DEPARTMENT OF THE INTERIOR 

FRANKLIN K. LANE, Secretary 

UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, Director 

Professional Paper 108-L 

STRATIGRAPHY OF THE. HANNA BASIN, WYOMING 

BY 

C. F. BOWEN 

Published May 7,1918 

Shorter contributions to general geology, 1917 , I 

<.t;ages 227-235) 

WASHINGTON 

GOVERNMENT PRINTING OVFICE 

191 8 
CONTENTS. 

Introduction .............. __ ... _ ........ . ..... _. : . .......... ......... -... ---.-----.----- -------.---.-----

stra~~~:!i ~~~t-i~~- _- _- ~ ~ --~ _- _- _____ ~: : : : : : : : : : : ~ ~ : : : : : : : : : : : : : : : : : : : : : :·: : : : : : : : : : : : : : : : : : : : : : : : : : : : : :_: : : : : ~ ~ ~ ~ 

~=r~~~i~~::: ~o~~a~~~~: : : : : : : : : : : : : : : : : : : : : : : : : : : :·: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :_: : :: 

Hanna formation._ .. _______ _____ _____ ___ . __ . ______________ . ___ . _______ .. _ ........ _. ___ .. ... _ . . _. __ .. . 

North Park formation .. c • .•.. . . ..••••.••••••••...... ..•..•• • •••••• - ••••••••• ------------ - ------------

Structure ..... : ..... _ .......................... · ......... : ............ -.------.------------- ~- ------ ----- Folding and faulting ____________ ... ___ .. .. _ . _ ... __ ... _ . ____ .. _ . ___ _____ ... ___ . _ ... __ . _______ . ~ _____ . 

Unconformities._ ... _ _" _. __ . __ .. _ .... _._ ... _ .. _________ .......... _. ____ ._. __ __ -.- __ . . ...... _ .. ______ .. 

Source of the materiaL ___ ~ __ .. ______ ...... _ ........... ___ .. _. __ . _ ... _. ___ .. __ . ___ . _ .. ____ ..... _-___ . ___ . . . 

Conclusion ....... . ... _ .. _ . ___ . ____ . _ .. ~ .. . ....... ___ __ ____ . ~ ____ ... __ ..... _ . _______ · ___ . _ . _ . _ ... _ . _____ .. . 

ILLUSTRATIONS. 

• PLATE LXVI. Chart showing thickness, character, and probable correlation of formations between Medicine 

Bow, Wyo., and Coalville, Utah .......... ______ ._._ ... _ ......... _ ................... __ ... . 

FIGURE 31. Key map showing location of Hanna Basin, Wyo .... _.: ............................. ..... .... . 

II 

·. 

Page. 

227 

228 

228 

229 

230 

231 

231 

231 

231 

231 

~34 

235 

Page. 

234 

227 
STRATIGRAPHY OF THE HANNA BASIN, WYOMING. 

By C. F. BowEN. 

INTRODUCTION. As the result of his work in the Hanna Basin 

Carbon CDounty, Vvyo., has attracted the ·(see fig. 31) in 1906, Veatch 1 subdivided this 

attention o geologists since the days of the group of rocks into two formations, which he 

territorial surveys under King, Hayden, designated "Lower- Laramie" and "Upper 

and Powell. During this earlier work all the Laramie," and made the statement that the 

50 o so 100 1501\files -~~~~======~~~~~====== 

FIGURE 31.-Kcy map showing location of Hanna Basin, Wyo. 

rocks (except the North Park formation) over..: 

lying the uppermost beds of marine origin 

were grouped in a single formation, for which 

the name Laramie was proposed. 

two were separated by an unconformity that 

involved the removal of 20,000 feet· of rocks. 

1 Veatch, A. C.,Coalin east-centralCarbonCounty, Wyo.: U.S. Geol. 

Survey Bull. 316, p. 246, 1906; The origin and definition of the term 

Laramie: Jour. Geology, vol. 15, pp. 526-549, 1907. · 

227 
228 . SHORTER CQNT'RIBUTIONS TO GENERAL GEOLOGY, 191i. 

Veatch's upper formation became the type of 

the "Upper Laramie formation," and the flora 

which it yielded was adopted as a standard for 

purposes of comparison in other fields. 

