RELATIONS OF LATE PALEOZOIC AND EARLY MESOZOIC FORMATIONS 

OF SOUTHWESTERN MONTANA AND ADJACENT PARTS OF WYOMING. 

By D. DALE CONDIT. 

SUMMARY OF CONCLUSIONS. 

The object of this paper is twofold-to present evidence found in southwestern Montana 

concerning the .great Jurassic base-leveling and 

its bearing on the solution of certain ·stratigraphic problems involving late Paleozoic, 

Triassic, and Jurassic formations, and to set 

forth the relations of those formations to· beds 

in western Wyoming. The conclusions briefly 

summarized are as follows: 

Prior to the encroachment of the sea from 

the northwest in late Jurassic time prolonged 

erosion and base-leveling occurred over much 

of the Rocky Mountain region. From the 

Idaho State line near Yellowstone National 

Park northward to the vicinity of Helena the 

erosion surface thus produced truncates beds 

of Triassic and Carboniferous age, through a 

stratigraphic range of about 1,000 feet. 

The Quadrant quartzite at the type locality 

in the northwestern part of Yellowstone Park 

is approximately equivalent to the Amsden 

and Tensleep formations in Wyoming. The 

Park City (Pennsylvanian and Permian), Dinwoody (Lower Triassic), and Chugwater (largely 

Triassic) of the Wyoming section are in part 

represented by the Teton formation of Yellowstone Park. The quartzitic cherty basal beds 

of the Teton, containing the phosphate rock, 

are equivalent to the Phosphoria formation of 

Idaho, which corresponds to the upper part of 

the Park City formation. In western Montana north of latitude 45° 30' the overlying 

Triassic shaly limestone and red shale were removed by the Jurassic erosion and the Ellis 

formation (Upper Jurassic) rests on the pt>"rtly 

eroded Phosphoria formation. 

FIELD WORK. 

The information set forth in this paper was 

obtained by the writer during the seasons of 

1913, 1915, and 1916. The first two years 

were spent in detailed mapping of the Permian 

phosphate beds along the northeast slope of the 

Wind River Mountains and throughout the 

Owl Creek Mountains of Wyoming. A reconnaissance trip was also made on both the east 

and west slopes of the Big Horn Mountains. 

In 1916 a reconnaissance examination occupying about three months was made in Montana 

from Helena south to Yellowstone Park and 

west to longitude 112°, and later in the same 

season a visit was made to exposures in the 

vicinity of Cody, Wyo. Nearly all the outcrops in Wyoming represented on the accompanying !nap (Pl. IX) except those near the 

Idaho State line were visited, and also practically all those in the Montana area. 

FORMATIONS IN SOUTHWESTERN MONTANA 

DISCUSSED IN TIDS PAPER. _ 

The Madison limestone, of Mississippian age, 

which ranges in thickness from 200 to 2,500 feet 

in different parts of Montana, Idaho, and Wyoming, forn1s an unmistakable unit throughout 

the region and a convenient datum in the study 

of the less constant higher beds. Its slightly 

uneven surface is in places capped by conglomerate made up of pebbles of the Madison 

limestone in a sandy matrix. No generalized 

section of beds above the Madison that is representative of all of southwestern Montana can 

be made, and therefore each formation will be 

described briefly in turn and illustrated by 

stratigraphic sections measured at a number of 

localities. 

QUADRANT QUARTZITE. 

The term Quadrant was introduced by 

Peale 1 to designate a formation consisting of 

150 feet of cherty limestones in the upper 

part and 200 f.eet of red limestones below, 

overlying the Madison limestone in the vicinity 

1 Peale, A. C., U. S. G_eol. Survey Bull. 110, pp. 39-43, pis. 1, 4, 1893. 

Ill 
112 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1918. 

·of Three Forks, Mont. The names for the defines the limits of the Quadrant ( ?) and 

Paleozoic formations in the Three Forks area Phosphoria formations as applied in that 

were stated by Peale 1 to have been determined area. 

''after consultation with the members of There has been considerable uncertainty 

Mr. Arnold Hague's division." The strata concernrng the age of the Quadrant quartzite. 

to which the name Quadrant was applied Peale's studies in the Three Forks quadrangle · 

were therefore doubtless correlated with the yielded fossils of Mississippian and Pennsylstrata, mostly quartzitic sandstone, found on vanian age. ColleGtions of fossils made years 

·Quadrant Mountain, in the northwestern part ago by Weed and others northeast of the Three 

-of Yellowstone Park, for which Arnold Hague Forks area were found to contain Mississippian 

and W. H. Weed, who surveyed the park be- forms, and more recent· collections northwest 

tween the years 1883 and 1893, had selected of the Three Forks area, within and near the 

the name Quadrant quartzite. The publica- Philipsburg quadrangle, have yielded Penntion of the Yellowstone Park folio, with four sylvanian forms. · Field work in 1916 showed 

geologic maps, was delayed until 1896. In that the typical Quadrant in the Yellowstone 

1894, however, the name Quadrant quartzite Park, as described b:y- Weed in Monograph 32, 

was again used, by Weed,2 for the rocks included representatives of · both the upper 

overlying the Madison limestone and under- Mississippian and the Pennsylvanian. 

lying the Ellis formation in the Livingston The Quadrant generally consists of three 

quadrangle, Mont., which doubtless were re- parts. The basal member is chiefly sandy 

garded as equivalent to the typical Quadrant red shale, slightly calcareous, containing few 

quartzite of the Yellowstone Park. · Since recognizable marine fossils. This red-shale 

1896 the name has been extensively used for member is only a few feet thick along the 

strata in many parts of western Montana Idaho State line but thickens northward to 

supposed to be equivalent to those at the type about 150 feet near Bozeman. Over the red 

locality. shale is more or less limestone and carbonPeale did not give any description of the aceous shale, absent locally c but present in 

formation at the type locality, and the first widely separated localities and containing abunpublished section of the rocks of Quadrant dant fossils, which are believed by G. H. Girty 

Mountain is that measured by Weeds and probably to denote early Pennsylvanian age. 

quoted on page 117 of this report. It will At the west boundary of Yellowstone Park 

be noted that the overlying cherty quartzitic this limestone is less than 50 feet thick and 

beds · described as the Phosphoria (Permian) sparingly fossiliferous, but it thickens westin this paper are included by Weed ih the ward to 2,50 feet in the Snowcrest Range, 

Teton formation. Although the Teton beds where it is 'rich in fossils. At Lombard, about 

of the Yellowstone Park region are also present 75 miles northeast of the Siiowcrest Range, 

in the south third of the Three Forks quad- it is nearly as prominent and equally fossiltangle, they were mapped as a part of the Ellis iferous, but at intervening pointsit is generally 

(Jurassic) in the Three Forks folio, except thin and contains poorly preserved fossils. 

that the lower· cherty quartzitic portion The limestone member is overlain by 100 to 

(Phosphoria) was considered a part of the 400 feet of quartzitic sandstone interbedded 

underlying Quadrant. The reference of the with a less amount of sandy dolomitic limelower part of the Teton to the Quadrant has stone and thin layers of smooth-textured 

been followed in all the geologic folios pub- argillaceous limestone, more or less cherty and 

lished for areas in western Montana, including containing traces of poorly preserved fossils. 

