. P. S. Smith, 1909.

6263 (9AE4). 6 miles north and 20 miles west from Nulato. Probably 1,000 

feet below 6262. P. S. Smith, 1909.

6264 (9AE5). About 50 feet below 6263, at same locality. P. S. Smith, 1909.

6265 (9AE6). 6 miles north and 23. miles west from Nulato. P. S. Smith, 

1909.

6266 (9AE1). Gisana-Nulato divide, about 17 miles north and 4 miles west 

from Nulato. P. S. Smith, 1909.

Below Nulato there are no exposures for about 4 miles to the 

vicinity of the Bush coal mine, where, according to Collier,92 the 

coal is contained in sandstone carrying fossil leaves. For about 

4 miles below the Bush mine there are exposures of highly folded 

sandstone and shale. Fossil leaves were obtained (2978) about li/^ 

miles below the mine. The rocks in the vicinity of the Bush mine

02 Collier, A. J., The coal resources of the Yukon, Alaska: IT. S. Geol. Survey Bull. 218, 

pp. 52-53, 1903.
408 MESOZOIC STRATIGRAPHY OF ALASKA

are part of the Kaltag formation and are believed to be the general 

equivalent of the coal-bearing beds near the Pickart mine and just 

above Nulato.

At the Blatchford mine,03 about 9 miles below Nulato, there are 

two thin beds of coal overlain by massive sandstone and underlain 

by sandstone and shale with fossil leaves (lot 3258). From the 

Blatchford mine to Kaltag the rocks strike northeast and dip northwest, exposing lower beds successively down stream. The rocks 

in this interval consist of shale and sandstone, which have yielded 

numerous collections of fossil plants and a few marine and fresh-water 

invertebrates. They dip at relatively high angles (15° to 50°) and 

would have a thickness of many thousand feet if there were no 

repetition by faulting. Several faults are known in this interval, 

but the amount of repetition is not known. The rocks between Nulato 

and Bluff Point, 21 miles below Nulato, have yielded only plants 

(lots 2978, 3258, 3260, 2980, 3261, 4639, 3259, 2981, 3262, and 3263) 

and fresh-water fossils (lots 2683 and 2932) and are believed to 

belong in the Kaltag formation, which forms the upper, coal-bearing 

member of the Cretaceous sequence. At Bluff Point and 2^ miles 

above Kaltag there are massive sandstones that have yielded marine 

fossils (lots 2931 and 4T93). These rocks, which have a thickness 

of 2,500 feet in the bluff 2y2 miles above Kaltag, are believed to be 

the oldest rocks exposed on this stretch of the river. Together with 

part but perhaps not all of the overlying plant-bearing sandstone 

and shale exposed between these two localities, which yielded the 

fossil plants of lots 3264, 2982, 3265, 2983, 3266, and 3267, they are 

probably to be correlated with the marine sandstone and shale exposed between the Pickart mine and Nulato and belong in the Nulato 

formation.

From 6 to 8 miles below Kaltag are exposures of sandstone dipping 

west. About 8 miles below Kaltag these beds yielded the fossil 

leaves of lots 2984, 3268, and 4640. At this place fragments of coal 

were seen in a slide. About 5 miles farther down the river, below an 

interval in which the rocks are concealed, is an outcrop of sandstone 

and coal. About 4% miles farther down the river are exposures of 

sandstone and shale. Marine fossils (lot 2684) were found at this 

locality. The rocks in the next 10 miles of river bank are lava and 

tuff that are believed to be post-Cretaceous. Their relations to 

the Cretaceous rocks are not known. The rocks between Kaltag and 

this volcanic area are believed to belong to the upper coal-bearing 

division of the Cretaceous, whicih has been named the Kaltag 

formation.

98 Collier, A. J., op. cit., pp. 53-55.
CRETACEOUS,, LOWER YUKON REGION 409

South of the volcanic area just described there are no rocks exposed in the river bank for about 12 miles. The next exposures are 

about 72 miles below Nulato, or 2 miles above the Williams coal 

mine. A series of bluffs beginning here extends to a point about a 

mile below the Williams mine. The coal bed at the Williams mine 

is about 314 feet thick and is interbedded with light-colored sandstone of different appearance from any Cretaceous rocks seen by 

the writer elsewhere on the river. The fossil plants of lot 2985 

came from sandstone immediately above the coal. This sandstone 

is cut off from the apparently younger rocks up the river by a fault 

about half a mile above the mine. Collier 94 states that " the coal 

bed is overlain by at least 2,000 feet of sandstones, conglomerates, 

and black shales," a thickness which apparently includes only the 

rocks between the coal and the fault. About a mile above the mine 

occur sandstone and shale which yielded the fresh-water invertebrates of lots 2683, 2933, and 4795 and also the plants of lots 3269 

and 4641. A little farther up the river, presumably higher in the 

sequence, the marine invertebrates of lot 4794 and the plants of lot 

4642 were obtained. Possibly all these rocks belong in the Kaltag 

formation, but it is also possible that the rocks up the river from 

the fault are of lower undetermined stratigraphic position.

Igneous rocks crop out for several miles along the river, beginning 

about a mile below the Williams mine. Thence no rocks show on 

the bank for several miles, the next exposure noted consisting of 

igneous rocks about 15 miles below the Williams mine.

At coal mine No. 1, about 20 miles below the Williams mine, there 

are sandstone and shale containing one or more thin beds of coal. 

The fossil plants of lots 2986 and 3270 were obtained from sandstone a short distance stratigraphically above (down the river from) 

the coal.

About 13 miles below mine No. 1 there are exposures of sharply 

folded shale and sandstone with a bed of coal 8 or 10 inches thick. 

The fossil leaves of lots 3271 and 4643 were obtained at this place. 

For about 15 miles below this locality there are exposures of shale, 

sandstone, and conglomerate from which no fossils have been obtained. These exposures are considered, in the lack of evidence to 

the contrary, to belong with the neighboring coal-bearing exposure 

at locality 3271, in the Kaltag formation.

No exposures, other than gravel, were seen in the next 15 miles, 

or as far as the upper end of Hall Rapids, about 30 miles above 

Anvik. The exposures at Hall Rapids consist of tuff which Collier 95

94 Collier, A. J., The coal resources of the Yukon, Alaska: U. S. Geol. Survey Bull. 218 

p. 55, 1903.

86 Idem, pp. 57-58.
410 MESOZOIC STRATIGRAPHY OF ALASKA

described as interstratified with some beds of impure lignite. Tuff 

and lava, presumably of the same age, are exposed at several places 

between Hall Rapids and Anvik. The writer believes that these 

rocks are post-Cretaceous.

The Cretaceous rocks along the Yukon and on its tributaries between Anvik and Andreafski have been described by Harrington 96 

as consisting of sandstone, argillite, and conglomerate. No detailed 

stratigraphic sections were measured, and only a few fossils were 

found. The rocks can not be certainty correlated with those exposed 

farther up the river, but the apparent absence of coal beds and of 

marine fossils, the presence of conglomerate, and the occurrence 

of the conglomerate in contact with pre-Cretaceous rocks suggest 

that most of the exposures represent the two lower divisions of the 

section between Melozi and Louden. Details concerning exposures 

at the several localities are given below.

The exposures on Anvik River include "mudstones or consolidated 

shales," fine-grained siliceous rocks that are locally cherty, and 

sandstone that is described as not so massive as those farther south. 

These sediments are interbedded at one locality, presumably near 

their top, with basaltic flows and tuff. No positive evidence as to 

the age of these rocks has been obtained, for they have yielded no 

fossils except indeterminate plant fragments. Harrington considered them presumably late Cretaceous or early Tertiary, although 

his map shows the sedimentary areas on Anvik River as Upper 

Cretaceous and the volcanic areas as Quaternary or late Tertiary. 

The writer suspects that none of the rocks on Anvik River described 

by Harrington are Cretaceous but that they are to be correlated with 

the Tertiary (?) volcanic and coal-bearing beds exposed ajong the

Yukon at Hull Rapids and other localities.

The exposures near Holy Cross and opposite Paimut consist of 

conglomerate, grit, and sandstone with some thin beds of argillite. 

No fossils were obtained from these strata, but their lithologic character and their position apparently directly above the supposed 

Paleozoic greenstone indicate that they are to be correlated with the 

lower conglomeratic division of the Upper Cretaceous section between Melozi and Louden.

The exposures near Dogfish village and at other localities between Mountain Creek and Johnson Island consist chiefly of finegrained rocks, including chert, quartzite, and shale, together Avith a 

few beds of grit and conglomerate. This area also adjoins a belt of 

pre-Cretaceous greenstone and therefore presumably includes basal 

beds equivalent to the Ungalik conglomerate. The presence of much

89 HarringtoD, G. L., The Anvik-Andrenf ski region, Alaska: U. S. Geol. Survey Bull. 

683, pp. 26-35, 1918.
CRETACEOUS,, LOWER YUKON REGION 411

fine-grained material suggests that the fresh-water shale and sandstone overlying the Ungalik conglomerate may also be represented. 

No fossils were obtained in this area.

The rocks exposed at Devils Elbow and elsewhere between Grand 

Island and Round Point include sandstone, argillite, and a variety 

of fine-grained siliceous and argillaceous sediments. The absence 

of conglomerate and the occurrence of most of these outcrops far 

away from the exposures of the pre-Cretaceous rocks suggest that 

these rocks are higher in the Cretaceous sequence than the Ungalik 

conglomerate. The apparent absence of marine strata or of coal 

beds suggests a correlation with the fresh-water shale and sandstone. 

The eastern margin of the area adjoins the pre-Cretaceous greenstone, and the equivalent of the Ungalik conglomerate may be present there. No such conglomerate has been described, however, and 

it may be that this contact is a fault.

The exposures near Marshall include sandstone, argillite, chert, 

and conglomerate, which crop out in close proximity to the pre-Cretaceous greenstone. These rocks are believed to represent the Ungalik conglomerate.

The rocks exposed on Chvilnuk River near Pilot Station and on 

Andreafski River include sandstone, argillite, and conglomerate. 

The presence of conglomerate suggests that the Ungalik conglomerate may be represented, but the absence of the pre-Cretaceous greenstone in or near this area indicates that the rocks may belong somewhat higher in the Cretaceous sequence. Some fresh-water invertebrate fossils collected on Andreafski River about 9 miles northeast 

of Andreafski indicate that the rocks at that locality probably belong 

in the upper coal-bearing division, but they may possibly represent 

the fresh-water shale and sandstone of the section between Melozi 

and Louden. Some fossil plants were obtained at the same locality, 

but they do not include species that are characteristic of any one subdivision of the Upper Cretaceous. Some marine fossils found near 

the mouth of Andreafski River indicate that one of the uppermost 

two divisions is represented there. The writer believes that all 

the fossil localities on Andreafski River belong in the upper coalbearing division (Kaltag formation).

Age and correlation. The Upper Cretaceous rocks of the lower 

Yukon are not known to be in contact with any formations other 

than the supposed Paleozoic rocks that underlie .them and the supposed Tertiary volcanic beds that may overlie them. There is consequently no evidence as to the precise age of the Upper Cretaceous 

rocks, except that afforded by the fossils, which have been found in 

all four of the Upper Cretaceous formations.
412 MESOZOIC STRATIGRAPHY OF ALASKA

The lower conglomeratic formation (Ungalik conglomerate) has 

yielded only some fragmentary plants and some indeterminate pelecypods, none of which give conclusive evidence as to the age. As 

these conglomeratic beds appear to underlie the other Upper Cretaceous rocks conformably, there is little if any doubt that they, too, 

are Upper Cretaceous.

The fresh-water shale and sandstone (Melozi formation) have 

yielded both fossil plants and fresh-water mollusks. The shells include chiefly some unidentified species of Unio, which afford no evidence as to the age of the rocks.

The marine sandstone and shale (Nulato formation) have yielded 

both fossil plants and marine invertebrates. Some fresh-water pelecypods (Unio) have been collected at one locality within the area of 

these rocks, but they were not obtained in place and are believed to 

have been derived from the underlying fresh-water shale and sandstone of the Melozi formation. Most of the marine invertebrates 

belong to unidentified species and have not been critically studied.97 

They indicate, according to Stanton,98 " That the horizon is within 

the Upper Cretaceous but probably not higher than the middle of 

the Upper Cretaceous."

The coal-bearing rocks (Kaltag formation) contain abundant 

fossil plants, some fresh or brackish water mollusks, and probably 

a few marine mollusks. It is possible that all the marine fossils 

that have been listed as coming from these beds were derived from 

older rocks that have been erroneously correlated with these beds. 

These marine fossils represent only a few genera and apparently 

do not include any species that have not been recognized in the 

underlying marine sandstone and shale. The fresh or brackish 

water fossils include oysters, and several genera of fresh-water 

mollusks that have not been recognized in the older fresh-water 

shale and sandstone.

The evidence yielded by the fossil plants, according to Hollick,99 

indicates with little doubt that the Upper Cretaceous flora of the 

Yukon as a .whole is approximately of Dakota age. This conclusion is practically in accord with the evidence yielded by the 

marine invertebrates.

The Ungalik conglomerate has yielded only undetermined plant 

fragments and pelecypods. The fossils of the other divisions of 

the Upper Cretaceous on the lower Yukon are listed below.

87 After this paper was practically finished a critical study of the Upper Cretaceous 

invertebrate fossils of Alaska was undertaken by W. R. Smith. The results of that study 

have not yet been published, but preliminary lists of fossils identified by Smith have 

been used in making .up the tables of fossils on pages 413-424.

86 Stanton, T. W., unpublished statement.

88 Personal communication.
CRETACEOUS, LOWEB YUKON REGION 413

Fossils from the Melozi formation 0

Asplenium foersteri Debey and EtPodozamites lanceolatus (Lindley

Qinkgo digitata (Brongniart) Heer.

Protophyllocladus polymorphic ...

Pinus?. .-.-...... ...-..--.. -

Sequoia fastigiata (Sternberg) Heer. 

Sequoia concinnaHeer.. ...........

Sequoia reichenbachi (Oeinitz)

Populites, n. sp~. . ____ . .......

Populites?, n. sp _ . ____ - ___

Quercus eamesi Trelease? ...........

Ficus daphnogenoides (Heer) Berry.

Daphnophyllum dakotense LesquePlatanus latior (Lesquereux)

Pseudoprotophyllum, n. sp .........

n. sp __ ....

Sapindus morrisoni Lesquereux

Cissites, n. sp. _______ ........

Trails..............................

Unio. ..............................

Viviparus? or Campeloma?.... _ ..

4782

d

2975 2976 4633

a

7715 1554

b

2963

a

a

a

a

3248

a

a

a

a

a

a

a

a

a

4634, 

4783

a

a .

a

a

a

d

3249

a

a

a

a

a

a

a

3250

a

a

a

a

3251 2922, 

3251a

7

c

2675

c

2923

c 

c 

d

d

" a, Identified by Arthur Hollick; b, identified by F. H. Knowlton; c, identified by W. E. Smith; d, 

identified by T. W. Stanton. The new species and new varieties of plants will be described in a monograph on the Upper Cretaceous flora of Alaska, by Arthur Hollick, now in preparation.

49448 26 28
414 MBSOZOIC STBATIGBAPHY OF ALASKA

4782(19). Yukon River, north bank, about 9 (?) miles below Melozi. Argillite associated with coarse conglomerate. W. W. Atwood, 1907.

2975 (2AC234). Yukon River, north bank, about 9 miles below Melozi. 

Thin bed of carbonaceous shale with "knife-edge" coal seams. A. J. Collier, 

1902.

2976 (2AC235). Yukon River, north bank, about 10 miles below Melozi. 

Talus at foot of bluff. A. J. Collier, 1902.

4633 (18). Yukon River, north bank, about 10 miles below Melozi. Soft 

shale dipping into hillside. W. W. Atwood, 1907.

7715. Yukon River, north bank, 15 or 20 miles below the mouth of the Melozi. 

I. C. Russell, 1889.

1554(9). "Below Melozikakat" [probably about 19 miles below Melozi 

River]. J. E. Spurr, 1896.

2963 (2AC236). Yukon River, north bank, 10 to 11 miles below Melozi. 

" Collected for about a mile along the foot of the cliff." A. J. Collier, 1902.

3248 (3AH11). Yukon River, north bank, about 12 miles below Melozi. 

Shaly sandstone about 300 feet above the river and talus on river bank. 

Arthur Hollick, 1903.

4634 (20),4783 (21). Yukon River, north bank, about 12 miles below Melozi. 

Sandstone and shale. W. W. Atwood, 1907.

3249(3AH12). Yukon River, north bank, about 12^ miles below Melozi. 

Talus on river bank. Arthur Hollick, 1903.

3250 (3AH13). Yukon River, north bank, about 13 miles below Melozi. 

Sandstone a short distance below small draw. Arthur Hollick, 1903.

3251 (3AH14). Yukon River, north bank, about 2 miles above Good Island, 

or 14 miles below Melozi. Talus. Arthur Hollick, 1903.

3251a (3AH14a). Yukon River, north bank,- just above upper end of Good 

Island. Gray sandstone. Arthur Hollick, 1903.

2922 (3AH14a). Yukon River, north bank, just above upper end of Good 

Island. Gray sandstone. Same locality as 3251a. Arthur Hollick, 1903.

2675 (2AC237). Yukon River, north bank, behind Good Island. Sandstone 

pebbles at mouth of creek. A. J. Collier, 1902.

2923 (3AH14b). Yukon River, north bank, behind Good Island.- Loose rock 

on river bank. Same locality as 2675. Arthur Hollick, 1903.
Fossils from the Nulato formation a

Dryopteris oerstedi (Heer) Knowlton? _._..._-......___._...____.

Podozamites lanceolatus (Lindley 

and Hutton) C. F. W. Braun ....

Sequoia reichenbachi (Geinitz) Herr

2924 2676

i

.........

....

Inoceramus cf. I. labiatus SchlotPleuromya, n. sp ..----..--.-. ......

d

2925

d

d

4784

2977, 

2678

d

2926

d

2927, 

3257

4637,

4785

d

4787

d

2677

Q

d

3255 2928

fl

d

2930 3256 2680

d

2929 2681 

.;..

....

....

d

1 a, Identified by Arthur Hollick: b, identified by F. H. Knowlton; c, identified by W. R. Smith; d, identified-
Fossils from the Nulato formation Continu

Pholadomya ______________

Thraciasp... _____________

Thracia?....--. _ ..................

Astarte, n. sp __ -...-. ............

Astarte? __ . __ __ __ .... ....

Opis?.. .-.-.... . ..............-.

Veneridae -.--.- _ .... ...

Meretrix, n. sp...... -..-.*._.. . .

Meretrix? ........

Tellinacf. T. ashburnerii Gabb ....

Tellina?.

Corbola--- . .....

Panope, n. sp .-..-..

Panope concentrica (Gabb) WhitPanopea__ ________ . __ _.*_

Panopea? _ .......... .

Turritella . .........

Aetaeonella (Volvalina), n. sp. . .

Actaeonella?- ____ __ ..........

Sonneratia? __ ....... . __ _ ...

Ammonites ___ ... ______ .....

 »

2924

d

2676

C

d

d

d

2925

rl

d

4784

d

*

2977, 

2678

c 

c

c

d

d

2926

c 

c

c

i

I

i

i

d 1 d

d L2927, 

3257

C 

C

d

d

c

d

d

d

4637,

4785

d

4787

d

o

d

2677

c

3255 2928

c

d

d

d

2930

d

3256 2680

c

c

c

2929

d

2681

d
CRETACEOUS, LOWER YUKON REGION 417

2924 (3AH15). Yukon River, north bank, just above Fossil Bluff, about 5 

miles above Louden. Rock fragments on beach. Arthur Hollick, 1903.

2676 (2AC238). Yukon River, north bank, at Fossil Bluff, 5 miles above 

Louden. Massive sandstone. A. J. Collier, 1902.

2925. (3AH15a). Yukon River, north bank, at Fossil Bluff, 5 miles above 

Louden. Sandstone and shale overlying " intrusive dike." Arthur Hollick, 

1903.

4784 (23). Yukon River, north bank, 5 miles above Louden. Sandstone and 

shale overlying " intrusive lava." In place. Probably same locality as 2676 

and 2925. W. W. Atwood, 1907.

2977, 2678 (2AC244). Yukon River, north bank at Bishop Mountain. A. J. 

Collier, 1902.

2926 (3AH17). Yukon River, north bank, at Bishop Rock. Crest of fold 

at upper end of exposure. Arthur Hollick, 1903.

2927, 3257 (3AH17a). Yukon River, north bank, at Bishop Rock. Talus at 

lower end of exposure. Arthur Hollick, 1903.

4785, 4637 (24). Yukon River, north bank, at Bishop Rock. W. W. Atwood, 

1907.

4787 (27). Yukon River, north bank, near Pickart mine. Sandstone about 

130 feet below the coal. (See section, p. 406.) W. W. Atwood, 1907.

2677 (2AC250). Yukon River, north bank. Strata below Pickart coal mine. 

A. J. Collier, 1902.

3255 (3AH18b). Yukon River, north bank, just below Pickart mine. Massive sandstone below the coal. Arthur Hollick, 1903.

2928 (3AH18c). Yukon River, north bank, a short distance below Pickart 

mine. Shale conformably beneath the sandstone that yielded lot 3255. Arthur 

Hollick, 1903.

2930 (3AH18d). Yukon River, north bank, for about 2 miles below 18c. 

Float. Arthur Hollick, 1903.

3256 (3AH18d). Yukon River, north bank. Sandstone just below 2930. 

Arthur Hollick, 1903.

2680 (2AC251). Yukon River, north bank, about 3 miles below Pickart mine. 

A. J. Collier, 1902.

2929 (3AH18e). Yukon River, north bank, opposite head of first island below 

Pickart mine. Sandstone. Arthur Hollick, 1903.

2681 (2AC252). Yukon River, north bank, 6 miles above Nulato. Massive 

sandstone. A. J. Collier, 1902.

4788 (28). Yukon River, north bank, 5% miles below Pickart mine. Talus 

below sandstone cliff. W. W. Atwood, 1907.

4789 (29). Yukon River, north bank, 6 miles below Pickart mine. Sandstone 

near lens of coaly stringers. W. W. Atwood, 1907.

4790 (30). Yukon River, north bank, 6% miles below Pickart mine. W. W. 

Atwood, 1907.

4791 (31). Yukon River, north bank, 6% miles below Pickart mine. W. W. 

'Atwood, 1907.

4792 (32). Yukon River, north bank, 6% miles below Pickart mine. Sandstone above 4788 to 4791. W. W. Atwood, 1907.

2179, 7471 (358). Yukon River, north bank, between Pickart mine and Nulato. 

F. C. Schrader, 1899.

3264 (3AH25). Yukon River, west bank, at upper end of Bluff Point, 24 miles 

below Nulato. Sandstone and shale. Arthur Hollick, 1903.

2931 (3AH25a). Yukon River, west bank, at end of Bluff Point. Coarse 

sandstone. Arthur Hollick, 1903.
418 MESOZOIC STRATIGRAPHY OF ALASKA

2982 (2AC263). Yukon River, west bank, 1 mile below Bluff Point. Sandstone. A. J. Collier, 1902.

3265(3AH26). Yukon River, west bank, about 3 miles below Bluff Point. 

Shale. Arthur Hollick, 1903.

2983 (2AC264). Yukon River, west bank, about 4% miles below Bluff Point. 

Massive sandstone. A. J. Collier, 1902.

3266 (3AH27). Yukon River, west bank, about 4% miles below Bluff Point. 

Shale near 2983 (?). Arthur Hollick, 1903.

3267 (3AH28). Yukon River, west bank, 3 miles above Kaltag. Shale associated with thin bed of coal. Arthur Hollick, 1903.

4793 (34). Yukon River, west bank, 3 miles above Kaltag. Thick sandstone. 

W. .W. Atwood, 1907.
Fossils from Kaltag formation °

 ^

Asplenium foersteri Debey and

Asplenium johnstrupi (Heer)

TTppr?

Onychiopsis nervosa (Fontaine)

Sagenopteris variabilis (VelePodozamites lanceolatus (Lindley and Button) C. F. W.

Oinkgo digitata (Brongniart)

Oinkgo?.. ........ --- ._--..-_

Nageiopsis angustifolia FonProtophyllocladus subintegrifole»

a

a

Tumion, n. so.- - __ .---.. _J a

O

i

a

a

a

N 

1

a

a

a

a

a

8

$

a

a

a

a

CO

3

cc

 <J<

CO

3

oT 

§

a

CO

§ 

ft

CO

*

CM

! "1

O

cl

CO O 

O

t- CO CO ,

CO

3CO

a

a 1

iCO

a

 *

_

a

|

..

2932, 326

a

CO ,

a

0 a, Identified by Arthur Hollick; b, identified by F. H. Knowlton; c, identified by W. R. Smith; d, identified 
Fossils from Kaltag formation Continu

Sequoia fastigiata (Sternberg)

Sphenolepis sternbergiana

Qlyptostrobus gronlandicus

Ficus melanophylla LesquerLiriodendropsis simplex (NewPlatanus, n. sp.......... _ ...

s CO

1

<N

el

CO

a

a

8

§

CO 

lO 

N 

CO

3 

S

oT

s

 * 

o»

CO

CO 

00

r~ *

GO

s *

N O

3

CO

h

2

^ n

n

a

W i

o>

i

'

§CO 1 » 

CO"

2932, 3262

CO 
Platanus? sp... ____ . ___ .

Vitis, n. sp. ....................

Aralia wellingtoniana LesqueMyrsine gaudini (Lesquereux)

Ostrca.. . ............ 0 
422 MESOZOIO STRATIGRAPHY OF ALASKA

o 

O

9ZZ6

SZZ6 '6S2Z

KL6

SW

U2£

Oi28

9862

S862

S6Z*

TW*

8862

6928

9892

f6Z*

2Wf

^892

8928

OW^

f862

8928

2928 '2862

1862 '8892

689*

T928

6S28

0862

0928

8S28

22U

8Z62

-OV2

2892

889*

98Z*

W28

W62 '6Z92

8928

S89*

2S28

98Z*

2962

o

t.

c

tn

t 

c 'f 

P

 G

 a

"O

 a

i

<: 

g

u

C

f

1 

g 

Pi

*c

c«

0

1

U

 c

-c

'S

1X 

O

 a

o1§X

a

03

 C

I

C

I

c.

C

f 

% 

£

1

c

 o

T

 a

 0

T3T3 -o

 a-aTS

. I

1

(Tubtoma), Viviparus spn. 

Vivinarus.---

1

1

c^- 

c

1S3

O

 0

C1-

tn v.

!|

o o '3 '3

0 0

OO
CRETACEOUS, LOWER YUKON REGION 423

2962 (2AC239). Yukon River, north bank, 4% miles above Louden. Hanging 

wall of coal bed about a quarter of a mile from the river and from the foot of 

a slide extending from the coal bed to the river. A. J. Collier, 1902.

4636 (22A). Yukon River, north bank, about 5 miles above Louden. Bedrock 

in place. W. W. Atwood, 1907.

3252(3AH16). Yukon River, north bank, about 4% miles above Louden. 

Slide that came down from vicinity of coal mine. Arthur Hollick, 1903.

4635 (22). Yukon River, north bank, about 5 miles above Louden. Weathered material. Probably same as 2926 and 3252. W. W. Atwood, 1907.

3253 (3AH18). Yukon River, north bank, about 2 miles above Pickart mine. 

Sandstone. Arthur Hollick, 1903.

2679 (2AC249). Yukon River, north bank, strata above Pickart coal mine. 

A. J. CoUier, 1902.

2964 (2AC249). Yukon River, north bank, XO miles above Nulato. Strata 

above Pickart coal mine. A. J. Collier, 1902.

3254 (3AHl8a). Yukon River, north bank, just above Pickart mine. Shale 

and sandstone overlying the coal. Arthur Hollick, 1903.

4786 (25). Yukon River, north bank, above Pickart mine. Sandstone about 

665 feet above the coal horizon. (See section, p. 405.) W. W. Atwood, 1907

4638 (26). Yukon River, north bank, above Pickart mine. Shale and sandstone about 168 feet above the coal. (See section, p. 405.) W. W. Atwood, 

1907.

2682 (2AC253). Yukon River, north bank, at Nulato. A. J. Collier, 1902.

 (2AC ). "Front Street, Nulato." A. J. Collier, 1902.

2978 (2AC255). Yukon River, west bank, 6 miles below Nulato. Shale and 

thin-bedded sandstone. A. J. Collier, 1902.

7122. Yukon River, west bank, " about 7 miles below Nulato " (probably near 

Blatchford mine). W. H. Dall, 1866.

3258 (3AH19). Yukon River, west bank, at Blatchford coal mine, 9 miles 

below Nulato. Shale and sandstone underneath the coal. Arthur Hollick, 

1903.

3260(3AH21). Yukon River, west bank, 3 miles below Blatchford mine. 

Sandstone. Arthur Hollick, 1903.

2980 (2AC260), Yukon River, west bank, about 15 miles below Nulato, or 

4% miles below Blatchford mine. Landslide. A. J. Collier, 1902.

