UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 847-F

GEOLOGY AND MINERAL RESOURCES

OF

NORTH-CENTRAL CHOUTEAU, WESTERN HILL

AND EASTERN LIBERTY COUNTIES

MONTANA

BY

W. G. PIERCE AND C. B. HUNT

Contributions to economic geology, 1934-36 

(Pages 225-264)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1937

For sale by the Superintendent of Documents, Washington, D. C. - - - - - Price 35 cents

CONTENTS

	Page 

Abstract----.-..------------------------------------------------- 225

Introduction. ___________-_-.____-_--.-._____-._..___.__-....-_..__ 226

Location and extent of area._...___..__--____-_--____._----..._ 226

Field work and acknowledgments.______________________________ 226

Publications relating to this area.________________________________ 228

Geography.----.... ____________________________ .......... 229

Surface features-__..----------._----------_----.--_---------- 229

Transportation._____.-_-__--.__......_---__---_--._-.--.--.-- 229

Culture and climate...--_-_-_----__._-_-----------_-----_--.__ 230

Stratigraphy. _ .__-----__------.--.-..-__------_---_----_------.-- 231

Rocks exposed-_______-_.-_-.-__--.__-_._--_.--.-_--_._-..-_--_ 231

Quaternary system.---._.--._..._----___.___--_-_----.-.-- 232

Recent series.__--___-_-_____-_-______---____-----_.._. 232

Pleistocene series.___-_---__.----..--.-_.---------..--- 232

Cretaceous, system -_______.______--_-__-_-_--__----__--_-- 232

Upper Cretaceous series_--___-_---__--_-_---------.-- 232

Judith River formation.___________________________ 232

Claggett shale___..._._..--_-._..--_..-_----..-... 236

Eagle sandstone.____-___-__-____-----_.____-..... 242

Colorado shale....---____--___--_---_-_--_-----_-- 246

Rocks not exposed-.___-----.-_--.___--__--.---.-.-..--.-.-.-. 248

Kootenai formation..._._..__-_._...____.__.____.----._,__ 248

Ellis formation.....----...__._.......-.._-._......._...-. 248

Madison limestone._--_.__--_._____.-.___-__-.____---.--_.. 249

Information from driller's log.------------------------------ 249

Igneous rocks_______-___-___-___-__________-___-_-_-____---_--___ 251

Structure. ___...---.--..----.-..--.-.-:.------..------..----.-..- 253

Regional structure.___------___________________-_.-_----__-_-- 253

Structure of the area._--__-____._--.-----_-__.--_-_..---.--._- 253

Faults.---___---_-__--_____________.______.____-_____-______. 254

Mineral resources._--_-__-------__-.-....----._._--___-._--.-.--.. 258

Oil and gas_-----_----------_._-----------_.---------------.-- 258

Results of drilling.._-_-......-.-........_-_-__.__---..-.-. 258

Wells near Kreinlin______.__.____._-________.._--___..__ 258

Utopia wells___----__-_--_-_. --_---__--_--_._------_-- 259

Other wells_________._..__..._._._.____......._..... 260

Oil and gas possibilities of the region._____---_-_____---_-_.- 260

Coal resources._______________________________________________ 261

Water resources_------_--__--_-_-__-_--. _____.___-___.._.._ 264

in
ILLUSTRATIONS

Page

PLATE 36. A, Cliffs of Judith River formation along Milk River; B, Crossbedding in Judith River formation_______-_-_____.___^-___ 236

37. A, Exposure of Eagle sandstone; B, View looking up Marias

River...._..........______-____________________ 237

38. A, Distant view of dike; B, Dike cutting upward through

Virgelle sandstone member of Eagle sandstone._----_-__-_ 252

39. A, View along trace of fault, showing steeply dipping Colorado 

shale thrust over horizontal beds of Eagle sandstone; B, View 

looking west across plateau surface of Liberty County toward 

Sweetgrass Hills_--_________-____!___:______:________ 253

40. Faults exposed along Sage Creek, about 3 miles south of Gildford.. _____--____-_____-_____________.___^___________ 256

41. Interpretation of logs of wells drilled hear Kremlin.________ 260

42. Coal in Judith River formation________--__-__-_-__.____ 260

43. Geologic map of north-central Chouteau, western Hill, and

eastern Liberty Counties, Mont___-_--__--__-__-_-_ In pocket 

FIGURE 57. Index map of Montana showing location of the area described- 227

58. Lenticularity and cross-bedding of strata in upper part of

Eagle sandstone in SW% sec. 1, T. 26 N., R. 7 E__ ___. ___ 246

59. Lobe of Judith River formation in dike of porphyritic lamprophyre along Milk River near the northwest corner of sec. 2, 

T. 37 N., R. 8 E__._________________-___-_-________ 251

60. Coal in upper part of Eagle formation, T. 26 N.,R. 12 E.,__. 262

IV
GEOLOGY AND MINERAL RESOURCES OF NORTHCENTRAL CHOTJTEAU, WESTERN HILL, AND EASTERN LIBERTY COUNTIES, MONTANA

By W. G. PIERCE and C. B. HUNT

This report describes a rectangular area of about 2,600 square miles in 

Chouteau, Hill, and Liberty Counties, Mont., adjacent to the international 

boundary. The area is a portion of the Missouri Plateau, a section, of the 

Great Plains province, and lies between the Highwood Mountains, Bearpaw 

Mountains, and Sweetgrass Hills, of north-central Montana. The southern part 

of the area is drained by the Missouri River and its tributary Marias River, 

but the northern part is drained by the Milk River. These streams are 

trenched in narrow valleys several hundred feet deep. The land surface 

between them is a rolling plain interrupted by very broad, shallow valleys that 

probably were eroded during the Pleistocene epoch by large streams whose 

courses were doubtless diverted from time to time by the continental glaciers. 

These valleys are now occupied only by very small creeks.

The exposed rocks include sedimentary formations of Upper Cretaceous age, 

Pleistocene glacial deposits, and a few dikes of igneous rock. The exposed 

Upper Cretaceous formations from oldest to youngest are the Colorado shale, 

Eagle sandstone, Claggett shale, and Judith River formation. The Colorado 

shale, as shown by deep wells, is about 1,800 feet thick, but only the upper 

500 feet is exposed in this area. The exposed parts of the formation consist 

mainly of dark-gray marine shale and some bentonite and calcareous concretions, and the upper 100 feet contains considerable sandstone and thus 

forms a transition zone between the Colorado shale and overlying Eagle 

sandstone. The Eagle sandstone, 200 to 225 feet thick, consists of a lower 

sandstone, the Virgelle sandstone member, overlain by sandstone, sandy clay, 

carbonaceous shale, and thin coal beds. The Claggett shale is a marine unit 

400 to 500 feet thick that thickens eastward. The lower half of the formation 

is brownish-black fissile shale containing dark-gray calcareous concretions 4 

feet or less in diameter. Four or more bentonite beds, 1 to 3 feet thick, occur 

in the lower 80 feet, and scattered pebbles of black chert are common in the 

lower 30 feet. The upper half of the Claggett is gray shaly sandstone with 

interbedded gray and black fissile shale and is transitional with the overlying 

Judith River formation. The Judith River formation, 500 to 600 feet thick, 

consists of continental and brackish-water sandstone, clay shale, carbonaceous 

shale, and coal. The lower 200 feet is made up of somber-colored beds with 

coal, generally most abundant at the top. The upper 300 to 400 feet consists 

of lighter-colored beds, non-coal-bearing in this area but containing coal where 

the top is exposed farther east.

225
226 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

Pleistocene gravel, loam, and glacial drift generally conceal the Upper 

Cretaceous rocks. The average thickness of these deposits is less than 15 

feet, but the maximum thickness is 50 feet or more.

The igneous dikes that intrude the Upper Cretaceous rocks are composed 

of porphyritic lamprophyre.

The sedimentary rocks dip northeastward at the rate of about 35 feet 

to the mile, and their -slope in this direction is modified by a few broad 

folds that plunge in the direction of the slope. The axis of the Utopia anticlinal nose, the most prominent fold of the area, is a few miles north of the 

main line of the Great Northern Railway. The Utopia nose plunges slightly 

north of east and has a structural relief of about 150 feet. The eastern 

extension of the Marias River syncline is just south of the Utopia nose and 

plunges east-northeast. Other folds that interrupt the regional dip have very 

little structural relief, and apparently none are closed folds. The rocks that 

are exposed in the vicinity of Kremlin have heretofore been regarded as 

having anticlinal structure, but they are interpreted by the writers as having 

been deformed by faulting. Here, as well as elsewhere in the eastern part of 

the area, there are numerous thrust faults of the type that are abundant in 

the region surrounding the Bearpaw Mountains, to the east.

Drilling has not revealed oil in commercial quantities, but small showings 

are present in several wells. Gas is apparently more abundant, for it was 

encountered in the Eagle sandstone in most of the wells.

Coal of subbituminous rank is present in lenticular beds, generally less than 

3 feet thick, in the upper part of the Eagle sandstone and the lower 200 feet 

of the Judith River formation. In general, however, the coal is of poor quality. 

A large number of small mines supply the local market, but none are worked 

continuously.

The ground-water resources of the area are not entirely adequate for domestic 

supplies and for stock. A sufficient quantity of water can usually be obtained 

by drilling wells into the Judith River or the Eagle formation, but the mineral 

content of these waters is fairly high, generally ranging from 1,000 to 2,500 

parts per million, and locally it may be as high as 5,000 parts per million. 

The principal mineral constituents of the water are sodium carbonate, sodium 

sulphate, and sodium chloride. The veneer of glacial drift, which covers most 

of the area, is generally too thin to yield water in shallow wells.

INTRODUCTION

Location and extent of the area. The parts of north-central Chouteau, western Hill, and eastern Liberty Counties that are described in 

this report form a rectangular area of about 2,600 square miles in 

north-central Montana adjacent to the international boundary. (See 

fig. 57.) The area extends southward 72 miles from the international 

boundary and is 36 miles wide; it includes Tps. 26 to 37 N., Rs. 7 

to 12 E.

Field work and acknowledgments. The field work in this area was 

undertaken by the United States Geological Survey to obtain the 

information necessary for the classification of public lands and for 

the proper administration of the laws governing the development of 

mineral resources on public lands. The examination was made by 

the writers during July, August, and September -1932. Topographic
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 227

maps of the Kremlin, Box Elder, Big Sandy (unpublished), and 

Lonesome quadrangles, prepared by the Geological Survey, were 

available for about one-fifth of the area and were used as base maps 

for field mapping. Sheets 26 and 27 of the international-boundary 

map, from the Gulf of Georgia to the north westernmost point of the 

Lake of the Woods, furnished precise topographic base maps of a 

strip about a.mile wide along the northern edge of the area. Planetable sheets, prepared during a previous survey of the coal resources 

by the Geological Survey, were available for Tps. 35 to 37 N., Rs. 10 

to 12 E., T. 26 N., Es. 11 and 12 E., and T. 25 N., R. 12 E., comprising 

one-sixth of the area. For the remainder of the area township plats 

prepared by the General Land Office were used as base maps. OutFIGURE 57. Index map of Montana showing location of the area described (shaded area).

crops were located approximately with respect to section lines, and 

altitudes were determined by traverses with a surveying aneroid. 

Practically all parts of the area could be reached by car, except those 

parts along the Missouri and Marias Rivers, where examinations were 

made on foot.

Rock outcrops are not abundant in the area, and information obtained from water wells was very helpful in supplementing that 

obtained from outcrops. The use of this information involved the 

interpretation of the driller's or owner's descriptions of lithologic 

units encountered in drilling the well, and although these descriptions are not invariably accurate, the water wells were the source of 

much valuable information.

The portion of the present report that relates to coal resources 

includes the results of field work in 1915 by Eugene Stebinger,
228 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

assisted by W. P. Woodring and J. D. Sears. This field work consisted of detailed areal mapping and tracing by plane-table methods 

: of coal beds along the Milk River and Canada Coulee in Tps. 85 to 

"37 N., Rs. 10 to 12 E:, and T. 3T N., R. 9 E. Similarly, in 1914 a 

party in charge of E. R. Lloyd made a detailed plane-table survey of 

T. 26 N., Rs. 11 and 12 E. No attempt was made during the earlier 

field work to determine the attitude of the strata and to map the 

geologic structure, but the present writers have used the earlier areal 

mapping as a basis for observations on the geologic structure of these 

townships.

The writers had a valuable and instructive field conference with 

their colleague C. E. Erdmann on the stratigraphy of the beds underlying the area considered in this report, which are exposed in the 

upturned beds of the Sweetgrass Hills. The project was under the 

supervision of H. D. Miser, and the writers are indebted to him and 

A. A. Baker for valuable suggestions and criticism of the report. 

The several oil companies furnished logs of their wells, and Mr. 

Lehfeldt, of Big Sandy, and the many residents of the region gave 

generous cooperation.

Publications relating to this area. Although the geology of most 

of this area has not been described or mapped previously except for 

a brief statement 1 of the results of the present investigation, the 

regional geology of north-central Montana has long been known 

through the work of authors of geologic reports and maps of adjacent 

or nearby areas. Some of these reports and maps are cited below.

Alclen, W. C., Physiography and glacial geology of eastern Montana and

adjacent areas: U. S. Geol. Survey Prof. Paper 174, 1932. 

Bowen, C. F., The Big Sandy coal field, Chouteau County, Mont.: U. S. Geol.

Survey Bull. 541, pp. 356-378, 1914. 

Bowen, C. F., The stratigraphy "of the Montana group,' with special reference

to the position and age of the Judith River formation in north-central

Montana: U. S. Geol. Survey Prof. Paper 90, pp. 95-153, 1915. 

Calhoun, F. H. H., The Montana lobe of the Keewatin ice sheet: U. S. Geol.

Survey Prof. Paper 50, 1906. 

Clapp, C. H., Bevan, Arthur, and Lambert, G. S., Geology an'd oil and gas

prospects of central and eastern Montana: Montana Univ., Bur. Mines and

Metallurgy, Bull. 4, 1921. 

Collier, A. J., The Kevin-Sunburst oil field and other possibilities of oil and

gas in the Sweetgrass arch, Mont.: U. S. Geol. Survey Bull. 812, pp. 57-189,

1930. 

Dobbin, C. E., and Erdmaun, C. E., Map of the Great Falls-Conrad region,

Mont., scale, 1:250,000, U. S. Geol Survey, 1930. 

Dobbin, C. E., and Erdmann, C. E., Structure contour map of the Montana

plains, scale, 1:1,000,000, U. S. Geol. Survey, 1932.

1 Pierce, W. G., and Hunt, C. B., Geology and mineral resources of north-central Chouteau, western Hill, and eastern Liberty Counties, Mont.: U. S. Dept. Interior Press Mem. 

72308, June 1933.
CHOUTEATJ, HILL, AND LIBERTY COUNTIES, MONT. 229

Erdmann, C. E., Preliminary structure contour map of. the Bears Den-FLat

Coulee-Whitlash districts, north-central Montana, U. S. Geol. Survey, 1930. 

Pepperberg, L. J., The southern extension of the Milk River coal field, Chouteau

County, Mont: U. S. Geol.'Survey Bull. 471, pp. 359-383, 1912. 

Perry, E. S., The Kevin-Sunburst and other oil and gas fields of the Sweetgrass

arch: Montana State Bur. Mines and Metallurgy Mem. 1, 1928. 

Reeves, Frank, Geology and possible oil and gas resources of the faulted area

south of the Bearpaw Mountains, Mont.: U. S. Geol. Survey Bull. 751, pp.

71-114, 1935. 

Reeves, Frank, Thrust faulting and oil possibilities in the plains adjacent to

the Highwop'd Mountains, Mont.: U. S. Geol. Survey Bull. 806, pp. 155-195,

1929. 

Stanton, T. W., and Hatcher, J. B., Geology and paleontology of the Judith

River beds: U. S. Geol. Survey Bull. 257, 1905. 

Stebinger, Eugene, The Montana group of northwestern Montana: U. S. Geol.

Survey Prof. Paper 90, pp. 61-68, 1915. 

Stebinger, Eugene, Possibilities of oil and gas in north-central Montana: U. S.

Geol. Survey Bull. 641, pp. 49-91, 1917. 

Weed, W. H., U. S. Geol. Survey Geol. Atlas, Fort Benton folio (no. 55),"1899.

GEOGRAPHY

Surface features. The area here under consideration includes part 

of the Missouri Plateau and lies between three mountain groups the 

Bearpaw Mountains on the east, the Highwood Mountains on the 

south, and the Sweetgrass Hills on the west. (See fig. 57 and pi. 