It is the purpose of the present paper (1) to 

show that the "Upper Laramie" as defined by 

Veatch consists of two formations separated by 

a marked unconformity; (2) to show that this 

unconformity is the one which he regarded as 

representing the · erosion of 20,000 feet and referred to the base of the "Upper Laramie formation"; (3) to present the facts so far as they 

can--now be interpreted for and against the existence of an unconformity at ·the . horizon 

~ndica ted by Veatch; and ( 4) to offer some suggestions as to the source of the material which 

goes to make up the enormous thickness of 

continental deposits of this era. 

STRATIGRAPHY. 

GENERAL SECTION. 

The formations exposed in or immediately 

adjacent to the area under consideration range 

in age from Cambrian (~)to probably Miocene. 

Those in the upper part of the section-that is 

above the base of Veatch's "Lower Laramie"-

are of chief interest and will be described somewhat in detail; the underlying formati-ons will 

be referred to but briefly. The sequence and 

gf:meral character of the Mesoz()ic and Cenozoic 

formations are shown in the following table: 

Mesozoic and Cenozoic jm:rnations in Hanna Basin, Wyo . 

. System. Formation. Thickness Characteristics. _(feet) . 

. Alluvium. Worked-over material from surrounding formations. 

Quaternary. 

Terrace gravel. 0-25± Waterworn pebbles of older sedimentary and crystalline rocks. 

North Park formation. 0-400± Whitish unconsolidated sand and clay with thin intercalated 

beds of limestone in some places; conglomeratic at base. 

........................... Unconformity ........... 

Alternating beds of dark-gray, yellowish, and carbonaceous 

shale; white, gray, and brown sandstones, massive to thin 

bedded and commonly cross-bedded; conglomerates and 

Tertiary. Hanna formation. conglomeratic sandstones containing pebbles of chert,-

7, 000± granite, quartzite, sandstone, Mowry shale, CloverlY.' con- glomerate, etc. (these conglomerates are distnbuted 

throughout the section but ~e most abundant in the lower 

half), and numerous beds of coal. Contains fossil bones of 

vertebrates, fresh-water shells, and an abundance of leaves. 

.......................... .. .. Unconformity .. ·_ ......... 

Light-colored, dark-gray, and carbona<;eous shale; buff to 

brown sandstone; in places extremely cross-bedded and 

showing great irregularity of deposition and numerous beds 

Tertiary (?). Ferris formation. I 6, 500± of coal. Pockets, ·lenses, and thin beds of conglomerate 

composed of pebbles of older rocks are distributed through a zone about 1,000 feet thick at the base of the formation. - Contains fresh-water invertebrates, land plants, and bones 

of vertebrates. -

Light-colored to gray carbonaceous shale; gray to brown 

sandstone showing cross-bedding, ripple marks, and -other 

Medicine Bow formation. 6, 200± features of irregular deposition; and thin irregular beds of 

coal. Fresh and br.ackish water, invertebrates, land plants, 

and bones of vertebrates. 

Cretaceous. 

Predominantly dark-gray shale with thin intercalated beds of 

shaly sandstone and some beds of light-colored massive to 

Lewis shale. 3, 300± heavy-bedded sandstone. N-ear the top of the formation 

is a persistent ledge-making gray sandstone about 270 feet 

thick. Marine. · 
STRATIGRAPHY OF THE HANNA BASIN, WYO. 229 

Mesozoic and Cenozoicjormations in Hanna Basin, Wyo.-Contlnued. 

System. Formation. Thickness Characteristics. (feet). 

An upper member of whitish sandstone alternating with gray 

and carbonaceous shale with a conspicuous resistant white 

sandstone at the top; contains thin irregular beds of coal in 

Mesaverde formation. some places. A midd~e member of brown to gray sandstone, 

2, 700 gray carbonaceous shale, and thin irregular beds-of coal; 

differs from upper member in its prevailingly brown color; 

fresh and brackish water fauna. A lower member of gray 

to white sandstone and gray shale; contains a marine fauna 

and is not coal bearing. 

Steele shale. 4, 000± 

Dark-gray shale with intercalated beds of sandstone and 

shaly sandstone, some of which form conspicuous ledges near top of formation. Shale contains concretions of cal- careous sandstone, dark limestone, and white crystalline 

calcite. Marine fauna. 

Niobrara formation. 370± Calcareous shale with considerable intercalated white crystalline calcite at top and bottom. -

Cretaceous. 

Carlile shale. 200 Dark-gray to black shale with some thin sandy layers. 

An upper member composed of thick beds of sandstone alterFrontier formation. 700 nating with thinner beds of shale and a lower member 

. composed of dark-gray shale . 

Mowry shale. 170 Fissile shale, dark brown on fresh surface but weathering to 

silver gray or white. _ . . 

