POSSIBILITIES OF OIL AND GAS IN NORTH-CENTRAL

MONTANA.

By EUGENE STEBINGER.

INTRODUCTION.

The search for oil and gas in Montana has become very active, 

and there is an insistent demand for information concerning the 

occurrence of these substances in the State. The extension into 

Montana of the Wyoming fields that are producing high-grade oils, 

the development of valuable gas fields in southern Alberta, the discovery of some oil within a few score miles of the northern boundary 

of Montana, and, finally, the recent drilling in of a large gas well 

at Havre, in Hill County, have led petroleum engineers and oil 

operators to give serious attention to " wildcatting " in this State. 

The thick bodies of Upper Cretaceous shale with which most of the 

oil and gas in both Wyoming and Alberta are associated are known 

to be continuous between these two localities under the plains 

portion of Montana, making it apparent that favorable structural 

features, in this area especially anticlines and domes similar to those 

that are productive in Wyoming and Alberta, offer a chance of success with the drill.

The purpose of the report here presented is to summarize all the 

available data concerning the possible occurrence of oil and gas in 

a considerable area in the north-central part of Montana, extending 

from the latitude of Great Falls northward to the international 

boundary. By no means all of this area has been searched for 

favorable structures, but the general character of the Cretaceous 

formations present under most of the area is well known. Furthermore, it is proposed to point out a number of anticlines and other 

upward-arching structures occurring in parts of Hill, Chouteau, 

Blaine, and Fergus counties which, according to experience at Havre, 

seem to be favorable for prospecting.

The facts observed seem to warrant the statement that considerable gas territory, on a scale comparable with the Alberta fields, may

49
50 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

be found and also that the area shows some probability of yielding 

oil. It can not be too strongly emphasized, however, that a rational 

search for oil and gas in the State should begin with operations in 

the areas where the rocks are most strongly arched. Only after these 

areas have been successfully prospected should the areas be tested 

which involve a much greater risk, namely, those in which the deformation of the beds is less pronounced or the bedrock is concealed by 

glacial drift.

LOCATION AND SURFACE FEATURES.

The part of north-central Montana herein described extends southward from the international boundary a distance of about 106 miles 

to the latitude of Great Falls and eastward a distance of 192 miles 

from K. 8 W. to E. 24 E. of the General Land Office surveys for 

Montana. (See fig. 11.) The area contains about 22,000 square

loo. , , , y. . . ,9 ioo Miles

FIGURE 11. Index map of Montana showing areas covered by Plates IV-VII.

miles. The principal towns are Great Falls, Fort Benton, and Havre. 

The area includes all of Blaine, Hill, Tdole, and Chouteau counties 

and parts of Fergus, Cascade, Teton, and Phillips counties. Plate IV 

is a geologic sketch map of the entire region.

For the most part the region is a treeless plains country, slightly 

rolling and covered with glacial drift. Along the principal streams, 

Missouri and Milk rivers and their tributaries, there are extensive 

areas of badlands, affording excellent exposures of the Cretaceous 

formations present. The region is further diversified by four small 

mountain groups, the Sweetgrass Hills, Bearpaw Mountains, Little
OIL AND GAS IN NOETH-CENTBAL MONTANA. 51

Rocky Mountains, and Highwood Mountains, which are from 20 to 

40 miles across and rise island-like 2,000 to 4,500 feet above the general level of the plains. They are partly forest covered and well 

watered, in contrast with the semiarid plains that surround them.

BASIS OF THE REPORT AND MAPS.

Only a small part of the region here described has been examined 

with a view to reporting specifically on its oil and gas possibilities. 

Many of the map data and other details presented are taken from 

work done during the last 10 years by members of the Geological 

Survey while studying the coal resources of the region. These surveys cover about a quarter of the area here described. In the examinations for coal the general features of the geology, especially near 

the coal outcrops, were carefully mapped, but naturally many details 

that are of prime importance in the search for oil and gas, particularly those pertaining to structure and to possible surface showings 

of oil and gas, were not recorded. Fisher 1 in 1906 examined the 

area extending from the vicinity of Great Falls northwestward to 

and beyond Teton River. Much of the information concerning the 

Kootenai formation in Montana is based on his observations. In 1908 

and 1909 Pepperberg 2 mapped the area along the Milk River valley 

from Harlem to a point a few miles west of Havre. Many of the 

data on Plate V, showing the geology in the vicinity of Havre, 

and on Plate VI, showing the tilted and folded rocks lying south 

of T. 35 N., were compiled from Pepperberg's maps and notes. In 

1912 Bowen 3 examined 10 townships lying southeast of Big Sandy 

between Missouri River and the Bearpaw Mountains and also a 

considerable area near the east end of the mountains in the vicinity 

of Cleveland. The data on the area lying north of Missouri River 

shown on Plate VII are taken from Bowen's reports. E. R. Lloyd 

in 1914 mapped all the area south of Missouri River shown on Plate 

VII extending eastward to R. 17 E. Lloyd's work has not been 

published and the descriptions of the area here given are taken from 

his original notes and maps. During the summer of 1915 the writer, 

assisted by Wendell P. Woodring and Julian D. Sears, examined the 

area in the vicinity of Winifred, in northern Fergus County, and

1 Fisher, C. A., Geology of the Great Falls coal field, Mont.: U. S. Geol. Survey Bull. 

35G, 1909; Geology and water resources of the Great Falls region, Mont?: U. S. Geol. 

Survey Water-Supply Paper 221, 1909.

a Pepperberg, X.. 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.

3 Bowen, C. F., The Cleveland coal field, Blaine County, Mont.; The Big Sandy coal 

field, Chouteau County, Mont.: U. S. Geol. Survey Bull. 541, pp. 338-378, 1914.
52 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

then spent the remainder of the season mapping the northern portion 

of the Milk Eiver coal field, lying in the tiers of Tps. 35 to 37 S". 

Gas was discovered at Havre during this period, and a few days were 

spent in that vicinity. A description by the writer x of the geology 

of the northwestern part of the region here considered has already 

been published.

GEOLOGY.

SEDIMENTARY BOCKS. 

GENERAL FEATURES.

The sedimentary rocks in north-central Montana range in age 

from Cambrian to Kecent. The formations, older than the Kootenai 

formation (Lower Cretaceous), however, are exposed only in the 

mountain uplifts and offer meager prospects of yielding either petroleum or natural gas. These older rocks, of Jurassic or earlier age, are 

best exposed in the Little Eocky Mountains and the Sweetgrass Hills. 

They are mainly hard, compact limestones that are not known to be 

petroliferous at any point in the region. This character, together 

with the fact that in the plains areas they generally lie too deep to 

be readily reached with the drill, makes them of little interest to 

the oil and gas prospector. In southern Montana and Wyoming 

these older formations contain a larger proportion of shale, which 

in places attains a considerable thickness, and there they may be of 

some importance as a source of oil and gas.

The extensive plains of northern Montana are underlain within 

reasonable drilling depth almost exclusively by Lower and Upper 

Cretaceous formations, and the sandstone beds associated with the 

thick bodies of shale in these rocks offer the best reservoirs for oil 

and gas in the region. Generalized sections showing the sequence 

and character of the formations, one for the eastern part and one 

for the western part of the region, are given below. These sections 

are also shown graphically on Plate IV.