3259(3AH20). Yukon River, west bank, 2 to 10 miles below Blatchford 

mine. Float along shore. Arthur Hollick, 1903.

3261 (3AG22). Yukon River, west bank, 6 miles below Blatchford mine. 

Shaly sandstone. Arthur Hollick, 1903.

4639 (33). Yukon River, west bank, 16 miles below Nulato. Shale and sandstone. Same locality as 3261. W. W. Atwood, 1907.

2683, 2981 (2AC262). Yukon River, west bank, about 20 miles below Nulato, 

or 3V2 miles above Bluff Point, at foot of slide. A. J. Collier, 1902.

2932, 3262 (3AH23). Yukon River, west bank, about 20 miles below Nulato. 

Same as 2683. Arthur Hollick, 1903.

3263 (3AH24). Yukon River, west bank, about 22 miles below Nulato. 

Sandstone overlain and underlain by shale. Arthur Hollick, 1903.

2984 (2AC266). Yukon River, west bank, about 8 miles below Kaltag. 

A. J. Collier, 1902.

4640 (35). Yukon River, west bank, about 8 miles below Kaltag. Shale and 

sandstone. W. W. Atwood, 1907.

3268 (3AH29). Yukon River, west bank, about 8 miles below Kaltag. Sandstone and shale. Arthur Hollick, 1903.
424 MESOZOIC STRATIGRAPHY OF ALASKA

2684 (2AC272). Yukon River, west bank, 18 or 20 miles below Kaltag. 

Loose pieces lying on dark shale. A. J. Collier, 1902.

4642 (36). Yukon River, west bank, 1% miles above Williams coal mine. 

W. W. Atwood, 1907.

4794 (37). Yukon River, west bank, 1% miles above Williams mine. W. W. 

Atwood, 1907.

2685 (2AC282). Yukon River, west bank, 1 mile above Williams mine. 

Black shale. A. J. Collier, 1902.

3269 (3AH30). Yukon River, west bank, about 1 mile above Williams mine 

near 2685. Sandstone. Arthur Hollick, 1903.

2933 (3AH30). Yukon River, west bank, about 1 mile above Williams mine, 

a few yards below 3269. Arthur Hollick, 1903.

4641 (38),4795 (39). Yukon River, west bank, 1 mile above Williams mine. 

W. W. Atwood, 1907.

2985 (2AC284). Yukon River, west bank, at Williams coal mine. "Fossils 

mostly taken from sandstone immediately above coal bed." A. J. Collier, 1902.

2986 (2AC289). Yukon River, west bank, just below "mine No. 1." Crossbedded sandstone the base of which is 28 feet above the coal. A. J. Collier, 

1902.

3270 (3AH31). Yukon River, west bank, near "mine No. 1." Shale. Arthur 

Hollick, 1903.

3271 (3AH32). Yukon River, west bank, about 18 miles below mine No. 1. 

Float at outcrop of sandstone and shale with thin coal bed. Arthur Hollick, 1903.

4643 (40). Yukon River, west bank, about 18 miles below mine No. 1. 

W. W. Atwood, 1907.

9774 (16AHal34). Andreafski River, east bank, 9 miles northeast of 

Andreafski. G. L. Harrington, 1916.

7259 (16AHal36),9775 (16AHal35). Andreafski River, east bank, 9% miles, 

northeast of Andreafski. G. L. Harrington, 1916.

9776 (16AHal40). Andreafski River, west bank, 1% miles below Andreafski. 

G. L. Harrington, 1916.

The foregoing lists show that a relatively large proportion of the 

ferns and gymnosperms range throughout two or more of the formations, but that most of the angiosperms are restricted to one formation. This difference evidently means that the angiosperms, being 

merely highly organized, were more sensitive to changes in environment and consequently are better horizon markers. It is shown 

statistically by the fact that, among the angiosperms, 80 per cent of 

those in the fresh-water shale and sandstone, 37^ per cent of those 

in the marine sandstone and shale, and 86 per cent of those in the 

coal-bearing rocks are characteristic of one formation, whereas 

among the gymnosperms and lower plants only 24 per cent of those 

in the fresh-water shale and sandstone, 33 per cent of those in the 

marine sandstone and shale, and 56 per cent of those in the coalbearing rocks are characteristic of one formation.

A similar difference between the angiosperms and the lower plants 

is shown in the stratigraphic range of those species that occur in 

other regions. Although most of the species of fossil plants from
CRETACEOUS, LOWER YUKON REGION 425

these beds that are known in other regions occur in the Dakota sandstone or in beds that have been correlated with it, there are about a 

dozen species which have been generally regarded as characteristic 

of the Lower Cretaceous, as well as a few species that have been regarded as Montana or possibly Laramie. Every one of these supposed Lower Cretaceous and late Upper Cretaceous species are 

among the gymnosperms or lower plants, whereas all the previously 

described species of angiosperms that have been found in the Upper 

Cretaceous rocks of this region are known elsewhere only in the 

Dakota sandstone or in rocks of approximately equivalent age.

Stratigraphic range of Upper Cretaceous fossils from the lower Yukon

Fucusn. sp ___ . ________________ . ............

Cladophlebis n. sp ____________ . ____ . _____

Aneimian. var ... ____ .. .. _ .....-- . _ --------

Cycadites?-.. __ _____ _____ . ...... ...

Nilssonian. sp... ___ . ___ . ___ . _____ . _ .. __ .

Nilssonian. sp.-.. .. _ ..-_ .. _ .-.-- ----------

Nilssonian. sp... ________________________

Pterophyllum n. sp _ . ____ __ . _____ . ______ .

Podozamiteslanceolatus (Lindleyand Hutton) C. F.W. Braun.

Qinkgo?. .....-.....-.--.-.......... ..-.':.-....-- _ -----

Oinkgon. sp........ ___ _ . ___ ... ______ .. .........

Qinkgon. sp.. ____________________________

Nageiopsis augustifolia Fontaine ______________ - _ -

Protophyllocladus n. sp._ .....................................

Protophyllocladus n. sp_. ____________________

Cephalotaxopsis n. sp... ______ . ______ . __ .... _ .

Cephalotaxopsis n. sp.... __ .. ____ ....... ___ .. __ ..

Cephalotaxopsis ____ -...- ____ . __ .-.--.... _ . __ ..

Tumion n. sp _______ . __________ . __ ... ........

Firms? ........................................................

Sequoia ambigua Heer __ . _ _ _ _ .................. ...

Sequoia fastigiata (Sternberg) Heer ________ ...... ___

Sequoia reichenbachi (Qeinit?.) Heer ____________ -... __ _

Range on 

lower Yukon

Ungalik

....

Sequoia, n. var. ___ . ___ ................................!....

Sequoia subulata Heer?...... _ . _ ...... __ .............. _ l ....

Sequoia __ ...... ____ .... ... _ ........ . .......... ....

Sequoia? (Cones).. _ --.--.. __ . _ .. __ ...... ............ ....

Taxodium sp. Knowlton __ .. _.__---.__._.. .........

Glyptostrobus gronlandicus Heer _ ............ ....... . ..

Qlyptostrobus, n. sp... __ ; __ ..... _ . ___ ... _ . ___ ..

2ingiberites, n. sp..... __ ... _ . _ . __ ...... ___ ....... .. .

Piper, n. sp.. ____ ........... _ ..... __ ............. _ ... ....

Melozi

X

X

X

X

y

X

X 

X 

X

X

X

X

X 

X

v

X

X

X

X

Nulato

X

X

X

X

X 

X

X

X

X

X

M

"a3

M

X

X 

X 

X 

X

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X

xxxx

X

X 

X

"x"

X

X

X 

X 

X

xxxxx

Range in other regions

Lower Cretaceous. 

Raritan. lower Atane. 

Lower Cretaceous.

Lower Cretaceous. 

Magothy.

Dakota? 

Lower Cretaceous. 

Lower Cretaceous. 

Laramie, Nanaimo, etc.

Lower Cretaceous.

Laramie. 

Dakota.

Magothy, Koine, etc. 

Dakota. 

Magothy, Patoot. 

Dakota. 

Lower Cretaceous.

Lower Cretaceous. 

Lower Cretaceous. 

Lower Cretaceous.
426 MESOZOIC STRATIGRAPHY OF ALASKA

Stratigraphic range of Upper Cretaceous fossils from the lower Yukon Contd.

Populites, n. sp ___ ... __ .......... ___ .... __ ... _ --

Populites, n. sp... ___ .......................... __ .........

Populites? n. sp........ .........................................

Betulites, n. var.... ...... . . ..--..-..-.- .. --.....----

Quercus eamesi Trelease?.. _ ........ _ ................ _ ...

Castaliites, n. sp... .... ........................................

Cinnamomum, n. sp...._.... . . .. ---

PseudoprotODhyllum n. sp.... ...-..-.--.-.-..-.....-...--.----

Range on 

lower Yukon

a a

S £

1"3

S

X

X

X

X

X

X

X

X

X

X

X

X

X 

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

2

_ri "3 

£

X

X

X

X

toeS

"3

M

X 

X 

X

X 

X 

X

X

X X1 

X

X

X 

X 

X

X 

X

X 

X 

X 

X 

X

X

X

X

X 

X 

X 

X

X 

X 

X 

X 

X

X

"x"

X 

X 

X 

X 

X 

X 

X

X 

X 

X 

X 

X

Range in other regions

Dakota. 

Dakota.

Dakota.

Dakota. 

Dakota.

?British Columbia.

Dakota. 

Dakota. 

Raritan, Magothy.

Dakota.

Dakota. 

Dakota.

Dakota. 

Dakota. .
CRETACEOUS, LOWER. YUKCW REGION 427 

StratifjrapMc range of Upper Cretaceous fossils from the lower Yukon Contd.

Pseudoprntophyllnm? n. sp

Pseudoprotophyllum... ___ . __________ ... _ . ......

Pseudoaspidiophyllum n. sp...__ _____ ... _ . ____ ...

Pseudoaspidiophyllum n. sp..... _____ . _________

Pseudoaspidiophyllum n. sp... ______ . _____ .......

Leguminosites n. sp.. ____ . ___ . _________ .......

Cassia n. sp _ ...... _ . .

Cotinusn. sp...... _ ... ________ ... __ . .... _ .....

Acer n. sp __ . _ ..... _____ . _____ ........ _ ......

Sapindus morrisoni Lesquereux MS. Heer __ .. ........... .

Rhamnitesn. sp.. ___ . __ . _ . __ . . ....... .

Zizyphus n. sp __ _ '............

Vitis n. sp __ . _______ .... ___ . ________ .......

Vitis n. sp __ ___ ....

Vitis n.sp... ........ . . .

Cissites n. sp ____ ...

Cissites n. sp __ .......... . _ _ .

Cissites n. sp.. _____ ... ___ ... _ ... .............

Ampelopsis? n. sp ___ . ______ . __ . ___ ....

Tilian. sp . ........

Grewiopsis n. sp.... ...... ...

Stercuha n. sp.... ...... ________ ... ___ .. __ . ...

Aralia wellingtoniana Lesquereux... __ . ___ . _ . __ .....

Aralia, n. sp. __ ... ...... . .

Aralia polymorpha Newberry ___ .-........-.....---..,... ..

Hederan. sp _____ . ___ .. ... . __ . .. _ . .

Andromeda? ___ . ...

Myrsine gaudini (Lesquereux) Berry. ...... __ .......... .

Sapotacites n. sp _ . _ ............. __ ... _ . _ .... .

Viburnum, n. sp....... _ ....... .. _ . _ ......

Viburnum n. sp. ..........

Viburnum n. sp. . .

Viburnum _ .......

Phyllites n. sp. __ . _ ... _ . . .

Phyllites...........

Undetermined plant fragments.. .. ......... ... ....

Hemiaster........ ___ ... __ . .. . _

Worm burrows.... _ .....

Trails...............

Nucula? n. sp....... ____ . _ .. __ ... ......

Nucula? _ . _ 1 ............ . .... .. . ... . ... .. ...

Leda n. sp... .................... .. ..... ...

Cucullaea mathewsoni Gabb

Cucullaea truncata Gabb?.

Cucullaea..-.--.. _ . ______ _ ... ....

Cucullaea?......-...... __ .'....

Pinna............... _ ...

Inoceramus cf . I. labiatus Schlotheim. . ..... ______ ...

Inoceramus.... __ ............. _______ . _ . ...

Inoceramus?. . ......

Ostrean. sp.......... __ . _ . _ .. ... _ .....

Ostrean. sp. ........................ ..... ...

Ostrea n. sp_. ......

Ostrea _ ........... . ....

Unio n. sp. .........

Union, sp.. _ ......... _ ..... _ ... .. _ .. .....

Unio..........................................

Trigonia leana Gabb ____ ....

Trigonia no wcombei Packard ?...... .......

Trigonia n. sp.... _ ............... . __ ..

Trigonia......................................................

Pectenn. sp _ ... ______ .. ___ ...... __ . __ . __ ..

Anomia.... _____ . ____ . _______ ... . _ .. ...

Mytilus.. ... _ .. . ..

Pleuromyan. sp... __ ... __ .............. .....

Pholadomya n. sp. ...........................

Pholadomya...................... __ ........ .....

Thracia sp...... __ .... _ . ______ . _ . . ......

Thracia? n. sp. ____ ..... ___ __ ..

Thracia?. _ . ___ . ____________ ..

Astarte n. sp _ . __ ............ _ ... ......

Range on 

lower Yukon

Ungalik

X

'5

O"3

X

X

X

X

X

X

X

X 

X

X

X

X

y

y

Nulato

X

X

X

y

y

y

y

y

y

y

X 

v

X

y

y

y

y

y

X

X

X

X

to

a

"3 

M

X 

X

X 

X 

X

X

xxxx

X

X 

X

X

X 

X 

X

X 

X 

X 

X 

X -X 

X 

X 

X

X

X

X 

X

X

X

X

Range in other regions

Dakota. 

Dakota. 

Magothy?

Dakota. 

Raritan

Dakota, Magothy.

Eocene (Martinez formation). 

Chico.

Chico, Colorado group.

Chico. 

Haida formation.
428 MESOZOIC' STRATIGRAPHY OF ALASKA

Stratigraphic range of Upper Cretaceous fossils from the lower Yukon Contd.

Astarte. _ ___ ....... _ .... _ ... __ .. ___ ____ ..

Astarte? n. sp ______ . ___ ....... _ ____ .. __ .. .....

Astarte?..... _ .... _ ............................. _ ........

Opis?................,.... .....................................

Corbicula? ______ ___ .. _ .... ___ .. ___ __

Meekia? _______ .. _ .. __ ........ _____ . ___ ...

Lucina n. sp _____________ . .........................

Lucina?... ... ...... ... . .............................

Cardium (Trachydium) n. sp ..................................

Protocardia n. sp. ________________________

Protocardia. _____ ___ _ .... __ 1 _ __ ____ .....

Veneridae __________ . ..... ........ .................

Meretrix.J _________ . __________________

Meretrix? __________ .... ___ . .......................

Tellinacf. T. ashburnerii Oabb ................. ...............

Tellina?.. .....................................................

Corbula.... ........ __ ... ......................... _ ......

Panopen. sp...... ............................................

Panope concentrica (Gabb) Whiteaves var. __________

Panopea? ____________________________

Turritella... -..-_ __ .........................................

Qoniobasis.. ___________ .... ___________ . .. 

Goniobasis? ____________ ..... .......................

Anchura cf. A. transversa Gabb.. .............................

Sonneratia? _____________ .* .........................

Ammonites _____ __ ____ __ . _ ____ _ ., _ ..

Range on 

Lower Yukon

Ungalik

X

8"3 

%

X

X

Nulato

y

v

y

V

y

y

X

v

v

v

X

X

X

V

X 

X

X

X

v

Y

X

X

X

X

"3 I

M

X 

X

X

"x"

X 

X

X

X 

X

Range in other regions

Chico. 

Chico.

Chico.

In conclusion it may be stated that the Upper Cretaceous rocks of 

the lower Yukon region seem to correspond in age, in a general 

way, with the Dakota sandstone. The evidence of the plants and of 

the marine mollusks is practically in accord, most of the previously 

*described species of plants occurring in the Dakota sandstone and 

the marine mollusks indicating "that the horizon is within the 

Upper Cretaceous but probably not higher than the middle of the 

Upper Cretaceous." The writer believes, however, that these rocks 

probably have a considerably greater range in age than the Dakota 

sandstone. This is indicated by the thickness of the rocks, which 

probably exceeds 8,000 feet; by their divisibility into four distinct 

formations; and by the fact that a large proportion of the plants, 

including almost all the angiosperms, do not range up from one of 

the formations into another. If it were possible to make a comparison of the floras with modern lists of fossil plants occurring at sue-
CRETACEOUS, INNOKO AND IDITAROD VALLEYS 429

cessive horizons throughout the Upper Cretaceous of a near-by 

region, the comparison would probably indicate that a considerable 

part, very likely the lower half or two-thirds of the Upper Cretaceous is represented by the Upper Cretaceous rocks of the lower 

Yukon.

INNOKO AND IDITAROD VALLEYS 

GENERAL FEATURES

The Upper Cretaceous rocks of the Innoko and Iditarod Valleys, 

which are probably the southern extension of the Upper Cretaceous 

rocks of the lower Yukon region, consist chiefly of marine shale and 

sandstone. Some terrestrial (coal-bearing) sandstone which is 

closely associated with them may be intercalated Upper Cretaceous 

deposits or may be infolded Tertiary sediments. These Upper Cretaceous strata are believed to rest everywhere upon Paleozoic rocks, 

no Lower Cretaceous or earlier Mesozoic rocks being known in this 

region, unless some chert and argillite exposed along the divide between the Innoko and the South Fork of the Sulatna, which Mertie 

and Harrington 1 referred tentatively to the Mesozoic, should prove 

definitely to be of Mesozoic age. The chert and argillite beds in 

the writer's opinion, are certainly pre-Cretaceous. The thickness of 

the Upper Cretaceous rocks is not known but is believed to be several thousand feet. They may be overlain unconformably by the 

supposed Tertiary conglomerate, grit, and sandstone of the upper 

Susulatna Valley (see pp. 431-432), by the possibly Tertiary coalbearing sandstone 2 on Poorman Creek and near Iditarod, and by the 

supposed Tertiary lignite-bearing beds 3 on the lower Innoko.

UPPER CRETACEOUS

SHALE AND SANDSTONE

Historical review. The Upper Cretaceous shale and sandstone 

of this district were first mentioned by Maddren, who made a hurried 

geologic reconnaissance of the Innoko placer district in 1908. Maddren described,4 under the heading "Mesozoic rocks in the Innoko 

basin," some "hard limy sandstones and shales" exposed near the 

point where the Innoko leaves the mountains; and also conglomerate, grit, and shale exposed south of Ganes Creek. Maddren found 

no local evidence as to the age of these rocks, except that they unconformably overlie rocks which he believed to be Devonian and

1 Mertie, J. B., jr., and Harrington, G. L., The Ruby-Kuskokwim region, Alaska : U. S. 

Geol. Survey Bull. 754, pp. 22-24, 1924.

2 Idem, pp. 26-27, 34, 119-120.

8 Maddren, A. G., The Innoko gold-placer district, Alaska: U. S. Geol. Survey Bull. 410, 

pp. 56-57, 1910. 

4 Idem, p. 55.
430 .MESOZOIC STRATIGRAPHY OF ALASKA

that they are more indurated than some beds farther down the 

Innoko which he supposed were Tertiary. His conclusion as to their 

age is that they "are considered to be of Mesozoic age and t6 be 

northeasterly outliers of the extensive Mesozoic formations found by 

Spurr on Kuskokwim River."

Maddren also described 5 black slate exposed on Innoko River 

from a point 10 miles below Ophir to the divide south of Ganes 

Creek, which he regarded as unconformably underlying the " Mesozoic rocks in the Innoko basin" and as Devonian or Silurian, but 

which subsequent writers have considered Mesozoic.

In 1910 Maddren again visited .the Innoko-Iditarod district, but 

the geologic results of this field examination have been published 

only in a preliminary statement,6 in which it is said that

The sedimentary rocks of the Kuskokwim Mountains are a series of alternating beds of sandstones, carbonaceous and calcareous shales, shaly and 

siliceous limestones, granitic arkoses, volcanic tuffs, and conglomerates. The 

sandstones are generally rather thinly bedded and flaggy. The shales range 

from soft to fairly hard rocks and in the Innoko district appear to be partly 

altered to slates. Near their contacts with granitic intrusives they have been 

locally hardened into blocky quartzites and argillites.

The few fragmentary fossil remains of land plants and marine-shell forms 

that have so far been found in these sediments point to an undoubted Mesozoic age for the series and a probable Cretaceous age for its younger members, 

of which the arkose sandstones appear to form a part.

Another geologic reconnaissance of the Innoko-Iditarod district 

was made in 1912 by Eakin,7 who gave a general description of the 

distribution and character of the Cretaceous rocks. The Cretaceous 

rocks are described as chiefly sedimentary, but with some basic 

flows, breccia, and tuff irregularly distributed among them. The 

sedimentary rocks comprise coarse and fine conglomerate, sandstone, 

shale, and slate". The conglomerate is found chiefly near the base 

of the series, in proximity to the old metamorphic rocks from which 

it was derived. By far the larger part of the sedimentary series is 

composed of sandstone and shale or slate. Marine Upper Cretaceous 

fossils, collected on Ophir Creek, are mentioned but not listed.

A geologic reconnaissance from Lake Clark to Iditarod was made 

by P. S. Smith in 1914. Although the area described and mapped 

by Smith lies south of the Innoko-Iditarod district, some of the rocks 

which he describes, namely, the "Mesozoic sedimentary rocks north 

and west of the Holitna," 8 were traced from the Kuskokwim to

"Maddren, A. G., op. dt., pp. 49-50.

6 Maddren, A. G., Gold placer mining developments in the Innoko-Iditarod region: 

U. S. Geol. Survey Bull. 480, pp. 243-245, 1911.

7 Eakin, H. M., The Iditarod-Ruby region, Alaska: U. S. Geol. Survey Bull. 578, pp. 

23-24, pi. 3, 1914.

8 Smith, P. S., The Lake Clark-central Kuskokwim region, Alaska: U. S. Geol. Survey 

Bull. 655, pp. 77-84, 1917.
431

Iditarod, and exposures near Iditarod undoubtedly were in part the 

basis of the description, though they are not specifically mentioned. 

In discussing the age and correlation of these rocks, Smith quotes a 

previously unpublished statement by Stanton 9 on some Upper Cretaceous fossils collected by Eakin in the Innoko district in 1912.

The geology of the Innoko-Iditarod district was studied by Mertie 

in 1915, and a preliminary report on this work contains a brief general description of the Cretaceous rocks.10

The Tolstoi placer mining district was visited in 1917 by G. L. 

Harrington, who has given a brief general description of the Cretaceous rocks.11

The final report on the Kuby-Kuskokwim region by Mertie and 

Harrington contains a full description of the Upper Cretaceous beds 

under the heading "Upper Cretaceous and Eocene rocks." This 

account 12 contains a general discussion of the distribution, lithology, 

'stratigraphy, structure, fauna, flora, and age of the Upper Cretaceous and Tertiary rocks of the entire region, of which the area 

occupied by Upper Cretaceous rocks not only includes parts of the 

Innoko and Iditarod valleys but extends southward to the Kuskowim. 

Local details concerning the rocks in several geographic subdivisions 

of the region are given under separate headings. Lists of fossils as 

identified by Stanton are quoted. The supposed Tertiary rocks were 

not mapped separately from the Upper Cretaceous rocks in the 

field, but the separation is indicated in a general way in the text.13 

Most of the description is believed to apply to the Upper Cretaceous 

rocks. The fossils listed 14 in lots 9364, 9365, 9366, and TOOT are 

believed to be Tertiary.

Stratigraphic description. The Upper Cretaceous rocks of the 

Innoko and Iditarod valleys consist chiefly of shale and sandstone, 

with some intraformational conglomerate. Their thickness is not 

known, but according to Mertie and Harrington it is to be measured 

in thousands of feet. Their base has not been recognized, but they 

are believed to lie unconformably upon Mesozoic (?) chert and 

argillite and Paleozoic rocks. They are overlain, with probable 

unconformity, in the writer's opinion, by conglomerate, grit, and 

sandstone that are exposed in-the upper Susulatna Valley and.contain fossil plants,1 * which Hollick believes to be Tertiary, together

8 Smith, P. S., op. cit, p. 83.

10 Mertie, J. B., jr., and Harrington, G. L., Mineral resources of the Ruby-Kuskokwim 

region: TJ. S. Geol. Survey Bull. 642, p. 233, 1916.

11 Harrington, G. L., The gold and platinum placers of the Tolstoi district: TJ. S. Geol. 

Survey Bull. 692, p. 344, 1919.

12 Mertie, J. B., jr., and Harrington, G. L., The Ruby-Kuskokwim region, Alaska: U. S. 

Geol. Survey Bull. 754, pp. 24-41, pis. 3, 4, 1924.

18 Idem, p. 30. ' * 

14 Idem, p. 40.
432 MESOZOIC STBATIGEAPHY OF ALASKA

with fossil shells which Stanton says are " probably not lower than 

Upper Cretaceous." The coal-bearing sandstone found in and near 

the Upper Cretaceous areas near Iditarod and at other places may 

be a member of the Upper Cretaceous sequence or may be infolded 

Tertiary beds. These coal-bearing beds have yielded no fossils.

Age and correlation. The Upper Cretaceous shale and sandstone 

of the Innoko and Iditarod valleys have yielded fresh-water and 

marine fossils, concerning which Stanton 16 has submitted the following statements:

7822 (12 AE 2). Ridge north of Folger Creek, 21 miles from margin of flats. 

Collected by H. M. Eak^n in 1912. Unio sp. Casts of a very small undescribed 

species. Specimens of a small Unio, possibly belonging to this species and in 

closely similar rock, were collected by Collier at Good Island, on the Yukon 

above the mouth of the Koyukuk. The fossils give no direct information as to 

the age, as similar types occur in both Cretaceous and Tertiary, but from geographic relations the locality at Good Island ought to be near the base of the 

Upper Cretaceous.

7823 (12 AE 3). Ophir Creek 1 mile above town. Float in creek bed. Collected by H. M. Eakin in 1912. Inoceramus sp. Several fragmentary distorted 

specimens that may belong to Inoceramus digitatus Sowerby, an Upper Cretaceous species. Whether it is really this species or not, it is believed to be an 

Upper Cretaceous type.

9367 (4). 1.1 miles from southwest peak of Camelback Mountain and 1.3 miles 

from northeast peak at head of Bonanza Creek. Collected by J. B. Mertie, jr., 

in 1915. Inoceramus sp. related to 7. laMatus Schlotheim. Probably Upper 

Cretaceous.

KUSKOKWIM REGION 

GENERAL FEATURES

' The Cretaceous rocks of the Kuskokwim region include marine

Lower Cretaceous sandstone and conglomerate on the western front 

of the Oklune Mountains, east of Kuskokwim Bay, and fresh-water 

and marine Upper Cretaceous shale, sandstone, and conglomerate 

exposed along Kuskokwim River and its tributaries. The Lower 

Cretaceous rocks are known only from float material at a single locality and are not believed to have any great areal extent, although they 

may be present in much of the unmapped area south of Kuskokwim 

River. The Upper Cretaceous rocks .are the direct southern extension of the Upper Cretaceous rocks of the Iditarod-Innoko district 

and are believed to extend throughout broad areas on both sides of 

the Kuskokwim.

The lower Cretaceous rocks of the Kuskokwim region consist of 

sandstone and conglomerate and probably shale. Their thickness 

and stratigraphic sequence have not been determined. The fauna as

16 Stanton, T. W., cited by Myrtle, J. B., jr., and Harrington, G. L., The Ruby-Kuskokwim region, Alaska: U..S. Geol. Survey Bull. 754, pp. 39, 40, 1924.
CRETACEOUS, KUSKOKWIM REGION 433

now known includes only Aucella crassicollis, which is the characteristic fossil of the^ Lower Cretaceous of Alaska., These rocks 

are believed to rest unconformably on late Carboniferous or early 

Mesozoic volcanic rocks and are probably overlain unconformably 

by the Upper Cretaceous rocks described below.

The Upper Cretaceous rocks of the Kuskokwim region consist of 

conglomerate, sandstone, and shale having a thickness of many thousand feet. It is believed that in the lower Kuskokwim region they 

rest unconformably on the Lower Cretaceous sandstone and conglomerate. Farther up the river, where the Lower Cretaceous rocks are 

absent, the Upper Cretaceous rocks lie unconformably on Devonian 

limestone. The Upper Cretaceous rocks include both marine and 

nonmarine members, which are believed to be the equivalents and 

perhaps the continuous southward extensions of some or all of the 

Upper Cretaceous formations exposed on the lower Yukon.