Thermopolis shale. 140 Dark-gray shale with thin sandy layers. 

Cloverly formation. 231 An upper me~ber of sandstone, a midd-le member of shale, 

and a lower member of conglomeratic sandstone. 

-----------------------------· 

Cretaceous (?). Morrison formation. 350 Shale, mostly gray or greenish, alternating with sandy shale 

and sandstone. Contains .bones of. dinosaurs. 

\ 

-----------------------------

Jurassic. Sundance formation. 85 Chiefly green, olive, and drab shales with a few thin intercalated beds of sandstone~ 

I 

Triassic. Chugwater f~rmation. 1, 000- Chiefly red shale with· intercalated red, buff, and yellow 

sandstone. 

For stratigraphic study the most important 

of the formations given in the table are the 

Mowry shale, the Frontier, anu the Mesaverde, 

because they possess characteristics which render them valuable as horizon markers. This is 

especially true of the silver-gray fish-scale shale 

of the Mowry. 

·MEDICINE BOW FORMATION. 

Above the highest marine formation-the 

Lewis shale-is a mass of continental deposits, . divisible into four formations having a 

maximum thickness of more than 20,000 feet. 

For the lowest of these formations the name 
230 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1917. 

Medicine Bow is here proposed, because the formation is best exposed and most easily studied 

along both sides -of North Platte River at the 

mouth of the Medicine Bow. The Medicine 

found that are sufficiently diagnostic for even 

generic determination. 

FERRIS FORMATION. 

Bow formation. is the equivalent of the "Lower The Medicine Bow formation is terminated 

Laramie" as defined by Veatch. The latter above by a conglomeratic zone taken as the 

term is not applicable, for the _" Upper Lara- base of the Ferris formation, so named because 

mie," in the sense in which that term was it is best exposed from the old Ferris ranch, on 

originally used, · is not of Laramie age. As the North Platte River, ea~tward to the top of the 

relation of the Medicine Bow formation to the hill north of "Middle Ditch" at its junction 

Laramie ·of the Denver Basin can not be deter- with "Big Ditch." As defined the Ferris formined by field re~ations, and as paleontologists mation is approximately equivalent. to the 

are not agreed as to the relation of the fossil lower half of the "Upper _Lara:p1ie" of Veatch. 

remains found in the two formations, the use -The conglomerate at the b.a,se _of the: Ferris forof the unqualified term "Laramie" is not ad visa- mation ranges through an iiJterval of aheut 

ble, and it is thought that confusion may be 1,000 f~et, in which massive sandstone, more 

avoided by the use of an entirely new name or less conglomeratic, . alternates with nonfor the formation hitherto called ''Lower conglomeratic sandstone and shale. · The conLaramie." glomerate is sparingly developed at the · base 

The Medicine Bow formation rests-conform- of the zone but increases in amoun_t upward. 

ably on the Lewis and consists of an alternating It is succeeded by an alternating series of sandsuccession of shale and massive to thin-bedded, stone and shale containing .numerous beds of -

ripple-marked, and cross~bedded sandstones, eoal. The maximum thickness of the formawith several beds of coal in the lower third of tion is about 6,500 feet. 

the formation. The massive and thick-bedded Both the matrix and the pebbles of the consandstones are .commonly somewhat coarser glomerate consist of materials of the same kind 

-than the thin-bedded varieties and in some as make up the sandstone of the underlying 

places contain clay balls and an occasional Medicine Bow formation. The · pebbles conpebble the size of a pea. sist mainly of chert and white quartz or 

Microscopic examination -shows that the quartzite; then follow in about the order 

sandstone is composed of fragments of quartz, named red and gray quartzite, porphyries, ~nd 

quartzite, feldspar, chert, schist, volcanic rocks, conglomerate, with subordinate amounts of 

limestone, and other minor constituents. In other constituents. Three facts impress the 

other words, it has been derived from both student of this conglqmerate: (1) It · is m~de 

sedimentary and igneous rocks. The grains up of only the most resistant kinds of rock; (2) 

show considerable variation in the degree of it is lacking in several kinds of ;rock now exsorting and rounding, but on the whole are posed in the surrounding mountains-for 

decidedly angular. One section ~howed well- example, granite, Iimestone,sandstone,C~overly · 

rounded grains, 20 per cent; subangular grains, conglomerate, and Mo~y shalej (3) It co~-

