RELATIONS OF THE E~1BAR AND CHUGWATER FORMATIONS IN 

CENTRAL WYOMING. 

By D. DALE CoNDIT. 

FIELD DATA. 

The information set forth in this paper was 

obtained in field work during the seasons of 

1913 and 1915. During 1913 the writer was 

engaged in the detailed mapping of the phosphate beds of the Embar formation on the 

northeast slope of the Wind River Mountains 

and in the Owl Creek Mountains as far east as 

Bighorn River canyon. In 1915 the mapping 

was continued eastward as far as Holt, from 

which a reconnaissance examination was made 

east and north along both flanks of the Bighorn 

Range as far as the latitude of Tensleep. A 

visit was also made to the west end of the 

Rattlesnake Mountains and neighboring points 

in Natrona County, to the Conant Creek anticline, in the eastern part of Fremont County, 

and to the Sheep Mountain anticline, in the 

Bighorn Basin. 

GENERAL CHARACTER OF THE EMBAR 

FORMATION. 

The term Embar was introduced by Darton 1 

to designate strata believed to be of " PermoCarboniferous" age and lying between the Tensleep sandstone (Pennsylvanian) and the Chugwater formation (red beds of Triassic~ age) in the 

Owl Creek Mountains of Wyoming. The type 

locality is at Embar post office, about 25 miles 

west of Thermopolis, where the formation is 

about 250 feet thick and consists largely of 

shaly to massive marine limestone, for the 

most part fossiliferous. Followed laterally 

eastward, the marine limestones gradually give 

place to red shales containing many gypsum 

beds. In the Bighorn Mountains, 70 miles 

east of the type locality, the transformation of 

the Embar beds is so complete that they can 

only with difficulty be distinguished from the 

1 Darton, N.H., GeologyoftheBighornMountains: U. S. Geol. Survey 

Prof. Paper 51, p. 35, 1906. 

overlying red beds composing the Chugwater 

formation. 

The Embar has in recent years attracted attention on account of its yield of petroleum in 

the Wind River basin and also on account of its 

phosphate beds, which · have been traced and 

mapped by the United States Geological Survey throughout the Wind River and Owl Creek 

mountains in the course of land classification. 

The stratigraphy of the Embar formation as 

found in the Wind River and Owl Creek mountains has been outlined in a reconnaissance 

report by Eliot Blackwelder,2 and those areas 

will be only briefly reviewed in this paper, the 

object of which is a consideration of the formation in its eastward extensions from the Owl 

Creek Mountains into the Bighorn Mountains 

and from the Wind River range into the 

Rattlesnake Mountains. (See Pl. LXI.) 

As found in typical development, the Embar 

consists of two principal parts, of ·which the 

upper is largely shaly and the lower is chiefly 

limestone, but includes phosphatic and calcareous shale and nodular chert. The name 

Park City has been adopted by the United 

States Geological Survey for the lower part, on 

the recommendation of Blackwelder, who identifies these beds with the Park City formation 

of Utah. He has also suggested the name Dinwoody formation for the upper shaly part, from 

Dinwoody Canyon, in the Wind River Mountains, where the formation, about 200 feet thick, 

consists of pale-green to white clay and shaly 

limestone weathering brown and containing obscure pelecypod shells. The Park City and Dinwoody beds as found at these localities are described by Blackwelder in a bulletin on the 

stratigraphy of the Wind River Mountains, 

submitted for publication by the United States 

2 A reconnaissance of the phosphate deposits in western Wyoming: 

U.S. Geol. Survey Bull. 470, pp. 452-481,1911. 

263 
264 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

Geological Survey. The somewhat meager 

evidence at hand seems to indicate that the 

Dinwoody beds are of Triassic age and are to 

be correlated with the Woodside shale and 

Thaynes limestone of southeastern Idaho. 

Toward the east the Dinwoody beds thin 

and change to gypseous greenish or brownish 

shales devoid of fossils. Outcrops of this character are found in the vicinity of Bighorn River 

canyon near . Thermopolis. Still farther east 

the beds become increasingly gypseous and 

assume a lithology that can only with difficulty 

be distinguished from that of the Chugwater. 

There is likewise a gradual transformation in 

the Park City beds as followed eastward from 

the Owl Creek and Wind River mountains. 