1 Stebinger, Eugene, Geology and coal resources of northern Teton County, Mont.: TJ. S. 

Geol. Survey Bull. 621, pp. 117-156, 1915 (Bull. 621-K).
OIL AND GAS IN NORTH-CENTEAL MONTANA. 53

Formations exposed in the plains of north-central Montana east of the 112th 

meridian in the area, described in this report.

System.

Quaternary.

Tertiary.

Tertiary (?).

Cretaceous.

Series.

Recent.

Pleistocene.

Eocene.

Eocene (?),

Upper Cretaceous.

Lower Cretaceous.

Group and formation.

Ailuvium.

Glacial drift.

Fort Union formation.

Lance formation.

. &

a

! ia

o

a

Bearpaw shale.

Judith Eiver 

formation.

Claggett shale.

Eagle sandstone 

with Virgelle 

sandstone 

member a t 

base.

Colorado shale.

Kootenai formation.

Thickness 

(feet).

0-200

"700+

700-800

500-800

450-550

350-500

250-400

1,500-1,700

400-600

Character.

Silt, sand, and gravel along flood 

plains of larger streams.

Bowlder clay, gravel, and lake silt 

and clay. Contains bowlders 

and cobbles of granite, gneiss, 

quart/ite, etc., transported from 

the northeast.

Clay shale, sandstone, and coal 

beds. Present only in smaU 

areas. Poorly exposed.

Alternating gray clay shale and 

.sandstone with irregular coal 

beds. Present in relatively 

small areas only.

Dark-gray clay shale with a few 

limestone concretions. Contains 

many marine shells. Forms a 

subdued, rounded topography 

and gumbo soil.

Light-gray clay and clay shale with 

irregular beds of gray or brown 

sandstone, and coal beds. Contains many oyster and other 

shells besides fossil bones.

Like the Bearpaw in character of 

rocks and fossils, except for the 

occurrence of sandy beds near the 

top.

Upper part gray clay shale and sandstone with coaly shale and thin 

coal. Lower part white to buff 

thick-bedded massive sandstone, 

Virgelle sandstone member. 

Contains gas in the Havre district.

Bluish-gray to black shale with a 

few limestone concretions. Contains many marine shells. Includes three or four sandy beds 5 

to 70 feet thick in lower 800 feet. 

Probably contains gas and oil in 

some localities of favorable structure.

Eed clayey shale and irregular 

gray sandstone with a few thin 

beds of limestone. Contains 

coal near the base and fossil plant 

remains of fresh-water origin. 

Probably contains gas and oil in 

some localities of 'favorable structure.

o Estimated.
54 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

Formations exposed in the plains of north-central Montana west of the 112th 

meridian in the area described in this report.

System.

Quaternary.

Cretaceous.

Series.

Recent.

Pleistocene.

Upper Cretacoous.

Lower Cretaceous.

Group and 

formation.

Alluvium.

Glacial drift.

Montana group.

Bearpaw shale.

Two Medicine 

formation.

Virgelle sandstone.

Colorado shale.

Kootenai formation.

Thickness 

(feet).

0-200

450-550

1,900-2,100

200-290

I.. 600-1, 750

600-700

Character.

Silt, sand and gravel along flood 

, plains of larger streams.

Bowlder clay, gravel, and lake silt 

and clay. Contains bowlders 

and cobbles of granite, gneiss, 

quartzite, etc., transported from 

tne northeast.

Dark-gray clay shale with a few 

limestone concretions. Contains 

many marine shells. Forms a 

subdued, rounded topography.

Gray to greenish-gray clay and soft 

irregular sandstone, which is 

most abundant in the lower 250 

feet. In places thin beds of red 

clay and nodular limestone. 

Contains an abundant reptilian 

 fauna of Judith River types, besides leaves and shells. Contains 

coal beds near the base and at the 

top.

Gray to buff coarse-grained, much 

cross-bedded massive sandstone, 

with many ferruginous concretions in upper half. In lower 

half slabby gray sandstone, becoming shaly toward the base.

Bluish-gray to black shale with a 

few limestone concretions. Contains many marine shells. Includes three or four sandy beds 5 

to 70 feet thick in lower 800 feet. 

Probably contains gas and oil in 

some of the areas of favorable struc- 

 ture.

Shale, red in upper part, but remainder grayish to black. Contains irregular sandy beds up 

to 100 feet thick. Fresh water. 

Probably contains gas and oil in 

some of the areas of favorable structure.

As shown by the tables given above, the differences between the 

geologic sections of the eastern and western parts of the region occur 

in the Montana group in the interval between the Virgelle sandstone and the Bearpaw shale. This is due to the fact that the marine 

invasion during which the Claggett shale was deposited in the east 

did not extend westward beyond the 112th meridian. An account of 

these relations has already been published.1

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

Prof. Paper 90, pp. 61-68, 1915 (Prof. Paper 90-G).
OIL AND GAS IN NORTH-CENTRAL MONTANA. 55

FORMATIONS IMPORTANT IN THE SEARCH FOR OIL AND GAS. 

KOOTENAI FORMATION.

In this region all the strata so far examined lying between the 

marine Jurassic beds and the Colorado shale have been placed in the 

Kootenai formation. Farther south in Montana, "however, on the 

flanks of the Little Belt Mountains and elsewhere, the variegated 

shales of the Morrison formation have been recognized in the lower 

part of this interval. The Kootenai formation crops out over a considerable area in the vicinity of Great Falls, on the outer slopes of 

the Little Rocky Mountains, and on the east end of the Bearpaw 

Mountains. It has also been penetrated by the drill near Kevin, in 

Toole County, and in the Sweetgrass Hills district. In the Great 

Falls area, where the fossil plants characteristic of the formation 

in the type area in Canada are present, the entire formation can be 

referred to the Kootenai with considerable certainty. In other areas 

where outcrops of these rocks have been examined in the mountain 

uplifts, although the typical fossil plants have not been found, the 

thickness and general sequence remain much the same. However, 

the distinctive red color of the shales present along the southern edge 

of the area mapped becomes less prominent toward the north and 

northeast.

In the Great Falls district the formation is between 400 and 500 

feet thick and is made up of red sandy shale, clay, and gray sandstone, together with a few irregular limestone beds. The red color 

of the rocks is a prominent feature, the soils on its outcrop being 

strongly colored. The sandstones range in thickness from 10 to 60 

feet, are more or less massive in character, and occur chiefly in the 

lower half of the formation. They contain a large amount of water.

Near Kevin, in Toole County, as shown by the well log given on 

page 90, there are beneath the Colorado shale 635 feet of beds that 

probably belong to the Kootenai. The section there is essentially 

an alternation of sandstone and shale, but the only red material 

present is'near the top of the formation. There are in this sequence 

five sandstone beds between 30 and 70 feet thick.

In the Sweetgrass Hills district, as shown by the well log on 

page 89, there are at least 610 feet of strata containing near the top 

a prominent bed of red shale that should probably be assigned to 

the Kootenai. The sandstones at the base are reported to contain gas.

