DEPARTMENT OF THE INTERIOR

Ray Lyman Wilbur, Secretary

U. S. GEOLOGICAL SURVEY 

George Otia Smith. Director

m 800

GEOLOGY AND MINERAL DEPOSITS 

OF SOUTHEASTERN ALASKA

BY

A. F. BUDDINGTON

AND

THEODORE CHAPIN

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>V*9 *0 9>«0t O V 

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON: 1929
ADDITIONAL COPIES

OF THIS PUBLICATION MAT BE PROCURED FROM

THE SUPERINTENDENT OF DOCUMENTS

U. 8. GOVERNMENT PRINTING OFFICE

 WASHINGTON, D. C.

AT

85 CENTS PEE COPY (Paper covers

 
CONTENTS

Introduction..---------. ___________________________ _______________

Scope of report ___.__-_-____-__________-_--__-___-_________

Nature of the field work ____ ______________________________

Responsibility of authorship... ______________________________

Acknowledgments. _ _ ________________________________________

Earlier explorations and surveys, by Theodore Chapin.___ _________

Notes on history of mining development- _____-______----__--____

Geography _. 

Location and extent___-_______-___________________---_____--__

Population and settlements... -..___ ____________---_--______

Transportation _ ______ -__________-______________-___________

Climate.---. ----_----_-_-----_--------_---------------_--____

Vegetation and timber supply, by Theodore Chapin . 

Agricultural land--__--__-___________.___ _ __-____---_-_______

Water power _ ____________________________________________

Outline of geology _________ _______________________ ________

Main structural features. _________ _________________________

Bedrock geology ___.____-_____--____.-._ __._.___--_________

Physiographic history.. _ ___________________ __________________

Topography __________ 

General features ________ _______ __ .IVL^i'i'JiLi. _> ___._ 

Pleistocene glaciation_______ ___________________________________

Height of the ice surface________-_________-_.___--_________

Direction of flow.- ________ __ _ _________________________

Valleys. ___..__ ______________ _______ ______ ___

Fiords_________ _ .. ____ . _______ __ ______

Cirques- .. . ___ __ ___ _ ___ _

Modern glaciers.... _ ... __ _________________________________

Marine erosion. __ ________________________ _________

Sea-cut benches and platforms.______________________. -_-__--___

Karst topography __ __ 

Relation of topography to structure __ _____ _ __ _ ____________

The rocks __ _ _ _ _ ______._. __ ... _. _

Stratigraphic column, by Theodore Chapin and A. F. Buddington___ 

General lithology _ ___!-. _ _____ __ __________.____-__--__.__

Volcanic rocks____________________________________________

Graywacke------_---_--_--_--_-__-__-_---___------_-_-.__

Sandstone __ __-__-___-__-________________---_--_____

Limestone-________--_____________________________________

Conglomerate. _________________________________________

Intraformational conglomerate.------.--..-,---------------.

Slate. ___________________________________ 

Chert_.____. ____-____---__ ...__-_-.__._. .._______......

Phyllite, schist, and gneiss _ ___._...___..-______-_-__--____

nz
IV COXTEBTTS 4

The rocks Continued. Page *

Wales group, by Theodore Chapin and A. F. Buddington_________ 45

Wrangell-Revillagigedo belt of metamorphic rocks.________________ 49

Character and distribution________________________________ 49

Ketchikan district.._______________________________________ 52

Vicinity of Wrangell Island...._____________________________ 57 4

Le Conte Bay___________________________________________ 59

Thomas Bay....____________________________ 60 A

Port Houghton__ ____________________________ 66

Hobart and Windham Bays______-____-__-______________--_ 68 *

Holkham Bay and Tracy Arm__________________________.._ 68

Juneau district..... ____________--___-____-_-. 70

Schistose greenstone and phyllite between Port Houghton and

Juneau... . __>-______________________--_____-_-_ 71

Age ....... . __.___._____._____________.__---- 73 _,

Ordovician rocks._____________________________________________ 74

Prince of Wales and neighboring islands.____________________ 74 \

Character and occurrence.______________________________ 74

Fossils..------.__-_--____-_--_____-_.-_--__-_-----_ 75

Kuiu Island-_---_-__-__-_-_--__-_-_-_-___-_-_-_--___.--_- 77

Silurian rocks__---__-_-_-_-_-_---.______-___..___-___..__.--__ 79 *

Distribution._____________________________________________ 79

Lower Silurian slate and graywacke____-____-_-___-_-___-___ 81

Volcanic rocks and conglomerate__-___-_-_____---_-_-___---_ 82 '^

Limestone and conglomerate._______-___-______-__-___.---- 83

Shale_________--_--_---__..____.___._--_______-__._-_.-- 88

Sandstone and graywacke._________________________________ 88

Dikes....-._-..______________.___.---._______ 90

Age and correlation______________________________.________ 90

Devonian rocks________________-_______-__________-_---__---_ 94 *

Distribution and character.________________________________ 94

Middle Devonian rocks-___________________________________ 94

Southern Ketchikan district, by Theodore Chapin_______. 94 .4- Northern Ketchikan district_-_--_-____-------___----. 101

Middle (?) and Upper Devonian rocks of northern part of

Kupreanof Island_-_--------_--__i--____-_--__-___----__ 106

Upper Devonian rocks of other parts of southeastern Alaska, >*

by Theodore Chapin______________________.____________- 107

Carboniferous rocks.--_-____--___-_-__--__-_____--__-_-___-_-- 109 *

Distribution and character.________________________________ 109

Mississippian rocks______-_-______--___-____--__--__------ 110 .

Distribution and character_____-_-___-___-------_-_--_- 110

Age and correlation.___________._.._.______________-___ 110

Pennsylvanian (?) rocks, by Theodore Chapin.________-__--__ 117

Permian rocks____-_.__-_--________-----___---------__---- 118

Character and occurrence._____-___-______--_--_-__-_-_ 118

Age and correlation____-^__________-______-_-___---__- 121

Lower division of the Permian___________-_-_______--.- 122

Upper division of the Permian_________________---_-__- 127

Triassic rocks (Upper Triassic)_________-----__-__----_-_-_----- 130

Distribution. _ ______-________--_____________---_---_-_---- 130

Character and stratigraphic relations______-___i-______-__--_ 131

Gravina and Revillagigedo Islands, by Theodore Chapin....... 132

Screen Islands._________-__________-_-_-____-----__-__---_ 134
t CONTENTS

** The rocks Continued.

Triassic rocks (Upper Triassic) Continued.

Keku Strait...... _.__--._.-..__---_-.--.-------.-_-.----- 134

Admiralty Island ______________________-______--_--------- 137

Volcanic rocks with Pseudomonolis-bearing beds _ ____________ 138

t Volcanic rocks of Kuiu and Hound Islands. __________________ 142

Age and correlation, by Theodore Chapin ____________________ 144

* Jurassic (?) rocks_________________. ___________________________ 156

Distribution and character. ________________________________ 156

* Sedimentary division________________________________-_-___ 157

Juneau district _ _____________________________________ 157

Seymour Canal-Fanshaw-Kupreanof area _ ____-_____-_-- 158

Kupreanof- Mitkof-Etolin Islands area ___________________ 163

Chichagof Island_____--_____---__-__-__-_------_------ 164

»' Felsite volcanic rocks. __.__-______-_-___-___-___-_---------- 165

Greenstone volcanic rocks. __________ __ ___________________ 165

* Distribution.. ________________________---_---.-_------ 165

Ketchikan district, by Theodore Chapin_ __,________-___-- 167

Age and correlation____________________. ______________ 168

Upper Jurassic or Lower Cretaceous intrusive rocks. ______________ 173

* General character. ________________________________________ 173

Border zone east of the Coast Range batholith.. _ _____________ 175

Coast Range batholith__----_______---_-_____-_-_---_---_-_ 177

^ Wrangell-Revillagigedo belt of metamorphic rocks--___-_-_---_ 181

Prince of Wales-Chichagof belt... _______ ... ________ 183

Kuiu-Heceta belt. ________________________________________ 186

Dall-Baranof belt._... ._.._...._- _ ....... ___ ..__._____ 186

Rock types_-_-_______-___________-_____________-_-_------ 188

Ultrabasic group. _-_________---_-_______-_-_---_-----. 188

* General features............ _________________ 188

Dunite.. ___________________________ 190

___-_________-_.______. ________________ 192

_-_-___-___-_____-_____-_-_- _ ______ 193

Hornblendite... __ _ ___ - ____ - _______ 194

Gabbro--.____ _ .-.__ ____________________ 199

Gabbro-diorite ___________________________ 201

Diorite __ ___ _________________________ 202

Monzodiorite. ____-_________-_-_-_-_____-___-_-_-_-_-_ 204

Syenite. ______________________________ 206

Quartz diorite. ______ ___ ._ __ ._ __ __ __ _________ 207

Granodiorite _ ___-_-___-____--_---_-_----__-_-_------ 214

Quartz monzonite_---_-_-___-_---_---_---_-_-_-------- 220

Granite _______________________________ 222

Pegmatite and aplite________-_-_______-___-___-------- 223

Malchite dikes. ________ _ _____________ ___ _ 229

Lamprophyre dikes _ _________________________________ 229

Structure of the intrusive rocks___-_-___-____-____-___---_-_ 231

Origin of variations in intrusive rocks_________ _______________ 235

Differentiation in place________________-_-_-_---_-_--_- 236

Successive intrusions-------------.-.------------------ 239
VI CONTENTS

The rocks Continued.

Upper Jurassic or Lower Cretaceous intrusive rocks Continued.

Origin of variations in intrusive rocks Continued. Page

Summary of relations of variants__________________ 242

Field relations____________________ ._ 242

Order of crystallization._________________________ 244

Rate of cooling and mineralizers____________________ 248

Ultrabasic rocks______._______________- ___________ 248

Gabbro, diorite, and alkalic-siliceous rocks _______________ 250

Age____________________________________ 252

Lower Cretaceous (?) rocks.________..________--_-_--__---_----_ 253

Distribution and character___--__________-__-_-_---__-.--__ 253

Gravina Island, by Theodore ChapiD______________________ 254

Rocky Bay, Etolin Island_________________-_-_--__-_-____ 255

Point Hamilton and vicinity.______________________________ 256

Pybus Bay________________________________ 257

Age and correlation_______________________________________ 258

Tertiary rocks.___-___-_________-_____________.-__-----__---_. 260

Eocene rocks_-__-__-______________________-______------__ 260

Distribution and character______________-.______-_______ 260

Basal conglomerate and sandstone.___________________ 262

Conglomerate of lava cobbles and rhyolitic flows, breccia,

and tuff _______________________________ 263

Basaltic and andesitic lava flows and associated rocks. _____ 266

Origin________________________..___...___ 267

Age.......--..___-___-_____-_-._- -_---_- .-_ 267

Pliocene (?) deposits___________.__________________________ 269

Lituya Bay_-____._______________________ 269

Suemez Is]and-__________-__________-_____---_--_---_- 270

Intrusive rocks___________________________________________ 271

Distribution_________:_________________ 271

Dikes... ____________________________________________ 271

Diabase....-____ ________ _ 273

Dacite porphyry___________.__________________________ 273

Olivine gabbro-________________________.______________ 274

Analcite gabbro.._______________-_-____------_------__ 274

Granite porphyry_____________________________________ 275

Quaternary rocks______________________________.._-_----------- 275

Glacial deposits----_______________________________-------- 275

Marine deposits and terraces_________________-_-_____-_--__ 276

Basalt and tuff..........._________________.----_. 278

Delta and current deposits____________________-____--_--___ 279

Relations between formations__-___-_____-----------___-------- 281

Wales group (Ordovician, Silurian, and Devonian)____________ 281

Middle and Upper Devonian, by Theodore Chapin_________>_. 283

Devonian and Carboniferous._______________________------_ 284

Paleozoic and Upper Triassic.______________________----_--_ 284

Unconformity within the Upper Triassic_____________________ 285

Jurassic (?), Lower Cretaceous (?), and older formations.______ 285

Upper Jurassic or Lower Cretaceous intrusive rocks and Mesozoic

orogeny._______________________________________________ 287

Tertiary and older formations.______________-____-___-----_ 288

Quaternary ______________________________________________ 289

Summary ________________________________________________ 289
» CONTENTS VH

I* Page

Structure. _------__.___-.______________________ 289

* General features_____-_-------__---_____---__-_--___________-_ 289

Jurassic (?) rocks of the Hyder district..... 292

Coast Range batholith and Wrangell-Revillagigedo belt of meta-

^ morphic rocks-____--_-----______-_-__---______-_-_--_-_____ 292

Juneau synclinorium-_________________________________________ 298

P- Duncan anticlinorium__________.__________________________ 299

Keku-Gravina synclinorium._________________________________ 300

^ Gravina synclinorium, by Theodore Chapin___.._________.. 300

Rocky Bay area, Etolin Island.-..__-_-_.______--__-_._-_ 302

Keku synclinorium_______________________________________ 302

Frederick Sound axis of cross folding__________________________ 303

Prince of Wales-Kuiu anticlinorium.________________________ 304

i General features_-_-______-___-_______________________ 304

Kuiu anticlinorium____________________________________ 307

P North coast of Prince of Wales Island---__-__---_-_----___-_ 307

Shakan Bay syncline__________-____-______-_-_____________ 308

Kosciusko-Tuxekan-Heceta synclinorium-_________________ 308

Maurelle Islands____________________________ 309

t San Fernando anticlinorium______________________ _______ 310

Kashevarof anticlinorium______________-___________________ 310

Vicinity of San Alberto and Bucareli Bays......__--____._. 311

r Southern half of Prince of Wales Island and adjacent islands,

by Theodore Chapin____________________ _____ 311

Dolomi-Sulzer anticlinorium, by Theodore Chapin__________ 314

Dall anticlinorium-_____________ _______________._ 314

Chichagof-Glacier Bay anticlinorium-_________ ___________ 315

Freshwater Bay syncline________.___-___________ 315

* Sitka Mesozoic belt____________________________________ 315

Mineral deposits.________________.____________ 316

Types of deposit_____________________________ 316

. Metalliferous deposits.___________________________ 320

Ores and associated minerals__________-___________________ 320

Gold___________________________ __________________ 320

Copper______________________________ 322

p- Iron__________________________________ 325

Silver and lead___________________________ 327

* Zinc_________________________________ 328

Nickel...____________________________________ 329

Molybdenum__________________________ 329

Tungsten.____________________________ 330

Antimony-______ _ 331

Y Titanium...___________________________ 331

Arsenic.-______________________________ 331

h Bismuth..____________________________ 332

Gypsum.._____________.______________ 332

* Garnet_______________________________ 332

Barite_______________________________ 333

Graphite. ______________________________ 333

^ Mica.________________________________ 334

Sillimanite, cyanite, and andalusite__________________ 335

^ Quartz... ____.___ _....__...___ 335

Carbonates. ______________ __________ 335
CONTENTS

Mineral deposits Continued.

Metalliferous deposits Continued.

Ores and associated minerals Continued. Page

Epidote____ ______.._____________________ 336

Pyroxene. _ ___________________________ 336

Amphibole------______-----___-__________ 337 -«

Albite. __________-____.___-____.___________ 337

Chlorite-_________.__________________________________ 337 *

Apatite______________________________ 337

Tourmaline....__________________________ 338 *

Lithologic and stratigraphies association of ore deposits-_______ 338

Wales group, by Theodore Chapin_____________________ 338

Wrangell-Revillagigedo belt of metamorphic rocks _ _______ 339

Ordovician and Silurian graywacke and slate_____________ 340

Silurian greenstone and limestone...--_________________ 340 -4

Middle Devonian rocks, by Theodore Chapin.___________ 341

Upper Devonian rocks, by Theodore Chapin_____________ 341 *

Mississippian rocks, by Theodore Chapin ________________ 341

Permian rocks, by Theodore Chapin_____________________ 342

Triassic rocks, by Theodore Chapin _____________________ 342

Jurassic (?) greenstone and slate._______________________ 342

Jurassic (?) graywacke and slate________--____-__-______ 343

Upper Jurassic or Lower Cretaceous intrusive rocks.______ 344

Gold________________________-_.______ 345

Gold-silver-lead._____________________ 347

Molybdenum________ ___________________________ 347

Nickel-copper____________________________ ___ 348

Copper and copper-palladium...._________________ 351

Iron.._____________________________ 351

Chromium. ______________________________________ 353

Lower Cretaceous (?) rocks____________________ ____ 353

Tertiary rocks______________________________________ 353

Quaternary deposits_________________________ 354

Belts of mineralization___________________________________ 356

Eastern border belt__________________________________ 357

Central Coast Range batholith______________________ 358

Western belt of schist and gneiss._______-_____________ 360

Zinc___-___________________________ 361

Silver-lead..________________________ 362

Gold____-___________________________._______. 362

Graphite.__________________________ 363

Garnet..____________________________ 363

Juneau gold belt______________________ 364

Funter Bay-Hawk Inlet belt.._________________ 366

Prince of Wales belt..._____..__.___________ 366

Copper____________________________ 368

Gold___- ______________ _ _ ____-_-___ 370

Chichagof gold belt___.____________________._ 371

Sitka belt___-________________________________ 373

Genetic relations of the metalliferous deposits_______________ 373

Character of country rock__________-_-___---_-__------- 374

o Type of associated igneous rock and type or stage of magmatic differentiation____________________--__-------_ 375

Mode of occurrence of igneous mass______________------_ 382
ILLUSTRATIONS IX

Mineral deposits Continued.

Metalliferous deposits Continued.

Genetic relations of the metalliferous deposits Continued. Page 

Temperature and pressure____________________________ 383

Hy drothermal alterations in the igneous rocks ____________ 386

Conclusions ________________________________________ 389

Limestone.. __________________________________________________ 390

Building and ornamental stone________________________________ 393

Index.. ___________________________________-___-._ 395

ILLUSTRATIONS

Page 

PLATE 1. Geologic map of a part of southeastern Alaska________ In pocket.

2. Generalized geologic map of southeastern Alaska..____ In pocket.

3. Coast Range topography, Hyder district: A, View near lower 

part of Chickamin Glacier; B, View near head of Chickamin 

Glacier._______________________________ 22

4. Mountains of Prince of Wales Island: A, Panorama from head

of Klakas Inlet; B, Panorama from head of Twelvemile Arm. 22

5. A, Cirque occupied by glacier 7^ miles N. 70° W. of Whiting 

Point, Port Snettisham; B, Cirque occupied by lake, Kane 

Peak, Kupreanof Island________________________________ 22

6. A, Rock ridge forming front edge-or lip of cirque occupied by 

lake at head of Cann Creek, Lisianski Inlet, Chichagof Island; 

B, Ridge between the heads of two cirques, Kane Peak, 

Kupreanof Island______________________________ . 22

7. A, Glacial lake in valley of Cascade Creek in Coast Range near 

Thomas Bay; B, Glaciated surface of quartz diorite showing 

roches moutonne'es, Thomas Bay________________________ 22

8. A, Rounded top of mountain below level of Pleistocene glaciation, Tracy Arm, Holkham Bay; B, Serrate peak of mountain above level of Pleistocene glaciation, near head of 

Chickamin Glacier, Hyder district.______________________ 22

9. A, Tracy Arm, a fiord in southeastern Alaska; B, Glacierfaceted headlands along fiord on east side of Baker Island __ 30

10. A, U-shaped glaciated valley with recent gorge in the bottom, 

Bergs Creek, Wrangell district; B, Pass at head of Goat 

Creek, Hyder district___________________________-______ 30

11. A, Baird Glacier and outwash plain, Thomas Bay; B, Trees

overthrown by advance of Baird Glacier in 1923___________ 30

12. A, Icebergs from Baird Glacier buried in outwash plain; B, 

Pit lake being formed in outwash plain of Baird Glacier by 

melting of iceberg____________________________________ 30

13. A, Dawes Glacier, Endicott Arm; B, North Dawes Glacier, at

the head of Endicott Arm______________________________ 30

14. A, Remnants of three uplifted wave-cut terraces in limestone, Keku Islets; B, Elevated wave-cut bench in limestone, 

Cornwallis Peninsula, Kuiu Island...___________________ 30

15. A, Coastal plain along southwest coast of Annette Island; B, 

Elevated wave-cut bench opposite Dolomi, Prince of Wales 

Island. _______________________________ 38
X - ILLTJSTBATIONS

Page

PLATE 16. A, Closely folded limestone of the Wales group, Dall Island; 

B, Greenstone schist of the Wales group, Port Johnson, 

Price of Wales Island-_______________________ 38

17. A, Mount Calder, Prince of Wales Island; B, Silurian conglomerate, Kuiu Island_______________________________ 86

18. A, Massive white Silurian (?) limestone, Dall Island; B, Flow 

breccia of Middle Devonian age, Hessa Peninsula, Prince 

of Wales Island....__________________._____ 86

19. A, Black chert of Mississippian age, Madre de Dios Island; 

B, Fossiliferous massive white limestone of Pennsylvanian 

age, Soda Bay, Prince of Wales Island__________________ 118

20. A, Permian limestone bluffs on northeast side of Saginaw Bay, 

Kuiu Island; B, Overturned fold in graywacke and phyllite, 

east side of Frederick Sound___________-________________ 118

21. Silicified stump and trunk of tree of Eocene age, Kuiu Island,

4 miles east-southeast of Point Camden__________________ 262

22. Structure sections in southeastern Alaska.__________________ 294

FIGURE 1. Diagrammatic structure section of Silurian and adjacent rocks

on east coast of Dall Island___________________________ 283

2. Structure section on Clover Bay, Prince of Wales Island.____ 313

3. Diagram showing relative amounts of different metals deposited

in lodes at six different positions on their parent batholiths__ 383
GEOLOGY AND MINERAL DEPOSITS OF SOUTHEASTERN ALASKA

By A. F. BUDDINGTON and THEODORE CHAPIN

INTRODUCTION

SCOPE OF REPORT

The object of the present report is to give a summary of all available data on the general geology of southeastern Alaska. The 

report is accompanied by a reconnaissance geologic map of the southern and eastern part of southeastern Alaska, which is the only part 

of that area so far covered in sufficient detail to warrant the publication of such a map. This report is not and can not be a comprehensive treatise on the geology and mineral deposits of this extensive 

area of Alaska, as the information now available is utterly inadequate for such a treatise.

Practically all the geologic work so far carried on in southeastern 

Alaska has been of a reconnaissance nature, and because of the small 

number of workers, the great area to be covered, and the dense 

undergrowth which clothes the mountains up to timber line and 

practically buries the bedrock except along very steep slopes, this 

reconnaissance has been confined chiefly to the coast. The strip 

along the coast has been mapped geologically by making landings at 

intervals averaging about half a mile. On the mainland certainly 

not more than 10 per cent of the Coast Kange batholith in southeastern Alaska and the adjoining territory of British Columbia 

can be said to have been sampled in even the roughest reconnaissance 

fashion; that is, by, the study of one hand specimen and one thin 

section for each 16 square miles of intrusive rock. About 125 batholiths and stocks are shown on the map, and there are many more 

stocks and sheets too small to be shown; yet only four of these have 

been studied in more than a superficial manner, many are known 

only by one or two thin sections, and many have not been studied 

at all.

A few areas in southeastern Alaska have been mapped in detail. 

These include the Kasaan Peninsula, 86 square miles, and the Cop1
2 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

per Mountain region, 45 square miles, on Prince of Wales Island; 

200 square miles in the Eagle River region; 50 square miles in the 

Berners Bay region; 103 square miles in the Juneau area, of which 

35 miles was subsequently resurveyed on an even more detailed 

scale; and 130 square miles in the Hyder district.

The strip of southeastern Alaska north of Cross Sound and the 

geology of Chichagof and Baranof Islands are referred to only briefly 

in this report.

A section containing many details concerning the intrusive rocks of 

the Coast Eange is included because of their possible bearing on the 

origin and distribution of mineral deposits.

NATURE OF THE FIELD WORK

The field work done by both authors wa.s conducted from a motor 

boat of sufficient size to serve for living quarters. The outcrops 

available for examination consisted of the wave-eroded rock beach, 

which is more or less continuous around the coast except at the heads 

of bays and inlets, where the rocks are usually concealed, and the 

ridges above timber line that were more or less free from moss 

covering. The examination of the rocks along the shore line was 

made from a rowboat fitted with an outboard motor. In some places 

it was possible to traverse the shore on foot for some distance, in 

other places this was impracticable, and in yet other places it was 

impossible even to land except in favorable weather.

The United States Coast and Geodetic Survey charts were used as 

a base for the geology. Actual examination of the geologic formations was confined almost exclusively to the coast line, though in 

the Ketchikan district Chapin made a few trips inland.

In the years 1915 to 1917, in a total of 9^ months' field work, 

Chapin completed an areal geologic map of the Ketchikan district 

south of latitude 55° 40' and an investigation of its mineral deposits. 

His map and completed report on this area, though unpublished, were 

available to Buddington when he began work in southeastern Alaska. 

In the years 1921 to 1925 Buddington spent a total of 13 months in 

reconnaissance areal geologic mapping of the coast of the northern 

half of the Ketchikan district, the Wrangell and Petersburg districts, 

and the southern half of the Juneau district. In addition, he investigated mineral deposits at numerous places throughout southeastern Alaska, mapped the west coast of Dall, Suemez, and Baker 

Islands, and covered in considerable detail the northern part of the 

Hyder district.

RESPONSIBILITY OF AUTHORSHIP

In 1918 Chapin resigned from the United States Geological Survey, 

and it devolved upon Buddington to write the present report, which 

includes the results of his own work and most of the general geology
INTRODUCTION 6

of Chapin's report. It has therefore been difficult to accredit responsibility for the statements and descriptions in the chapter on 

stratigraphy and yet maintain a coherent account for the reader. 

The stratigraphy that had been worked out by Chapin in the southern part of the Ketchikan district before Buddington entered the 

field has been found applicable, in the main, to the region farther 

north and has only been amplified and slightly modified by Buddington. Wherever possible, appropriate sections have been taken bodily 

from Chapin's report and credited to him. Where Chapin is cited 

as authority for certain statements or descriptions, without any 

specific reference, the source is Chapin's original report. Except 

where material in this report is credited to Chapin or others, Buddington is responsible for the statements or descriptions. But it 

will be readily understood that Buddington's views must necessarily 

have been influenced to a considerable extent by Chapin's work, and 

that he is thus indebted to Chapin even where the obligation is not 

specifically acknowledged. There has been no opportunity for conferences between Chapin and Buddington on the report here presented.

ACKNOWLEDGMENTS

In addition to his use of Chapin's material, the writer had access 

to the following unpublished reports and maps: The geology and 

mineral resources of the area east of Behm Canal, by Lewis G. 

Westgate; A geologic reconnaissance of the Glacier and Lituya 

Bay regions, by F. E. and C. W. Wright; A geologic map of Glacier 

Bay, by J. B. Mertie, jr.; and Geology of the vicinity of Juneau, by 

A. C. Spencer and H. M. Eakin. Specific acknowledgment of matter 

obtained from these reports is made at the appropriate places in the 

text. The writer has consulted also the many reports and articles by 

other geologists who have written upon different areas and mineral 

prospects or mines in southeastern Alaska and is indebted to them 

for much pertinent material.

Both authors are indebted to Mr. A. H. Brooks for the benefit of 

his broad knowledge of the geology of Alaska. In 1916 Mr. Brooks 

was in the field with Chap.in for a conference and field examination 

of critical localities, and in 1924 he accompanied Buddington for 

three weeks in an investigation of mineral deposits in the Juneau and 

Sitka districts. The authors are indebted also to Messrs. W. H. 

Dall, Edwin Kirk, G. H. Girty, Arthur Hollick, T. W. Stanton, 

J. B. Reeside, jr., and Rudolf Ruedemann for determination of 

fossils.

Mr. Walter Waters, of Wrangell, served very ably and satisfactorily as navigator for both Chapin and Buddington through seven 

field seasons. In the field the authors were the recipients of favors
4 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

from many operators and prospectors, whose assistance they gratefully acknowledge. Buddington is indebted to those who served as 

his assistants Messrs. Ben Larson, of Ketchikan, in 1921, George A. 

Wiggan in 1922 and part of 1923, Chauncey Deming in 1923, and 

Willard B. Jewell in 1924 and 1925, all of whom rendered consistently efficient service in furthering the work.

Buddington had the use of 2,500 thin sections of rocks collected 

from southeastern Alaska by F. E. and C. W. Wright, and rough 

volumetric mineral analyses were made on about 50 of these rocks 

by the Eosiwal method for this report. Particularly valuable was 

a collection of sections made from specimens obtained by F. E. 

Wright across the Coast Kange batholith along Stikine River.

EARLIER EXPLORATIONS AND SURVEYS

By THEODORE CHAPIN

The geographic features of the coast of southeastern Alaska first 

became known to the civilized world through the explorations of the 

English navigators Cook and Vancouver and the Spaniards Perez, 

Quadra, and Arteaga. Capt. James Cook with his assistants made 

extensive and accurate surveys of this coast in 1778, and after his 

death George Vancouver, one of his midshipmen, continued the survey of the coast of southeastern Alaska in 1793 and 1794. The accuracy of Vancouver's work is attested by the fact that some of his 

charts made over a hundred years ago have hardly been changed by 

the recent surveys made under modern conditions and improved 

methods.

The influence of the Spaniard^ is suggested by the large proportion 

of Spanish names retained in southeastern Alaska. The first of the 

Spanish explorers was Perez, who, in an expedition sent out from 

Mexico, discovered Queen Charlotte Islands in 1774. Bodega y 

Quadra explored the coast in 1775, and again in 1779 with Arteaga 

he made explorations on the west coast of Prince of Wales Island. 

Since the transfer of Alaska to the United States the Coast and Geodetic Survey has been engaged yearly in surveying the coast line and 

publishing sailing charts and navigation aids.

Casual observations on the geology of southeastern Alaska appear 

in the writings of some of the travelers who visited the region during 

the Russian occupation. The most valuable of the early papers is 

one by Dr. Constantin Grewingk, a Russian, who, although he never 

visited Alaska, published in 1850 a paper 1 which contains many geographic and some geologic data concerning southeastern Alaska,

1 Beitrag zur Kenntniss der orographischen und geognostischen Beschaffenheit der Nordwest-Kiiste Amerikas mit den anliegenden Inseln : Russ. k. mineral. Gessel. St. Petersburg 

Verb., 1848-49, 76-842, 1850.
EARLIER EXPLORATIONS AND SURVEYS 5

based largely on collections and data obtained by a Kussian naval 

officer.

The first knowledge of the geology of southeastern Alaska published in English was obtained from a report made by William P. 

Blake,2 who in 1863 accompanied a Kussian expedition sent to Stikine 

River to establish the boundary between Russian and English 

possessions.

In 1891 Reid 3 described Muir Glacier in Glacier Bay, and Gushing * 

made a geologic map of the vicinity. The Juneau gold belt w,as 

briefly described by Garside.5

Among the geologic investigations touching southeastern Alaska 

were those conducted by George M. Dawson,8 of the Geological Survey of Canada; C. Willard Hayes,7 William H. Dall,8 George F. 

Becker,9 and Alfred H. Brooks,10 of the United States Geological 

Survey; B. K. Emerson " and Charles Palache,12 of the Harriman 

Alaska Expedition; and others, all of whom contributed valuable 

information regarding the broader geologic features, the glaciers, and 

the coal, mineralogy, and ore deposits.

A brief discussion of the Ketchikan district by Brewer 18 was 

published in 1901.

In 1901 Brooks 14 made a reconnaissance of the Ketchikan district 

and outlined the main structural and stratigraphic features of southeastern Alaska. The correlations suggested and conclusions drawn 

in this hasty reconnaissance of 60 days, made primarily to describe 

the ore deposits, have proved substantially correct and have been but 

slightly amended as the result of later, more detailed geologic work.

3 Blake, W. P., Notes upon the geography and geology of Russian America and the 

Stikeen River: 40th Cong., 2d sess., H. Ex. Doc. 177, pt. 2, 1868.

"Reld, H. F., Studies of Mulr Glacier, Alaska: Nat. Geog. Mag., vol. 4, pp. 21-55, 1892. 

* Gushing, H. P., Notes on the geology of the vicinity of Muir Glacier: Idem, pp. 56-74.

5 Garside, G. W., The mineral resources of southeast Alaska: Am. Inst. Mln. Eng. Trans., 

vol. 20, pp. 815-823, 1893.

6 Dawson, G. M., Report on an exploration In the Yukon district and adjacent northern 

portion of British Columbia: Canada Geol. Survey Ann. Rept., new ser., vol. 3, pt. 1, pp.

I-277 B, 1888; Geological record of the Rocky Mountain region In Canada: Geol. Soc. 

America Bull., vol. 12, pp. 57-92, 1901.

7 Hayes, C. W., An expedition through the Yukon district: Nat. Geog. Mag., vol. 4, pp. 

99-162, 1892.

8 Dall, W. H., Coal and lignite of Alaska: U. S. Geol. Survey Seventeenth Ann. Rept., 

pt. 1, pp. 763-908, 1896.

8 Becker, G. F., Gold fields of southern Alaska: U. S. Geol. Survey Eighteenth Ann. 

Rept., pt. 3, pp. 1-86, 1898.

10 Brooks, A. H., A reconnaissance from Pyramid Harbor to Eagle City, Alaska: U. S. 

Geol. Survey Twenty-first Ann. Rept., pt. 2, pp. 374-376, 1900.

"Emerson, B. K., Notes on the stratigraphy of igneous rocks: Alaska, vol. 4, pp.

II-66, Harriman Alaska Expedition, 1904.

12 Palache, Charles, Notes on the minerals collected: Idem, pp. 92-96.

"Brewer, W. T., The Ketchikan mining district: Eng. and Mln. Jour., vol. 72, pp. 

630-632, 1901.

"Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska: U. S. 

Geol. Survey Prof. Paper 1, 1902.
6 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

In 1903 A. C. Spencer,15 assisted by C. W. Wright, made a study of 

the ore deposits in the vicinity of Juneau, and Wright 16 made a reconnaissance of Admiralty Island and studied the placer deposits on 

Porcupine Creek.

In 1904 and 1905 F. E. and C. W. Wright 17 made geologic investigations, including in their two seasons of work a reconnaissance of 

the Ketchikan and Wrangell mining districts, structural studies of 

the Coast Eange, stratigraphic investigations on Admiralty, Kuiu, 

Kupreanof, and Baranof Islands, and studies of the principal mining 

districts of southeastern Alaska.

In 1906 a geologic reconnaissance survey was carried northwestward from Lynn Canal to Lituya Bay by F. E. and C. W. Wright,18 

and C. W. Wright 19 made further economic and stratigraphic studies.

In 190T C. W. Wright 20 and Sidney Paige began the detailed 

geologic mapping and study of the ore deposits of Kasaan Peninsula 

and Copper Mountain, on Prince of Wales Island.

In 1908 C. W. Wright 21 continued his annual reconnaissance of the 

mining camps of southeastern Alaska and completed his study of 

Kasaan Peninsula and Copper Mountain, the report on which is a 

valuable contribution to our knowledge of the occurrence of the ore 

deposits of the Ketchikan district, especially the character of the 

contact deposits.

In 1906 and 1908 some investigations of mineral deposits were 

carried out in the Sitka district, and in 1909 Adolph Knopf 22 made 

a reconnaissance survey. In 1909 Knopf 23 made a geologic survey 

of the Berners Bay district, and in 1909 and 1910 he completed the 

detailed geologic mapping of the Eagle Eiver region.

18 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, 1906.

i8 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

pp. 138-154, 1906; The Porcupine placer district: U. S. Geol. Survey Bull. 236, 1904.

17 Wright, F. E. and C. W., Economic developments in southeastern Alaska : U. S. Geol. 

Survey Bull. 259, pp. 47-68, 1905; Lode mining in southeastern Alaska: U. S. Geol. Survey Bull. 284, pp. 30-54, 1906; The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, 1908. Wright, C. W., Nonmetallic deposits of southeastern 

Alaska: U. S. Geol. Survey Bull. 284, pp. 55-57, 1906.

is Wright, F. E. and C. W., A geologic reconnaissance of the Glacier and Lituya Bay 

regions (unpublished manuscript).

i» Wright, C. W., Lode mining in southeastern Alaska: U. S. Geol. Survey Bull. 314, 

pp. 47-72, 1907; Nonmetalliferous mineral resources of southeastern Alaska: Idem, pp. 

73-81.

20 Wright, C. W., Lode mining in southeastern Alaska, 1907: U. S. Geol. Survey Bull. 

345, pp. 78-97, 1908. Wright, C. W., and Paige, Sidney, Copper deposits of Kasaan 

Peninsula, Prince of Wales Island: Idem, pp. 98-115.

21 Wright, C. W., Mining in southeastern Alaska: TJ. S. Geol. Survey Bull. 379, pp. 

67-86, 1909 ; Geology and ore deposits of Copper Mountain and Kasaan Peninsula, Alaska : 

TJ. S. Geol. Survey Prof. Paper 87, 1915.

s* Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, 1912.

83 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, 1911; The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 502, 

1912.
EABLIER EXPLORATIONS AND SURVEYS 7

In 1909 and 1910 Knopf,24 incidental to other geologic work 

in southeastern Alaska, made brief visits to the operating mines in 

the Ketchikan district.

In 1912, after a lapse of one year, geologic work was resumed in 

the Ketchikan district by E. F. Burchard, who made a study of the 

marble deposits of the Ketchikan and Wrangell districts 26 and in the 

following year extended his studies to the Juneau, Skagway, and 

Sitka districts.26 A complete report on the marble resources of 

southeastern Alaska was published in 1920. 27

In 1913 stratigraphic studies of the Ketchikan district were carried 

on by Philip S. Smith.

In 1915 and 1916 Chapin continued the stratigraphic studies, and 

in 1917 he spent five weeks in a reconnaissance of mineral deposits 

in this district. The result of this work was Chapin's report and 

map of the Ketchikan district south of latitude 55° 40', previously 

mentioned.

In 1915 Gerald A. Waring 28 studied the mineral springs and hot 

springs of Alaska, and his report included a chapter on those of 

southeastern Alaska.

In 1917 R. M. Overbeck 29 prepared a geologic map and report on 

the west coast of Chichagof Island and Peril Strait.

In 1920 L. G. Westgate studied the geology of the coast along 

Behm Canal in the Ketchikan district and the geology and mineral 

deposits of the east side of Salmon River in the Hyder district.

In 1916 and 1921 A. C. Spencer and H. M. Eakin made a detailed 

study of the area in the vicin,ity of Juneau.

The reports by Westgate, Spencer, and Eakin have not yet been 

published.

In 1919 J. B. Mertie, jr., 29" carried on a reconnaissance of the 

geology and mineral resources of the Glacier Bay and Lynn Canal 

regions and visited all the producing mines in the Juneau and Ketchikan districts.

84 Knopf, Adolph, Mining In southeastern Alaska: U. S. Geol. Survey Bull. 442, pp. 

139-143, 1910; Mining In southeastern Alaska: U. S. Geol. Survey Bull. 480, pp. 98-102, 

1911.

28 Burchard, E. F., Marble resources of the Ketchikan and Wrangell districts: U. S. 

Geol. Survey Bull. 542, pp. 52-77, 1913.

28 Burchard, E. F., Marble resources of the Juneau, Skagway, and Sltka districts: U. S. 

Geol. Survey Bull. 592, pp. 95-107, 1914.

27 Burchard, E. F., Marble resources of southeastern Alaska: U. S. Geol. Survey Bull. 

682, 1920.

is Waring, G. A., Mineral springs of Alaska: U. S. Geol. Survey Water-Supply Paper 

418, pp. 19-49, 1917.

28 Overbeck, R. M., Geology and mineral resources of the west coast of Chichagof 

Island: U. S. Geol. Survey Bull. 692, pp. 91-136, 1919.

290 Mertie, J. B., jr., Lode mining in the Juneau and Ketchikan districts: U. S. Geol. 

Survey Bull. 714, pp. 105-128, 1920; Notes on the Salmon-Unuk River region: Idem, 

pp. 129-142.

6137 2£ 2
8 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

During the field seasons of 1921 to 1925 Buddington was engaged 

in a reconnaissance survey somewhat more detailed than .the older 

surveys along the coast of the northern Ketchikan, Wrangell, Petersburg, and southern Juneau districts, together with a reconnaissance 

of mineral deposits at numerous places throughout southeastern 

Alaska.

In addition to the reports already cited, special reports on individual mineral prospects and mining developments in southeastern 

Alaska are contained in the following yearly reports on the mineral 

resources of Alaska, by A. H. Brooks and others, published as 

bulletins of the United States Geological Survey: 1912, Bulletin 

542, pages 31-34; 1913, Bulletin 592, pages 75-117; 1914, Bulletin 

622, pages 95-102; 1915, Bulletin 642, pages 53, 73-104; 1916, Bulletin 

662, pages 66-100; 1917, Bulletin 692, pages 85-89; 1918, Bulletin 

712, pages 27-30, 53-90; 1919, Bulletin 714, pages 15-19, 69, 70, 76, 

105-142; 1920, Bulletin 722, pages 34r-38; 1921, Bulletin 739, pages 

20-22, 51-75; 1922, Bulletin 755, pages 23-25; 1923, Bulletin 773, 

pages 10-12, 71-139; 1924, Bulletin 783, pages 41-62; 1926, Bulletin 

797, pages 8-11.

NOTES ON HISTORY OE MINING DEVELOPMENT

Most of the data for the following brief notes on the history of 

mining development in Alaska are taken from Government reports 

on the several districts.

The Eussians were aware of the occurrence of gold in Alaska while 

they owned the Territory, prior to 1867, but they did no mining. 

The first mineral location in southeastern Alaska is reported 30 to 

have been made in 1867 on a copper deposit near New Kasaan, on 

Prince of Wales Island, by Charles Vincent Baranovich, a Russian 

trader.

In 1869 Mix Sylva and other disappointed miners from the Cassiar 

gold district, on the Canadian side of the international boundary, 

traveled northward from Fort Wrangell and discovered placer 

deposits at Windham Bay and on Powers Creek at Holkham Bay.81 

It is reported that $40,000,was extracted from these placers in 1870-71 

and that this represents the first considerable quantity of gold produced from Alaska. The first attempts at lode mining in Alaska 

under the American regime were made in the vicinity of Sitka in

80 Ulmer, Joseph, Mining in the Ketchikan district: Min. and Sci. Press, vol. 121, p. 493, 

1920.

31 Wright, C. W., in Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey 

Bull. 287, p. 2, 1906.
NOTES ON HISTORY OP MINING DEVELOPMENT 9

1871.32 By 1880 many auriferous ledges had been discovered in the 

district around Silver Bay, but they have been little worked to the 

present time, and none have been put on a productive basis. In 1880 

placer gravel was found near the mouth of Gold Creek, Gastineau 

Channel, and auriferous quartz veins were found on what is now the 

property of the Alaska-Juneau Co. by Joe Juneau and Richard Harris, who had been sent out from Sitka by N. A. Fuller on the strength 

of a favorable report by John Muir relating to the mainland of southeastern Alaska. The first official record of the Treadwell property is 

dated 1881, and most of the properties in the Juneau district which 

proved of value were discovered between 1881 and 1885.

The beach gold placers east of Lituya Bay were found and worked 

in the early nineties.

One of the first recorded events in the development of the gold lode 

mining industry of the Ketchikan district is the discovery by James 

Bowden of gold-bearing rock on Annette Island in 1892. In 1897 

and 1898 came the discovery of the Gold Standard lode, on Helm 

Bay; the deposits near Dolomi; the Sea Level lode, on Thorne Arm, 

Revillagigedo Island; and the mineralized area back of Hollis on 

Twelvemile Arm, Prince of Wales Island.

From 1896 to 1906 intensive prospecting was carried on throughout 

southeastern Alaska, and many of the copper, gold, and marble 

properties which have proved valuable were discovered. Placer gold 

was first discovered in the Porcupine area of the Skagway district 

in 1898; the total output from this area up to and including 1916 is 

estimated at about $1,200,000. During 1900 and 1901 considerable 

work was done on gold deposits on Woewodski Island, in the Wrangell district. The gold lodes on which the Chichagoff mine, in the 

Sitka district, is still operating were found in 1905. In 1920 gold 

veins were discovered on Lisianski Inlet, Chichagof Island, from 

which the first gold was produced in 1924 by the Apex-El Nido Co.

Between 1897 and 1901 many copper and gold properties were 

located in the Ketchikan district. Between 1899 and 1905 the mineralized belt east of Wrangell was discovered, systematic mining was 

carried on, and smelting of copper was begun. Copper ore was produced in the Ketchikan district first in 1905, to the amount of 

30,400 tons, with an average value of $10.79 a ton. The average 

quantity of copper obtained from the ore was about 3 per cent. In 

1906 there were 10 producing copper mines in the Ketchikan district; 

in 1924 there were only 2. The total production from 1905 to 1920 

is given below.

88 Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, p. 8. 

1912.
10 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA 

Production of copper mines wi the KetcMlcan district, 1905-1920

Mixed ore _____ _________ __ _

Gold.............................................

Silver ________________________........... ........ do..-

Quantity

550, 787

33, 102, 689

26, 896. 6

242,677

Value

$6, 107, 202. 00

566, 802. 00

159, 000. 00

12.41

The first nickel-copper deposits were found in 1911 on an island 

off the west coast of Chichagof Island. In 1921 and 1922 other 

nickel-copper1 lodes were located on Yakobi Island, also on the west 

coast of Baranof Island and on Funter Bay, Admiralty Island. No 

ore has yet been shipped.

Metal-bearing lodes, chiefly of gold and silver, were found at the 

head of Portland Canal in British Columbia in 1898, and similar 

discoveries were made on the Alaskan side between 1898 and 1901. 

They received little attention until 1909, when a small boom was 

started on the Canadian side. This boom subsided in a few years, 

but interest was again revived in 1917 by the discovery of rich silver1 

ores on the Canadian side. In 1918 large bodies of rich silver ore 

were found at the Premier mine. In 1923 gold-silver-lead ores were 

discovered on the West Fork of Texas Creek in the Hyder district, 

and in 1925 the Eiverside mine, in the Salmon Kiver Valley north of 

Hyder, produced gold-silver-lead ore.

A little marble was quarried in the early nineties on Ham Island, 

in the Wrangell district, and worked up into tombstones, which were 

sold at near'-by localities. Marble tombstones were in considerable 

demand by the natives, who substituted them for the crudely carved 

wooden totems. The first shipments of marble from Alaska were 

made in 1902 from quarries opened at Calder, on Prince of Wales 

Island, and since 1904 there has been a steady increase in the output, 

practically all of which has come from a few quarries in the vicinity 

of Shakan, on Prince of Wales Island.

Gypsum has been produced since 1906 from the deposit on Chichagof Island.

GEOGRAPHY

LOCATION AND EXTENT

Southeastern Alaska, which is often called the panhandle, extends 

southeastward from Mount St. Elias on the north to Dixon Entrance 

on the south and is bordered on the south, east, and north by British 

Columbia. This coastal belt, with its contiguous islands, has an area 

of nearly 40,000 square miles and is included between parallels 54° 30' 

and 60° 30' and meridians 130° and 141°. It forms a strip 400 miles
GEOGRAPHY 11

long and 100 to 150 miles wide, with a narrow extension northwest 

of Mount Fairweather 100 miles long and 25 to 50 miles wide. More 

than one-third of the land surface of southeastern Alaska is comprised in the 1,100 islands of the Alexander Archipelago. The seaward islands, Chichagof, Baranof, and Kruzof, together with a few 

smaller ones, have a total area of about 4,500 square miles. Prince 

of Wales Island is the largest island, with an area of 2,800 square 

miles. The other large islands ate Admiralty, about 1,500 square 

miles; Revillagigedo, 1,120 square miles; Kupreanof, 1,080 square 

miles; and Kuiu, T50 square miles. There are many smaller islands, 

such as Dall, 275 square miles; Etolin, 330 square miles; Mitkof, 200 

square miles; Zarembo, 180 square miles; Kosciusko, 160 square miles; 

Annette, 133 square miles; and Gravina, 102 square miles.

The territory under consideration (see pi. 1) is covered by the 

charts of the United States Coast and Geodetic Survey listed below, 

each of which is published on a scale of 1:200,000, except Nos. 

8152 and 8002, which are on smaller scales. No. 8002 covers all of 

southeastern Alaska. Large-scale charts of most of the harbors and 

channels can also be obtained.

8200. Frederick Sound and Sumner Strait.

8300. Lynn Canal and Stephens Passage. *

8102. Hecate Strait to Etolin Island.

8152. Dixon Entrance to Chatham Strait.

8250. Chatham Strait and Baranof Island.

8002. Dixon Entrance to Cape St. Elias.

There are two national monuments in southeastern Alaska. The 

Sitka National Monument comprises about 57 acres of great natural 

beauty and historic interest. The Glacier Bay National Monument 

comprises some 1,820 square miles and includes a number of tidewater glaciers of the first rank in a setting of magnificent snowcapped mountain ranges.

POPULATION AND SETTLEMENTS

The population of southeastern Alaska is mostly concentrated in 

the mining and fishing centers. About 160 of the small islands are 

now being utilized for fox ranches, and permanent caretakers live 

on them.

Skagway is the northernmost town and is the terminus of the 

White Pass Railway. Juneau is the capital of the Territory, the 

distributing center for the north end of the panhandle region, and 

the location of the Alaska-Juneau Mining Co. Douglas is opposite 

Juneau, across the Gastineau Channel, and near it was the plant of 

the Treadwell Mining Co. Sitka, on the west coast of Baranof 

Island, was the first capital of Alaska and contains many points of 

historic interest and valuable relics of the Russian occupation. The
12 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

agricultural experiment station is here, and the town is the general 

supply point for the adjacent region. Wrangell and Petersburg 

are the supply centers for the central part of the region, and Wrangell 

is the outfitting station for expeditions up Stikine Kiver. Ketchikan 

is the distributing point for the southern part of the region; it is 

the first port of entry in southeastern Alaska. The population of the 

principal towns, as given in the 1920 census, is as follows: Juneau, 

3,058; Ketchikan, 2,458; Sitka, 1,175; Wrangell, 821; Petersburg, 879; 

Skagway, 494.

There are several small native villages, including Klawak and 

Hydaburg, on Prince of Wales Island, and Kake, on Kupreanof 

Island. Craig is a small village on the west coast of Prince of Wales 

Island. There are also scores of small settlements at or near canneries or mines, to which regular mail service is maintained and 

where boat supplies, fuel, food, and clothing can be purchased.

TRANSPORTATION

Regular service is maintained by coastwise steamers all the year 

round from Seattle and Vancouver to Skagway, Juneau, Sitka, 

Wrangell, Petersburg, and Ketchikan. Freight rates are reasonable, 

and costs compare favorably with those at Seattle. In the summer 

season tourist boats leave Prince Kupert for the major ports of southeastern Alaska.

Boats run regularly from Ketchikan carrying mail, passengers, 

and freight to settlements on the west coast of Prince of Wales 

Island. Similar service is maintained from Juneau to Fanshaw Bay, 

Windham Bay, Sumdum, Snettisham, and Taku; from Petersburg to 

Kake; from Juneau to Auke Bay, Tee Harbor, Eagle Landing,

Comet, and Skagway; and from Juneau to Tenakee, Gypsum, 

Hooniah, Chichagof, Cape Edward, and Sitka.

Four rivers of considerable size the Alsek, Chilkat, Taku, and 

Stikine have their sources in the interior plateau and reach the sea 

after traversing the Coast Eange. During the open season regular 

sailings are maintained on Stikine River by high-powered river 

boats between Wrangell and Telegraph Creek, British Columbia, at 

the head of navigation, a distance of about 170 miles. Chickamin 

and Unuk Rivers can be ascended with difficulty in small boats to 

points well within the heart of the Coast Range.

Transportation facilities on land are poorly developed. The 

rugged nature of the land, with its many swampy areas and luxuriant 

growth of vegetation, and the numerous deep fiords and channels 

that cut into or separate the islands, preclude the extensive construction of railroads or even of wagon roads, except at unwarranted expense. The need of railroad construction is in large part obviated,
GEOGEAPHY 13

however, by the intricate system of waterways which penetrates the 

entire region, providing excellent highways for deep-sea vessels and 

numerous deep-water harbors in sheltered bays.

CLIMATE

The climate of southeastern Alaska is characterized by moderate 

temperature the year round, including mild winters and cool summers, and by heavy precipitation, except at the head of Lynn 

Canal and in an area bordering Frederick Sound, including the 

north end of Kupreanof Island and the southwest end of Admiralty 

.Island. The ports are open to navigation the year round. Near 

sea level the first frosts occur in September or October and the last 

in May or June. The average length of the growing season is 

about 180 days. The snowfall is slight except on the mountains and 

the inland areas. Near sea level, except at the heads of the mainland fiords, even in winter, the precipitation is mostly in the form 

of rain, which is heaviest in the fall and winter. The heavy precipitation, although it is disagreeable and occasions considerable 

inconvenience in travel and prospecting, is a very valuable asset in 

providing water power.

The prevailing winds at most places are from the south and southeast. At Sitka the winds are prevalently from the east, and in the 

vicinity of Calder and Kake they may in some years be prevalently 

from the west. A change from a southeast to a north wind almost 

invariably brings fair weather. During the winter fierce land winds 

ofteji blow down the fiords and at their height interrupt the normal 

passage of coastwise traffic.

Tables presenting the average monthly and annual precipitation 

and the ayerage annual mean temperature at stations in southeastern 

Alaska and an adjacent part of British Columbia are given below. 

The averages for Alaska have been computed from data given in 

publications of the Weather Bureau, United States Department of 

Agriculture, for 1923 and earlier years. The data for Stewart, 

British Columbia, are taken from records by the Dominion Meteorological Service.38

Except at the head of Lynn Canal, near Skagway and Klukwan, 

the minimum temperature is rarely below zero and very rarely 

below 7°. On the average zero readings occur less than twice a 

year at Juneau and less than once a year at Sitka. The maximum 

recorded temperature is 99°. The winter temperature commonly 

ranges from 10° to 20° above zero and the summer temperature 

from 70°' to 80°.

88 Schofleld, S. J., and Hanson, George, Geology and ore deposits of Salmon River district, 

B. C.: Canada Geol. Survey Mem. 132, p. 7, 1922.
14 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The total snowfall at Skagway averages about 3^ feet; at Juneau, 

9 feet; at Sitka, a little over 4 feet; and at Stewart, British Columbia, a little over 18 feet.

The number of rainy days averages about 200, except at the head 

of Lynn Canal, where it is less than 100. With few exceptions the 

rains are gentle, mostly in the form of drizzle or mist.
Average monthly precipitation, in inches, at stations in southeastern Alask

Calder..-. ___ ..... ________ ...... _ .. ............

Kake _ ..-.. ___ . __ .. __ .. ____ . __ . ______

Ketchikan ____________________________

Killisnoo _____________________________

Sitka . .. . .. ...

Speel River. ................................................

Wrangell ___________________________ ..

Jan.

8.9

9.97

11.54

4.37

12.90

4.93

6.88

7.36

1.53

10.48

7.65

7

OO

Feb.

8.0

8.02

11.24

4.02

11.44

4.17

5.27

6.13

1.35

10.55

6.94

5.87

Mar.

5.41

7.92

11.36

2.62

12.11

4.02

5.10

5.25

1.11

10.34

3.94

i. 5Q

Apr.

5.14

9.12

12 12

1.73

12.84

3.02

5.28

3.57

1.36

8.45

5.04

3.69

May

4.3

6.11

8.25

2.97

7.84

2.64

5.14

4.00

.67

5.79

3.33

June

3.0

3.69

5.72

1.80

5.71

2.00

3.76

3.30

.89

4.51

3.04

1 OO

Average monthly and annual mean temperatures, in degrees Fahrenheit, at stations in sou

Calder--. ____ .. __________ . ____ . _ . ___ .

Juneau. _____________________________

Sitka _ . ______ . _____________________

Wrangell. ____ . __ . ____________________

Stewart.. _______ .. ________ . __________

Jan.

27.7

25.4

26.9

31.8

19.1

27.1

19.3

Feb.

31.3

30.2

29.8

34.1

24.6

30.6

25.9

Mar.

29.7

34.2

34.5

33.4

36.5

28.0

31.6

30.5

Apr.

40.2

39.0

40.4

40.8

42.8

39.9

42.4

39.2

May

45.5

45.0

47.3

47.9

46.9

48.8

47.9

48.2

June

53.7

50.0

54.1

54.2

51.4

55.6

55.1

54.4
16 GEOLOGY AND MINEEAL DEPOSITS, SOTJTHEASTEEN" ALASKA

VEGETATION AND TIMBER SUPPLY 

By THEODORE CHAPIN

Most of southeastern Alaska lies within the Tongass National 

Forest, formerly known as the Alexander Archipelago National Forest. The hillsides, where not too steep, from sea level up for many 

hundred feet are covered with a luxuriant vegetation, which is so 

dense that it effectively conceals the underlying rocks, tends to confine 

prospecting to the stream courses, and renders detailed geologic 

mapping slow and expensive. Up to an altitude that may reach about 

2,500 feet but is dependent upon local conditions, the lowlands and 

slopes are forested with a heavy growth of timber. Among the 

conifers of the forests are species of hemlock, spruce, cedar, pine, and 

balsam fir. An estimate of their relative abundance furnished by 

W. G. Weigle, former forest supervisor of Alaska, is given in the 

following table:

Per cent 

Western hemlock (Tsuga, Tieteroplvylla,') .

, 60 Black hemlock (Tsuga mertensiana).

Sitka spruce (Picea sitchensis) _____________________ 25

Western red cedar (Thuya plicata) ____ ______ __ 7

Yellow cedar (Chamaecyparis nootJeatensis) _____ 5

Lodgepole pine (jack pine) (Pinus contorta). 

White balsam (AHes lasiocarpa )_____ _.

As seen from this table hemlock is the most abundant, and of the 

two species noted the western hemlock is much more plentiful. The 

hemlock is less susceptible than spruce to the borings of the teredo 

worm, and for this reason and on account of its superior weight it 

has been in great demand for piling used in fish traps and wharf 

and dock construction, purposes for which it is well adapted, as it 

tapers but little in the length required for piles. It is now used 

extensively also for planking, for which use it is better adapted than 

fir, as it does not splinter so badly and lasts longer. A great amount 

of planking is used in wharf, road, and tram construction, as the 

streets of most towns in southeastern Alaska are built of planks 

placed upon piling. Hemlock makes a very satisfactory grade of 

newsprint paper, and the trees, which range from 18 inches to 3 feet 

in diameter, are said to be especially well adapted to this use.

For general purposes spruce has found the most universal use. 

It grows to fine proportions, reaching 225 feet in height and 4 feet 

in diameter 100 feet from the butt. It averages 2,500 board feet to 

the tree, and exceptional trees yield 20,000 feet. On account of its 

toughness and lightness the Sitka spruce is suitable for airplane 

construction and during the World War was used in England and 

France as well as in the United States.
GEOGRAPHY 17

The western red cedar is used for shingles and for boat timber. 

The yellow cedar also is used in boat construction and is suitable for 

furniture and pattern making but is not easily obtained, as there is 

but little of it found below an altitude of 500 feet above sea level.

Among other trees common to this region may be noted mountain 

ash, cottonwood, quaking aspen, crab apple, and varieties of willow 

and alder. From sea level to a height of 1,500 feet or so the forests 

have a dense undergrowth of berry bushes and other t shrubs which 

in places form an impassable barrier except where trails are cut. 

The most objectionable of these shrubs is the devil's club, a luxuriant 

bush whose stalks and stems are thickly covered with sharp, fine 

thorns. Salmonberry is the most abundant and forms impenetrable 

thickets. Huckleberries are plentiful; they include two varieties with 

blue berries and one with red. There are also high-bush cranberries 

and black currants.

The best timber is found on the well-drained areas, which are 

confined to the steep hillsides and the vicinity of the large streams. 

It is not likely that in the near future much timber will be cut for 

export, but there is an ample supply suitable for mine timber arid 

other local requirements. There is, moreover, a great quantity of 

poorer-grade timber suitable for paper pulp, and it is believed that 

this region, with its abundant water power and large deposits of highgrade limestone, will become a pulp and paper producing region.

AGRICULTURAL LAND

Owing to the mountainous character of the topography, few of the 

flat or gently sloping tracts well adapted to agriculture are large. 

All the indented arms of the sea, however, are being gradually filled 

with material brought down by rivers. Except for some low-lying 

flat islands and low valleys on the larger islands these deposits constitute practically the only large areas of level land in the region. 

A number of homesteads have been taken up on the deltas of the 

mainland, and there is opportunity for many more. The largest 

available tract is that of the Stikine River delta, which is 1 to 3 

miles wide and extends upstream for 20 miles or so. This tract 

contains between 12,000 arid 15,000 acres of land apparently suited 

for diversified agriculture. North of the mouth of Stikine River, 

on the old, slightly uplifted delta of Patterson River, there is an 

additional 2,000 acres or more. There is also a considerable acreage 

available on the islands and mainland at the mouth of Glacier Bay. 

These areas are suitable for growing berries and vegetables.

WATER POWER

The heavy precipitation insures an abundance of water, and the 

deep lakes in many of the troughlike valleys form natural reservoirs 

whose capacity could readily be increased. Many of the streams
18 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

have an abrupt descent at or near the coast line, thus affording many 

fine water-power sites. The abundance of water power, the cheap 

water transportation, and the proximity of forests suitable for pulp 

wood afford opportunity for the present and future development of 

pulp and paper mills. One such mill is already in operation on the 

north arm of Port Snettisham, and others are contemplated.

Investigations by the Geological Survey and the Forest Service 

indicate a potential water power of more than 450,000 horsepower in 

southeastern Alaska. Only a small percentage of this is now utilized, 

but each year shows increased development of power for mining, 

milling, and other uses.

OUTLINE OF GEOLOGY

MAIN STRUCTURAL FEATURES

All of southeastern Alaska is a rugged mountainous region lying 

within the Pacific Mountain system, which, as defined by Brooks,84 

includes a broad zone of ranges forming a concave belt parallel to 

the southern coast of Alaska.

Farther southeast, in the vicinity of Vancouver Island, this system 

includes two prominent ranges the Coast Kange of the mainland 

and the Vancouver' Kange of Vancouver Island which, according 

to Clapp,35 are separated by the submerged northern part of the Pacific coast downfold that extends from the Gulf of California through 

British Columbia and Alaska and includes Haro, Georgia, Johnstone, 

and Broughton Straits and Queen Charlotte Sound. Hecate Strait 

constitutes a further extension o.f this downfold and separates the 

Queen Charlotte Range of Graham Island from the mainland.

Within southeastern Alaska the dominating feature of the mainland is the Coast Range, a high mountain mass many peaks of which 

rise to altitudes of 6,000 to 8,000 feet. Brooks 86 describes it as 

follows:

The Coast Range extends from near the boundary of Washington northward 

through British Columbia into southeastern Alaska, where it lies partly in 

Alaska and partly in Canadian territory. Following the coast line for nearly 

900 miles, it passes inland behind the St. Elias Range near the head of Lynn 

Canal. Thence it can be traced northward, decreasing in altitude and gradually losing definition until it finally merges with the interior plateau near 

Lake Kluane, in longitude 138° 30'. This range has no well-defined crest line 

but is rather a complex of irregular mountain masses, occupying a coastal strip 

between the Pacific Ocean and the Central Plateau region.

»* Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska: U. S. 

Geol. Survey Prof. Paper 1, p. 14, 1902.

88 Clapp, C. H., Sooke and Duncan map areas, Vancouver Island: Canada Geol. Survej 

Mem. 96, pp. 23-24, 1917.

38 Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 

45, p. 28, 1906.
OUTLINE OF GEOLOGY 19

Chapin describes Clarence Strait, Kevillagigedo Channel, Nichols 

Passage, and the lowlands bordering them as occupying the site of a 

down-warped trough. This trough extends northwestward beneath 

the Tertiary formations of Eagle, Zarembo, Kashevarof, Prince of 

Wales, Kupreanof, Kuiu, and Admiralty Islands. It is evidently 

one of the series of basins constituting the Pacific coast downfold. 

Tertiary formations are exposed at least locally in or on the borders 

of all the basins of the downfold that are not completely submerged.

The mountainous islands and peninsulas to the east of this Tertiary 

belt may, in the absence of more definite knowledge, be grouped with 

the Coast Kange of the mainland.

To the west of the trough lies what is here named the Prince of 

Wales Kange, dominated by a complex group of short, rugged mountains that reach an altitude of about 4,000 feet. This range includes 

Prince of Wales Island, all of Kuiu Island except the eastern part, 

and the island groups lying west of Prince of Wales Island, with 

the probable exception of Forrester Island. The Prince of Wales 

Eange is composed almost wholly of Paleozoic formations with 

associated intrusive rocks of Upper Jurassic or Lower Cretaceous age.

The trough between the Coast Range and the Prince of Wales 

Range appears to be terminated by Chatham Strait. Chatham 

Strait and Lynn Canal, according to the Wrights,87 constitute a great 

fiord eroded along a faulted zone. This fiord is 250 miles long, 3 to 

6 miles broad, and 1,000 to 2,900 feet deep. It traverses the general 

trend of the mountain ranges and of the bedrock structure at an 

angle of about 30°.

To the north there is no satisfactory means for discriminating 

between the Coast Range on the one side and the mountain ranges 

of Admiralty and Chichagof Islands, the Glacier Bay region, and 

the peninsula west of Lynn Canal on the other.

Mount Fairweather and the associated mountains, which are part 

of the St. Elias Range, lie along the line of trend of the ranges of 

the Alexander Archipelago, but are much higher, 8,000 to 15,000 feet, 

and probably in part of later origin. Their youth is indicated by 

the fact that in the vicinity of Mount St. Elias Pleistocene beds have 

been uplifted on their flanks and folded and faulted.88

BEDROCK GEOLOGY

The predominant features of the bedrock geology of southeastern 

Alaska (pi. 2) comprise the composite Coast Range batholith of the 

mainland and the associated outlying intrusive bodies on the islands

87 Wright, F. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

Geol. Survey Bull. 347, pp. 21-22, 1906.

88 Russell, I. C., Second expedition to Mount St. Elias, in 1891: tJ. S. Geol. Survey 

Thirteenth Ann. Kept., pt. 2, pp. 1-91, 1892. Maddren, A. G., Mineral deposits of th« 

Yakataga district: U. S. Geol. Survey Bull. 592, p. 132, 1913.
20 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

of the Alexander Archipelago and in the Glacier Bay region; a 

metamorphic-complex belt that lies adjacent to the Coast Range 

batholith and consists of injection gneiss, crystalline schist, marble, 

phyllite, and highly schistose greenstone; three belts of Mesozoic 

formations one through Juneau and Mitkof Island, one through 

Keku Straits and Gravina Island, and one through the west coast 

of Chichagof and Baranof Islands; a belt of Tertiary formations on 

Zarembo, Kupreanof, Kuiu, and Admiralty Islands, and another 

along the outside mainland coast northwest of Icy Point; and Paleozoic formations which form probably two-thirds of the country rock 

of the Alexander Archipelago and the Glacier Bay region. The 

metamorphic complex is in part of Carboniferous age but may include 

beds ranging from Ordovician to Upper Jurassic or Lower Cretaceous. Recent lava flows form Mount Edgecombe, on Kruzof Island, 

and are found in several small separated areas in the vicinity of 

Thorne Bay, on Revillagigedo Island, and the east side of Behm 

Canal and along the Lava Fork of Unuk River.

Paleozoic beds form practically all of the Prince of Wales Range, 

the northeastern part of Chichagof Island, and the area in the vicinity 

of Glacier Bay. These beds are of pre-Ordovician (?), Ordovician, 

Silurian, and Devonian age. A considerable part of Kupreanof and 

Zarembo Islands is composed of middle Paleozoic formations. Carboniferous formations are found within the Alexander Archipelago, 

in the Keku synclinorium on the northeast end of Kuiu Island and 

the northwest end of Kupreanof Island and on Admiralty Island. 

They are also exposed on the mainland" along both borders of the 

Juneau synclinorium in the Juneau and Skagway districts and locally 

along the borders of the Gravina synclinorium in the Ketchikan 

district.

The Prince of Wales Range and the mountain ranges on the northeast end of Chichagof Island and in the Glacier Bay region are 

characterized by the predominance of middle and lower Paleozoic 

formations, in contrast to the Queen Charlotte Range of Graham 

Island, where only Mesozoic formations are reported to be present, 

and the Vancouver Range, where there are Mesozoic and upper Paleozoic formations. The only parts of the Pacific Mountain system 

south of Alaska which are known to be composed in considerable 

part of rocks as old as the middle Paleozoic are the San Juan 

Islands,89 the Klamath Mountains of California and Oregon, and the 

northern part of the Sierra Nevada.40

Tertiary formations are found in and adjacent to the great trough 

between the Coast Range and the Prince of Wales Range. This

88 McLellan, R. D., The geology of the San Juan Islands: Washington Univ. Pub., vol. 2, 

pp. 91-99, 1927. ° 

*°Diller, J. S., U. S. Geol. Survey Geol. Atlas, Redding folio (No. 138), p. 1, 1906.
OUTLINE OF GEOLOGY 21

trough must have originated in late Cretaceous or early Tertiary 

time, for its northwestward continuation forms the lowland area 

upon which lies the belt of Tertiary beds of Union Bay, on the Cleveland Peninsula, Eagle Island, the west side of Zarembo Island, the 

Kashevarof Islands, the northeast side of Prince of Wales Island, 

the west side of Kupreanof Island, the east half of Kuiu Island, and 

the southwest end of Admiralty. Island. The Tertiary deposits of 

Kasaan Bay, Duncan Canal, and Ernest Sound indicate the sites of 

Tertiary erosion valleys which lead into the major trough.

PHYSIOGRAPHIC HISTORY

The mountain ranges of the Pacific system are commonly referred 

to as resulting from the deep dissection of an elevated plateau or 

uplifted and warped peneplain 41 of Tertiary age. In the southern 

part of the Coast Range 42 the upwarping of this peneplain is assumed to have taken place at the end of the Pliocene or in early 

Pleistocene time. The upwarping of the peneplain at the south 

end of the Vancouver Kange is placed by Clapp 43 in the early 

Pliocene.

Wright 44 has offered an alternative explanation of the approximate uniformity of summit level within the Coast Range:

It is possible that both the observed tendency toward planation in the 

uplands and also in the forelands noted above owe their present character to 

ice action. It is significant in this connection that the upper limit of ice action 

coincides with the upland base level. If the ice sheet remained long enough at 

approximately the same level its surface might well have functioned, like a 

large water surface, as a datum plane toward which the exposed masses 

tended to be beveled. Sufficient evidence has not yet been gathered to determine definitely the rOle which such ice-cap beveling may have played in the 

formation of the observed upland surface.

The Pleistocene ice cap was undoubtedly an important factor in 

the modeling of the present upland surface. The data, however, 

are inadequate for a satisfactory discussion of the relation of peneplains, of cycles of erosion, and of the former ice cap to the present 

physiography of the mountains.

*» Spencer, A. C., The Pacific Mountain system in Alaska: Geol. Soc. America Bull., vol. 

14, pp. 117-132, 1903. Brooks, A. H., The geography and geology of Alaska: U. S. Geol. 

Survey Prof. Paper 45, pp. 286-290, 293, 1900. Dawson, G. M., On the later physiographical geology of the Rocky Mountain region in Canada: Roy. Soc. Canada Trans., vol. 

8, sec. 4, pp. 3-74, 1891. Clapp, C. H., Geology of the Victoria and Saanlch map areas, 

Vancouver Island, B. C.: Canada Geol. Survey Mem. 36, p. 8, 1913. Hanson, George, 

Reconnaissance hetween Eitsault River and Skeena River, B. C.: Canada Geol. Survey 

Summary Rept. for 1922, pt. A, p. 38, 1923.

42 Cairnes, C. E., Coquihalla area, B. C.: Canada Geol. Survey Mem. 139, p. 29, 1924.

43 Clapp, C. H., Sooke and Duncan map areas, Vancouver Island: Canada Geol. Survey 

Mem. 96, p. 363, 1917.

44 Wright, F. B., Excursions in northern British Columbia and Yukon Territory: Twelfth 

Internat. Geol. Cong. Guidebook 10, Prince Rupert-Skagway section, pp. 41-51, 1913.
22 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Schofield and Hanson 45 state that in the Salmon Kiver district, 

B. C., the Coast Kange was worn down to a condition of peneplanation during the Cretaceous period and that the present valleys were 

eroded during the Tertiary period.

In the Ketchikan district Eocene sediments occur at and below 

sea level on Union Point, Cleveland Peninsula, and on Coal Bay, 

Prince of Wales Island. The pre-Eocene rocks in this general 

vicinity reach altitudes of 2,800 to 3,300 feet. There is no evidence 

of faulting between the formations, but there may have been some 

slight warping. It seems very probable, however, that the Eocene 

rocks were formed for the most part in a great downwarped basin 

but also in small part in deep valleys eroded in a mountain range. It 

therefore follows that an adolescent or mature topography had been 

developed, at least locally, within this region prior to the deposition 

of the Eocene sediments and volcanic rocks.

There is little evidence available from which to determine the 

date of the uplift of the Coast Eange in southeastern Alaska. It 

must have been post-Eocene and may have been Pliocene or early 

Pleistocene, as seems to be indicated farther south in British Columbia. The uplift of the St. Elias Kange certainly went on throughout 

the Pliocene and Pleistocene and has probably continued to the 

present time, as indicated by faulting on Yakutat Bay.

TOPOGRAPHY

GENERAL FEATUBES

The mountainous topography of southeastern Alaska, with its 

associated forests, glaciers, waterfalls, and fiords, has a scenic beauty 

that is one of the great economic assets of the region. A maze of 

deep, intricate .inland waterways thread among the thousands of 

islands of the Alexander Archipelago. Skagway may be reached 

from Seattle, 1,000 miles away, through the " inside passage," without once entering the open ocean. The archipelago consists in part 

of flat, low-lying islands, forested practically to the water's edge; in 

part of smooth, rolling mountains, likewise completely forested, that 

rise to a height of several thousand feet; and in lesser part of high 

ranges composed of bare rounded mountains gouged by cirques or of 

bare serrate peaks with talus slopes. On the mainland magnificent 

fiords, equivalent in origin and scenic character to the famous fiords 

of Norway, penetrate into the granitic heart of the Coast Range; at 

many places cliffs rise sheer from the water's edge to altitudes of 

2,000 to 5,000 feet; and a short distance back from the shore snowy

45 Schofield, S. J., and' Hanson, George, Geology and ore deposits of Salmon River district, B. C.: Canada Geol. Survey Mem. 132, p. 31, 1922.
U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 3

A. VIEW NEAR LOWER PART OF CHICKA.MIN GLACIER 

The medial moraine is from Through and Greenpoint Glaciers

X. VIEW NEAR HEAD OF CHICKAMIN GLACIER 

Serrate peaks in background are abonl 8,000 feel in altitude

COAST RANGE TOPOGRAPHY, HYDER DISTRICT
5 - 

U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 4

.1. PANORAMA FROM HEAD OF KLAKAS INLET

B. PANORAMA FROM HEAD OF TWELVEMILE ARM 

MOUNTAINS OF PRINCE OF WALES ISLAND
D. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 5

A. CIRQUE OCCUPIED BY GLACIER 7M MILES N. 70° W. OF WHITING POINT,

PORT SNETTISHAM

Back wall in crystalline limestone. Altitude )!,000 feet . .

B. CIRQUE OCCUPIED BY LAKE, KANE PEAK, KUPHEANOF ISLAND 

Baek wall in diorite
TJ. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 6

A. ROCK RIDGE FORMING FRONT EDGE OR LIP OF CIRQUE OCCUPIED BY LAKE 

AT HEAD OF CANN CREEK, LISIANSKI INLET, CHICHAGOF ISLAND

Allitude 1,300 feet. Rock is diorite . * '.

Ji. RIDGE BETWEEN THE HEADS OF TWO 

CIRQUES, KANE PEAK, KUPREANOF ISLAND
U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 7

A. GLACIAL LAKE IN VALLEY OF CASCADE CREEK IN COAST RANGE NEAR

THOMAS BAY

B. GLACIATED SURFACE OF QUARTZ DIORITE SHOWING ROGUES MOUTONNfiES, THOMAS BAY
U. «. GEOLOGICAL SURVEY BULLETIN 800 PLATE 8

A. ROUNDED TOP Of MOl '.NTAIN BELOW 

LEVEL OF PLEISTOCENE GLACIATION, 

TRACY ARM, HOLKHAM BAY

Altitude 4,000 feet

B. SERRATE PEAK OF MOUNTAIN ABOVE LEVEL OF PLEISTOCENE GLACIATION, 

NEAR HEAD OF CHICKAMIN GLACIER, HYDER DISTRICT

Altilade 8,000 feet ' . ,
TOPOGRAPHY 23

peaks 6,000 to 7,000 feet high are common. High peaks like the 

Devils Thumb, which rises to a height of 9,077 feet, with a shaft 

projecting more than 1,600 feet above the general level, are visible 

on a clear day for over a hundred miles. Thousands of small 

glaciers occur in the mountains, some clinging to slopes so steep as 

to cause wonder how they can remain there, and some terminating in 

ice cliffs from which huge masses are continually falling. Some of 

these valley glaciers discharge icebergs into the sea. Here and 

there waterfalls, starting hundreds or thousands of feet high on the 

mountain sides, plunge down in a series of cascades into the valleys 

or into the sea. So steep are many of the mountain slopes that great 

landslides are common, and long triangular scars, both old and 

recent, are a feature of many views. The unusual coastal forms and 

the contrasts of color afforded by the green of the forest on the lower 

slopes, the dark to light grays of the bare rock and the talus above 

timber line, and the white of the snow patches and the glaciers lend 

variety to the scene.

The topography is that of an adolescent rugged mountainous 

region, in which the ranges have been deeply dissected by river 

erosion, modified by the great Pleistocene ice sheet, and sculptured 

by alpine glaciers of Pleistocene and Recent- age. A panorama of 

part of the Coast Range at the head of Chickamin River, near the 

international boundary, is shown in Plate 3, A and B. The highest 

peak in the Coast Range south and east of Lynn Canal is Kate's 

Needle (10,002 feet), on the international boundary east of Thomas 

Bay. The relief is usually several thousand feet. In the general 

vicinity of the international boundary all the divides are filled with 

ice and the ridges bear snow or ice caps, from which flow valley 

glaciers, many of them 20 to 30 miles long, the general effect being 

that of a snow or ice field with many projecting nunataks. Literally 

thousands of small alpine glaciers are present on the mainland, and 

there are many also on Baranof and Chichagof Islands and perhaps 

on Admiralty Island. The Prince of Wales Range comprises a 

group of short, rugged glaciated mountains as much as 4,000 feet 

in height, such as are shown in the panoramas of Plate -1.

The evidences of the great ice flood of Pleistocene time are found 

in the fiorded coast line, in the modified shape of most of the preexisting river valleys, in the presence of hanging valleys, in polished, 

grooved, and striated surfaces, and in roches moutonnees. The re- .O i >

suits of extensive alpine glaciation are seen in the many cirques, 

tarns or mountain lakes in rock-rimmed basins, knife-edged or comb 

ridges between cirques, and Matterhorn-like peaks, on both the mainland and the larger islands of the archipelago. (See pis. 5-7.) 

6137 29 3
HEIGHT OF THE ICE SURFACE

During the Pleistocene epoch all the valleys and most of the 

mountains of both the mainland and the islands were buried under 

an ice sheet that extended across the whole region to the Pacific 

Ocean. During the period of maximum flooding ice to the depth of 

a mile or so must have flowed out through these parts of the mainland valleys that now constitute fiords.

The height of the surface of this ice field was not everywhere the 

same. In the vicinity of the head of Portland Canal its surface was 

at an altitude of about 6,000 feet; south of Stikine River and about 

14 miles east of Wrangell, 5,000 feet; on Cascade Creek, in Thomas 

Bay, about 5,000 feet; on Whiting River about 15 miles east of 

Snettisham, 4,500 feet; and in the Eagle River region, about 3,400 

feet.46 Below the altitudes noted the mountains are smoothed and 

rounded on their tops (see pi. 8, A), though on the mainland and 

locally on the islands their higher slopes are marked by cirques. 

But the highest peaks, though furnishing sites for local glaciers and 

snow accumulations, stood above the surface of the great ice field and 

are serrate, pinnacled-, and frost-riven. (See pis. 3, Z?, and 8, B.)

Information as to the rate of decline of the ice surface outward 

from the centers of accumulation is scanty. On Etolin Island the 

mountains, about 3,500 feet high west of Mosman Inlet, are rounded 

and glaciated, whereas the peak, about 4,500 feet high several miles 

east of Quiet Harbor, on Stikine Straits, is serrate at the top. On 

the Portage Mountains, Kupreanof Island, glacial striae occur at 

an altitude of 3,000 feet, and on the Kasaan Peninsula mountains 

up to 2,840 feet in height are glaciated. On Chichagof Island the 

mountain 2,800 feet high just west of East Point, Tenakee Inlet, is 

rounded and glaciated, whereas the 4,000-foot peak back of Tenakee 

is serrated and probably stood above the ice surface. On Yakobi 

Island, which lies directly on the Pacific, the mountain back of 

Bohemia Basin, 2,300 feet high, is rounded, grooved, and polished. 

Knopf states that Doolth Mountain, on the west side of Chichagof 

Island, 2,100 feet high, was probably overridden by the ice sheet.

DIRECTION OF FLOW

The ice apparently had, in general, a southwestward flow toward 

the Pacific Ocean. Observations of the direction of striae made by 

the ice current near sea level suggest, however, that the flow here was 

to a considerable extent influenced by the topography. These striae

49 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

602, p. 12, 1912.
TOPOGKAPHY 25

were doubtless made during the waning stages of glaciation and may 

therefore indicate a concentrated flow of the ice along former valleys 

at a late stage of the ice flood. At some places they may be the 

markings of local valley glaciers. The direction of the striae observed on Kupreanof and Kuiu Islands suggests that an axis extended 

southwest through the Portage Mountains, the south end of Keku 

Straits, and the unnamed bay north of Alvin Bay. Northwest of 

this axis the ice moved to the west or northwest that is, on the 

north side of Kupreanof Island, west-northwest; on the west side of 

Kupreanof Island north of Keku Straits, west; and through Keku 

Straits, Keku Islands, Threemile Arm, and Port Camden, northwest. 

Southeast of this axis the ice moved to the west, southwest, or south 

that is, across the peninsula at the mouth of Thomas Bay, southsouthwest ; at the head of Duncan Canal, south; at the mouth of Dimcan Canal, southwest; on Level Islands, west through Sumner Strait; 

north of Point Barrie, southwest; through Alvin Bay, west; and 

through Sumner Strait, Port Beauclerc, and Affleck Canal, south. 

The radiating movement of the ice currents is particularly marked 

in the vicinity of the bay at the south end of Keku Straits. The ice 

from this area flowed north and northwest through Keku Straits, 

west-northwest through Threemile Arm, west through Alvin Bay, 

southwest north of Point Barrie, and south through Sumner Strait. 

It is also worthy of note that at Kell Bay the ice flowed across the 

narrow neck of land to join the ice in Chatham Strait.

Erratic boulders of Tertiary conglomerate, breccia, and lava are 

abundant along the south shore of Mitkof Island and along Frederick Sound southeast of Cape Strait. It seems possible that these 

boulders were brought down by the Pleistocene glacier that flowed 

doAvn the Stikine River valley, as similar rocks are now found in place 

on Iskoot River, a branch of Stikine River. Many fine roches 

moutonnees on the west coast of Prince of Wales Island show that 

the ice moved west-southwest across Orr, Tuxekan, and Marble 

Islands, west through the passages north and south of Noyes and 

Lulu Islands, and south through the lower end of Bucareli Bay.

VALLEYS

Most of the large valleys on the mainland are broad, flat-floored, 

and U-shaped as the result of the glaciation, which widened, deepened, and straightened the preexisting river valleys. On the islands 

there are many " through valleys," with broad, flat floors sloping 

very gradually up to a divide that is low, broad, and rounded. Such 

valleys were formed by the passage of ice that flowed up one valley, 

across the divide, and down another valley, or by valley glaciers 

that flowed in opposite directions from the same head, planing down 

the intervening divide.
26 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

A valley from which the ice has not yet wholly retreated is shown 

in Plate 10, B. Other such valleys are the one running a little south 

of west from Petersburg to Duncan Canal, one running northwest 

from the slough opposite Petersburg to the head of Portage Bay, 

one on Wrangell Island, and one running from Fools Inlet a little 

west of north to Eastern Passage.

In some glaciated valleys the profile is not a simple U, but the 

profile of each side may be composed of two or more intersecting 

curves, concave upward, each successively lower scallop having a 

steeper inclination. The scallops on one side of the valley may or 

may not correspond to those on the opposite side. This suggests 

that the valley is a composite of two or more superimposed U valleys, 

the upper and older one being broader and shallower than the lower 

and younger ones. This indicates that the history of the waning 

stages of the Pleistocene glaciation was not one of continuous decline, 

and it may indicate that there was more than one period of glaciation. The successively narrower valleys suggest successively narrower glaciers, which maintained the same relative size for a sufficiently long time to cut new valleys into the old one. The asymmetric character of the valley can be explained as due to the glacier's 

eroding its new channel at one side of the old valley, rather than in 

the middle. Since the glaciers have retreated streams have cut 

gorges and canyons in the rounded, flat-floored valleys, many of 

them several hundred feet deep. (See pi. 10, A.)

A few valleys show practically the V shape resulting from normal 

river erosion, with only slight glacial modification. An example is 

the valley on the south side of Tracy Arm, about 12% miles east 

of the elbow. The movement of the ice through such valleys must 

have been slight during the Pleistocene ice flood, and the glaciers 

apparently did not persist in them sufficiently long during the waning stages of the ice to erode them deeply.

Lakes and broad sphagnum bogs are characteristic features of the 

glaciated valleys. Many of the Jakes occupy deep troughlike basins 

gouged out of the rock by the ice. The lake in the valley of Cascade 

Creek, which enters Thomas Bay (see pi. 7, A), and the lake in the 

valley north of Tracy Arm, which is tributary to Port Snettisham, 

are apparently of this type. Such lakes have great potential value as 

storage reservoirs in connection with water-power development. 

Submergence of valleys containing such lakes beneath sea level would 

produce typical fiords.

FIORDS

The magnificent fiords for which southeastern Alaska has long 

been justly famous have resulted in part from glaciation. (See pi. 

9, A, B.) These fiords are thought to be former river valleys which
TOPOGRAPHY 27

were eroded and deepened by the ice currents. Some submergence 

of the region as a whole may also have accompanied the erosion. 

As a result of one or both of these factors, the sea invaded the valleys 

to a greater or less degree upon the melting of the ice, forming passages that are locally called channels, canals, straits, inlets, reaches, 

coves, bays, sounds, or arms. Those of the mainland are exceedingly 

important in giving easy access to part of the Coast Range back 

from the main coast line that would otherwise be relatively inaccessible. Many of the valleys tributary to the fiords enter at high levels, 

so that their streams have an abrupt descent at or near the coast line. 

Tfcis gives rise to many fine water-power sites.

All the arms of the sea on the mainland are typical fiords with 

such characters as very steep, straight, parallel walls, truncated or 

partly eroded mountain spurs, hanging valleys, and a deep central 

basin or basins with a shallower threshold at the entrance. The 

walls often show beautiful grooving, fluting, and polishing, and 

locally a more deeply curved, billowy, flowing type of surface known 

as roche moutonnee. (See pi. 7, B.) Fine examples of fiords are 

Lynn Canal, Taku Inlet, the north arm of Port Snettisham, Endicott Arm and its branches, Thomas Bay, Le Conte Bay, Bradfield 

Canal, Rudyerd Inlet, and Portland Canal. The fiords are continued 

inland by U-shaped valleys with characters similar to the seaward 

part.

The main channels between the islands, such as Gastineau Channel, 

Stephens Passage, Frederick Sound, Sumner Strait, Stikine Strait, 

Zimovia Strait, Clarence Strait, Eastern Passage, Ernest Sound, and 

Behm Canal, likewise exhibit fiord characteristics but usually not 

to so marked a degree as those of the mainland, though Blake 

Channel and Seward Passage are as typical as any of the mainland 

fiords. Fiords are found also on Etolin, Prince of Wales, Baker, 

Chichagof, Baranof, and Dall Islands. The other islands show this 

feature to a much less marked degree.

An idea of the amount of deepening accomplished, at least locally, 

by the glaciers may perhaps be gained from consideration of the 

following facts: The lowest point of exit for Clarence Strait is 263 

fathoms at the mouth of Dixon Entrance, and throughout much of 

its course the depth is not over 225 fathoms, yet a depth of 347 

fathoms occurs off Lemesurier Point and 369 fathoms in Ernest 

Sound, east of Brownson Island, a difference of about 100 fathoms 

(600 feet). If this difference of 600 feet has been excavated in bedrock it might afford an estimate of the minimum deepening due to 

the ice, as presumably the channel as a whole would likewise have 

been lowered by erosion.
28 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The north arm of Holkham Bay, Tracy Arm (pi. 9, ^L), is perhaps the most impressive fiord in southeastern Alaska. Its entrance is a narrow channel between a long sand bar always studded 

with stranded icebergs on the east side and a rocky coast on the 

west. Through this entrance the strong tide rushes in swirls. The 

arm makes a right-angled turn 9 miles north of its entrance, practically at the western face of the Coast Kange batholith, and then 

for 13 miles runs directly across the granitic rock of the batholith 

and into the very heart of the mountains. The arm is only threequarters of a mile wide, the walls of quartz diorite rise sheer from 

the water's edge to a height of several thousand feet, and the water 

has a depth of 1,000 feet or more. So steep are the walls that for 

a considerable part of their length little or no vegetation has gained 

a foothold. On the contrary, much of the resistant granitic rock 

still retains the polished grooving, fluting, and striation produced 

by the great glacier, 5,500 feet or more thick, which formerly flowed 

through this arm. Hanging valleys are abundant, and many waterfalls plunge from: them down steep declivities to the sea. So deep is the 

water, even along the shore, that anchorage is impossible except at 

a few places where the larger streams have built out small deltas. 

Two great glaciers, each about 20 miles long, enter the head of the 

fiord and discharge bergs into its waters. The valleys through 

which these glaciers flow have all the characters of the fiord except 

that of being submerged, and if the land should subside 2,000 feet 

their lower parts would become simply two branches of the fiord, 

extending 5 miles inland.

Another fiord of most impressive grandeur is Fords Terror. Avhicli 

forms a narrow arm extending north from a point near the center 

of Endicott Arm. Its central part is very narrow, only 1,000 feet 

or so wide for a couple of miles, with walls of quartz diorite rising 

almost sheer from the water's edge to heights of 3,000 to 4,000 feet. 

It is of true canyon or gorge character and yet is an arm of the sea. 

The entrance to the canyon is particularly impressive, for it is a 

rock rim across which tidal currents have cut a narrow passage 20 

to 25 feet deep, through which the tide rushes with great velocity 

except at or about slack water. Potholes several feet deep have 

been drilled in the rock of the rim, between high and low tide levels, 

by the currents. Inside the rock rim are depths of as much as 500 

feet, and outside the rock rim in Endicott Arm, depths of more than 

1,200 feet. At one time Brown Glacier entered the east arm of 

Fords Terror, but it has now retreated so far that it no longer 

reaches tidewater. At the head of the west arm of Fords Terror is 

a beautiful hanging valley, with a stream plunging down a steep 

slope to sea level.
TOPOGRAPHY 29 

CIRQUES

Cirques, which are horseshoe-shaped basins similar to great stadia 

or amphitheaters carved out of solid rock, are found at the heads of 

many of the valleys. These basins are the result of erosion by 

present or former mountain glaciers. On the mainland the higher 

cirques are even now occupied by glaciers, but on the islands there 

are many such basins that are either empty or occupied by lakes. 

(See pi. 5.) Near the coast many of the cirque floors are at altitudes 

of 800 to 1,000 feet, as at the head of Bergs and Porterfield Creeks, 

east of Wrangell, on the mainland; at the head of Jumbo Creek, on 

Prince of Wales Island south of Hetta Inlet; and at the Apex-El Nido 

and Pinta Bay prospects, on Chichagof Island. They may, however, 

be as low as 400 to 500 feet, as on Baker Island.

In the heart of the mountains cirques do not in general occur at 

altitudes as low as on the islands. For instance, in the Salmon River 

district, even where the valleys are now free of ice, little or no 

evidence of cirques is found below an altitude of 4,000 feet. The 

cirques are believed to have been formed to a very considerable extent 

during the lowering of the snow line consequent upon the oncoming 

glacial epoch before the maximum accumulation of snow and ice of 

Pleistocene time. With the advance of the ice cirques that had been 

formed at low levels on the slopes of the major valleys of the mainland were almost or completely destroyed, and renewal of cirque 

formation at low or moderate altitudes was prevented because the 

valleys were filled with ice to considerable but varying depths up to 

relatively recent time. Many of these valleys are still partly filled 

with ice. Cirques at similar altitudes on the islands, however, were 

merely smoothed and modified. The ice filling the fiords and marine 

channels between the islands must have been melted away by the 

relatively warm ocean waters much more quickly than that in the 

valleys of the mainland, thus affording opportunity for individual 

glaciers to form or persist for some time at low levels and continue 

the process of cirque formation.

Knifelike ridges remaining between two cirques cut .back from 

opposite directions into the mountains are common (pi. 6, B) ; lateral riblike ridges are abundant; and in high mountains that stood 

above the surface of the Pleistocene ice, Matterhorn-like peaks, 

carved by several glaciers, each excavating its basin in the same 

ridge from a different direction, are conspicuous features of the 

landscape.

MODERN GLACIERS

Within the Wrangell, Ketchikan, Hyder, and Petersburg districts 

glaciers are restricted to the mainland, but they constitute there one 

of the main features of its scenic grandeur. Thousands of small
30 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

glaciers occupy cirques or cling to the precipitous faces of the mountains. There are many valley glaciers ranging in size from those 

which barely flow out from their sites of accumulation to those 

like Chickamin, Baird, Dawes, Sawyer, and Taku Glaciers, which 

extend 20 to 30 miles. Le Conte Glacier is the southernmost of the 

glaciers that reach the sea. Other tidewater glaciers in this district 

include Dawes Glacier, at the head of Endicott Arm; the two Sawyer 

Glaciers, at the head of Tracy Arm; and Taku Glacier, at the head 

of Taku Inlet. The two arms of Baird Glacier, Dawes Glacier, 

and the Sawyer Glaciers head in what is practically the same snow 

and ice field, with the divides at 5,500 to 6,500 feet. The glacier 

flowing into Knygs Lake, on Stikine River, several other glaciers 

draining toward Stikine River, and Le Conte and Popof Glaciers are 

supposed to head in the same field of ice.

All the glaciers seen, by the writer in the area described show 

evidences of recent retreat within the last score of years, except a 

very few tidal glaciers, which maintain essentially their former position, and Baird Glacier, which was advancing a little in 1922 and 

1923.

Baird Glacier, as shown on the map of the International Boundary Survey, consists of two arms. The southern arm has a maximum length of 30 miles, heading at an altitude of about 6,000 feet 

on the east side of Mount Ratz, in British Columbia, where it forms 

a through glacier with the ice that flows into Stikine River through 

Flood Glacier. The northern arm has a length of about 16 miles. 

Several through valleys filled with ice connect it with Dawes Glacier. 

The altitude of the surface of this ice field ranges from about 4,300 

feet to 6,500 feet. The glacier does not enter tidewater but reaches 

within about a mile of it. An outwash plain about a mile wide 

stretches in front of the ice and is being built forward into the bay. 

(See pi. 11, A.) In 1922 observations showed that between June 25 

and August 24 the front of the ice had advanced in general 10 to 15 

feet, with a slight retreat at some points. The retreat was particularly noticeable on the south side, where the ice had melted back from 

a group of. trees which it had previously overridden, probably in the 

preceding spring. At one place the ice about 12 feet above the 

ground had been thrust forward 5 feet over that below and had produced overthrust folds in the lower ice. The whole lower part of the 

ice was black from incorporated detritus. Only a very small ridge 

of terminal moraine, 15 feet or so high, was present at the edge 

of the ice. The ice in the forward part of the glacier showed many 

deep crevasses. On June 3, 1923, the glacier was slightly in advance of its position in 1922. On the south side spruce trees 7 inches 

in diameter had been overthrown by the advancing ice. (See pi. 

11, B.) On the north side a big snowslide, remnants of which were
U. S. GEOI.Or.ICAL SURVEY BULLETIN- 800 PLATE 9

.1. THACY AKM, A FIOKD IN SOUTHEASTERN ALASKA

View looking east. Three-fifths of a mile wide at sea level, 1,000 to 1,200 feet deep; walls more

than a mile hijrh

B. GLACIER-FACETKD HEADLANDS ALONG FIOHD ON EAST SIDE OF BAKER

ISLAND
. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 10

A. U-SHAPED GLACIATED VALLEY WITH RECENT GORGE IN THE BOTTOM, 

BERGS CREEK, WRANGELL DISTRICT

II. PASS AT HEAD OF GOAT CREEK, HYDER DISTRICT

View looking into drainage basin of middle fork of Chickamin River. Divide at head of a through 

valley from which the glacier has not wholly retreated
U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 11

A. BA1RD GLACIER AND OUTWASH PLAIN, THOMAS BAY

B. TREES OVERTHROWN BY ADVANCE OF 11AIHD GLACIER IN 1923
U. S. GEOLOGICAL SURVEY BULLETIN S(M 1T.ATK 12

,1. ICEBERGS FROM BAIRD GLACIER BURIED IN OUTWASH PLAI-N

B. PIT LAKE BEING FORMED IN OUTWASH PLAIN OF BAIRD GLACIER BY

MELTING OF ICEBERG
U. S. GEOLOGICAL SUKVBY BULLETIN 800 PLATE 13

A. DAVVES GLACIER, ENDICOTT ARM 

View from the south headland of the north arm in June, 1923

B. NORTH DAWES GLACIER, AT THE HEAD OF ENDICOTT ARM 

View showing high terminal moraine and glaciated walls of valley. Appearance in June, 1923
U. S. GEOLOGICAL SURVEY BULLETIN 800 1'I.ATE 14

A. HKMXAINTS OK THHI-;i-: I I'l.IKTED WAVE-CUT TERRACES IN LIMESTONE,

KEKU ISLETS

B. ELEVATED WAVE-CUT BENCH IN LIMESTONE, COHNWALUS PENINSULA,

KUIU ISLAND
TOPOGBAPHY 31

still present, appears to have dammed the river temporarily and resulted in a flood that tore away from the north edge of the glacier 

huge blocks of ice as much as 20 feet in diameter, scattered them 

along all tho way to the sea, and spread over them a deposit of 

coarse gravel, which built up the outwash plain at least 10 feet higher 

than it was in 1922. (See pi. 12, A.) In June may of the blocks of 

ice were partly or completely melted and had formed pit lakes. (See 

pi. 12, B.) The cobbles and boulders of the outwash plain are similar in size to those of the present river channel. Only little patches 

of moraine were present in front of the ice on June 3, 1923. On 

September 29, when the glacier was revisited, the ice front was found 

to be in essentially the same position, but a moraine whose surface 

ranged from sea level to a height of 30 feet (average about 15 feet) 

lay in front of the ice and marked the maximum advance of the 

summer. On the north side the stranding of icebergs in the river 

channel had diverted the river so that it flowed for a quarter of a 

mile along the front of the ice and cut a new channel to the bay. 

The glacier was again visited on July 28, 1924. At that time the 

moraine lay in about the same position as on June 3, 1923; the ice 

front was slightly behind the moraine; the icebergs that had remained buried in the outwash plain on June 3 were all gone, and their 

sites were marked by sand-covered pits in the coarse gravel. Otto 

J. Klotz,47 of the Canadian Boundary Survey, made some very interesting observations on Baird Glacier in 1894. He found that the 

slope at the front was 1 to 3, whereas for 15 miles inland it was only 

1 to 20; that between May 15 and August 11, 1894, the mass of the 

glacier at the ice front was lowered through ablation a little more 

than 2 feet a day; and that its rate of motion was a fraction over a 

foot a day.

The most conspicuous case of glacial retreat seen by the writer on 

the mainland is that of Brown Glacier, at the head of the east arm of 

Fords Terror. As shown on Coast and Geodetic Survey chart 

8200, published in 1920 but based on surveys made several years 

prior to that date, this glacier entered tidewater. In June, 1923, the 

position of the ice front was about 2 miles behind the position marked 

on that chart and about 1,100 yards from high-tide level. An old 

terminal moraine, breached by the river, lies several hundred yards 

from the beach. Beginning at the position formerly occupied by the 

ice front, as indicated by the chart, remnants of lateral moraine may 

be seen along the steep slopes of the east side of the arm and thence 

to its head. The moraine is deeply trenched by the side, streams and 

is overgrown with alder as far as the point where the arm turns eastward. Beyond that point the moraine is of comparatively recent

47 Klotz, O. J., Experimental application of the phototopographical method of surveying 

to the Baird Glacier, Alaska: Jour. Geology, vol. 3, pp. 512-518, 1895.
32 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

origin. Near the present terminus of the ice there is one lateral 

moraine at a height of somewhat more than 200 feet above sea level 

and another at a height of about 80 feet. The latter is still underlain 

by ice. The glacier lies in the valley, with lateral branches, buried 

under moraine extending up the side hills. The whole south arm of 

Brown Glacier is buried under an ablation moraine. The rock of 

the valley walls, recently exposed by the retreat of the glacier, is 

excessively shattered and is sloughing down rapidly.

The front of Dawes Glacier, on Endicott Arm (pi. 13, A), appears 

to be in essentially the same position as that indicated on the coast 

chart, but Eugene Owens, a prospector familiar with the region, 

reports that it has decreased in height considerably, and this statement is confirmed by the zone of barren rock immediately above the 

glacier. The head of the arm was filled with ice in June, 1923, and 

approach could not be made nearer than the east headland of the 

north arm.

North Dawes Glacier does not reach tidewater. A high terminal 

moraine (pi. 13, #), with outwash plain, lies between the ice front 

and the sea.

The Sawyer Glaciers enter the head of Tracy Arm, and both were 

actively discharging ice in August, 1923. South Sawyer Glacier 

heads in the same snow field as Sawyer Glacier and North Dawes 

Glacier. The altitude of the ice in the through valleys is about 

5,500 feet. South Sawyer Glacier has a length of about 22 miles 

and Sawyer Glacier about 20 miles. A field of broken ice was 

jammed in front of South Sawyer Glacier, and it could not be 

approached closer than the island. Ice was falling into the sea from 

Sawyer Glacier about every 15 minutes, but the current was sufficiently strong to keep the arm in front clear of bergs, and a boat 

could be taken practically to the edge of the ice.

Le Conte Glacier is reported to have retreated a considerable 

distance within the last 10 years. In June, 1922, the bay was so 

full of ice that approach could not be made closer than Thunder 

Point.

Great Glacier lies in a valley about 3 miles east of Popof Glacier, 

along the valley of Stikine Kiver. A lake lies between the ice front 

and an old terminal moraine breached by the river that drains the 

glacial valley. A second moraine lies below the first, and an outwash 

plain of sand and gravel occupies the space between the two. It is 

reported that as late as 1870 this glacier bordered the river.

Mendenhall Glacier, north of Juneau, has been described by 

Knopf. 48

«Knopf, Adolph, The Eagle. River region, southeastern Alaska: U. S. Geol. Survey 

Bull. 502, pp. 11-13, 1912.
TOPOGRAPHY 33

In the Hyder district Boundary Glacier, which is shown on the 

International Boundary Survey maps as a tributary of Salmon 

Glacier, now fails to join Salmon Glacier by several hundred feet.

The west front of Chickamin Glacier is reported to have retreated 

4,600 feet between 1902 and 1925, and 600 feet between July, 1923, 

and July, 1925.

As already stated, all the glaciers on the mainland that do not 

reach tidewater, with the single exception of Baird Glacier, so far as 

known, show marked evidences of recent retreat. In addition to 

actual observations on the retreat of the ice evidences of this retreat 

are found in old concentric terminal moraines hundreds or' thousands 

of feet in front of the present ice front, old lateral moraines scores 

to hundreds of feet above the present ice level, and bare rock surfaces 

above the present glacier surfaces upon which vegetation has not yet 

gained a foothold.

MARINE EROSION

The characters of the coast line are influenced to a marked degree 

by the nature and structure of the rocks, both in the results of erosion 

by glaciers, rivers, and weathering and in erosion by the ocean waters 

themselves. The granitoid rock of the Coast Range is massive and 

resistant, and in the fiords which cross it deep water occurs right up 

to the shore line. As a result, little or no erosion by the sea has taken 

place in this rock; indeed, at many places not even the glacial polish 

or striations have yet been worn off. But here and there, where the 

granitic rock occurs in small outlying stocks and is much jointed, 

reentrants, coves, sea stacks, and terraces have been carved out by the 

sea; examples of these are found at the north headland of the entrance to Hobart Bay and in the first cove to the east.

The gneiss, as a result of recrystallization and injection and permeation by aplitic and pegmatitic solutions, has acquired an essentially uniform character and therefore resists erosion by the sea in 

much the same way as the granitic rocks.

The less uniform schist, phyllite, and graywacke have a tendency 

to develop offshore reefs whose linear extension is parallel to the 

foliation or bedding. The tendency to develop reefs, however, is 

most pronounced in the slate and phyllite. These two types of rock 

are structurally and physically weak, so that erosion by the sea has 

in many places been extensive, resulting in a multitude of dangerous 

low-lying reefs along the coast and uplifted wave-cut terraces inland. 

Rocky Bay, at the south end of the northwest half of Etolin Island, 

and the islands and reefs in Seymour Canal and Pybus Bay, Admiralty Island, are typical examples of erosion in the Jurassic and 

Cretaceous slate and graywacke. Ordovician and Silurian graywackes, with intercalated slates, likewise give rise to a coast charac-
'34 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

terized by dangerous reefs. The beds of slate weather away, and the 

more resistant beds of graywacke stand up as long, narrow reefs. 

Most of the borders of Kuiu Island, much of the northwest coast of 

Prince of Wales Island, and Kashevarof Passage, off Lake Bay, 

Prince of Wales Island, show this development.

Where the slates, phyllites, and graywackes are intruded by Tertiary basalt dikes the dikes have weathered out in relief at many 

places, forming narrow linear reefs. They are particularly conspicuous in the vicinity of the Barrier Islands, which lie off the northwest coast of Prince of Wales Island, and near the south end of 

Brownson Island and Windy Bay, Etolin Island.

Bad as the slate, phyllite, and graywacke are as reef formers, however, the Tertiary volcanic rocks are uniformly worse. Without 

exception, the 'coast line developed from them is bordered by a wide 

fringe of jagged reefs. This is the result of the irregular jointed 

character of the lava. Many of the rhyolites have a platy structure 

that renders them an easy prey to the sea, but the basalts are the 

rocks out of which the more peculiarly treacherous reefs have been 

carved. Intricate passageways and coves have been cut in the lavas 

by the sea working along fracture zones. Along the entire south end 

of Kupreanof Island, for 2 miles offshore, there is a multitude of 

reefs in part above water and in part submerged. Keku Straits, 

from 1 to 2 miles wide, between Kuiu and Kupreanof Islands, is a 

maze of basaltic islands and reefs; the channel is tortuous and is 

passable only for small boats.

Some of the older lavas likewise tend to develop reefs, as exemplified in the Silurian andesitic volcanic rocks in Labouchere Bay and 

just east of Lake Bay, in Prince of Wales Island.

Along the islands off the west coast of Prince of Wales Island the 

sandstone and conglomerate show everywhere a most pronounced 

development of reefs, as along San Christoval Channel, Naukati Bay, 

Tuxekan Passage, the bay northeast of Point Ildefonso, Nossuk Bay, 

Tonowek Bay, and the south side of Marble Island.

The limestone, as a result of solution, has a finely pitted to coarse 

pockety surface, with many irregular needlelike or knifelike projections. Potholes are very common. So characteristic is the weathered surface of the limestone that it may be distinguished as such 

from considerable distances offshore. Marine erosion of massive 

limestone, such as the Silurian, takes place along joints, with the 

resultant development of chasms and long, straight, narrow channels. 

A peninsula may thus be dismembered into a string of islands, such 

as those off the north headland of Cone Bay, Heceta Island, or south 

of Cosmos Pass, Kosciusko Island. Nearly vertical bluffs, with deep 

water at the foot, are very common in the massive limestone. This 

is exemplified on the charts by such names as Bluff Island, at the
TOPOGEAPHY 35

mouth of Shipley Bay; White Cliff, on the southwest end of Heceta 

Island; and White Cliff Island, in Davidson Inlet. In the thinbedded limestone erosion proceeds parallel to the bedding.

On the outer coasts of the islands, where they are exposed to the 

full force of the waves, a most conspicuous feature is the number of 

long, deep, narrow, gorgelike chasms, which have been driven into 

the cliffs, and are still being cut in, by the waves working along two 

or more closely parallel joints.

SEA-CUT BENCHES AND PLATFORMS

Both on the mainland and on the islands rock benches or remnants 

of rock benches are common, except in the massive quartz diorite and 

injection gneisses of the mainland, where they are rarely found 

because of the recent glaciation and more resistant character of 

these rocks and because along the fiords which penetrate it the water 

is deep right up to the shore. The most pronounced and best 

developed benches are found in the limestone, slate, phyllite, and 

Tertiary volcanic rocks.

At low tide, broad rock benches with a very gentle seaward slope 

are exposed at many localities. These benches have been cut largely 

by wave erosion and are of recent origin. (See pi. 21.)

Benches that are conspicuous because they are very obvious from 

a boat lie within a zone several feet above and below hjgh-tide 

mark.40 Benches at this height appear to be developed locally on 

all the islands and on the mainland. (See pis. 14, and 15, B.) 

Very good examples may be seen along the south side of Taku Inlet; 

the south side of Holkham Bay; the southeast side of the Cornwallis 

Peninsula, on Kuiu Island; Totem Bay, on Kupreanof Island; Rocky 

Bay, Etolin Island; and near Dolomi.

A number of explanations have been advanced for coastal benches 

which occur at about high-tide level. They have been ascribed to 

protection offered by seaweed below high-tide mark; 50 to control 

by approximately horizontal structural features 51 such as bedding 

or joints; to recession of cliffs due to atmospheric weathering down 

to a ground-water level, which has a direct relation to high-tide 

level; 52 to wear by storm waves at and near the.time of high tide; 

to the interference of tide rips with storm waves except at slack tide; r's 

and to uplift.

40 Buddington, A. P., Abandoned marine benches in southeastern Alaska: Am. Jour. 

Sci., 5th ser., vol. 13, pp. 45-52, 1927.

80 Dawson, G. M., Report on the Queen Charlotte Islands: Canada Geol. Survey Kept, 

of Progress, p. 96, 1878.

51 Ferrar, H. T., and others, The geology of the Whangarei-Bay of Islands subdivisions : 

New Zealand Geol. Survey Bull. 27, new ser., 1925.

62 Bartruin, J. A., "Abnormal " shore platforms: Jour. Geology, pp. 793-807, 1926.

63 McLellan, R. D., The geology of the San Juan Islands: Washington Univ. Pub., vol. 

2, p. 24, 1927.
36 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Except for a few benches obviously due to structural control or 

to a coincidence of a glaciated level topographic surface with the 

present high-tide level, all the benches at about the level of high 

tide are believed by the writer to be due primarily to erosion by the 

sea and, where the tidal range is greater than 10 feet, to a relative 

uplift by an amount somewhere between 10 and 16 feet. The mean 

tidal range in southeastern Alaska, except in the vicinity of the outer 

coast, is 11 to 14 feet. At a level just above high tide there are 

many broad, flat rock benches, some of which bear numerous sea 

stacks. Though storm waves at high tide will completely cover such 

benches, it does not seem probable that they could have been cut 

under the present relations of land and sea. Other benches occur 

just below high-tide level or just below the upper limit of the rockweed growth, and some of these benches also bear sea-cut arches or 

sea stacks. These benches are interpreted as resulting from the 

partial erosion of relatively uplifted benches that formerly stood 

at slightly higher levels. The coincidence of many benches with the 

level of the approximate upper range of the rockweed is explained 

by the greatly retarded rate of erosion due .to the protection 

afforded by this rank growth of vegetation. The benches several feet 

above or below high-tide level, as a whole, are therefore believed 

to be due to erosion and uplift, followed by erosion which has lowered them in varying amounts. It seems highly probable that some 

former benches of similar origin have been entirely destroyed by 

subsequent erosion. Chapin suggests that as the benches occur only 

locally, it is probable that the uplift was of a differential character 

and that parts of the region are sinking below sea level and others 

are rising, owing to the warping nature of the movement. Buddington found no evidence in the Juneau and Wrangell districts to substantiate this idea, but the data are not sufficiently accurate to be 

decisive one way or the other.

Benches considerably above low-tide level are present also on 

the outer coast, where the mean tidal range is about 8 feet. These 

have not been carefully studied, and their origin is not known.

Extensive lowlands are developed locally on the softer rocks, such 

as slate, phyllite, and limestone. The groups of islands, such as 

those of Keku and Zimovia Straits, Seymour Canal, Kashevarof 

Passage, Saginaw and Security Bays, on Kuiu Island, Kocky Bay, 

on Etolin Island, and the Keku group, all have relatively flat surfaces at low altitudes. The extreme south end of Etolin Island, the 

south end of its northwestern part, and the north shore of Kupreanof 

Island all show low-lying land near the coast. The part of Gravina 

Island south of Dall Head, the bold promontory that marks the 

south end of the highlands of the island, is a flat that stands a few
TOPOGEAPHY 37

feet above sea level at the coast and slopes gently upward toward the 

highlands that rise abruptly from the plain. Similar features are 

found on the south end of Annette Island. (See pi. 15, A.) Too 

little is known of these lowlands to make any specific statement as 

to their character and altitude; but they appear to rise to altitudes 

of several hundred feet and locally have wide, relatively flat areas at 

a height of 160 to 200 feet. The low plains here referred to are in 

part coincident with those considered by Gilbert 54 to be low partial 

peneplains. It seems probable that they may be in lar'ge part the 

product of subaerial erosion and glaciation, subsequently modified 

by marine erosioJ^ between successive relative uplifts. That recent 

uplift to the amount of 600 feet has taken place in this region is indicated by deposits of postglacial clay, sand, and gravel containing 

a marine fauna, which have been found up to this height.

KARST TOPOGRAPHY

A typical karst topography has been developed on some of the 

large belts of uniform limestone. A very good example is the belt 

of sink holes in the form of crevasses, wells, pits, and deep longitudinal depressions, interspersed with narrow ridges and pinnacles, 

which occurs within the band of limestone extending from Grace 

Harbor to Waterfall Bay, on Dall Island. Practically the whole 

drainage is underground. So difficult to traverse is this belt that 

even deer trails are absent.

RELATION OF TOPOGRAPHY TO STRUCTURE

The structural factor that has most strongly influenced the topographic development of this region is the prevalent northwest strike 

of the formations. This is reflected in the general northwesterly 

trend of the major physiographic features as well as of many of the 

minor features.

The relatively flat-lying Tertiary volcanic rocks, where they occupy 

large areas, have tended to result in a plateau type of topography, 

but one which is reaching a mature stage of dissection. Buttelike 

forms are, however, developed here and there, as well as cuesta scarps 

and dip slopes. The outlying masses of granitoid igneou's rock intrusive into the sediments form resistant bosses and usually constitute 

a group of high mountain peaks.

The Tertiary sandstone, conglomerate, and volcanic rocks on the 

southwest side of Port Camden, with their low dips of only about 

8° SE., have been so eroded as to develop a marked set of steep cuesta 

 scarps and gentle dip slopes. .

"Gilbert, G. K., Glaciers and glaciatlon.: Alaska, vol. 3, p. 131, Harrlman Alaska Expedition, 1904. .
38 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Most of the bays in a belt comprising the west coast of Prince of 

Wales Island and the islands adjacent thereto, the area adjoining 

Keku Straits, and the south end of Admiralty Island in the vicinity 

of Pybus Bay have been eroded along synclinal troughs, and the 

youngest formations appear on the islands in the bays.

A very striking example of a depression eroded out of the trough 

of a syncline otf Silurian limestone is shown by Davidson Inlet and 

Sea Otter Sound. Taken in a rough general way, the west half of 

Kosciusko Island, the line of islands running south to Whale Head, 

Heceta Island, Tuxekan Island, Orr Island, and Marble Island, which 

are composed predominantly of Silurian limestone, together form 

the rim of the basin. The basin is almost separated into two parts 

by Orr, Marble, Hoot, Owl, and Eagle Islands, which together form 

a minor anticline or dome within the major syncline. Along the 

northwest-southeast axis of the basin, on the east side, there are 

several outcrops of upper members of the Silurian, comprising sandstone and conglomerate, as in the bay at the south end of Tuxekan 

Passage, along Karheen Passage, on the north .side otf the east end 

of Heceta Island, and at the south end of Orr and Marble Islands. 

Heceta and Kosciusko Islands are essentially cuestas, with steep 

scarps along the south and north sides, respectively, as on Bald 

Mountain and Mount Francis, and gentle though irregularly eroded 

dip slopes into and beneath Sea Otter Sound and Davidson Inlet. 

The two landmarks Mount Francis and Bald Mountain are outcrops 

of the same formation at opposite borders of the basin.

Other examples of lowlands or valleys which have been worn out 

of the troughs of synclines or synclinoria are the lower half of 

Pybus Bay, on Admiralty Island, the bay at the north end of Keku 

Straits, Shakan Bay and the lowland of the Barrier Islands, at the 

northwest end ctf Prince of Wales Island, Edna Bay, on Kosciusko 

Island, Tokeen Bay, the bay at the south end of Marble Island and 

the southwest end of Orr Islands, the south end of El Capitan 

Passage, Naukati Bay and the wide expansion of Tuxekan Passage, 

the bay at the south end of Tuxekan Passage, Karheen Passage, 

Nossuk Bay, San Christoval Channel, St. Nicholas Channel, Portillo Channel, Klawak Inlet and the lowland to the west and north 

ends of &an Alberto Bay, Bucareli Bay, the basin at the head of 

Port Refugio, on Suemez Island, Trocadero Bay, Soda Bay, Cordova Bay, and Tlevak Straits.

Some channels and bays originated as valleys eroded along the 

arches of anticlines. Frederick Sound appears to have been eroded 

along the broad dome of an anticlinal arch in Tertiary volcanic rocks. 

Other examples are the channels lying east of the line of islands 

southwest of Kake, on Kupreanof Island, Kashevarof Passage, Port 

Protection, Labouchere Bay, and Warmchuck Inlet, on Heceta Island.
U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 15

A. COASTAL PLAIN ALONG SOUTHWESTERN COAST Ob' ANNETTE ISLAND

S. ELEVATED WAVE-CUT BENCH OPPOSITE DOLOMI, PRINCE OF WALES

ISLAND
U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 16

A. CLOSELY FOLDED LIMESTONE OF THE WALES GROUP, BALL ISLAM)

£. GREENSTONE SCHIST OF THE WALES GROUP, PORT JOHNSON, PRINCE OF

WALES ISLAND

' View showing recumbent folds
THE BOOKS 39

Evidences of marked and profound faulting are common throughout the area west of the mainland, but the writer saw no place where 

faulting had had a direct influence on the present topography. The 

indirect results from faulting, however, are very evident in many 

places. The weaker rock of shear and breccia zones is more easily 

eroded, and faulting brings into contact rocks of unequal resistance. 

The straight deep marine channel formed by Chatham Strait and 

Lynn Canal, which extends for 250 miles and forms one of the most 

conspicuous features of southeastern Alaska, is thought to have been 

eroded along a fault zone. A good discussion of this feature is 

given by Martin and Williams.55

Other places where the results of faulting were especially noted 

are the east side of San Christoval Channel between San Fernando 

Island and the west coast of Prince of Wales Island; the east side 

of Bocas de Finas, on the southwest side of Heceta Island; the east 

side of the lower half of Orr Island; the west face of the Mount 

Calder limestone range, on the northwest end of Prince of Wales 

Island; and the south end of Zarembo Island.

Many of the features of the topography have been controlled by 

the presence of great fractures and intersecting fracture systems 

along which there has been only slight movement. The location of 

many erosion features such as river valleys and fiords, with their 

numerous abrupt changes of direction, is due primarily to such planes 

of weakness. Additional data would be needed, however, for an adequate discussion of this subject.

THE ROCKS

STBATIGRAPHIC COLUMN 

By THEODORE CHAPIN and A. F. BTTDDINGTON

The stratigraphic column in southeastern Alaska comprises a very 

thick series'of formations, which includes the Wales group (metamorphic rocks) and beds of Lower and Middle Ordovician, Silurian, 

Middle and Upper Devonian, Mississippian, Pennsylvanian (?), 

Permian, Upper Triassic, Jurassic, Lower Cretaceous (?), Eocene, 

Pliocene, and Quaternary, with a possible total maximum thickness 

of about 50,000 feet. The stratigraphic sequence is shown in the 

accompanying table. The general distribution of the systems and 

formations is shown on Plates 1 and 2. The Wales group comprises 

a series of metamorphosed beds whose age and relation to fossil 

horizons are not definitely known. They were classified as pre-SiluM Martin, Lawrence, and Williams, F. E., An ice-eroded fiord; the mode of origin of 

Lynn Canal, Alaska: Geog. Review, vol. 14, pp. 576-596, 1924.

6137 29 4
40 GEOLOGY AND MINEEAL DEPOSITS, SOUTHEASTERN" ALASKA

rian by Chapin, before the presence of Ordovician beds in the Ketchikan district was known. Their relation to the Ordovician beds has 

not yet been ascertained. The group as mapped may be in part preOrdovician and it may in part include Silurian beds or even some 

Devonian, owing to a failure to recognize and properly separate the 

Devonian. Other metamorphic rocks, mapped as the "WrangellKevillagigedo belt of metamorphic rocks," probably range in age 

from Ordovician to Jurassic or later.

Strati graphic sequence in southeastern Alaska 

.[By A. F. Buddington and Theodore Chapin]

System

laternary.

O1

!>.

.2

|H

EH

Series

Pliocene (?).

Eocene.

Character

Chiefly sand and gravel deposited 

by streams.

Basaltic lava and tuff.

Glacial drift .and marine bench 

and terrace deposits of interstratified gravel, sand, and clay.

Conglomerate, sandstone, and 

shale, with coal seams.

Basaltic and obsidian lava.

Basaltic and andesitic lava with 

minor amounts of interbedded 

breccia and conglomerate, associated with thin coal seams, at 

Murder Cove, Admiralty Island. Tentatively assigned' to 

Eocene.

Rhyolitic and andesitic volcanic 

rocks and conglomerate.

Coarse sandstone with basal and 

intercalated beds of conglomerate. Associated with thin coal 

seams in Port Camden, Kuiu 

Island; Hamilton Bay, Kupreanof Island; Kootznahoo Inlet, 

Admiralty Island; and Coal 

Bay, Prince of Wales Island.

 Tin f>rm f nrm i f: v 

Thickness 

(feet)

1,000±

2, 500±

1, 500±

1, 350±

Distribution

Mount Edgecombe, Kruzof Island; Canon Creek and Blue 

River, tributary to Unuk 

River; Revillagigedo Island; 

mainland, Ketchikan district.

Douglas Island, Funter Bay, 

Port Snettisham, Wrangell, 

Oravina Island, Salmon River 

at head of Portland Canal, 

west coast Prince of Wales 

Island, Stikine River.

Lituya Bay.

Suemez Island.

Kupreanof, Kuiu, and Admiralty Islands.

Gravina, Zarembo, Kupreanof, 

and Kuiu Islands.

Coal Bay, Prince of Wales Island; Union Bay, Cleveland 

Peninsula; Kupreanof, Kuiu, 

and Admiralty Islands.
THE BOOKS 

Stratigraiphio sequence m southeastern Alaska Continued

41

System

Cretaceous(?).

Cretaceous.

Jurassic 01

_O

£

Dnifefous.

-I

o

Series

Lower Cretaceous (?).

Upper Triassic.

Pennsylvanian (?).

Mississippian.

Character

Slate and graywacke, with a few 

chert nodules and thin layers 

of impure limestone; locally 

with intercalated beds of conglomerate.

Schistose greenstone; porphyry 

breccia, predominantly hornblende, rarely augite, with intercalated beds of tuff, lava 

flows, black slate, and graywacke.

Graywacke, dark-gray slate, and 

conglomerate with sparse intercalated beds of tuff and thin 

layers of impure limestone. 

May be in part the same as the 

Lower Cretaceous (?) slate and 

graywacke.

Andesitic rocks, including breccia 

with'limestone matrix and lava 

flows (in part with pillow structure), locally inter bedded with 

slate and other sediments.

Conglomerate, sandstone, and 

limestone; in the Ketchikan 

district includes considerable 

black slate in upper part.

Thick-bedded limestone; with 

common to abundant intercalated layers of white chert.

Conglomerate, limestone, sandstone, andesitic and basaltic 

lava, tuff, and, locally, rhyolitic volcanic rocks.

White massive limestone.

Interbedded coarsely crystalline 

limestone and black chert, overlain by interlayered dense gray 

quartzite and cherty limestone; 

sparse conglomerate.

Thickness 

(feet)

1, 400+

1,600±

1,000

3, 000±

100+

1,000

Distribution

Pybus and Herring Bays, Admiralty Island; northern part 

of Kupreanof Island; Rocky 

Bay, Etolin Island; Oravina 

Island; and northwest part of 

Annette Island.

East side of Lynn Canal; Douglas Island; Glass Peninsula, 

Admiralty Island; Fanshaw 

Peninsula; Vank Island; Anita 

Bay, Etolin Island; Onslow 

Island; Cleveland Peninsula; 

Gravina and Annette Islands; 

Cape Fox.

Point Young, Seymour Canal, 

Admiralty Island; Fanshaw 

Peninsula; north end Kupreanof Island; west coast Chichagof Island; Salmon River dis 

trict.

Northwest end of Kupreano, 

Island; east side of Hamilton 

Bay; Hound Island; northeast side of Kuiu Island.

Gravina, Revillagigedo, and 

Annette Islands; Keku Islets; 

northwest end of Kupreanof 

Island; Pybus Bay, Admiralty 

Island; Screen Islands.

Saginaw Bay, north side of Kuiu 

Island; Keku Islets; Pybus 

and Gambler Bays, Admiralty 

Island; eastern end of Suemez 

Island; Taku Harbor.

Saginaw Bay, north side Kuiu 

Island; Keku Islets; Snettisham Peninsula, 1 mainland; 

Windfall Harbor, Admiralty 

Island.

Soda Bay, west coast of Prince of 

Wales Island.

Suemez, Madre de Dios, and 

Robber Islands; Soda Bay, 

Prince of Wales Island; Klawak; Saginaw Bay, Kuiu 

Island; lyoukeen Peninsula, 

Freshwater Bay, and Port 

Frederick, Chichagof Island.
42 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA 

Stratiffraphio sequence m southeastern Alaska Continued

System

Devonian

Silurian. - 

Series

Upper Devonian.

Middle Devonian.

Character

Basalt, andesite (in part pillow 

lava), tuff, limestone, sandstone, slate, and conglomerate.

Limestone.

Andesitic green to gray tuff GOcally cherty) and graywacke, 

with locally, fine conglomeratic 

layers, intercalated limestone, 

and a minor amount of andesitic lava and breccia. 

Andesitic lava (in part pillow 

lava), breccia, tuff, conglomerate, and, locally, rhyolitic lava. 