35 per cent; angular grains, 45 per cent. These tains materials that seem to be foreign to this 

proportions suggest that the grains are chiefly region, namely, quartzite, porphyry (quartz 

the result of mechanical disintegration and latite), and rhyolite. These features lead to 

rapid transportation with little or no subse- the inference that the conglomerate and also 

quent reworking. ._ · the associated s.andstone- were derived from 

The formation contains remains of fresh and some distant source rather than from the 

brackish water invertebrates, land plants, and · f h 

d near-by- mountains. This In erence .· . as a. n bones of vertebrates. The plants are regarde f d - h important bearing on the unco_n ormities -Is- by F. H. Knowlton as of the same age as t_ e · f h D B · cussed on pages 231-234. 

plants of the Laramie o t e enver asin. The Ferris formation contains fresh-water The invertebrates are considered by T. W. 

Stanton to belong to the .fauna of the Lance invertebrat~s, land plants, and bones of verteformation. The bones J>elong in part to the brates. -- The shells and plants, which· are 

ceratopsians, but no specimens have been found chiefly above the conglomerate z.one, are 
STRATIGRAPHY OF THE HANNA BASIN, WYO. 231 

regarded as of Fort Union age, whereas the 

vertebrate remains, thus far found only in the 

conglomeratic zone, consist of bones of turtle8, 

indeterminable fragments of ceratopsians, and 

a few specimens that have been identified by 

_C. W. Gilmore as Triceratops. The bones of 

Triceratops tend to show that the basal part of 

the formation should be correlated with the 

Lance of Wyoming and Montana and the 

Denver foTmation of the Denver Basin. There 

is, however, no conclusive proof of an unconformity below the bone horizon in the Hanna 

Basin, as there is said to be in the Denver 

Basin. 

HANNA FORMATION. 

For the upper part of the "Upper Laramie" 

as defined by Veatch the name Hanna formation is proposed, because the formation is well 

exposed to the west and north of the townof 

Hanna and yields all the coal mined at that 

place. The Hanna formation rests unconformably on the Ferris formation. A conglomeratic sandstone marks its base, above which 

conglomerate, sandstone, shale, and coal beds 

alternate to the top of the formation, some 

7,000 feet above the ba;se. 

This formation differs from the Ferris . in 

being highly feldspathic, in being conglomeratic 

throughout, and in the fact that the conglomerate contains an abundance of local 

material, notably granite, Mowry shale, and 

Cloverly conglomerate. The relative abundance of these constituents varies from place to 

place in accordance with ·the character of the 

surrounding rocks. Thus near outcrops of the 

Mowry shale and the underlying Cloverly 

those rocks constitute most of the pebbles, 

near outcrops of granite that rock is the most 

abundant material in the conglomerate, and in 

the center-of the basin granite, sandstone, and 

conglomerate pebbles are associated with 

chert, white quartz, quartzite, etc. 

This formation contains an abundance of 

plant remains, all of which are referred to the 

Fort Union by Mr. Knowlton. The invertebrates are also regarded by Mr. Stanton as 

chiefly indicative of Fort Union age, though 

species found near the top are said to resemble 

the Wasatch fauna. Only a few fragmentary 

remains of vertebrates have thus far been 

found in this formation. They include fish 

scales, fragments of turtle shells, and a fragmentary mammalian jaw identified by J. W. 

Gidley as a creodont, -probably Claenodon, 

which may belong to either the Fort Union or 

Wasatch. 

NORTH PARK FORMATION. 

The North Park formation rests unconformably on the underlying rocks. This form·ation 

consists of conglomerate, unconsolidated sand 

and marl, and local thin beds of limestone. 

A peculiarity of the formation is that in many 

places its surface is thickly strewn with 

boulders of white, vitreous quartzite as much 

as 2 ·feet in diameter, -but none of these haveever been . found actually embedded in -the 

formation~ -· 

No fossils have been found in the North 

Park, and its age is therefore largely a matter 

of conjecture, but it is thought to be Miocene. 

STRUCTURE. 

FOLDING AND FAULTING. 

Folding is the dominant structural feature 

of the Hanna Basin, though faulting has 

occurred - to some extent. A characteristic 

of the folds is that they are all oversteepened 

toward the west or southwest. 

All the rocks up to and _including the Ferris 

formation seem to have been equally deformed 

and were folded, faulted, and deeply eroded 

before the deposition of the Hanna formation. 

After the deposition of this formation there 

was another disturbance, which followed chiefly 

the lines of the earlier movements and served to 

emphasize the features of structure already 

produced. By this disturbance the Hanna 

formation was tilted in some places into _a 

vertical position and was locally faulted. A 

third disturbance seems to have taken place 

subsequent to the deposition of the North 

Park formation, for this formation is now 

tilted in some places 40° or more. 