39, B.) The surface of the plateau is gently rolling but is trenched 

by deep valleys that are occupied by the principal streams. The 

relief in the area is about 1,270 feet, the altitude above sea level 

ranging from 2,500 feet along the Missouri River to 3,770 feet on 

Goosebill Butte. However, most of the area is a plateau surface 

between 2,900 and 3,300 feet above sea level.

The Missouri River flows northeastward across the southeast corner 

of the area. Marias River flows southeastward across the southwestern part of the area and joins the Missouri south of the area. 

The Milk River enters the United States from Canada and flows 

across the northeastern part of the area. These three streams have 

cut steep-walled valleys 200 to 300 feet below the general plateau 

surface, which is otherwise gently rolling and little dissected. (See 

pi. 37, B.) Broad valleys, some of which are probably the abandoned courses of major streams but are now occupied only by small 

creeks, form a large part of the surface for example, the valley of 

Sage Creek, which parallels the course of the Milk River; the valley 

of Lonesome Lake, in T. 29 N., Rs. 10 to 12 E.; and the valley of 

Big Sandy Creek, just east of the area.

Transportation. The main line of the Great Northern Railway 

crosses the central part of the area, and a branch line from Havre to 

Great Falls crosses the southeastern part.
230 CONTKIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

United States Highway 2 parallels the main line of the Great 

Northern Railway. It is a gravel road, in part oiled. State Highway 

29, which extends south westward from Havre through Big Sandy 

and Fort Benton to Great Falls, more or less follows the branch line 

of the railway. At the time of the field work this road was in part 

dirt and passable only with difficulty in wet weather. However, parts 

were being improved, and probably it will soon be serviceable in all 

weather.

Only the principal county roads are indicated on plate 43, but 

nearly all the section lines are traversable by automobile.

Culture and climate. The towns within the area Joplin, Inverness, Rudyard, Hingham, and Gildford are closely spaced along 

the main line of the Great Northern Railway; each had a population 

of a few hundred inhabitants in 1930. Havre, 20 miles east of the 

area, is the largest commercial center serving this region. Its population in 1930 was 6,372. It is a division point on the Great Northern 

Railway, and the Great Falls branch joins the main line there. Fort 

Benton, on the north bank of the Missouri River 10 miles south of 

the area, was an important trading post in pioneer days, for it was 

at the head of navigation and was reached by steamers that slowly 

plied their way up the river. Its population in 1930 was 1,109. Big 

Sandy, on the east boundary .of the area, had a population of 633, and 

Chester, 3 miles west of the area, had a population of 387.

The average annual precipitation in the area is about 11 inches, 

but through a period of a few years it may vary several inches. The 

annual mean temperature is about 42° F., but the extremes are 

great generally between 105° in the summer and 45° in the winter. 

The prevailing winds blow from the west and southwest.

Practically all the inhabitants are engaged in raising wheat by dryfarming methods, though some livestock is raised in the northwestern part of the area. Good crops of wheat are usually obtained 

in years of more than average rainfall, but in the years when the rainfall is below the average the crops are very poor. Water supply for 

domestic use and for stock is a problem throughout the area. Surface 

water is available only along the major streams. Most shallow wells 

yield only small supplies of water and none in dry seasons. A sufficient yield for domestic use and for a few head of stock can usually 

be obtained by drilling a few hundred feet, but the water is mineralized and not entirely satisfactory. As water supply is a foremost 

problem in this region, some consideration of it is included in this 

report (p. 264).
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 231

i STRATIGRAPHY

BOCKS EXPOSED

The rocks exposed in the area covered by this report are sedimentary deposits of Upper Cretaceous age, Pleistocene glacial deposits, 

and a few dikes of igneous rocks. The Upper Cretaceous rocks include sandstone, shale, and bentonite deposited in marine waters; 

sandstone and shale deposited in brackish waters; and continental 

deposits of clay, shale, sandstone, and coal. The sedimentary rocks 

can readily be separated into four formations, as described in the 

following table:

Upper Cretaceous formations exposed in the area

Age

Upper Cretaceous.

Formation

Judith 

Kivor 

formation

Claggett 

shale

Eagle 

sandstone

Colorado 

shale

Canadian 

equivalent

Pale beds

Foremost 

formation

Pakowki 

formation

Milk River 

formation

Colorado 

shale

Thickness 

(feet)

500-600

400-500

200-225

1, 800±

Character

Mostly light-colored continental and brackish-water deposits of thin-bedded sandstone, thick massive sandstone, 

clay shale, carbonaceous shale, and coal. Most of the coal 

beds are found near the top of the formation and within 

200 feet of the base. Locally there is a massive tan, probably marine sandstone about 50 feet thick at the base. 

Beds of oyster shells are common. The lower 200 feet, of 

more somber-colored beds, is equivalent to the Foremost 

formation, and the upper 300 to 400 feet, of a slightly 

lighter hue, to the Pale beds of the Canadian classification.

Upper half thin-bedded gray shaly sandstone, with interbedded gray and black fissile shale. Lower half brownishblack fissile marine shale containing dark-gray calcareous 

concretions 4 feet or less in diameter, which disintegrate 

into small angular pieces. Four or more bentonite beds 

1 to 3 feet thick occur in the basal 80 feet. Contains 

scattered small black chert pebbles in the lower 30 feet.

Upper half white and buff sandstone, sandy clay shale, 

carbonaceous shale, and thin coal beds. A thin bed of 

black chert pebbles in some places is present at or near 

the top. Contact with overlying Claggett shale is sharp. 

Lower half massive light-colored sandstone, the Virgclle 

sandstone member, which contains water and gas. The 

base is usually transitional into the Colorado shale.

Only-'the upper 500 feet is exposed in this area, consisting of 

interbedded tan sandstone and gray shale, which is more 

sandy in the upper 100 foot. The formation is composed 

principally of dark-gray marine shale with .some beds of 

bentonite, sandstone, and calcareous concretions; the 

lower part is sandy and is known as the "Blackleaf sandy 

member."

Pleistocene gravel, silt, and glacial till, which were deposited by the 

continental glaciers, were not mapped in detail. These deposits, however, are present throughout the area and generally conceal the 

Upper Cretaceous rocks.

The- dikes intruded into the Upper Cretaceous formations consist 

of porphyritic lamprophyre.
232 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

QUATERNARY SYSTEM

RECENT SERIES

The Recent deposits include flood-plain and alluvial deposits composed of clay, sand, and gravel. They lie unconformably on the 

earlier formations along the valleys of the principal streams of the 

area. The thickness is less than 25 feet.

PLEISTOCENE SERIES

The Pleistocene ice sheets deposited clay, sand, gravel, and boulders. This drift is generally less than 15 feet thick, except in 

morainal deposits or valley fill. The maximum observed thickness 

is 50 feet. This material covers nearly all of the area, except where 

it has been removed by streams, and unconformably overlies the 

earlier formations.

CRETACEOUS SYSTEM

UPPER CRETACEOUS SERIES

JUDITH RIVER FORMATION

The Judith River formation was named by Hayden 2 in 1871, but 

the stratigraphic position of the formation was not proved until 

1903, when Stanton and Hatcher 3 determined that it is a part of the 

Montana group and a time equivalent of part of the Pier re shale. 

The Judith River and Eagle formations thicken westward in northcentral Montana, and west of this area, where the Claggett thins out, 

they join. The combined series, exclusive of the Virgelle sandstone, 

is called the "Two Medicine formation", and the Virgelle is there 

treated as a distinct formation.

In the area here described the Judith River formation consists 

largely of sandstone and shale of fluviatile origin with some interbedded brackish-water deposits. The formation conformably overlies the Claggett shale; the contact is exposed at a few localities. 

The Bearpaw shale, which normally overlies the Judith River formation, has been completely eroded from the area.

The Judith River formation crops out in nearly all of the northern 

two-thirds of the area but has been eroded from the southern third. 

The formation attains a maximum thickness of about 600 feet in 

the northeast corner of the area.

The Judith River consists of very lenticular beds of sandstone, 

shale, and coal. (See pi. 36, B.) The lower 200 feet includes more

2 Hayden, F. V., Geology of the Missouri Valley: U. S. Geol. Survey Terr. [4th Ann.] 

Preliminary Kept., p. 97, 1871.

8 Stanton, T. W,, and Hatcher, J. B., Geology and paleontology of the Judith River 

beds: U. S. Geol. Survey Bull. 257, pp. 62-66, 1903.
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 233

coal, carbonaceous beds, shale, and in general more somber-colored 

deposits than the upper 300 to 400 feet, which consists predominantly 

of light-colored sandstones, generally friable, and which in this 

area contains little or no coal but to the east, near Havre, contains 

coal beds near the top of the formation. Ferruginous brown sandstone : beds containing brackish-water fossils are common in the lower 

200 feet but are rare in the upper 400 feet of the formation. On the 

other hand, vertebrate fossils are most common in the upper beds. 

Canadian geologists have long recognized these differences within 

the Judith River formation and have, divided the strata into two 

formations applying the name "Pale beds" to the upper part and 

"Foremost formation" to the lower part. (See pi. 36, A.) At many 

places it is difficult to draw a sharp boundary between these lithologic 

subdivisions.

Near the top of Goosebill Butte, in sec. 26, T. 27 N., R. 7 E., there 

is a prominent tan to buff: massive sandstone about 50 feet thick, 

which in places has slumped so that now large blocks are lower than 

their original position. A few feet above this sandstone are beds 

of oyster shells and some thin coal beds in strata that consist predominantly of sandstone. These coal-bearing beds are undoubtedly 

Judith River, whereas the massive sandstone below is. probably 

Claggett as originally defined (p. 236), but lithplogically it is a part 

of the Judith River and consequently is mapped as a part of that 

formation and so treated in this report. Furthermore, this massive 

sandstone bed is not present everywhere at the base of the Judith 

River, and in some places a massive cross-bedded sandstone that 

contains a Judith River fauna occurs near the base of the formation.

The base of the Judith River is also exposed across the northeast 

sections of T. 30 N., R. 7 E., along Dobie Ridge, where, however, 

there is complete gradation through an interval of 160 feet from 

the shale of the Claggett to thin-bedded sandstone of the Judith 

River, as indicated by the following section:

Section of upper part of Claggett shale and lower part of Judith River formation in the JE/% sec. 2, T. 30 N., R. 7 E.

Judith River formation : Ft. in. 

Sandstone, friable, tan; contains lenses of crossbedded sandstone and brown concretions in upper 

part________________' ___- - 17 

Shale, gray, very thinly laminated; breaks into fine

pieces _____ - 11 

Sandstone, tan, arkosic? _ _ 5 

Bed of oyster shells_ _ ; 4 

Shale, sandy, brown, carbonaceous- 1
234 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

Section of upper part of Cl&ggett shale and lower part of Judith River- formation in the &y2 sec. 2, T. 30 N., R. 7 E. Continued

Judith River formation Continued. Ft- inSandstone, light green gray, cross-bedded, lenticular;

forms irregular ledge____ ____________ 13 

Shale, hard, brown; contains plant fragments_____ 1 6 

Sandstone, friable, tan with orange-yellow streaks__ 12 

Shale, gray; contains plant remains and is -carbonaceous in upper 6 inches; oyster shells at very top 2 6 

Claggett shale:

Shale, brown and tan, thinly laminated; weathers to 

purple along joint cracks; contains light-gray to tan 

cross-bedded sandstone concretions 1 to 4 feet in 

diameter; some thin sandy beds with oyster shells 

in upper part; black fissile shale at top_______ 36 

Mostly concealed; sandy shale where exposed____ 33 

Sandstone, friable, tan; some clay with thin concretionary beds of buff sandstone_____________ 17 

Shale, tan to light gray, sandy; contains calcareous 

concretions that break into small conchoidal pieces. 11

The base of the Judith River is exposed in the fault blocks along 

the Milk River, in the center of T. 34 N., R. 13 E., just east of this 

area, where the contact with the underlying Claggett also is transitional. The transition beds consist of massive sandstone, 10 to 25 

feet thick, separated by dark shale of approximately equal thickness, 

so that it is a matter of interpretation whether the contact should 

be drawn at the top of the highest shale or at the base of the lowest 

massive sandstone bed.

About 200 feet above the base of the Judith River there is a carbonaceous zone that contains coal at many localities. This zone crops 

out in Canada Coulee in T. 37 N., R. 9 E., where coal is mined from 

it. The same zone is poorly exposed along Sage Creek and Little 

Sage Creek in the northwestern part of the area but has been recognized in water wells as a persistent coal-bearing unit. Several shafts 

have been put down to the coal, and although most of the mines are 

now little used, they have supplied a considerable quantity of coal 

for the surrounding territory and can do so in the future. The 

general lithologic sequence in the faulted blocks of the Judith River 

formation along Sage Creek, south of Gildford, suggests that the 

coal exposed in the mines there is from the same zone at the top of 

the lower 200 feet of the Judith River formation.

The following section of the Judith River, measured along Milk 

River at the international boundary, is the most nearly complete 

section measured by the writers, but neither the base nor the top of 

the formation is present.
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 235

Incomplete section of the Jitdith, River formation measured along Milk River 

at the international boundary, near north lime of sec. 2, T. 37 N., R. 8 E.

Glacial drift and soil.

Judith River formation: Ft i/( 

Sandstone, pale pink at base, light yellow at top; 

badly weathered fossil bone at top______ 22

Clay, light-colored________ ___ 24 

Sandstone, friable, fine-grained; weathers light gray; 

forms slope______ 15

Sandstone, light gray but weathers brown; fine to 

medium grain; considerable dark material in 

the sand, giving it a salt-and-pepper appearance; 

cross-bedded; forms ledge; lenticular..^ 3 

Shale, gray, with thin beds of yellow sandstone 16 

Shale, carbonaceous, with streaks of coal _____ 1

Shale, gray, with thin beds of yellow sandstone__ 11 

Shell bed containing fragments of Unios(?) and other 

. fossils ________:___________________ 3 

Shale, gray, with thin beds of yellow sandstone 15 

Shale, dark gray, fissile _ 1 

Shale, gray, with thin beds of yellow sandstone____ 8 

Shale, brown, 'carbonaceous ___ _ 1 5 

Shale, gray, with thin beds of yellow sandstone___ 16 

Shale, gray; some black carbonaceous shale near base 

but grades upward to lighter-colored shale with thin 

beds of sandstone____________________ 27 

Shale, carbonaceous, with thin streaks of coal____ 1 

Shale, gray and brown, locally carbonaceous_____ 11 6 

Bentonite___________ ____________ 2 

Shale, carbonaceous____________________ 1 6 

Coal __ __________________________ 2 8 

Shale, dark gray, carbonaceous; contains a few fossil

shells; grades upward to yellowish-brown shale__ 11 

Shell bed; lower part sandy shale, upper part darkgray shale________________________ 3

Coal, shaly_________________________ 1 2 

Sandstone, light gray, massive; contains some clay; 

dark-brown ferruginous concretions 1 foot thick and 

3 to 15 feet long in zone about 6 feet above base 

of unit___________________________ 22 

Clay, banded, tan, light gray, and chocolate brown;

increasingly sandy toward the top_________ 18 

Shell marl, mostly oyster shells____________ 4 

Shale, carbonaceous, with thin streaks of coal____ 1 

Sandstone, light gray, massive, resistant______ 10 

Shale, gray, silty, containing hard tabular concretions

1 to 4 inches thick, and banded clayey sandstone_ 27 

Shale," gray, sandy______________________ 35 

Shale, dark gray, with bands of dark-tan sandy shale- 20 

Alluvium in valley of Milk River. Lowest exposed bed is 

less than 50 feet above base of Judith River.

326
236 CONTKIBUTIONS .TO ECONOMIC GEOLOGY, 1934-36

The uncertainties of recognizing horizons within the Judith River 

and the complete absence of the Bearpaw shale contribute to the difficulties of determining the thickness of the Judith River in this area. 

About 200 feet of somber-colored beds (Foremost formation of 

Canadian geologists) are exposed along Milk River, and an estimated 

thickness of 300 feet of the Pale beds of the Canadian classification 

overlies them. The Bearpaw shale, which is present a few miles east 

of the area, is probably not more than 100 feet stratigraphically 

above the highest Judith River beds within the area, so that the estimated total thickness of the Judith River is between 500 and 600 

feet.

CLAGGETT SHALE

In 1905 Stanton and Hatcher 4 gave the name "Claggett shale" to 

the formation that overlies the Eagle sandstone and underlies the 

Judith River formation. The formation was named from the exposures near Judith (old Fort Claggett), on the Missouri River near 

the mouth of the Judith River. It consists chiefly of shale but includes more or less sandstone in the upper part. Elsewhere in Montana, where the formation contains a large percentage of sandstone, 

the name "Claggett formation" is applied to it.

The Claggett shale crops out in a broad belt in the southern part of 

this area and in fault blocks along Sage Creek and the Milk River. 