LOWER CRETACEOUS

Historical review.. The Lower Cretaceous rocks of the Kuskokwim region were included by Spurr 17 iri the " Oklune series," which 

he defined as including the larger part of the consolidated sedimentary rocks between Kuskokwim and Nushagak bays. This area includes rocks of diverse character, which probably do not constitute 

a stratigraphic unit. The only evidence that any of them are Lower 

Cretaceous was found in a boulder of sandstone and conglomerate, 

containing Aucella crassicollis, which Spurr obtained on Kanektok 

River near the western front of the " Oklune " (Ahklun) Mountains. 

Spurr believed that this boulder "undoubtedly came .from rocks 

in the immediate vicinity," which he described as "sandstones, arkpses, conglomerates, and carbonaceous shales." These rocks lie 

on the edge of the area occupied by the " Oklune series," which Spurr 

defined as including shale, limestone, chert, arkose, lava, and tuff.

His description includes a detailed account of the lithology and 

structure of the rocks observed at several localities and general statements concerning the character, age, and correlation. A statement 

by T. W. Stanton concerning the fossils from Kanektok River is 

repeated.

A brief discussion of the age and relations of the " Oklune series " 

was given by Brooks,18 who referred it to the "Jura-Cretaceous," 

but no new information was presented.

The southwestern extension of the " Oklune series " in the Goodnews Bay district was mapped by Harrington as "Mesozoic (?)

17 Spurr, .T. E., A reconnaissance in southwestern Alaska in 1898: U. S. Geol. Survey 

Twentieth Ann. Kept., pt. 7, pp. 133-134, 163-169, 181-182, 1900.

18 Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 

45,, p. 236, 1906.
434 MESOZOIC STRATIGRAPHY OF ALASKA

sandstones, slates, argillites, cherts, and graywackos, with some included flows and tuffs of basalt." Harrington's description 19 of 

these rocks is very brief and does not clearly indicate the distinction 

between the supposed Mesozoic and the supposed Carboniferous 

rocks, which are separated on the map.20 Harrington obtained no 

fossils and gives no stratigraphic details or any evidence of the age 

of the rocks.

Stratigraphic description. The "Oklune series" was defined by 

Spurr as follows: 21

Lithologically the series consists of beds which are in a general way similar 

throughout, being shales, impure limestones, and cherts, often organic, with 

beds of arkose, derived from granites or other coarse-grained igneous rocks. 

In nearly every district are abundant volcanic rocks, of ancient appearance, 

having a greenish color due to alteration, and associated with these are sedimentary tuffs, which are evidently derived from the same volcanic sources. 

Volcanic material is more abundant in certain districts than in others but is 

thoroughly characteristic of the series.

Age and correlation. The only fossils that have been obtained 

from the rocks referred to the " Oklune series " are some specimens of 

Aucella crassicollis which Spurr obtained in a large boulder of sandstone and conglomerate on Kanektok River just below Nukluk 

Creek and which he believed came from the near-by beds of arkose, 

sandstone, conglomerate, and carbonaceous shale. The position of 

these beds in the " Oklune series," the general stratigraphic sequence 

and thickness of the " Oklune series," and the identity of the rockfe 

that underlie and overlie it have not been determined.

The writer believes that the " Oklune series " as defined by Spurr 

constitutes a heterogeneous assemblage of rocks having a wide 

stratigraphic range. The volcanic members are probably not Cretaceous and may perhaps be correlated in part with the late Carboniferous or early Mesozoic tuff that overlies an upper Carboniferous 

limestone on the Kuskokwim just above Ohagamut and in part with 

the Tertiary volcanic rocks of the lower Yukon and Bristol Bay 

districts. The identity of part of them with the late Carboniferous 

or early Mesozoic volcanic rocks is suggested by the fact that in the 

southwestern extension of this area, near Goodnews Bay, Harrington found a limestone which he considered as possibly Carboniferous. 

The " Oklune series " may also include the equivalent of part of the 

Upper Cretaceous shale and sandstone that cross the Kuskokwim 

above Kolmakof. Possibly only a small part of the rocks that were 

included in the " Oklune series " is Lower Cretaceous.

18 Harrington, G. L., Mineral resources of the Goodnews Bay region, Alaska: U. S. 

Geol. Survey Bull. 714, pp. 215-218, 1921.

20 Idem, pi. 7.

21 Spurr, J. E., pp. clt., p. 168.
CRETACEOUS, KUSKOKWIM REGION 435

It may be concluded that there are. Lower Cretaceous Aucellabearing rocks in the lower Kuskokwim region which include sandstone and .conglomerate and probably shale. The thickness and 

stratigraphic sequence of these rocks are not known. They probably 

lie unconformably upon late Carboniferous or early Mesozoic volcanic rocks and are probably overlain unconformably by Upper 

Cretaceous conglomerate,, sandstone, and shale.

UPPER CRETACEOUS

Historical review. The Upper Cretaceous rocks of the Kuskokwim region were described 22 by Spurr as the "Holiknuk series." 

Spurr also described 23 some supposed Cretaceous rocks as the " Kolmakof series," which he regarded as the probable lateral equivalent 

of the " Holiknuk series " but as differing from it in being composed 

largely of volcanic material. The writer believes, as will be shown 

below (see p. 440), that probably only part of the " Kolmakof series " 

is Cretaceous. Spurr's descriptions of the "Holiknuk" and "Kolmakof series" include detailed statements concerning the rocks 

observed at several exposures and general discussions of the distribution, composition, structure, and age o'f the series. A statement by T. W. Stanton concerning fossils from the "Holiknuk 

series" is quoted.

In a brief discussion of the Mesozoic rocks of the Kuskokwim 

Valley, Brooks 24 suggests that the " Holiknuk series " may belong to 

the Jurassic or Triassic and that the "Kolmakof series" and 

" Oklune series " may be younger.

The quicksilver deposits on Kuskokwim River 15 miles above 

Georgetown and 5 miles below Kolmakof were visited in 1914 by 

P. S. Smith and A. G. Maddren,25 whose report contains some 

observations concerning the Cretaceous rocks in the vicinity. The 

rocks at the Parks prospect, 15 miles above Georgetown, which had 

been included by Spurr in the "Holiknuk series," were described 

by Smith and Maddren as Cretaceous sandstone and shale cut by 

dikes and sills. The rocks at the prospect 5 miles below Kolmakof, 

which had been included by Spurr in the "Kolmakof series," were 

described by Smith and Maddren as sandstone and shale aggregating at least 4,000 to 5,000 feet in thickness and cut by dikes and sills. 

It should be noted that although Spun- described the "Kolmakof

22 Spurr, J. E., A reconnaissance in southwestern Alaska in 1898: TJ. S. Geol. Survey 

Twentieth Ann. Kept., pt. 7, pp. 125-128, 159-161, 182, 1900. 

2« Idem, pp. 129-131, 161-163, 182-183.

24 Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 

45, p. 236, 1906.

25 Smith, P. S., and Maddren, A. G., Quicksilver deposits of the Kuskokwim region : 

U. S. Geol. Survey Bull. 622, pp. 275-278, 281-286, 1915.
436 MESOZOIC STRATIGRAPHY OF ALASKA

series " as dominantly volcanic, a critical study of his detailed observations shows that the rocks for about 14 miles below Kolmakof 

are shale and sandstone, like those of. the " Holiknuk. series," cut 

by dikes and sills and without true volcanic members, and that 

the undoubtedly volcanic members of the series were found farther 

down the river, where they are not associated with any supposed 

Cretaceous shale and sandstone, but where Maddren subsequently 

found that they are intimately associated with a Carboniferous 

limestone.

The 'Mesozoic sedimentary rocks exposed along Kuskokwim River 

between the mouth of the Holitna and Georgetown and in an area 

situated chiefly on the headwaters of the Holitna but extending 

southward into the valleys of the Mulchatna and Chulitna were described by P. S. Smith 26 under four subdivisions, including, from 

oldest to youngest, the " conglomerate of Cairn Mountain," the 

"Mesozoic shales south of the Kuskokwim," the "Mesozoic sandstones south of the Kuskokwim," and the "Mesozoic sedimentary 

rocks north and west of the Holitna." Smith believed that the first 

three of these subdivisions are in part Jurassic, but this opinion 

was not based on paleontologic evidence. The writer suspects that 

all the subdivisions may be conformable members of the Upper 

Cretaceous. Smith's description of these rocks includes discussions 

of the distribution, topographic expression, lithologic character, 

structure, age, and correlation of each subdivision, with statements 

by T. W. Stanton concerning fossils from the "shales south of the 

Kuskokwim" which he considered as indicating an indefinite position in the Mesozoic, probably Jurassic or Cretaceous, and from the 

" rocks north and west of the Holitna " which he regarded as probably Upper Cretaceous.

The Upper Cretaceous rocks of the area between Kuskokwim 

River and Iditarod were described by Mertie and Harrington 27 

under the heading "Upper Cretaceous and Eocene rocks." These 

rocks were " thought to be mainly of Upper Cretaceous age, though 

grading upward into the Eocene," but the supposed Eocene beds are 

not known within the Kuskokwim region. The description includes 

a general account of the supposed Upper Cretaceous and Eocene 

rocks of the entire Ruby-Kuskokwim region, with local details concerning certain areas, among which are the Takotna and Tatalina 

Valleys 28 and the district from "Iditarod to Kuskokwim River,29

28 Smith, P. S., The Lake dark-central Kuskokwim region, Alaska: U. S. Geol. Survey 

Bull. 655, pp. 57-84, 1917.

27 Mertie, J. B., jr., and Harrington, G. L., The Ruby-Kuskokwim region, Alaska : U. S. 

Geol. Survey Bull. 754, pp. 24-41, pi. 4, 1924.

28 Idem, pp. 31-32. 

28 Idem, pp. 35-36.
CRETACEOUS, KUSKOKWIM REGION 437

which lie within the region here under discussion. The description 

of the district from Iditarod to Kuskokwim River is an abstract of 

the description by P. S. Smith. The discussion of the " flora, fauna, 

and age " 80 contains lists of fossils as identified by Stanton and by 

Hollick. Among these fossils are several collections from the Kuskokwim region.

Stratigraphic description. No detailed stratigraphic studies of 

the Cretaceous rocks of the Kuskokwim region have yet been made, 

but the published observations of Spurr and Smith furnish the basis 

for some tentative generalizations concerning the general stratigraphic sequence. The general succession of beds appears to be, as 

might be expected, somewhat similar to the section on the Yukon.

The base of the Upper Cretaceous rocks was found, according to 

Spurr,31 about 10 miles below Vinasale, where Devonian limestone is 

overlain unconformably b}^ thin-bedded gray arkose and conglomerate. These younger rocks are comparatively unaltered and, according to Spurr, closely resemble the Cretaceous rocks of the Yukon. 

The conglomerate is coarse, containing some pebbles 5 or 6 inches in 

diameter. Spurr states that " rocks of this same appearance outcrop 

all along the river as far as the Holiknuk." The shale and sandstone show lateral intergradations within short distances. No fossils 

were seen except abundant but poorly preserved plant remains. 

One specimen of a post-Jurassic dicotyledonous leaf was collected. 

The strike from the contact with the Devonian rocks to the mouth 

of the Holiknuk is in general but not everywhere parallel to the 

course of the river, and the dip is in general but not uniformly to the 

northwest. Both in this section and in that on the Yukon River 

near Melozi the basal Cretaceous rocks are conglomerate, shale, and 

sandstone, which overlie limestone that is presumably Devonian. In 

each section obscure plant remains are abundant, but well-preserved 

plants are rare, and marine fossils are absent. The writer believes 

that the Cretaceous rocks on the Kuskokwim above the mouth of 

the Holitna are to be correlated with the basal conglomeratic rocks 

(Ungalik conglomerate) of the Yukon section and possibly with 

part or all of the overlying fresh-water shale and sandstone (Melozi 

formation). The rocks south of the Kuskokwim that were described 

by Smith 32 as the " conglomerate of Cairn Mountain " resemble the 

lower conglomeratic division of the Cretaceous sections on Yukon 

and Kuskokwim rivers in lithologic character and in stratigraphic 

relations and are, in the writer's opinion, to be correlated with that 

division. The " conglomerate of Cairn Mountain " consists of beds

3°Mertie, J. B., jr., and Harrington, G. L., op. cit., pp. 39-41.

<" Spurr, J. E., op. cit., p. 125.

*> Smith, P. S., op. cit, pp. 58-63.

49448 26 29
438 MESOZOIC STRATIGRAPHY OF ALASKA

of coarse and fine conglomerate with some coarse sandstone. Cobbles a foot or more in smallest diameter are by no means uncommon, 

but most of the pebbles are less than 3 inches in diameter. Most of 

the larger pebbles consist of igneous rocks, and the smaller ones of 

dark slate, with some limestone, chert, quartzite, and vein quartz. 

A pebble of calcareous sandstone containing Devonian fossils was 

found. Smith does not state the thickness of the conglomerate, but 

it may be inferred33 to be much more than 300 feet. Although no 

rocks are exposed directly beneath the conglomerate, it dips away 

from a supposed Devonian limestone, on which it is believed to rest 

unconformably.

The rocks exposed on Kuskokwim Itiver from the moutli of Urn 

Holitna to a place about 14 miles below Kolmakof were described 

by Spurr 34 as limestone, shale, and arkose. Some of the shale is 

carbonaceous and contains coal fragments. Abundant plant remains 

were noted, but they are presumably only fragmentary, as no fossil 

plants were collected. Marine fossil shells (Inoceramus) were obtained at two localities. The rocks exposed along the Kuskokwim 

between the mouth of the Holitna and the Parks quicksilver mine 

and in the hills between the mouth of the Holitna and Iditarod were 

described by Smith 35 as chiefly shale and sandstone. Some coarse 

sandstone and fine conglomerate with a calcareous matrix was found, 

but no limestone was seen. The sandstone contains abundant fragments of vegetable remains, but no well-preserved fossil plants were 

found. Marine fossils (chiefly Inoceramus) were found at several 

localities. The rocks exposed on the Kuskokwim near Kolmakof 

were described by Smith and Maddren 30 as thin-bedded sandstone 

and shale aggregating at least 4,000 to 5,000 feet in thickness, over 

lain conformably by arkosic sandstone at least 1,000 feet thick. Ma 

rine fossils (Inoceramus) were obtained in the arkosic sandstone.

The rocks exposed along the Kuskokwim from the mouth of the 

Holitna to a place about 14 miles below Kolmakof and in the hills 

north of the river are chiefly shale and sandstone, which have yielded 

marine fossils at several localities. The writer believes that these 

rocks correspond to the marine sandstone and shale (Nulato formation) of the Yukon section. This area may also contain some rocks 

corresponding to the coal-bearing Kaltag formation, which overlies the Nulato, and to the fresh-water shale and sandstone (Melozi 

formation), which underlie the Nulato, but no evidence of them has 

been recorded.

»» Smith, P. S., op., fit., p. 61. 

34 Spurr, J. B., op. cH., pp. 126-180. 

38 Smith, P. S., op. cit, pp. 77, 84.

36 Smith, P. S., and Maddren, A. G., Quicksilver deposits of the Kuskokwim region: 

U. S. Geol. Survey Bull. 622, p. 282, 1915.
CRETACEOUS, KUSKOKWIM REGION 439

South of the Kuskokwim, throughout an area extending southward 

from the divide between Stony and Hoholitna Rivers across the 

valley of the Mulchatna to Chulitna River just west of Lake Clark, 

Smith found some Mesozoic shale and sandstone overlying the " conglomerate of Cairn Mountain" (see pp. 437-438), which he considered as at least partly Jurassic but which, in the writer's opinion, 

should be correlated with the Upper Cretaceous rocks exposed on the 

Kuskokwim.

The rocks described by Smith 37 as " Mesozoic shales south of the 

Kuskokwim " are composed mainly of nearly black shale, but include 

in almost every large exposure some beds of sandstone. These rocks 

are believed to lie conformably upon the "conglomerate of Cairn 

Mountain" and are apparently overlain unconfofrmably by the 

"Mesozoic sandstones south of the Kuskokwim." No estimate of 

their thickness has been made. Organic remains are very uncommon in them, but small fragments of plant remains were seen in some 

of the finer sandstone and fragments of pelecypod shells (probably 

a Jurassic or Cretaceous Inoceramus) were found at one locality at 

the contact with the overlying sandstone. Smith states that these 

rocks "resemble so closely the Upper Cretaceous rocks described 

elsewhere [north of the Kuskokwim] that the two must be separated 

not by differences in lithology but by differences in structure." The 

lithologic character of these rocks, as well as their relation to the 

underlying conglomerate, indicates, in the writer's opinion, that they 

are to be correlated with the fresh-water shale and sandstone (Melozi 

formation) of the Upper Cretaceous section on the Yukon and probably with some of the unfossiliferous shale and sandstone exposed 

on the Kuskokwim.

The rocks described by Smith 38 as " Mesozoic sandstones south of 

the Kuskokwim " consist of a great thickness of beds which are composed dominantly of sandstone but contain also some conglomerate 

and shale. In many of the exposures it is difficult to tell whether the 

sandstone or the shale predominates. What is supposed to be thje 

basal bed is a fine conglomerate which appears to rest unconformably on the underlying shale. The only traces of organic remains 

are fragmentary bits of vegetable material. The writer believes that 

these rocks are the equivalent of some of the sandstone and shale 

exposed along the Kuskokwim and are possibly to be correlated with 

the upper arkosic sandstone near Kolmakof and with the marine 

sandstone and shale (Nulato formation) of the Upper Cretaceous 

section on the Yukon.

37 Smith, P. S., The Lake dark-central Kuskokwim region, Alaska: U. S. Geol. Survey 

Bull. 655, pp. 63-72, 1917. 

88 Idem, pp. 72-77.
440 MESOZOIC STRATIGRAPHY OF ALASKA

The rocks exposed along the Kuskokwim from a point 14 miles 

below Kolmakof to the bend about 8 miles below Ohagamut are 

chiefly volcanic. They were included by Spurr 39 in the " Kolmakof 

series," which he regarded as Cretaceous and as the volcanic lateral 

equivalent of the " Holiknuk series." Maddren 40 has shown, however, that these rocks include upper Carboniferous limestone and 

tuff. The writer believes that the rocks described by Spurr as the 

"Kolmakof series" include three or four distinct units, namely, 

Upper Cretaceous sandstone and shale, which are the direct western 

extension of Spurr's " Holiknuk series," the associated igneous rocks, 

which are dikes and sills and not lava; late Paleozoic or early 

Mesozoic tuff (and lava?) associated with upper Carboniferous 

limestone; and possibly late Tertiary volcanic rocks like those on 

the lower Yukon.

Age and correlation. The Upper Cretaceous rocks of the Kuskokwim region have yielded the fossils listed in the following table:

Upper Cretaceous fossils from Kuskokwim River*

Inoceramus...... __ . __ .-.. __ .... __ ....

- 11

h

13

h

9087

h

9088

b

9219

h

9222

h

9223

h

9224

h

9225

h

9226

h

h

9227

h

9228

h

h

a a, Identified by F. H. Knowlton; b, identified by T. W. Stanton.

 . Kuskokwim River about halfway between the Chagavenapuk aud 

Vinasale. J. E. Spurr, 1898.

11. South bank of Kuskokwim River midway between Yukwonilnuk River 

and camp of August 5. J. E. Spurr, 1898.

13. North bank of Kuskokwim River about 3 miles above Kolmakof. J. E. 

Spurr, 1898.

9087. North bank of Kuskokwim River about 1% miles above Kolmakof. 

A. G. Maddren, 1914.

9088. North bank of Kuskokwim River about 3 miles below Kolmakof. 

A. G. Maddren, -1914.. .. ..,.,..

9219 (14AS82). Hill south of camp of July 17, north of Mulchatna River. 

P. S. Smith, 1914.

9222 (14AS134), 9223 (14AS135), 9224 (14AS136), 9225 (14AS136a). Station LXIII, George-Kuskokwim divide. P. S. Smith, 1914.

9226 (14AS166). Station LXXXVII. P. S. Smith, 1914.

9227 (14AS167). Near station LXXXVIII, near Georgetown-Iditarod trail. 

P. S. Smith, 1914.

9228 (14AS170). 1 mile west of station LXXXVIII, Georgetown-Iditarod 

trail. P. S. Smith, 1914.

39 Spurr, J. E., A reconnaissance in southwestern Alaska in 1898: U. S. Geol. Survey 

Twentieth Ann. Kept., p. 7, pp. 130-131, 161-163, 182-183, 1900.

40 Maddren, A. G., unpublished notes.
CRETACEOUS, KOYUKUK VALLEY 441

The fossils listed above, though including no identifiable species, 

clearly indicate the Upper Cretaceous age of the rocks from which 

they came. The Inoceramus of lot 9087, according to Stanton, is of 

an Upper Cretaceous type, and the two lots of dicotyledonous 

leaves are also indicative of the Upper Cretaceous. It has also 

been shown on the preceding pages that the lithologic character of 

the rocks and the stratigraphic sequence are very similar to those of 

the section of Upper Cretaceous rocks on the lower Yukon. The 

lower plant-bearing conglomerate above the mouth of the Holitna 

is probably to be correlated with the Ungalik conglomerate and possibly with part or all of the Melozi formation. The marine shale 

and sandstone exposed along the Kuskokwim from the Holitna to a 

point 14 miles below Kolmakof and in the hills north of the river 

are to be correlated with the Nulato formation. The " conglomerate 

of Cairn Mountain " south of the Kuskokwim is probably the equivalent of the Ungalik conglomerate. The "Mesozoic shales south of 

the Kuskokwim," which lie conformably on the "conglomerate of 

Cairn Mountain," are probably to be correlated with the Melozi 

formation. The apparently unconformably overlying "sandstones 

south of the Kuskokwim " are possibly the equivalent .of the marine 

sandstone of the Nulato formation. The equivalent of the coalbearing Kaltag formation has not been recognized in the Kuskokwim 

Valley.

KOYUKUK VALLEY 

GENERAL FEATURES

The Cretaceous rocks of the Koyukuk Valley include the Lower 

Cretaceous limestone, lava, and tuff of the Koyukuk group; the 

Upper Cretaceous shale, sandstone, and conglomerate near the mouth 

of the river; and the Upper Cretaceous (?) sandstone, arkose, grit, 

and conglomerate of the Bergman group. The base of the Koyukuk 

group has not been recognized, and the rocks that may underlie it 

are not known. The writer suspects that the lava and tuff that have 

been described as part of the Koyukuk group may belong to an 

underlying formation. The Bergman group, which is supposed to 

rest upon the Koyukuk group where that group is present, directly 

overlies Paleozoic rocks along the northern border of its area. The 

Upper Cretaceous rocks in this district are not overlain by any strata 

other than unconsolidated Quaternary deposits, unless the coalbearing beds at Tramway Bar, which have been tentatively included 

in the Bergman group, should prove to be Tertiary deposit^ younger 

than the Bergman.
442 MESOZOIC STRATIGRAPHY OF ALASKA

LOWER CRETACEOUS 

KOYUKUK GROUP

Historical review. The Lower Cretaceous rocks of the Koyukuk 

Valley were first recognized in 1899 by Schrader,41 who described 

them as extending down Koyukuk Kiver for about 30 miles from a 

point about 15 miles above Waite Island, as consisting of impure 

limestone associated with amygdaloidal lava and andesitic tuff and 

as bearing a fauna determined by Stanton as Lower Cretaceous. 

A brief reference to the occurrence of these rocks has been made by 

Brooks.42 Schrader 43 described these rocks in somewhat greater 

detail in 1902, naming them the Koyukuk " series." The final report 

on his investigations in northern Alaska 44 contains a redescription 

of the Koyukuk "series" and shows, for the first time, its areal 

distribution on a map.

In 1910 Smith and Eakin, crossing from the Koyukuk to the 

Kobuk, just west of Hogatza River, studied and mapped some rocks 

in the Zane Hills, which were described as the Koyukuk group.45 The 

description is based primarily on the rocks in the Zane Hills, but 

information derived from Schrader's description of the rocks on the 

Koyukuk, especially concerning the age of the rocks, is included. 

The map shows the known areal extent of the Koyukuk group, not 

only in the Zane Hills but also on the Koyukuk, where as represented 

it occupies a somewhat less extensive area than that shown on 

Schrader's map. No fossils were found in the Zane Hills, but the 

rocks there are correlated with those on the Koyukuk on the basis of 

being " lithologically similar." Although Schrader's descriptions

indicate that limestone is the typical and most abundant constituent

of the Koyukuk group, it is stated by Smith that " limestones were 

entirely absent" in the Zane Hills.

A large area lying between the Yukon and the Koyukuk was 

mapped and studied geologically by Eakin in 1913. The Cretaceous rocks of this area, which were described by Eakin 40 as 

"Mesozoic sedimentary rocks," are chiefly Upper Cretaceous but 

may be partly Lower Cretaceous. The area which Eakin mapped 47

 " Schrader, F. C., Preliminary report on a reconnaissance along the Chandalar and 

Koyukuk Rivers, Alaska, in 1899 : U. S. Geol. Survey Twenty-first Ann. Report, pt. 2, pp. 

476-477, 1900.

42 Brooks, A. H., The coal resources of Alaska: U. S. Geol. Survey Twenty-second Ann. 

Rept., pt. 3, p. 529, 1902.

48 Schrader, F. C., Geological section of the Rocky Mountains in northern Alaska: 

Geol. Soc. America Bull., vol. 13, p. 246, 1902.

44 Schrader, F. C., A reconnaissance in northern Alaska: U. S, Geol. Survey Prof. 

Paper 20, pp. 53, 77, 97, pi. 3, 1904.

45 Smith, P. S., The Noatak-Kobuk region, Alaska: U. S. Geol. Survey Bull. 536, pp 

55, 80-82. 1913.

48 Eakin, H. M., The Yukon-Koyukuk region, Alaska: U. S. Geol. Survey Bull. 631, pp. 

41-50, 1916.

"Idem, pi. 2.
CRETACEOUS, KOYUKUK' VALLEY 443

"as " Upper Cretaceous (possibly including some Lower Cretaceous) 

conglomerates, grits, sandstones, slates, and shales" includes areas 

along Koyukuk River which were placed in the Koyukuk group by 

Schrader and by Smith. The description by Eakin contains no 

mention of any beds that resemble.the Lower Cretaceous rocks described by Schrader and Smith and may be regarded as applying 

only to the Upper Cretaceous rocks of this region. Eakin stated that 

the rocks which he described " may be in part of Lower Cretaceous 

age," and mentioned the Lower Cretaceous fossils (p. 444) found by 

Schrader.

Stratigraphic description. The Koyukuk "series" was described 

by Schrader 48 as follows:

The rocks of the Koyukuk series consist of pink and reddish limestone, dark 

shale, slates,, and some sandstone or arkose, with occasional associated igneous 

rocks. The latter include dioritic dikes, amygdaloids, and andesitic tuffs, which 

denote volcanic activity during and subsequent to Lower Cretaceous time.

Owing to wide breaks in the sequence of outcrops and the changing attitude of the rocks, no attempt will be made at present to form an estimate of 

the thickness of the series. It may be noted, however, that at one point where 

fossils were collected, near the southern edge of the map, on the right (or 

west) bank of Koyukuk River, the limestone exhibits a thickness of about 800 

feet.

The rocks that were referred to the Koyukuk group by Smith 49 

were described as follows:

In the Zane Hills, where similar rocks were examined by the Survey party 

in 1910, limestones were entirely absent and the group consisted of agglomeratic and arkosic beds associated with basic intrusives and effusives cut 

by acidic intrusives. Some conglomeratic beds were recognized.

It may be seen from the foregoing statements that the Lower 

Cretaceous rocks on Koyukuk River have not been adequately described. The stratigraphic sequence and thickness of the Koyukuk 

group, the character of its basal and upper contacts, and the identity 

of the rocks which underlie and overlie it are all unknown. The 

Koyukuk group, in the writer's opinion, is a heterogeneous aggregate composed of rocks of very diverse character, origin, and age. 

It includes Lower Cretaceous limestone containing Aucetta crassi^ 

collis and having a thickness estimated by Schrader at about 800 

feet, and it may include some other rocks, notably some or all of the 

shale, slate, arkose, and conglomerate mentioned by Schrader and 

Smith. The "associated igneous rocks" have not been described 

as interbedded with the Aucetta-be&rmg beds, although they certainly 

are intimately associated with those beds. The writer suspects that

48 Schrader, P. C., A reconnaissance in northern Alaska : U. S. Geol. Survey Prof. Paper 

20, p. 77, 1904.

*fl Smith, P. S., The Noatak-Kohuk region, Alaska: U. S. Geol. Survey Bull. 536, p. 81 

1013.
444 MESOZOIC STEATIGEAPHY OF ALASKA

they may possibly consist of pre-Cretaceous and post-Cretaceous 

volcanic rocks like the volcanic rocks " associated with " the Upper 

Cretaceous deposits on the lower Yukon. (See pp. 404, 410.) 

Some of the sedimentary rocks that have been included in the 

Koyukuk group may possibly be Upper Cretaceous.