These changes may be summarized briefly as 

follows: (1) Increasing thickness; (2) lithologic 

changes, including thinning of limestone beds 

and an increasing amount of shale almost entirely of red color; (3) the appearance of beds of 

massive white sediment-free gypsum in all but 

the basal portion; (4) the gradual eastward disappearance of marine fossils except in the basal 

beds of the formation; (5) the increasing prevalence of calcareous conglomerates at the principal limestone horizons; (6) the disappearance 

of concentrated beds of phosphate rock. With 

these changes the equivalents of the Park City 

and Dinwoody units as found in the Bighorn 

Mountains so little resemble the typical Embar 

of the Owl Creek Mo~ntains that the relation 

would hardly be suspected. The same is true 

of the Park City beds in the Rattlesnake Mountains as compared with those in the Wind River 

Range. The one member common to all localities is the nodular chert of the upper part of the 

Park City beds. It is largely through the 

persistence of this rock that the relations of the 

Embar and Chugwater beds have been determined. 

The eastward thinning of the Dinwoody formation and its apparent disappearance at 

about the head of No Wood Creek, in the southern part of the Bighorn Mountains, may be· 

attributed to nondeposition, although it is possible that the beds have been eroded, or, less 

probably, that they are present but so closely 

resemble the Chugwater red beds in lithology 

as to be unrecognizable. 

The character and relations of the Em bar and 

associated strata in the Wind River, Owl Creek, 

and Bighorn mountains are represented in the 

accompanying diagram (fig. 26). It is believed 

that the Embar includes strata ranging in 

age from Pennsylvanian to Triassic, and that 

its beds in the Owl Creek Mountains (see Pl. 

LXII, A) grade laterally into beds that 

were included in the lower part of the Chugwater formation as interpreted by Darton in 

the Bighorn Mountains. The beds as followed 

northeast approach the Chugwater more and 

more closely in lithologic character, and a 

difficulty arises in determining just how far the 

name Embar as a formational designation 

should be carried. Certainly the Embar facies 

is recognizable for some distance northward 

into the Bighorn Range, and throughout this 

part of the field the term Chugwater should be 

restricted to the overlying red beds, probably 

of true .Triassic age, rather than to all the ~eds, 

as the term is applied in the Laramie Range and 

Black Hills, where strata apparently as old as 

Pennsylvanian are included. 

FACIES OF THE EMBAR FORMATION. 

ILLUSTRATIVE SECTIONS. 

The lithologic character of the Embar in its 

typical development in the Wind River and 

Owl Creek mountains and in its gradual .eastward gradation into gypsiferous red beds in the 

Bighorn Mountain region (Pl. LXII, B) is illustrated by the series of sections in figure 25, and 

·also by figure 26, a diagrammatic cross section 

from the Wind River Range northeastward to 

the Bighorn Mountains. The first section in 

figure 25, measured in Bighorn Canyon near 

Thermopolis, is with slight modifications representative of the marine facies of the Wind 

River and Owl Creek mountains. The second 

section was measured near the head of No 

Wood Creek, T. 41 N., R. 89 W., near the . 

southwest extremity of the Bighorn Mountains. 

The conditions of deposition here were evidently intermediate between the marine conditions of the west and the shallow-water or 

lacustrine conditions that prevailed farther 

east. The third section, measured at the south 

end of the Sheep Mountain anticline, near 

Greybull, illustrates conditions not greatly 

different from those indicated at the No Wood 

Creek locality. The presence of fossils at several horizons records temporary marine invasions which alternated with partial emergence 

or shoaling, thus favoring evaporation and concentration into beds of gypsu~ and possibly 
U. S. GEOLOGICAL SURVEY 

Base from U. S. G. S. map of Wyoming 

MAP OF CENTRAL AND NORTHWESTERN WYOMING 

SHOWING OUTCROPS OF EMBAR FORMATIO 

In the Bighorn Mountains and n orth of Cody, w h ere the Embar formation Is thi n or 

possibly lacking, the outcrop of he Ch ugwater for mation 1. I ncl u d d 

JO 0 

tO 0 

Embar formation 

s 

lO 

)0 40 

1916 

:;o J{ilom t :•s =-1 

Embar and Chugwater formati ons 

PROFESSIONAL PAPER 98 PLATE LXI 

A HOLN a co e.l\l"TIMOAE, ,...O. 
RELATIONS OF THE EMBAR AND CHUGWATER FORMATIONS, WYOMING. 