The Kootenai formation is not known to be petroliferous at any 

point on the outcrop in the areas mapped, although gas is reported 

from the locality just mentioned. The prominent sandstones in 

the formation seem to offer excellent reservoirs for either oil or gas 

if these substances are present at any. locality.
56 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

COLORADO SHALE.

The formation overlying the Kootenai is the Colorado shale, a 

great body of bluish-gray to black shale containing in its lower half 

a number of sandstone beds. This formation, which ranges between 

1,500 and 1,750 feet in thickness in north-central Montana, is of 

marine origin that is, it was laid down on a sea bottom and contains fossil sea shells in great variety. The rock materials deposited 

during this marine submergence are continuous northward into 

Canada and southward across Wyoming and beyond. The interval 

of time during which they were laid down is called the Colorado 

epoch, and the rocks themselves when divided into two or more 

formations constitute the Colorado group.

The Colorado shale seems to be of first importance as a possible 

source of oil and gas in Montana. The only surface showings of oil 

so far found in north-central Montana are seeps from the lower part 

of this formation, and pay sands either in the formation or associated 

with it have been found in adjoining areas both to the north and to 

the south of the State. In northern Wyoming the greater part of 

the oil produced in the Salt Creek field and most of the fields in 

the Bighorn Basin comes from sands lying mainly in the lower half 

of this group of rocks. In the Province of Alberta the gas of the 

important field at Bow Island, east of Lethbridge, is derived from 

a sand reported to be the Dakota. It is probable, however, that 

this sand is actually in the lower part of the Colorado shale. Likewise, as reported by Dowling,1 the small quantity of high-grade 

oils obtained from several wells in two anticlines lying southeast 

of Calgary, in the same province, comes from sands at the same 

position with respect to this shale.

The similarity of the Colorado shale in northern Wyoming and 

Montana is also emphasized by the presence in both States of a 

peculiar shale or shaly sandstone carrying abundant impressions of 

fish scales. In Wyoming this shale, known as the Mowry shale, is 

about 200 feet thick and occurs in the lower half of the Colorado 

group. The presence of this fish-scale bed in so many productive 

oil fields has often been referred to as suggesting that fish remains 

may have been the source of at least part if not all of the oil found 

in the associated sands. These peculiar beds are present in at least 

the east half of the north-central Montana region. In the vicinity 

of Lewistown, in the central part of Fergus County, a short distance 

south of the area mapped, a bed about 900 feet above the base of the 

Colorado shale contains an abundance of fish scales, and has been 

considered 2 as representative of the Mowry of Wyoming. About

1 Dowling, D. B., Correlation and geologic structure of Alberta oil fields : Inst. Min. 

Eng. Bull. 102-A, pp. 1360-1364, 1915.

2 Calvert, W. R., Geology of the Lewistown coal field, Mont.: U. S. Geol. Survey Bull. 

390, p. 30, 1909.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 57

75 miles northeast of this locality, on the outer slopes of the Little 

Eocky Mountains, there are, according to Weed and Pirsson,1 in a 

thick shale formation occupying the stratigraphic position of the 

Colorado shale, some "white porcelanous beds in which there are 

abundant impressions of fish scales. This rock weathers into a 

porcelain-like debris whose light color attracts attention wherever 

the rocks are exposed." This description is typical of the .Mowry 

throughout large areas in Wyoming. On the east end of the Bearpaw Mountains Bowen 2 found fish scales in abundance in the Colorado shale, at approximately the same horizon. In the Great Falls 

area the Mowry was noted by Fisher 3 but is not conspicuous. It 

has not been found elsewhere in the western part of the region here 

described, although it may be present, the lower part of the formation being poorly exposed and having been little studied.

Sandstone beds, in some places as much as 80 feet or more in 

thickness, are present in the lower half of the Colorado shale in all 

parts of central Montana where the formation has been examined 

along the outcrop or has been pierced by the drill. These sandstones, sealed in by great thicknesses of shale, seem to offer favorable 

receptacles for the accumulation and retention of oil and gas, and 

they may contain these substances in commercial quantities where 

inclination of the strata has permitted their concentration, forming 

the so-called pools of the oil industry. The sandstone beds in the 

Colorado shale noted in four widely separated localities in the region 

are shown graphically in figure 12. The first two of these sections 

were measured on outcrops of the formation and are taken from reports by Calvert 4 and Fisher. 5 The last two are made up from well 

logs, which are given in detail on pages 90 and 89. The general prevalence of sandstone beds in the lower half of the Colorado shale is 

evident from this diagram. It is very probable that these sands are 

more or less lenticular, for the arrangement and thickness of the beds 

in adjoining areas are such as to make it unlikely that individual 

sands persist throughout the intervening distances. In general character, thickness, and spacing or distribution in the shale these sandy 

beds are comparable with those in the Colorado group of the Bighorn Basin oil fields, in northern Wyoming.6

1 Weed, W. H., and Pirsson, L. V., Geology of the Little Rocky Mountains : Jour. Geology, 

vol. 4, p. 409, 1896.

2 Bowen, C. F., The Cleveland coal flcld, Blaine County, Mont. : U. S. Geol. Survey Bull. 

541, p. 343, 1914.

3 Fisher, C. A., Geology of the Great Falls coal field, Mont.: U. S. Geol. Survey Bull. 356, 

1909.

4 Calvert, W. E., op. cit., p. 30. 

D Fisher, C. A., op. cit, pp. 36-37.

0 Lupton, C. T., Oil and gas near Basin, Big Horn County, Wyo.: U. S. Geol. Survey 

Bull. 621, pp. 168-173, 1916.

43768° Bull. 641 17 5 .
58 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

The only noteworthy surface showing of oil so far reported from 

north-central Montana occurs, according to W. A. English,1 of 

the United States Geological Survey, in one of the sandstones of 

the lower half of the Colorado shale on the north side of West Butte, 

in the Sweetgrass Hills, a short distance south of the Canadian 

boundary. Here, in a spring on the Roscoe ranch near the line 

between sees. 11 and 12, T. 37 N., E. 1 E., there are slight showings 

of light-greenish oil which collects to the extent of about a teaspoonful in 24 hours. Mr. English also reports that extraction tests made 

on samples from the sandstone outcrops in the lower part of the 

Colorado on West Butte give a good show of oil. The petroliferous

° COLORADO SHALE fl>

 Between Highwood Mts. From log of* 

tral Fergus Co. anc' Great Falls Kevin, Too 

h of Lewistown

^z/Thinl}' bedded ss.

(contains fish sca/esj

8' Coarse Jrayishbrown sandstone

100' "Rusty -beds"

*

Not examined

vKwSS

.......... .....~

sSiS

Report

so,' 

10 Dark-gray ss.

20 Impure sandstone 

50 Gray sandstone

180'Shale with 

massive sandstone

ed to contain sma/I ' f/o

From 1

/ell near 5weet*ri 

le Co.

5'x 

JO*

10 Black sandstone

zs'>

iv of gas

o| of v 

iSsHil

veil in 

s district

I0'« Gray ss.

50'Gray ss. 

70'xGray ss.

5', «r 

60'x Conglom. 

and gray ss.

cale £oo a.

 ipoo

 500. 