Age and correlation. The only fossils that have been found in the 

Lower Cretaceous rocks on Koyukuk Kiver are several small lots 

collected by Schrader in 1899 and tabulated below. The presence 

of Aucella crassicollis shows the Lower Cretaceous age of at least the 

limestone members of the Koyukuk group and indicates a general 

correlation with the limestone and other rocks containing Aucella 

crassicollis in other Alaskan districts.

Lower Cretaceous fossils from Koyukuk River a

Ostrea sp, (a small simple form).. _ ................. _ ... _ .

Aucella crassicollis Keyserling... __..__.._ __ .................

230

X

X

V

X

X

261 262 315

v

" Identified by T. W. Stanton.

230. North bank of Koyukuk River about 5 miles above Waite Island. F. C. 

Schrader, 1899.

261. North bank of Koyukuk River about 3 miles above lower end of Waite 

Island. Limestone at least 800 feet thick. F. C. Schrader, 1899.

262. North bank of Koyukuk River about 3 miles below lower end of Waite 

Island. Limestone and tuff. F. C. Schrader, 1899.

315. Koyukuk River near north end of Roundabout Mountain. Boulder on 

river bank. F. C. Schrader, 1899.

UPPER CRETACEOUS 

SHALE AND SANDSTONE ON THE LOWER KOYUKUK

Historical review. On the lower reaches of Koyukuk River, between Kateel River and the mouth of the Koyukuk, Schrader observed some sedimentary and associated igneous rocks which have 

proved to be in part Upper Cretaceous. These rocks are not described specifically in Schrader's text, but are referred to in the 

statement that the Nulato sandstone " probably also covers a considerable area in the lower part of the Koyukuk Basin, near the mouth 

of the river." 50 The map 51 accompanying Schrader's report indi60 Schrader, F. C., Preliminary report on a reconnaissance along the Chandalar and 

Koyukuk Rivers, Alaska, in 1899: U. S. Geol. Survey Twenty-first Ann. Kept., pt. 2, p. 

478, 1900.

"Idem, pi. 60.
CRETACEOUS, KOYUKUK VALLEY 445

cates "sandstone, arkose, grit, conglomerate, limestone, shale, mud 

rock with plant remains, volcanic tuff, breccia, and altered igneous 

rocks " as exposed along the lower part of the river. The sedimentary rocks of this area were mapped by Smith and 'Eakin 52 as the 

Shaktolik group, and the volcanic rocks as Tertiary or Kecent basalt, 

but no description was given of the exposures on the Koyukuk.

Stratigraphic description. The Upper Cretaceous rocks on the 

lower Koyukuk were described by Schrader as including sandstone, 

shale, conglomerate, and limestone. No information concerning 

the details of the stratigraphy is available, but it is believed that 

these rocks probably include the equivalent of several and perhaps 

all of the members of the Upper Cretaceous section exposed on the 

Yukon between Melozi and Louden. The exposures next below 

Kateel Eiver include grit and conglomerate that are probably the 

equivalent of the lower conglomeratic member near Melozi. The 

igneous rocks exposed along the lower 30 miles of the Koyukuk 

are the northern extension of some of the post-Cretaceous volcanic 

rocks of the Yukon. The intervening exposures are possibly the 

equivalent or one or more of the subdivisions of the Upper Cretaceous on the Yukon. No estimate of the thickness of the Upper 

Cretaceous rocks on the lower Koyukuk has been made. Their base 

has not been recognized, but it is believed that basal conglomerate 

rests upon pre-Upper Cretaceous rocks near the mouth of Kateel 

River. Their upper contact is probably beneath the Quaternary 

silt in the high bluff about 20 miles (35 or 40 miles by the river) 

north of Koyukuk village. This bluff separates exposures of Upper 

Cretaceous plant-bearing sandstone and shale from exposures of 

the supposed Tertiary volcanic rocks, which are probably the next 

younger consolidated rocks.

Age and correlation. Fossils have been obtained at only one 

locality in the Upper Cretaceous rocks on the lower Koyukuk. These 

fossils include both plants and a marine invertebrate, as listed below, 

and are too few to give any conclusive evidence on the precise position of these beds relative to the section of the Yukon. One of the 

plants is known only at this locality; the other occurs tin the lower 

fresh-water shale and sandstone (Melozi formation) of the Yukon 

section. The marine invertebrate indicates that the beds may correspond to either the marine sandstone and shale of the Nulato formation or to one of the marine beds in the Kaltag formation of 

the Yukon section.

82 Smith, P. S., and Eakin, H. M., A geologic reconnaissance in southeastern Seward 

Peninsula and the Norton Bay-Nulato region, Alaska: U. S. Geol. Survey Bull. 449, pi. 5, 

1911.

49448 26 30
446 MESOZ01C STRATIGRAPHY OF ALASKA

7472(333). West bank of Koyukuk River about 40 miles above mouth. 

Sandstone and shale. F. C. Schrader, 1899. Hedera n. sp., Platanus n. var. 

Identified by C. A. Hollick.

2183 (334). West bank of Koyukuk River about 40 miles above mouth. 

From sandstone and shale at the same locality as 7472. F. C. Schrader, 1899. 

My a?. Identified by T. W. Stanton.

UPPER CRETACEOUS (?) 

BERGMAN GROUP

Historical review. The supposed Upper Cretaceous rocks of the 

upper course of Koyukuk River were first described by Schrader53 

as the Kenai "series." The description states that the rocks are 

" composed of impure sandstone, arkose, grit, and conglomerate, indiscriminately carrying more or less lignite and remains of fossil 

plants. On account of its fossil contents and its resemblance to 

the Kenai found elsewhere in the Yukon district, this formation is 

provisionally referred to the Kenai." These rocks were subsequently 

named the Bergman " series " by Schrader.54 The later description 

contains a brief general account of the lithologic character, a statement that on the north these rocks rest unconformably on supposed 

Silurian schist and on the south they are apparently infolded with 

the Koyukuk " series," and a discussion of age in which it is said that 

" no fossils beyond undeterminable lignitic plant remains have thus 

far been found in the Bergman series. From its apparent close relations, however, to the Koyukuk series it seems that the Bergman 

series is probably Cretaceous."

Mendenhall, while on his way from Fort Hamlin to Kotzebue 

Sound in 1901, crossed the Koyukuk Valley by way of Kanuti and 

Alatna rivers. He gives a description 55 of the lithologic character 

of the Bergman " series " at the localities where he observed it and 

shows its areal distribution on geologic maps. The description contains no account of the stratigraphic sequence and no conclusive 

evidence as to the age.

The Bergman "series" was redescribed by Schrader 56 in 1904. 

The description includes a general account of the lithologic character, structure, and relation to the adjacent rocks and a statement 

that these rocks are referred tentatively to the Cretaceous because 

of " the seemingly close relationship of the Bergman series to the

53 Schrader, F. C., Preliminary report on a reconnaissance along the Chandalar and 

Koyukuk Rivers, Alaska, in 1899 : U. S. Geol. Survey Twenty-first Ann. Kept., pt. 2, p. 

477, 1900.

64 Schrader, F. C., Geological section of the Rocky Mountains in northern Alaska: 

Geol. Soc. America Bull., vol. 13, pp. 246-247, 1902.

65 Mendenhall, W. C., Reconnaissance from Fort Hamlin to Kotzebue Sound, Alaska: 

U. S. Geol. Survey Prof. Paper 10, pp. 39-41, pis. 5, 7, 1902.

M Schrader, F. C., A reconnaissance in northern Alaska: U. S. Geol. Survey Prof. Paper 

20, pp. 53, 77-79, 97, pi. 3, 1904.
CEETACEOiJS, KOYUKUK VALLEY 447

Lower Cretaceous or Koyukuk series, and the bituminous character 

of its coal content."

The structural and stratigraphic position of the Bergman " series " 

was briefly discussed by Brooks,57 who stated that the Bergman 

"series" may underlie the Koyukuk "series" and "be chiefly lower 

Mesozoic, with some infolded Kenai beds."

The upper part of the Koyukuk Valley was visited .in 1909 by 

Maddren, but his description of the Cretaceous rocks 58 was based 

chiefly on the earlier observations by Schrader and Mendenhall, as 

his observations were mostly outside the area occupied by these 

rocks. The description apparently applies to the Cretaceous rocks 

of the entire Koyukuk Valley and includes both the Bergman and 

Koyukuk " series," although the Koyukuk does not occur within the 

area covered by Maddren's map.

The exposures of these rocks in the Koyukuk and Kobuk Valleys 

were described by Smith 59 as the Bergman group which he referred 

to the Upper Cretaceous. Smith's description was based largely on 

his observations of the western extension of these rocks along Kobuk 

River (see pp. 449-451) but includes information derived from his 

own observations of the exposures on the lower courses of Alatna 

River and from Schrader's and Mendenhall's observations on the 

Koyukuk and its tributaries, including John, Alatna, and Kanuti 

Rivers. The resemblance of these rocks to the Upper Cretaceous 

Ungalik conglomerate and Shaktolik group of the Nulato-Norton 

Sound district is noted. This resemblance and the fact that the 

Bergman group is supposed to overlie and is less deformed than the 

Koyukuk group form the basis of its assignment to the Upper Cretaceous.

In a report on a district lying between the Koyukuk and the 

Yukon Eakin 00 described "Mesozoic sedimentary rocks," which are 

represented on his map as extending into the type area of the Bergman group. The main part of the description deals with the southwestern extension of this area, where these rocks are mapped as 

forming a continuous belt extending from the type locality of the 

Bergman group to the well-known exposures of Upper Cretaceous 

rocks on Yukon River below Melozi, which have already been described. (See pp. 401-404.)

67 Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 

45, pp. 235-236, 237, 1906.

68 Maddren, A. G., The Koyukuk-Chandalar region, Alaska: U. S. Geol. Survey Bull. 

532, pp. 32, 34, 53-55, 56, pi. 5, 1913.

68 Smithf P. S., The Noatak-Kobuk region, Alaska: U. S. Geol. Survey Bull. 536, pp. 

55, 84-87, pi. 2, 1913.

""Eaton, H. M., The Yukon-Koyukuk region, Alaska: U. S. Geol. Survey Bull. 631, pp. 

24, 41-50, pi. 2, 1916.
448 MESOZOIC STRATIGRAPHY OF ALASKA

Stratigraphic description. The Bergman " series " was described 

by Schrader 81 as follows:

The term Bergman is here employed to designate a group of comparatively 

uniform rocks covering a large area in the Koyukuk Basin and forming in 

large part the Koyukuk Plateau. This series lies north of the Koyukuk series 

and has a north-south extent of 60 to 70 miles. On the north it rests unconformably on the schists of the Totsen series, while on the south it is apparently infolded with the Koyukuk series, to which it is supposed to be closely 

related and which it is supposed to succeed in geologic age.

The Bergman series consists essentially of thin or medium bedded impure 

gray or brownish sandstone and dark slate, with some dark shale and occasionally conglomerate, but along the north it is bordered by a belt of conglomerate about 10 miles wide, which is apparently the basal member. The sediments of the series have been derived very largely from igneous rocks, as is 

shown by the generally feldspathic constituents of the sandstones and the 

presence of basaltic, diabasic, and granitic pebbles or finer detritus in the 

conglomerate on the lower part of Alatna River and at Lookout Mountain. 

The supposed basal belt of conglomerate along the northern border, however, 

so far as it was observed in the John River region, is composed essentially of 

the dfibris of limestone and mica schist derived from the Skajit formation and 

the Totsen series, on which latter it uuconformably lies. This conglomerate 

is normally coarse and in some instances contains boulders.

Owing to the wide separation of the outcrops visited, data for forming an 

adequate estimate of the thickness of the Bergman series have not been obtained. From a general impression, however ? it seems safe to suggest that it 

is probably at least 2,000 feet.

Age and correlation. The Bergman group has yielded no fossils, 

but its assignment to the Cretaceous and probably to the Upper 

Cretaceous is believed to be well grounded. The beds of the Bergman group seen by the writer near Settles are not unlike the Upper 

Cretaceous shale and sandstone of the Innoko and Iditarod districts.

They also resemble some of the Lower Cretaceous slate and quartzite 

of the Upper Yukon and may possibly include both Upper and 

Lower Cretaceous beds. It is also possible that some of the beds 

that have been included in the Bergman group, notably the coalbearing beds at Tramway Bar, may be Tertiary.

KOBUK VALLEY 

GENERAL FEATURES

The only rocks in the Kobuk Valley that have been assigned to 

the Cretaceous are the supposed western extension of the Bergman 

group, which has been mapped as trending westward from the 

upper Koyukuk across the headwaters of the Kobuk and along the 

divide between the Kobuk and Selawik. The rocks that have been 

referred to the Bergman group in the .Kobuk Valley consist of con81 Schrader, F. C., A reconnaissance in northern Alaska : U. S. Geol. Survey Prnf. Paper 

20, pp. 77-78, 1904.
CRETACEOUS, KOBUK VALLEY 449

glomerate, sandstone, and shale, which lie uncomformably upon 

Paleozoic rocks and are succeeded, though they are not known to be 

I directly overlain, by supposed Tertiary coal-bearing rocks.

, UPPER CRETACEOUS (?)

BEKGMAN GROUP

Historical review. The supposed Upper Cretaceous rocks of the 

Kobuk Valley were observed by Mendenhall in an exploratory jour-

[ ney down the Kobuk in 1901. These rocks were described by Mendenhall 02 as the Bergman "series," the description consisting of brief 

statements concerning the lithology and structure of the rocks seen

, at various places on the upper Kobuk with a general discussion coni cerning the possible age of the " series."

The exposures of these rocks in the upper part of the Kobuk 

j ; Valley and in the hills south of the Kobuk were studied in 1910 by 

'i Smith and Eakin,63 who included them in rocks that they briefly 

described as "Mesozoic and Tertiary (?) ,rocks." The same field 

observations were recorded in greater detail by Smith,04 who described these rocks as the Bergman group and discussed their distribution, lithologic character, structure, and age. Part of the rocks 

/ described by Smith as the Bergman group had been included by 

jy Mendenhall 05 in a "metamorphic complex,*' which he described as 

' probably chiefly Paleozoic.

StratigrapMc description. The exposures of the Bergman group 

in the Kobuk Valley were described by Mendenhall,66 as follows:

On the Kowak, a few miles above the outlet of Lake Nutavukti, conglomerates are exposed which, although exhibiting sonu- variations from the type, 

are regarded as belonging to the Bergman series. The conglomeratic beds are 

here interbedded with red and green shales, and a considerable body of soft 

red sandstones occurs in one locality. In the conglomerate occur pebbles of 

slate, greenstone, and other types, which are recognized as derived from the 

older rocks to the north.

Through the mile gorge, a short distance above the outlet of Norutak Lake, 

the Kowak flows along the strike of a slaty phase of the Bergman, which is 

very similar lithologically to a belt crossed along the Alien nearly due east 

of here. The slates in the canyon of the Kowak carry small limestone lenses 

and are cut by narrow quartz stringers. They have been only very slightly 

metamorphosed.

Below the gorge the river enters a broad filled valley with no rock exposures 

until the mouth of the Reed River is reached. Here slaty shales, similar to

63 Mendenhall, W. C., Reconnaissance from Fort Hamlln to Kotzebue Sound. Alaska,: 

U. S. Geol. Survey Prof. Paper 10, pp. 39-42, pis. 5, 7, 1902.

03 Smith, P. S., and Eakin, H. M., The Shungnak region, Kobuk Valley: U. S. Geol. 

Survey Bull. 480, pp. 284-286, 1911.

«* Smith, P. S., The Noatak-Kobuk region, Alaska: U. S. Geol. Survey Bull. 536, pp. 

84-87, pi. 2, 1913.

» Mendenhall, W. C., op. cit., pp. 31-37.

" Idem, pp. 39-40.
450 MESOZOIC STRATIGRAPHY OF ALASKA

those in the gorge above, are found in outcrop and exhibit a northerly dip, ' 

while those in the gorge dip toward the south. Five or six miles farther down- * 

stream soft green fractured sandstones and graywackes, frequently weathering ( 

red, are encountered. / 

A short distance above the mouth of Pah River the hills south of the Kowak I 

are found to be composed of these same Bergman beds. The shales predomi- \ 

nate here, and the topographic forms to which they give rise extend westward 

to the head of the Kuikcherk River and eastward as far as can be seen.

The following description was given by Smith: ° 7

Dominantly, the Bergman group is a series of dark greenish-gray arkosic j 

conglomerates and sandstones. The base of the section exposed on Alatna j 

River, on the lower part of John River, and on the upper part of the Kobuk 

is a conglomerate made up of pebbles of the older rocks, namely schists, limestones, vein quartz, and igneous rocks, such as greenstones and granites. The i 

beds are thoroughly indurated and are usually more resistant than the higher \' 

sandstones. As a result, they form conspicuous pinnacled ridges, particularly ( 

in the range north of the Kobuk from Beaver River westward to the Mauneluk. 

It is because of similarity in topographic expression in this particular that the \ 

hills south of the Kobuk from Ambler River westward are correlated with the (' 

areas of Upper Cretaceous rocks. This division corresponds closely in all ^ 

physical features with the Ungalik conglomerate, of probable Upper Cretaceous 

age, described in the extreme eastern part of Seward Peninsula and the adjacent Norton Bay region.

Toward the top of the lower division sandstones become more numerous, and 

at its top the group is composed almost entirely of sandstones which are practically indistinguishable from the sandstones of the Shaktolik group of the \ 

more southern part of the Koyukuk basin. The rock is medium fine grained, \ 

of rather uniform texture, and generally ,of a greenish-gray color. It is thoroughly indurated and offers fair resistance to weathering, not so great resistance, however, as most of the rocks already described. As a result, the sand- j 

stone portion of the Bergman group generally forms somewhat rounded, 

coarsely dissected hills of medium elevation.

The rock contains abundant fragments of rather angular ferromagnesian 

minerals and feldspars, whose glittering faces and partial crystal outline resemble the phenocrysts of an igneous rock. Generally, the beds are rather 

massive, showing no pronounced stratification. At many places, however, beds 

of dark shale interlaminated with the sandstones serve to bring out the structure. No extensive exposures of the shales were observed by the expeditions 

of 1910 or 1911, but Mendenhall notes belts of shale many hundred feet thick. j 

He also notes red and green shales in the Kobuk basin near Lake Nutavukti, 

but such shales have not been recognized in other parts of the region.

Fragments of what appears to be wood and lignitic beds have been found here 

and there in the sandstone member. A bed of lignite occurs in the hills immediately east of Pah River, and another near Tramway Bar on the North Fork 

of the Koyukuk, but both beds are apparently thin and of poor quality. Owing 

to the absence of determinative fossils some areas in the central part of the 

Kobuk basin mapped provisionally as Tertiary may prove to be Upper Cretaceous, in which case workable lignite beds may on closer examination be 

found in the Bergman group.

"Smith, P. S., op. cit. (Bull. 636), pp. 84-85.
CRETACEOUS, COLVILLE VALLEY 451

J Age and correlation. Neither the rocks in the Kobuk Valley re- 

' ferred to the Bergman group nor the rocks of the type area of the 

i group in the Koyukuk Valley have yielded any fossils, and their 

] assignment to the Upper Cretaceous is not beyond doubt. The evidence on the age of the Bergman group in the Koyukuk Valley is 

' discussed on page 449.

COLVILLE VALLEY 

GENERAi, FEATURES

{ The Cretaceous rocks of the Colville Valley include marine Lower 

Cretaceous and Upper Cretaceous rocks exposed on Anaktuvuk River, 

a tributary of the Colville. As most of the Arctic slope is unexplored, the extent of the Cretaceous rocks is not known. They are not 

present in the Canning River district, 100 miles east of the Colville, 

or along the Canadian boundary. They probably extend westward

1 for a considerable distance and may extend as far as Cape Lisburne, 

nearly 400 miles west of the Colville, where Jurassic rocks are overlain by rocks that are probably Lower Cretaceous.

The Lower Cretaceous rocks of the Colville Valley, which have 

been described as the Anaktuvuk "series," consist of sandstone at 

least 2,000 feet thick with subordinate amounts of conglomerate and

1 shale, contain Aucella crassicollis, and are believed to rest uncon-;

,/ formably upon Carboniferous and possibly Devonian rocks, although 

the actual contact is concealed beneath a broad belt of Quaternary - 

deposits. The Upper Cretaceous rocks of the Colville Valley, which

1 have been described as the Nanushuk " series," consist chiefly of sandstone, limestone, and shale of undetermined thickness, with some coal 

beds, contain marine fossils, apparently overlie the Lower Cretaceour unconformably, and are probably overlain unconformably by 

/ Tertiary beds.

[ LOWER CRETACEOUS 

'| ANAKTUVUK GROUP

/ The Lower Cretaceous rocks of the Anaktuvuk group were first 

described by Schrader 6S as the Anaktoovuk " series." The description consists of a brief general discussion of the character, occur-

) rence, structure, and age of the rocks. Reference is made to the determination by Stanton of Lower Cretaceous fossils (Aucella crassicollis}, but Stanton's report on the fossils is not quoted in full. 

These rocks were subsequently described by Schrader in somewhat 

great:r detail,69 but on the basis of the same field work, as the Anak88 Schrader, F. C., Geological section of the Rocky Mountains la northern Alaska: Geol. 

Soc. America Bull., vol. 13, pp. 245-246, 1902.

09 Schrader, F. C., A reconnaissance in northern Alaska: U. S. Geol. Survey Prof. Paper 

20, pp. 53, 74-76, pi. 3, 1904.
452 MESOZOIC STBATIGRAPHY OF ALASKA

tuvuk " series." The localities (544 and 545, on "Anaktuvuk Eiver, 

cross ridge below camp of August 1") where Schrader collected fossil 

plants from the rocks of the Anaktuvuk group were cited by Ward,70 

but no list or description of the fossils was given. The fossils from 

these localities consist of indeterminate stems. A description of the 

Anaktuvuk group based wholly on Schrader's description has been 

'given by Smith.71

Stratigraphic description. The AnaktuVuk group was described 

by Schrader as consisting chiefly of impure sandstone or arkose 

with a little fine conglomerate. The sandstone is mostly heavy 

bedded, many beds being 6 or 8 feet thick, and is generally fine 

or medium grained, but some beds are so coarse as to be 

almost a grit. The color ranges from dark or bluish gray to dirtygreen. The coarser rock commonly has a speckled appearance and 

seems to be composed of grains of variously colored flint. Some of 

the beds contain detritus from igneous rocks, such as fragments of 

feldspar and ferromagnesian minerals. The igneous rocks from 

which this detritus came have not been recognized. Conglomerate 

seems to be rare, having been seen at only one locality 2 miles below 

the mouth of Willow Creek. It is rather fine, few of the pebbles 

being more than three-quarters of an inch in diameter. The pebbles 

are notably angular and consist mainly of white quartz and dark 

slate-colored flint. The cementation is firm but not as strong as in 

the neighboring Paleozoic rocks. The exact stratigraphic position 

of this conglomerate has not been determined, but it seems to be 

above the middle of the group. No accurate measurement of the 

thickness of the Anaktuvuk group has been made, but Schrader 

estimates it to be at least 2,000 feet.

The Anaktuvuk group was believed by Schrader to rest unconformably on Carboniferous or Devonian rocks, but the basal contact 

is concealed beneath a belt of Quaternary deposits 8 miles wide. It 

is possible that this concealed interval contains Triassic or Jurassic 

rocks, such as Leffingwell has described (see pp. 103-105, 262-268) 

as overlying the Carboniferous rocks 100 miles east of Anaktuvuk 

Eiver. The Anaktuvuk is succeeded on the north by the Upper 

Cretaceous rocks of the Nanushuk formation. Schrader believed that 

these Upper Cretaceous rocks immediately overlie the Anaktuvuk ' 

group and that the structural discordance between the two suggests 

unconformity.

Age and correlation. The evidence on the age of the Anaktuvuk 

gro"up is found in several lots of fossils collected by Schrader at dif70 Ward, L. F., Status of the Mesozoic floras of the United States (second paper) : 

U. S. Geol. Survey Mon. 48, p. 146, 1905.

71 Smith, P. S., The Noatak-Kobuk region, Alaska: U. S. Geol. Survey Bull. 536 pp 

82-84, pi. 2, 1913.
CRETACEOUS, COLVILLE VALLEY 453

ferent localities on Anaktuvuk River. The fossils of lot 538-540, 

which were obtained from the lowest of the known fossiliferous 

beds, near the base of the exposures of the Anaktuvuk group on 

Anaktuvuk River, include Aucella crassicollis, which is regarded 

as characteristic of the Lower Cretaceous rocks of Alaska. The 

other lots of marine fossils including 546-548, obtained near the 

middle of the group, 551-556, somewhat higher; and 560, near the 

top of the group are less characteristic and are said by Stanton 

to be " probably of Cretaceous age, though they do not include any 

strictly characteristic genera." These fossils offer no evidence that 

the upper part of the Anaktuvuk group may not be Upper Cretaceous.

Lower Cretaceous fossils from Anaktuvuk group °

Worm burrow ___ . _ ...... _ ..... ....

Trails.............. ....... .. .. v . ---------

Inoceramus ?sp. (young).... _ . _ .....

538-540

X

544

..........

545

X

546-548

X

X

V

551-556

X

X

X

X

V

X

560

y

0 Identified by T. W. Stanton, except as noted. 

»Identified by W. M. Fontaine.

538-540. Mountain east of camp of July 29 on Anaktuvuk River."" Impure 

calcareous sandstone. F. C. Schrader, 1901.

544. Ridge east of camp of August 1 on Anaktuvuk River. Dark dirty-gray 

sandstone or arkose. F. C. Schrader, 1901.

545. River bank in canyon below camp of August 1 on Anaktuvuk River. 

Dark dirty-gray sandstone or arkose. F. C. Schrader, 1901.

546-548. River bank in canyon below camp of August 1 on Anaktuvuk 

River. Fine-grained gray sandstone at same locality as 545. F. C. Schrader, 

1901.

551-556. Anaktuvuk River at mouth of Willow Creek. Fine-grained gray 

sandstone. F. C. Schrader, 1901.

560. Anaktuvuk River 2 miles below camp of August 4. Rusty-gray arkose. 

F. C. Schrader, 1901.

UPPER CRETACEOUS

NANUSHUK FORMATION

Historical review. The Upper Cretaceous rocks of the Nanushuk formation were first described by Schrader 72 as the Nanushuk 

"series." The original description includes a brief account of the 

occurrence and character of the rocks, with a list of fossils identified

TIB The position of these camps is given in, Prof. Paper 20, pi. 3.

72 Schrader, F. C., Geological section of the Rocky Mountains in northern Alaska: 

Geol. Soc. America Bull., vol. 13, pp. 247-248, 1902.
454 MESOZOIC STRATIGRAPHY OF ALASKA

by T. W. Stanton. A later account by Schrader,73 though based 

on the same field work, describes the rocks in greater* detail.

Stmtigraphic description. The Nanushuk formation was described by Schrader 74 as follows:

The rocks of the Nanushuk series are best exposed in the north bank of the 

Anaktuvuk about 5 miles above the mouth of Tuluga River. The exposure 

occurs in a bluff about three-eighths of a mile long that rises steeply 120 feet 

above the river. The rocks, which here have a steep dip, are mainly thin 

bedded. The beds range from 3 to 6 inches in thickness and exhibit rapid 

alternation. They consist of gray and brown sandstone, generally fine grained 

and sometimes friable, with some gray and impure fossiliferous limestone, dark 

shale, fine-grained gray quartzite, drab-colored and green chert, and black 

slate, stained reddish along the joints. Coal of good quality is also present.

The Nanushuk formation is believed to overlie the Anaktuvuk 

group unconformably, Schrader stating that " the unconformity between the Anaktuvuk and the Nanushuk is inferred from the differ 

ence in the topography and the marked change in the character and 

attitude of their rocks. In the most northern observed exposure 

of the Anaktuvuk the dip is north, while in the most southern of the 

Nanushuk it is steeply south."

The Nanushuk formation is succeeded by the Tertiary beds of the 

Colville " series." Schrader 75 states that the Colville " series " " apparently overlies " the Nanushuk formation but does not describe the 

precise relations on the contact.

Age and correlation. The Nanushuk formation has yielded the 

marine fossils listed below. Concerning lot 3206 Stanton said: 

" This lot is certainly of Upper Cretaceous age. The species are all 

apparently different from those with which I am familiar, but several of them are of types known only in the Upper Cretaceous."

Upper Cretaceous fossils from Nanushuk formation a

Thracia? ______ - _________

3206

' b

a

a

3207

b

Tellina, n. sp ___ . _____ ... ...

Tellina_-~ -~-~-

3206

b

b

3207

0 a, Identified by W. R. Smith; b, identified by T. W. Stanton.

3206 (565-606). Anaktuvuk River 5 miles above mouth of Tuluga River. 

Gray sandstone. F. C. Schrader, 1901.

3207 (609-612). Anaktuvuk River about 7 miles below mouth of Nanushuk 

River. Gray calcareous sandstone. F. C. Schrader, 1901.

73 Schrader, F. C., A reconnaissance in northern Alaska: U. S. Geol. Survey Prof. Paper 

20, pp. 53, 79-81, pi. 3, 1904.