UNCONFORMITIES. 

Perhaps the most interesting structural 

problem in the field relates to the occurrence 

and magnitude of the unconformities. There 

_are certainly two and possibly three unconformities present. The highest of these _is at 

the base of the North Park formation, which 

overlaps all -other formations in the field. 
232 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1917. 

TIH~ next lower un·conformity is that at the 

base of the Hanna formation, formerly assigned 

to the base of the Ferris formation. It repre-

. sents the removal of more rather than less 

than the 20,000 feet assigned by Veatch. 

The existence of this unconformity is demonstrated by the following field relations: (1) 

There is a :inarked angular discordance between the underlying and overlying formations; 

(2) the Hanna formation transgresses all the 

underlying formationS at least down to the 

Cloverly and possibly down to· the granite; 

(3) the Hanna formation has been less intensely 

deformed than the . underlying formations; 

(4) the conglomerate _at the base of .the Hanna 

formation has clearly · been derived from all 

the underlying rocks and is chiefly of local 

origin. 

That this unconformity is the one assigned by 

Veatch to the base of his "Upper Laramie" is 

evident froni the following considerations: 

(1) It is the most conspicuous break in the field; 

(2) it is the only unconformity present at some 

of the typical places observed by Veatch, the 

lower beds being there cut by overlap; (3) the 

Ferris formation nowhere transgresses the 

"Lower Laramie" and overlaps older rocks, 

as was postulated by Veatch; (4) all the rocks 

between the Medicine Bow ("Lower Laramie") 

and North Park were included by Veatch in a 

single formation. 

Veatch's mistake was a natural one to make 

in rapid reconnaissance work. In the east~ 

ern part of the basin, where the unconformity 

is most evident,· the conglomerate of the Ferris 

formation is either cut out by overlap or is 

directly overlain by the conglomerate of the 

Harina formation, all the intervening strata 

being eroded. These relations were not 

detected in a rapid examination, but are perfectly clear when studied and mapped in detail. 

On the west side of the ·basin the two con:.. 

glomerates are separated by a stratigraphic 

inter·val of nearly 6,000 feet and by a horizontal· distance of 5 to 7 miles. In that area 

Veatch appears to have recognized only the 

lower of the two conglomerates and to have 

unhesitatingly correlated it with the unconformity he saw farther east. 

Th.e next question that arises is regarding 

the significance of -the conglomerate at the base 

of the Ferris formation. It has been held that, 

because this conglomerate is made up in part 

of pebbles containing Paleozoic fossils, it necessarily represents a period of uplift and erosion 

between the deposition of the Medicine Bow 

and that of the Ferris formation ("Upper 

Laramie" and .. "Lower Laramie") sufficient 

to expose the Paleozoic , rocks. This would 

naturally f~llow if it could be proved that Paleozoic rocks did not contribute materials to the 

underlying formation or th1;1t the pebbles of 

the conglomerate came from a different source 

than the sand- and clay of the underlying 

formation. As previously stated, microsco.pic 

study shows that the constituents of this conglomerate are all represented in the sandstone 

of 'the Medicine Bow formation. This seems 

to indicate that both were derived from· the 

same source and · that Paleozoic rocks contributed material to the Medicine Bow formation, as well as to the conglomerate above it. 

It is therefore not necessary to assume a great 

interval of uplift and ~r~sion between the 

periods of deposition of the two formations to 

account for the Paleozoic pebbles· in this conglomerate any more than it is necessary to 

assume a great interval of uplift and erosion 

to account for each of the successive conglomerates in the Hanna formation, or the conglomerates of · earlier formations, such as the 

Beckwith in Uinta County and the Frontier ( ~) 

at Coalville, Utah. The presence of P.aleozoic 

pebbles in these conglomerates, as well as in 

the Cloverly, is proof that the Paleozoic formations had been exposed somewhere in the 

region atleast since.the beginning of the Cretaceous period. That is, in so far as the evidence furnished by the conglomerate alone· is 

concerned, it seems to the writer that there is 

no more ·argument for assuming an · unconformity ·between the Ferris and Medicine Bow 

formations than there is for assuming an unconformity at the ~ase of each of the conglom- · 

erates in the Beckwith, Frontier, and Hanna 

formati~ns. Each of these conglomerates contains pebbles of Paleozoic rocks. 