The thickness of the Quadrant is in most the Philipsburg.4 Pardee,5 however, in a 

recent report on the Philipsburg regi~n, places a little more than 300 feet, but from 

the Gravelly Mountains west to the Snow1 Idem, p. 14. 

2 Weed, W. H., U.S. Gaol. Survey Gaol. Atlas, Livingston folio (No. 

1), 1894. 

aU. S. Gaol. Survey Mon. 32, pt.' 2, p. 34, 1899. 

4 U.S. Gaol. Survey Geol. Atlas, Philipsburg folio (No. 196), 1915. 

5 Pardee, J. T.,The Garrison and Philipsburg phosphate fields, Mont.: 

U.S. Gaol. Survey Bull. 640, pp. 206--211, 1917. 

crest Mountains the thickness increases from 

about 500 to nearly 1,000 feet. The formation also thickens northeastward from Lombard, a point on Missouri River about 35 miles 

northwest of Bozeman. 
U. . GEOLOGICAL SURVEY 

G 

Point where stratigraphic section was 

measured. Number refers to section 

on Plate X . 

Sc ale 1.od:ooo 6 o 6 12 18 24 30 Mi les 1 

~~----==~---c===---- 1918 

Base from 1 : 1, 000,000-scale maps of 

Montana, Wyom ing and Idaho 

Compiled in 1913 

MAP WING DISTRIBUTION OF PHOSPHORIA FORMATION IN MO 

AND EMBAR FORMATION IN WYOMING 

PROF ESSIONAL PAPER 120 PLATE IX 

Geology by D. Dale Cond it 
PALEOZOIC AND MESOZOIC FORMATIONS OF MONTANA AND WYOMING. 113 

,J»HOSPHORIA FOl!-MATION. Lingulidiscina utahensis, together with fossil 

bones. In some places the phosphatic mate~ial 

The Quadrant proper is overlain by 100 to appears as a resinous brown substance, formrng 

250 feet of dark-gray cherty quartzite, layers a cement for the quartz sandstone. At 30 to 

and ropy masses of n9dular chert and shale, 60 feet above the base of the Phosphoria occur 

with one or more beds of phosphate rock. The other phosphatic beds consisting of one _or 

sequence _is regarded as equivalent to par~ of more layers of gray to black oolitic phosphonte 

the Park City formation of Utah and Wyomrn?, and perhaps a few feet of dark shale overlain by 

but more :nearly equivalent to the Phosphoria chert either in thin wavy layers or as nodular 

formation of Idaho, as was recognized in 1913 masses mixed in an irregular manner with 

by Richards 1 and later by Stone and Bo1_1ine,Z brownish quartzitic sandstone. At irregu~ar in whose rep~rt the name was first pubhs~ed intervals in the sandstone there . are peculiar 

for those beds in Montana. Peale, 3 in mapprng distorted cylindrical columns of lighter-colored 

the geology of the Three Forks quadrangle, in- sandstone 1 to 4 inches in diameter, perpencluded the Phosphoria beds as a part of the dicular, or nearly so, to the bedding planesw 

Quadrant, and he has been followed by Calkins 4 Both the shale and the phosphate beds are 

in mapping the Philipsburg quadrangle. W e~d lacking a short distance northeast of a line 

and others,5 however, included these beds rn drawn from Helena to the northwest corner of 

the Teton formation of the Yellowstone Park yellowstone Park. The uppermost beds of the 

region, which . comprises beds ran?in~ in age Phosphoria contain poorly preserved brachifrom late Pennsylvanian to Triassic, and opod shells and fish bones, probably of Performing thre~ dissimilar lithologic units. The mian age. 

grouping is somewhat sim~ar to _tha~ of the 

Embar formation of··Wyoming, which Includes 

PennsyJvaniah and · Permian limestone and 

·Triassic· shale. 

The plane of contact between the Phosp~oria 

and Quadrant proper is not easily drawn m all 

places, for the reason that there is no mar~ed 

change in the lithology -of the beds. T~e hne 

of division is commonly marked by a few Inches 

of conglom~rate , and a nonpersistent bed of 

phosphate: rock, apparej}tly of clastic origin. 

It is suspected that· these beds denote an unconformity. The : overlying rock is dark-gray 

cherty quartzi~e with scattered phosphorite 

granules, diff~ring chiefly in color _fro~ the_ pu~er 

quartzitic. s~ndst<?ne below, whiCh Is. pmki~h 

gray, cross-bedded, and intercalated With argillaceous creamy limestone. 

The Phosphoria is notably siliceous, being 

either cherty or. quartzitic almost throughout. 

In Y ello~stone Park and to the west along and 

near the Idaho State line the irregular la:yer of 

phosphate rock at the base is made up of_ fragments ofphosphatized shells of the brachiOpod 

1 Richards, R. W., unpublished manuscript. 

2 Stone;R. W., and Bonine, C. A., The Elliston phosphate field, Mont.: 

U.S. Geol. Survey Bull. 580, p. 375, 1914. 

3 Peale, A. C., u. S. Geol. Survey Geol. Atlas, Three Forks folio 

(No. 24), 1896. 

4 Calkins, F, C., and Emmons, W. H., U.S. Geol. Survey Geol. A.tlas, 

Philipsburg folio (No. 196), 1915. 

5 Hague, Arnold,)'ddings, J.P., Weed, W. H., Walcott, C. D., Girty, 

G. H., Stanton, T. '\\'.;and Knowlton, F. H ., Geologyofthe Yellowstone 

National P~k: U_. S. Geol. Survey Mon. 32, pt. 2, 1899. 

TETON FORMATION. 