Good. exposures are few and are confined mostly to the walls of 

large .valleys and coulees. In places where there is no glacial drift 

there are local weathered exposures of the shale.

The Claggett is chiefly dark shale with a slightly brownish cast. 

The lower half contains calcareous concretions and beds of bentonite, 

but the upper half is progressively more sandy toward the top. The 

concretfons are most common in the upper part of the lower half or 

shaly unit of. the Claggett, They are isolated oblate spheroids from 

1 to 4 feet in diameter, composed of dark-gray limestone. They are 

usually 10 feet or more apart horizontally but locally occur with a 

regularity that suggests definite beds or zones. Horizontally the individual zones merge with higher or lower zones and consequently cannot be used for precise stratigraphic horizon markers or "key beds." 

Individual concretions disintegrate into small, angular conchoidal 

pieces, but the whole concretion tends to maintain its unity through 

cementation by calcite. Cone-in-cone structure occurs at the top and 

base of many of the concretions. At each concretion examined the 

cone structure points toward the concretion that is, the cones at 

the top point downward and those at the base point upAvard. The

4 Stanton, T. W., and Hatcher, J. B., Geology and paleontology of the Judith River 

beds: U. S. Geol. Survey Bull. 257, p. 13, 1905.
U. S. GEOLOGICAL SURVEY BULLETIN 847 PLATE 36

.4. CLIFFS OF JUDITH RIVER FORMATION ALONG MILK RIVER, IN SEC. 3, T. 37 N.

R. 9 E.

The lower third of the strata exposed (b) represents the Foremost beds of the Canadian classification, 

underlying the Pale beds of Canada (a). View looking north.

B. CROSS-BEDDING IN JUDITH RIVER FORMATION.

Due to overlap of shaly sandstone on a carbonaceous shale and coal bed. NWU sec. 28, T. 37 N.,

R. 9E.
TJ. S. GEOLOGICAL SURVEY 

A. EXPOSURE OF EAGLE SANDSTON

Shows gradational contact between Virgelle sandstone member (white) (white) and overlying overlying dark beds ofr uppe

12 E., about 2 miles northeast of Virgelle

B. VIEW LOOKING UP MARIAS RIVER IN CENTER OF SH 

Shows Claggett shale (Kc) in extreme upper right and left, underlain by Eagle sandstone (Ke) with Virgelle sa

through a transitional zone of shale and sandstone into Col
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 237

concretions are locally fossiliferous, with the fossils usually most 

abundant at the top of the concretion, just below the cone-in-cone 

structure if it is present.

Beds of bentonite from 2 inches to 3 feet thi,ck are characteristic 

of the "lower part of the Claggett. Eight beds of bentonite were 

found in the sections measured at Goosebill Butte and at the butte 

5 miles northeast of it that is sometimes called "Middle Goosebill 

Butte." In one section the highest of the eight beds of bentonite is 90 

feet above the -base of the Claggett, and in the other section 71 feet 

above the base. Individual beds of bentonite in these two sections 

cannot be correlated either by intervals between the beds or by the 

thickness of the bentonite, but this may be due in part to inaccuracies 

in the measurements, for in the weathered exposures it is difficult 

to determine the thickness of the bentonite, and slumping, which is 

not uncommon, may have caused errors in recording the position and 

intervals between bentonite beds. In these two sections, however, 

four beds of bentonite, from 5 to 6 feet apart and from 8 to 21 inches 

in thickness, occur between 30 and 60 feet above -the base of the Claggett. A similar succession of bentonite beds was also observed at several other localities within the area. These four bentonite beds are 

near the general stratigraphic position of the three beds of bentonite 

observed by Keeves,5 but these may be higher if, as Reeves states, the 

triple bed is at the base of the Ciaggett.

The upper half of the Claggett in the vicinity of Goosebill Butte 

consists of buff or dark-gray sandstone and sandy shale containing 

various amounts of calcareous matter. At some horizons, where 

there is a large proportion of calcareous material, a ledge-forming 

sandstone a foot or two thick is produced. At other horizons, where 

there is irregular distribution of calcareous material, there are sandy 

calcareous concretions 18 inches or less in diameter. Beds of gray 

sandy shale 10 to 15 feet thick merge imperceptibly into predominantly sandstone units.

The massive marine sandstone about 50 feet thick near the top of 

Goosebill Butte is in this report included as a part of the overlying 

Judith Eiver, as mentioned under that formation (p. 233).

In the northern half of the area the upper part of the Claggett 

is exposed only in fault blocks. These exposures show that the 

upper part is composed of sandstone and shale; the thicker sandstones are usually shaly and silty, and the thinner beds contain 

small .sandy calcareous concretions. The upper part of the Claggett 

is more variable in lithology than the lower half, and in some of the 

fault blocks it is difficult to determine the top. This variability is

"Reeves, Frank, op. cit. (Bull. 751), tf. 82. 

90380 37- 2
238 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

to be expected, however, for the upper part of the formation represents a recession of the sea with sedimentation passing from marine 

to littoral and brackish-water and then to continental conditions. 

This change was repeatedly interrupted by minor oscillations.

Fossils, which are not abundant in either number or species, are 

most common in the limy concretions in the lower half of the Claggett 

and are scarce in the upper half of the formation. The principal 

species found have been identified by J. B. Keeside, Jr., as Baculites 

ovatus, Baculites comf^essus^ Inoceramus barabina cf. sagensis, Liopistha montanensis, and Corbula perundata.

Apparently the Claggett thickens from about 400 feet in the 

western part of the area to about 500 feet in the eastern part. This 

thickening, however, is not determinable directly within this area 

but was estimated from well data and measured thicknesses in adjoining or neighboring areas.

The best exposure of the Claggett in this area is on the east side 

of Goosebill Butte in T. 27 N., R. 7 E., where the following typical 

section was measured:

. Section of Claggett shale on ea*st side of Goosebitt Butte

Ft. in.

Glacial drift and gravel (to top of butte) ___ ___ 15± 

Judith River formation:

Sandstone and shale, interbetlded____________ 50 

San'dstone, massive, cross-bedded, greenish gray;

weathers brown; many oyster shells at top_____ 6 

Shale, with thin beds of sandstone and carbonaceous

shale ___________________________ 30 

Sandstone, massive, buff, capped by hard brown crossbedded sandstone which on weathering forms cap 

rock of pillars; top is fossiliferous (oysters, clams)_ 50 

Claggett shale:

Shale, gray, sandy, with some black shale______ 99 

Shale, gray, an'd sandstone, light gray________ 1 6 

Shale, gray; lower part has purple hue on weathered 

fracture __________ ______________ 20

Sandstone, calcareous, buff, concretionary_______ 1 

Sandstone and shale; dark-gray sandstone and olivegray shale, interbedded- _'_ _ ___ 12 

Sandstone, buff, calcareous, irregularly bedded.___ 6 

Shale, gray-________ ____________ 23

Sandstone, friable, gray__ _ __ 6 

Sandstone, hard and calcareous in places __ 1 

Sandstone, gray, friable - ___ 1 2 

Sandstone, buff, hard, calcareous _____________ 1

Sandstone, gray, slightly nokiular___________ 3

Sandstone, hard, fine-grained, buff,, calcareous_____ 7 

Sandstone, drab, fine-grained, friable _ ______ 15

o Shale, gray, slightly sandy ___ 25
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 239 

Section of Clatfgett -shale on east side of GoosebUl Butte Continued

Claggett shale Continued. Ft. in. 

Shale, dark gray; contains at least seven beds of limestone concretions; concretions are 4 feet in diameter, 

are compose'd of gray limestone, and disintegrate 

into small chunks; cone-in-cone structure common 

at both top and bottom of concretions ____ 120 

Bentonite __ __ 1 3 

Shale, olive gray, fissile 13 

Bentonite __ 2 

Shale, gi'ay; contains limestone concretions similar 

to those described above_ __ __ ____ 16

Bentonite, with 1-inch bed of gray shale, 2 inches

above base_____ _ _ _ 9 

Shale, .dark olive gray___ ______ ____ 1

Bentonite _________ __ _ ____ 5

Shale, olive gray; contains limestone concretions 

similar to those described above_____ ____ 5 6

Bentonite __ _ _____________ _ __ 1 9

Shale, gray; contains limestone concretions similarto those described above________________ 5

Bentonite ________________________ 1 6

Shale, gray, clayey________ ____ 6

Bentonite __________________________'. 1 

Shale, gray, fissile_____________________ 15 

Sandstone, gray, shaly, crumbly____________ 6 

Shale, black, fissile; weathers to brownish cast___ 4 

Shale, olive gray________ ____________ 9

Sandstone, friable, yellow, am;! interbedded shale__ 1 

Shale, brown, with plant fragments__________ 1 6 

Bentonite ________._________________ 3 

Shale, gray___________ _ ________ 3

Eagle sandstone:

Sandstone, friable, buff and gray; contains more or 

less clayey material; weathers white_______ 

Total section measured., _ _ __ 581 1 

Total thickness of Claggett_____________ 420 1

The Claggett is well exposed 5 miles northeast of the above section, 

and the following section was measured there. Although this section differs in detail from the section just given, the general character of the two is the same.

Section of Clagyett shale measured at Middle Goosebilll Butte, in the EYn 

sec. 1, T. 27 N., R. 7 E.

Ft. in.

Glacial drift and soil______________________ 10 

Judith River formation:

Sandstone, gray and buff; sandstone concretions 5 

feet or less in diameter; cross-bedded; irregular 

hard sandstone 5 feet thick at top __ 22
240 .CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

Section of Claggett shale measured at Middle Gvos£l)ill Butte, m the 

sec. 1, T. 21 N., R. 7 E Continued

Judith River formation Continued. Ft., in. 

Sandstone, cross-bedded, gray; weathers brown; resistant__________________________ 1 6 

Sandstone, gray to buff_________ -______ 12 

Claggett shale:

Shale, olive green to gray, 2-inch bed of dark-gray 

concretionary limestone 10 feet above base; interbedded with argillaceous sandstone in upper part- 55 

Shale, sandj ; contains dark-gray limestone concretions 1 to 3 feet in diameter that weather to 

reddish brown__ __ _ ________ 10

Shale, brownish gray, fissile; becomes very sandy and 

oljive gray upward_ _______ .. __ 56

Sandstone, light gray, calcareous in places______ 3 

Shale, some black and fissile, some gray and sandy, 

with some argillaceous sandstone__________ 56

Shale, sandy, gray and tan; concretionary calcareous

sandstone at top_____________________ 38 

Sandstone, gray, calcareous in part_ _______ 2 

Partly concealed; probably brownish-gray shale, becoming sandy and less fissile upward_______ 66 

Shale, brownish gray, fissile; zone of dark-gray to 

black limestone concretions at top; these concretions, from 1 to 4 feet in diameter, also occur downward from the top of the unit to a horizon within 

30 feet of the base of the Claggett_______ 55 

Bentonite_ _________ _ ____ 1 3

Shale, brownish gray, fissile _ 21

Bentonite __________________________ 8 

Shale, brownish gray, fissile _ 6 

Bentonite __ ___ 10 

Shale, brownish gray, fissile________________ 5 

Bentonite___________________________ 11 

Shale, brownish gray, fissile___ ______ __ 5 

Bentonite_________ ________________ 1

Shale, brownish gray, fissile______________ 13 6

Bentonite__________._________________ 1 

Shale, dark gray, fissile.______ _ _ _ 3 6 

Bentonite___ _ _ ___ _____ 3

Shale, brownish gray____________________ 10 

Bed composed of a single layer of flat-lying black chert

pebbles from % to % inch in diameter_______ % 

Shale, dark gray, fissile ____ _ 9 

Bentonite___________________________ 3 

Shale, dark gray 1 

Eagle sandstone:

Sandstone, light gray, laminated _ 4 

Shale, brown, carbonaceous _ 1 

Shale, gray , _ 15 

Shale, dark gray, containing many plant fragments 3
CHOUTEAU, HILL, AND. LIBERTY COUNTIES, MONT. 241

Section of Claggett sJiale measured at Middle Goosebill Butte, in the J0% 

sec. 1, T. 21 N., R. 7 #. Continued

Eagle sandstone Continued. Ft. in. 

Shale, gray, grading upward into buff sandstone 5 

Shale, brown, carbonaceous_ _ 8 

Sandstone, shale, and siltstone; locally contains a 

massive light-gray sandstone in the middle of the 

unit ___________________ 60

Total section measured 546 2^ 

Total thickness of Claggett- 412 %

The base of the Claggett is fairly distinct and well exposed along 

Marias River in the southwestern part of the area. There is commonly a sharp lithologic break between the dark shale of the Clagget and the lighter-brown carbonaceous and plant-bearing beds at 

the top of the Eagle. Furthermore, the lower 30 feet of the Claggett 

contains scattered pebbles of black chert. These pebbles are locally 

present elsewhere in the section, but they are generally present and 

most abundant near the base of the Claggett. In the southeastern 

part of the area higher beds of the Claggett are only poorly exposed.

Along Sage Creek in T. 32 N., R. 11 E., the base of the Claggett 

is brought up by faulting. The following section was measured in 

the steeply dipping lower part of the Claggett exposed in sec. 15:

Section of lower part of Claggett shale in sec. 15, T. 82 N., R. 11 E.

Top concealed. Ft. in. 

Shale_______________________________ 48 

Sandstone, bedded _ ___ 5 

Shale___,_______:___________________ 15 

Bentonite____________________________ 4 

Shale_______________________________ 120 

Bentonite _____________ ________ 1 8 

Shale_______________________________ 6 

Bentonite __________________________ 1 1 

Shale_____________________________ 4 

Bentonite ____ _____ _______________ 8

Shale_______________________________ 4 

Bentonite__ ________:__:_______________ 2 

Shale______________________________ 8 

Base concealed. 

211 2

The presence of four beds of bentonite with thin bands of shale separating them strongly suggests that the base of this section is very 

nearly the base of the Claggett shale. However, no black pebbles 

were found at this locality.

Along the Milk River in the center of T. 34 N., R. 13 E., just east 

of this area, steeply dipping beds in. the Claggett are fairly well
242 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

exposed in fault blocks, but minor faulting has disturbed the stratigraphic succession so that no reliable section could be measured. 

Four attempts to determine the thickness of the Claggett at this locality gave results ranging from about 350 feet to nearly 500 feet. This 

information is presented because the exposures are sufficiently good 

to encourage attempts to measure a section, and a single measurement 

would leave little doubt of its correctness. For example, Stebinger 6 

gives the thickness of the Claggett as 285 feet in a supposedly complete section measured in sec. 8, T. 34 N., K. 13 E. It seems probable, 

however, that a concealed strike fault has cut out part of the Claggett 

in this section. In sec. 6 of the same township about 675 feet of 

Clagget is exposed, probably because of repetition of beds by one or 

more concealed faults.

EAGLE SANDSTONE

The name "Eagle sandstone" was first used by Weed 7 in 1899 for 

the beds of sandstone, shale, and thin coal that immediately overlie 

the Colorado shale at the mouth of Eagle Creek, along the Missouri 

River a few miles east of this area. In this area the formation is 

separable into a lower bed of massive sandstone and an upper series 

of sandstone and shale. Bo wen,8 in 1915, applied the name "Virgelle 

sandstone member" to the lower massive sandstone, which is exposed 

at the type locality near the town of Virgelle, in T. 26 N., R. 12 E., 

within the area considered in this report.

In the immediate vicinity of its type locality the Virgelle is a white 

argillaceous friable sandstone, but elsewhere in the area it is more 

commonly buff to light brown and massive. (Compare pi. 37, J., 

and pi. 37, B.} Over most of the area it is about 100 feet thick, and 

it generally crops out in cliffs or steep slopes. The upper part of the 

Eagle consists of massive sandstone, thin-bedded sandstone, clay shale, 

carbonaceous shale, and thin streaks of coal; it measures 100 to 150 

feet in thickness. At places it contains thick massive beds of white 

sandstone that are similar to the Virgelle.

Although the Virgelle sandstone member contrasts sharply with 

the higher beds of the Eagle, it is impossible to determine precise 

stratigraphic boundaries of the Virgelle in this area. In the western 

part of the area 100 feet of interbedded sandstone and shale lies at 

the top of the Colorado shale, forming a zone transitional into the 

Eagle (pi. 37, B}. Locally in this zone the sandstone beds thicken

6 Stebinger, Eugene, Possibilities of oil and gas in north-central Montana: TJ. S. Geol. 

Survey Bull. 641, p. 67, 1916.

7 Weed, W. H., U. S. Geol. Survey Geol. Atlas, Fort Benton folio (no. 55), p. 2, 1899.

8 Bowen, C. F., The stratigraphy of the Montana group, with special reference to the 

position and age of the Judith River formation in north-central Montana: U. S. Geol. 