It is recognized, however, that _a conglomerate indicates a more or less pronounced 

change in conditions of sedimentation. This 

change could be accomplished by a rejuvenation of the streams of an already existing land 

mass, by climatic changes, or by a combination of these and possibly other causes. The 

point made here is that the existence of a conglomerate is not positive proof of a great un-
STRATIGRAPHY OF THE HANNA BASIN, WYO. 233 

conformity. This is especially true of a conglomerate occurring in the midst of a great 

mass of continental deposits that have · the 

same lithologic character throughout-conditions entirely different from those presented 

by a conglomerate that separates two marine 

deposits or one deposit of marine origin and 

another of continental origin. 

The field relations of the Ferris conglomerate 

and the underlying formation show (1) that the 

two have ·been equally deformed; (2) that 

there is no angular discordance between them 

either in the Hanna Basin or in other areas 

where both are present; (3) that the Ferris 

formation is nowhere known to transgress the 

Medicine Bow formation and overlap older 

rocks; ( 4) that, as previously indicated, the 

conglomerate seems to have been derived from 

the same source as the Medicine Bow; (5) that 

there appears to be a gradual transition from 

the Medicine Bow formation to the Ferris formation. The contact between the two is not 

sharply defined, coarse sandstone of the Medicine Bow being followed by grits in which a 

few small pebbles occur, and these giving place 

higher up to pockets, lenses, and thin beds of 

conglomerate, which are fina.lly succeeded by 

thick beds of sandstone that are conglomeratic 

throughout. Interbedded in this transition 

zone are several beds of dark-gray shale, some 

.of which attain a thickness of 30 feet. 

This transition zone is very significant, occurring in all areas where both the Medicine 

Bow and Ferris formations or their equivalents 

are present. In the sou.thern pa~t of -the 

Great Divide Basin it is; according to Smith, 1 

800 feet thick and consists chiefly of clay with 

interbedded thin rusty-brown sandstone, which 

becomes increasingly conglomeratic toward the 

top. In the northern part of the Great Divide 

Basin, according tQ the same author, the transition zone is still thicker. 

Similar conditions in the Little Snake River 

- field are described by Ball and Stebinger. 2 

This thick . transition zone between the assumed unconformity and the principal conglomeratic zone supposed to represent it seems 

to the writer to be a fatal objection to the idea 

of an unconformity. It is difficult to conceive 

1 Smith, E. E., The eastern part of the Great Divide Basin coal field, 

Wyo.: U.S. Geol. Survey Bull. 341, p. 224, 1907. 

2 Ball, M. W., and Stcbinger, Eugene, The eastern part of thE' Little 

Snake River roal field, Wyo.: U. S. Geol. Survey. Bull. 381, p. 190, 1910. 

19437°-18--2 

of a basal conglomerate occurring several hun~ 

dred feet above the base it is assumed to repre-:-

sent. These conditions lead to the inference 

that no unconformity exists between the two 

formations. 

The arguments in favor of an unconformity 

are (1) the conglomerate at the base of the, 

Ferris formation, which, if the above reasoning · 

is sound, has no weight; (2) a considerable 

thinning of the Medicine Bow formation in 

some places, which is pattly offset by the fact 

that the Lewis and Mesaverde show just as 

great variations in thickness within as short 

distances; and (3) the fact that at the base of 

the Evanston formation of Uinta County, correlated with the Hanna at Carbon, there is an 

unconformity which ·has been assumed to represent the interval between the Medicine Bow 

("Lower Laram~e ") and Ferris ("Upper Laramie'') epochs. 

The question now arises whether the Evansron formation should be correlated with the 

Ferris or with the Hanna .formation. There · 

are three lines of evidence which suggest that 

it should be correlated with the Hanna. (1) 

The flora of the Evanston is said to correspond 

to that obtained from the old town of Carbon, 

which in all probability came chiefly if ~ot 

entirely from the Hanna formation and there:-

fore tends to support the correlation of the 

Evanston with that formation; (2) the Evans"'" 

ton is conformable with the overlying Wasatch, 

a relation which is not known to exist between 

the Wasatch and older rocks in any other place 

in southern Wyoming; (3) the relation of the 

Evanston to the Adaville ("Lower Laramie") 

is largely a matter of inference, for it nowhere 

rests on the Adaville, and sonie of those most 

familiar with the Evanston section now believe 

that the Adaville formation, formerly thought 

to represent the "Lower Laramie," is really 

Mesaverde. 