The Teton formation, as defined by Weed for 

Yellowstone Park, included the rocks now 

named Phosphoria formation, and the overlying Triassic brown shaly limestone . and r~d 

3andy shale. The brown limestone IS ~nmistakably related to the Dinwoody formatiOn of 

western Wyomin~. This relation was suspected 

by Blackwelder, 6 who states that the low~r part 

of the Teton formation is probably equivalent 

to the Embar of Wyoming. The overlying red 

shale is in part equivalent to the Chugwater 

formation of Wyoming and probably to the 

Thaynes limestone of Idaho. The p~rt ?f the 

Teton beds ove ~ying the Phosphona IS approximately 800 feet thick along the Idaho 

State line west of Yellowstone Park, but -as 

shown by figure 14 this part was beveled by 

the Jurassic erosion and completely· removed 

north of latitude 45° 30', both west and east of 

Yellowstone Park. 

Fossils of Triassic age are plentiful in the· 

shaly brown limestone. No fossils were found 

in the red shales but above them is locally a. 

bed of richly fos~iliferous limestone which at 

one point along the Idaho State line sou~h of 

Red Rock Lakes was found to contaln a 

pleurot.omarioid gastropod, possibly identical 

6 Blackwelder, Eliot, A reconnaissance of the phosphate deposits in 

western Wyoming: U. S. Geol. Survey Bull. 470, p. 455, 1911. 
114 SHORTER CONTRIBUTIONS TO GENERAL GEO.I OGY, 1918. 

with or closely resembling one that occurs in pods. These beds, which are wholly nonthe Thaynes limestone in southeastern Idaho. marine, lie between the marine Jurassic and 

The paleontologic and lithologic evidence at marine Upper Cretaceous beds. On the basis 

hand does not warrant positive statements 

as to the relations of the upper part of the 

Teton to the Idaho or Wyoming sections. 

Exclusion from the Teton of the basal portion, 

equjvalent to the Phosphoi-ia formation, leaves 

the higher shaly brown limestone and red 

beds of Triassic age to which the name 

Teton could be applied, but this seems inadvisable for several reasons, one of which is that 

the name has not been used for areas outside 

of Yellowstone Park. It is therefore believed 

that the use of the name Teton will be discontinued when enough additional field work 

shall have been done both in Montana and 

southeastern Idaho to permit the proper application of formation names now in use in 

Idaho and Wyoming. 

ELLIS FORMATION. 

In late Jurassic time, subsequent to a long 

erosion interval during which there was more 

or less tilting of the strata, a subsidence brought 

in from the northwest an arm of the sea in 

which were deposited the sediments of the 

Ellis formation. The rocks consist of fossiliferous greenish shale and limestone and a 

variable amount of rust-brown weathering 

sandstone and conglomerate. At Elkhorn 

mining camp, near Helena, and for 70 miles 

to the south, the Ellis beds rest on more or less 

disturbed strata of the Phosphoria formation, 

but farther south the Ellis and Phosphoria 

are separated by Triassic shaly beds that 

thicken southward and constitute a portion of 

the Teton formation. The Ellis beds are 

abou~ 200 feet thick in Yellowstone Park but 

thicken northward and northwestward . to 

about 400 feet in the Livingston and Philipsburg regions. It is suspected that the Ellis 

represents only the basal portion of the several 

thousand feet of the marine Jurassic beds in 

southeastern Idaho but corresponds closely 

with the Sundance ;formation of Wyoming. 

KOOTENAI FORMATION. 

Overlying the Ellis formation is a motley ., "d ' N'A ~a VlO\IVO , :... "d "N'A JO srm :__ .>ld:J.VN.lNOJ.Sh\OmA ~0 NOB.L 

aggregation of beds consisting in great part of 

red and green shale with conglomeratic sand- of lithology they are correlated with the 

stone and quartzite, and including near the Kootenai formation of the Philipsburg quadtop ·a limestone member. crowded with gastro- rangie, which is Lower Cretaceous. They 
FEET 

2,000 

1,900 

1,700 

1,600 

1,500 

1#()0 

1,300 

1,200 

1,100 

1,00.0 

900 

800 

700 

500 

400 

Near Cardwell, · Mont. -

2 

1,.;-dian Creek 

T.8S.,R.2E. :Montana 

principal meridian 

bed 

3 

Snowcrest Mountains 

T.IO S.1R.3W. 

Montana 

principal meridian 

4 

Idaho-Montana 

State line near Red Rock Lakes 

5 

Quadrant Mountain 

Yellowstone 

National Park 

------

// 

//,/' 

// 

// 

/ 

// 

/ 

/// 

6 

Dinwoody Lake,Wyo. T.4N.

1 R.5W. 

Wind River meridian 

FEET I 

2,500 

2,460 

2,300 

z,<:oo 

2,100 

2,000 

1,400 

1,300 

1,200 

1,100 

1,000 

900 

l '~ '-~ ~ 'LfG£•·'J 'o MAOI~ON LIMESTONE 

STRATIGRAPHIC SECTIONS IN SOUTHWESTERN MONTANA AND YELLOWSTONE NATIONAL PARK . . 

LEGEND 

Limestone 

~ 

812] 

Sandstone 

~ 

Nodul ~ ar chert; 

Ill 

Shale 

Red • bed.s 

J l 

PALEOZOIC AND MESOZOIC FORMAT'IONS OF MONTANA AND WYOMING. 115 

may possibly include_ the equivalent of the 

Morrison · formation. The thickness of the 

Kootenai ranges from 1,000 to 1,500 feet. 

The most conspicuous beds of the Kootenai 

are the gray gastropod limestone and a bed 

of conglomeratic sandstone in about the 

middle of the formation, the pebbles of which 

are dark chert. Both the beds are reported 

at many places in western Montana, in Yellowstone Park, and in the adjacent country in 

Wyoming. They form hogbacks projecting 

above the poorly exposed shaly. red beds of 

the Kootenai and the dark shale of the overlying Colorado formation. 

STRATIGRAPHIC DETAILS IN THE MONTANA 

AND YELLOWSTONE PARK AREA. 

[See Pl. X.] 

JEFFERSON RIVER .CANYON NEAR CARDWELL. 