 0

FIGURE 12. Sections showing sandstones in lower half of Colorado shale, north-central

Montana.

nature of the lower part of the Colorado shale in this portion of 

Montana seems to be clearly demonstrated by this occurrence.

The principal outcrops of the Colorado shale in northern Montana 

are shown on Plate IV. The largest one is in an extensive area occupying parts of five counties, extending from the vicinity of the Sweetgrass Hills southward to Great Falls. Over most of the interstream 

areas the shale is hidden under a cover of glacial drift, but along 

the streams it is generally well exposed.

EAGLE SANDSTONE, INCLUDING YIBGELLE SANDSTONE MEMBER.

Above the Colorado shale throughout north-central Montana there 

is a group of sandy beds from 250 to 400 feet thick, which constitute 

the Eagle sandstone. The lower part consists of a persistent

1 Personal communication.
. ' OIL AND GAS IN NORTH-CENTRAL MONTANA. 59

unit of cliff-making massive sandstone from 100 to 225 feet thick, 

named the Virgelle sandstone member because of its excellent exposures along Missouri Kiver below the town of Virgelle, in Chouteau 

County. The Virgelle sandstone is by far the most persistent of the 

sandstone strata in northern Montana and should serve as an excellent key rock in all drilling operations in the areas under which it 

is present. Its principal outcrop in the region mapped outlines a 

broad, oval-shaped area and extends from Missouri River in eastern 

Chouteau County northward and westward to the Sweetgrass Hills 

and then turns southward to.a point beyond Sun River. (See PI. 

IV.) West of the Sweetgrass Hills it forms the prominent escarpment known as " the rim," which extends from these hills southward 

for about 40 miles. Along the Missouri below Virgelle it forms the 

features long known as the " stone walls," which extend for about 

30 miles along the river.

The strong flow of gas encountered at Havre (see p. 73) comes 

from the Eagle sandstone. The gas produced at Medicine Hat, in 

Alberta, is also found at about the same horizon. The porous nature 

of the Eagle sandstones, together with their position immediately 

above the Colorado shale, makes it probable that gas and oil in 

notable quantities are present where the structural conditions are 

favorable.

FORMATIONS LYING ABOVE PROBABLE OIL AND GAS BEARING BEDS.

Above the probable oil and gas bearing formations there is a considerable thickness of shale, clay, and sandstone, comprising a number 

of formations of Upper Cretaceous and Tertiary age. They occupy 

all of the area indicated by the absence of shading on the map 

(PI. IV), including nearly half of the region described in this report. 

East of the one hundred and twelfth meridian they include the 

Claggett shale, Judith River formation, Bearpaw shale, Lance formation, and Fort Union formation, and their total thickness is between 2,700 and 3,350 feet. West of the one hundred and twelfth 

meridian they include the Two Medicine formation and the Bearpaw 

shale, and have a total thickness between 2,350 and 2,650 feet. 

The thickness and character of the individual formations are given 

in the tables on pages 53-54.

The thickness of these overlying formations is very important 

to any one contemplating drilling to the base of the Colorado shale. 

Drilling from a horizon above the base of the Bearpaw shale to the 

base of the Colorado will involve depths greater than 3,000 feet. 

Obviously the addition of a large part of the 2,000 feet or more of 

the Bearpaw, Lance, and Fort Union formations would make the 

base of the Colorado far too deep for " wildcatting." The full thick-
60 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PAET II.

ness of the Bearpaw, not over 800 feet, might be added, but areas 

containing the Lance and Fort Union formations should be avoided. 

Fortunately, these formations occupy only relatively small areas in 

Blaine, Fergus, and eastern Chouteau counties. In Chouteau County 

the Fort Union rocks are present in a small area east of Big Sandy.1 

The Lance, and probably the Fort Union, are present in northern 

Blaine County in all of the area lying northeast of the Cherry Patch 

Ridge, escarpment. In Fergus County the Lance formation is present 

along Missouri River east of Dog Creek.

GLACIAL DRIFT.

Glacial drift 2 of Pleistocene age, consisting chiefly of gravels 

and bowlder clay containing pebbles and bowlders of all dimensions, 

including many of great size, is present over a large part of northcentral Montana. It forms an effective cover, concealing the bedrock 

formations over large areas, and is of more than academic interest 

to one prospecting for oil and gas in this region. .To its presence 

over so large a proportion of the area may be due the comparative 

scarcity of oil seeps or gas escapes coming from the underlying 

bedrock formations in north-central Montana, the compact bowlder 

clay readily concealing any indications that may have been present 

before it was laid down. The drift also makes it impossible to decipher the structure of the underlying formations over extensive 

areas lying between the principal streams.

The drift ranges from a thin veneer to deposits several hundred 

feet thick and is usually thickest in the morainic areas, which have 

a rough " kettle and knob " topography. All this material was laid 

down by a continental ice sheet that overrode the region, coming 

from a center lying west of Hudson Bay. At least two separate invasions of the ice in this region are recorded. The only parts of the 

plains of north-central Montana that have not been glaciated are 

(1) the area along Missouri River south of the Bearpaw and Little 

Rocky mountains and east of R. 15 E., the ice sheet being held back 

from this area by the topographic barrier formed by these mountains; (2) the area lying west of R. 4 "W. in the part of southern 

Teton County shown on Plate IV.

RECOGNITION OF FORMATIONS IN THE COURSE OF DRILLING.

The general similarity of the rock materials composing the Cretaceous and Tertiary formations of north-central Montana tends to

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

Bull. 541, pp. 364-365, 1914.

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

Prof. Paper 50, 1906,
OIL AND GAS IN NORTH-CENTRAL MONTANA. 61

make uncertain the recognition of the various formations encountered 

in the course of drilling unless certain features are carefully observed. The rocks of the entire section are mainly shale, clay, and 

sandstone, repeated so many times in the succession of the beds that 

they are likely to be lumped together in large units of " shale and 

shells" by the driller.-

The principal features on which the recognition of the various formations must depend are (1) differences in the color tone of the 

various bodies of gray or neutrally tinted rocks; (2) position of the 

beds of coal or black coaly shale; and (3) position of the thick beds 

of sandstone. The differences in the color of neutrally tinted shale 

and clay are the most important and consist of alternations in thick 

groups of strata of dark-gray, bluish-gray, or nearly black tones 

with those that are prevailingly light gray, ash gray, or nearly 

white. These differences are readily distinguished in the course of 

drilling as the material is poured from the bailer.

In starting at the top of the Judith River formation and going to 

the Kootenai, the drill will encounter the following succession in 

the color tones of the gray shale, clay, and sandstone: (1) Judith 

River formation, light; (2) Claggett shale, dark; (3)" Eagle sandstone, light; (4) Colorado shale, dark until the easily recognized 

" red rock' of the Kootenai is reached. Coals or black coaly shale 

will generally be found near the top and near the base of the Judith 

River and at the top of the Virgelle sandstone member of the Eagle. 

The sandstone beds are apt to be confusing because of the frequent 

recurrence of beds of various thicknesses, but the general presence 

of sandy strata over 100 feet thick in the Eagle sandstone should 

make this formation easily recognizable.

COMPARISON WITH CANADIAN CLASSIFICATION OF FORMATIONS IN 

SOUTHERN ALBERTA AND SASKATCHEWAN.