Interbedded limestone, slate,

chert, andesitic lava, breccia, 

tuff, and, locally, conglomerate.

Conglomerate and graywacke-like 

sandstone, with, locally, interbedded limestone.

Green-gray graywacke with 

sparse conglomerate beds. Interbedded red, green-gray, and 

gray graywacke-like sandstone 

with a small amount of shale.'

Green-gray shale with intercalated red beds and thin-layered 

fine-grained gray sandstone, 

shale, and dense limestone.

Predominantly thick-bedded 

dense limestone; intercalated 

with thick beds of coarse conglomerate, thin-layered limestone, nodular and shaly argillaceous limestone, and sandstone. Limestone, 3,000 ± feet; 

conglomerate, 1,500 ± feet.

Andesite (in part pillow lava) and 

andesite porphyry lava; conglomerate; with some associated 

graywacke, tuff, breccia, and 

limestone.

Indurated graywacke with associated black slate and sparse 

conglomerate and limy sediments.

-TTnnmifnrmit:v (f\ .

Thickness 

(feet)

1,000

600+

2,400+ 

2,000

2,000

5, 000+

500+

4,500±

3, 000±

Distribution

Freshwater Bay, Chichagof 

Island; Suemez and San Juan 

Bautista Islands; northern part 

of Kupreanof Island.

Long and Round Islands, Kasaan 

Bay; San Alberto, Clam, Coronados, and Fish Egg Islands; 

north end of Kupreanof Island.

Northwest side of Kupreanof 

Island; islands in Saginaw Bay, 

Kuiu Island; Prince of Wales 

Island.

Prince of Wales, Dall, Sukkwan 

Baker, Suemez, and Noyes 

Islands. 

Duncan Canal and northwest,

end Kupreanof Island; north 

side of Noyes Island; Baker 

Island. 

San Christoval Channel, head of 

San Alberto Bay, north side 

San Fernando and Lulu 

Islands.

North half Prince of Wales Island, Tuxekan Passage, Naukati Bay, east end Heceta 

Island.

West of Edna Bay, south side of 

Kosciusko Island.

Dall Island; north part of Prince 

of Wales Island; Kosciusko, 

Heceta, and Tuxekan Islands; 

southwest side of Saginaw Bay 

and locally on east side of Kuiu 

Island; Kashevarof Islands, 

Tenakee Inlet and Freshwater 

Bay, Chichagof Island; Glacier 

Bay.

Kashevarof Islands; Prince of 

Wales Island; El Capitan Passage; Kuiu and Sumner Islands.

San Fernando, Lulu, Dall, and 

Noyes Islands; Klakas Inlet, 

Prince of Wales Island; Glacier 

Bay(?).
GENERAL LITHOLOGY 

Stra,tigra\pliio sequence in southeastern Alaska* Continued

43

System

Ordovician.

Probably pre-Ordovician Devonian t 

Series

Middle Ordovician.

Lower Ordovician.

Wales group 

(metamorphic rocks).

Character

Indurated graywacke with associated black slate and sparse 

conglomerate and limy beds; 

locally andesitic pillow-lava and 

volcanic rocks.

Thin-layered black chert with 

black graptolitic slate partings, 

graywacke, and, locally, andesitic volcanic rocks.

Greenstone schist with intercalated or interbedded limestone. 

Limestone. 

Schist with beds of limestone and 

slate. 

Schist.

Thickness 

(feet)

Distribution

Thorne, Stevenson, Lulu, Heceta, 

and Kuiu Islands; El Capitan 

Passage and Klawak Salt Lake.

Kuiu, Lulu, and San Fernando 

Islands; mouth of Klawak Salt 

Lake; head of Van Sants Cove, 

Kosciusko Island.

Long Island and 'southern part 

of Dall and Prince of Wales 

Islands.

GENEBAL LITHOLOGY

Volcanic rocks. Volcanic rocks, predominantly andesite or basalt, 

form a considerable part of the Wales group and of the Lower and 

Middle Ordovician, Middle and Upper Devonian, lower Permian, 

Upper Triassic, Jurassic, Lower Cretaceous (?), Tertiary, and Quaternary divisions. Rhyolite is present but very sparse in the Silurian, 

Middle Devonian, and lower Permian but is an important member 

of the Eocene and Pliocene (?) volcanic rocks and occurs within the 

Wales group.

Many of the volcanic rocks of the Paleozoic and Mesozoic eras 

are closely folded and metamorphosed and constitute greenstone 

schist, whereas those of the Tertiary are relatively flat-lying and 

unaltered. Pillow lava is abundant in the Lower and Middle Ordovician, Silurian, Middle and Upper Devonian, lower Permian, and 

Upper Triassic formations, where it is invariably associated with 

marine fossils. No pillow lava whatever was found in the Tertiary volcanic flows, which are associated with beds carrying fossil 

land plants. These facts suggest that submarine conditions are distinctly more favorable than land conditions to the development of 

pillow structure in basic lava.

G-raywacke. Aside from the volcanic rocks, sheared graywacke 

and slate form the bulk of the rocks classified as Jurassic or Cretaceous. Highly indurated graywacke, with a little slate, forms most 

of the Ordovician and a considerable part of the Silurian formations. 

Massive tuffaceous graywacke of great thickness also forms a large 

part of the Devonian formations. Indeed, the vast quantity of
44 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

greenish graywacke Avith associated slate, possibly over a third of the 

total section, is the most striking and peculiar feature of the entire 

stratigraphic sequence of southeastern Alaska. Graywacke is found 

in every system of the Paleozoic and Mesozoic and in many places 

presents a problem of correlation difficult or impossible of solution 

without extremely careful detailed work. The abundance of graywacke is doubtless the result of the widespread and active volcanism 

throughout most of the geologic time interval represented by formations in southeastern Alaska.

Sandstone. Relatively clean quartzose sandstone is practically 

absent. Red beds of any description are likewise very sparse and 

restricted to local areas, such as the west coast of Prince of Wales 

Island in the vicinity of Tuxekan, Karheen, and El Capitan Passages, 

where beds of graywacke-like red and green sandstone are prominent. 

.Some typical consolidated but unmetamorphosed sandstones are 

found in the Eocene section.

Limestone. Limestone forms a very considerable part of the 

Paleozoic systems with the exception of the Ordovician, but it is 

unimportant in the Mesozoic except for the Upper Triassic, and is 

absent from the Cenozoic. The most widespread, most uniform, and 

thickest formation of limestone is of upper Silurian age, but thick 

uniform beds are found also in the Middle Devonian. Cherty limestone of considerable thickness forms a part of the Carboniferous 

system. The limestone is almost wholly calcite limestone, and that 

of the upper Silurian is for the most part a very high calcite 

limestone.

Where the limestone is intruded by stocks of granitoid igneous 

rock it is locally metamorphosed to marble. On the mainland and 

in the Glacier Bay region most of the limestone has been coarsely 

recrystallized as a result of contact metamorphism on a regional 

scale due to the vast volume of the intrusive rock.

Conglomerate. Beds of coarse cobble and boulder conglomerate 

form conspicuous and thick members of the Silurian formation.?. 

They are prominent also in the lower Permian and Tertiary formations and locally in the Jurassic or Cretaceous. Pebble and coarse 

conglomerate beds are also prominent locally at the base of the 

Middle Devonian section. A peculiar and characteristic conglomerate composed of andesite and limestone pebbles and cobbles in a 

greenish tuffaceous matrix is very common in the Silurian and Middle Devonian formations associated with the volcanic rocks. Conglomerate composed chiefly of lava boulders forms very thick beds 

in the Eocene formations.

Intraformational conglomerate. A characteristic feature of the 

Paleozoic systems in southeastern Alaska is the abundance of coarse 

waterworn intraformational limestone conglomerate. Beds occur
WALES GROUP 45

in the Silurian, Devonian, lower division of the Permian, and Triassic, in all of which the cobbles of limestone were found to carry the 

same fauna as the formation to which the conglomerate belongs. 

Limestone conglomerate of intraformational origin occurs in beds 100 

feet or more in thickness in the Silurian. The prevalence of intraformational conglomerate is probably genetically connected with 

movements accompanying local volcanic activity during these periods.

Sla&e. Black slate and argillite are widely distributed and occur 

interbedded or intercalated in practically all the Mesozoic and 

Paleozoic formations. Black slate is particularly prominent in the 

Jurassic or Cretaceous beds. Earely shale is present.

Chert. Thin-layered black chert several hundred feet thick 

occurs in the Ordovician and Mississippian formations. Thick-bedded chert and cherty tuff occur in the Middle Devonian, intercalated 

thin black chert layers are common in the Mississippian limestone^ 

and layers and beds of white chert are common in the upper Permian 

limestones. Chert which has been described by some geologists as 

quartzite is locally prominent in association with the lower division 

of the Permian beds. Small cherty nodules are found in the Lower 

Cretaceous (?) slate.

Phyllite, schist, and .gneiss. Two types of metamorphism prevail throughout southeastern Alaska. One has resulted mainly in the 

formation of a slaty or schistose foliation in the rocks, without 

marked coarse recrystallization or the formation of high-temperature 

minerals. It was caused in large part by intense nonuniform 

stresses and occurred chiefly in the beds away from large bodies of 

the Mesozoic intrusive rocks. The other type affected particularly 

a wide belt adjoining the Coast Range batholith. It resulted in 

the formation of phyllite, schist, and gneiss, with marked recrystallization and change in character of the constituent minerals, caused 

by the higher temperature and permeating hot solutions attendant 

upon the emplacement and solidification of the vast volume of 

magma, in addition to nonuniform stresses as intense as those effective in the other type. The contrast between the rocks produced by 

the two types may be illustrated by the slate and schistose greenstone that are common in the Alexander Archipelago, as compared 

with the phyllite and the biotite, hornblende, and garnetiferous 

schists in the Wrangell-Revillagigedo belt of rocks of the mainland.

WALES GBOTJP 

By THEODORE CHAPIN and A. F. BUDDINGTON

The Wales group comprises a series of metamorphic rocks, including crystalline schist, quartzitic and slaty beds, limestone, and greenstone. The greenstone is predominantly schistose (pi. 16, Z?), and
46 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

much of the limestone is crumpled (pi. 16, A), cleaved, and sheared ' 

or metamorphosed to marble. On Prince of Wales Island the Wales 

rocks occupy a semicircular area extending across the island from 

Dolomi to Sulzer and along the east shore of Hetta Inlet to Lime 

Point. The other main area covers all of Long Island, in Cordova 

Bay, and the southern part of Dall Island. The str,atigraphic 

horizons to which the divisions of the group should be assigned are 

uncertain, owing to lack of fossils and difficulty in recognizing the 

formations because of metamorphism, and formations of more than 

one period are very probably included. Their age is probably 

Silurian and older, but perhaps some Devonian is included. The 

structurally lowest schist members can not be correlated certainly on 

lithologic grounds with any beds of the known Ordovician formations, and they may possibly be of pre-Ordovician age.

The schists include quartz-mica schist and related types derived 

from sedimentary rocks, greenstone schist including epidote and 

chlorite schists derived from basic lava flows and tuff, and some lightcolored schist derived from altered rhyolitic volcanic rocks. Both 

tuffaceous rocks and flows are interbedded with limestone which 

passes into the greenstone schist by an increasing amount of intercalated igneous material. Slate and other argillaceous rocks are 

interbedded with mica schist and greenstone. The limestones are 

white crystalline rocks and contain many beds of workable marble. 

Where they are interbedded with igneous rocks a great variety of 

colored and variegated marbles have been formed.

The base of the Wales group is nowhere evident. The lowest part 

exposed is a thick series of crystalline schist, predominantly of sedimentary origin but containing beds of limestone and altered basic 

and rhyolitic volcanic rocks. In the upper part of the schist series 

limestone is more abundant and ranges in thickness from less than 

100 feet to more than 1,000 feet. There is at least one thick massive 

bed of pure limestone several hundred feet thick and a great many 

smaller ones. In its upper part the limestone contains a great deal of 

intercalated greenstone tuff into which the limestone member seems 

to grade. The general sequence is schist, schist and limestone, limestone, greenstone and limestone, in a gradationally conformable 

series in which the limestone intergrades with both schist and greenstone. The greenstone schist associated with the limestone is largely 

altered to secondary quartz, epidote, chlorite, hornblende, calcite, 

mica, zoisite, talc, serpentinous material, and other secondary 

minerals.

The schists were originally sandstone, shale, lava flows, and tuff. 

They are interbedded with the limestone and were evidently laid 

down on the sea bottom. The greenstone probably represents sub-
WALES GBOUP 47

marine lava flows and volcanic ejectments collected in the sea. Even 

the coarser tuff and breccia are well stratified and apparently waterlaid. The alteration of these rocks is regarded as largely regional 

metamorphism produced by tectonic forces, in combination with 

magmatic intrusions. The intrusive rocks are only partly exposed 

at the present surface.

In 1925 Buddington spent 18 days in mapping the formations along 

the west coast of Dall Island. His observations follow. In the 

southern half of the island the oldest rocks are almost exclusively 

schist, which forms a belt through the center of the island from a 

point midway between Port Bazan and American Bay southeastward 

through the Essowah Lakes and the head of Security Cove to and 

including the Cape Muzon peninsula and McLeod Bay. The schist 

is light colored and includes very little if any limestone. A belt of 

light-colored feldspathic quartz schist forms the island and adjacent 

headland on the north side of McLeod Bay. It can be traced northward as far as the mountains at the head of Port Bazan and crops 

out also along the shore at the head of Security Cove. This schist 

can be identified in part as highly sheared, plicated, and folded rhyolite porphyry, and it is probable that a considerable part of this 

belt consists of metamorphosed rhyolitic volcanic rocks. Biotite 

metacrysts are common and, locally, crushed phenocrysts of plagioclase, orthoclase, and quartz. The Cape Muzon Peninsula consists 

almost wholly of thick-bedded schist with a very little limestone. 

The schist comprises quartzite schist, dark micaceous siliceous schist, 

and, locally, black hornblende schist. Dikes of quartz diorite, also 

pegmatite and aplite, are common. Locally black graphitic phyllite 

is present.

The schist core of the south end of the island is flanked on each 

side by a belt of schist with intercalated or interbedded limestone. 

The schist comprises light-gray to greenish quartzose varieties, 

sericitic schist, and greenstone schist, the last in minor amount.

North of Port Bazan the belt of schist and limestone is overlain 

by a thick band of limestone with intercalated schist in minor 

amount. This passes upward into schist ^and limestone, the schist 

largely of greenstone origin, and then into greenstone schist with 

only a little limestone. A similar belt of greenstone and limestone 

forms the area between the bay north of American Bay and Coco 

Harbor.

In the schist derived from sedimentary rocks quartz is the predominant mineral, though feldspar, epidote, arid mica (sericite and 

biotite of two kinds, one a dark green) are in places very abundant. 

Garnet, sillimanite, hornblende, magnetite, and pyrite are common 

accessory minerals.
48 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The limestone is in general fine-grained crystalline material.

The greenstone schist associated with the limestone is largely 

altered to secondary quartz, epidote, chlorite, calcite, hornblende, 

mica, zoisite, talc, serpentine, and other secondary minerals, which 

have entirely replaced the original minerals of the rock.

On American Bay there are beds of crystalline schist with large 

radiating clusters of hornblende crystals on the foliation planes in 

a light-colored groundmass composed of quartz with sillimanite or 

of plagioclase, muscovite, and epidote. Associated beds consist essentially of hornblende and epidote, feldspathic quartz-mica schist, hornblende schist, and mica schist, with many narrow quartz seams parallel to the foliation planes, and beds of dense limestone.

The schist on the east coast of Dall Island south of the harbor 

north of American Bay has the appearance of having been formed as 

a result of metamorphism associated with igneous intrusions. This 

applies also to the beds on the west side of the island as far north as 

Port Bazan. There are a number of small intrusive dikes and sills 

throughout this belt and, locally, an injection gneiss. In the bay 

south of Gooseneck Harbor, in Gooseneck Harbor, and in Coco Harbor and Kose Inlet the pronounced metamorphism found is the effect 

of dynamic metamorphism only. The relative sparseness of exposed 

intrusive masses, however, is in contrast to the widespread crystallinity of the schist, and more extensive bodies of intrusive rocks 

doubtless underlie the south end of the island at no great depth 

The limestone beds between Cape Lookout and View Cove and 

between Diver Islands and Eolus Point are believed to belong to the 

same formation. The limestone of the southern band is foliated, and 

that of the northern band is practically massive, indicating that the 

dynamic metamorphism decreased toward the north.

Chapin considered the limestone of the belt between Waterfall 

Bay and Grace Harbor a member of the Wales group, but Buddington 

questions this. The rock is foliated and metamorphosed but not 

more so than the similar bed of limestone extending from the Diver 

Islands to Eolus Point. The latter Chapin considered to be of 

Silurian age, as it occupies a synclinal relation with respect to fossiliferous Silurian slate. The limestone of Waterfall Bay Chapin considered to be overlain by the greenstone and limestone of the Wales 

group. The strike and dip of the greenstone would indeed appear 

to indicate that the limestone bears an anticlinal relation to it; but 

the lithology of the limestone and the presence of crinoids ally it to 

the limestone of Silurian age on Dall Island, and it has been mapped 

as such by Buddington. The extension of this belt of limestone to 

the southeast through Long Island and also the belt along the northeast coast of Long Island have been mapped as Silurian by Budding-
WBANGELL-REVILLAGIGEDO BELT OF METAMOEPHIC BOCKS 49

ion, though originally assigned to the Wales group by Chapin. If 

the greenstone does overlie the limestone belt near Waterfall Bay o . *

it is probably of Devonian age and does not belong to the Wales 

.group. The actual relations are not known.

The fossils collected from the rocks of the Wales group were 

 examined by Edwin Kirk, who reports as follows:

15 ACh 150. East coast of Prince of Wales Island, 5 miles south of Chasina 

.Point:

Organic remains are present, but it is impossible to determine what they

are. 

15 ACh 192. Lime Point, Prince of Wales Island:

Possibly fragments of coral but not determinable. Lithologic appearance

like Silurian.

15 ACh 66. Cholinondeley Sound, first cove west of Cannery: 

Crinoid columnals. Paleozoic.

The lithology and poorly preserved fossils are not diagnostic but 

suggest that some of the limestone intercalated with the greenstone 

schist is of Silurian age. The schist and the schist and limestone 

.are pre-Silurian but are not lithologically similar to the known 

Ordovician beds and may be of pre-Ordovician age.

WBANGELL-BEVILLAGIGEDO BELT OF METAMOBPHIC BOCKS 

CHARACTER AND DISTRIBUTION

A great belt of metamorphic rocks occurs adjacent to the Coast 

Uange batholith. It includes injection gneiss; crystalline schist with 

interbedded marble or medium to coarsely crystalline limestone; 

schistose greenstone and green phyllite with interbedded black and 

.gray sericitic slaty phyllite and, locally, sparse limestone and schistose 

chert; phyllite with interbedded black slate; and, intermingled in 

all to a minor or major extent, intrusive masses of quartz diorite 

(with variations toward granodiorite). These rocks are for convenience called the Wrangell-Kevillagigedo belt of metamorphic rocks, in 

contradistinction to the Wales group of metamorphic rocks, which is 

restricted to Long Island and the southern part of Prince of Wales 

and Ball Islands.

The belt is in general narrower at the north, with relatively fewer 

masses of intrusive rock, and pinches out toward the northwest; in 

the vicinity of Thomas Bay and the Lindenberg Peninsula the 

number of intrusive masses is much greater, and their volume increases toward the southeast, where the belt is wider. The Coast 

Range batholith probably underlies the southern part of the belt more 

or less continuously at no great depth. The present surface relations 

are comparable to those that would appear if the batholith at the 

southeast end of the metamorphic belt had a highly irregular but 

gentle surface slope to the southwest beneath the belt.
50 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

At the south end of the belt in the vicinity of Kevillagigedo Island and Bradfield Canal there is a width of 30 to 35 miles, measured 

across the strike, of intermingled schist, injection gneiss, and intrusive quartz diorite; near Wrangell there is 15 miles of phyllite, 

crystalline schist, and gneiss, with some intrusive masses of quartz 

diorite; along Thomas Bay, 6 miles of phyllite, schist, and gneiss, 

or, if the phyllitic rocks of the Lindenberg Peninsula are included, 

20 miles. On the mainland the width of phyllite and crystalline 

schist, measured across the strike, is 15 miles in the vicinity of Port 

Houghton, 10 miles near Endicott Arm, 5 miles near Holkham Bay, 

3 miles at Taku Inlet, and 2 miles in the Eagle River region.

Much of the western boundary of the Wrangell-Revillagigedo belt 

of metamorphic rocks is formed by the resistant Mesozoic greenstone, as along Revillagigedo Channel, Gravina Island, the west 

side of Cleveland Peninsula, the west side of Etolin Island, Glass 

Peninsula, Onslow Island, and Douglas Island. It is not, however, 

a natural boundary, for the contact type of metamorphism fades out 

gradually, though very irregularly, toward the areas with the least 

number of intrusive bodies. The irregularity is in part caused by 

the great differences in strength and character of yielding or response to stress of the very different lithologic units and by the 

localization of shear zones.

The rocks of the belt are the result of contact metamorphism on a 

regional scale combined with the effects of dynamic metamorphism, 

or intense stress. Rocks that have been mechanically metamorphosed 

and sheared and schist that has been dynamically metamorphosed 

under intermediate temperature are very common in the islands to 

the west of this belt of metamorphic rocks; but outside the belt 

highly crystalline schist and marble are restricted to local zones 

adjacent to intrusive bodies.

The crystalline schist of the Wrangell-Revillagigedo metamorphic belt comprises in general varieties of hornblende and feldspathic hornblende schist, micaceous quartz schist, garnetiferous 

quartz-mica schist, and quartz-feldspar schist. Sillimanitic schist 

is found occasionally. Garnetiferous, staurolitic, cyanitic, and ottrelitic phyllites are locally abundant.

The map of the southeastern part of the the Ketchikan district by 

Wright 56 does not discriminate between gneiss and schist; the 

boundary lines between these rocks as shown on Plate 1 of this report are therefore based merely on Wright's descriptions and on the 

general relation of the rocks to the number and volume of the intrusive masses.

58 Wright, F. E., The Ketchikan and Wrangell mining districts, Alaska: U. S. Geol. 

Survey Bull. 347, pi. 2, 1908.
WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS 51

Injection gneiss forms a belt between the crystalline schist and 

the main batholith on Thomas Bay and to the southeast or is intermixed with the outlying intrusive masses in the southern part of 

the belt; but north of Thomas Bay it practically dies out west of the 

batholith and is restricted to bands within the batholith. On Port 

Snettisham the injection gneiss adjacent to the border of the batholith is only 600 feet wide, whereas on Thomas and Le Conte Bays 

and on Stikine River it is V/2 miles wide.

The veins associated with the belts of rocks that show varying 

degrees of metamorphism show a corresponding progressive change 

in general character as the batholith is approached. In the dynamically metamorphosed but relatively slightly recrystallized rocks in 

the Juneau and Funter Bay-Hawk Inlet gold belts and in the slate 

and schistose greenstone of the Prince of Wales Island belt the 

quartz veins are commonly milky, with some associated carbonates, 

and are in places metallized with sulphides or free gold or both. In 

the belt of phyllite the quartz veins are predominantly milky, with 

some carbonates, and only a few are metalliferous. In the crystalline schist the quartz veins are usually glassy and thin lenticular, 

.and many of them form injection schist. In the belt of injection 

gneiss adjacent to the main batholith the veins or vein dikes are 

aplitic or pegmatitic, and oligoclase is one of their major constituents in addition to quartz and potash feldspar. The injection gneisses 

are thus mixed rocks consisting in part of igneous material and in 

part of recrystallized and altered sediments.

The predominant new mineral formed in the early stages of metamorphism is mica, with which are associated disseminated graphitic 

 dust, and locally garnet and ottrelite. Andalusite is commonly associated with muscovite, which in part replaces it and is wholly restricted to local contacts of small intrusive bodies with slate.

The phyllite and crystalline schist consist of biotite, muscovite, 

quartz, cyanite, staurolite, garnet, sillimanite, and feldspar in the 

light-colored varieties and of hornblende, quartz, andesine, oligoclase, 

garnet, and calcite in the dark-colored varieties. The graphitic dust 

tends to be segregated in streaks, threads, clots, or lenses. Sillimanite occurs only in the crystalline schist where there has been 

intense metamorphism. Cyanite later in origin than the sillimanite 

is found occasionally. Cyanite, staurolite, and garnet occur predominantly as metacrysts but are in small part oriented parallel to 

the foliation. Biotite, muscovite, and hornblende are predominantly 

oriented parallel to the foliation but here and there, especially 

biotite, occur also as metacrysts. One specimen shows epidote in 

rods and grains contemporaneous with biotite and quartz and oriented parallel to the foliation. Magnetite and pyrrhotite are common accessory minerals and usually occur in irregular elongate blebs
52 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

parallel to the foliation. Pyrite and magnetite also occur as disseminated crystals. The sulphides are in part later than the silicates 

and occur along fractures.

In the injection gneiss the graphite is in crystalline flakes intergroAvn with biotite or disseminated through the rock with orientation 

parallel to the cleavage. The aluminum silicate minerals, such. as. 

andalusite, cyanite, sillimanite, staurolite, and ottrelite, are wholly 

absent from the injection gneiss, presumably because of reaction with 

the permeating alkalic solutions. Rarely, adjacent to or within 

aplite veins the hornblende of the injected hornblende schist has 

been altered to pyroxene. Garnet, though one of the early metamorphic minerals to form, is found through the entire range of metamorphic environment and is even common in the form of disseminated 

crystals in the igneous rocks themselves where they have disintegrated 

and reacted with schist inclusions, though it may have persisted here 

as an unstable relic.

Tourmaline is sparse to abundant as minute crystals in the phyllite 

and crystalline schist but is practically missing from the injection 

gneiss, pegmatite, and igneous intrusive rocks. Apatite, on the other 

hand, is more abundant in the crystalline schist and injection gneiss 

than in the phyllite. The magmatio solutions appear therefore to 

have carried the tourmaline to greater distances than the apatite 

before depositing their load. The tourmaline occurs as perfectly 

formed crystals apparently replacing any or all of the other minerals 

and later than the foliation.

KETCHIKAN DISTRICT

Westgate 57 has given the following descriptions of the rocks and 

their relations at the south end of the Wrangell-Revillagigedo belt of 

metamorphic rocks:

The following rock varieties occur within the metamorphic complex: Biotite gneiss, inica schist, quartzite and quartzitic schist, crystalline limestone, 

calcareous schist and gneiss, and phyllite. These are all metamorphosed sediments, so thoroughly metamorphosed that not a trace of original fragmental 

structure or of fossils has been found in them east of Behm Canal. Amphibolite is also included within the complex, although its relations to the other 

rocks are uncertain.

A belt of gneiss and schist with interbedded crystalline limestone and quartsite lies between the belts of greenstone east of Revillagigedo Channel and the 

diorite of the Coast Range batholith. The western boundary against the greenstone is sharply defined. The eastern boundary against the diorite is much 

harder to draw because the transition is through a broad belt in which the 

diorite has penetrated the metamorphic rocks along their structural planes in 

broad dikelike bands, giving a lit-par-lit structure on an immense scale. As

67 Westgate, L. G., The geology and mineral resources of the area east of Behm Canal 

(unpublished manuscript).
WEANGELL-BEVILLAGIGEDO BELT OF METAMOEPHIC BOOKS 53

one passes from the metamorphic rocks northeast he goes from an area of essentially all metamorphosed sediments through a belt with an increasing 

amount of quartz diorite in bands between the successive strips of metamorphic 

rocks until he comes to an area where the rock is a quartz diorite but still 

contains isolated bands of metamorphic rocks. Still farther northeast is the 

pure quartz diorite. This progress is irregular rather than steady; along the 

Boca de Quadra the transition belt is 10 miles in width.

Biotite gneiss. Biotite gneiss is the most common rock of the metamorphic 

complex. The most characteristic variety is a red biotite gneiss, usually well 

bedded and rusty in outcrop. Freshly broken pieces are reddish gray, flue 

grained, and indistinctly bedded. Biotite is abundant in oriented separate 

flakes. The microscope shows quartz, plagioclase (oligoclase-andesine), no 

orthoclase, and chestnut-red biotite. Garnet occurs in irregular orbicular 

grains. Graphite is common with the biotite. Pyrite occurs abundantly in 

crystals filmed with hematite and has caused the rusty color of the weathered 

ledges. Apatite and zircon are also present as accessories. The average size 

of grain is 0.25 to 0.5 millimeter; the texture is mosaic; no granulation is° 

found. Though the biotite gneiss shows no trace of original fragmental 

structure, its constant association with limestone and the general presence of 

graphite make its sedimentary origin reasonably certain.

With this red biotite gneiss are other varieties, less constant in mineral character. Some are more banded (possibly injection gneisses), carry muscovite 

or hornblende, and tend toward schist. Some of these, like the red biotite 

gneiss, carry abundant graphite.

Mica, schist and plMjllite. Mica schist is one of the common types of the 

metamorphic complex. It ranges from nearly white to dark gray in color. 

Lenses and bands of quartz are in places abundantly developed in the structure 

planes of the rock. The most abundant minerals are muscovite, biotite, and 

quartz; hornblende and chlorite are less abundant. Garnet is common, and 

sillimaiiite, staurolite, pyrite, and black carbonaceous matter are also present. 

The rocks are closely folded at many places.

Along the west side of Kanagunut Island, at its north end, the schist gives 

place to black thin-bedded and evenly laminated phyllite. This is exceptional 

in the metamorphic complex.

Qiiartzite. At several points in the general vicinity of Kah Shakes Cove beds 

of massive, nearly pure quartzite occur. The rock is light gray to white, 

glassy, with an indistinct cleavage marked with small amounts of sericite, 

green mica, and limonite. The thin section shows a mosaic of sutured grains 

of quartz as much as 1 millimeter in size and a few small flakes of white mica. 

No sand grains are recognized.

Besides the pure quartzite, rocks are found intermediate between quartzite 

and gneiss and schist quartzose gneiss and schist.

Crystalline limestone. Beds of crystalline limestone a few feet to perhaps 

several hundred feet in thickness occur within the metamorphic complex. 

They are most abundant in a belt which makes the shore of Revillagigedo 

Channel for 3 miles, beginning at a point 1% miles south of Point Sykes. The 

belt bears inland and comes to the shore of Boca de Quadra at Quadra Point 

It is well developed on Kah Shakes Cove and farther south along Very Inlet. 

Beyond that it was not traced. The belt is not exclusively limestone but includes limestone in beds of such size and number that it can fairly be mapped 

as a limestone band. It is impossible to say to what extent the different limestone bands represent different beds and to what, extent they are repeated by 

folding. Outside this mapped belt narrow bands of limestone are found at
54 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

many places in the gneiss, even in the narrow bands of metamorphic rocks 

that exist as xenoliths cut in the granite. The rock in the ledge is a creamcolored coarse-grained rock; on the freshly broken surface it. is white or graywhite, in places averaging a quarter of an inch in size of grain. The rock is 

quite pure and almost wholly without metamorphic lime silicates.

Calcareous gneiss and schist. Calcareous gneiss passing into schist is 

associated with the limestone at Kah Shakes Cove and to the northwest, on 

the shore of Behm Canal. The constituent minerals are quartz, in places feldspar (usually plagioclase, though orthoclase occurs), calcite, muscovite, commonly chlorite, biotite, and hornblende. Zoisite and colorless epidote are 

abundant in grains and short columnar crystals. The accessory minerals that 

may occur are titanite, rutile, garnet, apatite, magnetite, pyrite, and zircon. 

The rocks are clearly metamorphosed calcareous sediments or impure limestone and mark a gradation from limestone into gneiss. In the field alternating 

beds of pure limestone and calcareous gneiss and schist are common.

Amphibolite. Arnphibolite is abundant in a belt which can be followed from 

Sitklan Island north-northeastward by Naket Inlet, Vixen Bay, Weasel Cove, 

and Badger Bay to the shore of Behm Canal, near the entrance of Smeaton 

Bay. Between Weasel Cove and Behm Canal the belt appears to separate into 

two, one of which comes to Behm Canal south of Point Nelson, the other east 

of Point Nelson in Smeaton Bay. The former is continued by amphibolite 

bands on the west shore of Behm Canal north of Smeaton Island.

Amphibolite does not constitute the whole of this belt but occurs in bands 

as much as several hundred feet wide in the schist and gneiss of the metamorphic complex and with the gneissoid diorite of the batholith. Four miles 

south of Point Sykes it is interbedded in limestone. It is dark gray to black, 

well bedded, much of it platy and breaking into thin slabs. The banding strikes 

north-northeast with the course of the belt and has commonly a steep eastward 

dip, though in places vertical or even steep west.

In hand specimens the amphibolite is dark gray to black and of fine grain 

(1 to 2 millimeters). It contains commonly hornblende, plagioclase (oligoclase-andesine), biotite, epidote, and quartz. Accessory minerals that may be 

present are apatite, magnetite, titanite, rutile, zircon, and pyrite. They are 

allotriomorphic granular in texture and show no evidences of crushing.

The amphibolite is older than the diorite, which cuts it in lit-par-lit fashion 

on both a^large and a small scale. At places on Smeaton Bay alternating bands 

are only an inch or two in width. The diorite also cuts the amphibolite irregularly, producing a breccia of dark rock cemented by the diorite.

The relations of the amphibolite to the other members of the metamorphic 

complex are not clear. From its mineral character and general field appearance 

it is believed to be an igneous rock rather than a member of a sedimentary 

series. It is then intrusive into the metamorphic rocks. Whether it represents 

a distinct intrusion from the diorite or an earlier intrusion belonging to the 

general magmatic period of the diorite was not determined.

Along Ernest Sound and Bradfield Canal there are good exposures 

of the metamorphic rocks showing all gradations from slate and 

phyllite on the southwest to injection and relic gneisses on the northeast.

The western border of the belt is taken to be the highly schistose 

to massive greenstone of Lemesurier Point and Onslow Island. 

Between the diorite mass of Etolin Island and the quartz diorite of
WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIO ROCKS 55

Eaton Point there is a belt of phyllitic beds including sheared sandstone, phyllitic graywacke, and phyllite. Adjacent to the greenstone 

on Union Bay there are beds of slate with a 150-foot bed of limestone. The phyllite is gray, and much of it has a paper-thin fissility; 

it is cross crinkled and very susceptible to weathering and erosion. 

Near the pyroxenite and diorite mass on Union Bay there is a local 

contact zone of more intense metamorphism where the beds are 

severely contorted, puckered, sheared, and injected by aplitic veins. 

The sandstone is changed to mica schist, and calcareous nodules to 

banded zoisite and epidotic quartzite. Within the phyllite there is 

conspicuous evidence of isoclinal folding w,ith very steep axes. Beds 

with garnet or biotite metacrysts are present but rare. Toward the 

Eaton Point mass of quartz diorite the phyllite shows the effects of 

sintering and baking and becomes harder, and many beds contain 

biotite metacrysts. Adjacent to the intrusive mass itself the beds are 

injected by abundant quartz veinlets.

Northeast of the phyllite is a belt characterized by crystalline 

schist and beds intermediate between schist and phyllite. This belt 

includes the beds between the quartz diorite masses of Eaton Point 

and Santa Ana Inlet, the borders of Brownson and Deer Islands, 

and the southern half of Wrangell Island.

Between Eaton Point and Santa Ana Inlet the rocks are predominantly quartz schist with intercalated layers and beds of cyanite 

schist. Thin layers of hornblendic/ quartzite and local beds of 

staurolite and garnetiferous schist are present. Muscovite eyes are 

abundant in much of the schist. On Deer Island the rock predominant around the quartz diorite mass is a quartz-mica rock intermediate between a phyllite and a schist with beds and layers of 

garnet-sillimanite-mica schist. The sillimanite crystals in many of 

the beds average an inch in length and are very conspicuous. A few 

of them are 6 .inches or more in length. At Point Peters staurolite 

crystals are associated with the sillimanite. At the northeast end 

of the island zones several feet wide shot through with glassy quartz 

veins and knots are common, and at the southeast end many narrow 

pegmatite veins and sills of quartz diorite are intruded in the schist. 

Some of the veins are crumpled with the schist.

On the south end of Wrangell Island and along Zimovia Straits 

there are thick beds of quartz-mica phyllite and a series of thinbedded quartz-mica phyllite interbedded with staurolitic phyllite. 

Along Zimovia Straits staurolite, cyanite, and cyanite-staurolite 

phyllite are interbedded with micaceous quartz phyllite. North of 

Deserted Village, where the phyllite abuts against a mass of quartz 

diorite, sillimanite schist is formed. Amphibole layers are common, 

and near intrusive masses the crystallinity is noticeably increased. 

6137 29 5
56 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

East of the belt characterized by beds intermediate between 

phyllite and schist, along Bradfield Canal as far east as Duck Island, 

there is a belt of crystalline schist, marble, and injection gneiss.

The marble and interbedded schist, are exposed on the flanks of the 

nose of a northwestward-pitching overturned anticlinal fold whose 

axial, plane dips steeply northeast. The marble is exposed on the 

shore of Humpback Bay, where it has a northwest strike; it appears 

again on Ham Island in Blake Channel, and extends to the east for 

several miles a little north of the shores of Bradfield Canal. Along 

Bradfield Canal as far east as the intrusive mass of Mount Kapho 

the predominant rocks are aplitic or pegmatitic quartzose micaceous 

or hornblendic injection gneiss with here and there sills of granodiorite. The rocks for several miles west of Duck Island consist 

dominantly of amphibolite injection gneiss, with associated quartzmica injection gneiss, hornblende schist, thin beds of marble, and 

sills otf granodiorite. The amphibolite injection gneiss ranges in 

composition from, beds of hornblende schist or coarse amphibolite 

several hundred feet thick, with sparse pegmatite veins, to beds in 

which pegmatite veins form almost the entire rock, but beds intermediate in composition are the most abundant. The pegmatite veins 

at some places are as much as a score of feet in width and contain 

muscovite and biotite as accessories. The beds of marble range from 

several feet to a score of feet in thickness. The granodiorite sills 

are also injected by pegmatite and are locally garnetiferous as a 

result o»f .assimilation. The gneiss has many bands which weather 

to a rusty color due to disseminated pyrite and pyrrhotite. The 

quartz-.mica varieties usually have intercalated beds of hornblende 

schist or hornblende injection gneiss and marble.

At the\head of Bradfield Canal, within the outer edge of the main 

batholith, is a belt of mixed gneiss with several thin beds of marble. 

The mixed gneiss consists of relic injection gneiss and thick sheets of 

quartz diqrite. Kusty-weathering beds are common. The relic injection gneiss is the result of the almost complete disintegration of a belt 

of schist by intrusive pegmatitic material, so that only relics of the 

original matter ,are left. On some large surfaces a coarse breccia 

structure is very evident, yet the rock is almost wholly pegmatite, 

and only a ghost of the original blocks of schist remains to tell the 

story of their former presence. To the west of the belt of mixed 

gneiss the quartz diorite contains layers of gneiss and thin beds of 

marble. Where thus interbanded with sedimentary material pegmatite veins roughly parallel to the foliation of the quartz diorite 

are abundant. In masses of the quartz diorite that are more uniform, with a less pronounced gneissic structure, the veins oif pegmatite are sparse and do not conform to the foliation but cut across 

and intersect at sharp angles.
WBANGELL-REVILLAGIGEDO BELT OF METAMORPHIC BOCKS 57 

VICINITY OF WRANGELL ISLAND

Along Stikine Straits, the nprth end of Wrangell Island, and Mill 

Creek, Virginia Lake, and Porterfield Creek on the mainland the 

increase in the intensity of metamorphism toward the Coast Range 

batholith is again well shown.

The beds at the -northwest end of Etolin Island consist of black 

.date, sheared graywacke, and sheared to massive greenstone, produced largely through dynamic metamorphism. The effects of contact metamorphism are shown locally where intrusive stocks are 

present.

On the north end of Wrangell Island, from the cove north of 

Chichagof Peak on the west side around to the headland on the east 

side of the island that lies southwest of the mouth of Mill Creek 

on the mainland, the rocks forming the coast line comprise a series 

of recrystallized, more or less' foliated, prevailingly gray sandstone, 

usually biotitic, with intercalated layers of black slate, much of which 

is ottrelitic. The quartzose beds are too much metamorphosed and 

recrystallized to be called sandstone, too micaceous and foliated and 

in places too impure to be called quartzite, and not so much sheared 

and recrystallized as the typical quartz schist farther east, nearer 

the mainland batholith. Some of the beds comprising Point Shekesti are typical micaceous quartz phyllite. Southward along Eastern Passage and Zimovia Straits the rocks show an increasing degree 

of metamorphism due to the presence of stocks of quartz diorite that 

probably form much of the interior of the island. Many of the 

quartzose beds were originally argillaceous, and some calcareous beds 

are intercalated within the series.

Along the west side of Wrangell Island the quartzose beds are 

usually fine to medium grained and 1 foot to 10 feet thick. There 

are also beds of slate that are usually not over several inches thick 

but may be several feet, with quartzose, highly biotitic layers. 

Intercalated calcareous beds weather with a characteristic rounded 

corroded surface.

In thin section quartz is seen to be the predominant mineral in the 

recrystallized argillaceous sandstone members. The quartz occurs 

in elongate grains in a matrix of very fine white mica, both minerals 

oriented parallel to the foliation. The amount of micaceous matrix 

is highly variable, depending upon the original argillaceous character of the rock. A little feldspar is commonly present as an accessory mineral. Biotite is very abundant in many of the beds and 

is especially prominent in the thin quartzose partings within the 

slate beds. It is uniformly disseminated through the rock as chunky1 

equidimensional grains pleochroic from pale greenish brown to 

brown and bears the relation of a metacryst to the other minerals.
58 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

Black carbonaceous dust is abundant but more or less segregated in 

small lenticular areas. In the highly quartzose beds the quartz is 

in a very fine granular aggregate with a denticulate texture and local 

lenticles of coarser grain. Pyrrhotite is a sparse to abundant accessory mineral replacing the siliceous material in the form of small 

irregular grains elongate parallel to the cleavage. Small euhedral 

tourmaline crystals are a constant though sparse accessory mineral 

later than the other minerals. A trace of ottrelite or magnetite is 

present in some of the beds.

The slate has a dull black surface usually marked by the reflecting 

black cleavage surfaces of abundant disseminated ottrelite crystals. 

These range from 1 to several millimeters in diameter. In thin section the rock is seen to consist of an exceedingly fine aggregate of 

quartz and white mica thoroughly pigmented with disseminated black 

carbonaceous dust. There is a trace of small biotite metacrysts and 

a few small grains of pyrrhotite. The platy ottrelite crystals are in 

part parallel to the cleavage but for the most part oriented at all 

angles to the cleavage as replacing metacrysts. They are black and 

opaque in thin section because of the great quantity of included carbonaceous dust. A few are surrounded by a zone of clearer recrystallized quartz. A little tourmaline is present as a microscopic accessory constituent. Pyrrhotite also occurs as a thin film, surfacing 

fractures across the cleavage.

The rocks on the east side of Wrangell Island from Rock Point 

southeast along the coast for about 5 miles show a slightly greater 

metamorphism than those on the west side, although the fine-grained 

facies have not passed beyond the stage of slate. A characteristic 

specimen of the slate consists of black garnetiferous ottrelitic slate 

with thin partings of biotitic recrystallized sandstone. The ottrelite 

and garnet crystals are uniformly and abundantly disseminated 

through the slate and average about 1.5 millimeters in diameter. 

Pyrrhotite is locally an abundant accessory mineral. The cleavage 

surface of the slate here is not as dull as that of the ottrelitic slate 

on the west coast, but it is not as lustrous as a typical phyllite.

From the middle of the cove east of Babbler Point to the east end of 

Lake Virginia the rocks are predominantly gray micaceous quartz 

phyllite with thin black or mottled gray layers of hornblendic quartzite and quartzose hornblendic limestone from several inches to a foot 

in thickness and local beds of black ottrelitic phyllite and of dull 

dark-gray phyllite. Many narrow quartz veins and ,a number of narrow granite sills occur in these rocks.

The quartz phyllite is in part a thinly cleavable gray fine-grained 

rock with a conspicuous brown sheen from the mica which forms a 

more or less uniform coat over the cleavage surfaces though the indi-
WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS 59

vidual flakes are indistinguishable or indistinct. A typical specimen 

in thin section is found to consist predominantly of quartz (average 

diameter 0.5 millimeter) with abundant brown biotite. Hornblende 

crystals oriented at various angles in the plane of the foliation are 

common as an accessory mineral. Magnetite grains are common, 

and there is a trace of garnet. The rock is pigmented with disseminated graphitic dust more or less segregated in streaks. In part the 

quartz phyllite is a similar fine-grained thinly cleavable rock with the 

brown biotite uniformly disseminated as abundant chunky metacrysts. Rods of tourmaline are found in these rocks, in places oriented at right angles to the cleavage.

The hornblendic layers are gray with disseminated black hornblende crystals or black hornblendic layers. They have a more massive appearance than the phyllite and are not so thinly cleavable. 

In thin section a typical gray specimen is found to be a calcareous 

hornblende quartzite with hornblende and quartz constituting the 

major minerals. The hornblende crystals are oriented in the plane 

of the cleavage. Calcite is an abundant accessory mineral, and there 

is a trace of feldspar. A specimen of the black phase is found to 

consist of alternating thin layers of highly hornblendic material and 

quartzose limestone. Both are black and thoroughly pigmented 

with disseminated carbonaceous dust.

Toward the southeast in the direction of the large masses of quartz 

diorite along Blake Channel, there is a marked increase in the degree 

of metamorphism. The phyllite passes into beds intermediate between phyllite and schist or into typical schist. In the vicinity of 

Madan Bay the beds are staurolite and muscovite-cyanite schist 

with interbedded quartz schist and a few thin layers of amphibolite. 

The beds of Port Madan itself are staurolite phyllite. The rocks 

along the east side of Bergs Cove and along Aarons Bay are very 

much plicated. Beds of marble, with many narrow quartz veins and 

considerably sheared, crop out on the west side of the bay. The 

predominant rocks are quartz-mica schist.

LE CONTE BAY

The shores of Le Conte Bay give a diagrammatic illustration of 

the change from phyllite to injection gneiss. A sill of porphyritic 

quartz diorite forms the north headland at the mouth of the bay. 

This is adjoined on the east by a belt of phyllite V/2 miles wide, 

On the western border of this belt the phyllite has a sheeny surface 

and almost parallel cleavage. On the south side of the bay the predominant rock is quartz phyllite with intercalated beds of crinkled 

black slate. The quartz phyllite is hard and tough when fresh, 

more like a micaceous quartzite, but on weathering becomes fissile.
60 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

To the east the phyllite is somewhat more crystalline and crinkled. 

The phyllite is adjoined by a belt of quartz-mica schist about threequarters of a mile wide. On its eastern border the schist is intercalated with thin layers of marble and is penetrated by aplite and 

pegmatite veins, which still farther east become so numerous as to 

make of the schist an injection gneiss. The injection gneiss forms 

the belt adjacent to the Coast Kange batholith. It comprises hornblende and biotite gneisses and is conspicuous because of the many 

rusty beds. The aplite and pegmatite also carries disseminated 

sulphides.

Quartz veining is abundant in both the phyllite and the schist. 

In the phyllite the quartz veins tend to occur along localized shear 

zones, whereas in the schist they occur as thin flat veinlets along 

the foliation planes and form what might be called a quartz injection gneiss. The quartz veins in the phyllite usually form a series 

of more or less parallel narrow veins, for the most part an inch to 

several inches wide but locally larger, with associated knots or 

lenses of quartz. Many of the quartz veins are themselves involved 

in folds.

THOMAS BAY

The inlet of Thomas Bay cuts across three different belts of rock, 

and two additional belts in the mountains on the north side of Cascade Creek were examined.

The first belt on the outer side comprises a series of crystalline 

schists, which are well exposed on the peninsula west of Ruth Island 

and along the west coast of Ruth Island itself. The rocks that form 

the peninsula are predominantly micaceous quartz schist with intercalated beds varying toward a quartzite on the one hand and toward 

a typical quartz-mica schist on the other. They show an increasing 

degree of crystallinity toward the east that is, toward the main 

batholith. The beds along the southwest side of Ruth Island are 

rusty-weathering plagioclase-mica schist with accessory staurolite, 

cyanite, garnet, pyrrhotite, and pyrite. Tourmaline and apatite in 

perfectly formed small crystals are common to abundant accessories 

in these rocks and, with the pyrite and pyrrhotite and a few glassy 

quartz veins, appear to have been the only foreign materials introduced during the metamorphism.

The second belt is about 1% miles wide at the head of the southern 

arm of Thomas Bay and about 4 miles wide northeast of Spurt Point. 

The thinning of the belt toward the southeast is due in part to the 

crosscutting of the quartz diorite mass on the east. The belt comprises a series of mixed rt>cks in part of igneous and in part of sedir 

mentary origin. The rocks that form the north shore of the bay
WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS 61

from the base of Point Vandeput almost to Wind Point, those that 

form the major part of Ruth Island, and those south of Cascade 

Creek in the south arm are predominantly hornblende plagioclase 

schist, much of it in various stages of injection and partial replacement by aplite veins or aplitic material and associated with narrow 

intrXisive sheets of quartz diorite. Intercalated with the schist just 

east of the base of Point Vandeput, in the cove on the northwest 

side of Ruth Island, along the southeast shore of the northeast half 

of Ruth Island, and at intervals along the shore north of Cascade 

Creek are thin beds of medium-crystalline limestone. On Ruth 

Island the limestone is interbedded with fine-grained white quartzite 

resembling sheared and recrystallized chert and with intercalated 

hornblende schist. Blue-gray quartzite also occurs interbedded with 

hornblende schist overlying the series of beds of white quartzite and 

hornblende schist. Other common intercalated beds are, for .the 

most part, aplitized mica schist with accessory graphite. Along the 

shore east of Spurt Point there are all stages of gradation between 

a schist composed almost exclusively of hornblende and a quartz 

diorite with accessory garnet. Along the west side of the north arm 

of Thomas Bay, from a point a short distance south oif Wind Point to 

the quartz diorite belt, the rocks are interbedded garnetif erous quartzmica schist or quartz-mica schist, with garnetiferous hornblende 

schist or hornblende schist. These beds arte in all stages of injection 

or replacement by aplitic material or aplite veins and are intruded by 

sheets of quartz diorite. Many of these beds are impregnated with 

pyrite and pyrrhotite and weather to a conspicuous rusty-brown 

color. Many of them carry as an accessory mineral, graphite in 

crystalline flakes, conspicuous for its silvery appearance on the foliation planes. Quartz veins and veinlets are common in this belt of 

mixed gneisses. Shear zones shot through and through with quartz 

veins are also seen. The veins are in general composed of a glassy 

quartz characteristic of high-temperature veins. Many of the beds 

show small slips and slickensided surfaces along which mica has 

developed.

The third belt is the intrusive mass of quartz diorite, about 3 miles 

in width. The whole mass is more or less contaminated with inclusions, remnants, or assimilation products resulting from the breaking up or disintegration of the schist. Along the east side of the 

south arm of the bay from Cascade Creek north the quartz diorite 

contains narrow included blocks of the schist with intercalated beds 

of crystalline limestone. The eastern half of the belt is made up of 

quartz diorite with many to sparse stringerlike inclusions of gray 

schist, individualized bands or blocks of gray injection gneiss, and 

bands consisting of layers of schist disrupted and disintegrated into 

a host of small separated stringerrshaped inclusions. .Locally what
62 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

at first appears to be clean quartz diorite is found on closer inspection to be garnetiferous. Sparse inclusions are found in even the 

cleanest of the mass. A few dikes of white quartz diorite aplite cross 

the foliation.

The fourth belt, about two-thirds of a mile wide where examined 

in the mountains north of Cascade Creek, comprises alternating 

sheets of injection gneiss, injected and impure crystalline limestone, 

and sheets of granite. Both the gneiss and the limestone (dolomite 

in part) are broken up by granodiorite dikes, and locally the injection gneiss and granite form areas of breccia. The marble is predominantly rich in silicates, though a few thin beds of purer marble 

were seen. Tremolitic layers are common and occur in beds some of 

which are several feet thick. Some beds have a close meshwork of 

disseminated chondrodite. These may contain layers with abundant 

nodules of phlogopite mica associated with a few small octahedra of 

lavender-colored spinel. Green pyroxene is very common, disseminated through many of the beds or as masses of coccolite adjacent to 

injected pegmatite veins. Pegmatite veins are usually common, and 

locally quartz veins are abundant. The pegmatite veins usually contain abundant .disseminated pyroxene resulting from assimilation 

of the limestone and locally a little titanite. Some of the limestone 

contains a little disseminated graphite and mica. Graphite occurs 

also as a local concentration in some of the pyroxene nodules. White 

plagioclase feldspar and epidote and nodules of garnet are abundant 

in some beds. Inclusions of limestone with their borders changed 

to masses of coccolite were noted in some sheets of the granodiorite.

The fifth belt, of unknown width, consists of a very coarsely porphyritic granodiorite.

The rocks that form the peninsula on the south side of Thomas 

Bay between "Wood Point and the channel on the west side of Ruth 

Island are predominantly micaceous quartz schist, varying toward a 

micaceous quartzite on the one hand and toward a more typical 

mica schist or quartz-mica schist on the other. The beds show an 

increasing degree of crystallinity toward the east.

Two typical specimens taken from a place three-quarters of a 

mile east of Wood Point are described below. One is a mediumgrained gray rock with a coarse foliation roughly parallel to a plane 

and fine brown mica flakes on the cleavage surfaces. In thin section 

the rock is seen to consist predominantly of quartz with abundant 

hornblende rods oriented parallel to the foliation, a little brown 

biotite, and accessory disseminated pyrite, magnetite, garnet, and 

apatite. The pyrite is in elongate irregular grains parallel to the 

foliation. The hornblende is faintly pleochroic pale to light green. 

Most otf the quartz is in finely mashed laminae with a denticular 

texture and wavy extinction, but some is in narrow lenticles and
WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS 63

layers of clear granular recrystallized quartz. The other specimen 

is a dark-gray garnetiferous, micaceous quartz schist with a roughly 

plane-parallel foliation. The cleavage surfaces have a conspicuous 

uniform sheen due to the mica, but only here and there is the mica 

distinguishable as individual flakes. In thin section the rock is seen 

to consist predominantly of quartz with disseminated lenticles made 

up of brown biotite and colorless muscovite with a little quartz. 

The micas are oriented at slight angles to the foliation in these 

lenticles. A little mica in the groundmass is oriented parallel to 

the foliation. Small garnets are common, forming metacrysts with 

tails of quartz. The rock is thoroughly clouded with disseminated 

dots of black carbonaceous material, which is particularly abundant 

in the biotite. Pyrrhotite is common as very much elongated grains 

parallel to the foliation. Apatite and plagioclase are accessory minerals. One small euhedral crystal of tourmaline is present.

Along the west side of the channel west of Ruth Island the rocks 

are more markedly crystalline and are locally closely crenulated. A 

typical specimen is a grayish-white micaceous quartz schist. The 

cleavage surfaces are marked by well-individualized flakes of brown 

biotite several millimeters in diameter.

The west side of Ruth Island is formed of rusty-weathering plagioclase-mica schist. Narrow glassy quartz veinlets, some with 

pyrrhotite and pyrite, are common locally, and the rocks are considerably more pyritic and pyrrhotitic than the underlying schist. 

In thin section the predominant constituent is seen to be plagioclase 

in grains elongate .to the foliation. One typical specimen is a very 

closely foliated rock with a fine lenticular texture, the lenticles, 

about a centimeter in length, being set off by a wrapping of brown 

biotite or colorless muscovite. Abundant staurolite, cyanite, and 

garnet crystals are present. The staurolite, cyanite, brown biotite, 

and plagioclase are in part intergrown and belong to essentially the 

same period of crystallization; in part they succeed an earlier generation of brown biotite, muscovite, and quartz and contain inclusions 

of these minerals oriented parallel to the foliation. Small euhedral 

crystals of brownish-green tourmaline are abundant and replace 

each of the other minerals but more especially the biotite. The rock 

is full of disseminated black carbonaceous dust, in places oriented in 

a fine plicated schistose structure inclosed in the other minerals. 

Abundant small apatite crystals and a trace of very fine fibrous sillimanite are present. Another specimen consists of layers rich in plagioclase containing abundant inclusions of brown mica oriented 

parallel to the foliation, separated by highly micaceous laminaemade up mostly of biotite but with muscovite common. The pyrite 

and pyrrhotite are in irregular grains much elongated parallel to the 

foliation.
64 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Between Thomas Bay and Endicott Arm, for a distance of 40 

miles or so, the Coast Range batholith changes from its prevailing 

northwest trend parallel to the formational strike to a more truly 

north-south trend and cuts across the strike of the formations at an 

angle of about 15° to 40°. As a result there is a change in the 

character of the same group of rocks as distance from the batholith 

increases. For example, the belt of injection gneiss adjacent to the 

main batholith on Thomas Bay appears to be represented on Port 

Houghton, 35 miles distant along the strike and about 5 miles away 

from the batholith, by a belt of garnetiferous quartz-mica schist, 

whereas on Hobart Bay, 10 miles farther along the strike and at 

least 10 miles from the batholith, the rocks are phyllite.

A belt half a mile to 2 miles wide characterized by the predominance of hornblende schist extends from Spurt Point, on Thomas 

Bay, northwest to Port Houghton, west of Walter Island Arm.

On -Thomas Bay, in general, the penetration and replacement of 

the hornblende schist has been so complete that at many places it is 

only on a weathered surface that the rock in any way suggests the 

process of aplitic injection, and there only faintly. Locally the injection character is conspicuous and the narrow veins are well individualized. The schist as a rule has a well-developed cleavage 

roughly parallel to a plane. It is medium grained, with the hornblende oriented parallel to an axis. The garnets to a, slight extent 

have grown by pushing aside the adjoining laminae, but to a greater 

extent they bear the relation of replacing metacrysts developed, or 

at least enlarged, at the time of the introduction of the aplitic material. The hornblende is commonly moderately pleochroic from 

light to dark olive-green, but may be pleochroic from deep green to 

blue to yellowish green. The plagioclase ranges from an andesine 

(Ab6An4 ) to an oligoclase-andesine (Ab7An3 ). The amount of 

plagioclase varies widely, depending in part upon the degree of 

aplitization. With increasing abundance of feldspar the rocks 

assume a gray color of much lighter tone than normally. Minor 

accessory minerals found in varying amounts in different specimens 

are brown biotite, quartz, epidote or pyroxene, resulting from the 

aplitic alteration of hornblende, pyrrhotite, pyrite, magnetite, ilmenite, apatite, and titanite. The feldspars and quartz show a conspicuously wavy extinction.

A very conspicuous rock developed locally as the result of aplitic 

injection of the hornblende schists crops out along the north shore of 

Thomas Bay east of the base of Point Vandeput and at the southern 

tip of Ruth Island. It is predominantly a coarse garnetiferous hornblende-plagioclase (Ab7An3 ) schist with variations across the strike 

which indicate an original bedded character. The hornblende crystals
WRANGELL-REVILLAGIGEDO BELT OF METAMOEPHIC ROCKS 65

are prismatic, with a diameter of about 0.5 centimeter and a length 

of 1 to 2 centimeters, and are oriented parallel to an axis. They 

are inclosed in a meshwork of aplite that consists of plagioclase 

associated with a little quartz. The garnets are inclosed in the 

aplitic veinlets, and some at least are directly the result of the injection of the aplite. It is a common thing for a few of them to 

contain grains of pyrite or pyrrhotite. Minor accessory minerals 

found in varying amounts in the rocks are biotite, apatite, epidote, 

zoisite, pyrrhotite, pyrite, magnetite, and titanite. A few grains of 

staurolite were found in one thin section examined, which contained 

also an exceptional number of apatite crystals. The hornblende is 

pleochroic from deep green to blue-green to yellow-green (o=1.661, 

y =1.677).

Another rock is a black hornblende schist mottled with abundant 

disseminated small red garnets (2 millimeters) and intimately veined 

parallel to the foliation by paper-thin veins of glassy quartz intercalated between a medium-crystalline limestone below and an epidotic 

mica schist thoroughly injected by aplite above. Hornblende in 

long prismatic growth oriented parallel to an axis is the predominant 

mineral. The garnets are confined to the quartz veinlets. Magnetite 

in very long grains with irregular borders, oriented parallel to the 

roughly plane-parallel cleavage, is a common accessory. A few 

small apatite crystals and a trace of feldspar constitute the other 

minerals.

Another specimen is a hornblende schist without garnet but with 

about 20 per cent of plagioclase (oligoclase-andesine) replacing the 

rock in the form of veinlets and lenticles or disconnected incipient 

veinlets. Some of the hornblende is in an advanced stage of partial 

alteration and replacement by epidote, an unidentified high-birefringent aggregate, and an isotropic chloritic-appearing substance. The 

plagioclase bears a definite replacement relation to the hornblende. 

Traces of apatite, magnetite, and biotite are present.

The schist that is light colored on fresh surface is predominantly 

feldspathic, 'with abundant biotite and locally garnetiferous. In 

general it carries a higher percentage of sulphides, predominantly 

pyrrhotite, than the dark hornblende schist and weathers accordingly 

with a rusty-brown surface. Graphite is a characteristic accessory 

mineral that is nearly always present, in contrast to its almost complete absence in the hornblende schist, and it is conspicuous because 

of the s,ilvery luster of its scales disseminated through the rock. 

Plagioclase feldspar ranging from oligoclase-andesine (Ab7An3 ) to 

andesine (Ab6An4 ) is the predominant mineral and seems to be 

mostly of aplitic origin. Quartz is a widely varying constituent,
66

ranging from a minor accessory to considerably more than half the 

1-ock. Biotite is constantly present in abundant flakes and gives the 

characteristic foliated appearance to the schist. In thin section it 

is usually pleochroic from light yellowish brown to deep chestnutbrown, but a variety pleochroic from light to deep olive-green is also 

found. Orthoclase is present in some specimens but ,is usually absent. A specimen collected from one of the least-injected beds is 

composed of 54 per cent quartz, 20 per cent plagioclase, 9 per cent 

biotite, 6 per cent graphite, 6 per cent orthoclase, 5 per cent pyrrhotite, and a little accessory apatite; it is a graphitic, micaceous quartzfeldspar schist. The plagioclase feldspar ranges from an oligoclaseandesine to bytownite. Another bed which occurs intercalated within 

the hornblende schist and crystalline limestone series is an epidotic 

feldspar-mica schist. This rock consists of an intergrowth of 

plagioclase, biotite, epidote, quartz, and magnetite, named in order of 

abundance. The epidote is in long rods and rounded grains oriented 

parallel to the foliation. The magnetite is in perfect disseminated 

octahedra and in irregularly bounded grains. The biotite is pleochroic from pale yellowish olive-green to deep olive-green. The 

graphite is in crystalline flakes in part intergrown with the biotite 

and in part with the other minerals. Apatite is an abundant accessory mineral, and a trace of muscovite is present.

In other specimens the pyrrhotite occurs in small elongate grains 

associated with the graphite or in parallel intergrowths with biotite. 

A trace of zircon is seen occasionally in some of the biotite.

PORT HOUGHTON

The formation on Port Houghton consists of hornblende schist 

with intercalated beds of limestone several feet thick and a few 

beds of black slate or phyllite. The schist may vary widely in 

general aspect and character but is marked by the prevalence or 

dominance of hornblende as an almost constant accessory. It ranges 

from hornblendic, garnetiferous, muscovitic, or biotitic quartz schist 

to very dark hornblende schist with only a very little interstitial 

groundmass. Locally the crystals of hornblende may average an 

inch in diameter, but predominantly the rocks are medium grained. 

All show a highly schistose structure.

Plagioclase is variable in amount, and in the dominantly hornblende schist it is usually restricted to the interstitial groundmass, 

where it may serve as a matrix for radiating sheaves of hornblende 

crystals which have grown at an angle to the foliation. The plagioclase is for the most part clear and untwinned, but in part twinned; 

it was determined in three different specimens as an albite a^ trifle 

more sodic than albite-oligoclase (AbgAri!). Common accessory
WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS 67

minerals in all the schist are biotite and calcite and, in minor amount, 

apatite, magnetite, epidote, and pyrrhotite.

Thin layers of limestone are here and there isoclinally folded in 

the schist, which, but for their presence, would show little or no 

evidence of such close folding.

Much of the hornblende is fibrous, the plagioclase may be crushed 

or show irregular extinction, and the quartz may exhibit wavy extinction as a result of pressure following the crystallization of the schist.

On the south side of Port Houghton, east of the belt of hornblende schist, there is a wide .belt of garnetif erous quartz-mica schist, 

which is of a surprisingly uniform character and which forms the 

coast line from a point just west of Walter Island Arm eastward 

to a point within 2 miles of the bar at the entrance to the Salt Chuck. 

The beds strike northwest and, except for local folding, have a 

uniform steep northeasterly dip. The schist is exposed for a width 

of 6 miles, measured at right angles to the strike. Locally, sills of 

quartz diorite and dikes of aplite are intrusive in the schist, as in 

the vicinity of Walter Island Arm, and more rarely a few beds of 

the schist are intimately veined with narrow quartz veinlets. Layers 

of hornblendic quartzite as much as 6 inches thick are present in very 

minor amount in the schist.

The schist is very thinly cleavable, and its cleavage surfaces exhibit 

a bright brownish sheen and are studded with red garnets showing 

crystal faces. The garnets are prevalently about three-sixteenths of 

an inch in diameter but range generally from an eighth to a quarter 

of an inch and in local beds are as much as half an inch. In the 

prevalent type of richly garnetiferous schist the garnets form from 

10 to 20 per cent of the rock by volume. Locally there are thin 

layers and beds composed almost wholly of granular garnet, which 

on weathering has a friable character.

In thin section the predominant mineral is found to be quartz, 

with garnet and brown mica as abundant major accessories. The 

quartz may be either granular or in elongate plates, oriented with 

their longer diameters parallel to the foliation. The mica is predominantly biotite, oriented with its longer diameters parallel to the 

cleavage. Muscovite is common but usually in minor amount. The 

garnets have for the most part been formed through a process of replacement, for the banding of the minerals is in general cut off 

sharply at their edges and the original puckered structure of the 

schist is still preserved as a relic structure in the garnets. The garnets have to some extent forced aside the adjoining laminae. Black 

graphitic dust is abundant more or less uniformly disseminated 

throughout the minerals of the schist. Tourmaline in crystal rods 

is a common minor accessory mineral, as well as pyrrhotite, which
68 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

occurs in irregular-shaped grains, oriented with the longer diameter 

parallel to the foliation. In some beds staurolite, cyanite, or hornblende may occur as a minor accessory mineral.

The rocks forming the south and east sides of the Port Houghton 

salt chuck are almost uniformly rusty-weathering brown quartzfeldspar schist. In the northern part some aplitic injection is 

apparent, but usually the rocks do not show any banding. Their 

general strike is a little west of north and their dip from vertical 

to 50° W. In thin section they are found to consist predominantly 

of quartz and plagioclase (oligoclase to oligoclase-andesine), with 

orthoclase and biotite as major accessories. Garnet, muscovite, pyrite, magnetite, and apatite are common minor accessory minerals. 

Locally hornblende may be common.

Another belt of quartz-feldspar schist is found on Endicott Arm, 

about 10 miles from the head. The beds here are intimately injected 

by quartz lenticles, lenses, and veins. Beds of quartzite, in part 

chertlike, and hornblende schist are intercalated. Locally the schist 

consists of alternating thin layers of limestone, quartz, and mica 

schist. Most of the beds weather rusty.

About iy2 miles west of the bar at the head of Port Houghton 

there is a half-mile belt of a very peculiar calcareous hornblende 

schist, which weathers with a pockety cavernous appearance due to 

the solution of the limestone. Cherty quartzite beds with thin layers 

of limestone and quartz-feldspar schist are interbedded.

HOBART AND WINDHAM BAYS

A belt of phyllite is well exposed on Hobart Bay and on the west 

half of Windham Bay. It consists of interbedded dark and light 

silvery-lustered, sheeny crinkled phyllite, associated with sparse 

beds of muscovitic limestone and calcareous schist, which are better 

crystallized than the phyllite. Quartz, biotite, chlorite, sericite, and 

feldspar are common visible constituents. Hornblende is common in 

sparse layers. The phyllite on Hobart Bay is intimately veined 

with quartz, but in much of the belt on Windham Bay only a few 

strong quartz veins were observed. Masses of dark metadiorite 

(sills?) are abundant in the phyllite near the contact with the greenstone belt both on Hobart Bay and in parts of the belt on Windham 

Bay. Similar interbedded gray and black argillaceous phyllite is 

exposed on Sanford Cove, Endicott Arm.

HOLKHAM BAT AND TRACT ARM

Holkham Bay and Tracy Arm afford an excellent cross section 

of the Wrangell-Kevillagigedo belt of metamorphic rocks, ranging 

from dynamically metamorphosed, highly schistose fossiliferous
WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS 69

beds on Stephens Passage through beds of phyllite and schist to 

relic and injection gneisses occurring as bands within the western 

border of the batholith.

On the southwest there is a bed of phyllite and slate with sills 

and dikes of metadiorite about 2^ miles in width. This belt extends 

far to the northwest across Port Snettisham and Taku Inlet to a 

point about 10 miles north of Juneau and just south of Berners Bay, 

where it merges into a belt of schist adjacent to the batholith. North 

of Port Snettisham the belt narrows from V/2 miles to half a mile 

in width. This belt corresponds to the black slate band of Spencer.58

On Holkham Bay the beds consist of a series of interbedded 

whitish sericitic phyllite, green chloritic phyllite, and black argillaceous phyllitic slate, locally with dark-colored metadiorite sills 

or dikes. Adjoining these beds on the east is green chloritic phyllite with beds of intercalated argillaceous phyllite.

Normal black slate is not found in this area nearer than 5 miles to 

the batholith. Sheets of aplite are found up to a point 3 miles from 

the contact. Limestone 6 miles from the contact is highly schistose 

but not recrystallized.

Between the phyllite and the border of the batholith is a belt of 

schist 2 to 2,y2 miles in width. This belt comprises interbedded 

quartz-mica gneiss, hornblende schist, and a band of chloritic micaceous hornblende schist, all with sheared aplite sills. Adjacent to the 

batholith glassy quartz veinlets a fraction of an inch to an inch wide 

are abundantly injected parallel to the foliation, together with aplitic 

veins. Farther away local shear zones with quartz veins and bunches 

of quartz are common. Many of the beds weather rusty. The band 

of aplitic injection gneiss is not more than half a mile wide.

The east branch of Tracy Arm cuts across the Coast Kange batholith at an angle of about 60° to its trend for 15 miles. The walls of 

the fiord here afford a most extraordinary opportunity to study the 

phenomena of reaction between the magma of the Coast Range batholith and the sediments which it has included and metamorphosed. 

Most of the rock in this belt is a shatter breccia consisting of quartz 

diorite and granodiorite with fragments of schist in various stages 

of assimilation. Many large belts of injection gneiss are also included. 

It is doubtful if there is exposed anywhere within this 15-mile 

belt an area as much as 10 feet square which does not contain at least 

one small inclusion. It seems probable that one-third of the batholith in this section is included country rock. All gradations between 

blocks of clean sediment without injection, injection gneiss, and reaction or relic gneiss are found. The only clean belt of quartz diorite

68 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, p. 17 

1906.
70 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

is on the western border and is about 3% miles wide. Even this has 

abundant small isolated stringers of inclusions throughout, and near 

the contact these inclusions are common, probably amounting to several per cent of the rock. Pegmatite veins are noticeably absent in 

this belt of quartz diorite.

Kelic or reaction gneiss, together with relatively clean sheets of 

quartz diorite and beds of gneiss and marble, forms a belt 2 miles 

wide east of the belt of relatively clean quartz diorite, and each of 

the other belts mapped as quartz diorite is in reality of this mixed 

character. The relic or reaction gneiss is mostly diorite or granodiorite with a ghostlike breccia or banded structure inherited from 

the blocks of sediment which have been incorporated as part of the 

rock through reaction with the magma. Much of the reaction appears 

to have been brought about by pegmatitic material, and this appears 

at many places as veins in the inclusions.

The injection gneiss consists predominantly of dark micaceous 

varieties with more or less pegmatitic injection. Hornblende, actinolite, and quartz schists are intercalated. Medium to coarsely crystalline limestone occurs for the most part as beds several feet thick in 

the gneiss, but beds of relatively clean marble as much as 100 feet 

thick are found. Bunches of silicates are common in the limestone; 

these include green pyroxene, red garnet, yellow chondrodite, scaly 

brown phlogopite mica, and rarely a little lavender-colored spinel.

JUNEAU DISTRICT

Spencer 59 has described the schist belt in the vicinity of Juneau 

as follows:

Beds of quartz sand now indurated to quartzite and strata of limestone 

now partly changed to marble occur at different horizons, but the great mass 

of the series is garnet, mica, and hornblende schist, presumably derived for the 

most part from the crystallization of calcareous and argillaceous sandstones 

and shales. It has been proved that certain layers of hornblende schist are 

derived from gabbro rocks, such as are locally found in a relatively unaltered 

state.

Knopf 60 has described a belt of schist which lies between the slategraywacke formation and the quartz diorite of the batholith in the 

Juneau district and ranges in width from a few hundred feet at 

Berners Bay to 2 miles at Mendenhall Glacier.

The schists are most highly crystalline in the zone directly bordering the 

quartz diorite gneiss, but toward the southwest they grade through phyllites 

and biotitic slates into the clay slates and graywackes of the next adjoining

69 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, p. 16, 

1,906.

60 Knopf, Adolph, The Eagle River region, southeastern Alaska: TJ. S. Geol. Survey BulL 

502, pp. 20-22, 1912.
WRANGELL-EEVILLAGIGEDO BELT OP METAMORPHIC ROCKS 71

belt of rocks. * * * The schists comprise a variety of rocks, mainly of sedimentary derivation. * * * Biotite, garnet, and amphibole are the most 

common minerals of metamorphic origin that are easily distinguishable; 

* * * staurolitic and cyanitic schists are found locally. * * * Coarsely 

crystalline white limestone is interstratified with the schists in beds ranging up 

to 50 feet in thickness but is not particularly abundant and is usually restricted to the outlying masses of schist in the gneiss.

SCHISTOSE GREENSTONE AND PHTLLITE BETWEEN PORT HOUGHTON AND

JUNEATJ

A group of rocks consisting of schistose greenstone and green 

chloritic phyllite interbedded with black and gray sericitic slaty 

phyllite and sparse dolomite or limestone beds and schistose chert 

form the Kobert Islands and Point Walpole at the entrance to Port 

Houghton, the outer coast between Port Houghton and Windham 

Bay, and several belts on the land between Windham Bay and 

Endicott Arm. A particularly large belt forms the Harbor Islands 

and the broad peninsula at the south entrance to Endicott Arm and 

extends northwest through the Snettisham Peninsula, Limestone and 

Slocum Inlets, and along the east side of Gastineau Channel, being 

here well exposed between Point Salisbury and Bishop Point.

Along the coast between Port Houghton and Windham Bay the 

group consists of interbedded schistose green hornblende porphyry, 

green schist with aphanitic texture, and black and light-gray phyllite. 

The green schist does not form the major part of the group of rocks 

but is characteristic of it. Some beds show conspicuous evidence 

of having once been fragmental. The fragments are felsitic in 

texture and andesitic. Pyrite and pyrrhotite are locally disseminated through the black phyllite, which weathers red more commonly 

than the light-colored phyllite. The group of rocks is excessively 

veined with quartz, which occurs as bunches, as numerous thin 

plates and lenticles, and sparingly as strong wide veins. All the 

quartz is glassy and is associated with varying amounts of calcite. 

Masses of dark metadiorite cut the beds. Locally the beds are 

veined and intruded by aplite sills and dikes, which are folded with 

the series, as are also many of the quartz veins. The beds show 

every evidence of intense folding and plication. Overthrust 

isoclinal folds that dip 35° to 40° NE. are evident everywhere.

Most of the Snettisham Peninsula except the eastern part is composed of schistose and phyllitic greenstone with intercalated beds 

of schistose limestone, black slate and phyllite, and sparse beds of 

schistose chert and conglomerate. The beds strike about northwest 

and dip northeast. At the south end of the peninsula the succession 

of beds from southwest to northeast is as described below. The 

6137 29 6
72 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

lowest beds comprise interbedded schistose limestone, black slate, 

white chert, and a felsitic greenstone that appears to be in part a 

sheared amygdaloid with flattened calcite amygdules and is in part 

a yellowish-green chloritic epidotic schist. On the shore of the 

peninsula northeast of the Midway Islands there is a 100-foot bed of 

schistose limestone, with many layers full of corals or crinoids or 

both, of Carboniferous age. These beds are overlain by a thick 

series of schistose greenstone of felsitic texture. Part of this has a 

peculiar nodular or lenticular structure, as if formed from shearing 

of a fragmental rock; the matrix is similar to the nodules except 

that it is more sheared. Part of the greenstone is apparently mashed 

amygdaloidal andesite. About 2y2 miles due east of Point Coke, at 

the point at the entrance to Tracy Arm, the greenstone is overlain 

by a bed of white limestone with intercalated layers of schistose 

white chert. This bed of limestone is lithologically identical with 

the Carboniferous limestone of Taku Harbor. It strikes northwest, 

dips 55° NE., and is overlain by beds of black phyllitic slate with 

similar strike and dip. The contact between the limestone and slate, 

however, is faulted.

At the north end of Snettisham Peninsula the cove east of Point 

Anmer is carved out of limestone with poorly preserved silicified 

fossils. These beds are underlain by interbedded schistose limestone 

and greenish-gray schist and are overlain by greenstone with intercalated beds of schist. Eastward, toward Snettisham, the beds are 

successively quartz-mica schist, schistose conglomerate that consists 

in part of chert pebbles, and green schist that contains lenticles of 

limestone and intercalated beds of schistose white chert and black 

slate. Large sheared coral heads occur in some of the beds of green 

schist. Some of the greenstone shows what appears to be a welldefined pillow structure. The series is lithologically similar to the 

Carboniferous beds of Windfall Harbor, on Admiralty Island. The 

limestone with Carboniferous fossils on Stockade Point, Taku Harbor, has previously been described.61 It consists of thick, massive 

beds with rare layers of white chert. On the east this limestone is 

associated with black graphitic slate or phyllite and nodular limestone in a matrix of black bituminous limestone. On the south 

there are beds of fragmental schistose greenstone with associated 

black phyllite.

On the east side of Taku Harbor there is a series of green chloritic or calcareous phyllite with thin beds of limestone and white 

chert. On Limestone Inlet the greenstone volcanic rocks are more 

massive and consist of amygdaloidal rock and breccia.

61 Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

Geol. Survey Bull. 347, p. 55, 1908.
WRAETGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS 73

AGE

The determination of the age of the Wrangell-Revillagigedo belt 

of metamorphic rocks is a very difficult problem. Along the coast 

between Prince Eupert and the mouth of Portland Canal Dolmage ca 

maps it as the Prince Rupert formation, of .Triassic or Carboniferous 

age. The Wrights 63 make the following statement with respect to 

the Ketchikan and Wrangell districts:

In view of the comparatively weak paleontologic and stratigraphic evidence 

bearing on the precise age of these argillites and crystalline schists, it is possible that their period of deposition extended even beyond the Carboniferous 

period into the Triassic. * * * The evidence thus far gathered, however, 

indicates Carboniferous age for the greater portion of these crystalline schists 

and argillites.

Chapin,04 mainly on lithologic and structural grounds but with 

some paleontologic evidence, has described the phyllite and crystalline schist with associated conglomerate and limestone on George 

Arm, Revillagigedo Island, as including both Carboniferous and 

Triassic formations.

Kirk found fossils that he identified as of Ordovician age in beds 

at Wrangell, but the organic traces are very imperfectly preserved 

and to the writer the identifications seem open to question.

Fossils identified by Girty as Carboniferous (lot 5138: Batostomella? sp., Stenopoity? sp., and Spirifer? sp.) were collected by Buddington from schistose limestone associated with greenstone on the 

shore of the Snettisham Peninsula northeast of the Midway Islands. 

Carboniferous fossils (Productus aff. P. gruenewaldti] had previously 

been reported by Kindle from Stockade Point, on Taku Harbor. 

Eakin found Triassic fossils in the belt of slate east of Juneau. 

Martin has referred the greenstones or Gastineau volcanic group on 

the east side of Gastineau Channel to the Upper Triassic and the 

Thane volcanic group to the lower or Middle Jurassic (?). He 

refers the schist (Clark Peak schist) east of the slate and phyllite 

belt to the Paleozoic.

Buddington is of the opinion that the greenstone of the Snettisham 

Peninsula belt and its extensions to the northwest and southeast is 

largely of Carboniferous age and is to be correlated with a similar 

lithologic series of rocks exposed on the east side of Saginaw Bay, 

Kuiu Island. Both Triassic and Devonian rocks and perhaps some

63 Dolmage, Victor, Coast and islands of British Columbia between Douglas Channel and 

the Alaskan boundary : Canada Geol. Survey Summary Kept, for 1922, pt. A, pp. 9-34, 

1923.

. M Wright, F. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

Geol. Survey Bull. 347, p. 66, 1908.

64 Chapln, Theodore, The structure and stratigraphy of Gravina and Revillagigedo 

Islands, Alaska: U. S. Geol. Survey Prof. Paper 120, pp. 18, 90-91, 1918.
74 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Jurassic may be associated with the Carboniferous in minor amount. 

North of Taku Inlet most of the greenstones may be younger, as 

suggested by Eakin and Spencer and by Martin.

On the west side of the south arm of Port Snettisham and the west 

side of Prospect Cove schistose conglomerate is interbedded with 

black phyllite. This conglomerate is lithologically similar to the 

conglomerate in the Jurassic or Cretaceous slate on the west side 

of Seymour Canal, Admiralty Island.

It seems probable that the Carboniferous and Triassic formations 

constitute a very considerable part of the Wrangell-Revillagigedo 

belt of metamorphic rocks, but that possibly beds as young as Cretaceous and as old as Ordovician are included. The areal geology 

and formational relations in the vicinity,of Keku Straits, at the 

north end of the Kuiu Island, and the northwest end of Kupreanof. 

Island (Tertiary formations excepted) seem to Buddington to represent an approximation to the original character and relations of these 

metamorphic rocks.

ORDOVICIAN BOCKS

A thick series of beds of graywacke with associated slate and 

locally with andesitic volcanic rocks forms most of Kuiu Island and 

a considerable part of Prince of Wales and the neighboring islands. 

The beds have heretofore been assigned wholly to the Silurian system, but the work done by the writer has shown that they are predominantly of Lower and Middle Ordovician age but also in part 

early Silurian.

PRINCE OF WALES AND NEIGHBORING ISLANDS

Character and ocewn^ence. At the south end of El Capitan Passage, north of Cap Island, there is a series of andesitic volcanic rocks 

3,000 feet or so thick, overlain by about 1,000 feet of andesite conglomerate, in part with limestone cobbles and boulders. The conglomerate is of Silurian age, as some of the limestone fragments 

carry Silurian fossils. The greenstone volcanic rocks comprise 

porphyritic andesitic lava containing pyroxene phenocrysts, in part 

with pillow structure; andesite porphyry conglomerate, composed of 

fragments that are only slightly waterworn, or breccia; and some 

graywacke with associated slate. The graywacke and slate intercalated in the lower part of the volcanic series carry Middle Ordovician graptolites.

Fossiliferous slate of Ordovician age is interbedded with the 

andesitic volcanic rocks at the head of Van Sants Cove, Kosciusko
ORDOVICIAN ROCKS 75

I

Island, and at the south end of a small island in Tonowek Bay, about 

2 miles southwest of the west headland of Nossuk Bay. Beds 

carrying graptolites of Ordovician age are found also on Thorne 

and Stevenson Islands, the southwest side of Heceta Island, San

, v Fernando and Lulu Islands, and Thorne Bay and Klawak Salt 

Lake, Prince of Wales Island.

The Ordovician beds on the northeast side of Prince of Wales 

Island consist predominantly of indurated graywacke, prevalently 

in beds 1 foot to several feet thick with slate partings, but some 

of the beds are so uniform in character that the bedding can not 

be distinguished, even in large outcrops. In part the formation 

consists of thin-layered graywacke with slate laminae in zones interbedded with the thicker-bedded phases. Fine conglomeratic and 

gritty layers are common locally in the graywacke, and, sparingly, 

beds of conglomerate. Calcareous pockets are common in some of 

the beds of graywacke. Along the shores of the arm northwest of 

Thorne Island the formation consists predominantly of black slate 

with thin quartzitic laminae. Limestone nodules are common locally 

in these beds, and beds of schistose brecciated limestone as much as 

20 feet thick occur. On Stevenson Island slate predominates over 

graywacke, though the beds of graywacke are as much as 40 feet 

thick. On the east side of the island the beds are fractured and 

faulted on a minute scale, and breccia zones with thin calcite veinlets 

are common. Rarely a zone of thin-layered black chert is intercalated in the graywacke-slate series. The predominant fragments 

in the intercalated conglomerate are limestone, slate, felsite, and 

andesite porphyry.

Examination of typical specimens of these rocks with the microscope shows a common type to consist predominantly of more or 

less angular fragments of plagioclase, associated with a little quartz,

' orthoclase, bits of volcanic rock, including felsite and andesite with 

very irregular borders, and sparse particles of limestone and chert. 

The groundmass is in places slightly calcareous. Another less common type lacks quartz but contains plagioclase, abundant fragments 

of pyroxene, and bits of lava that is for the most part of andesitic 

type.

* The northwest shore of Klawak Salt Lake and the island barrier at 

its mouth consist of thin-layered black chert with partings of black 

graphitic graptolitic slate, nonfossiliferous black slate, and intercalated beds of dense banded green quartzitic graywacke and 

quartzite.

Fossils. The age of the beds on Prince of Wales and the neighboring islands is based on the dozen collections made by Buddington
76 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTEEN ALASKA

and identified by Rudolf Ruedemann, of the New York State 

Geological Survey. The specific identifications are given in the 

following table:

Ordovwwn graptolite fauna from Prince of Wales and neighboring islands

[Determinations by Rudolf Ruedemann]

Diplograptus (Orthograptus) 

calcaratus cf. var. incisus.. _ .

Diplograptus (Olyptograptus)

Diplograptus euglyptus _ _

Diplograptus amplexicaulis .......

Climacograptus bicornis var. triClimacograptus sp. cf. C. eximius

Didymograptus sp. cf. D. nitidus.

Tetragraptus cf. T. quadribrachiCryptograptus tricornis cf. var.

Hallograptus mucronatus cf. var.

Lower Ordovician

1995 

(1543)

X

2001 

(2052)

v

y

V

2004 

(2164)

X

X

1

Horizon undetermined

2003 

(2146)

X

1997 

(1796)

X

Normanskill

2000 

(1904)

X

X

X 

X

2002 

(2116)

X

X

X

y

X

X

X

X

(658)

X

(706)

X

Trenton

(1076)

X

1996 

(1671)

X

1995 (1543). Kosciusko Island, head of Van Sants Cove; black slate interbedded with greenstone volcanic rocks; last Deep Kill zone, top of Beekmantown or lower Chazy.

2001 (2052). Four localities on the islands forming the barrier at the niouth 

of Klawak Salt Lake; thin-layered black chert with black slate laminae; third 

Deep Kill zone, upper Beekmantown.

2004(2164). South side of Lulu Island at west end of Port Real Marina; 

black chert with slate laminae.

2003 (2146). South end of San Fernando Island, about 1% miles north-northwest of Point Amargura; black chert with slate laminae; Ordovician, horizon' 

undetermined.

1997 (1796). South end of small island in Tonowek Bay about 2 miles southwest of the west headland of Nossuk Bay and a little north of true west of 

large island with hill (altitude 430 feet) ; graptolitic slate and graywacke 

interbedded with pillow lava; Ordovician.

2000(1904). Cove about .3 miles northwest of Point Desconocida, Heceta 

Island; interbedded black slate and graywacke; Normanskill.

2002 (2116). Northwest side of Klawak Salt Lake, about 4 miles from the 

head; Normanskill.
OEDOVICIAN ROCKS 77

(658). About a quarter of a mile southwest of the northeast tip of Thorne 

Island off the northeast coast of Prince of Wales Island; late Normanskill or 

younger.

(706). Point one-fourth mile west of Point Barnes, Stevenson Island; interbedded slate and graywacke; Normanskill.

(1076). East headland of cove about the center of the southwest side of the 

northwest arm of Thorne Bay, Prince of Wales Island; probably younger than 

Normanskill.

1996(1671). El Capitan Passage, islets 2 miles west of Hub Rock; graywacke and black slate intercalated in andesitic volcanic rocks; Trenton.

Kirk 65 has reported supposed Ordovician graptolites in the slate 

and phyllite near Wrangell, as follows:

On the point forming the south side of Wrangell Harbor graptolites were 

found that seem to fix the age of this Wrangell series. The graptolites are 

found both in slate and schist. The slate specimens are unrecognizable unless 

one knows they are graptolites to begin with. The specimens occurring 

in the schist, though badly preserved, are easily recognizable as graptolites, 

and the generic affinities of one individual may be determined with a fair 

degree of certainty.

The specimen of chief importance and interest is referred with little doubt 

to Tetraffraptus. It is very like a large species known' in the early Ordovician of 

Idaho. Other specimens not so well preserved strongly suggest Phyllograptus. 

These fossils clearly point to the Beekmantown age of the sediments.

Kirk's determination thus suggests that the fauna of the beds near 

Wrangell is older than the fauna of Prince of Wales Island. These 

apparent organic structures are so poorly preserved, however, that 

their determination is open to serious question.

KUIU ISLAND

Most of Kuiu Island except the northeast part is formed of 

beds of graywacke and slate that lithologically resemble the known 

Ordovician and early Silurian beds of Prince of Wales and adjoining islands. They underlie greenstone-limestone conglomerate belonging to the lower part of the upper Silurian section. No fossils 

have been found in the gray\vacke or slates of Kuiu Island and their 

age is unknown. They are possibly mostly Ordovician, with some 

associated lower Silurian beds in locally infolded synclinal troughs.

The Kuiu Island beds consist predominantly and characteristically of fine to coarse grained pale-green to whitish-gray graywacke 

in beds 1 ifoot to 10 feet thick, with dark-gray slate partings. Intercalated in the graywacke are zones of interlayered limestone and 

slate, or slate and graywacke, or limestone, slate, and graywacke. 

In the thin-layered limestone-slate beds the limestone layers are an 

inch or less thick and the slate a fraction of an inch thick. Fine 

conglomeratic beds several inches thick are common in the gray85 Kirk, Edwin, An Ordovician fauna from southeastern Alaska [abstract] : Geol. Soc. 

America Bull., vol. 29, pp. 143-144, 1918.
78 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

wacke, and rarely a bed several feet thick occurs. Black impure 

limestone occurs sparingly in beds as much as 25 feet thick; also black 

graywacke. Karely beds of thin-layered black chert are intercalated.

The graywacke is usually fractured on a minute scale, and the 

thin-layered zones are crumpled and plicated. Faults of small displacement are common. The beds are highly indurated and brittle. 

Owing to the fragmental character of the rock, a fine to coarse 

hackly surface often results tfrom weathering. The weathered surface is usually brown, owing to the oxidation of disseminated particles of pyrite, or pale greenish gray where smoothed and polished 

by wave action.

On Reid Bay the graywacke is in beds 9 inches to 6 feet thick, 

commonly between V/2 and 2^ feet, with black slate partings a 

fraction of an inch to an inch thick. The slate weathers to a reddish hue. Along Affleck Canal and Port Beauclerc the beds are 

several feet to 10 feet thick with a few fine conglomeratic layers. In 

part the graywacke is uniform, with only scattered calcareous 

pockets. In part it is marked by layers of calcareous lenses, which 

in places grade into calcareous layers an inch or so thick and an inch 

to several inches apart.

The beds of thin-layered limestone, slate, and graywacke have at 

many places been infolded with the more competent thick-bedded 

graywacke. Many of them are isoclinally folded, plicated, overthrust, and brecciated. Locally they have been completely crushed 

to a fault breccia or even compressed to a schistose aggregate composed of eyes of limestone an inch to several inches in length in an 

argillaceous matrix. As a rule the thin beds have a much steeper dip 

than the graywacke. Where least (Jisturbed, the beds range from 

several feet to 100 feet or more in thickness, but where folded they 

have a very much greater thickness as a result of duplication. The 

individual layers usually range from a fraction of an inch to several 

inches in thickness.

The limestone is dense to very fine grained and nonfossiliferous; 

it is in part light bjue-gray on fresh surface, weathering white, and 

in part dark gray to black. The slate is black, locally weathering 

with a reddish hue. The graywacke is similar to that of the thickbedded phases.

The coarser graywacke is seen in the hand specimen to be composed 

of fragments of dense felsite, chert, black slate, graywacke, limestone, 

and particles of plagioclase, pyroxene, hornblende, orthoclase, and 

quartz. Felsite and plagioclase fragments are most abundant.

The felsite fragments are angular and pearl-gray or pale greenish 

gray to white, weathering white. In the hand specimen they are 

distinguished with difficulty from the chert fragments but in thin 

section they are found'to consist almost wholly of abundant microlites
SILURIAN BOCKS 79

of plagioclase in a microcrystalline groundmass. Karely fragments 

are found which appear to be composed of quartz and feldspar. The 

plagioclase laths are commonly in flowage alinement but occur also 

in crisscross arrangement. The large plagioclase fragments in the 

graywacke are oligoclase-andesine, and tKe angle of extinction of the 

microlitic feldspars in the felsite indicates that they are similar. 

Chert and slate fragments are next in abundance to the felsite and 

plagioclase. Limestone particles are practically everywhere present 

though locally sparse. The particles of pyroxene and hornblende 

are fresh and angular; rarely an almost euhedral crystal of hornblende is present. The pyroxene is more common than the hornblende, but both are subordinate in amount. Orthoclase and quartz 

occur only as minor accessory minerals.

The character of the fragments and their subangular to angular 

shape suggest that the graywacke is composed of more or less waterworn volcanic tuff.

On Eeid Bay and extending southeast to Sumner Island there is a 

synclinal trough of Silurian volcanic and sedimentary rocks overlying the graywacke series. On Edwards Island and along the 

southwest side of Port Beauclerc there is a basin of similar Silurian 

beds. The Silurian age of these beds is definitely proved by their 

local association with beds of limestone that carry Silurian fossils 

and by the presence of Silurian fossils in boulders in the conglomerates. There is no difficulty in distinguishing the characteristic 

graywacke of Ordovician (?) age from the typical Silurian beds; 

but between the two is a series of beds which are usually highly 

deformed, with structural relations obscured. They consist of thinlayered limestone with layers of slate and graywacke and locally with 

schistose beds of breccia or conglomerate.

In the narrows at the entrance to the salt lake at the head of the 

Bay of Pillars thin-layered argillaceous and siliceous limestone overlies the graywacke, and on the inner side of the narrows the limestone is in turn overlain by coarse conglomerate. The thin-layered 

limestone resembles certain beds of the Silurian and is probably of 

Silurian age.

SILURIAN ROCKS

DISTRIBUTION

Silurian beds have a wide distribution throughout the Alexander 

Archipelago and in the vicinity of Glacier Bay. They are exposed 

on the flanks of anticlinal arches or within subordinate synclines in 

anticlinoria of Ordovician formations. They comprise beds of widely 

varying character, possibly 14,000 feet in total thickness. The lowest formation of the system appears to be a series of interbedded 

black slate and graywacke with sparse limy layers and conglomerate
80 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

beds. This formation is indistinguishable lithologically from the 

Ordovician beds, but the slate carries graptolites identified by Kuedemann as of lower Silurian age. Overlying these beds are, in succession, a series of interbedded and^sitic volcanic rocks and conglomerate 

composed of lava and limestone; interbedded limestone and conglomerate or limestone with locally a little conglomerate; shale; and graywacke or gray wackelike sandstone. In general the graywacke is composed of particles of rock similar to the kinds that form the pebbles 

and cobbles in the conglomerate but in a more finely comminuted state 

and associated with a considerable percentage of plagioclase, potassic 

feldspar, and quartz. The limestone and higher formations are not 

older than late middle Silurian, according to identifications of fossils 

made by Kirk.

On Dall Island Silurian formations occupy practically the whole 

area between the Diver Islands and the small cove north of Cape 

Augustine and between Breezy Bay and Coco Harbor. Buddington 

believes that the belt of limestone between Waterfall Bay and Grace 

Harbor is also of this age. The Silurian rocks exposed here consist 

of a lower part made up of dark-gray to black slate with thin calcareous or siliceous layers and sparse intercalated graywacke and thin 

limestone; and an upper part of white limestone, estimated to be 

2,000 feet thick. Graptolites identified by Ruedemann as of lower 

Silurian age were found by Chapin in graphitic slate at View Cove 

and by Buddington in slate on the north arm of Sea Otter Sound.

On the northeast end of Forrester Island there is a narrow fringe 

of conglomerate of Silurian type bordering intrusive granodiorite.

On Long Island, in Cordova Bay, there are two belts of Silurian 

limestone. It is probable that a part of the Wales group of metamorphic rocks belongs to the Silurian system.

Kosciusko, Heceta, Tuxekan, Orr, and Marble Islands consist for 

the most part of thick massive Silurian limestone, which in general 

dips in toward Davidson Inlet and Sea Otter Sound and thus forms 

the rim of a great major synclinal basin, which is,, however, modified 

by many minor folds. The section of the Silurian exposed around 

the borders of this basin is very much more complete than that on 

Dall Island.

Silurian beds form much of the northern half of Prince of Wales 

Island and are well exposed on the Kashevarof Islands on the nose of 

a plunging anticline whose core is composed of Ordovician beds. 

On Kuiu Island they are exposed in several narrow synclinal troughs, 

as along the west side of Port Beauclerc, in a belt extending northwest 

from Summer Island, along the southwest side of Saginaw Bay, 

and at the narrows on the Bay of Pillars. They are also exposed on 

Tenakee Inlet and Freshwater Bay, Chichagof Island, and around 

Glacier Bay on the mainland.
SILURIAN ROCKS 81

If all the beds which on faunal evidence are assigned to the Silurian 

have been correctly identified, then the Silurian system comprises 

the most heterogeneous and the thickest set of rocks, about 14,000 feet, 

in the geologic column of southeastern Alaska.

LOWER SILURIAN SLATE AND GRAYWACKE

The lowest beds of Silurian age are exposed on the southwest side 

of Heceta Island, the north end of Lulu Island, the east side of Noyes 

Island, between Cape Augustine and Diver Islands and on .View Cove, 

Dall Island, and on Kassa and Klakas Inlets, Prince of Wales 

Island.

The predominant beds of this formation consist of dark to black 

graphitic slate with interbedded graywacke and some associated limy 

layers and sparse conglomerate. On the north end of Lulu Island 

layers of slate carrying lower Silurian graptolites are intercalated 

in conglomerate that contains pebbles of slate, diorite, rhyolite, and 

limestone. On Dall Island rocks assigned to the lower Silurian 

form the coast line from the first cove north of Cape Augustine north 

to the limestone belt of the Diver Islands. This belt extends across 

to View Cove on the east side of the island but pinches in this direction. The beds consist of dark-gray to black slate, thin bedded, with 

siliceous or calcareous layers and with sparse intercalated thin limestone. Graywacke is present but sparse. The predominant rock is 

slate. Slickensided graphitic surfaces are exceedingly abundant. At 

the mouth of Devils Lake and other places there is several hundred 

feet of limestone with sparse intercalated beds of black slate.

The age of these rocks is based on graptolites collected by Buddington and identified by Ruedemann and on graptolites collected 

by Chapin and identified by Edwin Kirk. Chapin found graphitic 

slate with locally abundant graptolites at Klakas and Kassa Inlets on 

the west coast of Prince of Wales Island and at View Cove on Dall 

Island. The fossils from Kassa Inlet (!7AChl24) were identified 

by Kirk as Monograxptus sp.

Graptolite fauna of lower Silurian age from southeastern Alaska 

[Determinations by Rudolf Ruedemann]

Monograptus?.... ___ . ______ .... _ . _ . _ .... ........

2006 

(2345)

X

X

2005 

(2207)

1999 

(1903)

X

1998 

(1902)

X

X

2070 

(3072)

X

2071 

(3073)

X

X
82 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

2006(2345). East side of Noyes Island, about 2 miles southwest of Point San 

Francisco; interbedded graywacke, black slate, and sparse intercalated limy 

layers and nodules; Silurian (lower).

2005(2207). Lulu Island, north end, opposite Marabilla Island; thiii slate 

layers intercalated in conglomerate; probably Silurian (near base).

1999(1903). About 1% miles southeast of White Cliff, Heceta Island; interbedded black slate and graywacke; Silurian (lower).

1998(1902). Dead Tree Point, about 3 miles south of Cape Lynch, Heceta 

Island; from slabs of black slate occurring as fragments., in a conglomerate 

at the base of a thick Silurian limestone formation ; early Silurian (?).

2070(3072). Dall Island, Sea Otter Harbor, near head of north arm on north 

side; poorly preserved graptolitesi in slate.

2071(3073). Dall Island, Sea Otter Harbor, south side of north arm in cove 

north of small island; finely preserved graptolites in slate; these graptolites 

allow no closer correlation than that they belong to the Clinton of North 

America and the Llandovery of Great Britain.

VOLCANIC ROCKS AND CONGLOMERATE

The next younger formation is predominantly volcanic and conglomeratic. It is well exposed in narrow synclinal troughs on Kuiu 

Island; on Prince of Wales Island at Labouchere Bay, Port Protection, the west side of Exchange Cove, and Thorne Bay; and on the 

Kashevarof Islands. Locally it is found on San Fernando Island, 

at the south end of El Capitan Passage, on the north end of Cap 

Island, and on some of the adjacent northern islands. It is believed 

to be exposed also at other localities. The volcanic rocks on the west 

side of Van Sants Cove, Kosciusko Island, are probably in part at 

least of Silurian age.

At many places this formation is easily confused with the very 

similar Devonian or Ordovician volcanic rocks unless structural or 

f aunal evidence is available to differentiate them.

This formation has not been recognized in contact with the lower 

Silurian graywacke-slate series. At some places it is definitely overlain by upper Silurian limestone, but the nearest identified and underlying formation is the graywacke-slate series or volcanic rocks of the 

Ordovician. Part of the volcanic material has probably been derived 

from erosion of the Ordovician volcanic rocks. The position overlying the lower Silurian graywacke-slate series assigned to it in the 

stratigraphic sequence is based in part on paleontologic evidence.

The formation consists chiefly of volcanic rocks and of conglomerate composed of lava pebbles. In one locality it may consist predominantly of lava flows; in another exclusively of conglomerate 

composed of lava pebbles, and in another of both lava and conglomerate. The beds of conglomerate resemble those at the base of and 

intercalated in the limestone of the overlying formation.

Several different types of rock are comprised in the formation, 

including the following:
SILURIAN ROCKS 83

1. A conglomerate composed almost wholly of well-rounded andesite or andesitic porphyry cobbles and boulders; the matrix may be 

calcareous, and lenses of limestone are intercalated, but limestone 

cobbles are sparse.

2. A conglomerate composed almost wholly of limestone cobbles 

or boulders in a limestone or andesitic tuff-like matrix; this type is 

rare, but beds 100 feet thick are found.

3. Peculiar conglomerates -intermediate between 1 and 2, consisting 

of pebbles and cobbles of andesite and limestone in a greenish tufflike matrix.

4. A homogeneous-appearing andesitic rock composed of fragments of andesite in a matrix of the same material; the structure, 

which is apparently that of a conglomerate or waterworn breccia, can 

be distinguished only on favorable surfaces.

5. A uniform hornblende andesite porphyry with conspicuous 

phenocrysts and andesite with small phenocrysts of plagioclase or 

pyroxene; these form flows and locally show pillow structure.

6. Sparse layers of slate, beds of graywacke, and lenses or beds of 

limestone as much as 100 feet thick.

Rarely cobbles of diorite or of gray and red felsite are found in the 

conglomerate. Fragments of slate are locally abundant in some of the 

finer-grained beds. Rarely, also, the volcanic rocks consist of rhyolite 

flows and breccias, as at Sarheen Cove, El Capitan Passage. The 

limestone pebbles, cobbles, and boulders of the conglomerates tend to 

weather out and leave a characteristic pockety, openwork structure. 

(See pi. 17, B.)

The limestone fragments are usually of a dense-textured limestone 

typical of the Silurian, and many carry fossils of Silurian age. The 

.fossils are the same as those from the overlying limestone. It is therefore believed that the limestone conglomerates are intraformational 

and that the limestone fragments are of practically the same age as 

the volcanic fragments. Vertical movements of the sea bottom, perhaps local, must have accompanied the volcanism and resulted in contemporaneous erosion and submarine slumping of slightly compacted 

fine lime muds. A part of the volcanic material, at least, must have 

been erupted from central volcanoes, which were built up above the 

surface of the ocean and were thus subject to erosion.

LIMESTONE AND CONGLOMERATE

The succeeding formation consists of a very great thickness of limestone with local thick lenses of conglomerate. It is economically important because of its present and potential value as a source of limestone and some marble.

It forms a belt from Breezy Bay to Diver Islands from View 

Cove almost to Cape Lookout, and from a point opposite Howkan
84 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

to Waterfall Bay on Dall Island. On Long Island, in Cordova 

Bay, it forms two belts. Heceta, Tuxekan, Orr, Marble, Eagle, 

Owl, Hoot, White Cliff, and Kosciusko Islands consist almost wholly 

of this formation. The east side of Tuxekan Passage from Naukati 

Bay to Sarkar Cove, El Capitan Passage from Sarheen Cove to 

El Capitan, the Mount Calder Kange running northwest from 

Calder Bay through the Hole in the Wall to Labouchere Bay, a 

part of Port Protection, several miles of coast east of Point Baker, 

Strait Islands, Red Bay, and the coast for several miles to the west, 

the northern islands of the Kashevarof group, including Bluff, 

Shrubby, and Bushy Islands, the west side of Exchange Cove and 

the headland to the north, Prince of Wales Island, are all made up 

of limestone. On Kuiu Island Beauclerc Peak and the mountain 

ridge along the southwest side of Saginaw Bay consist of Silurian 

limestone. On Chichagof Island the marble of Basket Bay, Tenakee, 

and Freshwater Bay is probably in the same formation. In Glacier 

Bay a great range of coarsely crystalline upper Silurian limestone 

runs through Willoughby and Drake Islands and the east side of 

Rendu Inlet. These belts comprise most of the known Silurian limestone, but many other small areas have been observed, and there are 

very probably others not yet known.

. The limestone-conglomerate formation appears locally to overlie 

the volcanic rocks conformably. In many places the basal part consists of conglomerate of lava boulders and interbedded limestone and 

thus grades downward into the conglomerate and volcanic formation; 

in other places the limestone appears to rest directly on the volcanic 

rocks, as at Labouchere Bay. In yet other places, owing to possible 

faulting or erosion, the limestone lies in an unconformable relation 

directly against an older graywacke formation, as southwest of Saginaw Bay, Kuiu Island, and on the southwest side of Heceta Island. 

On View Cove and Sea Otter Harbor, Dall Island, the limestone 

overlies the lower Silurian slate and graywacke.

At Dead Tree Point, about 3 miles south of Cape Lynch, Heceta 

Island, limestone directly overlies conglomerate. The conglomerate 

consists of limestone cobbles and boulders; of flakes, slabs, and 

chunks of black graptolitic slate and graywacke; and of cobbles of 

andesite porphyry, granite, diorite, and rhyolite. Some of the limestone cobbles carry Silurian fossils, and the slabs of slate carry lower 

Silurian graptolites. This conglomerate, therefore, must mark an 

unconformity. On Cap Island, El Capitan Passage, about 1,000 feet 

of conglomerate of well-rounded andesite boulders intervenes between 

the limestone and the volcanic rocks. On the Kashevarof Islands 

and likewise north of Sarheen Cove, El Capitan Passage, conglomerate composed 'chiefly of'lava cobbles is interbedded with the
SILURIAN KOCKS 85

lower part of the limestone formation. This conglomerate includes 

some limestone cobbles and pebbles.

On the east side of Tokeen Bay beds of conglomerate and. intercalated limestone, of probable Silurian age, lie unconformably on 

indurated isoclinally folded graywacke of probable pre-Silurian age. 

The conglomerate passes upward into interbedded conglomerate, 

graywacke, and slate. The graywacke consists of bits of quartz, 

plagioclase, and andesite, Avith shreds of chlorite and grains of 

magnetite.

Conglomerate is not, however, restricted to the basal part of the 

limestone formation but may appear abruptly as. thick or extensive 

lenses or as intercalated beds within and even at the top of the 

formation. In some sections conglomerate is sparse or is not present, 

and beds of limestone as much as 2,000 feet in thickness are wholly 

free of argillaceous, sandy, or conglomeratic intercalations.

The conglomerate that occurs within the limestone formation is 

very well exposed in Halibut Harbor where it has a thickness of 

1,500 feet; west of Van Sants Cove, Kosciusko Island; on the east 

side of El Capitan Passage opposite Aneskett Point; at the south 

end of Tuxekan Passage, Prince of Wales Island; at the Bay of 

Pillars, Kuiu Island;, and on the Strait Islands. Beds 200 to 1,000 

feet thick are found at Cone Bay, at the head of Warm Chuck Inlet, 

Heceta Island, in Nossuk Bay, at the south end of Marble Island, and 

at Pole Anchorage, Kosciusko Island. Some of the limestone cobbles 

in the conglomerate at Halibut Harbor carry a Silurian fauna.

Conglomerate occurs at the top of the limestone formation on 

Bushy Island, in the Kashevarof group, and on Saginaw Bay. At 

Saginaw Bay it is interbedded with limestone carrying, Silurian 

fossils.

East of Edna Bay, Kosciusko Island, the conglomerate is composed predominantly of red rhyolite porphyry, some of which shows 

flow structure. Intercalated red rhyolite flows also appear to be 

present here.

Along the south end of Marble Island about 2,000 feet of graywacke and conglomerate overlying limestone is exposed in a syncline. The lower part consists of very thin-bedded graywacke and 

shale; the central part of thick-bedded graywacke or grit and pebble 

conglomerate; and the upper part of medium-bedded fine-grained 

graywacke and slate. The graywacke beds resemble those of the 

Shakan syncline, and it is not certain whether they are of Devonian 

or Silurian age. A specimen of graywacke, examined with the microscope, was found to consist of particles of andesite, felsite, plagioclase, granophyre, quartz, spherulitic rhyolite, and orthoclase. The 

groundmass is chloritic and slightly calcareous.
86 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

On Orr Island Silurian limestone is overlain by interbedded red 

and green sandstone and coarse conglomerate in apparently unconformable relations. The north arm of Cyrus Cove is cut along the 

contact between the conglomerate and the shaly limestone. The limestone that forms the west side of the north arm is along the line of 

strike of the conglomerate. At several places, however, beds of sandstone and conglomerate occur apparently interbedded with the limestone. On the east and west sides of the peninsula at the south end 

of Orr Island limestone crops out along the line of strike of the 

conglomerate, even where the two are only a short distance apart. 

In the lower beds of the conglomerate the major part or even all of 

the pebbles and cobbles are of limestone.

It is a question whether the conglomerate of Orr and Marble 

Islands should or should not be correlated with the sandstone of 

Naukati Bay and Karheen Passage. If so correlated, it is of Silurian 

age, and the apparently unconformable relations may mean only an 

abrupt change in conditions within the same general period of time.

The conglomerate is of a type and character found in southeastern 

Alaska, so far as the writer's knowledge goes, .exclusively in the 

Silurian system. It is prevailingly coarse pebble to cobble conglomerate with only a minor amount of finer-textured beds and with 

a few boulders as much as 2 feet in diameter. In some beds the 

pebbles and cobbles consist almost wholly of red felsite, or of felsite 

porphyry and limestone; in others, almost wholly of green andesite 

and andesite porphyry with plagioclase or pyroxene phenocrysts; 

here and there, almost wholly of limestone; but usually of andesite 

porphyry, amygdaloidal red basalt, red and gray felsite porphyry, 

limestone, light-colored and pink diorite, quartz diorite, monzonite, 

granite, red jasper, and chert in varying proportions. The fragments of granitoid rocks are almost everywhere present, though 

locally in minor amounts, and resemble very closely the intrusive 

rocks of the Coast Kange, to which they can not possibly have any 

genetic relation, as the conglomerate beds are locally intruded and 

metamorphosed by those rocks and are interbedded with or intercalated in fossiliferous Silurian limestone.

Some cobbles and boulders of the limestone carry Silurian fossils 

and must be of intraformational origin. The pebbles and cobbles 

of lava are similar to those found in the underlying volcanic formation, but rhyolite appears to be much more predominant in the 

conglomerate than in the lava flows. This change in proportion 

may be due in part to superior resistance of the rhyolite, but must 

be due in part to derivation from a source in which rhyolite was 

more prevalent with respect to andesite than in any rocks at present 

exposed in the Silurian or older formations in southeastern Alaska.
U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 17

A. MOliiVr CALDER, PRINCE OF WALES ISLAND 

A mountain of Silurian limestone

B. SILURIAN CONGLOMERATE, KUIU ISLAND 

Rock is composed of limestone and andesite in a waterworn tuffaceous groundmass
U. S. GEOLOGICAL SURVEY BULLETIN' 800 PLATE 18

A. MASSIVE WHITE SILURIAN(i>) LIMESTONE, DALI, ISLAND

R. FLOW BRECCIA OK MIDDLE DEVONIAN AGK, HESSA PENINSULA, 1'RINCK OK

WALES ISLAND
SILURIAN ROCKS 87

Doubtless, however, a large proportion of the lava cobbles were derived from the equivalent of the underlying conglomerate and volcanic formation. The pebbles and cobbles of granitoid rock have not 

been traced to their source, despite the fact that their size and 

abundance indicate a near-by local origin. It is possible that preSilurian batholithic rocks may yet be found within areas of the Ordovician or pre-Silurian formations. Otherwise it seems necessary to 

assume that they were derived from a land area composed of older 

formations with associated batholithic intrusive rocks which formerly 

stood to the west where now are the depths of the Pacific Ocean.

The association of very thick beds of high-calcium limestone 

with thick beds of giant conglomerate and graywacke is a most 

peculiar one. The conglomerate has been interpreted by Kirk 06 as 

of glacial origin, but Buddington could find no confirmatory evidence 

of this. It appears possible that the great lens-shaped beds of conglomerate may be local deposits, made by torrential streams, and 

the graywacke may be in part the more finely comminuted offshore 

equivalent. The calcareous shale and argillaceous limy beds which 

are locally intercalated with the clean thick-bedded limestone may 

also be in part the offshore equivalent of the conglomerate. However, if these beds of conglomerate are simple stream deposits, it 

is strange that the source from which they were derived is not evident. 

They may be reworked glacial till. The problem of their origin is 

not solved, and they need further study.

The limestone is in part dense and massive with only rare, if any, 

evidence of bedding; in part the massive limestone is interbedded 

with thin-layered limestone, nodular and shaly limestone, calcareous 

shaly argillite, dense platy siliceous layers, green-gray shale, and 

sparse buff-weathering sandstone.

The massive limestone occurs in uniform beds as much as 2,000 

feet in thickness. (See pis. 17, A and 18, A.) The fresh rock is 

white, but the usual color of the weathered surface is a pallid brown. 

The rock is usually intensely fractured, and the fracture surfaces are 

coated with a thin facing of calcite or rarely dolomite, which often 

weathers out in relief as a network of veinlets.

The thin-layered zones are as a rule highly fossiliferous, but the 

massive limestone is usually devoid of fossils. Conglomerate lenses 

are associated with many of the thin beds. In some localities a zone 

of these interbedded calcareous, argillaceous, and conglomerate beds, 

as much as 800 feet thick, appears to occupy an intermediate position 

in the section, as at the south end of Tuxekan Passage. Very rarely

" Kirk, Edwin, Paleozoic glaciation in southeastern Alaska: Am. Jour. Sci., 4th eer., 

vol. 46, pp. 311-515, 1918. .

6137 29 7
88 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

and locally rhyolite or andesitic volcanic rocks occur within the 

limestone.

On the south side of the Keku Island group there is a string of 

three long, narrow islands with a general east-west trend. These 

islands are composed predominantly of dense white limestone with 

scarcely a trace of bedding, "minutely fractured and veined with 

calcite. There are intercalated beds of coarse conglomerate 20 feet 

or more thick, composed who.Uy of fragments of limestone in a limestone matrix. Some of the boulders are 2 feet in diameter. Very 

many of the boulders and cobbles are fossiliferous or are themselves 

waterworn coral heads. In addition to other corals, they contain 

abundant Hall/sites, which have been found nowhere else in southeastern Alaska. The writer is of the opinion that these are intraformational conglomerates and that the beds are of Silurian age.

SHALE

A horizon very high in the Silurian is represented by a formation 

about 500 feet thick, consisting of pale-green slaty shale with intercalated red beds and thin-layered very fine-grained gray sandstone, 

gray shale, and dense limestone, which forms the northern part of 

Edna Bay and the coast about halfway between Edna Bay and Cosmos Pass, on the north side of Kosciusko Island. The beds are 

gently folded in a synclinorium, with a steep to slightly overturned 

anticlinal fold on the west side of Edna Bay. The bay itself is 

carved out of a northward-pitching synclinorium. These beds overlie 

the limestone conformably.

SANDSTONE AND GRAYWACKE

A thick series of interbedded red, green-gray, and gray sandstone, 

in part of graywacke type, with a minor amount of shale, forms the 

trough of a synclinorium on Naukati Bay and for 3 or 4 miles to 

the south along Tuxekan Passage; similar beds are exposed again 

along the west side of Karheen Passage, the east end of Heceta 

Island, and the islands north of the east end. On Naukati Bay the 

beds of sandstone are folded with a true east-west strike into two 

anticlines and a syncline. South of Naukati Bay the beds form a 

broad, gentle syncline. The limbs dip about 25°, the axis strikes 

N. 80°-85° E., and the trough pitches about 10° E. There appears 

to be about 3,000 feet of sandstone exposed here. The sandstone 

overlies the upper Silurian limestone. They have a similar strike, 

but the limestone occurs at many places directly along the line 

of strike of the sandstone in a manner. suggesting unconformable 

relations.
SILURIAN BOOKS . 89

On the east side of Heceta Island the sandstone in general strikes 

northwest and dips 40°-60° NE. In addition to the beds of red, 

green-gray,, and gray sandstone there are sparse beds of fossiliferous 

white sandstone and conglomerate. Pebble layers are common in the 

sandstone. The pebbles here as in the Silurian conglomerate are of 

granite, diorite, and monzonite; red, gray, and white rhyolite; red^, 

green, and black chert; and rarely limestone. Layers of nodular 

sandstone and beds of fissile limestone are present but very rare. 

Kipple marks occur on some surfaces and cross-bedding is very 

common.

A specimen of sandstone from Staney Island is found in thin 

sections to be composed predominantly1 of angular bits of quartz in 

a calcareous groundmass. Plagioclase grains are common, and the 

matrix is permeated with hematite. Another specimen obtained 

about half a mile south of Staney Island is a graywacke consisting 

of angular quartz and plagioclase with a little associated microperthite and grains of epidote and chlorite. The green-gray color is -due 

to the epidote and chlorite with sparse hematite. Another specimen 

from the northeast tip of Heceta Island appears to be a tuff cornposed almost wholly of plagioclase with associated pyroxene crystals 

and abundant grains of magnetite and epidote in a groundmass of 

epidote.

The relation of these beds to the underlying limestone distinctly 

suggests unconf ormable relations, but the fossils obtained from beds 

on Karheen Passage were identified by Kirk as of Silurian age. 

The common fossil is Leperditia sp.

On the northern part of Prince of Wales Island Silurian limestone is apparently overlain by a thick graywacke formation of 

doubtful age. The graywacke forms the coast line between Point 

Colpoys and Exchange Cove, a considerable part of the coast west 

of Red Bay, and the trough of the Shakan Bay synclinorium. The 

graywacke occurs in beds 9 inches to several feet thick, with intercalated layers of green-gray slate several inches thick. In the upper 

part the slate is more abundant and the slate and graywacke1 are 

interlayered in beds as much as 9 inches thick. Rarely a bed oi 

pebble conglomerate is found. West of Shakan there is one bed oi 

very coarse conglomerate containing pebbles and cobbles of diorite, 

black and white chert, limestone,: and porphyry. Along the coast, 

from the contact with the limestone south to the north-end of the 

southeast Barrier Island, the beds have a uniform north-northwest 

strike and southwest dip, changing from 60° on the east to 25° and 

less on the west. This would make a thickness of 7,500 feet, which 

seems too much. Just east of Shakan the beds of graywacke grade 

downward through slate and calcareous slate into limestone upon
90 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

which they appear to lie conformably. On the nose of the Kashevarof anticline, on Bushy Island, a great thickness of coarse conglomerate overlies the Silurian limestone; whereas west of Exchange 

Cove, in a similar structural position, graywacke with intercalated 

conglomeratic layers 6 inches to a foot thick overlies the limestone. 

This suggests that the graywacke is the equivalent of the conglomerate formation.

The graywacke resembles the Devonian graywacke formation of 

Saginaw Bay, but it is also similar in character, though it is without 

red beds, to the graywacke-like sandstone of Tuxekan and Karheen 

Passages, which are of Silurian age. It is here tentatively correlated 

with the Silurian beds.

When examined in thin section the graywacke is found to consist 

of angular bits of quartz, microperthite, orthoclase, plagioclase, limestone, epidote, chert, slate, and sparse particles of volcanic rock, 

Locally the groundmass is calcareous.

DIKES

At the north end of Prince of Wales Island numerous dikes of 

altered basic rock and of felsite cut the Silurian beds and are in 

turn cut by the intrusive rocks of the Coast Range. The older dikes 

were doubtless formed during one or more of the several periods of 

volcanism that intervened between the Silurian and the period of 

intrusion of the rocks of the Coast Range.

AGE AND CORRELATION .

Silurian fossils were found by E. M. Kindle in limestone at a 

locality just east of the third cove northeast of Meade Point, west of 

Saginaw Bay, Kuiu Island. The following fossils were identified 

by him:

Diphyphyllum? sp. Holopea servus. 

Conchidium knighti. Murchisonia sp. 

Whitfieldella sp.

Many small collections were made by Buddington from a great 

many widely separated localities. Edwin Kirk identified the species 

which are given in the table below. Kirk states that 933 (2042), 

1530 (2023), 1531 (2041), 1536 (2024), 1540 (2025), 1602 (2007), 

1625 (2044), 1665 (2036), 1679 (2046), 1680 (2047), 1696 (2029), 

1715 (2030), 1719 (2031), 1730 (2032), 1735 (2035), 1748 (2033), 

1752 (2034), 1766 (2037), and 1882 (2039) are Silurian and not older 

than late middle Silurian; 225, 233, 357, 399, 403, 540, 545, 546, 

623, 638, 654, 933, 972, 985, 1082, 1130, 1133, 1092, 1172, 1191 are 

Silurian; and 1562 (2027), 1688 (2045), 2230 (2018), 1761 (2008),
SILURIAN" ROOKS 91

1837 (2010), 1862 (2009), 1912 (2040), 611, and A are probably 

Silurian.

Collections were made by Buddington and Chapin from the limestone at the head of Waterfall Bay, Dall Island. Edwin Kirk reports as follows on these collections (2069 and 15 ACh 302): "All 

that remain in this limestone are poorly preserved crinoid columnals 

and what appear to be Cladopora-likQ corals. Judging from the 

scant evidence afforded by the lithology and the traces of fossils it 

would appear that Silurian age is indicated."
Silurian fossils from southeastern Alask

[Collected by A. F. Buddington; identified by Edwin 

Stromatopora. __ _ __ .... __

Diphyphyllum ..................

Ptychophyllum. ..

Cyathophyllum __ . __ ... __

Favosites.-.. ___ ... __ ......

Syringopora ____________

Aulopora...... __ .......

Cladopora. .............. . _ ..

Alveolites? ......................

Heliolites...... _________ .

Orthoceras. __ _______ . ...

Lissatrypa?. ____ _______

Hormotoma ......... ............

Sieberella... .......

Spirifer.... ________ ......

Schuchertella ___________

Meristina...... .. .. ......

Athyris. ........................

Coelospira... __________

Coelocaulus? ....................

Trochonema.. ..................

Holopea _____________

Dalmanites.. _________ ..

Proetus. ........................

Lichas.. ........................

Leperditia.. ___________

Clorinda... ________ .--.

Halysites.... _________ .-

Qypidula.. ______ . _ . _ 

Gastropods.-.. ___ ___ _ .

Capellinia _ .. _________

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SILURIAN ROCKS 93

1. Limestone, Prince of Wales and adjacent Islands.

2. Limestone interbedded with conglomerate and graywacke, Prince of Wales Island 

and Saginaw Bay, Kuiu Island.

3. Red and green graywackelike sandstone and shale, Prince of Wales and adjacent 

islands.

4. Cobbles in Silurian volcanic and conglomerate formation and intercalated slate and 

limestone, Kuiu and Prince of Wales Islands. 

6. Cobble in Silurian conglomerate.

140. About 6 miles east of Cape Bendel, Kupreanof Island.

223." Pair of long islets about 2% miles northwest of the conspicuous headland about 10 miles southeast of Point Cornwallis, Kuiu Island.

233. Same as 223.

357. East end of island in unnamed bay on Kuiu Island about 4 miles west 

of the northwest end of Conclusion Island.

399. Point at southeast end of Sumner Island, Sumner Strait.

403. Three miles west-southwest of the southernmost tip of Conclusion Island.

540. East side of Shrubby Island, Kashevarof Group.

545. South side of the island south of the middle part of Shrubby Island.

546. Islets southwest of point indicated by 1%-fathom mark on chart 8200, 

at southwest end of Shrubby Island.

623. Two miles east of Pine Point, north coast of Prince of Wales Island.

638. West headland of Exchange Cove, Prince of Wales Island.

654. Southern island of pair northeast of Exchange Island, off northeast coast 

of Prince of Wales Island.

933. (2042). Head of Saginaw Bay, west side of Kuiu Island.

973. Same as 223.

985. Southwest end of Shrubby Island, Kashevarof group.

1092. North of Sarheen Cove, El Capitan Passage, Prince of Wales Island.

1130. Islet at head of east arm of Labouchere Bay, Prince of Wales Island.

1133. Head of northeast arm of Labouchere Bay.

1172. South side of Sarkar Cove, near its head, El Capitan Passage.

1191. West side of El Capitan Passage about 1 mile north of Devilfish Bay.

1530 (2023). West side of small cove northwest of Green Island, on south 

side of Kosciusko Island.

1531 (2041). Point halfway between Edna Bay and Cosmos Pass, south 

side of Kosciusko Island; interbedded red and green shale.

1540 (2025). Kosciusko Island, east side of peninsula on east side of Edna 

Bay, about 0.7 mile north of south tip of point.

1562 (2027). Dead Mans Pass, east side of Marble Island, near center.

1602 (2007). Southwest end of Orr Island, west side of peninsula east-northeast of the south tip of Marble Island.

1625 (2044). South tip of Owl Island, off west coast of Prince of Wales Island.

1665 (2036). Head of bay on east side near the center of Orr Island.

1679 (2046). North side of third cove north of south tip of Orr Island.

1680 (2047). North headland of second cove north of southeast tip of Orr 

Island.

1688 (2045), Arm at north end of Tuxekan Island just east of Cap" Island.