Bighorn River· canyon 

200' 

160' 

Near head of No Wood Creek 

-..... .. ... 

Sheep ~ol.!ntain; ant1CI1ne 

... ............... ... 

····· ·· 

--

. , 

,, 

Ten sleep 

Canyon 

FIGURE 25.-Sections of the Embar formation in central Wyoming. 

LEGEND 

I 

Limestone 

I = 

. 

- Nodular chert 

II -

Red shale 

Gypsum 

Sandstone 

265 
266 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

other salts. The fourth section, measured at 

Tensleep Canyon, is representative of the formation as found on the west slope of the Bighorn Mountains. Red shales with many thick 

beds of gypsum and insignificant beds of limestone make up the section. Similar conditions 

are recorded on the east slope of the same 

range. The local detailed evidence of the 

several facies outlined is presented below. 

MARINE FACIES OF WIND RIVER AND OWL 

CREEK MOUNTAINS. 

The Park City portion of the Embar formation in the Wind River and Owl Creek mountains consists largely of limestone with calca~ 

reous shale and nodular chert. The general 

sequence, in ascending order, is (1) dolomitic 

gray fossiliferous limestone, resting with slight 

unconformity on the Tensleep sandstone; (2) 

argillaceous shaly limestone and sandy calcahorizons, one in the upper part and the other 

near the base. The lower bed is of considerable value in the Wind River Range but is 

missing in the Owl Creek Mountains. 

Section of Park City formation on South Fork of Little Wind 

River, on the northeast slope of the Wind River Mountains. 

Ft. in. 

Limestone, chalky in upper portion, dolomitic 

and cherty, grayish below ... _____ ._. __ ....... 12 0 

Limestone, brownish gray, crystalline, fossiliferous; Leioclema, Fenestella, Spirijerina pulchra, 

Derbya, and small crinoid segments plentiful._. 22 0 

Chert, nodular, in bluish-gray shaly matrix...... 14 0 

Shale, siliceous, bluish gray and cherty near top, 

drab to sepia brown, with phosphate bands, in 

lower part. ________ .. _ . ___ .......... . . _ - . - - . . 37 8 

Upper phosphate bed: 

Phosphate, dark, oolitic, sandy; Pugnax only 

fossil recognized (tricalcium phosphate, 

41.14 per cent)_ . __ . ___ ... __ . _ . _ ....... - . - 1 4 

Phosphate, sandy; Productus nevadensis and 

Pugnax common (tricalcium phosphate, 

43.74 per cent) ........ _ ... _ ............ -. 1 6 

Oinwoody Canyon Bi~horn River canyon 

Wind River Mts Owl Creek Mts 

reet~l~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

FIGURE 26.-Diagrammatic cross section from Wind River Mountains to Bighorn Mountains, Wyo. 

reo us shale of yellowish color; (3) limestone 

with geodes, chert masses, and many fossils, 

among which are Productus nevadensis, Leioclema, Spirijerina pulchra, and Productus subhorridus; (4) phosphatic shale of sepia-brown 

color, with one or more layers of granular phosphate rock and phosphatic limestone at the 

base; (5) nodular greenish phosphatic chert 

interbedded with many shale laminre; (6) siliceous greenish limestone grading up into gray 

resistant limestone, with abundant fossils, including Derbya, Pseudomonotis, Leioclema, 

and Spirijerina pulchra. These and other 

forms mentioned in this paper were identified 

by G. H. Girty. 

The detailed stratigraphy in the Wind River 

Mountains is further illustrated by a section 

measured on South Fork of Little Wind River 

in T. 1 S., R. 2 W. Wind River meridian. It 

will be noticed that phosphate occurs at two 

Limestone, brownish gray, thin bedded; Productus 

nevadensis and Spirifer aft. S. cameratus plentiful. In the lower portion are abundant specimens of Chonetes aff. C. geinitzianus __ . _ . . . . . . 12 

Limestone, massive, yellowish brown, crystalline; 

many fossils, Leioclema especially abundant .. _ 11 

Limestone, dolomitic, interbedded with laminated chert and sandy shale .... _ . _ ... . -.... - - 84 

Limestone, gray, coarsely crystalline, massive; 

abundant molds of diminutive pelecypods and 

gastropods ... _ ............. - . . . . .. -......... 31 

Lower phosphate bed: 

Limestone, phosphatic, gray, with dark spots; 

Lingulidiscina utahensis present .. - . . . . . . . . 1 

Phosphate rock, calcareous, dark, granular 

(tricalcium phosphate, 36.51 per cent) .. -.. 