74 Idem, p. 79.

75 Idem, p. 81.
MESOZOIC STRATIGRAPHY OF ALASKA 455

NORTHWESTERN ALASKA 

GENERAL FEATURES

The supposed Cretaceous or Jurassic rocks of northwestern Alaska 

include the plant and coal bearing beds that have been described 

as the Corwin formation, which are apparently entirely of nonmarine origin, and an overlying unnamed formation composed of 

sandstone and shale. These rocks apparently have a wide distribution, for they are exposed continuously along the coast from a 

point about 25 miles east of Cape Lisburne, near Corwin Bluff, to 

a point about 50 miles farther east, near Cape Beaufort, and occur 

also near Wainwright Inlet, which is 180 miles northeast of Cape 

Lisburne, and at several inland localities, at some of which coal has 

been reported. The Corwin formation has been studied in detail 

along the coast between Cape Lisburne and Cape Beaufort, where 

the general sequence of Mesozoic and associated rocks may be represented as in the following section, which is a modification of a section given by Collier.70 The principal changes from Collier's section 

are indicated by asterisks (*).

Section of Cretaceous or Jurassic and associated rocks near Cape Lisburne and

Gorwin Bluff

Feet

Quaternary* : Sand, gravel, silt, talus, ground ice, etc_ 100+ 

Unconformity. 

Lower Cretaceous (?)*: Sandstone interbedded with

shale, nonfossiliferous____________________ 10, 000+ 

. Conformity.

Cretaceous or Jurassic * : Corwin formation, composed of 

calcareous and carbonaceous shale with sandstone and 

conglomerate at infrequent intervals. Many coal beds 

and plants. No marine fauna______________ 15,000+ 

Unconformity or hiatus due to faulting.* 

Upper Triassic *: Thin-bedded shale, slate, chert, and

limestone. Marine invertebrate fauna____ _____ 1,000+ 

Unconformity or hiatus due to faulting.* 

Lower Carboniferous (Mississippian) :

Lisburne formation, composed of massive limestone 

interbedded with white chert. Extensive coral and 

bryozoan fauna___ __'_______________ 3,000+ 

Hiatus due to faulting, conformity (?).* 

Thin-bedded black shale, slate, and limestone, and 

several coal beds. Lower Carboniferous flora 

and fauna (?)_____________________ 500+ 

Conformity (?).

Devonian (?) : Calcareous sandstone and slate. No 

fossils found___________________________ 2, 000+

76 Collier, A. J., Geology and coal resources of the Cape Lisburne region, Alaska: U. S. 

Geol. Survey Bull. 278, p. 16, 1906.
456 MESOZOIC STEATIGKAPHY OF ALASKA 

CRETACEOUS OR JURASSIC 

COBWIN FORMATION

Historical review. The first accounts of the rocks now referred 

to the Corwin formation were given by Beechey 77 and by Collie,78 

who was surgeon on Captain Beechey's voyage on the Blossom in 

1825 to 1828. Collie described briefly the lithologic character of the 

coal-bearing rocks 35 miles from Cape Lisburne and near Cape 

Beaufort and noted the presence of " carbonized impressions of reedsr 

botforiiuted and plain, generally flat." These accounts were the basis 

of tile description by Grewingk,79 who erroneously assigned the rocks 

at Cape Beaufort to the Carboniferous because of the presence of 

coal at that locality and of Carboniferous fossils not far away at 

Cape Lisburne and Cape Thompson.

The next account of these rocks was given by Woolfe,80 who collected some fossil plants at an undescribed locality on the coast 

northeast of Cape Lisburne. These plants formed the basis of the 

first description of the fossils of the Corwin formation by Lesquereux,81 who subsequently described 82 a larger collection that 

was also obtained by Woolfe, presumably at the same locality. 

These fossils were assigned by Lesquereux to the Neocomian. They 

have been discussed by Ward,83 who regarded them as " Lower Cretaceous or possibly Upper Jurassic," and by Knowlton,8 * who accepted Lesquereux's age determination without comment. The coalbearing rocks at Cape Beaufort were described by Dall and Harris 85 

and also by Dall 86 under the heading " Cape Beaufort coal measures." With Dall's paper is an appendix by Knowlton 87 which

77 Beechey, F. W., Narrative of a voyage to the Pacific and Beering's Strait. Pt. 1, 

p. 270, London, 1831.

78 Collie, Alex., in Buckland, William : The zoology of Captain Beechey's voyage, pp. 

173-174, London, 1839.

79 Grewingk, C., Beitrag zur Kenntniss der orographischen und geognostischen Beschaffenheit der nord-west Kiiste Amerikas mit den anllegenden Inseln: Russ. ka. min. Gesell. 

St. Petersburg verb., 1848-49, pp. 163-164, 323, 333, 344.

80 Woolfe, H. D., The seventh or Arctic district: Report on population and resources of 

Alaska at the Eleventh Census, pp. 132-133, 1893.

81 Lesquereux, Leo, List of recently identified fossil plants belonging to the United 

States National Museum, with descriptions of several new species: U. S. Nat. Mus. Proc., 

vol. 10, p. 36, 1887.

82 Lesquereux, Leo, Recent determinations of fossil plants from Kentucky, Louisiana, 

Oregon, California, Alaska, Greenland, etc., with descriptions of new species: U. S. Nat. 

Mus. Proc., vol. 11, pp. 31-33, 1888.

83 Ward, L. F., The geographical distribution of fossU plants: U. S. Geol. Survey 

Eighth Ann. Rept, pt. 2, p. 926, 1888.

84 Knowlton, F. H., A review of the fossil flora of Alaska, with descriptions of new 

species: U. S. Nat. Mus. Proc., vol. 17, pp. 211, 213, 215, 216-217, 232-236, 1894.

85 Dall, W. H., and Harris, C. D., Correlation papers Neocene: U. S. Geol. Survey 

Bull. 84, p. 249, 1892.

80 Dall, W. H., Report on coal and lignite of Alaska: U. S. Geol. Survey Seventeenth 

Ann. Rept., pt. 1, pp. 819-820. 1896.

87 Knowlton, F. H., Report on the fossil plants collected in Alaska in 1895 as well as 

those previously known from the same region : Idem, pp. 876-897.
CRETACEOUS, NORTHWESTERN ALASKA 457

< contains a list of the fossil plants from the Cape Lisburne region 

similar to that published by Knowlton in 1894.

The Corwin formation was named in 1902 by Schrader,88 who

described it as the Corwin " series," the type locality being at Cor-

} win Bluff, about 30 miles east of Cape Lisburne. The reason why

Schrader used this new formation name instead of the older name,

"" Cape Beaufort," of Dall and Harris or Beaufort, was evidently a

suspicion that Grewingk's reference of the rocks at Cape Beaufort to

/ the Carboniferous might be at least partly correct. Schrader said:

i "" It is possible that the rocks at Cape Beaufort may on further research prove to be older than the Jura-Cretaceous, but for the present 

it seems best to include them in the Corwin series." Schrader gave 

a more detailed account 89 of the Corwin in 1904, describing the 

formation as extending as far along the coast as Wainwright Inlet,

j 180 miles northeast of Cape Lisburne, where he obtained fossil plants 

similar to those at Corwin Bluff. The fossil plants collected by 

Woolfe in 1884, together with some additional material obtained by 

H. D. Dumars in 1890 and by Schrader in 1901, have been described 

in detail by Fontaine,90 who considered that their age is " not older 

than the Lower Oolite and not younger than the Lower Cretaceous

1 but probably is between them." 

} These rocks were studied in considerable detail in 1904 by Collier,91

J who described them as the Corwin formation. Collier's report includes a brief discussion of the fossil plants by Knowlton,92 who

x referred them to the Jurassic. Knowlton subsequently 93 gave a

j detailed description of the fossil plants collected by Collier, with a

/ full discussion of their age.

1 The rocks exposed along the northwest coast of Alaska, especially 

in the valleys of Kukpowruk, Utukok, and Meade Rivers and near

1 Wainwright Inlet, were studied by Paige, Foran, and Gilluly in 1923 

in connection with the investigation of Naval Petroleum Reserve

( No. 4. A preliminary report on these investigations 04 contains a

} general description of the supposed Cretaceous or Jurassic plantj M Schrader, F. C., Geological section of the Rocky Mountains in northern Alaska :

 Geol. Soc. America Bull., vol. 13, pp. 244-245, 1902.

89 Schrader, F. C., A reconnaissance in northern Alaska in 1901: U. S. Geol. Survey 

Prof. Paper 20, 1904, pp. 72-74.

00 Fontaine, W. M., Plants from the vicinity of Cape Lisburne, Alaska (in Ward, L. P., 

Status of the Mesozoic floras of the United States, second paper) : U. S. Geol. Survey 

Mon. 48, pp. 153-175, pis. 39-45, 1905.

/ 61 Collier, A. J., Geology and coal resources of the Cape Lisburne region, Alaska : U. S. 

! <3eol. Survey Bull. 278, pp. 16, 27-30, 36-42, 1906. 

! 93 Knowlton, F. H., Report on Mesozoic fossil plants from northwestern Alaska: U. S.

 Geol. Survey Bull. 278, pp. 29-30, 1906.

93 Knowlton, F. H., The Jurassic flora of Cape Lisburne, Alaska: U. S. Geol. Survey 

0 Prof. Paper 85, pp. 39-64, pis. 5-8, 1914.

64 Paige, Sidney, Foran, W. T., and Gilluly, James, A reconnaissance of the Point 

Barrow region, Alaska: U. S. Geol. Survey Bull. 772, pp. 11-20, 1925.
458 MESOZOIC STRATIGRAPHY OF ALASKA i

bearing and coal-bearing rocks that are believed to be the northeast 

extension of the Corwin formation, with detailed descriptions of the 

exposures on Kukpowruk, Utokok, and Meade Rivers and on the 

streams tributary to Wainwright Inlet. Discussions and lists by 

Knowlton, Hollick, and Reeside of the fossils obtained by Paige and j 

his associates are given. These new collections of fossils yield evidence, which will be discussed on pages 465-466, that the flora of the 

Corwin formation may belong in the Lower Cretaceous, where it was 

placed in the earlier investigations, rather than in the Jurassic, where \ 

it was placed by Knowlton. <

StratigrapMc description. The Corwin formation, according to 

Collier,95

consists of rather thinly bedded shales, sandstones, conglomerates, and coal 

beds. Fossil plants occur in the shales wherever they have been closely examined. The shales which comprise the greater part of the formation vary 

in composition from greenish-brown calcareous to black carbonaceous beds and 

in texture from mudstones to fine-grained sandy shales. The sandstones, which 

occur at infrequent intervals throughout the formation in beds usually less than 

10 feet thick, are easily traceable over eroded areas, since their outcrops rise 

in relief above the surrounding shales. The conglomerates are made up mainly 

of quartz and chert pebbles from one-half inch to 4 inches in diameter. 

The most definite bed of this kind, which is about 15 feet in thickness and 

reaches the coast at Corwin Bluff, forms a prominent ridge from 100 to 200 

feet high. \

The coal beds are a very striking and characteristic feature of the * 

formation, 40 coal beds being indicated by Collier 9e in his columnar 

section. The coal is in general distributed throughout the formation, j 

but the thicker beds occur in two groups about 8,000 feet apart. r

The Corwin formation apparently contains no beds of marine * 

deposition. Coal beds and plant-bearing shale are distributed 

throughout the formation. Marine fossils and deposits of probable 

marine origin, such as limestone, have not been found, except the 

limestone reported by Schrader as occurring near Wainwright Inlet 

and Cape Beaufort. In view of the apparent terrestrial, origin of ' 

the formation and of its great thickness, the prevalence of finegrained material is noteworthy. ;

The thickness of the Corwin formation is stated by Collier to be 

at least 15,000 feet, as estimated from the exposures along the coast. 

These exposures are fairly continuous, and it seems improbable that 

there can be any duplication of the beds by faulting, unless it is by 

faults that are nearly parallel to the bedding. Collier 95 states that 

"there is no evidence of faulting other than minor shearing movements parallel with the bedding planes." The writer suggests that a

1)5 Collier, A. J., op. cit., p. 28. 

"" Idoin, pi. !).
CRETACEOUS, NORTHWESTERN ALASKA 459

multitude of such small faults might cause a considerable aggregate 

amount of thickening which would be very difficult to detect, and 

that in view of the apparent enormous thickness of the formation and 

more especially in view of the apparent range of a single flora 

throughout so great a thickness of strata, it may perhaps be safe to 

assert the probability of a considerable aggregate amount of duplication in thickness by small movements on numerous bedding faults.

The base of the Corwin formation has never been observed, nor 

is it known what formation underlies it. The next oldest rocks occurring in this district are the Triassic beds at Cape Lisburne (pp. 

106-112). These have not been observed in contact with the Corwin 

formation, except possibly at Cape Thompson, where the Triassic 

beds are overlain conformably by black shale which Kindle 97 has 

suggested may be the equivalent of the Corwin formation. No 

definite evidence in support of this correlation or on the age of this 

shale has yet been obtained.

The Corwin formation is overlain, probably conformably, by the 

Cretaceous (?) sandstone and shale described on page 467.

The rocks exposed on Kukpowruk, Utukok, and Meade Rivers and 

near Wainwright Inlet that are supposed to represent the northeast 

extension of the Corwin formation were described by Paige, Foran, 

and Gilluly 98 as follows:

A thick series of sandstone, shale, thin-bedded limestone, and associated beds 

of coal extends from Cape Beaufort westward to the Cape Lisburne region. 

These rocks are believed to extend eastward to and beyond Cape Simpson and 

inland at least 80 miles south of the coast at Meade River.

The sandstone is gray where fresh but weathers to a yellow or buff color. 

It is medium to fine grained, grades in places into shale and rarely into conglomerate, and in general is of normal types that were laid down at the margin of or in the sea by rivers and streams that entered it. Cross-bedding and 

ripple marks are locally abundant.

The shale is gray to yellow, many beds are fine grained mud rocks, and some 

beds are darkened by an appreciable amount of carbonaceous d6bris. In places 

it grades into sandy shale or sandstone, of which shale is the normal accompaniment in deposition of the type suggested above.

The limestone is gray to brownish and occurs in beds intercalated with the 

shale, into which it grades. It was noted only in very thin layers or as 

nodular concretions.

The coal that accompanies these rocks is abundant and occurs in beds of 

workable thickness. In the regions of strong folding it is of bituminous rank, 

and in the less disturbed regions it is of subbituminous rank.

The bottom of the series was not seen, nor is it possible to estimate from the 

data in hand how many feet of strata have been removed by erosion. By direct 

measurement and by estimates from observed dips it is known that the coal07 Kindle, E. M., The section at Cape Thompson, Alaska: Am. Join-. Sci., 4th ser., vol. 

24, p. 528, 1909.

88 Paige, Sidney, Foran, W. T., and Gilluly, James, A reconnaissance of the Point Barrow 

region, Alaska: U. S. Greol. Survey Bull. 722, pp. 12, 17, 1925.
460 MESOZOIC STRATIGRAPHY OF ALASKA

bearing portion of this sedimentary series is not less than 7,000 feet thick and } 

may be considerably more and that a non coal-bearing portion beneath the coal i 

is at least 2,000 feet thick and in all probability much more. An estimate of 

the entire thickness of these rocks can not be made at this time, though it may 

be stated with considerable assurance as more than 15,000 feet. The series is 

therefore comparable in thickness to the Corwin formation. j

Age and correlation. The evidence on the age of the Corwin formation is to be found almost wholly in its fossil plants. The field 

relations of the rocks indicate merely that they are post-Triassic, 

and the fossils other than plants are few and not characteristic. The 

fossils of the Corwin formation and of the beds that are believed to 

be equivalent to it are listed in the following table. In the table an 

attempt has been made to indicate the stratigraphic occurrence of 

the species as far as possible. The first 17 lots, all collected by Collier and his assistants from the type section of the Corwin formation, are arranged in geographic order from east to west. This 

order, unless undetected faults are present, is also the stratigraphic 

sequence, beginning at the base. The other lots could not be placed 

in similar order but are arranged in several groups, including miscellaneous collections from the type area of the Corwin formation, 

which could not be placed in stratigraphic sequence, followed by collections from Kukpowruk River, Utukok River, Wainwright Inlet, 

and Meade River in geographic sequence. i
Fossils from the Corwin formation

Coniferous leaves __ .....---..-.--,.--..-.-..-----.-...---

4AW25 |

b

b

b

b

0

b

b

b

b

o 

O

b

b

o 

O

h

b

b

b

i

i

b b

i "I"

i

ib

i

4AW18 |

b

"1" "

CO

b

b

b

h

b

5

S3

O *

- 

i

!

i

b

I

b

b

4AW12 ]

»

«<

b b

b

I

i

i

b

?

b

I £ £ 

 4

b

1

.. b

i

i

i

Ih

I

b b

b

--

jjj

b

b

b

b

b

b

b

b

b

«!

--

a

s

a

b

b

b

Q 

Q 

W *

b

a '

b

i

i

i

§

CO

3 

« a, Identified by W. M. Fontaine; b. identified by F. H. Knowlton; c, identified by T. W. Stanton; d, identifi
Fossils from the Gorwin formation Con

Coniferous wood. __ .... __ ---------------.-_-_-___-__ _

Worm burrows __________ _ . _____ ... ..........

Ostrea sp., large simple form. __ ---_-_-_-._____________.

Pelecypod related to Anisocardium but probably a new 

genus..... ____________________ . ..........

Tbraciasp.- __ __ ... _ .-.. __ ------------ __ ---.....

Tellinasp __ ____ ........ _ ....-.-.- __ ... _ .1......

Trails of crustaceans?- _.. _ .... _ _ .....................

10 

<M

«!

O

<

o 

O 

<J

CD

O

<

oo

£ <

00

O

<J

t~

O

<J

IM

00

O

 <

s

<J

(N

% 

<

00

^

 <

t*

%<

ct>

^

<J

i 

<1

^

<i

lO

£ 

 <

i

<1

^'

ft

B

^ 

p

H

 ^J*

 ^

o 

tc

I

1
CRETACEOUS, NORTHWESTERN ALASKA 463

4AW25. Shale about 4 miles east of the mouth of Thetis Creek, in sea 

cliff, about 1 mile east of Cape Sabine and about 400 or 500 feet below 

Thetis seam No. 5. C. W. Washburne, 1904.

4AC11. 4 miles east of Corwin Bluff. A. J. Collier, 1904.

4AC10. 3 miles east of Corwin Bluff. A. J. Collier, 1904.

4AC9. 2% miles east of Corwin Bluff. A. J. Collier, 1904.

4AW18. Thetis Creek about iy2 miles from mouth. C. W. Washburne, 1904.

4AC8. 2% miles east of Corwin Bluff. A. J. Collier, 1904.

4AC7. 2 miles east of Corwin Bluff. A. J. Collier, 1904.

4AC82. Beach at mouth of creek east of Corwin Bluff. A. J. Collier, 1904.

4AW26. Mouth of creek east of Corwin Bluff. Boulder. C. W. Washburne, 

1904.

4AW12. Mouth of creek east of Corwin Bluff. C. W. Washburne, 1904.

4AW8. Boulder at mouth of creek 100 yards east of Corwin Bluff. C. W. 

Washburne, 1904.

4AW1T. Shale at base of conglomerate at Corwin Bluff. C. W. Washburne, 1904.

4AW9. Foot of Corwin Bluff. C. W. Washburne, 1904.

4AW1. Shale above the big conglomerate at Corwin Bluff. Mostly from 

16-foot coal bed 1 mile west of Corwin Bluff. C. W. Washburne, 1904.

4AW4. Concretions in shale just west of mouth of small creek about 1^ 

miles west of Corwin Bluff. C. W. Washburne, 1904.

4AW5. Scattered through shale for 200 feet west of 4AW4. C. W. Washburne, 1904.

4AW11. Carbonaceous shale 3% miles west of Corwin Bluff. Below a big 

sandstone. C. W. Washburne, 1904.

H. D. W. "Near Cape Lisburne" (probably near Corwin Bluff). Henry 

D. Woolfe,. 1884.

H. D. D. Corwin coal mine. H. D. Dumars, 1890.

664, 666. Cape Beaufort. F. C. Schrader, 1901.

672. "Lisburne coal mines," near Corwin Bluff. F. C. Schrader, 1901.

4AC12. Cape Beaufort. A. J. Collier, 1904.

O. H. Labeled " 4 miles south of Cape Lisburne " but probably from Corwin 

mine. Oscar Hershey, 1906.

7640 (1). Low ridge 10 miles east of Cape Beaufort. Stratigraphic position 

probably near the top of the Kukpowruk coal series. W. T. Foran, 1923.

7641 (11). Kukpowruk River 5 miles from mouth, near bottom of coal series. 

W. T. Foran, 1923.

7644 (14). Shale below 10-foot bed of coal 5 miles up Kukpowruk, near 

bottom of coal series. W. T. Foran, 1923.

7645 (15). Shale below 1-foot bed of coal 5 miles up Kukpowruk. W. T. 

.Foran, 1923.

7646(16). Sandstone associated with coal 5 miles up Kukpowruk River, 

near bottom of coal series. W. T. Foran, 1923.

7647 (17). Kukpowruk River 4% miles from mouth, near bottom of coal 

series. W. T. Foran, 1923.

7648 (18). Parting in 10-foot bed of coal,, Kukpowruk River 5 miles from 

mouth, near bottom of coal series. W. T. Foran, 1923.

7649(19,20,21,22). Kukpowruk River 6 miles from mouth, approximately 

2,000 feet stratigraphically above 10-foot coal bed mentioned above. W. T. 

Foran, 1923.

7650 (23). Kukpowruk River 10 miles above mouth, approximately the same 

position as 22. Axis of shallow syncline; rocks nearly horizontal. W. T. 

Foran, 1923.
464 MESOZOIC STRATIGEAPHY OF ALASKA

7651 (24). Kukpowruk River 17 miles from mouth, at junction of forked, 

stream. Position in series not known; probably near top. W. T. Foran, 1923.

7653 (28). Kukpowruk River 18 miles from mouth, probably near top of coal 

series. W. T. Foran, 1923.

7652 (27). Kukpowruk River 22 miles above mouth, probably near top of coal, 

series. W. T. Foran, 1923.

7654 (35). Kukpowruk River 40 miles from mouth, approximately 1,000 feet 

stratigraphically below coal series, in zone of disturbance. W. T. Foran, 1923.

12178 (100,101). Thin conglomerate bed 43 miles above mouth of Kukpowruk 

River. About 1,000 feet stratigraphically below coal series. W. T. Foran, 1923.

7665 (C). Utukok River 15 miles from mouth. The strata on Utukok River 

are nearly horizontal, therefore all specimens collected on this river (7664, 7665,. 

7666, 7668) must be approximately in the same stratigraphic position. W. T.. 

Foran, 1923.

7666 (E). Utukok River 17 miles from mouth. W. T. Foran, 1923.

657. About 7 miles southwest of Wainwright Inlet. Slightly calcareous shaleF. C. Schrader, 1901.

658. About 7 miles southwest of Wainwright Inlet. Slightly calcareous sandstone. F. C. Schrader, 1901.

660. About 7 miles southwest of Wainwright Inlet. Dense slightly calcareoussandstone. F. C. Schrader, 1901.

661. About 7 miles southwest of Wainwright Inlet. Indurated shale. F. C.. 

Schrader, 1901.

7699(1). About 27 miles up Meacle River, on right bank. Poor exposure,, 

possibly float of coal-bearing shale and sandstone. Sidney Paige, 1923.

7700 (2). Right bank of Meade River 33 miles above mouth. Poor exposure 

of sandstone and shale. Sidney Paige, 1923.

7701 (3). Meade River 67 miles above mouth. Horizontal shale, sandstone,, 

and coal. Sidney Paige, 1923.

The flora of the rocks that were subsequently described as the 

Corwin formation was considered by Lesquereux 1 "probably Neocomian." Additional collections, which were also obtained from, 

the type locality of the Corwin formation, were studied by Fontaine,2 who said:

The age of the formation yielding the Alaskan fossils, as indicated by them,, 

is not older than the Lower Oolite and not younger than the Lower Cretaceous but is probably between them.

The larger collections that were obtained by Collier from the type 

section of the Corwin formation were studied in detail by Knowltion,3 who concluded that

The Corwin formation of the Cape Lisburne region is undoubtedly Jurassic 

in age, belonging either in the upper part of the Middle Jurassic or Brown

1 Lesquereux, Leo, Recent determinations of fossil plants from Kentucky, Louisiana, 

Oregon, California, Alaska, Greenland, etc., with descriptions of new species : U. S. Nat. 

Mus. Proc., vol. 11, p. 31, 1888.

2 Fontaine, W. M., Plants from the vicinity of Cape Lisburne, Alaska (in Ward, L. F., 

Status of the Mesozoic floras of the United States; second paper) : U S. Geol Survey 

Mon. 48, p. 175, 1905.

8 Knowlton, F. H., The Jurassic flora of Cape Lisburne, Alaska : U. S. Geol. Survey 

Prof. Paper 85-D, p. 43, 1914.
465

Jura, or the extreme lower portion of the Upper Jurassic or White Jura 

that is to say, it is probably not older than the Bathonian and certainly not 

younger than the Oxfordian.

Knowlton regarded the flora 'of the entire formation as a unit, 

saying,4 "so far as the data at hand indicate, there is little or no 

variation in the flora throughout the whole thickness of the formation."

The fossil plants collected by Paige and Foran in 1923 at several 

localities on the supposed northeastern extension of the Corwin 

formation include fossils that are similar to some of those in the 

type section of the Corwin formation, together with dicotyledenous 

leaves and other fossils that are indicative of the Lower Cretaceous. 

Knowlton 5 made the following statements concerning some of these 

collections:

7650. Kukpowruk River 10 miles above mouth. This is by all odds the most 

puzzling lot in the whole collection. The Ginkgo, although large and well 

-enough preserved, is of little value in fixing the age, as Ginkgo has come down 

to us from the Jurassic to the present with very little change. The fragment 

of a fern seems to be the same as a form from Cape Lisburne, but the welldefined dicotyledons absolutely preclude a reference to the Jurassic. On the 

basis of present knowledge it can hardly be older than the middle or upper 

part of the Lower Cretaceous.

7653. Kukpowruk River 18 miles from mouth, probably near top of coal 

series. These forms are similar to forms found in the Cape Lisburne Jurassic, 

but considering the report on No. 7650, I hesitate to call it Jurassic. No 

dicotyledons are present.

7668. Utokok River 43 miles above mouth. The age appears to be Lower 

Cretaceous, in the approximate position of the Kootenai or Wealden.

7665. Utokok River [15 miles from mouth]. Age can not be fixed by this 

specimen. May be Tertiary.

Arthur Hollick also examined the fossil plants collected by W. T. 

Foran along Kukpowruk and Utokok Rivers and made the following statements 8 concerning them :

Most of these collections consist of a single piece of matrix each. Plant 

remains are included in most of them, but they are fragmentary, and few are 

identifiable, even generically. Certain of the single specimens, however, if considered by themselves, would be regarded as almost certainly Jurassic; but 

at least one and possibly two of the collections undoubtedly represent Lower 

Cretaceous horizons, viz:

7650. Kukpowruk River, 10 miles above mouth. This collection, in addition 

to more or less well defined specimens of a fern (CladophleMs sp.) and a 

gymnosperm (Ginkgo sp.), contains fragmentary remains of leaves of angiosperms. This precludes the possibility of Jurassic age for the rock in which 

they occur. The age is Lower Cretaceous and apparently about the equivalent 

of the Potomac group.

* Knowlton, F. H., op. cit., p. 40.

5 Knowlton, F. H., quoted by Paige, Sidney, Foran, W. T., and Gilluly, James, op. 

cit., pp. 13-14.,

° Hollick, Arthur, idem, pp. 14-15.
466 MESOZOIC1 STRATIGRAPHY OF ALASKA

 7668. Utokok River, 43 miles above mouth. This collection, consisting of a 

single piece of matrix, contains plant remains, mostly fragments of ferns, 

among which are specimens of OleandriMum sp. and Cladophlebis sp. The age 

appears to be Lower Cretaceous and equivalent to the Kootenai formation.

The only identifiable fossils, other than plants, that have been 

obtained from the Corwin formation or from its supposed extension 

along the northwest coast of Alaska are some marine shells collected 

by W. T. Foran in 1923 from a thin conglomerate bed 43 miles from 

the mouth of the Kukpowruk and about 1,000 feet stratigraphically 

below the coal series. Concerning these fossils (lot 12178) Keeside 7 

said:

I have not been able to identify this fauna with any degree of certainty. The 

species present are probably all new and might come equally well from the 

Upper Jurassic, Lower Cretaceous, or Upper Cretaceous. It impresses me as 

more likely to be Upper Cretaceous than older.

The flora of the Corwin formation does not show a close relationship with any of the undoubted Jurassic floras of southern Alaska. 