A few miles east of Cardwell, which is on 

Jefferson River near the mouth of Boulder 

River, the broad valley narrows to a sharp 

canyon just wide enough for the tracks of the 

two railroad lines between the river and steep 

cliffs. On the south side of the valley (locality 

1, Pl. IX) are complete exposures of the 

Quadrant and Phosphoria formations, dipping 

steeply northwestward. Several faults introduce some doubt as to the total thickness, but 

the sequence of the beds is clear. A condensed 

section Of the beds measured here follows: 

S ection near Cardwell, Mont. 

Ellis formation: Feet. 

Limestone, sandy, impure, . cross - bedded; 

weathers to rust-brown color; lower beds 

contain fossils.... . . .. . .. .. .. .. . .. .. . . .. . .. . 36+ 

Phosphoria formation: 

Quartzite, dark gray, containing a few quartz. 

pebbles and bands of chert and a layer of 

travel-rounded chert pebbles at top......... 42 

Chert in thin shaly layers ................... 1.. 6 

Phosphatic beds consisting of phosphate rock, 

limestone, sandstone, shale, and chert, mostly 

in thin beds. . . .. .. .. .. .. .. .. .. .. . .. .. .. .. 35 

Sandstone, dark gray, slightly dolomitic and 

cross- bedded, containing peculiar ropy 

masses and markings...................... 29 

Quadrant quartzite: 

Quartzite, alternating with dolomitic limestone 

and thin chert layers; poorly preserved fossils 

in lower part.. . .. . .. .. .. . .. .. .. . .. .. .. .. . . 140 

Limestone, dolomitic and arenaceous, containing 

alternating thin layers of chocolate-brown shale 

and nodular chert; fossils fairly abundant in limestone but poorly preserved .............. _ . . . . . . 91 

Feet. 

Shale, brick-red .... _............................ 56 

Conglomerate, with matrix of limestone containing 

rounded pebbles of chert, limestone, and sandstone ..... _ ............... _ . . . . . . . . . . . . . . . . . . . 4 

Shale, brick-red, alternating with shaly sandstone, 

with conglomerate made up of pebbles of Madison 

limestone resting on uneven surface of Madison 

limestone... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 

INDIAN CREEK, MADISON VALLEY. 

Indian Creek joins Madison River from the 

east a few miles south of Cameron. Its 

branches drain a rugged area containing numerous alpine peaks in the heart of the Madison 

Range. From a densely timbered basin in the 

Mesozoic rocks the upper waters of the stream 

unite and flow westward through a sharp canyon (Pl. XI, A) in pre-Cambrian rocks bordered on the east by Paleozoic rocks that dip 

steeply northeastward. In sees. 20 and 21, T. 

8 S., R. 2 E ., on the north canyon wall (locality 2, Pl. IX), there are complete exposures of 

strata from the Madison limestone to the top of 

the Kootenai, stratigraphically nearly 2,000 

feet higher. A fault of large displacement cuts 

the lower Paleozoic strata at this point but 

does not affect ·the sequence of the higher 

strata. A condensed section of beds measured 

here is given below. 

S ection on Indian Creek, Mont. 

Kootenai formation: Ft. in. 

Limestone, gray, smooth textured, crowded 

with gastropods in basa.l portion........... 50 

Shale, ferruginous, with a few sandy layers 

and a layer of ocher-yellow blocky limestones, lavender-colored on fresh fracture .. 400 

Sandstone, quartzitic.. ..................... 38 

Shale, variegated red and brown. _ .. ·. . . . . . . 64 

Sandstone, coarse, with irregular conglomeratic layer in the midst, the pebbles mostly 

dark chert..... . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

Shale and clay with carbonaceous layers...... 49 

Sandstone, coarse, arkosic, with undulating 

base. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 

Shale, yellowish gray, with sandy layers...... 59 

Shale, reddish, with sandy layers..... . . . . . . . 109 

Ellis formation : 

Shale, bluish gray to green, with layers of impure limestone. . .. . .. .. . .. .. . . .. .. . . . . . . 98 

Sandstone, green, friable.................... 14 

Limestone, granular, gray, rich in fossils..... 32 

Shale, greenish, weathering yellow. . . . . ... . . . l8 

Limestone, gray, sparingly fossiliferous...... 51 

Limestone, gray, shaly, richly fossiliferous ... · 88 

Shale, calcareous, gray, fossiliferous......... 28 

Unconformity (?). 
116 SHORTER CONTRJBUTIONS TO GENER~L GEOLOGY, 1918. 

Ellis formation-Continued. Ft. in. 

Basal member of Ellis or possiblyequivalent 

of Nugget sandstone of western Wyoming: 

Shale, ocherous, sandy, gypseous in upper 89 

part............ ..... ............... 89 

Shale, calcareous, sandy....... . . . . . . . . . 12 

· Limestone, impure, sandy. . . . . . . . . . . . . . 13 

Sandstone, cross-bedded, yellowish, friable................................. 42 

Unconformity. 

Triassic marine beds: 

Shaie, sandy, grading downward into thinbedded limestone that weathers sepiabrown, closely resembling the Dinwoody 

of Wyoming, containing Lingula n. sp. and . 

other fossils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 

Phosphoria formation: 

Sandstone, dark gray, containing irregular 

chert layers and columnar rods of lightercolored sandstone ...................... . 

Chert in thin dark wavy layers ............. . 

Phosphatic beds: 

Phosphate rock, gray, coarsely oolitic ... . 

Limestone, dark gray .................. . 

Shale ................................. . 

Phosphate rock, black, oolitic, friable, 

with 2 inches of shale near middle; 

59.52. per cent tricalcium phosphate .. 

. Shale, carbonaceous ................... . 

Phosphate rock, impure, containing fish 

bones .............................. . 

Sandstone, cherty ........................ . 

Quartzite, dark gray ...................... . 

Shale ..................................... . 

Limestone, sandy, ·containing phosphatized 

fossil fragments and travel-rounded chert 

pebbles ................................. . 

Quadrant quartzite: 

Sandstone, quiutzitic, ·gray, cross-bedded, 

not measured. 

65 

33 

2 

1 

0 6 

4 

10 

2 

11 

10 

4 

12 

3 

6 

There is some question as to the lower limit 

of the Ellis formation in the preceding section. 

It seems clear that the position of the· great 

unconformity is at the base of the yellow sandstone that rests on the Triassic marine beds, 

but the overlying shaly gypsiferous beds apparently represent continental sedimentation 

in Jurassic time prior to the encroachment of 

the Ellis Sea and if so would not appropriately 

be included in the Ellis. Possibly these gypsiferous beds and the . yellow sandstone represent the Nugget sandstone of western Wyoming, as suggested in the diagram (fig. 14). 