The general succession of formations present in northern Montana extends into Canada, where the rocks have been known for 

many years to the Canadian geologists. The changes in the Montana group, including the disappearance of the Claggett shale toward 

the west, which first became apparent in studying the section in 

Montana, are also present and are in every way similar in southern 

Alberta, where they have been recognized by Dowling.1

The differences in the formation names used on either side of the 

Canadian boundary relate chiefly, so far as the probable oil and gas 

bearing formations are concerned, to the Colorado shale and Eagle

1 Dowling, D. B., Correlation and geologic structure of Alberta oil fields: Am. Inst. 

Min. Eng. Bull. 102, pp. 1355-1359, 1015. Dowling describes the stratigraphy in Montana but does not refer to the literature previously published on the subject.
62 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

sandstone, which the Canadian classification divides into three 

units the Dakota sandstone, Benton shale, and Niobrara sands.1 

The "Niobrara sands" are identical with the rocks described as 

Eagle sandstone in this report. The fact that all fossil evidence is 

against using the name Niobrara in connection with this sandstone 

was long ago emphasized by Stanton.2 Although in the early days 

the Dakota was supposed to be present in Montana, it is absent 

wherever the strata in which it should be present have been examined, 

and its existence in southern Alberta is believed to be equally uncertain. The sandstone at Bow Island and elsewhere referred to as 

Dakota by Clapp and others is very probably the sandstone in the 

lower part of the Colorado shale as described in this report and 

illustrated in figure 12. The fact that the logs of wells at Bow 

Island show dark shale beneath the pay sand called " Dakota " is very 

suggestive of this. Marine fossils found in the basal sandstones of 

the Colorado shale, described as " rusty beds" in the section from 

central Fergus County (see fig. 12), seem to prove the marine origin 

of all these sandstone beds. The use of the name Benton for shale 

overlying the supposed Dakota in northern Montana is also inadvisable, for no evidence has been found, either paleontologic or lithologic, to warrant recognition of the Benton and Niobrara subdivisions 

of the Colorado. The simple expedient of applying the term Colorado shale to all these strata in northern Montana has long been 

in use.

IGNEOUS BOCKS.

Igneous rocks in large areas are present only in the mountain uplifts of north-central Montana, where they occur in laccolithic 

masses. According to Weed and Pirsson 3 the igneous rocks of all 

these detached mountain groups belong to a single general type of 

highly differentiated alkaline rocks, usually high in silica. Dikes 

and sills of these rocks radiate from the mountains, some of them to 

considerable distances, and cut the Cretaceous beds of the plains. 

They are especially abundant in a belt from 15 to 20 miles wide between the Highwood and Bearpaw mountains. These dikes and sills 

have had little effect on the inclosing strata, baking of the beds and 

displacement having occurred only to a minor extent. They may be 

of importance in relation to the occurrence of oil and gas, especially 

where they are abundant, but it is difficult to determine what effect 

they have had on any hydrocarbons that might be present.

1 Clapp, F. G., and others, Petroleum and natural gas resources of Canada, vol. 2, pp. 

265-272, fig. 27, 1915.

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

beds : U. S. Geol. Survey Bull. 257, p. 64, 1905.

3 Weed, W. H., and Pirsson, L. V., Geology of the Little Rocky Mountains : Jour. Geology, 

vol. 4, p. 426, 1896.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 63

STRUCTURE. 

IMPORTANCE OF STRUCTURE IN THE SEARCH FOR OIL AND GAS.

The lay of ,the beds in sedimentary rocks is referred to as the 

structure. If a competent source of supply of oil and gas and a 

proper receptacle for their accumulation and retention namely, 

"sands" are at hand, structure that permits the concentration of 

these hydrocarbons into relatively small areas from an originally 

disseminated condition then becomes of paramount importance in 

the search for oil and gas. In order to permit the concentration of 

these substances into commercial pools, it seems necessary that the 

strata shall have been flexed, tilted, and folded in some manner. It 

can be said without reservation that oil and gas do not generally 

accumulate in commercial quantities if the rock layers are perfectly 

flat. Experience has amply proved the statement of the late Edward 

Orton that in horizontal beds " you will get a little oil, a little gas, 

and a little salt water, but not much of anything." '

The structural forms that have proved the most productive are 

domes or anticlines, produced by upwarps or bulges in the strata. 

Others of less importance are terraces, monoclines, synclines, and 

strata bent by faulting. The essential factor is that the beds be tilted 

or bent, but the degree of tilting varies greatly. In many places it 

is so slight that it is imperceptible to casual inspection and can not 

be detected except by close instrumental work, as in the Kansas, 

Oklahoma, and Texas fields. Elsewhere the tilting may be strongly 

developed, as in the California and Wyoming fields, where its presence can be ascertained at a glance by a trained observer.

The presence or absence of water in the " sands" is a further 

qualifying factor in determining the location of pools. The following statements with reference to the presence of water have been 

proved again and again in developed fields: If the pay sands are 

saturated with water, the gas and oil, being lighter, will be found 

above the water in the crests of domes or anticlines or on the flats 

or terraces of monoclines. If the sands are .only partly saturated 

with water, the gas and oil will be found down on the flanks at the 

upper level of saturation. If the sands are dry, the oil and gas 

will have migrated downward to the troughs of the synclines or 

to a point where further shifting has been prevented. ' Finally, it is 

generally although not invariably true that if oil and gas are present 

in the same stratum, gas, being the lighter, will be found above the 

oil that is, farther up on the flanks of the fold.

It is very probable that in Montana large quantities of gas or oil 

will be found, if at all, only in strongly developed folds, with relatively high dips, such as those in Wyoming, rather than in folds
64 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

having very low dips, such as are characteristic of the Mid-Continent 

fields. This belief is based on the fact that most of the oil fields 

so far developed in the Cretaceous rocks of the region adjacent to the 

Kocky Mountains, from Colorado to Alberta, are on strongly developed anticlines. There seem to be no conditions present in Montana which will make that State an exception to the general rule 

for the Rocky Mountain ahd Great Plains fields.

STRUCTURE OF NORTH-CENTRAL MONTANA. 

GENERAL ASPECT. '

Viewed as a whole the structure of north-central Montana is that 

of a large area of nearly horizontal beds of sedimentary rock that 

have been intruded by igneous rocks and uplifted in four isolated 

mountain groups. A general idea of these relations can best be 

obtained 'from the section extending entirely across the region 

through the Bearpaw Mountains, given on Plate IV. On a drawing 

covering so wide an area the vertical scale is necessarily exaggerated, 

making the dips in the areas of nearly flat strata appear greater 

than they really are. Sections made in the same manner, but in 

different directions, through others of the mountain uplifts, show 

the same general setting of large areas of nearly horizontal strata 

intruded and uplifted in the mountains. In relatively small tracts 

in the areas of nearly horizontal rocks, especially in the region surrounding the Bearpaw Mountains, the beds are much tilted and 

bent. These upturned beds, however, are nowhere extensive enough 

to offset the prevailing horizontality of the rocks.

SWEETGRASS ARCH.