Limestone, phosphatic, dense textured, dark; 

a fossil, probably Composita, present._ .. -. 

Phosphate rock, calcareous; green granules of 

glauconite(?) abundant; phosphatic shells 

of Lingulidiscina abound (tricalcium phosphate, 48.13 per cent). _ ....... -- ...... -- 1 

Phosphate rock, dark, calcareous; few traces 

of fossils (tricalcium phosphate, 39.92 per 

cent) _ ... - - -.... -.. - - - -... - - - . - - - - - - - - -· · 

0 

0 

0 

0 

0 

6 

10 

0 

8 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE LXII 

A. EMBAR AND ASSOCIATED FORMATIONS ON SOUTH FLANK OF OWL CREEK MOUNTAINS 

NEAR SHOT GUN CREEK, WYO., IN T. 7 N., R. 1 E. 

Upturned shales of Chugwater formation at left; resistant upturned I imestone of Park City formation at right, 

underlain by Tensleep sandstone, which forms the highest hill in the foreground at right. 

B. RED BEDS IN MIDDLE OF EMBAR FORMATION ON EAST SLOPE OF BIGHORN MOUNTAINS 

NEAR BARNUM, WYO., IN T. 42 N., R. 84 W. 

At top of hill is calcareous conglomerate. The beds below consist of structureless friable sandy red shale 

with irregular lamince of limestone, much distorted and faulted. These beds rest on even, undisturbed 

layers of limestone that form the basal part of the Embar formation. Thickness to top of hill is about 

90 feet. 
U. S. GEOLOGICAL SURVEY 

A. BED AND VEINLETS OF GYPSUM IN LOWER 

PART OF EMBAR FORMATION NEAR SOUTH END 

OF SHEEP MOUNTAIN ANTICLINE, WYOMING. 

About 17 feet above the 4-foot layer of gypsum is limestone 

filled with marine fossils. The veinlets of gypsum are 

in structureless red shale. 

PROFESSIONAL PAPER 98 PLATE LXIII 

B. NODULAR CHERTY SHALES OVERLAIN BY LIMESTONE IN UPPER PART OF EMBAR FORMATION 

NEAR HEAD OF NO WOOD CREEK, WYO., IN T. 41 

N., R. 89 W. 

At the base is phosphatic limestone in the geologic position of 

the principal phosphate bed found elsewhere. 
RELATIONS OF THE EMBAR AND CHUGWATER FORMATIONS, WYOMING. 267 

Limest-me, granular, thick bedded, having small 

calcite vugs; granules of glauconite(?) present. 

Ft. in. · cia ted Derbya and other fossils characteristic 

12 0 of the upper part of the Park City formation. 

0 No gypsum beds were discovered here, but 

0 some have been noted by C. J. Hares at Alcova, 

Limestone and dolomite, argillaceous, gray, with 

cherty layers and localized green stains........ 31 

Chert, white and gray, laminated................ 7 

Limestone, buff, dolomitic, resting on Tensleep 

sandstone .................................. . 4 0 

At certain points along the Wind River 

Mountain front the limestone beneath the lower 

phosphate bed is rich in cephalopod and gastropod forms believed by Mr. Girty to indicate 

Pennsylvanian age. 'I'he upper phosphate bed 

contains the Spirijerina pulchra fauna, which is 

regarded as of Permian age. 

TRANSITIONAL FACIES. 

The exposures at the Sheep Mountain anticline and near the head of No Wood Creek 

illustrate conditions intermediate between the 

marine facies of the west and the shallowwater, arid conditions of the east. 