SNOWCREST MOUNTAINS. 

The Snowcrest Mountains are west of Ruby 

River, about 20 miles a little west of south 

from Viiginia City. The highest pea.ks, more 

than 10,000 feet in elevation, are capped by 

the resistant Quadrant quartzite. (See Pl. 

XI, B.) The most interesting -features of the 

stratigraphy of this range are the unusual 

thickness of the Q1,1adrant formation as compared with its thickness in the section in the 

Gravelly Range, 10 miles to the east, and 

the prominent development of the dark, 

richly fossiliferous limestone in its lower portion. The following fossils were identified by 

G. H. Girty, who regards them as of early 

Pennsylvanian age: 

Lingula sp. 

Lingulidiscina sp. 

Schizophoria n. sp. 

Derbya robusta? 

Productus cora. 

Productus aff. P . coloradoensis. 

Productus aff. coloradoensis var. 

Productus n. sp. 

Spirifer rockymontanus. 

Composita subtilita. 

Hustedia mormoni. 

The subjoined section shows all but the uppermost beds of the Quadrant as measured in 

sec. 26, T. 10 S., R. 4 W. (locality 3, Pl. IX): 

Section of Quadrant quartzite in Snowcrest Mountains, Mont. 

Feet. 

Limestone, dolomitic, with gray sandy layers........ 80 

Sandstone, quartzitic, gray, with two thin layers of 

brownish-mottled shale ........................... 207 

Limestone, cherty, dolomitic, with thin sandy layers. 29 

Sandstone, quartzitic, gray, with thin layer of black 

shale in upper part and interbedded layers o£ dolomitic and smooth-textured dark-gray limestone. 0 0 0 0 247 

Limestone, dark gray, sparingly fossiliferous; several 

quartzite ]ayers ......................... -... . . . . . 55. 

Quartzite, pinkish.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 

Limestone, dark -gray, shaly to massive layers, with 

scattered brown to black chert nodules; fossils extremely abundant, especially in shaly limestone 

(see list above) ..................... · ............. 253 

Rocks poorly exposed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 

Sandstone, conglomeratic at base, possibly basal member of Quadrant formation; approximate thickness. 20 

Rocks not exposed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Limestone of fissile shaly structure, rich in fossils. 

This is apparently a part of the Madison but represents a phase not found elsewhere to the east or 

southeast. 

IDAHO-MONTANA STATE LINE OPPOSITE RED 

ROCK LAKES. 

On the State line between Idaho and Montana, in the Centennial Range south of the Red 

Rock Lakes (Pl. XII), about 35 miles southeast of the locality in the Snowcrest Mountains 

above described, the Quadrant formation 

proper is greatly reduced in thickness, being 
U. S. GEOLOGICAL SURVEY 

A. CANYON OF INDIAN CREEK, MADISON RANGE, MONT. 

Showing cliffs of quartzite of the Phosphoria formation (b) overlain by shaly Mesozoic beds (a). 

PROFESSIONAL PAPER 120 PLATE XI 

B. PRINCIPAL PEAK IN SNOWCREST RANGE, MONT. 

Consisting of: Madison limestone (lowest exposures in view), overlainikby shaly limestone of the Quadrant quartzite capped by quartzitic beds which form the talus slopes in the foreground. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 120 PLATE XII 

A. VIEW WESTWARD ALONG CREST OF CENTENNIAL RANGE FftOM POINT NEAR MONTANA PRINCIPAL 

MERIDIAN. 

Bed Rock Lakes in distance. The rocks are Phosphoria formation, Quadrant quartzite, and Madison limestone. 

B. SHALY CALCAREOUS BEDS ALONG CREST OF CENTENNIAL RANGE, EQUIVALENT TO DINWOODY FORMATION 

OF WYOMING. 
PALEOZOIC AND MESOZOIC FORMATIONS OF MONTANA AND WYOMING. 117 

probably no more than 200 feet thick, as compared with 900 feet in the Snowcrest locality. 

The upper sandy beds and underlying fossiliferous limestone are present, however, and a 

fossil collection shows close relation with the 

fauna of the thick shaly limestone in the Snowcrest section. The red shale usually o bs~rved 

at the ·base of the Quadrant is absent, and 

there is only a few feet of ocherous sandy beds 

resting on the massive white saccharoidal Madison limestone. · 

The Phosphoria formation at this point resembles in lithology the beds exposed on Indian 

Creek but contains in addition a valuable bed 

of phosphate rock at the base, nearly 4 feet 

thick and carrying 70 per cent of tricalcium 

phosphate. This bed, which is evidently of 

clastic origin, consists chiefly of fragments of 

phosphatized shells of the fossil Lingulidiscina. 

At the base there is a few inches of quartz or 

chert conglomerate marking the lower limit of 

the Phosphoria formation. 

QUADRANT MOUNTAIN, YELLOWSTONE •PARK. 

Quadrant Mountain, a . prominent topographic feature in the northwestern part of 

Yellowstone National Park, presents bold exposures of the quartzitic beds which have been 

named Quadrant quartzite, as . explained on 

pages 111-112. Below is given part of a section . 

measured by Weed 1 at the southeast end of 

the mountain (locality 5, Pl. IX). The portion 

of the Teton assigned to the Phosphoria under 

the new classification is indicated. 

Section on Quadrant Mountain, Yellowstone National Park. 

Teton: 

[Measured by W. H. Weed.) 

Feet. 

Sandstone, red and orange-colored, coarsely 

granular; weathers in blocks. __ ._.___________ 15 

Calcareous shale, dark slate-colored, fossiliferous. 5 

Limestone, bright yellow, fissile, . with platy 

debris, grading into yellow and red spotted calcareous sandstones below_ .. _ . _ ....... _ . _ .. _ _ 40 

Shales, light greenish drab, changing to red and 

grading into overlying beds._ ... _ ..... _._.... 75 

Conglomerate of red and gray quartz pebbles in 

limestone matrix .......... _ . _ . __ ..... _ . __ .. _ 10 

Cherty sandstone, the lower part without chert, 

is brown; slightly calcareous at base, becoming 

more so above [Phosphoria formation]_ . _ ..... _ 100 

Quadrant: 

Limestone, dense, white, weathering same color.. 10 

Sandstone and limestone in alternating bands ... _ 15 

Limestone, light gray and dense and pure .. _. __ . 12 

1 U. 8. Geol. Survey Mon. 32, pt. 2, p. 34, 1899. 

Quadrant-Continued. Feet. 