1696 (2029). El Capitan Passage, islet about 2 miles north of Cap Island.

1715 (2030). El Capitan Passage, cove southeast of Hub Rock; islet of thinlayered limestone.

1719 (2031). North side of Naukati Bay near entrance.

1730 (2032). East shore of Tuxekan Passage about 2 miles south of Staney 

Island.

1735 (2035). Southwest tip of islet on east side of Tuxekan Passage, opposite 

south tip of Tuxekan Island.
94 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

1748 (2033). West side of Tuxekan Passage opposite locality 1730.

1752 (2034). West side of Tuxekan Passage opposite Staney Island.

1761 (2008). Islet in middle of bay east of Point Swift, Tonowek Bay.

1766 (2037), Head of cove a little more than 1 mile south of Point Swift, 

Tonowek Narrows.

1837 (2010). Small islet at north end of group about 2y2 miles south of 

Karheen.

1862 (2009). Southeast tip of island about 2% miles due west of Karheen.

1882 (2039). West headland of cove on the north side of Heceta Island, about 

4y2 miles west of Karheen.

1912 (2040). Little islet about a mile northwest of northwest tip of Anguilla 

Island.

A. Quarry at Tokeen, Marble Island. Collected by E. F. Burchard.

B. Near the middle of the north side of Heceta Island. Collected by E. F. 

Burchard.

DEVONIAN ROCKS 

DISTRIBUTION AND CHARACTER

Kocks belonging to the Devonian system are widespread throughout southeastern Alaska and have been studied particularly on Prince 

of Wales, Annette, Sukkwan, Suemez, Ball (north end), Baker, 

Noyes, San Juan Bautista, and Kupreanof Islands and on Freshwater 

Bay, Flynn Cove, and Port Frederick, Chichagof Island. They 

comprise great thicknesses of basic volcanic rocks, graywacke, and 

tuffaceous sediments, considerable limestone, black slate, conglomerate, 

and a little chert.

The stratigraphic relations of the different formations of the system 

have not been worked out because there is a great variation in the 

lithologic character of the Devonian sections from place to place, no 

complete sequence has been found, fossils are relatively sparse in most 

of the beds, intense deformation and covered contacts obscure the 

relations at some places, and no detailed mapping has been done. 

Part of the tuff and graywacke on the northwest end of Kupreanof 

Island, mapped as Middle Devonian is certainly of Upper Devonian 

age, but just how much is not certain.

MIDDLE DEVONIAN ROCKS

SOUTHERN KETCHIKAN DISTRICT

By THBODOBB CHAPIN

The stratigraphic relations of the Middle Devonian rocks are not 

plain. The best evidence at hand points to three conformably gradational groups of rocks an upper group, purely sedimentary in character; a lower group, purely igneous; and an intermediate group, 

made up of igneous pyroclastic rocks with interbedded slate and 

limestone. The rocks of the lower group appear to be volcanic 

breccias and flows which unconformably overlie the lower Paleozoic
DEVONIAN ROCKS 95

and Silurian rocks. Overlying the volcanic rocks is a series of conglomerate ; sandstone, and slate, in part tuff aceous, with interbedded 

flows and breccias, and fossiliferous limestone. The rocks of this 

group appear to grade upward into the more dominantly sedimentary 

formations, which culminate in beds of massive limestone several 

hundred feet thick. The age of the upper and intermediate groups 

is known positively by the fossils which they carry. No fossils have 

been found in the lower group of igneous rocks, but from their conformable relations with and similarity to some of the underlying 

rocks they are regarded as also Middle Devonian, though somje may 

possibly be Lower Devonian.

Middle Devonian rocks exposed on Vallenar Bay on Gravina 

Island were called the Vallenar " series " by Brooks ° 7 and were further described by Chapin 68 as the Vallenar formation. The Devonian rocks of Gravina Island are probably the equivalent of rocks 

that occur on Prince of Wales Island and at other places, but the 

Middle Devonian section is now known to include considerably more 

than the rocks exposed on Gravina Island and probably contains a 

number of formations, although it is not possible to recognize in other 

parts of the region the exact equivalent of the Middle Devonian rocks 

of Gravina Island. At no place is the entire section of the Middle 

Devonian rocks exposed in undisturbed sequence, and the following 

section is constructed mainly from exposures on Prince of Wales 

Island.

StratigrapMo section of Middle Devonian rocks in the southern KetohiJcan

district

Massive limestone. 

Conglomerate and limestone. 

Conglomerate and graywacke. 

Graywacke and slate. 

Black slate and tuff. 

Tuffaceous conglomerate, sandstone, slate, limestone, and interbedded

flows and breccias. 

Volcanic breccias and flows.

The flows are fine-grained, dense, green to gray rocks composed 

essentially of secondary epidote, chlorite, calcite, sericite, quartz, and 

feldspar. The only evidence of the original character of the rock is 

found in the few remnants of plagioclase feldspar, probably andesine, 

and hornblende or pyroxene. The rock was originally andesite.

Interbedded with the lava flows are coarse breccias that consist of 

a dark-green matrix, of essentially the same composition as the lava, 

and angular red and black glassy fragments. In places the red ap87 Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska: U. S. 

Geol. Survey Prof. Paper 1, p. 42, 1902.

68 Chapin, Theodore, The structure and stratigraphy of Gravina and Revillagigedo 

Islands, Alaska: U. S. Geol. Survey Prof. Paper 120, p. 87, 1916. "
96 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

pears to predominate. Flow breccia, a type of rock intermediate in 

origin between the lava and breccia, is of common occurrence. It 

appears to be composed of fragmental volcanic ejectamenta, but 

shows flow structure. (See pi. 18, B.)

The coarse angular breccias .grade into finer-grained breccias and 

stratified, water-laid tuffs. They are composed of explosive volcanic 

material, including glass and microlites and fragments of feldspar 

and hornblende, and were evidently collected in water with little or 

no transportation by streams. The water-laid tuffs are nearly all 

calcareous, the amount of limestone varying from minute particles to 

lenses and beds. Even the coarser breccias are limy and in places 

contain large blebs of calcite. These calcareous parts of the rock 

dissolve out easily where exposed along the shore and give to these 

stratified rocks a slaglike appearance resembling the flow structure 

of lavas.

The tuffs also grade into tuffaceous conglomerate, sandstone, and 

slate, which by a decrease of volcanic material pass into purely sedimentary beds. The graywacke and feldspathic sandstone are composed largely of volcanic detritus.

On the southwest coast of Prince of Wales Island sediments and 

tuffs appear to be conformable on the flows and breccias. On Brownson Bay and Hetta Inlet graywacke carrying Middle Devonian fossils conformably overlies the volcanic rocks. The red and green 

breccias grade up into finer-grained tuff with Middle Devonian 

plants overlying graywacke with Middle Devonian marine fossils.

These tuffaceous sediments, which appear to be near the base of 

this group, contain interbedded black slate and limestone that also 

carry Middle Devonian fossils. Fossiliferous limestone that appears 

to occupy this horizon is exposed on Keete Inlet, Max Cove, Klakas 

Inlet, Hunter Bay, and Tah Bay, and with it are correlated some 

similar beds of limestone at the head of Nichols Bay. This same 

horizon is possibly represented also in the limestone interbedded with 

tuffaceous sediments on Dickman Bay and other places on Moira 

Sound.

Schistose rocks are associated with greenstone at a number of places. 

Some of these appear to be contact-metamorphic rocks formed along 

the borders of masses of intrusive quartz diorite and others are possibly infolded schist of older formations.

Round Island, in Kasaan Bay, is composed entirely of limestone 

similar in appearance to the limestone of Long Island and of the same 

age. Berry Island, much of Kasaan Peninsula, and parts of Skowl 

Peninsula are made up of conglomerate, graywacke, tuff, and interbedded limestone, but the relation of these beds to the fossiliferous 

limestone of Long Island is nowhere evident. The limestone is a 

dark-blue brittle rock, similar to the fossiliferous limestone of Long
DEVONIAN ROCKS 97

Island. The conglomerate is made up of pebbles and large cobbles 

of graywacke, chert, porphyry, .rhyolite, and limestone, set in a matrix 

of angular sand. The graywacke is a banded arenaceous rock composed of quartz and feldspar, angular rock particles, ferromagnesian 

minerals, and slate. It is essentially the same in composition as the 

conglomerate, into which it grades by increase of coarse material.

If the synclinal structure of Long Island extends across Kasaan Bay 

to Kasaan and Skowl Peninsulas the massive fossiliferous limestone 

of Long Island is stratigraphically the highest of the Middle Devonian rocks known. Some of the thick beds of limestone on Kasaan 

Peninsula may be correlated with it or they may be even higher but 

these interstratified limestone, conglomerate, and tuffaceous beds are 

believed to occupy a position just below the massive limestone of 

Long Island and are correlated with similar rocks on Skowl 

Peninsula.

A thick uniform limestone member of the Middle Devonian is exposed on Long and Round Islands, Kasaan Bay, and on Coronados 

and Fish Egg Islands and the islands to the north, on the east side of 

San Alberto Bay. Similar limestone of Middle Devonian age is exposed on the north end of Kupreanof Island, where it is very highly 

sheared, and in Duncan Canal. The limestone is highly fossiliferous 

and on Long Island it is dark gray to blue and fine grained. The 

limestone of Long Island was described by Kindle as overlying buff 

or cream-colored siliceous beds of igneous origin, but these supposed 

beds are reported by Buddington to be platy rhyolites with local flow 

structure and spherulitic texture, of Tertiary age, and to rest unconformably on the limestone.

The limestone on the Coronados Islands range from a white 

crystalline rock to brown and gray beds with a little argillaceous and 

sandy material. The limestones on the islands on the east side of San 

Alberto Bay are fine grained, gray, and thin to thick bedded. On 

the island halfway between Clam Island and East Alberto Island a 

thick bed of graywackelike sandstone is intercalated in the limestone. All the limestones are very richly fossiliferous, and the fauna 

has been identified by Edwin Kirk as of late Middle Devonian age.

The basalts are dark-green and black fine-grained rocks with visible 

phenocrysts of augite, feldspar, and olivine set in a groundmass composed essentially of secondary minerals.

The andesitic pillow lava, breccia, and tuff which overlie Middle 

Devonian interbedded limestone, slate, and chert on Duncan Canal, 

Kupreanof Island, may be of Middle Devonian age.

The age determination of the Vallenar formation of the southern 

Ketchikan district is based upon large collections of fossils made 

from the massive limestone at the top of the group and from the
98 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

underlying thin-bedded limestone which is interbedded with the tuffs 

and lava flows. Edwin Kirk, who has made a study of these faunas, 

states:

Some of the faunas here referred to the Middle Devonian as represented in 

the collections might be referred to the Lower Devonian. There are, however, 

no truly diagnostic Lower Devonian forms present, as there are no truly diagnostic Middle Devonian species. There is in addition a general homogeneity 

of the faunas from the base of the Devonian as drawn up to the Stritnffocephalua 

horizon, which elsewhere marksi the upper part of the Middle Devonian. There 

also appears to be a fairly close relation between the faunas of the Stringocephalus horizon and the faunas underlying it. For these reasons it has seemed 

best for the present to refer all the Devonian faunas below the StrinffOcephaHus 

horizon to the Middle Devonian.

The thin-bedded limestone and associated tuffaceous limestone have 

yielded a number of collections of fossils, all of which are regarded 

as Middle Devonian.

Fossils collected at Vallenar Bay, Gravina Island, by Brooks in 

1901 were determined by Charles Schuchert as Devonian. More collections were made in 1905 and 1906 by the Wrights and E. M. 

Kindle,69 who give the following report on a collection obtained 1 

mile west of Vallenar Bay, Gravina Island:

The material from this locality, while generally insufficient for specific determination, is much better than that obtained last year (1905) and leaves no doubt 

as to the Devonian age of the beds west of Vallenar Bay. Several specimens of 

Atrypa reticulwris are present. This fixes the horizon as not later than 

Carboniferous, while the association of Clwnetes cf. mmwtobensis, Spirifer sp., 

Proetus sp., and Cyclonema sp. indicates a horizon of Devonian age, probably 

Middle Devonian.

The following collections made by the writer were also regarded 

by Kirk as Middle Devonian:

15ACh 9, 21, 22, and 311, Hotspur Island:

Favosites hemisphericus. Zaphrentis type of Z. gigantea. 

Favosites limitaris. Favosites cf F. emmonsi. 

CJadopora sp. Rhipidomel,la sp. 

Favosites sp. Alveolites sp. 

Syringopora sp.

15 ACh 151, 153, and 155, Clover Bay, Prince of Wales Island: 

Cladopora sp. Favosites hemisphericus. 

Syringopora sp. Cyathophyllum sp.

15 ACh 180, Hessa Inlet, Prince of Wales Island: 

Cladopora sp. Crinoid columnals.

15 ACh 188, Hunter Bay, Prince of Wales Island: 

Atrypa reticularis. Cyathophyllum sp. 

Favosites hemisphericus. Syringopora sp. 

Alveolites sp.

88 Wi-ight, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

Geol. Survey Bull. 347, p. 50, 1908.
DEVONIAN ROCKS 99

15 ACh 203, Max Cove, Prince of Wales Island: 

Favosites hemisphericus. Alveolites sp.

The following collection was made by Kirk:

East shore of Keete Inlet, Prince of Wales Island: 

Atrypa reticularis. Chonetes sp. 

Stropheodonta sp. ' Orthoceras sp. 

Reticularia sp. Grammysia sp. 

Martinia cf. M. maia. Pterinea sp. 

Leiorhynchus sp. Modiomorpha sp. 

Rhynchonel,la sp.

Most of the species listed above are undescribed.

This fauna is clearly referable to the Middle Devonian as defined 

in southeastern Alaska. It belongs to a group of faunas found 

within the great series of argillite, quartzite, and greenstone overlying the Silurian and known not only in Prince of Wales Island but 

also in the northern part of Chichagof Island.

Fossil plants that occur in the graywacke beds associated with 

the limestone of Hessa Inlet were submitted to David White, who 

reports as follows:

The collection which constitutes lot 17339 of the paleobotanic collections of 

the Geological Survey consists of fragments of a slender, distantly forking 

algoid type with slender, but slightly thickened medial axis. It is probable 

that the ultimate divisions were more or less distinctly flat and ribbonlike, conforming largely to the characteristics of the genus Taeniocrada.

A few of the fragments, as preserved, have fades suggestive of one of the 

slender forms from the Middle Devonian of Canada, identified in some of the 

collections under the name Psilopliyton.

The aspect of the material and the absence of pteridophytic features suggest Middle or possibly even Lower Devonian age for the beds.

The massive limestone beds of the upper part of the Vallenar 

formation have yielded large faunas of Middle Devonian fossils. 

Kindle 70 lists a fauna collected in the massive limestone of Long 

Island, Kasaan Bay, which he considers to be Lower and Mjj^dle 

Devonian. Subsequent collections made by the writer and by Kirk 

have shown that the faunas of the upper and lower parts of the 

limestone series are essentially homogeneous and that the limestones 

form a stratigraphic unit. Kirk's report is as follows: . Many of the species represented in the limestones of Long Island, Kasaan 

Bay, are either new or are represented by specimens too imperfect for exact 

specific identification. Because of this there is at present no reason for changing Kindle's original faunal lists. In the lower portion of the limestone series 

he identified the following fossils:

Stictopora sp. Spirifer cf. S. sulcatus. 

Cladopora sp. Sanguinolites sp.

70 Kindle, E. M., Notes on the Paleozoic faunas and stratigraphy of southeastern Alaska: 

Jour. Geology, vol. 15, pp. 324-39-7 1907.
100 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Cardiola sp. 

Hercynella nobilis. 

Hercynella bohemica. 

Holopea sp. 

Murchisonia angulata. 

Murchisonia sp. 1. 

Murchisonia sp. 2. 

Planitrochus cf. P. amicus.

Loxonema sp. 

Holopella sp. 

Trochonema sp. 

Euoinphalopteris? sp. 

Operculum. 

Beyrichia? sp. 

Leperditia sp.^_ 

Orthoceras sp.

In the upper portion of the series Kindle lists; the following forms as collected 

from one zone:

Favosites cf. F. radiciformis. 

Cyathophyllum sp. 

Orthophyllum? sp. 

Zaphrentis sp. 

Calceola cf. C. sandalina. 

Syringopora sp. 

Lingula cf. L. bohemica. 

Atrypa reticularis. 

Atrypa hystrix. 

Gypidula optatus. 

Gypidula cf. G. interyenicus. 

Meristella cf. M. barrisi. 

Stropheodonta stephani. 

Spirifer sp. 

Spirifer hians? 

Spirifer thetidis. 

Spirifer subcomprimatus. 

Spirifer sp. 

Spirifer indeferens. 

Spirifer sp. 

Reticularia? sp. 

Rhynchonella cf. R. amalthea. 

Rhynchonella livonica. 

Pugnax sp. 

Dalmanella occlusa. 

Schizophora macfarlani? 

Schizophora striatula. 

Streptorhynchus sp. 

Stropheodonta comitans.

Camarotoechia? sp.

Cypricardinia? sp.

Conocardium cf. C. bohemicum.

Conocardiurn sp.

Lucinia cf. L. proavia.

Leptodesma sp.

Mytilarca sp.

Nuculites sp.

Telinopsis sp.

Holopella? sp.

Loxonema? sp.

Murchisonia sp. 2.

Murchisonia sp. 1.

Naticopsis sp. . Oriostoma sp.

Oriostoma princeps var.

Euomphalus cf. E. planorbis.

Tremanotus cf. T. fortis.

Tentaculites sp.

Ooceras sp.

Gomphoceras? sp.

Orthoceras sp.

Cytherella? sp.

Entomis pelagica.

Leperditia sp.

Cyphaspis sp.

Proetus sp.

Proetus cf. P. romanooski.

Somewhat below the fauna given above he notes the following species;

Cladopora? 

Cyathophyllum sp. 

Camarotoechia sp. 

Meristella cf. M. ceres. 

Spirifer sp.

Spirifer cf. S. thetidis. 

Spirifer cf. S. cheiropteryx. 

Stropheodonta comitans. 

Orthonota sp.

The " Cardiola" identified by Kindle in the lowest fauna is Pcmenka,. This 

ranges upward into the higher faunas and was found near the top of the section 

as shown in Long Island. Fragments of Hercynella,. likewise were seen assoSchizodus sp.

Conocardium cf. C. bohemicum.

Euomphalus planorbis.

Oriostoma princeps var.

Tentaculites.

Cyphaspis sp.

Orthoceras sp.

Proetus cf. P. romanooski.
DEVONIAN BOOKS 101

dated with the higher faunas. In the basal portion of the limestones numerous 

corals were found, chiefly referable to the genera Fav&sites, Cladopora, and 

Striatopora. These are specifically identical with corals associated with the 

higher faunas referred to the Middle Devonian, not only in this section but also 

in other parts of southeastern Alaska. There is no good reason then for drawing 

a stratigraphic line within the limestone series of Long Island.

The question of the age assignment of the limestone series involves then the 

contained fauna as a whole. Of Asiatic and European affinities as it is, and 

differing widely from the Devonian faunas of eastern North America, the task 

is not an easy. one. The general aspect of the fauna, and this carries with it 

even lower faunas found elsewhere in southeastern Alaska, is more Middle than 

Lower Devonian. In my opinion the best course is to call these faunas Middle 

Devonian. If Lower Devonian be present in southeastern Alaska it is more apt 

to be found within the sediments now referred to the Silurian. The final 

settlement of this question depends in great part, however, on the final disposition of disputed stratigraphic units elsewhere in North America, Europe, and 

Asia.

Collections were also made by the writer from massive limestone 

beds of Coronados and Fish Egg Islands and Port Bagial, on the 

west coast of Prince of Wales Island, which are correlated with the 

Long Island rocks. Kirk reports:

15 ACh 278. Coronados Island:

Cyathophyllum sp. Productella sp. 

Favosites, 2 sp. Stropheodonta sp. 

Stringocephalus burtini. Straparollina sp. 

Atrypa reticularis var. Bronteus sp. 

Leiorhynchus sp. Stromatopora? sp. 

Camaratoechia sp.

15 ACh 280, Port Bagial, Prince of Wales Island: 

Crania sp. Amplexus sp. 

Atrypa reticularis. Aleveolites sp. 

Eunella sp. Favosites hemisphericus. 

Ambocoelia umbonata. Cyathophyllum sp. 

Bellerophon? sp. Syringopora sp. 

Murchisonia sp. Cladopora sp. 

Strophostylus sp. Striatopora sp. 

Actinostroma sp..

The fauna obtained near the east end of Coronados Island is of great interest 

in that it gives a datum plane for correlation with faunas outside Alaska. Associated with the fauna listed from Port Bagial is found Strmgocephalus ~burtmi Defrance. This brachiopod marks a well-defined zone in the upper part of 

the Middle Devonian of Europe. It is also found in the Yukon Valley of 

Alaska and in the Mackenzie River region of Canada. In southeastern Alaska 

it has also been found in San Alberto Bay, west of Klawak. Here it occurs 

almost immediately underlying the Upper Devonian. Another interesting European element in the fauna is the trilobite genus Bronteus.

NORTHERN KETCHIKAN DISTRICT

On the southwest side of Saginaw Bay upper Silurian beds consisting of interbedded fossiliferous limestone and conglomerate are 

overlain by interbedded conglomerate and andesitic lava of probable
102 GEOLOGY AND MINEBAL DEPOSITS, SOUTHEASTERN ALASKA

Devonian age. Some of the lava is reddish, with abundant phenocrysts of pink plagioclase; it resembles trachyte but in thin section is 

found to be andesite.

The waters of Saginaw Bay cover the beds intervening between 

the conglomerate and lava formation and the formation exposed on 

the adjacent string of islands which parallels the shore. This group 

of islands is composed of thick-bedded greenish graywacke with 

intercalated beds of conglomerate and thin-layered platy sandstone 

and slate. Beds of thin-layered black argillite occur sparsely and 

also beds of andesitic breccia. The thin-layered argillites carry 

Devonian fossils, in part marine and in part carbonized plant remains. The conglomerate is composed of bits of red felsite, green 

andesite, and andesite porphyry; it is usually fine grit, but is rarely 

coarse and in beds 15 feet thick. The graywacke is in beds 2 to 20 

feet thick. There appears to be at least 2,000 feet of this formation 

exposed on these islands, and the total thickness is probably considerably greater. These beds structurally overlie the lava and conglomerate formation that appears to the southwest, and a few fossils 

collected from them are reported by Edwin Kirk to be of probable 

Middle Devonian age.

The predominant rock of Suemez, Baker, St. Ignace, and Noyes 

Islands consists of andesitic lava (predominantly with pillow structure) and breccia with associated limestone-andesite conglomerate 

and locally intercalated beds of bright-red shale or thin-bedded darkgray slate and graywacke. The limestone-andesite conglomerate is 

composed of limestone and andesite cobbles in a green tuff-like 

groundmass. Limestone occurs also in great, irregular masses as much 

as 10 feet in diameter. In one bed the limestone cobbles were found 

to carry Devonian fossils, and they are probably of intraformational 

origin. The conglomerate resembles the similar beds of the upper 

Silurian. The andesite is normally of felsitic texture and sagegreen to dark green-gray color. Along Port Heal Marina, at the 

north end of Santa Rita Island, beds of gray and red felsite breccia 

and tuff with sparse beds of thin-banded green and gray slate overlie 

the andesitic volcanic rock.

On Baker Island the peninsular headland east of the Gaviota 

Islands is formed by a syncline of thin-bedded dark and light gray 

calcareous slate, sandstone, or graywacke and intercalated conglomerate, overlying the andesitic volcanic rocks. There is 500 feet or so 

of, schistose limestone also exposed. The conglomerate consists of 

pebbles of chert and dense sage-green greenstone. At the extreme 

northeast end of St. Ignace Island there are exposures of similar interbedded limestone, conglomerate, sandstone, and slate overlying the 

volcanic rocks. On Noyes Island, between Point San Francisco and
DEVONIAN ROCKS 103

Steamboat Bay, there is a series of interbedded conglomerate, sandstone, graywacke, and dark-gray to black slate, with intercalated limestone and local andesitic lava and breccia. On Steamboat Bay there 

is a thick chert bed. The limestone carries Devonian fossils.

The beds overlying the andesitic volcanic rocks on the northwest 

side of Suemez Island are of a different type. They consist of interbedded graywacke, slightly waterworn andesitic tuff, banded darkgray slate, light-colored dense graywacke, and conglomerate composed of cobbles of limestone and andesite. Beds of limestone, tuff, 

and breccia are sparsely intercalated. The graywacke is predominant.

On Duncan Canal, Kupreanof Island, there is a series of beds consisting in part of dark-gray slate with intercalated beds of chert and 

thin layers of black chert and limestone and in part of thick-bedded 

limestone interbedded with slate, green and white chert, and schistose 

andesitic volcanic rocks. The slate series appears to pass upward 

into the more dominantly limestone beds. The limestone carries a 

Middle Devonian fauna identified by Edwin Kirk. The beds are 

overlain by sage-green andesitic lava (in part with pillow structure), 

breccia, and tuff.

A series of beds of conglomerate or graywackelike sandstone or 

both forms the group of islands at the head of San Alberto Bay and 

in San Christoval Channel, the north end of San Fernando and 

Lulu Islands, Blanquizal Island, and a group of small islets west of 

the north end of Anguilla Island, in the Maurelle group. San Christoval Channel is carved out of a syncline of these beds. The east limb 

is vertical to slightly overturned toward the west; the slope of the 

west limb is more gentle. At the north end of San Fernando Island 

there is exposed about 2,500 feet or more of conglomerate beds that 

overlie a graywacke series or, locally, conglomerate of typical Silurian aspect. The Silurian (?) part of the conglomerate series is here 

composed predominantly of limestone cobbles and boulders and of 

pale-colored rhyolite porphyry. Local beds are composed almost, 

wholly of andesite. Granite and chert pebbles are present. These 

beds appear to be overlain conformably by pebble conglomerate 

with interbedded sparse sandstone and shale. The upper conglomerate beds contain many chert pebbles and seem to be less metamorphosed than the lower conglomerate beds, though this difference may 

be only apparent. Locally conglomerate beds resembling the upper 

conglomerate overlie a graywacke series with apparent unconformity. At the north end of Lulu Island there is 2,000 feet of the 

pebble conglomerate in which chert forms a considerable part, limestone pebbles are rare, and slaty fragments are locally abundant. 

The conglomerate beds are overlain conformably by dense nonfossiliferous limestone at Point Santa Gertrudis.

6137 29 8
104 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Blanquizal Island consists of interbedded graywackelike sandstone 

and conglomerate, with the sandstone predominating. In the conglomerate the pebbles are greenstone, chert, graywacke, quartz, rhyolite, and rarely diorite and granite. There appears to be 1,800 feet 

of these beds exposed here. About 1% miles northwest of Point 

Ildefonso there are beds of fossiliferous sandstone intercalated in a 

giant conglomerate, which appears to overlie unconformably a graywacke formation. Some of the sandstone is white, but most of it is 

gray. The matrix of the conglomerate is calcareous, and the cobbles, 

which are predominantly 6 to 12 inches in diameter and well rounded, 

consist of limestone, green, white, and black chert, slate, greenstone, 

felsite, granite, diorite, and banded dense cherty quartzite. In some 

conglomerate beds on the islands in San Christoval Channel cobbles 

of greenstone or diorite or both are abundant.

The age of these beds is uncertain. Structurally they must lie 

between the Silurian and the Middle Devonian. At the head of San 

Alberto Bay they pinch out, and Middle Devonian limestone is practically adjacent to Silurian volcanic rocks. As the contacts are 

covered it is not certain whether this relation is due to a local lenslike character of the conglomerate formation, to an unconformity, or 

to faulting. The beds probably belong either to the upper part of 

the Silurian system or to the lower part of the Devonian. Kirk 

states that the few fossils obtained from the formation at a place 1% 

miles northwest of Point Ildefonso indicate a probable Middle Devonian age. Chert is not a characteristic cobble of the Silurian conglomerate, though it is present in them; but granitoid and volcanic 

rocks are characteristic both of the beds under consideration and of 

the known Silurian conglomerates.

Limestone carrying abundant silicified fossils forms Ham Island, 

a small islet in Karheen Passage. A collection from this locality was 

identified by Kirk as of Middle Devonian age. This limestone apparently occupies the trough of a syncline in red sandstone with conglomeratic layers. The sandstone locally carries abundant LeperdHtia, 

which are referred to the Silurian by Kirk. At the head of San 

Alberto Bay Middle Devonian limestone overlies conglomerate and 

graywackelike sandstone, as has been described. This suggests a 

correlation of the sandstone of Karheen Passage and the conglomerate and sandstone of San Christoval Passage and the head of San 

Alberto Bay. But the sparse fossils from the two formations are 

referred by Kirk to the Silurian and probably Middle Devonian 

respectively, and there is considerable difference in lithology. On 

San Fernando Island at Fern Point Middle Devonian limestone 

overlies graywacke of probable Silurian or older age. These relations suggest that an unconformity exists at the base of the limestone formation.
DEVONIAN ROCKS 105

A number of collections of fossils, identified by Edwin Kirk as 

of Middle Devonian age, were made by Buddington from formations north of the southern part of the Ketchikan district. These 

are listed in the following tables:

Middle Devonian fossils from southeastern Alaska 

(Collected by A. F. Buddington; identified by Edwin Kirk]

Spirifer........... ........................

Rhynchonella... _____________

Hercynella? ...............................

Tentaculites. .............................

Pterinea. _________ ... ............

Orthoceras _________________

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1. Limestone, Kupreanof and Noyes Islands.

2. Limestone, Prince of Wales and adjacent Islands.

3. Graywacke, Saginaw Bay, Kuiu Island.

l-P-6. Middle arm of Duncan Canal, Kupreanof Island.

Q-16. East shore of Duncan Canal, southwest of islet northwest of Castle 

Islands.

Rr-2. First islet south of peninsula between middle and east arms of Duncan 

Canal, Kupreanof Island.

P-3. First islet northwest of Duncan point, west arm of Duncan Canal, 

Kupreanof Island.

Z-9. Head of Emily Island arm of Duncan Canal, Kupreanof Island.

2232(2019) and 2230(2018). Northeast end of Noyes Island, east of Steamboat 

Bay.

140. About 6 miles east of Cape Bendel, Kupreanof Island.

1841(2038). Ham Island, about 1% miles south of Karheen, off west coast of 

Prince of Wales Island.

2030(2012). Clam Island, north of Fish.Egg Island, and Klawak Reef, off west 

coast of Prince of Wales Island.

2031(2013). Alberto Island, off west coast of Prince of Wales Island.

2057(2014). Island1 halfway between Clam Island and Bast Alberto Island, 

San Alberto Bay.
106 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

2085(2016). Small islet off northeast end of the island on which there is a 

cemetery, north of Klawak.

2132(2017). Fern Point, east side of San Fernando Island. 

939(2022). Island about center of Saginaw Bay, Kuiu Island.

A peculiar fauna occurs in a bed of sandstone intercalated in giant 

conglomerate on the east side of San Christoval Channel. Bark 

identified the fossils as Camarotoechia sp., Orbiculoidea sp., and 

Cypricardella sp. and referred them to a probable Middle Devonian 

horizon.

MIDDLE ( ?) AND UPPER DEVONIAN ROCKS OF NORTHERN PART OF 

KUPREANOF ISLAND

A thick series of beds, predominantly tuffaceous, of known Devonian age, is exposed in the northern part of Kupreanof Island. 

They are well exposed in the vicinity of Kake and again for 2 miles 

along Frederick Sound about 2 miles east of Cape Bendel. The 

fossils included are in part of Upper Devonian age and in part of 

indeterminate age but either Middle or Upper Devonian.

The formation comprises, characteristically, very thin bedded tuff 

with sparse chert layers; thick-bedded tuff with intercalated calcareous tuff or tuffaceous limestone; and a few flows of pillow lava with 

beds of banded chert and becls of slate. It is possible that a series 

of rocks east of Cape Bendel consisting of black slate and chert with 

interbedded limestone lying between the typical beds of tuff and 

Permian limestone belong to this formation. The tuff is in general 

very fine to medium grained and green to green-gray. Impalpably 

fine grained beds are very common. One of the most striking and 

characteristic features of this series is the presence of beds of tuff of 

a color most unusual in rocks, a light blue to blue green. Beds and 

layers of white chert are found in minor amount intercalated in the 

tuff, and black chert is associated with the slate in the belt east of 

Cape 'Bendel. The tuff and chert are exceedingly fractured by short 

cracks and minute offsetting faults, and the rocks break down into 

small angular fragments. They weather along the coast line with a. 

glazed appearance, the result of the prevalently fine grain, and acquire yellowish-brown, greenish, or reddish-brown hues.

The thin-bedded facies is well shown at Point Macartney, where it 

consists of greenish tuff with chert in layers a fraction of an inch to 

several inches thick, with a few beds of tuff several feet thick. 

Crinoid stems are visible in many hand specimens of the tuff and in 

practically all specimens when examined in thin section.

A specimen of typical medium-grained green tuff from. Point 

Macartney is found, on microscopic examination, to be a crystal tuff 

and to consist almost wholly of angular particles of sodic plagioclase
DEVONIAN ROCKS 107

with a few grains of hornblende and andesite (plagioclase) porphyry. 

Cross sections of crinoid stems are very common. The green color 

is due to disseminated chlorite. A pale greenish-blue tuffaceous limestone from a locality about 5 miles southeast of Kake is found to 

consist of abundant rounded particles of plagioclase and of andesite 

porphyry with plagioclase phenocrysts in a calcareous groundmass. 

Quartz grains occur sparingly. Crinoid stems and corals with wellpreserved cell structure are abundant. A few particles of dense green 

chert are present. A specimen of dense green tuff from a locality 

about 3 miles southeast of Kake exhibits in thin section a compressed 

indistinct groundmass with abundant small particles of plagioclase 

and many traces of devitrified glass shards, some with evidence of a 

scoriaceous structure. Another specimen from the islet about a mile 

southwest of Kake is a dense striped green vitric tuff, slightly calcareous, composed almost wholly of fragments of devitrified glass 

with abundant particles of feldspar in an indistinct groundmass. 

Many small crinoid stems are seen in thin section. Crystal tuff and 

vitric-crystal tuff, with accessory fragments of andesite, are thus seen 

to be the predominant types of rock.

The series is evidently marine, comprising in considerable part tuff 

consisting of volcanic ash of primary origin and in minor part 

detrital tuff consisting of volcanic ash washed in from land surfaces, normal mud resulting from weathering processes, calcareous 

skeletons of organisms, and siliceous precipitates or organic secretions.

The stratigraphic positions and relations of the divisions of the 

Devonian system are only partly known. The beds described include 

andesitic volcanic rocks; interbedded conglomerate, limestone, slate, 

and andesitic volcanic rocks; interbedded slate, chert, andesitic volcanic rocks, and limestone; limestone; graywacke with waterworn 

andesitic tuff; and interbedded predominantly cherty conglomerate 

and graywacke-like sandstone. In the absence of fossils and in our 

ignorance of the stratigraphic sequence it is impossible to distinguish 

Middle Devonian volcanic rocks from Upper Devonian volcanic rocks 

on lithology alone; and it is not certain that there is not more than 

one horizon within the Middle Devonian represented predominantly 

by limestone, or by graywacke and tuffaceous sediments, or by volcanic rocks.

UPPER DEVONIAN ROCKS OF OTHER PARTS OF SOUTHEASTERN ALASKA

By THEODORE CHAPIN

Kocks of known Upper Devonian age are not extensive in southeastern Alaska, though it is quite probable that, owing to the absence 

of fossils, rocks of this age have been included with Middle Devonian
108 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

or Carboniferous formations. They are found on the west coast of 

Prince of Wales, Suemez, and San Juan Bautista Islands and on 

Freshwater Bay, Chichagof Island. The rocks comprise melaphyre 

pillow lava and tuff on Freshwater Bay and limestone, calcareous 

sandstone with some conglomerate, interbedded limestone, and argillite, and basalt on Suemez and San Juan Bautista Islands. The 

lower yellow impure limestone on Port Refugio, Suemez Island, and 

the argillite on San Juan Bautista Island contain fossil plants. The 

limestone contains abundant marine fossils.

The age of the Upper Devonian rocks is known from a number of 

fossil collections from various places. Fossil plants from the lowest 

member of the Upper Devonian limestone of Port Refugio, Suemez 

Island, collected in July, 1917, were submitted for identification to 

David White, who reports as follows:

7388 (17 ACh 7). Port Refugio, Suemez Island, southeastern Alaska. The 

limestones contain indistinct fragments of what appears to have been a rather 

dense filamentose alga resembling somewhat some of the fossils identified by 

various paleontologists as Buthotrephis. These fragments do not seem to admit 

of more exact determination. Two specimens in the collection appear to belong 

to vascular types, though they are so macerated as to leave doubt as to their 

exact affinities. One of them, however, is similar to certain Devonian plant 

remains from Canada described as Rachiopteris. Material of this sort is to be 

expected from the Middle Devonian, though it might perhaps occur in the lower 

part of the Upper Devonian.

Marine invertebrates collected from the overlying beds were determined by Edwin Kirk, who reports as follows:

16 AOh 132, 141, 142, 143. Port Refugio, Suemez Island, west coast of Prince 

of Wales Island:

Spirifer disjunctus. Orthothetes cf. O. chemungensis. 

Schizophoria striatula var. Ambocoelia sp. 

Productella cf. P. hallana. Plant remains. 

Camarotoechia (?) duplicata.

The faunas of all these lots are essentially the same, most of the species being 

found in each lot. The age of the strata is clearly Upper Devonian.

Fossils collected from San Juan Bautista Island were examined 

by Kirk, whose report follows:

16 ACh 158:

Cyathophyllum sp. Pentamerella sp.

Syringopora sp. Gomphoceras sp1.

Aulopora sp. 16 ACh 162:

Atrypa reticularis. Productella cf. P. hallana.

Productella cf. P. hallana. Atrypa sp.

Near these two localities Wright made a collection which adds the 

following species to the above lists: 

Productella cf. P. lachrymosa. Spirifer disjunctus.
CARBONIFEROUS BOOKS 109

These faunas are of Upper Devonian age. Stratigraphically the 

beds containing them underlie those carrying the faunas listed from 

Suemez Island.

Fossils collected by Buddington from the west headland of a cove 

about 2 miles north of Point Refugio, Suemez Island, were identified 

by Kirk as Pugnax pugwis, Productella sp., and Spirifer disjunct/us, 

of Upper Devonian age. Fossils were also collected by Buddington 

from green andesitic calcareous tuff beds underlying limestone on 

Hamilton Bay, Kupreanof Island, about Qy2 miles southeast of Kake. 

These were identified by Kirk as Fenestella? sp. and crinoid columnals, of either Upper Devonian or Mississippian age, with the 

chances rather favoring the former.

CARBONIFEROUS ROCKS 

DISTRIBUTION AND CHARACTER

Rocks of the Carboniferous system are distributed throughout 

southeastern Alaska, but in the Alexander Archipelago they occupy 

only small, widely separated areas. On the mainland they form a 

considerable part of the schist series in the Juneau district and are 

possibly present in the schist of the Ketchikan district.

It seems highly probable that a considerable part of the WrangellRevillagigedo belt of metamorphic rocks of the mainland is of Carboniferous age, including the mapped belts described as schistose 

greenstone, green phyllite interbedded with black and gray sericitic 

slaty phyllite, and sparse beds of limestone and schistose chert. One 

such belt forms most of the outer part of the mainland coast line 

from Port Houghton northwest to Taku Inlet, and other belts lie 

to the east. On Admiralty Island a part of the belt of rocks that 

passes through Windfall Harbor is likewise believed to be of this 

age. A description of the schistose beds of the Wrangell-Revillagigedo belt of metamorphic rocks will be found on pages 49-74.

In the Ketchikan district metamorphic rocks composed of schist 

and limestone with tongues of intrusive granitoid igneous rocks 

border the Coast Range batholith. Many of the beds of limestone 

contain a great abundance of crinoid stems, and on that basis they 

have been referred by Kindle to the Carboniferous.

The most complete section of the Carboniferous system in the least 

metamorphosed condition is exposed on Saginaw Bay and the Cornwallis Peninsula, at the north end of Kuiu Island, and on the Keku 

Islets.

Considered lithologically the Carboniferous rocks may be divided 

into three groups a lower group, of Mississippian age, which consists of interbedded coarsely crystalline limestone and black chert 

overlain by interlayered dense gray quartzite and cherty limestone
110 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

with sparse sandstone and conglomerate; an intermediate group, of 

Pennsylvanian or lower Permian age, which comprises conglomerate, 

limestone, sandstone, andesitic, and basaltic lava and tuff, and possibly at some places rhyolitic volcanic rocks; and an upper group, 

of Permian age, which consists of thick-bedded limestone with common to abundant intercalated layers of white chert. All three divisions have very richly fossiliferous beds.

MISSISSIPPIAN ROCKS 

DISTRIBUTION AND CHARACTER

The Mississippian rocks are exposed over a considerable area in 

the vicinity of Klawak, on the west coast of Prince of Wales Island. 

They form the east side of Klawak Inlet, a belt between Klawak 

Inlet and Klawak Lake, Klawak Island, and the islands to the north 

up to the entrance of Klawak Salt Lake. They are exposed also at 

Point Bocas Peninsula, Suemez Island, on small islands at the mouth 

of Soda Bay, and on Madre de Dios and the Robber Islands, Bucareli Bay.

The beds consist of coarsely crystalline highly fossiliferous limestone and black thin-layered chert (pi. 19, A) overlain by interbedded dense gray quartzite and cherty limestone with sparse sandstone, conglomerate, and limestone. The base of the beds is reported 

by Chapin to be a thin strip of conglomerate 'and calcareous arkose. 

Much of the fossiliferous coarsely crystalline limestone has a fetid 

odor when first broken.

In Saginaw Bay, Kuiu Island, the beds form a long peninsula and 

its continuation in islands and reefs in the center and at the head of 

the bay, also the string of islands at the head of the east side of the 

bay and the outer edge of the coast for over a mile south of Halleck 

Harbor. On Chichagof Island Mississipian beds form the lyoukeen 

Peninsula.

The contacts between the Mississippian and older formations are 

either covered or obscured by faulting, but all the beds here described 

as Mississippian overlie Upper Devonian or late Middle Devonian 

beds.

AGE AND CORRELATION

Fossils collected from Soda Bay by the Wrights 71 in 1905 were 

determined by G. H. Girty, who reported as follows :

Zaphrentis sp. Chonetes sp.

Menophyllum? sp. Productus aff. P. punctatus.

Derbya sp. Productus aff. P. mesialis.

Schizophoria? sp. Productus aff. P. setiger.

t, F. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska : U. S. 

Geol. Survey Bull. 347, p. 54, 1908.
CARBONIFEROUS ROCKS 111

Productus hirsutiformis. Spirifer aff. S. keokuk. 

Productus aff. P. cora. Spiriferina sp. 

Productus aff. P. concentricus. Reticularia aff. R. setigera. 

Productus aff. P. burlingtonensis. Athyris aff. A. lamellosa. 

Spirifer aff. S. bisulcatus.

This lot clearly belongs to the lower Carboniferous fauna.

The following collections made by Chapin were also identified by 

Girty, who reports:

1803 (15ACh234). Island at entrance to Soda Bay:

Zaphrentis sp. Productus sp. 

Lithostrotion aff. L. portlocki. Spirifer striatus? 

Productus semireticulatus.

1803 a (15 ACh 233). Island at entrance to Soda Bay:

Zaphrentis sp. Productus aff. P. cora or P. giganteus. 

Lonsdaleia? sp. Reticularia? sp. 

Syringopora sp.

1803 b (15 ACh 232). Island at entrance to Soda Bay:

Aulopora? sp. Productus giganteus. 

Lonsdaleia? sp. Martinia? sp.

1803 c (15 ACh 233). Island at entrance to Soda Bay:

Lithostrotion sp. Productus giganteus. 

Campophyllum? sp.

1803 d (15 ACh 230). Island at entrance to Soda Bay:

Productus giganteus. / Composita? sp. 

Pustula sp. Bdmondia? sp. 

Girtyella? sp. Euomphalus? sp. 

Martinia? sp.

1804 (15 ACh 238). Northeast coast of Suemez Island 1V2 miles southeast of 

Point Bocas:

Fenestella sp. Pustula aff. P. biseriata.

Hemitrypa sp. Pustula sp.

Batostomella? sp. Productella concentrica.

Batostomella? sp. Spirifer aff. S. keokuk.

Schizophoria sp. Reticularia aff. R. setigera.

Orthotetes aff. O. keokuk. Composita sp.

Chonetes aff. C. illinoisensis. Griffithides sp.

Productus semireticulatus. Paraparchites aff. P. carbonarius.

Productus aff. P. ovatus. Eumetria sp.

Avonia? sp.

Girty says:

The Carboniferous collections represent at least thi*ee distinct faunas. One 

of these belongs in the upper Mississippian and apparently represents 

the Mountain limestone or Pro&uctus giganteus zone of European geologists. * * * The Mississippian lots, then, are in ascending order 234, 232, 

233, and 230. They belong to the Lisburne fauna and correlate the rocks from
112 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

which they came with the formation of that name in northwestern Alaska and 

with the Mountain limestone of Europe. The Mountain limestone is generally 

correlated with the upper Mississippian of North America. Another collection 

representing the same fauna is that numbered 238.

2434 a (16 ACh 105). Eastern island of group east of Madre de Dios Island, 

entrance to Trocadero Bay:

Fusulinella? sp.

Endothyra aff. E. bowmani.

Crinoid stems.

Batostomella sp.

Fistulipora sp.

Fenestella sp.

Polypora sp.

Pinnatopora sp.

Coeloconus sp.

Rhabdomeson sp.

Goniocladia? sp.

Cystodictya aff. C. pustulosa.

Orthotetes? sp. -

Streptorhynchus? sp.

Schizophoria n. sp!

Productus semireticulatus.

Productus aff. P. undatus?

Diaphragmus n. sp.

Tegulifera? sp.

Pustula aff. P. eximia.

Pustula aff. P. distorta.

Pustula aff. P. spinulosa.

Pustula sp.

Shumardella missouriensis?

Girtyella sp.

Brachythyris aff. B. suborbicularis.

Brachythyris n. sp.

Spirifer aff. S. pellensis.

Martinia n. sp.

Composita n. sp.

Cleiothyridina aff. C. sublamellosa.

Eumetria verneuiliana.

Edmondia sp.

Sphenotus? sp.

Cardiomorpha? sp.

Caneyella? n. sp.

Leptodesma sp.

Pterinopecten n. sp.

Aviculipecten n. sp.

Aviculipecten sp.

Pleurotoinaria sp.

Euomphalus sp.

Naticopsis? sp.

Bulimorpha sp.

Platyceras sp.

Orthoceras sp.

Nautilus sp.

Gastrioceras sp.

Goniatites sp.

Grifflthides sp.

Paraparchites sp.

Bairdia sp.

16 ACh 106. Robber Islands, entrance to Trocadero Bay:

Litliostrotion? sp. 

Zaphrentis sp. 

Stenopora? 2 sp. 

Anisotrypa? sp. 

Batostomella sp. 

Fenestella sp. 

Polypora sp.

Cystodictya aff. C. pustulosa. 

Orthotetes? sp. 

Schizophoria? sp. 

Chonetes aff. C. illinoisensis. 

Productus giganteus. 

Productus semireticulatus.

Productus sp.

Pustula aff. P. magnituberculata.

Pustula punctata.

Pustula sp.

Productella? aff. P concentrica.

Camarotoechia sp.

Spirifer aff. S. striatus.

Syringothyris? sp.

Reticularia aff. R. pseudolineata.

Cliothyridina aff. C. incrassata.

Conocardium sp.

Platyceras sp.

Phillipsia sp.

16 ACh 107. Madre de Dios Island, entrance to Trocadero Bay:

Zaphrentis sp. 

Lonsdaleia? sp. 

Cystodictya? sp. 

Rhombopora sp:

Schizophoria sp. 

Productus semireticulatus. 

Brachythyris sp. 

Ostracoda indet.
CAEBONIFEEOUS BOOKS 113

16. ACh 115. Klawak Island, a quarter of a mile north of Klawak cannery:

Michelinia sp. 

Zaphrentis sp. 

Lithostrotion sp. 

Lithostrotion sp. 

Lonsdaleia sp. 

Crinoidal fragments. 

Schizophoria aff. S. swallowi. 

Orthotetes? sp. 

Streptorhynchus? sp. 

Chonetes aff. C. illinoisensis. 

Chonetes sp. 

Productus giganteus. 

Productus aff. P. longispinus. 

Productus aff. P. gallatinensis. 

Productus aff. P. inflatus. 

Productus aff. P. striatus. 

Productus aff. P. ovatus. 

Productus sp. 

Pustula aff. P. plicatilis. 

Pustula aff. P. pilosa. 

Pustula aff. P. spinulosa. 

Pustula sp.

Overtonia? aff. O. fimbriata.

Productella? aff. P. concentrica.

Camarotoechia ? sp.

Cranaena? sp.

Spirifer aff. S. cameratus.

Spirifer, 2 sp.

Spiriferina? sp.

Squamularia? sp.

Martinia? sp.

Cliothyridina? sp.

Composita sp.

Sphenotus sp.

Nucula? sp.

Pterinopecten sp.

Leptodesma sp.

Bellerophon aff. B. sublevis.

Pleurotomaria? sp.

Platyschisma ? 2 sp.

Platyceras sp.

Proetus sp.

Paraparcnites sp.

Bairdia sp.

16 ACh 145. East shore of island in Klawak Inlet, 21/4 miles north of Klawak:

Lithostrotion sp.

Lonsdaleia? sp.

Fenestella several sp.

Polypora several sp.

Pinnatopora? (Ptilopora?) sp.

Rhabdomeson sp.

Schizophoria (or Rhipidomella) sp.

Orthotetes? sp;

Productus semireticulatus.

Productus ovatus?

Pustula aff. P. wallacianus.

Rhynchopora sp.

The following collections were made by Buddington and identified 

by Girty, who reports:

930 (5443). Northwest end of long island at head of Saginaw Bay, Kuiu 

Island, on east side; 40-foot bed of limestone intercalated in series of interlayered chert, slaty quartzite, and cherty limestone:

Leiorhynchus? aff. L. greenianum.

Brachythyris aff. B. suborbicularis.

Spirifer aff. bifurcatus?

Syringothyris? sp.

Spiriferina sp.

Reticularia sp.

Martinia? sp.

Hustedia sp.

Conocardium sp.

Naticopsis? sp.

Proetus sp.

Eudothyra? sp. 

Cyathaxonia sp. 

Lonsdaleia sp. 

Amplexus? sp. 

Triplophyllum sp. 

Clisiophyllum sp. 

Platycrinus sp. 

Batostomella? sp. 

Leioclema sp.

Glyptopora n. sp. 

Cystodictya aff. C. lineata. 

Crania n. sp. 

Rhipidomella n. sp. 

Derbya? sp. 

Chonetes aff. C. capax. 

Productus n. sp. aff. P. samsoni. 

Productus aff. P. cora. 

Productus aff. P. gallatinensis.
114 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Productus aff. P. ovatus var. minor. 

Pustula aff. P. wallaciana. 

Pustula aff. P. curvirostris. 

Pustula aff. P. millespinosa. 

Pustula aff. P. concentrica. 

Pustula sp. a. 

Pustula, 3 sp. indet. 

Pustula? sp.

Marginifera? cf. M. juresanensis. 

Camarophoria sp. 

Rhynchopora aff. R. beecheri. 

Dielasma aff. D. formosum. 

Dielasma aff. D. arkansanum. 

Dielasma? sp.

Spirifer aff. S. missouriensis. 

Spirifer n. sp.

Spirifer sp.

Brachythyris aff. B. subcardiiformis

var.

Spiriferina aff. S. panderi. 

Spiriferina aff. S. cristata. 

Squamularia aff. S. perplexa. 

Martinia? sp. 

Composita n. sp. 

Hustedia sp. 

Schizodus? sp.

Deltopecten aff. D. wyandotte. 

Aviculipecten aff. D. similis. 

Euphemus? sp.

Euomphalus aff. E. planidoreatus. 

Platyceras sp. 

Griffithides sp.

932 (5444). Head of Saginaw Bay, Kuiu Island:

Fusulina sp.

Ortonia? sp.

Stenopora sp.

Fenestella several sp.

Semicoccinium? n. sp.

Polypora, several sp.

Septopora? sp.

Acanthocladia n. sp.

Streblotrypa? n. sp.

Chainodictyon ? sp.

Coeloconus sp.

Cystoclictya? sp.

Crania n. sp.

Crania sp.

Rhipidomella aff. R. carbonaria.

Schizophoria? sp.

Derbya? sp.

Chonetes aff. C. capax.

Productus aff. P. cora.

Productus semireticulatus.

Productus aff. P. koninckianus.

Productus aff. P. ovatus var. minor.

Productus aff. P. sampsoni?

Productus sp.

Pustula aff. P. indianensis.

Pustula aff. P. concentrica.

Pustula aff. P. morbilliana.

Pustula aff. P. pseudaculeata.

Pustula aff. P. rugata?

Pustula sp. a?

Pustula sp. d.

Pustula? sp.

Strophalosia ? sp.

Camarophoria aff. C. bisinuata.

Rbynchopora aff. R. beecheri.

Dielasma n. sp.

Dielasma aff. D. formosum.

Dielasma aff. D. arkansanum.

Spirifer aff. S. missouriensis.

Spirifer n. sp.

Spiriferina aff. S. cristata.

Brachythyris aff. B. subcardiiformis

var.

Squamularia aff. S. perplexa. 

Ambocoelia aff. A. planiconvexa. 

Cliothyridina aff. C. orbicularis. 

Hustedia n. sp. . \ 

Edmondia sp. 

Sphenotus, 3 sp. indet. 

Sphenotus? sp. 

Goniophora? n. sp. 

Nucula aff. N. shumardiana. 

Leda? sp. 

Parallelodon sp. 

Aviculipecten aff. A. similis. 

Aviculipecten chesterensis? ; 

Aviculipecten aff. A. edwardsi. 

Aviculipecten aff. A. edwardsi var. 

Aviculipecten aff. A. hardinensis. 

Aviculipecten, 2 sp. indet. 

Aviculipecten n. sp. 

Deltopecten aff. D. caneyanus. 

Deltopecten, 2 sp. indet 

Leiopteria? sp. 

Conocardium n. sp. 

Myalina sp.

Cypricardina aff. C. consimilis. 

Cypricardella sp.
CARBONIFEROUS ROCKS 115

200 (4304). About 8 miles southeast of Point Cornwallis, on Keku Strait, just 

north of conspicuous sea arch in limestone:

Fusulinella sp. Productus sp.

Zaphrentis? sp. Pustula sp.

Crinoid. Camarophoria sp.

Polypora? sp. Spirifer sp.

Diplopora? sp. Spiriferina sp.

Batostomella? sp. Husteclia sp.

Rhipidomella sp. Pleurotomaria ? sp.

Chonetes sp. Straparollus? sp.-

Productus ovatus? Grifflthides sp.

Productus n. sp.? Bairdia sp.

2053 (5445). About 1 mile northwest of Klawak: 

Schizophoria aff. S. swallowi. Dielasma? sp. 

Orthotetes? sp. Spirifer aff. S. mosquensis. 

Productus semireticulatus var. Cliothyridina? sp. 

Productus aff. P. gallatinensis.

2069 (5446). Northwest end of island about 2% miles north of Klawak:

Triplophyllum sp. Pustula sp. b.

Spirorbis sp. Marginifera? aff. M. splendens.

Fenestella sp. Marginifera? n. sp.

Schizophoria sp. Camarotoechia sp.

Productus giganteus. Spirifer aff. S. mosquensis.

Productus aff. R. gallatinensis. Cliothyridina? sp.

Pustula aff. P. semicostata. Euomphalus n. sp.

2090 (5446). Small islet about 1% miles north of Klawak:

Fusulina sp. Productus aff. P. cora.

Lithostrotion? sp. Pustula aff. P. pseudaculeata.

Cainpophyllurn? sp. Marginifera? n. sp.

Triplophyllum sp. Squamularia perplexa.

Rhipidomella aff. R. nevadensis. Composita? sp.

Productus semireticulatus var. Euomphalus aff. E. utahensis.

2095 (5447). Just east of cemetery on island north of Klawak:

Rhombopora sp. Productus sp.

Rhabdomeson sp. Pustula aff. P. alternata.

Cystodictya sp. Pustula sp. c.

Derbya? sp. Pustula, 2 sp. indet.

Chonetes aff. C. illinoisensis. Marginifera? sp.

Chonetes aff. C. geinitzianus. Camarophoria? sp.

Chonetes sp. Dielasma? n. sp.

Productus aff. P. cora. Squamularia aff. S. perplexa?

Productus aff. P. ovatus var. minor. Grifflthides sp.

2108 (5449). Little islet about 1% miles north of Klawak. Gray sandstone 

with intercalated calcareous beds:

Triplophyllum sp. Pustula aff. P. punctata.

Rhipidomella aff. R. nevadensis. Pustula aff. P. blairi.

Schizophoria? sp. Marginifera? aff. M. splendens.

Chonetes sp. Squamularia? sp.

Productus semireticulatus. Ambocoelia sp.

Productus aff. P. cora. Cliothyridina aff. C. sublamellosa.
116 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Sphenotus, 2 sp. indet. 

Parallelodon n. sp. 

Cypricardella n. sp. 

Schizodus? sp. 

Aviculipecten aff. A. similis. 

Laevidentalium aff. L. venustum. 

Bellerophon sp. 

Bucanopsis sp. 

Euphemus carbonarius. 

Phanerotrema aff. P. .grayvillense. 

Phanerotrema? aff. P. wortheni. 

Solenospira? sp. 

Goniatites? sp.

Bembexia aff. B. swallowiana. 

Trepospira? sp. 

Pleurotomaria sp.

Pleurotomaria n. sp.

Pleurotomaria, 2 sp. indet,

Solenospira? sp.

Anomphalus? n. sp.

Aclisina? sp.

Sphaerodorna sp.

Meekospira sp.

Straparollus aff. S. spergenensis var.

planorbiformis. 

Naticopsis aff. N. carleyana. 

Naticella n. sp. 

Naticella? sp. 

Zygopleura n. sp. 

Orthoceras sp. 

Phillipsia n. sp. 

Ostracoda indet.

2257 (5450). Bast side of small islet in Klawak Harbor:

Pustula aff. P. spinulosa.

Pustula, 2 sp. indet.

Marginifera? n. sp.

Camarophoria sp.

Camarophoria? sp.

Girtyella? sp.

Dielasma? n. sp. "

Spirifer aff. S. incertus.

Squamularia aff. S. perplexa.

Delthyris? n. sp.

Brachythyris aff. B. subcardiifonnis.

Spiriferina sp.

Cliothyridina sp.

Hustedia aff. H. remota.

Platyceras sp.

Clisiophyllum sp. 

Batostomella sp. 

Chainodictyon? sp. 

Rhombopora sp. 

Schizophoria aff. S. swallowi. 

Schizophoria ? sp. 

Rhipidomella sp. 

Derbya? sp.

Chonetes aff. C. illinoisensis. 

Productus semireticulatus. 

Productus aff. P. gallatinensis. 

Productus aff. P. cora. 

Pustula aff. P. pustulata. 

Pustula aff. P. carringtoniana. 

Pustula aff. P. rugata. 

Pustula aff. P. pseudaculeata.

Girty makes the following comments on the collections by Buddington:

I am inclined to refer [them] to the upper Mississippian (Lisburne horizon), 

yet not without some doubt. Their fauna at least marks a pronounced change 

from that of the Permian, whether of the dark sandy beds or of the whitish 

limestone. Nor are they equally open to doubt, for lots 2257 and 2069 I would 

identify with considerable confidence as Mississippian. The several faunas 

contained in these collections differ from one another considerably, and all 

may not belong to the same period. On the other hand, severaj collections are 

not without strong suggestions of Pennsylvanian time. In the United States 

I should regard FusuUna and Squamularia, and to a less degree Hustedia, as 

indexical of Pennsylvanian, but there the evidence of these forms is not uncontradicted. It is obvious, however, that these Alaskan faunas have no counterpart of any age in the United States, and that the criteria which one 

would safely employ there can not be employed here. As to FusuUna, the form 

which has been recognized in two of the collections is very rare, very small, 

and very primitive, and furthermore, not only the related genus Fusulinella 

but Fusulma itself is known in the Mountain limestone (upper Mississippian)
CARBONIFEROUS BOCKS 117

of Russia. It seems best, then, to refer these eight collections to the upper 

Mississippian and to account for their diverse facies and their, in some cases, 

Pennsylvanian leanings by the fact that the upper Mississippian faunas of 

Alaska are extremely varied, that they are widely different from the Mississippian faunas of the United States, and that they are imperfectly known 

and have never been described in detail.

Partly for the reasons just given, I have made few if any unqualified identifications of the species collected, and in making comparisons I have "employed 

species best known to me and probably to others most likely to use the faunal 

lists; or else I have employed ,less known species that are more similar than 

the familiar ones. My object has been to convey some notion of the faunas 

shown by the collections, so that the very diverse and conflicting faunal relations suggested by the comparisons should carry little weight. In fact, not a 

few of these species of supposed Mississippian age are compared with late 

Pennsylvanian species figured by Tschernyschew in his monograph on the 

Gschelian fauna of Russia. This is partly because parallel species were lacking 

in our own Mississippian and Pennsylvanian faunas. Furthermore, the 

Gschelian fauna contains many types not found in our own Pennsylvanian 

faunas at all, some of them even recalling our Mississippian faunas. This is so 

true that I have not been able wholly to divest myself of the suspicion that 

some of the collections included in the Gschelian monograph came from 

Mississippian horizons.

PENNSYLVANIAN ( ?) ROCKS 

By THEODORE CHAPIN

The Pennsylvanian (?) fauna occurs in the massive white limestone which is confined to the small bay on the southeast corner of 

the island in Soda Bay, on the west coast of Prince of Wales Island, 

about east of the north end of Dall Island. The limestone, which is 

at least 100 feet thick, overlies conformably the limestone of Mississippian age and appears to occupy the trough of a syncline, the 

axis of which is about coincident with the axis of the bay. (See 

pi. 19, #.)

The following collection of fossils was identified by G. H. Girty:

16 ACh 228 (1803-e). Southwest corner of island in the mouth of Soda Bay, 

Prince of Wales Island:

Chaetetes milleporaceus. Lophophyllum sp. 

Lophophyllum sp. Euomphalus sp.

The highest of the [Soda Bay] collections (228, 1803-e) is probably of Peuusylvanian age. It contains little that is really diagnostic, but we note a complete faunal change from the Productus giganteus fauna below. The coral 

genera Chaetetes and Lophophyllum, though not really confined to the Pennsylvanian, are especially characteristic of its fauna. In North America the 

genus Chaetetes appears to be practically restricted to rocks of Pennsylvanian 

age. Indeed, no Mississippian occurrences are generally known, though I have 

recognized the genus in two or three Mississippian collections, a fact not yet 

made public. Provisionally, lot 228 may be assigned to the Pennsylvanian, and 

it may be compared with the Moscovian of Russia. Additional evidence, however, is needed to give force to either correlation.
118 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

PERMIAN ROCKS 

CHARACTER AND OCCURRENCE

The rocks here 'classified as Permian comprise two divisions, both 

of which are tentatively assigned to the Permian by Girty. The 

lower division comprises a very great variety of rocks, including 

thick conglomerate; black calcareous shale with layers of brownweathering limestone or buff calcareous sandstone; basaltic and 

andesitic lava, in part with pillow structure; andesitic tuff and 

breccia; thick-bedded medium-grained white limestone with layers of 

white chert; brownish-weathering thin-bedded dense limestone; sandstone; and perhaps at some places felsite breccias, tuffs, and flows. 

The upper division is more uniform and consists of white limestone 

with intercalated layers of white chert.

The most characteristic and most complete sequence of unmetamorphosed Permian beds is exposed on the Cornwallis Peninsula of Kuiu 

Island and on the Keku Group of islands.

In the Ketchikan district the known Permian is exposed only on 

the small narrow peninsula at the extreme eastern side of Suemez 

Island. These beds belong to the upper division of the Permian and 

are described by Chapin as consisting of about 300 feet of closely 

folded blue and gray limestone, which appears to have unconformable 

relations to the older formations. Beds of the lower division of the 

Permian are found on lower Porcupine Creek in the Skagway district.

The upper division of the Permian is exposed locally beneath the 

Upper Triassic formations along the north shore of Hamilton Bay, on 

the long island several miles south of Kake, and southeast of Pinta 

Kocks, on the eastern flank of the Cape Bendel syncline, Kupreanof 

Island. These beds also form the conspicuous mountain about 5 miles 

north of Kake. On Admiralty Island they are known in Pybus and 

Herring Bays. On the mainland; the upper division of the Permian 

is found at the south headland of Taku Harbor and about 2*^ miles 

east of Point Coke, at the entrance to Holkham Bay, in the Juneau 

district.

Highly metamorphosed Carboniferous formations, that may be of 

Permian age, are found on the west side of Windfall Harbor, Admiralty Island. The rocks consist predominantly of amygdaloidal 

and porphyritic andesitic lava with zones of chert, black slate, and 

one thick zone of interbedded conglomerate, limestone, chert, and 

green andesitic tuff and lava with intercalated red beds comprising 

shale, sandstone, and conglomerate. Several of the limestone beds, 

though highly sheared, are coralline and crinoidal, and the fauna was 

identified by G. H. Girty as of Carboniferous age.
TJ. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 19

A. BLACK CHERT OF MISSISSIPPIAN ACE, MADRE DE DIGS ISLAND

B. FOSSILIFEROUS MASSIVE WHITE LIMESTONE OF PENNSYLVANIAN AGE, 

SODA BAY, PRINCE OF WALES ISLAND
U. S. GEOLOGICAL SURVEY BULLETIN 800 PLATE 20

A. PERMIAN LIMESTONE BLUFFS ON NORTHEAST SIDE OF SAGINAW BAY,

KUIU ISLAND

B. OVERTURNED FOLD IN GRAYWACKE AND PHYLLITK, EAST SIDE OF FREDERICK SOUND
CARBONIFEROUS ROOKS 119

The Snettisham Peninsula on the mainland consists of schistose 

greenstone volcanic rocks with intercalated beds of limestone, conglomerate, and argillaceous and quartz-mica schists. On the shore 

northeast of the Midway Islands a 100-foot bed of schistose limestone 

has many layers containing abundant corals or crinoids. A fauna 

from this limestone submitted to G. H. Girty was identified as of 

Carboniferous age. About 2^ miles east of Point Coke, at the point at 

the entrance to Tracy Arm, there is an exposed bed of limestone with 

layers of schistose white chert which is lithologically identical with 

similar Carboniferous beds. The cove east of Point Anmer, at the 

north end of Snettisham Peninsula, is carved out of limestone which 

contains poorly preserved silicified fossils and resembles the upper 

division of the Permian.

At Taku Harbor, in the Juneau district, limestone carrying Carboniferous fossils (probably Permian) occurs in association with 

schistose greenstone, phyllite, thin bedsi of limestone and chert, and 

black graphitic slate.

The stratigraphic succession in the lower division of the Permian 

appears to be variable. In Saginaw Bay the beds immediately overlying the Mississippian appear to be brown to buff weathering calcareous gray sandstone, with lenses of coarse conglomerate and interbedded limestone and shale. The sandstone predominates, and the 

beds lie conformably on the Mississippian. The conglomerate consists of cobbles of andesite, red rhyolite, white chert, red jasper, and 

limestone. At the head of the bay the sandstone beds are overlain 

by a thick series of black calcareous slate interlayered with buffweathering siliceous limestone and calcareous sandstone. On the 

south side of Halleck Harbor the sandstone is overlain by a thick 

series of basaltic or andesitic breccia with sparse small limestone pebbles and cobbles that carry Carboniferous fossils. To the southeast 

the volcanic rocks appear to thin out and inter digitate as green tuff 

with interbedded sandstone, shale, and limestone. On the islands 

opposite the cannery the cherty dolomite of the upper division of the 

Permian overlies andesitic pillow lava and tuff with interbedded 

limestone and calcareous sandstone full of carbonized plant remains. 

On Halleck Harbor the same beds overlie brownish-weathering sandy 

limestone and black calcareous shale. The lower Permian beds are 

cross folded and warped so that estimates of thickness are difficult.

On the northeast side of Cornwallis Peninsula and in the Keku 

Islets Permian formations are again exposed, but though not more 

than 4 miles apart across the strike, the lithology of the formations 

is in some respects quite different. Conglomerate beds predominate. 

The lowest beds appear to be exposed along the northeast coast of 

6137 29 9
120 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Cornwallis Peninsula from the point about 10 miles southeast of 

Point Cornwallis. The beds comprise interbedded conglomerate, 

conglomeratic limestone, sandstone, and limestone with intercalated 

basalt and andesite flows. The conglomerate consists of pebbles and 

cobbles of andesite, white chert, limestone, red jasper, and other 

rocks. Some of the limestone has intercalated layers of white chert. 

Rhyolite of unknown age forms part of the coast in this vicinity. 

About 4 miles southeast of Point Cornwallis there is a series of 

volcanic rocks and conglomerate exposed locally along the coast for 

a mile and also on the west side of the long islet. These beds are 

overlain unconformably by Upper Triassic limestone and are probably of Permian age. They consist of rhyolite breccia and tuff of 

red, white, and greenish hues, with interbedded lava and conglomerate, and of basaltic breccia and amygdaloidal basalt with many 

veinlets of brilliant red jasper.

The small islet and reefs about 4 miles southeast of Point Cornwallis, opposite a conspicuous sea arch, are composed of about 400 

feet of interbedded conglomerate and brown sandstone overlain by 

limestone and underlain by limestone with white chert layers. The 

conglomerate is composed predominantly of fragments of red felsite 

and green andesite with abundant limestone, chert, and bits of red 

jasper; many of the limestone cobbles are highly crinoidal. Toward 

the northeast andesitic tuff is intercalated in the conglomerate. The 

age of these beds is indeterminate except as indicated by the fact that 

on the next islet to the east about 250 feet of fossilif erous limestone 

which belongs to the lower division of the Permian, interbedded with 

andesitic flows and tuffs, is exposed in a position structurally overlying the conglomerate. On the next large island to the east there 

is exposed about 1,000 feet of conglomerate, consisting largely of 

cobbles and pebbles of limestone and chert, with intercalated sandstone. These beds are in a structural position that would place them 

higher in the series than the limestone and volcanic rocks, and they 

are in turn overlain conformably by the limestone with intercalated 

chert layers carrying a fauna characteristic of the upper division 

of the Permian. The uppermost beds of the conglomerate series are 

brown-weathering sandstone with intercalated limestone and conglomerate. Some of the limestone cobbles in this conglomerate carry 

a fauna identified by Edwin Kirk as of Silurian age.

On the large northwesternmost island of the Keku group there is 

about 1,200 feet of black platy or shaly limestone or calcareous shale 

with a few intercalated layers of buff-weathering sandy limestone 

and a 75-foot bed of conglomerate. These beds form a triangular 

area in the middle of the island leaving only a narrow strip at the 

west side of the base of the peninsula on the north side of the island
CARBONIFEROUS ROCKS 121

and a wide area on the east. They are adjoined on the west by infolded or infaulted Upper Triassic beds, and on the east by limestone and chert. The beds of buff-weathering limestone are highly 

fossiliferous with a fauna identified by G. H. Girty as belonging to 

the lower division of the Permian.

Carbonized plant remains are frequently found in the sandstones 

of the lower division of the Permian.

The upper division of the Permian is characteristically exposed 

on the Keku Islets, on Cornwallis Peninsula of Kuiu Island (pi. 

20, A) and on Pybus and Herring Bays, Admiralty Island. The 

formation consists of about 1,000 feet of limestone with intercalated 

layers or interbeds of white chert. The relative amount of chert is 

variable in different sections. On the Keku Islands the chert layers 

usually range from about 9 inches to several feet in thickness and 

the limestone beds from 5 to 50 feet. Lenticular veinings of chert 

are also common in the limestone. Many of the chert layers are considerably brecciated. Locally, as on the south side of Admiralty 

Island west of False Point Pybus, there is as much as 200 feet of 

white chert with only a very little limestone, and elsewhere there are 

relatively clean beds of limestone several hundred feet thick. The 

beds are highly fossiliferous, and faunas collected from many localities have all been identified by G. H. Girty as of Permian age.

AGE AND CORRELATION

The age of the formations listed here as Permian is based on 

several collections of fossils made by Wright and on later collections 

gathered from many localities by Buddington. The identifications 

are all by G. H. Girty.

Girty's report on collections made by Buddington in 1922 from 

both the upper and lower divisions of the Permian follows:

Where I have seen the Permian rocks of southeastern Alaska, they consist oi 

an upper group of whitish cherty limestones and a lower group of blackish sandj 

limestones. The fauna's also of these two divisions of the Permian, though 

related, are appreciably different. The existence of this lithologic and faunal 

distinction raises the question whether, as the upper division is classed as 

Permian, the lower should not be classed as upper Pennsylvania!!. On this 

question I am inclined to take the negative side, for the present ab least. The 

difference between the lower and upper faunas seems too slight for a boundary 

as important as that between the Peunsylvanian and the Permian.

He reports further on the collections made by Buddington in 1923:

Lots 5135 (966-c) and 5136 (976) contain the fauna of the white cherty 

Permian limestone correlated with the Artinsk sandstone of Russia, that is so 

well exposed on Kuiu Island (Saginaw Bay) and is also found in other parts 

of Alaska.

The white Permian limestone is underlain by dark sandy limestones which 

are exposed on Kuiu Island and on the Keku Islets. To this horizon I would
122 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

refer lots 5126 (918-B), 5127 (920-A), 5122 (921), 5130 (925), 5129 (926), and 

5132 (929). This fauna, if well represented, is readily distinguishable from 

that of the white limestone, though related to it, and should, I am inclined to 

think, be classed as Permian if the other is. It might well be classed, however, 

as upper Pennsylvanian if the Pennsylvanian was followed by the Permian 

without any marked lapse of time or change of conditions. Lots 5124 (913), 

5131 (928), and 5134 (965) should also probably be included in this group, 

though they have a somewhat different fauna; and in the group, though less 

definitely, should probably be included the small collections 5123 (906) and 

5125 (918-A). The paleontologic evidence which 5125 contains is too meager 

to indicate clearly where its affinities lie. Lot 5125 (905) is unique in consisting largely of Goniatites, but it does not contain enough other species to indicate 

its geologic age. This lot may go either with 5124, 5131, or 5134, or it may be 

much older. The Goniatites suggest certain Mississippian types, but they are 

also related to some that occur in the Pennsylvanian.

The accompanying lists show the species contained in the collections. But 

few positive identifications have been made. The faunas are so fundamentally 

unlike any that have been described in the United States proper that comparisons with our own Pennsylvanian and Permian species would be for the 

most part futile. The faunas most closely related to these, so far as known, 

are found in Russia, but the Russian faunas are so remote as to cast doubt in a 

general way upon the exact identity of many of the Alaskan species, and as no 

Russian specimens are available for direct comparisons, it has seemed best now, 

as in the past, merely to suggest relationships and to leave such final identifications as can be made to the course of a comprehensive study in which all of our 

specimens of each species can be employed.

LOWER DIVISION OF THE PERMIAN

The collections listed below were all made by Buddington, except 

as otherwise specified; the identifications are by G. H. Girty, who 

makes the following comments:

Lots 917 and 2349 contain a rather characteristic fauna which occurs in 

dark-colored siliceous and calcareous beds that underlie the whitish Permian 

limestone of Artinskian age. This fauna differs materially from that of the 

whitish limestone and at the same time is undoubtedly related to it. This 

horizon has been included along with the other in the Permian, but it may 

prove to be highest Pennsylvanian.

917 (5451). East side of peninsula on southwest side of Halleck Harbor, Kuiu 

Island:

Fenestella sp. Marginifera aff. M. splendens.

Derbya? sp. Marginifera aff. M. splendens var.

Chonetes aff. C. granulifer. Marginifera aff. M. lebedevi?

Chonetes n. sp. Camarophoria aff. C. mutabilis.

Productus aff. P. mammatus. Camarophoria aff. C. pentameroides ?

Productus sernireticulatus var. Rhynchopora sp.

Productus aff. P. koninckianus. Dielasma? sp.

Productus cora? Spiriferella arctica var.

Pustula aff. P. fasciata. Squamularia aff. S. perplexa.

Pustula aff. P. wallaciana. Martinia? aff. M. simensis var. sub

Avonia aff. A. porrecta? stricta.
CARBONIFEROUS ROCKS 123

Spirifer cameratus Tschernyschew Aviculipecten aff. A. rnontpelierensis.

[not Morton]. Aviculipecten sp. 

Anibocoelia n. sp. Lima aff. L. retifera. 

Cliothyridina? sp. Bellerophon sp. 

Aviculipecten aff. A. delawarensis.

Halleck Harbor, Kuiu Island; black carbonaceous shale, calcareous sandstone, and conglomerate; lower division of upper Carboniferous; collected by 

Wrlght: 

Fusulina aff. F. longissima. Spirifer cameratus Tschernyschew

Crania sp. [not Morton?].

Schizophoria? sp. Squamularia n. sp.

Derbya aff. D. robusta. Martiniopsis sp.

Chonetes sp. Rhynchopora aff. R. geinitziana.

Chonetes aff. C. trapezoidalis. Dielasma sp.

Productus aff. P. humboldti. Streblopteria sp.

Productus aff. P. porrectus. Aviculipecten aff. A. mccoyi.

Productus aff. P. semireticulatus. Aviculipecten, 2 sp.

Productus aff. P. schrenki. Entolium aff. E. aviculatum.

Productus cora. Solenopsis? sp.

Spirifer aff. S. ufensis.

5125 (918-A). First niche in coast line southeast of the southwest headland 

of Halleck Harbor, Kuiu Island; thin-layered buff-weathering siliceous limestone underlying 5126 (918-B) either unconformably or in faulted relations:

Lonsdaleia sp. Productus aff. P. undatus. 

Productus aff. P. gruenwaldti.

5126 (918-B). First niche in coast line southeast of the northwest headland 

of Halleck Harbor, Kuiu Island; gray sandstone underlying conglomerate:

Fusulina aff. F. elongata. Productus aff. P. koniuckianus.

Chonetes aff. C. geinitzianus. Pustula aff. P. humboldti.

Productus aff. P. ischmensis. Rhynchopora sp.

Productus aff. P. ischmensis var. Reticularia? n. sp.

5128 (926). Just southeast of cannery on northeast side of Saginaw Bay; 

buff-weathering interbedded calcareous sandstone and shale, overlain by 

conglomerate:

Fusulina aff. F. elongata. Pustula aff. P. humboldti. 

Fenestella sp. Marginifera sp. 

Orthotichia? aff. 0. morgauiana. Rhynchopora aff. R. nikitini. 

Streptorhynchus sp. Dielasma sp. 

Chonetes aff. C. tinmnicus. Spiriferina aff. S. cristata. 

Chonetes aff. C. granulifer. Reticularia? n. sp. 

Productus aff. P. ischmensis. Squamularia? sp. 

Productus aff. P. ischmensis var. Spirifer aff. S. cameratus. 

Productus aff. P. koninckianus. Euchondria? aff. E. neglecta. 

Productus aff. P. mammatus? Aviculipecten sp. a. 

Productus aff. P. gruenevvaldti. Aviculipecten sp. b? 

Productus sp. Aviculipecten sp. d. 

Pteria aff. P. longa. Aviculipecten aff. A. occidentalis. 

Pinna sp.

72 Wright, P. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska : U. S. 

Geol. Survey Bull. 347, p. 52, 1908.
124 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

5122 (921). First cove southeast of Halleck Harbor, Saginaw Bay, Kuiu 

Island; shaly limestone overlying interbedded andesitic breccia, tuff, and limestone :

Fusulina aff. F. elongata.

Fenestella sp.

Rhombopora sp.

Orthotich.'a? aff. O. morganiana.

Enteletes? n. sp.

Derbya aff. D. grandis.

Chonetes aff. C. geinitzianus.

Chonetes aff. C. granulifer.

Productus cora.

Productus aff. P. koninckianus.

Productus aff. P. mammatus.

Productus aff. P. gruenewaldti.

Pustula aff. P. juresanensis?

Pustula sp.

Acanthopecten aff. A. carbonifer.

Lima n. sp. a.

Lima n. sp. b.

Lima aff. L. retifera.

Marginifera aff. M. typica var. septentrionalis.

Marginifera aff. M. aagardi. 

Rhynchopora aff. R. nikitini. 

Dielasma aff. D. bovidens. 

Dielasma aff. D. supracarbonicurn. 

Spirifer aff. S. cameratus. 

Spiriferina aff. S. cristata. 

Spiriferina aff. S. holtzapfeli. 

Splriferiua sp.

Squamularia aff. S. perplexa. 

Euchondria? aff. E. neglecta. 

Aviculipecten sp. a. 

Aviculipecten sp. b. 

Aviculipecten sp. c. 

Naticopsis n. sp. aff. N. nana.

5130 (925). North end of round island opposite cannery on northeast side of 

Saginaw Bay, Kuiu Island; limestone associated with andesitic volcanic rocks:

Orthotichia? aff. O. morganiana. Productus aff. P. ischniensis.

Derbya aff. D. grandis. Productus aff. P. ischmensis var.

Chonetes aff. C. geinitzianus. Pustula aff. P. humboldti.

Chonetes aff. C. trapezoidalis. Reticularia? n. sp.

Chonetes sp. Euchondria? aff. E. neglecta.

Productus aff. P. koninckianus. Phanerotrema sp.

5131 (928). About two-thirds of a mile southeast of cannery on northeast 

side of Saginaw Bay, Kuiu Island; calcareous slate with many basalt dikes; 

Tertiary:

Sponge?

Striatopora sp.

Fenestella sp.

Pinnatopora sp.

Rhombopora sp.

Chonetes sp.

Productus aff. P. gruenewaldti.

Productus aff. P. koninckianus.

Margiuifera aagardi. 

Pustula aff. P. wallaciana? 

Rhynchopora? sp. 

Ambocoelia? sp. 

Anthraconeilo ? sp. 

Aviculipecten sp. f. 

Nautilus? sp. 

Phillipsia sp.

5132 (929). Northeast side of Saginaw Bay, about 1% miles southeast of 

cannery; buff-weathering interbedded calcareous sandstone and shale:

Fusulina aff. F. elongata. 

Zaphrentis sp. 

Triplophyllum sp. 

Amplexus? sp. 

Batostomella sp. 

Fenestella, 2 sp. 

Polypora, 2 sp. 

Crania sp. 

Derbya aff. D. grandis.

Chouetes aff. C. geinitzianus. 

Chonetes aff. C. trapezoidalis. 

Chonetes aff. C. granulifer var. 

Productus aff. P. koninckianus. 

Productus aff. P. mammatus. 

Productus aff. P. gruenewaldti. 

Pustula hurnboldti. 

Pustula aff. P. fasciata. 

Pustula aff. P. tuberculata.
CARBONIFEROUS ROCKS 125

Pustula aff. P. juresanensis? 

Marginifera aff. M. typica var. septentrionalis.

Spirifer aff. S. cameratus. 

Spiriferina sp. 

Reticularia? n. sp. 

Squaniularia aff. S. perplexa. 

Parallelodon sp. 

Aviculipecten sp. b? 

Aviculipecten sp. d?

Aviculipecten sp. e.

Pernipecten n. sp.

Lima sp. b.

Conocardium? sp.

Schizodus? sp.

Bellerophon sp.

Pleurotomaria n. sp. aff. P. conulus.

Naticopsis n. sp. aff. N. nana.

Platyceras.

Ostracoda indet.

2349 (5452). Head of Saginaw Bay, east side of cove on east side of bay:

Zaphrentis sp.

Campophyllum sp.

Spirorbis? sp.

Leioclema sp.

Polypora sp.

Thainniscus? sp.

Crania sp.

Schizophoria n. sp.

Derbya? sp.

Chonetes aff. C. granulifer.

Chonetes aff. C. verneuilianus.

Chonetes aff. C. ostiolatus?

Productus cora.

Productus aff. P. tenuistriatus..

Productus aff. P. koninckianus.

Productus aff. P. cancriniformis.

Productus sp.

Productus semireticulatus var.

Productus aff. P. gruenewaldti.

Avonia aff. A. porrecta.

Pustula aff. P. irginae.

Pustula aff. P. subhorrida.

Pustula aff. P. wallaciana.

Pustula aff. P. pseudaculeata.

Pustula sp.

4308 (206). Northernmost Keku Islet, west side; black limestone with buffweathering layers and conglomerate beds:

Marginifera aff. M. splendens. 

Caniarophoria aff. C. pentameroides. 

Rhynchopora sp. 

Spirifer cameratus Tschernyschew

[not Morton]. 

Spirifer aff. S. nikitini. 

Spirifer aff. S. fasciger. 

Brachythyris aff. B. ufensis. 

Spiriferella ? aff. S. artiensis. 

Spiriferina sp. 

Spiriferina sp.

Squaniularia aff. S. perplexa. 

Reticularia? sp. 

Ciiothyridina aff. C. roisayana. 

Aviculipecten aff. A. delawarensis. 

Aviculipecten aff. A. montpelierensis. 

Aviculipecten sp. 

Pernipecten aff. P. aviculatus. 

Pteiia n. sp. 

Schizodus? sp. 

Pleurotomaria sp. 

Naticopsis sp. 

Platyceras sp. 

Griffithides sp.

Derbya? sp.

Chonetes sp.

Productus aff. P. cancrini.

Productus aff. P. mamrnatus.

Productus aff. P. semireticulatus.

Marginifera aff. M. involuta.

Marginifera aagardi.

Same as 4308; collected by Wright:

Eusuliua aff. F. longissima. 

Scenopora sp. 

Rhombopora sp. 

Meekella? sp.

Schizophoria sp. 

Camarophoria aff. C. crumena. 

Spirif erella? arctica var. 

Squaniularia aff. S. perplexa. 

Ciiothyridina n. sp. 

Aviculipecten sp. 

Myalina? sp.

Perbya? sp.

Chonetes aff. C. trapezoldalis. 

Productus aff. P. cora. 

Productus aff. P. humboldti.

73 Wright, F. B. and C. W., op. cit, pp. 53-54.
126 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Productus aff. P. koninckianus. 

Productus aff. P. fasciatus. 

Productus aff. P. tartaricus. 

Productus aff. P. lineatus. 

Productus seraireticulatus. 

Productus aff. P. jakovlevi. 

Streblopteria sp. 

Aviculipecten aff. A. mccoyi. 

Aviculipecten, 2 sp. 

Myalina aff. M. perattenuata. 

Pinna ?sp. 

Schizodus sp. 

Capulus sp. 

Straparollus sp. 

Bulimorphia aff. B. peracuta. 

Productus n. sp. aff. P. tuberculatus. 

Productus sp. 

Marginifera aff. M. juresanensis.

4309 (215). East side of northernmost large Keku Islet; black calcareous shale 

with intercalated1 beds of buff-weathering limestone:

Spirifer cameratus Tschernyschew [not

Morton?]. 

Spirifer arcticus? 

Spiriferina aff. S. pyramidata. 

Squamularia sp. 

Pugnax aff. P. Utah. 

Rhynchopora aff. R. geinitziana. 

Rhynchopora aff. R. nikitini. 

Camarophoria aff. C. purdoni. 

Camarophoria aff. C. superstes. 

Pseudomelania sp. 

Loxonema aff. L. subgracilis. 

Turbonellina aff. T. chatzepovkensis. 

Pleurotomaria, 2 sp. 

Bellerophon sp. 

Medlicottia aff. M. orbignana. 

Leperditia sp.

Zaphrentis? sp. 

Cladochonus sp. 

Botostomella sp. 

Derbya? sp.

Productus aff. P. mammatus. 

Productus aff. P. timanicus. 

Productus aff. P. cancrini. 

Pustula aff. P. humboldti. 

Marginifera aagardi. 

Marginifera? aff. M. lebedevi. 

Marginifera? aff. M. involuta.

Camarophoria aff. C. crumena. 

Rhynchopora aff. R. nikitini. 

Dielasma sp. 

Spiriferella? arctica var. 

Spirifer aff. S. dieneri. 

Spirifer aff. S. fasciger. 

Spiriferina sp.

Squamularia aff. S. perplexa. 

Cliothyridina n. sp. 

Aviculipecten sp. 

Fleurotomaria? sp.

5128 (905). Kuiu Island, just west of the point on Keku Strait where the 

coast line turns from north to northwest, limestone overlying conglomeratic 

limestone, and andesitic lava involved in an indeterminate relation:

Lonsdaleia sp. Gastrioceras aff. G. nolinense. 

Platyceras sp.

5123 (906). Just northwest of locality 5128; coral reefs interbedded with 

basaltic flows:

Triplophyllum sp. Striatopora? sp.

4305 (231). Kuiu Island, west of south end of Keku Island group; limestone with interbedded basaltic lava:

Syringopora? n. sp. 

Zaphrentis? sp. 

Clisiophyllum sp. 

Lonsdaleia n. sp. 

Lonsdaleia? sp. 

Polypora sp. 

Rhombopora sp.

Schizophoria sp.

Productus aff. P. gruenewaldti.

Productus cora Tschernyschew [not

D'Orbigny].

Camarophoria margaritovi ? 

Spirifer aff. S. striatus Tschernyschew

[not Martin].
CARBONIFEROUS ROCKS 127

5124 (913). North end of long island about 3 miles southeast of Cornwallis 

Point, Keku Strait; highly crinoidal limestone, lower beds with chert layers:

Lonsdaleia sp. 

Fistulipora sp. 

Batostomella sp. 

Derbya? aff. D. bennetti. 

Rhipidomella aff. R. uralica. 

Orthotlchia? aff. 0. morganiana. 

Chouetes aff. C. granulifer var. 

Productus aff. P. cora. 

Productus sp. 

Pustula sp.

Pustula aff. P. tuberculata. 

Pustula aff. P. pustulata?

5134 (965). Islet in Keku Strait about 1% miles east-northeast of point 4 

miles southeast of Point Cornwallis; limestone interbedded with andesitic flows 

and tuff:

Avonia aff. A. porrecta.

Marginifera aff. M. juresanensis?

Marginifera aff. M. aagardi?

Marginifera sp.

Richthofenia aff. R. lawrenciana.

Dielasma? sp.

Spirifer aff. S. marcoui.

Squamularia aff. S. guadalupensis.

Cliothyridina? sp.

Aviculipecten ? sp.

Grifflthides? sp.

Syringopora sp. 

Favosites sp. 

Striatopora sp. 

Lonsdaleia sp. 

Stenopora sp. 

Batostomella sp. 

Rhipidomella aff. R. uralica. 

Orthotichia? aff. O. morganiaua. 

Productus aff. P. gruenewaldti. 

Productus aff. P. koninckianus. 

Productus n. sp.? 

Marginifera aff. M. juresanensis. 

Productus (Marginifera?) sp. 

Avonia aff. A. porrecta.

Pustula aff. P. fasciata? 

Pustula aff. P. wallaciana? 

Dielasma sp. 

Spirifer sp. 

Martinia? sp.

Squamularia aff. S. perplex a. 

Brachythyris sp. 

Cliothyridina? sp. 

Cypricardinia sp. 

Aviculipecten? sp. 

Schizodus? sp. 

Euconospira? sp. 

Platyceras sp. 

Euomphalus? sp.

5137. West side of Windfall Harbor, Seymour Canal, Admiralty Island; 

schistose limestone interbedded with conglomerate, chert, and andesitic volcanic rocks:

Stenopora sp. 

Batostomella? sp. 

Leioclema sp.

Polypora sp. 

Rhabdomesa? sp.

UPPER DIVISION OF THE PERMIAN

Wright made a collection from beds on Halleck Harbor in Saginaw Bay, Kuiu Island. His description 74 follows:

Beds of white cherty limestone 450 feet or more in thickness overlie a series 

of black, carbonaceous shales, calcareous sandstones, and conglomerates with 

an exposed thickness of 125 feet. * * *

Wright, F. E. and C. W., op. cit, pp. 54-55.
128 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

In the overlying limestone beds belonging to the upper series Girty reports 

the following:

Fossils from Halleck Harbor, Kuiu Island; upper division of upper Carboniferous :

Zaphrentis? sp.

Crinoid fragments.

Stenopora sp.

Streptorhynchus aff. S. pelargonatum.

Chonetes, 2 sp.

Productus aff. P. timanicus.

Productus aff. P. aagardi.

Productus aff. gruenewaldti.

Productus aff. P. humboldti.

Productus aff. P. mammatus.

Productus aff. P. lineatus.

Productus aff. P. occidentalis.

Productus sp.

Spirifer aff. S. alatus. 

Spirifer aff. S. blasii. 

Spirifer articus. 

Spirifer n. sp. aff. S. marcoui. 

Spirifer aff. S. dieneri. 

Spiriferina aff. S. cristata. 

Squamularia sp. 

Cleiothyris sp. 

Camarophoria margaritovi. 

Camarophoria aff. C. purdoni. 

Rhynchopora aff. R. nikitini. 

Rhynchopora aff. R. geinitziana. 

Dielasma sp.

The fossils listed in the accompanying table were identified by 

Girty from collections made by Buddington.

Fossils fwm upper division of Pei'mian of Kuiu, KeJcu, and Kupreanof Islands

Stenopora?..-.- __ . ______ ... ____ .

Zaphrentis?... __________ . .............

Polypora.... ______________ . .......

Productus horridus _______________

Productus aff. P. longus Tschernyschew [not 

Meek?]....................... ............

Productus aff. P. inflatus Tschernyschew [not

Camarophoria margari to vi. . . . . ____ . _ . _

Pustula aff. P. horrida. ..-.-.-...-.-..-......

Dielasma?. ____ . ____________ -.

Spiriferella? arctica. ...........................

to

iTH

X

X

X

X

X

X

(69) 4302 

X

X

X

X

X

X

I

Tt<

X

X

X

X

X

r~

0

 ^

X

X

X

(217) 4310 

X

X

X

5? 

g

p 1

9

X

X

X

X

X

X

X

X

X

X

(235) 4312 

X

X

X

I 

§

2"O

X

X

X

X

X

X

X

(976) 5136 

X

X

X

X

X

X

X

X

X

X

X

X

X

X
CARBONIFEROUS ROCKS 129

4301 (61). Little islet with east-west axis about 7 miles southeast of Kake, 

on Hamilton Bay, Kupreanof Island;' 1922.

4302 (69). About 6% miles southeast of Kake on Hamilton Bay, Kupreanof 

Island; thick massive white crinoid limestone overlying green tuff; 1922.

4303 (75). Small islet off tip of southeast prong of northern half of long island 

about 2% miles south of Kake, Kupreanof Island; limestone with thin conglomeratic layer; 1922.

4307 (203). Reef with conspicuous sea stack about half way between Kuiu 

Island and the northernmost Keku Islet; 1922.

4310 (217). Northern reef of Keku Islands, about 5 miles west-southwest of 

Kake; limestone with white chert layers; 1922.

4311 (234). Southern tip of southernmost large island of Keku group; about 

5 miles west of Point Hamilton; 1922.

4312 (235). Islet southeast of locality 4311; 1922.

5135 (966-c). Long, narrow island in south-central part of Keku group; limestone overlying conglomerate of the lower division of the Permian; 1923.

5136 (976). Island about 1 mile north-northeast of conspicuous headland 10 

miles southeast of Point Cornwallis; from limestone cobbles in a conglomerate 

probably of Upper Triassic age; 1923.

A collection of fossils was made by Chapin from Suemez Island 

and identified by Girty as follows:

1805 (15 ACh 240). South shore of east point of Suemez Island:

Zaphrentis sp. Dielasma aff. D. bovidens.

Fistulipora sp. Dielasma sp.

Slenopora sp. Camarophoria aff. C. margaritovi.

Lt-ioclema sp. Spirifer aff. S. tastubensis.

Chonetes aff. C. verneuilianus. Spirifer aff. S. interplicatus.

Productus aff. P. humboldti. Spirifer aff. S. schellwieni.

Pclypora sp. Spirifer sp.

Productus cora var. Cliothyridina? sp.

Productus aff. P. mammatus. Griffithides sp.

Productus sp.

Fossils collected by Burchard 7B from the west side of Pybus Bay, 

Admiralty Island, about 2^ miles from the entrance, were identified 

by Girty as of Artinskian age:

Batostomella sp. Tegulifera? sp.

Camarophoria aff. C. margaritovi. Dielasma sp.

Chonetes aff. C. morahensis. Rbynchopora aff. R. nikitini.

Productus aff. P. timanicus. Spirifer aff. S. cameratus.

Productus aff. P. gruenewaldti. Spiriferella? arctica.

Productus seinireticulatus. Squamularia aff. S. perplexa.

Productus aff. P. multistriatus. Modiola? sp.

Productus sp. Murchisonia? sp.

78 Burchard, B. F., Marble resources of southeastern Alaska: U. S. Geol. Survey Bull. 

682, p. 55, 1920.
130 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The lower limestone, which is exposed on the more northerly of 

the Screen Islands, in Clarence Strait, yielded the Carboniferous 

(?) fossils collected by G. C. Martin in 1914, of which Girty says:

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 the Screen Islands:

Pseudomonotis? sp. Aviculipecten ? aff. A. fasciculatus. 

Pleurotomaria ? sp.

Kindle also obtained from the lower limestone 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.

DISTRIBUTION

Fossiliferous Upper Triassic rocks are found on Gravina Island, 

in the northern half of Kuiu and Kupreanof Islands, on some of 

the islands at the north end of Keku Strait, on Turnabout Island, 

Frederick Sound, on the Screen Islands, Clarence Strait, on the south 

end of Admiralty Island, in Pybus Bay, at Gambier Bay and between 

Mole and Windfall Harbors, Seymour Canal, and on the mainland 

near Juneau. Lithologically similar rocks, presumably of the same 

age, occur on Carroll Inlet, George Arm, and Annette and Hotspur 

Islands, in the Ketchikan district. Triassic beds form a portion of 

the schistose greenstone, phyllite, and crystalline schist of the mainland, but fossils of Triassic age have been found in those beds at only 

one locality in the area covered by this report.

Triassic rocks occur on Gravina Island in a belt along the southwest coast from Threemile Cove, opposite Dall Bay, northward for 

about 7 miles. On Kupreanof Island they are exposed along the 

flanks of a southeastward-pitching anticline which passes through 

the town of Kake and within a major syncline which lies east of the 

Kake anticline; good outcrops are found on Frederick Sound east 

of Cape Bendel and on the north shore of Hamilton Bay. On the 

Keku group of islands they occur within a narrow pinched synclinal
; TRIASSIC ROCKS (UPPER TRIASSIC) 131

trough, in part with isoclinal folds, extending across the two large 

northeastern islands of the group. They also form Hound Island. 

On Kuiu Island they extend southeastward for about 2y2 miles, with 

local interruptions, along the northeast side of Cornwallis Peninsula, 

from a point about a mile southeast of Point Cornwallis. Triassic 

beds also form the coast west of Hound Island for 7 miles or more,

CHARACTER AND STRATIGRAPHIC RELATIONS

The succession, variation, and thickness of the Triassic formations 

have not been satisfactorily worked out because of structural disturbances and the interruption of the continuity, of the exposures 

by waterways or by forest cover. The Triassic rocks in the vicinity 

of Keku Straits include three groups one consisting of sediments 

and the two others of volcanic rocks with a little intercalated sedimentary material.

The sedimentary formation of the Upper Triassic here comprises 

conglomeratic limestone and calcareous conglomerate, calcareous 

sandstone, and sandy limestone, black shale, and medium-bedded 

gray limestone. The limestone is usually fine grained and at many 

places contains black slaty layers. The conglomerate and sandstone 

are restricted to the basal beds.

The volcanic formations are differentiated on the basis of their 

faunas; their character and their structural relations over wide 

areas are insufficiently known and their lithology is too similar to 

separate them otherwise. They comprise green andesitic flows, breccia, and tuff with local intercalated sedimentary beds. The lava predominantly shows a pillow structure but is in part amygdaloidal and 

in part polygonally jointed. Much of the breccia has a limestone 

matrix and is in considerable part the result of a primary disaggregation of the radial-jointed pillows an autoclastic structure. The 

basal part of the volcanic rocks on Kuiu Island consists of interbedded limestone and green andesitic tuff and lava with local conglomeratic beds. On Kupreanof Island the other volcanic formation has locally a bed of conglomerate 150 to 200 feet thick at its 

base. The volcanic rocks of Kuiu Island rest directly on the lower 

division of the Permian beds, whereas the volcanic rocks of Kupreanof 

Island rest on the sedimentary division of the Upper Triassic.

On Gravina Island Chapin includes in the Upper Triassic a series 

of slate with interlayered graywacke-like sandstone which he describes as overtying the conglomerate, fossiliferous limestone, and 

slate of the basal part of the Upper Triassic. To Buddington it 

seems possible that this formation may be, at least in part, of 

Jurassic age.
132 GEOLOGY AND MINERAL, DEPOSITS, SOUTHEASTERN ALASKA 

GRAVINA AND EEVILLAGIGEDO ISLANDS 

By THEODORE CHAPIN

On Gravina Island 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 and intercalated sedimentary beds which are, 

at least in part, of Upper Jurassic or Lower Cretaceous age and possibly in part of Upper Triassic 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, 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 gradational beds of grit. 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 76 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 limestone 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 aive 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, 

in which corals are especially abundant. On Threemile Cove it is 

more closely folded, is considerably silicified, and weathers out brick78 Threemile Cove has appeared in the literature as " cove 3 miles north of Ball Head."
TRIASSIC BOOKS (UPPER TRIASSIC) 133

red. The limestone here is less fossiliferous, and the fossils are 

poorly preserved. The greater amount of deformation of the limestone 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. 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 the Dall Ridge north of Dall Head. Similar rocks 

are exposed on Bostwick and Seal Cove and extend northwestward 

in a belt from 2 to 3 miles wide as far as Vallenar Bay and North 

Vallenar Point.

The dominant rock of this series is black clay slate that has a 

pronounced cleavage. Intercalated with the slate are thin beds of 

quartzose sandstone, quartzite, conglomerate, and sandstone. The 

limestone beds are not numerous but ate usually fossiliferous. The 

interbedded limestone layers are 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 folds are sharply contorted. The 

beds on Vallenar Bay are much more regular, and show none of the 

close folding.

Associated conglomerate, limestone, schistose slate, and phyllite 

on Revillagigedo Island are correlated with the sedimentary series of 

Gravina Island on the basis of the similarity of lithology and sequence and the stratigraphic and structural relations. The beds are 

exposed on George Arm, Carroll Inlet, and Thorne Arm. The 

lithologic similarity of these rocks to the Triassic rocks of Gravina 

Island is marked, notwithstanding their more schistose nature, which 

is due to their proximity to the large masses of intrusive rocks. The 

conglomerate is very schistose, and the cobbles are mashed and deformed. The limestone is white and crystalline. The slate is in part 

schistose and might more correctly be termed phyllite and schist. 

Similar slate, phyllite, and schist occur on the north end of Tongass 

Narrows.

The base of the Upper Triassic series of Gravina Island is not 

visible. The lowest part exposed occurs at Threemile and Thompson 

Coves, where the actual base of the conglomerate is concealed by 

water. At Vallenar Bay the Triassic rocks overlie Devonian sediments that come to the surface along the axis of an anticline, but 

the contact is covered by Quaternary deposits. The presence of 

Devonian pebbles in the conglomerate of Threemile Cove indicates an 

underlying Devonian rock. On George Arm the supposedly Triassic 

rocks rest upon rocks that are probably Carboniferous. A marked 

unconformity at the base of the Upper Triassic rocks is thus evident.
134 GEOLOGY AND MINERAL, DEPOSITS, SOUTHEASTERN ALASKA

On Gravina and Revillagigedo Islands the Triassic rocks are overlain in places conformably by volcanic beds of Upper Triassic or 

Jurassic age and in places unconformably by slate and graywacke 

of Jurassic or Cretaceous age.

Greenstone and slate made up of an interbedded series of altered 

tuff, flows, and black slate, with some intrusive rocks, occur on Gravina, Duke, Annette, and Kevillagigedo Islands, in the Ketchikan district. The greenstone and slate overlie the Upper Triassic rocks with 

apparent conformity. On the evidence of a few fossils found in the 

intercalated sediments and on the grounds of structure and analogy 

with rocks of known age, these rocks are regarded as Upper Triassic 

or Jurassic.

SCREEN ISLANDS

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 thick, massive conglomerate; the upper limestone and 

the conglomerate are probably Upper Triassic, and the lower limestone is Carboniferous. On the northernmost islands there are exposed beds about 900 feet thick, comprising limestone with intercalated beds of conglomerate 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. Some of the limestone cobbles carry Carboniferous faunas, 

indicating an unconformity at the base of the Upper Triassic.

KEKU STRAIT

The sedimentary division of the Upper Triassic is again well shown 

near the north end of Keku Strait. Where exposed on the flanks 

of the Kake anticline it consists of calcareous beds which rest unconformably on Paleozoic beds; the basal Triassic beds contain fragments of the Paleozoic rocks. At the north end of the long island 

several miles south of Kake limestone and conglomerate carrying 

Upper Triassic fossils overlie unconformably tuff with chert and 

calcareous layers of Devonian age. Many fragments of the Devonian 

rocks are found in the Upper Triassic conglomerate. At the southeast end of the anticline the Upper Triassic rests unconformably on 

the Permian cherty limestone, and fragments of the Permian carrying typical fossils are incorporated in the Upper Triassic conglomerate. At most places the Upper Triassic sedimentary beds overlie the 

upper division of the Permian. The succession, variation, and thickness of the beds intervening between the Paleozoic formations and
TEIASSIC ROCKS (UPPER TRIASSIC) 135

the Upper Triassic volcanic rocks differ locally and are confused by 

faulting and unconformable relations with the underlying rocks. At 

no place was there found a complete section suitable for measurement. 

About 4 miles from the head of Hamilton Bay, Kupreanof Island, 

on the north side, where the coast line swings to the northwest, is a 

small elongate island composed of Permian limestone with a narrow 

belt of Triassic limestone overlying it unconformably at the east end 

and south side. No sandstone or basal conglomerate occurs between 

the Triassic and the Permian formations here as it does on the near-by 

shore of Kupreanof Island. The dip of the Triassic beds is about 

20° less than that of the underlying Permian, but the strike seems 

to be the same. No evidence of faulting was seen, though it may 

be present. The Triassic limestone weathers a dove-gray; the Permian limestone weathers a pale buff and may also be distinguished 

by the presence of chert beds and layers.

On the shore of Kupreanof Island just north of the elongate island 

4 miles from the head of Hamilton Bay good exposures of the lower 

portion of the Upper Triassic appear at the tip of the partly eroded 

Kake anticline. The basal beds are about 100 feet thick and consist of coarse conglomerate with a calcareous matrix. The cobbles 

in the conglomerate are predominantly limestone with Permian fossils, white chert, and fragments of green tuff and chert of Devonian 

age, named in the order of abundance. The actual unconformable 

contact between the conglomerate of the Upper Triassic and the 

Permian limestone with white chert layers may be seen here. The 

conglomerate toward the top is interbedded with sandstone and 

passes upward into calcareous sandstone and sandy limestone about 

50 feet thick, above which is about 125 feet of interbedded calcareous 

sandstone and limestone, succeeded in turn by 100 feet of blue-gray 

limestone in beds 6 inches to 2 feet thick intercalated with black 

limestone, much of it shaly, from several inches to a foot thick. The 

limestone beds are fossiliferous. (See lots 11243, 11241, 11242, 11240 

in table, p. 151.) The exact contact between the limestone and the 

overlying volcanic rocks is covered, but the covered beds can not 

be more than 25 feet thick at this place. One outcrop between the 

limestone and the volcanic rocks consists, of interlayered dense 

quartzite and limestone carrying fragmentary imprints of Pseudomonotis subcircularid*? (see lot 11437), which is characteristic of the 

volcanic series that overlies the HcHobia, beds of- the sedimentary division. The beds of this section have in general a northwest strike 

and a northeast dip; the dip changes from 30° at the base of the section in the southwestern part to 70° where the volcanic rocks come in.

The west side and lower half of the large island south of Kake 

are composed of the Triassic formations that constitute the south6137 29 10
136 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

west limb of the Kake anticline. The extension of these formations 

to the northwest may be followed in the extreme outer line of reefs. 

The southeastern part of the island is composed of Triassic conglomerate and limestone, resting on Permian limestone, which is 

exposed locally, and overlain by the Upper Triassic volcanic rocks. 

At the extreme southeast tip of the island conglomerate with a calcareous matrix forms the lowest member, but its base is not exposed. 

Overlying the conglomerate is about 100 feet of limestone in beds

 ranging from 6 inches to 2 feet thick, with black slaty limestone 

partings. Many of these beds are richly fossiliferous. The lime- 

.stone is in turn overlain by a series of thin-bedded rocks consisting 

,of black quartzitic or cherty layers interbedded with limestone; 

the hard, resistant layers become more abundant near the top. About 

three-quarters of a mile north of the extreme southeastern tip of 

.the island the basal conglomerate of the Triassic is cut out by faulting, and the overlying limestone is brought directly against the 

Permian beds, as indicated by the fault breccia zone. From the 

southeast end of the island northwestward the beds swing around to 

an east-west strike, with a southerly dip. The Carboniferous lime- 

.stone, which is exposed here and there as a fringe beneath the Triassic, shows a similar change of direction. At the southeast end of 

the narrow neck joining the two parts of the island, on the west side, 

.several hundred feet of interlayered limestone, black calcareous 

:shale, and chert, somewhat crumpled, are overlain by about 125 feet 

of interbedded conglomerate and sandstone with intercalated black 

slate. The conglomerate is overlain by the volcanic rocks, but the 

.contact is covered. The conglomerate is probably the equivalent of 

that found on the islets to the northwest of this island and described 

with the Upper Triassic volcanic series.

On the eastern peninsula of the northwest end of the same large 

island south of Kake the lower formation of the Upper Triassic is 

.again exposed. The basal conglomerate of the Upper Triassic here 

apparently rests directly on the chert and tuff of the Upper (?) 

Devonian, and the beds have a similar strike and direction of dip, 

though the conglomerate dips more steeply than the chert. The basal 

conglomerate is medium grained, with pebbles averaging half an 

inch to an inch in diameter. The pebbles are almost exclusively 

.chert with a few of green tuff that corresponds to the underlying 

Devonian beds. Limestone nodules are present in the conglomerate 

and are highly fossiliferous. (See lot 11237 in table, p. 151.) There 

are here about 100 feet of thin-bedded limestone, calcareous sandstone, and slate with the intercalated basal conglomerate. These 

.beds are overlain by limestone that is too much disturbed for measurement. Overlying the limestone is a most extraordinary breccia,

-which is described with the volcanic rocks on page 139. The Tri-
TRIASSIC ROCKS (UPPER TRIASSIC) 137

assic beds have a general northwest strike and southwest dip. The 

nearest underlying Devonian beds exposed dip, about 35° SW., the 

Upper Triassic limestone dips about 70° SW., and the agglomerate 

is vertical.

On the northwest tip of Kupreanof Island about halfway between Point Macartney and Cape Bendel the basal conglomerate 

of the Upper Triassic appears as the east limb of the Kake anticline, with a very gentle dip. The pebbles and cobbles, as usual., 

comprise limestone, chert, and green tuff, one or the other being the 

more common in different beds. To the east is red shale conglomerate, succeeded by variolitic pillow lava and breccia. The contacts 

are covered.

About 2!/2 miles northeast of Cape Bendel the Upper Triassic 

basal conglomerate reappears as the east limb of a syncline with a 

vertical dip. There is about 100 feet of conglomerate with several 

sills (?) of andesite lying between the Permian limestone and the 

Upper Triassic volcanic rocks.

On the north side of Cornwallis Peninsula, about a mile southeast

 of Point Cornwallis, the contact between the Triassic beds and the 

upper division of the Permian is exposed. The beds of Triassic lime- 

.stone, which are very gently warped and folded, extend along the 

shore line, with local interruptions, ior 2y2 miles to the southeast. 

At the northern contact the gently folded Triassic beds rest on 

Permian limestone with layers of white chert. The Permian beds 

strike N. 35° W. and dip 65° NE. The basal beds of the Triassic 

limestone are conglomeratic, and the cobbles and pebbles are wholly 

of white chert. At the southern contact the Triassic limestone overlies unconformably a series of volcanic rocks that probably belong 

to the dower division of the Permian. The contact is covered. The 

limestone is in beds from 1 foot to several feet thick and is very fine 

grained. The beds are locally fossiliferous. (See lots 11931 and 

.11932, p. 151.)

ADMIRALTY ISLAND

On the east side of the east arm of Pybus Bay, Admiralty Island, 

Permian cherty limestone is overlain by 200 feet of conglomerate of 

Tipper Triassic age, which consists almost exclusively of cobbles and 

pebbles of limestone and white chert from the underlying formation. 

The conglomerate is in turn overlain by crumpled beds of interlayered gray limestone and dark-gray to black calcareous slate, and 

"these beds are overlain unconformably by Lower Cretaceous slate.

Edwin Kirk reports the presence of Upper Triassic fossils in interlayered slate and limy layers at the head of Mole Harbor, Seymour

 Canal.
138 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

Triassic formations are found in a narrow strip extending along 

Seymour Canal southeast from the east headland of Windfall Harbor. 

The succession of beds is as follows: Conglomeratic limestone, white 

layered chert, slate, and greenstone, and very highly sheared limestone. The limestone crops out along the coast for 1% miles; for 

another iy2 miles along the coast the beds consist predominantly of 

andesite Avith intercalated zones of bedded limestone and black chert.

VOLCANIC ROCKS WITH PSEUDOMONOTIS-BEARING BEDS

The volcanic rocks with intercalated sedimentary beds carrying the 

characteristic fossil Pseudonwnotis overlie, probably unconformably, 

the calcareous, wholly sedimentary division of the 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 these volcanic rocks. 

This bed was not found on Kupreanof Island and may represent 

only a local development.

The long island south of Kake is contracted near .the center to a 

narrow neck. At the southeast end of this neck, on the west side, 

above the interlayered limestone, black calcareous shale and chert, 

there is about 125 feet of interbedded conglomerate and sandstone 

with intercalated black slate, with the top not exposed. 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, with 

feldspar crystals common in the groundmass. Many of the fragments are angular; those of sedimentary rock are from underlying 

formations, but the volcanic fragments are similar to the lava°of the 

Upper Triassic horizon. The beds are overlain by andesitic lava with 

associated thin beds of black slate, calcareous quartzite, and limestone. Fossils from layers between pillow lavas (lot 11246, 88BN) 

were submitted to T. W. Stanton, who identified them as 

Pseudomonotis subcirculffiris and Halobia sp. (Upper Triassic).

Along the line of strike to the northwest of the northwest tip of 

the large island south of Kake are two small islands which are 

formed in part of volcanic breccia and in part of beds partaking 

of the nature of both a breccia and a conglomerate. The rocks 

are in a much sintered condition and consequently weather with the 

characteristic glazed surface. There are about 200 feet of the^e beds, 

consisting of very coarse conglomerate at the base and medium conglomerate (average diameter of fragments 2 inches) in the upper 

part. The top is not exposed. The fragments comprise black slate, 

andesite, andesite porphyry, chert, green tuff, calcareous quartzite.
TEIASSIC KOCKS (UPPER TR1ASSIC) 139

and limestone. Some of the chert fragments are fossiliferou^ and 

are presumably derived from the upper Carboniferous, whereas the 

green tuff is doubtless from the 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 zonep completely surrounding them. Fragments of unmistakable perlite were 

identified; vesicular and amygdaloidal volcanic rocks are abundant; 

and feldspar fragments are very common. These constituents suggest that volcanic material and perhaps fragments of underlying 

sedimentary beds shattered by volcanic explosions fell where normal 

conglomerates were accumulating. Hence the beds are correlated 

with the volcanic series.

The volcanic rocks are exposed along the southwest limb of the 

Kake anticline on the southwest side of the long island south of 

Kake. The series here comprises pillow lava 5 to 20 feet thick, 

massive and polygonal jointecl flows 10 to 30 feet thick, and sedimentary beds of interlayered black slate, quartzite, and limestone 1 

inch to 10 feet, commonly several feet thick. Pseudommiotis subcircularis and Halobia are common fossils. A very extraordinary type 

of rock is found on the extreme northwest headland of this island. 

Here the sedimentary beds are broken to fragments and involved in 

a glassy andesitic matrix. As a rule each fragment is inclosed in a 

ball of glass, so that on weathering the appearance is that of a very 

coarse agglomerate. The average diameter of the fragments is about 

9 inches, but fragments 2y2 inches in diameter are common, and some 

blocks are as much as 18 by 300 feet. The upper part is predominantly finer, with fragments ranging from the size of a hickory nut 

to that of an apple. The breccia beds stand about vertical and 

measure 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.

Fragments of andesite occur in the breccia at the north end. Immediately adjacent to the inclosed fragments there is usually a zone 

of dense pearl-gray lava, which changes abruptly to a green glass. 

The pearl-gray zone, when examined under the microscope, is found 

to be less crystalline than the dominant green groundmass. Phenocrysts of plagioclase occur sparingly, and microlites are very abundant in the groundmass. Calcite veinlets are abundant in both the 

gray and the green rock.

The volcanic rocks are also exposed within the Cape Bendel syncline, along the north side of Hamilton Bay. The series here consists of amygdular and pillow lavas, in part variolitic, with intercalated sedimentary beds. The interstices between the pillows are
140 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

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 pseudobreccia structure in which the fragments have 

not been displaced from one another 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 and gray quartzite interlayered with limestone 

in bands measurable in inches. Many of the layers are highly 

fossiliferous. (See lot 11245, table, p. 151.)

In the northern part of the cove just south of Cape Bendel the basal 

part of the Upper Triassic appears to consist of interbedded conglomerate and lava to a thickness of a hundred feet or more. Devonian beds of green tuff adjoin them on the west. The cobbles of 

the conglomerate are limestone, chert, and fragments of green 

Devonian tuff. Some beds are composed almost wholly of fragments 

of red shale. Similarly 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. (See lot 11933, table, 

p. 151.) The beds here overlie the Permian. Overlying these basal 

beds comes a series of volcanic rocks that consists chiefly of green 

andesitic lava, predominantly with pillow structure but in part 

amygdaloidal. Variolitic texture is very common. The total thickness of the lava, including the conglomerate at the base, was estimated 

as approximately 1,400 feet. About 1*4 miles northeast of Cape Bendel, on the east headland of a cove due south of Pinta Rocks, there 

occurs intercalated in the lava a zone of about 50 feet of conglomerate 

which grades upward into sandstone and is overlain by about 225 

feet of isoclinally folded thin-bedded limestone. The limestone is in 

layers about 6 inches thick, with black shaly limestone partings. 

Many of the layers are highly fossiliferous. (See lot 11934, table, 

p. 151.) These beds are overlain by more pillow lava.

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 show pillow structure. Rarely a chalcedony vein is present. The sandstone lies on the east side of a bight 

on the south side of the island and contains intercalated layers of 

calcareous sandstone and conglomerate 1 inch to several inches thick, 

some of which are richly fossiliferous. (See lot 11405, table, p. 155.) 

Traces of carbonized plant stems are common.

Shale with Upper Triassic fossils is found on both the large islands 

of the outer line of islands of the Keku group. On the northwesternmost island the beds consist of black shale with intercalated impure 

brecciated limestone and nodular layers in possible isoclinal folds
TEIASSIC ROCKS CUPPER TRIASSIC) 141

with a general dip of about 30° SW. On the east side of the north 

end of the island the beds are adjoined by eastward-dipping black 

limestone with buff-weathering sandy layers carrying Permian fossils. These beds are associated with beds of conglomerate. The contact between the Triassic ,and Permian is covered. The relations may 

be explained as representing an infolded trough of Triassic beds 

unconformable to the Permian. Fossils (see lot 11436, table, p. 151) 

gathered from the black shale on the southwest side of the island were 

reported by T. W. Stanton as Upper Triassic. At the north end of 

the southeastern island black shale adjoin limestone beds of white 

chert. The limestone and chert are probably Permian; the shale contains fossils identified by T. W. Stanton as Halobiat sp., indicating a 

Triassic age for the beds. The beds are vertical, and faulting is 

probably the cause of the relations of the Triassic to the Carboniferous.

The lava is mostly felsitic or basaltic in texture but is locally distinctly porphyritic, with phenocrysts of albite. It ranges from 

green-gray to very dark gray. In thin section it is found to consist 

in general of a felt of porphyritic plagioclase laths in a groundmass 

of very irregular texture. The groundmass may be a clear green or 

it may consist of a deep-green matrix crowded with microlites of 

plagioclase. Grains of augite are abundant in some sections and 

absent in others. Magnetite is commonly present as abundant grains 

or skeletal plates through the groundmass. The groundmass is in 

part interstitial to the plagioclase laths, a typical intersertal texture, 

and in part segregated into knots. Locally the microlitic patches are 

spherical and weather like variolites 0.2 to 0.3 millimeter in diameter. 

The green groundmass is of peculiar character. At first glance it 

resembles some chloritic alteration products, but with crossed nicols, 

in some sections, it is seen to consist of isotropic or nearly isotropic 

glass locally crowded with minute microspherulites made up of 

birefringent fibers. In other sections the birefringent fibers are 

oriented at right angles to cracks in the glass, and in yet other sections the amygdular parts are found to consist of concentric shells of 

nearly hemispherical spherulites arranged parallel to the borders 

with a central core rock of microspherulitic aggregates. The interstitial parts of the groundmass are commonly composed of an 

aggregate of birefringent microspherulites. There appears to be no 

difference between the interstitial material and that of the amygdulelike parts. The plagioclase laths also project into the amygdular 

parts in such a fashion as to suggest that these spherulitic amygdules 

were an integral part of the rock at the time of consolidation. The 

green groundmass may constitute as much as 30 or 40 per cent of the 

rock, and it is believed to represent simply an uncrystallized or
142 GEOLOGY AND MINERAL DEPOSITS, .SOUTHEASTERN ALASKA

spherulitically crystallized part of the lava. Inclusions identical in 

character with the green groundmass are found also in the feldspar.

It is possible that all of the green groundmass was originally glass 

and that the spherulitic crystallization is the result of subsequent 

devitrification. With crossed nicols, all the spherulites show welldefined uniaxial crosses. The green spherules weather to resemble 

amygdules of chlorite, for which they were mistaken in the field. 

It may be that the groundmass corresponds, in part at least, to what 

is commonly called palagonite, an altered basic glass. True amygdules of chlorite are found in some of the andesite east of Cape 

Bendel.

The porphyritic feldspar was determined by the index of refraction method in four different specimens and in eacji was found to 

be albite instead of a more calcic plagioclase, such as might be 

expected. Albite is reported to characterize certain pillow lavas 

(spilites) of Great Britain,77 but Us sodic character is ascribed to 

secondary replacement. There is nothing to suggest that the sodic 

character of the plagioclase .iii the Alaskan lavas is other than primary. The plagioclase of the groundmass commonly has a very 

low extinction angle and may be oligoclase.

In the Juneau district Eakin and Spencer 78 have described as 

the Gastineau volcanic group a series of beds in which they found 

Upper Triassic fossils. These volcanic rocks were examined on 

Taku Arm by the writer, and the basal part found to resemble very 

closely the volcanic rocks of Hamilton Bay, which are of Upper 

Triassic age. Some of the flows show a rough polygonal jointing, 

others exhibit a well-defined though distorted ellipsoidal or pillow 

structure with interstitial limestone, and still others show the peculiar pseudobreccia structure in which the lava is broken up into 

angular fragments that show no rotation and are separated from one 

another only by thin films of limestone. All three features are 

common to the volcanic rocks of Kupreanof Island. The Gastineau 

volcanic group is overlain by the Thane volcanic group.

VOLCANIC ROCKS OF KUIU AND HOUND ISLANDS

A volcanic formation lithologically similar to the rocks just described but carrying a different fauna is found on the northeast end 

of Kuiu Island and on Hound Island, Keku Straits.

Directly south of the southeast end of the Keku group of islets 

the coast line of Kuiu Island has an east-west direction for l1/^ miles. 

Along this coast are exposed very gently folded beds of limestone

77 Dewey, Henry, and Flett, J. S., On some British pillow lavas and the rocks associated 

with them : Geol. Mag., new ser., decade 5, vol. 8, p. 203, 1911.

78 Eakin, H. M., and Spencer, A. C., Geology and ore deposits of Juneau, Alaska : U. S. 

Geol. Survey Bull. [in preparation].
TRIASSIC ROOKS (UPPER TRIASSIC) 143

with intercalated conglomerate, conglomeratic limestone, sandstone, 

and andesite. The limestone beds are locally fossiliferous (lots 

4305, 5128, 5123), and are reported by Girty to belong probably to 

the lower division of the Permian. (See pp. 123, 126.) Just east of 

the point where the shore line turns southward these beds are overlain by sandstone with conglomeratic layers, followed by interbedded 

limestone and green andesitic tuff with a few conglomerate layers. 

The beds have in general a northeast strike and a dip of 20° SE.r 

though at the point they are almost horizontal and cross folded. 

About three-fifths of a mile south of the point the limestone is fossiliferous. (See lot 11406, table, p. 155.) The limestone beds range 

from 5 to 50 feet in thickness, and the tuff beds from 10 to 20 feet. 

The limestone is fine grained and of a brownish hue. These beds 

pass upward into a predominantly volcanic series, with similar strike 

and dip, consisting of basaltic and andesitic lavas, breccias, and 

tuffs with interbedded limestone, which is in part sparsely conglomeratic with andesite pebbles. At the head of Six and a Quarter 

Fathom Cove, on the southwest side, coarse green agglomerate striking northwest and dipping gently northeast is overlain by about 300 

feet of thin-bedded sandstone and shale with a few limestone layers, 

the shale predominating. These beds are exposed on the west headland of Six and a Quarter Fathom Cove and appear to be in the 

trough of a syncline. They may belong with the series at Point 

Hamilton, like the beds of shale exposed in the string of islets immediately to the north.

The entire peninsula between Six and a Quarter Fathom Cove and 

the cove to the south is composed of interbedded coarse agglomerate 

and pillow lava. The agglomerate 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 pass gradationally upward into breccia with a limestone 

matrix, and the lack of a marked dividing line suggests autoclastic 

structure. The breccia in general consists of amygdular green-gray 

andesite of felsitic texture in angular fragments ranging from 1 inch 

to 9 inches in diameter with many bombs 2 feet in diameter and a 

few blocks as much as 10 feet in diameter. The average is about 10 

inches. The matrix is limestone, which locally may form as much 

as one-third of the rock but predominantly is merely interstitial to 

the fragments. At a point on the east side of the peninsula, about 

due west of Pup Island, there is conspicuous pillow lava with layers 

of limestone as much as a foot in thickness molded to the surface of 

the ellipsoids. This limestone is baked to a pinkish-brown hornstone 

adjacent to the contact with the lava. Some of the limestone pockets 

are extraordinarily rich in well-preserved fossils. (See lots 11407 

and 11962, table, p. 155.)
144 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Hound Island and several islets to the northwest consist, of gently 

folded coarse green andesitic breccia with a limestone matrix. Commonly the fragments run) from an inch to a foot in diameter, but 

finer beds occur sparingly, and rarely a bed of dense buff-weathering 

limestone or of agglomeratic limestone is intercalated.