One of the species occurring in the Corwin formation, Fieldenia 

nordensMoldi Nathorst, has been doubtfully identified from the 

Middle Jurassic Tuxedni sandstone of Cook Inlet. Phoenicopsis 

speciosa Heer occurs in the Upper Jurassic Chinitna shale of Cook 

Inlet. Coniopteris bu/rejensis (Zallesky) Seward occurs in the Upper Jurassic Shelikof formation of the Alaska Peninsula. Zamites 

megaphyllus (Phillips) Seward occurs in the Upper Jurassic Naknek formation of the Alaska Peninsula. The flora of the Corwin 

formation shows a closer relationship with the flora of the Kennicott 

formation, which is regarded as Lower Cretaceous. Four species, 

Otozamites leani (Lindley and Button) Seward, Zamites megaphyllus (Phillips) Seward, Taxites zamiodesl (Leckenby) Seward, 

and Elatides cwvifolia (Dunker) Nathorst, have been identified as 

occurring in the Corwin and Kennicott formations.

The probability that the Corwin formation is Cretaceous instead 

of Jurassic is suggested by the above-cited apparent lack of relationship with any of the undoubted Jurassic floras of Alaska, by its 

closer relationship with the Kennicott formation, which is classified as 

Lower Cretaceous (see pp. 335-349), by the presence of several species 

which Lesquereux, Fontaine, and Ward considered Lower Cretaceous, and especially by the presence of dicotyledonous leaves.

LOWER CEETAOEOUS (?)

SANDSTONE AND SHALE NEAR CAPE LISBUBNE

The youngest of the supposed Cretaceous rocks near Cape Lisburne 

comprise sandstone and shale, which overlie the Cretaceous or Juras7 Reeside, J. B., jr., quoted by Paige, Sidney, Foran, W. T., and Gilluly, James op cit 

p. 15. ''
SUMMABY, STBATIGBAPHY 467

sic rocks of the Corwin formation with apparent conformity. They 

have yielded no fossils but are believed to be possibly Lower Cretaceous and perhaps the general equivalent of the Anaktuvuk group. 

They are the youngest rocks known in the Cape Lisburne district.

These rocks were described by Collier 8 under the heading " Upper 

Mesozoic beds" and were mapped as " Cretaceous (?) sandstones 

and shales." Collier described briefly the lithology and the stratigraphic and structural relations of these beds to the adjacent socalled Carboniferous and Jurassic rocks and discussed their thickness and age and correlation. The southern extension of these rocks 

is possibly found in some shale that overlies the Upper Triassic 

rocks at Cape Thompson and has been briefly mentioned by Kindle."

The Corwin formation of the Cape Lisburne district, which has 

been described above (see pp. 456-466) and which is of Cretaceous or

Jurassic age, is apparently overlain conformably by nonfossiliferous 

sandstone and shale, which are estimated to be at least 5,000 feet 

and perhaps 10,000 or 15,000 feet thick. These beds have been described by Collier 10 as an unnamed formation of upper Mesozoic 

and probably of Cretaceous age. They consist.of sandstone and 

shale, the former predominating. They differ from the beds of the 

underlying Corwin formation in that the sandstone is less gritty 

and contains no conglomeratic material, they include no coal, and 

fossils are absent or at least so rare that they have not yet been 

found. The only evidence of the age of these beds is their apparently conformable .superposition on the Cretaceous or Jurassic beds 

of the Corwin formation. No younger rocks are known in this district, these beds being overlain by Triassic rocks that are thrust over 

them.

SUMMARY 

STRATIGRAPHY 

LOWER CRETACEOUS

The Lower Cretaceous rocks of Alaska consist of shale, sandstone, 

limestone, and conglomerate, which have been recognized at many 

localities throughout much of the Pacific coastal region and of the 

Yukon and Kuskokwim Valleys and at more isolated localities in 

northern Alaska.

In the Pacific coastal belt these rocks rest, for the most part, on 

Upper Jurassic sedimentary rocks. In the interior region, where

8 Collier, A. J., Geology and coal resources of the Cape Lisburne region, Alaska: U. S. 

Geol. Survey Bull. 278, pp. 30-31, pi. 1, 1906. '

9 Kindle, E. M., The section at Cape Thompson, Alaska : Am. Jour. Sci., vol. 28, p. 

528, 1909.

10 Collier, A. J., op. cit., pp. 30-31.
468 MESOZOIC' STRATIGRAPHY OF ALASKA

Jurassic rocks are absent, they rest either on Triassic beds or on 

different Paleozoic sedimentary formations or on schist of undetermined age. In northern Alaska the basal relations of the Cretaceous rocks are not known.

The Lower Cretaceous rocks contain a scanty marine fauna which 

has not been thoroughly studied but which contain two or more 

species of Aucella related to Aucella crassicollis Keyserling and 

Aucella piochii Gabb, together with a few other fossils, most of 

which are not known to be characteristic of definite horizons.

The Lower Cretaceous rocks of the Alaska Peninsula include two 

supposedly conformable formations, the Staniukovich shale, containing Aucella piochn, below, and the Herendeen limestone, containing Aucella crassicollis, above. The Staniukovich shale is underlain with apparent conformity by Upper Jurassic rocks. The 

Herendeen limestone is overlain with probable unconformity by 

Upper Qretaceous rocks.

In the Matanuska Valley the Lower Cretaceous rocks include 

conglomeratic tuff and arkose with Aucella crassicollis at the base, 

overlain conformably by the Nelchina limestone. The basal Lower 

Cretaceous beds rest with apparent conformity on Upper Jurassic 

rocks. The Nelchina limestone has been observed only on hilltops 

but is believed to be succeeded unconformably by Upper Cretaceous 

rocks.

The Lower Cretaceous rocks of the Chitina Valley as herein described include the Kennicott formation, which is composed of yellowish sandstone and greenish sandy shale that carry several species 

of Aucella, abundant ammonites, and other marine fossils and a 

fossil flora that Knowlton has referred to the Upper Jurassic. The 

Kennicott formation lies unconformably on Upper Triassic rocks 

and is believed to be succeeded conformably by Upper Cretaceous 

shale. The Kotsina conglomerate and some limestone and sandstone 

that probably overlie it are believed to be possibly Lower Cretaceous 

and possibly to represent lateral westward gradations from the 

Kennicott formation. Some conglomerate and grit on Nikolai and 

Dan Creeks may also be the equivalents of the basal Kennicott beds. 

The Lower Cretaceous rocks of the Nutzotin Mountains consist 

of shale and graywacke that contain Aucella crassicollis. They have 

not been accurately separated from some Upper Jurassic shale and 

graywacke that are supposed to underlie them conformably. The 

next younger rocks at present known are Tertiary sedimentary and 

volcanic beds.

The rocks that have been assigned to the Lower Cretaceous in 

southeastern Alaska consist for the most part of shale or slate, sandstone or graywacke, and conglomerate. They are distinguishable, 

in the writer's opinion, from the somewhat similar slaty rocks that
SUMMARY, STRATIGRAPHY 469

have been referred to the Upper Jurassic by containing the Cretaceous rather than the Jurassic type of Aucella, by containing no volcanic beds, by containing conglomerate with granitic pebbles that 

are believed to have been derived from the supposed Jurassic intrusive rocks, and by showing in some places a lesser degree of 

metamorphism than the Jurassic slate. The Lower Cretaceous beds 

.are believed to lie unconformably on Upper Jurassic and older rocks. 

They are overlain unconformably in some places by Tertiary beds, 

no Upper Cretaceous rocks having been found in southeastern 

Alaska.

Along the upper Yukon between Eagle and Woodchopper there 

are Lower Cretaceous slate and quartzite, several thousand feet 

thick, carrying Aucella crassicollis, that are believed to lie unconformably on Upper Triassic and Paleozoic rocks and to be succeeded unconformably by Upper Cretaceous beds.

In the Rampart-Tanana district Lower Cretaceous quartzite and 

slate of undetermined thickness overlie Silurian and Devonian rocks 

and are overlain, probably unconformably, by Upper Cretaceous 

shale.

Lower Cretaceous rocks are known in. the Kuskokwim region only 

from sandstone and conglomerate float carrying Aucella crassicollis 

on the west front of the Oklune (Ahklun) Mountains, east of Kuskokwim Bay. From this occurrence the rocks in the vicinity have 

been described as the " Oklune series," which is believed to rest 

unconformably on late Carboniferous or early Mesozoic volcanic 

rocks and to be overlain unconformably by Upper Cretaceous conglomerate, sandstone, and shale.

The Lower Cretaceous rocks of the Koyukuk Valley have been included in the Koyukuk group, which, as originally described, includes limestone, lava, and tuff. The limestone contains Aucella 

crassicollis and is doubtless Lower Cretaceous, but the writer suspects that the supposedly associated lava and tuff may include preCretaceous or post-Cretaceous volcanic rocks like those " associated 

with " the Upper Cretaceous rocks on the lower Yukon. The rocks 

beneath the Koyukuk group are not known. The Koyukuk group is 

supposed to be overlain unconformably by the Upper Cretaceous (?) 

rocks of the Bergman group.

In the Colville Valley the Lower Cretaceous rocks have been described as the Anaktuvuk group, which consists of sandstone with 

some conglomerate and shale. The Anaktuvuk group is at least 

2,000 feet thick, contains Aucella crassicollis, and is believed to rest 

unconformably on Carboniferous and Devonian rocks and to be 

overlain unconformably by Upper Cretaceous rocks.

49448 26 31
470 MESOZOIC STRATIGRAPHY OF ALASKA

The Lower Cretaceous may be represented on the northwest coast 

of Alaska by the coal-bearing rocks of the Corwin formation and 

by the overlying sandstone and shale. The Corwin formation, which 

has been considered to be more than 15,000 feet thick, is composed of 

shale, sandstone, and conglomerate, with many coal beds. It contains a flora which has previously been referred to the Jurassic but 

which the writer believes may be Lower Cretaceous. The Corwin 

formation probably lies unconformably on Upper Triassic rocks and 

is overlain with apparent conformity by shale and sandstone that 

may also be Lower Cretaceous. No Upper Cretaceous or Tertiary 

beds are known in this region.

TJPPEK CRETACEOUS

The Upper Cretaceous rocks of Alaska consist of shale, sandstone, 

and conglomerate, of which some are marine and some are noninarine. The nonmarine rocks contain coal beds and fossil plants. 

The Upper Cretaceous rocks cover smaller areas than the Lower 

Cretaceous rocks but nevertheless are widely distributed throughout 

many parts of the Territory, including much of the Pacific coastal 

belt, exclusive of southeastern Alaska, much of the Yukon and 

Kuskokwim Valleys, especially in their lower and middle parts, and 

some localities in northern Alaska.

The Upper Cretaceous plant-bearing beds of Alaska include the 

middle and upper members of the Chignik formation of the Alaska 

Peninsula; the four formations of Upper Cretaceous shale, sandstone, and conglomerate of the lower Yukon region, some of which 

extend into the lower part of the Koyukuk Valley; and the shale, 

sandstone, and conglomerate near Seventymile Kiver on the upper

Yukon. Fossil plants are known to occur also in the Upper Cretaceous shale and sandstone near Wolverine Mountain, south of 

Rampart, but no determinable specimens have been available for 

study. Marine Upper Cretaceous rocks, in which no determinable 

fossil plants have yet been found, are known in the Matanuska, 

 Chitina, Innoko, Kuskokwim, and Anaktuvuk Valleys.

The Upper Cretaceous rocks of the Alaska Peninsula have been 

described as the Chignik formation, which includes a lower member 

about 200 feet thick that consists of shale with marine fossils and 

no known fossil plants; a middle member about 300 feet thick that 

consists of shale with many coal beds and some sandstone and that 

contains fossil plants with a few marine mollusks; and an upper 

member 300 to 500 feet thick that consists of conglomerate, sandstone, and shale with fossil plants and marine invertebrates. The 

Chignik formation rests in some places upon Lower Cretaceous limestone with possible unconformity, and where the Lower Cretaceous
SUMMARY, STRATIGRAPHY 471

limestone is absent it rests unconformably upon Upper Jurassic 

rocks. It is overlain, unconformably in at least some places, by 

Tertiary strata. The plant-bearing beds of the Chignik formation 

on the Alaska Peninsula are underlain by and interbedded with 

marine fossiliferous strata. Most of the marine fossils were obtained from the lower member of the Chignik formation that is, 

from rocks beneath the plant-bearing beds. This fauna, according 

to Stanton, is related to that of the Chico of California. This opinion is in reasonable accord with the evidence of the plants from the 

overlying beds, which Hollick believes to be possibly equivalent to 

the Montana.

The Upper Cretaceous rocks (Matanuska formation) of the Matanuska Valley consist of marine shale and sandstone having an 

aggregate thickness of at least 4,000 feet, of which the lower half 

is practically all shale containing abundant marine fossils, and the 

upper half consists of sparsely fossiliferous alternating beds of sandstone and shale, the sandstone predominating. The base of the 

Upper Cretaceous shale has not been observed, but the areal distribution of the formation indicates that it probably rests unconformably 

upon a surface of profound erosion cut across rocks that range in 

age from Lower Jurassic to Lower Cretaceous. The Upper Cretaceous Matanuska formation is overlain unconformably by Tertiary 

arkose and conglomerate.

The Upper Cretaceous rocks of the Chitina Valley consist of marine shale with some interbedded sandstone, having a total thickness 

of probably 7,000 or 8,000 feet. They are underlain with apparent 

conformity by conglomerate and sandstone that may be either basal 

Upper Cretaceous or Lower Cretaceous. They are believed to be 

succeeded by conglomeratic rocks that have been tentatively assigned 

to the Upper Cretaceous or basal Tertiary, above which is lava that 

is probably Tertiary.

The Upper Cretaceous rocks of the upper Yukon region consist 

of shale, sandstone, and conglomerate at least several hundred feet 

thick, which are believed to be underlain unconformably by Carboniferous limestone and which may be overlain by Tertiary coalbearing rocks. The only fossils that have been obtained from these 

Upper Cretaceous rocks are fossil plants which indicate a correlation with the upper coal-bearing division (Kaltag formation) 

of the section on the lower Yukon.

The Upper Cretaceous rocks of Wolverine Mountain, in the 

Rampart-Tanana district, probably rest unconformably on the 

Lower Cretaceous slate and quartzite, consist of black, rather massive carbonaceous sandy shale, probably 200 or 300 feet thick, and 

contain marine mollusks and poorly preserved fossil plants. Ter-
472 MESOZOIC STRATIGRAPHY OF ALASKA

tiary rocks, although present elsewhere in the district, are absent 

at this locality, and the only beds known to overlie the Upper 

Cretaceous rocks are Recent UP consolidated deposits.

The Upper Cretaceous rocks of the lower Yukon region consist 

of sandstone, conglomerate, and shale, that have an aggregate 

thickness of perhaps 8,000 feet. They may be separated into four 

formations, from the base upward (1) the Ungalik conglomerate, 

consisting of conglomerate, sandstone, and sandy shale about 3,000 

feet thick and containing no known fossils except a few worm 

tubes, trails, and unidentifiable shells and vegetable remains; (2) the 

Melozi formation, consisting of fresh-water shale and sandstone 

at least 1,000 feet thick and containing fossil plants and freshwater mollusks; (3) the Nulato formation, consisting of marine 

sandstone and shale perhaps 3,000 feet thick and containing marine 

invertebrates and a few fossil plants; and (4) the Kaltag formation, 

consisting of coal-bearing rocks at least 800 feet thick, which comprise 

fresh-water sandstone, shale, and coal beds with possibly some thin 

marine members, and containing fossil plants, fresh-water mollusks, 

and perhaps a few marine fossils. The Upper Cretaceous rocks of 

the lower Yukon are underlain by Paleozoic rocks and are believed 

to be overlain in some places by Tertiary volcanic rocks.

The Upper Cretaceous rocks of the Innoko and Iditarod valleys, 

which are probably the southern extension of the Upper Cretaceous 

rocks of ths lower Yukon region, consist chiefly of marine shale and 

sandstone. Some beds of terrestrial (coal-bearing) sandstone that 

are closely associated with thes3 rocks may be intercalated Upper 

Cretaceous deposits or may be infolded Tertiary sediments. These 

Upper Cretaceous strata are believed to rest everywhere upon Paleozoic rocks, no Lower Cretaceous or earlier Mesozoic rocks being 

known in this region. Their thickness is not known but is believed 

to be .several thousand feet.

The Upper Cretaceous rocks of the Kuskokwin region consist of 

conglomerate, sandstone, and shale having a thickness of many 

thousand feet. They are believed to rest uncomformably on the 

Lower Cretaceous sandstone and conglomerate of the lower Kuskokwim region. Farther up the river, where the Lower Cretaceous 

rocks are absent, the Upper Cretaceous rocks lie unconformably on 

Devonian limestone. The Upper Cretaceous rocks include both marine and nonmarine members, which are believed to be the equivalent 

and perhaps the continuous southward extension of some or all of 

the Upper Cretaceous formations exposed on the lower Yukon.

The Upper Cretaceous rocks exposed on the lower Koyukuk are 

the northern extension of the Upper Cretaceous rocks of the lower
SUMMARY, STRATIGRAPHY 473

Yukon and may include all the formations exposed on the Yukon. 

They have yielded only a few fossil plants and marine mollusks that 

do not furnish sufficient evidence as to which of the formations exposed on the Yukon may be represented. The Bergman group of 

the upper Koyukuk and of an adjacent area on the headwaters of 

the Kobuk may also be Upper Cretaceous. The Bergman group consists of sandstone, arkose, grit, conglomerate, and shale. It is believed to be at least 2,000 feet thick. It overlies Paleozoic rocks 

along its northern border and is infolded with the Lower Cretaceous 

rocks of the Koyukuk group on the south. The Bergman group has 

yielded no fossils, but there is believed to be little doubt that it is, at 

least in part, Upper Cretaceous.

The Upper Cretaceous rocks exposed on Anaktuvuk Eiver, a tributary of the Colville, which have been described as the Nanushuk 

"series." consist chiefly of sandstone, limestone, and shale of undetermined thickness, with some coal beds, contain marine fossils, apparently rest unconformably upon'the Lower Cretaceous sandstone 

of the Anaktuvuk group, and are probably overlain unconformably 

by Tertiary beds. As most of the Arctic slope is unexplored, the extent of the Upper Cretaceous rocks is not known. They are not present in the Canning River district, 100 miles east of the Colville, 

or along the Canadian boundary. They probably extend westward 

for a considerable distance and may extend as far as Cape Lisburne, 

nearly 400 miles west of the Colville, where the Cretaceous or Jurassic rocks of the Corwin formation are overlain by sandstone and 

shale that may be Upper Cretaceous.

The beds succeeding the Upper Cretaceous rocks in the Alaska 

Peninsula, the Matanuska Valley, the Chitina Valley, the upper 

Yukon district, the Rampart-Tanana district, and on the Arctic 

slope are Tertiary (probably Eocene) coal-bearing shale, sandstone, 

and conglomerate with no recognized members of marine origin, 

except at one locality on the Alaska Peninsula. In the Nutzotin 

Mountains and in southeastern Alaska, where no Upper Cretaceous 

rocks are known, these Tertiary deposits directly overlie the Lower 

Cretaceous rocks. The writer believes that there is an unconformity 

between the Cretaceous and the Tertiary rocks in all these districts. 

In several of the districts direct proof of unconformity is lacking, 

the Tertiary rocks not having been observed in contact with the 

Cretaceous rocks. The fact, however, that the Tertiary rocks rest 

upon other than the Cretaceous rocks which should normally underlie them is in itself an indication of unconformity at the base of the 

Tertiary.
474 MESOZOIG STRATIGRAPHY OF ALASKA

CORRELATION

The probable relations of the Cretaceous rocks of the several 

Alaskan districts to one another and to the Cretaceous rocks of other 

regions is indicated in the table facing page 474.

The Lower Cretaceous rocks contain in general only a scanty 

marine fauna, which has not been fully studied and which does not 

permit precise correlations. Most of the Lower Cretaceous rocks 

of Alaska contain few identifiable fossils except species of Aucella 

related to Aucella crassicollis Keyserling and Aucella piochii Gabb. 

The Cretaceous Aucetta-bear'mg beds of Alaska are believed to be 

approximately equivalent to the upper part of the Knoxville formation of California.

A somewhat younger horizon may be represented by the sandstone 

of the upper Chitina Valley, which the writer has referred to the 

Kennicott formation and which contains marine fossils that, according to Stanton,11 indicate a horizon in the basal part of the Upper 

Cretaceous or near the top of the Lower Cretaceous. The fossil 

plants from the same beds, according to Knowlton.12 are Upper 

Jurassic.

The Upper Cretaceous plant-bearing beds of Alaska represent two 

distinct horizons. Those of the Yukon Valley are low in the Upper 

Cretaceous, including at least the approximate horizon of the Dakota 

sandstone and perhaps the entire lower half of the Upper Cretaceous, 

and those of the Alaska Peninsula are somewhat higher in the Upper 

Cretaceous, possibly including the equivalent of part or all of the 

Montana group.

The most comprehensive section of the older plant-bearing beds is

on the lower Yukon, where the rocks may be separated into four 

formations, of which the upper three contain floras of the same general type but specifically distinct, especially in so far as the numerous new species of angiosperms are concerned. All three formations 

contain species that occur elsewhere in the Dakota flora, as well as 

some more persistent species, notably of ferns and gymnosperms, 

part of which range elsewhere down into the Lower Cretaceous and 

Jurassic or up into the Eocene. The great thickness of these plantbearing beds and the specific distinctness of the floras of the several 

formations suggest that these rocks may represent considerably more 

than the Dakota sandstone, possibly the entire lower half or twothirds of the Upper Cretaceous.

The section on the lower Koyukuk, which is the northward continuation of the section on the lower Yukon, is very imperfectly

11 Stanton, T. W., quoted by Mofflt, F. H., The upper Chitina Valley, Alaska: U. S. 

Geol. Survey Bull. 675, pp. 37-42, 1918. 

u Knowlton, F. H., quoted, idem, pp. 42-44.
Tentative correlation of Cretaceous rocks of Alaska

Age

Post-Cretaceous.

Upper Cretaceous.

Lower Cretaceous.

Pre-Cretaccous.

Alaska Peninsula

Eocene coal-bearing rocks underlain locally by Eocene tufls.

Upper member.

ChnSn. f°r- Middle member.

jLower member.

Herendeen limestone. 

Staniukovich shale

Upper Jurassic.

Matanuska Valley

Eocene coal-bearing 

rocks.

Matanuska formation (marine shale 

and sandstone) .

Nelchina limestone.

Conglomerate tun? and 

arkose.

Upper Jurassic.

Chitina Valley

Late Tertiary to Recent lava underlain 

by one or more small 

patches of Eocene(?) 

coal-bearing rocks.0

? Conglomerate, arkose, and shale of 

hills near Young 

Center. (May be 

basal Eocene.)

Shales of Chititu and 

Young creeks.

Kennicott formation 

(sandstone and 

sandy shale) .

Upper Triassic.

Nutzotin Mountains

Eocene coal -bearing 

rocks."

.AwceZZa-bearing beds 

of Chisana and 

White rivers (shale 

and graywacke) .

Upper Jurassic.

Southeastern Alaska

Eocene coal-bearing 

rocks of Hamilton 

Bay and Kootznahoo Inlet.0

Aucella-beariag beds 

of Pybus Bay and 

Etolin Island (sandstone, shale, and 

conglomerate) .

Upper Jurassic (?) .

Upper Yukon

Eocene shale, sandstone, and conglomerate with lignite.0

Shale and sandstone 

near Seventymile.

jlMceZZo-bearing beds 

of Washington Creek 

and Charley River 

(slate and sandstone) .

Upper Triassic and 

Paleozoic.

Rampart-Tanana 

district

Eocene coal-bearing rocks."

Marine Upper 

Cretaceous near 

Wolverine 

Mountain.

Aucetta - bearing 

beds of Minook 

Creek (quartzite).

Lower Yukon and NulatoNorton Bay districts

Late Tertiary (?) volcanic 

rocks.

(contem- Shaktolik grup poraneous) .

Kaltag formation 

(coal-bearing rocks) .

Nulato . formation 

(marine sandstone 

and shale) .

Melozi formation 

(fresh-water shale 

and sandstone) .

Ungalik conglomerate.

Paleozoic. j Paleozoic.

Innoko Valley

Tertiary (?) plantbearing beds.

Shale and sandstone.

Paleozoic.

Kuskokwim Valley

"Holiknuk series."

.AwceZZa-bearing beds 

of "Oklune series" 

(sandstone and conglomerate) .

Late Paleozoic (?) volcanic rocks.

Koyukuk Valley

? Coal-bearing beds at 

Tramway Bar.

Bergman group (Upper Cretaceous?) .

Shale, sandstone, and 

conglomerate on the 

lower Koyukuk.

.dMceZZa-bearing beds 

of Koyukuk group 

(limestone, shale, 

sandstone, and volcanic rocks?) .

Arctic slope

Marine Pliocene and 

coal - bearing (?) 

Eocene (?) beds.

Nanushuk formation 

(position within the 

Upper Cretaceous 

not established) .

/IwceZZa-bearing beds 

of the Anaktuvuk 

group (sandstone, 

conglomerate, and 

shale) .

Cape Lisburne

Nonfossiliferous sandstone and shale, of 

doubtful age, overlying the Corwin 

formation. (May 

be Lower Cretaceous.)

Corwin formation 

(Cretaceous or Jurassic) .

Europe

Eocene.

Cretaceous. Upper 

Cretaceous. Lower 

Danian.

Senonian.

Turonian.

Cenomanian.

Albian 

(Gault).

Aptian.

Barremian.

Neocomian.

Jurassic.

Atlantic coast

Manasquan.

Rancocas.

Monmouth.

Matawan,

Magothy.

Raritan.

Patapsco.

a

id 

uo

o 

"o Arandel.

P-i

Patuxent.

Texas

Gulf series.

Comanche series.

Navarro.

Taylor.

Austin.

Eagle Ford.

Woodbine.

Washita.

Fredericksburg.

Trinity. 

?

Great Plains

Fort Union (Eocene) .

Lance, Laramie, and 

associated formations.

Montana 

group.

Colorado group.

Fox Hills.

Pierre.

Niobrara.

Benton.

Dakota.

Purgatoire. '

Pacific States

Chico.

Horsetown.

CD

1

CO

00

Knoxville.

1 These are the oldest post-Cretaceous rocks of the district, but they have not been observed directly overlying the Cretaceous rocks. 49448 26. (Face p. 474.)
SUMMARY, CORRELATION 475

known and may represent either part or all of the lower Yukon section. The fossils that it has yielded are neither abundant nor distinctive. They clearly indicate the presence of floras and faunas of 

the general type and age of those on the lower Yukon but are not 

sufficient to show which of the formations of the lower Yukon section may be represented at the fossiliferous localities on the Koynkuk.

The section on the upper Yukon contains no Upper Cretaceous fossils other than plants. Its flora clearly represents that of the coalbearing Kaltag formation of the section on the lower Yukon. The 

writer believes that the upper part of the Yukon Valley did not 

receive Upper Cretaceous sediments for a long time after the beginning of Upper Cretaceous sedimentation on the lower Yukon, and 

that the Upper Cretaceous sea never extended up the Yukon as far as 

the Seventymile district.

The Chignik formation of the Alaska Peninsula includes three 

members. The lower member has yielded no fossils except marine 

invertebrates, which according to Stanton " indicate correlation with 

a horizon in the Chico as developed in California and in the Nanaimo 

of Vancouver Island * * * but the beds at Chignik are probably not older than basal Senonian." The middle member has yielded 

fossil plants and a few marine mollusks, but neither the mollusks 

nor the plants are indicative of the precise horizon. The upper 

member has yielded both plants and marine invertebrates. The 

fauna suggests a correlation with the upper part of the Colorado 

group, but the flora contains elements suggestive of the Montana 

group.

The Upper Cretaceous fossils of the Matanuska Valley, according 

to Stanton,18 " belong to the Upper Cretaceous fauna which has been 

recognized at several points on the Alaska Peninsula and is part of 

the general Indo-Pacific fauna found in the Chico formation of 

California, on Vancouver Island, in Japan, and in India."

The fauna of the Upper Cretaceous shale of the Chitina Valley is 

believed to belong at about the same horizon.

The Upper Cretaceous rocks of the Innoko and Kuskokwim valleys have yielded no fossils that are indicative of the exact horizon. 

The character and sequence of the rocks and their geographic position on the southern border of the Upper Cretaceous rocks of the 

lower Yukon suggest that they probably represent approximately 

the same horizon.

The fauna of the Nanushuk formation of the Anaktuvuk Valley 

has practically nothing in common with the other Cretaceous faunas 

of Alaska and can not be placed relative to them.

13 Stanton, T. W., quoted by Martin, G. C., and Katz, F. J., Geology and coal fields of 

the lower Matanuska Valley, Alaska: U. S. Geol. Survey Bull. 500, pp. 88-39. 1912.
476 MESOZOIC STRATIGRAPHY OF ALASKA

CHRONOLOGIC RECORD

o .Before describing in detail the events of Cretaceous time in 

the area which is now Alaska, it is necessary to consider the preceding conditions that furnished the setting and, to a large extent, 

determined the details of the Cretaceous history.