The structure of the western half of the region described is characterized by a very broad anticline or arch that extends in a general 

northerly direction and is here called the Sweetgrass arch. This 

broad uplift brings the Colorado shale to the surface in an area about 

75 miles wide, surrounded on all. sides but the south by outcrops of 

the Virgelle sandstone. (See PI. IV.) The arch extends southward 

from the Sweetgrass Hills to the region beyond Teton Kiver, where 

it flattens out because of the presence of gentle northward dips 

induced by the uplift of the Belt Mountains,.still farther south. On 

the north this broad uplift extends to and beyond Belly River in 

Alberta, but it pitches slightly, allowing the overlying rocks of the 

Montana group to arch over its crest. On. the geologic maps of 

southern Alberta it appears as a broad belt of " Belly River beds," 

flanked on each side by the overlying marine shale. The Bow 

Island gas field of southern Alberta lies near the center of this broad, 

arch.
U. S. GEOLOGICAL SURVEY BULLETIN 641 PLATE IV

EXPLANATION

Igneous rocks, intrusions and flows

Folded and faulted Cretaceous formations

Mountain uplifts, partly igneous, on whose flanhs 

Colorado shale and Virgelle sandstone are 

exposed in places

Area in which Colorado shale and Virgelle 

sandstone occur beneath younger formations 

(Depth to Virgelte sandstone generally, less than l.tOO1

Sweetgrass

fa:r, H

SASKATCHEWAN 

MONTANA T

 v. Oil seepage

 * Small flo«/ of gas 

Gas well 

Show of oil and gas

/figures indicate depth of vrel/sj

Section of Cretaceous formations for 

area mapped west of 112th meridian

Section of Cretaceous formations fop 

mapped east of 112th meridian

rpaw shale

Claggett shale 

(marine)

Ea^le sandstone

sandstone member

Colorado shale 

(marine)

SECTION ALONG LINE

GEOLOGIC SKETCH MAP AND SECTION SHOWING OIL AND GAS PROSPECTS IN NORTH-CENTRAL MONTANA.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 65

The location of the axis or crest of a very broad fold of this kind 

is extremely difficult. In fact, it is not improbable that this arch has 

no well-defined crest but culminates in an area of slightly undulating, nearly horizontal rocks along its middle part. (See section, PL 

IV.) Most of the arch in northern Montana has not been examined 

geologically. The possibility of the occurrence of minor folds within 

the area of the broader arch must be considered, and if any such 

are present they are important in relation to the occurrence of oil 

and gas, offering the possibility of getting oil from the Colorado 

shale at comparatively shallow depths. The oil and gas developments in this area are noted under the local descriptions in this 

report.

REGION OF TILTED AND FOLDED ROCKS SURROUNDING THE BEARPAW

MOUNTAINS.

In the plains surrounding the Bearpaw Mountains for 30 to 40 

miles on all sides there are many folds and faults in the nearly 

horizontal Cretaceous rocks that are irregular in their trend and 

distribution. The causes of this peculiar and irregular faulting are 

not well understood, but they are probably related to the extensive 

igneous intrusions in the Bearpaw Mountains. The faults are all of 

the thrust type, older formations having been carried upward beside younger rocks that lie for the most part undisturbed. The 

largest of these faults average about 12 miles in length, but most 

of them can not be traced more than 4 to 6 miles. The cross section 

of the Meili fault (PL V) illustrates the general type of these 

faults, although in many of them only the'beds on one side of the 

break are tilted, those on the opposite side remaining undisturbed 

practically up to the fault plane. The trends of the faults cover 

all points of the compass, although in small areas a single direction 

may be dominant for instance, south of the Bearpaw Mountains 

many of the faults trend about N. 55° W., while north of these 

mountains the two principal trends are approximately N. 40° E. and 

N. 70° W.

These faults have produced in the strata upward arches, which, 

if the impervious shales overlying the sands have not been broken 

by the faults, should be as effective reservoirs as anticlines for the 

storage of gas or oil, or if the impervious cap has been broken the 

movement along the fault plane has tended to seal the pores in the 

sand and thus retain any oil or gas that may have accumulated there. 

The discovery of gas at Havre seems to prove that these faults have 

not unsealed the underlying sands and suggests that conditions 

favorable at least for gas and probably for oil are present throughout the wide extent of territory occupied by these faulted structures.
66 CONTBIBimONS TO ECONOMIC GEOLOGY, 1916, PABT II.

On Plates VI and VII are represented 32 of these faults, including 

all the principal ones mapped in the areas north and south of the 

Bearpaw Mountains. Detailed accounts of these areas are given 

under the local descriptions.

DISTURBED BELT ADJACENT TO THE FRONT RANGE OF THE ROCKY MOUNTAINS.

A small area in the vicinity of the North and South Forks of Sun 

Kiver, in the southwest corner of the region here described, forms 

a part of an extensive belt of strongly folded and faulted Cretaceous 

and Tertiary rocks lying adjacent to the front range of the Rocky 

Mountains. This disturbed belt extends northward into Alberta, to 

Calgary and beyond. The discovery of gas and oil in faulted anticlines in this disturbed belt in the vicinity of Calgary has led to 

considerable excitement in the last few years. Little is known of the 

details of the part of the disturbed belt lying in the area described in 

this report, but it is not improbable that anticlines are present there. 

If so, they are very likely to be much faulted and trend northwest. 

Where they are underlain by the Colorado shale and Kootenai formation at reasonable depths they offer a probability of obtaining 

oil and gas with the drill.

LOCAL FEATURES.

AREA OF TILTED AND FAULTED ROCKS NORTH OF THE BEARPAW

MOUNTAINS.

HAVRE GAS FIELD. 

INTRODUCTION.

The first recorded discovery of gas in the vicinity of Havre was 

made at Fort Assinniboine by the Quartermaster's Department, 

United States Army, between June, 1892, and November, 1893, while 

making a deep boring in the hope of getting artesian water. This 

well was drilled to a depth of 1,500 feet and obtained a small flow 

of gas, although no water was encountered below the gravel and 

sand of the glacial drift. Nothing further was developed until 

the Havre Natural Gas Co., composed of prominent citizens of Havre, 

finally obtained a large flow of gas under high pressure 2 miles 

northeast of the town in July, 1915. The company had previously 

drilled two wells in Havre, one at the race track and the other at 

the brewery, at opposite ends of the town. A small flow of gas was 

obtained in each of these wells, and with commendable persistence 

the company made a new location, which resulted in the important 

find just noted! All these locations were made at random, without 

regard to surface showings of gas or of geologic structure, the guiding principle of those interested being simply the firm conviction
OIL AND GAS IN NORTH-CENTRAL MONTANA. 67

that the gas fields of southern Alberta extended southeastward into 

Montana.

Acknowledgments are due to Brig. Gen. J. F. Morrison, United 

States Army, for the well record and information concerning the 

drilling at Fort Assinniboine, made while he was in command of 

the post. The writer is also indebted to Dr. J. A. Wright, president 

of the Havre Natural Gas Co., and to other members of that company for information concerning their operations and for the gas 

analysis on page 74.

GEOLOGIC FORMATIONS EXPOSED IN THE VICINITY OF HAVRE.