Survey Prof. Paper 90, p. 97, 1915.
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 243

and merge into the massive Virgelle, and the lithologic boundary is 

far below the top of the transition zone as developed elsewhere. 

Farther east, where the transition zone at the top of the Colorado is 

less sandy, the base of the Virgelle may be more definite. No regional 

trend or pattern of such changes could be determined. Similarly the 

boundary at the top of the Virgelle is arbitrary. The upper part of 

the Eagle locally, becomes more sandy and the sandstones merge into 

the underlying Virgelle. These irregularities at the top and base of 

the Virgelle are well exposed along Marias Kiver in the southwestern 

part of the area.

Few fossils were found in the Eagle in this area. Locally fragments of fossil wood are abundant, and elsewhere marine invertebrates are common.

Chert pebbles that have a black exterior are abundant in some 

places near the top of the Eagle. They are commonly flattened 

ellipsoids from one-fourth to 1 inch in length and are invariably 

very smooth or well rounded. Some of them are concentrated in thin 

beds, and others are scattered through a zone several feet thick. These 

chert pebbles have been regarded by some workers as a reliable indication of the top of the Eagle. In the area examined by the writers 

these pebbles are most abundant at the top of the Eagle, but they are 

not restricted to that horizon. In sec. 6, T. 34 N., K. 13 E., the upper 

part of the Colorado shale is exposed in a fault block. About 40 

feet below the top of the Colorado shale is a 10-inch bed of reddishbrown limestone (with marine shale above and below) containing 

pebbles of green, gray, and black chert. The pebbles are from onefourth to 1 inch in diameter and are most abundant near the center 

of the limestone bed. About 31^ feet above this bed is a similar bed, 

5 inches thick, which also contains chert pebbles.

Chert pebbles are not uncommon in the basal part of the Claggett 

shale, although they may be widely scattered. They were found as 

high as 30 feet above the base of the shale. Chert pebbles similar to 

those in the Eagle and Claggett were found in glacial drift at several 

localities. Near the center of the west line of sec. 11, T. 30 N., 

K. 11 E., there are many chert pebbles lying on the surface of the 

ground. The Judith River formation is at the surface at this locality, 

and presumably the pebbles have weathered out from it, although 

possibly they were left there with a thin veneer of ground moraine. 

These pebbles are similar in appearance to those in the older formations that is, they have the same range in size, all of them are dark 

gray or black on the outside but are composed of black, gray, white, 

yellow, or red chert, and all are smooth or well "rounded." Some 

of the pebbles from this locality were submitted to W. T. Schaller,
244 CONTRIBUTIONS TO ECONOMIC\ GEOLOGY, 1934-36

of the United States Geological Survey, for a determination of the 

nature and origin of the black coating, and he reports as follows:

The black coating could not be removed by ignition; hence it is not organic. 

Treatment with various acids did not remove it; hence it is not due to a 

surface coating of iron or manganese oxides.

Examination of a thin section showed that the chert composing the pebbles 

is full of a black substance, much of it in rhombohedral crystals that suggest 

one of the rhombohedral carbonates (calcite, siderite, etc.). It also showed 

that the material of the black coating not only occurs on the surface but 

forms a narrow zone that penetrates each pebble a short distance and also is 

present in streaks, probably following healed fractures from the surface that 

penetrate the pebbles for greater distances than the thickness of the outer 

zone. * * *

It is suggested that the black coating on the pebbles is explainable as follows: Permeating solutions dissolved parts of the original carbonate mineral 

(magnesia-bearing siderite?) disseminated throughout the chert and on 

reaching the surface of the pebbles were oxidized and precipitated their 

load, probably chiefly iron, as black iron oxide in a narrow zone whose thickness would depend on the distance to which the oxidizing atmospheric conditions could operate and also, in lesser degree, along fractures (since healed) 

in which the same oxidizing conditions could operate. As this oxidized and 

precipitated iron oxide is embedded in the chert for a distance equal to the 

narrow zone of permeability of atmospheric oxidizing conditions, it cannot be 

removed by simple treatment with the common acids such as hydrochloric, 

sulphurous, or sulphuric.

Subsequent abrasion polished the outside surface of the zone containing the 

precipitated oxidized iron oxide and accentuated the black color.

The best exposures of the Eagle are in the southern and southwestern parts of this area, especially along the Missouri and Marias 

Eivers, but there are other exposures in the northeastern part of the 

area, in fault blocks along the Milk River.

Section of Eagle sandstone measured near south line of sec. 85, T. 28-N., R. S E.

Claggett .shale.

Eagle sandstone: Ft. in. 

Shale, somber-colored, in lenticular beds, and carbonaceous dark shale"; locally contains carbonized 

wood; some interbedded massive sandstone. locally 

in thick beds___________,__ ___ 122 

Virgelle sandstone member:

Sandstone, white, friable, massive, coarsegrained near top; locally dark bluish-purple 

ferruginous concretions . 50 

Sandstone, buff orange, containing large ironstained calcareous concretions; interbedded 

lenses of light-gray to white sandstone . 11 

Colorado shale (top of transitional zone):

Sandstone, gray; becomes increasingly arenaceous and

less consolidated toward the top___ 32 

Sandstone, white to light gray _ 1 6
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 245

Section of Eagle sandstone ineasured near.south line of sec. 35, T. 28 N.,

R. 8 E Continued

Colorado shale (top of transitional zone) Continued. Ft- inSandstone, dark gray, loosely consolidated, massive- 13 6 

Shale, very sandy, thin-bedded, with %- to 1-inch beds

of loosely consolidated buff to gray sandstone. 72 

Sandstone, calcareous 1 

Shale, sandy, thin-bedded, dark olive gray 11 6 

Sandstone, shaly, gray__ 1 

Sandstone, calcareous, gray __ % 

Sandstone, shaly, gray, with some laminae of buff

sandstone____-__ . 3 

Sandstone, calcareous, gray ___ ___ _ 1 

Sandstone, buff, with laminae of bluish-gray shale 1 

Shale, sandy, bluish gray, laminated, with buff sandstone beds as much as 2 inches thick; limestone concretions at base ____________ __ 6 6

Total section measured________________ 325 2% 

Thickness of Eagle sandstone_________ _ 183

In the SWi/4 sec. 1, T. 26 N., R. 7 E., the Eagle above the Virgelle 

sandstone member is well exposed. These upper beds are about 100 

feet thick and consist largely of sandstone near the base but become 

increasingly shaly upward. The sandstone beds are strongly crossbedded, and all the beds are very lenticular. (See fig. 58.)

The thickness and lithology of the upper part of the Eagle near 

the center of the south line of sec. 35, T. 28 N., K. 8 E., are shown 

in the preceding section.

Section of Eagle sandstone on Marias River in the SE1/^ sec. 25, T. 29 N., R. 7 E.

Feet

Glacial drift and soil________________________ 15 

Claggett shale: Shale, dark gray, containing black chert pebbles ; no bentonite beds observed_'._____________ 20 

Eagle sandstone: .

-Mudstone, gray, to somber-colored shale; brown and carbonaceous shale; thin hard light-gray sandstone beds; 

contact with the Virgelle sandstone gradational through 

25 feet_____________________________ 132 

Virgelle sandstone member: Mostly light gray, some buff; . 

friable sandstone, weathering into fluted columns; contains lenticular gray and brown sandstone concretions; 

60 feet above the base is an irregular but fairly persistent hard brown concretionary sandstone; the lower 15 

feet of the Virgelle not exposed________________ 115

Total thickness of section measured___________ 282 

Total thickness of Eagle sandstone___________ 247
246 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

COLORADO SHALE

The name "Colorado" was first used on one of the atlas sheets of

the Fortieth Parallel Survey (published 

in 1876) and described in 1878 by King.9 

As originally designated, the group 

included equivalents of the fFort 

Benton,10 Niobrara and fFort Pierre 

groups of Meek 11 and was a lithologic 

unit consisting almost entirely of shale. 

However, as paleontologic information 

grew, a marked break was recognized between the faunas of the Niobrara and 

Pierre (fFort Pierre of Meek). In 

1878 White 12 proposed, among other 

changes in nomenclature, that the term 

"Colorado group" be restricted to include 

only the fFort Benton (Benton) and 

Niobrara. In 1899 Eldridge 13 strengthened the evidence for restricting the 

usage of the term, and in 1893 

Stanton 14 used the term "Colorado 

formation" for only the fFort Benton 

(Benton) and Niobrara. The present 

usage of the United States Geological 

Survey is threefold: (1) The term 

"Colorado group" is used where the 

rocks can be divided into distinct formations; (2) "Colorado formation" is used 

where there are sandstone and shale beds

I

0 O.

8 King, C. E., Systematic geology; U. S. Geol. Expl. 

40th Par. Kept., vol. 1, p. 305, 1878..

10 A dagger (t) preceding a geologic name indicates that the name has been abandoned or rejected 

for use in classification in publications of the U. S. 

Geological Survey.

11 Meek, F. B., A report on the invertebrate Cretaceous and Tertiary fossils of the upper Missouri 

country: U. S. Geol. Survey Terr. Kept., vol. 9, 

pp. 24, 25, 1876.

12 White, C. A., Report on the geology of a portion 

of northwestern Colorado: U. S. Geol. and Geog. 

Survey Terr. 10th Ann. Kept., for 1876, pp. 3-60, 

1878.

13 Eldridge, G. H., Some suggestions upon the 

methods of grouping the formations of the middle 

Cretaceous and the employment of an additional 

term in its nomenclature: Am. Jour. Sci., 3d ser., 

vol. 38, pp. 313-321, 1889.

14 Stanton, T. W., The Colorado formation and its 

invertebrate fauna: U. S. Geol. Survey Bull. 106, 

1893.
OHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 247

that cannot be separated into mappable units; and (3) "Colorado 

shale" is used where the beds are chiefly shale that cannot be subdivided. In conformity with this usage, the name "Colorado shale" 

is used in the area considered in this report.

Only the upper 500 feet of the Colorado shale crops out in this 

area. These beds are well exposed in the southern part of the area 

along the Missouri River and Marias River. The upper 100 feet is a 

series of interbedded sandstone and shale that is transitional into 

the overlying Virgelle member of the Eagle sandstone. This sandy 

transition zone grades eastward into shale. In the southwestern 

part of the area the proportion of sandstone increases upward, and 

to locate consistently the base of the overlying Virgelle sandstone 

member of the Eagle is nearly impossible, whereas in the southeastern part of the area, although there is a sandstone in the upper 

500 feet of the Colorado, it is less prominent than farther west, and 

the base of the Virgelle is fairly distinct. The lower 400 feet of 

the beds exposed consists almost entirely of dark-gray shale. The 

Colorado shale weathers into nearly vertical walls along the cliffs of 

the Missouri River. In contrast with the Colorado shale, the Claggett and Bearpaw shales commonly weather into slopes. In places 

the Colorado shale is slightly sandy, with some beds of yellow 

micaceous crumbly sandstone from one-fourth inch to 1 inch in 

thickness. Ovate concretions of black limestone from 6 inches to 2 

feet in length, with septaria or veins of calcite, are common in the 

formation. The concretions apparently are not confined to specific 

horizons and occur sporadically, although locally they may be 

abundant.

In the northern part of T. 34 N., R. 12 E., several hundred feet 

of the upper part of the Colorado shale and part of the overlying 

Eagle sandstone and Claggett formation are exposed in a fault 

block. There the contact between the Colorado shale and the Eagle 

sandstone is sharp, with practically no transition zone, but possibly 

it is a fault contact. At 44 feet below the apparent top of the 

Colorado shale there is a peculiar reddish-brown bed of limestone 

containing pebbles of black, gray, and green chert from one-fourth 

to 1 inch in diameter. The bed is 10 inches thick and has a rough 

columnar jointing. Beds of this type were not observed elsewhere 

in the area, but similar chert pebbles occur in the overlying formations. (See pp. 241, 243.)

Fossils in the Colorado shale are most abundant in the concretions. 

Collections include Scaphites ventricosus, Scaphites vermifomiis, 

BacuUtes asper. Inoceramus grandis, and Ostrea congest®. Scaphites ventricosm was found in the lower 25 feet of the sandy transition zone between the Colorado shale and the Virgelle sandstone,
248 , CONTRIBUTIONS TO ECONOMIC GEOLOGY-, 19 34-36

indicating that at least the lower part of tHis zone is of Colorado 

age. Possibly the uppermost 75 feet of the transition, zone is of 

Montana age, equivalent to the beds that to the east contain the 

Telegraph Creek fauna, but in the absence of paleontologic data in 

this area the top of the Colorado is determined on the basis of 

lithology.

Partial section of upper part of sandy transition zone at top of Colorado shale 

in Skit Coulee, sec. 21, T. 26 N., R. 8 E.

Virgelle sandstone member of the Eagle sandstone.

Colorado shale: Feet

1. Sandstone, ferruginous and friable; very thin beds of

shale_____________________________ 12

2. Sandstone, ledge-forming, laminated owing to thin films 

of shale along bedding planes___'. ________ __ 1

3. Sandstone (like no. 1)_____________________ 4

4. Sandstone (like no. 2)____________________ 1

5. Shale, black, with a few beds of brown sandstone about

an inch thick_________________._______ 7

6. Sandstone (like no. 2)__________________ 1

7. Shale (like no. 5)_______________________ 7

8. Sandstone (like no. 2)____________________ 1

9. Shale and sandstone interbedded in irregular lenses onesixteenth to one-fourth inch in thickness; proportion 

of sandstone increases upward by increase in number 

of sandstone lenses___________:_________ 2

10. Sandstone (like no. 2)____________________ 1

11. Shale and sandstone (like no. 9)______________ 2

12. Sandstone (like no. 2)___________________ 1

13. Shale and sandstone (like no. 9) ________ ___ 36 

Alluvium in Skit Creek. . 

76

The total thickness of the Colorado shale, determined from well 

logs and measurements made by others outside this area, is about 1,800 

feet. Apparently it is of nearly uniform thickness over a wide area.

Some information concerning the lower part of the Colorado shale 

and underlying rocks is available from drill records and outcrops in 

nearby areas.

Kootenai formation. The Kootenai formation, of Lower Cretaceous age, consists of 350 to 500 feet of variegated red, green, and 

gray shale with lenticular cross-bedded sandstone and thin beds of 

limestone. Beds of gray sandstone, 50 feet or more in thickness, are 

present in places. To the west the base of the formation is marked 

by a sandstone known as the "Sunburst sand."

Ellis formation. The Ellis formation, of Upper Jurassic age, is 

composed of 200 to 300 feet of dark-gray limestone, black limy shale,
CHOUTEAU, - HILL, AND LIBERTY COUNTIES, MONT: 249

arid some calcareous sandstone, with a sandstone locally present -at 

the base. It rests unconformably upon the Madison limestone.

Madison limestone. The Madison limestone, of lower Mississippian age, consists of about 1,000 feet of white to bluish-gray limestone, generally in thick massive beds but locally in beds 6 to 12 

inches thick. " " ,

Information from driller's log. An approximate section of these 

older rocks and the authors' interpretations of the formations penetrated is given in the following driller's log of a well drilled by the 

California; Co. on the Utopia anticlinal nose, about 2 miles west of 

the area.

Log of the California, Co.'s Ross No. 1 well, in the NEy^SEy^NEy^ sec. 8,

T. S3 N., R. 6 E.

[Altitude 3,565 feet. Commenced drilling Nov. 9, 1931. Completed drilling Apr. 21, 1932]

Judith River formation: - - Feet

Cellar _____ ______ _ _____________ __ 0- 13

Shale, yellow ; shows coal _____________ 1 13- 36 

Shale, dark gray _____ _ __ ___ ____ _ ___ 36- 81

Claggett formation : ~ " ' . Shale, gray __ _ __ _____ .. _ 81- 515

Eagle sandstone: ' " ' "

Shale, gray, sandy ___ _ ________ : _____ 515- 530 

Shale, gray _________ __.:-_ ___ __ 530- 590 

Shale, gray, sandy _ ___ _ __ j _ __ _ 590- 600

Shale, gray ___ _ ___ _ ___ __ __ __ 600- 605 .