AGE AND CORRELATION

By THEODOKE CHAPIN

The term " Gravina series" was first applied by Brooks 79 to 

massive conglomerate overlain by black slate or shale occurring on 

the south end of Gravina Island. He included in his mapping of 

this " series " the someAvhat similar massive conglomerate and associated black slate and arenaceous sediments of the west coast, Bostwick Inlet, and Blank Inlet and suggested its possible extension to 

other places. As a result of recent investigations, however, the sedimentary rocks of Gravina Island originally defined as the " Gravina 

series " are now known to include two sedimentary formations one 

of Triassic age and one of Jurassic or Cretaceous age. These two 

sedimentary formations are associated with volcanic rocks of intermediate stratigraphic position. Brooks first regarded the " Gravina 

series" as Cretaceous and correlated it with the Queen Charlotte 

series of Vancouver and Queen Charlotte Islands, but later he stated 

that its identity with the Vancouver (Triassic) seemed equally 

probable.80 His correlations with Triassic and Cretaceous formations, 

which were made without any fossils, proved substantially correct.

A large number of fossil collections made later have shown the age 

of the limestone, conglomerate, and black slate of Gravina Island to be 

Triassic, probably Upper Triassic.

Fossils collected by G. C. Martin and R. M. Overbeck from the 

massive conglomerate at the exposed base of this series were determined by T. W. Stanton as f olloAvs:

8831 (G. C. M. No. 3). Gravina Island, south ami, of cove 3 miles north of 

Dall Head. Large limestone nodule in conglomerate. The whole nodule is 

a nautiloid with deeply lobed suture, possibly referable to Cosmanautilm. 

On the back is a Rhynchonellaf. Probably Triassic.

8833 (G. C. M. No. 5). Gravina Island, south arm of cove 3 miles north of 

Dall Head. Near zone of nodular masses of limestone in conglomerate. This 

lot appears to be Devonian.

Mr. Martin's opinion, with which the writer agrees, is that the 

Triassic conglomerate rests unconf ormably upon Devonian rocks, and 

the Devonian fossils from Threemile Cove were obtained either

79 Brooks, A. H., Preliminary report on the Ketchikan mining district, Alaska: U. S. 

Geol. Survey Prof. Paper 1, p. 45, 1902.

80 Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Pr9f. Paper 

45, p. 226, 1906.
TRIASSIC ROOKS (UPPER TRIASSIC) 145

from boulders in the conglomerate or from unrecognized Devonian 

rocks occuring in complex structural relations with the Triassic beds. 

The beds on Threemile and Thompson Coves are faulted and also 

closely folded and contorted, being thus thrown into complex structural relations. From the wording of the locality description above 

it would appear quite possible that the fossils were collected from 

included masses of limestone in the conglomerate. In 1916 A. H. 

Brooks and the writer collected fossils from narrow bands of limestone interbedded with the conglomerate. J. B. Keeside, jr., reports 

on these as follows:

9899 (16 ACh 136). Threemile Cove, Gravina Island. Echinoid spine, possibly 

of Cidwris. Age undetermined.

Fossils were first collected from Threemile Cove in 1905 by the 

Wrights.81 The exact locality is uncertain, but the matrix of the 

fossiliferous rocks is described as calcareous schist, which is evidently 

the siliceous limestone. The fauna was regarded by G. H. Girty as 

coming from the uppermost part of the Carboniferous or from the 

Mesozoic. The beds were thus doubtfully referred to the Mesozoic 

for some years, but recent collections have shown them to be without 

much doubt Triassic and probably Upper Triassic.

Collections made by Martin and Overbeck from the limestone beds 

oif Threemile"Cove occurring beneath the black slate were determined 

by T. W. Stanton as follows:

8830 (G. C. M. No. 2). Gravina Island, south arm of cove 3 miles north of 

Dall Head; outcrop of massive limestone near anchorage behind wooded island: 

Undetermined corals of Mesozoic type, two or three genera represented. 

Ostrea? sp.

Pseudomelania ? sp., internal cast. 

Arcestes?? sp., fragment; may not even be an ammonite.

Probably Triassic.

8832 (G. C. M. No. 4). Gravina Island, near south foreland on arm of cove 

3 miles north of Dall Head, near contact with conglomerate: 

Undetermined coral fragment. 

Pentacrinus sp., segment of column.

Probably Triassic.

8834 (G. C. M. No. 6). Graviua Island, north arm of cove 3 miles north of 

Dall Head; massive limestone in reef west of cabin, probably about 100 feet 

below 8704 (see p. 147) :

Corals, probably several genera. 

Cassianella sp. 

Myophoria?? sp. 

Natica sp. 

Murchisonia? sp. 

Triassic.

81 Wright, F. B., and C. W., op. cit, p. 52.
146 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

8835 (G. C. M. No. 7). Gravina Island 20 or 30 feet below 8834; thin-bedded 

limestone interbedded with shale:

Corals; several genera represented. 

Spiriferina? sp. 

Myophoria? sp. 

Natica sp. 

Turritella? sp. 

Pseudomelania ? sp. 

Trachyceras? sp., small fragment 

Triassic.

The following collections made .by the writer in 1915 from the limestone overlying the massive conglomerate were determined by Mr. 

Stanton:

9531 (15 ACh 111). West coast of Gravina Island, cove 2% miles north of 

Ball Head:

Bchinoid spines.

Undetermined corals.

Ostrea? sp.

Gryphaea? sp.

Pecten sp.

Natica? sp.

Turritella? sp. 

The fossils in this lot are poorly preserved and mostly fragmentary

They are apparently Mesozoic and may be Triassic. 

15 (ACh 121). Northeast shore of Thompson Cove, Gravina Island:

Corals, genus undetermined.

Pentacrinus sp.

Echinoid spine.

Ostrea? sp.

Solemya? sp.

Turritella? sp.

Spiriferina? sp. 

Probably Triassic.

9534 (15 ACh 122). Northeast shore of Thompson Cove, Gravina Island:

This lot includes undetermined corals, Ostrea?, Turritella?, and undetermined gastropods. Probably Triassic.

9535 (15 ACh 123). North shore of Thompson Cove, Gravina Island:

Pecten ? sp.

Gryphaea? sp.

Halobia sp.

I Undetermined ammonite. 

1 Triassic.

9536 (15 ACh 129). Fivemile Cove, Gravina Island; limestone apparently 

overlying massive conglomerate:

Corals, several undetermined genera. 

Bryozoa? 

Pecten sp. 

Purpurina?? sp.

Undetermined slender gastropod. 

Probably Triassic.
TEIASSIC ROCKS (UPPER TRIASSIC) 147

9537 (15 ACh 130). Fivemile Cove.,' Gravina Island: 

Corals, several genera. 

Bryozoa? 

Myophoria sp. 

Purpurina?? sp. 

Turbo? sp. 

Triassic.

9538 (15 ACh 132). Fivemile Cove, Gravina Island, immediately north of 

1*537:

Gryphaea sp. 

Probably Triassic.

Two lots of fossils collected by P. S. Smith from the black slate of 

Threemile Cove (8704) and also from Fivemile Cove (8705) were 

submitted to Mr. Stanton, who reported as follows:

The only fossil species recognized in these two lots is a Halobia which is 

closely related to if not identical with H. supero^ Mojsisovics, an Upper Trias- 

§ic species. The rocks from which these collections came are therefore referred 

to the Triassic.

The writer made the following collections in 1915 from the black 

slate and interbedded limestone and sandstone beds of Threemile 

Cove, Thompson Cove, and Dall Ridge. Stanton reports:

15 ACh 112. Threemile Cove, Gravina Island, 300 yards north of 15 ACh 111. 

Spiriferina? sp. 

Halobia? sp. 

Probably Triassic.

9532 (15 ACh 113). Threemile Cove, Graviua Island, 300 yards southeast 

of north end of cove and about 700 yards north of 15 ACh 112; fossils from 

black slate and limestone:

The black slate shows fragmentary specimens of Halolia cf. H. superla 

Mojsisovics, of Upper Triassic age, while the limestone shows imperfect 

specimens which seem to be referable to Aicoella* and hence is probably of 

Upper Jurassic age.

The limestone and black slate from which the fossils regarded as 

Upper Triassic and Upper Jurassic were obtained are apparently 

interbedded. This anomalous occurrence may be due to very closely 

infolding of Jurassic rocks, but it appears more probable that the 

doubtful Jurassic forms are not correctly identified.

9533 (15 ACh 115). Thompson Cove, Graviua Island; Halobia slates in 

fault block:

Cidaris? sp., imprint of surface. 

Halobia cf. H. superba.

Triassic.

15 ACh 124. Dall Ridge, 4 miles north of Dall Head, Gravina Island. 

EcMnoid spines, 'etc. 

Probably Triassie.
148 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The following collection was identified by J. B. Eeeside, jr.:

9900 (16 ACh 137). Threemile Cove, Gravina Island: 

Cerithiurn ? sp., fragment showing part of two whorls. 

Isastraea ef. I. profunda. 

Thamnastraea cf. T. rectilamellosa. 

Spongiomorpha? sp. 

Hydrozoau, undetermined.. 

Natica? sp.

These forms are apparently of the Upper Triassic coral fauna referred 

by J. P. Smith to the Noric.

The conglomeratic sandstone near the crest of Dall Ridge contains 

Devonian fossils, but as these are fragmentary and occur in pebbles 

they indicate nothing more than the post-Devonian age of the rocks. 

Edwin Kirk reports:

15 ACh 126. Dall Ridge, 4 miles north of Dall Head. Fragmental fossils 

apparently occurring as pebbles in conglomerate. At least one of the fossils 

is Devonian. It is a coral, probably Alveolites.

Black slate and sandstone exposed on the west coast of Bostwick 

Inlet are correlated on structural grounds and lithologic similarity 

with the upper part of the Tria§sic rocks on the west coast of the 

island. The fossils listed below were collected in 1914 by Martin 

and Overbeck from the west shore of BostAvick Inlet and identified 

by T. W. Stanton:

8836 (G. C. M. No. 8). Gravina Island, Bostwick Inlet, west shore near 

entrance; from angular nodules in a brecciated (?) nodular limestone: 

Terebratula sp. 

Spiriferina? sp. 

Pecten sp. 

Plicatula? sp. 

Cassianella sp. 

Myophoria sp. 

Myophoria or Trigoriia sp. 

Nucula sp. 

Astarte? sp. 

Arcestes? sp.

Triassic. This assemblage suggests the fauna of the lower part of 

the Moclin formation in California, which was tentatively assigned to the 

Jurassic.

Near this same locality P. S. Smith 82 also collected fossils on 

which G. H. Girty reports as follows:

Three lots from Bostwick Inlet, Gravina Island, contain round criuoid 

stems (13 AS 170) and a single compressed pelecypod (13 AS 169), suggesting 

the genus Posidonomya. The third lot (13 AS 171) contains a pelecypod fauna 

interesting and varied' but entirely new to me. As these fossils at best show 

only the shapes and some of them the sculpture, and as pelecypods of similar 

external appearance may belong to widely different genera, the identifications 

made here are offered with doubt. Though similar doubt tacitly surrounds

82 Notes on the geology of Gravina Island, Alaska : Prof. Paper 95, p. 103, 1915.
TRIASSIC BOOKS (UPPER TRIASSIC) 149

many pelecypod identifications in faunal lists and elsewhere, I have expressed 

it in this case by the use of question marks because the age of the whole fauna 

is involved in such uncertainty. In lot 171 five types are represented more or 

less abundantly and by specimens more or less good. These are Olossitesf 

cf. G. linffualis, Schizodusf cf. 8. appressus, Paracyclas? cf. P. elliptivus, Crenipecten? cf. G. crenulatus, Eli/melln? cf. E. nuctiloides. Besides these, however, 

there are a good many indeterminate forms, some of which suggest the genera 

Leda, Chonetes??, Pseudomonotis??, Aviculipeoten, and Niicula. The age of the 

fauna is quite uncertain. You declined for the time being to admit it into 

the Triassic, and nothing resembling it has thus far been brought in from the 

Alaskan Carboniferous. The generic and specific resemblances suggested above 

might indicate a Devonian fauna, but neither has any Devonian fauna related 

to this been obtained from Alaska. The genus Chonetes, if definitely present, 

would at least limit the geologic age to the upper Paleozoic, but the specimen 

is so imperfect that even the identification as a brachiopod is doubtful.

Thus the age of this, the best fauna in the collection, must for tbe present 

remain undesignated. It would be highly rash to attempt any definite age 

determination or conclusion for the other lots, containing, as they do, for the 

most part, only crinoid stems (even that being doubtful in some cases), though 

they may tentatively be placed in the Paleozoic.

Regarding this report Smith suggests that the doubtfully determined fauna from Bostwick Inlet, "which is unknown elsewhere in 

Alaska, may mark a Lower Triassic horizon, also unknown in 

Alaska. He states:

As Mr. Girty points out, this fauna is entirely unlike any other from Alaska. 

It therefore affords little aid in solving the stratigraphic position of the beds 

on Gravina Island. Certain significant deductions, however, suggest themselves. In general in southeastern Alaska the known Carboniferous rocks are 

limestones and not lithologically similar to the rocks of Gravina Island. The 

rocks here discussed are much less dynamically metamorphosed and are less 

intensely deformed than the known Devonian or Carboniferous rocks of the 

region. Their relation to the andesitic agglomerates and flows fits in better 

with an assumed Mesozoic age than with a Paleozoic age. The almost uninterrupted succession of beds from a basal (?) conglomerate to shales containing unquestioned Triassic fossils .on the southwestern coast suggests that 

the doubtfully determined genera from that locality, provisionally assigned to 

the Carboniferous, justify the suggestion made by Mr. Girty at that time that 

they may mark a Triassic horizon. No Lower Triassic is known in Alaska. 

Is it'not possible that this fauna from Bostwick Inlet, which is unknown elsewhere in Alaska, fits into this as yet unfilled gap?

Its reference to the Lower Triassic, however, seems improbable, for 

the fauna is in the upper part of the formation, above the position 

of the Zfafofo'a-bearing slate (determined as Upper Triassic) and 

immediately below the Upper Jurassic or Lower Cretaceous volcanic rocks. It£ reference to the Upper Triassic or the Lower or 

Middle Jurassic would be more in keeping with the observed 

relations.

The term Vancouver series was first applied by Dawson 88 to the 

entire mass of volcanic materials and interbedded limestone, flaggy

53 Dawson, G. M., Canada Geol. Survey Ann. Kept, for 1886, p. 10b, 1887.
JL50 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

. argillite, and quartzite that unconformably underlie the Cretaceous 

jocks of Vancouver Island. At that time, on the evidence of intercalated fossiliferous bed^, this series of rocks was regarded as largely 

Triassic, although the possibility of its including both Jurassic and 

(Carboniferous rocks was recognized. The Vancouver series was later 

subdivided by Clapp,84 who has shown that it is in part Jurassic 

and possibly also in part Carboniferous. The Triassic rocks of 

(jravina Island are probably the equivalent of parts of the Van-

-couver series of Vancouver and Queen Charlotte Islands. 

 Triassic rocks are widespread throughout Alaska and occur at.

 many places in southeastern Alaska. Fossils of Upper Triassic

#ge have been found on Admiralty, Kupreanof, and Screen Islands.

Martin 85 states that the abundant corals in some of these Triassic 

rocks of Gravina Island suggest that they may represent the lower 

Noric coral fauna of Iliamna Lake. He considers that the Triassic 

limestones of southeastern Alaska, which in general are characterized 

by faunas containing Halobia cf. H. superba Mojsisovics, correspond 

at least approximately in position to the Chitistone limestone of the 

popper Eiver Valley.

The age and correlation of the Triassic formations in the vicinity 

of Keku Strait and the Screen Islands in Clarence Str'ait have been 

discussed by Martin,86 whose statement is here quoted in its entirety.

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 tables. Most of these collections include well-known Upper 

Triassic species that are characteristic of the Triassic rocks of other Alaskan 

localities, such as Pseuaomonotis subcircularis (Gabb) and Halobia cf. H. 

stiperba Mojsisovics, as well as some of the ammonites that are customarily 

associated with the Halobia.

84 Clapp, C. H., Southern Vancouver Island : Canada Geol. Survey Mem. 13, p. 37, 1912. 

83 Martin, G. C., Triassic rocks of Alaska: Geol. Soc. America Bull. vol. 27, p. 700, 1916. 

80 Martin, G. C., The Mesozoic stratigraphy of Alaska : U. S. Geol. Survey Bull. 776, 

pp. 83-89, 1926.
Upper Triassic fossils front, north end of Re

[Identified by T. W. Stantonj

Plant stems?. ___ _ _

Corals? _ _ __ .

Rhynchonella.. __ ......

Terebratula? __ .... _ ... . .

Spiriferina borealis? ___________

Spiriferina?.. ..............

Brachiopods ___ ........

Pseudomonotis subcircularis. . ........

Pseudomonotis? _ . ____ . . .

Halobia cf. H. superba ________

Halobia... ................

Ostrea?... _____ . _____ ... .

Lima?.. ___________ .

Modiolus _______ _ .

Pleuromya? _________ _a

Astarte?... _ .............

Undetermined pelecypods ____ .

Mojsvaroceras? ____________

Tropites. __________ .

Paratropites _____________ ..

Discotropites sandlingensis? .............

Sagenites?.... _______________

Ceratites? _______________

Clionites?.. ____ . ________ . .....

Placites? ______________ _ .

Atractites... ___ . __ _ __ .....

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152 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

11931 (No. 910). Kuiu Island about 3 miles southeast of Point Cornwallis, on 

Keku Strait side; gently folded limestone; A. F. Buddington, 1923.

11932 (No. 961). .Kuiu Island, opposite round island about 4 miles southeast of 

Point Cornwallis; limestone that apparently overlies 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 part 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; from a boulder in limestone conglomerate; W. W. Atwood, 1907.

4821 (6). Same locality as 4822; from 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) r Same as 8845; G. C. Martin, 1914.

8841 (15). Hamilton Bay, about three-quarters of a mile up the northernmost creek entering the head of the bay; from 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). One and one-fourth miles northeast of Cape Bendel, Kupreanof 

Island, on east headland of cove due south of Pinta Rocks; fossils from near 

top of limestone; A. F. Buddington, 1923.

11237 (39). About 2 miles south of Kake, on northwest point of large island; 

fossils in 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). Seven miles southeast of Kake, Kupreanof Island; limestone overlying conglomerate and sandstone; A. F. Buddiugton, 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; 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; from beds that seem to overlie the limestone conglomerate that 

yielded lots 4821 and 4822; W. W. Atwood, 1907.

9543. Islet in Frederick Sound, a quarter of a mile southwest of Kake; 

Mrs. Theodore Chapin, 1915.

10196. South end of northernmost large island of Keku Islets; G. H. Girty, 

1918.
TEIASSIC BOCKS (UPPER TRIASSIO) 153

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 

beds of white chert; shale probably same formation as 215 and 205; A. F. 

Buddington, 1922.

11436 (205 Bu). Southwest1" side of northernmost large Keku Islet; same 

formation (?) as 215 but more sheared; A. F. Buddington, 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 beds similar 

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; from 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 sO'Utheast of Kake; from the same series of beds that yielded lot 4820, apparently 

a few feet lower; W. W. Atwood, 1907.

8844 (18). North side of Hamilton Bay, 2 miles below head of bay; 40 or 

50 feet above lot 8843; G. C. Martin, 1914.

(16B). Near head of Hamilton Bay; float; E. M. Kindle, 1905.

The fossils of lots 11245 to 16B are indicative of the Upper Noric Pseudomemoes-bearing beds that constitute the uppermost known Triassic rocks of other 

Alaskan regions. The fossils of lots 11934 to 11436, all of which contain 

Hdloltia, 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. sup&rlta-, are indicative of the Middle or Upper Karnic JloJo&ia-bearing beds 

that generally underlie the Pseudomonotis-bearing beds of other regions.

The fossils of lots 11931 to 8841, in which both Pseudortwnotis and Halo'bia 

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 

Halo'bia,, 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 were not recognized in the observed outcrops." The fossils at 

localities 8842 and 8845 include species related to Spiriferina borealis Whiteaves 

and Traohyceras (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.
154 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The Triassic rocks of Liard 'River, according to McConnell,87 " 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,88 include eleven species, among which 

are Spirifenna lorealls Whiteaves and Dawsonites canadense Whiteaves, which 

have been doubtfully identified from Hamilton Bay. Mojsisovics so has pointed 

out that some of these fossils are indicative of Karnic age. Three of the Liard 

River species (Dawsonites canadense, Nathorstites mcconnelli, and Nathorstites 

lentivularis'), one of which occurs at Hamilton Bay, have been found, according 

to Bohm,00 in the Upper Triassic rocks of Bear Island, between Norway and 

Spitsbergen. 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 01 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, which has not been 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 large number 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 species do not 

show important characters that are necessary for positive generic assignment, 

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."

^McConnell, R. G., Report on an exploration in the Yukon and Mackenzie Basins, 

Northwest Territory: Canada Geol. Survey Ann. Kept., new ser., vol. 4, pp. 19D, 49D, 

1890.

88 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, 18, 1889.

88 Mojsisovics, Edmund von, Beitrage zur Kenntniss der obertriadischen Cephalopoden-. 

Faunen des Himalaya: K. Akad. Wien Denkschr., Band 63, p. 697, 1896.

80 B5hm, Johannes, Ueber die obertriadische Fauna der Bareninsel: K. Svenska VetenBkaps-Akad.. Handlingar, Band 37, No. 3, pp. 56-58, 61-64, 73-76, 1903.

01 Freci^ Fritz, Die zirkumpaciflsche Trias: Letbaea geognostica, Teil 2, Das Mesozoicum, 

Band 1, Trias, pp. 488-491, 508, 1908.
TRIASSIC ROCKS (UPPER TRIASSIC) 155

Fossils from Upper Triassic (?) limestone and, calcareous sandstone associated 

^oith lava ana tttff on Kekit Strait

[Identified by T. W. Stanton]

Sponge?.. __ . _____ .... ....

Cidnris? and other echinoids

Rhynchonella... ___ . ____ .

Terebratula __ . ______ .

Gervillia?. .................... ..

ribs)...............-...........

t^

§

X

y

v

X

X

X

N

to 

Oi

X

X

X

X

X

X

X

X

v

X

1

v

X

10

§

X

y

X

ribs) ______ . ..............

Cardita?..... .............. ......

Trochus? (a sinistral specimen) ..

Platyceras? ___ . ______ ..

t~

o * t-l

X

X

X

X

X

X

X

X

X

X

X

X

IN

to 

en

X

y

X

v

X

X

y

X

X

X

X

X

X

X

X

X

o 

o »<

X

"O

o V

!-H 

*-H

11407 (256 Bu). Kuiu Island, 3 miles a little north of west of Point Carnden 

on west side of 9%-fathom cove about half way 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 pinkishbrown hornstone; fossils are all from this pocket; A. F. Buddingtou, 1922.

11962 (256 Bu). Same locality as 11407 but on different pocket; 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 commpn in the limestone and abundant in the sandstone; A. F. 

Buddiugton, 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 flaZo&ia-bearing limestone would accord with the occurrence of volcanic 

rocks immediately beneath the JTaZofria-bearing limestone in other parts of
156 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Alaska, notably in the Chitina Valley and on Cook Inlet. There are difficulties, 

however, in the assignment of the rocks to this position. The JETaZo&to-bearmg 

beds at near-by localities rest unconformably upon Devonian and Permian 

rocks. If the beds that contain the fauna in question belong under the Halobiabearing beds they are separated from the -HaZoZmj-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 that of Pseudomonotis rather than of a horizon 

below that of HaloMa cf. H. 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 Rhaetic. The volcanic beds that overlie the Triassic rocks of 

Gravina Island, which the writer has referred tentatively to the Lower or 

Middle Jurassic, may possibly belong at the same horizon.

The upper limestone, on the Screen Islands, Clarence Strait, which crops 

out only on the southernmost island, yielded the Triassic (?) fossils represented 

in the following table: 91a

Fossils from upper limestone on Screen Islands 

[a, Identified by T. W. Stanton; b, identified by O. H. Oirty]

Corals ___ _ _ __ ... _ ... __ ... _ .. _ .......

Crinoidal fragments ______________ ........

ArchaeocidarisVsp... ___ ___ - _____ ........

Burrows.. ...........................................

Terebratula?.. _ ............ _ ....... _ ...........

Cyrtiasp. __ ___ _ __ ______ ........

Spiriferina? . ______________________

Pecten?. _._.__ ___ ................................

Pelecypods.. _ .... _______ ... __ . .....

Murchisonia? sp .. _ -.... _ _ ... __ ___ .. ....

Tuberculopleura?sp.. ___ ____ ................

Ammonite........ _ ... . _ . _ _ .... . .

8839

a

8838 (220)

b

b

b

b

b

b

b

b

b

11075 11076

a

(2)

b

(3)

b

(4)

b

b

8839. Near south end of the southernmost of Screen Islands, 100 or 200 feet 

below 8838; G. C. Martin, 1914.

8838. South end of the southernmost of Screen Islands; from nearly the 

highest beds exposed on this island; G. C. Martin, 1914.

(22G). Screen Islands; B. 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.

JURASSIC (?) BOCKS 

DISTRIBUTION AND CHARACTER

The rocks herein classified as Jurassic (?) include several distinct 

formations of uncertain stratigraphic relations. At a few localities 

slate carrying the fossil Aucella crassicollis has been found, and

Martin, G. C., op. cit., p. 78.
JURASSIC (?) ROCKS 157

these beds of slate, with the associated grayw.acke and interbedded 

thin limestone and conglomerate, have been mapped separately and 

grouped as probably of Lower Cretaceous age, although they may be 

Upper Jurassic. Most of the sedimentary beds and volcanic rockB 

are unfossiliferous; they are considered to be of Jurassic (?) age 

because of their structural relations and lithologic similarity to 

formations of known age elsewhere. They may include beds as old 

as Lower Jurassic and as young as or younger than the AuceUa 

wassicollis zone. It may be that beds even as old as Ordovician have 

been erroneously mapped as belonging to this group, and it is highly 

probable that some Upper Triassic beds have by error been included. 

On the other hand, it is possible that the slate with thin-layered 

graywacke-like sandstone described by Chapin as occurring on Gravina and Annette Islands and included by him in the Upper Triassic 

may be for the most part of Jurassic age.

The definite stratigraphic sequence of the formations which belong 

to the Jurassic (?) is unknown.

Considered lithologically, the rocks believed to be Jurassic (?), 

exclusive of the Aucella-be&riiig beds, are here divided for mapping 

and discussion into two groups (1) a predominantly sedimentary 

facies consisting of graywacke, black slate, and conglomerate; (2) a 

predominantly volcanic facies consisting of schistose greenstone volcanic rocks, mainly hornblende and rarely augite porphyry breccia, 

with intercalated tuff and flows, black slate, and graywacke.

SEDIMENTARY DIVISION 

JUNEAU DISTRICT

Knopf 92 described and mapped as the " Bernerp formation" a 

belt of interbedded slate and graywacke with some greenstone, of 

supposed Upper Jurassic or Lower Cretaceous age, which occurs 

along the coast on the east side of Lynn Canal from Comet southeastward, including part of Douglas Island and the north end of 

Admiralty Island. It is now known that ^ome rocks of Jurassic, 

Triassic, and probably Paleozoic age were erroneously included in 

this belt, but it seems probable that most of it is Jurassic or 

Cretaceous.

Knopf describes the graywacke as

composed of grains of plagioclase feldspar and quartz together with fragments of other minerals and rocks, embedded in an argillaceous cement. The 

composition is somewhat variant; at Berners Bay, for exampje, the gray wackes 

contain considerable augite and hornblende derived from it, so that hand 

specimens might be mistaken for tuffs or even porphyries. As a rule, however,

82 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, pp. 15-17, pi. 5, 1912.
158 GEOLOGY AND MINEBAL DEPOSITS, SOUTHEASTERN ALASKA

none of the constituents, except the glassy grains of quartz and the fragments of black slate, are recognizable by the eye. * * * Conglomeratic 

graywacke was seen at only one locality * * * where it forms a belt 

several hundred feet wide. * * * North of Berners Bay [the graywackes] 

contains little or no quartz, but south of the bay quartz becomes more prominent. * * * It will be apparent from the foregoing description that at 

some localities it may be difficult to distinguish the graywackes from tuffs; 

this difficulty becomes pronounced near the vo,lcanic areas.

Spencer and Eakin °3 have mapped as the Treadwell slate, a formation composed of dominantly black clay slate with some conglomerate 

and considerable graywacke which occurs along the east coast of 

Douglas Island. The Treadwell slate is overlain by the Douglas 

Island volcanic group and underlain by the Thane volcanic group; 

jt is assigned to the Upper Jurassic (?) by Martin.

SEYMOUR CANAL-FANSHAW-KTTPREANOF AREA

A belt of rocks so similar in lithology and structure as to make 

it seem highly probable that they belong to the same formation 

extends across Admiralty Island between Point Young and Oliver 

Inlet and southeastward, appearing locally along the borders of 

Seymour Canal. Farther southeast it includes the Five Fingers, the 

western part of the Fanshaw Peninsula, and a part of the north end 

of Kupreanof Island.

On the north side of Admiralty Island between Point Young and 

Oliver Inlet are exposed a series of conglomerate, graywacke, and 

slate. The rocks that form Point Young consist predominantly of 

highly cleaved and mashed conglomerate with interbedded graywacke and some black slate. The pebbles and cobbles in the conglomerate consist of limestone, green-gray felsite porphyry, and 

other rocks. The island west of Point Young is of greenstone 

breccia. The beds east of Point Young for some distance are covered 

with sand and gravel. For 4 miles west of Oliver Inlet graywacke 

and slate, with sills of andesite porphyry, containing hornblende 

phenocrysts, are exposed. These beds are intruded by a /small mass 

of granodiorite just west of the entrance to the inlet. East of-the 

inlet for several miles are exposed intrusive masses of quartz diorite 

with included strips of graywacke and slate; these in turn are adjoined by the typical greenstone of Douglas Island with intrusive 

sills and dikes of quartz diorite, which together form the peninsula 

for 1% miles west of Point Arden.

Along Seymour Canal the lowest beds are exposed on Windfall 

Harbor. For a few miles around this harbor the formations are 

Carboniferous and Triassic. (See pp. 118, 138.) The contact of 

the older beds with the graywacke-slate formation mapped as Juras83 Spencer, A. C., and Eakin, H. M., manuscript report on the Juneau district.
JURASSIC (?) BOCKS 159

sic (?) is 3 miles southeast of Windfall Harbor, but this contact 

is covered. The lowest beds of the Jurassic (?) formation are 

graywacke with conglomeratic lenses overlain by black slate which 

passes upward into a thick bed of conglomerate with a black slate 

matrix. The strike and dip are indeterminate. The predominant 

component of the conglomerate is a gray-green felsite porphyry with 

small plagioclase phenocrysts; some limestone cobbles are included, 

and limestone nodules occur sparingly; rarely granitoid rock is 

present. The fragments range from 1 to 9 inches in diameter. This 

conglomerate is adjoined along the coast to the southeast by black 

slate and graywacke with local beds of fine conglomerate. The beds 

along the coast for 15 miles northwest of Mole Harbor have a general 

northwest strike and a dip of 70°-90° W., probably due to a slight 

overturning toward the east. In the vicinity of Mole Harbor, both 

to the north and to the south, black slate with sparing nodules and 

nodular layers of dense blue-gray limestone is cut by many dikes of 

diorite of the Coast Range type. These slate beds are lithologically 

identical with those typical of the graywacke-slate series.

North of Windfall Harbor to a point within about 2 miles of the 

head of the next bay the rocks along the coast consist of schistose 

chert, greenstone, and slate. Black slate of the graywacke-slate 

series forms the head of the first bay north of Windfall Harbor, the 

peninsula to the east, Swan Island, and Tiedeman Island. Rarely 

a sill of green andesite occurs in it. Interlayered slate and graywacke form the second peninsula north of Swan Island on the west 

side. The beds here have a northwest strike; the dip is 50° SW. 

in the southwestern part and changes to vertical toward the northeast. The line of islets on the east side of Seymour Canal about 

3 miles from its head consist of interbedded coarse graywacke and 

fine conglomerate with a vertical dip. The Glass Peninsula consists 

of greenstone schist containing hornblende or pyroxene phenocrysts, 

with intercalated slate and graywacke. The rocks along the east 

side of Seymour Canal consist of interbedded schistose greenstone, 

black slate, graywacke, and local conglomeratic beds and thus constitute a transition between the interbedded slate and graywacke 

with occasional greenstone sills found farther west and the predominantly greenstone series that forms most of the Glass Peninsula. 

The beds in general strike northwest. The dip along the west side 

of Seymour Canal is in general to the west; farther northeast across 

the strike it steepens to vertical; and on the east side of Seymour 

Canal it is vertical or steep eastward. Along the east side of the 

Glass Peninsula the dip is 35°-65° NE.

Bedded rocks similar to those along Seymour Canal are found on 

Fanshaw Peninsula, along the coast from a locality about 1% miles 

west of Bay Point to the point south of Point Walpole, and along
160 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

the stream at the head of the north arm of Farragut Bay, also on 

Whitney Island, Storm Islands, and the Five Fingers. The beds 

consist of graywacke, slate, and thin-bedded graywacke and slate. 

Any one of these types of rocks may dominate locally, but graywacke 

is the more common. Conglomeratic slate beds and rarely a tuffaceous 

bed occur locally intercalated with the graywacke. The graywacke 

varies from a very fine-grained rock with a fissile parting to a coarsegrained rock of more massive character. The more massive type is 

found on the Storm Islands, where the beds of coarse-grained graywacke with intercalated black slate and fine conglomerate are 1 foot 

to several feet thick. The beds of graywacke contain many lenses 

of conglomerate; but they are particularly characterized by an abundance of small calcareous pockets from one-fourth of an inch to several 

inches in diameter, which weather out and leave the rock exceedingly 

pitted with holes. Much larger lenses of calcareous material or limestone are also common in the graywacke and slate. Beds as much as 

a foot thick containing abundant fragments of black slate occur intercalated with the graywacke. In thin section the graywacke is found 

to consist almost wholly of waterworn fragments of plagioclase and 

of andesite porphyry with feldspar phenocrysts; it might be called a 

waterworn tuff.

The more fissile facies of the graywacke occur in beds from 1 to 6 

feet thick with layers of slate several inches thick. The graywackes 

are a greenish gray on the fresh surface and a whitish or ash gray 

on the water-rounded surface. On weathering they break down along 

the cleavage planes and resemble the slates. In thin section they are 

seen to consist of quartz, plagioclase (albite-oligoclase), and fragments of other rocks in varying amounts in a very fine-grained 

groundmass. Locally fragments of black slate are common..

Limestone layers several inches thick are commonly intercalated 

with the graywacke and slate in the thin-bedded zones. Limestone 

occurs also as nodules and persistent thin layers in the thick-bedded 

slates and here and there in beds as much as a foot thick. Calcareous 

lenses are common in the graywacke.

The slates are thin-cleaving dark-gray to black argillaceous rocks 

of normal character.

The conglomeratic slates occur in beds that are usually not more 

than 20 feet thick but at some places are as much as 100 feet, as just 

north of Point Highland. The fragments are commonly a fraction 

of an inch to 2 inches in diameter. In the 100-foot bed cobbles 1 foot 

and boulders 5 feet in diameter are present. The fragments are 

exclusively a gray-green feldspar porphyry, locally Avith border outlines resembling those of a breccia. The phenocrysts are albiteoligoclase. The matrix ranges from a slate to a very fine graywacke. 

The pebbles and cobbles have been very much flattened by pressure,
JURASSIC (?) ROCKS 161

and the groundmass has a slaty cleavage. Just southeast of Point 

Highland a bed of uniform massive green tuff about 30 feet thick 

occurs intercalated in conglomeratic slate. In thin section this rock 

is found to consist mostly of fragments of felsite porphyry with 

euhedral crystals of plagioclase (albite-oligoclase) and pyroxene in a 

microfelsitic groundmass.

The north end of Kupreanof Island from a point about 10 miles 

east of Cape Bendel to a point 4 miles west of Portage Bay is composed of rocks similar to those of the Fanshaw Peninsula and the 

north end of Admiralty Island. About 10 miles east of Cape Bendel 

a series of beds comprising graywacke and black slate with intercalated conglomerate comes in overlying, presumably unconformably, 

Devonian limestone, slate, and green chlorite schist. The contact is 

covered, but the Devonian beds have a very steep dip, in general to 

the west, whereas the overlying formation has a moderate dip to the 

northeast. Overlying the basal beds of the group of rocks mapped 

as Jurassic (?) is a great thickness of isoclinally folded black slate, 

which was evidently crumpled as a result of drag folding between the 

more massive beds below and above. At the" headland about 12 miles 

east of Cape Bendel the slate is overlain by about 1,000 feet of conglomeratic beds with intercalated graywacke and slate. The lower 

part of these beds consists of thick conglomerate, which passes upward through interbedded conglomerate and graywacke into interbedded conglomeratic slate and black slate, and finally into a series 

of slate and gray phyllite. The slate-phyllite series is exposed 

almost continuously for a width of more than 10 miles at right 

angles to the prevailing strike. The general strike of the cleavage is 

N. 10°-40° W., and the dip 40° E. So great an apparent thickness 

is best explained as the result of repeated duplication through isoclinal folding and crXimpling. Minor folds with a southeast pitch and 

a uniform crosscutting cleavage were seen repeatedly within the beds. 

About 4 miles west of West Point the slate-phyllite series gives way 

abruptly to several hundred feet of Devonian rocks, which consist 

of a series of thin-bedded black slates with layers of chert and sills 

or dikes of intensely altered intrusive rock that weathers pale greenish 

gray. The contact between the two formations is covered, but the 

Devonian (?) rocks are intensely crumpled near the contact.

The conglomerates range in texture from a coarse graywacke to 

beds with cobbles 3 to 9 inches in diameter. Beds with pebbles half 

an inch to several inches in diameter predominate. The beds have 

been severely compressed, and the pebbles and cobbles are very much 

flattened and tr'aversed by many close-set minute faults. The pebbles 

and cobbles are mostly felsite porphyry, with fragments of slate next 

in abundance. Quartz, black and white chert, and limestone are less
162 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

common. A typical cobble of the felsite porphyry, viewed under the 

microscope, consists of abundant phenocrysts of albite-oligoclase and 

a few crystals of much altered augite in a cryptocrystalline groundmass. The felsite porphyry is commonly slightly impregnated with 

pyrite, and its color ranges from pale gray-green to grayish white, 

depending in part on the denseness of texture.

Thin layers of limestone and layers with limestone nodules occur 

sparingly throughout the slates and the slate-phyllite series. The 

gray phyllite is probably a sheared very fine-grained graywacke. 

Limestone also forms the matrix of a few of the conglomerate beds.

The only traces of organic remains in these beds were found in 

graywacke from the northeasternmost tip of Whitney Island, Cleveland Passage. These were submitted to Arthur Hollick, who states 

that they are casts and impressions of what are apparently branching 

fronds of a fucoid plant resembling " Ghondrites heeri " Eichwald 

and that even if the specific identity of these remains could be established it would not possess any special significance, as the stratigraphic position of the species has never been definitely determined.

A significant feature o*f the rocks of the Seymour Canal-FanshawKupreanof area, however, is the predominance, of similar green-gray 

felsite or felsite porphyry pebbles in the conglomerates or conglomeratic slates of each locality.

Specimens of pebbles from the conglomerates of Point Young, Seymour Canal, Fanshaw Peninsula, and Kupreanof Island were examined with the microscope. The porphyritic rocks usually have a 

cryptocrystalline unidentified groundmass, and the dominant phenocrysts are usually a sodic feldspar (albite-oligoclase) but locally 

augite is equally abundant. A specimen from the conglomerate of 

Seymour Canal is microcrystalline in texture and is composed predominantly of plagioclase with interstitial quartz. The feldspars 

are so altered that the presence or absence of orthoclase could not be 

positively determined. The rocks in general have the appearance of 

quartz keratophyre or keratophyre. No pebbles or cobbles of porphyry with large phenocrysts of hornblende or pyroxene, such as 

characterize the greenstone rocks of the Glass Peninsula and Douglas 

Island, were found in these conglomerates. The conglomerate beds 

might therefore be older than the greenstones, so far as this evidence 

is concerned.

Pebbles of a granitoid rock similar to the Upper Jurassic or Lower 

Cretaceous intrusive rocks are present, but rare, in the conglomerates; 

this need not mean that the conglomerate beds are younger than the 

intrusive rocks, for pebbles of similar granitoid rocks are found also 

in Silurian conglomerates.
JUBASSIO (?) ROCKS 163

The conglomerate-graywacke-slate beds on Seymour Canal lie 

between the Carboniferous beds (perhaps with some Upper Triassic 

and younger beds) on the west and the greenstones of the Glass 

Peninsula on the east. Sills of greenstone occur in the sedimentary 

series, which grades through transitional interbedded greenstone, 

slate, and graywacke into the dominantly volcanic series. All the 

formations are cut by the Upper Jurassic or Lower Cretaceous intrusive rocks. These phenomena, taken in connection with the structural 

relations, suggest that the sedimentary series overlies the Carboniferous and probably the Upper Triassic series and underlies the 

greenstones. Such an interpretation is equally applicable to the 

Kupreanof and Fanshaw areas.

KUPREANOF-MITKOF-ETOLIN ISLANDS AREA

A series of fine-grained foliated, more or less fissile graywacke with 

black slate partings forms a large part of a northwestward-trending 

belt through Etolin Island, Mitkof Island, and the Lindenberg 

Peninsula. These beds are intruded by a great many masses of 

granitoid rocks and are more broken up and metamorphosed than the 

beds in the Seymour Canal-Fanshaw-Kupreanof area.

The fissile dark-gray graywacke occurs in beds from 1 to 6 feet 

thick, with beds 1^ to 2 feet very common. The slate partings range 

from a fraction of an inch to a foot or more in thickness and average 

several inches. Persistent layers of fine-grained black impure limestone occur sparingly, and layers of limestone lenses several inches 

thick are common. Lenticles of limestone an inch in length are common in some beds of graywacke, and weathering results in a pockmarked sufrace. Fragments of black slate flattened along the foliation planes are abundant locally in the graywacke. On the west side 

of Wrangell Narrows the fissile graywacke weathers with a pseudoporphyritic or tuffaceous aspect. Thin-bedded slate-graywacke zones 

are intercalated in the prevailingly thicker-bedded rocks. Locally 

sheets of melaphyre are found in the formation, as in the mountains 

on the west side of Wrangell Narrows and on the north end of Etolin 

Island, southeast and southwest of Chichagof Pass. A bed of melaphyre breccia is intercalated in the graywacke on the east side of 

Blind Slough on the south side of Mitkof Island. Two large blocks 

of melaphyre breccia are found at the head of Portage Bay, on 

Kupreanof Island, but it is not certain that they are in place.

The southern peak of the Portage Mountains is composed of a 

series of beds of fine to medium grained tuff underlain by slate. 

The tuff is green on the fresh surface and weathers to a gray hue. 

It consists of angular fragments of melaphyre crowded with pheno-
164 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA .

crysts of plagioclase and of augite almost wholly altered to hornblende.

The graywackes are usually fine-grained gray rocks with a distinct 

foliation which results in a more or less thin cleavage. In many 

beds the cleavage planes are so accentuated by weathering that the 

graywacke resembles slate or phyllite. In thin section the rock is 

found to consist typically of altered fragments of plagioclase (andesine to oligoclase) with a variable amount of quartz in a sericitic, 

argillaceous, or chloritic groundmasjs. Quartz may be absent or it 

may form a large percentage of the rock and constitute a quartzitic 

facies. Particles of andesitic rocks are occasionally present, and 

slate fragments are common in some beds. Near intrusive masses 

the graywacke is garnetiferous, and many dots of graphitic matter 

are arranged along certain of the foliation planes; hornblende is 

present in the calcareous phases, and a trace of tourmaline or 

apatite may be disseminated throughout the rocks. Other minerals 

that may be present are pyrite, magnetite, pyrrhotite, and epidote.

The beds of slate are of the usual black or bluish-black clay slate 

and locally form the bulk of the formation.

No fossils were obtained in the graywacke-slate beds of this belt. 

The stratigraphic position must therefore be surmised from structural relations and from a comparison with similar formations of 

known age in adjacent regions.

These beds of graywacke and slate are similar in lithology to 

those of the Seymour Canal-Fanshaw-Kupreanof area, but they are 

much more broken by intrusive granitoid rocks and locally are more 

metamorphosed. The conglomerates, which form so marked a feature of the northern belt, have not been found within the belt under 

discussion. The two belts may belong to different formations, 

though they are grouped together in this report.

CHICHAGOF ISLAND

Overbeck 94 has described fossiliferous slate and graywacke from 

the head of Slocum Arm on Chichagof Island. Stanton reported the 

fossils as Aucella sp. related to A. focheriana D'Orbigny, with the 

following comment on age:

The form of Aucella in these two lots appears to be distinct from the forms 

identified as A. piocliii Gabb and A. crassicollis Keyserling in previous collections 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 AwoeWo-bearing rocks of southeast Alaska may belong in the same series.

9* Overbeck, R. M., Geology and mineral resources of the wegt coast of Chichagof 

Island: U. S. Geol. Survey Bull. 692, p. 108, 1919.
JURASSIC (?) ROCKS 165 

FELSITE VOLCANIC ROCKS

The beds at the south end of the Fanshaw Peninsula between Bay 

Point and Farragut Bay and for several miles north of Bay Point 

constitute a series of rocks not found elsewhere in the district. 

They comprise very fissile schists that weather white or rusty brown, 

intercalated black slate and conglomeratic slate, and schistose green 

andesite porphyry. The light-colored schists are of volcanic origin 

and include schistose felsite porphyry flows, breccias, and tuffs. The 

tuffs are often found in thin beds alternating with slate. A specimen 

of one of these schists, seen in thin section, is found to consist of 

plagioclase (albite-oligoclase) in a cryptocrystalline groundmass. 

The groundmass is much altered; in it secondary pyrite, calcite, and 

epidote are common, and needles of amphibole are abundant. The 

characters are those to be expected in a sheared felsite porphyry flow. 

In the beds of breccia black pyroxene crystals are conspicuous against 

the light-colored groundmass.

The correlation of these beds is an unsolved problem. The presence of andesite porphyry volcanic rocks, which may be sills, suggests 

a correlation with the Jurassic (?) greenstone volcanic series which 

adjoins them on the west. The fine conglomeratic slates resemble 

very closely those in the sediments of F'anshaw Peninsula to the 

north and may be of the same age, although they appear to be 

interbedded with the volcanic rocks. The cobbles in the conglomerates of the Jurassic (?) conglomerate-graywacke-slate series are 

similar to the felsite volcanic rocks of these beds; this similarity 

suggests that the volcanic beds are older than the conglomerates.

Knopf 95 states that some quartz porphyry schists are associated 

with the Jurassic or Cretaceous graywackes and slates in the Berners 

Bay area. Dolmage 96 describes dacite associated with the Vancouver 

group of volcanic rocks, which are believed to be Triassic in age.

GREENSTONE VOLCANIC ROCKS 

DISTKIBUTION

Greenstone volcanic rocks of Jurassic or Cretaceous age have been 

mapped by Knopf 97 as occurring in a belt on the mainland on the 

x east side of Lynn Canal north of Point Sherman; on the coast from 

Berners Bay to Auke Bay; on Douglas Island; and on the east side of 

Gastineau Channel. Near Juneau part of the greenstone is probably 

of Upper Triassic age and the remainder is of unknown age; this 

portion of the belt has been mapped for this report with the schists.

88 Knopf, Adolph, U. S. Geol. Survey Bull. 446, p. 14, 1911.

M Dolmage, Victor, Canada Geol. Survey Summary Kept, for 1920, pt. A, p. 14, 1921.

87 Knopf, Adolph, op. clt., pi. 5.
166 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

To the southeast the greenstone volcanic rocks form most of the 

Glass Peninsula, Admiralty Island, and a belt striking across Farragut Bay, on the mainland. They are again exposed as a narrow 

band intercalated in graywacke on the east side of Blind Slough and 

as a belt east of Point Alexander, Mitkof Island. They form Vank 

and Sokolof Islands and a belt on the north end of Etolin Island 

at Olive Cove and Anita Bay. In the Ketchikan district they form 

Onslow Island and the west part of the Cleveland Peninsula and 

extend southeast along Tongass Narrows, Gravina, Annette, and 

Mary Islands, and the coast north of Cape Fox.

Beds of black clay slate are intercalated with the greenstone at 

most places, but the amount is variable and in some thick sections 

they are absent. On the borders of many of the greenstone belts 

greenstone and slate are interbedded, and locally greenstone sheets 

are intercalated in the graywacke series.

On favorable weathered surfaces the breccia structure of the greenstone is well exhibited. The fragments may range in size from a 

fraction of an inch to a foot but are usually a few inches; they have 

been very much compressed and are elongated parallel to the foliation. In many beds the fragments form most of the rock with only 

a little groundmass. The most conspicuous feature of the rock is 

the abundance of black hornblende crystals, which are almost always 

present and are 0.2 to 0.3 inch in diameter and as much as 0.5 inch 

in length.

In thin section the rocks all show extensive alteration and parallel 

orientation of the secondary minerals. The component secondary 

minerals are amphibole, epidote, chlorite, calcite, quartz, a little magnetite, and often albite.

The least metamorphosed facies consists of phenocrysts of augite 

in process of alteration to hornblende in a groundmass composed of 

crowded fibers of uralite and actinolite in a microcrystalline plagioclase aggregate with large grains of epidote. Locally amygdules 

filled with calcite or chlorite are present. Usually the augite has 

been completely altered to hornblende and the groundmass consists 

of epidote, chlorite, sericite, actinolite, uralite, and microcrystalline 

secondary plagioclase, perhaps with some quartz. Local phases of 

the rocks, probably metamorphosed tuffs, consist almost wholly of 

hornblende with a trifle of biotite and muscovite and a few grains 

of epidote. Others have a little quartz. The rocks have been called 

augite melaphyres by Knopf.

Knopf 98 reports that in the Eagle River region conglomerates are 

associated with the breccias and consist essentially of pebbles and 

well-rounded boulders of volcanic material in a matrix of tuffaceous

88 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, pp. 19, 20, 1912.
JURASSIC (?) BOCKS 167

or waterworn material. He notes further that between Yankee and 

Bridget Coves the lavas display a remarkable development of ellipsoidal structure. This is the only reported occurrence of ellipsoidal 

structure in the Jurassic or Cretaceous volcanic rocks, and for this 

reason a question arises as to whether these particular lavas do not 

belong to some other system.

KETCHIKAN DISTRICT 

By THEODORE CHAPIN

In the Ketchikan district interbedded altered tuffs, flows, and black 

slate with some intrusive rocks occur on Gravina, Duke, Annette, 

and Kevillagigedo Islands. The greenstone and slate overlie the 

Upper Triassic rocks with apparent conformity. On the evidence of 

a few fossils found in the intercalated sediments and on structural 

grounds and analogy with rocks of known age these rocks are regarded as Upper Triassic or Jurassic.

On Gravina Island the greenstone and slate occupy three parallel 

belts one extending from South Vallenar Point to Seal Cove, another from the east shore of Bostwick Inlet to Vallenar Point, and 

the third along Tongass Narrows from Old Indian Town to Gravina 

Point. Northeast of Tongass Narrows similar rocks extend from 

Kadio Station to Herring Bay. On Annette Island the greenstone 

arid slate occupy two belts along the east and west coasts of the island.

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; and an upper series of mixed water-laid 

tuff and black slate and limestone, with porphyritic basic rocks of 

similar composition, evidently partly intrusive and partly extrusive. 

No sharp line separates the two parts, and the writer has not differentiated them on the geologic map. The black slate passes into 

green fissile tuffs and these into more massive varieties, so that as a 

rule no sharp line of contact can 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 

parts of California Ridge. It is a fine-grained green rock with large 

angular fragments set in a dense matrix of the same composition.

The breccia passes upw,ard into finer-grained tuff, in part at least 

water-laid material, with which are intercalated black slate and thin

6137 29 12
168 GEOLOGY AND MINERAL, DEPOSITS, SOUTHEASTERN ALASKA

beds of crystalline limestone. The black slate is typical clay slate 

that has ,a well-developed cleavage, with bedding planes discernible 

in places. The beds of slate are plainly conformable with green tuff. 

The black slate and green bedded tuff are best developed along the 

north shore of Tongass Narrows from Ketchikan to Mountain Point. 

The black slate is in places considerably metamorphosed and schistose 

and might more correctly be called phyllite. It is closely interbedded 

with and grades into fissile green tuff, both of which are interbedded 

with more massive tuff. The green tuff also is schistose and in places 

is completely recrystallized. The greater part of the town of Ketchikan stands on rocks of this character, ,and excavations for street 

building show both 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.

AGE AND CORRELATION

Chapin 80 has discussed the age and correlation of the greenstone 

and slate in the Ketchikan district as follows:

The age determination of the greenstone and slate rests upon rather slender 

paleontologic foundation. The collections from Bostwick Inlet were submitted 

to Mr. Stanton, who reports as follows:

9528 (15 ACh 104). Bostwick Inlet, Gravina Island.

9529 (15 ACh 105). Bostwick Inlet, Gravina Island. 

Aucella sp. 

Probably Upper Jurassic; possibly Lower Cretaceous.

9530 (15 ACh 106). Bostwick Inlet, Gravina Island. 

Pecten? sp.

Not sufficient for determining age but probably from 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 from which the Triassic and doubtful collections 

were made. The fossils occur in sedimentary beds apparently interbedded with 

the volcanic breccias and overlying the Triassic sediments, but the relations are 

somewhat obscured by the gravel covering.

Some correlations with rocks of known age are suggested. The greenstone 

and slate series extends more or less continuously along the mainland and 

adjacent islands of southeastern Alaska. In the Juneau region the recent detailed work of Spencer and Eakiu shows a section similar to that exposed along 

Tongass Narrows and adjacent islands, and Brooks, who has studied both 

sections, believed that the black slate and greenstones of Ketchikan should be 

correlated with the andesitic flows and black slates of Juneau, which carry 

Triassic fossils. The finding of Upper Triassic fossils by Spencer and Eakin 1

88 Chapin, Theodore, The structure and stratigraphy of Gravina and Revillagigedo 

Islands, Alaska: U. S. Geol. Survey Prof. Paper 120, pp. 96-97, 1919. 

1 U. S. Geol. Survey Thirty-eighth Ann. Rept., p. 90, 1917.
JURASSIC (?) BOOKS 169

in the slate and greenstone series of Juneau suggests, to the writer* the possibility that the rocks of Tongass Narrows are of similar age. Smith 2 notes the 

similarity between the volcanic rocks of Gravina Island and the augite 

melaphyres of the region north of Juneau, referred by Knopf 3 to the Upper 

Jurassic or Lower Cretaceous, and it is not at all unlikely that the upper portion 

of the slate and greenstone series of the Ketchikan district may be the equivalent 

of the volcanic rocks associated with the " Beruers formation." The slate and 

greenstone of the Ketchikan district may thus be correlated with both the 

Triassic and Jurassic rocks of the Juneau region.

Martin 4 has given a thorough discussion of the Jurassic system in 

southeastern Alaska, from which the following quotation is taken:

Although Jurassic rocks1 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 Aucelldr 

bearing 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 Aucellabearing beds, and this interpretation undoubtedly is in part correct. Others 

have been assigned to the Carboniferous, for which there apparently is strong 

evidence. Another part of these rocks contains 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 pre-Jurassic, 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-Oetaceous or post-Cretaceous; if they are intruded by granitic rocka 

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

a Smith, P. S., Notes on the geology of Gravina Island, Alaska: U. S. Geol.. Survey 

Prof. Paper 95, p. 164, 1916.

8 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, p. 18, 1912.

* Martin, G. C., The Mesozoic stratigraphy of Alaska: U. S. Geol. Survey Bull. 776, pp. 

245-247, 1926.
170 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

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 evidenceagree, 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 melapbyre breccia of the Wrangell district. The Jurassic rocks of Gravina Island and the Juneau district are included in the following sections:

Section of Mesozoic rooks* on Gravina Island"

Lower Cretaceous (?) : Conglomerate, graywacke, and Feet 

black slate with Belemnites_______________ ___ 800±

Unconformity.

Upper Jurassic: Slate and limestone interbedded with tuffs'

and containing Aucella- 1,200±

Lower or Middle Jurassic (?) : Breccia, tuff, and lava__

Unconformity (?).

Upper Triassic: Limestone, slate, and conglomerate___ 1, 600±

Stratigraphic section near Juneau 6

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).

8 Complied by G. C. Martin from Information given by Chapin (U. S. Geol. Survey Prof. 

Paper 120, pp. 83-100, 1918).

8 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 G. C. Martin.
JURASSIC (?) ROCKS 171

Buddington seriously questions the validity of certain criteria 

suggested by Martin as a basis for separating the Jurassic and 

'Cretaceous systems in southeastern Alaska. These criteria are that

 the presence of granitic boulders in conglomerates indicates a probable post-Jurassic age, and that if the beds are intruded by granitic 

.rocks they are early Jurassic or pre-Jurassic.

Lithologically the nonfossiliferous sedimentary beds mapped as 

.Jurassic (?) resemble the fossiliferous rocks mapped as Lower

 Cretaceous (?). The former differ from the latter, however, in 

that they are in part more metamorphosed, and they are definitely

 cut by masses of the Upper Jurassic or Lower Cretaceous intrusive 

rocks. The greater metamorphism is, however, directly correlated 

with proximity to these intrusions, and it is therefore not an argument against a correlation of the two formations. The fossils, if

 originally present in the Jurassic (?) beds, may have been largely 

'destroyed by the greater metamorphism.

The nonfossiliferous slates of Seymour Canal appear to be structurally the equivalent of the Au'ceUa-be&ring slates of Pybus Bay.

 Conglomerate beds of similar character occur intercalated in both 

ioraiations, and both overlie Upper Triassic beds. A very marked 

unconformity exists between the similar Jurassic (?) sedimentary 

formation on the north end of Kupreanof Island and the underlying 

.Devonian formation. The Aucetta-bQ&rmg slates of Point Pybus are 

Jiot cut by any intrusive rocks, but they are cut by quartz veins, 

~vvhich are restricted to the proximity of the diorite masses of The 

Brothers Islands and are therefore believed to be genetically connected with those intrusive masses.

Cobbles of diorite, granodiorite, and granitoid rocks occur in the

 conglomerate beds both along Seymour Canal and at Point Pybus. 

On Seymour Canal the beds associated, with the conglomerates are 

cut by diorite at Mole Harbor. The presence of these cobbles, which 

are, it is true, so similar to the Upper Jurassic or Lower Cretaceous 

intrusive rocks that they can not be distinguished therefrom, nevertheless does not point to a postbatholithic age for the conglomerates. 

On the contrary, similar rocks are found also as cobbles and boulders in Silurian conglomerates throughout southeastern Alaska.

The conglomerates and associated beds at Point Young, Admiralty 

Island, were correlated by Wright 7 with the Aucella-be&rmg beds 

of Lower Cretaceous (?) age on Pybus Bay. This seems to Buddington a reasonable interpretation, although it is questioned by Martin.

No fossils were found with the volcanic rocks in these districts, 

and an opinion as to their stratigraphic position must be gained from

7 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

p. 143, 1906.
172 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

a comparison with similar rocks of known age in other districts and 

from their structural position.

On the Glass Peninsula, Admiralty Island, the volcanic rocks 

appear structurally to overlie the Jurassic (?) sedimentary beds of 

Seymour Canal. An alternative explanation would be to consider 

that the volcanic rocks are overturned and that the sediments overlie them and are isoclinally folded in a major syncline. The 

absence of cobbles of the volcanic rocks in the conglomerates of the 

sedimentary series and the presence of sills of andesite porphyry in 

them suggest that the first interpretation is the correct one.

On Etolin Island, north of Rocky Bay, similarly, the volcanic 

rocks appear to overlie the fossiliferous Lower Cretaceous (?) sediments, which here are Atycella-bQ&ring slates.

If the age determination and the interpretation of the structural, 

relationship of the sediments of Eocky Bay are correct, they would 

indicate that the volcanic rocks are at least as early as Lower Cretaceous. The evidence, however, is too uncertain to warrant assigning these volcanic rocks definitely to the Lower Cretaceous, and they 

are mapped as Jurassic (?). All the volcanic rocks are definitely 

older than the Coast Range batholith.

Schofield and Hanson 8 describe as the " Bear River formation " a 

series of Mesozoic volcanic rocks that occur at the head of Portland 

Canal on the east side of the Coast Range batholith. Their description follows:

This group of rocks is almost entirely of volcanic origin, and the name 

" greenstone " commonly applied to it is suitable in a general way. The lower 

members are largely fragmental rocks of agglomerate character. Their constituent fragments are angular purple and green masses of andesite in an andesitic 

matrix. They vary in size from minute particles to pieces a foot or more across. 

In thin section they show phenocrysts of a plagioclase of intermediate composition, probably an andesine, scattered through a highly altered matrix in 

which hornblende and plagioclase are the main constituents. The rock is 

highly altered, and many secondary minerals such as calcite, epidote, and 

chlorite are present. In some places bands of tuff are interbanded with the 

agglomerates. * * * The agglomerates are overlain conformably by finegrained tuffs that form the upper part of the Bear River formation.

The " Bear River formation " is overlain conformably by the Salmon River conglomerates, which in turn pass upward into the conformable Nass argillites or slates with some interbands of sandstone 

and fine conglomerate. Schofield and Hanson 9 obtained fossils from 

the conglomerates near the base of the Nass formation which were 

identified by McLearn, who suggests that they indicate a Jurassic 

age, although the evidence is not conclusive.

8 Schofield, S. J., and Hanson, George, Geology and ore deposits of Salmon River district, 

B. C.: Canada Geol. Survey Mem. 132, pp. 11-12, 1922.

"Schofleld, S. J., and Hanson, George, Canada Geol. Survey Summary Rept. for 1920, 

pt. A, p. 8a, 1921.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 173

From the literature quoted it is evident that a volcanic formation 

of probable Jurassic age and very similar lithologically to that under 

discussion is widespread throughout southeastern Alaska and British 

Columbia.

It may be that the volcanic rocks here included under the term 

Jurassic (?) comprise more than one formation that part belong 

to the Jurassic and underlie the Aucetta-bearmg beds and part to the 

Lower Cretaceous and overlie the AuceUa-bB&Ting beds. The evidence at hand is not sufficiently determinative to indicate positively 

that part of the volcanic rocks are younger than the Aucella-bestfing 

beds, but Buddington believes this to be the case.

UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 

GENERAL CHARACTER

The Upper Jurassic or Lower Cretaceous intrusive rocks are the 

dominant geologic feature of southeastern Alaska. They are but a 

part of a great composite batholith and its satellitic intrusions that 

extend for more than 1,100 miles northwestward into Yukon Territory from Fraser Eiver, in British Columbia. From Vancouver to 

Skagway, on the mainland, the batholith forms the backbone of the 

Coast Range and is exposed either1 at the shore line or not far inland. 

Outlying dikes, stocks, and batholiths that are believed to be of 

the same general period of intrusion as the Coast Range batholith 

and genetically allied to it are found locally on Vancouver Island 

and the Queen Charlotte Islands and abundantly throughout most 

of the Alexander Archipelago. The Coast Range batholith is the 

largest on the North American continent.

It is much wider south of Skeena River, in British Columbia, than 

north of it, and reaches a maximum width of 110 miles. The part of 

the main batholith in southeastern Alaska and the adjacent strip of 

British Columbia is 35 to 60 miles wide, with an average of about 

50 miles, and about 350 miles long.

The term " batholith " is applied to intrusive igneous bodies that 

occupy considerable areas and show no observable evidence of a 

bottom; the term " stock" is applied to smaller similar bodies. 

Daly 10 has proposed that " batholith " .be confined to bodies more 

than 40 square miles in area.

The rocks in southeastern Alaska grouped as Upper Jurassic or1 

Lower Cretaceous intrusive rocks include a minor amount of widely 

varying ultrabasic rocks and a predominant more siliceous, sub10 Daly, R. A., Igneous rocks and their origin, p. 90, New York, McGraw-Hill Book Co., 

1914.
174 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

alkalic series. The ultrabasic rocks comprise the oli vine-rich rocks 

dunite, wehrlite, and saxonite; the pyroxenites hypersthenite or 

bronzitite, diallagite, and augitite; and hornblendites. There are 

all gradations between hornblendite, hornblende diorite, and pyroxenite, and between pyroxenite and dunite.

The normal subalkalic series includes norite; augite gabbro and 

gabbro-diorite; diorite, monzodiorite, quartz diorite, granodiorite, 

quartz monzonite, granite, and exceedingly rare monzonite and syenite. Albite and albite-oligoclase Varieties of diorite, monzodiorite, 

quartz diorite, granodiorite, and quartz monzonite are found in small 

volume associated with the predominant varieties of these rocks 

which carry a more calcic plagioclase. Pegmatitic f acies of the hornblendite, pyroxenite, and norite are found, and pegmatitic and 

aplitic facies of the other subalkalic rocks.

The Upper Jurassic or Lower Cretaceous intrusive rocks may be 

discussed with respect to six approximately parallel belts, based 

upon the mode of occurrence, the environment, and the character and 

range in variation of the intrusive masses. These belts, beginning on 

the northeast, are the border zone east of the Coast Eange batholith, 

the Coast Eange batholith of the mainland, the Wrangell-Kevillagigedo belt, the Prince of Wales-Chichagof belt, the Kuiu-Heceta 

belt, and the Dall-Baranof belt.

In classifying the rocks Johannsen's system 11 has been used with 

some modifications which are noted here. An upper limiting ratio 

of about 10 per cent of potassic feldspar to total feldspar, instead 

of 5 per cent, is chosen to delimit quartz diorite from granodiorite, 

and rocks with as much as 10 per cent of quartz are grouped with the 

diorite. Only rocks with a ratio of 10 per cent or more of potassic 

feldspar to total feldspar are included in the monzodiorite. The 

plagioclase is divided according to the following system: Albite 

(Ab10An0 to AbgAnJ, oligoclase (AbgA^ to Ab7An3 ), andesine 

(Ab7An3 to Ab5An5 ), labradorite (Ab5Ang to Ab3An7 ), bytownite 

(Ab3Anr to AbiAng), anorthite (AbxAn9 to Ab0An10 ). .

In the following tables minerals due to hydrothermal alteration 

or replacement have been counted as part of the minerals which they 

are replacing. The estimates of the minerals are based on Rosiwal 

analyses of thin sections, and the percentages are given by weight. 

The term potassic feldspar includes microcline, microperthite, and 

orthoclase.

The table below gives for the major types of rocks their average mineral composition and the range in composition of the 

specimens of intrusive rock which were studied. Some rocks which

11 Johannsen, Albert, A quantitative mineralogical classification of igneous rocks, revised : 

Jour. Geology, vol. 28, Nos. 1-3, pp. 38-60, 158-177, 210-232, 1920.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 175

slightly exceeded the upper limiting ratio of potassic feldspar for a 

given type were nevertheless treated with this type if they were 

closely associated with it in minor amount in the field. The table 

therefore shows ranges differing slightly from those adopted as a 

standard. ' The term " granodiorite " is often used in the field for any 

or all facies of the Coast Range batholith where a more precise 

designation is not essential. Many geologists use the term " albite 

syenite " in preference to " albite diorite " and " albite granite " or 

" sodic granite " in preference to " albite-quartz diorite."

In contrasting the average alkalic content of the rocks of the 

several belts it is recognized that potassium occurs both in the potassic feldspars and in biotite, and that some rocks of the same 

gross chemical composition would be classed either as biotitic quartz 

diorite or as granodiorite relatively free from biotite, the classification depending upon whether the potassium molecule is present as 

the biotite or the feldspar molecule.

Average and range in composition of major types of the Upper Jurassic or 

Lower Cretaceous intrusive rocks

Qabbro:

Gabbro-diorite:

Diorite:

Monzodiorite:

Quartz diorite:

Albite or sodic quartz diorite:

Granodiorite: 

Average. ____ . ........

Oligoclase granodiorite:

Quartz monzonite: «

Oligoclase-quartz monzonite:

Granite: 

Average. .................

Labradorite

51

35-65

Andesine- labradorite

46

30-75

Andesine

63

60-70

56

50-75

54

40-60

50

38-60

"35

30-50

Albite or

oligoclase

73

65-75

56

49-65

31

13

10-15

Potassic feldspars-

(\->\

1

0-5

1.5 0-8

19 9-30

4

0-8

2

0-5

12.5 9-28

12

10-15

33

25-45

37

6t

55-73

Pyroxene

31 0-60

6

0-20

Hornblende

10 0-50

42

35-65

27

20-30

17 0-35

9.515-

1

0-5

7.58-

1

0-2. 5

2

0-10

0

1

Biotite

2

2.5 0-12

2

0-7

12

23

2

0-10

8.5

25

2

1.5-4

3.5 0-8

1.5

2

a>

1 

a

S

5

3

?:-

N

 e 

o*

i

0-5

4

0-10

4

0-10

19.5

15-30

22

15-30

20

15-30

29

20-35

25

20-35

30

23

12-40

Accessories

?,

1

1 5

1 5

0 5

o Plagioclase is oligoclase to andesine, averaging possibly about AbyAnj.

BORDER ZONE EAST OF THE COAST RANGE BATHOLITH

The border zone east of the Coast Range batholith lies mainly 

within British Columbia and is for the most part relatively inaccessible. The country has been but little studied, except very locally,
176 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

and there is very little exact information as to the character of the 

intrusive rocks.

The most striking phenomenon in this border zone is the absence of 

contact metamorphism on a regional scale "and the meager evidences 

of local contact metamorphism produced by the Coast Range batholith. The rocks are closely folded; argillaceous rocks have been 

changed to slaty types and, locally, andesitic volcanic rocks to greenstone; but there is practically no phyllite and no crystalline schist 

away from the immediate contact with intrusive bodies.

The number of intrusive stocks or batholiths varies markedly 

within this eastern border zone. Hanson 12 states that between 

Skeena and Nass Rivers the eastern border of the batholith is irregular and there are a number of apophyses and outlying stocks of 

granodiorite but that between Nass River and Portland Canal the 

border is approximately straight.

Near or adjacent to the eastern border of the batholith in the 

Hyder district there is a mass of hornblende granodiorite that is 

close to quartz monzonite in composition. This mass, which the 

writer has named the Texas batholith, is cut by many dikes of 

younger quartz monzonite and granodiorite and has been locally very 

intensely mashed and altered by the thrust from the intruding quartz 

monzonite magma. The Texas batholith must be markedly older 

than the quartz monzonite and granodiorite which cut it, and there 

is a question as to whether it should be interpreted as an older facies 

of the intrusive rocks of the Coast Range or whether it is so much 

older as to warrant its exclusion from that group. It is not known 

whether the quartz diorite mapped by Dolmage to the south, at the 

head of Hastings Arm and Observatory Inlet, should be grouped 

with the Texas batholith. This batholith is sparsely porphyritic, 

with large crystals of microperthite, except locally, where it plunges 

beneath a cover of sediments and is an even-grained quartz diorite. 

These features suggest that it is a stock differentiated in place and 

older than at least the bulk of the intrusive rocks of the Coast Range. 

It is intrusive, however, into the "Bear River series" and Nass 

argillite of Jurassic age. Its average composition is 48 per cent 

andesine, 20 per cent potassic feldspar, 19 per cent quartz, and the 

rest hornblende, with a little accessory biotite.

In the Hyder district the problem is thus complicated by the fact 

that there are two batholiths of similar composition but of different 

age. The Texas batholith of granodiorite with local border facies 

of quartz diorite underlies much of the country between Salmon 

River and the north and south branches of Chickamin Glacier. 

West of Mount Bayard there is a mass of granodiorite that is intru12 Hanson, George, Reconnaissance between Skeena River and Stewart, B. C.: Canada 

Geol. Survey Summary Rept. for 1923, p. 37a, 1924.
UPPEE JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 177

sive into the Texas batholith and is either an outlying stock or an 

apophysis of the eastern part of the main Coast Range batholith, 

which in this region is quartz monzonite. The younger f acies of the 

Upper Jurassic or Lower Cretaceous intrusive rocks also exhibits 

sparse local masses of diorite. North of Long Lake on the Canadian 

side there is a stock of augite porphyrite or porphyritic gabbrodiorite, which is cut by dikes of quartz diorite and granodiorite 

belonging to the younger series of intrusive rocks.

Between the head of Portland Canal and the Atlin district the 

country is relatively unknown. In the Atlin district, according to 

Cairnes,13 there are a number of stocks of granodiorite or quartz 

monzonite. Descriptions of the outlying intrusive masses in the 

Whitehorse district, Yukon Territory,14 suggest that albite or oligoclase quartz monzonite predominates. One mass of gabbro-diorite 

with considerable potassic feldspar is present.

The scanty data suggest that the more common intrusive rocks 

within this belt range from quartz diorite through granodiorite to 

quartz monzonite, with local development of more basic f acies. They 

appear to be in general more alkalic and siliceous than the stocks in 

the Prince of Wales-Chichagof belt, west of the batholith, where the 

country rocks show a similar degree of metamorphism.

The data at hand are insufficient for an adequate description of 

even the grosser variations in composition of the Coast Range batholith. Only general statements applicable to local sections can be 

made.

The rocks of the batholith are often called by the general term 

" granite " or " granodiorite," as it is difficult or impossible in the field 

to distinguish their character more precisely. Detailed examination, 

however, shows that only a relatively very small proportion of the 

batholith is true granite that is, a quartzose rock in which twothirds or more of the total amount of feldspar present is potassic 

feldspar and in which the plagioclase is a sodic variety.

Of 78 specimens taken ,at intervals across the batholith along the 

west side of Portland Canal and along Chickamin and Stikine Rivers, 

28 were granodiorite, 26 quartz monzonite, 16 quartz diorite, 2 granite, 2 hornblende-biotite diorite, 2 monzonite, 1 hornblendite, and 1 

gabbro. These figures give an approximate idea of the probably relative quantitative distribution of the different types of igneous rock

13 Cairnes, D. D., Portions of the Atlin district of British Columbia: Canada Geol. 

Survey Mem. 37, p. 57, 1913.

u Cockfleld, W. E., and Bell, A. H., Wbitehorse district, Yukon : Canada Geol. Survey 

Mem. 150, pp. 29-32, 1926.
178 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

within the southern part of the mainland Coast Kange batholith in 

Alaska and show that granodiorite, quartz monzonite, and quartz 

diorite are predominant.

Analyses of 19 specimens taken at intervals completely across the 

batholith along Stikine Eiver and 23 specimens taken at intervals 

along Portland Canal show the average composition to be that of a 

granodiorite with 19 to 24 per cent of potassic feldspar, about 22.5 

per cent of quartz, 40 to 46 per cent of oligoclase andesine, 6 per 

cent of hornblende, 5 per cent of biotite, and the rest accessory minerals. These averages are given in the table on page 180 as Nos. 1 

and 3. A weighted average of 18 specimens taken along Chickamin 

Kiver is given as No. 2.

There is variation in composition both lengthwise of the batholith 

and across it, but in this area the variation lengthwise is much less 

marked than that crosswise. The variation across the batholith along 

Stikine and Chickamin Rivers and along Portland Canal is in general from a hornblende-biotite-andesine-quartz diorite on the southwest to a biotite-oligoclase-quartz monzonite on the northeast, with 

rock whose composition averages that of a granodiorite in the core. 

This gradation is not continuous, however, but irregular. Along 

Portland Canal, in the core of the batholith, there are at least two 

broad belts of quartz monzonite interbanded with broad strips of 

granodiorite, which in turn is locally interbanded with quartz diorite. 

On Stikine and Chickamin Rivers no quartz monzonite was noted in 

the core of the batholith, but quartz diorite bands are found; and on 

Stikine River there are in places small masses of diorite and of more 

basic rocks. There is a tendency toward increase of potash feldspar 

and sodic plagioclase and decrease of ferromagnesian minerials from 

the southwestern to the northeastern border of the batholith. Hornblende is wholly and biotite almost wholly absent from the quartz 

monzonite of the eastern part. Wherever reaction and injection 

gneisses are present the rocks may be extremely variable within 

very short distances, owing probably in part directly to the nature 

of the original country rock and in part indirectly to the influence of 

the original rock in shortening or prolonging the period of crystallization of the magma and thus permitting greater or less differentiation. Inclusions of country rock ranging from large belts to disintegrated shreds are found within the batholith; these are usually 

restricted to certain belts, where all gradations may be found from 

schist through injection and reaction gneisses to normal intrusive 

rock.

The western portion of the batholith throughout southeastern 

Alaska is known to be composed of quartz diorite for a width of
UPPEE JURASSIC OB LOWEE CEETACEOUS INTENSIVE EOCKS 179

5 to 15 miles from the contact. The average composition of 20 

specimens from this belt is given in the table on page 180 as No. 4.

The core of the batholith consists predominantly of granodiorite, 

with some associated quartz monzonite and quartz diorite and a few 

small masses of diorite and more basic rock. The average of 44 

specimens from the core of the batholith between Portland Canal 

and Stikine Kiver is given as No. 5.

The quantitative petrography of the eastern flank of the batholith 

is practically unknown. For a width of about 12 miles and a length 

of about 25 miles between Portland Canal and Chickamin River 

the rock is quartz monzonite. The average of 16 specimens from 

this belt is given as No. 6. On the Stikine River the rock of the 

eastern border is an oligoclase quarz monzonite. An average of 

5 specimens is given as No. 7. At the head of Hastings Arm 

and Alice Arm, 40 miles south of Portland Canal, the eastern border 

of the batholith for a width of 5 to 10 miles from the eastern 

contact is mapped by Dolmage 15 as quartz diorite.

In the Stikine River section the predominant rock of the west 

flank of the batholith in a belt 5 to 10 miles wide is quartz diorite (see 

No. 9), and near the east flank is a belt of oligoclase-quartz monzonite 

about 10 miles wide (see No. T). The successive rock belts from west 

to east contain increasing amounts of alkali feldspars and quartz 

and decreasing amounts of hornblende, biotite, and calcic feldspars. 

But although taken as a whole the changes are toward increasing 

alkalies (both of K2 0 and Na2 0) and increasing silicity, the series 

of sections examined by the writer does not show a uniform gradation from west to east but a very abrupt change from a belt of 

quartz diorite to one predominantly of granodiorite, then to one practically all quartz monzonite. Quartz diorite occurs locally and diorite rarely (see No. 10) within the predominantly more alkaline core 

of the batholith.

The writer is indebted to W. B. Jewell for a description of the 

Chickamin River section. At the mouth of the river, adjoining 

a band of crystalline schist and injection gneiss, there is a narrow 

band of quartz diorite. To the northeast is a belt of granodiorite 

about 14 to 15 miles wide, adjoined in turn to the northeast by a belt 

of quartz monzonite 10 to 12 miles wide. A belt of granodiorite very 

low in potassium intervenes between the normal granodiorite and 

the quartz monzonite. The average of six specimens of the normal 

granodiorite from the western half of the batholith is given as 

No. 11.

"Dolmage. Victor, Coast and islands of Brtish Columbia between Douglas Channel and 

the Alaskan boundary : Canada Geol. Survey Summary Rept. for 1922, pt. A, map facing 

p. 10, 1923.
180 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

In the Portland Canal section the southwestern border zone of the 

batholith, 10 to 12 mile^ wide, consists of quartz diorite; the core, 45 

miles or so wide, of granodiorite and quartz monzonite (see Nos. 12 

and 13), with local bands of quartz diorite; and the eastern border 

zone of quartz monzonite. This section is different from that on 

Stikine and Chickamin Kivers in that at least two broad bands of 

quartz monzonite occur within the granodiorite of the core. This 

quartz monzonite of the core, however, is considerably more basic 

than that of the eastern border, as shown by Nos. 6 and 13.

Boundary Peak, on Unuk Kiver, is composed of quartz monzonite 

(see No. 14), indicating that here, too, quartz monzonite forms the 

eastern border facies of the batholith.

Approximate mineral composition of Coast Range batholith

1

2

3

4

5

6

7

8

9

10 

11

12

13

14

Average of 23 specimens taken at intervals across batholith

Weighted average of 18 specimens taken at intervals across

Average of 19 specimens taken at intervals across batholith

Average of 44 specimens from core between Portland Canal

Average of 16 specimens of quartz monzonite from east border

Average of 5 specimens of oligoclase quartz monzonite from

Average of 5 specimens of granodiorite from core, vicinity of

Average of 5 specimens of quartz diorite from west half along

Average of2specimens of diorite from core along StikineEiver. 

Average of 6 specimens of granodiorite from west side along

Average of 7 specimens of granodiorite from core along PortAverage of 6 specimens of quartz monzonite from core along

Oligoclase or 

andesine

40.5

46

46

44

37.3

31

50

61

52 

49

46.5

33

43

2 2

 S !s 

o

PW

24

20

1Q

2

21.6

32.7

37

17

2

2.5 

20

15

32

37

aa <y

22.7

22

22.5

20

20

24.5

30

21

18.5

2 

20

21.5

22

18

Hornblende

5 8

3.5

6

6

.1

0

5

11

22 

3.5

9

7

 +3 S

O

S

.5

7 1

5

12

7

4

1.5

5

6.5

20 

6.5

6

4

1

Accessories

2-

1.2

1.5

1+

1.4

1.5

.5

2

1

1.5 

1

2

2

1

0 Furnished by W. B. Jewell.

It is interesting to note that the intrusive rocks of the Coast Range, 

in the Atlin district of British Columbia, far to the northwest, on the 

eastern border of the batholith, are described by Cairnes 16 as granodiorite or quartz monzonite. An analysis of a specimen described by 

Cairnes as typical is quoted below. It is on the border line between 

a granodiorite and a quartz monzonite.

10 Cairnes, D. D., Portions of the Atlin district, British Columbia : Canada Dept. Mines 

Mem. 37, pp. 57-59, 1913.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 181 

Analysis of granodiorite from the Atlm district, British Columbia

Analysis

SiOj...... ... .......... ............

AlaOs - ...... .......... ......... ...

FeO................. .................

MgO...................... ...........

OaO.......... . -.... . .-..

NasO . .................

KtQ.......... ........................

HiO at 110° C.. ........ ..............

HjO above 110° C. . ..................

TiOs...... ....... .... .................

P|05~- ----- -~ ...................

MnO.... ............................

....... 69.08

....... 13.93

....... 2.72

....... 1.62

....... .80

....... 3.38

....... 3.55

....... 3.99

....... .03

....... 1.05

....... .23

....... .07

___ Trace.

100.45

Norm

Quartz ...............................

Orthoclase.. _____________ .

Albite................................

Anorthite ______ ____ .

Magnetite ______________ .

Ilmenite... _____________ .

........ 26.22

........ 23.35

........ 29.87

........ 10.6ft

........ 4 81

........ 3.94

........ .4ft

In summary, the meager data on the Coast Range batholith suggest 

that for 150 miles between Portland Canal and Stikine Eiver there 

is a pronounced variation in the composition across the batholith 

from southwest to northeast. The southwest border facies of the 

batholith, in a belt 5 to 15 miles wide, is quartz diorite; the core, 15 

to 25 miles wide, has the average composition of a granodiorite and is 

composed predominantly of granodiorite, quartz monzonite, ajnd 

quartz diorite; and the eastern border facies, 10 to 15 miles wide, is 

quartz monzonite. Dolmage,17 however, in describing about 150 miles 

of the Coast Range batholith to the south of Portland Canal, writes: 

" These more acid types [granodiorite and quartz monzonite] show a 

general tendency to lie toward the central part of the batholith, but 

there are exceptions to this." The changes from one type of rock 

to another appear to take place rather abruptly, but no evidence of 

brecciation of one variant by another was seen, except in the small 

masses of gabbroic and ultrabasic rocks. Nevertheless, certain features suggest that we may be dealing with a group of very closely 

related interlocking batholiths.

WRANGELL-REVILLAGIGEDO BELT OF METAMORPHIC ROCKS

The Coast Range batholith is paralleled on the southwest by a belt 

of injection gneiss, crystalline schist, and phyllite intruded by abundant batholiths, stocks, sheets, and dikes, believed to be outlying 

masses genetically associated with the main batholith. This belt will 

be designated here the Wrangell-Revillagigedo belt of metamorphic 

rocks. It is narrow and loses its individuality at the north but widens 

and is very well defined toward the south. Near the mouth of 

Gastineau Channel and west of Thomas Bay this belt has a width of 

about 13 miles; opposite the mouth of Stikine River, about 25 miles;

17 Dolmage, Victor, Coast and islands of British Columbia between Douglas Channel and. 

the Alaskan boundary : Canada Geol. Survey Summary Kept, for 1922, p. 16A, 1923.
182 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

and at the south end of Eevillagigedo Island, about 35 miles. This 

composite belt of sedimentary and intrusive rocks appears to swing 

from a northwest strike northwest of the Cleveland Peninsula to a 

north-south strike south of the peninsula. But this apparent change 

in strike is due essentially not to a change in the general strike of- the 

formations but to the fact that at the south the intrusive rocks, including both the main batholith and the outlying stocks, have worked 

over farther to the west.

Within this belt about half the siliceous intrusive rocks are hornblende-biotite-andesine-quartz diorite with only a trace to 2 per cent 

of potassic feldspar, and half are hornblende-biotite-andesine granodiorite with usually 7 to 12 per cent of potassic feldspar. The average composition of 20 specimens from this belt is given in the table 

on page 188. The differences between these outlying intrusive rocks 

and the quartz diorite of the western border of the batholith are 

slight. The percentage of andesine, biotite, and quartz is practically 

the same; the potassic feldspar is considerably higher in the intrusive rocks of the Wrangell-Kevillagigedo belt, and the hornblende 

somewhat lower.

There appears to be a regional variation in the potassic feldspar 

content of the intrusive rocks, most of those between Cleveland 

Peninsula and Windham Bay being on the border line between 

quartz diorite and granodiorite and those in the vicinty of the north 

end of Kevillagigedo Island being quartz diorite. The average composition of 13 specimens of granodiorite and quartz diorite between 

Cleveland Peninsula and Windham Bay is given in the table as 

No. 2, and that of 7 specimens of quartz diorite from the Cleveland 

Peninsula and the vicinity of the north end of Kevillagigedo Island 

is given as No. 3. North of Windham Bay quartz diorite is again 

common.

There are more than a score of small stocks and sheets of hornblendite distributed throughout this belt. The hornblendite is usually cut to pieces on the borders by diorite or granodiorite intrusions. 

A few masses of dunite, pyroxenite, and peridotite are also present.

Distributed through the entire length of this belt are small stocks, 

sheets, and dikes of granodiorite and quartz diorite which are relatively very low in ferromagnesian minerals and usually higher in 

sodium, and all of them show an intense state' of alteration of similar 

character. The plagioclase is usually an oligoclase and if unaltered 

would range usually from 60 to 70 per cent; the potassic feldspar is 

microcline or microperthite and ranges from a trace to 12 per cent; 

the quartz ranges from 20 to 30 per cent. Hornblende is either 

absent or present only as an accessory mineral. Biotite usually 

ranges from 4 to 6 per cent. The plagioclase is partly replaced by a
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 183

latticework of muscovite plates and by irregular grains of epidote 

and occasional zoisite. The biotite and potassic feldspars are practically fresh and unaltered or unreplaced. Calcite is abundant in 

some masses and absent in others.

PRINCE OF WALES-CHICHAGOF BELT

West of the Wrangell-R'evillagigedo belt and parallel to it is the 

Prince of Wales-Chichagof belt, in which intrusive masses are 

common but of different character, and the country rock consists 

predominantly of slate, limestone, graywacke, greenstone, and 

dynamically metamorphosed schistose rocks, with locally some crystalline schist and marble. The stage of metamorphism in general is 

much less advanced than in the Wrangell-Revillagigedo belt, though 

locally, adjacent to large igneous bodies, it may be intense.

This belt includes Chichagof Island, Admiralty Island except the 

northeastern part, the west side of Lindenberg Peninsula, the southwestern part of Mitkof Island, the east side of Zarembo Island, all 

of Etolin Island except the northeast end, and the northern and 

eastern parts of Prince of Wales Island. It is 40 miles wide at the 

north, but may not be much more than 5 miles wide on Kupreanof 

Island; it widens on Etolin Island and is about 25 miles wide through 

Prince of Wales Island.

The igneous masses consist predominantly of hornblende-andesine 

diorite and monzodiorite and quartzose variants of these rocks. 

Hornblende diorite predominates. A few large masses of younger 

granite are present in the southern part. Granodiorite and quartz 

diorite occur as variants of the predominant less quartzose masses 

and here and there as separate stocks. A few masses of ultrabasic 

rocks are present. Locally, the diorite grades into hornblendite and 

gabbro as marginal variants. Throughout this belt there are local 

marginal variants of the albite or albite-oligoclase type of diorite, 

monzodiorite, granodiorite, and quartz diorite, as well as dikes of 

albite and albite-oligoclase trachyte. Thus though certain types of 

intermediate igneous rocks predominate in this belt, extreme differentiates, such gabbro and gabbroic hornbjendite on the one hand and 

albite varieties of diorite, monzodiorite, and quartz diorite on the 

other, are common. The rocks of this belt thus differ in general 

from those to the east in that they are predominantly diorite rather 

than quartz diorite and that differentiates of highly contrasted composition are more abundant.

The average composition of 65 specimens from this belt is given 

in the table on page 188 as No. 4. The younger granites are not 

included here. The average is that of a quartzose hornblende diorite

6137 29 13
184 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

with considerable potassic feldspar. As contrasted with the average 

composition of the rocks in the belt to the east, it shows a very 

marked decrease in quartz and biotite and a very marked increase 

in the amount of hornblende almost to the exclusion of biotite; the 

total content of ferromagnesian minerals is considerably higher, and 

magnetite and pyroxene are the predominant accessory minerals. 

About half of the rocks studied were diorite; the rest were equally distributed between monzodiorite, quartzose diorite, quartzose monzodiorite, granodiorite, and quartz diorite.

As in the Wrangell-Kevillagigedo belt, there is in a very general 

way a greater proportion of potassic feldspar in the rocks of a certain portion of the belt that includes the western parts of the Lindenberg Peninsula and Mitkof Island and the southern part of Admiralty Island. The rocks here are predominantly monzodiorite or its 

quartzose variants, whereas to the north and south' within the Prince 

of Wales belt the predominant rocks are diorite or quartzose variants. 

The stock at Copper Mountain, Prince of Wales Island, is an exception to this grouping. The average composition of 27 specimens 

from Prince of Wales and Etolin Islands is given in the table as No. 

5. The average of 6 specimens from Kupreanof, Mitkof, and southern Admiralty Islands is given as No. 6. The data from the northern 

islands are not so extensive as those from the southern part of the 

belt, but they indicate a much higher content of potassic feldspar 

and lower content of ferromagnesian minerals.

Wright 18 describes the main intrusive rock of the Kasaan Peninsula as a quartz-bearing diorite with the following characters:

The quartz is scarcely more than an accessory, generally forming not more 

than 5 per cent of the mass. Orthoclase appears in about the same amount. 

Plagioclase, which makes up 50 to 70 per cent of the rock, is basic andesine, 

ranging chiefly from Ab3An3 to AbiAni. The range of the composition of the 

individual plagioclase crystals is about the same. For this reason zoning is not 

pronounced. Twinning according to both the albite and the Carlsbad laws is 

very common in the plagioclase. Hornblende is everywhere present, constituting 

10 to 25 per cent of the weight of the rock. It is the common variety; it is pleochroic in various yellow-greens; it is optically negative, showing a large optic 

axial angle; its maximum extinction angle, measured from the trace of the 

cleavage, is from 20° to 25°, corresponding to an angle of 15° to 20° on (010) ; 

and its indices of refraction are considerably higher than those of other 

recorded measurements; namely, from 1.665 to 1.680, determined by the immersion method. Some fades of the diorite contain about 15 per cent of yellowbrown or orange-brown biotite. The rock contains small amounts of augite 

less than 10 per cent. The minor accessories are apatite, titanite, and magnetite. * * *

18 Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

Alaska: U. S. Geol. Survey Prof. Paper 87, pp. 74, 75, 1915.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 185

Near some of its margins the diorite becomes basic and passes into gabbro, 

the hornblende giving place to augite and the plagioclase becoming richer in 

lime. Specimens from the mines and prospects north of Karta Bay illustrate 

this transition.

In addition to the predominant diorite and its local gabbroic 

variants just described, there are large masses and dikes of diorite, 

quartz diorite, and monzodiorite with albite or albite-oligoclase as 

the predominant plagioclase in place of andesine. The large masses 

occur principally as differentiation variants of the dioritic magma. 

The sodic variants, however, occur principally as dikes of porphyritic texture. The Mount Andrew mass on Kasaan Peninsula appears to be prevalently an albite-oligoclase-hornblende monzodiorite.

A great many batholiths and stocks of Upper Jurassic or Lower 

Cretaceous intrusive rocks are found on Prince of Wales Island. The 

types of rock forming the intrusive masses in the vicinity of Copper 

Mountain and Kasaan Peninsula have been described in detail by 

Wright and Merwin. 19 The main Copper Mountain and Beaver 

Mountain batholiths range in composition from granodiorite to monzodiorite, with a very local development of gabbro. Near the contact the masses are locally syenitic or more sodic. The igneous 

mass exposed along the coast between Skowl Arm and Cholmondeley 

Sound is in general a quartzose hornblende diorite, as exemplified by 

the average mineral composition of six specimens, given in the table 

as No. 7. The mass is heterogeneous and comprises local variants 

of hornblendite, diorite, and granodiorite. The Kendrick Bay 

igneous mass is likewise a quartzose hornblende diorite with local 

marginal variants toward diorite. The average composition of four 

specimens is given as No. 8. In the more hornblendic and less 

quartzose diorites there is a relative concentration of apatite and 

magnetite. The apatite forms more than 1 per cent and magnetite 

more than 2 per cent of the rock.

At the head of Brownson and Nichols Bays there is a mass of 

highly siliceous quartz diorite with diorite as a local marginal 

variant.

Chichagof Island appears to resemble Prince of Wales very closely 

in its geology. The prevailing country rocks, except on the southwest coast, are the same and are in a similar stage of metamorphism, 

and the predominant intrusive rocks and range of variants are likewise similar. The chief intrusive rock on Chichagof Island is hornblende-andesine diorite. Of 30 samples collected from various parts 

of the island, more than half were diorite. The other common types 

are hornblende-biotite-quartz diorite and granodiorite. Locally

18 Idem, pp. 33-37, 74-84.
186 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

there are developed alkalic siliceous marginal variants and dikes of 

albite-quartz diorite, oligoclase granodiorite with sparse ferromagnesian minerals, or highly hornblendic gabbro-diorites. These variants, however, are small in volume. Masses of hornblendite, bronzitite, and norite are also found on the main island and the islands 

off its west coast. The average approximate mineral composition 

of 30 specimens (18 diorite, 6 quartz diorite, 4 granodiorite, and 2 

gabbro-diorite) from Chichagof Island is given in the table on 

page 188 as No. 9. The plagioclase commonly ranges from 50 

to 75 per cent, potassic feldspar from 0 to 10 per cent, quartz from 

0 to 30 per cent, hornblende from 0 to 40 per cent, biotite from 0 to 

10 per cent, and magnetite from a trace to 4 per cent.

The area from Lynn Canal and Chilkat Inlet west to the Pacific 

Ocean, with the possible exception of the eastern part, probably lies 

within the Prince of Wales-Chichagof belt. Wright 20 reports 

granodiorite and diorite as the predominant types in the Glacier 

Bay region.

KUIU-HECETA BELT

The Kuiu-Heceta belt includes the western fringe of the north 

half of Prince of Wales Island, the north end of Dall Island, San 

Fernando, Heceta, Tuxekan, Kosciusko, and Kuiu Islands, Kupreanof Island with the exception of the Lindenberg Peninsula, and 

the southwestern part of Admiralty Island. This belt is somewhat 

elliptical in shape, as it includes the parts of the Prince of WalesChichagof belt on the east and of the Dall-Baranof belt on the west 

in which intrusive rocks are relatively sparse and the degree of metamorphism is correspondingly slight. The stage of metamorphism of 

the pre-Tertiary rocks in this belt is less than in any other area in 

southeastern Alaska. Many of the oldest beds contain great numbers 

of comparatively well preserved fossils.

Near the head of Washington Harbor, Kuiu Island, and at the 

north end of the west side of Kupreanof Island there are masses of 

augite gabbro. The stock on Marble Island, Davidson Inlet, has 

not been studied.

DALL-BARANOF BELT

The Dall-Baranof belt includes Dall, Forrester, Suemez, Baker, 

Lulu, Noyes, Warren, Coronation, and Baranof Islands. Within 

this belt stocks and batholiths are more numerous than in the adjoining Kuiu-Heceta belt, and the composition of the more common

20 Wright, F. E. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript).
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROOKS 187

intrusive rocks appears to differ from that of the prevailing types 

in the Prince of Wales-Chichagof belt. But here again our knowledge of the composition and relations of the intrusive masses is 

scanty, and any inferences drawn need further substantiation.

The average composition of 21 specimens (13 quartz diorite, 4 

granodiorite, 3 diorite, and 1 gabbro-diorite) exclusive of ultrabasic 

types, collected at different points within the belt, is given as No. 10. 

The rocks, on the average, are much more siliceous and carry less of 

ferromagnesian. minerals than the average of the Prince of WalesChichagof belt and are slightly more feldspathic and carry less of 

ferromagnesian minerals than the average of the Wrangell-Revillagigedo belt.

On Baranof Island highly mashed hornblende diorite and hornblende gabbro occur on Bear Lake and Silver Bay; serpentine .on 

the north side of Red Bluff Bay; and amphibolite with associated 

nickeliferous pyrrhotite on Snipe Bay. On Dall Island augite diorite and gabbro occur near Squaw Mountain.

There is a wide variation in the types of intrusive rocks, but 

quartz diorite and to a less extent granodiorite are predominant. 

The quartz diorite varies from a leucocratic type, which contains less 

than 5 per cent of ferromagnesian minerals (mostly biotite), 60 to 

65 per cent of plagioclase (oligoclase or oligoclase-andesine), and 

30 to 35 per cent of quartz to quartzose hornblende-andesine diorite. 

Leucocratic oligoclase granodiorite also occurs.

On Dall and Suemez Islands moderately to coarsely crystalline 

schists are restricted to the immediate vicinity of the intrusive masses.

But few data on the rocks of Baranof Island are available. Of 

seven specimens from the larger masses, all except one were quartz 

d,iorite; the exception is an oligoclase granodiorite of leucocratic character. The rocks are peculiar (see table on p. 188, No. 11) in their 

low percentage (8.5) of ferromagnesian minerals.

The intrusive mass on Baker Island is a leucocratic quartz diorite 

composed of about 30 per cent of quartz, 65 per cent of plagioclase 

(oligoclase or oligoclase-andesine), and 5 per cent of less of biotite 

and accessory minerals. Warren Island is composed of hornblende 

or biotite granodiorite with about 10 per cent or so of potassic feldspar, 50 per cent of andesine, and 22 per cent of quartz. A small 

intrusive mass on Indiada Island, in Santa Cruz Harbor', Suemez 

Island, is a quartzose feldspathic hornblende diorite. A specimen 

from the south side of Lulu Island is a very highly feldspathic (90 

per cent andesine) hornblende diorite.
188 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Approximate average mineral composition of tlie Upper Jurassic or Lower 

Gretaoeous\ intrusive rocks in the Alexander Archipelago

1

2

3

4

5

6

7

8

q

10

11

Locality

WRANGELL-REVILLAGIGEDO BELT

Average of 20 specimens distributed throughout the

belt..............................................

Average of 13 specimens taken between Cleveland

Average of 7 specimens from vicinity of northern

PRINCE OF WALES-CHICHAGOF BELT

Average of 65 specimens from Prince of WalesChichagof Belt ......................... ........

Average of 27 specimens from Prince of Wales and

Etolin Islands ____________________

Average of 6 specimens from Kupreanof, Mitkof,

Average of 6 specimens, Skowl Arm to Cholmondeley

Average of 4 specimens from Keudrick Bay, Prince

DALL-BARANOF BELT

Average of 21 specimens distributed throughout the

belt............ ..... .. . .............

ndesine

^

54

51.5

60

57.5

55

63

58.5

67

58.5

62

62

feld- otassic 

spar

PH

6.5

9

1.5

5

6

16

4

0

3

5.5

5

 e'

a

O31

19

19

19

9.5

9

5

9

9

11

20

83.5

ornblende

B

8

8 '

9

20.5

20

11

25

20

21

6.5

' 3.5

o

W

11' 5

11.5

10.5

3.5

4

3

1

1

4

3.5

5

yroxene

PH

1.5

3.5

.5

[agnetite

£

2

2

2

2

2

ccessories

^

1

1

.5

.ft

'f,- -

ft

1

5

2

1

ROCK TYPES

ULTRABASIC GROUP

GENERAL FEATURES

The ultrabasic and gabbroic rocks in southeastern Alaska are relatively sparse compared with the great volume of more siliceous and 

alkalic siliceous intrusions, but they are, nevertheless, widely distributed throughout the Alexander Archipelago and near the western border of the mainland batholith. Taken together, they form 

a very considerable volume, and there is no doubt that there are a 

great many masses which have not been reported. They are important economically because of the local association of ilmenitic 

magnetite with the diallagite or hornblende-augite varieties and of 

pentlandite and chalcopyrite-bearing pyrrhotite with certain of the 

norite, amphibolite, bronzitite, and troctolite varieties.

The ultrabasic group includes such types as dunite, pyroxenite, 

hornblendite, peridotite, troctolite, saxonite, wehrlite, and probably 

many others. More than a score of stocks and sills of ultrabasic rock 

have been found along the coast line of a northwest-southeast belt 

about 200 miles in length and 50 miles in width, paralleling a straight 

line drawn between Ketchikan and Juneau. These masses range in 

size from sheets 100 feet thick, intruded parallel to the cleavage of the 

inclosing schist, to stocks 2 or 3 miles in diameter.
UPPEE JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 189

Ultrabasic rocks have been noted by the writer as follows: Hornblendite on the north side of the entrance to Taku Harbor; hornblendite and hornblende-pyroxenite with ilmenitic magnetite ore 

bodies on the north end of the Snettisham Peninsula at Snettisham; 

saxonite on the north side of Tracy Arm, about 7 miles east of the 

first elbow, and pyroxene hornblendite on the south side, about southeast of the saxonite; dunite near the head of the east arm of Fords 

Terror, on the south side; hornblendite with many widely divergent 

pegmatitic variants on the Midway Islands; hornblendite at Point 

Lookout and south of Point League; hornblendite and pyroxenite on 

the north side of Windham Bay, about 3 miles east of Point Windham} hornblendite at the mouth of Shuck River, on the west side; 

hornblendite on the south side of Port Houghton, at the west side 

of the entrance to Walter Island Arm; hornblendite at the east side 

of the entrance to Portage Bay; hornblendite, dunite, wehrlite, and 

pyroxenite in the vicinity of Kane Peak, Kupreanof Island; hornblendite southeast of Frederick Point, Mitkof Island, and on the 

Sukoi Islets; hornblendite with disseminated sulphides at Circle Bay, 

on the south side of Woronkofski Island; hornblendite in patches 

along Zimovia Straits; dunite and pyroxenite on the Blashke Islands; 

pyroxenite with titaniferous magnetite on the east side of Union 

Bay, Cleveland Peninsula; and a dike of troctolite near Funter Bay, 

Admiralty Island.

In the Ketchikan district the occurrences of ultrabasic rocks are 

reported by Chapin 21 as follows: Pyroxenite with titaniferous magnetite on the east side of Union Bay, Cleveland Peninsula; peridotite 

in the mountains on the west side of Helm Bay; pyroxenite at the Salt 

Chuck mine, at the head of Kasaan Bay, Prince of Wales Island; 

peridotite and pyroxenite on the Percy Islands, Duke Island, Cat 

Island, Annette Island near Metlakatla, and the south end of Sukkwan Island.

Northwest of Juneau, according to Knopf, hornblendite occurs near 

Herbert Glacier, in the Eagle River area,22 and about 2 miles north 

of the mouth of Johnson Creek, in the Berners Bay area,23 and 

highly hornblendic gabbro, hornblendic pyroxenite, and augitic hornblendite, locally associated with considerable titaniferous magnetite, 

occur on Chilkoot Inlet and the adjacent mountains near Haines,24

21 Chapin, Theodore, unpublished report on the Ketchikan district.

22 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, p. 25, 1912.

23 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, pp. 25-26, 1911.

24 Knopf, Adolph, The occurrences of iron ore near Haines: U. S. Geol. Survey Bull. 

442, pp. 144-145, 1909.
The Wrights 25 report hornblendite, pyroxenite, and basic gabbro 

as different facies of a gneissoid body on the west side of Dixon 

Harbor.

On Chichagof Island Knopf 26 noted a mass of hornblendite at the 

head of Port Althorp; Overbeck 27 noted hornblendite on Lisianski Strait near Miner Island and gabbro (norite) near Nickel and 

on Lisianski Strait north of Canoe Pass; the writer 28 has noted norite, 

bronzitite, and hornblende gabbro at Bohemia Basin, Yakobi Island, 

and hornblendite at the Apex-El Nido property, on Lisianski Inlet.

On Baranof Island the only masses of ultrabasic rock so far reported are amphibolite on Snipe Bay and serpentine on Ked Bluff 

Bay.

A specimen collected from Mount Cook, in the St. Elias Kange, by 

I. C. Russell, is reported by Williams 29 to be troctolite.

DUNITB

The true dunite consists almost wholly of olivine with an accessory 

opaque spinellid mineral, possibly pleonaste or magnetite. The 

dunite rocks weather typically with a pale reddish to yellowish hue 

and have the appearance of a very uniform fine grain. On fresh 

surface they range from olive-gray to yellowish gray. Locally, 

partial alteration to serpentine or talc has occurred, and on Tracy 

Arm the olivine contains abundant needles of secondary tremolite. 

A mass of serpentine occurs on the north side of Ked Bluff Bay, 

Baranof Island. Gradations between dunite and pyroxenite are 

found, both hypersthene and augite occurring in association with the 

olivine.

A stock of differentiated ultrabasic rocks forms the core of the 

Blashke Islands, in Clarence Strait. This stock deserves a more 

detailed examination, as it is easy of access, is well exposed, and 

exemplifies a striking case of magmatic differentiation within this 

type of rock. A cursory examination seems to indicate that the 

essential features are a core of dunite about a mile in diameter with 

an encircling ring of pyroxenite and an outer border of hornblende 

gabbro-diorite. The two rings of pyroxenite and hornblende gabbrodiorite are together roughly about three-eighths of a mile wide,

25 Wright, F. E. and C. W., A geologic reconnaissance of Glacier and Lituya Bays (unpublished report).

28 Knopf, Adolph, The Sitka mining district, Alaska : U. S. Geol. Survey Bull. 504, p. 15, 

1912.

27 Overbeck, R. M., Geology of the west coast of Chichagof Island: U. S. Geol. Survey 

Bull. 692, pp. 109-112.

28 Buddington, A. F., Mineral investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, pp. 101-102, 118, 1925.

28 Williams, G. H., Notes on some eruptive rocks from Alaska: Nat. Geog. Mag., vol. 4, 

p. 68, 1892.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 191

though accompanied by outlying masses of diorite in the adjacent 

sediments. No evidence of one rock intruding another was noted, 

but the gradations must be abrupt. The dunite is relatively less 

resistant to weathering and erosion than the gabbro-diorite and 

pyroxenite. As a result a most striking and peculiar phenomenon has 

arisen. A basin has been worn out of the dunite and is occupied by a 

salt lake. The rim rock of the basin is the pyroxenite and gabbrodiorite, through which there are three gorgelike entrances to the 

basin. The tide rushes in and out through these narrows with great 

velocity, and they constitute three "salt chucks" or "skookum 

chucks."

Around this salt lake the fresh dunite is dark yellowish olive-green, 

fine grained, and close jointed with ,a fissile and platy structure. 

Many of the joint surfaces are coated with a thin film of magnesite or 

dolomite. In thin section a specimen from the east side of the salt 

lake is found to consist exclusively of olivine in a state of partial 

alteration to serpentine, with about 3 per cent of idiomorphic opaque 

pleonaste octahedra.

The pyroxenite is a dark-green granular rock. In thin section a 

specimen from the north side of the stock is found to consist predominantly of monoclinic pyroxene with about 17 per cent of hornblende, 12 per cent of olivine, and a little hypersthene. The hornblende is mostly secondary after the pyroxene.

The gabbro-diorite is a medium-grained dark rock of mottled 

appearance, composed predominantly of black hornblende with .associated white plagioclase. A specimen from the northeast corner of 

the salt lake was found on microscopic examination to consist of 61 

per cent of hornblende, 30 per cent of plagioclase (andesine-labradorite), 6 per cent of pyroxene, and 3 per cent of titaniferous 

magnetite.

The intrusive mass lies within a belt of Silurian greenstone. A 

storm prevented the writer from examining the southeastern part of 

the islands, but the geology of the northwestern part suggests that 

the mass is encircled by a ring of the graywacke-slate formation 

which stratigraphically underlies the greenstone. Hence it is concluded that the magma was forced upward as a plug, doming the 

overlying rocks and shoving the beds to one side. Dikes of diorite 

are common in the surrounding rocks. The sedimentary beds have 

been baked to dense, hard rocks and the hornblende andesitic greenstones altered to epidote-hornblende rocks as a result of the intrusion.

At the head of Fords Terror, on the mainland, Juneau district, on 

the south side of the east arm at the bend where the coast turns 

north, there is a mass of dunite with associated highly hornblendic 

gabbro. These ferromagnesian rocks are intruded and brecciated by 

quartz diorite and granitic pegmatite veins. The dunite consists
192 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

almost wholly of olivine and secondary talc with accessory hypersthene and secondary magnetite. The talc is in part in well-crystallized plates and in part in fibrous aggregates. Veinlets of fibrous 

tremolite traverse the dunite.

On Kupreanof Island the range of hills south and southwest of 

Cape Strait is composed of igneous rocks. Kane Peak itself and 

the mountains to the west appear to be of monzodioritic character, 

but on the southeast flank of Kane Peak there is a very conspicuous 

bare reddish-brown area visible from Frederick Sound. This color 

is due to the oxidation and weathering of ultrabasic rocks comprising pyroxenite and dunite and intermediate gradations between 

these two types. A core of pyroxenite is encircled along the south 

and east sides by a border of dunite and wehrlite. Kock^ of this 

character also appear within the outer borders of ,tne pyroxenite ,in 

vertical dikes or dikelike forms. The pyroxenite forms a bare nubbin with very steep cliff faces and is marked by bouldery spheroidal 

weathering. A long vein which weathers bright red and another 

which weathers brown occur in the pyroxenite; this coloring is probably due to sparse disseminated sulphides. The pyroxenite consists 

of a granular aggregate of pale-green diallage. On the north side 

of the pyroxenite core, along the shores of Frederick Sound for 114 

miles southeast of Cape Strait, hornblendite appears to be the predominant rock. A specimen of the subalkalic rock from Kane 

Peak near the pyroxenite mass along its western border is a hornblende-pyroxene monzodiorite, a very peculiar variant of the normal 

monzodiorites. It has probably resulted from partial reaction of 

normal intrusive monzodiorite with pyroxenite. A specimen of 

dunite just southeast of Cape Strait is a very dark rock which on 

fresh surfaces shows a mottling of black and dull greenish-yellow. In 

thin section it is found to consist of granular olivine altered to 

serpentine clouded with black opaque magnetite dust. A trifle of 

talc is also present. A specimen of wehrlite from Kane Peak, near 

the pyroxenite mass on its south side, consists of about 78 per 

cent of olivine, 20 per cent of monoclinic pyroxene, and 2 per cent 

of magnetite. The rock is fresh and wholly unaltered.

SAXONITE

On the north side of Traey Arm, about 7 miles ea^t of the first 

elbow, is a. small point about 3^ miles west of another conspicuous 

elbow. In the inner bend on the east side of the point is an exposure of ultrabasic rock that has weathered yellowish to reddish 

brown. The fresh color is yellowish gray to olive gray. About 500 

yards is exposed, though included beds of gneiss or intrusive sills of 

quartz diorite occur. The rock is fissile and is traversed locally
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 193

by closely spaced veinlets of white fibrous tremolite from a quarter 

of an inch to 6 inches wide. Films of serpentine coat the joint planes. 

Microscopic examination of a specimen shows it to be a variety of 

peridotite called saxonite, consisting of about two-thirds olivine, onethird orthorhombic pyroxene, and a small percentage of magnetite. 

The hypersthene contains rounded inclusions of the olivine. The 

magnetite occurs in part as disseminated grains and in part as 

dust and dots throughout the olivine and pyroxene. The rock is 

practically unaltered, except for abundant tremolite needles in the 

olivine. Some specimens show flakes of talc visible in the hand 

specimen.

PYROXENITB

The pyroxenites include varieties made up of a monoclinic pyroxene composed almost wholly of the diopside molecule or of a monoclinic pyroxene composed of diallage with a percentage of an aluminous and ferric iron molecule and locally in association with the 

norite of the orthorhombic pyroxene bronzite. The diopside and 

diallage pyroxenites are light to dark green granular rocks. The 

bronzitites are of a prevailing bronze color.

The diopside pyroxenites are associated with the dunite and other 

olivine-rich rocks; the diallagites are associated with hornblendite 

and gabbro. So far as studied in this region, magnetite with a 

little associated ilmenite occurs in marked magmatic concentrations 

and segregations entirely with the diallagites and hornblende-augite 

rocks, the latter usually associated with hornblendite. Apatite tends 

to be markedly concentrated in many of the hornblendites and hornblende-augite rocks, and pyrrhotite with a little associated pentlandite 

and chalcopyrite is concentrated in the norite, hypersthenite, hornblendite, troctolite, and gabbroic rocks.

A large mass of pyroxenite of the diallagite variety crops out 

along the east side of Union Bay, on the Cleveland Peninsula, from 

the saltery north to the head of the cove on the east side of Union 

Point. The pyroxenite is a medium-grained granular dark-greenish 

rock, locally with a gneissic structure as the result of flowage, 

Coarse pegmatite veins are present, some of which are gabbroic to 

highly feldspathic. Dikes of intrusive diorite cut the pyroxenite. 

In thin section the pyroxenite is seen to consist almost wholly of 

pyroxene with a variable amount of ilmenitic magnetite. A trifle of 

the magnetite occurs as minute inclusions in the pyroxene, but most of 

it is present as large grains with the borders molded against the 

pyroxene and with projecting points or threads interstitial to the 

pyroxene. Some pyroxenite boulders, presumably from this mass, 

carry as much as 30 per cent of magnetite. The pyroxene has indices
194 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

of refraction considerably higher than those of diopside and probably 

consists in part of the augite and hedenbergite molecules. A trace 

of green spinel is associated with the magnetite.

The ultrabasic rocks north of Karta Bay in which the palladiumcopper ores of the Salt Chuck mine occur have been described by 

Wright 30 and by Mertie. 31 Mertie describes the country rock as

in general a pyroxenite, with gabbroic and gabbro-pegmatitic phases. * * * 

The chief rock-forming mineral is augite, and the subordinate constituents are 

biotite, iron oxides, plagioclase, apatite, and titanite, though not all of these 

are invariably present in any one specimen.

Merwin describes one facies of this mass as consisting of about 55 

per cent of augite, 25 per cent of biotite, and 10 to 15 per cent of 

magnetite, and states that the biotite is much later than both the 

augite and magnetite, and the magnetite in part later than the 

pyroxene.

At Cobb's prospect, on Karta Bay the rock consists of about 8 

per cent of biotite, 15 per cent of magnetite, 10 per cent of plagioclase, and 67 per cent of augite. The biotite and plagioclase are 

interstitial to the pyroxene but nearly contemporaneous with the last 

of the pyroxene.

The hornblendite masses are readily recognizable by their rich 

black color on the fresh surface. Locally they weather with a rusty 

reddish-brown hue as a result of disseminated sulphide particles.

The most marked and characteristic feature of the hornblendite 

masses is their wide and abrupt variation in texture and the local 

abundance of pegmatitic facies which may vary widely in composition. Usually the hornblendite ranges from a coarse, massive, evengrained rock with individual grains a centimeter or so in diameter 

to a rock in which the hornblende crystals are conspicuously columnar 

with a length of several millimeters and a diameter of a millimeter. 

In the finer-grained rock a gnessic structure is usually present as a 

result of the rough parallel orientation due to flowage. Locally the 

mass may be composed of hornblende in crystals averaging 6 inches 

in length and 2 or 3 inches across.

In a few places, hornblendite masses have developed as marginal 

facies to monzodiorite, quartz diorite, granodiorite, or diorite.

The hornblende is variable in composition, as is indcated by the 

variation in the indices of refraction, which are the same as those of 

the hornblende in the diorites a from 1.650 to 1.680 and y from 1.672 

to 1.700. Hornblendites are common members of the Upper Jurassic 

or Lower Cretaceous intrusive rocks west of the main batholith.

30 Wright, C. W., U. S. Geol. Survey Prof. Paper 87, p. 75, 1915.

31 Mertie, J. B., Lode mining in the Juneau and Ketchikan districts: U. S. Geol. Survey 

Bull. 714, p. 122, 1921.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 195

A chemical analysis of hornblende from hornblendite on Knight 

Inlet is given in a report by Bancroft. The analysis' of hornblende 

from hornblendite on Vancouver Island has been calculated by Clapp 

from an analysis of the rock. These analyses are given in the table 

below, together with the composition obtained by averaging the two. 

This average probably closely approximates the composition of the 

hornblende of the hornblendites under discussion.

Chemical composition of hornblende in, hornblendite

SiOa . . ................

AlaOj.--. ....... ...... ...

FeaOs. - ... -

FeO. ....................

TiOa.. ...................

CaO. ....................

1

41.0

14.6

4.1

10.5

2.7

11.6

2

42.8

14.6

3.3

7.3

1.1

11.4

3

42.0

14.6

3.7

8.9

1.9

11.5

MgO............... ......

KS 0. ....................

NazO.------ .............

HaO. ....... .............

PzOi. ....................

1

13.2

.4

2.7

2

14.9

1.1

1.9

.5

.8

3

14.0

.8

2.3

1. Analysis of hornblende from hornblendite about 2 miles beyond the Aknuati Valley on the north 

shore of Knight Inlet, B. C. Analyst, W. B. Campbell. Bancroft, J. A., Geology of the coast and islands 

between the Strait of Georgia and Queen Charlotte Sound, B. C.: Canada Geol. Survey Mem. 23, p. 87, 

1913.

2. Analysis (calculated) of hornblende from hornblendite northwest of Prospect Lake, southeast end of 

Vancouver Island. Clapp, C. H., Geology of the Victoria and Saanich map areas, Vancouver Island, 

B. C.: Canada Geol. Survey Mem. 36, p. 70, 1913.

3. Average of Nos. 1 and 2.

Biotite, plagioclase, magnetite, pyrite, pyrrhotite, apatite, and 

titanite are the common accessory minerals. Biotite usually occurs 

as hexagonal plates disseminated throughout the rock. It is common as large plates in some of the pegmatitic variants. In feldspathic varieties of the hornblendites or the highly hornblendic gabbros 

the plagioclase is an andesine (Ab65An35 ); but in the coarse pegmatitic facies the feldspar appears to be exclusively an almost pure 

albite. Pyrite and pyrrhotite are variable in amount and give rise 

on weathering to a rusty-brown outcrop. Magnetite shows, in part, 

a tendency to concentrate with the pyroxenitic facies of the hornblendite. Apatite is uniformly more abundant than in any other type 

of the Upper Jurassic or Lower Cretaceous intrusive rocks. Titanite 

is locally very abundant in some of the pegmatitic facies. Epidote 

occurs locally in some of the pegmatitic facies as a primary mineral. 

Epidote, quartz, and calcite occur as secondary minerals.

Each of the minerals albite, orthoclase, and magnetite locally occurs 

in the form of veins in the hornblendic rocks. Plagioclase is usually 

present, and with an increase in this mineral the hornblendite becomes 

feldspathic and grades toward highly hornblendic gabbro.

A coarse-grained granular aggregate, with crystals of hornblende 

that average about 0.5 millimeter in diameter and are as much as 2 

centimeters in length, forms the headlands of Southwest Cove, Etolin 

Island, and crops out along the coast for several miles to the north. 

It consists almost entirely of hornblende with a little interstitial 

feldspar and aggregates of quartz, epidote, and calcite. The horn-
196 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

blende contains many corroded remnants of pyroxene and a few of 

brown biotite.'

Another specimen from the west headland at the south entrance to 

Zimovia Straits consists almost exclusively of hornblende with a 

little biotite and abundant interstitial microscopic accessory apatite 

and crystals of magnetite. The hornblende crystals are about a 

millimeter in diameter and several millimeters in length.

Another facies of the hornblendite is found on the Lindenberg 

Peninsula, Kupreanof Island, about 4 miles northwest of Duncan 

Peaks. The hornblendite here occurs as narrow lenses or sheets near 

the border of a monzodiorite stock. The main mass of hornblendite 

is composed almost wholly of columnar hornblende showing euhedral 

basal sections with disseminated hexagonal crystals of biotite. Near 

the contact with the normal diorite the hornblendite contains abundant phenocrysts of plagioclase which have been completely altered 

to an aggregate of epidote and zoisite with a groundmass of hornblende. In the border zones lenses of normal diorite occur in the 

hornblendite, suggesting that the hornblendite is intrusive into the 

diorite. It appears, however, to grade transitionally into the diorite 

through a gradual increase in the number of plagioclase phenocrysts.

A gabbroic hornblendite consisting of about 80 per cent of hornblende, 18 per cent of plagioclase, and 2 per cent of quartz, magnetite, 

and biotite occurs at the mouth of Fords Terror, on the mainland 

in the Juneau district. It is shattered and cut to pieces by dikes of 

quartz diorite. At the foot of Brown Glacier a highly hornblendic 

rock, possibly of gabbroic origin, forms a shatter breccia with intrusive quartz diorite.

A marginal development of hornblendite from quartz diorite on 

the northwest side of Herbert Glacier, in the Eagle Kiver area, has 

been described by Knopf.32

A hornblendite that occurs about 2 miles north of the mouth of 

Johnson Creek, in the Berners Bay area, has been described by 

Knopf 33 as follows:

The hornblendite is a heavy black rock composed mainly of hornblende. 

Abrupt variations in texture and composition are of general occurrence and 

give the rock a wide range in appearance. The hornblende in places forms 

prisms up to 2 inches in length and is characterized by its brilliant cleavage 

faces and metallic luster on cross-fractured surfaces. Locally feldspar, in part 

converted to epidote, occupies the triangular interstices between the hornblende 

prisms.

About 7 miles east of the first elbow of Tracy Arm, on the south 

side, there is a small mass of pyroxene hornblendite, shattered and

82 Knopf, Adolph, The Eagle River region, southeastern Alaska: TJ. S. Geol. Survey Bull. 

502, p. 25, 1912.

83 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, pp. 25-26, 1911.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 197

reticulated by granitic pegmatite veins. The rock consists of many 

black hornblende crystals about half an inch in diameter in a mediumgrained granular groundmass. In this section the rock is found 

to consist of about 50 per cent of brown hornblende, 5 per cent of 

labradorite, 1 per cent each of quartz and magnetite, and the remainder of pyroxene, including both monoclinic pyroxene and hypersthene, the former about twice as abundant as the latter. The large 

hornblende crystals have abundant corroded inclusions of both 

pyroxenes.

The northern portion of the Snettisham Peninsula, on the mainland, is composed of a mass of diorite and hornblendite about 2% 

miles.in width as exposed along the coast at the entrance of Port 

Snettisham. The eastern 1^ miles of this mass is hornblendite with 

associated variants. The most marked characteristic of this hornblendite mass, as of all the other masses of hornblendite in southeastern Alaska, is the abrupt and extreme variation in its texture. The 

predominant rock, however, is a black medium-grained variety composed almost wholly of hornblende, with accessory magnetite, apatite, and plagioclase. Coarse-grained pegmatitic variants occur 

within the mass and may consist of long columnar hornblende, of 

hornblende and biotite, or hornblende and pyroxene, of pyroxene and 

magnetite, or of magnetite. Occasionally chlorite, in large wellcrystallized plates, is intergrown with the other minerals. Rarely an 

epidote veinlet cuts the pegmatitic veins. The hornblendite is intruded by dikes of diorite and of aplite. Narrow vein dikes of white 

albite occur sparingly, and rarely one composed almost wholly of 

pink orthoclase is found.

About 100 yards east of the first point opposite the post office at 

Snettisham there is a 6-foot vein of practically solid ilmenitic magnetite. The country rock is a medium-grained hornblende pyroxenite, consisting of about 56 per cent of pyroxene, 26 per cent of brown 

hornblende, 14 per cent of magnetite (with ilmenite), and 4 per cent 

of apatite.

A magnetite amphibolite from Snipe Bay, Baranof Island, has 

previously been described by the writer. 34 This amphibolite is associated with nickeliferous pyrrhotite. Only one specimen was examined in detail, and this consisted of 49 per cent of brown hornblende, 39 per cent of ilmenitic magnetite, 7 per cent of plagioclase, 2 

per cent of chlorite, 2 per cent of pyrrhotite, and 1 per cent of apatite.

Magnetite-bearing hornblende-pyroxene rocks and coarsely crystalline gabbro and diorite on Chilkoot Inlet from a point 4 miles south

34 Buddington, A. F., Mineral Investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, pp. 106-107, 1925.
198 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

of Haines to a point 2 miles north of Haines have been described by 

Knopf,35 as follows:

The rock mass exposed along the shore north of Haines is a remarkable 

occurrence geologically. Specimens collected from the finest-textured portions 

show a rock composed of coarsely crystalline aggregate of feldspar, hornblende, 

and pyroxene, throughout which are scattered some visible grains of magnetite. 

The dark minerals (hornblende and pyroxene) make up half the bulk of the 

rock. When examined microscopically the rock is found to consist of an allotriomorphic granular assemblage of plagioclase feldspar (bytownite), hornblende, and augite. Magnetite and apatite are present as accessory constituents 

in unusually large amounts. From this normal type of rock, which would be 

termed a gabbro, abrupt variations in texture and mineral composition are 

encountered. In places the cliffs for hundreds of feet are composed solidly of 

formless hornblende individuals 6 inches long by 3 inches broad. Commonly 

this hornblende rock contains more or less grayish-green augite admixed with 

it and is ramified by coarse white feldspathic dikelets or blotched by masses of 

gabbro. In places it even forms a breccia cemented by such material. Locally 

the hornblendite contains numerous lumps and particles of magnetite. * * * 

Near Fort Seward, which is situated just west of Haines, the rock exposed consists of a coarsely granular aggregate of pyroxene, hornblende, and black mica 

(biotite).

Knopf has described an amphibolite from the vicinity of the 

Crystal mine at Port Snettisham, and gives a chemical analysis. 

He suggests that the rock is the result of alteration of a porphyritic 

basalt, but the writer believes it to be an altered hornblendite. 

Knopf's description 36 follows:

In thin section the rock proves to be composed largely of amphibolite, zoisite, 

and epidote, with subordinate albite, which is largely associated with the epidote 

minerals. The amphibole comprises two varieties, a brown-green strongly pleochroic variety, and a light-green feebly pleochroic variety. Other constituents 

are ilmenite, titanite, chlorite, and muscovite. The chemical analysis of a 

specimen of this rock obtained near the entrance to the upper tunnel of the 

mine is as follows:

Analysis of amphibolite from Port Snettisliam 

[J. G. Faircbild, analyst]

SiO2 _________________ 46.87 H-0+________________ 2.23

AUOs _________________ 15.14 TiOi_________________ 2. 20

Fe2O3 ________________ 3. 87 CO2 ________________ None.