In the Sheep Mountain region the fossiliferous limestones of the upper two-thirds of 

the formation show that deposition for the 

most part took place in sea water. A little 

below the middle, however, persistent beds 

of gypsum (Pl. LXIII, A) alternate with the 

fossiliferous limestones, indicating intermittent 

restrictions of the sea and concentration of the 

water, which temporarily favored precipitation. The fine-textured arenaceous evenbedded red shales of the lower part denote 

deposition for the most part at or a little below 

sea level. The general absence of coarse 

sandy sediments here and elsewhere at the 

Park City horizon indicates that the land 

areas supplying the sediments were reduced 

nearly to base-level and that the products of 

erosion were carried by streams of low gradient. 

The source of the sediment is a matter of 

speculation but may have been land to the 

east, for the beds thicken in that direction. 

Evidence of depositional conditions equiv~ 

alent to those recorded near Greybull and at 

the head of No Wood Creek is found at the 

west end of the Rattlesnake Range, inN a trona 

County. The Park City beds, where observed 

near the Jamison ranch, in T. 33 N., R. 88 W., 

are about 300 feet thick and consist largely 

of red shales with~ few impure limestone beds 

and one limestone member about 25 feet thick 

near the base. The upper part of the formation contains much reddish-brown nodular 

chert (Pl. LXIII, B), with which are asso308300--17--,--18 

about 35 miles to the southeast. 

SHALLOW-WATER FACIES. 

Arid conditions, favoring concentration of 

brines and deposition of thick beds of gypsum 

and probably other salts, prevailed in the 

Bighorn Mountain region almost from the 1 

beginning of Embar time. · The basal 20 feet 

or so of strata resting on the nearly even upper 

surface of the Tensleep sandstone consist of 

dolomitic cherty limestones with a few marine 

fossils, overlain by green and red shales containing locally a layer of impure fine-textured 

curly brown limestone, apparently of algal 

Origin. Higher strata have little regularity 

of sequence, but there is a predominance of 

arenaceous red beds which are gypseous 

throughout and contain an increasing amount 

of gypsum toward the top. The thickest 

gypsum beds in the upper part of the formation are locaUy 100 feet or more thick and consist of numerous clean white layers 5 to 10 feet 

thick, lacking mechanical sediments and alternating with thin layers of red shale and 

laminre of dolomitic limestone, generally a few 

inches thick. In the upper part of the formation there is a persistent layer of nodular 

purplish-red chert in the midst of the gypseous 

beds. The chert bed bas been traced continuously eastward from the Owl Creek Mountains and is believed to lie at the same horizon 

as the greenish chert above the phosphate bed 

of that region. 

The gypsum beds are prominent at Tensleep 

Canyon, at Cherry Creek near Redbank, and at 

numerous other points on the west slope of 

the Bighorn Mountains, being 50 to 100 feet 

or more in thickness at a number of places. 

Deposits even thicker than this are found on 

the east slope of the mountains, along the several forks of Crazy Woman Creek, and to the 

south, along branches of Powder River. 

One of the noteworthy features concerning 

the gypsum beds is that they are not persistent. They grade laterally into red beds and 

conglomeratic limestone of vesicular, tufaceous texture. The gypsum and conglomerate 

beds lie approximately at the same horizon 

and are found in the same general vicinity, but 
268 SHOR.TER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

are not as a rule associated in any one section. 

The gradation from one to the other not uncommonly takes· place within a distance of a 

few hundred yards. This mode of occurrence 

is in large part a result of the conditions of 

deposition, which favored prolonged evaporation in numerous small basins, the margins of 

which · were above water from time to time, 

permitting a drying and cracking of the calcareous muds . and slight erosion. The fragments were rolled along and cemented by calcareous deposits of tufaceous character. The 

conglomerate pebbles, consisting of red shale, 

friable sandy material, limestone, and chert, 

all of local origin, occlir at several horizons. 

A peculiar result of weathering of this rock is 

the removal, partly by solution and partly by 

wind erosion, of many of the pebbles, leaving 

the calcareous matrix of vesicular texture with 

rounded cavities as much as 4 to 6 inches in 

diameter. 

The nonpersistence of the gypsum beds is in 

part attributed to solution in recent times. 