Quartzite, pure white, thin bedded; forms a persistent band along face of mountain........... 6 

Quartzite, more thickly bedded, white.......... 65 

Limestone, very light gray, somewhat dense, containing very small fragments of light-colored 

chert_ . _ . _ . _ . _ . ___ .... __ . . . . . . . . . . . . . . . . . . . . 10 

Quartzite, white, calcareous, with intercalated 

bands of limestone carrying quartzite fragments 30 

Limestone, light gray, with angular fragments of 

sandstone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Quartzite, white, weathering pink and rust color 

but appearing black when seen from a distance, 

owing to the growth of lichens upon it. . . . . . . . 130 

Limestone, light gray, dense................... 2 

Sandstone, well banded, white, saccharoidaL.... 6 

Sandstone, very calcareous, saccharoidal, white 

and rust color. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Talus slope of sandstone blocks; also of cherty 

limestone ___ ..... _ . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 

Additional sections measured at several 

places on Quadrant Mountain during the present investigation are given below. The Phosphoria exposures were found at the south end 

of The Pocket, a peculiar natural amphitheater 

cut into the plateau surface of the mountain 

top. Complet e exposures of the Quadrant 

quartzite were found about 2 miles to the 

southwest, on the north face of Bannock Peak. 

(See Pl. XIII, A.) 

Detailed section of Quadrant and higher formations on Quadrant Mountain. 

Triassic beds: Ft. in. 

· Limestone, gray, thin bedded; weathers 

sepia-brown; grades up into shaly, sandy 

yellowish beds overlain by red shale; 

Lingula n. sp. is plentiful in the limestone 60+ 

Phosphoria formation: . 

Sandstone, dark· gray, with scattered chert 

nodules ... . .......... l ................... 15± 

Chert, in ropy masses and wavy layers, with 

irregular sandy layers in upper part....... 30 

Sandstone, dark, gray, with cauda-galli markings on , bedding and scattered siliceous 

nodules and ropy masses; fishbones plentiful. __ ... _ . _ . _ ..... _ . _ ............... _ . 9 

Phosphatic rock, gray, with green specks.... 1 

Sandstone, dark gray, with markings; chert 

and fishbones similar to those in 9-foot 

sandstone above.......................... 23 

Quartzite, dark gray_ .. . . _ ... _._ .. _ .. ____ ~ ~ 16 

Phosphate rock, sandy, resinous; has brown 

appearance on fresh fracture; contains fragments of Lingulidiscina . ................ _ 3 

Quartzite, gray, phosphatic in upper part... 18 

Quadrant quartzite: 

Limestone, dolomitic, white, finely crystalline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Sandstone, gray, cross-bedded ............ _. 16 

Limestone, dolomitic, white, . finely crystalline ...... . ................. _ ..... _ . . . . . 23 

2 

2 
118 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1918. 

Quadrant quartzite-Continued. Ft. in. 

Sandstone, quartzitic, alternating with sandy 

dolomitic beds; poorly preserved fossils 

plentiful -near base ....... . ... . . . ......... 350 

Shale, red, sandy, slightly calcareous........ 11 

Sandstone, conglomeratic, yellow and red, 

resting on Madison limestone. . . . . . . . . . . . . 18 

The beds above the Quadrant quartzite rn 

this section constitute the Teton form.ation. 

FORMATIONS IN WEST-CENTRAL WYOMING. 

The sequence of late Paleozoic and early 

Mesozoic formations in west-central Wyoming 

is represented in the following table. Their 

probable equivalence with the section to the 

northwest in Yellowstone Park and Montana 

is indicated in Plate X. 

Late Paleozoic and early Mesozoic formations in westcentral "fVyoming. 

Feet. 

Sundance formation (Jurassic), limestone, green 

shale, and sandstone ........................ 200- 300 

Chugwater formation (Triassic), largely red 

sandy shale, with sandstone and more or less 

gypsum.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800-1, 400 

Din woody formation (Triassic), shaly brownish 

fossiliferous limestone.. . . . . . . . . . . . . . . . . . . . . 50- 200 

Park City formation (Permian and Pennsylvanian), fossiliferous limestone and shales ... 150- 225 

Tensleep sandstone (Pennsylvanian).......... 200- 500 

Amsden formation (Pennsy~ vanian and late 

Mississippian), sandstone, limestone, and 

shale ...................................... 200- 300 

It has been shown by the writer 1 that 

although the Chugwater red beds are in large 

part Triassic, the lower portion in the Big 

Horn Mountains and elsewhere in central 

Wyoming is of earlier Triassic, Permian, and 

Pennsylvanian age and was deposited contemporaneously with the marine Triassic 

(Dinwoody) and Permian and Pennsylvanian 

(Park City) beds to the west. 

AMSDEN FORMATION AND TENSLEEP 

SANDSTONE. 

The Amsden formation, which rests on the 

Madison limestone, is somewhat similar in 

lithology to the lower portion of the Quadrant 

quartzite of Montana, with which it is correlated, but at no place has it been found to 

contain richly fossiliferous beds, such as have 

been discovered in Montana. In the western 

part of the Wind River Mountains the Amsden 

consists of massive white sandstone at the 

1 Condit, D. D., Relations of the Embar and Chugwater formations in 

central Wyoming: U.S. Geol. Survey Prof. Paper 98, pp. 263-270, 1916. 

base, overlain by interbedded gray to yellowish 

shale, sandstone, and thin beds of limestone. 

Some of . the shale beds are deep red. 

The Tensleep consists almost entirely of 

sandstone, with a few interbedded dolomitic 

layers that locally contain marine fossils. The 

beds correspond so closely in position, thickness, and lithology with the upper portion of 

the Quadrant quartzite that there is no question as to their correlation. It is suggested also 

that the Tensleep may be in part equivalent . 

to the Weber quartzite of southeastern Idaho 

and Utah. 

PARK CITY FORMATION. · 

Above the Tensleep sandstone in the Wind 

River Mountains is a sequence of prevailingly 

calcareous beds correlated by Blackwelder 2 

with the Park City formation of Utah on the 

basis of paleontologic and lithologic evidence. 