It seems to the writer, therefore, that the 

weight of evidence so far as it can now be interpreted is opposed to the existence of a great 

unconformity at the base of the Ferris formation, but it is freely admitted that more detailed field work over wider areas is necessary 

to decide this question. It is of course possible that a considerable unconformity near 

the margin of the ancient land mass from which 

the sediments were der.ived may give place to 
234 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1917. 

· apparent conformable relatiori.s at a considerable distance from that place. But it is ,still 

a fact that unconformity between the Fort 

Union and Wasatch is the most widespread and 

significant break that had been produced up to 

that time since the beginning of the Cretaceous 

period. · 

SOURCE OF THE MATERIAL. 

The source of the enormous amount of sediment represented in these continental deposits 

is an interesting problem. 

For the Hanna formation it can be stated 

with considerable confidence that the material 

was derived from all the underlying formations 

and is of more or less_ local origin. 

For the underlying formations the case· is not 

so simple. Even if it. coUld be demonstrated 

that the Ferris for!Jlation is of local-derivationJ 

it would still be necesSary to explain the SOUrCe 

of the 6,200 feet of the Medicine Bow formation 

to which the immediately underlying rocks did 

not contribute. A study of at least all the 

Cretaceous formations is therefore necessary 

to throw light on the problem. 

A few suggestions may be offered by comparing the sections in the accompanying 

chart (Pl. LXVI). These sections extend from 

_the east side of the Hann~ Basin westward 

through Rawlins, Rock Springs, and Evanston 

to Coalville, Utah. In constructing them the 

Mowry shale was taken as a datum plane. 

To consider first the sandstone fo'rmations ' these sections show that from east to west the 

Mesaverde and Frontier thicken regularly, the 

materials become coarser with pronounced 

development of conglomerate in the Frontier 

and with slight indications of conglOmerate 

in the upper part of the Mesaverde, and there 

is a marked development of coal in both 

formations. ' 

The 700-foot interval represented by the 

Morrison and Cloverly· near Medicine Bow . is 

represented by the several-thousand feet of 

Bear River and the, upper part of the Beckwith 

· in Uinta County. Although individual units 

{)f this group can not be exactly correlated, 

their upper and lower limits are definitely 

fixed, the upper by the Mowry shale and the 

lower by the Jurassic (Sundance and Twin 

Creek) formations, which are correlated with 

each ·other by their marine faunas. 

The Beckwith includes many beds of coarse 

sands~one· and conglomerate containing pebbles 

of Paleozoic rocks, and the Bear River is coal 

bearing. There is no coal ·in this interval in 

the Medicine Bow . area, and the conglomerate 

of the Cloverly is composed almost entirely of 

small -pebbles of black chert rarely exceeding 

half an inch in diameter. These pebbles 

show by their fineness and thorough. assortment that they have been transported for 

long distances. 

Of the shale fo~mations the Lewis thins 

from east to west-that is, i~ th~ direction in 

which the sandstones thicken. The Mowry 

and the Hilliard and Steele shales, however, do 

not. The westward thickening_ of the Mowry 

is doubtless due to the fact that it is coarser 

and contains .a considerable amount of interbedded sandstone in . its western 'part. The 

Hilliard also carries large lenses of sandstone 

in Uinta County, hut its apparent t.Q.ickening 

toward the west .may be due to the difficulty 

of accurately determining its thickness because 

of lack of exposures, inability to m~~sure dips 

except in the overlying and underlying formations, and the possibility that its boundaries 

have not been .. drawn at the same horizon in 

the several fields. 

·The evidence of these sections seems to 

indicate that all the Cretaceous formations up 

to the top of the .Lewis . were derived from a 

western source. 

As the Medicine Bow formation, or its 

equivalent the "Lower Laramie," rests conformably . on the Lewis and shows some tendency to become coarser westward, as indica.ted by !ts slightly Qonglomeratic character 

in places in the Rock Springs field, the inf-erence is that it was derived from the same source 

as the underlying formations. 

The fact that the Ferris Jormation seems to · 

be more closely related to the Medicine Bow 

both lithologically and structurally than to 

the overlying . formation, together with the 

evidence that the conglomerate cam·e from 

some distant source, would seem j;o indicate 

that this formation also came from the west. 