Shell, sandy; little water ___ u ____ _____ _ 605- 610

Shale, gray, shelly ___ _ ___ __ ___ __'__" 610- 625

Shale, gray, and sandy shells _ ___ _ 625- 650 

' ' Shale, gray _ __ ________ __ ___ _ ___ ____ 650- 688

Virgelle sandstone member: 

Sand, water-bearing ______ __ ___ _ __ _ 688- 720

Shale ________________________ 720- 725 

Sand ______________________ '___ 725- 785

Colorado shale:

Shale, sandy __ _ ______ 785- 820 

Shale, gray _______________________ 820- 826 

Shale, gray, sandy ___ _ ___________ _ _ 826- 830 

Shale, gray ________________ .! _____ 830-1, 015 

Shale, black _________ ____________ 1, 015-1, 050 

Shale, blue _____________________ ____ 1, 050-1, 074 

Shell, lime _______________________ 1, 074-1, 077 

Shale, blue ______________________ 1, 077-1, 085 

Shale, gray ______________________ 1,085-1,120 

Shale, black _____________________ 1, 120-1, 190 

Shale, gray _______________________ 1, 190-1, 220 

Shale, black ______________________ 1, 220-1, 230 

Shell, lime _______________________ 1, 230-1, 235 

Shale, black ____________ . __________ 1,235-1,740
250 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

Log of the California Co.'s Rosa No. 1 well, % tjfie NE^SE-y^NEy^. sea. 8, 

T. 33 N., R. 6 #. -Continued

Colorado shale Continued. Feet 

Shell, lime________________ ____ 1,740-1,743 

Shale, black________________________ 1, 743-1, 907 

Shell, lime_______________________ 1,907-1,910 

Shale, black______________________ 1,910-2,050 

Shell, sandy; show of gas_______________ 2, 050-2,055 

Shale, black______________________ 2,055-2,215 

Shale, gray*._______________________ 2,215-2,240 

Shale, black_______________________ 2,240-2,320 

Shale, gray, sandy__________________ 2,340-2,400 

Sand, water-bearing________________ 2,400-2,415

Lime, dark gray, sandy, hard____________ 2,415-2,420 

Shale, dark gray, sandy; shells__________ 2,420-2,430 

Shale, gray, sandy__________________ 2,430-2,535 

Sand; water at 2,553 feet_____________ 2,535-2,565 

Shale, gray, sandy__________________ 2,565-2,590 

Shale, dark gray, sandy_________________ 2, 590-2, 595 

Shale, black______________________ 2,595-2,608 

Shale, gray______________________ 2,608-2, 610 

Sand; water, 1 bailer an hour____________ 2,610-2, 615 

Shale, gray_______________.._______ 2, 615-2, 660

Kootenai formation:

Shale, gray, green, and red______________ 2, 660-2,725 

Shale, brown______________________ 2, 725-2, 730 

Shale, gray_______________________ 2, 730-2,955 

Shale, brown______________________ 2,955-2,960 

Red beds_________________________ 2, 960-2,970

Shale, gray, sandy__________________ 2,970-2,980 

Shale, gray, sandy; lime shells__________ 2,980-3,000 

Shale, sandy______________________ 3,000-3,005 

Shale, light gray, lime shells-.___________ 3,005-3,015 

Sand, dry ("Sunburst" of drillers)________ 3.015-3,060 

Shale, brown______________________ 3,060-3,065

Bllis formation:

Lime, black, hard___________________ 3,065-3,075 

Shale, black, and lime shells____________ 3.075-3,090 

Shale, black______________________ 3,090-3,120 

Lime, black_______________________ 3,120-3,150 

Shells, black, lime; gray shale___________ 3,150-3,200 

Shells, black, lime; gas at 3,202 feet when dumping

bailer___ ___________________ 3. 200-3, 210 

Shale, dark gray, dry________________ 3,210-3,215 

Lime, sandy, gray__________________ 3,215-3,220 

Shale, gray_____________1________ 3,220-3,226 

Sand, water-bearing__________________ 3,226-3,265 

Lime, white, sandy__________________ 3,265-3,280 

Lime, brown, sandy__________________ 3, 280-3,285 

Lime, sandy_______________________ 3, 285-3, 288

Madison limestone______________________ 3, 288-3, 337
OHOUTEATJ, HILL, AND LIBERTY COUNTIES, MONT. 251

IGNEOUS ROCKS

Pikes of igneous rock crop out at four localities in the area, but 

there may be many more similar dikes that are concealed by the 

glacial drift. The dikes are composed of porphyritic lamprophyre 

that is closely related in composition to the large bodies of igneous 

rocks in the adjacent Bearpaw and Highwood Mountains and the 

Sweetgrass Hills. All the dikes are deeply weathered and are only 

slightly more resistant to weathering and erosion than the UpperCretaceous rocks which they intrude. The dikes crop out only in 

the valleys, where they generally protrude a few feet above the 

surrounding surface; no outcrops were observed on the old erosion 

surface, which forms a sort of tableland between the abrupt and 

narrow valleys of the present drainage system. (See pi. 38, A, B.) 

It is uncertain whether the dikes are irregular and discontinuous or

.' Judith River formation .'.'.'.'.'.

Ji ' '. '. ' '. Judith River formation ..'...'.'. _','. / .' 

FIGUBB 59. Lobe of Judith River formation In dike of porphyritic lamprophyre along 

Milk River near the northwest corner of sec. 2, T. 37 N., B. 8 E.

simply concealed. The maximum width of the dikes is usually 

about 6 feet, but at one locality a width of 15 feet was observed. 

The intrusion of the dikes did not cause any alteration or disturbance of the adjacent sedimentary rocks except for a slight 

baking near the contact.

A dike that trends N. 60° E. emerges from a cover of glacial drift 

near the top of the bluff along the Milk River at the international 

boundary, near the northwest corner of sec. 2, T. 37 N., R. 8 E., 

and extends into Canada about 500 feet. The dike is 6 feet wide 

near the boundary but narrows northeastward to about 1 foot at 

the edge of the alluvium in the valley of Milk River. The contacts 

of the dike are irregular. At one point a lobe, about 2 feet wide, 

of Judith River sandstone and shale extends into the dike (fig. 59). 

The dike is broken by irregular joints developed at high angles to 

the contacts. The sedimentary rocks in the Judith River formation apparently are not baked at the contact beyond a zone about 1 

inch wide, immediately adjacent to the igneous rock. The dike
252 CONTRIBUTIONS TO. ECONOMIC .GEOLOGY, 1934-36

is a porphyritic iamprophyre that contains phenocrysts of biotite 

in an altered groundmass that consists chiefly of anhedral feldspar, 

probably mostly potash feldspar, and euhedral biotite. The flakes 

of biotite are clearly oriented, with trends roughly parallel to the 

trend of the dike. . A second dike, which also trends about N. TO 0 E., occurs about 100 

feet northwest of the one just described.- It is apparently of the 

same composition.

In the NE% sec. 15, T. 26 N., R. 9 E., a dike 3 feet wide trends 

N. 30° E. and dips 85° E. At the outcrop the dike intrudes the sandy 

transition zone at the top of the Colorado shale. The inner part of 

the dike is easily weathered and has no discernible jointing, but on 

each side of this part the rock is jointed in columns that are about 

1 foot thick and nearly horizontal and normal to the contacts. No 

platy jointing was found along the contact. The central part of the 

dike contains phenocrysts of biotite and augite in a fine-grained 

groundmass whose index of refraction is higher than that of balsam. 

The biotite is more abundant than pyroxene. There is little parallelism of the phenocrysts. The columnar-jointed border zones are 

holocrystalline, with only a few phenocrysts of pyroxene (probably 

augite) in a groundmass of euhedral biotite, magnetite, and anhedral 

feldspar, probably potash feldspar.

A dike in the SW*4 sec. 33, T. 26 N., R. 12 E., intrudes the upper 

part of the Eagle (pi. 38, A). It trends northeast, and its maximum 

width is 15 feet. It has outer zones about 1 foot thick that are 

broken into small plates by jointing parallel to the dike; the central 

zone is massive, with joints normal to its linear extent, a character 

which is typical of most of the dikes in this area. The rock is a 

porphyritic Iamprophyre containing numerous large corroded phenocrysts of biotite and a few subhedral phenocrysts of augite. The 

groundmass is composed chiefly of au'gite and a nontwinned feldspar 

with an index of refraction lower than that of balsam. There is relatively little biotite in the groundmass. The phenocrysts of biotite 

are not only corroded but thoroughly leached and exhibit only a 

slight pleochroism or absorption. The phenocrysts have a nearly 

parallel orientation, but there is practically no parallelism of the 

minerals in the groundmass.

A dike of igneous rock trends N. 8° E. diagonally across a small 

valley in the SW^ sec. 20, T. 26 N., R. 12 E., and is exposed for a 

distance of about 300 feet in the valley walls but does not protrude 

above the old erosion plain bordering the valley. (See pi. 38, B.) 

It intrudes the Virgelle sandstone and the upper part of the Eagle. 

The dike is 6 inches to 1 foot wide and is practically vertical. It 

contains abundant large phenocrysts of mica.
U. 8. GEOLOGICAL SURVEY BULLETIN' 847 PLATE 38

A. DISTANT VIEW OF DIKE IN SWJ4 SEC. 33, T. 26 N., R. 12 E. 

The dike does not protrude above the plateau surface.

B. DIKE IN SWJ4 SEC. 20, T. 26 N., R. 12 E.

Cutting upward through undisturbed and unaltered sandstone in upper part of Virgelle sandstone

member of Eagle sandstone.
U. S. GEOLOGICAL SURVEY BULLETIN 847 PLATE 39

A. VIEW ALONG TRACE OF FAULT SHOWING STEEPLY DIPPING COLORADO SHALE 

THRUST OVER HORIZONTAL BEDS OF EAGLE SANDSTONE, SWJ.J SEC. 4, T. 26 N., R. 

11 E.

B. VIEW LOOKING WEST ACROSS PLATEAU SURFACE OF LIBERTY COUNTY TOWARD

SWEETGRASS HILLS.
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 253

STRUCTURE 

REGIONAL STRUCTURE

The principal structural feature in the north-central Montana 

region, including the area here described, is a northeastward- to 

eastward-dipping homocline, but the regional dip is modified by 

folding and faulting in some of the isolated mountain groups. The 

bomocline rises to the southwest and west, continues for 40 miles or 

more west of the area, and forms the east side of the broad Sweetgrass arch, on the crest of which are the Kevin-Sunburst, Pondera, 

and other oil fields. The Bearpaw Mountains are circumscribed by 

a belt of thrust faults, some of which occur in the southeastern and 

eastern part of this area. The laccolithic intrusions of igneous rocks 

in, the Sweetgrass Hills have domed up the sedimentary beds, so 

that they dip at high angles near the hills, but the dips flatten out 

and merge with the regional dip a few miles distant. The eastern 

limit of this doming is in the northwest quarter of the area. The 

igneous activity in the Highwood Mountains, to the south of this 

area, does not appear to have had any local structural effect, for the 

uniform northeastward dip continues through the area of igneous 

rocks in the mountains 15 and into the southern part of the area here 

described.

STRUCTURE OF THE AREA

The interpretation of the structure of the area is shown on plate 

43 by means of contours drawn at intervals of 100 feet on the top 

of the Eagle sandstone. The contours are based in part on altitudes 

obtained at exposures of recognizable stratigraphic horizons; most 

of these altitudes were obtained at localities along the Missouri and 

Marias Rivers and Canada Coulee and in the northeastern part of 

T. 30 N., R. 7 E. In other parts of the area the contours are based 

on altitudes at outcrops of rocks whose position in the formation 

was not accurately known, on information obtained from about 100 

wells drilled for water, and on the logs of 7 wells drilled for oil or 

gas in or near this area, exclusive of wells drilled west of Kremlin. 

Much of the information on which the contours are based is indefinite, 

but the maximum error in the altitude of the top of the Eagle sandstone, as indicated by the contours, probably does not exceed 100 

feet, and for most of the area the error is believed to be less than 

5.0 feet.

15 Reeves, Frank, Thru?*- faulting and oil possibilities in the plains adjacent to the Highwood Mountains, Mont.: U. S. Geol. Survey Bull. 800, pi. 44, 1929. 

90380 37 3
254 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

The predominant structural feature throughout the area is a homoclinal dip; the rocks in the southern part of the area have a nearly 

uniform dip toward the northeast of about 35 feet to the mile, except in the immediate vicinity of faults; through the central and 

northern part of the area the homoclinal dip gradually swings to 

the east. Transverse to this general northeast or east homoclinal 

dip are several minor undulations. In the southwest a broad indistinct anticlinal nose plunges north-northeastward past Brinkman, 

About 10 miles to the southeast another nose parallels it. They ar& 

merely broad warps in which the structural relief, transverse to the 

axes, does not exceed 40 feet in 6 miles. The axis of a syncline that, 

plunges east-northeast passes near Joplin, Inverness, and Kudyard.. 

This syncline is the eastern extension of the Marias River syncline,. 

which trends eastward across the Sweetgrass arch. An eastwardplunging anticlinal nose, commonly known as the "Utopia nose",, 

lies a few miles north of the main, line of the Great Northern Railway ; its trend is slightly north of east. The Utopia nose is slightly 

asymmetrical, the southern flank being the steeper. The structural 

relief of the nose is about 150 feet, but the exposed beds do not show 

any closure on the west side. Possibly there are smaller anticlinal, 

noses north of the Utopia nose and more or less parallel to it that 

are concealed by glacial drift and cannot be determined from th& 

small and isolated outcrops of Judith River beds. The northeastern 

part of the area is concealed by glacial cover, except along the Milk 

River, and there practically all the exposed rocks are in the Judith 

River formation, in which there are no recognizable stratigraphic 

horizons; the beds, however, appear to be nearly horizontal. The 

so-called Kremlin "anticline" is interpreted by the writers as theresult of faulting. The structure at that locality is described under 

the Kremlin wells. (See pp. 258-259.)

FAULTS

No normal faults were found in this area, but several thrust faults 

of an unusual type are exposed, principally along the Missouri River 

in the southeast corner of the area and along the Milk River in the 

northeastern part. Other faults are doubtless present in the area 

between these exposures, most of which is covered by glacial drift. 

No faults were observed in the western half of the area. A line 

indicating the western limit of known thrust faulting is shown on 

plate 43.

The faults are a part of the system of thrust faults that occurs in 

the region encircling the Bearpaw Mountains, to the east of thisarea. They have been noted by many geologists who have w.orked
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 255

in this part of Montana and have been the subject of a special study 

by Reeves.10

In the published descriptions of the fault system Keeves presents 

evidence to show that the faulting is shallow and does not extend 

below the upper part of the Colorado shale. Briefly, this evidence, 

consists of the following features: (1) Although some of the thrust 

faults show that a stratigraphic displacement of more than 1,000 feet 

may occur in faults of this type, none of the faults expose strata below the middle of the Colorado shale, even where faulting begins 

well below the top of the Colorado shale; (2) thrust faults of this 

type are absent where strata below the Colorado shale are at the 

surface; (3) the lowest beds exposed along the faults have approximately the same inclination as the fault plane, suggesting that the. 

fault began as a movement along a bedding plane and passed upward', 

along a curving surface; (4) the fault planes apparently flatten with 

depth; (5) well data indicate that the Kootenai formation below the 

thrust faults is in its normal position and not at a higher level 011. 

the up thrust side of the hypothetically extended fault; (6) mathematical calculation of the depth of faulting gives an average of 900 

feet below the Eagle sandstone. The writers found no evidence that 

does not accord with Reeves' conclusions concerning the depth of the 

faulting.

The. faults observed in this area are all of the reverse type, and 

the dip of the fault planes is 30° to 60°. The dip and strike of the 

strata on the upthrown side of a fault are about the same as the dip 

and strike of the fault plane that is, the bedding planes within the 

upthrust block are parallel to the fault plane. The steep dip of beds 

in the upthrust block near a fault flattens to the regional dip within 

a quarter of a mile and locally within less than 1,000 feet from the 

fault. The strata on the footwall side of the fault appear to be undisturbed ; they are nearly flat and conform with the regional structure. (See pi. 39, A.) So far as can be ascertained, that part of 

the area containing thrust faults is neither higher nor lower structurally than the adjoining region, and, except for the steeply upturned beds on one side of the fault, the structure continues with its

16 Reeves, Frank, Geology and possible oil and gas resources of the faulted area south' 

of the Bearpaw Mountains, Mont.: U. S. Geol. Survey Bull. 751, pp. 97-103, 1924; Thrust 

faulting and oil possibilities in the plains adjacent to the Highwood Mountains, Mont.: 

U. S. Geol. Survey Bull. 806, pp. 165-185, 1929; Structure of the Bearpaw Mountains 

and adjacent plains, Mont, (unpublished manuscript) ; The structure of the Bearpaw 

Mountains, Mont.: Am. Jour. Sci., 5th ser., vol. 8, pp. 296-311, 1924; Shallow folding; 

and faulting around the Bearpaw Mountains: Am. Jour. Sci., 5th ser., vol. 10, pp. 187 

200, 1925 ; The landslide origin of the thrust faults around Bearpaw Mountains [abstract] : 

Washington Acad. Sci. Jour., vol. 17, no. 5, p. 127, 1927 ; Thrust faulting adjacent to theHighwood Mountains, Mont, [abstract] . Washington Acad. Sci. Jour., vol. 17, no. 9,. 

p. 232,.-1927. (See also other papers listed in bibliography, pp. 228-229.)
 256 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

regional trend undisturbed through a faulted area. (See structure 

contours, pi. 43.)