FeO_________________ 8.41 P2O5_________________ .15

MgO________________ 6.10 S ___________________ None.

CaO_________________ 11.27 MnO_________________ .17

Na,O _________________ 3. 02 

KiO _________________ . 30 "' 73

Norm: Albite, 26.2; anorthite, 28.1; orthoclase, 1.7; magnetite, 5.7; ilmeuite, 

4.2; diopside, 24; olivine, 8.0; hypersthene, 2.1.

86 Knopf, Adolph, The occurrence of iron ore near Haines: U. S. Geol. Survey Bull. 442, 

pp. 144-146, 1910.

3a Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, pp. 39-40, 1912.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 199

GABBRO

The gabbroic rocks include hypersthene gabbro or norite, augite 

gabbro, augite-biotite gabbro, and hornblende gabbro. The distinction between gabbro and diorite is in this report based upon the composition of the feldspar rocks with labradorite or more calcic feldspar are grouped with the gabbros. The gabbros are relatively sparse. 

Their association locally with the ultrabasic group of rocks has already been referred to. Small masses, in part isolated, are also 

found.

The only noritic masses so far reported are on Chichagof Island and 

the adjoining islands to the west. Only two masses have been studied, 

and these only in a reconnaissance fashion.

At Bohemia Basin, Yakobi Island, about 2^4 miles southwest of 

Miner Island, there is an elliptical mass of gabbroic rock about 1% 

miles wide and 2 miles long. The rock is of very diversified character and comprises such facies as hornblende gabbro, norite, bronzitite, and amphibolite. As observed at the head of the basin, the 

country rock is a greenstone schist and the outer border of the intrusive mass is a light-colored quartz diorite about 500 feet wide. The 

following table shows the composition of the diorite, gabbro, norite, 

and bronzitite.

Composition of igneous rocks from intrusive mass at Bohemia Basin, Yakobi

Island a

1

55

(Ab3An2)

16

10

18

2

52

(AbsAns)

39

8

i

3

50

(AbjAns)

47

2

1

4

34

(AbiAm)

60

5

1

5

12

(AbajAnes)

84

4

6

Trace.

10

82

6.5

1.5

° Secondary minerals have been considered as part of the minerals which they are replacing.

1. Quartz diorite 100 feet from outer border of intrusive mass.

2. Quartzose diorite 500 feet from outer border of intrusive mass and adjacent to norite.

3. Hornblende gabbro from'northern outer margin of norite mass.

4. Norite, fine-grained facies.

5. Feldspathic bronzitite.

6. Olivine bronzitite.

The bronzite is a bronze-colored pyroxene on the border line between hypersthene and enstatite and was determined as a variety 

with about 86 per cent of the enstatite molecule MgSiO3 and 14 

per cent of FeSiO3 .

Locally the ultrabasic facies are extensively altered. Masses of 

sulphides occur in lenslike form or as disseminations. The sulphides 

comprise pyrrhotite, pentlandite, and chalcopyrite; the pyrrhotite 

6137 29 14
200 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

predominates. The disseminated sulphide blebs are primary late 

magmatic minerals and an integral part of the rock.

The basic rocks associated with nickeliferous pyrrhotite near 

Nickel, on the west coast of Chichagof Island have been briefly 

described by Overbeck.37 The rock that makes up most of the intrusive body is reported to be diorite, and the most basic facies 

hornblende gabbro and norite are found close to the outcrops of the 

ore bodies. A facies with disseminated sulphides is reported as 

consisting chiefly of hornblende, pyroxene, and feldspar, together 

with a little biotite and disseminated sulphides that consist predominantly of pyrrhotite with associated pentlandite and chalcopyrite. Kerr ?8 has described a pyroxene gabbro which is also associated with the ore deposits; the pyroxene is described as diopside 

with a little hedenbergite molecule in solid solution.

On the property of the Admiralty-Alaska Co., on Funter Bay, Admiralty Island, at an altitude of 1,650 to 1,700 feet, there is a dike of 

troctolite in schist. The fresh troctolite consists of 55 per cent of 

labradorite, 39 per cent of olivine, 4 per cent of pyroxene, and 2 

per cent of magnetite. The texture is diabasic. Locally sulphides 

are disseminated throughout the rock. These sulphides consist predominantly of pyrrhotite with a little associated pentlandite and 

chalcopyrite. In places the rock is extensively modified by hydrothermal alterations.

Knopf 39 reports hornblende gabbro at the head of Tenakee Inlet, 

Chichagof Island, and gabbro along Nakwasina Passage and Katlian 

Bay, Baranof Island.

Gabbro was noted by Chapin on the eastern shore of Duke Island, 

in the Ketchikan district. Highly hornblendic gabbro was noted by 

Wright 40 in the Copper Mountain area, and augite gabbro on the 

Kasaan Peninsula north of Karta Bay, Prince of Wales Island; The 

peak of Thunder Mountain, north of Sakie Bay, Dall Island, is made 

up of gabbro, which occurs as a local marginal facies to a diorite stock.

The gabbros may be fresh and massive, altered and massive, or 

very intensely mashed, depending upon local conditions.

The approximate mineral composition of a few representative types 

of the gabbroic group of rocks is given in the table below. The 

gabbros show no unusual features. A trace of orthoclase is present

" Overbeck, R. M., Geology and mineral resources of the west coast of Chichagof 

Island: U. S. Geol. Surrey Bull. 692, pp. 129-133, 1919.

88 Kerr, P. F., A magmatic sulphide ore from Chichagof Island, Alaska: Bcon. Geology, 

Tol. 19, pp. 371-372, 1924.

89 Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, p. 15, 

1912.

«° Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

Alaska : U. S. Geol. Survey Prof. Paper 87, pp. 36, 75, 1915.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 201

in many of them, and in a few microscopic veinlets of orthoclase 

 cross the grains. A noteworthy feature is the concentration of 

magnetite.

Mineral composition of gabliroic types of rock from southeastern Alaska

South side of Nakwasina Passage, Baranof Island _____

Mountain (altitude 3,035 feet) at north end of Kupreanof

Bohemia Basin, Yakobi Island, pocket marginal to norite. .

Hornblende-augite gabbro, Kasaan Peninsula, Prince of

Labradorite

59

64

38

57

50 

20

45

42

Pyroxene

»30

'35

44

41

"16"

30

35

Hornblende

2

6

47 

70

15

I 

a

8

1

12

.5

10

8

O

1

1.5

Accessory minerals

3

Biotite

......

15

0 Pyroxene partly altered to hornblende. 

» Pyroxene partly altered to serpentine.

GABBBO-DIORITE

The dioritic rocks, including gabbro-diorite, diorite, monzodiorite, 

and quartzose variants of these, ,are almost wholly restricted to the 

area between Lynn Canal and the Pacific Ocean and the islands of 

the Alexander Archipelago, where they are further localized in certain belts. They form the predominant type of rock within the 

Prince of Wales-Chichagof belt and the area west of Glacier Bay. In 

addition, stocks are found here and there in the northern part of the 

.Juneau belt adjacent to the main batholith, rarely within the mainland batholith itself, and on the islands west of Prince of Wales 

Island.

Commonly the most basic variant of the intrusive rocks of the 

Coast Kange after the ultrabasic group of rocks and their associated 

variants, is gabbro-diorite. Rock of this type forms separate stocks 

and occurs also as marginal variants of the predominant more alkalic 

 or siliceous and less ferromagnesian types. It is relatively sparse, 

however, and forms only a very small percentage of the total mass 

of intrusive rock. The gabbro-diorite locally grades into very highly 

hornblendic variants.

The approximate mineral composition of several representative 

types is given in the table below. The feldspar is usually near 

Abj^Ajii, an andesine-labradorite. Hornblende is commonly the predominant ferromagnesian mineral and forms 35 to 65 per cent of the 

rock. Pyroxene may be present as an accessory mineral and in some 

rocks may be the predominant ferromagnesian mineral. Quartz and 

orthoclase may be present as accessory minerals. Magnetite is always
202 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

present and in certain rocks shows a marked concentration, reaching 

10 per cent or more. Biotite may be present but is usually restricted 

to the more typical hornblende-andesine diorite and the more siliceous 

and alkalic types.

Mineral composition of typical gabbro-diorite from southeastern Alaska

Three-quarters of a mile southwest of Hetta Mountain, Prince of Wales Island _____________

South side of Portage Bay, Prince of Wales Island ....

Blashke Islands, Kashevarof Passage ........ .........

21 miles west of Tenakee, Chichagof Island ...........

4 miles northwest of Hadley, Kasaan Peninsula. .....

i *

 5*®"S

fl-°

«!~

15

50

30

50

55

77

3

ao>

 B

ow

70

47

60

36

35

3

£

o

PQ

0

*-8

oS

PH

5

S

O1

5

1

o> 

a

M

PM

10

5

18

>. °"i

w a> o> n

 <

3

5

a03

^

5

13

1

A belt of augite diorite (gabbro-diorite) on the mainland near 

Eagle River, in the Juneau district has been described by Knopf.41 

It forms a mass about 5 miles long and from a tenth to a quarter of 

a mile wide, of sill-like form. The rock is described as consisting 

of plagioclase partly converted to epidote, augite in abundance, 

biotite, sporadic hornblende, and orthoclase filling the triangular 

interstices between the plagioclase feldspars.

Knopf 42 has described as the Jualin diorite a stock of gabbrodiorite in the Berners Bay region of the Juneau district. The 

stock is about 5y2 miles long, in a direction parallel to the general 

trend of the structure of the country, and has a maximum width of 

1.1/2 miles. The rock consists essentially of labradorite near AbjAn1? 

hornblende, and biotite. Orthoclase and interstitial quartz are 

present in subordinate amounts, and locally the rock grades into 

granodiorite. Magnetite, titanite, and apatite are accessories. Hornblende is the most prevalent dark mineral; biotite exceeds it in 

prominence locally but in other places is absent.

DIORITE

The diorite differs from the gabbro-diorite essentially in having 

a slightly more sodic plagioclase (andesine), and a smaller percentage of hornblende. The diorite and monzodiorite very commonly show a local marginal development of hornblendite. With 

an increase in quartz the monzodiorite grades locally into granodio41 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, p. 29, 1912.

42 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, pp. 24-25, 1911.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 203

rite, and the diorite into quartz diorite. In many of the dioritic 

masses the plagioclase shows considerable alteration.

The predominant mineral in the diorite is an andesine feldspar. 

This usually forms 60 to 70 per cent of the rock but ranges from 50 

to 90 per cent. Hornblende usually forms 20 to 30 per cent and 

ranges from 6 to 45 per cent. Biotite is practically absent in half 

the specimens of diorite examined and in the other half ranges from 

1 to 12 per cent. Quartz ranges from 1 to 10 per cent. Potassic 

feldspar, including orthoclase and microperthite, ranges from 1 to 8 

per cent but is usually present only as a trace. Magnetite is usually 

present to the extent of 1 to 2 per cent but in a few places forms 

as much as 5 per cent of the rock. Titanite is usually present as an 

accessory mineral and may constitute 1 per cent or so of the rock. 

Apatite is practically always present and locally forms as much as 2 

per cent of the rock. Zircon is a common accessory in minor amounts.

The approximate mineral composition of representative types of 

diorite is given below.

Approximate mineral composition of types of diorite in southeastern Alaska

Average of 16 specimens from Chichagof Island. ___ .. 

Point south of entrance to Ingraham Bay, Prince of Wales 

Island. _____ ... ______ ... ___________

Qrindall Point, Prince of Wales Island. ___________

Andesine

62

63

48

24

64.5

66

68

71

75

73

63

83

90

62

42

Hornblende

26.5

28

45

64

30

26

19

28

22

6

20

15

7

21

25

Biotite

3

2

7

1

1

11

13

26

Potassic 

feldspar

2

1

1

6

7

1

6.5

SI

Sa 

cy

4

4

6

3

4

7

4

7

1

3

1

Magnetite

1.5 2-

1

5

2.5

1

2

1

Accessory minerals

1

(«)

2

.5

.5

1

2

1

2

1

.5

0 Present.

A chemical analysis of a representative specimen of diorite from 

the east side of Burnett Inlet, Etolin Island, is given below. The 

plagioclase of this rock is an andesine-labradorite, and the ferromagnesian mineral is almost exclusively hornblende. Only about 1 per 

cent of biotite is present. The hornblende is slightly altered to 

uralite, and the plagioclase slightly sericitized. A little microperthite is present.
204 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Analysis of diorite from Bur'nett Inlet, Etolim Island 

[J. Q. Fairchild, analyst]

Si02 ... ... .

AhOs 

FeaOs-. .

FeO... . ......

MgO. ........

CaO..... .....

NaaO. .

KS 0.... ......

HaO-. .

H2 0+........

TiOs... .......

P205 ..........

Analysis

.............................. 50.24

..-. . . -........,..... 17.86

. . .. 2.00

. .. 6.56

........ ...-.. ....... 5.47

 . .. . . 10. 59

. ....................... 3.51

........-.-.. .............. 1.40

.............................. .03

....... .. ............... 1.39

.............................. 1.32

.............................. .24

100. 61

Norm

Albite- ................................... 28.5

........ 28.8

........ 8.3

........ .8

........ 14.0

........ 12.5

........ 2.8

........ 2.4

........ 1.9

100.0

Quartzose diorite intermediate between normal diorite and quartz 

diorite is common in the Prince of Wales-Chichagof belt. The approximate mineral composition of nine specimens from this belt is 

given below in column 1.

A more feldspathic type is shown in column 2. These rocks have 

closer affinities with the diorite than with the quartz diorito. They 

have slightly less hornblende and more quartz than the normal 

diorite but are markedly distinguished from the quartz diorite by 

their small content of biotite.

Approximate mineral composition of quartzose diorite from southeastern Alaska/

Andesine... ...........................

1

fi3

?3

10

2

70

15

Biotite 

1

. 1

1

2

2

1

1

21

1. Average of 9 specimens from Prince of Wales-Chichagof belt.

2. Average of 2 specimens from Dall-Baranof belt.

MONZODIORITE

Monzodiorite occurs both as separate stocks, particularly on Mitkof 

Island and the Lindenberg Peninsula, Kupreanof Island, and as 

marginal variants of diorite or granodiorite stocks. Locally the monzodiorite has marginal hornblendite variants or grades into granodiorite or, rarely, into monzonite.

The predominant mineral of the monzodiorite is normally an andesine plagioclase, which forms 50 to 75 per cent of the rock. Potassic 

feldspar forms 9 to 30 per cent. In most places the potassic feldspar 

is microperthite, in small part microcline without perthitic intergrowths ; and in the Copper Mountain region, Prince of Wales Island, 

according to Wright, the potassic feldspar is orthoclase. Hornblende
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROO£S 205

ranges from several per cent to 35 per cent, but usually is around 20 

per cent. Biotite ranges from a trace to 7 per cent. Quartz is commonly present as an accessory mineral and ranges from 1 to 10 per 

cent. Magnetite, apatite, titanite, and zircon are other common 

accessory minerals. In the monzodiorite mass on the east side of 

Portage Bay, Kupreanof Island, epidote. is present to the amount of 

several per cent and seems to be a primary magmatic mineral; it 

occurs as fresh grains and euhedral rods and is locally corroded on 

the edges by the feldspar. In many of the monzodiorite stocks the 

plagioclase is intensely altered to epidote, zoisite, and muscovite.

The average approximate mineral composition of hornblendeandesine monzodiorite from the Prince of Wales-Chichagof belt is 

given below.

Average mineral composition of seven specimens of hornblende-andesme monzodiorite from the Prince of Wales-Chichagof belt

Andesine __________________________________ 56

Potassic feldspar__________________________ 19

Hornblende______________________________ IT

Biotite _________________________________ 2

Quartz _____________________________ 4

Accessory minerals_______________:__________ 2

100

An analysis by George Steiger of quartzose monzodiorite from the 

Jumbo Basin, Prince of Wales Island, is given by Wright.43

Analysis of quartzose monisodiorit& from Jumbo Basin

8102 ....

AljOa. .....

FeaOs ----..

FeO.. ........

MgO. .....

CaO..........

NajO.--.....

KaO... .......

HaO- ..

HaO+ .....

TiOa.. .......

Zr02 ....

COj.. ........

PjOs .

S. ............

MnO.. ....

BaO.... ......

SrO.........

Analysis

.............................. 59.44

.............................. 17.40

.............................. 3.30

......... ..................... 2.77

.............................. 1.81

.............................. 6.51

.............................. 4.22

.............................. 3. 12

.............................. .00

........... --, ... ....... . 56

fifi

.............................. .28

.............................. .02

.. . . ...... ........... .17

.............................. .07

.............................. .05

100. 44

Norm

Albite.... ... ................ ........

/\Vfl *-or\

........ 8.94

........ 18.35

........'35.63

........ 19.48

........ 8.68

........ 1.93

........ 4.87

........ ' 1.37

........ .67

........ .62

100.52

Albite and albite-oligoclase monzodiorites occur locally in small, 

masses on Prince of Wales Island. Such rocks form a marginal 

variant to the Copper Mountain stock and are found also at the

43 Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

Alaska : U. S. Geol. Survey Prof. Paper 87, p. 106, 1915.
206 GEOLOGY o AND MINERAL DEPOSITS, " SOUTHEASTERN ALASKA

Mamie mine, on Kasaan Peninsula. These sodic variants carry much 

less ferromagnesian mineral, consisting of only a small percentage 

of hornblende. The orthoclase is interstitial to the plagioclase and 

locally contains apatite crystals. Accessory magnetite and titanite 

are usually present. They locally grade into albite diorite. A typical specimen obtained near the Mamie mine consists of 71 per cent 

of albite, 23 per cejit of orthoclase. 5 per cent of hornblende, and 1 

per cent of apatite and magnetite. Another from a dike near the 

head of Hole in the Wall is described by Merwin as consisting predominantly of albite, with 15 to 20 per cent of orthoclase, 10 per cent 

of biotite, and accessory apatite, titanite, and magnetite.

SYENITE

Syenite is exceedingly rare, both in the islands of the Alexander 

Archipelago and in the mainland batholith. Only three specimens 

were found by the writer in the whole district covered by him. A 

specimen collected 2 miles south of McLean Arm, Prince of Wales 

Island, is a syenite composed almost wholly of microperthite with a 

little interstitial meshwork of oligoclase and accessory interstitial 

quartz. The approximate mineral composition of a specimen from 

the Copper Mountain region, Prince of Wales Island, and of two 

specimens from the mainland batholith is given below.

Approximate mineral composition of syenite from southeastern Alaska

1

75

5

10

8

2

67

20

5

3

74

10

1

1 2

6

1

1

3

4.5

.5

1. Near contact of main granitic mass, 1,000 feet east of Jumbo No. 4 mine, Copper Mountain region, 

Prince of Wales Island. Described by H. E. Merwin in Wright, C. W., U. S. Geol. Survey Prof. Paper 

87, p. 36,1915.

2. River Point, Portland Canal, Hyder district.

3. North center, Chickamin Bay, Behm Canal.

Merwin 44 has described the syenites from the Copper Mountain 

district, on Prince of Wales Island, as follows:

The syenites are medium-grained light-gray to pale-pink rocks composed 

essentially of orthoclase and plagioclase (oligoclase variety) in different proportions, with hornblende as the principal dark mineral and pyroxene, magnetite, apatite, and titanite as accessories. * * * The syenite forms a part 

of the batholithic masses occurring near its margin. It is also found in outlying dikes and in tongues branching from the main intrusive masses.

The Wrights 45 report that no syenite was discovered in the Glacier 

Bay region.

** Merwin, H. E., In Wright, C. W., Geology and ore deposits of Copper Mountain and 

Kasaan Peninsula, Alaska: U. S. Geol. Survey Prof. Paper 87, p. 36, 1915.

«Wright, F. E. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript).
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 207 

QUARTZ DIOBITE

Quartz diorite forms the western border of the mainland batholith, 

and perhaps a part of the extreme eastern border. It also occurs 

locally within the Coast' Kange batholith. It is one of the predominant igneous rocks of the Wrangell-Revillagigedo belt adjacent 

to the batholith on the west and is the predominant intrusive rock of 

the Dall-Baranof belt. Elsewhere in the Alexander Archipelago it 

is common but is exceeded in prominence by less quartzose, more 

typically dioritic rocks. It also occurs as local marginal developments on the borders of masses of dioritic or granodioritic rocks.

In the Coast Range batholith of the mainland the quartz diorite 

commonly grades into granodiorite toward the core. Locally on the 

 outer borders small masses of hornblendite are developed as marginal 

variants of it. In the Wrangell-Revillagigedo belt it grades into 

granodiorite, low in potassium, the dividing line between the two 

being taken at 8 per cent potassic feldspar.

A mass of quartz diorite forms a marginal border to a mass of 

norite at the Bohemia Basin, on Yakobi Island, near Chichagof 

Island.

. The quartz diorite is mottled in black and white with a generally 

predominant light-gray to white color. In the hand specimens a 

well-defined gneissoid structure is usually^evident. The hornblende 

occurs in black prismatic crystals without terminal faces, and the 

biotite in hexagonal flakes and chunky crystals. The hornblende and 

biotite may occur separate and oriented, or segregated in small patches 

or in short, indistinct narrow linear lenticles. Locally titanite crystals are common, though they are of erratic distribution. The rock 

is essentially of even grain with here and there a slight, inconspicuous 

tendency toward a porphyritic texture. The plagioclase of first 

crystallization may appear in euhedral tabular crystals of very 

slightly larger diameter, many of which weather more easily in the 

center.

The average grain of the mainland batholith is between 1 and 2 

millimeters, with local facies averaging 3 millimeters. Some of the 

slightly porphyritic plagioclase crystals may have a longer diameter 

of more than 0.5 centimeter; and some of the larger hornblende prisms 

are 1 centimeter in length. In many of the specimens examined by 

the writer some of the larger plagioclase crystals show a slight to 

conspicuous zoning. In the outlying stocks zoning of most of the 

plagioclase is common.

The hornblende of the granodiorite in the Wrangell-Revillagigedo 

belt, which is near quartz diorite in composition, must have a considerable variation in composition, as the indices of refraction range 

from 1.660 to 1.680 for a and 1.681 to 1.700 for y.
208 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

The approximate mineral composition of representative types of 

quartz diorite from the mainland batholith is given in the table on 

page 212. Andesine is the predominant mineral and ranges usually 

from 40 to 60 per cent. Hornblende and biotite together commonly 

form 15 to 23 per cent, but in a few specimens reach 35 per cent and 

very rarely are as low as 6 per cent. Usually, where the amount of 

hornblende and biotite together is between 19 and 27 per cent, hornblende predominates slightly over biotite; if the combined percentage 

of both constituents is 18 per cent or less biotite usually predominates 

over hornblende, but there are exceptions to both generalizations. 

Quartz commonly forms about 20 per cent but ranges from 15 to 30 

per cent. Potassic feldspar is absent in about half the specimens find 

where present may form as much as 7 per cent. The accessory minerals include titanite, magnetite, apatite, and zircon. Titanite is 

variable in distribution but is usually present and_may form more 

than 1 per cent of the rock. Apatite and magnetite may likewise 

locally form more than 1 per cent. A few of the quartz grains 

inclose abundant needles that may be rutile.

The .average composition of five specimens in which hornblende 

exceeds biotite is given in the table on page 212 as No. 3. These 

rocks have a slightly higher f erromagnesian content than those shown 

by No. 2, in which the hornblende and biotite are about equal. No. 4 

shows the average composition of eight specimens in which biotite 

exceeds hornblende. The ferromagnesian content of such rocks is on 

the average somewhat lower, 15 per cent as compared with 19 per 

cent, than that of the rocks in which hornblende and biotite are 

approximately equal and considerably lower, 15 per cent as compared 

with 22 per cent, than that of the rocks in which hornblende greatly 

exceeds biotite. The biotite granodiorite is also slightly more 

quartzose.

The abnormally high content of hornblende and biotite in a few of 

the specimens, Nos. 5 and 6, may be due in part to assimilation or 

reaction with inclusions of sediment and schist.

The average composition of the siliceous intrusive rocks in the 

Wrangell-Revillagigedo belt adjacent to the mainland batholith on 

the west is given as No. 7. It shows only slight difference from the 

average composition of the rocks of the western border of the main 

batholith. There is a slight increase in the percentage of pot.assic 

feldspar and an apparent decrease in hornblende, but this apparent 

decrease might not be substantiated if more extensive data were 

available. The quartz diorite of this belt grades into granodiorite in 

the stocks in the vicinity of Wrangell and Mitkof Islands, and this 

raises the average of the potassic feldspar content. The intrusive 

rocks of this belt are otherwise similar to the western portion of the 

main batholith.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 209

The average composition of five specimens from the .WrangellRevillagigedo belt in which biotite and hornblende are approximately equal is given as No. 8. In No. 9 is given the average of 

three specimens in which biotite considerably exceeds hornblende. 

Rocks of this type have a trifle less ferromagnesian minerals than 

those in which hornblende and biotite are approximately equal. The 

average of six specimens of biotite-quartz diorite, which forms small 

stocks and masses in the vicinity of Revillagigedo Island, shows a 

.marked decrease in the total amount of ferromagnesian minerals

 and a preponderance of biotite almost to the exclusion of hornblende. 

There is a correlative increase in the amount of quartz in similar

 quartz diorite from the Coast Range batholith. The smaller amount 

of potassic feldspar in these rocks, as compared with those that contain more hornblende, is due to the fact that these were collected 

from a part of the Wrangell-Revillagigedo belt in which the potassic 

content is low, whereas most of the hornblende rocks came from the 

high-alkali part of the belt.

A very detailed, careful petrographic study of the composition 

of certain of the Upper Jurassic or Lower Cretaceous intrusive 

rocks in the Ketchikan and Wrangell districts has been made by the 

Wrights.40 They do not state whether the specimens selected for 

study came from the mainland or the islands, or from both. The 

average composition obtained by them is that characteristic of the 

western border of the batholith and of the intrusive rocks in the 

Wrangell-Revillagigedo belt. Their results are quoted herewith:

Although the composition of the Coast Range granodiorites varies considerably

 from point to point, it is desirable to ascertain the approximate average composition of the entire mass. To this end seven typical specimens were selected 

from different parts of the range. These specimens were chosen with special 

regard to their abundance and general distribution throughout the area, abnormal and rare types being disregarded altogether. Each of these specimens 

was studied in detail under the microscope, and a careful estimate of the rejative

 quantity of each mineral in the rock was made from the thin sections by the 

Rosiwal method. Although the values thus obtained are necessarily only first 

approximations, they represent roughly the general mineral content of the 

Coast Range granodiorite. 

The following average mineral composition was thus obtained:

Average mineral composition of the Coast Range intrusive

Quartz________________ 19.4 

Orthoclase _____________ 6.6 

Andesine (AbcoAn^)_______ 47.4 

Hornb.lende ____________ 7.6 

Biotite________________ 11.6 

Apatite _______________ . 6 

Magnetite __ . 9

Pyrite ________________ . 1

Titanite ______________ 1. 3

Epidote__.____________ 3. 5

Chlorite_______________ . 1

Calcite_______________ . 1

Kaolin and muscovite______ . 8

100.0

«° Wright, F. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

 Geol. Survey Bull. 347, pp. 63-65, 1908.
210 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The average specific gravity, 2.77, was determined by weighing the hand 

specimens in air and then in water.

From these data the average chemical composition was calculated by assuming for the hornblende and biotite the compositions of like minerals from a 

similar rock from Butte, Mont.

Average chemical composition and norm of the Coast Range intrusive

Constituent

SiOj.... ........ ........... .....................

TiOa........--...-.-.-.................,.....__

AljOa .. ... .. .....................

F&Oi..... ................ ... ...................

FeO..... .......................................

MnO...... ................... ..................

MgO... ........ ................................

CaO..- ....... ...............................

NaaO........ ...................................

KiO . ....................................

HtO.. ..........................................

PaOs........................ ...... ..............

Per cent

61.0

1.0

17.5

1.6

2.7

.1

2.4

fi 9

3.3

2.3

.9

.3

100.0

Molecular 

ratio

1.017

.013

.171

.010

.038

.001

.060

.123

.053

.024

.050

.002

Norm

Q. .............. 16.14

Or.............. 13.32

Ab- ... ..... . 27.78

An.............. 27.02

Di. ............. 4.81

Hy.... .......... 5.75

Mt.. ......... 2.32

11. .............. 1.97

Ap.............. .67

.

184. 26

68.121

10. 56J

1 4 on 15.52 4.29

99.78-

This chemical and mineral composition places the rock in the family of the 

quartz diorites, of the type tonalite according to the usual classification. In the 

new quantitative classification of Cross, Iddings, Pirsson, and Washington the 

rock is dosalic, dosalane, quardofelic, alkalicalcic, and dosodic, and belongs in 

Class II, order 4 (austrare), rang 3 (tonalase), and subrang 4 (tonalose). In 

short, it is tonalose of the ordinary type.

The amount of titanite is unusual and is characteristic of many of the Coast 

Eange intrusives. The highly lustrous, well-shaped crystals of this mineral 

glisten in the sunlight and attract the attention of the most casual observer.. 

The hornblende occurs usually in dark prismatic crystals, noticeable for the 

excellent prismatic cleavage and the lack of terminal faces. Many biotite flakes 

are hexagonal and deep brown in transmitted light. A few apatite crystals are 

visible tp the unaided eye, but this mineral occurs generally in fine hexagonal 

crystals of microscopic dimensions. Pale-green veinlets of secondary epidote,. 

which follow fracture planes in the granodiorite, are not rare.

These even-grained rocks usually have the normal, sharply defined, granitoid 

texture. However, gradations to holocrystalline porphyritic phases, due to the 

superior development of the feldspars, occur. Gneissic structure is common near 

the western margin of the Coast Range belt. In some places the development 

of gneissic structure in the granite has been so far advanced and the recrystallization of the neighboring invaded sediments to gneiss has been so thorough 

that it is difficult to define the precise limits of the original intrusive granite.

A chemical analysis of a composite sample of 14 specimens collected 

by Buddington from the western part of the Coast Range batholith 

and from outlying masses is given below:
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROOKS 211

Ohemical analysis of composite sample of quartz diorite 

[J. G. Faircliild, analyst]

SiOn.. ........

AhOj... ... ...

FeaOs ... ...

FeO..........

MgO. ........

 CaO... .......

NajO.........

K»0..........

HaO- ..

H.O+ ~

Ti08..........

PiOa-.-. -.

Analysis

. ..... ................... 69. 55

.......... .................... 16. 18

.............................. 1.94

.-.-....-...-._-.._-..._.._.. 6.61

2 86

........... ................... 6.26

.............................. 3.40

.............................. 2.62

.............................. .04

__-.-._ _.....-_-..._.....__ .82

.............................. .96

..-... ...-......_._.___.... .26

100. 50

Norm

Albite-.. ..........................

........ 10.69

........ 15.57

........ 28.82

........ 20.85

........ 4.S9

........ 13.62

........ 2.37

........ .79

........ 2.79

99.79

Only four specimens of quartz diorite from the Prince of WalesChichagof belt were studied. These are given in the table on 

page 212 as No. 12. They differ from the Coast Range type in that 

hornblende is the predominant ferromagnesian mineral, even where 

the combined percentage is less than 15 per cent. They are essentially more quartzose and less ferromagnesian mineral variants of 

dioritic masses, and the data are not sufficiently extensive to warrant 

detailed discussion.

Four specimens of quartz diorite from Chichagof Island are similar to those of the Coast Range batholith. Their average composition is given as No. 13. Hornblende usually exceeds biotite in these 

rocks except where their combined percentage is 18 or less. The 

rocks are slightly more basic and less quartzose than the normal

 Coast Range type. Magnetite averages 1 per cent or more in these 

rocks and seems to be slightly more abundant on the average than 

in any of the other belts in which quartz diorite occurs.

The average approximate mineral composition of seven specimens

 of quartz diorite from Baranof Island is given as No. 14. Quartz 

diorite appears to be the predominant type of intrusive rock on this 

island. It is more quartzose and has a far smaller percentage of 

ierromagnesian minerals than the normal Coast Range type of quartz 

diorite. Biotite commonly predominates over hornblende, but there 

are exceptions. The ferromagnesian minerals together form 6 to 14 

per cent, andesine 57 to 75 per cent, quartz usually 20 to 30 per cent, 

.and potassic feldspar from a trace to 8 per cent. The accessory 

minerals include magnetite, apatite, titanite, and zircon, but they 

iire usually small in amount.
212 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The average composition of three specimens of biotite-quartz 

diorite from Baranof Island is given as No. 15. The total ferromagnesian content is lower than the average, quartz is higher, and 

biotite preponderates almost to the exclusion of hornblende. The 

percentage of accessory minerals is low.

Approximate mineral composition of quartz diorite in southeastern Alaska

1

2

3

4

5

6

7

8

ft

10 

11

12

13

14

15

COAST RANGE BATHOLITH

Average of 21 specimens from west border of Coast Range

batholith.. _ . _____ .... ___ . _ . ______ . ......

Average of 4 specimens; hornblende and biotite approximately

equal _ .... ____ . ___ . ________ . ............

Average of 2 highly ferromagnesian specimens; hornblende in

excess of biotite ___ . ___ . ____ . __ . _ -... _ ...

Average of 3 highly ferromagnesian specimens; biotite in excess

WRANGELL-REVILLAGIGEDO BELT

Average of 5 specimens; biotite and hornblende approximately

Average of 6 specimens; biotite greatly in excess of hornblende.

PRINCE OF WALES-CHICHAGOF BELT

DALL-BARANOF BELT

Average of 3 specimens, Baranof Island; biotite in excess of

hornblende _ ' __ . ___ . ____ . __ . ..................

.9

"a

 <

54

59

54.5

59

44.5

43.5

54

54.5

56.5

63 

39

65

56

62

26

a> O

a

a>

g

W

11

10.5

15

3

22

12

8

9

1. 5

17

7

13.5

3.5

1

co

o

«

12

8.5

7

12

14

22

11.5

10.5

12.5

10 

19

3

11

5

6

fi

O1

20

19

19

23

18

19

19

19

18

24 

17

22

16.5

23.5

29

u

CO Q, 2$

PH

2

1

3

2

2

6.5

6

6

1

7

2

1

5

1

f»

o

"§ 

o> o

«°>fl

1-4 

2

1.5.

1

1.5.

1.5.

1

1

1

.5. 

1

1

2

1

.5.

A study of the mineral relations of the diorite to the quartz diorite 

as given in the table on page 213 shows that up to a certain limit an 

increase of quartz in the diorite, though it may be accompanied by 

a decrease in the amount of ferromagnesian minerals, particularly 

hornblende, is not normally accompanied by a change of hornblende 

to biotite; but on the other hand, in the change from quartzose diorite to quartz diorite there is normally a corresponding change of part 

of the hornblende to biotite. A study of the mineral' relations within 

the quartz diorite also shows that the amount of hornblende or hornblende and biotite combined may vary markedly though the amount, 

of quartz remains constant. The data are inadequate for determin-- 

ing positively whether or not a decrease in the quantity of ferro-- 

magnesian minerals within the andesine-quartz diorite is accom-- 

panied by a slightly increased sodic content of the plagioclase.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 213

Average mineral composition of diorite and quartz diorite of soutlieastern

Alaska

11 specimens of quartzose diorite from Prince of Wales-Chichagof

belt.............................................................

21 specimens of quartz diorite from west border of Coast Range

20 specimens of quartz diorite from Wrangell-Revillagigedo belt....

7 specimens of quartz diorite of Coast Range batholith near Vancp

a

<3 a 

3

62.5

63

54

54

62

64.5

a> a

a

VJ

o

w

27

23

11

8

3.5

9.6

a>

,J^

o

W

2.5

1

12

11.5

5

1.5

u

rft Q.

GQ 'O

oS 

PH

1.5

1

2

6.5

5

C4

^

C3

a

4

10

20

19

23.5

21.7

t>>

0*73

W tl

a> d

I1

2.5

2

1+

1

1

3-

0 Averaged from data given by Burwash, E. M. 3., The geology of Vancouver and vicinity, 

Univ. Chicago Press, 1918.

Albite and oligoclase quartz diorites, so far as known, form a very 

minor portion of the Upper Jurassic or Lower Cretaceous intrusive 

rocks and are restricted to very small stocks, to dikes, or to local marginal variants of larger dioritic stocks. The mineral composition of 

several specimens of rock of this type is given in the table below. 

The albite-quartz diorite locally varies toward albite diorite, as in 

No. 7, and toward albite granodiorite, as in Nos. 3 and 6. Accessory 

minerals include magnetite, titanite, apatite, and zircon, but they are 

usually sparse.

Analyses of sodic quartz diorite from Alexander Archipelago

1

?!

3

4

5 

fi

7

Average of 3 specimens of sodic quartz diorite, Dall and

Dike north of Karta Bay, Prince of Wales Island «.. .........

V/i miles southeast of Boggs landing, Kasaan Peninsula,

o

63

......

S 

3

3

73

71

70

68-73

74

'90

Potassic 

feldspar

1

2

5

......

SI

aa <y

32

25

24

20

25-30 

15

10

Hornblende

0 5

......

3

+3

0

3

2.5

10

< Wright, 0. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, Alaska: U. S. 

Qeol. Survey Prof. Paper 87, p. 86,1915. 

' Contains 15 per cent dissolved orthoclase molecule.

The stock on Baker Island appears to be composed of a quartz 

diorite very low in ferromagnesian minerals, with biotite predominating almost to the exclusion of hornblende, and with the plagioclase varying from albite-oligoclase to andesine..

Albite-quartz diorite from Lisianski Strait near Miner Island and 

from the Porcupine Islands, off the west coast of Chichagof Island, 

has been described by Overbeck.47 Albite to albite-oligoclase quartz

47 Overbeck, R. M., Geology and mineral resources of the west coast of Chicbagof 

Island: U. S. Geol. Survey Bull. 692, pp. 109-110, 1919.
'214: GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

.diorite also forms the country rock at the border of a stock of diorite 

.about 41/2 miles north of the head of Pinta Bay, Chichagof Island.

GRANODIORITE

Granodiorite is one of the major types of rock forming the core of 

.the Coast Range batholith in the region under consideration, and it is 

found also as outlying stocks and local variants of other types of 

;rock throughout the Alexander Archipelago and on the mainland 

to the northwest. The Texas batholith, a small batholith of granotdiorite older than the bulk of the Coast Range intrusions, forms an 

area in the Salmon River district on the east side of the Coast Range 

'batholith.

In the Wrangell and Petersburg districts stocks and sheets of 

 granodiorite on the border line of quartz diorite in composition are 

found throughout a belt about 20 miles wide paralleling the main 

batholith of the Coast Range. This belt includes a wide strip of the 

jnainland and the adjoining islands, comprising the eastern half of 

ithe Lindenberg Peninsula and Mitkof Island, the group of islands 

:at the mouth of Stikine River, and Wrangell Island. Other outlying masses are found on Prince of Wales, Forrester, Dall, and 

"Warren Islands, in the Ketchikan district, and on Chichagof Island.

The Wrights 48 have described granodiorite as forming stocks on 

:the west side of Queen Inlet about 3 miles from the entrance point, 

;north of Morse Glacier and at the head of Muir Inlet, Glacier Bay, 

;at the head of the east arm of Excursion Inlet, at the south entrance 

;to Chilkoot Inlet, and in Lituya Bay.

The granodiorite as seen in the field closely resembles the quartz 

.diorite, and in many places the two rocks grade imperceptibly into 

one another. However, much of the granodiorite is of a slightly 

more pinkish hue, owing to the higher percentage of potassic feld- 

.spar; this is particularly true within the Coast Range batholith, 

where the potassic feldspar is a prominent component.

The predominant type of rock is a hornblende-biotite granodiorite, 

though locally biotite alone or hornblende alone may constitute practically the whole amount of ferromagnesian mineral. In places 

within the core of the Coast Range batholith and the intrusive masses 

,of the Alexander Archipelago there are more siliceous alkalic variants, such as oligoclase granodiorite with very low ferromagnesian 

.content. In the Alexander Archipelago such masses usually form 

small stocks, local marginal variants, or dikes.

Very rarely an augitic variant of the andesine granodiorite is 

found. The predominant granodiorite is prevailingly a mediumgrained light-colored rock, mottled with black ferromagnesian minerals, with locally a tendency toward an inconspicuous porphyritic or

^Wright, F. E. and C. W., Geology of Glacier and Lituya Bays (unpublished msinuscript).
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 215

inequigranular texture, and usually a gneissoid. structure. With the 

naked eye the rock is seen to consist of plagioclase, potassic feldspar, 

quartz, biotite, hornblende, and scattered crystals of titanite. The 

feldspar grains are usually about 3 to 5 millimeters in length, but the 

average grain diameter is about 1 to 2 millimeters. Near the bordering schist, or near inclusions of schist, the rock may contain a little 

disseminated pyrite or pyrrhotite and more rarely minute garnets. 

Locally, also, as a result of reaction with inclusions of hornblende 

gneiss, the rock carries a higher percentage of hornblende than 

normally.

When examined in thin section, the texture is seen to be hypidioinorphic granular, with local traces of granulation of the feldspars 

and cataclastic structure. Where a porphyritic texture is developed 

the; phenocrysts are usually andesine feldspar, but microcline phenocrysts as much as 2 inches in length are common in a granodiorite 

mass which forms the mountains about 4% miles northeast of Spray 

Island, Thomas Bay, and .microperthite locally occurs in part as 

phenocrysts.

The plagioclase feldspar crystals are prevailingly subhedral, with 

a length several times greater than the width. They commonly show 

a conspicuous zonal structure, particularly in the border facies of 

the quartz diorite masses. The plagioclase ranges from Ab55An45 to 

Ab80An20 . In the low-potash feldspar facies the plagioclase averages about andesine (Ab6An4 ), and in the high-potash feldspar 

facies it probably averages about oligoclase-andesine. The hornblende has a prismatic development without terminal faces and is 

associated with biotite and accessory minerals. The biotite occurs 

in chunky crystals with frayed ends and is deeply pleochroic from 

light yellowish-brown to deep chestnut-brown. The potassic feldspars include microperthite, microcline, and locally orthoclase.

Near contacts with schist inclusions and usually in the outlying 

masses on the islands the rock is slightly altered. In such places the 

plagioclase is flecked with sericite or muscovite fibers and zoisite or 

epidote rods and grains; and the hornblende may be partly replaced 

by epidote. The unaltered portions of the minerals are fresh and 

clear. Epidote and zoisite usually form several per cent of the rock. 

The Horn Cliffs stock and several masses in Hobart Bay show an 

unusually high degree of alteration; the plagioclase is almost entirely replaced by well-crystallized plates of muscovite and grains 

of, epidote with a little zoisite, but the microperthite is entirely 

unaffected.

The. approximate average mineral composition of specimens of 

granodiorite from the core of the Coast Range batholith is given in 

the table on page 217 at Nos. 1 to 4. Plagioclase is the predominant 

6137 29 15
216 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

mineral and ranges from 38 to 60 per cent but usually runs between 

38 and 46 per cent. Quartz ranges from 15 to 30 per cent but is 

usually near 20 per cent. Potassic feldspar ranges from 10 to 28 

per cent but is predominantly between 13 and 20 per cent. Hornblende and biotite together range from 8 to 25 per cent, but are predominantly between 10 and 18 per cent; when the combined percentage of the ferromagnesian minerals is greater than 13 per cent 

hornblende usually exceeds or equals biotite, and when the combined 

percentage is 12 or less biotite usually exceeds hornblende, but exceptions are common. Hornblende predominantly ranges from 0 to 

14 per cent, and biotite from 0 to 15 per cent. The plagioclase 

usually ranges in composition from oligoclase to andesine, and the 

average for a given rock may be an oligoclase-andesine.

The accessory minerals are the same as those of the quartz diorite magnetite, apatite, titanite, and zircon. Magnetite is usually 

the most abundant accessory mineral and may form as much as 2 

per cent of the rock. Titanite is usually present, but is variable in 

concentration; it may form 1 per cent or more of the rock. Apatite 

is always present and locally may form 1 per cent or more. Zircon 

is usually very minor in amount.

A chemical analysis of a composite sample of six specimens of 

granodiorite from the core of the Coast Range batholith in the 

Hyder district is given below.

Chemical analysis of composite sample of granodiorite from the Coast Ranffe

batholith

[J. O. Fairehild, analyst]

SiOs.. ........

AljOs.........

"FpoOa

FeO.... ......

MgO. ........

CaO.. .....

NajO.........

K2 0... .......

H8O-_.-...-.

H20+.. ......

TIOj..........

P2 05 .... 

Analysis

.............................. 64.87

.. . . . . ... 16.26

.....--.-..........__-......- 1.51

................... ........... 2.89

.............................. 1.72

.............................. 4. 72

..................... ......... 3.82

.............................. 3.30

....-.._..-. .-.-.. .-.-. .00

................. ... . . 28

...................... ........ .70

.............................. .19

100.26

Norm

Albite...............-...... ......

A nnHtA

.:...... 1(5.98

........ 19.46

OO AQ

n

ftA

........ 2.17

........ 7.36

1 7ft

........ .45

o no

100.02

In the Hyder district, just west of the international boundary, 

along Boundary Glacier, there is a mass of granodiorite which constitutes a contact facies of the quartz monzonite that here forms the 

eastern portion of the Coast Range batholith. It is not certain 

whether this granodiorite is an apophysis or a stock. Its approximate average composition is given in the table on page 217 as No. 5. 

It differs from the granodiorite of the core of the batholith in having 

less ferromagnesian mineral and a little more plagioclase.
UPPEE JUEASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 217

The average composition of specimens of granodiorite from the 

Wrangell-Revillagigedo belt of outlying stocks and batholiths adjacent to the main batholith is given in the table below as Nos. 6 

to 8. In comparison with the more abundant granodiorite of the 

Coast Range batholith, these outlying stocks are considerably more 

basic and less alkalic. The combined percentage of hornblende and 

biotite is considerably higher and that of potassic feldspars considerably lower. In average composition the plagioclase is an andesine. 

Andesine ranges from 40 to 60 per cent, quartz from 15 to 25 per 

cent, combined ferromagnesian minerals from 13 to 30 per cent, and 

potassic feldspars from 7 to 10 per cent. The accessory minerals 

are similar to those in the granodiorite of the Coast Range batholith. 

Where the combined percentage of ferromagnesian minerals is 18 per 

cent or more, biotite is usually only slightly in excess of hornblende, 

if at all; where the combined percentage is less than 18, biotite commonly greatly exceeds hornblende; but there are numerous exceptions to both generalizations. Hornblende ranges from 0 to 15 per 

cent, and biotite from 11 to 18 per cent.

The approximate average mineral composition of nine specimens 

of granodiorite from the Alexander Archipelago west of the 

Wrangell-Revillagigedo belt is given in the table as No. 9. The 

average shows that the rocks are relatively low in ferromagnesian 

minerals and high in andesine. The data are too meager to warrant 

further discussion, as the average might be considerably affected by 

more samples.

Approximate mineral composition of granoddorite in southeastern Alas/fat,

COAST RANGE BATHOLITH

Average of 15 specimens ...... __ ___ .. _____ ......

Average of 5 specimens, hornblende in excess of biotite _ ...

Average of 4 specimens, hornblende and biotite approximately

equal. _________________________ . ......

Average of 6 specimens, biotite in excess over hornblende. ....

Average of 5 specimens of granodiorite stock on east side of

Coast Range batholith, in the Hyder District.. __ .......

WRANGELL-REVILLAGIGEDO BELT

Average of 10 specimens. .'. __ ... _ .. __ .. ....

Average of 5 specimens, biotite slightly in excess of hornblende. 

Average of 4 specimens, biotite in great excess over hornblende.

ALEXANDER ARCHIPELAGO, WEST OF WRANGELL-REVILLAGIGEDO BELT

Average of 9 specimens -..-... __ __ ... _ ..... _ ........

%n 

1

a

<

"46

45.5

40

46

48

50.5

49 

54

56

<D a

q

a) 

3 

a

s

w

8.5

12

102-

4

7

10 

2

7

<o

o

3

7.5

2

10

6

13

13 

13

5

i

3<y

21. 5

19

21.5

24

10 IP. Oa

18

16.5 

20

10 ia

2

«s

3 !s 

]l

o

fe

15

20

17.5

17

17

10

10 

10

12

c

1

fcja

Si

g»

Q

 <

2

1.5

2

1

9 1 £~ \>

1.5

l.ft 

1

1

1 Oligoclase-andesine.
218 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Locally an augitic variant of the usual hornblende-biotite-andesine 

granodiorite is found. One rock of this type has been described by 

Merwin 49 from samples collected north of Green Mountain, Prince 

of Wales Island, and another occurs in a sill in injection gneiss north 

of Duck Island, Bradfield Canal. Their composition is given in 

the table below.

Approximate mineral composition of augite granodiorite

Andesine __ . ___ - ________

Potassic feldspars..... ________

1

47

11

24

2

40

10

25

Hornblende ____ - _________

1

8

9

1

2

10

10

5

1. Sill in injection gneiss, north of Duck Island, Bradfield Canal.

2. North of Green Mountain, Prince of Wales Island. H. E. Merwin, in Wright, C. W., U. S. Qeol. 

Survey Prof. Paper 87, pp. 35-36, 1915.

Oligoclase granodiorite is found throughout the Alexander Archipelago as very small stocks, as dikes, or as local variants of the 

andesine granodiorite. Usually in the stocks or dikes it is intensely 

altered and replaced by muscovite and epidote. It grades into oligoclase and albite-quartz diorites and into andesine granodiorite. The 

.combined percentage of hornblende and biotite is low, and accessory 

minerals are relatively sparse. A study was made of specimens of 

oligoclase granodiorite from four widely separated localities on Chichagof Island, Dall Island, Revillagigedo Island, and Portland Canal. 

The average composition of two specimens from Tenakee, Chichagof 

Island, is given in the table on page 219 as No. 1. These rocks are 

characterized by a very high content of quartz and very low content 

of ferromagnesian minerals, and accessory minerals are sparse. The 

rock that forms the small islets at the entrance of Port Bazan, Dall 

Island, is of almost the same composition.

On the west side of Portland Canal, about halfway between Hidden 

Inlet and Edward Passage, there is a mass of light-colored oligoclase 

granodiorite which brecciated and injected a block of schist. The 

composition of this rock is given in the table as No. 2. The oligoclase 

is Ab4An15 and the potassic feldspar is microperthite. The accessories include apatite, zircon, titanite, and magnetite. This rock from 

the core of the Coast Range batholith is similar to those from the Alexander Archipelago just described. A specimen from Revillagigedo 

Island is given as No. 3.

49 Merwin, H. E., in Wright, C. W., Geology of Copper Mountain and Kasaan Peninsula, 

Alaska: U. S. Geol. Survey Prof. Paper 87, p. 35, 1915.
UPPER JURASSIC OR LOWER .CRETACEOUS INTRUSIVE ROCKS 219

Approximate mineral composition of oligoclase granodiorite from southeastern

Alaska

1

2

3

West side of Portland Canal, halfway between Hidden Inlet

|-

*Q

bo

a

O

53

49

65

o

"S

(fl CO

OS

fc

10

15

11

N

a

Ofl1

33

34

20

 o 

§

ft

W

2

0

«

1.5

1.5

4

t>>

ki in 

CO 2

CO CD

a>g °'d 

u 9

 <

0.5

The Texas batholith, a small batholith of granodiorite, occupies an 

area in the Salmon Kiver district at the head of Portland Canal on 

the east side of the Coast Kange batholith. This mass of granodiorite 

is intruded into graywacke, slate, tuff, and breccia of probable 

Jurassic age, and is itself intruded by apophyses and dikes genetically connected with the quartz monzonite and granodiorite of the 

Coast Range batholith. It is therefore older than the bulk of the 

intrusive material of the Coast Range batholith but still belongs to 

the 3eries of Jurassic or Cretaceous intrusions. It is grayer and 

more gneissoid than the younger granodiorite and quartz monzonite, 

and near its contact with those rocks is mashed and crushed for a 

width of a mile or more as a result of the pressure exerted by their 

intrusion. The granodiorite of the Texas batholith is well exposed 

along Texas Creek and its tributaries. The average composition of 

this granodiorite is given in the table below as No. 1. The ferromagnesian minerals are so altered in most of the rock that a distinction between hornblende and biotite can not be made. In the 

few sections in which this can be done hornblende predominates and 

biotite forms from 2 to 5 per cent of the rock. Titanite and magnetite locally may form as much as 1 per cent each, and apatite is 

usually present as an accessory mineral.

The granodiorite of the Texas batholith locally develops a less 

alkalic facies at or near the contact with the country rock, as at the 

head of the West Fork of Texas Creek. The average composition 

of this type is given in the table as No. 2. A still more basic facies 

is developed locally within a few feet of the contact, such as the 

monzodiorite whose composition is given as No. 3.

Approximate mineral composition of granodiorite of the Texas batholith

Average of 22 representative specimens... ....................

Quartz diorite facies near western end at head of West Fork,

Monzodiorite a few feet below contact with roof of graywacke.

 g§

-d

 <

48

60

66

05 O

ao>

£1

O

W

12

1^

17.4

£

"o

W

.5

.5

1.6

 p

a

o19

20

4

0

CO 3

o2

PH

20

5

11

o'd

CO 0>

0 a

O R

«<1

0.5

.5

-"--
220 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

QUARTZ MONZONITE

Quartz monzonite is one of the three major types of rock forming 

the Coast Range batholith. Between Stikine River and Portland 

Canal it constitutes a belt 10 to 15 miles wide, and on Portland Canal 

it forms wide belts within the core of the batholith. It is very rare 

in the intrusive rock of the Alexander Archipelago but has been 

found as local variants of the other prominent types there.

The average composition of 16 specimens from the northeastern 

belt of the Coast Range batholith is given in the table on page 221 as 

No. 1. Immediately adjacent to the contact the quartz monzonite is 

locally less alkalic or siliceous and may carry more ferromagnesian 

minerals, as shown by No. 2.

The quartz monzonite of the central part of the core (see No. 3) is 

in general highest in hornblende and biotite (10.52 per cent), and 

hornblende is greater in amount than biotite. In the quartz monzonite of the eastern part of the core, on Portland Canal (see No. 4), 

the total amount of hornblende and biotite (8 per cent) is smaller 

than in the central core, and biotite (5 per cent) exceeds hornblende 

(3 per cent). Along the eastern flank of the batholith (see No. 1) the 

total amount of ferromagnesian minerals is still l6ss (4 per cent), 

hornblende is practically absent and quartz is high.

In the border belt also the quartz monzonite varies considerably, 

as is indicated in Nos. 5, 6, and 7. The combined percentage of 

ferromagnesian minerals is much lower in the quartz monzonite than 

in the granodiorite and the content of potassic feldspar is, of course, 

much higher.

Along Portland Canal the potassic feldspar of the quartz monzonite is microperthite (hypoperthite), and only locally does it show 

microcline structure; it never shows more than a slight amount of 

the plagioclase phase, and in some rocks none. The gridiron structure of microcline is, however, usually present in the potassic feldspar 

of the quartz monzonite of the eastern belt.

The plagioclase of the quartz monzonite along Portland Canal 

appears to average about oligoclase-andesine; along Stikine and 

Chickamin Rivers it averages oligoclase. The plagioclase is markedly zoned in the belt between Portland Canal and Chickamin River 

but zoning is inconspicuous on Stikine River. Myrmekite is only 

rarely present in more than slight amounts.

The biotite occurs as chunky crystals and is in many places intergrown with thin chlorite leaves as a result of partial alteration, or 

locally it is wholly altered to chlorite.

The accessory minerals are more abundant in the quartz monzonites 

high in ferromagnesian minerals than in the more siliceous and 

alkalic facies. Magnetite forms on the average about half of the
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 221

accessory minerals, and titanite, apatite, and zircon the other half. 

Zircon is relatively rare. Magnetite appears to be more common 

than in the quartz diorite. One specimen of quartz monzonite contained 2 per cent of titanite and a small percentage of magnetite and 

apatite with accessory zircon.

The quartz monzonite on Devilfish Bay, Kosciusko Island, is a 

marginal variant of a large stock of dioritic character whose predominant composition is unknown. This f acies is unusually quartzose 

and contains about 5 per cent of magnetite and 1 per cent of titanite. 

It contains both microperthite and microcline, the latter in interstitial relations. Apatite, magnetite, and titanite are present as 

accessory minerals. The plagioclase is a very sodic andesine.

Approximate average mineral composition of quarts monzonite from southeastern. Alaska

16 specimens from cast border facies of batholith 

between Portland Canal and Stikihe River. ... 

2 specimens of chilled contact part of quartz mon9 specimens from core of Coast Range batholith.. 

6 specimens from eastern part of core of batholith, 

Portland Canal.... _ . __ . __ .... ___ ...

4 specimens from northwest of Hyder........ _ .

Stikine River __ .. __ ... . __ ........

Dike rock cutting schist on east side of Hetta 

Lake, Prince of Wales Island « __ ... _ ......

Oligoclase-andesine

37.3 

45

37 

38

39

3f3

31

50

feldspar Potassic 

32.7 

30

30.5 

32

30.5

34

37

30

N

£

03

3

cy

24.5 

14

20 

20

23.75

26.5

30

15

Hornblende

0.1 

4

6.5

(»>

Biotite

4 

6

4

5

5

2.5

1.5

(»>

3

0.6

......

.75

(»)

<D

1

0.5 

1.0

2.0 

2.0

.9

1.0

.5

(»)

4O

I

0.25

......

.20

' "Wright, 0. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, Alaska: U. 8. 

Geol. Survey Prof. Paper 87, p. 36,1915. 

6 5 per cent of accessory minerals, including hornblende, biotite, diopside, magnetite, and titanite.

A chemical analysis of a composite sample of six specimens of 

quartz monzonite from the Hyder district is given below:

Chemical analysis of composite sample of quartz monzonite from eastern part 

of Coast Range fta-tholith, Hyaer district

[J. Q. Fairchild, analyst]

Analysis Norm

SiOj.... ....... ...

AhOs ....

FesO«..._. -..-.

FeO. ......... ... ....

MgO...... .... ... ...

CaO... . ....

NajO .............

KiO. .. . . HiOH.O+.. -... ....

TiOj....... .......

PaOi ...... . ....

........................ 70.86

........................ 14.96

........................ 1.06

........................ 1.43

................'........ .41

........................ 2.23

........................ 3.90

........................ 4.60

........................ .00

........................ .40

 -.-.-. ........... .34

........................ .11

- 100. 30

Albite..... ............. .....

Titanite. ..-........ ......

................ 24.72

................ 27.24

................ 33.01

................ 9.73

2 72

................ .79

................ .35

................ 1.52

100.08
222 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA 

. GRANITE . .

Granite occurs as stocks throughout the Alexander Archipelago 

and to the northwest, but it forms only a minor element in the intrusive complex. In all places so far described it bears an intrusive 

relation to the Wrangell-Revillagigedo belt of metamorphic rocks. 

It appears to be very rarely present within the Coast Range batholith.

In the Ketchikan district Chapin has mapped and described large 

masses of granite occupying the central part of Annette Island and 

a part of the south end of Prince of Wales Island. Small bodies 

of granite are found on Gravina Island and about a mile north of 

Hadley, on the Kasaan Peninsula, Prince of Wales Island.

Large masses of granitic rock occur in the Wrangell district, but 

it is not positively known whether they should be grouped with the 

Upper Jurassic or Lower Cretaceous intrusive rocks of the Coast 

Range or with the Tertiary intrusive rocks. They comprise granite, 

granite porphyry, and rhyolite porphyry and occur in a belt th4t 

extends from the northwest end of Zarembo Island southeast across 

the central part of Etolin Island to Ernest Sound. Small stocks of 

granite are found on the northwest side of Etolin Island at thje 

second point north of Steamboat Bay and at Quiet Harbor. Near 

Round Point, Zarembo Island, there are small masses of granite 

porphyry and rhyolite porphyry intrusive into slate. The rhyolite 

porphyry is exceptionally miarolitic, and the volume of the druses as 

measured on the polished surface of a hand specimen is about 4.5 

per cent. The druses range from a fraction of a centimeter to a 

centimeter in diameter. These druses are lined with terminated 

quartz crystals projecting into the cavity and are associated or 

flecked with many small plates of crystalline hematite (specularite). 

The druses are further partly or completely filled with a microcrystalline aggregate of kaolinite, usually with calcite in the center.

The sto°ck which cuts the diorite on Etolin Island ranges from a 

medium-grained granite on the southeast to a granite porphyry on 

the northwest. The porphyry has a very prominent miarolitic structure. The druses average about 0.5 centimeter in diameter and are 

lined with terminated quartz crystals and well-bounded crystals of 

microperthite projecting into the cavities. There are also many 

masses of granite porphyry forming the islands in Ernest Sound. 

Many of these are miarolitic; and hexagonal biotite crystals are 

common in the druses in addition to the quartz and feldspar.

These granitic masses differ from the intrusive rocks of the Coast 

Range in their more massive character and miarolitic structure and 

in certain features of texture characteristic of volcanic rocks. They 

are similar to the known Tertiary granite near Point St. John,
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 223

Zarembo Island. It is possible that they are either of Tertiary age 

or a very late phase of the Upper Jurassic or Lower Cretaceous 

intrusions of the Coast Range.

A sill of granite is intrusive into black slate on the southwest side 

of Endicott Arm, in the Juneau district, and rarely a granitic facies 

develops in the main Coast Eange batholith, as near Tombstone Bay, 

Portland Canal.

A stock of granite 3 miles wide, intrusive into diorite gneiss, on 

the east side of the North Arm of the West Bay of Dundas Bay, 

on the mainland north of Cross Sound, has been described by the 

Wrights.50

The predominant mineral in the granite is a potassic feldspar 

which may be orthoclase, microperthite, or microcline. Microperthite 

is most common in the stocks of the Ketchikan and Wrangell districts. It forms 55 to 73 per cent. The plagioclase ranges from 10 

to 15 per cent and is albite or .albite-oligoclase. Quartz ranges from 

12 to 40 per cent. The accessory minerals are usually sparse; they 

include magnetite, apatite, and zircon. Hornblende or biotite is 

usually present, but their total amount forms only a small percentage. 

The granites ,are usually of a distinctly pinker or redder hue than 

the dioritic and quartz dioritic types of rock.

PEGMATITE AND APLITE

Pegmatite is a facies of the Upper Jurassic or Lower Cretaceous 

intrusive rocks which occurs predominantly as dikes or sheets near 

the borders of the stocks or batholiths, either in the igneous rock 

itself or in the adjoining schist and country rock. It is usually considerably coarser grained than the main mass of the igneous rock. 

Aplite has a similar relation and mode of occurrence but is finer 

grained than the igneous rock with which it is associated.

In the central part of the mainland batholith, in the igneous rock 

itself at ,a distance from included slabs or blocks of schist, pegmatite and aplite are rare; but along the western margin, in the Ketchikan and Wrangell districts and the southern part of the Juneau district, they are abundant, and the .adjacent schist as far north as 

Juneau is usually intimately penetrated by them parallel to the 

schistosity, so as to constitute injection gneiss over belts several 

miles in width.

North of Juneau, in the Eagle River and Berners Bay region, the 

development of aplitic ,and pegmatitic differentiates and the resulting 

injection gneisses is not so extensive as in the southern part. Near

60 Wright, F. E. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript) .
224 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

and in large inclusions of schist, even in the central part of the 

batholith, pegmatite dikes and veins are common. Where the pegmatite and aplite are not abundantly developed aplite is usually the 

more common; it may be found as dikes far away from the nearest 

igneous intrusion and widely distributed.

In the sedimentary rocks of the Hyder district around the borders 

and in the roof of the Texas batholith dikes of aplite and less commonly pegmatite occur within several hundred feet of the contact.

Wright, in describing the mode of .occurrence of pegmatite and 

aplite in the neighborhood of stocks in the Copper Mountain 

area, Prince of Wales Island, says that they form in places a network of small dikes and stringers within a zone of fractured schist, 

though they are more prominent as separate dikes traversing the 

granitic intrusive masses. In general, pegmatite and aplite dikes are 

present in the borders of intrusive stocks and the adjacent metamorphic rocks in the Alexander Archipelago, but they are not 

plentiful.

Wright calls particular attention to the relative .absence of pegmatite and aplite dikes in the intrusive rocks in the vicinity of 

Glacier Bay. Pegmatite is relatively more rare than aplite.

The pegmatite dikes along and near the west flank of the Coast 

Eange batholith typically consist predominantly of albite (Ab95An8 ) 

to oligoclase-andesine (Ab65An35 ) plagioclase with quartz. Microcline or microperthite is usually present in small amounts.

The dikes are usually light colored and coarse grained, and only 

the common accessory minerals are present. Crystals of muscovite 

or of biotite are common in the pegmatite dikes along Bradfield Canal 

and at the head of Knygs Lake, on the mainland, and on Fools Inlet, 

Wrangell Island. In a typical pegmatite dike about a mile east of 

Bergs Basin the dominant feldspar is oligoclase-andesine (AbgAnJ 

accompanied by a little orthoclase, accessory muscovite, and about 30 

per cent quartz. Most of the feldspar is untwinned, but its identification as a plagioclase may be made by its index of refraction.

Near the head of Knygs Lake on the west side there are albite pegmatite veins with abundant small miarolitic cavities in which platy 

hexagonal barrel-shaped crystals of prehnite about 0.75 centimeter 

in diameter are found. Some of the pegmatite veins here carry considerable pink orthoclase and grains of black magnetite. Others are 

remarkable for a graphic intergrowth of garnet and quartz interstitial to the albite feldspar.

The pegmatites of the core and the eastern part of the Coast Range 

batholith have not been seriously investigated. The few observations 

available suggest that these pegmatites, like the igneous rocks with
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 225

which they are associated, are higher in potassic feldspars and are of 

a quartz monzonitic or granitic composition.

Aplite occurs in part as discrete dikes but for the most part as 

narrow veins intimately penetrating the belt of injection gneiss 

adjacent to the Coast Range batholith on the mainland or adjacent to 

some of the outlying stocks. In the discrete dikes quartz constitutes 

as much as 30 per cent of the rock, but in the injected veinlets whose 

borders fade into the adjoining schist layers quartz is present only 

as an accessory. In both modes of occurrence, however, the feldspars 

are similar. The decrease of quartz in the veinlets of the injection 

gneisses must be the result of reaction with the original minerals of 

the schist.

In composition, the aplite shows a wide range of variation similar 

to that of the granular igneous rocks. Such varieties as oligoclasequartz diorite aplite, oligoclasite, quartz monzonite aplite, granite 

aplite, syenite aplite, and granodiorite aplite are found. The highly 

sodic aplites are usually found in conjunction with the more sodic 

granitoid rocks, such as quartz diorite and granodiorites low in potassium, and the more potassic aplites are found predominantly with 

granodiorite and quartz monzonite.

Near the southwestern border of the Coast Range batholith aplite 

dikes are common. Soda-lime feldspar is the predominant mineral in 

most of these aplites, and they are characteristically oligoclase-leucoquartz diorite aplite or granodiorite aplite; or in the injection gneisses, 

oligoclasite (probably as a result of reaction with the sediments).

A typical specimen of aplite from sharply defined dikes in the 

quartz diorite south of Thomas Bay is a fine-grained white rock with 

a trace of porphyritic texture. (Soe table on p. 227, No. 1.) The 

aplitic material in the body of the schists of Thomas Bay is almost 

entirely plagioclase feldspar, ranging from oligoclase-andesine 

(Ab7An3 ) to andesine (Ab6A4 ) with locally a little quartz. At 

Thunder Point, Le Conte Bay, a sheet of aplite intrusive into hornblende schist consists almost wholly of plagioclase (Ab7An3 ) with a 

small percentage of quartz and shredded corroded remnants of hornblende torn from the adjoining schist. The aplitic injection gneisses 

of the Groundhog Basin consist almost exclusively of oligoclaseandesine (Ab72An28 ) with accessory hornblende, biotite, garnet, pyroxene, or epidote that have been torn from the adjoining schist and 

corroded or formed by reaction. Quartz is present as an accessory 

mineral only. Muscovite is common in many of the aplite dikes.

Typical examples of oligoclase-quartz diorite and oligoclase granodiorite aplite from the western border zone of the Coast Rango 

batholith are given in the table as Nos. 1 to 4.
226 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Aplite of the potassic type also occurs both as discrete dikes and 

as veinlets in injection gneiss of the western border zone of the batholith. Typical examples of discrete dikes are found southeast of 

Groundhog Basin. The rock is white and fine grained (average diameter about 0.2 millimeter); microperthite and microcline constitute 

the predominant feldspar and are accompanied by a little plagioclase 

and about 30 per cent of quartz. In the injection gneiss along Bradfield Canal, some of the aplite veinlets are composed almost exclusively of microcline and microperthite, and others of oligoclase-andesine and quartz with a trifle of orthoclase or microcline. Both types 

may appear in the same layers of gneiss, and in such occurrences the 

microcline-microperthite variety seems to be the older. Both the 

sodic and the potassic aplites have only a little quartz in the injection 

gneiss but are normally quartzose in the discrete dikes.

Analyses of typical examples of oligoclase-quartz monzonite aplite 

from the core and the eastern part of the Coast Range batholith 

are given in the table as Nos. 5, 6, and 7; of two examples of granite 

aplite from the eastern part of the batholith as Nos. 8 and 9; and 

of two examples of potassic aplite, associated with an outlying stock 

on Prince of Wales Island as Nos. 10 and 11.

An unusual type of granite aplite dike on the Kasaan Peninsula 

has been described by Wright.51 Its composition is given as No. 12. 

The unusual feature is the occurrence of calcite as a primary mineral. 

Merwin writes that

Two periods of crystallization can be made out. In the first period quartz, 

orthoclase, and a little calcite formed an even-grained mass penetrated by spiderlike stringers of the mother liquor. In the second the mother liquor solidified in 

a partly granular, partly poikilitic mass. Orthoclase and calcite are much 

more abundant in the later crystallization, and the calcite is coarser grained 

and anhedrai.

The data available on rocks within the Coast Range batholith suggest that in the aplites associated with a particular type of igneous 

rock the plagioclase is more sodic than that of the genetically associated rock and the percentage of potassic feldspar is higher in the 

aplite than in its parent rock.

si Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula. 

Alaska: U. S. Geol. Survey Prof. Paper 87, p. 81, 1915.
UPPEE JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 227 

Mineral composition of typical aplite

1

?

3

4

5

6

7

8

9

10

11

12

Oligoclase granodiorite aplite, Hobart

Bradfleld Canal, Wrangell district- ... 

Oligoclase-quartz monzonite aplite, 1

Oligoclase-quartz monzonite aplite, head

Quartz monzonite aplite, Chickamin

Granite aplite, north side of Texas

Goat Mountain, near head of ChickaAdamellite aplite, near Jumbo mine,

Calcite alaskite aplite, Kasaan PeninPlagloclase

62

52 .

45

57

(AbrAm) 

31

28

26

14.6

16

f 45 

< (Ab4Ant to

I AbjAn,) 

10-15

(Albite)

Quartz

25

36

30

28

27

36

47

34

30

1 8 f 8

30-55

30

Potassic 

feldspar

12

6

22

15

41

35

21

51

45

45

40-50

60

Calcite

9

Accessory 

minerals

6

(Muscovite)

1

1

6

.4

2

« Collected and described by W. B. Jewell (personal communication).

*Described by Merwin, H. E., in Wright, C. W., U. S. Geol. Survey Prof. Paper 87, pp. 40, 81, 1915.

The Wrights 52 state that in practically all the aplites and pegmatites in the Glacier Bay region a little orthoclase or microcline is 

present. Oligoclase and quartz are the predominant minerals. Hornblende, biotite, magnetite, titanite, and apatite may occur as accessory 

minerals.

Knopf ,53 in describing the Sitka mining district, writes:

Pegmatite and aplite dikes accompany the quartz diorites. * * * The 

aplite dikes are of greater importance and are widely distributed, though nowhere present in large numbers * * * and consist essentially of andesine 

(AbzAni) with minor amounts of biotite or hornblende. Pyrite, calcite, muscovite, and chlorite appear as secondary minerals.

In the ultrabasic rocks pegmatitic f acies are restricted almost wholly 

to the hornblendites, but in these they are common. Predominantly 

they are very coarse and consist of hornblende and albite with accessory plates of biotite; some contain abundant crystals of titanite or 

apatite or both. Locally the veins are highly feldspathic or consist 

wholly of albite. In a mass of hornblendite on Mitkof Island pegmatitic facies with large plates of biotite several inches in diameter 

are common.

The Midway Islands, in Stephens Passage, are formed of hornblendite with abundant pegmatitic facies, consisting of very coarso 

columnar black hornblende; hornblende with biotite; hornblende and

83 Wright, F. E. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript).

M Knopf, Adolph, The Sitka mining district, Alaska : U. S. Geol. Survey Bull. 504, p. 16, 

1912.
228 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

albite; hornblende with pyroxene and magnetite; hornblende and 

albite with abundant pyrite, apatite, and titanite; albite and epidote. 

or albite alone. The albite in the last-mentioned f acies occurs as discrete veinlets.

One such pegmatitic facies of hornblendite consists of columnar 

crystals of hornblende as much as 6 inches in length and half an inch 

in diameter, with interstitial white albite. The basal sections of the 

hornblende crystals are euhedral and approximately equidimensional. 

The albite is almost exclusively molded against the crystal faces of 

the hornblende, but locally small veinlets and threads of albite Break 

across the hornblende and slightly replace it. A little epidote and 

titanite are associated with the albite. The epidote is of contemporaneous crystallization and in part occurs interstitial to the hornblende and molded against its crystal facies.

Another facies is a very coarse pyroxene-hornblende rock with black 

hornblende predominant in crystals averaging 2 inches in length. A 

considerable percentage of magnetite is associated with the pyroxene. 

Traces of titanite, albite, and epidote occur interstitial to the hornblende and pyroxene and molded against their crystal faces. Here 

and there a magnetite or pyrite crystal with idiomorphic outlines 

occurs in the albite.

; Another variety is composed of about three-fourths epidote of a 

pale greenish-amber color and one-fourth albite, in a granular aggregate with accessory titanite. The epidote shows crystal faces against 

the albite, and the albite occurs interstitial to the epidote and locally 

sends off thin veinlets across it.

Still another facies is predominantly a medium-grained granular 

aggregate of black hornblende with very abundant apatite and pyrite 

and idiomorphic crystals of titanite a quarter of an inch in diameter. 

In the weathered rock the titanite can be picked out as perfect crystals. In an albite-rich facies of this rock pyrite forms a triangular 

area between large albite plates, is molded against the albite, and is 

probably of late pegmatitic origin. A small vug with crystals of 

epidote occurs in the pyrite. Epidote also coats cleavage surfaces of 

the albite and locally replaces the albite along the border of the 

albite and pyrite. Apatite crystals are abundant as inclusions in the 

hornblende.

Pegmatitic veins consisting of hornblende and albite with hornblende predominating, of albite, of albite and biotite, of microperthite and pyroxene, and of calcite and albite occur in the ultrabasic 

rocks of Kane Peal?:, Kupreanof Island.

In the hornblendite pegmatites the accessory minerals are the first 

to crystallize but finish late. The order of crystallization among the 

accessories is apatite, magnetite, titanite. Hornblende is the first of
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 229

the major minerals to form but is soon joined by albite, with a little 

epidote. The crystallization of the albite overlaps that of the hornblende and epidote. Locally a little pyrite succeeds the albite. This 

completes the distinctly pegmatitic stage. Epidote* of a later generation locally replaces the hornblende and albite.

MALCHITE DIKES

In the Hyder district dikes of malchite are common in the country rock to the east and north of the eastern border of the quartz 

monzonite of the Coast Kange batholith. They also cut granodiorite 

porphyry dikes, which are offshoots of the quartz monzonite or are 

genetically connected with it.

The malchite is a green-gray or dark-gray rock of fine grain or 

sparsely porphyritic felsitic texture. When exajnined microscopically it is seen to consist typically of small phenocrysts of plagioclase 

and locally of plagioclase and hornblende in a groundmass composed 

of a mat of plagioclase laths with subordinate green hornblende rods 

and a little interstitial quartz and potassic feldspar. Abundant 

minute crystals of magnetite are distributed throughout the groundmass, and apatite occurs here and there. The variety of the plagioclase is difficult to determine, but it appears to range from an albiteoligoclase to andesine. These dikes appear to be in part late f acies of 

the Coast Range batholithic intrusions in this area, grading toward 

lamprophyres, and in part simply quickly chilled, less differentiated 

facies of the magma.

LAMPKOPHYRE BIKES

Dikes of lamprophyre, dark green-gray to gray-black rocks of fine 

grain, are found at many places cutting batholithic intrusive masses 

and the surrounding country rock. They are locally very abundant 

within the Coast Range batholith. On Tracy Arm they are particularly well shown. They occur here in the quartz diorite throughout 

the length o,f the arm, but are especially abundant in certain belts 

at one place 13 dikes were counted within 100 feet. They range in 

width from 1 foot to 10 feet. On the bare walls of the fiord they may 

be seen to form ribbon-like bands extending upward from sea level 

several thousand feet to the tops of the mountains. They are also 

well shown in certain belts along Portland Canal.

Spessartite, garganite, kersantite, minette, and vogesite are types 

of lamprophyre which have been found in this district. The predominant type1 is allied to spessartite; the ferromagnesian mineral 

is predominantly brown hornblende, and the feldspar is almost 

wholly the oligoclase or andesine variety of plagioclase. Lamprophyre composed of these minerals will here be classed as spessartite. 

Augite is present locally, and there the rock varies toward the gar-
230 GEOLOGY AND MINEBAL DEPOSITS, SOUTHEASTEBET ALASKA

ganite type. Brown hornblende usually forms 10 to 50 per cent of 

the spessartite of southeastern Alaska, but may be as high as 75 per 

cent or even more. Plagioclase is usually the predominant mineral. 

Potassic feldspar *is only rarely present.

The spessartite usually consists of long prismatic rodlike crystals 

of brown hornblende with or without a few a.ugite crystals, in a 

groundmass formed by a felt of oligoclase or andesine laths with or 

without associated rods of broAvn hornblende. Magnetite is usually 

present as disseminated abundant small crystals, and apatite in long, 

slender rods. Titanite is found occasionally. There is commonly 

a trace of interstitial quartz. Secondary minerals are always present 

and may be very prominent; they comprise calcite, chlorite, and 

epidote. Calcite is usually abundant in the groundmass, and much 

of it shows replacement relations to the other minerals, but in part 

it is interstitial to the plagioclases and molded against them. It must 

belong to a late magmatic stage and phase of alteration.

On the Commonwealth claims, about 14 miles below Hyder, on 

Portland Canal, a tunnel has been driven along an augite minette 

dike that occurs in quartz monzonite in the eastern part of the Coast 

Eange batholith. The dike rock consists of augite and dark-brown 

biotite phenocrysts in a groundmass of orthoclase with accessory 

apatite and ilmenite. The biotite is locally altered to chlorite and 

secondary magnetite. The orthoclase is flecked with sericite and is 

partly replaced by chlorite and calcite. Augite in rods forms about 

two-fifths of the rock, biotite about one-fourth, and orthoclase with 

secondary and accessory minerals the remainder.

West of the Coast Range batholith the presence of younger Tertiary basic dikes and of older basic porphyritic dikes complicates the 

study of the lamprophyre and lamprophyrelike dikes, which may 

be genetically associated with the Upper Jurassic or Lower Cretaceous intrusive rocks. The types described include vogesite- a 

highly augitic variety and spessartite, with rarely a minettelike 

type. Diabase dikes are locally common arid in places cut the ore 

deposits, but many of them give no evidence as to whether they 

belong to the Tertiary intrusive rocks or to the Upper Jurassic or 

Lower Cretaceous.

A dike of hornblende minette on the inland shore of Gastineau 

Channel about 2 miles southeast of Juneau has been described by 

Spencer. 54 This rock is said to. consist mainly of biotite and basaltic 

hornblende, with some feldspar, a small amount of augite, and accessory magnetite and titanite. Mertie reports a sodic augite minette 

from the west side of Lynn Canal which consists of biotite and 

augite, with accessory iron oxide and apatite and interstitial albite.

M Spencer, A. C., The Juneau gold belt, Alaska : U. S. Geol. Survey Bull. 287. p. 19, 

1906.
UPPER JURASSIC OR LOWER CEETACEOUS INTRUSIVE ROCKS 231

Lamprophyric dikes in the Eagle River region, where they are of 

widespread occurrence, have been described by Knopf.56 A common 

variety is said to consist of phehocrysts of augite in an altered 

isotropic groundmass containing smaller crystals of augite and some 

brown hornblende.. Another -^variety, of basaltic appearance -that is 

not so common is described as consisting of hornblende, augite, and 

biotite in a groundmass of brown hornblende with sporadic augite 

and interstitial labradorite. also accessory magnetite and apatite. 

Still another, type consists of pyroxene, olivine, biotite, and hornblende in a matrix of analcite (?), zeolite, and probably orthoclase. 

Knopf 56 also describes la.mprophyre dikes in the Berners Bay region, 

where one variety consists of augite phenocrysts in a groundmass of 

augite and a little biotite, brown hornblende, and interstitial labradorite, and another variety consists of hornblende phenocrysts in a 

much altered groundmass of plagioclase.

In the Sitka district Emerson 57 noted a spessartite dike at Hot 

Springs, near Sitka; F. E. Wright has determined others from the 

same locality to be vogesite.

A spessartite dike on the west side of Baker Island, about 1% 

miles north of Veta Bay, in the Ketchikan district, consists of brown 

hornblende with some interstitial plagioclase and abundant minute 

crystals of magnetite. The hornblende occurs both as phenocrysts 

and in the groundmass. Sparse augite phenocrysts are also present. 

Merwin 58 has described a spessartite type of lamprophyre .from the* 

Copper Mountain region. It is reported to consist of 35 per cent of 

green hornblende, part of which occurs as phenocrysts, plagioclase- 

(andesine to acidic labradorite), 10 per cent of magnetite, and accessory minerals.

STRUCTURE OF THE INTRUSIVE ROCKS

In the mainland batholith the rocks are prevailingly ..gneissoid.. 

The banded character is most accentuated near the borders of the 

batholith or near inclusions within the batholith. Local schistose 

zones are found along intensety sheared narrow bands. In the central parts of the batholith masses of considerable extent show only an. 

indistinct gneissic structure.

Where evidences of shearing and mashing are absent or practically 

so, as is usually the case, the two most distinctive gneissoid character55 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, pp. 31-32, 1912.

58 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S.'Geol. Survey Bull.. 

446, pp. 18-19, 1911.

67 Emerson, B. K., Alaska, vol. 4.'p. 18. Harriman Alaska Expedition, 1904.

58 Merwin, H. E., in Wright, C. W., Geology and ore deposits of Copper Mountain andj 

Kasnan Peninsula, Alaska : U. S. Geol. Survey Prof. Paper 87. p. 42, 1915.

6137 29 1(5
232 GEOLOGY AND MINERAL, DEPOSITS, SOUTHEASTERN ALASKA

istics are (1) the parallel dimensional orientation of the inequidimensional mineral grains, such as the more or less lath-shaped or tabular feldspars, the prismatic hornblendes, and the lenses or leaves of 

quartz; and (2) the relative indistinct segregation of the light and 

dark minerals in flat en echelon lenses or in small patches. It is noteworthy that most of the abundant biotite crystals are chunky in form 

and that many of them are oriented with the c axis parallel to the 

foliation, which is contrary to the usual orientation in secondary or 

recrystallized gneiss.

The gneissic structure is for the most part interpreted as having 

arisen during the period of crystallization of the magma and before 

its completion, and the rock is therefore a primary gneiss. Flowage 

currents, nonuniform stresses, the pressure of the shouldering effect 

of the intruding magma upon the walls of the batholith, and locally 

a gneissic structure inherited from reaction with slabs of schist have 

all contributed to produce the structure which we now find.

The writer examined 20 specimens of gneissoid quartz diorite from 

the west side of the mainland batholith between Portland Canal and 

Taku Inlet and found not a trace of crushed or granulated minerals 

in any of them. Most of the quartz shows strain shadows, and some 

of the biotite crystals may show distortion and slip planes, but these 

comprise the only evidences seen of the effects of stress upon the 

rocks subsequent to their consolidation.

The structure of the rocks near Behm Canal has been described by 

Westgate 59 as follows:

Structural variations in the granitoid rocks are marked and have an important bearing on origin. The rocks are dominantly gneissoid. Even in the most 

massive types well in toward the heart of the batholith it is difficult to find 

ledges without some parallel structure, either a faint banding and orientation 

of the dark minerals or drawn-out streaks of darker rock (Schlieren). And 

even in these more massive parts frequent transitions take place to a conspicuously banded rock, the bands of which are commonly bent, sometimes 

intricately folded. These folded gneissoid granitoid rocks are not the result 

of mountain-making forces acting after the solidification of the rocks. * * * 

They result from the flow of yet unsolidified magma. * * * Sederholm 60 

has likened the banding of the gneiss to twisted lines of sawdust seen on a 

flowing stream.

The gneissic character * * * is accentuated because * * * the intrusion is not simple but took place by successive advances of somewhat different magmas. Injection of later magma along planes already determined in 

the earlier magma probably not then fully consolidated would emphasize 

the banded character of the resultant complex.

68 Westgate, L. G., The geology and mineral resources of the area east of Behm Canal 

(unpublished manuscript).

60 Sederholm, J. J.r Ober ptygma.tisehe Faltungen : Neuea Jahrb., Beilage-Band 36, pp. 

491-512, 1913.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 233

It is certain, however, that the mainland batholith has been subjected to very considerable stresses subsequent to its complete consolidation. Yielding has taken place through extensive mashing 

along local belts or zones, which may be of considerable width and 

great length (75 miles or more), or through intensive shearing along 

narrow zones, or through slipping along many planes of various 

orientation throughout a zone. In most of the specimens examined 

in thin section the quartz shows strain shadows or locally and less 

commonly is irregularly broken into ribbons or has a sutured or 

denticulate texture typical of recrystallization. In spe-cimens from 

the shear zones the quartz is mashed and the feldspar grains are 

extensively comminuted on their borders.

A belt of highly mashed rock 15 miles or so wide is crossed by 

Stikine River from the head of Little Canyon to and below Flood 

Glacier. The varieties of rock included within this belt are diorite, 

quartz diorite, granodiorite, quartz monzonite, and granite.

In 15 specimens chosen by the writer at intervals along the west 

side of Portland Canal 4 show very pronounced cataclastic structure, 

7 show neither crush phenomena nor strain shadows in quartz, and 4 

show on]y strain shadows in quartz. The writer found no evident 

relation between the type of rock and the degree of crushing or between the degree of crushing and proximity to the border of the batholith. In the shear zones the quartz is completely granulated, as is 

also a very considerable part of the peripheral zone of the feldspar.

Knopf 61 has described a rock in which cataclastic effects, resulting 

from stress acting upon the completely consolidated igneous rock 

with its primary gneissoid structure, predominate and accentuate 

the original gneissic character:

The gneissic structure of the quartz diorite, like the foliation of the adjoining 

schists, trends northwest and southeast and dips steeply to the northeast at 

about 70°. It is in part a primary structure assumed by the magma during 

solidification but is mainly a result of dynamic metamorphism, the most obvious 

effect of which has been the reduction of the large feldspar crystals to augen. 

In a few places the feldspars were sufficiently crushed and drawn out to form 

narrow white bands. The foliation of the gneiss is most pronounced near the 

contact, where it is in places so strongly developed as to form a black diorite 

schist carrying porphyritic eyes of feldspar; toward the northeast the gneissic 

structure gradually and progressively gives way to the massive granular texture 

characteristic of the normal granitic rocks.

The structure of the stocks and batholiths of the Alexander Archipelago is variable and depends upon several factors. The margins 

of the masses show locally a gneissoid structure. The granodiorite is 

usually gneissoid, whereas the diorite and gabbro are more commonly

81 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, pp. 23-24, 1912.
234 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

predominantly massive. In the Glacier Bay region, also, the 

Wrights 62 noted that, with the exception of a few bodies of diorite 

gneiss, the diorites are fairly fresh, massive rocks. Knopf 63 has 

described the Jualin diorite stock in the Berners Bay area and an 

augite diorite stock in the Eagle Eiver area 64 as generally massive. 

In describing the geology of the Sitka district Knopf ° 5 writes :* " The 

intrusive rocks are commonly fresh and unaltered and are little 

affected by schistose or gneissic structure. The marginal portions of 

some of the intrusive masses, however, show gneissic foliation."

The outlying intrusive masses, like the mainland batholith, also exhibit local shear zones in which the minerals are crushed and mashed. 

On the w«st coast of Chichagof Island, according to Overbeck,66 

most of the area mapped is not far from the contact between the intrusive igneous rocks and other rocks, and consequently the rocks of 

the intrusive body are greatly sheared. Though this is a common 

phenomenon it is far from being uniformly true.

At some places west of the Coast llange batholith extensive belts, 

including intrusive igneous 'stocks, dikes, and' sills constitute a local 

shear zone or zone of close folding; the larger masses of igneous rocks 

may show considerable mashing, and the thin sills may be closely 

folded together with the schists.

In a belt adjacent to Stephens Passage, from Port Houghton north 

to Point Astley on the mainland, outlying stocks of igneous rocks 

have been considerably crushed and recrystallized and altered. The 

inclosing rocks are likewise intensely sheared and plicated. The extension of this belt of shearing is apparently indicated by the mashed, 

character of the intrusive masses on Grand Island and near Point 

Arden, Admiralty Island. The pegmatites are mashed as well as the 

main bodies of intrusive rock. The Tertiary basaltic dikes, however, 

are unaffected.

The Wrights 6T describe the quartz diorite on the west side of Sullivan Island and granodiorite at-the south .entrance to Chilkat Inlet as 

much crushed and suggest that this crushing is the result of movement along a great shearing plane, in the course of which the west 

shore of Lynn Canal rose relatively to the east shore.

"Wright, F. B. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript).

63 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

466, pp. 13-14, 1911.

84 Knopf, Adolph, The Eagle River region, southeastern Alaska : U. S. Geol. Survey Bull. 

502, pp. 29-30, 1912.

88 Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504. p. 15r 

1912.

68 Overbeck, R. M., Geology and mineral resources of the west coast of Chichagof Island :: 

U. S. Geol. Survey Bull. 692, p. 109, 1919.

67 Wright, P. E. and C. W., The geology of Glacier and Lituya Bays (unpublished manuscript) .
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 235

These zones evidently mark an area of unusually intense shearing 

of an age subsequent to that of the Upper Jurassic or Lower Cretaceous intrusions.

The ultrabasic rocks are in general massive, and though some f acies 

may show a gneissic structure they are usually without any evidences 

of crushing; locally, however, they are severely sheared and mashed. 

The diorites are almost uniformly massive, and only rarely are 

mashed. The hornblendites are generally massive in the coarser f acies 

but may be slightly gneissoid in the medium-grained facies. The 

gabbroic hornblendites usually show a well-developed gneissic structure due to flowage.

The granites are uniformly massive.

The structure of the pegmatite and aplite dikes is variable, some 

being gneissoid and mashed and others massive. In thin section some 

show crushing of the feldspars, undulatory extinction in the quartz 

and feldspars, and recrystallized quartz; others show a massive texture of primary crystallization without any evidence of crushing or 

gneissic character.

Knopf C8 found the same relations in the Eagle River region. He 

writes: "A period of dynamic deformation set in during the pegmatitic stage, for some of the pegmatite and aplite dikes are sheared 

like the gneiss, but others have escaped the general dynamic metamorphism."

The various types here described as Upper Jurassic or Lower 

Cretaceous intrusive rock all appear to cut the Jurassic or Cretaceous 

formations and to be unconformable beneath the Eocene. They must, 

therefore, have been intruded after the formation of the Jurassic or 

Cretaceous beds which they cut and before the Eocene epoch. The 

possible length of time for their intrusion is thus restricted to a relatively short period geologically, though this period may have been 

very long in terms of years. Because these rocks belong to the same 

general period of intrusion and because their composition and character are such as to suggest genetic relations, they are commonly 

believed to have been derived through very complicated interaction 

of processes and differentiation from an original common magma.

We do not yet know the processes entering into magmatic differentiation sufficiently well to solve the problems of origin of a suite 

of simple rock types of the same magmatic period, even when we 

have adequate data as to the rock types and their interrelations, and 

as the data on the types and interrelations of the Upper Jurassic or

48 Knopf, Adolph, The Eagle River region, southeastern Alaska: TJ. S. Geol. Survey Bull. 

502, p. 14, 1912.
236 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Lower Cretaceous intrusive rocks in southeastern Alaska are wholly 

inadequate, we are therefore not in a position to speak with any 

defmiteness as to their origin. It is desirable, however, to bring out 

certain interrelations which may have a bearing upon any theory of 

magmatic differentiation proposed to explain the origin of these 

various types and associations of rocks. Two major problems arise 

in this connection; one concerns the amount and character of differentiation in place; the other the number, importance, and relations 

of successive intrusions.

The types of the Upper Jurassic or Lower Cretaceous intrusive 

rocks of southeastern Alaska are essentially similar qualitatively and 

quantitatively to those characteristic of the intrusive rocks belonging 

to the same period far to the northwest and to the southeast. The 

genetic problems involved are therefore essentially the same; hence 

the data accumulated and the inferences drawn by workers elsewhere 

within the Coast Eange and the adjoining islands are pertinent to 

the consideration of the origin of the intrusive rocks in this area.

DIFFERENTIATION IN PLACE

Significant data covering variations within a single mass of the 

Upper Jurassic or Lower Cretaceous intrusive rocks have been established by workers in other areas.

Burwash 69 writes of the southern part of the mainland batholith:

Quartz diorite is easily the dominant type for the area under consideration. 

The more quartzose phases occur at a distance from Paleozoic contacts, and the 

more basic as the contacts are approached. This marginal differentiation generally takes the form of a decrease in quartz and an increase in hornblende. 

* * * In some cases, as in the vicinity of The Lions, the hornblende becomes 

so predominant that the rock over small areas might be properly described as 

hornblendite. This type of differentiation occurs in contact with the basic 

eruptives and limestones of the Texadan series, and where it occurs at a distance from roof pendants it probably indicates that the roof originally existed 

in close proximity to the remaining differentiation rocks.

Bancroft 70 in discussing the geology of the intrusives of the Coast 

Range in the vicinity of the Strait of Georgia and Queen Charlotte 

Sound, B. C., writes:

In general, the sequence of intrusions has been marked by an increasing 

acidity of the magma with a corresponding decrease in the specific gravity. 

The hornblendites and some of the larger bodies of dark basic rocks are the 

oldest, while the light-colored quartz diorites, granodiorites, and granites 

are the youngest. As a rule, differentiation has likewise taken place in the 

individual batholiths in such a manner as to form a peripheral zone of rela88 Burwash, E. M. J., The geology of Vancouver and vicinity, p. 50, Univ. Chicago Press, 

1918.

70 Bancroft, J. A., Geology of the coast and islands between the Strait of Georgia and 

Queen Charlotte Sound, B. C.: Canada Geol. Survey Mem. 23, p. 103, 1913.
UPPER JUBASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 237

tively basic rocks such as dark diorites and gabbros, which shade gradually 

into an interior of more siliceous and homogeneous character. For example, 

near Kwalate Point in Knight Inlet the hornblendites, which seem to be an 

ultrabasic marginal modification of the oldest batboliths within this area, pass 

gradually into a dark diorite.

Wright 71 and Merwin have described in detail certain of the intrusive rocks on the south end of Prince of Wales Island. In the 

vicinity, of Hetta Inlet the main batholiths of Copper Mountain and 

Beaver Mountain range in composition from granodiorite to monzonite. Near the contacts the rocks are locally syenitic. Gabbro (in 

part hornblendite) and quartz diorite are local variants. On the 

Kasaan Peninsula the main intrusive rock is diorite, with accessory 

quartz. Local variants include gabbro, monzonite, albite, diorite, 

and a little granite (sodic and potassic-sodic). Marginal variants 

of the diorite include gabbro, which is found north of Karta Bay, 

and monzonite, which occurs at the contact at the Mamie mine.

Knopf 72 describes marginal phenomena of the Coast Range batholith in the Eagle River region as follows:

Various modifications of the quartz diorite gneiss are found along the contacts with the rnain o schist belt and with the outlying bands ,of schist. The 

most common change, as already alluded to, is the passage from the coarsetextured, imperfectly oriented gneiss of gray color to a dark, closely foliated, 

fine-grained gneiss. Locally, as on the northwest side of Herbert Glacier, the 

hornblende becomes segregated so as to form a coarse hornblendite in which 

the interstices between the hornblende prisms are filled with biotite and 

pyrrhotite.

The evidence in southeastern Alaska and in regions immediately 

to the south where the relations have been studied is positive in 

indicating that quartz diorite is in many places a marginal border 

variant to more alkalic types such as granodiorite. It forms a border 

zone on the west flank of the Coast Range batholith from Portland 

Canal to Stildne River for a distance of 150 miles, whereas granodiorite types predominate farther in toward the core.

The average composition of four contact phases and eight subcontact phases of the Coast Range batholith in the vicinity of Vancouver, B. C., is given in the table below. The contact phases are 

hornblende diorite with an andesine-labradorite plagioclase, and the 

subcontact variants are hornblende-quartz diorite with an intermediate andesine plagioclase.

71 Wright, C. W., Geology and ore deposits of the Copper Mountain and Kasaan Peninsula, Alaska: U. S. Geol. Survey Prof. Paper 87, pp. 33-41, 73-83, 1915.

72 Knopf, Adolph, The Eagle River region : U. S. Geol. Survey Bull. 502, p. 25, 1912.
238 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Average volumetric composition of contact and su^contact phases of the Coast 

Range batJwlith w the vicinity of Vancouver, British Columbia °

Andesine .................

Quartz ____ ........

Hornblende. .- ............

Biotite...!. ..............

l

64.45

21.66

9.68

1.49

2

65.38

4.33

26.55

2.46

Titanite ...............

1

0.95

.13

.08

1.66

2

0.98

.09

.21

 Based on data given by Burwash, E. M. J., The geology of Vancouver and vicinity, p. 47, Univ. 

Chicago Press, 1918.

1. Average composition of eight specimens of quartz diorite; subcontact phases of Coast Range batholith.

2. Average composition of four specimens of diorite; contact phases of Coast Range batholith.

The average quartz diorite of the Coast Range batholith in the 

vicinity of Vancouver appears to have a considerably greater percentage of andesine than the quartz diorite in southeastern Alaska 

and only half the amount of f erromagnesian minerals; and, in keeping with this, hornblende is by far preponderant over biotite in the 

southern type. The quartz diorite of the Coast Range batholith in 

southeastern Alaska does not show a contact variant to diorite, as 

in the vicinity of Vancouver. These differences may be explicable by 

the hypothesis that in the vicinity of Vancouver th'e adjacent country 

rock was not so thoroughly and highly heated as in southeastern 

Alaska, and that consequently more rapid chilling with the subse- 

, quent difference in relations resulted.

Clapp 73 in discussing the Saanich granodiorite on Vancouver 

Island writes:

Near its contacts, especially with the Suttou limestones, the granodiorite 

becomes in places more dioritic and passes into quartz and quartz-bearing 

diorites, and also into feldspar-rich, quartz-poor rocks, which are best considered as quartz-bearing feldspathic diorites, although some of them are 

inonzonitic in character. The quartz diorites differ from the normal granodiorites in their lack or small amount of potash feldspar.

The origin of the quartz diorite masses which occur within the 

Coast Range batholith is an unsolved problem. The evidence is 

insufficient to determine whether they are older and are intruded by 

the more alkalic "types surrounding them, or whether they represent 

chilled contact variants against deeply penetrating portions of the 

roof of the batholith, or against earlier intruded magmas.

In the Hyder district the eastern part of the main batholith is 

quartz monzonite. (See table, p. 180, No. 6.) An apophysis or large 

outlying stock in the vicinity of Boundary Glacier is a granodiorite 

(see table, p. 217, No. 5), with a tendency toward a porphyritic texture 

and a finer-grained groundmass. Large dikes in this same area and 

of the same age are granodiorite porphyry and quartz diorite por73 Clapp, C. H., Sooke.and Duncan map areas, Vancouver Island: Canada Geol. Survey 

Mem. 96, p. 192, 1917.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROOKS 239

phyry with a felsitic groundmass, whereas narrow dikes that are 

almost wholly felsitic in texture are quartzose diorite. L The relation 

of degree of differentiation to size of mass and slowness of crystallization is well shown by this sequence. .

The Texas batholith, in the Hyder district, which is predominantly 

granodiorite, passes locally at or near the contact with the country 

rock into a quartz diorite facies or even, immediately adjacent to the 

contact, into a monzodiorite.

Among the mediosilicic rocks there is a tendency for differentiation within a single intrusive mass to produce locally a more basic 

variant on the periphery and a more alkalic-siliceous variant in the 

core. Some of the ultra-basic group of rocks show the reverse phenomena. The dunite stock on the Blashke Islands, in Kashevarof 

Passage, appears to consist of a core of dunite with a narrow peripheral zone of pyroxenite, which changes abruptly through gabbrodiorite to diorite on the outer borders.

In Bohemia Basin, Yakobi Island, the mass of norite with bronzitite segregations appears to be surrounded by diorite, which toward 

one part of the border, at least, grades into quartz diorite. Dikes of 

diorite, however, appear in the norite.

At Kane Peak, on the north end of Mitkof Island, pyroxenite 

appears to form the core of a stock and to be partly surrounded by a 

shell of dunite on its southern edge and hornblendite on its northern 

edge. The relations here have not been thoroughly studied.

SUCCESSIVE INTRUSIONS

Except in the Texas batholith the writer has not seen in the areas 

in which he has worked brecciation phenomena or other unequivocal 

evidences of intrusive relations between such varieties as diorite, 

monzodiorite, quartz diorite, granodiorite, or quartz monzonite. In 

a rapid reconnaissance survey, however, such evidence might easily 

be overlooked. There is, however, abundant and positive evidence 

that members of the diorite-monzonite group of rocks locally intrude 

and brecciate members of the ultfabasic group and gabbro, though 

abrupt apparent transitions, such as have been previously described, 

also occur. The hornblendite masses in particular are in general 

severely brecciated on the borders by intrusive diorite or quartz 

diorite.

There is also abundant and positive evidence that the highly potassic granite batholiths and stocks in the islands of the Alexander 

Archipelago intrude and brecciate older diorite, monzodiorite, and 

quartz diorite.

On the east side of the Coast Range batholith, in the Hyder district, the small Texas batholith probably intrudes Jurassic beds but 

is itself intruded by granodiorite of the main Coast Range batholith
240 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The Wrights n make the following very interesting statement concerning the problem of intrusion, with particular respect to the 

mainland batholith:

The variations across the range [Coast Range batholith] are apparently 

not so gradual as those along its trend. The Coast Range massif consists of 

many interlocking batholiths, or batholiths within batholiths, intruded at 

successive epochs .but during the same general period of'irruption. In the 

southern part of Alaska, especially in the Unuk River, .Stikine River, and 

Portland Canal sections, the contacts between the different batholiths are 

less sharp than in the northern Skagway cross section. The geologic evidence 

indicates that the granite in the southern section was intruded into more 

deeply buried rocks than that in the northern region, and this fact may 

account for the difference in contacts. * * * In this portion of the Alaskan 

Coast Range rapid gradations from one type to another occur and indicate 

in many ways intrusion within intrusion besides variation due to differentiation and assimilation. Naturally it is not probable that intrusion was or could 

be accomplished over such a wide area at one time and by one huge magma. 

For the gradual relief of strains and stresses due to the transfer of so much 

material and also for the action of a viscous magma the lapse of considerable 

time must be assumed.

Dolmage 7B writes as follows concerning the eastern side of the 

Portland Canal sections:

Quartz diorite and granodiorite form over 90 per cent of the total exposed 

bulk of the batholith. These two rocks are very similar in appearance and 

the one often merges into the other, making it difficult to map the two types 

separately. However, the granodiorite, granite, and quartz monzonite have 

sharp intrusive contacts with the gabbro.

Knopf 76 describes the northern part of the batholith as follows:

At Skagway and at the upper end of Taku Inlet it is found that the batholith 

is.of composite origin and that more salic rocks were intruded subsequently to 

the quartz diorite.

Knopf says further:

.The Jualin diorite is undoubtedly of younger age than the quartz 'diorite 

gneiss and has escaped the widespread crushing to which the older rock has been 

subjected.

The general geologic history of southeastern Alaska suggests that the irruption of the quartz diorite and the Jualin diorite took place during one broad 

epoch of intrusion, which so far as known extended through the greater part 

of the Jurassic period. At Berners Bay powerful deformational forces have 

been operative between successive intrusions.

74 w right, F. E. and C. W., The Ketchlkan and Wrangell mining districts, Alaska : U. S. 

Geol. Survey Bull. 347, pp. 61-62, 1908.

'"Dolmage, Victor, Coast and Islands of British Columbia between Douglas Channel and 

the Alaskan boundary: Canada Geol. Survey Summary Rept. for 1922, pt. A, p. 15, 1928.

78 Knopf, Adolph, The Eagle River region, southeastern Alaska : U. S. Geol. Survey Bull. 

502, p. 24, 1912.

77 Knopf, Adolph, Geology of the Berners Bay region, Alaska : U. S. Geol. Survey Bull 

446, pp. 13-14, 1911.
UPPEB JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROOKS 241

Concrete evidence of intrusion of one type of intrusive into another 

appears to be more abundant on the islands west of the Coast Range 

batholith than within the central part of the batholith.

Clapp 78 discusses the relations among the intrusive rocks at the 

south end of Vancouver Island as follows:

Intrusive into the pre-Upper Jurassic .rocks described above are'batholi'ths and 

stocks of plutonic rocks and smaller masses of injected rocks. All the plutonic 

or batholithic rocks were irrupted during the same general period of batholithlc 

intrusion, but nevertheless they may be subdivided into three principal types, 

Irrupted in a definite sequence. These types are, in the order of their irruption; Wark gabbro-diorite gneiss, Colquitz quartz diorite gneiss, and Saanich 

granodiorite. * * * The Wark [gabbro-diorite] and Colquitz [quartz diorite] 

gneisses form virtually a single batholith, but the Colquitz gneiss is clearly 

intrusive into the Wark gneiss. * * * The Saanich granodiorite * * * 

is clearly intrusive into the Wark gneiss, and is quite certainly younger than 

the Colquitz gneiss. * * * It seems clear that the batholithic rocks were 

irrupted during two main periods, which have been called the Wark and Saanich 

periods. During the first period the Wark and Colquitz gneisses were irrupted 

independently. Thus the Wark period is divided into two subperiods, the second subperiod being characterized by the irruption of a more acid or salic 

magma than that first irrupted. A similar division into two subperiods is made 

of the Saanich irruptive period. The first subperiod, during which the basic or 

mafic rock, the Beale diorite, was irrupted, is possibly represented in the Duncan 

map area only by some of the contact phases of the Saanich granodiorite, such 

as the quartz gabbro.

Again Clapp 79 states:

Perhaps preceding, but chiefly during and closely following, the deformation 

[Jura-Cretaceous], batholiths and stocks of granitic rocks, and sills, dikes, and 

irregular masses of porphyrites were intruded into older surface-formed volcanic and sedimentary rocks of the Vancouver group. * * * Those granitic 

rocks irrupted during the deformation were foliated and pulled out into bands, 

the Wark and Colquitz gneisses, while the younger granitic rocks, the Saanich 

Kranodiorite, irrupted after a greater part of the deformation had ceased, are 

still largely unfoliated. The earlier injected porphyrites, the Tyee and Sicker, 

were injected into the Sicker series and were folded arid sheared. The later 

porphyrites were injected into the Saanich granodiorite to form dikes, and their 

injection apparently closed the irruptive cycle begun long before by the eruption 

of the volcanic rocks.

Wright,80 in discussing the intrusive rocks of Kasaan Peninsula, 

Prince of Wales Island, writes:

The granitic intrusives include diorite, gabbro, syenite, and a little granite. 

These intrusives differ considerably in mineral composition and probably represent several periods of igneous invasion during one general epoch, though some 

of the differences can undoubtedly be attributed to segregation of minerals 

within the igneous magma while it was becoming solidified.

78 Clapp, C. H., Sooke and Duncan map areas, Vancouver Island: Canada Geol. Survey 

Mem. 96, pp. 172, 195, 197, 202, 1917. 

TO Idem, pp. 360-361. 

80 Wright, C. W., op. cit. (Prof. Paper 87), p. 74.
242 GEOLOGY AND MINERAL DEPOSITS^ SOUTHEASTERN ALASKA

At the contacts of these granitic batholiths with the country rock there are 

masses of slightly altered and locally sheared diorite surrounded by unaltered 

diorite. At some places these masses show sharp contacts, though at others 

the two kinds of rock merge gradually into each other, suggesting a peripheral 

solidification of the igneous batholith, a fracturing of its outer part, and 

subsequent injection of molten rock into the interstices.

Bancroft 81 discusses the phenomena of intrusion as follows:

The vast majority of these intrusive bodies may thus safely be assumed as of 

Jurassic age, probably being injected during the latter part of that geological 

period. It would seem that at that time this area was resting upon a deepseated magma which, by its intrusion in one locality and then in another, relieved 

the accumulating stresses. A number of batholiths of more basic magmas were 

the first to invade the region. They may be looked upon as the introduction 

to the chapter of igneous activity which followed. Although within a given 

locality periods of quiescence seem to have alternated with periods of renewed 

advance on the part of the magma, such periods of quiescence in one locality 

may have corresponded to periods of activity in another. The upward progress 

of some of the individual batholiths seems to have been of this periodic character. A single batholith must have advanced to a certain level and remained 

stationary for a sufficient length of time to permit the accumulation of more 

basic magma at its margins and solidification through crystallization to a certain depth. Then followed a renewed demand for relief of stress in this locality, 

the still molten and more acid magma of the interior ruptured the more basic 

and solidified peripheral portions of the batholith and proceeded upward once 

more. For example, it seems difficult otherwise to explain how in some localities 

the granite batholith which comprises the majority of the islands in Queen 

Charlotte Sound merges gradually with its basic marginal modifications, and 

in other places the granite is in sharp contact with the same basic rocks. ,

SUMMARY OF RELATIONS OF VARIANTS 

FIELD KHUA.TION8

From' the foregoing descriptions and interpretations, and from the 

data presented elsewhere in this report, the following conclusions may 

be stated.

West of the Coast Kange batholith, more particularly on the 

islands off the coast from Vancouver to Icy Strait and Cross Sound, 

there is a group of ultrabasic intrusive rocks which, though relatively 

minor in amount wheni compared to the immensely greater mass of 

intrusives of more siliceous-all^alic character, yet are numerous and, 

taken together, form a not inconsiderable volume. These include 

hornblendite, pyroxenite, dunite, peridotite, and intermediate variants ; they are older than the group of more siliceous-alkalic types.

Hornblendite occurs also as a local marginal variant to more alkaline and siliceous rocks such as diorite, monzodiorite, quartz diorite, 

and granodiorite. Hornblendite of this origin and relation may be

81 Bancroft, J. A., Geology of the coast and islands between the Strait of Georgia and 

Queen Carlotte Sound, B. C:. Canada Geol. Survey Mem. 23, p. 104, 1913.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 243

of slightly different age from the separate discrete intrusive masses 

of hornblendite, though it too may locally be intruded by the rock 

which forms the more siliceous-alkalic core.

Diorite and gabbro-diorite occur both as discrete stocks and batholiths, and also to a minor extent as marginal variants of quartz diorite 

and granodiorite. Locally gabbro-diorite and augite gabbro form 

marginal variants to diorite. The gabbro-diorite and gabbro are 

locally intruded by diorite, quartz diorite, and more siliceous-alkalic 

types. Locally they form marginal zones to ultrabasic stocks.

Granodiorite in stocks and small batholiths may show marginal 

variants to quartz diorite, gabbro-diorite, diorite, monzodiorite, and 

very rarely to syenite. A decrease in potassic feldspar and quartz 

locally on the margins is a common feature of the granodioritic stocks 

and small batholiths. Clapp reports that quartz diorit© and more 

basic rocks are cut by the granodiorite. Quartz monzonite in the 

eastern part of the batholith locally shows border apophyses or stocks 

of granodiorite and outlying dikes as basic as quartzose diorite.

Granite (potassic) is the youngest of the major members of the 

plutonic complex, and. is uniformly found with intrusive relations 

toward the older members.

It is noteworthy that west of the Sierra Nevada batholith in California there is a similar older group of ultrabasic intrusive rocks 

and a younger group of more alkalic-siliceous intrusive rocks, including quartz diorite, granodiorite, quartz monzonite, and granite.

Accompanying each of the prevalent rock types, such as diorite, 

monzodiorite, quartz diorite, and granodiorite of andesine variety in 

the Alexander Archipelago, there is a relatively very small volume of 

more sodic (albite or oligoclase) leucocratic variants, such as oligoclase or albite diorite and oligoclase or albite quartz diorite, with a 

relatively smaller amount of accessory minerals, such as magnetite, 

apatite, and titanite. These usually occur locally in small volume as 

marginal variants or perhaps more commonly as satellitic dikes, 

sheets, apophyses, and small stocks.

A pegmatitic facies may be associated with each of the major rock 

types except dunite and peridotite. The plagioclase of the pegmatite 

is usually more sodic than the rock with which it is associated. Aplite 

dikes are associated with each of the rock types from diorite to 

granite, and in these, too, the plagioclase is usually of a more sodic 

variety than that of the rock with which it is associated. Veins of 

albite or of albite and calcite and orthoclase in sparse amounts accompany the ultrabasic rocks. In general it seems probable that the 

aplite associated with a particular type of igneous rock contains a 

more sodic plagioclase and a higher percentage of potassic feldspar 

and quartz than the rock with which it is genetically associated.
244 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Lamprophyre dikes are the youngest members of the intrusive 

series, but it is not known whether or not they vary in relation to the 

rock with which they are associated.

ORDEE OF CRYSTALLIZATION

A theory of differentiation which is very prominent at the present 

time is based upon the principle of fractional crystallization. Stated 

in the broadest terms, it is based upon the facts that magmas crystallize not at any one temperature but throughout a temperature interval, and that the average composition of the crystals separated at 

any one time is different from that of the liquid with which they 

are in equilibrium at the given temperature; and it involves the conceptions that if through the action of gravity these crystals sink or 

rise through the liquid or if the liquid is removed from the crystals 

through a process of deformation or filter pressing at a stage when 

the crystals have separated to a sufficient extent to form a crystal 

meshwork, then we would have an original common magma differentiated into two or more portions in which the crystal aggregates 

are of different composition from the liquid residuum or from the 

expressed liquid, as the case may be, and each submagma will form 

a different type of rock. Modifications of this simple type of differentiation are introduced by alternating periods of deformation and 

quiescence, by the effects of the relatively volatile substances termed 

mineralizers, by marginal chilling with differentiation proceeding in 

the core, and by other factors. The influence of fractional crystallization has been especially developed and stressed by Bowen.82

As the major unit in such a theory of differentiation is the crystal, 

it is necessary to know the order of crystallization in order to study 

its relation and effect on the order of differentiation. The period 

of crystallization of the different minerals varies essentially with the 

composition of the magma in which crystallization is proceeding.

In the normal hornblende diorites plagioclase is the first of the 

major minerals to begin to separate. The hornblende is in part contemporaneous with the plagioclase and in part interstitial to the 

plagioclase. Euhedral crystals are common. Quartz and potassic 

feldspars occur only in an interstitial position.

In the monzodiorites plagioclase is in general the first mineral toseparate. The potassic feldspar either begins very soon after the 

plagioclase and is intergrown with the plagioclase, or it begins at a 

much later stage and is interstitial, depending upon the percentage 

of potassic feldspar present. Microcline is more common in the interstitial groundmass, and microperthite is most common at the early

82 Bowen, N. L., The evolution of the igneous rocks, Princeton TJniv. Press,. 19,28.
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 245

stage of separation. Hornblende separates after the plagioclase 

and may crystallize together with the potassic feldspar or cease 

before the feldspar begins, according to its composition. Myrmekitic intergrowths of plagioclase and quartz locally replace the potassic feldspars, along their borders.. .Quartz.is.restricted ,to interstices 

and is uniformly the last mineral to finish crystallization.

In the quartz diorites the order of crystallization is similar to 

that of the granodiorites. Plagioclase is the first mineral to crystallize and at a later stage is accompanied by hornblende, biotite, and 

quartz. The potassic feldspars, myrmekite if present, and quartz, 

form the last stages in the crystallization of the magma. The accessory minerals are for the most part concentrated and associated with 

the ferromagnesian minerals, but in part they occur as inclusions in 

the other minerals.

In the quartz diorites and the granodiorites of both the Coast 

Range batholith and the adjoining Wrangell-Revillagigedo belt hornblende and biotite are usually approximately equal in amount if the 

combined percentage is 18 or thereabouts;''whereas if the total 

amount of both is greater than about 18 per cent, hornblende usually 

exceeds biotite, and if less than 18 per cent, biotite usually exceeds 

hornblende. Where biotite predominates over hornblende there is a 

correlative increase in quartz, as if the biotite and quartz were formed 

by the breakdown and modification of hornblende.

A similar relation between hornblende and biotite is found;in the 

quartz monzonites. Here, however, the average total ferromagnesian 

content of all variants is lower, and the combined percentage around 

which hornblende and biotite are approximately equal in amount is. 

much smaller.

In the quartz diorites of Baranof Island the total ferromagnesian 

content is low; and in them also where the combined percentage 

of hornblende and biotite is lower than the average for the region, 

biotite preponderates'over hornblende, and -is-accompanied-1 by* an 

increase, of quartz.

The quartz diorites differ from the diorites in an increase from 4 

per cent of quartz to 19 or 20 per cent, and in a. considerable decrease 

in total content of ferromagnesian minerals, plagioclase, and magnetite. The ratio of biotite to hornblende increases markedly in the 

average type of quartz diorite from that of the diorites. Indeed, a 

part of the increased percentage of quartz in the quartz diorites may 

have originated from the breakdown and modification of the hornblende molecule.

In the albite-leucoquartz diorites the plagioclase is the first major 

component to crystallize, and in the porphyritic facies it forms the 

phenocrysts. In the alaskitic granites microperthite appears to be 

the first mineral among the major components to separate, though
246 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

the evidence is not certain, and in the porphyritic facies it forms the 

phenocrysts. At a later stage the ferromagnesian minerals, plagioclase, and quartz accompany the microperthite.

In the granodiorites the plagioclase feldspars are, in general, the 

first of the major mineral components to separate, and in the porphyritic facies, with only two exceptions noted, they were found to form 

the phenocrysts. At a later stage of precipitation they are accompanied by the ferromagnesian minerals and by the potassic feldspars 

and quartz. Quartz forms in part an interstitial groundmass to 

the other minerals.; Myrniekite, a vermicular intergrowth of quartz 

and andesine, is characteristically present, locally replacing the potassic feldspars on their borders; it seems to have preceded at least 

a portion of the quartz. In the granddiorite porphyry from the 

mountains near the head of Cascade Creek on Thomas Bay and in an 

augite granodiorite sill on Bradfield Canal microperthite forms large 

phenocrysts; these' are the only rocks noted in which the potassic 

feldspar might be interpreted as having crystallized at the. earliest ( 

stage. In the crystallization of the potassic feldspars microcline or 

orthoclase is more common in the later stages and microperthite in 

the earlier stages; locally microperthite forms the core of the crystal 

and microcline the outer zone. Here and there hornblende is full of 

rounded inclusions of quartz, and more rarely plagioclase contains 

similar inclusions of quartz.

In the quartz monzonites along Portland Canal minute euhedral 

and rounded quartz crystals occur within and on the borders of the 

feldspars. The ferromagnesian minerals occur in slight part as 

minute idiomorphic inclusions wi thin the feldspars but are mainly 

contemporaneous with the feldspars. Most of the feldspar, quartz, 

and ferromagnesian minerals are essentially contemporaneous. In 

part the microperthite forms large crystals which have a porphyritic aspect, but they usually contain inclusions of the other minerals 

and, though they may have started early, they must have grown 

with relative rapidity throughout a considerable period of time. 

Quartz may finish crystallization a trifle later. Microcline is later 

than microperthite.

The accessory minerals occur to a slight extent as minute inclusions 

in any or all of the other minerals; but there is a tendency for them 

to occur within the outer borders of the ferromagnesian minerals, 

especially in the biotite or between the boundaries of the other minerals. The zircons in particular tend to be restricted to minute rods 

in the biotite. Some large titanite crystals seem definitely to be contemporaneous with the major minerals, and such crystals may inclose 

minute euhedral crystals of apatite and magnetite. The magnetite 

grains are frequently found in groups of idiomorphic crystals, many 

of them with associated apatite. Euhedral crystals of magnetite and
UP^ER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 247

apatite are often found clustered around the borders of titanite 

crystals.

In the quartz monzonite on Stikine River the first minerals to 

begin to crystallize were the accessories magnetite, apatite, and 

titanite. These occur also in quartz of late crystallization and are 

therefore in part contemporaneous with the other minerals. Quartz 

occurs as idiomorphic crystals in the plagioclase or as large grains, 

in part interstitial and molded on the feldspars and in part showing 

crystal faces against microperthite; it appears to have begun early 

and finished last. The biotite is sparse and appears for the most part 

to be in the quartz, but locally it occurs as included crystals in the 

feldspars. The plagioclase is hypidiomorphic and occurs in part as 

included crystals in the microperthite. The biotite is almost entirely 

altered to chlorite. The crystallization of the microperthite and 

plagioclase was for the most part contemporaneous, though plagioclase may have started first.

In the granites at many places microperthite bears a porphyritic 

relation to the other minerals, and plagioclase occurs in the groundmass or interstitial to the microperthite. This might suggest that 

the microperthite started crystallization before the plagioclase were 

it not for the fact that many of the large microperthite crystals contain included small crystals of plagioclase. In the granite, as in the 

quartz monzonite, the crystallization of the microperthite and plagioclase must for the most part have been contemporaneous, though 

plagioclase may have started first.

It is exceedingly difficult to tell the exact period of crystallization 

of the accessory minerals, such as magnetite, apatite, zircon, and 

titanite. In general they occur as minute inclusions in the other 

minerals, particularly in the ferromagnesian minerals, or mainly 

as small grains of early crystallization; but in part, where they are 

present in unusual abundance, they occur within or on the borders 

of the ferromagnesian minerals or interstitial to the major minerals. 

The interstitial mode of occurrence is particularly noticeable in some 

of the pyroxenite and hornblendite where magnetite or apatite, respectively, is in considerable abundance. In general, apatite is associated with the magnetite crystals and may occur as inclusions in 

them. Both apatite and magnetite may occur as euhedral crystals 

inclosed in titanite.

In hornblende diorite that contains 2 per cent of magnetite and 

1 per cent of apatite practically all the magnetite and apatite occur 

as inclusions in the hornblende crystals. The hornblende in these 

rocks began to crystallize after the plagioclase and is in part interstitial to it. In slight part" magnetite occurs interstitial to the other 

minerals or as included crystals in interstitial quartz. 

G137 29- 17
248 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

In the ultrabasic rocks the predominant accessory mineral is magnetite. Where this is small in amount (less than 1 or 2 per cent) 

it occurs as minute euhedral crystals in the other minerals. Where it 

is more than a few per cent, as in the diallagites and hornblendites 

only 1 per cent or so occurs within the other minerals and the remainder belongs to a later stage of crystallization. In the augitite 

from Union Bay the magnetite (20 per cent) forms irregular-shaped 

blebs interstitial to the pyroxene with offshooting threadlike streamers between the borders of the pyroxene grains. In a hornblendemagnetite augitite from Snettisham practically all of the magnetite 

and apatite form a mesh interstitial to the pyroxene and hornblende. 

The apatite is in part inclosed as euhedral crystals in the magnetite. 

In a hornblendite from Kupreanof Island practically all the magnetite (3 per cent) and apatite (4 per cent) are in euhedral crystals 

situated between and intersecting the borders of the grains of hornblende; they belong to a late stage of crystallization. The same is 

true of the hornblendite from Etolin Island. In the hornblendite 

from Snipe Bay, Baranof Island, thei apatite is in perfect crystals 

in the interstitial labradorite.

RATE OF COOLING AND MINEKALIZERS

In a consideration of the theory of differentiation through the separation of crystals from the solution in which they are growing and 

of the action of mineralizers, the rate of cooling, or the length of time 

during which the magma consists of both solid and Jiquid phases, 

is a most important factor affecting the degree and character of differentiation. Other factors being the same, the slower the rate of 

cooling the longer will the usual magma consist of crystalline and 

liquid phases and the greater will be the opportunity for differentiation. Rapid cooling will tend to check differentiation and will result 

in a rock closely similar in composition to the original magma, except 

for the loss of most of the more volatile constituents. A relatively 

high content of mineralizers reduces the viscosity and tends to facilitate crystallization and produce a coarse texture; it may also have 

an influence in determining the particular assemblage of minerals 

which crystallize from the magma. The mineralizers may also act 

as agents to transfer more soluble or volatile constituents and thereby 

themselves directly cause differentiation.

ULTRABASIC ROCKS

The data on the field relations of the dunites, peridotites, and 

pyroxenites are inadequate for a discussion of their origin.

The hornblendites present certain features which must be taken 

into consideration in explaining their origin. There is no doubt 

that in part they bear intrusive relations to the sediments, for they
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 249

are repeatedly found as sills, and southeast of Petersburg, on Mitkof 

Island, intrusive masses of hornblendite have produced contact metamorphism in the adjoining slates, with the formation of such 

minerals as andalusite.

The most pronounced feature of the hornblendite masses is their 

wide and abrupt variation in texture and the local abundance of 

pegmatitic variants which may differ widely in composition. Some 

bands of hornblendite are composed of crystals averaging 6 inches 

long and 3 inches broad. The most common mineral of the pegmatite 

facies, in addition to the hornblende, is albite; biotite is locally 

common, and in many places titanite and apatite are abundant. 

Albite may occur as separate veinlets. Locally ilmenitic magnetite 

veins are present. In thin section many of the hornblendite masses 

are found to be unusually rich in apatite, containing as much as 4 per 

cent. All these features suggest that a very potent factor in the 

origin of these rocks has been a relatively high percentage of volatile 

constituents, especially water, in the magma.

Some, at least, of the hornblendites, especially the feldspathic 

types, are of such a composition that if calculated in terms of anhydrous minerals they may be shown to be equivalent to an olivine 

gabbro. For example, an analysis of the amphibolite from Port Snettisham,, recalculated in terms of normative minerals, gives andesinelabradorite 54.3 per cent, orthoclase 1.7 per cent, ilmenitic magnetite 9.9 per cent, diopside 24 per cent, hypersthene 2.1 per cent, and 

olivine 8 per cent. A hornblendite northwest of Prospect Lake, 

Vancouver Island, is reported by Clapp 83 to consist of hornblende 

85.2 per cent, augite 8 per cent, magnetite 5.5 per cent, and apatite l.S 

per cent. The chemical analysis recalculated in terms of the norm 

gives 31.8 per cent of labradorite-bytownite, 5 per cent of orthoclase, 

19.64 per cent of diopside, 22.02 per cent of olivine, 9.28 per cent of 

magnetite, 3.04 per cent of ilmenite, 2.79 per cent of apatite, and 3.41 

per cent of nephelite. The relatively high percentage of apatite 

shown here is in accord with the composition of many of the hornblendites in southeastern Alaska.