Three of the six Cretaceous formations present in north-central 

Montana crop out along the Milk Kiver valley in the vicinity of 

Havre. These are the Claggett shale, the Judith Kiver formation, 

and the Bearpaw shale. (See table, p. 53.) Because of the thick 

cover of glacial drift over all the level areas in the region, the exposures of these rocks are limited to the steeper slopes along the 

stream valleys and coulees. There they are well exposed in freshly 

eroded badlands, in which the identity of the various units is readily 

determinable.

The Claggett shale, the oldest formation in this vicinity, is exposed 

only in the faulted areas lying west of Havre. It consists of soft 

dark-gray clay shale, about 285 feet thick, characterized throughout by an abundance of the glassy crystals of selenite, a variety of 

gypsum. The thickness given was obtained in sec. 8, T. 34 N., R. 

13 E., where the only complete section of the formation so far found 

in the Milk Kiver valley is exposed. The shale weathers to a dark 

gumbo soil that becomes very tenacious when wet. Its most extensive 

outcrop in the Havre district is in the lower part of Meili Coulee, 

about 5 miles northwest of Havre, where it is well exposed north of 

the fault in that vicinity. (See map, PL V.)

The Judith River formation is the most extensively exposed formation in the region and crops out in the badlands that extend for 

many miles along the Milk Kiver valley. It is composed of lightcolored clay, clay shale, and sandstone containing lenticular coal 

beds near the top and a few thin seams at the base. Soft clay beds 

make up the bulk of the formation, and the rapidity of erosion in 

these soft strata has produced the extensive badlands. The sandstones are cross-bedded and ripple marked, but in no place are they 

persistent enough over considerable areas to serve as key rocks. Fossil shells of fresh and brackish water types are present at many 

horizons. The coal has burned along the outcrop, baking and fusing 

the overlying beds into prominent brick-red scoria or clinker, a common feature in the badlands of Montana, where coal or lignite beds 

are present. These "burnt-rock streaks" are clearly due to this
68 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

cause, being present only at the coal horizons, and should not be 

attributed to the burning of oil-bearing shale, as has been maintained 

by persons interested in the oil prospects of the region.

The best exposures of the Judith River formation in the vicinity 

of Havre are on the north side of Milk River, where all the coulees 

leading to the river valley show continuous outcrops of these rocks. 

The total thickness of the formation in the vicinity of Havre is about 

480 feet, according to a measurement made by V. H. Barnett in 

1908 across the upturned edges of the formation, the Claggett shale 

appearing below and Bearpaw shale above, as exposed 3 miles west 

of Havre, near the mouth of Beaver Creek on the south side of the 

railway. This is the only exposure known in the Milk River valley, 

where a complete section of the Judith River beds apparently not disturbed by faulting can be measured.

The Bearpaw shale conformably overlies the Judith River formation. It is a dark gumbo-forming shale, very similar to the Claggett, and is the youngest purely marine formation in northern Montana. It is not distinguishable either by its fossils or by the character of its rocks from the Claggett unless a complete stratigraphic 

section is present and its position above the Judith River can be 

definitely determined. In the vicinity of Havre it is exposed only 

on the south side of Milk River, where it appears in numerous isolated areas, in most of them associated with faults. All these 

areas are shown on the map (PL V). Not more than 350 feet of 

this shale is present in the area mapped, although the total thickness 

of the formation is much greater.

Glacial drift covers a large part of the area in the vicinity of 

Havre, completely obscuring the structure of the underlying Cretaceous formations and therefore greatly increasing the difficulty 

of prospecting the area for gas and oil. The gravel and bowlder 

clay of this cover of drift are irregular in thickness but in places 

probably measure over 100 feet. They form the surface of all the 

areas shown without shading on Plate V. The areas along Milk 

River and its principal tributaries mapped as occupied by alluvium 

contain recent stream deposits of sand and silt and a little gravel.

EAGLE SANDSTONE AND COLORADO SHALE.

The Eagle sandstone and Colorado shale are not exposed in the 

vicinity of Havre, but they underlie most of the area within reasonable drilling depths and seem to offer the best possibilities for obtaining gas and oil. The large flow of gas obtained by the Havre Natural 

Gas Co. comes from the Eagle sandstone and proves that important 

quantities of gas are present in that formation. It is noteworthy 

that the gas at Medicine Hat, about 115 miles northwest of Havre, 

is produced from sands at the same geologic horizon.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 69

The exposures of the Eagle sandstone nearest to the Havre area 

lie about 25 miles to the northwest, on Milk River, in T. 34 N., R. 

13 E. Here, in the W. -| sec. 8, the sandstone is brought to the surface in a prominently faulted area, shown on Plate VI. A section 

across the upturned strata, which strike N. 34° E. and dip 31° SE., 

is as follows:

Section of Eagle sandstone in W. \ sec. 8, T. 3^ N., R. 13 E.

Claggett shale.

Eagle sandstone: Fee*- 

Sandstone, buff, indurated, with .a 6-inch pebble bed near

the middle __________________________ 23 

Shale, carbonaceous, brown to black____________ 15 

Clay shale, gray, with thin bands of buff sandstone____ 220 

Sandstone, very massive, almost white____________ 30 

Sandstone, very massive, light gray, cross-bedded______ 100 

Bottom not exposed. 

388

An inspection of the above section shows that the formation is 

composed essentially of tAvo sandstone members, with a thick shale 

member between them. The sequence and character of the beds are 

identical with those of the same formation in the Missouri River 

section. The thickness, however, is somewhat greater. The 130 feet 

of massive sandstone at the base of the section corresponds to the 

Virgelle sandstone member of the Eagle and apparently differs little 

from that member in the type section on Missouri River, the 30-foot 

white sandstone being especially like the white sandstone forming 

" the stone walls " on the Missouri.

The details of the Colorado shale are not known in the vicinity of 

Havre. The formation has not been drilled through so far as known, 

but its main features are not likely to be very, different from those it 

exhibits generally in north-central Montana, as described on pages 

56-58. The presence of sandstones in the lower half of the Colorado 

shale, shown in the section on Plate V, is entirely inferential, being 

assumed from the general prevalence of sandstones in the Colorado 

in all parts of north-central Montana.

STRUCTURE.

Main features. The dominant structural feature in the vicinity 

of Havre is a belt of deformation in which the rocks are folded and 

faulted, extending about 15 miles in a northwesterly direction across 

the district. This belt is one of many of similar character and proportions on all sides of the Bearpaw Mountains. The deformation 

at its southeast end, on Boxelder Creek, seems to have produced two 

parallel gentle anticlines, here referred to as the Boxelder anticlines. 

Farther northwest the movement in the rocks appears to have been 

taken up by several parallel faults that have approximately the same
70 CONTRIBUTIONS TO ECONOMIC GEOLOGY/1916, PART II.

trend as the anticlines. The most extensive of these is the Meili 

fault. (See sections on PL V.)