In Pennsylvanian or early Permian time there was a widespread 

marine submergence, which carried the sea and spread deposits of 

limestone over areas in all parts of Alaska if not over the entire 

area. The fact that there are no extended areas in which these 

deposits have not been found and the absence of any known lithologic er^fanual facies in the deposits indicate that the orogenic 

features which exist to-day and of which we find indications throughout the deposits of Mesozoic and Tertiary time probably had not be°n 

outlined before the end of the Paleozoic era.

The absence of late Permian and of Lower and Middle Triassic 

sediments in most if not all of Alaska indicates a pronounced withdrawal of the sea toward the end of Paleozoic time. A thick and 

widespread accumulation of lava, which lies between the Pennsylvanian or early Permian and the Upper Triassic sediments at many 

places south of the Alaska Range, but not north of it, where the 

Upper Triassic and Carboniferous limestones are in direct contact, 

indicates that the withdrawal of the sea at the end of the Paleozoic 

era was accompanied or closely followed by widespread volcanic outbursts throughout the region south of the present Alaska Range. 

These volcanic deposits are sharply limited by the present axis of the 

Alaska Range, a fact which indicates that the present position of 

the Alaska Range was determined by differential movements that 

began at the end of Paleozoic time.

In Upper Triassic time there was another profound marine submergence, which carried the sea into the areas of the present major 

mountain axes of Alaska. The restriction of Upper Triassic deposits to these mountain areas and the apparent existence, during 

the earlier part of the Upper Triassic epoch, of faunal facies that 

are characteristic of the several mountain provinces suggest that the 

Upper Triassic deposits were laid down in three geosynclinal basina, 

which occupied the sites of the present Brooks Range, Rocky Mountains, and Alaska and Coast ranges. In later Upper Triassic 

(Noric) time deposition was still restricted to the vicinity of the 

present mountains, but it was more widespread than formerly, and 

in the deposits then laid down there are no indications of faunal 

facies. At the end of the Triassic. period the sea probably withdrew from the entire Alaskan area, the uppermost Triassic (Rhae-
SUMMARY, CHRONOLOGIC RECORD 477

tic) and possibly the earliest J'urassic (Lower and Middle Lias) not 

being represented anywhere in the Territory.

In Jurassic time there was another more or less gradual marine 

transgression. Lower Jurassic deposits are known only on the Pacific and Arctic seaboards. Middle Jurassic deposits have a somewhat wider extent in the Pacific coastal region. Upper Jurassic deposits are believed to have been laid down throughout the area south 

of the Alaska Range. The entire absence of marine Jurassic deposits north of the Alaska Eange, except, for some Lower Jurassic 

beds on the Arctic coast should be especially noted. In Jurassic 

time there was again a persistent shore line in or near the present 

position of the Alaska Eange.

In Lower Cretaceous time the sea again swept over the greater 

part of Alaska. The submergence covered not only the site of 

Jurassic sedimentation south of the Alaska Range but most of the 

Yukon V.alley,- the greater part of which had been land since the 

end of the Paleozoic era, and much of the area of northern Alaska, 

from which the sea had been excluded since the end of the Triassic 

period. The deposits of Lower Cretaceous time generally include 

basal conglomerate succeeded in most places by limestone and shale 

that are indicative of the absence of vigorous erosion in any near-by 

regions. Sandy beds are present throughout the Lower Cretaceous 

sections in some places, notably in the vicinity of the present mountains. Volcanic rocks are notably absent in the Cretaceous of 

Alaska, the only apparent exceptions being the conglomeratic tuff 

of the Matanuska Valley, which the writer believes to be reworked 

Jurassic volcanic material, and the supposed Cretaceous volcanic 

beds of the Kuskokwim and Koyukuk Valleys, which the writer 

believes to be partly Carboniferous volcanic beds and partly postCretaceous intrusive rocks. The Lower Cretaceous faunas of Alaska 

consist chiefly of boreal species of Aucella.

At the beginning of Upper Cretaceous .time the sea had receded 

from the Alaskan area, and when Upper Cretaceous sedimentation 

began it was of a different type and occurred in different areas from 

those of the earlier Cretaceous deposits. The major tectonic features of Alaska appear to have been well outlined by the beginning 

of Upper Cretaceous time, so that the distribution of the Upper 

Cretaceous deposits bears a very definite relation to the existing 

geographic features. For example, the marine Upper Cretaceous 

rocks do not occur along the present major mountain axes but are 

found for the most part on the Pacific and Arctic coasts and in the 

lower, broader parts of the Yukon and Kuskokwim Valleys. The 

Upper Cretaceous strata also include terrestrial deposits that were
478 MESOZOIC STRATIGRAPHY OF ALASKA

laid down in embayments that were the direct predecessors of the 

existing major valleys.

The initial Upper Cretaceous sedimentation of Alaska may be 

represented by some beds of sandstone in the upper Chitina Valley 

which Stanton regards as either basal Upper Cretaceous or Gault 

but which Knowlton believes to be Jurassic.

The oldest undoubted Upper Cretaceous deposits of Alaska are 

found on the lower Yukon and probably extend into the Koyukuk 

and Kuskokwim Valleys. The strati graphic succession on the lower 

Yukon includes conglomeratic beds at the base, followed in sequence 

by fresh-water shale and sandstone, then by marine sandstone and 

shale, and finally by terrestrial coal-bearing rocks which may be 

interbedded with a few thin marine strata. Upstream on the Yukon 

the full sequence outlined above is present as far as Melozi. The 

next exposures of Upper Cretaceous rocks are in the Rampart district, where the basal conglomerate and the fresh-water ehale and 

sandstone are absent and marine Upper Cretaceous sandstone rests 

directly on the Lower Cretaceous rocks. Still farther up the Yukon, 

in the Seventymile district, the only Upper Cretaceous rocks are 

shale and sandstone which contain a flora that indicates a correlation 

with the upper member of the section on the lower Yukon. This 

correlation shows that there was a gradual submergence of the 

Yukon Valley in Upper Cretaceous time which permitted the younger 

beds to extend progressively farther up the river. The sequence of 

beds on the lower river, ranging from conglomerate and coarse sandstone with very few fossils at the base, through shale and sandstone 

with fresh-water mollusks and abundant plants, followed by marine 

beds, to coal-bearing rocks at the top, also indicates the gradual submergence of a large valley. The cycle began with the rapid reworking of the large volume of coarse residual detritus which had probably accumulated during the long time, possibly since the end of the 

Paleozoic era, during which this region had been above the sea. This 

process was followed by the deposition of finer detritus, which now 

forms the fresh-water shale and sandstone. The submergence afterward went far enough to permit the incursion of marine waters 

throughout the lower and middle parts of the Yukon Valley. 

Finally the submergence slackened, and the marshes, in which the 

present coal beds were formed, were permitted to spread over the 

surface of the marine sediments, while contemporaneous deposits now 

represented by plant-bearing shale and sandstone extended up the 

valley into areas where the Upper Cretaceous sea had never reached.

The events of Upper Cretaceous time in the Yukon region, as outlined above, probably occupied approximately the earlier half of the 

Upper Cretaceous epoch and the area affected not only included the
SUMMARY, CHRONOLOGIC RECORD 479

valley of the Yukon but extended north into the lower part of the 

Koyukuk Valley and south across the valley of the Kuskokwim 

nearly to Clark Lake. The Upper Cretaceous succession in the 

Kuskokwim Valley appears to be very closely parallel to that on 

the lower Yukon. Some of the Cretaceous rocks on the upper 

Koyukuk and on Kobuk River may mark the northern border of this 

province, and the Upper Cretaceous rocks of the Arctic coast, though 

doubtless laid down i.\ a different basin, may date from the same 

time. The Upper Cretaceous rocks of the southern part of Alaska 

are of later date, and it is believed that while Upper Cretaceous 

sedimentation was in progress in the Yukon Valley the rest of 

Alaska was land.

During the later half of Upper Cretaceous time, when sedimentation had probably ceased in the Yukon region, the sea invaded parts 

of the southern coastal region of Alaska. In the Alaska Peninsula 

the deposits include marine shale, followed by coal-bearing shale, 

and then by conglomerate, sandstone, and shale that are probably of 

mixed marine and terrestrial origin. The sequence of events seems 

to have been a submergence which permitted the encroachment of the 

sea, a quiet period in which coal-forming marshes spread over the 

surface of the marine sediments, and a period of differential movement in which the marshes were submerged beneath marine waters 

and renewed erosion delivered large volumes of coarse gravel intothe sea. The end of Cretaceous time on the Alaska Peninsula appears to have been marked by a renewal of mountain growth which 

finds its expression in the increasing coarseness of the youngest Cretaceous deposits. The next succeeding deposits consist of Eocene 

tuff, which shows that the diastrophic movements that began in late 

Cretaceous time afterwards culminated in volcanic outbursts.. On 

the Alaska Peninsula, as probably everywhere else in Alaska, Cretaceous time was free from volcanism. The Upper Cretaceous deposits of the Alaska Peninsula are known near the west end of the 

peninsula at Chignik and Herendeen Bays and near the east end m 

the vicinity of Cape Douglas. It is believed that Upper Cretaceous 

deposits were laid down in the intervening area and removed by 

subsequent erosion.

The late Upper Cretaceous sea also extended into the sites of thepresent Matanuska and Chitina valleys, where there are shale and 

sandstone carrying a marine fauna that probably was approximately contemporaneous with the fauna of the lower member of the 

Chignik formation. The absence of Upper Cretaceous coal-bearing 

rocks in the Matanuska and Chitina valleys may mean either that 

marine conditions persisted there until the end of Cretaceous time.
480 MESOZOIC STRATIGRAPHY OF ALASKA

or that these districts were raised well above the sea while the coalforming marshes existed on the Alaska Peninsula.

The notable absence of Upper Cretaceous rocks along most of the 

Pacific seaboard, especially beneath the Tertiary coal-bearing rocks 

on Cook Inlet, at Controller Bay, and in southeastern Alaska, may 

mean either that the deposition of the Upper Cretaceous rocks was 

restricted to a few districts, or that early Tertiary erosion removed 

all traces of the Upper Cretaceous rocks except in a few places where

 conditions were especially favorable for their preservation. There 

is also the possibility that the slate and graywacke of Kodiak Island, 

Kenai Peninsula, Prince William Sound, the Controller Bay district, 

Yakutat Bay, and the west coast of Chichagof Island include Upper

 Cretaceous rocks that have been subject, throughout their entire 

linear extent, to folding and metamorphism that were much more 

intense than those which affected either the rocks on the margin of 

the belt of slate and graywacke or the Upper Cretaceous rocks of 

neighboring districts.

Upper Cretaceous time ended with .the complete withdrawal of the 

sea from the Alaskan area and probably was closely followed by 

the folding and erosion of the Cretaceous rocks. The Cretaceous 

rocks of Alaska are highly folded almost everywhere, and many of 

them are cut by intrusive rocks and by metalliferous veins. In 

many places it is not possible to determine the exact date of the folding, intrusion, and mineralization, especially as some of the Tertiary 

rocks have been similarly affected. It is believed, however, that at 

least part of the folding, intrusion, and mineralization dates from 

about the end of Cretaceous time. The earliest post-Cretaceous 

rocks in most of Alaska are the "widespread Tertiary coal-bearing 

beds. Although these rocks are highly folded in some places and 

have been cut by dikes and veins, they are in general notably less 

indurated, folded, and altered than the Cretaceous rocks. In some 

places there is clear proof of an unconformity at the base of the Tertiary rocks, and the writer believes that the Cretaceous rocks of 

Alaska were subjected to uplift and erosion, if not folding, immediately at the end of Cretaceous time in all parts of the Territory.

ROCKS OF UNDETERMINED AGE, MESOZOIC OR OLDER

SLATE, GRAYWACKE, AND GREENSTONE OF THE PACIFIC COAST

GENERAL FEATURES *

The slate and associated rocks, including graywacke, in some 

places phyllite, and both intrusive and bedded volcanic rocks, 

usually described as greenstone, that occur at scattered localities
ROCKS OF UNDETERMINED AGE 481

along the Pacific coast from Sitka to Kodiak offer a complex arid 

difficult series of problems in correlation and in determination of 

age. These problems have not been indisputably settled at any 

one point, and taken as a whole they constitute one of the most 

inviting fields of broad correlative study that still remain unworked in Alaska.

These rocks cover large areas along much of the Pacific shore 

north of latitude 57°, bordering the Gulf of Alaska for 800 miles 

and extending inland in places as far as the Alaska Range. The 

slaty rocks of this belt resemble one another in composition, in 

degree of metamorphism, in the general absence of characteristic 

fossils, and in the different structural and correlative problems 

which they present. They differ from one another sufficiently to

have been subdivided into several formations in some of the districts, to have been designated by one or more new formation names 

by most of the earlier observers, and to have been assigned to every 

geologic period from the Silurian to the Pleistocene.

It is obviously impossible to place these rocks among the undoubted Mesozoic strata that have been described in the preceding 

chapters. Brief references to the principal descriptions of the 

rocks in each of the districts will be given, followed by a statement of the writer's opinion on their age.

LOCAL DESCRIPTIONS 

SLATE AND GEAYWACKE OF KODIAK ISLAND

Parts of Kodiak and the neighboring islands contain slate and 

graywacke of undetermined age. These rocks were described by 

Dall,14 who considered them older than the Middle and Upper 

Jurassic rocks which he had seen on the mainland of Alaska and 

who accepted their provisional reference to the Triassic on the 

basis of Hyatt's identification of the fossils which Dall collected.15 

These rocks have been described briefly by Emerson,16 Martin,17 

and Maddren,18 and their fossils have been described by Ulrich,19

"Dall, W. H., Report on coal and lignite of Alaska: U. S. Geol. Survey Seventeenth 

Ann. Rept, pt. 1, pp. 871-872, 1896.

16 Hyatt, Alpheus, Report of the Mesozoic fossils (appendix to Ball's Report on coal 

and lignite of Alaska) : Idem, p. 907.

10 Emerson, B. K., General geology; Notes on the stratigraphy and igneous rocks: 

Alaska, vol. 4, pp. 51-53,, Harrim'an Alaska Expedition, 1904.

17 Martin, G. C., Mineral deposits of Kodiak and neighboring islands: U. S. Geol. 

Survey Bull. 542, pp. 128-129, 1913.

18 Maddren, A. G., The beach placers of the west coast of Kodiak Island: U. S. Geol. 

Survey Bull. 692, pp. 301-302, 1919.

19 Ulrich, E. O., Fossils and age of the Yafeutat formation : Alaska, vol. 4, pp. 125-146. 

Harriman Alaska Expedition, 1904.
482 MESOZOIC STRATIGBAPHY OF ALASKA

who referred them to the Lower Jurassic. Ulrich described the 

following fossils from the deposits near Kodiak:

Terebellina palachei Ulrich. 

Inoceramya concentrica Ulrich. 

Chondrites divaricatus Fischer-Ooster. 

Chondrites alpestris Heer. 

Palaeodictyon inagnuin laxum Ulrich. 

Palaeodictyon singulare Heer. 

Arthrodendron diffusum Ulrich. 

Cancellophycus rhoinbicum Ulrich. 

Retiphycus hexagonale Ulrich.

Gyrodendron emersoni Ulrich. 

Gilbertina spiralis Ulrich. 

Helminthoida exacta Ulrich. 

Helminthoida subcrassa Ulrich. 

Helminthoida abnormis Ulrich. 

Helminthoida vaga Ulrich. 

Helminthopsis magria Heer. 

Helminthopsis? labyrinthica Heer 

Myelophycus cunatum Ulrich.

SUNRISE GROUP

The slate and graywacke of Kenai Peninsula have been generally 

described as the Sunrise group. The latest and most comprehensive 

descriptions are those by Martin.20 Johnson,21 and Grant.22 The 

following description by Martin'" contains reference to previous 

descriptions:

Slates and graywackes compose the greater part of the Kenai Mountains, 

the only other known rocks they contain being intrusive masses, which are 

most abundant on the southern and eastern coasts, the greenstones near Resurrection Bay, the volcanic beds iuterstratified with the slate and graywacke 

in the western part of the peninsula, and the Mesozoic and other sediments 

that compose the foothills along the southern shore of Kachemak Bay.

These rocks have been mapped as a unit in the northern and central parts 

and along the western front of the Kenai Mountains, but on the southern 

coast of the peninsula Grant has recognized four formations, each composed 

partly of slates and graywackes but differing in degree of metamorphism and 

to some extent in composition. The writer believes -that most or all of these 

formations extend into other parts of the Kenai Mountains where the rocks 

were mapped as a unit, not because of their lithologic homogeneity but because 

the field work was not sufficiently detailed to justify the mapping of the subdivisions. The slaty rocks of Kenai Peninsula are not a lithologic -unit of uniform stratigraphic character but constitute a stratigraphic and structural complex containing rocks of moderately diverse lithologic character and probably 

of widely differing ages.

The slate and graywacke of Seldovia Bay underlie the ellipsoidal basalts, 

which in turn apparently lie beneath the presumably Upper Triassic cherts. 

They are consequently either Paleozoic or early Triassic. The slates and 

graywackes in the vicinity of Turnagain' Arm contain fossils which are 

apparently either Jurassic or Cretaceous. This locality is within the type 

district of the Sunrise group as described by Mendenhall 24 and by Moffit,25

20 Martin, G. C., General features of Kenai Peninsula: U. S. Geol. Survey Bull. 587, 

1915, pp. 33-35; The western, part of Kenai Peninsula: Idem, pp. 44-52.

21 Johnson, B. I/., The central and northern parts of Kenai Peninsula: Idem, pp. 

113-119.

22 Grant, U. S., The southeastern coast of Kenai Peninsula: Idem, pp. 211-227. 

as Idem, pp. 33-35.

24 Mendenhall, W. C., A reconnaissance from Resurrection Bay to the Tanana River, 

Alaska, in 1898 : U. S. Geol. Survey Twentieth, Ann. Kept., pt. 7, pp. 305-307, 1900.

25 Mofflt, F. H., Gold fields of the Turnagain Arm region : U. S. Geol. Survey Bull. 277, 

pp. 17-19, 1906.
ROCKS OP UNDETERMINED AGE 483

which has been generally regarded as the probable equivalent of the Valdez 

group 29 and has been generally assigned to the Paleozoic.27 The slaty rocks 

on the south coast of the peninsula include slates and graywackes consisting 

of two probably unconforniable members, occurring from Day Harbor to Nuka 

Island Passage, regarded by Grant as the equivalent of the Sunrise group; 

slate and graywacke in relatively small volume associated with greenstones, 

occurring on Day Harbor and the east shore of Resurrection Bay, regarded 

by Grant as the equivalent of the Orca group of Prince William Sound ; slate, 

graywacke, and conglomerate, less altered than the rocks regarded by Grant 

as equivalent to the Sunrise group, occurring on the forelands from Nuka 

Island Passage to Chugach Bay ; and graywacke and slate, associated with 

cherts, limestones, and basic igneous rocks, occurring on the bays from Nuka 

Island Passage to Port Chatham, and apparently the direct areal extension of 

the slate and graywacke of Port Graham and Seldovia Bay.

The evidence of the age of these slaty rocks indicates that the type area 

of the Sunrise group contains beds that are middle or late Mesozoic, possibly

as young as Upper Cretaceous, whereas the slates of the southern part of the 

district are probably Paleozoic, certainly not being younger than Triassic. 

The data now available afford no grounds for separating these rocks, either 

cartographically or by description, so that the term Sunrise group can not 

be used at present for a lesser aggregate than all the slaty rocks of the Kenai 

Peninsula. The Sunrise group, in such a usage of the term, therefore doubtless 

includes beds which are equivalent to the Valdez group of Prince William 

Sound. The correlation of the Sunrise and Valdez as exact equivalents is, 

however, of very doubtful validity. As the rocks of the type district of the 

Sunrise group are probably high rather than low in the stratigraphic sequence 

of rocks in the Kenai Mountains, and as the Valdez group is generally regarded 

as including the older rather than the younger slaty rocks of Prince William 

Sound, it seems probable that if the slates of the Kenai Mountains and of 

Prince William Sound are in general equivalent, as they are supposed to be, 

then the rocks of the type area of the Sunrise group on Turnagain Arm and 

vicinity are probably more nearly equivalent to the slates of the Orca group 

than to those of the Valdez group. The equivalent of the Valdez group is 

probably to be sought in the unfossiliferous pre-Triassic slates south of Kachemak Bay or in the more altered lower member of the slates on the coast from 

Resurrection Bay to Nuka Island rather than in the fossiliferous Jurassic 

or Cretaceous slates in the vicinity of Turnagain Arm. It should be noted 

that the fossils which were obtained at Nuka Bay from the upper member of 

the slates and graywackes that extend from Resurrection Bay to Nuka Island 

are identical with the fossils collected by the writer on Kenai Lake, and that 

these fossils occur on Prince William Sound in the Orca and not in the Valdez 

group.

Sidney, and Knopf, Adolph, Geologic reconnaissance in the Matanuska and 

Talkeetna Basins, Alaska: U. S. Geol. Survey Bull. 327, pp. 15-16, 1907.

27 Grant, U. S., and Higgins, D; P., Reconnaissance of the geology and mineral resources 

of Prince William Sound, Alaska : U. S. Geol. Survey Bull. 443, p. 24, 1911.
484 MESOZOIC STKATIGBAPHY OF ALASKA 

VALDEZ AND OBCA GBOUPS

The slate, graywacke. and greenstone of Prince William Sound 

have been described 2S as the Valdez and Orca groups, which are supposed to include all the sedimentary and metamorphic rocks of 

Prince William Sound. The Valdez group has been generally regarded as underlying the Orca group and as being probably Paleozoic, whereas the Orca group has been generally regarded as probably Mesozoic. The relative sequence of the Valdez and Orca 

groups is somewhat in doubt, and even the validity of their differentiation has been questioned. As to their .age, there is very little evidence on which a positive opinion can be based. The only fossils 

that have been found on Prince William Sound, which came from 

various undetermined positions in the Valdez-Orca sequence, are 

fucoids and worm tubes like those of the Yakutat group and the 

slate and graywacke of Kodiak Island, indeterminate fragments of 

plants, crinoid remains 29 that suggest the " Cretaceous or later," and 

cephalopods 30 that apparently are early Paleozoic.

SLATE AND GRAYWACKE OF STTSITNA VALLEY

Slate, graywacke, and conglomerate of undetermined age have 

been found in various parts of the upper Susitna Valley. These 

rocks include the " Susitna slates" described by Eldridge,31 the 

" slates and schists of the Susitna and Talkeetna Valleys " 32 and the 

" undifferentiated Paleozoic rocks in the headwater region of the 

Susitna " 33 described by Brooks, the " Jurassic (?) rocks " 34 and the 

" undifferentiated Mesozoic (?) rocks " 35 of the Broad Pass region 

described by Moffit, the " argillites, slates, and graywackes " of the

28 Schrader, F. C., A reconnaissance of Prince William Sound and the Copper River 

district, Alaska, in 1898 : U. S. Geol. Survey Twentieth Ann. Kept, pt. 7, pp. 404-408, 

1900. Schrader, F. C., and Spencer, A. C., The geology and mineral resources of a portion of the Copper River district, Alaska (U. S. Geol. Survey special publication), pp. 

34-40, 1901. Grant, U. S., and Higgins, D. F., Reconnaissance of the geology and 

mineral resources of Prince William Sound, Alaska: U. S. Geol. Survey Bull. 443, pp. 

22-23, 1910. Capps, S. R., GeneMl geology [of the Bllamar district] : U. S. Geol. 

Survey Bull. 605, pp: 30-46, 1915. Johnson, B. L., Copper deposits of the Latouche and! 

Knight Island districts, Prince William Sound : U. S. Geol. Survey Bull. 662, pp. 197- 

200, 1918; Mineral resources of the Jack Bay district and vicinity, Prince William 

Sound: U. S. Geol. Survey Bull. 692, pp. 158-163, 1919.

28 Johnson, B. L,., op. cit. (Bull. 662), p. 198.

30 Moffit, F. H.., unpublished report.

81 Eldridge, G. H., A reconnaissance in the Susitna basin and adjacent territory, 

Alaska, in 1898: U. S. Geol. Survey Twentieth Ann, Rept, pt. 7, pp. 15-16, 1900.

82 Brooks, A. H., The Mount McKinley region, Alaska: U. S. Geol. Survey Prof^Paper 

70, p. 65, 1911.

ss Idem, pp. 68-69.

M Moffit, F. H., The Broad Pass region, Alaska: U. S. Geol. Survey Bull. 608, pp.. 

32-38, 1915.

85 Idem, pp. 39-40.
BOCKS OF UNDETERMINED AGE 485

Chulitna Valley described by Capps,36 and the "slate and graywacke series " of the Kahiltna Valley described by Mertie. 87

The only evidence on the age of the slate and graywacke of Susitna. 

Valley is yielded by some specimens of Inoceratmus that are suggestive of Upper Cretaceous age (see pp. 309-310) and by some fossils 

collected by R. M. Overbeck in 1919, concerning which T. W. Stanton 38 has submitted the following statement:

10240 (Fl). Ridge west of Portage Creek, Eakin's station sub. 9, Susitna 

Valley. These fragments of slate show no fossils except a number of slender 

tubular bodies which resemble small specimens of Terebellina palachei Ulrich, 

a species from the Takutat group whose definite place in the Alaskau stratigraphic column is still unknown, though it was believed by Ulrich to be Lower 

Jurassic.

SLATE OF CONTROLLER BAY

The metamorphic rocks of the Controller Bay region crop out on 

Wingham Island and in Ragged Mountain west of Katalla. The 

rocks consist 39 of black slate having a well-developed cleavage, of 

graywacke, of a variety of highly colored fine-grained rocks of uncertain origin, and of greenstone and other rocks of igneous origin 

which probably include both bedded and intrusive masses. The only 

fossils that have been discovered are numerous but poorly preserved 

specimens of Globigerina of indeterminate species. The rocks of 

both areas are overthrust upon Tertiary shale. The degree of metamorphism shows the rocks to be pre-Miocene, and the occurrence of 

Globigerina (assuming that the lower range of Globigerina has been 

finally determined) shows them to be post-Carboniferous. More 

definite evidence of their age is lacking.

YAKTTTAT GROUP

The rocks of the Yakutat group have been described by Russell,40 

Novarese,41 Tarr and Butler,42 and Blackwelder.43

38 Capps, S. R., Mineral resources of the upper Chulitna region: U. S. Geol. Survey 

Bull. 692, pp. 217-218, 1919.

37 Mertie, J. B., Jr., Platinum-bearing gold placers of the Kahiltna Valley: U. S. Geol. 

Survey Bull. 692, pp. 236-237, 1919.

88 Personal communication.

88 Martin., G. C., Geology and mineral resources of the Controller Bay region, Alaska: 

U. S. Geol. Survey Bull. 335, pp. 26-27, 1908.

40 Russell, I. C., An expedition to Mount St. Elias: Nat Geog. Mag., vol. 3, p<p. 130- 

J31, 140, 167, 170, 1890; Second expedition, to Mount St. Elias, in 1891; U. S. Geol. 

Survey Thirteenth Ann. Kept. pt. 2, pp. 24-26, 34, 52, 90, 1893.

41 Novarese, I. V.. Rocks and minerals of South Alaska: The ascent of Mount St. 

Elias, Appendix E, pp. 232-239, 1900.

«Tarr, R. S., and Butler, B. S. Areal geology [of the Yakutat Bay region] : U. S. 

Geol. Survey Prof. Paper 64, pp. 152-160, 1909.

48 Blackwelder, Eliot, Reconnaissance on the Pacific coast from Yakutat to Alsek River: 

U. S. Geol. Survey Bull. 314, pp. 82-87, 1907.

49448 26 32
486 MESOZOIC STRATIGRAPHY OF ALASKA

The Yakutat "system" was described by Kussell as consisting of 

gray and brown sandstone and nearly black shale or slate.

Tarr and Butler described it as a complexly folded and faulted 

series of rocks in which the three most prominent elements are (1) 

a series of thinly bedded black shale and gray sandstone, (2) a black 

shale conglomerate, with crystalline pebbles and boulders, and (3) a 

massive crystalline rock, the most prominent rock in the Yakutat 

group, which was tentatively classed as an indurated tuff. The 

Yakutat group is of unknown thickness, its relation to the adjoining rocks has not been satisfactorily determined, and it has yielded 

no fossils, except the supposed worm tube Terebellina palachei Ulrich and a supposed irregular echinoid which Stanton 44 believes to 

be post-Triassic.

The Yakutat group was divided by Blackwelder into an upper 

member consisting of graywacke, conglomerate, and hard black shale, 

and a lower member consisting of black shale conglomerate of possible glacial origin.

AGE

Fossils have been found in the slate and graywacke of the Pacific 

coast of Alaska in the vicinity of Kodiak, at several places on Prince 

William Sound, and near Yakutat. The fossils from Kodiak consist of 16 species of fucoids, a pelecypod, and a supposed worm tube.