These results indicate that the hornblendites may have resulted 

from the crystallization of a magma of a composition which would 

usually have produced an olivine gabbro but which in the presence 

of a relatively high content of volatile materials, particularly water, 

formed hornblendite.

The hornblendites are as a rule severely brecciated and intruded by 

the more alkalic-siliceous types, such as diorite and quartz dioritey 

and are therefore older. For that reason it is permissible to consider

83 Clapp, C. H., Geology of the Victoria and Saanich map areas, Vancouver Island, B. C. t 

Canada Geol. Survey Mem. 36, p. 70, 1913.
250 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

them as belonging to the same sequence as the younger intrusive 

rocks of the Coast Range and as representing an early intruded 

magma very rich in volatile constituents and relatively undifferentiated because of quick crystallization, due to the relatively small size 

of the masses and to the fact that the country rock must have been 

relatively cooler than it was later, when large volumes of magma 

.reached the same level and gave out great quantities of heat.

The hornblendite masses in part appear to be the result of differentiation in place from the predominant alkalic-siliceous group of rocks 

and bear a definite relation to marginal or contact phenomena connected with included blocks of country rock. This is in accordance 

with the idea that the hornblendites represent relatively quickly crystallized imdifferentiated portions of the magma which have a high 

percentage of volatile constituents. Why there should be this local 

concentration of volatile constituents is an unsolved problem.

GABBRO, DIORITE, AND ALKALIC-SILICEOUS ROCKS

If the order of differentiation corresponds to the order of crystallization, gabbro, gabbro-diorite, diorite, quartz diorite, granodiorite, 

quartz monzonite, and granite should appear in the order named.

The most basic type of intrusive rock in southeastern Alaska, exclusive of the dunite, pyroxenite, and related types, is gabbro or its 

equivalent, hornblendite. The gabbro is restricted to sills, small 

stocks, or very local marginal developments of moderate-sized stocks, 

and should represent approximately the relatively little differentiated, quickly cooled original magma. Almost all of the gabbro and 

gabbro-diorite is found on the islands of the Alexander Archipelago.

The extreme alkalic-siliceous differentiate among the major rocks is 

a potassic granite, which is usually intrusive into the other major 

types of rock and is therefore the youngest. This determination of 

relative age accords with the order suggested by the succession of 

crystallization.

Very slow cooling in the deep core of the batholith still deeper 

than that exposed by the present erosion level may have permitted 

maximum differentiation and the formation of a granitic solution 

which under stresses was intruded locally into the less differentiated, 

more quickly cooled stocks and batholiths of the Alexander Archipelago, which are smaller and were intruded in a belt of cooler country rock than the Coast Range batholith. Thus the effects of relative 

rate of cooling may afford a partial explanation of the fact that the 

locks of the Prince of Wales-Chichagof belt are predominantly diorites of various types (gabbro-diorite, diorite, monzodiorite, and 

quartzose variants), with associated low potassic granodiorite and 

quartz diorite (the average composition of 65 specimens is that of a
UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS 251

quartzose hornblende diorite containing 8 to 11 per cent of quartz), 

whereas the rocks of the Coast Range batholith are predominantly 

the more alkalic-siliceous types, such as granodiorite and quartz 

monzonite with peripheral quartz diorite (the average composition 

of 37 specimens is that of a granodiorite with about 20 per cent of 

potassic feldspar and 20 per cent quartz).

Within a given stock or batholith differentiation may have been 

checked at different stages in different portions as a result of different rates of cooling and local conditions. Normally, if there is a 

variation within a given stock due to different rates of cooling, the 

more quickly cooled portion will be on the borders, and a more basic 

type of rock, representing an early stage of differentiation, will be 

formed there. Many examples of local and peripheral basic borders 

in stocks and batholiths of the Alexander Archipelago have already 

been referred to.

The belt of quartz diorite on the western flank of the Coast Range 

batholith likewise bears a position and relation to the more alkalicfeldspathic rocks (granodiorite and quartz monzonite) of the core, 

explicable as a marginal, relatively more quickly cooled variant. 

There is a question, however, whether the relations observed here 

are due to differentiation in place or to successive intrusions, of more 

advanced differentiated magma toward the northeast; the latter 

seems more probable.

The quartz diorites with relatively low ferromagnesian content, 

which seem to predominate on Baranof Island, are not readily 

explained, and further data are needed.

The leucocratic sodic types of rock, such as albite diorite and 

albite monzodiorite, albite, and oligoclase quartz diorite, oligoclase 

granodiorite, oligoclase monzonite, and the pegmatites and aplites 

which are associated in minor amount with each of the similar but 

respectively more basic andesirfe types, apparently have not originated through the same complex processes of differentiation that 

gave rise to the submagmas constituting major types of rocks but are 

due to local causes and processes acting upon the individual sub-0 

magma. The sodic variants do not lie within the same sequence 

of differentiation as the more calcic major types. Their composition 

is that of late-stage differentiates from the local submagmas. Many 

of them occur as apophyses and outlying dikes, and this mode of 

occurrence is compatible with what might be expected of a late differentiate of small volume. It is probable that the mineralizers have 

played an active part in the origin of these facies.

It is certain that some of the intrusive rocks the quartz diorite 

and granodiorite of the Wrangell-Revillagigedo belt in particular 

have had their composition locally very considerably modified by 

reaction with incorporated fragments of schist and sediment. This
252 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

is true also of portions of the core of the Coast Range batholith immediately adjacent to included or shredded blocks of schist. The 

resultant variations in composition are in part due directly to the 

differences in composition of the assimilated rock and in part indirectly to the same differences because of their effect in prolonging or 

shortening the period of crystallization of the magma and thus 

permitting varying degrees of differentiation.

AGE

The age of the Mesozoic intrusive rocks has not been definitely 

determined. To the northeast, on the east side of the batholith in the 

Whitehorse district, Yukon Territory, the intrusive rocks are reported by Cockfield 8 * to cut rocks of Middle Jurassic age and therefore to be probably of Upper Jurassic age or later. Hanson 85 reports 

that on the east side of the batholith, in British Columbia, between 

Skeena River and Stewart, the Coast Range batholith intrudes the 

Hazelton group (Jurassic) but does not intrude the Skeena (Lower 

Cretaceous) series. He says: " It is therefore probably mainly of 

Upper Jurassic age, but parts of the batholith may be of later age." 

Dolmage,86 in describing the Tatla-Bella Coola area, writes: "In 

Taseko Lake district what appears to be the main Coast Range 

batholith cuts a thick series of coarse fragmental volcanic rocks in 

which the writer found plant remains, determined by E. W. Berry 

to be of Cretaceous age. * * * This evidence proves that this 

part at least of the batholith is younger than the lowest Cretaceous, 

and the evidence found in Tatlayoko Lake, Taseko Lake, and Bridge 

River districts strongly suggests that much of the eastern part of 

the batholith is of postbasal Lower Cretaceous." Cairnes 87 suggests that at the southeastern part of the batholith, on the eastern 

border, there are intrusions of two ages. Masses of intrusive rocks 

that cut probable Jurassic beds are reported by him to be overlain 

unconformably by beds of Lower Cretaceous age, and the Lower 

Cretaceous beds are in turn cut by intrusions of pre-Tertiary age. 

On Vancouver Island the Mesozoic intrusive rocks are known definitely to be older than Upper Cretaceous.

In southeastern Alaska all the intrusive rocks classed as Mesozoic 

are definitely known to be older than the Eocene. On Chichagof

84 Cockfleld, W. E., and Bell, A. H., Whitehorse district, Yukon : Canada Geol. Survey 

Mem. 150, pp. 32-33, 1926.

85 Hanson, George, Reconnaissance between Skeena River and Stewart, B. C.: Canada 

Geol. Survey Summary Rept. for 1923, pt. A, p. 37, 1924.

88 Dolmage, Victor, Tatla-Bella Coola area, Coast district, B. C.: Canada Geol. Survey 

Summary Rept. for 1925, pt. A, p. 161, 1926.

87 Cairnes, C. E., Coquihalla area, B. C.: Canada Geol. Survey Mem. 139, pp. 71-77, 

89-105, 1924.
LOWER CEETACEOUS (?) ROCKS 253

Island intrusions of the Coast Kange type are proved by Overbeck 88 

to cut fossiliferous beds of Upper Jurassic age. The writer is convinced that on Admiralty Island intrusions of the Coast Kange type 

cut beds which, where not metamorphosed, carry the fossil Aucella 

crassicollis and which are therefore probably of lower Cretaceous 

age. At the head of Portland Canal there is positive evidence of two 

epochs of intrusion; the older batholith cut beds of the Hazelton 

series (Jurassic) and is in turn intruded by the quartz monzonite 

of the Coast Range batholith.

It is evident that for the most part the youngest beds with which 

the Mesozoic intrusive rocks are found in contact are of Middle or 

Upper Jurassic age; at a number of localities intrusive rocks of the 

Coast Range type cut Lower Cretaceous formations; there were at 

least two epochs of intrusion; and the Mesozoic intrusive rocks are 

all older than the Upper Cretaceous. So far as southeastern Alaska 

is concerned, the writer is aware of no evidence to disprove the 

assumption that all the Mesozoic intrusive rocks may be of Lower 

Cretaceous age, but the data given for adjacent territory suggest 

that they may be in part of Upper Jurassic and in part of Lower 

Cretaceous age.

The writer would emphasize the fact that in southeastern Alaska 

there are thick conglomerate beds that have been found throughout 

a length of 175 miles which are of known Silurian age but which 

contain pebbles, cobbles, and boulders similar in every way to the 

Mesozoic intrusive rocks. Similar pebbles are also found in beds intercalated with slates carrying the fossil Aucella crassicollis^ and the 

writer believes that this formation, too, is cut by the Mesozoic intrusions. It is therefore essential that the occurrence in conglomerates 

of fragments resembling the Mesozoic intrusive rocks should be used 

only with the greatest caution as a criterion to indicate the age of the 

conglomerate bed with respect to the Mesozoic intrusions.

LOWER CRETACEOTTS(P) ROCKS

DISTRIBUTION AND CHARACTER

Fossiliferous beds definitely recognized as of Upper Jurassic or 

Lower Cretaceous age are known at only five localities in southeastern 

Alaska the vicinity of Point Pybus and other places on the south 

side of Admiralty Island; the north end of the peninsula between 

Hamilton Bay and Keku Strait, in the northern part of Kupreanof 

Island; the south end of the northwest half of Etolin Island in the 

vicinity of Rocky Bay; Blank Inlet, Gravina Island; and Slocum 

, Chichagof Island. The beds comprise black slate or shale and

88 Overbeck, R. M., Geology and mineral resources of the west coast of Chlchagof Island : 

U. S. Geol. Survey Bull. 692, pp. 91-112, 1919.
254 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

graywacke with intercalated beds of conglomerate and calcareous 

sandstone and thin layers of impure limestone. The beds of Slocum 

Arm, Chichagof Island, may possibly be somewhat older than those 

of the other localities. As explained on pages 156-157, the f ossiliferous rocks of Jurassic or Cretaceous age have on the map been 

separated from the nonfossiliferous Jurassic or Cretaceous rocks and 

have been tentatively designated Lower Cretaceous (?).

GRAVINA ISLAND 

By THEODORE CHAPIN

A formation consisting essentially of interbedded conglomerate, 

graywacke, and black slate exposed along a wedge-shaped strip extending from Blank Inlet to the northeast coast of Gravina Island is 

determined on fossil evidence to be Upper Jurassic or Lower Cretaceous. Similar rocks just northwest of Ward Cove, Revillagigedo 

Island, and on Annette Island are correlated with this formation.

The conglomerate is composed of rather small pebbles with a few 

boulders as much as a foot in diameter. The matrix is essentially 

a graywacke but contains a considerable amount of fragments of 

igneous rock. The pebbles and cobbles are mostly igneous and resemble 

the volcanic rocks of Gravina Island. Pebbles of dioritic rocks that 

resemble 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 increase in fineness and decrease of 

igneous material into typical-looking graywacke containing angular 

fragments of slate and decomposed particles of dioritic rocks, hornblende, pyroxene, and epidote.

The slates are very fissile black clay slates and are closely interbedded with the graywacke members. The slates have a marked 

cleavage.

The stratigraphic sequence of the conglomerate, slate, and graywacke was not determined, as the beds are very closely folded and 

overturned in places. The conglomerate does not appear to be the 

basal member but occurs at intervals throughout the formation, interbedded with the slate and graywacke.

The conglomerate, graywacke, and slate are the products of normal 

deposition in a shallow sea. The changes in character of the deposits 

indicate corresponding constant 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.
LOWER CRETACEOUS (?) ROCKS 255

These Upper Jurassic or Lower Cretaceous beds overlie the volcanic rocks of Gravina Island, which are regarded as Triassic or 

Jurassic, but in most places the relations are rather obscure. On the 

northeast shore of Bostwick Inlet, near1 the entrance, the slate and 

graywacke overlie the eroded surface of the volcanic rocks with 

marked, unconformity. On the northeast shore of Gravina Island 

conglomerate 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 Gravina Island 

occupy the trough of a closely folded overturned syncline in which 

are involved also the older Mesozoic rocks, which actually overlie 

them along the eastern flank of the syncline. The slate has a distinct 

cleavage and the graywacke and conglomerate are sheared in places 

but are not schistose. There appears to be about 800 feet of these 

sediments.

ROCKY BAY, ETOLIN ISLAND

The rocks that occur in the vicinity of Rocky Bay, on the south 

side of the northwest part of Etolin Island, comprise in part a series 

of beds characterized by the prevalence of graywacke and in part a 

closely folded black slate formation. Structurally the graywacke 

series appears to overlie the slate.

The slate formation consists essentially of a very cleavable black 

argillaceous slate with thin layers and partings of graywacke. Intercalated thin layers of rusty-weathering impure limestone are common, and nodules of limestone and nodules and thin bands of blueblack chert are conspicuous in many of the beds. Rarely a thin 

layer of fine-grained conglomerate is present. The pebbles of the 

conglomerate consist of felsite and felsite porphyry, andesite, chert, 

limestone, slate, and graywacke. A thin section from a leaf of graywacke in the slate examined under the microscope is found to consist 

of angular fragments of plagioclase (oligoclase-andesine), finegrained rock fragments that are possibly chert, and a trace of quartz, 

in an argillaceous, very finely sericitic groundmass. Plagioclase 

fragments are found also in the limestone layers in the slate.

The graywacke series comprises massive-looking graywacke beds as 

much as 10 feet thick, interbedded with slate, and thin-bedded graywacke and slate. The graywackes are greenish-gray or gray and 

medium to coarse grained. They consist, in general, principally of 

fragments of plagioclase (labradorite), with intermingled grains of 

melaphyre and augite. Some layers consist principally of fresh fragments of green augite with a minor amount of fragments of plagio-
256 GEOLOGY- AND MINERAL, DEPOSITS, SOUTHEASTERN ALASKA

clase and melaphyre. Occasionally it is difficult to say whether the 

rock is detrital or a true volcanic tuff. The groundmass is argillaceous, and in places a little calcite is present. Quartz is sparse or 

absent. The feldspars are usually considerably altered to sericite. 

Many of them show zonal growth; some are partly bounded by crystallographic outlines; some are angular; and others have rounded 

corners. Accessory minerals are hornblende, rounded grains of 

epidote, apatite, pyrite, and magnetite. Locally thin bands of red 

slate are intercalated with the graywacke, but usually the slate layers 

are black.

In the vicinity of Marsh Island waterworn volcanic breccias are 

interbedded with black slate and graywacke. Nodules of limestone 

occur in the slate, and dikes of pyroxene and plagioclase porphyry 

are common. The waterworn fragments composing the breccia beds 

consist predominantly of light gray-green keratophyre and amygdaloidal plagioclase and pyroxene porphyries in an argillite groundmass. These beds are very similar to those of doubtfuFage found on 

the Fanshaw Peninsula. Structurally overlying these beds is a series 

of volcanic rocks, which consists predominantly of plagioclase and 

pyroxene porphyry breccias with interbedded thin flows of similar 

rock. Both red and green beds are present. These breccias, in part, 

have the appearance of flow breccias.

The interbedded waterworn volcanic breccia and slate are structurally underlain by beds of slate and graywacke that carry Aucella. 

It thus appears that the volcanic beds overlie the Aucetta-beaxing beds 

and are as young as Lower Cretaceous. The possibility that the beds 

are overturned and that the AuceHlw-bearmg beds are unconf ormable 

on Triassic and Jurassic and structurally overlie the volcanic beds 

must, however, be borne in mind in view of the close folding and 

complex structure of the district. This possibility, however, does 

not seem probable to the writer.

POINT HAMILTON AND VICINITY

A series of Lower Cretaceous or Upper Jurassic sedimentary beds 

is exposed on the peninsula at the north end of Kupreanof Island, 

between Hamilton Bay and Keku Straits. East of Point Hamilton 

these beds are intruded by a mass of Tertiary gabbro; south of Point 

Hamilton they are overlain unconformably by Eocene sandstone containing typical Kenai plant fossils. They comprise about 1,000 feet 

of j thin-bedded gray shale and sandstone 1 inch to several inches 

thick, with intercalated beds or nodular layers of fine-grained limestone from 6 inches to a foot thick. The beds have a general northwest strike and dip 10°-20° S. At Point Hamilton a slightly calcareous sandstone crops out in a bed 1 foot thick, and it is present also
LOWER CRETACEOUS (?) ROCKS 257

in the abundant weathered blocks scattered over the tidal flats. This 

sandstone is moderately fossiliferous, but the shells are mostly in 

fragments and poorly preserved. (See lot 11404, p. 260.) Karely a 

thin bed of tuff is intercalated, and traces, of carbonized plant remains 

are found. The beds are the least metamorphosed of all the Jurassic 

or Cretaceous formations in this region.

Beds .of similar type, predominantly shale, are found again 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.

Again on the west headland of the cove, about 3 miles southwest of 

Hound Island, somewhat more than 300 feet of thin-bedded sandstone and shale with a few limestone layers is exposed. Beds of 

sandstone as much as 2 feet thick occur in the basal part. These beds 

apparently overlie Upper Triassic volcanic rocks, but the contact is 

covered and the beds are nonfossiliferous.

PYBTTS BAY

The Cretaceous (?) beds in Pybus Bay have been briefly described 

by Wright.89 Some additional data are given here. The main body 

of Pybus Bay is eroded out of the Aiwetta-loQarmg slates, which lie 

in a synclinal relation to the older formations. The south end of the 

peninsula between Gambier Bay and Pybus Bay appears to be 

formed by the southeastward-plunging nose of a broad anticline, 

though this suggestion needs further confirmation.

The succession of formations is best shown on the east arm of 

Pybus Bay. In the upper half of the bay the beds consist predominantly of cherty layers several inches to 9 inches thick, with associated slate, calcareous material, and tuff. The chert is blue-green, 

green, gray, and black, with intercalated layers of brilliant red to 

reddish-brown jasper. The beds are closely folded and very much 

broken and faulted. The strike is more or less parallel to the bay 

and the dip is vertical. These beds may be of Devonian age. Overlying them comes the upper Permian white limestone with intercalated layers of white chert and abundant silicified fossils. On the 

east side of the bay the Permian beds form a line of isjets, and 

toward the south they are overlain by 200 feet of Upper Triassic 

conglomerate. This consists almost exclusively of cobbles and 

pebbles of limestone and white chert that resemble the Permian 

formations, with an interstitial groundmass of limestone. The conglomerate is in turn overlain by crumpled beds of interlayered gray 

limestone and dark-gray to black calcareous slate of the Upper

80 Wright, C. W., A reconnaissance of Admiralty Island : U. S. Geol. Survey Bull. 287, 

p. 144, 1906.
258 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Triassic. These are overlain by the Aucetta-bQ&r'mg beds, which 

-consist of dark-gray slate with sparse small black cherty nodules and 

lenses of limestone from 1 foot to several feet in diameter and 6 

inches or so thick. The contact between the formations is covered 

but only for a narrow width. The Triassic and Permian formations 

are approximately vertical; the Aucetta-be&riug beds dip about 50° 

SW. These slates pass upward into beds in which thin graywackelike sandstone is interbedded with the slate in certain zones. The 

beds are closely folded, and zones with Aucella are common.

Point Pybus is composed of conglomerate, and the channel between 

it and the first small -islet to the south is cut along the axis of an 

asymmetrical anticline in the conglomerate. At Point Pybus the 

conglomerate beds dip 30°-35° N. and on the islet about 80° S. The 

conglomerate must be several hundred feet thick, as about 300 feet 

appears to be exposed. The beds are predominantly of the pebble 

type, but cobble beds also occur. In most of the beds the pebbles 

and cobbles are almost exclusively of chert, but in some beds a greengray felsite predominates. Limestone, granodiorite, rhyolite, and 

andesite pebbles occur sparsely. Small nodular lenses of limestone 

occur in the conglomerate. North of Point Pybus the conglomerate 

passes upward through sandstone into dark-gray slate interbedded 

with sandstone. The beds of slate are almost isoclinally folded 

within an asymmetrical syncline which strikes approximately east, 

and the conglomerates come to the surface again on the conspicuous 

headland about 2% miles northeast of Point Pybus. Several of the 

conglomerate beds are richly fossiliferous with Aucella. The next 

headland to the northeast, about iy2 miles southwest of False Point 

Pybus, is composed of Permian white limestone with white cherty 

layers and abundant silicified fossils. These beds are vertical. 

South of the headland thin-bedded sandstone and slate are crumpled 

and broken as in a fault zone.

At Point Pybus and in the islands to the south the beds are cut by 

shear zones along which quartz veins have been formed. Quartz 

veins do not occur to the north or west, and their presence here is 

attributed to a genetic connection with the diorite mass of The 

Brothers Islands.

AGE AND CORRELATION

Martin 90 makes the following statements concerning the Lower 

Cretaceous (?) formations in southeastern Alaska:

The rocks in southeastern Alaska that are believed by the writer to be of 

Cretaceous age include the AwceZZo-bearing sandstone, shale, and conglomerate 

of Pybus Bay and other localities in the southern part of Admiralty Island;

80 Martin, G. C., The Mesozoic stratigraphy of Alaska : U. S. Geol. Survey Bull. 776, 

p. 375, 1926.
LOWER CRETACEOUS ( ?) ROCKS 259

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 of Blank Inlet, on Gravina Island; and possibly some graywacke, slate, and conglomerate on Prince of Wales Island. These rocks aredistinguished from the somewhat similar slaty rocks that have been described 

as Jurassic 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 the 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 uncpnforrnably upon the 

Upper Jurassic and older beds after those rocks were folded and metamorphosed 

and after the intrusive rocks of the Coast Range had been partly unroofed. 

No Upper Cretaceous rocks have been recognized in southeastern Alaska.

As previously stated, Buddington is of the opinion that the Cretaceous (?) formations referred to are not necessarily younger than 

the Coast Kange batholith but may be older. Though cobbles of 

granodiorite and diorite similar to the rocks of the Coast Kange 

batholith occur in the Lower Cretaceous (?) conglomerates, cobbles 

of similar rock occur also in Silurian conglomerates. This feature, 

therefore, has no value as a criterion of age. Furthermore, quartz 

veins believed to be genetically allied with the intrusive rocks of the 

Coast Range cut the ^m?eZfa-bearing beds, and slate and conglomerate 

lithologically similar to and geographically allied to the AioceUabearing beds are actually intruded by masses of diorite.

The age determination of the conglomerate, sjate, and graywacke 

of Gravina Island rests on fossils collected by Chapin. Only one 

form was identified. Mr. Stanton reports:

9527 (ACh 99). Blank Inlet, 1% miles north of Blank Point, Gravina Island. 

Belemnites sp. 

Jurassic or Lower Cretaceous.

Fossils were collected on Etolin Island by G. C. Martin in 1914 

from the black clay slate near the cabins on Johnson Cove, a small 

harbor on the west side of the island, just east of the north end of 

the Screen Islands. They were determined by T. W. Stanton as 

distorted specimens of Aucella crcessicolUs Keyserling?, signifying 

a probable Lower Cretaceous age if the specific identification is 

correct.

Fossils were also collected by the writer from the same belt of rocks 

on the island off the mouth of Johnson Cove. The rocks here are 

slate with a few thin beds of graywacke, calcareous rock, and fine 

conglomerate. Chert nodules are common in the slate. The fossils 

are abundant but distorted, and it is difficult to obtain good specimens because of the close-set fracture cleavage which crosses the
260 GEOLOGY AND MINEBAL DEPOSITS, SOUTHEASTERN ALASKA

bedding. They were identified by Mr. Stanton as Aucella crass'icollis 

Keyserling? and Belemnites sp., imprint. Aucellas in a poor state 

of preservation were found also in black clay slate at the head of 

Rocky Bay, Etolin Island.

At the northwest end of Kupreanof Island, at Point Hamilton, a 

slightly calcareous sandstone bed 1 foot thick occurs intercalated in 

the shales, and weathered slabs are abundant over the tidal flats. 

These slabs are fossiliferous, but the shells are mostly fragments and 

poorly preserved. A collection from this place was submitted to 

T. W. Stanton, who identified the fauna and gave the age as Upper 

Jurassic or Lower Cretaceous.

.11404. Point Hamilton, Kupreanof Island. 

Worm trails or burrows. 

Rhynchonella ? sp. Fragment. 

Aucella sp. 

Pteria? sp.

The determination of the age of the beds at Point Pybus is based 

on collections of Aucella made by C. W. Wright and described by 

T. W. Stanton 91 as follows:

The specimens of Aucella from Pybus Bay, Admiralty Island, are apparently 

referable to species that in California and1 adjacent States are characteristic of 

the Lower Cretaceous, Aucella piocMi occurring in a lower zone than Auoella 

cras»icollis. 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.

TERTIARY BOCKS

The only fossils found in Tertiary rocks of the Alexander Archipelago are of Eocene age. In Lituya Bay on the mainland rocks 

with Pliocene fossils are found.

The Wrights 92 report a belt of probably Tertiary lavas ranging 

from acidic andesite to basalt on the south side of Pleasant Island, 

in Icy Strait, and on the southwest shore of Excursion Inlet.

EOCENE BOCKS 

DISTRIBUTION AND CHARACTER

The Eocene rocks of southeastern Alaska are now for the most 

part restricted to separate areas within a belt about 200 miles long 

and 20 miles or less in width that extends southeast from the southwest end of Admiralty Island, roughly parallel to Keku and Clarence

91 Stanton, T. W., cited by Wright, C. W., A reconnaissance of Admiralty Island : D. S. 

 Geol. Survey Bull. 287, p. 144, 1906.

82 Wright, F. E. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript).
TERTIARY ROCKS u 261

Straits. Within this belt they were once doubtless more continuous; 

the remnants now exposed are those which have not yet been removed 

by erosion. They are found in Kootznahoo Inlet and form most of 

the southwest end of Admiralty Island, the northeast side of Kuiu 

Island, the west side of Kupreanof Island, and the west half of 

Zarembo Island. Kesidual patches are found on certain of the 

Castle Islands, Duncan Canal; at the southeast end of Onslow Island; 

at the east headland of Union Bay, Cleveland Peninsula; near Dall 

Head, Gravina Island; in Coal Bay, Prince of Wales Island; and on 

Long and Daisy Islands, Kasaan Bay.

A small area of Tertiary volcanic rocks outside the main belt 

forms the southwestern part of Suemez Island: in the Ketchikan district. These rocks may be younger than those on Admiralty, Kupreanof, and Kuiu Islands.

The Eocene beds are considered on the basis of their lithologic 

character and associations, in three groups. The group of beds 

believed to be the lowest, which are found in Port Camden, Kuiu 

Island, and in Hamilton Bay, Kupreanof Island, comprise 1,350 feet 

or more of sandstone with intercalated conglomerate. The second 

group consists predominantly of rhyolitic volcanic rocks and conglomerate of lava cobbles, or both, with some associated basaltic and 

andesitic volcanic rocks; these are believed to represent a horizon 

higher than the sandstone series, for in Port Camden they definitely 

overlie sandstone. The third group comprises dominantly basaltic 

and andesitic lavas, with some rhyolitic flows and minor amounts of 

intercalated breccia and conglomerate of lava cobbles; these overlie 

the rocks of the other two groups and at several localities there is the 

suggestion of a slight unconformity. It is possible that future work 

will show that the upper group is not Eocene.

The most complete section of the Eocene rocks is! found in Port 

Camden, Kuiu Island. For about 6 miles south of the west headland at the entrance to Port Camden the mountains along the shore 

are composed of sandstone, conglomerate, and rhyolitic volcanic 

rocks, with sills of basalt; the strike is northeast and the dip 8°-10° 

SE. The point at the north headland is formed by a mass of basalt 

with very coarse polygonal jointing, which is intrusive into sand' 

stone; each of the five points along the coast to the south is similarly 

formed from a sill of basalt.

The thickness of the formations from their base in the cove west of 

the headland at the entrance of Port Camden to the point west of 

Cam Island, as given below, has been estimated on the basis of an 

average dip of 8 P , with allowance made for sills of basalt. South-
262 GEOLOGY 4A.ND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

west of Cam Island there is great variation in the strike and dip, 

with the attendant probability of duplication of beds, and basaltic 

volcanic rocks and conglomerate are present in relations suggestive 

of the possibility of a slight unconformity. The rhyolitic breccia 

and tuff, the conglomerate of lava cobbles, and the basalt flows southwest of Cam Island are therefore not included in the estimate.

Section of Eocene rocks at Port Camden, Kuiu Island

Conglomerates of lava cobbles with interbedded tuff and Feet

breccia, predominantly rhyolitic______________ 1,000+ 

Rhyolite breccia and tuff____________________ 500± 

Sandstones with intercalated conglomerate near top___ 1,200± 

Basal conglomerate with intercalated sandstone_____ 150± 

Unconformity. 

Upper Triassic andesitic volcanic rocks.

BASAL CONGLOMERATE AND SANDSTONE

The contact between the Tertiary and Upper Triassic volcanic 

rocks on Kuiu Island in the cove west of Point Camden is covered. 

The pebbles and cobbles of the lowest exposed beds of the Tertiary, 

however, consist predominantly of andesite with some rhyolite; the 

andesite cobbles are such as might have come from the underlying 

Triassic volcanic rocks.

At the head of Port Camden, on the east side, there is a narrow belt 

of sandstone and normal conglomerate, which strikes southeast into 

Threemile Arm. The beds dip 20°-30° NE. and are overlain by conglomerate of lava cobbles with associated felsite flows and breccias. 

The base of the sandstone series is not exposed. The pebbles in the 

interbedded conglomerate are predominantly quartz, granite, and 

phyllite. The beds are similar to those at the mouth of the arm and 

may represent the same formation exposed here either by faulting or 

by flexing.

The main sandstone belt of Port Camden strikes northeast and is 

found on Kupreanof Island south of Point Hamilton and on the 

south side of Hamilton Bay. The beds, are predominantly coarse 

white feldspathic sandstone with abundant small fragments of black 

slate and other rocks. They weather a light-brownish hue. Intercalated beds of dark-gray shale and shaly sandstone and of conglomerate are present. The former are usually fossiliferous. Thy 

pebbles in the conglomerate are of rocks common to neighboring preTertiary formation; they usually include quartz, slate, phyllite, quartz 

diorite, and granite.

On the west side of Port Camden the conglomerate includes pebbles 

of chert and locally red jasper in addition. The chert and jasper are
U. S. GEOLOGICAL SURVEY 

SIUCIFIED STUMP AND TRUNK OF TREE OF EOCENE AGE, KUIU ISLAND, 
TERTIARY ROCKS 263

probably derived from the Carboniferous formations that are exposed on the north. Locally thin seams of coal are found in the sandstone. A noteworthy feature of the sandstone series is the practically 

complete absence of volcanic rocks either as flows or as fragments.

On the Cleveland Peninsula, in the Ketchikan district, normal 

coarse conglomerate crops out for a short distance along the shore 

just south of Union Point. On the north the conglomerate overlies 

beds of slate and sandstone and consists almost wholly of fragments 

of slate and phyllite, some of which are 4 feet in length, with sparse 

boulders of quartz diorite as much as 5 feet in diameter; intercalated 

in the conglomerate are light-colored sandstone and pale-brownish 

shaly sandstone with a few veinlets of bitumen filling cross fractures. 

On the south the conglomerate is dark-colored to black and consists 

predominantly of angular to rounded slate cobbles, with abundant 

boulders of pyroxenite and some of quartz diorite; as the hills southeast of Union Point are formed by a boss of similar pyroxenite with 

intruded dikes of quartz diorite, the source of all the materials in the 

conglomerate is near at hand. This deposit bears every resemblance 

to a coarse delta or alluvial-fan deposit built up by torrential streams 

flowing down mountain slopes lying to the east. The fact that there 

are no fragments of volcanic rocks in the 1,000 feet or more of basal 

conglomerate suggests the possibility that these beds belong to the 

same horizon as the sandstone and conglomerate of Port Camden.

At Coal Bay, on the north coast of Skowl Peninsula, Prince of 

Wales Island, there is a small area of sandstone carrying thin beds 

of coal. The sandstone beds occupy a small local basin and unconformably overlie Devonian greenstone and sediments. The beds arp 

flat-lying and apparently are not more than 100 feet thick.

On Admiralty Island, Wright 93 found a series of conglomerate, 

sandstone, and shale, with a few coal beds, which occupies an area of 

about 36 square miles at Kootznahoo Inlet.

CONGLOMERATE OF LAVA COBBLES AND RHYOLITIC FLOWS, BRECCIA, AND

TUFF

The rhyolite breccia and tuff of Port Camden are white and 

medium to coarse, with fragments one-fourth of an inch to an inch 

in diameter. It is possible that some flow material may be present 

here also. Overlying these rhyolite beds is a conglomerate of lava 

cobbles that is markedly different from the normal conglomerate of 

the sandstone series. It is characteristically coarse; most of the

93 Wright, C. W., A reconnaissance of Admiralty Island : U. S. Geol. Survey Bull. 287, 

pp. 144-147, 1906.

6137 29 18
264 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

cobbles are 6 to 12 inches in diameter and well rounded. In the 

lower part of the formation the cobbles are predominantly felsite 

and felsite porphyry, but the conglomerates of the upper part contain basalt cobbles and are associated with basalt and andesite flows. 

Intercalated with the conglomerate are uniform fine-grained white 

tuff or tuffaceous sandstone. Many of the bedding planes of these 

fine-grained rocks are covered with the carbonized remains of plants, 

mostly sprays of Sequoia. The conglomerate formation is also noteworthy for the common occurrence of silicified wood. Locally, abundant silicified stumps still in place and silicified trunks lying where 

they fell (pi. 21) indicate the site of a buried forest. About 3% 

miles south of the west headland of Port Camden, on the low beach 

on the north side of the conspicuous point, six stumps were counted 

in place in a tract 50 yards square. The remnants of another such 

forest are exposed on the west side of Keku Straits, about 4 miles 

southeast of Point Camden, on the south side of the cove.

A series of conglomerate beds composed of lava cobbles and associated with rhyolite and andesite volcanic rocks is exposed on the 

east side of Port Camden near the head. This belt strikes southeast 

and is exposed again near the head and along the west side of Threemile Arm. It comprises flows of white, gray, and, locally, red rhyolite and andesite interbedded with corresponding breccia and conglomerate. All the conglomerate beds are coarse, and some are very 

coarse; one such bed is composed of lava boulders 3 to 5 feet in diameter in a conglomeratic groundmass. The white rhyolite and rhyolite 

breccia usually contain disseminated pyrite and weather a rusty 

brown. The andesite is a dense green-gray rock and commonly 

shows a rough indistinct polygonal jointing with a platy structure 

at right angles to the columns. Much of the red and white rhyolite 

likewise shows a platy fissility. White rhyolite is exposed at the 

head of Seclusion Harbor and is adjoined on both the east and the 

west by basalt, which appears to overlie it.

A coarse conglomerate of lava cobbles and boulders, some of which 

are as much as 2 feet in diameter, is exposed in the vicinity of Point 

Nesbitt, Zarembo Island. The cobbles are predominantly felsite and 

felsite porphyry; basalt and basalt porphyry are secondary. Beds 

of basaltic breccia and. basalt flows are associated with the conglomerate. The beds strike northeast and dip about 30° NW. The total 

thickness is doubtless more than 1,000 feet.

In the Wrangell district, on both the north and the south sides of 

Zarembo Island, in Kah Sheets Bay, Kupreanof Island, and in the 

cove just east of the east headland of Steamer Bay, Etolin Island,
TERTIARY ROCKS 265

rhyolitic volcanic rocks, accompanied by conglomerate composed of 

cobbles of rhyolitic lava, overlie Devonian beds unconformably at 

ihe eastern boundary of the Tertiary formations.

The coast line for 3 miles south of the southwest headland of Seclusion Harbor, Conclusion Island, the islands and reefs north of Conclusion Island, and the islands at the entrance to Keku Straits are 

composed of a series of gray to black felsitic or finely porphyritic 

lava or vitrophyre, which commonly weather along the coastal cliff to 

a bright reddish or orange hue. A little breccia is interbedded with 

the lava, and on Conclusion Island there are many beds of coarse conglomerate with lava pebbles, cobbles, and boulders as much as 4 feet 

in diameter of the same material as the flows. Many of the lava 

flows show a well-developed columnar jointing and a platy parting 

at right angles to the columns. Locally the upper parts of the flows 

are amygdaloidal, with chalcedony, quartz, and calcite fillings. One 

flow near the northwest end of Conclusion Island shows a flow breccia 

at the base, which passes upward into columnar-jointed felsite. The 

basal part consists of great boulderlike or pillowlike masses with 

radial jointing, set in a matrix made up chiefly of angular fragments 

that evidently resulted from the disaggregation of similar masses. 

Some of the pillows have an outer surface of obsidian.

The vitrophyres of Conclusion Island, south of Seclusion Harbor, 

and the west side of Threemile Arm, in general strike northwest and 

dip northeast, whereas those of the other islands strike northeast and 

dip southeast.

Khyolitic lava and breccia are exposed on Kupreanof Island opposite Conclusion Island, in Totem Bay, in Little Totem Bay, about 3 

miles west of Totem; Bay, and at the eastern contact in Kah Sheets 

Bay. A little more than 6 miles east of Point Barrie green and 

purple felsites are exposed. The beaches here are of waterworn 

pebbles of varicolored tuff, breccia, felsite, and porphyry, many of 

which are very beautiful. The shores of Little Totem and Totem 

Bays are composed of green, white, red, and gray rhyolite. Many 

of the rocks show marked fluxion banding, others are porous, and 

others spherulitic; some are very much altered. Quartz and feldspar 

phenocrysts are common in some,phases of these flows and feldspar 

in others. Shingle Island is composed of a fissile platy rhyolite with 

abundant vesicles lined with crystals of chalcedony and quartz. Very 

beautiful flow structure exemplified in swirling green and white bands 

is found in flows of rhyolite associated with basalt on the Level 

Islands. Much of the rhyolite lava there is minutely spherulitic. 

The rhyolite at the head of Totem Bay is so platy that it might
266

easily at a superficial glance be mistaken for shale or slate. West 

of the rhyolitic lava on the west side of Totem. Bay is basaltic lava 

overlying tuff and breccia, with intercalated beds of sandstone and 

conglomerate. One bed of tuff is greenish and contains fragments 

of black, green, and red glass or obsidian.

At several localities rhyolite flows overlie older formations unconformably and are generally believed to) be of Tertiary age. In the 

Ketchikaii district, near the south tip of Gravina Island, a rhyolite 

flow overlies granite and greenstone, and at Long Island, Kasaan 

Bay, platy rhyolite overlies Middle Devonian limestone.

BASALTIC AND ANDESITIC LAVA FLOWS AND ASSOCIATED BOCKS

Basaltic and andesitic volcanic rocks, mostly flows, occupy large 

areas at the southwest end of Admiralty Island, a belt 15 to 18 miles 

wide on Kupreanof and Kuiu Islands paralleling Keku Straits, and 

an area at the west side of Zarembp Island. Small patches are found 

on certain of the Castle Islands, Duncan Canal, and on the group of 

islets southeast of Onslow Island, in the Ketchikan district. These 

lavas and pyroclastic beds have a maximum thickness of 2,500 feet. 

The greater part appear to be the result of fissure eruptions that 

filled existing valleys and even submerged the tops of mountains. On 

Port Camden they overlie the sedimentary formations carrying Kenai 

(upper Eocene) fossils.

In the vicinity of Point Mitchell, Kupreanof Island, the lava is 

olivine basalt; it is light gray and has a fissile, platy structure parallel to the surface of the flows. For 6 miles east of Point Barrie the 

lavas are predominantly basalt porphyry with labradorite phenocrysts. Local layers are highly amygdaloidal.

The rocks along Keku Straits from the mouth to the head are basalt 

with some associated green platy andesite. The basalts are in part 

red and felsitic to finely uniform in grain, in part dark-weathering 

porphyry; the former variety shows a very pronounced close-set 

vertical jointing. Rarely globules of brown glass are uniformly distributed throughout the rock. Here and there the phenocrysts are 

pyroxene. Well-developed polygonal jointing in basalt is very beautifully shown on one of the Castle Islands, in Duncan Canal, on the 

Level Islands, Sumner Strait, and at Arena Cove, Suemez Island. 

Some of the flows consist of a gray-black basalt porphyry at the 

center with an oxidized red highly amygdaloidal or vesicular upper 

surface.

Locally the andesitic lavas are altered, with the development of 

secondary minerals, such as zeolitized glass, calcite, epidote, chlorite, 

serpentine, sericite, and magnetite, and the introduction of pyrite.
TERTIARY ROCKS 267

The amygdules consist for the most part of chalcedony or calcite, 

or both, but many of the vesicles are only lined or partly filled with 

drusy quartz; chlorite is locally a common filling, and in one area 

heulandite is abundant; a zeolite supposed to be stilbite is reported 

by Wright.

At Murder Cove, on the south side of Admiralty Island, coal beds 

are interstratified with the basaltic tuff, breccia, and lava.

ORIGIN

The Tertiary formations accumulated in a great depressed trough 

or structural valley between mountain ranges with differences in altitude probably equal to those of the present time; also, to some extent, 

in erosional valleys leading into the major valley. Mountains 2,000 

feet in height appear to have been buried under the Tertiary lavas. 

The beds of coarse conglomerate are of the nature of alluvial fans 

spread at the mouths of rivers with very steep gradients, where they 

debouched upon the more level floor of the valley. The sandstone 

deposits were probably formed by the interlacing of alluvial fans 

that spread out toward the center of the trough and valley and 

formed a gentle piedmont slope such as is found to-day at the foot 

of the Sierra Nevada and the Coast Ranges in San Joaquin Valley, 

California.

The andesitic and basaltic lavas were probably erupted mostly from 

fissures, though in part from local volcanoes. The dominance of 

fissure eruptions is suggested by the abundance of dikes and sills in 

the adjacent country rock.

There are no known marine deposits associated with the Eocene 

beds in southeastern Alaska.

AGE

The age of the sedimentary formations has been determined as 

Tertiary by Knowlton and Hollick, from' fossils collected at several 

localities.

The original collection made by F. E. and C. W. Wright was 

determined by Knowlton and referred to as probably of Kenai age 

(upper Eocene). Hollick assigns their later collection to the "Arctic 

Miocene," which is the equivalent of the Eocene. The lists are 

given in the accompanying table.
268 GEOLOGY AND MINERAL, DEPOSITS, SOUTHEASTERN ALASKA

Eocene flora of southeastern Alaska 

la, Identified by Arthur Hollick; b, identified by F. H. Knowlton]

Pteris sitkensis . . . ....................... _ ..... _ .. _ .

Taxcdiumoccidentale. _____ ......... ____ . .......

Taxodium distichum miocenum. __ .................. __ .

Taxitesolriki........ _ . __ ........................... ....

Sequoia couttsiae ?.. _________ . __ . ...............

Sequoia nordenskioldi ?.. __ . ............................

DIoon praespinulosum n. sp. (ined.) _____________

Flabellariagronlandica. __ . __ . ______ _ . .........

Populus. ____________________ . .............

Populus balsamoides. _____ . ____ . _________

Castanea castaneaefolia. __ ....... _ .. _ ..... ............

Oreodaphne.... _ _.._ _ ......... __ ..... _ ....... ...

Magnolia inglefieldi.. ________ ... ...................

Vitis olriki. ................................................

Corylus macquarri . . ___________ ...... ............

Osmunda doroschkiana _____ ...... __ . ................

Planera ungeri ____ . __ . _______ . ................

Juglna snigella _______ .. ____________ . ....

Laurus.... _ .. _ ______ .. ........

Castalia... _ __ _ ................ ____ __ .........

Lastraea stiriaca.. _ ................ _ ........ _ .........

7565 

(55)

a

a

a

a

A

b

b

b

b

b

b

b

b

b

b

7581 

(258)

b

7582 

(291)

b

7580 

(271)

b

b

b

b

b

B 7518

b

7565(55). Dark gray, almost black, friable shale, associated with coal seam 

intercalated in coarse white sandstone and conglomerate. South side of Hamilton Bay, Kupreanof Island.

A. Collection made by F. E. and C. W. Wright, probably from the same locality 

as 7565.

7581(258). White rhyolitic tuff with silicifled tree stumpsi and fragments of 

trunks and branches. Tuff underlies coarse volcanic conglomerate. North side 

of point about 3 miles southwest of Point Camden, Kuiu Island.

7582(291). White sandstone layers intercalated in very coarse conglomerate 

of volcanic cobbles between basalt flows.

7580(271). White rhyolitic tuff and breccia. Port Camden, Kuiu Island, 3 

miles southwest of Cam Island.

B. Collection made by F. E. and C. W. Wright 3 miles south of entrance to 

Port Camden. Fine-grained gray argillaceous sandstone interstratifled with 

conglomerate composed of lava cobbles.

7518. Just south of fourth brook south of McNamara Point, Zarembo Island.

Although the lower part of the Tertiary formations is thus of 

Eocene age, it is by no means certain that the upper part may not 

belong to a later epoch of the Tertiary. Locally the basaltic and 

andesitic lavas of the highest formation appear to bear unconformable relations to the sedimentary beds; but this is not sufficiently 

pronounced, especially in view of the disturbances which accompany 

volcanism, to warrant their definite assignment to a later epoch.
TERTIARY EOCKS 269 

PLIOCENE ( ?) DEPOSITS 

LITUYA BAY

The Tertiary deposits of Lituya.Bay are described by the Wrights 9 * 

as follows:

The strata along the shore line between Lituya Bay and Icy Point consist 

of conglomernte, sandstone, and shale, and constitute the low, uonincised foreland fringe, which is characteristic of this part of the coast and extends northwest to Yakutat Bay and beyond. The strata strike parallel with the shore 

and dip at low angles seaward; they are coastal shelf deposits that have 

derived their materials from the adjacent mountains. The formation is well 

exposed on Cenotaph Island in Lituya Bay. On the north end of this island the 

sandstone and conglomerate beds are more highly tilted than usual, and dips as 

steep as 55° S. 60° W. have been observed; on the south end of the island 

the dip is considerably less and averages about 20°. * * * The sandstone 

and conglomerate of Cenotaph Island consist of subangular fragments to rounded 

pebbles of different sizes, the largest 6 inches or more in diameter, of granodiorite, amphibolite gneiss, greenstone, slate, and vein quartz, intermixed and 

distributed in the manner characteristic of coastal shelf deposits. Most of 

the rocks have a greenish tinge, as a result, no doubt, of the relatively large 

amount of greenstone material present. In Lituya Bay the field relations indicate that the Tertiary deposits probably rest directly on the greenstone.

These beds occur only in low-lying basins adjacent to the shore. The materials were deposited by the streams from the mountains in the background, in 

part as a piedmont assemblage of the interlacing fans extending to the ocean, 

and they were worked over by wave action, deposited in bands, and finally 

loosely consolidated. The character of the material, especially the coarse conglomerate, indicates that at the time of deposition of these beds the mountains 

rose rather abruptly from sea level, as at present. It is significant that these 

deposits and also the sand beaches end with the recession inland of the high 

peaks capable of supplying much material for such deposits.

Similar relations exist with respect to the Eocene beds on Admiralty and 

Kupreanof Islands to the southeast and furnish an argument against the hypothesis that the Coast Ranges underwent peneplanation during Tertiary 

(Miocene) time.

On the north end of Cenotaph Island a volcanic agglomerate consisting of 

lava intermixed with considerable sandstone was discovered. The field relations indicate that the eruption was submarine and probably took place while 

the deposition of the sediments was still in progress. The lava is basaltic and 

deep red and contains visible plagioclase and pyroxene. The fragments of 

sandstone in the agglomerate are dark brown and apparently less fresh. This 

lava is the youngest volcanic rock that has been observed in the Glacier Bay 

region.

On the east side of Cenotaph Island fossils were found in several of the 

sandstone beds. They were referred to W. H. Dall for examination. His report 

is given below:

" The fossils from Cenotaph Island, Lituya Bay, Alaska, are marine mollusks, 

etc., contained in much-crushed blackish shale and sandstone; they have a 

strong similarity to those collected by I. C. Russell in the foothills or mountains

M Wright, F. E. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript).
270 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

near Mount St. Elias, and like them have a rather northern facies. Russell's 

specimens, however, were much better preserved. The present fossils are mostly 

so crushed that any exact comparison with the analogous species of the recent 

fauna is impracticable. It can only be said that they resemble certain recent 

forms and, in part, may be identical. The age of the fauna is either Pliocene 

or Pleistocene, probably the former. There are no characteristic Miocene 

species. The list is as follows: Area, sp., Cardiitm near 0. groenlandicum, Car.- 

dium near G. vslandicum, Cardium near C. corUs, Panomya n. sp., TJya, near U. 

ar&naria, Leda sp., Yoldia near Y. montereyensis, Nucula, sp., Acila sp., Macoma 

near M. saibulosa,, Macomo.. near M. btiltMca, cast of large pholad burrow like 

that of Parapholas califoi-ma, Diplodwtiu sp. near D. aleutica, Pandora near 

P. grand/is, Saxicava sp., Hinmtes? sp,, Purpura sp. near P. crispata, Chrysodomust sp., Lunatia, sp., worm tube, EcMnarachnius sp., an impression apparently 

fucoid, other fragments of vegetable matter."

Fragments of wood gathered from the same locality were examined by F. H. 

Knowlton, who reports as follows:

" This material consists of a considerable quantity of minute fragments of 

wood, some of which, possibly all, is evidently coniferous; but beyond this it is 

impossible to go. Thin sections of this wood could be cut, but it is doubtful if 

they would show much of value, as it would doubtless prove to be new."

These fossils were not taken from the base of the formation, and it is 

possible that several Tertiary horizons are represented here as they are farther 

west in the Yakataga section 95 and in the marine Tertiary of Controller Bay.M 

It is significant that the Pliocene rocks of the Mount St. Elias region, as 

described by Russell w and Maddren, are intensely folded; in the Lituya Bay 

area they are little disturbed.

At several points on Cenotaph Island coal seams were observed interbedded in 

the sandstone and shale, but at no point are the beds of sufficient size to be 

commercially valuable.

The total thickness of the exposed Tertiary deposits can not be estimated 

with any degree of exactness from the data at hand. No time was available in 

the field for careful stratigraphic work. The best estimate which can at present 

be made is possibly several thousand feet.

STTEMEZ ISLAND

At the south end of Suemez Island the broad, flat valley that 

extends from Arena Cove northeast to Port Refugio is occupied by 

an area of Tertiary volcanic rock. These include rhyolite, obsidian 

flows, andesite, and basalt. In Arena Cove the east side and Lontano 

Point are composed of andesitic lava with intercalated red shale of 

Devonian (?) age. The peninsula a little west of the middle of the 

cove consists of platy andesitic lava of Tertiary age. The coast line 

north of Cape Felix is composed of Devonian (?) volcanic rocks, 

but the high mountains back of Cape Felix appear to be formed by 

the Tertiary volcanic flows. Just east of Cape Felix there is a small 

cove. The headland in front of this cove is formed by a great dike

95 Maddren, A. G., Mineral deposits of tie Yakataga district: U. S. Geol. Survey Bull. 

592, pp. 126-132, 1913.

98 Martin,, G. C., The Controller Bay region, Alaska: U. S. Geol. Survey Bull. 335, 1908.

97 Russell, I. C., Second expedition to Mount St. Elias, in 1891: U. S. Geol. Survey 

Thirteenth Ann. Kept'., pt 2, pp. 1-91,1893.
TEETIARY ROCKS 271

of basalt with conspicuous columner jointing, and the shore of the 

cove is a flow of rhyolite. A part of the rhyolite flow is obsidian, 

consisting of layers of greenish-black glass and a considerable mass 

of yellow glass with black glass nodules. A little south of the head 

of Port Refugio basaltic lava appears in small outcrops along the 

streams. It is reported that coal seams have been found within this 

formation.

This formation resembles lithologically the Tertiary volcanic rocks 

of Kupreanof, Kuiu, and Admiralty Islands and also in part the 

Tertiary volcanic rocks of Graham Island, to the south in British 

Columbia. Its geographic location allies it with later volcanic rocks 

that are assigned by MacKenzie 98 to the early or middle Pliocene.

INTRUSIVE ROCKS 

DISTBIBTJTION

The Tertiary intrusive masses are of very minor extent compared 

with the older (Upper Jurassic or Lower Cretaceous) intrusive 

masses. Nevertheless they are locally conspicuous. A belt 12 to 15 

miles wide parallel to and surrounding the borders of the present 

Tertiary formations is characteristically riven by sills and dikes of 

basalt and andesite and locally to a minor extent by rhyolite. A belt 

in which there are several intrusive masses of Tertiary diabase and 

gabbro passes through Eva Island, the peninsula on Kupreanof 

Island, between Hamilton Bay and Keku Strait, Pup Island, Point 

Camden, and the head of Threemile Arm, Kuiu Island. At the 

north end of Keku Strait there is a sill or laccolith of dacite 

porphyry.

DIKES

The dikes and sheets are most common in the phyllite, slate, and 

graywacke, and are sparse or absent in the granite. In the phyllite 

and slate they are predominantly parallel to the foliation, but in the 

graywacke they are most common as dikes. The dikes are usually 

most abundant near the present outcrops of the Tertiary formations. 

Within the Tertiary formations themselves dikes and sills of basalt 

and andesite are common, especially in the sandstone and conglomerate series of Port Camden and in the rhyolitic volcanic rocks and 

lava conglomerates throughout the areas of their distribution. The 

Level Islands, Sumner Strait, are composed of basaltic, andesitic, 

and rhyolitic lava of Tertiary age, which is locally intensively intruded by basaltic and andesitic dikes 3 to 10 feet wide and spaced, 

on the average, not more than 50 feet apart. On the west side of 

Zarembo Island also dikes are very abundant in the Tertiary lavas.

08 MacKenzie, J. D., Geology of Graham Island, B. C.: Canada Geol. Survey Mem. 88 

pp. 76-82. 1916.
272 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Near the mouth of Saginaw Bay, Kuiu Island, and on the Keku 

group of islands dikes of basalt are sparse, but near the head of 

Saginaw Bay they are abundant. There is a similar concentration 

of dikes near the head of Bay of Pillars. On the southeast side of 

Kuiu Island dikes are common between Port Beauclerc and the outcrop of the Tertiary lavas. There are several basalt dikes at the 

head of Port Beauclerc and a few on Edwards Island, but none were 

noted on the south arm of the bay. Several great dikes of basalt 50 

to 75 feet wide strike through the second island south of Point 

Amelius and appear again in the bay 3 miles southwest. None were 

seen along Affleck CanajL

The part of Prince of Wales Island northwest of a line running 

from the south end of the Barrier Islands to the west headland of 

Red Bay is cut by a very great number of basalt dikes striking northnortheast. The northeast, side of Prince of Wales Island, including 

the east headland of Red Bay and the east half of Thorne and 

Stevenson Islands, is crossed by a very great number of basalt dikes 

striking northwest. Between these two areas dikes are present but 

not abundant.

On the north coast of Kupreanof Island sills of basalt are abundant 

in the upper half of Portage Bay and there are a few dikes of felsite, 

but none were noticed on Frederick Sound east of Boulder Point. 

Sills of basalt are very abundant in the bay opposite the Castle 

Islands, Duncan Canal.

On the north side of Zarembo Island basalt and andesite sills and 

dikes are very abundant in the slate for 5 or 6 miles east of the border 

of the Tertiary formations, but they are sparse in the quartz diorite 

mass. On the southeast side of Zarembo Island, where the Tertiary 

formations adjoin the Devonian (?) slate, great masses of rhyolite 

porphyry are exposed, and the slate east to and including Round 

Point is cut by many dikes of rhyolite porphyry.

Sheets of intrusive basalt are common in the Lower Cretaceous (?) 

slate of Etolin Island. On the southeast s,ide of Canoe Passage, at 

the lower end, the phyllite for a mile and a half is intruded by a 

great many sheets of rhyolite and basalt. The basalt cuts the rhyolite. 

The slate forming the east headland of Windy Bay, in particular, is 

very closely intruded by sills of basalt. The number of basalt sheets 

and dikes increases notably toward the present area of Tertiary lava 

on Eagle Island. On Deer Island and along Seward Passage basalt 

dikes are rare.

On the mainland basic dikes are locally very abundant in the 

granitic rocks, but they are probably genetically connected with the 

Coast Range batholith and are not of Tertiary age. Dikes similar 

to the typical Tertiary basalt are very rare on the mainland. At
TERTIARY ROCKS 273

Point Coke, at the entrance to Holkham Bay, however, there is a 

typical dike of Tertiary basalt 200 feet wide. This dike is fractured and has many gash veinlets of albite and calcite, locally with 

sparse galena and ilmenite.

Rock from a typical basalt dike in Tertiary sandstone on the west 

side of Zarembo Island was studied in thin section with the microscope. It has a diabasic texture and consists essentially of labradorite laths with intersertal reddish pyroxene and greenish glass 

with a microspherulitic crystallization. Magnetite is abundant in 

disseminated crystals, plates of ilmenite are common, and apatite is 

sparse.

A sheet of basalt on the west border of the Tertiary formations on 

Kuiu Island, west of the north end of Conclusion Island, has a 

typical diabasic texture. It consists of a felt of labradorite laths 

(Ab2An3 ) with intersertal colorless pyroxene and interstitial radiate 

fibrous crystallized glass. The glass is brownish and gives a black 

cross with crossed nicols. Abundant accessory grains of disseminated 

magnetite are present.

A sample of andesite taken from a dike in the slate at Baht Harbor, 

Zarembo Island, as seen in thin section, is found to consist of a felt 

of andesine laths with considerable interstitial decomposed greenish 

glass. There is a trace of interstitial quartz and abundant plates of 

ilmenite. This rock is a very common type.

DIABASE

Pup Island, Eva Island, and Point Camden, at the north end of 

Kuiu Island, are formed of diabase intrusive into Tertiary sedimentary beds.

DACITE PORPHYRY

At the north end of Keku Strait there is a mass of dacite porphyry 

extending north-northeast. This is believed to be a thick sill or laccolith which thins out to the west. It is intruded between the sandstone and the volcanic conglomerate of the Tertiary. The rock is 

light green-gray to ash-colored and shows lath-shaped phenocrysts 

of feldspar and a few of pyroxene. On the big island at the south 

side of the mass the rock is drusy and the cavities are lined with 

crystals of quartz and riebeckite. The rock is characterized throughout by a platy fissility, mostly in the vertical plane, but locally parallel to the plane of intrusion. Rarely, flat blocks of sandstone and 

conglomerate are included within the dacite, and it is cut by dikes 

of basalt.

In thin section the rock is found to be composed of euhedral crystals 

of plagioclase and pyroxene in a groundmass of interstitial brown
274 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

glass and a micrographic intergrowth of quartz and feldspar. The 

plagioclase ranges from andesine to albite-oligoclase. Small partly 

resorbed crystals occur locally.

OLIVINE GABBRO

On Kupreanof Island,. between Hamilton Bay and Keku Strait, 

there is a small mass and several sills of olivine gabbro intruded into 

the Tertiary sediments that form the peninsula just south of Point 

Hamilton. The gabbro mass is oval, with a longer diameter of somewhat more than a mile. The beds on the east, west, and north dip 

gently beneath it, and it is overlain by beds that dip gently southsoutheast. It appears to form a small basin-like mass with the lower 

beds on three sides depressed beneath it. Directly east of Point Hamilton, on the east side of Hamilton Bay, there is a diabase sill, intrusive into Devonian sediments, which is probably of Tertiary age.

The gabbro is very heterogeneous in texture. Coarser-grained gabbroic veins rich in feldspar are common. They grade imperceptibly 

into the normal type of rock. In thin section the rock is found to 

range from diabasic to ophitic texture. It consists of labradorite, 

monoclinic pyroxene, and olivine, with accessory magnetite. The 

olivine is in places partly altered to dark-green serpentine and the 

pyroxene to chloritic aggregates, and locally there are bundles of 

actinolite needles. In specimens from the chilled contact f acies there 

is some interstitial dark-brown glass. Much of the magnetite is in 

skeletal crystals.

ANALCITE GABBRO

About 3 miles northeast of Point Camden a very irregular peninsula makes out from Kupreanof Island. The outer part of this 

peninsula is composed of a gabbro sill intrusive into Tertiary sandstone. The rock is highly pyroxenic and consists of labradorite 

(AbxAn2 ) and monoclinic pyroxene with analcite and secondary 

thomsonite and accessory magnetite and apatite. The rock texture is 

ophitic. The analcite occurs as grains and as interstitial fillings between the other minerals and may form 10 per cent or more of the 

rock. It appears to belong to a late stage in the primary crystallization of the magma. Much of the analcite is partly replaced by thomsonite, which usually Avorks into it from the borders and may completely replace it. Veinlets of massive microfibrous pectolite with 

considerable associated analcite also occur in the gabbro. The identity 

of the analcite was checked by a chemical analysis made for the writer 

by Prof. A. H. Phillips, of Princeton University.

On Kuiu Island, at the head of Threemile Arm on the southwest 

side, there is exposed a mass of gabbro which may form the group of 

high mountains that lie between Port Camden, Seclusion Harbor,
QUATERNARY ROCKS 275

and Threemile Arm. This gabbro mass lies along the belt of Tertiary 

intrusive gabbro bodies that passes through Point Camden, Pup 

Island, Point Hamilton, and Eva Island and may be of the same age. 

If so, its intrusion probably accounts for the uplift of the lower 

Tertiary beds at this point and the absence of the basal sandstone and 

conglomerate. The rock consists of labradorite and of pyroxene 

that is considerably altered to green hornblende and chlorite.

GRANITE PORPHYRY

At the north end of Zarembo Island south of Point St. John there 

is a mass of granite porphyry exposed along the shore. This granite 

porphyry is associated with Tertiary volcanic rocks and is probably 

of the same age. It consists of feldspar in a groundmass of micrographic intergrowth of quartz and feldspar. The feldspar is much 

altered but appears to be microperthite. Small druses rilled with 

kaolinite and chlorite are present.

QUATERNARY ROCKS 

GLACIAL DEPOSITS

Glacial deposits are usually inconsiderable in this region, except 

where directly connected with modern glaciers. The general submergence of the glacier fronts at the time of recession, the steep fiord 

walls of the valleys of the mainland and in part of the islands, and 

the rapid rate of erosion, due to heavy rainfall and steep slopes, 

account in part for the generaji lack of glacial deposits on land.

The most conspicuous evidence of glacial deposits is found in the 

boulder beaches, or accumulations of partly reworked boulders and 

gravel, which occur locally along the coast. Knopf eo reports that in 

the Eagle River region a mantle of tough glacial till covers much oi 

the bedrock and extends up to an altitude of 2,500 feet.

At Thomas Bay Point Vandeput and the bar that forms a convex 

barrier almost across the mouth of the bay are parts of a terminal 

moraine composed predominantly of granitic cobbles and boulders; 

the terrace at Wood Point is studded with glacial boulders of the 

terminal moraine; and along the south shore of the bay lateral 

morainal material is found. At the head of Port Houghton the " salt 

chuck" is separated from the main arm by a terminal moraine 

through which a narrow channel has been cut. Both at Thomas Bay 

and at Port Houghton the moraines appear to have been reworked 

«find leveled by marine planation and then uplifted.

M Knopf, Adolph, The Eagle River region, southeastern Alaska : U. S. Geol. Survey Bull. 

502, p. 32, 1912.
276 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Boulder clay is found at the head of Portage Bay, Kupreanof 

Island.

Convincing evidence of at least two advances of the ice with a 

recessional stage are found in Glacier Bay; in the vicinity of Mendenhall Glacier, in the Eagle Kiver region; and in the Porcupine district, northeast of Haines. In Glacier Bay an extensive forest grew 

above glaciated bedrock and was covered by thick deposits of gravel 

belonging to an interglacial stage; it is now being uncovered by the 

retreat of the glaciers and the erosion of modern streams.1 In the 

Porcupine River district interglacial gravel and glacial deposits are 

found in interglacial canyons. Knopf 2 reports a buried forest in the 

outwash plain in front of Mendenhall Glacier.

Eakin 3 has described the interglacial canyons with interglacial 

stream gravel in the valleys of Glacier and Porcupine Creeks, tributary to the Klehini River, as follows:

In places in the Porcupine Valley at the side of the present canyon there are 

so-called bench deposits, which consist of stream gravels overlain by glacial 

detritus. It is evident that these deposits occupy sections of a canyon, older 

than the present but of similar origin, which was in some places followed and in 

others missed by the course of the stream when the last intrenchment began. 

Two distinct ice advances are1 thus indicated, each of which was followed by 

intrenehment of the hanging-valley streams. * * * In the Glacier Creek 

Valley also there is evidence of two distinct advances, with a period of stream 

erosion intervening. An extremely deep and narrow bedrock gorge filled with 

glacial detritus has been traced for some distance along the lower part of the 

 valley beneath the modern gravels. A base level of erosion much lower than the 

present is indicated the same as in the lower Porcupine Valley.

Benches and terraces of fossiliferous marine gravel, °sand, and clay 

are found locally at altitudes up to 600 feet throughout southeastern 

Alaska.

In the Hyder district marine interlaminated clay and sand occur up 

to altitudes of 450 feet near Elevenmile on Salmon River at the head 

of Portland Canal and are reported by Hanson 4 at similar altitudes 

on Bear River.

In the Ketchikan district Chapin found fossiliferous gravel and 

blue clay on Gravina Island, about half a mile northwest of the 

cabin at the head of Dall Bay, at an altitude of about 80 feet. The

1 Cooper, W. S., The recent ecological history of Glacier Bay: Ecology, vol. 4, pp. 

93-128, 223-246, 355-365, 1923.

2 Knopf, Adolph, The Eagle River region, southeastern Alaska : U. S. Geol. Survey Bull.. 

502, p. 12, 1912.

3 Eakin, H. M., The Porcupine gold placer district, Alaska : U. S. Geol. Survey Bull. 

699, p. 20, 1919.

* Hanson, George, Reconnaissance between Kitsult River and Ske-ena River, S. C.: Canada Geol. Survey Summary Rept. for 1922, pt. A, p. 44, 1923.
QUATERNARY ROCKS 277

outcrop is covered on all sides by vegetation. The exposed base 

contains about 2 feet of glacial till and blue clay and is overlain by 

stratified beds of glacial gravel 5 or 6 feet thick. Fossils occur in 

both the blue clay and the stratified gravel. A collection was submitted by Chapin to W. H. Dall, who reports the following species:

Cylichnella n. sp. Macoma calcarea. 

Bela violacea. Saxicava arctica. 

Coins sp., fragment. Mya intermedia. 

Cardiuin (Cerastoclerma) ciliatum. Balanus sp., fragment. 

Axinopsis viridis.

The assembly naturally indicates the colder climate associated with 

the period of glaciation.

Buddington is indebted to Mr. Harper Keed, of Wrangell, for 

directing him to a fossil locality in British Columbia on Goat Creek, 

a small tributary of Stikine River from the west about 40 miles 

above its mouth and about 5 miles above the international boundary. 

The fossiliferous beds are about half a mile up the creek at an altitude estimated as 175 to 200 feet above sea level. The beds crop out 

in the steep bank of the brook and consist of clay with fossil shells 

overlain by coarse gravel. The shells are so leached as to crumble 

in the fingers. A collection was submitted to W. H. Dall, who 

reported the following species:

Cardium ciliatum. Leda minute. 

Pecten islaudicus. Chrysodomus liratus. 

Macoma balthica. Barnacle, fragments. 

Mytilus edulis.

Mr. Dall also made the following comments:

In 1899 on Douglas Island I traced elevated beaches with Quaternary shells 

along a ditch for the town of Douglas water pipe to an altitude of 200 feet. 

Other fossils from the same source were collected by Spencer in 1903. There 

is no doubt that there was an elevation of some 200 feet in the coast region of 

southeastern Alaska during Quaternary or later time. The Goat Creek 

fossils are probably of about the same age as those of Douglas Island but 

were deposited in silt at the end of a glacier, whereas the Douglas Island fossils 

are in ordinary beach gravel.

Shells of similar character and age were found in September, 1922, 

by Buddington in the moraine of Great Glacier on the west bank of 

Stikine River above the mouth of Iskoot River. The fossils were 

lying on the surface, where they had been washed out of clay at the 

top of the moraine just in front of the ice. Clay with marine shells 

is reported to have been struck in digging the foundations for the old 

cable office at Wrangell.

Uplifted gravel deposits of marine origin are found at several 

localities. Along the east side of Frederick Sound there is a gravel 

terrace from the point about 3 miles north of Point Agassiz south to
278 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

and including Brown Cove. This terrace may be'continuous across 

to Patterson River and may represent uplifted former delta deposits. 

Just north of Point Agassiz the coastal edge of the terrace is about 

20 feet above low-tide level. At the mouth of Patterson River, 

Thomas Bay, there are terraces of sand and gravel at least 40 feet 

above the river level.

Dall has reported beach deposits on Douglas Island at an altitude 

of 200 feet, and, Spencer reports sea shells and old beach deposits in 

the vicinity of Juneau at altitudes of 600 feet or more above the 

present sea level.

Knopf 5 reports fossiliferous marine gravel on Lemon Creek, Eagle 

River, and at an altitude of 100 feet on the summit of the divide 

through which the Amalga tramway passes after leaving the flats of 

Eagle River.

A remnant of an ancient uplifted delta of Stikine River forms the 

point at the south entrance to Le Conte Bay, extending out to Camp 

Island; this terrace consists of clay beds at the base and fine sand at 

the top. Its altitude at one point measured 60 feet above sea level. 

Remnants of uplifted deltas of sand and gravel are common at the 

mouths of many of the streams, such as Powers Creek, on Endicott 

Arm; Patterson River, in Thomas Bay; and Harding Creek, in 

Bradfield Canal.

BASALT AND TUFF

Basaltic lava of Quaternary age occupies small areas at many 

places along the mainland and on Revillagigedo Island. On the 

mainland the lavas are reported by Wright 6

to have been, extruded near the granite contact and, following Canon Creek and 

Blue River valleys to the Unuk River, spread over its valley floor and forced 

its waters to the south wall, where now they pass by way of the three narrow 

canyons indicated on the map. The volcanic ash from these eruptions can still 

be seen as black patches on the glaciers of the mountain peaks 8 to 10 miles 

distant.

Westgate 7 writes of the volcanic rocks along Behin Canal as follows:

Lava, chiefly basalt, and associated tuff are found at several points along 

the shore of Behm Canal north of Smeaton Bay. The largest' area, 3 miles 

long, is at Point Trollop, at the entrance of Smeaton Bay. Two small areas 

are found on the west side of Behm Canal and another at the south end of the 

Punchbowl, a small bay on the south side of Rudyerd Bay. On the east shore

5 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, pp. 32-33, 1912.

"Wright, F. E., The Unuk River mining region of British Columbia: Canada Geol. Survey-Summary Kept, for 1905, pp. 50-51, 1906.

7 Westgate, L. G., Geology and mineral resources of the area east of Behm Canal (unpublished manuscript).
QUATERNARY ROCKS 279

there is a small mass at Edith Point and another 2 miles north. These may 

liave been once continuous with the basalt of some of the adjacent small 

islands, including New Eddystone Rock.

These lavas and tuffs are essentially flat-lying, still in their original position. 

'They were extruded after the region had reached essentially its present surface

 development and are confined to the lowlands. Their flat upper surface is a 

constructional surface; on Point Trollop it is hardly over 100 feet above the 

level of the sea. New Eddystone Rock, 234 feet high, is a pillarlike remnant

 cut by the waves from a flow which may not have arisen originally to a much 

.greater height.

The rocks are dark to black and weather a characteristic red-brown. At 

Point Trollop two flows are found, each vesicular in its upper part. The base

 of a the lower one is below water level. The rock is1 very fine grained, gray-

 black, and massive, and under a hand lens shows a few tabular phenocrysts as 

jnuch as 5 millimeters in length. The microscope1 shows unoriented labradorite 

microlites 0.2 millimeter in length, small grains of augite, crystals of horn-

 blende, and grains of magnetite in a fine-grained plagioclase groundmass. 

Pyroxene isi much more abundant than the hornblende.

At the north end of Winstanley Island another type is found, light gray, fine 

..grained, and containing scattered phenocrysts of feldspar as much as 3 millijneters in length. The thin section shows phenocrysts of feldspar and green 

augite in a groundmass of plagioclase laths, irregular grains of augite and 

hornblende, magnetite, and brown iron oxide. The rock is rather an augite 

.andesite than a typical basalt.

The lava flows which came into Behm Canal originally had greater extent 

than they show to-day. The present distribution seems to be the result of a

 considerable amount of stream erosion, which must have taken place when the 

land stood higher in reference to sea level than it does to-day. Since the 

present position of land and sea was reached wave erosion has been going on. 

New Eddystone Rock is a pillar left standing above a wave-cut platform, a 

remnant of an originally much larger mass. Several reefs of lava near Edith 

Point have been formed by the complete truncation of small islands. Study 

,has not been sufficiently detailed to determine what part of the erosion of the 

.basalt was preglacial, what part postglacial, and recent.

Quaternary lava and tuff make up the volcanic cone of Mount 

Edgecombe, on Kruzof Island, in the Sitka district. The volcanic 

rocks comprise mainly basic andesite and basalt and are briefly

 described by Knopf .8

DELTA AND CURRENT DEPOSITS

All the indented arms of the sea are being gradually filled, particularly at their heads, by material brought in by rivers. These

 delta deposits constitute practically the only large level land areas 

in the region, except for some low-lying flat islands and through

 valleys on some of the islands.

8 Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, pp. 

14-15, 1912.

6137 29 19
280 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Many of the deltas at the heads of the fiords on the mainland 

are being built forward into deep water with very steep fronts. On 

the islands of the archipelago most of the arms of the sea were originally shallower, and the ice withdrew earlier; consequently, silting up 

of the bays and coves' has proceeded longer and has reached a more 

advanced stage. Very wide tidal flats are common, as along the 

west side and head of Duncan Canal, Portage Bay, and Hamilton 

Bay, Kupreanof Island; Blind Slough, Mitkof Island; Ked Bay, 

Prince of Wales Island; and Port Camden, Saginaw, and Security 

Bays, Kuiu Island.

The largest of the deltas is that of Stikine River, which at low tide 

completely blocks the connection between Frederick Sound and the 

passages on the south. Stikine River is of large volume and is fed 

by many glacial streams that carry great quantities of suspended 

material. Sediment brought down by the river is deposited not only 

on the immediate delta, which is being built forward, but along the 

shores of Frederick Sound as far as Thomas Bay and in Sumner 

and Zimovia Straits and Eastern Passage. Uplifted marine sediments with Recent fossils are found along Stikine River in front 

of Great Glacier at an altitude of about 200 feet. When these beds 

were deposited the land must have stood about 200 feet lower and 

the delta of the Stikine River could not have been built as. far as 

this point. A long fiord must therefore have extended to or beyond 

this point. To judge from such fiords as Bradfield Canal, Taku 

Inlet, and others, the probable minimum average depth was 500 feet. 

Depths of 500 feet occur within 3 miles of the front of the present 

face of the delta. The width of the arm is from iy2 to 2 miles. It 

thus seems evident that since the retreat of the glaciers from this 

region Stikine River has built forward a delta which, at a minimum 

estimate, must have a length of at least 46 miles, an average depth of 

at least 500 feet, and a width of iy2 to 2 miles.

This advance of the delta results in continued deposition of material 

upstream. According to the International Boundary Survey chart, 

the bed of the river is now at an altitude of about 250 feet above sea 

level at a point about 85 miles upstream from the edge of the delta 

at mean lower low water. The tributary streams, such as Iskut and 

Katete Rivers and Andrews Creek, are necessarily also depositing 

material in their valleys.

A conspicuous feature of many of the small inlets in or near the 

mainland is the steep boulder-paved shore line. The boulders were 

especially noted along Fools Inlet, Kupreanof Island, and Walter 

Island Arm, Port Houghton. They are residuary from the partial 

erosion of a veneer of glacial drift, and their arrangement appears
RELATIONS BETWEEN FORMATIONS 281

to be the result of aggregation accompanying erosion and of ice 

shove due to the expansive force of freezing water in the protected 

arms.

Sand and gravel beaches of large volume and extent are not 

abundant. Much of the north coast of Kupreanof and Prince of 

Wales Islands consists of sand and gravel. The gravel beaches are 

perhaps most conspicuous along the coast lines eroded in the Tertiary 

volcanic rocks, as on the Level Islands, the southwest side of Zarembo 

Island, and the south side of Kupreanof Island. On the west side of 

Port Camden the platy, jointed rhyolite and rhyolitic tuff have given 

rise to many shingle beaches composed of flat, platy fragments.

BELATIONS BETWEEN FORMATIONS 

WALES GROUP (ORDOVICIAN, SILURIAN, AND DEVONIAN)

The oldest fossiliferous rocks in southeastern Alaska are the Ordovician beds. The Wales group of metamorphic rocks may include 

formations as old as the Ordovician or may even be largely pre-Ordovician. It is overlain unconformably at some places by beds of Middle 

Devonian age; it is overlain at other places by beds of lower and 

upper Silurian age, but whether conformably or unconformably is 

not known. The Wales rocks are relatively much more deformed 

and metamorphosed than the known Silurian formations, but it is 

possible that this difference may be' due to excessive metamorphism 

resulting from the intrusion of large masses of igneous rock that are 

only slightly exposed at the present surface. The beds of the Wales 

group have not been observed in contact with rocks of known Ordovician age, and the relations between them are not known.

The graywacke and slate formations of the Ordovician and lower 

Silurian are isoclinally folded with nearly vertical axes wherever 

found, irrespective of the possible effects of the intrusion of igneous 

masses. The upper Silurian beds, on the other hand, show metamorphism and folding that are locally in part connected with the intrusion of igneous masses but are in general not so pronounced as in 

the underlying graywacke and slate. There are two possible explanations for this: The Ordovician arid lower Silurian beds may have 

been folded before the deposition of the upper Silurian, or the more 

intense folding of the older beds has resulted from folding of the 

incompetent graywacke and slate beneath arches of the thick, massive 

Silurian limestone, which acted as a competent bed. There is no 

doubt that the difference in competency has been an important factor 

in producing the difference in folding between the two groups of 

rocks, but whether it is the only factor is questionable.
282 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

At some places the upper Silurian limestone of Dall Island overlies 

upper Silurian volcanic rocks and conglomerate, whereas at others it 

directly overlies lower Silurian slate and graywacke; und in some 

localities upper Silurian volcanic rocks and conglomerate directly 

overlie the Ordovician graywacke and slate. These relations suggest a marked unconformity, but there can be. no certainty of this 

until more detailed work has been done and the possibilitj^ of faulting 

and changes-in lithology along the strike have been excluded.

On the east side of Tonowek Bay a conglomerate series with intercalated limestone of probably Silurian but possibly Devonian age 

overlies a series of graywacke. The conglomerate series strikes 

almost due north and dips west; the beds dip gently where they 

overlie the graywacke. The beds of graywacke in the vicinity of 

the passages to El Capitan Passage have a general north-northwest 

strike, are indurated, and are closely folded almost vertically. There 

is thus apparently a marked angular unconformity between the conglomerate and the graywacke.

At the north headland of Sarkar Cove, Prince of Wales Island, 

conglomerate of Silurian age with a northeast strike and a southeast 

dip overlies beds of graywacke that have a northeast strike and 

northwest dip. No fragments of graywacke^could, however, be found 

in the conglomerate.

In a cove west of Catalina Island, San Christoval Channel, apparently unconformable relations between Middle Devonian (?) conglomerate and underlying graywacke are well shown. Conglomerate 

that strikes east and dips 20° N. overlies graywacke that strikes N. 

75° E. and is nearly vertical. The contact is not exposed, but the 

conglomerate and the graywacke crop out not more than 10 feet apart. 

The conglomerate is composed predominantly of graywacke cobbles, 

though some chert, limestone, green-gray porphyry, and diorite are 

also present.

Chapin has studied the relations between the Silurian and Devonian formations in the southern half of Prince of Wales Island and 

on Dall Island. He finds that the Middle Devonian formations 

overlie the lower and upper Silurian beds unconformably. Thus the 

lower Silurian beds at Klakas Inlet, Prince of Wales Island, are surrounded by volcanic breccia regarded as the basal member of the 

Middle Devonian rocks, and the breccia appears to overlie unconformably the graptolite slates. On Kassa Inlet the lower Silurian 

beds are exposed in several small areas by the erosion of the Devonian 

breccia which unconformably overlies them. Similarly, on Dall 

Island the Devonian igneous rocks overlie unconformably the upper 

Silurian limestone and lower Silurian slatei of Breezy Bay and View 

Cove. (See fig. 1.)
RELATIONS BETWEEN FORMATIONS 283

In the vicinity of San AJberto Bay, Buddington finds that there is 

some evidence of unconformable relations between the thick limestone member of the upper part of the Middle Devonian section and 

the older formations. At the north end of San Alberto Bay the limestone is adjoined by coarse conglomerate which overlies Silurian 

formations. On Fern Point, San Fernando Island, the same limestone member overlies graywacke of Silurian age or older, and on 

Ham Island, in Karheen Passage, the limestone is adjoined by sandstone of upper Silurian age. The Devonian volcanic and graywacke 

formations are thus missing from beneath the limestone in these 

three localities. As the contacts are covered, however, no positive 

statement can be made that the relations are unconformable.

s. N.

V^ - Volcanic 

rocks of 

Vallenar 

A-4' formation

?3u

Horizontal scale

123 5 MILES

Vertical scale exaggerated

FIG.CHE 1. Diagrammatic structure section through the east const of Ball Island, 

showing Silurian antl adjacent rocks

MIDDLE AND UPPER DEVONIAN

By THBODOHB CHAPIN

The western part of the Coronados Islands, a small group at the 

mouth of Port St. Nicholas, Prince of Wales Island, is composed of 

fossiliferous limestone of Middle Devonian age. The eastern part of 

the islands consists of conglomerate, limestone, tuff, and amygdaloidal basalt, regarded as Upper Devonian, which stratigraphically 

overlie the massive Middle Devonian limestone with apparent unconformity. The relations are not clear, however, for the beds are 

closely folded and in places overturned. On a number of small 

islands in Trocadero Bay basalt and tuff with associated conglomerate similar to the Upper Devonian of Port Refugio, Suemez 

Island, overlie unconformably tuff and breccia regarded as Middle 

Devonian.
284 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA 

DEVONIAN AND CARBONIFEROUS

In the Ketchikan district Chapin reports that the limestone division of the Permian overlies the Upper Devonian unconformably. 

In the Keku Islands, of the Petersburg district, Buddington finds 

that the lower division of the Permian appears to bear unconformable relations to formations as old as Silurian. The southern islands 

of this group consist of upper Silurian limestone, the adjacent shores 

and island of Permian limestone, and there is not sufficient distance 

intervening between these two formations to allow for the presence 

of the Devonian and Mississippian formations. This might be accounted for by faulting were it not for the fact that on one of the 

central islands conglomerate beds of the lower division of the Permian directly underlie the upper division of the Permian and carry 

fossiliferous cobbles of the upper Silurian limestone.

Kocks bearing Permian fossils are described by Chapin as occurring on the small peninsula at the east end of Suemez Island, where 

they appear to overlie the Upper Devonian and the basalt and interbedded limestone and chert of Point Bocas and the Mississippian 

black chert and limestone of Ridge Island. The contact is concealed, 

but the relation is probably unconformable, as the Mississippian and 

Pennsylvanian beds are apparently absent.

The Wrights 9 believe that the pre-Upper Triassic formations were 

folded in a series of northeastward-trending folds at the close of the 

Paleozoic era. They write:.

By a consideration of the entire coastal province of southeastern Alaska, 

several important features which throw light on the dynamic history of the 

region are brought out. * * * Prior to the development of the main northwest-trending structural lines, which at present dominate this coastal province 

and are most pronounced adjacent to the wide areas of intrusive rocks, the 

prevalent structure was made up of northeasterly-trending folds. These folds 

btill form a minor system prominent in Chichagof, Admiralty, and Prince ol 

Wales Islands. The later and more intense folding of the beds on a broader 

scale, which forms the major system and trends northwesterly, has in general 

obliterated this minor system. But the evidence of the two systems is clearly 

presented on the north shore of Chichagof Island, where the minor system of 

small folds is the dominant structure at those places which are distant from 

the northwest-trending intrusive belts and which are not greatly disturbed 

and metamorphosed. Nearer the intrusive belts the larger system gradually 

prevails, and the minor folds as a whole are combined in the broader anticlines and synclines of the major northwest-trending folds. Complex minor 

folding and fracturing is thus produced in the beds. The fact that beds of

 Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

Geol. Survey Bull. 347, p. 39, 1906.
RELATION'S BETWEEN FORMATIONS 285

upper Carboniferous age have this northeasterly folding indicates that this was 

the dominant bedrock structure at the close of the Paleozoic era.

The only area in which any evidence for such folds was seen by 

Buddington is off the west coast of Prince of Wales Island in the 

vicinity of the Gulf of Esquibel and Bucareli and San Alberto Bays. 

If the Wrights are correct in their interpretation, the unconformity 

between the Upper Triassic formations and the Paleozoic indicates 

a time of pronounced orogeny corresponding to the Appalachian 

revolution of the eastern part of North America. More data, however, are needed for consideration of this problem.

The Upper Triassic formations bear unmistakably unconformable 

relations to the Paleozoic, as the basal conglomerates at many localities carry abundant fossiliferous limestone cobbles of Devonian and 

Permian age. At most places the Upper Triassic beds overlie the 

upper division of the Permian; but locally, as on Vallenar Bay, 

Gravina Island, and on the island south of Kake, Kupreanof Island, 

they directly overlie Devonian formations. On Clover Bay, Prince 

of Wales Island, they are infolded with Devonian formations.

UNCONFORMITY WITHIN THE UPPER TRIASSIC

An unconformity occurs within the Upper Triassic rocks. On 

Kupreanof Island and the islands southeast of Kake Upper Triassic 

sediments overlie the upper limestone division of the Permian and 

are overlain in apparent conformity by volcanic rocks of Upper 

Triassic age. Locally, there is a thick bed of coarse conglomerate of 

the Upper Triassic volcanic rocks. On the northeast side of Kuiu 

Island, however, the Upper Triassic volcanic rocks overlie the lower 

division of the Permian, without any apparent angular unconformity. 

The volcanic rocks on Kuiu Island also carry a different fauna from 

those on Kupreanof Island. Unconformities are indicated, therefore, 

within this series of beds.

JURASSIC ( ?), LOWER CRETACEOUS ( ? ), AND OLDER FORMATIONS

The rocks mapped as Jurassic (?) or Cretaceous are believed to 

overlie the Paleozoic and Triassic formations unconformably.

On Kupreanof Island about 10 miles east of Cape Bendel a series 

of beds comprising graywacke and black slate with intercalated conglomerate overlies, presumably unconformably, Devonian limestone, 

slate, and green chloritic schist. The contact is covered, but the 

Devonian beds have a very steep dip, in general to the west, whereas 

the overlying Jurassic or Cretaceous rocks have a moderate dip to 

the northeast. On Seymour Canal beds of the same graywacke-slate 

formation overlie Upper Triassic beds, but the formations here are 

very much disturbed and the relations are uncertain. No fossils have
286 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

been found in the younger formation, and its assignment to the 

Jurassic or Cretaceous is based on its lithology and structural 

relations.

The beds that carry Upper Jurassic or Lower Cretaceous fossils 

have been mapped as Lower Cretaceous (?); at the localities where 

they have been studied they overlie Upper Triassic formations.

Chapin reports that on Gravina and Revillagigedo Islands the 

Triassic rocks are in places overlain conformably by volcanic beds 

of Upper Triassic or Jurassic age and in; places unconformably by 

slate and graywacke of Jurassic or Cretaceous age. On the northeast 

shore of Bostwick Inlet, near the entrance, he finds that conglomerate 

and graywacke overlie, with marked unconformity, the eroded surface of the volcanic rocks, and that on Ward Cove they overlie with 

noticeable unconformity black phyllite which is correlated with the 

Upper Triassic.

On Pybus Bay, Admiralty Island, black fossiliferous slate with 

intercalated conglomerate and interlayered graywacke of Upper 

Jurassic or Lower Cretaceous age, carrying Aucella oraissicollis and 

Aucella piochii, overlies limestone and calcareous slate of the Upper 

Triassic. Similarly, on Etolin Island slate carrying Aucella crassicollis overlies Upper Triassic limestone and conglomerate, though 

here a considerable intervening zone is covered by water. In a cove 

on Keku Strait, on the northeast side of Kuiu Island, sandstone 

believed to be of Upper Jurassic or Lower Cretaceous age overlies 

Upper Triassic volcanic rocks.

The Lower Cretaceous or Upper Jurassic beds thus overlie unconformably the Upper Triassic formations, but no marked angular 

unconformity between them has been proved. A pronounced angular 

unconformity is known to exist at the north end of Kupreanof 

Island between the Jurassic or Cretaceous beds and the underlying 

Devonian formations.

On Fanshaw Peninsula, on the Glass Peninsula of Admiralty 

Island, and on Etolin Island the graywacke5)slate, and conglomerate 

formation appears to be overlain conformably by greenstone.

The Jurassic or Cretaceous slate and graywacke appear to be much 

less metamorphosed than the older Mesozoic formations, but this is 

certainly in part due to their character. In all the formations the 

argillaceous beds are most resistant to recrystallization, and their 

abundance in this series gives the Jurassic or Cretaceous formations 

a misleading appearance of minor metamorphism. The pebbles and 

cobbles of the intercalated conglomerate beds are very markedly flattened as a result of very strong pressure. In the Keku synclinorium 

the Jurassic or Cretaceous beds are very little metamorphosed, but 

this is true also of the underlying Upper Triassic formations in the 

troughs of the synciines.
RELATIONS BETWEEN FORMATIONS 287

UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROCKS AND MESOZOIC

OROGENY

The invasion of the vast volume of Upper Jurassic or Lower Cretaceous intrusive material and the erogenic folding which gave to 

the pre-Tertiary formations their dominant northwest trend came 

;after the formation of the beds described as Upper Jurassic or Lower 

 Cretaceous and probably in part at least after the formation of the 

.Aucella>-l)esirin.g beds assigned to the Lower Cretaceous (?). Folding, 

with the consequent development of cleavage^ no doubt took place 

'before the arrival of the intrusive magmas at the horizons where the 

rocks are now exposed. The folding was accentuated by the side 

thrust of the magma during the process of its emplacement; locally 

it was accompanied by recrystallization adjacent to the batholiths and 

stocks, with the production of the metamorphic complex, and by 

.shearing and mashing at greater distances from the intrusive masses.

Many of the older axes of folding have been swung around into the 

. general northwest trend by the orogenic forces that acted at this 

time along northeast-southwest lines. In some areas, however, northwest folds are superimposed upon previous northeast and northnortheast folds, and in other areas upon north-south axes of folding. 

Faulting and brecciation have thus resulted, and the relations are 

much confused.

The relations of the Coast Kange batholith to the country rock 

nave been described. In contrast to thje regional metamorphism produced by the great batholith, the smaller outlying1 stocks and batholiths have produced only zones or pockets of contact metamorphism. 

Their intrusion has, however, resulted in marked disturbance of the 

beds, with faulting and displacement. On Blashke Island an ultrabasic stock has domed up graywacke within an area of younger limestone. East of Shakan, Prince of Wales Island, where old sills and 

dikes occur in marble, the effects of the thrusting force exerted by 

the magma against its walls are very evident; the marble has flowed 

under the pressure exerted by the magma, sills parallel to the border 

of the intrusive mass have been squeezed into lenses, and dikes at an 

angle to the border are severely crumpled back on themselves.

The Copper Mountain region, on Prince of Wales Island, has been 

mapped in detail by Wright,10 who says:

The structure of the intruded rock beds apparently had little influence on or 

control of the intrusion of the main masses, for the intrusion evidently determined the present position of the bedded rocks. The larger dimensions of most 

of the smaller granitic masses, however, lie in the bedding planes of the stratified

10 \vright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

Alaska: U. S. Geol. Survey Prof. Paper 87, p. 39, 1915.
288 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

rocks. * * * The intruded schistose beds are usually bent to conform with 

the contact of the intrusive masses, though in places they are much crinkled and 

squeezed or even brecciated.

There has also been some "reactive" replacement of inclusions 

broken away from the country rook.

TERTIARY AND OLDER FORMATIONS

The Eocene formations rest with pronounced unconformity upon 

the Mesozoic intrusive rocks and all older formations. Many beds 

are folded, tilted, and faulted, but the dip is seldom greater than 30° 

and is usually less than 15°. The sedimentary beds are consolidated 

but not metamorphosed. Between them and the older formations 

there is a marked angular unconformity.

The general character of the structure has been appropriately described by Wright,11 who says: " The rocks of this formation have 

no definite strike or dip, but are characterized by frequent and great 

deviations in the attitude of their stratification, though the amount 

of flexuring and faulting is moderate." The strike is more or less 

parallel to the borders of the larger areas, a northeast strike being 

perhaps most prevalent.,

If the interpretation of the structure of the Eocene rocks is correct, the forces that effected their folding were exerted almost at 

right angles to those that acted upon the Mesozoic formations in 

pre-Tertiary time. MacKenzie 12 has drawn a similar conclusion with 

respect to the Tertiary formations of Graham Island, British Columbia ; he writes:

A third period of folding affected the island after the Masset formation had 

consolidated. The date of eruption of the Masset rocks has been placed in the 

Pliocene, so that this folding probably took place in the late Pliocene.

The direction of the stresses causing this folding has not been thoroughly 

worked out, but many of the folds seen run more nearly east and west than 

those in the pre-Tertiary rocks, and these stresses may well have acted in a 

southwest or southerly direction.

Beds of known Pliocene age are not found in connection with the 

Eocene rocks in the Alexander Archipelago or adjacent mainland, 

and their relations are therefore not known. The possible Pliocene 

beds on Suemez Island overlie Devonian formations with marked 

angular unconformity and are practically flat-lying.

11 Wright, C. .W., Reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

p. 144, 1906.

13 MacKenzie, J. D., Geology of Graham Island, British Columbia: Canada Geol. Survey 

Mem.. 88, p. Ill, 1916.
STRUCTURE 289 

QUATERNARY

The Quaternary deposits, exclusive of the glacial drift, consist of 

small local marine bench and terrace deposits of interstratified 

gravel, sand, and clay that bear unconformable relations to all the 

older formations.

The basaltic lava and tuff of the Mount Edgecombe volcano, Kruzof Island, according to Knopf, are post-Pleistocene. The lava and 

tuff of Canon Creek and Blue Eiver, tributaries to Unuk River, on 

the mainland, are reported by Wright to be post-Pleistocene and are 

the most recent volcanic rocks in the region.

SUMMARY

There appear to have been several disturbances between the Middle 

Ordovician and Middle Devonian time whose cumulative effect is a 

pronounced unconformable relation between the Middle Devonian 

and the older formations. Whether any one of these disturbances 

was of marked intensity, and if so, at what time it occurred, are 

unsolved problems. There is some inconclusive evidence to suggest 

that there was disturbance of considerable intensity between the 

Jower and the upper Silurian. A period of marked disturbance, perhaps one of major orogeny, occurred between the Permian and the 

Upper Triassic. It is certain that a period of pronounced orogenesis 

took place between the Lower Cretaceous (?) and the Eocene. The 

pre-Eocene revolution was accompanied by the continuing intrusion 

over a considerable period of time of vast bodies of magma, which 

tended to obliterate and modify the results and evidences of previous 

disturbances. At some time after the Eocene, possibly in the Pliocene, the Eocene beds were gently folded or warped and faulted. 

Far to the northwest, in the St. Elias Eange, Pleistocene beds have 

been closely folded and faulted with an intensity characteristic of 

orogenic deformation.

STRUCTURE

GENERAL FEATURES

Only the broader features of the structural geology of southeastern 

Alaska are known. Two outstanding major features are the great 

Coast Range batholith of the mainland, with its innumerable shreds 

and many large included slabs and narrow bands or belts of metamorphosed sedimentary and volcanic rocks, and the Prince of WalesKuiu anticlinorium, a great anticlinal axis which parallels the batholith and extends through Prince of Wales Island, Kuiu Island, the 

northeastern part of Chichagof Island, and Glacier Bay. Between
290 GEOLOGY AND MINEKAL DEPOSITS, SOUTHEASTEKN ALASKA

this anticlinorium and the mainland batholith lies the great Juneau 

synclinorium, which toward the southeast is split into two branches 

by the Duncan antic]inorium; the southwestern branch is called in 

this report the Keku-Gravina synclinorium. The major synclinorium 

constitutes a northwest extension of the Pacific coast downfold which 

involves the great valley of California, the Puget Sound Basin, the 

Strait of Georgia, and Hecate Strait. All these structural elements 

strike northwest.

A subsidiary cross axis of warping, which strikes east-northeast, 

parallels Frederick Sound, where it separates Admiralty Island from 

Kupreanof and Kuiu Islands, and as it affects Eocene rocks it must 

be of Tertiary age. Another east-northeast axis, not so clearly defined, includes the east side of Noyes Island, Lulu and San Fernando 

Islands, and the north side of Klawak Salt Lake. Ordovician formations are exposed along this belt with younger formations on each 

flank and infolded along northwest axes. There are insufficient data 

to determine the origin or significance of this structural element; 

The Wrights 13 report that in the Glacier Bay region the prevalent 

structural trends are northwest, but that locally secondary structural 

features and minor folds have been produced by movements accompanying the batholithic intrusions. The axes of the secondary folds 

superimposed on the large folds trend usually in a northeast or east 

direction.

On the east side of the Coast Range batholith Jurassic formations 

are exposed in the Hyder district and Paleozoic and Mesozoic rocks 

on Stikine River. Adjacent to the mainland batholith on the west, 

from Berners Bay southeast to Dixon Entrance, is the WrangellRevillagigedo belt of metamorphic rocks, which consists of formations of both Paleozoic and Mesozoic age, metamorphosed to phyllite, 

crystalline schist, and injection gneiss with abundant associated intrusive masses. In the trough of the.'synclinorium the Upper Jurassic 

or Lower Cretaceous formations are exposed. Tertiary formations 

overlie the Mesozoic unconformably and occupy a considerable part 

of the Keku-Gravina synclinorium. The formations exposed along 

the Prince of Wales-Kuiu anticlinorium are almost exclusively 

Paleozoic. On the west flank of the anticlinorium, along the west 

coast of Chichagof Island and Baranof Island, in the Sitka district, 

there is a belt of Mesozoic formations.

The relations of the various structural elements to each other and 

the general character of the folding are shown in the series of cross 

sections in Plate 22. The sections are necessarily somewhat generalized owing to our lack of knowledge of details.

13 Wright, P. E. and C. W., Geology of Glacier and Lituya Bays (unpublished manuscript) .
STRUCTURE 291

Isoclinal folds slightly or very markedly overturned toward the 

southwest predominate within a belt 15 to 30 miles wide adjacent to 

the west side of the Coast Range batholith. (See pi. 20, B.) Near 

the batholith the schist and gneiss predominantly dip 60°~90° NE.; 

in the outer part of the Wrangell-Revillagigedo belt of metamorphic 

rocks, or locally within the adjoining Jurassic (?) beds of the Juneau synclinorium the predominant dip is much lower, 300(-50° NE. 

being most common. On the east side of Prince of Wales Island 

in the vicinity of Moira Sound and at the northeast end of Prince 

of Wales Island isoclinal folds overturned toward the northeast are 

prominent.

Faulting on a small scale is prevalent throughout the sedimentary 

formations in southeastern Alaska. The geology has not been 

worked out sufficiently to afford satisfactory information as to the 

extent and character of large-scale faulting, but there is no doubt 

that it is much more prevalent than might be indicated by the few 

examples mentioned.

Lynn Canal and Chatham Strait were eroded along a fault zone.

In the Jimeau district the Silverbow fault, which has an approximately east-west strike and a downthrow on the north, has been 

mapped by Spencer and Eakiri.14 The beds as exposed at the surface show a horizontal displacement of about 1,600 feet. This fault 

is later than the Upper Jurassic or Lower Cretaceous intrusive rocks.

A highly mashed overthrust fault zone is indicated by the cataclastic texture of the rocks in a belt on the mainland adjacent to 

Stephens Passage from Port Houghton north to Point Astley and 

to the northwest in the vicinity of Point Arden and Grand Island. 

There are also many zones of intense shearing within the Coast Range 

batholith itself.

A noteworthy fault plane with a strike of about N. 38° W. occurs 

along the southwest side of Mount Calder, between the limestone and 

graywacke, and through the east side of Middle and Divide Islands, 

off the northwest end of Prince of Wales Island. Brecciation and 

crumpling and folding of the beds at the northeast end of this fault 

zone are intense.

Along Bocas de Finas, on the west side of Prince of Wales Island, 

there is a fault zone with a general N. 60° W. strike. The conglomerate, graywacke, and slate beds here are crumpled, brecciated, offset, 

slickensided, and generally shattered. Northwest of Point Desconocida the shattering is intense, and every specimen of rock shows narrow veinlets along the fractures. The graywacke-slate beds show 

many minute thrust faults, suggesting that the major fault may be of 

the thrust type.

14 Spencer, A. C., and Eakin, H. M., manuscript report on the Juneau district.
292 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Other fault zones were noted along the east side of the lower half 

of Orr Island, the east side of San Christoval Channel, and the south 

side of Zarembo Island.

JURASSIC (?) ROCKS OF THE HYDER DISTRICT

The structure of the Jurassic (?) formations on the east side of the 

Coast Range batholith north of Hyder has been described by Schofield and Hanson. 15 The formations are folded with a northwesterly 

strike, and one fold shows slight overturning toward the west.

Discordant features which are considered to be post-Jurassic but 

older than the main bulk of the intrusive rocks of the Coast Eange 

batholith are found in the vicinity of Salmon River, the West Fork 

of Texas Creek, and Texas Glacier, in the Hyder district. These are 

the Texas batholith of granodiorite and the Jurassic (?) slate and 

graywacke into which it is intruded. The trend of the gneissic structure of the Texas batholith averages about N. 70° E., and the strike 

of the sedimentary beds averages about N. 80° E. The sedimentary 

formations are closely compressed and isoclinally folded; south of 

the ridge between Texas Glacier and West Fork the dip is steep to the 

south, and north of this ridge it is generally steep to the north. The 

beds of the " Bear River series " along the international boundary in 

the Salmon River district, however, have the usual northwest strike. 

The approximately east-west discordant structure extends for a length 

of about 13 miles and a width of 10 miles.

COAST RANGE BATHOLITH AND WRANGELL-REVILLAGIGEDO 

BELT OF METAMORPHIC ROCKS

The Coast Range batholith and the Wrangell-Revillagigedo belt 

of metamorphic rocks can best be treated together, as one is genetically related to the other.

Along the entire western border of the batholith in southeastern 

Alaska the strike of the metamorphic rocks is northwest, parallel 

to the general direction of the belt, and the dip is steep northeast or 

vertical. In the vicinity of Behm Canal, according to Westgate, the 

dip averages about 50° NE.; in the latitude of Wrangell it is 70°-90° 

NE. and flattens out toward the southwest; in the latitude of Hobart 

Bay the formations are in approximately isoclinal appressed folds 

with dips of 70° NW. to 75° NE. for a width of about 12 miles adjacent to the batholith, but toward the southwest they flatten out to 

45° or so. In the Juneau district, as reported by Spencer, the dip 

is about 60° NE. in the vicinity of the Sheep Creek mines and somewhat less between Juneau Mountain and Mendenhall River. In the

15 Schofleld, S. J., and Hanson, George, Geology and ore deposits of Salmon River district, 

B. C.: Canada Geol. Survey Mem. 132, pp. 33-34, 1922.
STRTJCTUEE 293

Eagle River district, according to Knopf, the dip is usually 40°-60° 

NE., and in the Berners Bay district it averages 70° NE., though 

locally it is steep to the southwest.

In this region folds can be worked out only rarely except on a 

minor scale in the thin-bedded graywacke and slate, where it is evident that the axes of the folds are themselves acutely folded arid 

in places pitch almost vertically. As a result of this marked folding 

of the axes and of a common asymmetric relation of the limbs of the 

folds, adjacent strata in the graywacke, slate, and phyllite show at 

many places a marked discordance in strike and dip.

The schist and gneiss in the Ketchikan district are believed by 

Chapin to constitute the overturned limb of the Gravina Island part 

of the Keku-Gravina synclinorium. Similarly, the schist and phyllite in the Juneau district are considered by Spencer and Eakin to 

be the overturned east limb of the Juneau synclinorium. The minor 

structure of this limb shows overturned folds. A photograph of an 

overturned fold in graywacke and phyllite east of Frederick Sound 

is shown in Plate 20, B.

There seems to be a tendency for a generally steeper dip close to 

the batholith and a much more gentle dip away from it.

Throughout the Ketchikan and Wrangell districts and as far 

north as Thomas Bay the western border of the Coast Range batholith is in general parallel to the strike of the adjacent formations, 

(hough locally it shows crosscutting relations. Between Thomas Bay 

and Endicott Arm for a distance of 40 miles or so the border of the 

batholith changes from its prevailing northwest strike to a strike more 

nearly north, and swinging away from the formation strike it cuts 

across the formations at an angle of 15° to 40°. Northwest of Endicott Arm the border of the batholith swings again to the northwest 

at a slightly greater angle than the formations, and thus edges back 

across successive formations, terminating them on the north. The 

batholith thus appears to work across the east limb and trough of 

the Juneau synclinorium until it abuts against the Carboniferous 

formations of the west limb of the synclinorium on Chilkat River.

The intensity of metamorphism increases from west to east as the 

batholith is approached. The Wrights 16 comment on the metamorphism produced by the batholith as follows:

By comparing the metamorphic effects of the intrusive granite along its western and eastern flanks in the latitude of the Ketchikan district decided differences are apparent. On the coastal side the metamorphism is usually of the 

deep-seated type; gneisses and schists predominate and are cut by innumerable 

pegmatite dikes ramifying from, the granite. * * * Along the eastern 

border of the batholith, on the other hand, the metamorphism is of the contact

18 Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

Geol. Survey Bull. 347, p. 67. 1908.
294 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

type, argillites and slates predominate and are often indurated and heavily 

impregnated with sulphides. * * * The geologic interpretation of thesedata indicates clearly that the rocks east of the massifs were less deeply buried! 

at the time of intrusion than those of the coastal side.

Schofield 17 comments upon the ideas of the Wrights and proposesthe following explanation:

Another explanation the one favored by the author for the varying intensity of metamorphism of the two flanks may be given. It is well known; 

that the roof of a batholith is always intensely metamorphosed by the ascending 

hot solutions from the underlying molten magma. On the other hand, the 

deeper and more vertical contacts do not show contact metamorphism to the 

same degree, not only as regards intensity but also as regards areal extent.18 

If the batholith and the intruded rocks are exposed in a plane normal to thevertical axial plane of the batholith, the plane would consist of a core of granite 

surrounded by a contact zone of approximately the same width. On the other 

hand, if the batholith and the intruded rocks are cut obliquely, the roof rocks 

will be preserved higher up on the low side, whereas on the high side the highly 

metamorphosed roof rocks will be entirely removed and the contact will be undulating and fairly even. The contact-metamorphic zone will be very narrow on* 

the high side and very wide and irregular on the low side. In addition, the 

low side will be marked by many roof pendants of all sizes, whereas the high 

side will be almost free from them. Examination shows that the two sides 

of the Coast Range batholith correspond to the above distribution, as can beseen by the following table:

Eastern flank

1. Smooth-flowing contact.

2. Few roof pendants.'

3. Very narrow metamorphic zone.

4. Slates, sandstones, and tuffs characteristic.

5. Moderate-temperature conditions.

6. Gold-silver and silver-lead deposits

Western flank

1. Very irregular contact.

2. Many roof pendants.

3. Wide metamorphic zone.

4. Schists and gneisses characteristic^

5. High-temperature conditions.

6. Copper deposits of high temperatureand pressure.

of medium temperature and pressure.

7. Intruded rocks of roof type, gneisses, 

and schists reach the same elevation as the unaltered rocks along 

the steeply pitching contact.

These facts show that erosion on the western side of the Coast Range 

lith has not entirely removed the roof rocks and that the contact between thebatholith and these rocks is almost' flat. This conclusion is supported by the 

presence of a large number of roof pendants and the very irregular contact 

between the granite and the intruded rocks. On the eastern flank, however, 

erosion has exposed a deeper portion of the batholith, the roof being entirelyremoved, so that the margin of the batholith plunges very steeply beneath theintruded rocks. Also the contact is smoothly undulating and the roof pendants 

are absent.

17 Schofield, S. J., and Hanson, George, Geology and ore deposits of Salmon River district, British Columbia: Canada Geol. Survey Mem. 132, pp. 65-66, 1922.

18 Schofield, S. J., Canada Geol. Survey Mem. 76, p. 83, 1915.
U. S. GEOLOGICAL SURVEY

A

BULLETIN 800 PLATE 22

ea /eve/

"'"ISIP

^S Chobnondeley 

SoiULci'

wsl - wl

Kzshevarof'Passage- ~ * 

Screen Islands

TT - vt^-. ^ -v.y-MV^v---^^- ''<~'^^rr- .v... ^-^^-^nT-r--- "i »M» .iT

G ra vin'a . sy n c I r n o r i u nr'' '" ! ' ' '"' "'' -"''->'. i''\'\\'\' >s ' ' ' v ''' in'O'.-L'-"'!"^^''^" '''

Wran^ell-Revilla^i^edo belt of metamorphic rocks

Kupreanof Island 

"Sav Cpl "ft 

Ksg: Dgt "fcav !"fiav/ Dgt Da Dsa

 < Cmc Cpl "-P0 -. PC" 

SI Da DA -: Cpc h?cl Da\ Cpl ;Cpl Cpl 'l

Juneau synclinorium

Se

STRUCTURE SECTIONS IN SOUTHEASTERN ALASKA 

Seclions A and R by Theodore Cliapin
STRUCTURE 295

This points either to greater uplift on the eastern side of the batholith or to 

a depression on the western flank. The depression seems to be the more 

probable, since the western coast of British Columbia and southeastern Alaska 

has all the aspects of a depressed coast that protected the western flank from 

deep erosion.

It follows that, in the wide metamorphic zone on the western flank, ore 

deposits of high temperature and pressure would be characteristic, but on the 

eastern flank a few ore deposits of high temperature and pressure might occur 

along the immediate contact of the granite. Owing, however, to the very low 

conductivity of rocks, the zone for these deposits would be very narrow and 

would rapidly give way to ore deposits characterized by minerals of medium 

temperature and pressure. The deposits of the latter variety on the western 

flank are covered by the waters of the Pacific Ocean.

Schofield's correlation of the degree of metamorphism with the 

character of the contact of the batholith seems well supported by the 

phenomena in the Wrangell-Revillagigedo belt. But the data used 

to support, his suggestion that the eastern contact is the more deeply 

eroded are of very doubtful validity. Furthermore, the data at hand 

do not support his statement that the eastern contact is smoothly 

undulating, with a few roof pendants; on the contrary, there are 

numerous large blocks of sedimentary and volcanic rock within the 

eastern part of the batholith between the head of Portland Canal and 

Stikine River.

The Coast Range batholith shows an asymmetric character of differentiation, with the more highly differentiated variant quartz 

monzonite in the eastern part. This fact might be used to support 

Schofield's suggesion that the eastern part is the more deeply eroded 

if the whole batholith were the result of a single intrusion and if 

all the variations were the results of differentiation in place. But it 

is very doubtful if this is the case. The character of the contacts 

of the batholith appears to vary from place to place independently of 

the depth of erosion.

Schofield gives copper deposits as characteristic of the west flank 

of the batholith in British Columbia. The main copper deposits in 

southeastern Alaska are predominantly associated with outlying 

dioritic stocks in the Prince of Wales-Chichagof belt and not with the 

west flank of the Coast Range batholith. In the Juneau district 

auriferous quartz veins are associated with the west flank of the 

batholith.

As indicated in the discussion of the Wrangell-Revillagigedo belt 

of metamorphic rocks in this report, the conditions along the contact 

of the batholith in southeastern Alaska are very far from uniform, 

and there is as much difference between the northern and the southern parts along the western contact as there is between the eastern 

and western contacts in the latitude of the Ketchikan and Wrangell 

districts. The general upper surface of the west side of the batholith 

6137 29 20
296 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ATiASKA

appears to have a gentle slope in the Ketchikan and Wrangell 

districts but a relatively steep slope in the Juneau and Skagway 

districts.

South of Frederick Sound, in the Wrangell-Revillagigedo belt, the 

main surface of the batholith must lie at no great depth, as indicated 

by the abundant intrusions of quartz diorite, which probably represent cupolas or more elevated protrusions of the magma. Associated 

and genetically correlated with these bodies is a belt of injection 

gneiss, crystalline schist, and phyllite 20 to 35 miles wide.

North of Frederick Sound the western border of the batholith 

probably plunges with increasing steepness, as indicated by the 

marked decrease in the number of intrusive bodies and the appearance as far south as Port Snettisham of masses of diorite close in 

to the batholith assuming that the diorite is to be interpreted as a 

relatively early differentiation product due to quick cooling.

North of Thomas Bay the aplitic injection gneiss thins to a narrow 

strip immediately adjacent to the batholith, and the belt of crystalline schist and phyllite similarly narrows toward the northwest until 

in the vicinity of Berners Bay it, too, forms but a border too thin 

to map, immediately adjacent to the batholith. The decreasing extent of metamorphism may thus be correlated with the increasing 

depth of the batholith due to an increasingly steeply plunging 

contact.

The differences in degree and extent of intrusion, injection, and 

recrystallization along the western contact may thus be accounted 

for, but there remains the problem of the greater! degree of folding 

in the vicinity of the western border of the batholith. There is a 

most pronounced increase in the degree of crumpling, plication, foliation, and isoclinal folding as the border of the batholith is approched 

from the west, suggesting that the batholith has exerted a tremendous 

thrust. The manner in which the batholith has peeled off great 

slabs of schist constitutes further evidence. On the other hand, in 

the vicinity of the adjacent outlying stocks sintering and compacting 

of the phyllite and slate as the contact is approached indicate that 

the cleavage and foliation are in part younger than the intrusion.

The data are inadequate for a solution of the problem. But if we 

assume that the intrusion of the batholith took place within the 

same general period as the Jurassic or Cretaceous folding, then it is 

probable that at least two factors were involved an increased local 

intensity in the dynamic metamorphism above the location of the 

rising magma and a thrust exerted by the magma itself during its 

emplacement at horizons equivalent to those now exposed. Under 

the same stress and with other conditions the same rocks will be 

much more highly deformed under higher temperature. Thus it
STRUCTURE 297

might be that though stresses of essentially similar orders of magnitude affected beds both far to the east and far to the west of the 

present highly folded zones, the beds to the east and west, relatively 

much cooler, yielded by close folding and development of cleavage, 

whereas those in the intensely folded zone, at a higher temperature 

due to the rising magma with its advance wave of escaping highly 

heated vapors, yielded far more extensively. A preliminary foliated 

or cleaved character had thus already been induced before the arrival 

of the magma, which accentuated the dynamic effects by its own 

thrusting pressure and aided recrystallization by heat, vapors, and 

solutions.

Another important factor appears to have been the structural relations which the invaded formations bore to the magma. For example, where they were in steeply dipping attitudes above the rising 

magma conditions for penetration by magmatic solutions and vapors 

were favorable and metamorphism was correspondingly facilitated; 

such seems to have been the condition in the belt adjacent to the 

southern part of the batholith in southeastern Alaska. Where the 

contact plunges steeply the transfer of solutions and vapors was 

markedly obstructed by the relatively much greater impermeability 

across the foliation surfaces and that portion highly metamorphosed 

above and adjacent to the batholith must lie below the present topographic surface, deeper down on its flank.

The gneissic structure of the batholith suggests that the magma 

moved upward along planes dipping steeply to the northeast and 

that the maximum effect of its thrust was directed against the adjoining formations on the southwest. The country rock was probably irregularly domed up to a considerable extent by the invading 

magma, was fractured, faulted, and stoped to some extent, and was 

thrust aside to a very considerable degree. There is abundant evidence in residual structures and in the composition of the resulting 

rocks that, locally, narrow belts of sediment were wholly incorporated 

in the magma through a process of reactive replacement, but this 

was probably not the major factor in the process of emplacement of 

the batholith.

A series of lamprophyre dikes cut the Coast Range batholith and 

the country rocks. Those in the Eagle River and Berners Bay regions are reported by Knopf to strike in general parallel to the 

stratification. Within the Coast Range batholith they strike predominantly across the grain of the batholith, with trends of N. 10°- 

45° E., although to a minor extent they are approximately parallel 

to the gneissic structure or Jocally have a different trend. East of 

the Coast Range batholith, in the Salmon River district, many of 

them strike northwest. In the vicinity of the Strait of Georgia and
298 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Queen Charlotte Sound in British Columbia, according to Bancroft,1 * 

the dikes are somewhat irregular in their strike, " but the greater 

number of them assume a direction which is parallel or transverse 

to the trend of the Coast Ranges, thus corresponding to the regional 

system of joints."

In the Salmon River district and the adjoining territory to the 

east in British Columbia the predominant trend of the intrusive 

dikes genetically connected with the Coast Range batholith is northwest.

. JUNEATJ SYNCLINORIUM

The Juneau synclinorium extends southeastward through Juneau, 

the outer part of the Fanshaw Peninsula, and perhaps through Mitkof 

and Etolin Islands to a junction with the Keku-Gravina synclinorium. 

It includes a belt of rocks of Mesozoic age lying to the west of the 

belt of crystalline schist and gneiss along the east side of Lynn Canal 

from Comet southeast; Portland, Shelter, and Douglas Islands; the 

east side of Gastineau Channel; Glass Peninsula; the east side of 

Admiralty Island and the islands in Seymour Canal; probably a 

part of the slate and phyllite belts on the mainland along the east 

side of Stephens Passage; Sail Island and The Five Fingers; most 

of tjhe Fanshaw Peninsula; and the north end of Kupreanof Island. 

It is possible that the Lindenberg Peninsula, Mitkof, and Vank 

Islands, and the north end of Etolin Island belong to the same belt. 

At the northwest the belt is cut out by the edging over of the western 

border of the Coast Range batholith.

The beds comprise predominantly graywacke, slate, some conglomerate, and various types of greenstone. The slate and thinbedded zones are isoclinally folded and overturned. (See pi. 20, B.)

The synclinorjal structure is well exhibited in the latitude of Port 

Snettisham and Windfall Harbor, Admiralty Island. Formations 

with Carboniferous fossils are found on the west limb of the major 

syncline on Windfall Harbor and on the east limb in the Taku Haroor-Snettisham Peninsula belt. The Carboniferous beds of Windfall Harbor are adjoined on the southeast for about 1% miles along 

Seymour Canal by interbedded limestone and slate of Upper Triassic 

appearance; these beds are intensely plicated, folded, and faulted; 

at one locality isoclinal folds with a steep southwestward dip were 

observed. Southeast of these limy sediments are greenstone and then 

black slate and graywacke with intercalated conglomerate. The sedimentary beds are mapped as Jurassic(?). The Jurassic(?) slate 

and graywacke form the islands in Seymour Canal, and greenstone

19 Bancroft, J. A., Geology of the coast and islands between the Strait of Georgia and 

Queen Charlotte Sound, B. C.; Canada Geol. Survey Mem. 23, p. 116, 1913.
STRUCTURE 299

iind slate the Glass Peninsula. Beds with Upper Triassic fossils are 

found at the head of Mole Harbor. A steep westward dip seems to 

prevail throughout the beds in Seymour Canal. This westward dip 

changes through vertical to a steep eastward dip on the east side of 

the canal and to 65° NE. or less on the east side of the Glass Peninsula. The Carboniferous beds on the east limb along the Snettisham 

Peninsula dip usually 70°-80° NE. The structure here may thus 

be of the nature of a synclinal fan fold. To the northwest, near the 

head of Hawk Inlet, there are beds of schist which dip predominantly 40°-90° E. and structurally should form the west limb of the 

synclinorium.

East of the Carboniferous beds of the Taku Harbor-Snettisham 

Peninsula belt there is a belt of slate which passes northwest through 

the south arm of Port Snettisham, through Prospect Cove, and east 

o,f Juneau. Near Juneau Upper Triassic fossils have been found in 

the slate, and on Port Snettisham there are intercalated beds of very 

highly mashed conglomeratic black slate that resembles the Jurassic( ?) conglomerate of Seymour Canal. This belt is therefore probably an infolded syncline of Mesozoic beds. The dip ranges from 

75° NW. to steep northeast, and the Carboniferous beds of the Taku 

Harbor-Snettisham belt are exposed on an anticlinal fold.

To the southeast near Windham Bay there are apparently three 

major anticlines and two major synclines in the schistose greenstone, 

phyllite, and slate. The phyllite and slate exposed on Hobart Bay 

and in Sumdum Cove in the major synclines may be, in part at least, 

of Mesozoic age. This belt, including phyllite, slate, and greenstone 

west of the head of Windham Bay, may therefore belong within the 

great Juneau synclinorium.

The general strike of both the cleavage and the bedding in the 

Jurassic (?) slate and graywacke on the north end of Kupreanof 

Island and north of Cape Fanshaw on the mainland is N. 10°-45° W. 

The general strike of both the bedding and the cleavage in the same 

system of beds between Cape Fanshaw and Bay Point, on the other 

hand, is about N. 70°-90° E. In each of these areas the general trend 

of the cleavage is more constant than that of the bedding. The wide 

and uniform change of direction in the strike of the bedding in the 

belt between Cape Fanshaw and Bay Point is accompanied by a similar change in the strike of the cleavage. Local variations in the 

direction of dip of the cleavage suggest drag folding.

DTTNCAN ANTICLINOBIUM

The Duncan anticlinorium strikes southeast from the northwest end 

of Kupreanof Island east of Cape Bendel along Duncan Canal and 

across the central part of Zarembo Island. Devonian formations are
300 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

exposed in the core and form a belt that separates the Mesozoic beds 

of the Juneau synclinorium from the Mesozoic and Tertiary formations of the Keku-Gravina synclinorium. Very gently dipping volcanic rocks, presumably Tertiary, are exposed on one of the Castle 

Islands, Duncan Canal.

Along the core of the anticlinorium the beds are folded into several 

anticlines and synclines. Duncan Canal is eroded along the crest of 

a closely folded anticline. A synclinal axis lies along a line from the 

Castle Islands through Deception Point Cove, Woewodski Island; 

pillow lava and andesitic tuff and breccia are exposed in the trough. 

West of this the beds are thrown into a series of open folds. In the 

bay west of the Castle Islands a wide belt of slate is exposed; it has 

a uniform cleavage with a dip of 40°-60° E. or NE., which remains 

constant irrespective of the direction of the strike and dip in the beds 

affected by minor folds.

At the northwest end of Kupreanof Island the beds are closely 

folded and greatly disturbed; a thick bed of coralline limestone has 

been mashed and rendered very highly schistose, and the relations of 

the rocks are not well shown. At the southeast end of Zarembo 

Island the beds are much broken by faulting.

KEKU-GRAVINA SYNCLINORIUM

The Keku-Gravina synclinorium is one of the major features in 

the geology of southeastern Alaska. It includes the southwest end 

of Admiralty Island and extends 350 miles southeast from Kootznahoo Inlet, Admiralty Island, through the territory adjacent to Keku 

Strait, Clarence Strait, and Gravina Island to Cape Fox, at the 

entrance to Portland Canal, and has a width of 5 to 20 miles.

The predominant formations within the synclinorium at the southeast end are of Mesozoic age, with rare isolated remnants of overlying 

Tertiary beds; but in the northwest part the Tertiary formations 

predominate.

GRAVINA SYNCLINORIUM 

By THEODORE CHAPIN

The synclinorium in the latitude of Gravina Island, here called 

the Gravina synclinorium, has been described in detail in an earlier 

report.20 The structure section is shown in Plate 22, section A-B. 

The beds present a dominant northwest strike and, except locally, 

dip northeast, giving the appearance of a simple monoclinal structure over a wide area. The section is believed to represent truncated 

closely compressed folds overturned toward the southwest. The

20 Chapin, Theodore, The structure and stratigraphy of Gravina and Revillagigedo 

Islands. Alaska: U. S. Geol. Survey Prof. Paper 120, pp. 86-87, 1918.
STRUCTURE 301

overturned position of these beds is shown by the relation of the 

Mesozoic and Paleozoic beds; the younger beds dip beneath the older 

ones on the east side of the trough. 

The following description is quoted from the previous report:

On the southwest coast of Gravina Island Triassic conglomerate, limestone, 

and black slate are overlain by volcanic: rocks and intercalated sediments of 

Triassic or Jurassic age, which, in turn, are overlain by the slate and graywacke 

of Blank Inlet, determined to be Jurassic or Cretaceous. Succeeding the 

Jurassic or Cretaceous sediments are volcanic rocks, with black slates and tuffs. 

Here the section is interrupted by a boss of granite, beyond which are black 

slates and phyllites, limestone, and schistose conglomerate. Beyond the conglomerate occur crystalline schists and massive semicrystalline limestone bearing fossils regarded as certainly Paleozoic and probably Carboniferous. This 

anomalous position of the Paleozoic and Mesozoic rocks is probably due to an 

overturned position of one limb of the syncline.

From the slate and graywacke area of Blank Inlet the general sequence of 

rocks is the same toward the northeast as it is toward the southwest, and it is 

believed that the similar rocks are in fact the same beds exposed on two limbs 

of an overturned fold, the trough of which is exposed on Blank Inlet. The 

volcanic rocks on each side of the Blank Inlet area of slate and graywacke are 

similar and may be correlated, as there is little reason to doubt their identity. 

The slates and phyllites of Revillagigedo Island are much more schistose 

than the black slates and sandstones of Gravina Island, with which they are 

correlated, but this is evidently due to the contact inetamorphism caused by the 

adjoining intrusive granite. The other sediments of Revillagigedo Island are 

also more metamorphosed than their supposed equivalents on Gravina Island. 

The limestone is crystalline and the conglomerate is schistose, but these differences in metamorphism are also .easily accounted for, not alone by the small 

body of granite shown in the sketch but also by the immense batholith of the 

Coast Range.

Along this eastern limb of the syncline is a greatly disturbed belt which 

apparently continues the entire length of southeastern Alaska along the border 

of the intrusives of the Coast Range. In this disturbed belt the folding is much 

more close and the beds are more tightly compressed and, if correctly Interpreted, are in part overturned. The structural form is not a simple syncline 

and might more correctly be termed a " synclinorium," for one prominent anticline and a number of minor folds occur.