This view is somewhat strengthened by the 

fact that pebbles of quartzite occurring in the 

conglo~erate are similar to the quartzite in 

the Uinta Mountains. · 
PROFESSIONAL PAPER 108 PLATE LXVI 

U. S. GEOLOGICAL SURVEY 

Section at 

Coalville. Utah 

·p Ot' --

fO~,.V. --

/'.~C.;; - - - vJ"J - - ---- - -----

Conglom_erate 

.... ' ' .... Conglomerat e ', 

Coal r:~,, 

' ' 

Section in southwestern Uinta County 

\ Evanston) 

WASA1CH FORMATION 

-- -- -- - -

FORMATION 

- - -----

Probable gr_r~l!!t..! q_n - - -- --- ---·---

------~------ -­

-------------

I 

I 

I 

I 

I 

I 

Section in 

Rock Springs field 

(Schultz,t909) 

I 

I 

---

FORMATION 

___ _ .,.,. ---

LA RAM IE(?) FORMATION 

------ _-_:--=---=~ ~:: :::.::-~ ~:: ==· = == = ===--=-·-:_ _-:_~--_-_-. -: _- ------------------------------- LEWIS SHAI.E - -- - -------- ------- - -- -- --·-

ADAVILi E FORMATION 

M ESAVERDE fORMATIO"' 

------------

--- - --

H ILLIARD FORMATION 

.... 

FRON TIER FORMATION ' '-, 

' ' ' ' ----- - - --------- -------- ---- ---------------------- ---- ----- ---

·- ----87 mi les-----

- ---.... ----.,.,.,..--,.. 

--------- ------------- ----------------------------

--.. __ _ 

--------

------ ----- -------------------

Section at 

Section on westside of Hanna 

Basin 

Coal bearing HAN NA fORMATION 

sout h end of Great Divide 

Basin 

(Smith.l909) 

--- 35 m i les I 

--30 miles ----

-------------------------

UNDiffERENTIATED 

TERTIARY 

--------

LARAMIE FORMATION 

---- ---- ---

MESAVER DE FOR MATION 

Coal bearing 

----- -- ---

--- -----------------------

FORMATION= NIOBRARA SHALE 

AND BASAL SHALE PORTION 

OF M ONTANA 

FERRIS fORMATION 

------...... _ 

----------- MEDICINE BOW FOR MATION 

LEWIS SHALE 

MESAVERDE FORMAfiON 

STEELE SHALE 

Coal beds ------------- Conglomeratic sandstone 

--------------- - ----------- ---------- - - ---------------- - --·------- -------- ---------- ----- -·------ ------------- rRONT d:.R FORMATION ---------- ------------------ --------- - - ----- ------- - -------

Section on east s ide of Hanna 

Basin 

HANNA fORMATIO N 

f ERRIS FORMATION 

MEDICIN E B OW FORMATION 

MESAVERDE fORMATION 

Coal beds ~ ------ ---------·--- - -------- ------ - - ---------------------- --- ---- - -----·- ----=-------===....::-.::::.:::- - ---

-:~~~?t:::::: :: .!'-~~~5~~!== = = = -::.::-::-_-_-:::: ... --=----=---::.::.:::== = ===---- - ---- ------- -------------------- ---- ------- -------------- ---- - -------------------- ----------- -----

--- ------

' ' ' ' ' ' ' ' ' ' ' ' ' ' 

--:-_::-:-

-------·- --------------------- ----- --- - ------- ·- ----- ------- -----------------------· 

--- -~-- ------ -·- --- ----------------------

-----------------------------------

------ --- ------

TWIN CREEK LIMESTONf. 

---- -- ------

NU GG T SANOSTOIH 

---

---

------

-- ... - --

------

---- --

--- --- --

---- ----- --

---

-----

__ ... 

---

---

--- ---

----

-- -- --- ---- --- --- ---- -- -- ---- --

------ --- --- --- --- --- -- --- -- -- ---- --- --- -- ---- ------ -- ---- --- -- --- ---- --- --

Vertical scale 

s,oLo o~ __ _L __ L_~ ___ oL_ ______________ s~,oL o ______________ ~o~,oo~o~----------- 5~,ooo Feet 

CHART SHOWING THICKNESS, CHARACTER, AND PROBABLE CORRELATION OF FORMATIONS BETWEEN MEDICINE BOW, WYO., AND COALVILLE, UTAH 
STRATIGRAPHY OF THE HANNA BASIN, WYO. 235 

CONCLUSION. field relations do not suggest an unconformity 

By way of summary it may be said that the at the base of the Ferris formation; that 

great break, as indicated by structural a:n,d PaJeozoic rocks contributed to the sedimentary 

field relations, occurs at the base of the Hanna formations from at least the beginning of 

formation; that this formation is the equivalent Cretaceous time; a d that the sediments 

of the Wasatch of the Great Divide Basin and seem to have· been erived from the west or 

Rock Springs fields; that the structural and southwest.