Evidence supporting this conclusion is seen 

along the east slope, where sink holes are not 

uncommon, and also in the absence of gypsum in exposures extending a short distance 

up the mountain slope. This feature is especially noticeable near No Wood and Redbank, 

where there is an a bun dance of bedded gypsum up to about the 6, 700-foot contour and 

none at all in higher exposures. Stra.tigraphic 

measurements above and below this elevation 

show a corresponding difference in thickness. 

The irregularity of the gypsum beds is also 

in part attributable to partial solution at 

different times in the past, when it has been 

favored by the ever-changing ground-water 

conditions. The chief evidence of this process is the greatly distorted character of the 

rocks in all but the basal part of the formation. 

The distortion is noticed even in exposures 

along the base of the mountains. The arenaceous red clays are structureless and loosely 

cemented. Thin laminre of limestone distrib-

. uted through the section are faulted and tilted 

in edgewise blocks. The evident disturbance 

of these beds and the undisturbed character of 

the underlying beds indicate that there has 

been a widespread collapse through the removal 

of soluble parts of the beds, perhaps at different times. Possibly the soluble parts included 

salt as well as gypsum. In fact, the data 

would seem to indicate that they did, because 

a certain amount of distortion is noticed even 

in exposures where there is much gypsum. 

The possibility of the former presence of saline 

deposits leads to the query whether those salts 

may not still exist down the dip far below the 

surface. 

The evidence at hand seems to indicate that 

· the gypsum beds were deposited under conditions somewhat different from those prevailing 

during the deposition of the gypsum beds found 

in the upper part of the Chugwater, which are 

described by Branson.1 The red beds (Chugwater), which are coextensive with the Em bar 

in Wyoming and range from about 1,000 to 

1,400 feet in thickness, are believed by Branson 

to be for the most part of marine origin, and the 

presence of the gypsum in the upper part is 

regarded as pointing to marine origin for that 

part of the red beds in most of Wyoming. The 

reasons for his conclusions are set forth as 

follows: 

1. Uniformity in thickness of beds over wide areas. 

2. Uniformity in texture of rocks over wide areas. 

3. Ripple marking on horizontal beds through most of 

the formation. 

4. Chemical precipitation of limestone at the 800-foot 

level. 

5. Chemical precipitate of gypsum near the top over 

wide areas and at various levels in many places. 

6. Absence of sun cracks and fossils of land animals 

excepting in the Popo Agle beds. 

7. Presence of undoubted subaerial evidences in the 

Popo Agie beds, with textures and materials like much of 

the rest of the red beds. 

The succession of events is summarized as 

follows: 

1. The red beds began under marine conditions, and the 

sea gradually became more and more charged with calcium 

carbonate and magnesium carbonate until a dolomitic 

limestone was precipitated. 

2. Above the limestone the sea gradually filled with sand 

until the sediments were exposed, and the Popo Agie beds 

were formed under subaerial conditions. 

3. The sea in upper Triassic time readvanced and some 

200 feet of sandstone and shales filled the western margin. 

4. Subaerial deposition, mainly of wind-blown sand, 

succeeded and lasted while beds varying from a few feet to 

60 feet in thickness were deposited . 

5. The sea readvanced, but concentration of calcium 

sulphate had been in progress for a long time and soon 

resulted in widespread deposits· of gypsum. 

6. Usually some sandstone and some thin layers of limestone were deposited above the gypsum before the withdrawal of the sea a~ the close of the period. 

1 Branson, E. B., Origin of the Red Beds of western Wyoming; Origin 

of thick gypsum and salt deposits: Geol. Soc. America Bull., vol. 26, 

No. 2, pp. 217-242, 1915. 
RELATIONS OF THE EMBAR AND CHUGWATER FORMATIONS, WYOMING. 26'9 

Darton's conception of the history of Chug- the rule during the later part of the epoch, 

water red-bed deposition is as follows: 1 and aridity favored prolonged evaporation of 

In the latter part of Carboniferous [Pennsylvanian] 

time, and probably during the Permian also, there was 

a widespread emergence, resulting in shallow basins with 

very wide mud flats which occupied a large portion of 

the Rocky Mountain province. In these regions were 

laid down the last deposits of the Pennsylvanian division 

and the great mass of red clay and sands constituting the 

Chugwater formation. These beds probably were deposited by saline water under arid-climate conditions 

and accumulated in a thickness of 1,000 feet or more. 