The three faults along the Milk River are roughly parallel, trending northeastward, and each is a thrust to the northwest. No such 

generalizations, however, can be made for the faults along the Missouri River in the southeast corner of the area, for about half of 

them strike northwestward and the rest strike northeastward. The 

thrust side in four of the northwestward-trending faults is on the

-.southwest, and in one it is on the northeast. The thrust side in 

three of the northeastward-trending faults is on the northwest, and 

in three it is on the southeast. In the faults about 3 miles south of 

Gildford the principal fault seems to trend eastward, with the thrust 

side on the south.

Some of the thrust blocks are cut by several faults, so that the 

blocks are composed of a number of "slices." Measurements of 

stratigraphic sections across some of the thrust blocks showed rapid 

variation in the thicknesses of the stratigraphic units, which is 

ascribed to subsidiary faulting, although the faulting was not everywhere evident. A general picture of the complexity of some of the 

fault blocks may be obtained from the faults exposed in the banks 

of Sage Creek, south of Gildford. Plate 40 shows a block diagram 

<of this area drawn from a detailed plane-table survey.

Most of the faults are not actually exposed for more than a mile 

or two, and it is possible that some of those that are mapped as 

extending 3 or 4 miles may be in reality more than one fault. The 

throw or stratigraphic displacement of the faults ranges from a few 

feet to hundreds of feet; the largest stratigraphic displacement observed is in the northeast corner of T. 34 N., R. 12 E., where beds 

below the top of the Colorado shale are thrust against strata above 

the base of the Judith River formation, representing a stratigraphic 

interval of about 1,325 feet. Sufficient data were not obtained to 

make estimates of the amount of horizontal movement.

That part of the map published with the report by Reeves 17 in 

1924 based upon the earlier field work of Lloyd and Thorn includes T. 26 N., R. 12 E., of the present report. Reeves shows a fault 

passing through sees. 9, 10, 16, and 17, with the upthrown side on 

the northwest. Faults are exposed in the 8^/2 sec. 17 and the NW}4 

sec. 16, and there are steeply inclined beds in the S^ sec. 3 that suggest the presence of a fault there; the displacement of the fault in 

the northwestern part of sec. 16 is in the opposite direction from 

that of the faults at the other two localities. The writers believe

17 Reeves, Frank, Geology and possible oil and gas resources of the faulted area south 

of the Bearpaw Mountains, Mont.: U. S. Geol. Survey Bull. 751, pi. 13, 1924.
U. S. GEOLOGICAL SURVEY BULLETIN 847 PLATE 40

FAULTS EXPOSED ALONG SAGE CREEK, ABOUT 3 MILES SOUTH OF GILDFORD.

Based on plane-table survey.
OHOUTEAU, HILL, AND LIBEETY COUNTIES, MONT. 257

that instead of a single fault there are three faults en echelon, and 

that as one fault dies out another fault with reversed thrust begins. 

Reeves 18 makes the following statement concerning faults mapped as 

scissors faults elsewhere in the fault belt adjacent to the Bearpaw 

Mountains:

As formerly mapped, some of the faults show a reversal in throw along their 

strikes. A special study of this feature in areas of good exposures during the 

later part of the field investigations revealed the fact that such a structure 

consists of two or more faults, of opposite throw and ending in slightly offsetting 

positions.

The origin of the thrust faults has been discussed at length by 

Reeves in the previously cited papers, but his theory is stated very 

simply in the following abstract: 19

The thrust faulting in the plains on the north and south sides of the Bearpaw 

Mountains is apparently confined to the weak Upper Cretaceous and early 

Tertiary formations. The trend and extent of the faults indicate that they 

were produced by a thrust force acting outward from the mountains. The 

slight plainsward inclination of the strata toward the faulted area suggests the 

possibility that during the mid-Tertiary period of volcanic activity in the mountains these formations, being buried under an enormous load of extrusive material and subjected to violent and frequent earthquake shocks, slipped plainsward 

on wet bentonite beds in the upper part of the Colorado shale, resulting in the 

compression and thrust faulting of these formations in the plains.

Two points which have not received consideration in the development of the theory, yet which seem to be logical accompaniments 

of such postulated movements, are: (1) Either all of the area between 

the central part of the Bearpaw Mountains and the outermost thrust 

fault probably would be underlain by a thrust fault or there must 

have been openings or gaps in the strata above the fault plane and 

to the mountainward side of the trace of the thrust fault on the surface equivalent to the amount of horizontal shortening involved in the 

thrust. Inasmuch as no evidence of gaps or large breaks is recorded, a more or less continuous fault seems a necessary part of this 

theory. Furthermore, there should be an area in the central part of 

the BearpaAv region that has been stripped of the strata above the 

fault plane equivalent in horizontal extent to the total amount of 

areal horizontal shortening in the thrust faults. (2) If the faulting 

is due to an outward movement of material from a "center", the 

further the material was moved the greater would become its circumference, so that gaps or openings should be produced having a 

radial trend from the "center." Such gaps apparently have not been 

observed.

18 Reeves, Frank, Structure of the Bearpaw Mountains and adjacent plains, Mont, (unpublished manuscript).

"Reeves. Frank, The landslide origin of the thrust faults around Bearpaw Mountains [abstract] : Washington Acad. Sci. Jour., vol. 17, no. 5, p. 127, 1927.
258 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36 

MINERAL RESOURCESOIL AND GAS 

RESULTS OF DRILLING

Wells near Kremlin, Six wells have been drilled in a small area 

about 3 miles west of Kremlin. Drilling of the Kremlin Petroleum. 

well, in sec. 28, T. 33 N., E. 12 E., began in 1921, but the rest of the 

wells were drilled from 1927 to 1931. All the wells are located on 

a flat sod-covered plain of low relief, and the maximum difference 

in altitude of the tops of the wells is not over 20 feet. The EquitablePerkins No. 1 well, in the SW%SWV4 sec. 34, T. 33 N., R. 12 E., 

was drilled 3,765 feet, to the base of the Ellis formation, and was 

then plugged back to the Eagle sandstone at 1,080 feet, where gas 

had been found. The Perkins-Jones-Carruth well, a few hundred 

feet east of the Equitable-Perkins well, was drilled to a depth of 

1,160 feet. Small flows of gas were encountered in the Eagle sandstone between 1,005 and 1,075 feet, but were not of commercial size, 

and the well was abandoned. The Flynn No. 1 well, in the 

NEi/iNWi/4 sec. 3, T. 32 N., R. 12 E., struck a flow of gas reported 

to be 1,650,000 cubic feet at 1,090 feet. Drilling was continued to 

1,153 feet, where a strong flow of water was encountered that could 

not be shut off, and the well was abandoned. The Perkins-RobeckFederal Bank well, in the NEV4SE% sec. 33, T. 33 N., R. 12 E., was 

drilled to a depth of 1,240 feet. Gas was reported at 1,095 feet, probiibly from the Eagle sandstone, and a water-bearing sand was encountered from 1,225 to 1,240 feet. The hole was plugged and abandoned. The Kremlin Petroleum well, in the NW^SE^ sec. 28, 

T. 33 N., R. 12 E., was drilled with a diamond drill to a depth of 

.3,131 feet. Gas was reported from a depth of 689 to 703 feet probsibly from the Eagle sandstone and also from 1.631 to 1,680 feet

 and 2,810 to 2,839 feet. A bluish-black shale heavily saturated with 

oil or a tar, which flowed into the hole and prevented further drilling, is reported at the bottom of the hole. The Robeck No. 1 well, 

nlso in the NW^SE^ sec. 28, T. 33 N., R. 12 E., was drilled to a 

depth of 750 feet. Gas, reported to be about 200,000 cubic feet, was 

struck at 610 feet. The hole was cased to this depth and capped.

A showing of oil was found in only one of these wells, but gas was 

found in all of them. The gas flows in the Robeck No. 1 and Flynn 

No. 1 wells apparently were the largest. The depth to the gas flows 

an four of the wells is between 1,005 and 1,095 feet, but in the Kremlin 

Petroleum and Robeck No. 1 wells gas was struck between 610 and 

703 feet. Probably the gas in all the wells is from the same formation that is, the Eagle sandstone. There is, however, a difference of

 several hundred feet between the depth at which it is encountered in
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 259

the four wells and that in the two just mentioned. The logs of the 

wells, as interpreted by the writers, also place these two wells strati- 

.graphically higher than the rest. The formations encountered and 

their depths below the surface, as interpreted from well logs, are 

shown in plate 41.

In the Kremlin Petroleum and Robeck No. 1 wells gas-bearing 

sandstone was encountered at about 600 feet. In the Kremlin Petroleum well deeper drilling encountered more sandstone at about 

1,200 feet and the top of the Kootenai at about 3,100 feet (pi. 41). 

The sandstone encountered at 1,200 feet is probably the Eagle sandstone, undisturbed except for regional tilting, and the sandstone at 

600 feet is probably also the Eagle in a thrust block. If the sandstone at 600. feet is correlated with the Eagle, and the sandstone at 

1,200 feet is considered to be a sandstone in normal strati graphic 

sequence in the Colorado shale, the Colorado shale would be more 

than 1,000 feet thicker here than elsewhere in this region, and the 

sandstone at 1,200 feet, which has not been recognized at other localities, would be a local lens in the upper part of the Colorado. Similarly, if the sandstone at 1,200 feet is correlated with the Eagle, and 

the sandstone at 600 feet is considered to be a sandstone in normal 

stratigraphic sequence in the Claggett, the thickness of the Claggett 

Avould be about 500 feet greater here than elsewhere in this region, 

4tnd the sandstone at 600 feet would be a member not previously 

recognized in the shale.

The altitude of the surface at the six wells shown in plate 41 is 

about the same at each well, and the Eagle was encountered at about 

1,000 feet in each well except the Robeck No. 1, where drilling ceased 

at 750 feet. Apparently the Eagle sandstone and the older formations 

have a nearly uniform dip. The Perkins-Robeck-Federal Bank well 

was probabty drilled through an undisturbed stratigraphic sequence, 

but in the logs of the Equitable-Perkins, Perkins-Jones-Carruth, and 

Flynn No. 1 wells, as interpreted by the writers, the thickness of 

Claggett shale is abnormally great for this region. This unusual 

thickness may possibly be due to faulting that has repeated part of 

the Claggett, but because of the difficulty of recognizing the contact 

between the Claggett and Judith River formations, it seems probable 

that the apparent unusual thickness of the Claggett may be due to the 

inclusion of part of the Judith River.

Utopia wells. The Mid-Rocky Federal Land Bank well, drilled 

in 1927 in the NWi/4 sec. 7, T. 33 N., R. 7 E., tested the Utopia anticlinal nose to a depth of 1,475 feet. It was abandoned in the upper 

half of the Colorado shale. Two other nearby wells, on the Utopia 

nose but outside of this area, were drilled to the top of the Madison 

limestone in 1930-31 the Eleanor Association No. 1, in the SEi/4 sec.
260 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

11, T. 33 N., K. 6 E., to a depth of 3,310 feet, and in 1931-32 the 

California Co.'s Boss No. 1, in the NEVi sec. 3, T. 33 N., K. 6 E., to 

a depth of 3,337 feet. All three of these wells were dry holes.

The Newell well, in sec. 21, T. 35 N., K. 7 E., was drilled in 1926-27 

to the base of the Colorado shale, at 2,600 feet, and is reported to 

have obtained a daily flow of 5,000,000 cubic feet of gas from a sand 

500 feet above the base of the shale. The Square Deal Oil Co.'s 

well near Joplin was abandoned in the Madison limestone at a total 

depth of 3,710 feet. Gas is reported from a bed near the base of 

the Eagle sandstone and from the base of the Colorado shale, and a 

show of oil and gas at the top of the Madison.

Other wtells. Drilling on the Williston-Shelby-Flack well, in the 

NEV4 sec. 12, T. 28 N., K. 11 E., began in 1928 and has progressed 

intermittently. The well is reported to have reached a depth of 

more than 2,615 feet and has probably penetrated the Kootenai formation. The well of the Bohy Oil Co., in the SW^4 sec. 26, T. 29 N., 

R. 9 E., was drilled to a depth of only about 600 feet and is now 

filled with cavings. The Register Life Insurance Co.'s well, in sec. 

15, T. 30 N., R. 13 E., was a dry hole and was abandoned in 1928 

at 2,230 feet, within the lower half of the Colorado shale. The 

Twenty Dollar Bill Syndicate's well, in the SEi/4 sec. 9, T. 25 N., 

R. 9 E., penetrated the Madison limestone. Its total depth is 2, 378 

feet. The Cypress well, in the NWi/4 sec. 36, T. 28 N., R. 6 E., likewise penetrated the Madison. It was drilled in 1928-29 to a depth of 

2,789 feet. None of these wells struck oil, although several of them 

encountered some gas in the Eagle.

OIL AND GAS POSSIBILITIES OF THE REGION

Drilling has not revealed oil in commercial quantity, but small 

quantities are present in many wells. Gas has been found at several horizons, but the largest flows come from the Eagle sandstone. 

This formation crops out across the southern part of the area and 

dips regularly northward and eastward factors which reduce the 

probability of a large gas field being discovered in this sandstone. 

Where thrust faults break the regular dip, reservoirs for oil and 

gas may be formed, but several structural features of this type have 

been drilled without commercial success. Lower beds that are possible sources of oil and gas and are productive on the Sweetgrass 

arch are the Blackleaf sandy member in the lower part of the Colorado shale, the Sunburst sand or similar sandstones in the Kootenai, 

and the basal Ellis or top of the Madison limestone, but the attitude 

of the strata at the surface does not indicate the presence of any 

structural feature suitable for trapping a large quantity of oil or 

gas. The merging of sandy beds into shale up a homoclinal dip, a 

feature which conceivably might occur in the Colorado shale or other
U. S. GEOLOGICAL SURVEY BULLETIN 847 PLATE 41

Kremlin Petroleum 

NW{ SEi sec. 28 

T. 33 N., R. 12 E.

Robeck No. 1

3OO'~

/SOO'-

Perkins, Robeck, Federal Bank

NEiNE|SE*sec.33

T. 33 N., R. 12 E.

Equitable, Perkins No. 1 

SWJ SW} sec. 34 

T. 33 N., R. 12 E.

Perkins, Jones, Carruth

SE} SW£ SWi sec. 34

T. 33 N., R. 12 E.

Flynn No. 1

NE} NE'f NW} sec. 3

T. 32 N., R. 12 E.

EXPLANATION

Coal

INTERPRETATION OF LOGS OF WELLS DRILLED NEAR KREMLIN.
U. B. GEOLOGICAL SURVEY BULLETIN 847 PLATE 42

T.35N..R.8E. 

T. 31 N, R. 10 E. T. 32 N., R. 11 E. T. 33 H., R. 12 E. T. 33 N., R. 7 E. T. 33 N., R. 8 E. T. 35 N., R. 9 E. Measured by E. Stebiiiger T.36N..R.8E.

17 19 20 22

Ft. in. Ft in.

__ Reported 

Reported 25' below 

12' below 

surface ferf in water 

in auger well 

hole

Ft. in. ,__', Ft. In. ^^ Ft. in.

1? below ^1 Reported 

surface ^H 35' below 

te3) in mine |HJ surface 

in mine

T.36N..R.7E. T.37N..R.8E.

T.37N..R.9E. 

Measured by E. Stebinger

25 26 27 28 29 30 31 32 33 34

Ft. in. __Ft. in. _ _ Ft. in. _ _ Ft. in. _ _ Ft in. _ _ Ft in. Ft. in. Ft. in. Ft in. Ft. in.

i 6 i a II "B SS 3

Reported 43' below H ^ ' 6 

35' below ^| surface ^H 2 8 

|-i--sl surface H5 in mine 

in mine

2 i

2 11 3 2

2 7

T.37N..R.9E. 

Measured by E. Stebinger

35 36 37 38 39- 40 41 42 43

Ft. in. Ft. in. Ft. in. Ft. in. Ft. in. Ft. in. Ft in. Ft. in. Ft. in.

1 '<

1 9

2 

I

T.37N..R.9E. T. 37 N.. R. 10 E. T. 35 N.. R. 12 E. 

Measured by E. Stebinger Measured by E. Stebinger Measured by E. Stebinger

45 46 47 48 49 50

Ft. in. Ft. in. Ft. in. Ft. in. _ Ft in. _ Ft. in.

2 8 F3

135 

t 3 

t

EXPLANATION 

B Coal 

BBi Shalycoal 

HI Shale

COAL IN JUDITH RIVER FORMATION.
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 261

shale units, may possibly provide reservoirs for oil or gas; the 

location of such lithologic changes can be determined only by systematic drilling. It does not seem probable that sandstone beds in 

the Claggett would be sealed up the dip by a change to impervious 

shale, because the Claggett thins toward the west and the sandstones 

above and below it become thicker in that direction.