The Park City beds, together with overlying 

calcareous brownish shaly beds of Triassic age, 

constitute the Embar formation of Darton,3 

who applied this name to strata believed to 

be of ''Permo-Carboniferous" age, lying between the Tensleep sandstone and Chugwater 

red beds at a locality in the Owl Creek Mountains. This grouping into one formation of 

beds of Pennsylvanian, Permian, and Triassic 

age and of widely different lithology is comparable to the grouping of the beds in the 

Teton formation of Yellowstone Park, and 

the only reason for retaining Embar as a formation name is its convenience as a term for 

use in areas where the Dinwoody and Park 

City can not be differentiated. 

The portion of the Embar formation equivalent to the Park City beds in the Wind River 

and Owl Creek mountains (see Pl. XIII, B) 

consists largely of limestone with calcareous 

shale and nodular chert. The general sequence is as follows: 

Generalized section of Park City formation in Wind River 

and Owl Creek mountains, Wyo. 

Siliceous greenish limestone grading up into gray resist- . 

ant limestone, with abundant fossils including Derbya, · 

Pseudomonotis, Leioclema, and Spiriferina pulchra. 

Nodular greenish phosphatic chert interbedded with 

many shale laminae. 

2 Blackwelder, Eliot, Stratigraphy of the Wind River Mountains, 

Wyo.: U.S. Geol. Survey Bull.- (in preparation). 

a Darton, N. H., Geology of the Bighorn Mountains: U. S. Geol. Survey Prof. Paper 51, p. 35, 1906. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 120 PLATE Xlli 

A. NORTH FACE OF BANNOCK PEAK, YELLOWSTONE NATIONAL PARK. 

Showing Madison limestone (Cm) and Quadrant quartzite (Cq) at head of cirque valley. 

B. UPTURNED BEDS ON SOUTH SLOPE OF OWL CREEK MOUNTAINS, WYO., NEAR SHOTGUN CREEK, T. 7 N., R.l E. 

a, Tensleep sandstone , forming highest hills; b, Park City formation, with resistant upper limestone member; c, shale of Dinwoody formation, mostly covered by talus; d, shaly red beds of Chugwater formation. 

PALEOZOIC AND MESOZOIC FORMAT'ION OF MONTANA AND WYOMING. 119 

Phosphatic shale of sepia-brown color, with one or more 

layers of oolitic phosphate rock and phosphatic limestone at the base. 

Limestone with geodes, chert masses, and many fossils, 

among which are Productus nevadensis, Leioclema, Sp'i-

'rijerina pulchra, and Productus subhorridus. 

Argillaceous shaly limestone and sandy calcareous shale 

of yello'wish color. . 

Dolomitic gray fossiliferous limestone, resting with slight 

unconformity on the Tensleep sandstone. 

Paleontologic data recently presented by 

Branson 1 support the belief of Girty that the 

lower portion of the Park City beds is of Pennsylvanian age. Branson's conclusions are the 

result of study of both vertebrate and invertebrate fossils. 

DINWOODY FORMATION. 

The name Dinwoody formation has been 

adopted for the upper shaly portion of the 

Embar on the suggestion of Blackwelder, 

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 that weather brown and 

contain obscure pelecypod shells. The Park 

City and Dinwoody beds found at this locality are described by Blackwelder in an unpublished bulletin on the stratigraphy of the 

Wind River Mountains. The consensus of 

opinion of several observers is that the Dinwoody beds are to be correlated with the Woodside shale (Lower Triassic) of southeastern 

Idaho. The beds are lithologically identical 

with strata in the middle portion of the series 

of beds in Yellowstone Park designated the 

Teton formation by Weed. 

A complete section of the Embar measured 

by Blackwelder 2 at Dinwoody Canyon 1s 

given below. 

Section in Dinwoody Canyon, Wyo. 

Dinwoody formation: 

Pale-green to white clay, with local sandy 

and calcareous beds, overlain conformably. 

Ft. in. 

by bright-red sandy shale of the Chugwater 

formation......... . . . . . . . . . . . . . . . . . . . . . . . 130 

Gray shaly limestone, weathering brown..... 28 

Alternate calcareous and sandy shale and 

argillaceous sandstone in thin beds. . . . . . . 12 

Dark argillaceous limestone with shale partings containing many. obscure pelecypod 

shells.................................. 10 

I Branson, E. B., The lower Em bar of Wyoming and its fauna: Jour. 

Geology, vol. 24, pp. 639-664, 1916. 

2 Blackwelder, Eliot, A reconnaissance of the phosphate deposits in 

western Wyoming: U.S. Gool. Survey Bull. 470, pp. 476-477, 1911. 

Pa k City formation: • Ft. in. 

Grayish sandy shale, shaly limef;ltone, and 

shaly sandstone, in alternate beds. . . . . . . . 75 

Massive gray crystalline limestone with fossil 

Bryozoa and brachiopods ................ . 

Nodular greenish-gray day, greenish limestone, and chert i Spiriferina pulchra, Hustedia meekana, Derbya sp., crinoids, and 

Bryozoa in abundance ................... . 

Alternating sepia-brown phosphatic and calcareous shale and shaly limestone, with 

thin beds of chert near the top; abundant 

Productus nevadens-is? :near the bas~ ...... . 

Brown shale and soft nodular black and gray 

phosphate rock interlaminated (30.5 per 

cent tricalcium phosphate) ............. . 

Dark greenish-gray oolitic and argillaceous 

phosphate rock ( 41 per cent phosphate) ... 

Gray to sepia-brown shale, full of oval nodules 

somewhat more calcareous; abundant Spirije:r, Pi-oductus, etc. (average 8.5 per cent 

phosphate) ............................. . 

Hard greenish-brown p osphatic limestone, 

with glauconite grains (23. 7 per cent phosphate) .......... -..... -------· · · · · · · · -· · 

Brown argillaceous lime.stone and calcareous 

shale, nodular, as above; abundant Productus nevadensis, P. cora, P. subhorridus, 

Spinferina pulchra, P ttgnax utah, Bryozoa, 

etc. (8 per cent phosp ate) ............. . 

Dark-drab or brown fetid limestone in massive beds; upper la,yers crowded with 

16 6 

6 

35 6 

1 8 

1 

12 5 

7 

6 

Bryozoa .. '. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 21 

Green clay shale -with thjn beds of chert • 

and platy gray limestone................. 43 

Gray speckled phosphatic sandstone......... 1 

Earthy white sandstone .................... . 

Greenish-gray speckled phosphatic sandstone containing L~ ngulidiscina utahensis, etc. (27 .4 per cent tricalcium phosphate) ... . ............. -.. -... -.... -- ---

Light-gray earthy limestone ............... . 