Of the 16 fucoids, 10 are new species and are known only from 

this locality, 2 species are known also from the European Eocene, 

and 4 are restricted to the Lower Jurassic of the Alps. On this 

evidence Ulrich considers the Lower Jurassic age of the rocks as

proved.

The pelecypod was described as a new genus and species Inoceramya concentrica, known from this one locality. Ulrich assumed 

the genus to be the ancestor of Inoceramus, which he stated to be a 

"characteristic Cretaceous genus," and hence assumed the ancestor 

to prove the Jurassic age of the rocks containing it. But inasmuch 

as Inoceramus was well developed in the Jurassic, then the ancestor 

(if it is an ancestor) proves its terrain to be pre-Jurassic. Both the 

origin arid the validity of the genus are in doubt. Specimens of 

Inoceramus frorii the Upper Cretaceous of Alaska are very similar 

to Inoceramus concentrica.

The supposed worm tube is a new genus and species which is restricted to Alaska but which is known not only from Kodiak but 

also from Yakutat, Prince William Sound, and other places. The

** Stanton, T. W., cited by Tarr, R. S., and Butler, B. S., op. cit., p. 158.
ROCKS OF UNDETERMINED AGE 487

worm furnishes no evidence as to its absolute age and no satisfactory 

evidence as to the correlation of the rocks containing it.

The slate and graywacke of the Pacific coast of Alaska have been 

generally assigned to the Mesozoic, chiefly because of Ulrich's opinion 

concerning the fossils from Kodiak, but the writer believes that the 

evidence of these fossils is insufficient for a positive determination 

of age and is capable of a different interpretation from that which 

Ulrich placed upon it. Ulrich's conclusion from the evidence of the 

fucoids was based on the assumption 45 "that we are not dealing 

with the new horizon" and that "the slate of Kodiak must be 

referred to either the Lower Jurassic (Lias) or to the Eocene."

The writer believes that there is no basis for the assumption that 

the fucoids from Kodiak can not represent a "new horizon." In 

the immediately preceding sentence Ulrich himself cited the discovery 

of " new horizons " for a supposed Eocene fucoid in the Carboniferous and possibly in the Silurian. The writer is not influenced as 

much by Ulrich's final conclusion as he is by Ulrich's statements 4" 

that the evidence from the genera of fucoids " points perhaps quite 

as strongly to the Eocene as to the Lias " and that

we have seen black inosculating films in the Waverly shales of Kentucky and 

certain Carboniferous shales in Texas that we are really at a loss to distinguish from the Eocene species figured by Heer or from the Kodiak species.

The entire absence of any of these fossils in the richly fossiliferous 

Mesozoic beds of this region; the stratigraphic dissimilarity of the 

slate and graywacke to most of the undoubted Mesozoic strata, 

especially to those of the Jurassic and Triassic; the greater degree 

of alteration of the slate and graywacke as compared with that of 

the undobuted Mesozoic rocks; the absence of any known Paleozoic 

rocks in most of this region; and the position of the slate and graywacke of Seldovia Bay beneath the greenstone that underlies the 

fossiliferous Triassic and Lower Jurassic beds (see pp. 45-46) all 

suggest the Paleozoic age of the slate and graywacke.

There are doubtless some Mesozoic beds, probably chiefly of Cretaceous age, occurring within the area of the slate and graywacke, 

but the writer suspects that such Mesozoic rocks may represent small 

structural inclusions in a larger mass of early Paleozoic strata.

« Ulrich, E, 0., Fossils a«d age of the Yakutat formation : Alaska, vol. 4, pp. 129-130, 

Harriman Alaska Expedition, 1904. 

*6 Idem, pp. 130, 131.

INDEX

Admiralty Island, Triassic limestone on,

age and correlation of 91-92

Triassic limestone on. . 89-91 

Age of rocks, evidence on 246 

Alaska Peninsula, Cretaceous rocks on.... 289-308

Jurassic rocks on...-.-...-....-..-.-- 181-218

Kialagvik formation on-._ .... 186-191

Lower Jurassic (?) rocks on, age and correlation of. 185-186

stratigraphic description of-------- 183-185

studies of.. ..................... 182-183

Naknek formation on.................. 203-218

Shelikof formation on.....---..--..--.- 192-203

Triassic greenstone and chert on.....---. 60-61

Triassic shale and limestone on, age and

correlation of.... 63-64

stratigraphic description of... 62-63 

studies of..... . . 61-62

Tuxedni sandstone (?) on __.. ____. 191 

Alaska Range, Jurassic rocks of. __. __.. 232-235 

Anaktuvuk group, age and correlation of.. 452-453 

description of____. __.. _. 451-452 

Annette Island, Triassic (?) rocks on__... 73-75 

Arctic slope, Jurassic rocks of.... _.. _.. 262-268

Triassic rocks of......-....-..-------- 100-105

Atwood, W. W., cited.................. 79,294,297

Aucella, occurrence of..___.... ...... 175,

203-204, 206, 231, 244-245, 248, 282-283, 

292-295, 333, 343, 348, 377-381, 443, 468- 

469.

Aucella zone, fauna of.. .. . . 283 

flora of................................. 283

rocks of....-..--...-.-.-..---...--._. 273-274

stratigraphic place of___.__........ 279

B

Baranof Island, graywacke on ______ 260-262 

Bather, F. A., fossils determined by__.... 14,71 

Bergman group, description of__... 448,449-451

studies of..... ... .... 446-447,449 

" Berners formation," age and correlation of. 258-260

description of_______. __.. __. 256-258 

Brooks, Alfred H., cited ..- 233-234

Preface.-.----... . ...... ..... xi-xn

and Kindle, E. M., cited. . .. 97,385-386 

Brooks Mountain, Middle Triassic rocks

of....... -.. - 116-117

Buckman, S. 8., cited__... __..___ 196 

Buddington, A. F., cited. . 80-83,251,380

Cache Creek, slate and graywacke of..._ 308-310 

Cadoceras, occurrence of._______ 160,162,163

Cadoceras zone, fauna of_.____. __ 280-281 

flora of.. 280-281

rocks of....----.--..-..--.-.---------.- 271-272

Cape Lisburne, Lower Cretaceous (?) sandstone and shale near. .... 466-467 

section near.. . ..... 455 

Triassic shale, chert, and limestone

near........................... 108-112

Cape Thorn pson, Triassic chert and limestone

near........--.-..---.....---.- 112-115

section southeast of.... ...._........ 114

Capps, S.R., cited. . . .. - 63, 

184-185,189,197-198, 206-207, 209, 241-242, 244, 

253-254,309,372-374. 

with Mofflt, F. H., cited.... ........ 12-13,

19,28,356-357, 358-359,362-364

Castle Mountain, limestone north of, nature

and correlation of...... _.. 315-316

Cardioceras, occurrence of.........._.... 175-176

Cardioceras zone, fauna of__--......... 281

flora of. .. -- 281

rocks of................................ 272-273

stratigraphic place of....___...._... 281

Chapin, Theodore, cited.____._____ 69-70, 

73-74,75,231,381-382

Chert, Triassic, of Fohlin Creek.. ___.__ 25-26 

Triassic, of Kenai Peninsula_ . 47-49

Chichagof Island, graywacke of..__.__ 260-262

Chignik formation, age and correlation of.. 300-308 

stratigraphic description of.._.. __ 297-300 

studies of__________. ____. 295-297 

fossils from, found in other formations. 306-308

Chinitna Bay, section of Naknek formation

on.. ........................ 172-173

sections of Chinitna shale on___.... 160,161

Chinitna formation in Matanuska Valley.

age and correlation of .._.. 228-229 

in Matanuska Valley, description of.. 227-228 

stratigraphic place of.... _......--.. 280

Chinitna shale, age and correlation of.._ 163-168 

stratigraphic description of. _ __. 159-163 

studies of..-....--....-.-..-..--.-..... 158-159

Chisana River, Aucella-bearing beds of_.. 373-375

Chisik conglomerate, nature and age of __ 170-171

Chitina Valley, chert on Fohlin Creek in__ 25-26 

Chitistone limestone in_____...... 10-18

Cretaceous rocks of.__________ 327-372 

Jurassic rocks of _____________ 237-240 

McCarthy formation in........___.. 26-32,

Nikolai greenstone in.... ......_.... 7-10

Nizinalimestone in_...__......_... 18-22

Triassic rocks in. ______. __. ___ 6-32 

tuffaceous slate in......... .......'239-240

489
490 INDEX

Page 

Chitistone limestone, fauna of.._.......... 13-18

stratigraphic description of.. ___... _ 12-13 

studies of..... .. ....__..__.._ 10-12

Chititu Creek, Cretaceous shale on, age and

correlation of.____.____ 364-369 

Cretaceous shale on, stratigraphic description of__.__....__ 362-364

studies of...___-________ 360-362 

Chulitna Valley, Triassic rocks of.-__.__ 42-45 

Clark Peak schist, age of ..._._____ 94 

Clearwater Creek, Triassic limestone on__ 39-40 

Clover Bay, Prince of Wales Island, apparent

section on..__._.--.___ 74 

Cold Bay, section of Shelikof formation on 198 

Cold Bay district, generalized section of the

sedimentary rocks of..__.__ 181 

Collier, A. J., cited............ 107,109,110,115,458

Colville Valley, Cretaceous rocks of._... 451-454 

Conglomerate, Jurassic, nature and occurrence of................ 169-171, 236-239

Controller Bay, rocks of undetermined age on 485

Cook Inlet, Cretaceous rocks on__..._ 308-310

Jurassic rocks on_____._....__ 133-180

west coast, of, Jurassic porphyry and tuff

on............................. 137-139

Triassic rocks on.-__.__..._........ 51-57

Tuxedni sandstone on, age and correlation of....................... 145-158

description of...___._.._ 140-145 

C ooper Pass, Triassic rocks of- - - _......... 36-37

Coral-reef horizon of the Upper Triassic, occurrence of.-..__._____.. 122-123 

Correlation, interregional, of the Triassic- __ 128 

tentative, of Triassic rocks in Alaska..... 120

Corwin Bluff, section near__.__, .__- 455

Corwin formation, age and correlation of.. 460-466

stratigraphic description of.-..-------- 458-460

studies of.__..-___..-.__.__.. 456-458 

Cretaceous deposits, general distribution of. 286-289 

Cretaceous period, chronologic record of.... 476-480

Cretaceous rocks of Alaska, tentative correlation of....................... 474-475

Cretaceous, Lower, rocks, nature of at various

localities...____......__ 467-470

Upper, rocks, nature of, at various localities........................... 470-473

Crinoid bed of Firth River, nature and age of. 264-

265

D

Dan Creek, grit and sandstone of.___.. 358-360 

Daonella, occurrence of._.__..._...... 118

Dawson, O. M., cited...___._...._... 124

Dictyophyllum, occurrence of.....---------- 221

Douglas Island volcanic group, nature and

age of. . - - 255-256 

Dry Bay, section of Shelikof formation near.. 199

E

'Eichwald, Eduard von, fossils determined

by. ---------------------- 194

E tolin Island, Aucella-bearing beds of..-.-. 380-381

Page

Firth River, crinoid bed of-_. __ 264-265 

Triassic shale and limestone on, age and

correlation of. 101-103

description of_______ ___ 100-101 

Fontaine, W. M., fossils determined by . 295,

357, 453, 461-464 

Frech, Fritz, cited_____________.... 3-5

G 

Gastineau volcanic group of the Juneau

district, age and correlation of... 94-95 

description of ______ ___ 92-94 

Gidley, J. W., fossils determined by____ 215 

Girty, George H., cited . . 59,260 

fossils determined by.-.. 54,59,76-77, 78,98,112 

Granite Creek, section of Matanuska formation on.-..................... 319-320

Gravina Island, breccia, tuff, and lava on... 249-251 

conglomerate, graywacke, and slate on. 381-382 

Triassic conglomerate, limestone, sandstone, and slate on_______ 67-73 

Upper Jurassic (?) slate, limestone, and

tuff on -- 252-254

Greenstone, Triassic, of the west coast of

Cook Inlet......... ...-.... 51-52

Grewingk, C., fossils determined by..___. 192

H 

Halobia, occurrence of___. ..._ _ .. 7,

14,18, 23, 40,48-49, 50, 54, 70-73, 79,84, 92, 98, 

101-102, 104. 

cf. H. superba, zone of....------------- 120-122

Hayes, C. W., cited-....-.....-------.--.. 34

Herendeen Bay, sections of Chignik formation near........... ........ 298-299

Herendeen limestone, age and correlation of. 294-295 

stratigraphic description of- - ____ 294 

studies of 292-293

Herring Bay, Admiralty Island, section on.. 90

History, geologic, in Cretaceous time___ 476-480

geologic, in Jurassic time..-.....-_.. 283-286

in Triassic time......-----.-.--- 128-130

Hollick, Arthur, cited--.--...- ------- 465-466

fossils determined by.-..--------- 190,200,216,

300-305, 323, 324, 326,338, 341, 390, 394, 413-424 

Hyatt, Alpheus, cited...-..--------.-. 158,188

Ignek formation, nature and age of ___ 265-268 

Iliamna Lake, limestone on, age and correlation of. I .. 59-60 

limestone on, description of. .... 57-58

Triassic greenstone on and near... __... 57

Iniskin Bay, section of Chinitna shale on._ 161

section of Tuxedni sandstone on........ 144-145

Iniskin-Chinitna Peninsula, generalized section of Tuxedni sandstone on...- 144 

Innoko and Iditarod valleys, Cretaceous rocks

of---... 429-432

Juneau, stratigraphic section near..._..... 93

Juneau district, Gastineau volcanic group of.. 92-95

Upper Jurassic (?) rocks of------------ 255-256
INDEX 491

 Page 

Jurassic, Lower, faunas, table of._-...... 275-276

Lower, floras, table of. ------- 275-276

rocks, correlation of-.____.__ 274-277 

sequence of.-..-.....-....-.-.- 268-270

Middle, rocks, correlation of_.__... 277-279 

rocks, sequence of.......____.. 270-271

Upper, rocks, sequence of-...--..___ 271-274 

Jurassic period, chronologic record of.__ 283-286 

Jurassic rocks of Alaska, correlation table

of.........................Facing 270

distribution of...-......-..-.---.-.--.- 130-133

Jurassic rocks of North America, correlation

table of.___.............Facing 274

K

Kaguyak Bay, Cretaceous exposure on..... 299-300

Kaltag formation, fossils from__...._.. 419-424

Kamishak Bay, section of Naknek formation

on............................... 175

Kamishak chert, age and correlation of.._... 56-57 

description of -..-...--. .... ...- 55-56

Kantishna district, Triassic (?) limestone of 99-100 

Keku Strait and vicinity, Triassic rocks of,

age and correlation of.. ---------- 83-89

Triassic rocks of, description of.......... 78-83

Kenai Peninsula, Jurassic tuff of, age and

correlation of..---------------- 135-137

Jurassic tuff of, description of...__... 134-135 

Triassic rocks of............__....._ 45-51

Kennicott formation, age and correlation of. 335-349 

stratigraphic description of.. _.... _ _ 333-335

studiesof--.___--------------___ 330-333

Kialagvik formation, age and correlation of. 189-191 

stratigraphic place of.......... ___.. 270,277

studiesof-----..-.--.-.-.-.-.-.---.---- 186-189

Kindle, E. M., cited ................ 113-114,377

with Brooks, A. H., cited-- ...... 97,385-386

Kingak shale, nature and age of- ___._ 262-264 

Knopf, Adolph, cited__..._............. 258,259

with MofBt, F. H., cited.--......- 240-241,243

with Paige, Sidney, cited..--..__-_ 312,314-315 

Knowlton, F. H., cited...................... 221,

259-260, 267, 343, 344-346,464-465 

fossils determined by--...-...___.__ 29, 

146, 150, 158, 164/168, 185, 200, 216, 222- 

223, 226, 268, 336-342, 387, 392, 394, 413- 

424, 440, 461-464. 

Kobuk Valley, Upper Cretaceous (?) rocks

of.....-.-.....--..-.....-.l... 448-451

Kodiak Island, slate and graywacke of undetermined age on.__--..._ 481-482 

Triassic chert and lava on............... 64-65

Kotsina conglomerate, age and correlation

Of.... ...................... 353-355

stratigraphic description of..__. _ 351-353 

studies of..-----.---.------------------ 349-351

Kotsina Valley, general section of Triassic

rocks in-._.................... 7

Koyukuk Valley, Lower Cretaceous rocks

in, age and correlation of.-------- 444

Lower Cretaceous rocks in, stratigraphic

description of.._ ___... 443-444 

studies of-.--..-.--__- - 442-443

Upper Cretaceous rocks in, nature and

age of__- _ _ _ 444-446

Upper Cretaceous (?) rocks in, description of........._.............. 448

Page 

Koyukuk Valley, Upper Cretaceous (?) rocks

in, studies of .- . _ 446-447 

Kupreanof Island, Aucella-bearing beds of. 379-380 

Kuskokwim region, general features of the

rocks of ............._._. 432-433

Lower Cretaceous rocks of, age and correlation of.....-- ----_- 434-435

studies of-------.-----.-------... 433-434

Upper Cretaceous rocks of, age and correlation of.-.-......_........ 440-441

stratigraphic description of. .__ 437-440 

studies of._...___._-...:.... 435-437

Kuskulana formation, correlation of, with

the Nizina limestone-........... 20

fauna of.. --------------_... ....... 22-25

Kuskulana Valley, general section of Triassic

rocks in..._._._...... _ 7

Lava, ellipsoidal, of Kenai Peninsula........ 47

Leffingwell, E. de K., cited---...-......-. 263,266

Liard River, Triassic rocks on...__........ 87

Limestone, Upper Triassic, of the west coast

of Cook Inlet. . .- .'.... 52-54

Limestone and tuff, Triassic, ol Kenai Peninsula.---------------------------- 49-51

Lower Lias (?) horizon, rocks of..------.... 269

M

McCarthy Creek, conglomerate and overlying volcanic rocks of.. 371-372

McCarthy formation, fauna of.. . ...... 29-32

stratigraphic description of.---.-........ 28

studies of-...----..-.-..----- -.-.-.. 26-28

Maddren, A. G., cited . ........ 101,430

Martin, G. C., with Stanton, T. W., cited... 158-

159,175,176 

Matanuska formation, age and correlation

of 321-327

stratigraphic description of.. .._. 318-321

studies of--._...___.________ 317-318

Matanuska Valley, Cretaceous rocks of._ 310-327

Jurassic rocks of.- 218-232

Melozi formation, fossils from___-------- 413-414

Mendenhall, W. C., cited...... - 312,449-450

Mertie, J. B., jr., with MofBt, F. H., cited. 351,352 

Mesozoic history, importance of-- __ xi, 1,2 

Middle Lias (?) horizon, rocks of.......... 269-270

MofBt, F. H., cited 39,

41,143-144,163,171,237,239,335,364,370,371

and Capps, S. R., cited................ 12-13,

19,28,356-357,358-359,362-364 

and Knopf, Adolph, cited...... 32,240-241,243

and Mertie, J. B., jr., cited______ 351,352

N

Nabesna-White River district, Triassic rocks

of 32-37

Naknek formation, stratigraphic place of.... 282

in Matanuska Valley, age and correlation

Of 231-232

stratigraphic description of.- .... 230-231

studies of 229-230

on Alaska Peninsula, age and correlation

of----- 211-218

stratigraphic description,of....__ 206-211

studies of... .. 203-206
492 INDEX

Page 

Naknek formation, on Cook Inlet, age and

correlation of.___.... .. 175-180

stratigrapbic description of... _.. 170-175 

studies of...._....._....__.. 168-170

Nanushuk formation, nature and age of.... 453-454

Nation River, limestone near, age and correlation of........................ 97-100

description of....____._.. 95-97

Nelchina limestone, description and age of. 313-315 

Nikolai Creek, sandstone and conglomerate

on, age and correlation of...... 357-358

sandstone and conglomerate on, stratigraphic description of..-._... 355-357 

studies of.._____________- 355 

section of part of McCarthy formation

on.__.___........_____ 28

Nikolai greenstone, character and age of.__ 7-10

Nizina limestone, age and correlation of __ 22

stratigraphic description of.....____ 20-22

studies of.................._...._.... 18-20

Nizina Valley, general section of Triassic

rocks in.....___._____... 6-7

Noatak Valley, Triassic rocks of. ___..... 106

Northwestern Alaska, Cretaceous or Jurassic

rocks of..........__.__._ 456-466

general features of rocks of. __.... 455

Lower Cretaceous (?) rocks of.....__ 466-467

Triassic rocks of __________.__ 106-115 

Nulato formation, fossils from...__...-. 415-418 

Nutzotin Mountains, Aucella-bearing beds

of, age and correlation of_ __ 244-245 

Aucella-bearing beds of, stratigraphic description of.................... 243-244

studies of.............. ........- 242-243

Cretaceous rocks of............._.... 372-373

Jurassic rocks of.___.__.___... 240-245

0

Ohio Creek, Triassic rocks on....____.... 43-44

OihBay, section of Chinitna shale on.._... 162

section of Naknek formation on.......... 173

Orca group, features of....................... 484

Pacific coast, rocks of undetermined age on. 480-487 

Paige, Sidney, and Knopf, Adolph, cited.... 312,

314-315 

Foran, W. T., and Gilluly, James,

cited.......................... 459-460

Permian (?) strata, occurrence of.. 5 

Perseverance slate, age of _____.. _. 94 

Pickart mine, section of Upper Cretaceous,

rocks near.________..... 404-406

Pinnacle Mountain, section of Naknek formation on._______.. . 210 

Pompeckj, J. F., cited....................... 188

fossils determined by.._________ 196 

Pre-Triassic (?) slate, occurrence of.. ____ 5 

Prince of Wales Island, graywacke, slate, and

conglomerate of............... 382-383

Triassic (?) rocks of...................... 73-75

Upper Jurassic (?) rocks of...._____ 254

Pseudomonotis, occurrence of.. 6,7, 29,34,37,42,45, 

50,56-57,61-64,79,84,92,98,102,104,106,112 

subcircularis, identification of...____ 128 

Pseudomonotis-bearing beds, unconformity

at base of...................... 124-125

Page 

Pybus Bay, Aucella-bearing beds of, age and

correlation of..........___.. 378-379

Aucella-bearing beds of, description of. 376-378

Q . Quail Creek, quartzite and slate near... 390-392

R 

Rampart-Tanana district, Cretaceous rocks

of--........................ 390-395

Reeside, J. B., jr., cited_________.__ 176,

336-342,347-348,354-355,357

fossils determined by ____........ 14-15,

23, 29,71,95,178, 232,357,462 

Revillagigedo Island, Triassic (?) rocks of.... 73-76

Rocks of undetermined age, age of.____ 486-487

general features of..._________ 480-481

Roosevelt Lakes, conglomerate near...__ 236-237

St. Lawrence Island, Triassic (?) float on.. 115-116 

Schrader, F. C., cited................. 443,448,454

and Spencer, A. C., cited. 10,18,27,330-331,350 

Scope and purpose of the report....___... 1-3 

Screen Islands, Triassic (?) limestone on.._ 76-78 

Seventy-mile River, shale, sandstone, and

conglomerate near. ______ 387-390 

Seward Peninsula, Triassic rocks of._ __ 116-117 

Shelikof formation, age and correlation of.. 199-203

studies of-..------..-...-.............. 192-199

Shublik formation, nature and age of...... 103-105

Skolai Pass, Triassic (?) rocks of............. 33-35

Skwentna group, age and correlation of...... 234

description of.__________...._ 233-234

Skwentna Valley, Jurassic rocks of........ 232-235

Smith, J. P., fossils determined by....-.-... 59-60

Smith, P. S., cited..-......................' 443,450

Smith, W. R., fossils determined by. __.... 300,

303-306, 324-327,366-369, 413-124,454 

"Sookhom shores," location of.______ 195-196 

Sources of information.___________ xi-xu 

Southeastern Alaska, Cretaceous rocks of.. 375-383

general features of the rocks of. __.__ 65-66 

Jurassic rocks of..._________.__ 245-262 

Triassic conglomerate, limestone, sandstone, and slate of......____ 67-73

Spencer, A. C., with Schrader, F. C., cited.. 10,

18,29,330-331,350

Spiriferina, occurrence of.____......... 119-120

Springer, Frank, cited..___________ 263-264 

Spurr, J. E. .cited..................... 207-208,434

Staniukovich shale, nature and age of_.. 291-292 

Stanton, T. W., cited....._-___-_--_---_.___ 53,

55-56, 97, 100, 109, 189-190, 221-222, 261-262, 

263, 267, 291-292, 309-310, 313, 315, 321-322, 

331-332, 346-347, 352, 365, 374, 485. 

fossils determined by.....___.._._ 14-15,

23, 29, 35, 37, 40, 42, 44, 45, 50, 54, 64, 71, 75, 

78, 84, 87-89, 91-92, 98, 102, 104, 106, 112, 115, 

117,136-137,146-157,164-168,177-180,185-186, 

190-191, 200-203, 211-218, 222-223, 225-226, 

228-229, 232, 235, 240, 244, 264, 265, 268, 295, 

300-306, 324-327, 336-342, 354-355, 357-358, 

366-369, 375, 378, 379, 380,386-387, 392,394-395, 

407, 413-424, 432, 440, 444, 453, 454, 462. 

and Martin, G. C., cited...... 158-150,175,176

Steidtman, Edward, and Cathcart, S. H.,

cited........................... 116-117
INDEX 493

Page

Sunrise group, description of.._ _ 482-483 

Susitna Valley, Cretaceous rocks in....._ 308-310 

Jurassic rocks in____________ 236-237 

. slate and gray wacke of undetermined age

in..................... ..... 484-485

Talkeetna formation, age and correlation of. 221-223 

stratigraphic description of.. .. 220-221 

stratigraphic place of.......... 269-270,276-277

studies of...__._...-.....---...... 219-220

Talkeetna Mountains, Jurassic rocks of._ 218-232 

Taral, tuffaceous conglomerate near_._ 238-239 

Thane volcanic group, description of._.. 251-252 

Tordrillo formation, nature and age of.. _. 235 

Treadwell slate, nature and age of.___.. 255-256 

Triassic, early, (?) volcanic rocks, occurrence

of................................ 6

Lower, rocks, absence of.._____._ 129 

Middle, rocks, occurrence and correlation of. .........._...... 117-119

time, emergence during_______ 129

Upper, rocks, chert horizon of..____ 123

rocks, coral-reef horizon of....._ 122-123

correlation of._________ 279-283 

Dawsonites zone of ______ 119-120 

general distribution of. _ ___ 119 

Halobia zone of.._______ 120-122 

zone of Pseudomonotis subcircularis Of............... .... 123-128

time, submergence during. ____ 129-130 

Triassic rocks, general distribution of.... __ 3-5

Tuff, conglomeratic, and arkose of the Matanuska Valley, age and correlation of..........._........... 312-313

conglomeratic, and arkose of the Matanuska Valley, stratigraphic description of____........_. 311-312

studies of................. .... 310-311

Tuxednijjsandstone, age and correlation of.. 224-226 

fauna of________________ 278-279 

flora of................................ 278-279

section of, on south shore of Tuxedni

Bay................... ... 141-143

stratigraphic description of_______ 224 

stratigraphic place of_______ 270-271,277

Page

Tuxedni sandstone, studies of.______ 223-224 

Tuxedni sandstone (?), presence of, on the

Alaska Peninsula________ 191

U

Ulrich, E. 0., fossils determined by.....__ 482

Upper Lias (?) horizon, rocks of............. 270

Upper Susitna Valley, Triassic rocks of___ 37-42

Valdez group, features of..._________ 484 

Vancouver Island, age of fossils from___ 125-127 

Volcanic rocks, early Triassic (?), occurrence

of............................... 6

Jurassic, nature and occurrence of...... 134-139,

220-221, 233-234 

W

Washburne, Chester, notes by............... Ill

White, C. A., cited..-...-..-.-...-..-....-. 187

fossils determined by._______.__ 295 

White Biver, Aucella-bearing beds of...... 373-375

Windfall Harbor, sandstone and volcanic

rocks of.........._........... 254-255

Wolverine Mountains, shale near_.__ 392-395 

Wrangell district, melaphyre breccia of___ 251 

Wright, F. E., and C. W., cited.......... 382-383

y

Yakutat group, features of................. 485-486

Yentna Valley, Jurassic rocks of. _____ 232-235 

Young Creek, conglomerate of ridge south

of___..__._._.........__- 369-371

shale of, age and correlation of.------- 364-369

stratigraphic description of........ 362-364

Yukon, lower, region, Cretaceous rocks of,

stratigraphic description of._ 399-411 

lower, region, Cretaceous rocks of, studies

of....................... 395-399

region, stratigraphic range of Upper

Cretaceous fossils from__ 425-528 

Upper Cretaceous rocks of, age 

and correlation of__..._...- 411-429 

upper, region, Cretaceous rocks of..... 383-390

Yukon Eiver, Triassic rocks on......__. 95-100

Triassic rocks on, section of._......... 96

49448 26- -33 O