The Kremlin field, where gas has been encountered in the Eagle 

sandstone, contains but few rock outcrops, and those that were found 

seem to be in their normal position stratigraphically and to conform 

with the regional northeastward dip. The logs of the wells that 

have been drilled, however, show several anomalous features that can 

be explained on the assumption of thrust faulting. This interpretation is a logical one, for the field lies within the area of known thrust 

faulting that surrounds the Bearpaw Mountains. Other parts of the 

faulted area about the Bearpaw Mountains where thrust faults are 

exposed have been drilled, but most of them have not been productive, unless they form a part of a larger structural terrace or anticline. If there are thrust faults in the Kremlin field and they do 

not descend below the Colorado shale, then the strata below it would 

be no more likety to contain oil or gas than at any other place in 

the area.

The largest and most pronounced anticlinal fold in the area is the 

Utopia anticlinal nose, which rises toward the west without closure. 

Two wells on this fold, just beyond the west margin of the area here 

described, were drilled to the Madison limestone but failed to obtain 

commercial production of oil or gas.

COAL RESOURCES

In this area coal beds are present in the upper part of the Eagle 

and the lower 200 feet of the Judith Eiver formation. The coal is 

of subbituminous rank and generally is present in thin beds of local 

extent. The coal beds in general are too thin and remote from convenient shipping points for profitable commercial mining at this time. 

A few mines supply local needs but are not worked continuously. 

Thicker coal beds, in part more conveniently located with respect to 

shipping points, are present 20 miles east of this area, in the upper 

part of the Judith Eiver formation at Havre 20 and in the Fort Union 

formation 6 miles east of Big Sandy.21 Mining at these two localities is much more extensive than in the area considered in this report.

20 Pepperberg, L. J., The Milk River coal field, Mont.: U. S. Geol. Survey Bull. 381, 

pp. 82-107, 1910; The southern extension of the Milk River coal field, Chouteau County, 

Mont.: U. S. Geol. Survey Bull. 471, pp. 359-383, 1912

21 Bowen, C. F., The Big Sandy coal field, Chouteau County, Mont.: U. S. Geol. Survey 

Bull. 541, pp. 356-378, 1912.
262 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

Where coal is exposed in the banks of coulees, as in T. 37 N., 

R. 9 E., or in steeply dipping fault blocks, as in T. 32 N., R. 11 E., 

mines are developed by tunneling along the beds. Where the beds 

lie nearly flat, and the coal is several feet below the surface, as in 

T. 36 K, Rs. 7 and 8 E., the coal is mined through shafts.

EXPLANATION 

Coal

Shaly coal 

Shale

FIGURE 60. Coal in upper part of Eagle formation, T. 26 N., R. 12 E. Numbers refer to 

locations shown on plate 43.

The following description of the coal resources is based largely on 

E. R. Lloyd's examination of the Eagle coal beds in 1914 and Eugene 

Stebinger's examination of the Judith River coal beds in 1913 and 

1915. The writers made no attempt to study the coal beds in detail, 

but they visited most of the mines that have been opened since the 

earlier examinations.

Although the Eagle formation crops out extensively over the southern part of the area, potentially valuable coal beds are apparently 

confined to T. 26. N., R. 12 E. Other outcrops of the Eagle farther
CHOUTEAU, HILL, AND LIBERTY COUNTIES, MONT. 263

Avest were examined by the writers, but only very thin coal beds were 

seen. The average of tAvo analyses of samples collected by Lloyd in 

1914 from drift mines in T. 26 N., R. 12 E., gave a calorific value for 

the air-dried sample of 9,770 British thermal units. Coal \vas found 

at numerous places along the river bluffs and in the coulees. The 

beds are highly lenticular and contain many thin partings of shale 

and bone, so that it Avas necessary to measure numerous sections to 

show the true character of the coal. Thicknesses range from a feAV 

inches to 2y2 feet. Measured sections of the coal beds are shown in 

figure 60, and the locations are recorded on plate 43. Seven measurements on a coal bed exposed near locality 12 and tAvo measurements on another bed at locality 14 illustrate the variable lithology 

of the coal beds in the Eagle of this area.

The Judith River formation covers the northern two-thirds of the 

area, and locally coal beds are exposed where the loAver 200 feet of 

the formation is the surface rock. A fairly persistent zone of carbonaceous shale, containing someAvhat lenticular beds of coal, occurs 

about 200 feet above the base of the Judith River formation. This 

zone is particularly Avell developed in the northwest quarter of the 

area. The thickness of the coal beds is generally about 1 to l1/^ feet, 

although locally it exceeds 3 feet.

The folloAA'ing analyses of fresh coal from mines in sees. 2 and 28",, 

T. 37 N., R. 9 E., were made in the laboratory of the United States; 

Bureau of Mines, at Pittsburgh, Pa.:

Analyses of mine samples of coal in the Judith River formation, from Hill

County, Mont.

Laboratory no.

17841 F...

17892.....

of analyses

A

B

C

A

B

C

Proximate Ultimate

Moisture

24.1

31.4

Volatile 

matter

29.2

38.5

43.9

30.4

44.4

56.2

Fixed 

carbon

37.4

49.3

56.1

23.8

34.7

43.8

Ash

9.28

12.23

14.4

2.09

Sulphur

1.15

1.52

1.73

1.35

1.97

2.49

Hydrogen

5.98

4.35

4.96

Carbon

50.03

65. 95

75. 14

Nitrogen

1.02

1.34

1.53

Oxygen

32.54

14.61

16.64

Heating value

Calories

4,705

6,205

7,065

British 

thermal 

units

8, 470

11, 170

12, 720>

17841F, sample from NWHNWH sec. 28, T. 37 N., R. 9 E. 17892, sample from SAVJ4 sec. 2, T. 37 N., R.. 

9E.

Formsof analyses: A, analysis of sample as it comes from the mine; B, analysis after all moisture hasbeen eliminated; C, analysis after all moisture and ash have been theoretically removed.

Most of the coal beds measured are probably near the top of the 

lower 200 feet of the Judith River formation. Plate 42 shows the 

measured coal beds, and plate 43 shows the locations.
264 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36

WATER RESOURCES

Surface water and shallow wells do not furnish an adequate supply 

of water in this region, and consequently drilled wells are generally a 

necessary source of water supply for domestic use and livestock. 

The two formations that yield the greatest amount of water are the 

Judith Biver formation and the Eagle sandstone. Apparently water 

can be obtained at several horizons in the Judith River, but the 

amount is usually not large and may vary a great deal even locally. 

Several wells drilled for water in the Judith River formation have 

been dry holes. The water is confined under artesian pressure, but 

the pressure is not great enough to produce flowing wells. The 

wells drilled to the Eagle sandstone usually furnish an abundant 

supply of water, probably from the Virgelle sandstone member near 

the base of the formation. It is likewise confined under artesian 

pressure, but the wells do not flow. The Claggett shale, which lies 

between the Judith River and Eagle formations, does not yield 

water.

In that part of the area in which the Claggett shale is at the surface, or where there is not a> considerable thickness of Judith River 

strata, the objective for water wells is the Eagle formation. The 

structure contours on plate 43 will be of value in such areas in determining the depth to the top of the Eagle, if the altitude of the 

ground at the proposed drilling site is known, for the depth to the 

top of the Eagle at that locality is the difference between the surface 

altitude and the altitude of the top of the Eagle as shown by the 

contours.

The waters from the Judith River and Eagle formations are in 

most places not entirely satisfactory for drinking and may be unsuitable for irrigation. The total dissolved solids are about the same in 

each formation, generally from 1,000 to 2,500 parts per million but 

locally as high as 5,000 parts per million. Considerable variation in 

the amount of dissolved solids may occur within either formation. 

The principal mineral constituents of the water from both formations are sodium bicarbonate, sodium sulphate, and sodium chloride.
INDEX

Page

Abbott mine, work at 146

Abstracts of reports 1,

43-44, 121, 175, 189, 225-226

Acknowledgments for aid_ 2,

46-47, 123, 191, 227-228

Alice mine, features of_ _ 33

Alien no. 2 claim, ore deposit of _ 25

Alluvium in Rosebud coal field,

Mont., character and

distribution of-__ 66, pi. 11

Alma gas field, production from___ 220

Antelope mine, features of 29

Arizona mine, features of______ 37

Arkansas coal field, accessibility of__ 194

climate of______ _ _ 193

coal of, analyses of__ __ 210-213 

drainage of_______ __ 192-193 

geography of 191-194 

geologic work in___ __ 190 191 

land forms in__ _______ 191-192

location of__ _______ 190

population of___________ 194

vegetation of 193' 

western part of, age and character of rocks in____ 194-196 

coal of, analyses of___ 210-213 

coal of, production of__ 203-205 

coal of, rank, quality, and

uses of__________ 209 

coal beds of, distribution

and thickness of__ 205-208 

field work in_________ 190

geology of _______ 194-203 

map of, showing geologic 

structure and mineral 

resources pi. 35 

mining methods in _ 209 

natural gas in_______ 214-221

road material in 224 

sand and gravel in ___ 224 

shale for making brick in__ 224 

structural features favorable for accumulation 

of gas in-__ __ 221-224 

Atoka formation, character, distribut i o n, and thickness 

of __ _ 196-198 

correlation of- ________ 196 

fossils in___ ______ 197-198 

natural gas from_________ 215 

Avon area, Mont., geologic map and

structure sections of pi. 32 

See also Maxville, Philipsburg, 

and Avon areas.

B

Page

Ballbrach mine, work at 14ft 

Barnes mine, development workings

at,_____________ 188 

Bee Bluff fault, possibility of gas in

closure against_ 222 

Bellevue mine, features of 23-24 

Benton group, equivalent of 246 

Big Dirty coal bed, occurrence of, in 

Richey - Lambert coal 

field, Mont_____ 139-140, 

pis. 22, 27

occurrence and thickness of, in 

Rosebud coal field, 

Mont_______ 77-78, pi. 10 

quantity of coal in, in Rosebud

coal field, Mont_____ 83. 

Biswell Hill anticline, possibility of

gas in__ _ 221 

Blackleaf sandy member of Colorado 

shale, possibility of oil 

and gas in ______ 260> 

Blanchard Mountain area._____ 38, pi. 3 

Blue Bell mine, development workings at__ __' 188 

section of phosphate beds in_ pi. 34 

Blue Bird mine, features of_____ 28-29 

Blue Lode claim, ore deposits of-_ 33-34 

Boggy shale, character and thickness of_ _ _ 200 

correlation of _ ______ 196 

Boiler mine, work at__________ 146 

Bonanza mine, features of____ 35, pi. 3 

Boston mine, features of______ 41, pi. 3 

Brooklyn property, features of_ 19-22, pi. 3 

Bryan mine, features of __ 29 

Budka coal bed, occurrence of-____ 141,

pis. 22, 27

Burley coal bed, coal mined from_ 84

occurrence and thickness of 79, pi. ID

outlook for mining of______ 84

quantity of coal in__ ____ 83

Butterfleld coal bed, occurrence of_ 140,

pis. 22, 27 

Butterfleld mine, work at_______ 146

Carroll coal bed, occurrence of ___ 140;

pis. 22, 2T

Carroll mine, work at____ _ 146; 

Cavanal coal bed, occurrence of_ 208 

Cecil anticline, possibility of gas in_ 223. 

Charleston coal bed, occurrence and

thickness of 207-208, pi. 35

265
266 INDEX

Page

Chinaman mine, development workings. at_ _ 37, pi. 3 

Chouteau, Hill, and Liberty Counties, 

Mont., coal resources 

of________ 261-263, pi. 43 

field work in__________ 226-228 

geography of_______ 226,229-230 

geologic map of ___ pi. 43 

geology of __________ 231-257

oil and gas in__________ 258-260

possibilities of______ 260-261 

publications relating to___ 228-229 

water resources of _ 264 

Claggett shale, bentonite beds in 237 

character, thickness, and correlation of____ 231,236-242 

fossils in______________ 238 

oil and gas in_________ 259, 261

sections of______ 234r 238-241, 249 

Coal beds of Chouteau, Hill, and Liberty Counties, Mont.. 

general features of--- 261- 

263, pi. 43

Coal beds of Kiclu-y-Lambert coal 

field. Mont.. clinker 

formed by burning of- 145, 

pi. 25

details of, by townships____ 148- 

174, pi. 22

distribution and correlation of- 130-

142 

Coal beds of Rosebud coal field.

Mont., coal clinker in_ SI82, pi. 11 

details of, by townships----__ 85 

120, pis. 11-21

general features of 75-76, pis. 10, 11 

sections of__________ pis. 12-21 

stral igraphic relations and correlation of-_ ____ 74 

75, pis. 9,10

Coal beds of western part of Arkansas coal field, distribution and thickness of_________ 205-208 

Coal of Chouteau, Hill, and Liberty 

Counties, Mont., analyses of____ __ _ 263 

mining of_____________ 261-262 

a-ank of_______ ___ 261 

.resources of___________ 261-263 

sections of__________ 262, pi. 42 

Coal of Richey-Lambert coal field,

Mont., analyses of_ 144 

mining of________ __- 145-147 

nature and occurrence of____ 139-143

physical and chemical character

of____________ 142-143 

Coal of Rosebud coal field, Mont.,

occurrence of__ 78-74, pi. 9 

outlook for mining of______ 84 85

physical and chemical properties of__________ 80-81 

quantity of_______ __ 82-84 

Coal of western part of Arkansas coal

field, analyses of__ 210-213 

mining of___- __ 209

Page 

Coal of western part of Arkansas coal

field, production of 203-205 

rank, quality, and uses of _ 209 

Collier, A. J., correlation of formation divisions by__ 195-196 

Colorado shale, character, thickness,

and correlation of _ 231,

246-248, pi. 39

fossils in__________ __ 247

oil and gas in__________ 259-261 

sections of_________ 248, 249-250 

Contact mining district, Nev., claim

map. of- ______ pi. 3

geology of_____ __ 5-12, pi. 2 

history of______ _ 4-5

location of_____________ 2 

mineral deposits in, oxidation

and enrichment in__ 17 18 

types of__ ______ 13-17

mines and prospects in______ 18 41

outlook for__ __ ____ 18 

production of______ ____ 4-5 

topography of_____ ______ 2 4

Copper, p:oduction of. in Contact

district, Nev_____ _ 5

Copper King no. 2 claim, geology and

ore deposits of-____ 25 

Copper Shield group, work on___ 37, pi. 3

D

Delano no. 1 claim, geology of _ 25 

De.lano no. 2 claim, ore dep~si1s of_ 26 

Detvveiler mine, work at_______ 29 

Dissett Bros., production of phosphate rock from mine 

of______________ 177 

Dissett mine, development workings

on_____________ 188 

section of phosphate beds in:__ pi. 34

Eagle sandstone, character, thickness, and correlation 

of______________ 231, 

242-245, pis. 37-39

coal beds in____________ 261-263 

fossils in_____________ 243

oil and gas in______ ____ 258-2G1

sections of_________ 244-245, 249 

water ln__ _ __ ____ 264

Edgar. Chner, mine cf. development

at ______________ 188 

mine of, production of____ _ 177

 section in________ pi. 34

Effle Fay group, work on______ 37, pi. 3

Ellis formation, character and thickness of_________ 248-249 

oil and gas in__________ 258, 260 

section of_____ _______ 250 

Elvirio coal beds, occurrence of___ 141- 

142, pis. 22, 27 

Elvirio mine, work at__________ 146

Empire mine, work at__________ 22

Eplin & Horton, development workings on property of__ 188 

Erna gas field, production from___ 218
INDEX 267

F

Page

Field work___ 46, 123, 176, 190, 226-228 

Flaxville (?) gravel, Ricbey-Lambert 

coal field, Mont., character and thickness of- 132- 

133, pi. 26 

Florence group of claims, features

of________-__- 37, pi. 3 

Flowers coal bed, occurrence and

thickness of____ 80, pi. 10

outlook for development of 84

Fort Benton group, equivalent of_- 246

Fort Pierre group, equivalent of___ 246

Fort Smith formation, correlation

of_____________ 190 

Fort Union formation in RicheyLambert coal fl e 1 d, 

M o n t, distribution, 

character, and thickness of_________ 129 

Fort Union formation in Rosebud 

coal field, Mont., coal 

beds in__ 78-80, pis. 10,11 

occurrence and character of 57-64, 

pis. 5, 8-11

quantity of coal in__^______ 83-84 

Foster coal bed, occurrence and

thickness of __-__ 79, pi. 10 

quantity of conl in__ ____ 83

G

Gaines coal bed, occurrence of _ 141,

pis. 22, 27 

Game Hill anticline, possibility of

gas in____ ___ 222 

Gas. See Natural gas. 