The waters were shallow much of the time, and there 

were wide, bare wash slopes and mud flats, as is indicated 

by the frequent mud cracks, ripple marks, and impressions of various kinds on many of the layers throughout 

the formation. 

In contrasting the Embar of the Bighorn 

Mountains with the overlying Chugwater beds 

the following features are noted: 

1. Limestone is much more plentiful in the 

Embar, but, aside from that which occurs in 

the basal portion, it is in smaU patches laterally alternating with thick beds of gypsum. 

2. There is ample evidence of frequent 

emergence and slight erosion d.uring late 

Embar time, a feature not observed in the 

Chugwater. This is especially true of exposures on the east slope of the Bighorn Range. 

The conglomerates are, in part, composed of 

travel-rounded pebbles, denoting contemporaneous erosion. There are, however, other 

conglomeratic beds regarded as breccias. 

These consist of angular pebbles of various 

materials bound together by a spongy calcareous, travertine-like cement. The brecciated 

portion may be in part of secondary origin, 

produced by the solution of gypsum and possibly salt beds and the resultant collapse of 

the strata. Breccias and conglomerates such 

as these have not been observed in any part 

of the Chugwater formation. 

3. Although the evidence of contemporaneous erosion in the Embar denotes temporary emergence, it is believed that the materials were for the most part laid down beneath 

the surface of the sea. The persistence of the 

nodular chert and the similarity of certain 

other beds over nearly all the area indicate 

that throughout · Emb;tr time the sea waters 

frequently extended from the west over the 

entire region. Reductions of 'the sea were 

I Darton, N. H., Paleozoic and Mesozoic of central Wyoming: Geoi. 

Soc. America, Bull., vol. 19, pp. 465-466, 1908. 

the inclosed salt-water basins. 

SOURCE OF MATERIALS. 

The source of the materials of the Te:q.sleep, 

Embar, and Chugwater formations is largely a 

matter of speculation. That the Tensleep 

sandstone was at least in part deposited in the 

sea is indicated by its beds of arenaceous 

dolomite, some of which contain fossils. The 

following collection was obtained from beds a 

little above the middle of the formation on the 

east slope of the Bighorn Range in T. 44 N., 

R.84 W.: 

Crinoid stems. 

Nucula levatiformis var. obliqua. 

Deltopecten sp. 

Astartella subq uadrata? 

Schizodus ovatus. 

Plagioglypta canna? 

Lrevidentalium? sp. 

Bellerophon aff. B. sublevis. 

Euphemus? sp. 

Bucanopsis? sp. 

Phanerotrema aff. P. grayvillense. 

Mr. Girty reports that the fauna is too small 

to warrant positive statement as to its relations. It shows a new and very indefinite 

combination of specimens, which may be late 

Pennsylvanian or, less probably, Permian. 

Elsewhere reedlike, columnar plant remains 

have been observed in the Tensleep sandstone. 

It has been found that over the greater part 

of central Wyoming there is a general southward direction of inclination of the lines of 

deposition, suggesting a possible derivation of 

the sands from the north; but this view is not 

supported by the data as to thickness, for the 

formation at the north end of the Bighorn 

Range is 30 to 40 feet thick and increases southward to 200 or 300 feet in the Owl Creek Range 

and to more than 500 feet in the Wind River 

Range. 

The slight thickening of the Embar formation eastward from Bighorn River canyon into 

the Bighorn :Mountains has been mentioned. 

There is likewise a gradual increase to the 

southwest, where the beds become more and 

more calcareous. The change is not considerable westward along the Wind River Mountain front, and, in fact, the formation thins 

from about 430 feet at Dinwoody Canyon to a 
270 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

little more than 200 feet about 50 miles 

farther northwest, across the divide, on Buffalo 

Fork of Snake River at a locality measured 

by Blackwelder. 

ABSTRACT OF PAPER. 

The Embar formation of central Wyoming, which lies 

between the Tensleep sandstone and the Chugwater 

formation, comprises several distinct facies, each of which 

is considered in detail, and some of the formational 

boundaries in the Bighorn Mountain region are redefined. 

In connection with the description of the gypsum and 

associated strata it is suggested that conditions were 

possibly also favorable for accumulation of salt beds. The 

chance of finding such deposits down the dip below the 

surface is believed to be sufficient to merit further investigation.