On the west coast of Vallenar Bay about a mile east of South Vallenar Point is the crest of a very sharply folded anticline, which has 

involved the calcareous shale and argillite. This is believed to be the 

lowest of the! Devonian beds, and the limestone and conglomerate to 

the west are believed to be stratigraphically higher in the section and 

to occupy the overturned limb of a steeply pitching anticline overturned toward the west. The contact with the Mesozoic beds at the 

head of Vallenar Bay is covered by gravel. This anticline, along 

which the Devonian beds are brought to the surface on Vallenar Bay, 

is presumably the same fold which extends along Dall Ridge to Seal 

Cove and forms a minor fold in the broad synclinorium involving all 

the rocks between the west coast of Gravina Island and George Arm.
302 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The topographic features of the broad depression that connects Vallenar Bay and Bostwick Inlet and divides Gravina Island into two 

distinct parts were regarded by Brooks as indicative of faulting. 

The movement, however, does not appear to have involved the 

Devonian beds.

Middle Devonian rocks correlated with those on Gravina Island 

crop out on Hotspur Island, a small island about 3 miles long that 

lies between Duke and Annette Islands. The beds of Hotspur Island 

all strike northwest and have a dominant dip to the northeast. The 

Devonian beds form a narrow belt of fossiliferous gray limestone 

and calcareous shale carrying a coral fauna in which Fdvosites is 

especially abundant. To the north and south of the limestone are 

interbedded limestone, black slate, and tuff of probable Triassic age, 

which unconformably overlie the Devonian limestone. The structure 

of the island appears to be that of a closely folded anticline, in part 

overturned toward the southwest. The crest of the anticline is occupied by the Middle Devonian limestone, and the limbs are composed 

of slate and limestone of probable Triassic age.

KOCKY BAY AREA, ETOLIN ISLAND

The Lower Cretaceous (?) slate of the Rocky Bay area, on the west 

end of Etolin Isjland, shows apparently anomalous cleavage relations. 

On Clarence Strait and Stanhope Island the strike of the cleavage 

averages about N. 15° E. and is uniformly more easterly than the 

prevailing strike of the bedding. The dip of the cleavage is in most 

places nearly vertical. In Rocky Bay the strike of the cleavage 

swings more to the east, and finally, on the east side of the bay, it 

becomes northwest. The cleavage appears like a close-set fracture 

cleavage. The conditions are similar to those in the Jurassic (?) 

slate between Bay Point and Cape Fanshaw, on the Fanshaw Peninsula, but are somewhat more, complicated. The explanation of the 

peculiar conditions is not apparent to the writer.

KEKU SYNCLINORIUM

Between Etolin Island and the north end of Keku Strait the Mesozoic formations are buried beneath the Tertiary. At the north end 

of Keku Strait there are two major synclines, in the troughs of which 

Lower Cretaceous (?) beds' are exposed, and an anticlinal axis, on 

which Devonian beds are exposed. Carboniferous formations occupy 

the Cornwallis Peninsula and the Keku group of islets, except for 

a narrow belt of infolded or infaulted Upper Triassic beds and an 

anticlinal ridge of Silurian limestone. Between the Tertiary rocks 

of Point Camden and the Carboniferous formations of the Cornwallis Peninsula is a series of Upper Triassic volcanic rocks with
STRUCTURE 303

Lower Cretaceous (?) shale and minor associated sandstone occupying the trough of a synclinal basin between Kuiu Island and Hound 

Island, most of which is covered by water. Extending through 

Hound Island and several islands to the northwest is an anticlinal 

axis on which Upper Triassic lava is exposed. Lower Cretaceous (?) 

beds are again exposed in the trough of a syncline at Point Hamilton. 

The Lower Cretaceous (?) beds in these synclines are the least 

metamorphosed of all in southeastern Alaska.

The axis of a well-defined anticline passes northwest through the 

village of Kake on Kupreanof Island. Devonian beds are exposed 

on the core and Upper Triassic formations on the flanks. The fold 

pitches 20°-25° SE. and is carried beneath the waters of Hamilton 

Bay. The channel between the line of islands and reefs and Kupreanof Island is eroded along the core. The anticline is asymmetric, 

with a gentle dip on the northeast limb and a vertical dip on the 

southwest limb. The Devonian beds on the core show many minor 

folds and crumples, and there is' considerable faulting.

Adjoining the Kake anticline on the east is the Cape Bendel 

syncline, in which Upper Triassic formations are exposed. The syncline is asymmetric, with a gentle southwest limb and a vertical 

northeast limb. It includes several minor anticlinal axes. Permian 

limestone is brought to the surface on one of these axes and forms 

the conspicuous mountain north of Kake. Carboniferous and 

Devonian beds form the east flank of the syncline.

FREDERICK SOUND AXIS OF CROSS FOLDING

Jurassic (?) beds are exposed at intervals along the south side of 

Admiralty Island and form a considerable part of the coast line. 

These beds have not been carefully studied, but they appear to have 

been folded along two axes the usual north-northwest axis and 

another about parallel to Frederick Sound that is, east-west. The 

axis of cross folding is reflected in the east-west strike of the beds 

between Cape Fanshaw and Bay Point.

Tertiary formations cover the west half of Zarembo and Kupreanof Islands, the eastern part of Kuiu, and the southwest part of 

Admiralty Island. The Tertiary formations at the northwest end of 

Kupreanof Island and those at the southwest end of Admiralty 

Island appear to lie on opposite flanks of a broadly folded anticline 

whose axis strikes northeast. On Port Camden the beds dip 8°-10° 

SE. and on Hamilton Bay about 15° SE. Wright 21 states that on 

the southwest end of Admiralty Island the Tertiary lava beds are 

not folded, but show a general dip of 5°-10° NW. Frederick Sound

21 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

p. 146, 1906.
304 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

would thus appear to be eroded approximately along the core of the 

dome in the Tertiary formations. On the south side of Kupreanof 

Island and in the vicinity of the southern part of Keku Strait there 

is a lack of uniformity in the strike and dip. In the vicinity of 

Point Nesbitt, Zarembo Island, there is a series of lava conglomerate 

with associated volcanic rocks with a northeast strike and a dip of 

30° NW.

If the interpretation of the structure of the Tertiary formations is 

correct, then the forces that effected their folding were oriented 

almost at right angles to those that effected the folding of the Mesozoic formations in pre-Tertiary time.

PRINCE OF WALES-KTJIU ANTICLINORIUM 

GENERAL FEATURES

The Prince of Wales-Kuiu anticlinorium is one of the major features of the geology of southeastern Alaska. It comprises all of 

Prince of Wales Island, the entire archipelago off the west coast of 

Prince of Wales Island, including Dall, Suemez, Baker, Noyes, and 

Coronation Islands, and all of Kuiu Island except the northeastern 

part. The belt is more than 150 miles long and throughout most of 

its extent is 40 to 50 miles wide. It is possible that some of Baranof 

Island might be included. This anticlinal axis forms the Prince of 

Wales group of mountain ranges. A northwest extension is found 

across the northeast end of Chichagof Island and in the vicinity of 

Glacier Bay.

The formations exposed are exclusively Paleozoic except for a few 

small isolated areas of Tertiary sedimentary and volcanic rocks. 

The predominant formations are of Ordovician, Silurian, and Devonian age. Carboniferous formations are exposed only locally in 

the vicinity of Klawak, Trocadero Bay, and Ulloa Channel, on the 

west coast of Prince of Wales Island, and at the north end of Kuiu 

Island. Rocks possibly of pre-Ordovician age are exposed on Prince 

of Wales Island and on Dall Island.

East of the Prince of Wales-Kuiu anticlinorium lies the KekuGravina synclinorium, with its Mesozoic and Tertiary formations, 

and on the west lies the Pacific Ocean. The formations of Queen 

Charlotte Island, of Mesozoic and Tertiary age, if extended along 

their strike, would underlie the Pacific Ocean in this vicinity.

Within this major anticlinorium there are five large structural 

provinces, comprising three anticlinoria of a second order and two 

synclinoria.

The Kuiu anticlinorium includes all of Kuiu Island, except the 

northeastern part, and Warren Island. It is composed almost exclu-
STBUCTUEE 305

sively of Ordovician (?) rocks, with only a minor amount of 

Silurian.

The synclinorium of the northern half of Prince of Wales Island 

includes the Shakan Bay and Kosciusko-Tuxekan-Heceta synclines. 

Several other synclines with corresponding anticlines are present in 

the northern part of Prince of Wales Island, but they have been much 

 disturbed by the intrusion of a large stock of igneous rock. The 

formations within this synclinal province are mostly Silurian, with 

a little Ordovician and perhaps some Devonian.

The central anticlinorial province includes the southeast side of 

.Noyes Island, Lulu and San Fernando Islands, the. central part of 

Prince of Wales Island, comprising a belt north of Klawak Salt 

Lake, and the eastern part from a line west of the west arm of Whale 

Passage to Tolstoi Bay. The Maurelle Islands may belong with this 

province. The formations of the central anticlinorium are almost 

wholly of Ordovician age, with some associated lower members of 

the Silurian system and a little Devonian; they are similar and 

probably equivalent to those of the Kuiu anticlinorium. The principal structural features are the San Fernando and Kashevarof 

anticlines.

The southern synclinorium embraces the southern half of Prince 

of Wales Island south of Thorne Bay and Klawak Inlet, also the 

adjoining islands, including Baker, St. Ignace, San Juan Bautista, 

Suemez, and Sukkwan Islands, and the north end of Dall Island. 

Taken as a whole, this province is a synclinorium of Devonian with 

locally a little area of younger formations. It is divided into two 

parts by the Dolomi-Sulzer anticline, which exposes the Wales group 

of rocks.

The southern anticlinorium includes Long Island, in Cordova Bay, 

and most of Dall Island. Only rocks of the Wales group and Silurian 

formations are exposed.

There are several structural elements in the Prince of Wales-Kuiu 

anticlinorium whose relations to one another and whose significance 

are not clear. If the area were completely mapped the problem 

might be solved.

The graywacke formations of Kuiu Island (the core of the Kuiu 

anticlinorium), El Capitan Passage, Thorne and Stevenson Islands, 

Lake Bay (the core of the Kashevarof anticline), and Klawak Inlet, 

and the Salt Lake on Tuxekan Passage constitute one structural element. They are isoclinally folded with nearly vertical to very steep 

eastward-dipping axial planes. Although locally they have the normal northwest strike typical of southeastern Alaska, the predominant 

strike is about true north.

The two major structural features along the northwest coast of 

Prince of Wales Island the Shakan Bay and Kosciusko-Tuxekan-
306 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Heceta synclinoria are closely folded, but the folds are much more 

open than those within the graywacke described in the preceding 

paragraph. The strike here is northwest and the strike of the Silurian formations on the east side of Kuiu Island is also northwest.

In the south half of Prince of Wales Island and in the great island 

group to the west, south of the Gulf of Esquibel, the structure is 

exceedingly complex. There are folds trending approximately eastnortheast, such as those in the sandstone at and south of Naukati 

Bay, the San Fernando anticline of graywacke, and the Devonian 

formations of the east hajf of Baker Island and north half of 

Suemez Island; .folds trending north-northeast, such as those in the 

Devonian and Mississippian formations of San Alberto Bay; folds 

trending west-northwest, such as those on the north end of Dall 

Island and the Dolomi-Sulzer anticlinorium, on Prince of Wales 

Island; and folds trending northwest, such as those in the formations 

of the south half of Prince of Wales Island and Trocadero Bay. 

The folds that trend northwest are .locally superimposed on those 

that trend east-northeast for example, the northwestward-trending 

San Christoval Channel syncline upon the dominant east-northeast 

San Fernando anticline.

The graywacke formation with a general northern trend is partly 

and perhaps wholly of Ordovician and lower Silurian age, and the 

beds are very closely folded and compressed wherever found, irrespective of their proximity to outlying intrusive masses or to the 

Coast Kange batholith. Their attitude suggests that the structural 

element which they constitute originated in an erogenic period preceding the deposition of the upper Silurian formations. Apparent 

marked unconformity at several localities would seem to support this 

suggestion, but fuller and more exact data are needed before it can be 

accepted.

The east-northeast, northeast, and west-northwest folds in the 

island group in San Alberto Bay and Klawak Inlet and south of the 

Gulf of Esquibel present phenomena for whose explanation the 

writer has no satisfactory hypothesis. The formations at the south 

end of Prince of Wales Island have in general a considerably more 

westerly trend than the dominant northwest strike of the formations 

farther east, and on the west they reach the Pacific Ocean at angles 

of 60°-90°. The northwest structure may have been superimposed 

upon the east-northeast and northeast folds, and the west-northwest 

structure may be a modification of the northwest structure resulting 

from a preexisting east or northeast1 trend in underlying or adjacent 

formations. Another possibility is that the east-northeast and northeast folds are of Tertiary age and were'superimposed on the older 

northwest folds, but it is a question whether the Tertiary folding was 

sufficiently strong to accomplish this task.
STRUCTURE 307 

KUIU ANTICLINORIUM

The Kuiu anticlinorium includes all of Kuiu Island, except the 

northeastern part, and Warren Island. It is composed almost wholly 

of Ordovician (?) formations and constitutes an anticlinorial core 

with respect to the Keku synclinorium. The rocks consist predominantly of indurated tuffaceous graywacke with slate partings and 

local thin-bedded zones of slate, graywacke, and limy sediments. No 

fossils have been found, but on lithologic similarity the beds are 

regarded as probably largely of Ordovician age, though some may be 

early Silurian.

Greenstone conglomerate and volcanic rocks and locally limestone 

of Silurian age occur at several localities in the troughs of synclines, 

as on the west side of Port Beauclerc,, from Point Amelius northwest 

to Edwards Island; in a belt northwest through Sumner Island; at 

Point St. Albans; at the narrows 'on Pillar Bay; and probably at 

other localities not visited. These are of only minor volume in comparison with the predominant graywacke.

The Ordovician (?) beds of Kuiu; Island, like those of Prince of 

Wales Island, have a prevailing steep eastward to vertical dip; westward dips are rare. The structural relations are complex. The beds 

are probably duplicated through isoclinal folding and thrust faulting, and beds with strikes at right angles to each other in adjacent 

outcrops are noticed. Many of the thin beds between the more competent thick-bedded graywacke have been isoclinally folded, plicated, 

overthrust, and brecciated; locally they have been completely broken 

down to a mylonite or fault breccia or even compressed to a schistose 

aggregate composed of lenses of limestone 1 inch to several inches in 

length in an argillaceous matrix. For 5 or 6 miles south of Point 

Amelius the beds strike west and dip in general 30°-60° and apparently constitute a major anticlinal axis, but in general the strike of the 

beds is north in the southern half of the island and about northwest in 

the northern half.

NORTH COAST OF PRINCE OF WALES ISLAND

Along the north coast of Prince of Wales Island the formations are 

repeated .by folding but are very much disturbed, and the structure is 

complex. At Labouchere Bay there is a minor steeply southeastwardpitching anticlinal fold which exposes Silurian volcanic rocks, and 

Port Protection occupies the site of an anticlinal axis on which 

Silurian (?) graywacke and volcanic rocks are exposed. For several 

miles along the coast between Point Baker and Red Bay there are 

exposures of beds of graywacke, slate, and limestone, which have a 

general dip of 20°-40° NW. They are interpreted as occupying thu
308 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

trough of a syncline and overlying the Silurian limestone, but they 

may include both Silurian and Devonian. The relations of the 

Silurian limestone east of Eed Bay to the greenstone volcanic rock* 

of Point Colpoys and the tuffaceous graywacke farther east are not 

known. The dip is steep to the west at Point Colpoys, but this may be 

due to overturning. The beds along El Capitan Passage are very 

much disturbed by the intrusion of the batholith of igneous rock, as 

are all the beds surrounding this mass. The major structure hero 

appears to be that of a syncline containing in its trough upper 

Silurian conglomerates that dip 15°-40°. Graywacke and slate are 

exposed on the anticlinal core along the west side of El Capitan Passage south of Devilfish Bay and on the islands in the vicinity of Sarkar Cove. The graywacke has generally a steep dip and may be, in 

part at least, of Ordovician age.

SHAKAN BAY SYNCLINE

The Shakan Bay syncline comprises a belt of graywacke that is 

assumed to be probably of Silurian age and to occupy a synclinal 

trough"in Silurian limestone; this graywacke is exposed on the Barrier Islands, the adjoining coast of Prince of Wales Island, Hamilton 

Island, and the peninsula between Shakan Bay and Shipley Bay. 

The contact between the graywacke a ad the Silurian formations east 

of the Barrier Islands is a fault plane. The graywacke has a dip of 

70° W. on the east, near the Silurian (?) beds, and changes to 25° or 

less on the west. The southeast island of the Barrier Island group lies 

exactly in the trough of the syncline, the beds dipping in on all sides. 

At the west end of the peninsula between Shakan and Shipley Bays 

there are several gentle folds. There is evidence of marked faulting 

within these beds.

KOSCIUSKO-TUXEKAN-HECETA SYNCLINORIUM

South of the Shakan syncline is the Kosciusko-Tuxekan-Heceta 

synclinorium, which includes Kosciusko, Marble, Orr, Tuxekan, and 

Heceta Islands, other islands around Davidson Inlet and Sea Otter 

Sound, and a part of the west coast of Prince of Wales Island. This 

synclinal basin is 30 to 35 miles long and 20 to 25 miles wide. Tho 

strike is northwest. It includes chiefly Silurian formations with Ordovician formations exposed locally around the rims. The structure 

is complex, with many1 minor anticlines and synclines. The beds in 

general dip in toward Davidson Inlet and Sea Otter Sound. Eagle, 

Owl, White Cliff, and Hoot Islands mark the core of a gentle anticlinal dome within the major basin. The synclinorium includes broad, 

open folds with limbs dipping 30°-45° and narrow, tightly com-
STRUCTURE 309

pressed folds with limbs dipping 60° to vertical or slightly overturned 

toward the northwest. On Kosciusko Island the east limb consists of 

graywacke of probable Ordovician age and has a steep dip; the west 

limb consists of the steeply dipping graywacke of Warren Island.

Edna Bay occupies the site of a northward-pitching synclinal 

basin with several minor folds. On the west side of the bay there is 

an anticline the west limb of which is slightly overturned toward the 

west. The cleavage here dips steeply northeast. The axis of this 

anticline comes out on Davidson Inlet northwest of Green Island. 

To the west of this anticline is another synclinal trough in which the 

beds are gently folded back and forth and in which the youngest 

Silurian beds found in this area occur.

The graywacke and conglomerate beds (about 2,000 feet thick) 

at the south end of Marble Island and on the reefs between Marble 

Island and White Cliff Island occur in a synclinal basin in the 

Silurian limestone. The prevailing dip is 25°-40°.

At the head of Naukati Bay a formation of interbedded red and 

green sandstone is gently folded into two anticlines and a syncline. 

The folds' strike approximately east. South of Naukati Bay the 

same sandstone formation forms a broad synclinal basin whose axis 

strikes N. 80°-85° E. and pitches about 10° E. The limbs of the 

syncline dip about 25°. The cleavage throughout has a strike of 

about N. 70° E., nearly parallel to the axes of the folds. The sandstone overlies the Silurian limestone.

Karheen Passage, the east end of Heceta Island, and the bay 

southeast of Tonowek Narrows in a belt that is about 3 miles wide 

and extends N. 40° W. are carved out of a southeastward-pitching 

synclinorium of thin-layered Silurian limestone and overlying sandstone. The sandstone on the east end of Heceta Island has a general 

north to north-northwest strike and a dip of 4Q°-60° E. The thinlayered limestone shows abundant drag folds, which are closely compressed, with steep to vertical dips. This syncline is adjoined on 

the east at the south end of Tuxekan Passage by an anticline that 

pitches northwest.

Warmchuck Inlet, Heceta Island, is cut out along the nose of a 

northwestward-plunging anticline in Silurian formations. Graywacke of probable Ordovician age is exposed on the core of the anticline in the Salt Lake on the east side of Tonowek Bay.

MATJRELLE ISLANDS

Esquibel, Anguilla, Two< Crack, and San Lorenzo Islands, in the 

Maurelle group, are composed of Silurian and older formations exposed on an anticlinal core. The islands to the west are probably 

composed of Devonian formations exposed on the flanks of the anti-
310 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

cline. The general strike of the Devonian formations is northwest, 

but that of the Silurian and older formations is east-northeast. 

There are at least two anticlines and two synclines within the anticlinal core, and it is probable that beds as old as the Wales group 

are exposed.

The San Fernando anticlinal axis strikes across the dominant 

northwest structural trend and includes the southeastern side of Noyes 

Island, Lulu and San Fernando Islands, and a belt on Prince of 

Wales Island east of San Christoval Channel. The core of the anticline trends east-northeast and the beds exposed are graywacke 

and associated slate and chert of Ordovician and Silurian age. Along 

Portillo and San Christoval Channels younger Silurian conglomerate and sandstone are infolded into the older graywacke along 

northwest axes. Noyes Island and the Gulf of Esquibel occupy 

the trough of a syncline in which Devonian formations occur. The 

east limb of the San Christoval syncline is vertical to slightly 

overturned toward the west, and the west limb dips 10°-30° NE.

KASHEVAROF ANTICLINORIUM

The core of the Kashevarof anticlinorium includes Thorne and 

Stevenson Islands and extends south into an unknown portion of 

Prince of Wales Island. Kashevarof Passage is cut across its northward-plunging nose. The oldest beds, exposed on .the core, are the 

graywacke-slate series found on Thorne and Stevenson Islands and 

at Lake Bay. The slate carries Ordovician fossils. These beds are 

repeated many times by folding. The prevalent dip is steep eastward, but locally the dip is westward and some dips are as gentle as 

20°. Beds of thin-layered slate and graywacke are, practically without exception, in an approximately vertical attitude and commonly 

show very abundant slickensided surfaces, possibly as a result in 

part of drag folding due to thrust faults with an eastward dip. It is 

also probable that isoclinal folding "has occurred. Overlying the 

Ordovician beds on the nose and flanks of the anticlinorium is the 

greenstone-limestone conglomerate and volcanic formation of the 

Silurian, succeeded on the Kashevarof Islands by the Silurian limestone member, which in turn is succeeded on the northwest end of 

Prince of Wales Island by the Devonian tuffs and sediments. On the 

Blashke Islands the beds are domed up by an intrusion of dunite and 

associated dioritic rocks, and Ordovician graywacke is exposed on the 

borders of the igneous stock within a belt of the Silurian greenstone. 

In the vicinity of Eatz Harbor the beds are disturbed and interrupted by a small batholith of diorite. The Ordovician and Silurian
STRUCTURE 311

beds of the Kashevarof anticlinorium extend southeast to the Kasaan 

Peninsula, where they are believed to be overlain by Devonian formations. Fossilifefous Ordovician slate is found on the west side of 

Thorne Bay.

VICINITY OP SAN ALBERTO AND BTJCARELI BATS

Paleozoic rocks younger than Middle Devonian are found in the 

vicinity of San Alberto and Bucareli Bays and occur within a part 

of the southern synclinorium. They occupy at least two auxiliary 

complexly folded synclinal troughs one along Klawak Inlet and the 

islands of Trocadero Bay, the other including San Juan Bautista 

Island, the west side of Ulloa Channel, part of Port Refugio on 

Suemez Island, and the islands in Soda Bay. The peninsula between 

Trocadero and Soda Bays is an anticline on which the/ Middle Devonian formations are exposed. There are two structural trends almost 

at right angles to each other in the vicinity of San Alberto and 

Bucareli Bays, one northwest to west-northwest along Ulloa Channel 

and Trocadero Bay and the other in a general northeast direction 

along Bucareli and San Alberto Bays.

In the island group west of Klawak Middle Devonian and Mississippian beds are folded with a north-south strike and cross folded on 

east-west axes. The cleavage is north-south. East of Klawak the 

beds dip steeply eastward to vertical. At Point Bocas, on Ulloa 

Channel, Mississippian rocks occupy a- closely folded syncline and 

strike northwest, and on the northeast side of Suemez Island Upper 

Devonian beds strike northwest. The Middle Devonian beds of St. 

Ignace Island and the east half of Baker Island strike east to eastnortheast, and those on the north end of Suemez Island strike east 

to northeast.

SOUTHERN HALF OP PRINCE OF WALES ISLAND AND ADJACENT ISLANDS

By THEODORE CHAPIN

The Middle Devonian rocks-of the southern half of Prince of Wales 

Island and the islands to the west appear to occupy a synclinorium, 

with a great many auxiliary folds which trend generally northwest. 

The oldest rocks are the greenstone flows and breccias which occupy 

the southwest flank of the syncline. They cover the north end of 

Dall Island, Halibut Nose, the west coast of Sukkwan Island, and 

the southwestern coast of Prince of Wales Island from Keete Inlet 

to Cape Chacon. They are tentatively correlated with similar rocks 

on Moira Sound, on the southern branches of Kasaan Bay, and on 

Bucareli Bay.

6137 29 21
312 GEOLOGY AND MINERAL DEPOSITS, SOU THE ASTERN ALASKA

The rocks exposed along the shore from Port Johnson to the head 

of Moira Sound appear to present a conformable sequence composed 

of three zones of tuffs and sediments and two of igneous beds with a 

monoclinal dip toward the southwest. The apparent total thickness 

is 20,000 to 30,000 feet. This section, however, is believed to be a 

synclinorium composed of closely folded truncated beds overturned 

toward the northeast. The igneous beds are believed to be the equivalent of the red and green flows and breccias that occur on the southwest coast of Prince of Wales Island along closely compressed anticlines. The tuffs and sediments stratigraphically overlie them and 

occur along the synclines.

Twelvemile Arm and Polk and McKenzie Inlets are bordered by 

tuffaceous sediments, black slate, and conglomerate, with beds of 

lava and breccia apparently interbedded. The. structure here, as on 

Moira Sound, is believed to be that of closely compressed and overturned folds. The belt of igneous rocks that extends from the mouth 

of McKenzie Inlet across Skowl Arm to the Jervais Islands, if correctly correlated with the red and green andesite and breccia of the 

lower group, occupies the crest of a truncated anticlinal fold and is 

stratigraphically overlain by tuffaceous sediments and black slate. 

Toward the east end of Skowl Peninsula the beds are more dominantly sedimentary. They are essentially conglomerate, slate, and 

graywacke and are free from igneous and tuffaceous material. They 

comprise the base of the upper group of Middle Devonian rocks and 

are higher stratigraphically than any beds exposed on Moira Sound 

or Klakas Inlet. They are apparently conformable with the intermediate group into which they grade by an increasing amount of 

tuffaceous material. Interbedded with the conglomerate is considerable limestone, and overlying the limestone and conglomerate is the 

massive limestone of Long Island.

Long Island, a small island about 2 miles long in Kasaan Bay, is 

made up essentially of massive fossiliferous limestone of Middle 

Devonian age. The rocks of Long Island appear to occupy a syncline, 

but the structure is very complicated in detail. They are locally 

overlain unconformably by rhyolite flows of Tertiary age.

The rocks of Kasaan Peninsula consist chiefly of the igneous mass 

to which the term Kasaan greenstone was applied by Brooks,22 who 

described the formation as composed largely of effusive rocks but 

stated that intrusive rocks were also probably included and that some 

associated narrow belts of limestone were not separated from the 

greenstone on the map. Kasaan Peninsula was regarded by Wright 23

22 Brooks, A. H., Preliminary report on the Ketchlkan mining district, Alaska: U. S. 

Geol. Survey Prof. Paper 1, p. 49, 1902.

23 Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

Alaska : U. S. Geol. Survey Prof. Paper 87, p. 72, 1915.
STRUCTURE 313

as a closely folded synclinorium in which the beds in general strike 

northwest and dip northeast, and no doubt some of the older tuffaceous and igneous beds of Middle Devonian age were involved in this 

close folding and now appear as if interbedded with the younger 

conglomerate and limestone.

Clover Bay is a small indentation 4 or 5 miles north of the mouth 

of Cholmondeley Sound, Prince of Wales Island. A mass of sedimentary rocks too small to map occurs near the head of the bay, inclosed within a mass of intrusive quartz diorite; it comprises beds of 

conglomerate, graywacke, argillite, and fossiliferous limestone which

FIGURE 2.- Structure section on Clover Bay, Prince of Wales 

Island

strike N. 60° W. and stand at a steep angle. The following sequence 

of rocks is exposed:

Apparent section on Clover Bay, Prince of Wales Island

Quartz diorite. Feet

Limestone with Middle Devonian fossils_ 15

Conglomerate graywacke with fossils (probably Triassic)__ 12

Concealed___ ________ _________ _ _ 25

Argillite________________________________ 20

Limestone with Middle Devonian fossils___________ 10

Argillite________________________________ 10

Graywacke ____ ______ _______ ___ __ 30

Concealed____________:___________________ 43

Graywacke with fossils (probably Triassic)_________ 10

Limestone with Middle Devonian fossils__________ 22 

Graywacke _______________________________ 17

Argillite with dikes of quartz diorite_ __ __~_ _ __ 43 

Quartz diorite.

In the field this section was regarded as interbedded limestone and 

graywacke, but from the fossils it appears that the limestone is 

Middle Devonian and that the graywacke is probably Mesozoic and 

therefore younger. From these facts the structure is interpreted as 

shown in Figure 2. 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.
314 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

DOLOMI-SULZER ANTTCLINORIUM 

By THEODORE CHAPIN

The Dolomi-Sulzer anticlinorium extends between Hetta Inlet and 

Cholmondeley Sound and along the east side of the northern part of 

Cordova Bay and the west side of Hetta Inlet. The crest of the anticlinorium extends from Dolomi to a, point near Sulzer, at the head 

of Hetta Inlet, where it pitches steeply northwest beneath upper 

Paleozoic rocks. A belt of limestone and schist of the Wales group 

extends from Dolomi to Copper Mountain and occupies the crest of 

the fold which has brought these beds to the surface. The anticlinorium trends a little north of west. ;Its structure isi not simple, 

as it includes many minor folds. South of Dolomi the beds dip 

southwest along the south limb and disappear beneath the upper 

Paleozoic greenstone, slate, and conglomerate of Moira Sound. The 

Wales group is unconformably overlain by Devonian and Silurian 

formations.

DALL ANTICLINORIUM

The Dall anticlinorium includes the southern half of Dall Island 

and Long Island, in Cordova Bay. Its trend in the southern part of 

Dall Island is northwest, but in the northern part it swings around 

to true west and is cut off by the Pacific Ocean. The structural relations are very complex, and a combination of synclinal and anticlinal 

folds locally overturned toward both the southwest and the northeast 

is indicated. With the probable exception of narrow belts of Silurian rocks only the Wales group is exposed in this area. The beds 

of the Wales group contain a great number of minor folds and sharp 

flexures. The schist and greenstone are twisted and contorted, and 

even the massive limestone beds are closely folded or foliated. Bodies 

of intrusive rock have caused extensive recrystallization locally 

within the Wales group, and contact zones are common.

On Dall Island, between Cape Augustine and the Diver Islands, 

there is a large area of lower Silurian slate which is overlain on the 

north by upper Silurian limestone. The beds of lower Silurian slate 

strike true west or a little north of true west. They are isoclinally 

folded, with, a prevalent dip of 60° S. in and south of Salde Bay 

and a prevalent dip of 45°-70° N. in Sea Otter Sound. The limestone belt of Thunder Mountain lithologically resembles the upper 

Silurian limestone, but it appears to occupy a poorly defined synclinal trough in the lower Silurian slate, owing either to unconformable relations or to close folding of the underlying weaker beds.
. . STRUCTURE 315 

CHICHAGOF-GLACIER BAY ANTICLINOEIUM

The Chichagof-Glacier Bay anticlinorium is a northwest extension 

of the anticlinal axis that passes through Prince of Wales and Kuiu 

Islands. The formations on the northeastern half of Chichagof 

Island and on the islands and coasts of Glacier Bay are, so far as 

known, whoJQy of Paleozoic age. This belt constitutes, therefore, an 

anticlinorial core with respect to the Mesozoic formations of the 

Juneau and Sitka belts. The present knowledge of the geology of 

this part of southeastern Alaska is, however, inadequate for defining 

how much of the territory adjacent to Glacier Bay, how much of Chichagof Island, and how much, if any, of Admiralty Island should be 

included in this belt. The predominant rocks of the belt are- Silurian 

limestone and underlying graywacke-like beds and slate. A great 

belt of Silurian recrystallized limestone passes northwest through 

Willoughby and Drake Islands and the east side of Kendu Inlet, 

Glacier Bay. Similar limestone is found on the east side of Tenakee 

Inlet,

FRESHWATER BAY SYNCLINE

Knopf 24 reports that chert and banded quartzite resembling graywacke form the north shore of Chichagof Island between Idaho Inlet 

and Flynn Cove and from Port Frederick to Point Augusta. These 

beds are overlain by Silurian limestone and these in turn by Upper 

Devonian melaphyre lava flows and tuff, which form a belt extending 

northwest from the northeast side of Freshwater Bay to Port Frederick. These beds are overlain by 1,000 feet of Mississippian limestone, which forms the lyoukeen Peninsula and is exposed also in 

Port Frederick. It therefore appears that a synclinal trough, here 

called the Freshwater Bay syncline, in which Upper Paleozoic formations are exposed, strikes northwest through Freshwater Bay and 

Port Frederick. The beds on Freshwater Bay have been described 

by Kindle. 25

Upper Paleozoic beds (Permian) are exposed also east of Glacier 

Bay in the Porcupine district,26 and cobbles of upper Paleozoic formations are found in the glacial moraines at the head of Muir Inlet 

and Adams Inlet.

SITKA MESOZOIC BELT

The Sitka Mesozoic belt extends northwestward through Sitka 

along the west coast of Baranof and Chichagof Islands. It has been

2* Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, pp. 

11-12, 1912.

25 Kindle, E. M., Notes on the Paleozoic faunas and stratigraphy of southeastern Alaska: 

Jour. Geology, vol. 15, p. 322, 1907.

20 Bakin, H. M., The Porcupine gold placer district, Alaska : U. S. Geol. Survey Bull. 699, 

p. 11, 1919.
316 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

described by Knopf 27 and Overbeck. 28 Knopf reports that at Silver 

Bay, Sitka, and Klag Bay, on Baranof Island, the strike is northwest and the dip commonly 70° or more southwest. Overbeck describes the beds on the west coast of Chichagof Island as striking, in 

general, between west and N. 45° W., with a few striking N. 30° W., 

and as dipping almost unversally south to southwest at angles of 

40°-70°. Extensive faulting has occurred. Overbeck states that 

with the data available it is impossible to interpret the structure, but 

that there is undoubtedly duplication of beds due to folding and 

faulting, and that these beds may form the limb of an anticline.

MINERAL DEPOSITS

The mineral deposits of southeastern Alaska will be discussed in a 

general way with respect to the types of deposit, their relation to 

formations and to rock structure and character, their tendency to 

localization in belts or areas, and their relation to igneous rocks. 

Detailed descriptions may be found in the publications cited.

TYPES OF DEPOSIT

The types of deposit include contact deposits, fissure veins, stringer 

lodes, stockworks, replacement veins and impregnation zones, shearzone deposits, breccia veins, certain complex lode types, and placer 

deposits.

The most important known contact deposits are the copper and 

iron ores of the Ketchikan district. They usually occur at or near 

the borders between the intrusive masses and the surrounding rocks, 

which are chiefly limestone, graywacke, greenstone tuff, and schist, 

but locally they are found in blocks of country rock included within 

the intrusive masses. Among the best examples are those at the 

Mount Andrew, Mamie, Poorman, and It mines, on the Kasaan 

Peninsula; one of the Rush & Brown mines, on Karta Bay; and the 

Jumbo and Copper Mountain mines, on the west side of Prince of 

Wales Island. The marble deposits at the north end of Prince of 

Wales Island and the garnet deposits at the mouth of Stikine River 

are likewise due to contact metamorphism. Wright 29 summarizes 

the occurrence of the contact deposits as follows :

At the time of their intrusion the igneous rock masses or dikes forced their 

way through the sedimentary and volcanic rocks, to some extent folding and 

fracturing them. While they were cooling both the intruded and intrusive rocks

87 Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, pp. 

ia-14, 1912.

28 Overbeck, R. M., Geology and mineral resources of the west coast of Chichagof Island: 

D. S. Geol. Survey Bull. 692, pp. 95-112, 1919.

28 Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

Alaska: U. S. Geol. Survey Prof. Paper 87, pp. 86-87, 1915.
MINERAL DEPOSITS 317

naturally shrank somewhat, and the shrinkage caused cracks and fissures to 

form near the contacts. These fissures became channels for mineral-bearing 

solutions, derived presumably from great depths, where the temperature was 

high. On ascending along the contacts where the temperature was lower these 

solutions deposited their mineral content and to some extent replaced the rocks 

along their courses. The contact deposits therefore lie within the contact zone, 

between the intrusive and the intruded rocks, and are believed to have been 

derived from the same magma that formed the adjacent igneous rock. * * * 

The contact deposits are generally small irregular masses and are no more 

persistent in depth than they are laterally, but where masses have been found 

in a wide contact zone further exploration will probably reveal similar ore 

masses, both laterally and in depth.

The fissure veins occur along distinct fractures in the rocks and 

may be found at considerable distances from the surface exposures 

of the intrusive rock, or they may occur within the intrusive igneous 

rock itself. Examples of fissure veins are found in the gold quartz 

veins on the west coast of Chichagof Island, such as the Chichagoff, 

Hirst-Chichagof, and Apex-'El Nido; certain of the gold quartz 

veins in the diorite stock at Berners Bay, such as the Comet, Ophir, 

and Jualin; certain of the gold quartz veins in the Juneau district, 

such as the Bald Eagle, at Sumdum, and the veins at Funter Bay; the 

gold-silver-lead veins of the Hyder district, such as the Fish Creek, 

Mountain View, Riverside, Ibex, Homestake, and Comstock; the copper veins at the Cymru property, on the north end of Moira Sound, 

Prince of Wales Island, and at the head of Port Houghton, in the 

Juneau district; the molybdenite vein at Shakan, Kosciusko Island; 

the stibnite (antimony) lode at Point Camaano, Cleveland Peninsula ; and the barite veins at the north end of Kuiu Island.

In the Juneau district gold veins assigned by Lindgren 30 to the 

high-temperature, deep-seated type occur with a similar type of 

mineralization throughout a vertical range of over 4,500 feet. In 

the Hyder district gold-lead-silver veins assigned by Westgate 31 to 

a type representing intermediate temperature and depth occur with 

similar mineralization throughout a vertical range of over 5,000 feet. 

The veins at the highest altitudes, 5,000 feet, must have been formed 

at considerable depth beneath the surface, for erosion has been active 

over the mainland area since the intrusion of the batholith and must 

have removed a cover of very considerable thickness at least severaj thousand feet. It may therefore be reasonably assumed that 

exploration for ore shoots at depth is warranted on fissure veins of 

considerable length that show workable ore shoots at or near the 

surface.

The stringer lodes are narrow belts of schistose or slaty country 

rock ribboned with veinlets and lenses of quartz, mostly parallel to

80 Lindgren, Waldemar, Mineral deposits, McGraw-Hill Co., 1919.

81 Westgate, L. G., Ore deposits of the Salmon River district, Portland Canal region: 

U. S. Geol. Survey Bull. 722, p. 130, 1922.
318 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

the foliation or bedding, but in part reticulating. They are common 

in the slate and graywacke of the Juneau gold belt.

The stockworks are chimneylike or cylindrical masses of broken 

rock with a very large number of irregular small quartz stringers 

that intersect in an intricate manner. They are relatively scarce; 

examples are the gold quartz deposits at the Kensington and Eureka 

lodes, in the Jualin diorite of the Berners Bay district, and one of 

the gold quartz^iodes in the Lisianski* stock of diorite at the Apex-El 

Nido property, on Chichagof Island.

Replacement veins and impregnation zones consist, in part, of more 

or less tabular veins or zones that have resulted either from the partial or complete metasomatic replacement of a bed that is relatively 

more easily replaceable owing to its physical or chemical characters, 

or from impregnation or complete replacement of the rock adjoining a fracture which has permitted the ingress of the solution. 

They consist also in part of replacement and impregnation deposits 

along shear zones. The zinc deposits of the Groundhog Basin, east 

of, Wrangell; the barite deposit on the Castle Islands, in Duncan 

Canal; the silver-lead-zinc deposit of the Daly-Alaska property, in 

the Hyder district; and the Point Astley copper prospect, on Hoikham Bay, belong in this group.

The shear-zone deposits are in zones of rock crushed so that it has 

usually a fine foliation; the crushed rock may be replaced by metalliferous minerals; it contains closely spaced, generally small tabular 

veinings parallel to the foliation, either with or without replacement of the intervening wall rock. Brooks 32 has described the 

cupriferous shear-zone deposits of the Ketchikan district as follows:

The shear-zone deposits follow zones of fracture that are parallel to the 

schistosity of the country rock. They are found in various kinds of country 

rock, but primarily in greenstone schist, graywacke, and sheared diorite. 

There are two phases: of the shear-zone deposits. One consists of lenses or 

tabular deposits, many of which are made up largely of rich massive sulphide 

minerals. These have well-defined walls and are not unlike the cupriferous 

quartz veins described below. The other phase consists of disseminated deposits 

in which the sulphides are distributed through wide zones of sheared country 

rock, generally without well-defined walls. In some of the disseminated deposits 

the sulphide mineralization is rather evenly distributed throughout the entire 

mass, which may thus be a large body of low-grade ore. More commonly, 

however, the mineralization is concentrated along certain zones determined 

by the intensity of the shearing. * * * Examples of the shear-zone deposits, 

including both the concentrated and disseminated phases, are found at the 

Rush & Brown mines, on Karta Bay; at Niblack Anchorage and McLean Arm, 

on the east side of Prince of Wales Island; at the Corwin and Red Wing properties, near Hetta Inlet; and on Big Harbor (Trocadero Inlet), on the west side 

of Prince of Wales Island; and on McLeod Bay, Dall Island.

33 Brooks, A. H., Mineral resources of Alaska: U. S. Geol. Survey Bull. 714, pp. 17-20, 

1921.
MINEEAL DEPOSITS 319

Breccia veins are usually tabular in form and are found along a 

fault or fracture zone. They comprise masses of broken rock or 

breccia cemented and impregnated by quartz, calcite, or metallic 

sulphides. Some of the copper, deposits on Prince of Wales Island 

and the gold lodes near Dolomi are examples of this type. They are 

not common.

Ladder veins are rare in this district. One of this type on the Keku 

Islets consists of a dike of basalt with cross fractures filled with narrow veinlets of sphalerite; it is of no commercial value.

The ore bodies of the Tread well mines on Douglas Island, in the 

Juneau district, are dikes of albite diorite veined with metalliferous 

quartz and calcite and impregnated with auriferous pyrite. They 

constitute one of the complex types.

Deposits which do not fall readily into any of the foregoing types 

are found within the gabbroic and highly ferromagnesian igneous 

rocks. These .include the nickel-copper deposits of Chichagof and 

Baranof Islands; the copper-palladium deposit at the Salt Chuck 

mine, in the Ketchikan district; and the titaniferous magnetites at 

Haines, in the Skagway district, at Snettisham, in the Juneau district, and on Union Bay, Cleveland Peninsula.

The auriferous quartz veins of the Juneau gold belt are usually 

solid masses through which the sulphides are leanly distributed; but 

veins with drusy cavities or interlocking comb structure are also 

found. Banding is rare. In the veins of the Funter Bay-Hawk 

Inlet gold belt the quartz is mostly milky white and massive, but 

locally it is of comb or drusy structure.

The veins of the Apex-El Nido mine, on Chichagof Island, on the 

other hand, show a characteristic sheeted or ribbon structure that 

parallels the walls. The sulphides, on the average, form only a small 

percentage of the vein and are in streaks parallel to the banding. 

Thin shear zones and slickensiding are common within the veins, and 

new sulphides have been introduced along such planes. It is possible 

that such reopened veins will be found to be those that carry the 

richest ore shoots. At the Chichagoff, on Chichagof Island, the lodes 

show a well-marked ribbon structure, which is accentuated by the fact 

that the separate ribbons of quartz alternate with thin slabs of schistose graywacke. From the structural features of this body Knopf 33 

suggests that

From a principal level driven along the general trend of the shear zone 

numerous crosscuts should be made into both the hanging wall and the footwall. 

Not only do the apparent walls prove unreliable guides concerning the ore bodies 

but it is conceivable that where large horses of graywacke occur in the shear

83 Knopf, Adolph, The Sitka mining district, Alaska: U. S. Geol. Survey Bull. 504, pp. 

21-22, 1912.
320 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

zone the ledge may split and curve around the massive rock, and on resuming 

its general trend may follow a parallel course at a distance of some feet in 

either the footwall or the hanging wall of the original course.

In the veins associated with the Texas batholith in the Hyder district there is a very marked banding of the sulphides in the solid 

quartz, giving a ribbon structure parallel to the walls. In some veins, 

as on the Homestake prospect, the veins have been subjected since 

their formation to intense stresses, as indicated by flowage and mashing. The original medium-crystalline galena has been mashed to a 

densely crystalline aggregate, which has flowed and carried out into 

bands or lenses the associated more or less crushed pyrite and chalcopyrite. In the so-called steel galena of the Homestake prospect the 

solid sulphide mass resembles an augen gneiss, with eyes of granulated pyrite in a flow-banded galena. The quartz shows local crushing and strain shadows. At another prospect the galena has been 

recrystallized into long bands parallel to the walls. Faulting has 

also affected some of these veins, to what extent has not yet been 

determined.

METALLIFEROUS DEPOSITS 

ORES AND ASSOCIATED MINERALS

The basis for a considerable part of the discussion of the occurrence 

and economic importance of the metallic and nonmetallic minerals 

has been drawn from the reports of Spencer,84 Wright,35 Knopf,36 and 

Brooks,87 as well as from the more recent work of the present writers. 

To avoid repetition specific citations of these reports are generally 

omitted in the following pages.

GOLD

The gold occurs in quartz veins, in sulphide impregnation zones, 

and in lodes comprising both veins and metallized country rock. The 

impregnation zones are usually of very low grade. Gold in noteworthy amount has not been found in the contact-metamorphic 

copper deposits, though it is recovered as a by-product.

Gold lodes .do not appear to be concentrated in any particular 

formation but rather to be governed in distribution by structural 

conditions and the relations to intrusive bodies.

84 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, pp. 33-38, 

1906.

85 Wright, if. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: U. S. 

Geol. Survey Bull. 347, pp. 77-203, 1906.

89 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, pp. 29-31, 1911.

87 Brooks, A. H., The future of Alaska mining: D. S. Geo?. Survey Bull. 714, pp. 1-57, 

1921.
MINERAL DEPOSITS 321

Gold occurs in the veins and lodes in two ways. In some of the 

veins it is found almost entirely in fine flakes or spangles of native 

metal irregularly distributed in pockets or shoots. In the majority 

of deposits, however, most of the gold is invisible and is supposed 

to be distributed through the sulphides in minute films and particles; 

in this condition a part of the gold may be still free to amalgamate 

with quicksilver, but in many of the deposits the gold is so intimately 

associated with the sulphides that fine milling and amalgamation 

fail to extract it. With the gold some silver is usually present. 

Gold has been found to occur in pyrrhotite, pyrite, chalcopyrite, 

arsenopyrite, sphalerite, and galena. In the upper parts of some 

lodes it appears in bright-yellow particles embedded in iron ocher, 

where it has evidently been derived from the oxidation of a pyritic 

mineral. The gold usually occurs in a quartz gangue but has also 

been found in calcite.

In the Berners Bay region the presence of chalcopyrite in the vein 

is reported to be favorable to good tenor in gold; in the Windham 

Bay region high gold content is commonly associated with the presence of sphalerite and galena; in the region around Klag Bay, on 

Chichagof Island, according to Knopf, the presence of galena with 

pyrite indicates everywhere high gold; at the Londevan prospect, on 

George Inlet, gold is said to increase markedly where galena is 

abundant; and at the Dunton mine, near Hollis, on Prince of Wales 

Island, gold is said to be most plentiful where pyrite is most abundant in the quartz. Spencer reports that as a general rule in the 

Juneau region an increase in the amount of sulphides in a given 

deposit or vein is accompanied by an increase in the value of the ore. 

In the Hyder district gold occurs in quartz veins that carry shoots of 

solid sulphide, predominantly galena and pyrite, or shoots heavily 

metallized with sulphides. High gold tenor here is also shown by 

the tetrahedrite in the quartz fissure veins and locally by sphalerite 

that occurs in replacement and impregnation lodes in greenstone or 

in porphyry dikes.

Brooks wrote in 1919:

Auriferous lodes in Alaska have yielded $92,000,000 worth of gold, of which 

more than 80 per cent has come from the six large low-grade mines of the 

Juueau district. * * * Successful lode mining at Juneau, in complete contrast to m'ost of the placer operations, has been based on the exploitation of 

low-grade deposits on a very large scale. The mines have, indeed, been operated 

at a lower unit cost than any others in the world. The average value per ton 

of the gold and silver recovered from the ore produced in these mines since 

1882 [to 1919] is $1.95. The small margin of profit was offset by the very large 

tonnage handled.

Gold occurs also in placers in southeastern Alaska, A little placer 

gold was taken out in the early days from local deposits throughout 

the Juneau, Ketchikan, and Wrangell districts. Hill and gulch
322 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

placer deposits near Juneau are reported by Spencer to have yielded 

between $600,000 and $800,000 in gold prior to 1890, when they were 

practically exhausted and abandoned. A description of these placers 

is given by Spencer.

Other placer deposits were worked in the creeks tributary to Windham Bay in the early days. The placer deposits on Shuck River are 

being investigated with a view to the installation of a hydraulic 

plant or a dredge. The deposits are described by Wright in the 

report by Spencer.

Valuable placer deposits have been found in the Porcupine district 

on the tributaries of Chilkat River, particularly those of Glacier and 

Porcupine Basins, at the head of Chilkat Inlet, Lynn Canal. It is 

estimated that between 1898 and 1916 about $1,200,000 in gold was 

taken out here. The geology has been described by Wright 38 and 

Eakin.39

Placer gold is also won from the beach placers northwest of the entrance to Lituya Bay.

A little gold has been recovered from residual weathered deposits 

near the outcrop of auriferous veins, as on the west side of Helm 

Bay, in the Ketchikan district.

COPPER

The copper minerals found in southeastern Alaska include the 

primary minerals chalcopyrite, bornite, tetrahedrite, and chalmersite; 

and the secondary minerals metallic copper, malachite, azurite, chrysocolla, chalcocite, and covellite.

Metallic copper has been observed at only a few localities, whereit usually occurs in insignificant amount, as an oxidation product at 

or near the surface outcrop of copper pyrites. In this mode of occurrence the copper is in thin sheets along clay seams or slipping 

planes. At the Salt Chuck mine, at the head of Kasaan Bay, Prince 

of Wales Island, it has been found as low as 200 feet beneath the 

surface but is slight in amount.

Malachite and azurite are often found as alteration products at the 

surface outcrops or along fractures in or adjacent to the ore body, 

but do not anywhere themselves occur in sufficient quantity to constitute ore. Chrysocolla is reported by Wright from the surface 

workings of the Copper Mountain mine, on Prince of Wales Island. 

Chalcocite and covellite are occasionally found as secondary alteration products of chalcopyrite or bornite, but they nowhere occur in

88 Wright, C. W., The Porcupine placer district, Alaska : U. S. Geol. Survey Bull. 236, 

1904.

08 Eakin, H. M., The Porcupine gold placer district, Alaska : U. S. Geol. Survey Bull. 

699, 1919.
MINERAL DEPOSITS 323

sufficient amount to constitute an ore pocket. At the Salt Chuck 

mine chalcocite occurs as low as 200 feet beneath the surface.

Chalcopyrite forms the bulk of the copper ores in the deposits of all 

types. It is also common as an accessory mineral in the gold lodes. 

In the Berners Bay region it is, according to Knopf, next to pyrite, 

the most common metallic sulphide in the gold quartz veins. In the 

gold lodes of the Juneau district, as reported by Spencer, chalcopyrite 

is present in relatively small amounts as compared with the sulphides 

of iron, zinc, and lead. The association of chalcopyrite with pentlandite in pyrrhotite masses occurring in gabbroic or ultrabasic rocks 

has previously been described. It is the most valuable ore mineral 

at the present time in most of the contact deposits and is common i n 

shear zones, in greenstones, and in impregnation lodes.

Bornite is present rarely as an accessory in the mineral deposits 

of southeastern Alaska. Only in a few places does it form the major 

mineral of an ore deposit; one such occurrence is at the Goodro or 

Salt Chuck mine, at the north end of the Kasaan Peninsula, Prince 

of Wales Island, and another is at the copper prospect east of Point 

Astley, on Holkham Bay, in the Juneau district. In the Salt Chuck 

mine the bornite carries palladium and occurs as disseminations and 

veinlets in pyroxenite. At the Point Astley prospect the bornite is 

associated with pyrite, sphalerite, and galena and occurs in metallized 

quartz stringers in greenstone schist and in impregnated schist and 

partly replaced limestone layers. A small pocket of bornite was 

found on Francis Island, in Glacier Bay, at the contact of a diorite 

dike with limestone. In the vicinity of Dall Head, on Graviria 

Island, a little bornite is associated with chalcopyrite and stringers 

of specularite in a quartz gangue. At the Spik claim, 2 miles south of 

the head of McLean Arm, on Prince of Wales Island, bornite, chalcopyrite, and pyrrhotite occur in irregular masses in greenstone. 

Bornite is reported also from prospects on the ridge between Chilkat 

and Chilkoot Valleys, in the Skagway district, about 10 miles northwest of Haines. The quartz veins that carry bornite usually carry 

also hematite.

Tetrahedrite, though a copper ore mineral (often called gray 

copper), has not been observed in the deposits mined largely for their 

copper content. It is common and valuable where it occurs in veins, 

mainly because of the gold and silver which usually accompany it. 

Tetrahedrite may occur in very minor amounts in some of the gold 

quartz veins of the Juneau and Sitka districts, but if so it is very 

rarely reported. It has been found in gold quartz veins near Dolomi, 

on Prince of Wales Island; as narrow stringers in limestone and 

schist west of Crab Bay, on Annette Island; and as seams and veinlets in limestone at Mount Vesta, on Vesta Bay, Dall Island; and it
324 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

is reported to occur in veins in diorite on the west side of Rendu 

Inlet, Glacier Bay. Tetrahedrite is an abundant mineral in certain 

of the gold-lead-silver veins of the Hyder district. It is present 

locally in considerable amounts on the Cantu, Fish Creek, Mountain 

View, and Ibex properties, in the Salmon River district, and has 

been found in the veins on the Riverside property. The silver content usually increases with an increase in the amount of tetrahedrite 

in these veins; the tetrahedrite may carry as much as TOO ounces of 

silver a ton. The veins are fissure veins in quartz diorite or granodiorite and consist of quartz with shoots of galena, pyrite, tetrahedrite, and locally sphalerite, chalcopyrite, or pyrrhotite.

Chalmersite has been identified at only one locality, where it is in 

association with pyrrhotite.

A general discussion of the copper Deposits in southeastern Alaska 

has been given by A. H. Brooks:

All the productive copper mines, as well as the largest developed cupriferous 

ore bodies of southeastern Alaska, are in the Ketchikan district. Copper is 

widely distributed in the Ketchikan district and, as will be shown, occurs in 

deposits of several distinct types. The most important so far as present production and extent of proved ore bodes are concerned are the contact deposits, 

which have yielded more than 98 per cent of the copper produced in the 

Ketchikan district. * * *

It has been shown that the best developed of the Ketchikan copper deposits 

are those composed essentially of chalcopyrite, magnetite, and pyrite. Some 

of these have a considerable percentage of lime. Much of the successful mining of the past has been done because of the smelter demand for base ores 

and the premium paid for a high iron content. The change in metallurgic 

practice has decreased this demand, producing an adverse effect on copper mining in the district. Limestone is abundant in southeastern Alaska.

The Ketchikan copper deposits are not far from tidewater and are on good 

harbors open to navigation throughout the year. They are connected by 

sheltered waterways with the smelters at Anyox, Tyee, and Tacoma. This condition should give cheap freight rates. The strong topographic relief, excellent 

timber, and good water powers of the district all favor low mining costs.

A total of 543,498 tons of copper ore has been produced in the Ketchikan 

district since mining began in 1901. This ore yielded 34,056,376 pounds of 

copper, gold to the value of $545,000, and 255,440 ounces of silver. The average 

copper content of this ore is 62.66 pounds to the ton, equal to 3.13 per cent. 

The average value of the gold and silver content is $1.31 a ton. The average 

value of the total metallic contents of the ore is $12.71 a ton. No attempt has 

been made to concentrate the Ketchikan ore except by hand sorting. The small 

mines have normally maintained their shipping grade of ore at 5 per cent or 

more.

o

The facts above set forth clearly indicate that the Ketchikan district contains copper deposits which are well worth investigating by those who have the 

capital to develop and reduce ores on a large scale. The physical conditions 

seem almost ideal for cheap operations. Special attention should be directed to 

devising methods by which the iron content of the chalcopyrite-magnetite ores, 

as well as the copper, can be utilized.
MINERAL DEPOSITS 325 

IRON

The iron minerals include pyrrhotite, pyrite, magnetite, hematite, 

limonite, and marcasite.

Pyrite is the commonest metallic sulphide. It is present in the 

form of small but perfect cubes or irregular grains throughout most 

of the metamorphic schists, slates, and greenstones. In the intrusive 

masses it is usually present near contacts. It is the most common 

sulphide in the gold quartz veins and is the next most abundant 

mineral to galena in the fissure veins of the Hyder district. It is 

practically always associated with sulphide masses to a greater or less 

extent. Alone it is of little commercial value, except as a raw material 

for the manufacture of sulphuric acid, but where associated with gold 

it may form a valuable ore. Where it occurs as disseminated or 

replacement deposits it rarely carries more than very little gold. It 

gives rise on weathering to limonite and the characteristic brown, 

yellow, or reddish stains. Very large masses of pyrite occur at the 

Khayyam mine, on the summit of a mountain 2.8 miles southwest of 

Kiam, on McKenzie Inlet, Skowl Arm, Prince of Wales Island, as 

described by the Wrights.

Pyrrhotite is similar in mode of occurrence to pyrite, but it is not 

quite so widely distributed. It is abundant in all the copper contactmetamorphic deposits, in high-temperature fissure veins, and as disseminations and lenses in the gabbroic and ultrabasic group of rocks. 

Wherever pyrrhotite occurs either in or associated with the basic 

igneous intrusive rocks it should be tested for nickel, for at many 

places pyrrhotite in such association is known to carry noteworthy 

percentages of nickel. (See pp. 348-351.) Pyrrhotite in association 

with diorite or more granitic rocks, on the other hand, is not known 

to carry nickel, and the pyrrhotite of the contact and vein deposits 

genetically connected with this group of intrusive rocks carries only 

0.1 to 0.2 per cent of nickel. Chalcopyritef is commonly associated 

with pyrrhotite in small amounts and at certain places in sufficient 

quantity to constitute an ore. Pyrrhotite is the predominant metallic 

mineral in the zinc deposits and most of the sulphide lodes in the 

Wrangell-Revillagigedo belt of metamorphic rocks. It occurs in 

small amounts in many of the gold quartz veins and may be gold 

bearing but is by no means as common in such veins as pyrite.

Magnetite occurs in sufficient quantity to constitute ore bodies. It 

is rarely found in the gold quartz veins. Its principal mode of occurrence is in association with contact-metamorphic copper deposits and 

as disseminations or vein dikes in the pyroxenite and hornblendite. 

It is almost universally present as an accessory constituent in the 

igneous rocks. In the quartz diorite, granodiorite, quartz monzonite, 

and granite magnetite is rarely present in amounts greater than 2
326 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

per cent and normally is less than 1 per cent; in the diorite and monzodiorite it averages between 1 and 2 per cent and may be as high as 

5 per cent; in the gabbro it ranges from a trace to 12 per cent and 

averages about 5 per cent; and in the pyroxenite and hornblendite 

it reaches 30 per cent and may occur as vein dikes of almost solid 

magnetite. There is thus, in general, a very marked increase in the 

percentage of magnetite in the less siliceous and more basic rocks. 

In the diorite, however, magnetite appears normally to form only a 

small percentage. In the ultrabasic group of rocks a little ilmenite 

is associated with the magnetite as grains and in small amount is 

intergrown with it on a microscopic scale. The ilmenitic magnetite 

deposits are of future potential value and are described in connection 

with the Upper Jurassic or Lower Cretaceous intrusive rocks. (See 

pp. 193-198, 351-353.)

Brooks has discussed the magnetite ores of southeastern Alaska as 

follows:

In the absence of any considerable iron industry on the Pacific coast there 

has been no incentive to search for iron ores in Alaska. The largest deposits 

known consist of magnetite associated with copper ores the contact-inetamorphic deposits of the Ketchikan district. J. B. Mertie, jr., who has made a 

rough estimate of the quantity available from these deposits, places the minimum reserve at 10,000,000 tons, with possibly an average copper content of 0.5 

per cent. This estimate is based on an appraisal of the probable depth of the 

known deposits and on the assumption that all the ore would be available for 

mining. There are no accurate data at hand on the mean iron content of these 

ores, nor is it known whether the phosphorus contents are everywhere below 

the Bessemer limit. Some analyses of the Mount Andrew magnetite ore made 

many years ago gave a phosphorus content of 0.02 per cent. The possibility 

that these ores contain titanium should also be considered. On account of the 

presence of sulphides the sulphur content of the ores will be high. Similar 

deposits have been mined on Texada Island, in British Columbia, and these 

contain an average of 55 to 60 per cent of metallic iron,40 and the phosphorus 

content of most of them is low enough to make them fall within the Bessemer 

limit, but the sulphur content is high. * * *

The above brief review indicates that Alaska contains a number of iron-ore 

deposits, of which the most promising are those of the Ketchikan district. It 

would appear that the value of the Ketchikan deposits will depend on finding 

a commercial method of recovering the low copper contents as well as utilizing 

the iron.

Hematite occurs as disseminated grains or rosettes of specularite in 

the contact-metamorphic deposits and in a few quartz veins, in part 

associated with bornite and in part with pyrite. It has not been 

observed in the gold quartz veins. 0 ^

Limonite is nowhere found in quantity, although it occurs wherever iron minerals are altered under surface conditions. It forms 

a noteworthy capping on many of the pyritic or pyrrhotitic

40 Lindeman, Einar, Iron-ore deposits of Vancouver and Texada Islands, British Columbia : Canada Dept. Mines, Mines Branch, No. 47, 1910.
MINERAL DEPOSITS 327

sulphide bodies and is present in many rusty belts within the slates, 

phyllites, schists, and gneisses.

Marcasite is common in small amounts in the sulphide bodies as an 

alteration product along fractures or locally replacing the sulphides, 

especially pyrrhotite, in the upper portions of the deposits. The 

nickeliferous pyrrhotite bodies in particular are partly replaced by 

marcasite in the outcrop. Marcasite of this mode of occurrence is of 

secondary origin under surface conditions. Marcasite occurs also as a 

primary mineral associated with sphalerite in and near a basalt dike 

on one of the Keku Islets.41

SILVER AND LEAD

Native silver occurs in small amount at the Point Astley copper 

prospect, on Holkham Bay, and at the Daly-Alaska and Mountain 

View properties in the Salmon Eiver district, but most of the silver 

occurs in association with gold and with silver-bearing galena and 

tetrahedrite. Electrum, r, pale alloy of gold and silver, with silver 

in excess, is reported by Spencer to occur in ore from the Reagan 

shaft, and pyrargyrite is reported as a secondary mineral in the 

Silver Queen and Glacier mines, on Sheep Creek, in the Juneau district. Proustite has been identified as a rare secondary mineral in a 

vein on the Mountain View property, in the Salmon River district.

Galena occurs in extremely variable amounts in the gold quartz 

veins. Where it is present in considerable quantity the proportion of 

silver is likely to be higher, and it is in many places associated with 

sphalerite and a little chalcopyrite. Galena occurs also associated 

with sphalerite, pyrite, and tetrahedrite in complex sulphide deposits. It is the principal ore in the fissure veins at the Lake and 

Glacier Basin claims, east of Wrangell; in the replacement deposits 

at the Moonshine prospect,, on Cholmondeley Sound, Prince of Wales 

Island; in the fissure veins in the quartz xiiorite and granodiorite of 

the Salmon River district, where pyrite is associated with it as the 

next most abundant mineral; and in a fissure vein in dolomite at a 

prospect on Whiting River. In all these localities it carries moderate 

to low percentages of silver. Ore rich in tetrahedrite from the Fish 

Creek veins, in the Salmon River district, is reported to carry as 

much as 700 ounces of silver to the ton, and at some of the properties 

in this district f reibergite is present.

Most of the lead produced in southeastern Alaska up to the present 

time has come from the gold mines of the Juneau district, but it 

seems highly probable that a considerable amount will in the future

41 Buddington, A. P., Mineral investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, pp. 138-139, 1925.

6137 29 22
328 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

come from the veins of the Salmon River district, and that properties 

in other districts will be developed.

Cerusite commonly occurs as a white coating on the weathered 

surface of galena masses and particles, and anglesite occurs locally 

as a surface alteration product.

Galena, argentiferous galena, and argentiferous tetrahedrite are 

far more abundant in the mineral deposits along the east side of the 

Coast Eange batholith than they are within or west of the batholith. 

Native silver, pyrargyrite, proustite, and argentite are common ore 

minerals in the deposits on the east side of the batholith in British 

Columbia. These are thought to have been formed mainly as a result 

of enrichment but may in small part be primary.

ZINC

Practically the only zinc mineral in southeastern Alaska is sphalerite, commonly known as zinc blende. It is usually dark brown, red, 

or nearly black. When examined with the microscope much of it is 

found to contain abundant dots or rods of chalcopyrite oriented along 

its cleavage planes. The sphalerite from the zinc deposits of the 

Groundhog Basin is reported to be the variety martite with considerable iron.

Sphalerite is a common accessory mineral in the gold quartz 

veins of southeastern Alaska and is usually associated with sulphide 

bodies, including galena or chalcopyrite, where they occur in fissure 

veins and shear and impregnation zones. It is not an abundant constituent of the contact copper deposits and is usually present there 

only as an accessory mineral. At the Complex mine, between Mineral and Dora Lakes, on Kitkun Bay, Prince of Wales Island, some 

of the ore is essentially sphalerite, with a little chalcopyrite and 

galena, in a banded quartz fissure vein carrying gold and silver. 

Sphalerite has been found in considerable amounts at some prospects 

on Beaver Mountain, Prince of Wales Island. At no place in the 

Alexander Archipelago has sphalerite yet been mined by itself as 

an ore.

At the Groundhog Basin,42 east of Wrangell, on the mainland, extensive low-grade deposits of sphalerite with pyrrhotite and a little 

galena have been found as tabular replacement veins in a band of the 

metamorphic complex; they are discussed on page 361. Sphalerite is 

abundant in other metalliferous zones in this formation, and it seems 

highly probable that zinc will eventually be produced from bodies 

occurring in the Wrangell-Revillagigedo belt of metamorphic rocks.

43 Buddington, A. F., Mineral deposits of the Wrangell district, southeastern Alaksa: 

U. S. Geol. Survey Bull. 739, pp. 57-63, 1923.
MINERAL DEPOSITS 329 

NICKEL

There is only one known nickel mineral, pentlandite, that is of 

economic value in southeastern Alaska. It occurs usually in small 

amount within certain pyrrhotites and can not normally be seen in 

the ore, but on polished surfaces and under the microscope it is plainly 

visible. At the surface outcrops the pentlandite is altered to a secondary nickel mineral which may be bravoite,48 but this is only a 

local modification. Gray efflorescent salts are characteristic of the 

weathered outcrops. The nickel ores are described in connection with 

the Upper Jurassic or Lower Cretaceous intrusive rocks. (See pp. 

348-351.) The pentlandite is always associated with pyrrhotite and 

generally with chalcopyrite in genetic connection with .gabbroic or 

ultrabasic intrusive masses or dikes. Only one prospect has been 

developed to any extent. It is highly probable that other nickel 

deposits of similar type will be found in southeastern Alaska.

The ore reserves in the Sudbury mines are stated to be 150,000,000 

tons, and the New Caledonia deposits are estimated to contain 

160,000 tons of nickel. In view of these large reserves in the present 

major producing regions, it would be exceedingly difficult for a large 

new concern entering the field to dispose of its nickel, but a small 

producer would not have the same difficulty. The Alaskan deposits 

show a grade of ore and geologic associations which warrant their 

further investigation and prospecting when economic conditions 

justify an intensive search for new sources of nickel ore.

MOLYBDENUM

Molybdenum in the form of molybdenite is widely distributed in 

small amounts, but it is known in noteworthy concentrations at only 

a few localities. It occurs disseminated in contact-metamorphic deposits, as on Lemesurier Island, in Icy Strait; in pegmatitic quartz 

veins, as at Shakan; in quartz fissure veins in the dioritic and more 

gran,itic intrusive rocks; as facings of fractures in local areas; and 

disseminated in aplite and pegmatite veins. There is no record that 

any molybdenite has been produced in Alaska for sale.

Molybdenite has not been observed in general in the gold quartz 

veins of the Juneau district, according to Spencer, but occurs in 

certain zones of sheeting in the diorite of that district and was found 

in all parts of the Treadwell ore bodies. It also occurs here and 

there in small quartz fissure veinlets and as fracture facings in the 

granodiorite stock of the Salmon Eiver district and in schist at the 

north end of Noyes Island. On Prince of Wales Island it occurs 

both in the contact copper deposits and in the altered dioritic rock 

near these deposits. Very fine specimens of molybdenite quartz

48 Buddington, A. F., Alaskan nickel minerals: Econ. Geology, vol. 19, pp. 521-541, 1924.
330 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

veins have been brought from float on Brady Glacier and from Geikie 

Inlet, Glacier Bay. Molybdenite also occurs facing fractures in 

metamorphic rock at the entrance to Adams Inlet on the north side, 

and it is reported from the region north of the east fork of Skagway 

River extending from mile 6 eastward for 8 miles.

Development work has been carried on at only three molybdenite 

prospects a contact deposit in limestone on Lemesurier Island, in 

Icy Strait; 44 a deposit in the granitic rock of the Coast Range batholith on the White Pass & Yukon Route about 25 miles from Skagway,45 and a fissure vein in diorite near Shakan.46 Hess 47 says 

that near Shakan the mineralized zone crops out for 500 feet and 

quotes F. W. Bradley as authority for the statement that the ore 

averages from 1 to 2.28 per cent of MoS2 in large lots, that 100,000 

tons of ore assaying 1.58 per cent of MoS2 was indicated, and that 

6,270 tons of high-grade ore was blocked out. Hess writes further :47a

The world contains innumerable molybdenum deposits, mostly small, all of 

which, except in the oxidized parts, carry the metal, so far as is now known, 

in the form of molybdenite. Some of the molybdenite deposits, however, are 

extensive and contain large quantities of the metal. * * * A few, like those 

at Climax, Colo., and Yetholme, New South Wales, are very large, though of 

comparatively low grade, carrying only about 1 per cent or less of MoS2, and it 

is likely that under the stimulus of a continuous demand a larger number of 

such deposits might be found. There are numerous areas where such developments would not be surprising, such as the mountain region extending from 

Mexico to-Alaska.

TUNGSTEN

Tungsten in the mineral scheelite has been found at the Apex-El 

Nido property, on Lisianski Strait, Chichagof Island, and is reported 

by Brooks to have been found in a vein on .Baranof Island near Sitka. 

At the Apex-El Nido property the scheelite occurs in disseminated 

form in high-grade gold quartz veins associated with arsenopyrite 

and also in a shoot of solid scheelite 5 inches wide in a quartz 

stringer. The veins are in aplite dikes in diorite. In the Hyder district scheelite occurs also as abundant disseminated crystals associated 

with pyrite, barite, and tetrahedrite in a vein on the Mountain View 

property and less abundantly in other veins. A shoot of scheelite 

has also been found in a vein on the Riverside property.

** Buddington, A. F., Mineral Investigations In southeastern Alaska: U. S. Geol. Survey 

Bull. 783, pp. 55-56, 1926.

45 Brooks, A. H., The Alaska mining industry in 1916 : U. S. Geol. Survey Bull. 662, 

p. 25, 1918.

48 Chapin, Theodore, Mining developments in the Ketchikan district: U. S. Geol. Survey 

Bull. 692, p. 89, 1919. Mertie, J. B., Mining developments in southeastern Alaska: TJ. S. 

Geol. Survey Bull. 714, pp. 118-119, 1921.

*7 Hess, F. L., Molybdenum deposits: U. S. Geol. Survey Bull. 761, pp. 14-15, 1924.

*7a Idem, p. 33.
MINERAL DEPOSITS 331 

ANTIMONY

Antimony is found in the minerals stibnite, tetrahedrite, and bindheimite. Bindheimite (?) is a local yellowish alteration product of 

tetrahedrite in the surface outcrops of some veins in the Hyder district and has no commercial value. The occurrence of tetrahedrite 

has been discussed in connection with the copper ores. (See pp. 

323-324.) Stibnite is the only commercially valuable antimony ore. 

It has been found in quantity at only one locality, as a fissure vein 

of solid stibnite 3^ feet Avide where exposed in limestone at Camaano Point, at the south end of Cleveland Peninsula. A small test 

shipment of ore has been made from this locality. Stibnite occurs as 

abundant radiating clusters of needles or blades in certain low-grade 

gold quartz fissure veins in schist on the Clark prospect, 6^/2 miles 

east of Juneau, and is reported by Spencer to occur in minute 

radiating crystals in calcite at the Queen mine, in the Juneau district.

TITANIUM

The titanium minerals include ilmenite and rutile.

Kutile is reported by Spencer to be present in gold quartz veins 

which contain albite in the Juneau district and to have been characteristic of the Treadwell ores. In the veins that have been opened at 

several points along Gastineau Channel it occurs in drusy cavities in 

the veins or penetrating the albite, quartz, or calcite. A quartz vein 

near the head of Farragut Bay carries disseminated perfect crystals 

of rutile as much as half an inch in diameter. It has not been found 

in commercial, amount.

Ilmenite occurs for the most part associated with magnetite in the 

gabbroic and ultrabasic group of igneous intrusive rocks and in the 

andesitic and basaltic lavas. In a vein dike of magnetite at Snettisham it forms 8 per cent of the vein matter. It has also been noted 

in large plates associated with albite and calcite in gash veinlets in 

a basalt dike east of Point Coke, on Holkham Bay.

ARSENIC

The arsenic minerals include arsenopyrite. native arsenic, realgar, 

and orpiment. Spencer reports that in the Alaska-Treadwell mine 

a single specimen of native arsenic weighing several ounces was 

found with a coating of the secondary minerals realgar and orpiment. 

This is the only reported occurrences of these three minerals.

Arsenopyrite occurs in many places in sparse amounts in the gold 

quartz veins of the Juneau district and in some places is reported to 

carry much gold. It is the major sulphide in the high-grade gold 

quartz veins at the Apex-El Nido mine, on Chichagof Island. It 

also occurs as one of the major sulphides in a low-grade gold quartz
332 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

fissure vein on Thomas Bay and in a silver-lead fissure vein on Whiting River. In the Silver Bay area, Sitka district, according to 

Knopf, arsenopyrite occurs in sparse amount in the low-grade gold 

quartz veins, associated with insignificant amounts of pyrite and 

pyrrhotite. Arsenopyrite is not reported by Wright from the contact copper deposits on the Kasaan Peninsula or the Copper Mountain area, on Prince of Wales Island. Arsenopyrite is associated 

with sphalerite and pyrrhotite in certain veins in the sedimentary and 

volcanic rocks that form the roof and borders of the Texas batholith, 

in the Hyder district.

BISMUTH

The only bismuth minerajl so far reported in southeastern Alaska 

is tetradymite, a telluride of bismuth. This is said by F. E. and 

C. W. Wright to occur with the gold ores at the Hoadley claims, 

north of Ketchikan, and at the mines on Cleveland Peninsula. It 

is in insufficient quantity to have commercial value.

OTPSTJM

The only deposit of gypsum known in southeastern Alaska is the 

bed at lyoukeen Cove, on the east side of Chichagof Island,48 which 

has been worked since 1906. Neither the hanging wall nor the footwall is exposed. The bed overlies Carboniferous beds and is regarded 

as of Permian or possible Triassic age. The gypsum, because of its 

relatively great solubility, occurs in a valley, and prospecting is 

therefore difficult. It is possible that there are other similar occurrences of gypsum. If the stratigraphic succession of the beds at 

lyoukeen Cove could be worked out in detail, it might be possible 

to indicate favorable areas for prospecting elsewhere in southeastern 

Alaska.

GARNET

Garnet occurs almost exclusively in two associations as massive 

aggregates in the contact-metamorphic deposits and as disseminated 

crystals in the rocks of the Wrangell-Reviilagigedo belt. It is 

locally present in sparse amounts in the intrusive bodies near tiheir 

contacts. Rarely it is a prominent mineral in high-temperature 

quartz fissure veins, as in a copper vein on Port Houghton. The 

garnet in the crystalline schist at the garnet mine north of Wrangell 

is the iron-aluminum variety, almandite. (See also p. 363.) It is 

probable that most of the garnet in the crystalline schist is this 

variety. The occurrence of a widespread belt of garnetiferous schist 

in Port Houghton is described on page 67.

48 Wright, C. W., The building stones and materials of southeastern Alaska : U. S. Qeol. 

Survey Bull. 345, pp. 124-125, 1908.
MINERAL DEPOSITS 333

Garnet is one of the predominant gangue minerals in the contactmetamorphic copper and magnetite deposits. In the Copper Mountain region it is the calcium-iron variety, andradite. Though it commonly occurs in massive form, it appears also in crystal aggregates 

embedded in the altered limestone and in veins crosscutting the limestone beds and penetrating the intrusive rock. Garnet for use as an 

abrasive has been produced intermittently at the mine north of 

Wrangell. Production of garnet in southeastern Alaska could be 

markedly increased if demand should arise. Information concerning 

garnet in general is given by Myers and Anderson.49

BARITE

Barite occurs locally in fissure veins, where it forms practically 

the whole vein; as replacement deposits in limestone beds; and locally 

as a common gangue mineral in the gold-silver-lead veins of the 

Hyder district.

Barite 60 in fissure veins in limestone, conglomerate, and volcanic 

rocks occurs on Kuiu Island along the north side of the Cornwallis 

Peninsula and the south side of Saginaw Bay and in the Ketchikan 

district at the northeast end of St. Ignace Island. These veins may 

be 200 feet in length and as much as 2 feet wide, but they have not 

been prospected because of their small size.

Barite 51 as a replacement deposit in limestone beds occurs on the 

Castle Islands on Duncan Canal, Kupreanof Island, and at Lime 

Point, the south end of the peninsula between Hetta and Nutkwa 

Inlets, Prince of Wales Island. The Castle Island prospect is 

reported to have about 60,000 tons exposed above tide level, averaging about 93 per cent of barium sulphate. At the Lime Point locality, 

according to Chapin, the country rock is semicrystalline blue-weathering white limestone interbedded with schist. An opening has been 

made along the deposit for 100 feet, exposing a roughly tabular, 

nearly vertical body of barite about 30 feet wide. It is a finely 

crystalline white rock containing practically no visible impurities. 

Some of the barite was shipped to San Francisco and tested with 

satisfactory results.

GRAPHITE

The slate of the sedimentary formations and the phyllite are prevalently black from their carbonaceous content. With increasing intensity of metamorphism and recrystallization toward the northeast

*» Myers, W. M., and Anderson, C. 0., Garnet its mining, milling, and utilization: U. S. 

Bur. Mines Bull. 266, 1925.

M Buddington, A. F., Mineral investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, pp. 136-138, 1925.

«Buddington, A. F., Mineral deposits of the Wrangell district, southeastern Alaska: 

U. S. Geol. Survey Bull. 739, pp. 72-73, 1922. Burchard, E. F., A barite deposit near 

Wrangell: U. S. Geol. Survey Bull. 592, pp. 109-117, 1914.
334 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

as the border of the Coast Eange batholith is approached the carbonaceous material is increasingly segregated and recrystallized. In 

the incipient stages of this process, in the phyllite, the carbonaceous 

material first appears as disseminated dust; at a more advanced stage, 

in the phyllite and crystalline schist, this dust has collected into 

microscopic spherules or into clotlike aggregates of spherules; and 

finally in the injection gneiss it is found as individualized crystalline 

flakes of graphite. The graphitic schist and gneiss containing crystalline flakes of graphite occur only in the belts of thoroughly recrystallized schist and injection gneiss such as occur within or adjacent 

to the mainland batholith. (See p. 363.)

Carbonaceous material is occasionally found in sparse amount in 

gold quartz veins, and as it occurs also in the black slate that forms 

the wall rock for many of the veins it finds its way in considerable 

amount into the ore, where it interferes both with amalgamation and 

with the separation of finely divided sulphides.

Graphite is disseminated in certain beds of the crystalline limestone. No prospecting for this mineral has been carried on in southeastern Alaska. There is, however, a very large potential source of 

supply if demand for it arises in the future.

MICA

The micas include the varieties sericite, biotite, muscovite, and 

phlogopite.

Sericite is one of the most common minerals resulting from the 

alteration of the wall rock by vein-forming solutions. It also occurs 

sparsely disseminated through the gold quartz veins. A pale-green 

variety called mariposite occurs in small amounts in some of the 

veins.

Biotite (black mica) is a constituent of almost all the igneous rocks, 

but muscovite (light-colored mica) is found only in the granite, and 

there only rarely. Biotite and muscovite were noted in pegmatite 

veins as crystals 2 inches or more in diameter. Biotite occurs in 

larger crystals in some pegmatite veins associated with hornblendite 

masses but has no commercial value at the present time. Muscovite, 

to be of commercial value under present conditions, should be in 

crystals of such size that it can be punched to yield disks at least V/2 

inches in diameter.52 A yield of 5 to 10 per cent of sheet mica from 

all the pegmatite mined is considered very good if the sheets average 

at least 3 inches square.

Phlogopite (brown mica) occurs as disseminated flakes and nests in 

certain beds of the crystalline limestones of the Wrangell-Kevilla-

^Sterrett, D. B., Mica deposits of the United States: U. S. Geol. Survey Bull. 740, 

p. 26, 1923.
MINEBAL DEPOSITS 335

gigedo belt of metamorphic rocks. It is possible that pockets of 

phlogopite of commercial value occur near the contacts of the intrusive rocks with the crystalline limestones within the Coast Range 

batholith, though none have yet been found.

SILLIMANITE, CYANITE, AND ANDALUSITE

Sillimanite, cyanite, and andalusite are used as raw materials in 

the manufacture of certain refractory products. At the present time 

deposits of these minerals must be of high grade to warrant working. 

In southeastern Alaska sillimanite and cyanite have been found only 

in certain schists in the metamorphic complex, where they are common 

to abundant constituents. Andalusite is found only as disseminated 

crystals in slate at or near the contact with intrusive stocks. The 

largest sillimanite crystals seen by the writer are in crystalline schist 

at the south end of Deer Island.

QUARTZ

The principal nonmetalliferous mineral in the metalliferous veins 

is a white quartz of fairly coarse texture. Some of the veins exhibit 

a drusy structure; in these the quartz is partly bounded by crystal 

faces, and terminated crystals project into the vugs. In the veins of 

the Hyder district and the Apex-El Nido property, on Chichagof 

Island, the sulphides show a tendency toward banding in the quartz 

parallel to the walls.

In the crystalline schist adjacent to the injection gneiss of the 

Coast Kange batholith seams of thin glassy quartz occur parallel to 

the foliation of the schist in such a way as to form a quartz injection 

gneiss analogous to an aplite injection gneiss. Farther away from 

the batholith the veins are, in general, local and larger and the quartz 

is more milky and white and may carry sulphides and be otherwise 

metallized.

Quartz in the form of chalcedony and agate is found mainly in the 

Tertiary lavas as amygdules or small gash veins.

CARBONATES

The carbonates include calcite, ferriferous calcite, ankerite, and 

dolomite. Calcite is the major mineral in all the limestones and 

forms 95 to 99 per cent of the thick massive Silurian limestone. It 

occurs in subordinate amounts in the metalliferous quartz veins and 

as an alteration product in the wall rocks of the contact-metamorphic 

deposits. It usually does not form the predominant gangue mineral 

in veins except where it occurs in small stringers. Knopf reports 

that the altered diorite wall rock in the Bemers Bay region contains
336 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTEBN" ALASKA

sparry masses of reddish-brown carbonate which is easily soluble 

in cold hydrochloric acid and is probably a ferriferous calcite. In 

the Heckla Blanket gold quartz vein, on the Admiralty-Alaska property, Admiralty Island, there are sparry masses of brown-weathering 

carbonate which are difficultly soluble in cold hydrochloric acid. 

The indices of refraction are those of ankerite, a ferriferous dolomite. Dolomite is reported by Knopf as an alteration product of 

the diorite adjoining quartz veins in the Berners Bay region. In 

the absence of chemical tests it is readily confused with calcite. 

Dolomite also forms the major constituent of certain beds of marble 

in the Wrangell-Kevillagigedo belt of metamorphic rocks.

EPIDOTE

Epidote, a hydrous aluminum silicate of calcium and iron, is a 

mineral of bright yellowish-green color. It occurs largely as an 

alteration product of the igneous rocks and as a gangue mineral in 

the contact-metamorphic deposits. In the hydrothermally altered 

diorite and quartz diorite in the belts containing metalliferous veins 

it is present in a finely disseminated condition and in considerable 

measure causes the greenish hue that the dioritic rocks assume in 

the vicinity of ore bodies. It does not normally occur in the gold 

quartz veins. It forms under a wide range of conditions, for it has 

been found as a primary mineral of magmatic origin in a monzodiorite on the east side of Portage Bay, Kupreanof Island, and it is 

abundant as an alteration product and as deposits in amygdules 

by solutions and vapors of volcanic origin in the basic Tertiary 

lavas.

PYROXENE

Pyroxene is the predominant gangue mineral in some of the contact-metamorphic deposits and is common in all. It occurs also as 

local disseminated deposits, nests, and bands in the crystalline limestone of the Wrangell-Revillagigedo metamorphic belt. Diopside 

is reported to be the variety on Prince of Wales Island, and the ironrich variety hedenbergite is the gangue of a copper contact deposit 

on Kupreanof Island.

Pyroxene also forms large masses of the intrusive rock pyroxenite. 

The pyroxene of the pyroxenite is in part almost pure diopside, 

usually where associated with dunite; in part diopside with a percentage of an aluminous molecule (diallage) or a hedenbergite molecule, usually where associated with hornblendite or gabbro; and in 

part bronzite, where associated with norite. The pyroxenite is noteworthy because of the local association of magnetite with the diallage varieties and of nickeliferous pyrrhotite with the bronzite 

varieties.
MINERAL DEPOSITS 337 

AMPHIBOLE

The hornblende variety of amphibole, a calcium-magnesium-iron 

silicate, is a prominent gangue mineral in some of the contactmetamorphicj deposits. Hornblende occurs also as a prominent 

gangue mineral in a high-temperature copper quartz vein on Port 

Houghton. Hornblende forms large masses of the intrusive rock 

hornblendite, which locally carries magnetite deposits, as at Snettishairi, or nickeliferous pyrrho'tite deposits, as at Snipe Bay, Baranof 

Island.

The tremolite variety of amphibole, a calcium-magnesium silicate, 

occurs as a metamorphic mineral in some of the crystalline limestone 

of the Wrangell-Kevillagigedo belt of metamorphic rocks. Veinlets 

of fibrous tremolite with fibers as much as 18 inches in length are 

found in soapstone about 2% miles southwest of the head of Hobart 

Bay.

ALBITE

Albite occurs in small amounts in some of the gold quartz veins of 

the Juneau belt; at the Lon de Van claims, at the head of George 

Inlet, Revillagigedo Island; at the Birdseye claim, south of Ketchikan; and at other localities. At Glacier Basin, east of Wrangell, it 

forms veinlets cutting veins of sphalerite and galena. In the quartz 

veins mentioned it is associated with the carbonates calcite and 

dolomite, several metallic sulphides, and rutile. Albite forms veinlets in the dunite and hornblendite, where it may be associated with 

contemporaneous calcite. Albite occurs also as the result of alteration 

of the plagioclase in the diorite wall rock of veins in the Berners 

Bay region and as veinlets with quartz and calcite or dolomite in the 

altered diorite.

CHLOKITE

Deep-green chlorite occurs in the wall rocks of the metalliferous 

veins as an alteration product of hornblende, biotite, or pyroxene and 

in part replacing the feldspars; in some of the copper-bearing magnetite deposits on Kasaan Peninsula, where it occupies small druses 

and occurs in finely disseminated form; as crystals in the magnetite 

deposits occurring in the pyroxenite and hornblendite; in the greenstones and altered basic lavas; and as amygdules of the Tertiary 

andesite and basalt.

APATITE

Apatite occurs as a minor accessory mineral in practically all the 

igneous rocks. It may form as much as 1 per cent in the dioritic and 

more alkalic or siliceous rocks, but it is locally concentrated to form 

several per cent in the hornblendite and hornblende-rich gabbro. 

It occurs as an accessory gangue mineral in the disseminated magnet-
338 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

ite deposits at Haines. It is abundant in the wall rocks of the magnetite vein at Snettisham and may occur in the vein itself in minor 

amount.

TOURMALINE

Spencer reports the presence of tourmaline in some of the quartz 

veins of Gold Creek, in the Juneau district, where it occurs in minute 

needles. He suggests that its presence may indicate the possibility 

that the mineralization of the region was one of the effects of the 

great dioritic intrusions. Tourmaline and apatite occur also as minor 

accessory minerals in the crystalline schists, where they are thought 

to have been introduced by vapors and solutions given off by the 

Upper Jurassic or Lower Cretaceous intrusive magma. Very rarely 

tourmaline is found in the pegmatite veins.

LITHOLOGIC AND STRATIGRAPHIC ASSOCIATION OF ORE DEPOSITS

Mineral deposits are shown on Plate 1 by appropriate symbols. 

From this map it may be seen that metallization is very widespread 

and is not confined to certain rock formations or to any group of 

formations. Mineral deposits of value occur in schist, limestone, 

greenstone, tuff, quartzite, black slate, granodiorite, quartz diorite, 

diorite, hornblendite, pyroxenite, norite, peridotifce, conglomerate, 

graywacke, and quartz porphyry. The general distribution of these 

deposits, however, bears a definite relation to the rock structure and 

to the igneous masses, and certain formations appear to be favorable 

to certain types of mineralization. The following descriptions are 

intended to show this relation as well as the stratigraphic distribution 

of the mineral deposits.

WALES GROUP

By THEODORE CIIAPIN

The oldest rocks of the region are the schist, limestone, and greenstone of Prince of Wales, Dall, and Long Islands. The schist is 

composed of highly altered sediments with possibly some igneous 

rocks, all more or less recrystallized into mica and quartz schists. 

The schist is seamed with many quartz veins which in places are 

gold bearing and some of which have produced. The schist appears 

to be a promising formation for future prospecting for gold lodes.

The limestone beds are largely recrystallized into white marble and 

in the vicinity of the intrusive bodies into metamorphic contact rock 

consisting principally of garnet, epidote, and calcite. It is in the 

metamorphic bodies that the contact ore bodies of copper occur. In 

the search for these deposits the prospector should be guided first by 

the bodies of intrusive granitic rock and more specifically by the
MINERAL DEPOSITS 339

presence of the contact-metamorphic minerals which are indicative of 

metallization. The limestone also incloses some of the best bodies of 

commercial marble of both white and ornamental varieties. The 

overlying greenstone schist contains both gold-bearing fissure veins 

and shear-zone deposits of copper.

WKANGELL-B.EVILLAGIGEDO BELT OF METAMORPHIC BOCKS

The Wrangell-Revillagigedo belt of metamorphic rocks includes 

phyllite, various types of crystalline schist, schistose greenstone, limestone, marble, and injection gneiss. These rocks border the Coast 

Range batholith or are included as bands within the batholith. 

Within this group metallization is scattered and only locally concentrated in belts, and prospects are not as common as in some other 

formations. It is probable, however, that other metalliferous deposits will be found within the Wrangell-Revillagigedo belt of metamorphic rocks included within the batholith as they are further 

prospected.

In the more thoroughly crystalline schist and the injection gneiss 

sulphide deposits carrying chalcopyrite and sphalerite or both together have been formed by replacement or impregnation. Locally 

galena may be associated with them. Quartz fissure veins carrying 

chalcopyrite, gold, and argentiferous galena are also found.

In the phyllite and less intensively metamorphosed schist gold 

quartz fissure veins predominate.

Nonmetallic minerals or deposits of present or potential economic 

importance within the Wrangell-Revillagigedo metamorphic belt include garnet, graphite, marble, and perhaps phlogopite mica. The 

marble is described on page 394, graphite on page 363, and garnet 

on pages 67 and 363.

Phlogopite mica occurs locally as disseminated deposits and as 

nodular aggregates or nests in the crystalline limestone and dolomite 

of the bands inclosed within the batholith, but pockets of phlogopite 

with crystals of sufficient size to be of commercial value have not been 

found. It is not improbable, however^ that such pockets may occur 

along or near the contacts with the batholithic intrusive rock or 

with dikes.

Soapstone, associated with actinolite schist, crops out on the shores 

of the cove about 2y2 miles southwest of the head of Hobart Bay, 

just inside of the first conspicuous point on the west side of the bay 

going north. The soapstone and associated actinolite schist are bordered on one side by phyllite and on the other by granitic intrusive 

rocks. The soapstone forms the central part of the green actinolite 

schist, and about 50 feet of soft uniform rock is exposed. The soapstone consists of intergrown talc, chlorite, and siderite, with a little
340 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

accessory magnetite. The siderite weathers with a rusty color, 

Veinlets of coarsely crystalline talc and chlorite several inches wide 

cross the soapstone, and veinlets of carbonate are common. Veinlets 

of fibrous tremolite (slip fiber) with fibers as much as 18 inches in 

length occur along slippage faces. The soapstone has a distinct 

schistose structure but breaks out in large massive blocks. The 

actinolite rocks are cut by a dike of diorite, which is in turn cut by an 

aplite dike. Much of the actinolite schist shows conspicuous black 

hornblende crystals scattered through the rock. The evidence seen 

was insufficient to determine whether the soapstone and actinolite 

schist represent a metamorphosed bed of impure limestone intercalated in the phyllite or a metamorphosed igneous rock.

ORDOVICIAN AND SILURIAN GRAYWACKE AND SLATE

The indurated graywacke with dark to black slate partings, the 

thin-bedded zones of black slate with graywacke or limy beds, and the 

thin-layered black chert of the Ordovician and Silurian systems are, 

so far as now known, almost barren of metallization. There is a 

copper prospect in a brecciated zone in graywacke near Lake Bay, on 

Prince of Wales Island, and locally there are quartz veins which may 

be metallized but have not been prospected; but taken as a whole 

these formations appear to afford relatively poor ground for prospecting. This is certainly due in considerable part to the relative 

sparsity of intrusive masses in them.

SILURIAN GREENSTONE AND LIMESTONE

The Silurian rocks, exclusive of the graywacke-slate formation in 

the lower part, consist of greenstone and conglomerate, a thick limestone member that is massive to thick bedded, and graywackelike 

sandstone and shale. These rocks are locally cut by Mesozoic intrusions, and in places the limestone and greenstone are considerably 

altered and mineralized.

The marble quarries operated by the Vermont Marble Co. at 

Tokeen, on Marble Island, off the west coast of Prince of Wales 

Island, are in contact-metamorphosed Silurian limestone. The great 

belt of metamorphosed medium to coarsely crystalline limestone, 

with some marble on Glacier Bay, likewise belongs to the Silurian. 

The quarries of the Pacific Coast Cement Co. on Dall Island are in the 

Silurian limestone. Indeed, the Silurian limestone is a great potential source of high-grade limestone in southeastern Alaska.

On Lemesurier Island, in Icy Strait, there is a molybdenite prospect of contact-metamorphic type at the contact of limestone with 

diorite, and in Glacier Bay there are copper and molybdenite 

prospects.
t MINERAL DEPOSITS 341

MIDDLE DEVONIAN ROCKS 

By THEODORE CHAPIN

The Middle Devonian rocks contain altered volcanic flows and 

tuffs, limestone, black slate, graywacke, and conglomerate, all of 

which carry mineral deposits of value. The altered volcanic flows 

and breccias, which comprise the lowest members of this series, contain shear-zone deposits and appear to be a favorable locality to 

prospect for this type of ore deposit.

The overlying members of the Middle Devonian appear to be the 

most highly mineralized rocks of the Ketchikan region and contain 

deposits of various types. The contact and shear-zone deposits of 

Kasaan Peninsula, Karta Bay, and many other localities occur within 

this formation. The black slates and associated tuffaceous sediments 

are favorable for the deposition of gold-bearing quartz fissure veins. 

In the vicinity of Hollis on Twelvemile Arm veins of this type are 

prevalent. The sediments are cut by a large boss of quartz diorite 

and by associated porphyry dikes and veined by many quartz fissure veins which in places have bordered or cut the porphyry dikes 

mineralizing and replacing them. This area has yielded considerable ore from several small mines and offers possibilities for future 

output. The black slates all show more or less sulphide mineralization and should be prospected for possible gold-bearing lodes.

Both the thin-bedded and massive limestone members of this 

formation contain deposits of marble, some of which have been 

quarried.

In the Wrangell district the belt of Middle Devonian rocks that 

extends across Woewodski Island and along Duncan Canal, on Kupreanof Island, northwest to Frederick Sound contains gold and 

copper deposits, also limestone in beds of sufficient size to afford a 

supply of this material if desired.

UPPER DEVONIAN ROCKS 

By THEODORE CHAPIN

The Upper Devonian rocks consist of basalt, conglomerate, fossiliferous limestone, and probably also chert, green grit, and tuff. 

These rocks are not widely distributed and are not known to be 

mineralized.

MISSISSIPPIAN ROCKS 

By THEODORE CHAPIN

The Mississippian rocks are composed essentially of black chert 

and interbedded blue, gray, and brown limestone. These rocks are 

not known to be metallized but contain bodies of very handsome 

brown semicrystalline limestone that is composed of large flashing
342 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

crystals of calcite and contains a great number of fossils. The rock 

takes a brilliant polish and makes a beautiful ornamental stone.

PERMIAN ROCKS 

By THEODORE CHAPIN

The Permian rocks are not known to be metallized, but this may 

be due. to their small area of occurrence and lack of known intrusious 

rather than to their physical or chemical character. The limestone 

of the upper division of the Permian contains some thick beds fairly 

free from chert and affords a potential source of supply. The gypsum 

beds of lyoukeen Cove, Chichagof Island, appear to be associated 

with Carboniferous formations.

TRIASSIC ROCKS 

By THEODORE CHAPIN

The rocks of Triassic age comprise limestone, conglomerate, slate, 

and sandstone and their metamorphosed equivalents. On Gravina 

Island the Triassic rocks inclose deposits of both gold and copper. 

The Triassic limestones are soft gray rocks and do not contain any 

marble deposits. _

JURASSIC (?) GREENSTONE AND SLATE

The greenstones of Jurassic (?) age are mineralized at a number of 

places in the Ketchikan district and carry both gold and copper in 

fissure veins and shear-zone deposits. A mineralized belt occurs along 

the west side of Helm Bay, on the Cleveland Peninsula, in rocks of 

this age. Another mineralized zone extends along the shore of 

Tongass Narrows, northwest of Ketchikan, for about 2 miles; in 

this zone some locations have been made and a little prospecting 

done. The ore deposits are mineralized zones in the greenstone and 

black slate along the contact of quartz diorite and fissure veins of 

. quartz in the intrusive rock. The veins contain free gold associated 

with pyrite, chalcopyrite, and arsenopyrite. The ore bodies are very 

rich in pockets but are not persistent; very little development work 

has been done upon them.

In the Wrangell district practically no prospects have been located 

in this formation.

The greenstones are well exposed on Douglas Island, in the Juneau 

district, and with respect to them Spencer 5S writes:

Fractures filled with quartz and other vein minerals are present in many 

places on Douglas Island, but up to the present no strong or regular veins 

have been developed. From the manner in which veins occur in the corre63 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, p. 90, 

1906.
MINERAL DEPOSITS 343'

spending rocks on the mainland to the northwest it is believed that the most 

promising situations for the occurrence of strong veining are along the contacts of the greenstone masses with 'the slate. * * * All of the veins observed 

in the greenstones which form the mountain seem to be irregular and discontinuous gashes, and even these, though widely distributed, are by no means 

numerous. * * * In many places on Douglas Island considerable masses 

of greenstone contain large amounts of pyrite in disseminated crystalline 

grains. * * * Some of these bodies of impregnated rock have been prospected in the past, and they are thus known to contain a small amount of gold, 

though none of them have ever been successfully mined.

No prospects worthy of note have been found in the greenstones 

of the Fanshaw and Glass Peninsulas.

In the Hyder district greenstones form much of the country rock 

between Salmon Kiver and the international boundary. Small shoots 

of sulphide consisting of galena, sphalerite, pyrrhotite, and pyrite 

or of pyrrhotite and chalcopyrite are found as replacement lodes 

and impregnation deposits parallel to the schistose structure of the 

greenstones. Locally the sphalerite in this rock carries a very high 

tenor in gold. A little arsenopyrite is commonly associated with the 

sulphides, and quartz and calcite are abundant gangue minerals. 

Quartz fissure veins with shoots of sulphide in which galena predominates also occur.

JURASSIC (!) GEAYWACKE AND SLATE

Stringer lodes of quartz are present in much of the graywacke and 

slate of Jurassic ( ? ) age and are locally very abundant. They are 

generally low-grade gold veins and have been exploited mainly in 

the Eagle Kiver portion of the Juneau belt.84 Kich gold shoots are 

very sporadic in the veins ; generally the ore is of low grade.

On the west coast of Chichagof Island, however, according to 

Overbeck,55

Graywacke is economically the most important rock of the region at the present 

time, because all the gold prospects so far located are in graywacke, although 

there is no apparent reason why mineralization should not have taken place in 

the schistose series as well. One possible reason for the seeming localization of 

the mineralization in the graywacke is that the physical properties of the massive 

graywacke under great forces may have caused it to break with big, clean fractures that were of great extent and that furnished excellent pathways for the 

ore-bearing solutions.

The famous Chichagoff mine is on a metallized quartz vein occupying a shear zone which has been followed for more than 4,500 feet 

in argillitic graywacke. The Hirst-Chichagof mine is operating on

64 Knopf, Adolph, The Eagle River region, southeastern Alaska : U. S. Geol. 

502, 1912. 9-iqmr .

H Overbeck, R. M., Geology and mineral resources of the west coast of CMchngof Island :. 

U. S. Geol. Survey Bull. 692. p. 113, 1919. ,tt!Oq llTB'.mm^rri A

6137 29 2%
344 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

quartz fissure veins that occupy shear zones in black carbonaceous 

slate near the contact with a sheet of greenstone. The veins near 

Sitka are likewise in the gray wacke-slate series of the Jurassic (?) 

rocks.

A very rough estimate wasl made of the amount of quartz in the 

Jurassic (?) slate at a locality on. the north end of Kupreanof Island. 

The quartz occurs in stringer leads in shear zones within the slate. 

The shear zones are from several feet to several hundred feet apart 

and average about 25 feet apart. The quartz forms from one-fifth to 

one-third of the shear zone, and quartz veins form about 0.75 to 1 per 

cent of the total belt of rock. The beaches are in places composed 

wholly of quartz pebbles. The quartz is milky white and carries 

accessory calcite, but sulphides are rare, and the veins presumably 

are not sufficiently metallized to be of commercial value.

In the Hyder district, along the West Fork of Texas Creek, quartz 

fissure veins are found in the graywacke and slate carrying shoots 

of sulphide in which galena predominates. There are also basemetal veins parallel to the structure of the slate and graywacke. 

Sphalerite is a .major mineral in many of these veins and may be 

associated with a little arsenopyrite.

UPPER JURASSIC OR LOWER CRETACEOUS INTRUSIVE ROOKS

^4. number of valuable mineral deposits are known within the intrusiv£; rocks of Upper Jurassic or Lower Cretaceous age where these 

rocks jbcqur as outlying dikes, stocks, and batholiths east and west of 

the^majn^po^t Kange batholith. Practically no metalliferous deposits ha^e^.een^ocated within the igneous part of the main core of 

t|i.e m^i^lan^bajb|ip}itji. It seems probable, however, that metallized 

veins' will eventually be found within the quartz diorite or granodiorite in the vicinity of included belts of country rock, particularly tii!!k:o':riip/{j. tsyiOjasii odi^icv /loo't , . . , . .. wnere, the included rock has .not been intensively metamorphosed. ifejro.'iilii ,2#-w/'Y.*n3 fin via nslftooi . . J ,. .

diorite, granodionte, diorite, 

gold, gold-silver, silver-lead, 

gabbroic and ultrabasic

- , ite, hornblendite, and ;?I.-t,fo> avavfrfJj-a^ftflfocw ffcrfsithoJ l'.-a1 C".o Jnsix ' . ' norite copper-palladium, nickel-copper, and titamlerous iron deposits occur. -Q m^i' ' tt)'isuo bflSfJsm ..e -no. PI stfiimj.nv, n . ... Th6 metalliierous deposits witjiin the diqritic and granodiontic

 te'$ OOrLir (j',:d\ r-rrom aoti n9wo.l.iqt nose! sr.ii noiii^ ones 0!. n , . igneous rocks occur, predominantly as. fissure veins in well-defined ' -« f. snfni lay.r.fbLdG-iK'n.fcl. srli'i .e^osvrYKi^ :nj in zones of^intense shearing, also to a minor extent as

: aplilen dikes i-mefeallizatiQii^has -produeed Assure

veins, impregnations, or a combination of vei

.: &«jr:fsI.iossri3MO 5.0 ianoJ lasw 91!} To aaoinpas's linwiia Baa

A significant point to be borne in

S2 OS TS10
MINERAL DEPOSITS . 345

of the igneous mass in which metalliferous veins occur are altered 

the feldspars are decomposed and dull and waxy in color, the ferromagnesian minerals are partly chloritized or altered to carbonates or 

other secondary minerals and are soft, and the rock has lost its fresh 

. appearance. Narrow dark-colored schistose zones that include powdered or slickensided rock of greenish hue are common, and veinlets 

of yellowish-green epidote or white zoisite occur.

These relations have been observed near the gold-silver-lead veins 

in quartz diorite and granodiorite of the Hyder district, near the gold 

veins in the Jualin diorite of the Berners Bay district, and near the 

gold veins in the Lisianski stock of diorite on Chichagof Island.

Rarely quartz veins or siliceous variants are developed locally in 

bodies of pegmatite and carry deposits of molybdenite, as at Shakan, 

on Prince of Wales Island, or copper in the form of bornite or chalcopyrite, as at the Drum Lummon mine, in British Columbia.

GOLD

In the Berners Bay region, according to Knopf ,56 the largest number of gold-bearing ore bodies lie within a stock of gabbro-diorite, the 

Jualin diorite, which is intrusive into graywacke, slate, and metamorphosed basalt just west of the western border of the Coast Range 

batholith. Knopf describes 10 properties that have been located in 

this mass. The fissure veins are marked by a tendency to swell and 

pinch gradually along the strike and dip. In the Jualin diorite of the 

Berners Bay region the average vein has a mean thickness of 5 feet, 

and the maximum width of solid quartz known at any point is 15 feet. 

The gangue is usually almost wholly quartz with a little associated 

calcite and sparse sericite. The metallic minerals of the veins comprise pyrite, which is most abundant, chalcopyrite, the next commonest metallic sulphide, a little galena, and at two properties sphalerite. 

Gold is rarely visible in the low-grade ores but is reported to have 

been found intergrown with quartz in pockets in the Comet mine. 

The presence of chalcopyrite seems favorable to a good tenor in gold. 

The ores are in general of low grade.

The stockworks in the Jualin diorite are described by Knopf as 

consisting of masses of broken country rock intricately penetrated 

and gashed by quartz stringers that commonly average a few inches 

in thickness. At the Kensington mine the ore body approximates an 

ellipse, 160 feet long and 80 feet wide, and is known from development work to have a depth of at least 800 feet. The whole mass of 

country rock and included network of quartz veins constitutes the

M Knopf, Adolph, .Geology of the Berners Bay region, Alaska: U. S. Qeol. Survey Boll. 

446, 1911.
346 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

ore body. The Eureka stockwork is said to average $7 a ton over a 

width of 18 feet, and the Kensington from $3 to $5 over a width of 

80 feet. The strike of individual veins is reported to be fairly regular, but no system in the strike of the veins as a whole can be observed. The greater number, however, strike between north and 

northwest, with east or northeast dips ranging from 40° to 70°.

The Lisianski stock of diorite 57 occurs in the western part of 

Chichagof Island. Several gold quartz properties have been located 

within this mass of intrusive rock, but the best-known and only producing mine is the Apex-El Nido, on Lisianski Inlet. The metalliferous veins here are for the most part in dikes of altered aplite (or 

soda trachyte) in the diorite. Veins occur also in albite-quartz 

diorite variants of the stock at the Pinta Bay prospects and on Lisianski Strait, northwest of Miner Island, and in the diorite at other 

places. On the Apex-El Nido property the metallized fissure veins 

average from ll/2 to 2% feet in width, and the Apex vein has been 

traced for 2,000 feet in length and has been exposed through a vertical range of more than 600 feet. These veins range from milkywhite quartz with free gold and only a trace of sulphides to quartz 

with local pockets of arsenopyrite as much as 2 feet in width. In 

general the sulphide metallization is small. Arsenopyrite predominates, and pyrite, galena, chalcopyrite, gold, and scheelite are the 

metallic minerals. The gangue is uniformly a milky-white granular 

quartz, with here and there a little sericite and calcite, and with 

numerous vugs lined with quartz crystals. Usually the gold is not 

visible to the eye, but the rich shoots yield gold when the quartz is 

crushed and panned. The most gold is found where the quartz veins 

have been crushed and slickensided, and gold and sulphides have 

been introduced along cracks in the original vein. Some of the gold 

and sulphides are, however, of contemporaneous crystallization with 

the quartz. The Apex and El Nido veins show a sheeted or ribbon 

structure parallel to the walls. Ore shoots are reported to have given 

average assay values for lengths of a hundred feet of $33 to $57 a 

ton in gold. A small stockwork on the El Nido property consists of 

brecciated altered diorite with many stringers of quartz. The stockwork is pear-shaped with diameters of 20 and 30 feet. The veins 

range in width from a fraction of an inch to 4 feet, and carry a considerable percentage of coarse pyrite and black sphalerite. It is 

reported that a 13-foot sample across the stockwork, consisting of 

about 30 per cent of diorite and 70 per cent of quartz stringers, 

averaged $6.82 in gold and 0.44 ounce in silver to the ton. Of eight 

veins examined in the diorite stock all strike between N. 15° E. and

67 Buddington, A. F., Mineral Investigations In southeastern Alaska: TJ. S. Qeol. Survey 

Bull. 773, pp. 114-124, 1925.
MINERAL DEPOSITS 347

N. 60° E.; the average is about northeast. The dip is from 50° to 

80°, about equally divided between east and west.

The gold ores of the famous Treadwell mines, on Douglas Island, 

consisted of dikes of albite diorite, which had been fractured, the 

openings filled with metallized quartz, and the rock impregnated 

with auriferous pyrite; the dike as a whole was mined.

On Granite Mountain, on the west side of Twelvemile Arm, Prince 

of Wales Island, there is a small intrusive mass of quartz diorite 

which carries quartz veins metallized with free gold, pyrite, chalcopyrite, and galena; and near by, in the vicinity of Hollis, the associated porphyritic dikes are veined and replaced by auriferous quartz 

veins.

Another gold mine in granitic rock is the Surf Inlet mine, on 

Princess Royal Island, in British Columbia.88 The ore bodies are 

large pyritized quartz veins, in places 37 feet in width, in a zone of 

intense shearing in the rocks (mainly quartz diorite) of the western 

part of the Coast Range batholith. In 1920, 108,082 tons of ore was 

mined, yielding 9,687 tons of concentrates, which gave 44,051 ounces 

of gold, 20,104 ounces of silver, and 685,259 pounds of copper.

GOLD-SILVER-LEAD

In the Hyder district, on or near the eastern border of the Coast 

Range batholith, there is an older batholith of granodiorite, the Texas 

batholith, in which many metallized quartz fissure veins are found.69 

The sulphides are predominantly galena and pyrite, with variable 

amounts of sphalerite and tetrahedrite and other sulphides. Galena 

is the major sulphide. Where tetrahedrite is present the ores are 

usually richer in silver. The commercial ore usually forms shoots 

in the quartz veins. The gold occurs both as visible flakes and in 

invisible form. The gold and silver contents of the ores are variable, 

but the gold content is on the whole unusually high for mineralization 

of this type. Concentrates from the Riverside mine in 1$26 are 

reported by R. G. Mellin to have contained 1.4 ounces in gold and 32 

ounces in silver to the ton and 60 per cent lead.

MOLYBDENUM

The only mineral carrying molybdenum found in southeastern 

Alaska is molybdenite, which occurs in veins within diorite and more 

siliceous granitoid types, both in outlying stocks and on the borders

M Dolmage, Victor, Coast and islands of British Columbia between Burke and Douglas 

Channels: Canada Geol. Survey Summary Rept. for 1921, pt. A, p. 29, 1922.

69 Buddington, A. F., Mineral investigations in southeastern Alaska: U. S. Qeol. Survey 

Bull. 773, pp. 73-95, 1925; Geology and mineral deposits of the Salmon River area: Eng. 

and Min. Jour.-Press, vol. 123, pp. 525-530, 1927.
348 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

of the main batholith. The best known prospect is near Shakan, on 

Prince of Wales Island. It has been described by Mertie.60 The 

vein is in hornblende diorite near the contact of an intrusive stock 

with the country rock and is genetically allied to a pegmatite vein. 

The gangue is partly pegmatite and partly quartz, with a little calcite, epidote, and chlorite. The metallic minerals comprise molybdenite, pyrrhotite, pyrite, and chalcopyrite.

Molybdenite is reported to occur also in a quartz veinlet in the 

quartz diorite of the eastern border; of the batholith at the Texas 

Creek-Comstock property, on Texas Creek in the Hyder district, and 

in the Coast Range batholith near Skagway.

NICKEL-COPPER

Mineral deposits carrying nickel and copper have been found at 

several localities on Yakobi Island; on Fleming Island and the west 

coast of Chichagof Island about 25 miles northwest of Chichagof; on 

Snipe Bay, Baranof Island; on Tenakee Inlet, Chichagof Island; and 

on Funter Bay, Admiralty Island. In all these localities the metalliferous deposits occur exclusively within ultrabasic rocks or their 

gabbroic variants. The nickel-copper lodes at Bohemia Basin, 

Yakobi Island, occur in norite or bronzitite segregations of the 

norite; those at the Alaska Nickel mines in hornblende gabbro and 

norite; at Snipe Bay in an amphibolite dike with a high percentage 

of ilmenitic magnetite; at Tenakee Inlet in a schistose basic dike; and 

at Funter Bay in a troctolite or olivine diabase dike.

The lodes usually consist mainly of pyrrhotite, with a little pentlandite (Fe,MS) and chalcopyrite, and with varying amounts of the 

minerals of the country rock, particularly pyroxene, hornblende, and 

labradorite, as gangue. Magnetite occurs as residual remnants in 

the sulphides at Snipe Bay and as a minor accessory of early crystallization in the sulphides at Funter Bay. In the surface outcrops 

the pentlandite is as a rule partly or completely altered to a secondary mineral, possibly bravoite 62 (Fe,NiS2 ), which often weathers 

with a copper-red hue resembling niccolite. Marcasite partly or 

completely replaces the pyrrhotite in some of the surface outcrops. 

The rock with disseminated sulphides is conspicuous at the surface 

because of the iron stain on its weathered outcrop.

60 Mertie, J. B., Jr., Lode mining in the Juneau and Ketchikan districts: U. S. Geol. 

Survey Bull. 714, pp. 118-119, 1921.

81 Overbeck, R. M., Geology of the west coast of Chichagof Island: U. S. Geol. Survey 

Bull. 692, pp. 125-133, 1917. Kerr, P. F., A magmatic sulphide ore from Chichagof 

Island, Alaska: Econ. Geology, 1924, pp. 369-376. Buddington, A. F., Mineral investigations in southeastern Alaska: U. S. Geol. Survey Bull. 773, pp. 98-113, 1925; U. S. Geol. 

Survey Bull. 783, p. 46, 1926.

82 Buddington, A. F., Alaskan nickel minerals: Econ. Geology, vol. 19, pp. 521-541, 1924.
MINERAL DEPOSITS 349

The metalliferous minerals occur as almost solid sulphide lenses 

or bodies and also as disseminated blebs throughout a considerable 

portion of the rock. The relatively pure solid sulphide may carry 

4 per cent or more of nickel and as much as 3 per cent of copper. 

The disseminated ore has from 1 to 2^ per cent of nickel with 1 

per cent or more of copper. Lodes of the disseminated type.of ore 

occur in considerable volume. It is reported that on the 75-foot level 

at the Alaska Nickel mines there has been exposed and sampled 

37 feet of ore with an average width of 5 feet. The whole body 

has not been exposed. The nickel content is reported to range from 

1.85 to 5.05 per cent, and copper from 0.4 to 4 per cent, with an 

average of 3.42 per cent of nickel and 1.58 per cent of copper.

The distribution of the sulphides throughout the mass of igneous 

rock in which they occur is not uniform but heterogeneous and local. 

The sulphides are interpreted as having been originally more or less 

homogeneously in solution in the molten magma. As the magma 

cooled the sulphides separated as immiscible drops and were concentrated locally to varying degrees. The disseminated type of ore 

represents a relatively slight concentration of the sulphide where 

the sulphides remain molten longer than the silicates and crystallized 

at a late stage interstitial to the silicates. The more concentrated 

or solid sulphide masses represent a more complete concentration 

or segregation of the sulphides where they remained molten longer 

than the silicates and through subsequent movements came to bear 

a veinlike intrusive relation to the country rock.

Such variation in relations need not, therefore, be interpreted as 

indicating more than the complex phenomena .which may result 

during the solidification of a single magma essentially in place. In 

the Tenakee prospect, however, the sulphides, as they now occur, 

are definitely later than the dike that contains them; they occur in 

part as seams in a sheared zone within the dike and in minor part 

in metallized quartz or quartz-calcite stringers in the shear zone. 

Pyrrhotite, pentlandite, and chalcopyrite occur in the quartz-calcite 

fissure veinlets.

Analyses for nickel have been made on a number of samples of 

pyrrhotite from contact-metamorphic and fissure-vein deposits associated with diorite or more alkalic-siliceous rocks in southeastern 

Alaska, but they show only 0.1 to 0.2 per cent of nickel and a trace 

of cobalt. In the light of the present data it seems improbable that 

nickel deposits will be found associated with diorite or more siliceous 

variants, such as quartz diorite, granodiorite, quartz monzonite, or 

granite. On the other hand, it is highly desirable that all pyrrhotite 

or copper-bearing pyrrhotite sulphide masses found in association 

with gabbroic or ultrabasic masses or dikes (hornblendite, dunite, 

pyroxenite, etc.) should be investigated as to their possible nickel
350 GEOLOGY AND MINERAL DEPOSITS,; SOUTHEASTERN ALASKA

content. The nickeliferous sulphide masses so far found are all 

within the basic intrusive rock itself; but in the Sudbury region of 

Ontario the sulphide ore masses are found also in the adjoining 

country rock. It seems highly probable that there are on Chichagof 

and Baranof Islands and, perhaps, on other islands of the Alexander 

Archipelago many dikes and masses of gabbro, norite, and ultrabasic 

rocks which have not yet been discovered and with which nickel ores 

may be associated. Nickeliferous pyrrhotite has recently been reported from a basic pyroxenite dike on the east side of the Coast 

Eange batholith in the Yale mining division, B. C.63

The nickel-bearing intrusive masses so far discovered are closely 

allied in size and mode of occurrence with basic bodies carrying 

nickeliferous sulphide, such as those at the Friday claim, Julian, 

Calif., the old Gap mine, Lancaster County, Pa., and many masses in 

Norway and Sweden. Vogt 64 has made a careful study of the Norwegian deposits and has arrived at the conclusions that the variety of 

gabbro which favors the nickel-pyrrhotite deposits is one that carries 

hypersthene, that the deposits which are associated with small bodies 

of norite and peridotite are themselves of very small dimensions, and 

that the large deposits always accompany large intrusive masses, 

especially of norite; but that it must not be inferred that all large 

norite masses are necessarily accompanied by large deposits of nickel 

pyrrhotite or that the deposits which accompany large norite bodies 

are themselves necessarily large. Vogt cites the norite mass at Erteli, 

Norway, which has an area of about 240,000 square yards and from 

the ore bodies of which has been produced about 110,000 tons of 

nickel ore containing 1,250 tons of nickel and 600 tons of copper.

The Gap mine, in Lancaster County, Pa., was actively operated 

from 1863 to 1885 and was for a time the chief nickel producer of its 

day, but after the development of the nickel deposits in New Caledonia and at Sudbury, Ontario, it was closed. Its total production 

was 4,000,000 to 4,500,000 pounds of nickel.65 The ore as mined ran 

about 1 to 3 per cent of nickel and one-third to one-fourth as much 

copper. The deposit is described by Kemp 66 as pyrrhotite carrying 

pentlandite and chalcopyrite and occurring on the borders of a lens 

of amphibolite or hornblendic rock which yields evidence that it is 

an altered gabbro or norite or peridotite. This lenticular mass or 

stock is about 1,500 feet long and 500 feet in maximum width and is 

an intrusion in mica schist.

63 Cairnes, C. E., An occurrence of nickel ore In Tale mining division, B. C.: Canadian 

Min. Jour., vol. 45, p. 1164, 1924.

M Vogt, J. H. L., On the content of nickel in igneous rocks: Econ. Geology, vol. 18, 

p. 334, 1923.

88 U. S. Geol. Survey Mineral Resources, 1882-1886.

89 Kemp, J. P., The nickel mine at Lancaster Gap and the pyrrhotite deposits at Anthony's Nose, on the Hudson: Am. Inst. Min. Eng. Trans., vol. 24, pp. 620-633, 888, 1896.
MINERAL DEPOSITS 351

Vogt 67 states that:

For the larger noritic nickel deposits in Norway and Sweden it appears that 

the highest percentage of nickel is found in the norite richest in hypersthene, 

the lowest percentage of nickel in the norite relatively poor in hypersthene, and 

intermediate percentages of nickel in the rocks having an intermediate content 

of hypersthene. In other words, the percentage of nickel in the sulphides is 

dependent essentially on the content of hypersthene (or hypersthene plus 

diallage, primary amphibole, and biotite) in the rock.

The nickel content of the sulphide ores was also found to increase 

with the percentage of magnesium oxide in the rock. The norites 

adjacent to the ore at the Bohemia and Tasmania claims, on Yakobi 

Island, are hypersthene segregations in which the hypersthene 

(bronzite) is rich in magnesia (80 to 86 per cent MgSi03 ). Indications are therefore favorable for a high percentage of nickel in the 

sulphides, if Vogt's conclusions are of general application. At the 

Snipe Bay locality the rock appears to be made up largely of hornblende, which according to Vogt is likewise a favorable indication of 

nickel in the sulphides.

Wagner 68 has shown that many nickeliferous sulphide deposits 

accompany igneous masses that show pronounced magmatic differentiation. This is confirmed by the wide variation shown in the 

intrusive masses in the Chichagof belt.

COPPER AND COPPER-PAIXADIUM

The association of copper with nickel in certain of the gabbroic 

and ultrabasic group of igneous rocks has been described. At the 

Salt Chuck mine, near the north end of Kasaan Peninsula, Prince of 

Wales Island, there is a deposit unique because of its metallization 

with copper and palladium. The property has been described by 

Mertie.09 The ore occurs in a pyroxenite with gabbroic variants. 

The ore minerals consist of copper sulphides distributed in grains, 

small patches, and veinlets as ore shoots in the pyroxenite. Bornite 

is the chief copper mineral, but a small proportion of chalcopyrite 

also occurs locally. Practically no gangue minerals are found with 

the ore. In addition to the copper, gold, silver, platinum, and palladium are recovered. The ore deposit is believed to have formed 

later than the containing country rock and is of epigenetic rather 

than direct magmatic origin, as some of its features seem to indicate.

IRON

The locations of many small masses of black hornblendite and 

some of green pyroxenite have been described elsewhere. Near Union

<" Vogt, J. H. L., op. cit., p. 348.

"Wagner, P. A., Magmatic nickel deposits of the Bushveld complex, Rustenburg district, Transvaal: South Africa Geol. Survey Mem. 21, p. 148, 1924.

 »Mertie, J. B., Jr., Lode mining in the Juneau and Ketchikan districts: U. S. Geol. 

Survey Bull. 714, pp. 121-127, 1921.
352 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Bay, on the Cleveland Peninsula, in the Ketchikan district; Snettisham, in the Juneau district; and Haines, in the Skagway district, 

ilmenitic magnetite is associated with the ultrabasic rocks pyroxenite and hornblendite.70 The magnetite with a little associated 

ilmenite occurs both as disseminations in the rock and as vein dikes 

and veinlets. In the disseminated type the magnetite and ilmenite 

occur as irregular-shaped blebs interstitial to the silicates. The iron 

oxides may form as much as 30 per cent of the rock, equivalent to 

about 20 per cent of metallic iron. The disseminated type of metalliferous deposit occurs at all three localities in considerable volume. 

At Snettisham there is a 6-foot vein dike of practically solid ilmenitic magnetite. The ilmenite occurs in part as grains 0.2 to 1 millimeter in diameter, associated with the magnetite, and in part as 

lamellae of microscopic size parallel to the parting planes of the magnetite. At Snettisham the ilmenite in a typical specimen constituted 

about 8 per cent of the ore. The ore at Snettisham is reported to 

have carried 4 or 5 per cent of titanium dioxide, and a magnetic 

concentrate from the deposit at Haines is reported to contain 3.91 

per cent of titanium dioxide. Apatite is associated with the disseminated deposits.

These ultrabasic rocks with contained magnetite produce marked 

centers or zones of local magnetic attraction, which are noted in the 

Coast Pilot.71

Local attraction of the compass is very evident on the east side of 

Union Bay, where there is a belt three-eighths of a mile offshore in 

which the variation is 32°-39° E. On the small islet off the northeast point of the bay, to the south of Union Point, a variation of 

68° E. was observed in 1922.

On the east side of Port Snettisham a local attraction of considerable strength has been observed. The disturbance is felt over an 

area of 20 square miles of land and water and is strong over 8 square 

miles.

In Chilkoot Inlet local magnetic disturbances have been observed 

from Seduction Point to Indian Rock. The disturbance is 20° W. 

at Battery Point, 12° W. at Seduction Island, and 7° W. at Chilkat 

Inlet, south of Jenkins Rock.

As possible indications of other magnetite-bearing bodies the following additional areas of local magnetic attraction are noted: A 

magnetic disturbance has been observed in the vicinity of East Island, 

the small island which lies 2% miles south-southeast from the easternmost point of Duke Island, Dixon Entrance. It may be noted

70 Knopf, Adolph, The occurrence of iron ore near Haines: U. S. Geol. Survey Bull. 442, 

pp. 144-146, 1910. Buddington, A. F., Mineral investigations in southeastern Alaska: 

U. S. Geol. Survey Bull. 773, pp. 133-134, 1925.

71 U. S. Coast Pilot, Alaska, pt. 1, Dixon Entrance to Yakutat Bay, 7th ed., 1925.
MINERAL DEPOSITS 353

that bodies of pyroxenite occur in this group of islands. Local 

attraction has been observed at Shakan Strait and in Peril Strait 

between Otstoia and Povorolni Island.