Geologic maps:

Arkansas coal field, structure in

western part of_____ pi. 35

Avon phosphate area, Mont-__ pi. 32 

Chouteau, Hill, and Liberty 

Counties, Mont., parts 

of ____________ pi. 43 

Contact mining district, Nev__ pi. 2 

Maxville phosphate area, Mont- pi. 28 

Nevada-Bellevue mine- ____ pi. 4 

Philipsburg phosphate area,

Mont___________ pi. 29 

Richey-Lambert coal field, Mont_ pi. 22 

Rosebud coal field, Mont____ pi. 10 

Goomorphology of Rosebud coal field,

Mont___________ 71-73 

Gold, production of, in Contact district, Nev________ 5 

Graveley, C. A., mine of, features

of____________ 187-188 

mine of, production of_. __ 176 

section of phosphate beds

in ________ pi. 34

Gravels in Rosebud coal field, Mont., 

character and distribution of______ 64-66, pi. 11 

Gray Copper Corporation properties,

features of__ 32-35, pi. 3

H

Page 

Haddow coal bed, occurrence and

thickness of 80, pi. 10 

I-Iaddow Creek mine, production of 85 

Hartshoi'ne sandstone, character and

thickness of__--___ 198 

correlation of 196' 

distribution of__________- 198 

fossils in_________ ___ 198

Helen B. Smith claim, features of__- 34-35 

Hell Creek member of Lance formation, distribution and 

character of- 53-54, pis. 9-11 

Hendricks, T. A., and Parks, Bryan,

Geology and mineral . 

resources of the western part of the Arkansas coal field- 189-224, pi. 35 

Hice mine, features of _- 38 

Hickey mine, geology and ore deposits of ____ 30-31, pi. 3 

Hill County, Mont. See Chouteau, 

Hill, and Liberty Counties, Mont.

Hunt, C. B., with Pierce, W. G., 

Geology and mineral 

resources of north-central Chouteau, western 

Hill, and eastern Liberty Counties, Montana__ 225-264, pis. 36-43

Ho tunnel, dike in ___ _ 25, pi. 4 

Ivy Wilson group, production of__ 35-36

Tones mine, geology and ore deposits

of. ___________ 30-31

Jordan mine, work at _ _ 146 

Judith River formation, character, 

'thickness, and correlation of______ 231, 232-236 

coal beds in__ 232-235, 261-263, pi. 42 

sections of__ 233-234, 235, 249, pi. 36 

water in_______________ 264

K

Kootenai formation, character and

thickness of _ __ 248 

oil and gas in_____ 259; 260, pi. 41 

section of_____________ 250 

Kratz mine, geology and ore deposits of ____ 39-40 

Kremlin, Mont., wells near___ 258, pi. 41

Lance formation, coal beds in____ 75- 

78, pis. 10, .11

occurrence and character of__ 53-

57, pis. 6, 8,11

quantity of coal in_______ 83-84
268 INDEX

Page

Lane coal bed, occurrence of- 140, pis. 22, 27 

Lane mine, work at____ __ 146 

Lavaca gas field, production from- 218-219 

Lead, production of, in Contact district, Nev __ __ 5 

Lead-Silver mine, features of __ 30-31 

Lebo shale member of Fort Union 

formation in RicbeyLambert coal field, 

Mont., character and 

thickness of_____ 129-130, 

pis. 22, 24, 27

Lebo shale member of Fort Union 

formation in Rosebud 

coal field, Mont., coal 

beds in___ 77-78, pis. 10, 11 

correlation of __ 60-61 

occurrence and character of- 57, 

pis. 5, 8-9, 11

quantity of coal in________ 83-34 

relations of- _ _ -_ 58-59 

sections of_____________ 57-59 

thickness of_______-_ 59, pi. 10 

Lena shaft, ore body in__ 22 

' Liberty County, Mont. See Cbouteau, Hill, and Liberty 

Counties, Mont. 

Lower Hartshorne coal bed, analyses

of coal from_____ 210-213

coal below, occurrence of__ 205

occurrence and thickness of_ 205-

206, pi. 35

M

McAlester shale, character, distribution, and thickness of- 199 

coal beds in__ _ _ __ 199 

correlation of__________ 196 

fossils in__ ____-____ 199 

McKay coal bed, occurrence and

thickness of____ 80, pi. 10 

quantity of coal in_______ 83 

Madison limestone, character and

thickness of____ 249,250

oil and gas in_________ 259-261

Magnolia mine, lodes of_______ 33

Mammoth claim, deposits of __ 33-34

Manitou anticline, possibility of gas

in_____________ 222-223 

Mansfield gas field, history and production of______ 217-218 

Massard Prairie gas field, production

. from______________ 219

Maxville, Philipsburg, and Avon 

areas, Mont., field 

work in _ ___ 176 

geology of ___ 177-383, pis. 28-32 

phosphate rock in__ 183-188, pi. 34 

surface features of_____ _ 177 

Mill Creek fault, possibility of gas

in closure against___ 223 

Miller mine, work at _______ 146 

Mulberry fault, possibility of gas in

closure against-__ 223-224

N

Natural gas in Chouteau, Hill, and 

Liberty Counties, 

Mont., occurrence of__ 258- 

260

possibilities of__________ 260-261 

results of drilling for_____ 258-2GO' 

Natural gas in western part of Arkansas coal field, analyses of __- 216 

occurrence of_____-____ 214 216 

production of_ ___ __ 216 

Nevada mine, ore of__ 36 

Nevada-Bellevue mine, geology, ore 

deposits, and workings 

of_________ 22-26, pi. 4 

New Hope mine, development work

at______________ 188

Northwest Development Co., sections 

of phosphate rock on 

property of ___- pi. 34 

Northwestern Improvement Co., development workings on 

property of__ __ 187-188 

production of phosphate rock

from mine of __- 176-177 

Niobrara group, equivalent of__ 246

Oil. See Petroleum.

Palo Alto mine, features of __ 26-28 

Pardee, J. T., Phosphate rock near 

Maxville, Philipsburg, 

and Avon, Mont ___ 175- 

188, pis. 28-34 

Paris coal bed, analyses of coal

from_________ 211-212 

occurrence and thickness of_ 208,

pi. 35

Paris shale, correlation of__-__ 196 

Parker, Frank S., The Richey-Lambert coal field, Richland and Dawson Counties, Mont ___ 121- 

174, pis. 22-27

Parks, Bryan, with Hendricks, T. A., 

Geology and mineral 

resources of the western part of the Arkansas coal field- 189-224, pi. 35 

Petroleum in Chouteau, Hill, and 

Liberty Counties, 

Mont., occurrence of_ 258-260 

possibilities of_________ 260-261 

results of drilling for _____ 258-260 

Philipsburg area, Montana, geologic

map of __ pi. 29 

sections of phosphate beds in__ pi. 34 

structure sections and profile in- pi. 31 

See also Maxville, Philipsburg, 

and Avon areas.
INDEX 269

'Phosphate rock, beneficiation of 185-186

columnar sections of_ _ _ pi. 34

composition of _ _ 184-185

development workings on 187-188

markets for __ _ 177

occurrence of _ 183-184

production of__ 176

reserves of _ ____ 186-187

1'lerce, W. G., The Rosebud coal

field, Rosebud and Custer Counties, Mont 43-

120, pis. 5-21

and Hunt, C. B., Geology and 

mineral resources of 

north-central C h o u - 

teau, western Hill, and 

eastern Liberty Counties, Mont________ 225- 

264, pis. 36-43 

Pierre group, equivalent of ______ 246

Pierson mine, production of coal

from _ 84 

Pleistocene gravel, occurrence and

character of__ - 133- 

135, pis. 22, 24-26

Prittegurl coal bed, occurrence of 142,

pis. 22, 27

Pust coal bed, occurrence of 142,

pis. 22, 27 

Pust mine, work at_____ _ 146

Q

Queen of the Hills mine, features of_ SI32, pi. 3 

R

Rattler mine, features of ____ 32-33 

Red Metal mine, work at ____ 37, pi. 3 

Reeside, J. B., Jr., fossils identified

by____________ 238 

Rlchey-Lambert coal field, Montana, 

coal of, physical and 

chemical character of_ 142- 

143

coal of, reserves of__ _ 147-148

coal beds in, by townships____ 148-

174, pi. 27

T. 19 N., R. 50 E__ 148, pi. 27 

T. 20 N., R. 50 E 148-151, pi. 27 

T. 21 N., R. 50 E__ 151-152, pi. 27 

T. 22 N., R, 50 E____ 152, pi. 27 

T. 23 N., R. 50 E__ 152-153, pi. 27 

T. 21 N., R. 51 E- 153-154, pi. 27 

T. 22 N., R. 51 E_ 151-155, pi. 27 

T. 23 N., R. 51 E__ 155-156, pi. 27 

T. 24 N., R. 51 E__ 156-158, pi. 27 

T. 21 N., R. 52 E______ 158-159 

T. 22 N., R. 52 E____ 159, pi. 27 

T 23 N., R. 5-2 E_ 159-160, pi. 27 

T. 24 N., R. 52 E_ 160-162, pi. 27 

T. 21 N., R. 53 E__ 162, pi. 27 

T. 22 N., R. 53 E_ 162-163, pi. 27 

T. 23 N., R. 53 E_ 163-164, pi. 27 

T. 24 N., R. 53 E_ 164-166, pi. 27 

T. 21 N., R. 54 E__ 166, pi. 27 

T. 22 N., R. 54 E_ 166-168, pi. 27 

T. 23 N., R. 54 E- 168-169, pi. 27

90380 37 4

Page

Richey-Lambert coal field Continued, 

coal beds Continued.

T. 24 N., R. 54 E- 169-171, pi. 27

T. 21 N., R. 55 E- 171-172, pi. 27

T. 22 N., R. 55 E_ 172-173, pi. 27

T. 23 N., R. 55 E__ 173, pi. 27

T. 24 N., R. 55 E- 173-174, pi. 27

drainage of__ __ 126-127

field work in__ _ 123

geography of_ 125>-128

geomorphic history of 136-

139, pis. 22, 23, 26

land forms in__ ___ ___ 125-126 

location of___________ 121-122 

mining in____ ______ 145-147

previous geologic work in_ 124-125 

settlements in___________ 127-128

stratigraphy of__ 128-135, pis. 22-25 

structure of__________ 135-136 

transportation in__________ 127-128

water supply of_____ 126-127

Rosebud coal bed, coal mined from 84 

occurrence and thickness of 80, pi. 10 

outlook for mining of _ 84 

quantity of coal in__ _ 83 

Rosebud coal field, coal of, physical 

and chemical properties of__________ 80-81 

coal of, quantity of__ __ 82-84 

coal beds in, by townships __ 85- 

120, pis. 12-21

T. 2 N., R. 42 E__ 90-92, pi. 12 

T. 3 N., R. 42 E_______ 88-90 

T. 4 N., R. 42 E_______ 88-89 

T. 5 N., R. 42 E__ 86-88 

T. 6 N,, R. 42 E ____ 85-86 

T. 2 N., R. 43 E__ 96-97, pi. 14 

T. 3 N., R. 43 E__ 95-96, pi. 13 

T. 4 N., R. 43 E_______ 94-95 

T. 5 N., R. 43 E_______ 93-94 

T. 6 N., R. 43 E__-____ 92-93 

T. 2 N., R. 44 E 102-103, pi. 16 

T. 3 N., R. 44 E 101-102, pi. 15 

T. 4 N., R. 44 E______ 99-101" 

T. 5 N., R. 44 E_______ 97-99 

T. 6 N., R. 44 E_______ 97-98 

T. 2 N., R. 45 E____ 106 

T. 3 N., R. 45 E 105-106. pi. 18 

T. 4 N., R. 45 E__ 103-105, pi. 17 

T. 5 N., R. 45 E______ 103-104 

T. 3 N., R. 46 E__-__ 109-110 

T. 4 N., R. 46 E ___ 108-109 

T. 5 N., R. 46 E______ 106-108 

T. 3 N., R. 47 E 112-113, pi. 21 

T. 4 N., R. 47 E__ 111-112, pi. 20 

T. 5 N., R. 47 E__ 110-111, pi. 19 

T. 3 N., R. 48 E_____ 116-117 

T. 4 N., R. 48 E______ H3-U6 

T. 5 N., R. 48 E______ 113-114 

T. 3 N., R. 49 E_______ 120 

T. 4 N., R. 49 E______ 119-120 

T. 5 N., R. 49 E______ 116-H9 

drainage and water supply of__ 48-51 

faults in ______________ 68-69 

field work in____________ 46-47 

geomorphology of_________ 71-73 

location of___________1_ 45
270 INDEX

Page 

Rosebud coal field, Mont., magnetic

declination in_ 47 

outlook for development of_ 84-85 

population of_ ___ _ 51 

previous geologic work in_ _ 4.5-46 

stratigraphy of 53-66, pis. 7-10 

structure in__ 66-71. pis. 7, 8, 10,1.1 

topography of 47-48, pis. 5, 6,11 

transportation in_______ _ 52

vegetation in_ 51, pi. 5

Salmon River Mining Co., claims

of____________ 22,, pi. 3 

Salt Lake group, inactivity of__ 37, pi. 3 

Savanna sandstone, character and

thickness of____ 199-200

coal beds in ____ -_ 199-200

correlation of______-__-- 196

fossils in_______________ 200

Schaller, W. T., quoted________ 244

Schrader, F. C.. The Contact mining

district, Nevada____ 1-41, 

pis. 1-4 

Sbeckles mine. See Truro-Sheckles

mine.

Shibley gas field, production from__ 220 

Silkworm mine, ore deposit of _ 40-41 

Silver, production of, in Contact district, Nev________ 5 

Silver Circle mine, geology and ore

deposits of____ 31-32, pi. 3 

Silver King mine, geology and ore

deposit of________ 39-40 

Skylark claim, work on________ 37 

Snyder mine, production of______ 84 

Solack coal bed, occurrence of____ 141,

pis. 22, 27

Spadra shale, correlation of_____ 196 

Squires mine, work at _ 146 

Standard prospect, features of-__ 35, pi. 3 

Stark mine, work at_-________ 146 

Stillson coal bed, occurrence of___ 142,

pis. 22, 27

Stillson mine, work at_________ 146 

Sue group, development work on__ 35-36,

pi. 3 

Sunburst sand, possibility of oil and

gas in _ _____ 260

Terrace gravels in Rosebud coal field. 

Mont., character and 

distribution of 64-66, pi. 11 

Terret coal bed, coal mined from__ 84 

occurrence and thickness of__ 79-80.

pi. 10

outlook for mining of_______ 84 

quantity of coal in________ 83 

Tongue River member of Fort Union 

formation in RicbeyLambert coal field. 

Mont., character and 

thickness of____ 130-131, 

pis. 22, 23

Tongue River member of Port Union 

formation in Rosebud 

coal field, Mont., coal 

in, outlook for mining 

of_____________ 84 

coal in, Quantity of_____ 83 

coal beds in, features of _ 62-64, 

78-80, pis. 9-11

distribution and character of 61, 

pis. 5, 8, 11

fossils in __ _ __ 61

sections of _ __1 ___ 62-64

thickness of____ __ 61

Tongue River syncline, features of 68

Trail Creek ccal bed, quantity of coal

in _____________ 83 

Trail Creek coal zone, occurrence and

thickness of__ 78-79, pi. 10 

Truro-Sheckles mine, features of__ 37 

Tullock member of Lance formation,

coal beds in_ _ 55-56, 

76-77, pis. 10,11

coal beds in, quantity of coal in_ 83

distribution and character of 54-56,

pis. 6-li

fossils in_____________ 56 

section of_______________ 56 

thickness of_________ 55-56, pi. 10

U

United States Bureau of Mines, coal

analyses by ______ 263

Upper Hartshorne coal bed, occurrence of_______ 206-207

Utopia anticline, drilling on____ 259-261

Vache Grasse anticline, possibility of

gas in___________ 221

Vesta gas field, production from_ 218

Virgelle sandstone member of Eagle 

sandstone, correlation 

of-___________ 242-243 

sections of_____ ____ 244, 249 

water in_______________ 264

Vivian Tunnel Co., plans for development work by_____ 30

Vulcan mine, geology and ore deposit of__________ 38-39

W

Washington Phosphate & Silver Co., 

development workings 

on property of __ 188, pi. 33 

production of phosphate rock

from mine of- __ 177

Water resources of Chouteau, Hill, 

and Liberty Counties, 

Mont____________ 264

Wells, logs of, interpretation of___ pi. 41

Wright coal bed, quantity of coal in_ 83 

thickness of________.__ 76, pi. 10

Yellow Gir] mine, inactivity at. 37