Dark-green shale .......................... . 

Pale-gray smoky dolomite with seams of 

black chert and pores full of black bitu2 

2 2~ 

1 9~ 

1 3~ 

men. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

White calcareous sandstone and conglomerate of chert pebbles; lies with obscure 

unconformity upon the Tensleep sandstone ...................................... 1 7 

CHUGWA~['ER FORMATION. 

The Chugwater red beds, 800 to 1,450 feet 

t ick in west-central Wyoming, present prohl~s in sedimentation that have engaged the 

alt~ntion of a number of workers who are not 

i11 agreement as to the origin of these beds. 

Almong their striking features are the unif~rmity _in thickness and texture of individual 

embers over wide areas; the prevalence of 

~i1 pie marks on horizontal beds through much 
120 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1918. 

of the formation; the absen~e of sun cracks 

and fossils of land animals except in the upper 

portion; and the extensive occurrence of gypsum 

beds near the top. It is not the purpose of 

this paper to consider in det ail the peculiarities of the Chugwater or the different hypotheses concerning its origin. It is evident, however, that mature conclusions can be· reached 

only after a detailed study of the red beds 

throughout Wyoming and adjacent areas. 

The question of age alone illustrates this point. 

In western Wyoming the lowest red beds 

overlie marine fossil-bearing brown shales of 

Triassic age that are regarded by several 

observers as equivalent to the Lower Triassic 

Woodside shale of Idaho. Furthermore, it is 

suspected that the lower Chugwater beds of 

western Wyoming grade laterally into the 

marine Thaynes limestone of Idaho, which are 

of Lower Triassic age, or at least that they 

represent partial-time equivalents of these 

beds. 

A fossil collection made by Darton 1 in the Big 

Horn River canyon near Thermopolis, Wyo., 

is of interest in this connection. The fossils 

obtained in a limestone 150 feet below the top 

of the formation were found by G. H. Girty 

to include Natica lelia, Bakewellia, Pleurophorus, and Aviculipecten, undoubted marine 

types, constituting a fauna which is referred 

with considerable confidence to the Triassic. 

This occurrence is of additional interest as 

indicating the marine origin of a portion of 

the Chugwater, as contended by Branson.2 

In the Big Horn Mountains, in the central 

part of the State, the lowest red beds of the 

Chugwater have been shown by the writer 3 

to be of late Pennsylvanian age. 

The age of the uppermost beds of the Chugwater formation is uncertain. Wherever present in Wyoming they are overlain by the Sundance formation, which is Upper Jurassic, but 

it is a question whether the deposition of the 

gypseous shale, cross-bedded sandstone, and 

nonmarine limestone characteristic of the upper 

part of the Chugwater may not have been 

1 Darton, N. H., Geology of the Bighorn .Mountains: U. S. Geol. 

Survey Prof. Paper 51, p. 40,· ~906. 

2 Branson, E. B., Origin of the Red Beds of western Wyoming: Geol. 

Soc. America Bull., vol. 26, pp. 217-230, 1915. 

a Condit, D. D., Relations of the Em bar and Chugwater formations 

in central Wyoming: U. S. Geol. Survey Prof. Paper 98, pp. 263-270, 

1916. 

largely contemporaneous with the early Jurassic base-leveling so plainly recorded in the 

truncated beds to the north, in Montana. 

SUNDANCE FORMATION. 

The Sundance formation of Wyoming is regarded as the equivalent of the Ellis in :Montana, with which it agrees fairly well in lithology, thickness, and fossil content. The Sundance consists largely of greenish calcareous to 

sandy shale, with a resistant dark-gray limestone near the middle. Both the shale and the 

limestone are richly fossiliferous, and the most 

characteris'tic species are Belemnites densus, 

Gryphaea calceola, and stem segments of the 

crinoid P entacrinus asteriscus. 

RECORD OF JURASSIC BASE-LEVELIN~. 

The most striking evidence of pro longed 

.erosion in Jurassic time is furnished by the 

contact of the late Jurassic marine beds (Ellis) 

with successively older formations as followed 

northward across Montana. This feature is 

graphically shown in figure 14. The substrata. 

along the Idaho-Montana State line near Y el-· 

lowstone Park are limestone or red beds of 

Triassic age, ·and successively lower formations 

appear northward to Elkhorn mining camp, 

about 20 miles south of Helena, where the substrata are beds probably 75 feet below the top 

of the Phosphoria formation. Fisher4 has 

stated that in places in the Great Falls region, 

in northern Montana, the Ellis rests on the. 

Madison limestone. 

Study of the erosion surface from place to· 

place reveals the presence of peculiar yellowish. 

earthy sandstone, ferruginous gypseous shale, 

and local limestone beds, all making up a motley aggregate related neither to the overlying 

Ellis nor to the underlying formations. These 

heterogeneous materials constitute the sedi-· 

mentary record of events that preceded or accompanied the advance of the sea from the 

northwest in late Jurassic time. Their thickness, ranging from a few feet to little more .than 

100 feet, is direct evidence of the slight rehef of 

the land surface, the inequalities of which were 

leveled to form the floor: upon which the marine. 

Ellis beds were deposited. 

t Fisher, C. A., Geology of the Great ·Falls coal field, Mont.: U.S .. 

Geol. Survey Bull. 356, p. 27, 1909. 
PALEOZOIC AND MESOZOIC FORMATIONr OF MONTANA AND WYOMING. 121 

The thickness of strata removed by Jurassic sp culation, but 1n the writer's op1n1on .this 

erosion in northern Montana may have been erosion may have furnished the sediments of 

2,000 feet, if the Chugwater red beds once ex- th~ shale and sandstone series of southeastern 

tended over that area. The extent to which I1aho lying between the marine Lower Triassic 

the Chugwater was eroded in Wyoming is not C1haynes limestone) and JUarine Upper Jurasevident, but it seems probable that in the west- sic (Twin Creek limestone). It is probable 

central part of the State, where the beds are at in the meanwhile the Wyoming area, a 

1,400 feet thick, they remain almost intact, loF, nearly level plain, which was intermittently 

and that the upper portion, including the gyp- o9cupied by small bodies of water and in which 

seous beds, may be in part a product of Jurassic n~ither erosion nor deposition of considerable 

sedimentation. gnitude occurred, furnished the conditions 

The disposition of the great mass of material nJcessary for the forrnation of extensive but 

stripped from the northern area is a matter of v riable gypsum and limestone beds.