CHROMIUM

A little chromium in the mineral chromite occurs in the serpentine 

rocks of Duke and Percy Islands and of the Cleveland Peninsula, but 

it has not been found in commercial amounts.

LOWER CRETACEOUS (?) ROCKS

The slate, graywacke, and conglomerate mapped as Lower Cretaceous (?) nowhere carry veins that have been exploited. Stringer 

leads of quartz are locally very abundant in the slate, as in the vicinity of Rocky Bay, on Etolin Island^ and Point Pybus, on Admiralty 

Island. They have presumably been tested and found to be of very 

low grade, though there appears to be very little information concerning them. They carry very lean to no metallization with sulphides. By some geologists these beds are considered younger than 

the Mesozoic intrusive rocks and therefore younger than the period 

of metallization. This conclusion has not been proved, however, 

and to the writer it seems doubtful.

TERTIARY ROCKS

The Tertiary formations consist of sandstone, conglomerate, and 

shale, with rhyolitic, andesitic, and basaltic volcanic rocks. They 

were formed after the intrusion of the Coast Range batholith and 

therefore do not contain any metalliferous deposits associated with 

the magmas of the Upper Jurassic or Lower Cretaceous intrusive 

rocks. Indeed, no metal deposits of economic value have been found 

in the Tertiary formations. A little sphalerite of no commercial 

importance has been found in a Tertiary dike on the Keku Islets.72 

Veins of chalcedony and fluorite are found in the Tertiary volcanic 

rocks on the west side of Zarembo Island.78

Thin coal beds or seams are associated with Eocene formations on 

Kootznahoo Inlet and Murder Cove, Admiralty Island; 74 on Port 

Camden, Kuiu Island; on Hamilton Bay, Kupreanof Island; 75 and 

at Coal Bay, Prince of Wales Island. It is reported that efforts are

73 Buddington, A. F., Mineral investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, pp. 138-139, 1925.

73 Buddington, A. F., Mineral deposits of the Wrangell district, southeastern Alaska: 

U. S. Geol. Survey Bull. 739, p. 75, 1922.

74 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

pp. 151-154, 1906.

n Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts: U. S. Geol. 

Survey Bull. 347, pp. 59-61, 1908.
354 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

being made to produce coal on a commercial scale from the beds on 

Admiralty Island. Coal beds are reported to occur in the Tertiary 

beds of Lituya Bay.

QUATERNARY DEPOSITS

The Quaternary formations consist of glacial, marine, and stream 

deposits. The stream deposits are the only ones which have any 

economic importance. They include some interglacial stream deposits in the Porcupine placer region, but are mainly of Recent (postglacial) age; they are of value because of the local occurrence of gold 

placer deposits where streams that have traversed wide mineralized 

belts meet with other conditions favorable for the formation of 

placers. A little placer gold has been taken out from many little 

local deposits throughout the Ketchikan, Wrangell, Juneau, and 

Skagway districts, but the three most profitable localities are the 

Porcupine placer district,76 the Gold Creek placers, back of Juneau,77 

and the placers in the drainage basins of Spruce Creek and Shuck 

River, on Windham Bay.

The belt of mineralization from which the Porcupine placers have 

been derived is wide and consists of large areas of lean or barren 

rock and also wide belts in which sulphide minerals are abundant. ' 

One belt of this sort in a slate formation is 1,200 feet wide and 

shows abundant quartz veining and sulphide mineralization; a 

large number of samples taken at random across the belt assayed 

between $1 and $2 a ton. The Gold Creek placers of the Juneau 

district are derived from gold quartz veins which occur in a band 

of slate and phyllite 2,000 to 3,000 feet in width. The placer deposits of the Shuck River Basin are likewise derived from metallized 

quartz stringers and sulphide-impregnated zones in black slate and y 

schistose greenstone.

Gold placer deposits in Alaska have been discussed by Brooks,78 

and the following statements are based on his work. A placer is a 

deposit of sand, gravel, or other loose material containing a sufficient 

percentage of gold or other valuable minerals to permit profitable 

recovery. Southeastern Alaska has been intensely glaciated, and gla- *~ 

ciation of a region is usually unfavorable to the formation of placers, 

as the decomposed bedrock and stream gravel with local placers are 

eroded and the gold contents dissipated. There are, however, some 

glacio-fluviatile deposits that contain gold placers. These have resulted from the water sorting and transportation of material derived,

79 Eakin, H. M., The Porcupine gold placer district: U. S. Geol. Survey Bull. 699, 1919.

77 Spencer, A. C., The Juneau gold belt: U. S. Geol. Survey Bull. 287, pp. 42-43, 77-85, /- 

1906.

78 Brooks, A. H., Alaska's mineral resources and production: U. S. Geol. Survey Bull. 

773, pp. 15-28, 1925.
MINERAL DEPOSITS 355

often in very large bulk, from glacial scouring. The gold derived 

from glacial debris may be concentrated by stream or wave action. 

The floods that accompanied the retreat of the ice were favorable to 

stream sorting of this kind. There are three types of glacio-fluviatile 

placer deposits in southeastern Alaska (1) placers formed during an 

interglacial stage and preserved from ice scouring in canyons, such 

as part of the placers in the Porcupine district; (2) placers resulting 

from flooding during the disappearance of the ice sheets, such as 

most of those in the Porcupine district and some of the creek placers 

in the Juneau district; (3) placers formed entirely in post-Pleistocene 

time from reworking of debris originally scoured from the bedrock 

by glaciers. The placer deposits in amphitheaterlike basins or cirques, 

such as that of the Silver Bow Basin, near Juneau, are derived both 

from reworking of glacier-scoured material and from the product of 

rock weathering.

In addition to the glacio-fluviatile placers, residual, eluvial, and 

beach deposits are found.

Residual deposits rest directly on the bedrock source of gold and 

have resulted from weathering of the auriferous outcrop in place. 

A little gold has been taken from placers of such type in the belt of 

metallization on the west side of Helm Bay, in the Ketchikan district, 

but these placers are rare and their total yield is small.

Eluvial placers are deposits of loose rock containing a considerable 

amount of gold. The rock consists of angular and subangular fragments derived by weathering of bedrock and accumulated by soil and 

talus creep not far from its source. The " hill-slope " placers of the 

Juneau district were of this type and were found directly on or near 

the slope below the auriferous lodes that were later developed in the 

Alaska-Juneau, Perseverance, and Treadwell mines. The gulch deposits of the Juneau district are the result of a combination of eluvial 

and fluviatile concentration.

Beach placers are the result of concentration of gold by wave 

action. Most of the few beach deposits in southeastern Alaska are the 

result of reworking of auriferous glacial debris. A little gold has 

been taken from beaches near Yakutat, and valuable beach placers 

have been worked along the shore for a distance of about 10 miles 

northwest of Lituya Bay. The auriferous deposits consist of magnetite and garnet sands occurring in layers from a few inches to a few 

feet thick and extending in places for 100 yards back from tidewater. 

During periods of high tide and storms these auriferous sands are 

concentrated by the waves in layers high on the beach. Local beach 

placers have been found elsewhere, but little gold has been taken from 

them.
356

The placers are all dependent upon the presence of an auriferous 

mineralized belt as a source from which the gold is derived and 

concentrated.

Spencer 79 writes of the placers in Gold Creek Valley, near Juneau, 

as follows:

The early miners classified their locations as hill, gulch, and creek claims.

* * * The hill deposits are local masses of soil mixed with fragments of the 

country rock and veins, accumulated either practically in place or at no great 

distance from the parent outcrops. They represent the surface wash derived 

from the gold-bearing rocks, lodged at the base of declivities and in minor hollows on the hillsides. * * * In the formation of the gulch placers surface 

wash from considerable areas has been brought into the gulches from the side 

slopes and concentrated to a greater or less extent along the stream beds, where 

the rock and vein fragments are comminuted and the gold set free to lodge in 

natural riffles in the slaty bedrock. The materials which compose the creek 

deposits have been washed in from the side gulches and from the main tributaries of the creek. The tenor of these placers is lower than in the hill and 

gulch deposits, because the sources of the material are more widely distributed, 

and large amounts of debris have been furnished from practically barren rocks.

* * * The gulch and hill deposits are no longer of economic importance, but 

the gravel fillings in the main valley have yielded only a part of the gold which 

they originally contained. * * * The accumulation of gravels in certain 

reaches of Gold Creek Valley and not in others has resulted from an irregular 

distribution of grade along the bedrock profile; * * * where the grade is 

low or where depressions exist deposition went on until a slope was built sufficiently steep to allow the current to carry off all material subsequently washed 

into the stream.

Of the Porcupine district Eakin 80 writes:

The gold placers occur only in conjunction with the intrenchment of streams 

in the hanging valleys left after1 glaciation wherever their courses traverse zones 

of mineralized bedrock. The concentrations are generally found in a thin 

stratum of stream gravels on the bedrock bottoms of the canyons. The goldbearing stratum is generally overlain by barren or very low-grade gravels that 

are progressively deeper downstream. Their deposition is due to the rising 

base level afforded by the aggrading Klehini River.

The canyons appear to be of two ages, postglacial and interglacial. 

Eakin says:

The stream gravels in the bottoms of the older canyons, which are gold-bearing in places, are overlain by glacial detritus the depth of which is generally 

equal to the height of the canyon walls.

BELTS OF MINERALIZATION

Throughout southeastern Alaska and the adjoining territory of 

British Columbia metallization tends to occur in part in localized 

belts or areas. (See pi. 1.) Within each such belt deposits valuable

79 Spencer, A. C., op. cit., pp. 77-78.

80 Eakin, H. M., The Porcupine gold placer district: U. S. Geol. Survey Bull. 699, 1919.
MINERAL DEPOSITS 357

for a certain metal or group, of metals may predominate, and the 

type of metallization may differ for each belt. The tendency toward 

localization is, however, only, a tendency, not a rule, fpr mineral 

deposits that differ in character from the prevalent one are found in 

each belt, and mineralization is by no means confined to these localized 

belts.

The map shows a very obvious grouping of metalliferous deposits 

around or in the vicinity of masses of intrusive rock, though mineral 

deposits have not been discovered in association with all the intrusive 

masses. Intrusive rocks are relatively sparse in the Kuiu-Heceta 

belt, including Kuiu Island, the western part of Kosciusko Island, 

Heceta, Tuxekan, San Fernando, and Suemez Islands, and the adjacent western coast of Prince of Wales Island. It is surely significant 

that not a single metalliferous deposit of commercial value has been 

discovered in that belt.

EASTERN BORDER BELT

A metalliferous belt lies near or within the inland border of the 

Coast Range batholith, and its course may be traced by the prospects 

located wherever this eastern border is accessible, as at Alice Arm, 

ut the head of Portland Canal, and on Salmon, Unuk, Iskoot, Stikine, 

and Taku Rivers.

The mineral deposits of this belt are described by Schofield,81 

Dolmage,82 Hanson,83 Cairnes,84 Westgate,85 and Buddington.86 

They are of the following types: (1) A type rich in silver minerals, 

such as tetrahedrite, pyrargyrite, proustite, polybasite, argentite, and 

at some places native silver; examples of this type are the Premier 

and certain bodies in the Forty-nine, Big Missouri, and other mines 

at the head of Portland Canal, on the Canadian side of the boundary, 

which occur as veins and veinlike replacement deposits in quartz 

porphyry and at the contact of the porphyry and tuff, also the Esperanza, Golkish, and Dolly Varden, near Alice Arm, which occur as 

veins in argillite; (2) a low-grade complex type that contains predominantly pyrite, chalcopyrite, sphalerite, and galena with copper, 

lead, and zinc and locally a high content of gold or silver; this type

81 Schofleld, S. J., and Hanson, George, Geology and ore deposits of Salmon River district, 

B. C.: Canada Geol. Survey Mem. 132, pp. 61-62, 1922.

82 Dolmage, Victor, Coast and islands of British Columbia between Douglas Channel and 

the Alaskan boundary: Canada Geol. Survey Summary Kept, for 1922, pt. A, pp. 9-34, 

1923.

83 Hanson, George, Reconnaissance between Kitsult River and Skeena River, B. C.: 

Canada Geol. Survey Summary Rept. for 1922, pt. A, pp. 35-51,, 1923.

81 Cairnes, D. D., Portions of Atlin district, B. C.: Canada Dept. Mines Mem. 37, 1913.

85 Westgate, L. G., Ore deposits of the Salmon River district: U. S. Geol. Survey Bull. 

722, pp. 117-140, 1921.

88 Buddington, A. F., Mineral investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, pp. 71-139, 1925.
358 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

occurs usually as replacement or disseminated deposits in beds of 

greenstone or tuff and tuffaceous conglomerate and forms roughly 

tabular lodes, such as certain bodies in the Hercules, Big Missouri, 

Forty-nine, Daly Alaska, and other mines; the base-metal type occurs 

also in fissure veins; (3) quartz fissure veins in granodiorite and in 

sedimentary and volcanic beds metallized with ore shoots that consist largely of galena and pyrite with locally associated tetrahedrite, 

chalcopyrite, pyrrhotite, a little sphalerite, or native gold and that 

are valuable for lead, silver, and gold; examples are the Riverside, 

Fish Creek, Mountain View, and Homestake properties in the Hyder 

district; a similar type is found also,, according to Cairnes, as the 

most widely distributed type of vein in the Atlin district, where the 

veins occur in schist, basic volcanic rocks, and granodiorite; (4) 

gold quartz veins, such as are found in the Engineer mine, in the 

Atlin district, to the north, and in the Kitsumgallum district, to the 

south; (5) molybdenite-bearing quartz veins in a series of argillite, 

arkose, and argillaceous sandstone, such as occurs 4 miles east of 

Alice Arm.

In the Salmon River district, on the Alaskan side of the international boundary, observations on the strike and dip of 122 veins were 

obtained. Almost half of these strike northwest (N. 30°-60° W.) 

and dip 45°-70° NE.; a fifth of them strike between north and northnorthwest (N. 0°-30° W.) and dip 45°-70° E.; and another fifth 

strike within about 15° of east (N. 75° E.-N. 70° W.). In one narrow localized belt parallel to Casey Glacier and Homestake Gulch the 

veins strike N. 0°-35° E. In the Texas batholith of granodiorite 

about two-thirds of the veins strike within 15° of northwest, whereas 

in the graywacke, tuff, slate, and greenstone about half the veins 

strike within 15° of east, parallel to the bedding and the structure.

CENTEAL COAST RANGE BATHOLITH

The Coast Range batholith in southeastern Alaska and the adjoining part of British Columbia consists essentially of granodiorite, 

quartz monzonite, and quartz diorite, with a little associated diorite 

and more basic rocks and included belts of schist and injection gneiss. 

Few mineral deposits have been discovered within the core of the 

Coast Range batholith. In the past this has commonly been ascribed to an actual scarcity of metallization there; but it is now 

being recognized that the exceeding ruggedness of the country and 

its inaccessibility, with consequent slight prospecting, may also be a 

contributing factor. Mineral deposits of economic importance occur 

in the belts of metamorphic rocks inclosed within the batholith, as 

previously described, and there is no doubt that others will be found;
MINERAL DEPOSITS 359

but it will probably still be found to hold true that mineral deposits 

of commercial value are relatively sparse within the Coast Range 

batholith.

Prospecting has been carried on mainly along the western border 

of the Coast Range batholith, in the vicinity of outlying stocks on 

the islands of the Alexander Archipelago, and along the eastern 

border of the batholith at places where it is accessible. Recent developments are now directing attention to the fact that many blocks 

and belts of schist or gneiss are found within the batholith and that 

locally they may contain ore deposits.

The abundance of schist and gneiss inclusions in the Coast Range 

batholith is indicated by the fact that along the east side of Portland 

Canal about half of the batholith, along a cross section of 100 miles, 

is schist or gneiss. In a length of about 11 miles along Tracy Arm 

one-third of the batholith is schist or gneiss.

The predominant types of metalliferous deposits within the belts 

of crystalline schist and injection gneiss in the core of the Coast 

Range batholith include replacement and impregnation deposits 

carrying copper or copper and zinc (chalcopyrite and sphalerite). 

Quartz fissure veins with copper, rarely molybdenite, and bands of 

mineralized schist with galena, sphalerite, and tetrahedrite are also 

present.

Within the belts of schist and gneiss included in the batholith 

bands of oxidized rusty-weathering sulphide-impregnated rock are 

common. Most of these bands carry only pyrite or pyrrhotite or 

both, with a little chalcopyrite and a very low content in gold, and 

under present conditions they are of no value; but some carry combinations of pyrrhotite, chalcopyrite, sphalerite, and galena and deserve consideration. Both types of deposit the bands impregnated 

with iron sulphide and the bands of base metal have a similar 

weathered appearance, and the pyrite-pyrrhotite bands are so predominant that the base-metal bands carrying chalcopyrite, sphalerite, 

or galena, or a combination of these, are liable to be passed over 

through lack of careful examination of the fresh rock.

Sphalerite and pyrrhotite are the most abundant minerals in several metallized zones in the belt of schist and gneiss at or near the 

western border. It seems highly probable that other similar deposits will be found as these belts of metamorphic rock are more 

thoroughly prospected.

The low-grade copper deposit of the Hidden Creek mine, at Anyox, 

British Columbia, occurs in a belt of greenstone and argillite inclosed 

within the central portion of the batholith. In this mine there has 

been developed to date 13,215,000 tons of copper ore averaging 2.14

6137 29 24
360 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

per cent of copper.87 Seven miles west of the Hidden Creek mine, 

at Maple Bay, on the east side of Portland Canal, another copper 

mine is being developed in the same belt of schist. This schist belt 

is reported to occur also on the west side of Portland Canal. The 

common metallic minerals are pyrite, pyrrhotite, chalcopyrite, zinc 

blende, magnetite, and arsenopyrite. They are believed to be the 

result of the replacement of greenstone and argillite.

Wright 88 reports a 2-foot vein of copper ore in a belt of schist 

included within the Coast Eange batholith on Unuk River about 1 

mile below the international boundary. The vein consists of pyrite, 

pyrrhotite, and chalcopyrite.

A vein carrying considerable quantities of sphalerite is reported to 

occur on Taku River about 1 mile from the international boundary. 

The predominant minerals are pyrrhotite and sphalerite with a little 

pyrite, galena, and locally chalcopyrite. The ore gives low assays 

for gold and silver.

At the Whiting River prospect, in the Juneau district, there is a 

quartz fissure vein in a belt of marble inclosed in quartz diorite. The 

metallic minerals comprise arsenopyrite (predominant), pyrite, 

galena, sphalerite, and chalcopyrite. The silver content is moderate, 

and there is considerable gold. Quartz porphyry dikes cut the 

marble near the vein.

On Quartz Creek, a tributary about 30 miles from the mouth 

of Iskut River, there are bands of schist that are metallized with 

sphalerite and galena and have locally stringers of tetrahedrite 

carrying considerable silver.

Despite the known and probable occurrence of mineral deposits 

within the core of the Coast Range batholith it is still true that the 

batholith itself is not as favorable an area for prospecting as the 

eastern and western border belts or the Alexander Archipelago.

WESTERN BELT OF SCHIST AND GNEISS

*

The western belt of schist and gneiss comprises the metamorphic 

rocks west of the Coast Range batholith. It includes practically 

the same general area as the Wrangell-Revillagigedo belt of metamorphic rocks and, in addition, the narrow belt of schist and gneiss 

adjacent to the western border of the batholith, which tapers to a few 

hundred feet in width near Berners Bay.

The predominant metalliferous deposits in the more intensely metamorphosed crystalline schist and gneiss immediately adjacent to the

87 Dolmage, Victor, Coast and islands of British Columbia between Douglas Channel and 

the Alaskan boundary: Canada Geol. Survey Summary Kept, pt. A, p. 20, 1922.

88 Wright, F. E., The Unuk River mining region of British Columbia: Canada Geol. Survey Summary Kept, for 1905, p. 50, 1906.
MINERAL DEPOSITS 361

western border of the batholith include sphalerite replacement veins 

associated with pyrrhotite, chalcopyrite, or a little galena; a few 

low-grade quartz fissure veins; and a copper quartz fissure vein. In 

the less intensely recrystallized, more characteristically mechanically 

sheared beds at the south end of Revillagigedo Island there is a belt 

in which a number of gold quartz veins are found, and in the phyllite 

east of Wrangell silver-lead veins occur.

Schist and gneiss that contain disseminated crystalline flake graphite, garnet, and beds of marble or medium to coarse crystalline limestone are found within this belt.

A localized belt of mineralization occurs on the mainland about 13 

miles east of Wrangell. It includes the tabular zinc replacement 

veins at the Groundhog Basin, the silver-lead and zinc replacement 

veins at Glacier Basin, and the gold quartz fissure veins at Bergs 

Basin. The mineral deposits are associated with intrusive sheets 

and dikes of quartz porphyry. The replacement veins are of a 

high'-temperature type and are associated with typical contact-metamorphic minerals. This belt very probably extends northwest toward Stikine Eiver, for quartz porphyry is found in considerable 

quantity as float in Andrews Creek. The belt deserves further 

prospecting.

Ziiw. The extensive low-grade zinc replacement veins of the 

Groundhog Basin,89 about 13 miles east by northeast of Wrangell,

 occur in a belt of gneiss and schist within the western border zone of 

the Coast Range batholith. The main vein has been traced for a 

length of about 3,200 feet, through a range in altitude of 1,140 feet, 

and has been sampled for a length of 1,600 feet. The width for the 

1,600 feet sampled ranges from V/2 to 9 feet and averages about 3 

feet; the average of 24 assays, each made on the full width of the 

vein, is approximately zinc IT per cent, lead 2.5 per cent, silver 1.25 

ounces to the ton. The metallic minerals comprise pyrrhotite and 

dark-brown sphalerite, with small and variable amounts of pyrite

 and galena. The gangue is made up largely of unreplaced remnants 

of the country rock and includes plagioclase, pyroxene, hornblende, 

epidote, quartz, and biotite. The sphalerite is reported to be a variety carrying considerable iron. The veins are of the high-temperature type and are allied to contact-metamorphic deposits in origin. 

Small replacement bodies of magnetite slightly earlier in age than the 

sulphides are locally associated with the sulphide veins. The sulphide veins have a tabular form parallel to the banded structure of 

the inclosing crystalline schist and gneiss and are not located on a 

contact. The deposits in part replace intercalated limestone beds 

and in part replace injection gneiss.

89 Buddington, A. F., Mineral deposits of the Wrangell district, southeastern Alaska : 

U. S. Geol. Survey Bull. 739, pp. 57-63, 1922.
362 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

On Tracy Arm, in the Juneau district, about 1 mile south of the 

point at the first elbow, there is a prospect known as the Neglected 

Prize. The vein lies within a narrow belt of injection gneiss between the quartz diorite of the western border of the Coast Range 

batholithl and an outlying quartz diorite sill. Assays of samples 

from the full width in several prospect pits are reported to range 

from 1.5 to 4.1 per cent of copper and from 4.7 to 14.6 per cent of 

zinc. The sulphides predominate over the gangue and comprise 

pyrrhotite, sphalerite, chalcopyrite, and pyrite.

On Lynn Creek,90 north of Vancouver, in British Columbia, in a 

belt of crystalline schist bordering the west side of the Coast Range 

batholith, a zinc body is being developed. The veins occur near the 

contact with quartz diorite and are tabular deposits that 'have replaced limestone beds. The metallic minerals comprise a large 

amount of sphalerite, chalcopyrite, pyrite, and pyrrhotite.

Silver-lead. Silver-lead veins within the belt of schist, gneiss, and 

crystalline limestone are found at the Lake claims,91 10y2 miles east 

of "Wrangell, at the claims in Glacier Basin,91 14 miles east of Wrangell, and at the Whiting River prospect.82 At Glacier Basin they 

occur in part as tabular replacement bodies in gneiss and in part as 

veinings throughout a part of a brecciated felsite sheet. The ore 

minerals comprise galena and sphalerite, with associated pyrrhotite, 

chalcopyrite, and pyrite. At the Whiting River prospect the lode 

is a metallized quartz fissure vein in crystalline dolomite and lime-- 

stone. The metallic minerals comprise arsenopyrite, pyrite, galena, 

sphalerite, and chalcopyrite, with arsenopyrite predominant. Quartz 

porphyry dikes cut the marble near the vein.

Gold. The following descriptions of gold belts in the Ketchikan 

district are given by Chapin:

A strongly mineralized zone in the Wrangell-Revillagigedo belt 

of metamorphic rocks occurs along the south end of Revillagigedo 

Island from Tongass Narrows northwestward to the head of Thorne 

Arm and George Inlet. The gold-bearing lodes occur in the green-' 

stone, slate, and schist that border the wide belt of quartz diorite 

that extends nearly across the island from the mouth of Thorne Arm 

to Survey Point. The gangue of the lodes is essentially quartz which 

carries pyrite and galena. Pyrrhotite, sphalerite, and chalcopyrite 

are also found. The gold occurs both free and combined with sulphides and carries silver in varying amounts. The lodes are fissure 

veins.

wfiurwash, E. M. J., The geology of Vancouver and vicinity, pp. 56-60, Univ. Chicago 

Press, 1918.

91 Buddington, A. P., Mineral deposits of the Wrangell district, southeastern Alaska: 

U. S. Geol. Survey Bull. 739, pp. 63-«7, 1922.

83 Buddington, A. F., Mineral investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, p. 135, 1925.
MINERAL DEPOSITS 363

A strongly mineralized belt lies along the west side of Helm Bay, 

on the Cleveland Peninsula. The lodes are chiefly gold-bearing and 

occur as quartz fissure veins and as impregnated zones with gash 

veins in schistose greenstone with interstratified argillaceous beds. 

An unusual feature of certain of these lodes is the presence of the 

rare mineral tetradymite. The common association of minerals is 

free gold, iron pyrite, and a little galena in a quartz gangue. Chalcopyrite and bornite occur as accessory minerals in some veins.

Extending along the shore of Tongass Narrows northwest of 

Ketchikan for about 2 miles is a mineralized zone in which some 

locations have been made and a little prospecting done. The ore 

deposits occur as mineralized portions of the greenstone and black 

slate along the contact of the quartz diorite and as fissure veins in 

the intrusive rock. The veins contain free gold associated with 

pyrite, chalcopyrite, and arsenopyrite. The ore bodies are rich in 

pockets but are not persistent, and very little development work has 

been done on them.

At the Clark prospect, 6% miles east of Juneau, there are lowgrade gold quartz veins some of which are unusual because of the 

association of considerable stibnite in the veins.

Graphite. Beds of schist and gneiss with crystalline flakes of 

graphite were particularly noted north of Wind Point, on Thomas 

Bay; at the head of Knygs Lake, on Stikine River; in the schist belt 

crossed by Andrews Creek, on Stikine River; and near Duck Island 

Cove on Bradfield Canal. A specimen from Thomas Bay is a 

graphitic feldspathic quartz schist consisting of 54 per cent of quartz, 

26 per cent of feldspar, 9 per cent of biotite, 6 per cent of graphite, 

and 5 per cent of pyrrhotite. Other beds carry a very low content of 

mica. The graphite occurs as disseminated flakes with a diameter 

ranging from 0.2 to 0.7 millimeter and averaging 0.4 millimeter, and 

with an average thickness of 0.08 millimeter.

Garnet** Garnet has been mined at only one locality, the property 

of the Alaska Garnet Co., 7}/£ miles north of Wrangell. This is the 

locality from which come the garnets found in museums all over the 

world and many of them labeled " Fort Wrangell." The garnets 

are from one-fourth to three-fourths of an inch in diameter and 

occur disseminated through beds of quartz-mica schist 10 feet or 

more in thickness. They lie near intrusive quartz diorite and are 

of contact-metamorphic origin.

Another richly garnetiferous belt occurs on Port Houghton and 

has been described on page 67 of this report.

93 Buddlngton, A. F., Mineral deposits of the Wrangell district, southeastern Alaska: 

U. S. Geol. Survey Bull. 739, pp. 73-74, 1922.
364 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

JUNEAU GOLD BELT

Another well-defined belt, often referred to as the Juneau gold 

belt, lies along the west side of the Coast Range batholith, beginning 

north of Thomas Bay and extending for 175 miles to the northwest 

parallel to the contact, with a width of 5 to 10 miles. The main 

product of this belt has been gold, though this is always accompanied 

by varying amounts of silver. The geology of this belt has been 

described by Spencer,94 from whose report the following quotations 

are taken:

The gold occurs in various forms of lode deposits and in placers which 

have been formed by the breaking down of the lodes during general erosion of 

the rocks and the concentration of their contents through the sorting action of 

streams. * * * The lode deposits may be divided into three classes (1) 

veins; (2) impregnated masses of rock; (3) mixed deposits consisting of 

veins and impregnations together. * * * The vein stuff is ordinarily quartz 

or calcite, one or both, with variable proportions of other minerals, particularly 

sulphides of the metals which are commonly accompanied by gold and 

silver, * * * the most noteworthy differences being seen in the amounts 

of metallic sulphides present. As a rule these vary from little or none up 

to 3 or 4 per cent, or in ore shoots of limited extent up to a much higher proportion. * * * Throughout the district probably the greatest number of 

veins, and in general the larger ones, occur in fissure openings which follow the 

structure of the inclosing rocks. Practically all of the veining has been formed 

since the schistose and slaty structures were developed. * * * Those veins 

which occur between two sorts of rock possessing different rigidity (as between 

soft slate and greenstone or diorite) are apt to be the strongest and most 

continuous. In most cases, however, instead of solid veins lying between two 

different beds, one finds typical stringer leads composed of numerous nearly 

parallel veinlets occupying irregular openings in the slates adjacent to the 

contact. Stringer leads are characteristic of the slaty rocks, and they occur 

in many places irrespective of the proximity of massive strata. These stringer 

leads are commonly composed of series of parallel overlapping veinlets occupying openings along the slaty cleavage or in some places cutting across the 

structure. * * * In another form of stringer leads gashlike fractures have 

been opened in some rigid rock, and commonly these are confined to the vicinity 

of contacts with the inclosing slates. * * * Vein aggregates of this sort 

are sometimes traceable for several hundred feet. * * * Instances of crosscutting veins are comparatively rare, though they have been noted. * * * °in 

the vicinity of Yankee Cove several transverse veins have been prospected, and 

here they are confined to a certain band of massive greenstone. * * *

In this form of mineralization the metallic minerals are disseminated more 

or less irregularly through masses of country rock. * * * In many instances one of the products of this replacement is iron pyrites and other 

sulphide minerals also occur. * * * In most cases where rock masses containing disseminated sulphides have been prospected it has been found that the. 

gold present is not sufficient to constitute an ore. * * *

Veining and impregnation are combined in the ore bodies of the Treadwell 

mines on Douglas Island. * * * In the Treadwell deposits the masses of

94 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, pp. 22-38, 

1906.
MINERAL DEPOSITS . 365

igneous rock which have been transformed into ore have the form of dikes 

lying parallel with slate and an interbedded stratum of greenstone, between 

which they have been intruded. These dikes were fractured and in their 

broken condition became channels for the circulation of mineral-bearing waters, 

which deposited vein stuff in the open spaces and, soaking into the fragments of 

the broken rock, attacked them as they were able, destroying to a degree certain 

of the minerals present and depositing new minerals in their stead. Among 

these introduced minerals are various sulphides, of which the principal one 

is pyrite, which is accompanied by a small amount of gold. Pyrite and gold also 

occur in the veinlets, and the whole recemented mass constitutes the ore of the 

mines which comprise the famous Treadwell group. * * *

From the observable range of the vein fillings from elevations above 3,000 

feet to a depth of more than 1,000 feet below tide it may be safely assumed 

that the same sort of veins' must have been removed with the rocks which have 

been carried away by erosion and must be present in the existing rocks to a 

considerable depth. * * * In general, then, metalliferous veins and impregnations are probably distributed through the rocks to depths of several 

thousand feet in very much the same manner as to number and form as in the 

rocks which are exposed above tide level. * * * Continuous, well-defined 

outcrops and wide bodies of quartz may be regarded as indications favorable for 

continuance in depth, though, as shown by the Bald Eagle vein at Sumdum, this 

is no infallible rule, and it is regarded as especially liable to fail in soft, flexible 

rocks like slates. Swells and pinches, both horizontal and vertical, are common 

features of fissure veins in all regions where they have been followed by the 

miner. * * * Throughout the Juneau region the contacts between rocks of 

different rigidity are regarded as favorable situations for permanence in depth, 

though even in such cases great changes in the width of veins and their solidity 

are to be expected. * * *

The ores of the Juneau region usually carry more than half of their gold in 

a free-milling condition. * * * A general rule, to which a few exceptions 

could be noted, is that in a given deposit or vein an increase in the amount of 

sulphides is accompanied by an increase in the value of the ore. * * * Free 

gold and the gold and silver bearing sulphides occur either in veins of quartz 

and calcite or disseminated through masses of more or less altered rock. In 

general the vein ores contain the largest values per ton, deposits combining vein 

and impregnation features are intermediate in gold contents, and masses consisting entirely of disseminated sulphides are of low grade and commonly too 

poor to be mined with profit.

In the region here considered quartz forms the characteristic filling of the 

veins and is the principal nonmetalliferous mineral of the ores, though calcite 

is usually present and certain veins contain considerable amounts of albite.

The accessory gangue minerals include ankerite, rutile, sericite, and 

in places tourmaline and others derived from the wall rocks. Among 

the metallic minerals, pyrite is the most common, and pyrrhotite is 

present in many of the quartz veins. Galena and sphalerite are extremely variable in amount and are commonly associated with an 

increase in the proportion of silver. Chalcopyrite is nearly everywhere present but in small amounts. Arsenopyrite occurs in many 

places in the veins and in some places carries much gold. Gold 

occurs in two ways; as flakes or spangles of the native metal and in
366 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

an invisible form in the sulphides. Other primary metallic minerals 

restricted to one or a few veins include stibnite, tetrahedrite, and 

molybdenite.

FUNTER BAY-HAWK INLET BELT

A belt of schist and phyllite that shows considerable dynamic metamorphism and contains a great number of well-defined quartz fissure veins extends from Funter Bay to Hawk Inlet and perhaps 

farther south on Admiralty Island. This belt appears to be geologically similar to the Juneau belt. The mineralized belt on 

Funter Bay has been described by Wright,95 Eakin,96 Mertie,97 and 

Buddington.98

The schist includes three general types greenstone schist composed of combinations of chlorite, epidote, zoisite, mica, quartz, and 

albite, with a little calcite, titanite, and apatite; light-colored micaceous quartz schist; and black crinkled graphitic phyllite. Several 

varieties of igneous rock occur as sheets or dikes, including albitequartz diorite, albite diorite, and albite trachyte.

Near Funter Bay there are two sets of veins, one of which strikes 

N. 45°-60° E. and the other N. 20°-35° W., the latter approximately 

parallel to the strike of the schist. On the Hawk Inlet side of 

Mount Kobert Barren the veins strike prevalently N. 15°-30° E., 

which is 20°-30° more eastward than the strike of the schist and 

phyllites, and have a steep eastward dip.

Some of the quartz veins are very large; one has been traced for 

2,300 feet and is 20 feet wide at one point; another is over 2,000 feet 

long and 20 to 50 feet wide; and another has at one point a width of 

57 feet, said r to be ore. Some of the large veins have been proved 

to carry gold ore shoots of low or medium to high grade and some 

to have large volumes of quartz that yields low assays in gold. In 

general, the quartz is white, milky, and massive, but locally it shows 

comb or drusy structure and is associated with masses of ankerite or, 

in the weathered oxidized surface outcrop, with limonite. The goldbearing quartz is commonly iron-stained or sparsely metallized with 

one or more of the minerals pyrite, pyrrhotite, sphalerite, galena, 

chalcopyrite, specularite, and native gold.

PRINCE OF WALES BELT

The Prince of Wales belt of metallization is in part coincident 

with the Prince of Wales-Chichagof belt of intrusive rocks. The

85 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Geol. Survey Bull. 287, 

pp. 147-150, 1906.

* Eakin, H. M., Mining developments and water-power investigations in southeastern 

Alaska: U. S. Geol. Survey Bull. 662, pp. 84-92, 1917.

m Mertie, J. B., Mining developments and water-power investigations in southeastern 

Alaska: U. S. Geol. Survey Bull. 714, pp. 113-118, 1921.

88 Buddington, A. F., Mineral investigations in southeastern Alaska r U. S. Geol. Survey 

Ball. 783, pp. 42-50. 1926.
MINERAL DEPOSITS 367

bedded rocks comprise dynamically metamorphosed schist, local con"- 

tact-metamorphic zones around the intrusive bodies, graywacke, tuff, 

greenstone, limestone, and slate. The average of the Mesozoic intrusive rocks is equivalent to a quartzose diorite, and the predominant 

rocks are of dioritic types as compared with the more siliceous quartz 

diorite to the east.

The southern half of Prince of Wales Island is especially well 

metallized. The most abundant metals are iron and copper and to a 

less extent gold. The developed prospects or mines are predominantly 

magnetite-chalcopyrite contact deposits, chalcopyrite impregnated or 

veined shear zones, gold quartz fissure veins, and copper-bearing 

quartz veins and brecciated zones. Other types, of which there are 

only one or a few of each, comprise copper-palladium, silver-lead, 

molybdenite, and a base-metal type that includes zinc, lead, and 

copper with silver and gold. The greater production of gold and 

silver has come from the copper lodes. A little silver has been won 

from the argentiferous galena, but most of the silver recovered has 

come from the gold.

On the north end of Prince of Wales Island there are at least two 

large stocks of dioritic rock, one back of Ratz Harbor and another in 

the vicinity of Shakan. The belt in the vicinity of these two stocks 

deserves further prospecting. The Shakan stock is highly differentiated ; evidences of metallization in it or in its vicinity were noted in 

several places and include arsenopyrite veinlets, galena, and specularite in local contact-metamorphic pockets, the molybdenite lode at 

Shakan, and gold-bearing quartz veins. The country rock also is in 

part favorable to the formation of contact copper deposits.

The graywacke formations belonging to the Ordovician and 

Silurian systems appear to be relatively barren.

The extension of this metallized belt is indicated by the metallization in a belt parallel to Duncan Canal on Kupreanof Island 

extending northwest to Frederick Sound. The gold lodes of Woewodski Island and the copper deposits near the head of Duncan 

Canal and on Frederick Sound are included here. They have been 

described by the Wrights " and by Buddington.1

The copper-palladium and molybdenite deposits are described in 

connection with the Upper Jurassic or Lower Cretaceous intrusive 

rocks (pp. 347, 351). The silver-lead deposits are known as the 

Moonshine and Hope prospects and are located on the west side of 

the South Arm of Cholmondeley Sound. At the Hope claims the 

surface exposures show a lode cutting quartzite, schist, and limestone

« Wright, F. B. and C. W., The Ketchlkan and Wrangell mining districts, Alaska: U. 8. 

Geol. Survey Bull. 347, pp., 140-142. 182-184, 1906.

1 Buddington, A. F., Mineral deposits of the Wrangell district, southeastern Alaska: 

U. S. Geol. Survey Bull. 739, pp. 67-73, 1922.
368 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

country rock. The lode appears to be continuous but widens where 

it crosses the calcareous rocks. The ore bodies are due to the replacement of limestone and calcite lenses in the schist by epidote, garnet, 

and galena. The Moonshine vein has been described by the Wrights.2

The Complex prospect is midway between Mineral and Dora Lakes, 

on the south side of Cholmondeley Sound. The country rock is limestone and schist, and the lode is a fissure vein of banded quartz with 

considerable galena, sphalerite, chalcopyrite, and pyrite carrying gold 

and silver. Some of the ore is essentially sphalerite, with a little 

chalcopyrite, galena, gold, and silver; and in most of the ore zinc, 

copper, lead, gold, and silver all occur in sufficient amounts to be 

essential recoverable products.

Copper. The copper deposits have been described by Brooks and 

others.8 Brooks writes:

All the productive copper mines as well as the largest developed cupriferous; 

ore bodies of southeastern Alaska are in the Ketchikan district. Copper is 

widely distributed in the Ketchikan district and, as will be shown, occurs in 

deposits of several distinct types. The most important so far as present production and extent of proved ore bodies are concerned are the contact deposits, 

which have yielded more than 98 per cent of the copper produced in the 

Ketchikan district.

The largest of the developed contact lodes are essentially chalcopyrite-magnetite deposits. Others which are less common consist mainly of chalcopyrite and 

pyrrhotite. All the ores carry pyrite, molybdenite, and specularite as accessory 

minerals. Some of the ores contain small amounts of nickel and traces of cobalt. The ores that have been mined carry enough gold to increase their value 

materially. In some localities a shallow surface zone of copper carbonates and 

other secondary minerals has been formed, but these deposits are not large 

enough to be of commercial importance.

These deposits occur in or near the contact-metamorphic zone caused by the 

intrusion of granitic and dioritic material into the sedimentary rocks among 

which limestone predominated. Such deposits have also been found in the 

contact zone of schists, greenstone tuffs, and graywackes.

The gangue of the contact deposits consists principally of minerals resulting 

from the alteration of the country rock and includes garnet, epidote, pyroxene, 

amphibole, and calcite. Calcite is sufficiently abundant in some of the ores to 

give them special value as flux. Quartz also occurs in all the deposits but is 

usually not abundant.

The typical contact deposits are masses of irregular outline, and some have 

very poorly defined boundaries. In some places a little copper occurs in zones 

about 200 feet wide, but the ores thus far mined have been taken from the 

smaller and much richer shoots, which are irregularly distributed through the

a Wright, F. E. and C. W., op. cit, p. 187.

8 Brooks, A. H., The future of Alaska mining: U. S. Geol. Survey Bull. 714, pp. 12-19, 

1921. Wright, F. E. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, 1908. Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, Alaska: U. S. Geol. Survey Prof. Paper 87, 1915. 

Chapin, Theodore, Mining developments in southeastern Alaska: U. S. Geol. Survey Bull. 

642, pp. 83-100, 1916; Mining developments in the Ketchikan and Wrangell districts: 

U. S. Geol. Survey Bull. 662, pp. 63-75, 1918. Smith, P. S., Lode mining in the Ketchikan district: U. S. Geol. Survey BulL 592, pp. 75-94, 1914.
MINERAL DEPOSITS 369

contact rock or the larger bodies of low-grade ore. One difficulty that has beset 

the miner is the great irregularity in occurrence of the rich ore shoots. It is 

not uncommon to find an ore body whose horizontal cross section is almost 

square and which ends abruptly at the bottom. In many places search will reveal another ore shoot at greater depth. Hence there is little guide to the search 

for ore except the zone of contact rnetamorphism. The largest deposits thus far 

developed consist of huge bodies of magnetite in which chalcopyrite occurs, both 

flnely disseminated and in shoots of massive sulphides.

Incidentally to the search for rich ore shoots, which are as yet the principal 

source of the copper produced, a considerable tonnage of concentrating ore has 

been, blocked out. There are also much larger bodies of low-grade ore which 

contain too little copper to be now classed as commercial ores. The reserves of 

such ore have not been determined, and little is known of their average copper 

content. It is probably true, however, that if a magnetite ore carrying 0.5 per 

cent copper could be utilized, the developed reserves would be very large; also 

that the hope of finding other similar deposits is well founded.

Among the best examples of the contact copper deposits in the Ketchikan 

district are those at the Mount Andrew, Mamie, Poorman, and It mines, on 

Kasaan, Peninsula; the Rush & Brown mines, on Karta Bay; and the Jumbo 

and Copper Mountain mines, on the west side of Prince of Wales Island.

Another type of the copper deposits of the Ketchikan district is represented 

by those occurring in cavities formed by shear zones. Though those deposits 

appear to be largely cavity fillings, there is evidence in some places that they 

are in part formed by replacement of the country rock. The principal metallic 

minerals of the shear-zone deposits are chalcopyrite and pyrite, but they also 

contain some magnetite, pyrrhotite, sphalerite, and galena, as well as some 

gold and silver. Country rock, quartz, and calcite form the gangue of these 

deposits. The shear-zone deposits follow zones of fracture that are parallel to 

the schistosity of the country rock. They are found in various kinds of country 

rock but primarily in greenstone schist, graywacke, and sheared diorite.

There are two phases of the shear-zone deposits. One consists of lenses or 

tabular deposits, many of which are made up largely of rich, massive sulphide 

minerals. These have well-defined walls and are not unlike the cupriferous 

quartz veins described below. The other phase consists of disseminated deposits 

in which the sulphides are distributed through wide zones of sheared country 

rock, generally without well-defined walls. In some of the disseminated deposits 

the sulphide mineralization is rather evenly distributed through the entire 

mass, which may thus be a large body of low-grade ore. More commonly, however, the mineralization is concentrated along certain zones determined by the 

intensity of the shearing. In some of the deposits there has been marked 

silicification over a considerable width, but the sulphide minerals occur chiefly in 

ore shoots and stringer leads limited to certain parts of the whole mass. Practically all these disseminated deposits include ore shoots in irregular and tubular 

masses, and some are of sufficient size to form commercial ore bodies, as defined 

by the methods of mining and recovery that have existed in the past.

Up to the present time mining of the copper ore in shear zones has been 

confined to the lenses and tabular masses occurring either as separate deposits 

or as a part of the lower grade disseminated ore bodies. The larger bodies of 

low-grade disseminated ore have received relatively little attention, and little 

is known of their copper content. It will require much prospecting and careful 

sampling to determine whether they are of commercial importance.

Examples of the shear-zone deposits, including both the concentrated and 

disseminated phases, are found at the Bush & Brown mines, on Karta Bay; at
370 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

Niblack Anchorage and McLean Arm, on the east side of Prince of Wales 

Island; at the Corwin and Red Wing properties, near Hetta Inlet, and on Big 

Harbor (Trocadero Inlet), on the west side of Prince of Wales Island; and on 

McLeod Bay, Dall Island.

There are also in the Ketchikan district some copper-bearing quartz veins and 

brecciated zones. The deposits of this type thus far developed are small and 

have been exploited chiefly because of their silica content. They are essentially 

chalcopyrite-bearing quartz veins but contain also pyrite, sphalerite, tetrahedrite, 

and galena. All carry gold and silver. In some the gangue includes calcite 

and barite. These veins occupy true fissures with well-defined walls and cut 

both sedimentary and igneous country rock. In some the sulphides are well 

disseminated, but more commonly they occur in massive shoots separated by 

more or less barren vein matter. Chalcopyrite-bearing quartz veins are found 

in many places in the Ketchikan district, but most of them are too small to 

warrant development. The largest developments on this type of deposit are at 

the Cimru property, on the north arm of Moira Sound and at the south end of 

Gravina Island.

One other type1 of copper deposit in the Ketchikan district deserves mention, 

even though as yet only one example of it has been developed. This occurs in 

pyroxenite with gabbroic phases1 and appears to have been deposited in a very 

irregular zone of fracture. It carries bornite, chalcopyrite, and metals of the 

platinum group, chiefly palladium. The gangue is practically all country rock. 

This deposit, on which the Salt Chuck mine is located, was first opened as a 

low-grade copper deposit, but its present importance is due to its content of 

palladium and platinum.

Gold. Gold veins predominate in the area northwest of Dolomi 

and in the vicinity of Hollis, on Twelvemile Arm of Kasaan Bay, 

extending northwest toward Klawak Salt Lake. Gold quartz veins 

are reported in the diorite at Katz Harbor and in the diorite near 

Shakan. On Woewodski Island, in Duncan Canal, several veins have 

been prospected for gold. The mineralized belts near Dolomi and 

Hollis are described below by Chapin.

The Dolomi mineral belt is grouped around the two convergent 

valleys of Paul and James Lakes, which drain into the stream that 

enters the bay near the town. The ore deposits occur in the limestone, 

greenstone, and schist of the Wales group, and it is not unlikely that 

they are on the same mineralized belt in which occur the Dora Lake 

and Kitkun Bay deposits. The ore minerals are gold, pyrite, chalcopyrite, tetrahedrite, sphalerite, and galena, which occur in welldefined veins of quartz that are fairly persistent and may be traced on 

the surface for some distance. Some of the veins are of the breccia 

type and are formed along fracture planes or zones by the cementation of the broken-rock fragments by quartz and calcite, with some 

replacement of the country rock by mineralizing solutions.

Twelvemile Arm, on which Hollis is situated, is bordered by lava, 

tuffaceous sediments, and black slate of Middle Devonian age and by 

intrusive quartz diorite. The ore deposits are fissure veins, which 

occur largely in the black slate and associated sediments, and shear-
MINERAL DEPOSITS 371

zone deposits in the greenstone. The fissure veins are valuable 

mainly for their gold content. The vein matter is essentially quartz 

with a little calcite. The veins fill persistent joint planes and in 

places are associated with porphyry dikes, The ore minerals are free 

gold, pyrite, chalcopyrite, galena, zinc blende, and locally a little 

tetrahedrite. The shear-zone deposits in this vicinity are less valuable and have not been developed commercially. They consist of 

brecciated zones in the greenstone metallized by pyrite and chalcopyrite. The principal mining activity has been in the vicinity of Hollis, 

in a mineralized area that lies just south of the quartz diorite of 

Granite Mountain and extends from Hollis northwest for 7 miles or 

more. In this area gold lodes predominate. The country rock is 

mainly black slate and argillite, with some interbedded tuff and 

limestone and associated greenstone flows and breccias. A number of 

lodes have been opened in this gold quartz belt and several small 

plants installed, but none have made large production. This strongly 

mineralized region has never received the attention which it has 

deserved, but it will no doubt be developed in the future. The Kassan Gold Mining Co. is now operating the Dunton mine, on Harris 

Creek.

On Woewodski Island there are impregnated shear zones in greenstone and altered gabbro carrying auriferous pyrite and strongly 

defined quartz fissure veins metallized with sphalerite, pyrite, galena, 

and a little chalcopyrite and free gold. The mineralized belt on 

Kupreanof Island, in the Wrangell district, includes gold and copper lodes, none of which are now being worked. At the head of 

Duncan Canal there is a sulphide replacement deposit consisting 

largely of pyrite and pyrrhotite with a little chalcopyrite. At the 

northwest end of this belt, on Frederick Sound, float consisting of 

slate with chalcopyrite veinlets has been found, and quartz veins 

occur in the greenstone. The geologic conditions in this belt are 

such as to warrant further prospecting for new lodes of copper or 

gold, particularly within the belt of the Middle Devonian beds; 

these beds crop out along both sides of Duncan Canal and extend 

northwest from Duncan Canal to Frederick Sound, where they are 

exposed for 6 or 7 miles to the east of the Pinta Kocks.

CHICHAGOF GOLD BELT

All of Chichagof Island except the western part appears to be 

very similar geologically to Prince of Wales Island, both in the 

character of the county rock and in that of the intrusive masses. 

The number of mineral deposits so far found on Chichagof Island, 

however, is not comparable with the number found on Prince of 

Wales Island. It would seem that there should be contact-metamorphic copper or iron deposits on Chichagof Island locally where
372 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

some of the intrusive rocks come against greenstone and limestone; 

that shear zones with copper minerals should occur in the greenstones ; and that gold-bearing quartz veins should occur in local belts 

of slate or graywacke, or even in the intrusive masses themselves 

near their borders. The possibility of nickel-copper deposits occurring within basic intrusive masses should also be borne in mind.

The Chichagof gold belt has been described by Knopf ,4 Overbeck,5 

and Buddington.6 As now known it includes the belt of bedded 

graywacke, slate, and metamorphic rocks along the west coast of the 

island, west of the igneous batholith, and a part of the batholith 

itself, particularly the northern part. One of the most famous mines 

in southeastern Alaska, the Chichagoff, is in this belt, in the vicinity 

of Klag Bay. Another operating mine, the Hirst-Chichagof, is in 

the same general area, and a third, the Apex-El Nido, is in the 

dioritic batholith near Lisianski Strait. 

Overbeck,7 writing of the vicinity of Klag Bay, says: 

Graywacke is economically the most important rock of the region at the 

present time, because all the prospects so far located are in graywacke, although 

there is no apparent reason why mineralization should not have taken place 

in the schistose series as well. One possible reason for the seeming localization 

of the mineralization in the graywacke isi that the physical properties of the 

massive graywacke under great forces .may have caused it to break with big 

clean fractures that were of great extent and that furnished excellent pathways 

for the ore-bearing solutions. The soft schistose rocks, on the other hand, 

would not give clean breaks or persistent pathways, so the solutions would 

dissipate through the schist and would not concentrate at any one place. 

* * * The Chichagoff ore body is a vein deposit that has formed along a 

shear zone in the argillitic graywacke; * * * it has been followed for over 

4,500 feet [and] may range in width from less -than a foot to 10 feet. The 

ore * * * is distributed in shoots. * * * The gold is associated with 

quartz, which is white and glassy in appearance. * * * Sulphide mineralization and gold mineralization in the quartz seem to be genetically connected.

The Hirst-Chichagof mine is in gold quartz veins in black slate 

near a sheet of greenstone. There are many other prospects on 

auriferous quartz veins in the slate and graywacke. At the head of 

Falcon Arm a sulphide-impregnated diorite aplite dike is being 

prospected.

The gold veins in the dioritic stock are described on page 346.

Knopf,8 in discussing the economic geology of the Sitka district 

in 1912, wrote: " The indications afforded by present developments

* Knopf, Adolph, The Sitka mining district,, Alaska: U. S. Geol. Survey Bull, 504, 1912.

8 Overbeck, R. M., Geology and mineral resources of the west coast of Chichagof Island; 

U. S. Geol. Survey Bull. 692, pp. 91-136, 1919.

9 Buddington, A. P., Mineral investigations in southeastern Alaska: U. S. Geol. Survey 

Bull. 773, pp. 114-125, 1924.

7 Overbeck, R. M., op. cit., pp. 113, 116. 

'Knopf, Adolph, op. cit., p. 32.
MINERAL DEPOSITS 373

point strongly to the conclusion that the entire strip of territory 

contiguous to the west coast of Chichagof Island offers a more encouraging inducement to the search for new ore bodies than any 

other part of the region." This conclusion has been confirmed by 

later developments and still holds true.

In addition to gold, there are several nickel-copper properties 

associated with norite, bronzitite, and gabbroic rocks located in this 

belt at Nickel, also at Bohemia Basin and Surge and Takanis Bays, 

on Yakobi Island. These are described on pages 348-351.

SITKA BELT

In a northwestward-trending belt that parallels Silver Bay, near 

Sitka, on Baranof Island, there is a series of graywacke and slate 

carrying auriferous quartz lodes. This belt has been described by 

Knopf 9 as follows:

The ore bodies occupy shear zones in graywacke and strike parallel to the 

stratification of the country rock. The lodes form massive outcrops of white 

quartz up to 15 feet or more in thickness, which are apt to show a short lenticular structure along the strike and to split up into stringer lodes. They are 

irregular in shape, bellying out and constricting abruptly. Near the lodes the 

country rock is much sheared and is penetrated by numerous transverse 

stringers as well as by veins parallel to the shear planes.

A characteristic feature of the ore bodies is in the insignificant amount of 

metallic sulphides in many ledges almost a vanishing quantity contained in 

the vein quartz. Pyrite, pyrrhotite, and arsenopyrite are the principal sulphides; galena and sphalerite have been observed but are extremely rare. The 

sulphides are at many places concentrated in and around fragments of slate or 

sheared graywacke included in the ledges, even though the quartz itself is 

barren.

There is no producing mine in this belt at the present time, though 

some development work is being carried on.

GENETIC RELATIONS OF THE METALLIFEROUS DEPOSITS

A genetic association of most of the ore deposits in southeastern 

Alaska with the magmas that formed the intrusive rocks of Upper 

Jurassic or Lower Cretaceous age has been postulated by many geologists who have worked in this area.10 Succeeding work has tended 

to confirm this hypothesis. All the ore deposits except those formed 

as magmatic deposits within the basic or ultrabasic rocks are thought 

to have been formed by solutions that had their origin in these molten

 Knopf, Adolph, op. cit., pp. 26-27.

10 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, p. 30, 

1906. Wright, F. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska: 

U. S. Geol. Survey Bull. 347, pp. 41, 76, 1908. Brooks, A. H., Geologic features of 

Alaskan metalliferous lodes: U. 8. Geol. Survey Bull. 480, pp. 43-74, 1911. Knopf, 

Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 446, pp. 

35-30, 1912.
374 GEOLOGY AND MIFEKAL DEPOSITS, SOUTHEASTERN ALASKA

magmas. The solutions may have varied in character from a magmatic type such as that of a pegmatite to a more highly fluid and 

dilute type.

Accepting this generalization concerning origin as valid, we face 

the question whether a particular type of mineralization is prevalently associated with a particular type or mode of occurrence of 

igneous rock; or with a particular type or stage of differentiation of 

the magma; or with a particular type of country rock that has certain specific characters, chemical or physical, or both; or with a par 

ticular environment of temperature and pressure; or whether it is 

dependent upon two or more of these factors to varying degrees.

Hanson 11 has presented a very good statement of a part of the 

problem in a discussion of the origin of the ore deposits on the east 

side of the Coast Range batholith between Skeena River and Stewart, 

B. C.:

Although the mineral deposits along the interior mineral belt have a general 

similarity, the valuable metals are restricted to certain areas in the belt. The 

localization of certain metals into definite areas is of interest, and it would 

be of great importance to discover the explanation for such concentrations. The 

source of the metals is considered as all-important in this connection. If the 

source contains metals, mineral deposits may form. It is not certain that ore 

deposits will result, as other conditions may prevent the deposition and concentration of the metals into ore bodies. The main source of the mineral deposits 

of the interior belt is believed to be the magma of the Coast Range batholith. 

It is probable that there are valuable metals in one part of the batholith which 

are lacking in another part. By very careful discrimination between rock 

types in the batholith in areas of known mineral deposits, some general rules 

may be established which can be applied to other parts of the interior belt.

The country rock in which the ore bodies occur is also of importance, but the 

influence of the country rock pertains chiefly to the size and persistence of the 

veins and to the presence of ore shoots in the vein. The rock in which the ores 

are found has probably not had much influence on the localization of metals 

into areas within a mineral belt. The physical nature of the country rock, 

which has a bearing on the size of fracture, and the chemical nature, which influences replacement of the rock and precipitation of the metals, are here the 

two main factors. The depth at which the ore was formed is also important 

but will not explain the localization of certain metals into areas in one mineral 

belt.

This subject has been discussed by the writer in another publication.12

CHARACTEK OF COUNTRY ROCK

When fluid metalliferous solutions are present the character of the 

country rock has no doubt a very considerable influence in deter11 Hanson, George, Reconnaissance between Skeena River and Stewart, B. C.: Canada 

Geol. Survey Summary Rept. for 1923, pt. A, pp. 44-45, 1924.

12 Buddington, A. F., Coincident variations of types of mineralization and of Coast 

Range Intrusives: Econ. Geology, vol. 22, pp. 158-179, 1927.
MINERAL DEPOSITS 375

mining the type of ore deposit contact, impregnation, fissure vein, 

"stringer lead," or others and under some conditions in localizing 

its formation within certain types of rock or bed for example, the 

formation of the contact type of deposit in limestone or certain 

greenstone tuffs. The general relations of ore deposits to the formations in southeastern Alaska have been discussed on pages 338-356.

The copper-iron contact deposits of Prince of Wales Island occur 

predominantly in limestone, greenstoife tuff, and tuffaceous graywacke. The copper impregnation deposits tend to occur in schistose 

varieties of greenstone or tuffaceous graywacke and in limestone 

layers or lenses interlayered with them. The chemical character of 

the rock appears to have been a very potent factor here in localizing 

the ore deposits. Where schistose rock forms the walls of contact 

deposits the mineralization is less concentrated, and the sulphides 

are more disseminated in the contact rock and penetrate the schist 

for some distance from the contact with the intrusive.

Mineralized quartz veins are relatively uncommon in the limestone.

In the Hyder district, where mineralized veins occur in granodiorite, graywacke, slate, and greenstdne, pyrrhotite is abundant only 

in the replacement veins in the greenstone, and its relative restriction to rock of this type appears to be definitely related in some way 

to the composition of the greenstone.

The strength of the rock, of course, has its effect. Quartz veins 

in slate usually do not persist to great length and depth, though 

several or many may occur together to form a " stringer lead." 

However, along the contact between slate and a strong bed of graywacke or a dike, the veins may develop to great length and depth. 

Here the physical character of the country rock is the determining 

factor.

TYPE OF ASSOCIATED IGNEOUS ROCK AND TYPE OR STAGE OF MAGMATIC

DIFFERENTIATION

The genetic association of certain kinds of mineralization with certain kinds of ultra,basic and gabbroic igneous rock is clear and definite. Many of the metalliferous minerals or solutions did not travel 

outside of the igneous mass that gave them birth. Thus the nickelcopper deposits are absolutely restricted to and occur actually within 

rocks of the ultrabasic or gabbroic group; the ilmenitic magnetite 

tends to occur in concentrated amounts with the hornblendite and 

pyroxenite; the only copper-palladium deposit that has been found 

occurs in an ultrabasic rock, pyroxenite; apatite tends to be concentrated with the hornblende.

For the more siliceous and alkalic rocks, however, the problem of 

relating kinds of mineralization to kinds of igneous rock becomes 

6137 29 25
376 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

immensely more complicated. The metalliferous solutions may have 

wandered far from their parent magma; external factors may thereby 

have had a great influence; differentiation may have taken place 

within the solutions themselves; and there may have been overlapping 

effects due to the various stages of differentiation reached by individual bodies of magma within a particular region or by the magma 

of the same stock or batholith at successive times.

The relation of magnetite to the type of rock and degree of magmatic differentiation is especially clear, as shown by the table below:

Relation of magnetite to stage of magmatic differentiation

Content of magnetite (per cent)

Kange

Trace to 2.. .......... -.... .. ......

Trace to 12............... ..................

Average

±0.5

±1

1 to 2

5

There is a very marked increase in the percentage of magnetite in 

the more basic and less siliceous types of rock. In the dunite, however, magnetite normally forms at most only a few per cent of the 

rock. In the basic and ultrabasic rocks ilmenite is associated with 

the magnetite in small amounts. In the pyroxenite the magnetite 

occurs predominantly in disseminated interstitial blebs. In the hornblendite, which is believed to owe its origin in part to a relatively 

high content of volatile materials, the magnetite may occur as veinlets and vein dikes. The mobility of the iron solutions from the 

hornblendite magma has thus evidently been increased by the higher 

percentage of volatile material. In the diorite, monzodiorite, granodiorite, and more granitic masses this mobility of the metalliferous 

solutions is apparently still further increased, as indicated by the fact 

that magnetite and specularite occur locally in large amounts replacing the country rock near or adjacent to the intrusive mass.

The relationship of copper, which occurs predominantly in the 

form of chalcopyrite, forms a very interesting problem. It is found 

associated with a little pentlandite and a relatively large amount of 

pyrrhotite within certain types of gabbroic and ultrabasic rocks, 

where it occurs disseminated and in solid lenses; locally within certain gabbroic rocks it also forms veinlets in fractured zones. Bornite 

occurs at one place as disseminated deposits and veinlets in pyroxenite. 

Copper minerals are not concentrated along with magnetite and are 

not associated with it in the pyroxenite or hornblendite. In association with gabbroic and ultrabasic rocks chalcopyrite has a greater
MINERAL DEPOSITS 377

tendency than magnetite to occur in veinlike form, even where the 

associated rock is of the same type.

In association with diorite, monzodiorite, and granodiorite chalcopyrite, like magnetite, exhibits the results of a greater mobility than 

in association with basic and ultrabasic rocks, inasmuch as it occurs 

typically in the country rock as contact deposits adjacent to the intrusive body or in shear zones or impregnation deposits at considerable distances from the intrusive. Here also the chalcopyrite shows 

a relatively greater tendency to move out farther away from the 

same general magma than the magnetite.

Dolmage 13 has suggested as a possibility that chalcopyrite tends 

to occur to a greater extent with granodiorite than with diorite. 

He writes:

Copper occurs at numerous places along this part of the west coast. The 

occurrences are, without exception, of the contact-metamorphic type and are 

formed near the contacts between the limestones of the Vancouver group and 

the intrusions of granodiorite or diorite of the Coast Range butholith. At or 

near every observed contact of these two rocks copper and iron minerals were 

found in the altered limestones and in some places in large amounts. At the 

diorite contacts le.ss copper and more iron are found, but at the granodiorite 

contacts copper predominates. * * *

The deposits mny be found within a few feet of the granitic contact or at 

a distance of several thousand feet. They may be formed in thick beds of 

metamorphosed limestone free from any volcanic rock or, as is more often 

the case, they are in thin beds of limestone between beds of volcanic rocks 

which are also highly metamorphosed and metallized.

The Treadwell gold deposits on Douglas Island occur in fractured 

and metallized albite diorite and albite monzodiorite sheets. Knopf 14 

reports a number of albite diorite dikes between Juneau and Auke 

Lake, some of which have been mineralized and altered. He writes 

of them as follows:

This highly interesting kind of mineralization is essentially similar to that 

which has affected the Treadwell dikes, * * * but it by no means follows 

that mineralization of this character was everywhere accompanied by the 

formation of gold deposits of commercial value. Nevertheless, it is a favorable 

feature, and in view of the fact that such dikes contain enormously valuable 

ore bodies on Douglas Island, efforts should be made to prospect thoroughly 

the albite diorite dikes of the mainland.

Mertie 15 reports albite granite (or albite-quartz diorite), albite* 

syenite (or albite diorite), and albite trachyte associated with gold 

veins at Funter Bay, on Admiralty Island. He writes: ' a c

All the acidic and intermediate types of intrusive rocks examined by the 

writer contain albite or oligoclase-albite plagioclase feldspar. * * * This

13 Dolmage, Victor, West coast of Vancouver Island between Barkley and Quatsino 

Sounds : Canada Geol. Survey Summary Kept, for 1920, pt. A, p. 19, 1921.

14 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, p. 36, 1912.

16 Mertie, J. B., Lode mining in the Juneau and Ketchikan districts: U. S. Geoi. Survey 

Bull. 714, pp. 114-115, 1921.
378 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

feature is of more than passing interest when considered in relation to the 

sodic character of the intrusive rock at the Treadwell mines, on Douglas Island, 

about 15 miles to the east. It is not unlikely that mineralization at these two 

localities took place at the same general period and had a similar origin.

The gold-bearing veins with high-grade shoots at the Apex-El 

Nido mine, on Chichagof Island, are in fissures in aplite dikes which 

are so altered as to be indeterminate but may have been originally 

albite aplite or albite trachyte. Albite trachyte dikes are found 

near by. At the Pinta Bay and Miner Island prospects albite-quartz 

diorite is the country rock. Gold-bearing lodes are thus associated 

with highly sodic rocks at several widely separated localities, and the 

relation suggests that both may have had a more or less common 

genetic origin and have been dependent upon a certain type of magmatic differentiation. The local association of gold deposits with 

albite diorite and albite-quartz diorite in the Mother Lode* district 

of California has been described by Turner 10 and Reid. 17 McCann 18 

has described an association of gold quartz veins with albitite dikes 

in the Bridge River area, on the east side of the Coast Range 

batholith.

Gold quartz veins occur within the igneous rock of several stocks, 

such as the Jualin diorite stock, in the Berners Bay district; the 

Lisianski stock of diorite, on Ohichagof Island; and the quartz 

diorite stock on the west side of Twelvemile Arm, Prince of Wales 

Island. Quartz veins with gold-silver-lead shoots whose predominant value is in lead occur within the Texas batholith of granodiorite, 

in the Hyder district. This batholith must have had a relatively low 

percentage of water, as is indicated by its pronounced gneissic structure, the occurrence of hornblende almost to the exclusion of biotite, 

the practical lack of pegmatite dikes, the lack of contact metamorphism, and the sparseness of aplite dikes and their restriction to 

a zone within 500 feet of the contact.

It has been shown on pages 177-181 that there is a progressive 

though somewhat irregular change in the average character of the 

igneous rocks from the southwest in the Prince of Wales-Chichagof 

belt (quartzose diorite) through the Wrangell-Revillagigedo belt 

(quartz diorite) and the western part of the core of the main batholith 

(granodiorite) to the northeastern part of the core of the main 

batholith (quartz monzonite). The question arises whether these 

rocks, representing as they do increasingly more advanced stages of 

magmatic differentiation, can be correlated with a corresponding 

change in metallization.

18 Turner, H. W., Replacement ore deposits in the Sierra Nevada: Jour. Geology vol 7 

pp. 389-400, 1899.

17 Reid, J. A., The east country of the Mother Lode: Min. and Sci. Press, vol 94 pp 

279-280, 1907.

18 McCann, W. S., Geology and mineral deposits of the Bridge River map area, B. C.: 

Canada Geol. Survey Mem. 130, p. 67, 1922.
MINERAL DEPOSITS 379

The largest number of copper deposits are on Prince of Wales 

Island, where they are associated with rocks which, as exposed, represent an intermediate stage in the differentiation sequence of southeastern Alaska and which occur as small batholiths, stocks, and 

sheets. These rocks are described on pages 183-186. Their average 

composition is approximately that of a quartzose diorite. Gold veins 

are also common in this belt. Magnetite or pyrrhotite is associated 

with the copper deposits to such an extent that copper and iron may 

be said to be the predominant metallic elements.

To the east, between the Prince of Wales-Chichagof belt and the 

Coast Kange batholith, is the Wrangell-Revillagigedo belt of intrusive rocks, in which, on the average, a more advanced stage of 

differentation is represented and the igneous rocks have the average 

composition of quartz diorite. Metalliferous deposits in this belt are 

relatively sparse, though quartz veins are abundant. Gold is predominantly the metal sought in what mineral deposits there are. 

Only two copper deposits are reported in this entire belt. The gold 

veins are mainly in the western part of the belt adjacent to the batholith. The intensely recrystallized metamorphic rocks represent relatively high temperature and high pressure; and it seems probable that 

the chief causes of the relative absence of metalliferous deposits here 

may be temperature and pressure and the schistose character of the 

rock. Many zones impregnated with sulphides of iron carrying a 

little gold occur in the schist, and it is possible that the gold was 

disseminated through a large volume of rock rather than concentrated 

in workable veins. The Wrangell-Revillagigedo belt may overlie an 

upward outward major bulge in the batholith where most of its 

upper surface is .now at only shallow depths and the exposed stocks 

and batholiths are equivalent to hills on its surface. The country rock 

immediately above the batholith would be relatively highly heated by 

conducted heat and by the passing of highly heated vapors, and the 

metals might not be deposited in concentrated form until the solutions reached a less schistose and cooler rock higher up, which has 

since been eroded.

The Wrangell-Revillagigedo belt of schist and gneiss, with its 

associated abundant intrusive rocks, dies out toward the northwest. 

Its place is taken by the Juneau gold belt, with slate, graywacke, 

dynamically metamorphosed schistose greenstone, and relatively 

sparse associated intrusive rocks similar to those of the Prince of 

Wales-Chichagof belt. This decrease in number of intrusive bodies, 

their change in character, and the decrease in metamorphism and 

practical disappearance of aplitic injection gneiss are explicable on 

the assumption that the Wrangell-Revillagigedo bulge in the batholith has an irregular shelf or terrace-like form and drops away rela-
380 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

tively abruptly northwest of Thomas Bay, giving the western border 

of the batholith in the Juneau district a very steeply plunging slope 

that carries it to great depth. The rocks that now form the Juneau 

gold belt would therefore have been at a greater distance above the 

batholith and in a cooler environment than those to the southeast; 

what intrusive bodies there were would extend a long way vertically 

from their source, and the same would be true of the auriferous quartz 

veins. Such a hypothesis would suggest that temperature was the 

determining factor and that the ore deposits and the exposed dioritic 

and sodic intrusive rocks were both genetically associated with a 

common deeper-seated magma. Copper deposits are rare, perhaps in 

part owing to the relatively few intrusive stocks and in part to the 

character of the intrusions or of the country rock. Copper occurs in 

limestone and schistose greenstone at Point Astley and at William 

Henry Bay, on Lynn Canal.

Very few mineral deposits have been discovered in association with 

the quartz diorite of the western part of the batholith. There is a 

copper-zinc deposit at Tracy Arm and zinc and silver-lead deposits at 

Groundhog and Glacier Basins, east of Wrangell. The deposits at 

Groundhog and Glacier Basins are associated with quartz porphyry 

sheets, and it might be questioned whether they are genetically connected with the quartz diorite or with the porphyry. There is a silverlead deposit on Whiting Eiver. To the southeast,19 near Vancouver, in 

British Columbia, there is a zinc deposit with some galena at the contact with a basic marginal variant of the quartz diorite, and between 

Powell Kiver and Lund there is a prospect in which zinc is the prevailing metal. Copper deposits are also known. The data are too 

few to afford adequate evidence as to what is the predominant type 

of metallization in association with the western portion of the 

batholith. The occurrence of two contact-metamorphic zinc deposits 

is in marked contrast to the typical copper-iron contact deposits of 

the Prince of Wales belt. The few data available suggest that copper 

and zinc and to a lesser extent gold and silver-lead prevail.

The rocks within the core of the Coast Range batholith are predominantly granodiorite and quartz monzonite, with local developments of quartz diorite and other types, and they represent on an 

average a more advanced stage of differentiation than the rocks of 

the western border. Relatively few metalliferous prospects are 

known. The copper deposits of Anyox and Maple Bay, on Portland 

Canal, British Columbia, are the best known. Silver-lead and zinc, 

copper, and lead veins are found in the included sedimentary belt 

along Unuk and Iskoot Rivers. The known metallization is such as

18 Brewer, W. M., Some ore deposits of the Coast Range: Canadian Inst. Min. and Met. 

Monthly Bull., vol. 127, pp. 1176-1191, 1922.
M1NEEAL DEPOSITS 381

to suggest an increasing abundance of lead in the form of galena 

relative to zinc and copper.

The northeastern border belt of the Coast Range batholith between 

Portland Canal and Chickamin River is quartz monzonite. Quartz 

fissure veins carrying hematite or martite and pyrite are found, 

but no metalliferous deposits of economic value are known within 

this belt.

In the belt east of the batholith there are locally outlying masses of 

intrusive rock, but information as to their exact character is lacking. 

The problem is further complicated by the presence of Jurassic or 

Lower Cretaceous intrusive rocks of two ages. However, a number 

of stocks are known which consist predominantly of quartz diorite or 

granodiorite, or quartz monzonite. Galena and tetrahedrite are far 

more abundant in the veins here then in any other belt, and sphalerite 

and chalcopyrite are common. Native silver, pyrargyrite, proustite, 

and argentite are valuable ore minerals, but they are thought to have 

been formed mainly through processes of enrichment and are only in 

small part of primary origin. The metallization is marked by the 

relative predominance of silver and silver-lead ores in contrast to 

any of the other belts. Gold and base-metal (copper, lead, and zinc) 

lodes are also common. Mineral deposits with galena in association 

with typical contact-metamorphic minerals such as andradite garnet 

are reported to occur on Stikine River near Devils Elbow.

Green-gray to green-black dike rocks cut across many of the ore 

bodies. In part these dikes are of lamprophyric character, in part 

they may be younger basalt dikes of Tertiary age, and in part they 

may be malchite dikes genetically associated with a younger facies 

of the Coast Range batholith, as in the Salmon River district.

From the foregoing description it would appear that certain types 

of metallization are characteristic of certain belts and that the 

changes in the predominant types of metallization from one belt to 

another are in part coincident with changes in the predominant type 

or types of associated igneous rocks. But the type of metallization 

within a given belt is not wholly uniform; for instance, lead deposits 

and silver-lead veins are known within the Prince of Wales copperiron belt. Neither is the composition of the igneous rocks within 

a given belt completely uniform; albite-quartz diorite or granodiorite 

occurs within the Prince of Wales belt where andesine diorite or 

quartzose dioritic rocks predominate, ,and diorite is found within 

the core of the Coast -Range batholith where granodiorite and quartz 

monzonite predominate. If the stage or type of magmatic differentiation is a determining factor in the type of associated metallization we should therefore expect to find as wide ,a range in the types 

of metallization within a belt as in the types of igneous rocks within 

that belt.
382 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The known facts do not prove whether the change in the type of 

metallization is genetically related to the difference in stage of magmatic differentiation represented by the associated or underlying 

rocks, or whether the magmatic differentiation is only one of ,a 

number of factors; or whether the relation is one of mere fortuitous 

coincidence and some other factor or factors, such as temperature or 

rock type, and mode of occurrence of the igneous mass, has exercised 

the predominant control.

MODE OF OCCURRENCE OF IGNEOUS MASS

Emmons 20 has classified mineral deposits with relation to the 

contour of the roof of the parent batholith that is, with respect to 

the mode of occurrence of the genetically associated igneous mass. 

This grouping is given below:

1. Cryptobatholithic, near hidden batholiths which have not been exhumed by 

erosion.

2. Acrobatholithic, in and near cupolas or domes of batholiths, high points of 

larger underlying masses.

3. Epibatholithic, on batholiths, near their rims but below eroded cupolas or 

below the highest points of the roofs.

4. Embatholithic, among closely spaced outcrops which are probably parts of 

a single batholith. The outcrops of invaded rocks predominate.

5. Endobatholithic, in and near roof pendants of large batholiths. The invading rocks predominate.

6. Hypobatholithic, in deeply eroded batholiths where even roof pendants 

have been eroded.

In a general way the mineral deposits of the eastern border belt 

are in groups 2 and 3, acrobatholithic and epibatholithic; those of 

the Prince of Wales-Chichagof belt are in groups 3 and 4, epibatho 

lithic and embatholithic; those of the Wrangell-Kevillagigedo belt 

are in groups 4 and 5, embatholithic and endobatholithic; and those of 

the Coast Range batholith belt in groups 5 and 6, endobatholithic 

and hypobatholithic.

Emmons 21 gives a diagram, reproduced here as Figure 3, which 

shows the relative amounts of metals developed, as a rule, in each of 

the six groups.

The mineral deposits within the belts described in this paper conform in a general way to the appropriate mineralization for the 

type to which they belong, as described by Emmons, with the exception of the Coast Range batholith belt. Within this belt, according 

to Emmons's table, gold should predominate, but so far as the present information goes, this is not the case. Emmons says, how20 Emmons, W. H., Relations of the disseminated copper ores in porphyry to igneous 

intrusiyes: Am. Inst. Min. Eng. Trans., vol. 75, pp. 797-809, 1927.

21 Emmons, W. H., Relations of metalliferous lode systems to igneous intrusives : Am. 

Tnst. Min. Eng. Trans., vol. 74, p. 33, 1926.
MINERAL DEPOSITS 3S3

ever, that in the endobatholithic group "gold deposits greatly predominate, but a few valuable copper deposits and a small number of 

lead, silver, zinc, and other metals are found." Emmons states further that in groups 2 and 3 gold deposits are commonly found around 

and outside of the area of copper deposits, but that in group 4 the 

order may be reversed, with gold close to the batholith and copper 

farther out. Emmons's generalizations suggest that in the prospecting of the Coast Range batholith gold deposits might be sought for 

in the vicinity of included blocks of country rock.

Within each group of deposits, as classified by Emmons according 

to their environment, the stage and type of differentiation reached by

Jepfh oferosiop 

Of Ba+holi'+h

No ba+holith 

exposed

2. Acroba-fho/ifhic

In and near

cupolas

S.Epiba+holith/c

Saielliiie, bul bzlow 

eroded cupolas

Among closely spaced 

bo thoflrhs

5. Endoba+holH-hic 

In and near 

ro o fp en flan ~fs

6. Hypoba+holi-l~hic

In very deeply 

eroded baiholifhs

Au. Sn W Cu ZTI

FIGURE 3. Diagram showing the relative amounts of different 

metals deposited in lodes at six different positions on their 

parent batholiths. (After W. H. Emmons)

the intrusive magma must differ considerably within the same or different regions. Certainly this must introduce a factor that tends, 

even though only in a slight degree, to modify the character of the 

accompanying mineralization.

TEMPERATURE AND PRESSURE

All the metalliferous deposits associated with the intrusive rocks 

of Upper Jurassic or Lower Cretaceous age have been formed under 

conditions of intermediate to high temperature, as indicated by 

their associations and mineral content and by the type of alteration 

of the wall rock accompanying the introduction of the veins. They 

have been formed throughout a vertical distance of 5,000 feet, as 

determined by actual observation, and by inference throughout 10,000 

feet or more. They must have crystallized at considerable depth, for,
384 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

so far as we know, erosion has been taking place over the uplands ever 

since the intrusion of the Coast Range igneous masses in Upper 

Jurassic or Lower Cretaceous time. They are therefore intermediate 

to deep-seated and were formed under high pressure.

Schofield 22 has discussed the occurrence of different types of metallization in belts in British Columbia as follows:

There are two main mineral belts in British Columbia separated from each 

other by an elongated and curved area of granite batholiths belonging mainly 

to the early part of the Mesozoic era. This mass includes the Coast Range 

batholith and the majority of the batholiths occurring in the southern part 

of British Columbia. The belt which follows along the Pacific coast, including 

the island fringe, may be called the Pacific mineral belt; that on the eastern 

side of the same batholith the Interior mineral belt. It will be remarked that 

the two belts differ in the mineralogical composition -of their ore bodies. The 

ore deposits of the Pacific belt are sought mainly for their copper content; 

those of the Interior belt are sought mainly for their gold, silver, and lead 

content. * * * .

The reason for the separate occurrence of copper on the one border and of 

gold, silver, and lead on the other border' of the great complex of igneous intrusions is not at once apparent. A fact that may throw some light on the 

subject is that the copper deposits resemble conditions of high temperature 

and pressure, even bordering on those of contact deposits, whereas the goldsilver and silver-lead deposits are usually, though not always, associated with 

fissure veins filled under conditions of a moderate temperature and pressure. * * * Not only is there a contrast between the ore deposits on the 

two sides of these batholithie masses but also a contrast in the degree of 

metamorphism exhibited by the prebatholithic rocks.

The Wrights 23 ascribe the greater metamorphism on the west 

flank as compared with the east flank to deeper burial at the time of

intrusion of the batholith. Schofield,24 on the other hand, thinks that

. the difference in types of metallization and metamorphism is due

not to deeper burial on the west as compared to the east but to 

differences in the slope and relations of the upper surface of the 

batholith to the present topographic surface. He assumes that, 

owing to relatively less deep erosion, a relatively flat upper surface 

of the batholith is present at or beneath the surface on the west and, 

owing to deeper erosion, a steeply plunging contact on the east. 

Thus on the east the veins, except a few adjacent to the batholith, 

would be at considerable heights above the batholith, in a cooler zone, 

and would be of intermediate-temperature type, whereas those on 

the west would everywhere be only a relatively short distance above 

the surface of the batholith and therefore in a hot zone and of the 

high-temperature type.

22 Schofield, S. J., and Hanson, George, Geology and ore deposits of Salmon River district, B. C.: Canada Geol. Survey Mem. 132, pp. 63-64, 1922.

23 Wright, P. B. and C. W., The Ketchikan and Wrangell mining districts, Alaska : U. S. 

Geol. Survey Bull. 347, pp. 65-68, 1908.

-* Schofield, S. J., and Hanson, George, op. cit, pp. 65-66.
MINERAL DEPOSITS 385

Schofield's broad generalizations for British Columbia need to be 

considerably modified to be adaptable to the phenomena in southeastern Alaska. Slopes on the west side of the batholith are locally 

just as steep as those on the east side, and it seems probable that the 

differences are original and are not due to differences in depth of 

erosion. The main copper belt here is not associated directly with 

the western border of the batholith but with a belt of outlying stocks 

that are in general considerably more basic. A gold belt lies between 

the copper belt and the batholith, and zinc as well as copper appears 

to be abundant along the western border of the batholith. Schofield's explanation would make temperature conditions at the time of 

deposition the controlling factor in causing the differences in type 

of metallization found within the separate belts. This is also the 

factor considered in general to be of major importance in producing 

the variation in metallization of veins at increasing distances from 

a magmatic center with which they are connected, and also in producing the variation in metallization of veins with increasing depth 

types of phenomena both of which are found in many other metalliferous regions. The sequence in the types of predominant 

metallization in southeastern Alaska is similar to the usual sequence 

of ores occurring in zones, in both a vertical and a horizontal sense, 

the high-temperature iron-copper-gold types being on the southwest, 

nearer the magmatic center, and the intermediate-temperature silverlead-gold types on the northeast. These relations, therefore, seem to 

support Schofield's hypothesis, and there is no doubt that temperature 

is a major factor in the problem.

The relation of the western border of the batholith to the Juneau 

gold belt is similar to the relation of the eastern border of the batholith to the gold-silver-lead belt as described by Schofield. The gold 

veins in the Juneau belt are classified as high-temperature veins by 

Lindgren, though they must be close to the border line of intermediate-temperature veins, and the gold-silver-lead veins of the Salmon 

River district are intermediate. Temperature may therefore be a 

chief cause of the difference between them, though the degree of 

differentiation of the genetically associated magmas may also have 

been a cause.

The occurrence of contact copper deposits in the belt of dioritic 

rocks on Prince of Wales Island, of contact zinc deposits with the 

quartz diorite of the western border of the batholith. and of a contact lead-bearing deposit on the eastern border of the batholith associated with quartz monzonite, all in limestone, necessitates an appeal 

to some factor other than temperature to explain such differences in 

metallization.' This factor may be original differences in the composition of the magmas or in the stage of magmatic differentiation
386 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

with which the ore deposits were genetically connected. The magma 

that produced the lead deposit may itself have been at a lower temperature than the magma that produced the copper deposits, but 

both kinds of deposits are associated with typical contact-metamorphic 

minerals.

The origin of the contact deposits of Prince of Wales Island has 

been described by Wright 25 as follows:

In the limestone tremolite (or wollastonite) and diopside were formed by 

the introduction of silica; later, and in part contemporaneously, garnet was 

formed by the combination of lime (already present) with silica, ferric iron, 

and alumina, introduced by solution. While the quartz and feldspars were 

being removed from the diorite calcite, garnet and pyroxene (diopside) were 

added. Afterward chalcopyrite and pyrrhotite replaced part of the calcite in 

the contact zone without notably affecting the other minerals. Later the 

fissures, which probably held the solutions during the period of active metamorphism, were filled with pyrite. chalcopyrite, magnetite, and the other 

minerals above enumerated. Finally upon the older vein minerals were deposited notably zeolite and calcite. * * *

The garnet, some of which probably formed almost contemporaneously with 

the wollastonite, is a variety having distinct double refraction. Experiments 

made with this garnet by Doctor Merwin at the Geophysical Laboratory of the 

Carnegie Institution of Washington show that it loses its birefringence after it 

has been heated for a few hours at about 800° C., and does not regain it after 

several hours heating at 600° C. This fact indicates that most of the metamorphism took place at temperatures lower than 800° C.

Quartz occurs in the contact zone only in veins. Tests made on some of 

this vein quartz by F. E. Wright * * * indicated that it was formed at 

temperatures below 575° C.

Eskola 2G quotes Goldschmidt as authority for the statement that 

where wollastonite is present the temperature during metamorphism 

has exceeded a certain limit that varies with the pressure. At 

atmospheric pressure this limit should be about 500° C.; at increasing pressure the limit would rise, at first rapidly, then more and 

more slowly, being about 850° C. at 300 atmospheres and 950° C. at 

15,000 atmospheres. The temperature during the period of contact 

metamorphism, therefore, probably lay between 500° C. and 800° C.

HYDROTHERMAL ALTERATIONS IN THE IGNEOUS ROCKS

The igneous rock of the Coast Eange batholith is in general only 

very slightly altered except in local areas where metalliferous veins 

are present. The alteration products commonly found include chlorite altered from biotite in such a way as to resemble parallel intergrowths of biotite and chlorite and probably formed at a late mag2B Wright, C. W., Geology and ore deposits of Copper Mountain and Kasaan Peninsula, 

Alaska: U. S. Geol. Survey Prof. Paper 87, p. 108, 1915.

20 Eskola, Pentti, On the petrology of the Orijarvi region in southwestern Finland, pp. 

160-162, Helsingfors, 1914.
MINERAL DEPOSITS 387

matic stage, chloritically altered hornblende, here and there plagioclase slightly sericitized, and very rarely a bit of muscovite replacing 

biotite.

The outlyling stocks of grariodiorite, monzodiorite, and diorite, 

however, commonly show a noteworthy degree of alteration, at some 

places with accompanying metallization, at some places without. 

The feldspars and ferromagnesian minerals are considerably altered 

epidote with some zoisite and flecks or aggregates of sericite. Many 

of the very small stocks and the sheets and dikes are so altered that 

the determination of the original character of the rock is in doubt. 

The albite-leucoquartz diorite bodies are as a rule very highly altered, and muscovite is as abundant as epidote and zoisite in these 

smaller altered masses. A peculiar character of these alterations is 

that most of the potassic feldspar is fresh and unaltered, and the 

biotite is fresh and only sparsely replaced by epidote.

In a belt adjacent to Stephens Passage, from Port Houghton north 

to Point Astley, the igneous rocks have been subjected to considerable 

crushing and the inclosing schist has been isoclinally folded and plicated. The minerals of the igneous rocks have been almost entirely 

replaced by muscovite and zoisite with a little epidote or by muscovite and epidote with a little zoisite. The muscovite is commonly in 

plates forming a latticework parallel to the cleavage of the feldspar. 

The potassic feldspar is practically unaltered. On the contrary, 

many other highly mashed shear zones in the ultrabasic and more 

alkalic-siliceous granitic rocks, both in the stocks and within the 

Coast Kange batholith itself, do not show any intensification of 

alteration.

Alterations such as those noted would suggest that the invading 

solutions were of magmatic origin, highly heated, and with a relatively high potassic content to form the high-potassium mica muscovite and to leave relatively unaltered the iron-potassium mica biotite 

and almost completely unaltered the potassic feldspars microperthite, 

microcline, and orthoclase. These alterations, at most places, do not 

appear to have been associated with metalliferous veins.

On the other hand, in all the areas of intrusive rocks of Upper 

Jurassic or Lower Cretaceous age in which metalliferous veins occur 

the rock is more or less highly altered and has a consequent dull, 

dead appearance even on a fresh surface. Areas of such rock warrant prospecting.

In the Hyder district the belt of quartz diorite and granodiorite in 

which the gold-silver-lead quartz veins occur is much altered. The 

plagioclase is partly to completely altered to sericitic aggregates with 

associated epidote and carbonates, and the hornblende and biotite are 

altered to chlorite with associated epidote, zoisite, ilmenite, and
388 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

locally muscovite or biotite. The potassic feldspars are practically 

unaltered. The quartz is usually strained and ribboned by stress and 

crushing.

Similarly, the belt of the Lisianski stock of diorite on Chichagof 

Island in which the auriferous quartz veins occur is considerably 

altered. Veinlets of yellowish-green epidote and white zoisite are 

common. Adjacent to the vein$ the feldspars are almost completely 

altered to aggregates of sericite with a little chlorite and carbonate. 

Sericite, epidote, carbonates, and chlorite, with a little ilmenite, are 

the common alteration minerals.

The hydrothermal alteration of the adjoining igneous rocks that 

accompanied the invasion of the metalliferous vein-forming solutions 

in the Juneau gold belt at the Treadwell mine, in the Jualin diorite, 

and in other igneous rocks has been described in detail by Spencer 27 

and Knopf.28

At the Treadwell mine the original rock contained albite-oligoclase, microperthite, a little hornblende, and biotite. The original 

minerals are clouded with alteration products, and the secondary 

minerals include abundant albite (which in part replaces or veins 

microperthite), quartz, calcite, sericite, epidote, zoisite, chlorite, uralite, rutile, magnetite, and introduced sulphides.

In the Jualin diorite, according to Knopf, the general course of the 

alteration consisted in the chloritization and destruction of the f erromagnesian minerals, the partial sericitization of the plagioclase feldspar, the formation of albite, and the introduction of carbonates 

(dolomitic in part) and pyrite. Away from the most intensely 

altered parts epidote and chlorite appear as alteration products of the 

hornblende and epidote of the plagioclase. The biotite is partly 

chloritized. Knopf writes:

The chemical work done by the ore-depositing agencies shows that they were 

hot ascending solutions carrying carbon dioxide, sulphur (probably as hydrogen 

sulphide), silica, potash, gold, iron, and several heavy metals in small quantities, 

and doubtless other constituents that have left no record. * * * At one 

locality the solutions were capable of causing the formation of tourmaline as 

well as producing sericitization and carbonatization.

In the Eagle River region, near a network of auriferous veinlets, as 

described by Knopf, an amphibolite consisting mostly of actinolite 

with associated epidote and albite and a little biotite has been altered 

to an aggregate of albite and biotite with considerable associated

27 Spencer, A. C., The Juneau gold belt, Alaska: U. S. Geol. Survey Bull. 287, pp. 

99-103, 1906.

28 Knopf, Adolph, The Eagle River region, southeastern Alaska: U. S. Geol. Survey Bull. 

502, pp. 36-41, 1912; Geology of the Berners Bay region, Alaska : U. S. Geol. Survey Bull. 

446, pp. 31-34, 1911.
MINERAL DEPOSITS 389

zoisite and new apatite. It is believed that the chemical changes were 

a large addition of soda and potash for the formation of albite arid 

biotite, heavy losses in magnesia, lime, and iron, and an enrichment in 

phosphoric pentoxide to form apatite.

The work of Spencer and Knopf shows that in the Juneau gold 

belt albitization was a common and noteworthy mode of alteration 

of the wall rock and that sericite, epidote, zoisite, chlorite, and carbonates were other common secondary minerals formed. Locally 

rutile, apatite, or tourmaline was introduced, or a biotite-albite rock 

with zoisite was formed from an amphibolite with associated epidote 

and albite.

Throughout the crystalline schist and much of the phyllite tourmaline and apatite occur as accessory minerals in a manner suggesting that they have been introduced by solutions or vapors which permeated them. Albite similarly appears to have been introduced into 

schist during its metamorphism at many places, as in the belt containing auriferous quartz veins between Funter Bay and Hawk Inlet, 

on Admiralty Island.

The rocks in which the nickel deposits occur are in places considerably altered. At the Bohemia Basin claims, on Yakobi Island, 

and at the deposit on Funter Bay pyroxene and olivine have locally 

been altered to or veined by serpentine. This alteration was later 

than the introduction of the sulphides. Kerr 20 reports that at the 

Alaska Nickel mines, on Chichagof Island, the hornblende and pyroxene are locally replaced by tremolite that is later than the sulphides. 

These phenomena indicate that in these deposits the sulphide masses 

bearing nickel and copper are of magmatic origin, and that their 

segregation and concentration preceded the stages of hydrothermal 

alteration and tremolitic replacement.

CONCLUSIONS

On the whole, the phenomena are too complex and the data at 

hand are insufficient for an evaluation of the relative influence upon 

type of metallization of such factors as rock character and structure, 

stage or type of magmatic differentiation, mode of occurrence of the 

associated igneous rock and of the mineral deposit, and temperature 

and pressure. All the factors mentioned must enter to some extent 

into the formation of every deposit, and further study of the problem 

must await more detailed investigations and more extensive knowledge of territory that is as yet geologically unknown and unprospected.

28 Kerr, P. F., A magmatic sulphide ore from Chichagof Island, Alaska : Econ. Geology, 

vol. 19, p. 375, 1924.
390 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

LIMESTONE 80 ' '

The development of a pulp and paper industry in southeastern 

Alaska will cause a demand for limestone for use in the manufacturing processes. It is reported (1928) that the Pacific Coast Cement 

Co. has installed a large plant for the manufacture of cement at 

Seattle and that the limestone is to be quarried at View Cove, on 

Dall Island, Alaska, and brought to Seattle by vessel. The successful development of uses for limestone in southeastern Alaska will 

be of great benefit to that region, as large quantities of high-grade 

limestone are available at or near tidewater, in situations favorable 

both for a harbor and for quarrying.

The largest areas.and thickest beds of uniformly pure, very high 

calcite limestone occur in the islands off the west coast and at the 

north end of Prince of Wales Island. They are of Silurian age. 

Silurian limestone forms many of the islands in the Kashevarof 

group, in Clarence Strait. On the north end of Prince of Wales 

Island it forms the marble beds at Calder and El Capitan, in Dry 

Pass; the Mount Calder Range, which extends northwest from Calder Bay to Labouchere Bay; the coast north of the Barrier Islands; 

the east side of Port Protection; several miles of coast V/2 miles east 

of Point Baker; the coast in the vicinity of Red Bay nearly as far 

east as Point Colpoys; ,and a belt north.of Sarheen Cove and west 

of Aneskett Point, on El Capitan Passage. The largest area in 

which this limestone is exposed lies in the vicinity of Davidson Inlet 

and Sea Otter Sound and includes most of Kosciusko, Marble, Orr, 

Tuxekan, Eagle, White Cliff, Owl, Hoot, and Heceta Islands, the 

east side of Tuxekan Passage in the vicinity of Tuxekan, and the 

southern part of Staney Island. The limestone is exposed also on 

Dall Island and forms belts that strike northwest from Breezy Bay 

to the Diver Islands, from View Cove to Cape Lookout, and probably 

from Howkan to Waterfall Bay. On Long Island, in Cordova Bay, 

it forms two belts striking northwest across the island. On Kuiu 

Island it forms Beauclerc Peak; it is exposed on the passage south of 

Edwards Island; and a fine belt forms the range of mountains along 

the southwest side of Saginaw Bay. On Chichagof Island it is found 

at Basket Bay, Tenakee Inlet, and Freshwater Bay. In Glacier Bay 

a great range of coarsely crystalline upper Silurian limestone runs 

through Willoughby and Drake Islands and the east side of Rendu 

Inlet.

The Silurian limestones are in part of a dense texture and massive, 

in few places, if anywhere, showing any evidence of bedding; in 

part they are massive limestone and interbedded thin-layered lime30 This section is reprinted with slight revision from Buddington, A. F., Mineral investigations in southeastern Alaska : U. S. Geol. Survey Bull. 783, pp. 58-61, 1926.
MINERAL DEPOSITS 391

stone and nodular and shaly limestone, with calcareous shaly argillite, green-gray shale, and sparse buff-weathering sandstone. The 

massive limestone occurs in uniform beds as much as 2,000 feet thick. 

The fresh rock is white, but the usual color of the weathered surface 

is a pallid brown. The rock is in most places intensely fractured, 

and the fractured surfaces are coated with a thin facing of calcite or 

rarely dolmite, which at many places weathers out in relief as a network of veinlets. Conglomerate beds are commonly associated with 

the thin-layered zones. Where the limestones are intruded by 

igneous rocks they are recrystallized and form fine to coarsely 

crystalline limestones, some of which afford fine marble, as at Tokeen, 

on Marble Island, and at Calder and El Capitan, on Dry Pass, Prince 

of Wales Island. The Silurian limestones of Glacier Bay and Chichagof Island are likewise recrystallized by the contact-metamorphic 

fiction of intrusive masses.

The Silurian limestones are prevailingly high-calcite limestones 

with 95 to 99 per cent of calcium carbonate. Of the 11 analyses 

given in the table on page 393, 8 show 96 per cent or more of CaC03 . 

It is certain that large quantities of very high grade limestone are 

available in this formation.

Regarding the limestone on the property of the Pacific Coast 

Cement Co., on Dall Island, Mr. S. E. Hutton, chief engineer of the 

company, states 81 that

sampling and diamond drilling has proved the limestone to be of remarkably 

uniform composition, falling in a very few instances to 95 per cent calcium 

carbonate and rising in many instances to 99 per cent calcium carbonate. An 

average of a very large number of samples in the district we propose to work 

first showed insoluble 1.09 per cent, combined iron and aluminum oxides 0.42 

per cent, calcium oxide 53.87 per cent, magnesium oxide 0.69 per cent, as 

calcium carbonate 96.13 per cent. The average over the whole territory was 

about 97.5 per cent calcium carbonate.

Limestones of pre-Silurian age in beds from 100 to several hundred 

or even 1,000 feet thick, as well as a great many thinner beds, occur 

within a series of schist and greenstone in the vicinity of Sulzer and 

Copper Mountain and at the head of Cholmondeley Sound, on Prince 

of Wales Island. The limestone ranges from a white, coarsely crystalline marble to a dark-blue or nearly black limestone that is finely 

crystalline to granular or locally thin bedded and slaty. The only 

available analysis is that of a pure magnesian or dolomitic limestone 

(No. 20 in the table below).

Limestones of Devonian age in beds as much as 600 feet thick are 

exposed on Long and Round Island, in Kasaan Bay, Prince of Wales

31 Personal letter to A'. F. Buddington, dated Mar. Wf 1928. 

6137 29 26
392 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN" ALASKA

Island, and on the islands in San Alberto Bay, opposite Klawak. 

On Kupreanof Island they are found at the head of Duncan Canal, 

along the center and west arms, and at the head and along the east 

side of Emily Island Arm. No chemical analyses of these limestones 

are available. Some of the limestones in San Alberto Bay seem to 

be fairly pure, and all are worthy of investigation if their geographic 

location should make it desirable.

Limestones of Permian age form much of the Keku group of 

islands and the adjacent shore of Kuiu Island. They also form the 

line of conspicuous bluffs along the northeast side of Saginaw Bay, 

on Kuiu Island. They occur in a narrow belt on the mainland in the 

Juneau district, cropping out along the shore at Point Anmer, at the 

entrance to Port Snettisham, and striking inland to the southeast. 

Permian limestones are also exposed in Pybus and Gambier Bays, on 

Admiralty Island. The Permian limestones, which are about 1,000 

feet thick, usually have intercalated layers of chert. Locally, however, thick clean beds are present. On the island opposite the cannery on the east side of Saginaw Bay, Kuiu Island, there is a steep, 

high bluff of clean limestone. An analysis of a typical specimen 

(No. 14) shows it to be a high-calcite limestone.

Limestones of Triassic age crop out east of Point Cornwallis, on 

Kuiu Island, and probably form much of the peninsula inland. An 

analysis of a specimen obtained about 3 miles southwest of Point 

Cornwallis, on Keku Strait (No. 15), shows the rock to be an impure 

calcite limestone that contains about 11 per cent of insoluble matter. 

Upper Triassic limestones are exposed on the islands in Hamilton 

Bay, Kupreanof Island; on the Screen Islands, in Clarence Strait; 

on the west side of Gravina Island; and in Pybus and Gambier Bays, 

Admiralty Island. These limestones are usually medium to thin 

bedded and have intercalated layers of black slate. They are prob- 

.ably in the main impure argillaceous and siliceous calcite limestones.
MINEEAL DEPOSITS 

Analyses of limestones from southeastern Alaska

393

1

?

3

4

fi

fi

7

8

g in

n

10

13

14

15

Ifi

17

is

19

20

Locality

BEDS OF SILURIAN AGE

Marble, head of Red Bay, Prince of Wales Island ______ . ......

Marble, Marble Creek, north of Shakan, Prince of Wales Island. ....

BEDS OLDEK OR YOUNGER THAN SILURIAN

Marble, Dickman Bay, Prince of Wales Island........ ...............

Bluff of Permian limestone at southwest end of island opposite the

Triassic limestone, about 3 miles southwest of Point Cornwallis on

Limestone, near Jumbo mine, Copper Mountain region, Prince of 

Wales Island _ . ___ . _______ .. ______ .. .............

Calcium carbonate 

(CaCOs)

99.51

81.90

95.90

95. 35

R4. <lfi

98.99

99.12

96.90

99. 20 

96. 16

99.59

74.61

58.40

96.82

87.19

63.68

61.11

95.44

82.75

Magnesium carbonate 

(MgCCh)

0.94

14.93

1.40

2.04

13.18

1.01

.63

2.59

.63 

.89

1.03

3.25

6.61

.63

84

26.10

8.90

39.10

1.45

15.62

Insoluble0.01 .20>

3.50

2.95

13.18-

.12

.37

1.70"

Trace. 

2.56 .32-

22.84

37.32

2.79

11.32

19.06

28.19-

.91

3.61

1.84

Analyses 1, 5, 8, 10, 13, and 16-19 made by R. E. Bailey for E. F. Burchard; 0, 7, 14, and 15 by J. G. 

Fairchild for A. F. Buddington; 9 by E. F. Lass for the Alaska Marble Co.: 20 by George Steiger for C. W. 

Wright.

BUILDING AND ORNAMENTAL STONE

Wright 82 reports:

The granitic intrusive rocks occupy about one-half the aggregate land area 

of southeastern Alaska. * * * The metainorphism in the granite, its nonuniformity in color, and the presence of joint cracks, so far as observed, make 

most of the stone undesirable for building purposes. However, granitic masses 

of good quality, uniform in color, and favorably located for purposes of quarrying, were observed along the mainland up Portland Canal, in Behm Canal, 

at Thomas Bay, and Taku Inlet. On Baranof Island exposures of this rock 

of similar good quality occur at Gut Bay, on the east side, and at the head of 

Whale Bay and near Silver Bay, on the west side. * * * The prevailing 

color of the granite rock is a light gray and only in a few places were pink or 

reddish masses observed. The grains of the component minerals are ordinarily 

of medium size. < * * Evidence of the durability of the granite is afforded 

in many places where exposure to the influence of weathering has caused little 

or no disintegration of the surface.

Numerous stocks of granitoid igneous rocks occur on the islands, 

parts of which are massive and of uniform texture, though segregations of dark minerals, included fragments of country rock, and 

disseminated pyrite are present in many places and render the rocks 

less desirable as building stone.

33 Wright, C. W., Nonmetalliferous mineral resources of southeastern Alaska: U. 

Geol. Survey Bull. 314, pp. 77-78, 1907.
394 GEOLOGY AND MINERAL DEPOSITS, SOUTHEASTERN ALASKA

The masses of true granite, such as those on Canoe Pass, Etolin 

Island, and elsewhere in the Alexander Archipelago, are massive and 

uniform and have a characteristic pink color, in contrast to the light 

gray of the more dioritic rocks referred to by Wright.

Chapin describes certain of the serpentine and ultrabasic rocks 

of the Duke Island group, in the Ketchikan district, as being suitable 

for ornamental building stone and as giving a very pleasing effect 

when polished. In the serpentinized areas some of the rock is green, 

some is colored black by the presence of considerable magnetite, and 

some shows a combination with pale-green diopside. The rock composed of pure diopside without serpentine is pale green and somewhat translucent and takes a brilliant polish. Handsome combinations and great variety might be obtained by .selecting rocks 

containing different amounts of the constituent minerals, diopside, 

olivine, and the magnetite-bearing serpentine, thus combining the 

different shades of green and black.

The marble deposits of southeastern Alaska have been described 

by Burchard.33 Many types are available, and Buchard reports that 

there are undeveloped deposits which warrant prospecting whenever 

the demand for marble on the Pacific coast exceeds the present production. Marble and medium to coarsely crystalline limestone locally 

form thick beds within the Wrangell-Revillagigedo belt of metamorphic rocks on the mainland. Several such occurrences not described by Burchard are referred to by Buddington.34 The type 

which has thus far been exploited commercially on the largest scale is 

a fine to medium crystalline white to bluish-gray marble with gray to 

dark-bluish veins, bands, and clouded areas. The new State capitol of 

Washington is being built of marble from southeastern Alaska.

83 Burchard, E. P., Marble resources of southeastern Alaska: U. S. Geol. Survey Bull. 

682, 1920.

34 Buddington, A. P., op. cit, pp. 61-62.
INDEX

Acknowledgments for aid. __________ 3-4 

Agricultural land, distribution of .. _ 17 

Albite, occurrence of. .______.__ 337 

Amphibole, occurrence of..__..__...__ 337 

Andalusite, occurrence of__....__...__ 335

Annette Island, coastal plain on, plate showing.............................. 38

Antimony, occurrence of..._________ 331 

Apatite, occurrence of________.._ 337-338 

Aplite, occurrence and composition of..... 223-229

Arsenic, occurrence of. ................. 331-332

Authorship of the report.__________ 2-3

B

Bailey, R. K., analyses by.....__.__.__ 393 

Baird Glacier, description of.________ 30-3.1 

Baird Glacier and outwash plain, plates

showing_____________ 30 

Bancroft, J. A., quoted................ 236-237,242

Baranof Island, intrusive rocks on and near.. 186-

188,212

Barite, occurrence of_____________ 333 

Basalt, Quaternary, nature and occurrence

Of.... ....................... 278-279

Beaches, occurrence of....._._.__ . 280-281

Bench, wave-cut, in limestone, plate showing. 30 

wave-cut, on Prince of Wales Island,

plate showing__________ 38 

Benches, wave-cut, production of______ 35-36 

Bismuth, occurrence of __ .......__ 332

Bohemia Basin, Yakobi Island, composition

of igneous rocks from______ 199 

Boundary Glacier, retret-t of._____.__ 33 

Brooks, A. H., quoted. 18,318,321,324,326,368-370 

Brown Glacier, retreat of__________ 31-32 

Bucareli Bay, structure of rocks near....__ 311 

Buildinp stone, kinds and occurrence of 393-394 

Burwash, E. M. J., quoted_________ 236

C

Calcite, occurrence of___________ 335-336 

Carboniferous rocks, distribution and nature

of.................. ... 109-110

Chert, black, of Mississippian age, plate showing........................... 118

distribution of.._..__.. . 45 

Chichagof-Glacier Bay anticlinorium, features of.._________.._ 315 

Chichagof Island, intrusive rocks on and near. 183-

186,188,212

Chichagof gold belt, description of. . 371-373 

sedimentary Jurassic (?) rocks on____ 164

Page

Chickamin Glacier, plates showing_____ 22 

retreat of._............................ 33

Chlorite, occurrence of_._________ 337

Chromium, occurrence of-__________ 353

Cirque, occupied by glacier, plate showing.. 22

occupied by lake, plate showing..._... 22

lip of, plate showing..._______ 22

Cirques, cutting of...... . _ ... 29

ridge between heads of, plate showing._ 22 

Clapp, C. H., quoted.............__..... 238-241

Climate of the region_______. ____ 13-15 

Clover Bay, Prince of Wales Island, section

on.._..................._.... 313

Coal, occurrence of..____________ 353-354 

Coast line, erosion on.._______.____ 33-35 

Coast Range batholith, chemical composition

of................................ 210

intrusive rocks east of.-..______ 175-177 

metallization in__..__.._..._. 358-360 

mineral composition of. 177-181,209,212,217,238 

structure of.......__._............. 292-298

Conglomerate, nature and distribution of.... 44-45

Copper, deposits of, relation to types of

igneous rocks__. _____.. 376-377 

occurrence of.. 322-324,348-351,359-360,368-370 

Country rock, influence of, on metalliferous

deposits.____________ 374-375 

Cyanite, occurrence of.____________ 335

D

Dall, W. H., fossils determined by......... 269-270

Dall anticlinorium, features of_.____ 341 

Dall Island, intrusive rocks on______ 186-188 

Davidson Inlet, development of.._____ 38 

Dawes Glacier, decrease of._._______ 32 

plate showing.._____________ 30 

Delta deposits, occurrence of._______ 279-280 

Devonian and Carboniferous formations, re1 ations between..... _____ 283-284

Devonian rocks, distribution and nature of.. 94

occurrence and age of __________ 94-109

ore deposits in____._________ 341

Dikes, occurrence and age of_ _ ___.. 271-273

Diorite, occurrence and composition of._ 202-204

Dolmage, Victor, quoted_________ 240,377

Dolomi mineral belt, features of..._____ 370

Dolomi-Sulzer anticlinorium, features of__ 314

Dolomite, occurrence of....________ 335-336

Duncan anticlinorium, description of.__ 299-300 

Dunite, nature and occurrence of_____ 190-192

395
396 INDEX

E 

Eakin, H. M., quoted..................... 276,356

Eastern border belt, minerals in____ 357-358

Emmons, W. H., quoted__________ 382

Eocene rocks, age of ____________ 267-268

basal conglomerate and sandstone of.,. 262-263

conglomerate of lava cobbles in. _.... 263-266

lava flows and associated rocks in___ 266-267 

nature and distribution of.._..___ 260-262 

origin of.........__..-.......--...-.... 267

Epidote, occurrence of..._.___.._.__ 336 

Erosion, marine, results of..___...__... 33-35 

Etolin Island, sedimentary Jurassic (?) rocks

on............................. 163-164

Explorations and surveys, earlier...._._. 4-8

Fairchild, J. G., analyses by________ 198, 

204,211, 216, 221,393

Fanshaw Peninsula, felsite volcanic rocks on. 165 

sedimentary Jurassic (?) rocks on. __ 159-161 

Faulting, results of______________ 39 

Felsite volcanic rocks, occurrence of.-..__ 165 

Field work, record of..____________ 2 

Flow breccia, Middle Devonian, plate showing.....__............._..... 86

Fold, overturned, in graywacke and phyllite,

plate showing.._______ 118

Formations, relations between..__...... 281-289

Frederick Sound axis of cross folding, description of-.......---..-..___... 303-304

Freshwater Bay, syncline, features of____ 315 

Funter Bay-Hawk Inlet belt, minerals in__ 366

G

Gabbro, occurrence and composition of __ 199-201 

Gabbro-diorite, occurrence and composition

Of.. ._.-... .-.-. -- 201-202 

Garnet, occurrence of.___....__...._._. 332-333,363

Geology, bedrock, outline of.___.-..--... 19-21 

Girty, G. H., fossils determined by -....__ 110-117

121-127,128-130,143,148-149,156 

Glacial deposits, nature and occurrence of.. 275-276 

Glacial lake in valley of Cascade Creek, plate

showing_____________ 22 

Glaciation, headlands faceted by, plate showing.. ......................... 30

on quartz diorite, plate showing-..._.. 22 

Pleistocene, cutting of cirques by... __ 29 

deepening of fiords by..___..__ 26-28 

direction of flow of the ice______ 24-25 

height of the ice sheet during____ 24 

rounded top of mountain below level

of, plate showing_ _______ 22 

serrate peak of mountain above level

of, plate showing. ____..__ 22 

shaping of valleys by________ 25-26 

U-shaped valley shaped by, with recent 

gorge in the bottom, plate showing,... .......................... 30

Glaciers, modern, retreat or advance of..__ 30-33 

Goat Creek, Hyder district, pass at head of,

plate showing. _________ 30 

Gold, association of, with types of igneous

rock................... 377-378, 379-381

occurrence of_....__...... 320-322,345-347, 

354-356, 360, 362-363, 364-366,370-371

Page

Granite, occurrence and composition of__ 222-223 

Granodiorite, occurrence and composition

of ........................... 214-219

Graphite, occurrence of.. _______ 333-334,363 

Gravina Island, Lower Cretaceous (?) rocks

on............................. 254-255

Upper Triassic rocks on...__.__.. 132-134 

Gravina synclinorium, description of___ 300-302 

Graywacke, nature and distribution of___ 43-44 

Great Glacier, retreat of.___.______ 32 

Greenstone volcanic rocks, Jurassic (?), age

and distribution of.---.-..__ 165-173 

Gypsum, occurrence of.__________ 332

Hanson, George, quoted__________. 374 

Heceta Island, intrusive rocks on_____. 186 

Hess, F. L., quoted.................__.... 330

Hobart Bay, metamorphic rocks on.___.. 68 

Holkham Bay, metamorphic rocks on...__ 68-69 

Hollick, Arthur, fossils determined by__ 267-268 

Hollis, gold deposits near.--.--....-...._ 370-371

Hornblendite, occurrence and composition

Of .. . . ..-.....-- 194-198

origin of................_.......__ 248-250

Hound Island, Triassic volcanic formation

on............................. 142-144

Hutton, S. E., quoted-._...___...... 39

Hyder district, structure of Jurassic (?) rocks

in............................... 292

Icebergs buried in outwash plain, plates

showing..._________.. 30

Igneous rock, mode of occurrence of masses

of............................. 382-383

type of metalliferous deposits influenced

by type of---.....-....--..-..- 375-382

Injection gneiss, nature and distribution of. 50,51-52 

Intrusive rocks, Jurassic or Cretaceous, differentiation of, by successive intrusions. .-..--..-.-.....___ 239-242

Jurassic or Cretaceous, differentiation of,

in place................_.... 236-239

gabbro, diorite, and granite variants

of, origin of.................... 250-252

nature and distribution of____ 173-289 

ore deposits in___________ 344-353 

relations to older formations__.. 285-286 

structure of..... ................ 231-235

ultrabasic types of.._............ 188-198

origin of.._...........__.. 248-250

variants of, field relations of___ 242-244

order of crystallization of. __ 244-248

rate of cooling of________ 248

Mesozoic, age of..___________ 252-253

Tertiary, dikes in. _.__.___.... 271-273

distribution of ______ ___ 271 

kinds of........................... 273-275

Iron, occurrence of _____._325-327,351-353

Johannsen's system of classifying rocks,

modifications of_______ 174

Juneau district, metamorphic rocks in._. 70-72

sedimentary Jurassic (?) rocks in.__. 157-158
INDEX 397

Page

Juneau gold belt, minerals in_______ 364-366 

Juneau synclinorium, description of.___ 298-299 

Jurassic (?) greenstone and slate, ore deposits

in............................. 342-343

Jurassic (?) graywacke and slate, ore deposits

in................ . . .. 343-344

Jurassic (?) rocks, distribution and nature

of.-. .. 156-173

Karst topography, occurrence of_____.. 37 

Kashevarof anticlinorium, description of.. 310-311 

Keku Strait, Upper Triassic rocks on.__ 134-137 

Keku synclinorium, description of____ 302-303 

Ketchikan district, greenstone volcanic rocks

in. ....................... 167-168

metals in.............___._ ._ 368-370

metamorphic rocks in__ ________ 52-56 

northern, middle Devonian rocks in_ 101-106 

southern, middle Devonian rocks in.... 94-101

Kindle, E. M., fossils determined by........ 90, 98

Kirk, Edwin, fossils determined by_.._.. 49,

90-94,98,99-101,105-106,108-109,148

quoted____________.____. 77

Knopf, Adolph, quoted............. 70-71,157-158,

196,198,227,233, 237, 240,319-320, 373,377,388 

Znowlton, F. H., fossils determined by.... 267-268

Kosciusko-Tuxekan-Heceta synclinorium, description of...-...-.-..-.-.-... 308-309 

Kuiu anticlinorium, description of. _- 307 

Kuiu Island, graywacke, slate, and limestone

on............................... 77-79

intrusive rocks on____________ 186 

Triassic volcanic formation on..___ 142-143 

Kupreanof Island, Middle (?) and Upper

Devonian rocks on.....___. 106-107

sedimentary Jurassic (?) rocks on and

near______._______ 161-164

Lamprophyre dikes, occurrence and composition of.____________ 229-231 

Lead, occurrence of......._.__ 327-328,347,362

Le Conte Bay, metamorphic rocks on.._. 59-60 

Le Conte Glacier, retreat of____....__ 32

Limestone, fossiliferous Pennsylvanian, plate

showing-....___.___.__ 118

occurrence and nature of.____ 44,390-393

Permian, bluffs of, plate showing____ 118

Silurian, nature and distribution of___ 83-88

Lituya Bay, Pliocene (?) deposits on...... 269-270

Location and extent of the region.._..._. 10-11 

Lower Cretaceous (?) rocks, age and correlation of....................... 258-260

distribution and nature of.____... 253-254 

metallization in_____________ 353

M

MacKenzie, J. D., quoted................... 288

Magnetite, relation of, to stage of magmatic

differentiation................... 376

Malchite dikes, features of._........... - 229

Maps, geologic, of southeastern Alaska.. In pocket. 

Marine deposits and terraces, nature and

occurrence of..__... 276-278 

Martin, O. C., quoted......... 150,169-170,258-259

Page 

Maurelle Islands, structure of...._____ 309-310

Mertie, J. B., quoted.................. 194,377-378

Merwin, H. E., quoted..._......_..-.. 206,226

Metalliferous deposits, belts of........ . 356-357

genetic relation of...._ _.. ... 373-389

types of ............................. 316-320

Metamorphic rocks, nature and distribution

of 45-52

Metamorphism, two types of._____.. 45 

Mica, occurrence of.....__ .. 334-335

Mineral deposits, types of . ._ .. 316-320

Mining, history of._____.______.. 8-10

Mississippian rocks, age and correlation of. 110-117

distribution and features of.....__.. 110

ornamental limestone in________ 341-342 

Mitkof Island, sedimentary Jurassic (?)

rocks on....................... 163-164

Molybdenum, occurrence of....... 329-330,347-348

Monzodiorite, occurrence and composition

Of.............................. 204-206

Mount Calder, Prince of Wales Island, plate

showing..________...... 86

N

Nickel, occurrence of. __________ 329,348-351 

North Dawes Glacier, plate showing.____ 30

Ordovician and Silurian graywacke and slate,

ore deposits in.____.____ 340 

Overbeck, R. M., quoted.................. 343,372

P

Paleozoic and Upper Triassic formations,

relations between.._......_ 284-285

Palladium, occurrence of-_. _______. 351 

Pegmatite, occurrence and composition of. 223-229 

Pennsylvanian (?) rocks, features of...._. 117

Permian rocks, age and correlation of. .. 121-130 

nature and occurrence of........_.... 118-121

possibility of metallization of...____. 342 

Pit lake forming of, by melting of iceberg in

outwash plain, plate showing_ 30 

Placers, origin of..._____________ 354-356 

Platinum, occurrence of.. 351 

Point Hamilton, Lower Cretaceous (?) rocks

on and near......._ ...... 256-257

Population of the region . . 11-12 

Port Houghton, metamorphic rocks on and

near...____ .... _ 66-68,71

Precipitation, records of..._............... 15

Pressure of igneous rocks, influence of, on

metallization.................. 383-386

Prince of Wales belt, metals in............ 366-371

Prince of Wales Island, intrusive rocks on and

near..-......-..-.--... 183-186,188,212

mountains of, plates showing...__._. 22,86 

north coast of, structure of.___.__ 307-308 

Ordovician rocks on and near...._.__ 74-77

Silurian rocks on....._.__ .. .. 80

south half of, structure of rocks on and

near..__.___............ 311-313

Prince of Wales-Kuiu anticlinorium, general features of -------....-.. 304-308

Pseudomonotis beds, distribution of . 138-142 

Pybus Bay, Lower Cretaceous (?) rocks on.257-258 

Pyroxene, occurrence of.._._- 336 

Pyroxenite, description of....._____ 193-194
398 INDEX

Q Page

Quartz, occurrence of.. . 335 

Quartz diorite, occurrence and composition

of.--. . - -.... 207-214 

Quartz monzonite, occurrence and composition of 220-221 

Quaternary deposits, minerals in..____ 354-356 

unconformable relations with older formations..___ ..._____ 289

E

Reefs, development of...... .....__.... 33-34

Reeside, J. B., jr., fossils determined by... 145,148 

Relations between formations......___. 281-289

Revillagigedo Island, intrusive rocks on and

near........................... 212,217

metamorphic rocks on and near_ 181-183,188 

Upper Triassic rocks on__.___... 133-134 

Roches moutonn§es, plate showing..___ 22 

Rocky Bay, Etolin Island, Lower Cretaceous (?) rocks on....______ 255-256

structure of rocks on and near.... ___ 302

Ruedemann, Rudolf, fossils determined by.. 76-

77,81-82 

Ruth Island, metamorphic rocks on......... 63,64

San Alberto Bay, structure of rocks near_. 311 

San Fernando anticlinorium, features of __ 310 

Sandstone, absence of__.. ......_ 44

Sawyer Glacier and South Sawyer Glacier,

discharge of ice from..____.. 32 

Saxonite, features of.......... .......... 192-193

Schist, development'of... 45 

Schofleld, S. J., and Hanson, George, quoted. 172,

294-295,384 

Scope of the report......_.... ____ 1-2

Screen Islands, Upper Triassic rocks on__. 134 

Sea Otter Sound, development of...____ 38 

Seymour Canal, sedimentary Jurassic (?)

rocks on....-... ___.. 158-163 

Shakan Bay syncline, features of 308

Sillimanite, occurrence of ........ 335

Silurian conglomerate, Kuiu Island, plate

showing____.. . .. 86 

Silurian (?) limestone, massive, plate showing..- 86

Silurian rocks, age and correlation of_..... 90-94

distribution of . 79-81

limestone and conglomerate formation in. 83-88 

slate and graywacke in.... _ 81-82

ore deposits in.____._...__.._. 340 

sandstone and graywacke series in___ 88-90 

shale in._.................. _.. 88

volcanic rocks and conglomerate in..__ 82-83 

Silver, occurrence of.... ... 327-328,347,360,362

Sitka Mesozoic belt, gold-bearing quartz veins

in 373

structure of ___...... ...... 315-316

Slate, distribution of..____.. _.. 45 

Smith, P. S., quoted -. 149

Snettisham Peninsula, metamorphic rocks on. 71-72 

Spencer, A. C., quoted..... 70,342-343,356,364-365

Stanton, T. W., fossils determined by.___ 138,

141,144,145-147,148,151-156,164,168, 259, 260

Steiger, George, analyses by...... . 205,393

Stratigraphic column in the region... .. 39-43

Structure of the rocks, general features of.. 289-292

influence of, on topography._.____. 37-39

Page

Structure sections, plate showing______ 294 

Suemez Island, Pliocene (?) deposits on..., 270-271 

Syenite, composition of 206-

T 

Temperature of igneous rocks, influence of,

on metallization.....____.. 383-386

Terraces in limestone, remnants of, plate

showing.__._.__.____ 30 

Tertiary and older formations, relations between_______________ 288. 

Tertiary rocks, metals and coal in..___ 353-354 

Thomas Bay, metamorphic rocks on_. __ 60-66 

Timber, distribution of.___________ 16-17 

Titanium, occurrence of ___________ 331 

Topography, influence of structure on. ___ 37-39 

main features of__________ 18-19,22-23 

main features of, production of _____ 21-22 

Tourmaline, occurrence of ______ 338 

Tracy Arm, metamorphic rocks on_ __.. 68-70 

plate showing____________,_ 30 

Transportation, means of.___.._____ 12-13 

Tree, silicifled stump and trunk of, plate

showing_____.________ 262 

Trees overthrown by advance of Baird Glacier,

plate showing...._______. 30

Triassic rocks, ore deposits in._......... 342

Triassic, Upper, rocks, age and correlation

of...... . . 144-156

Upper, rocks, distribution of.. 130-131,137-138 

rocks, nature and stratigraphic relations of______________ 131 

Tungsten, occurrence of___________ 330

V

Vegetation of the region... ___.... 16-17 

Vogt, J. H. L., quoted .. . 351 

Volcanic rocks, nature and distribution of... 43-

W 

Wales group, closely folded limestone of,

plate showing_.._______ 38

description of. 45-49

ore deposits in________- _____ 338-339> 

recumbent folds in greenstone schist of,

plate showing. ..._... 38 

relations of.. 281-28&

Water power, facilities for_.________ 17-18- 

Western belt of schist and gneiss, minerals

in... 360-363

Westgate, L. G., quoted......_ 52-54,232,278-27*

White, David, fossils determined by _.._ 99,108- 

Windham Bay, motamorphic rocks on and

near...-...... ..____.. 68,71-72-

Wrangell, metamorphic rocks near. 181-183,188,212 

Wrangell Island, intrusive rocks on and near. 217 

metamorphic rocks on and near..___ 57-59 

Wrangell-Revillagigedo belt of metamorphic

rocks, age of____.______ 73-74 

nature and distribution of...______ 49-52 

ore deposits in___....._._____ 339-340

structure of..__... __..... 292-298.

Wright, C. W., quoted.... 184-

185,241-242,287-288,316-317,386

Wright, F. E., quoted... 21,27&

Wright, F. E. and C. W., quoted 73,127-

128,209-210,240,269-270.284-285,293-294

Z 

Zinc, occurrence of ...... 328,360-363

o