Boxelder anticlines. The extensive exposures of the Judith River 

formation along Boxelder Creek and the adjoining coulees show 

two parallel anticlines extending across sees. 8, 9,16, and 17, T. 32 N., 

R. 17 E. The outcrops affording the best exposures of the north anticline appear in the coulee that runs northward near the center of 

sec. 9. On the north side of the anticline dips of 4° NE. are apparent', 

on the south side the dips are at a maximum of 5° SW. These dips 

outline a rather narrow-crested fold, trending in a northwesterly 

direction. The dips outlining the south anticline appear on the east 

slopes of Boxelder Creek in sees. 8 and 17. In the SW. £ sec. 8 there 

is an average dip of 4° NE. in the Judith River beds on the northeast 

flank of the anticline. On the opposite flank the average dip is 

about 10°, as is shown in exposures in the SE. £ sec. 17. The 

Bearpaw shale is shown in two isolated outcrops surrounded by 

glacial drift in the S. ^ sec. 17 and seems to come in normally above 

the Judith River formation. Southwest of these outcrops there are 

probably some faults parallel with the general trend of the anticlines, for the next rocks exposed to the southwest are the Judith 

River beds, in such an attitude that the presence of a sharp synclinal 

fold with an axis lying near the outcrops of the Bearpaw shale does 

not seem probable. The axes of the two Boxelder anticlines are 

closely parallel. Their limits on the northwest and southeast are 

not -determinable because of the cover of glacial drift, but they are 

doubtless parallel to the general trend of the Meili fault, and their 

extension toward the immediate vicinity of Havre, where the large 

quantity of gas has been found, is very probable.

Meili fault. The Meili fault is the principal one of a group of 

parallel faults trending approximately N. 70° W., northwest of 

Havre. It can be traced continuously, except for several short covered stretches, for 2 miles, beginning at the edge of the alluvium in 

the NE. i sec. 34, T. 33 N., R. 15 E., and extending to the west line 

of sec. 28 of the same township. To the southeast, under the cover 

of the extensive tract of alluvium along Milk River, it may extend 

a considerable distance parallel with the minor faults that are 

exposed on the adjacent sides of the Milk River valley. That this 

fault may extend as far southeast as the center of sec. 5, T. 32 N., 

R. 16 E., a point about half a mile north of Havre, is suggested by 

the small exposure of the Claggett shale lying in normal relations 

beneath the Judith River strata in the NW. £ sec. 5. This exposure 

of the Claggett is probably part of a larger tract uptilted by faulting, but now concealed by alluvium, and is comparable with the area 

of the Claggett shale on the north side of the fault in Meiii Coulee,
U. S. GEOLOGICAL SURVEY BULLETIN 641 PLATE V

7^--NORTHS

Stnnjfellowx.''.' '/ -" ' -" . " '. .

Ranch

NacDevitL Ranch.

Gorman+Ranch + *

GENERALIZED SECTION OF ROCKS 

IN THE HAVRE REGION

A -r* JzoxelcLer CT* . -^^-\ Judith River formation

Afilk River 2,-aoo &

__I

'WOiiiEA fcont3' 5 coat beds) 

shale

and syncline(o)

ss^SSk Eaele sandstone

: ::::::::::o? Virielle sandstone member

SECTION ALONG LINE A-A ACROSS THE MEILOFAULX Feet above sea.ievet SECTION ALONG LINE B~B ACROSS THE-BOXELDER ANTICLINES ' * '-'/''-: ':" . ' ; -^

; , Scale of sections vxsvs^vr^a Colorado shale

Igneous frocks Cla|§ett shale Small flow 

of gas

GEOLOGIC MAP AND SECTIONS OF THE VICINITY OF HAVRE, MONT.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 71

On the north side of the Meili fault at the place where it crosses 

Meili. Coulee near the south line of sec. 28, T. 33 N., R. 15 E., there 

is a large area of the Claggett shale faulted in part against the 

Judith River beds and in part against the Bearpaw shale. The 

maximum stratigraphic displacement along this fault is about 800 

feet. The dips in the area of the Claggett shale along Meili Coulee 

are all northeastward. They average about 5° near the fault, but 

farther north, near the middle of sec. 28, they become steeper, an 

observed dip of 16° being noted, and still farther north, about 1£ 

miles from the fault, the dip has flattened to 1°. The structure thus 

shown is in effect that of a broad anticline which has been cut on 

the south by the Meili fault. (See section A-A', PI. V.) South of 

the Meili fault, at the same locality, the dips are also to the north, 

averaging as high as 40°, but a short distance to the southwest they 

reverse, making a sharp anticline, beyond which the beds assume 

a horizontal position.

West of sec. 28 the Meili fault may be continuous, though it 

changes slightly in trend, to a direction more nearly west, with the 

fault that crosses the coulee near the center of sec. 29, which also 

brings the Claggett shale into contact Avith the Judith River formation. A quarter of a mile north of. the latter fault is a closely folded 

anticline that follows the trend of the Meili fault and extends northwestward as far as Supenau Coulee, a distance of over 3 miles. This 

fold is much covered by glacial drift between the coulees, but the 

close alignment of all the exposed parts makes their unity very 

probable. The dips on either flank of this anticline are steep but 

irregular, ranging from 18° to 75° on the north side of the fold and 

from 13° to 38° on the south side.

Minor faults near Havre. Two faults paralleling the Meili fault 

and extending through sees. 35 and 36, T. 33 N., R. 15 E. (see PI. 

V), have a much smaller throw than the Meili fault and do not at 

any point bring the Claggett shale to the surface. As in the Meili 

fault, the dips on the north side of these breaks are northward, 

away from the faults, and the degree of tilting is similar to that 

along Meili Coulee.

West of Havre, just south of the railway, faulted beds are exposed 

across sees. 1 and 6 in steeply tilted blocks which are visible from 

the west end of the town. The formations involved include the 

Claggett, Judith River, and Bearpaw. The trend of the faults and 

the strike of the beds in this disturbed area are all apparently 

parallel to the trend of the Meili fault. The beds north of the 

northern fault dip betAveen 30° and 45° S. The tilted block north 

of this fault, if the strike continues, extends beneath Havre under 

the area covered by alluvium. This fact makes it probable that the
72 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

gas well near the brewery at the west end of the town is located in 

tilted beds, and there is also some likelihood that the well at the 

east end of the town is in the same -tilted block. South of the fault 

just mentioned the beds tilt northward, so that the structure here 

is in effect that of a syncline, broken along its axis by a fault.

GAS DEVELOPMENTS.

The gas in the well at Fort Assinniboine was encountered at a 

depth of about 1,200 feet.1 The pressure was not great. The gas 

burned freely when lighted, but the flow lasted only a few days. 

It is probable that the bed yielding this gas was in the Eagle sandstone. The rocks penetrated in this well are shown in the following 

log:

Log of well drilled by the Quartermaster's Department, United States Army, at 

Fort Assinniboine, Mont., between June, 1892, and November, 1893.

[Altitude of surface, about 2,660 feet.]

Probable formation.

Glacial drift.

Driller's description of the rock. Thickness.

Feet. 

65

375

30

108

312

170

440

Depth.

Feet. 

65

440

470

578

890

1,060-

1,500

The bedrock formations over a large area in the vicinity of the 

well are concealed by glacial drift, and therefore there is some uncertainty as to the formations pierced by the drill. The 375 feet of 

" soft gray slate rock " lying immediately below the gravel and sand 

of the glacial drift is very likely the Bearpaw shale. This is made 

fairly certain by the presence of the 30-foot member described as 

" black shale, with small portion of coal mixed," which, overlying a 

considerable thickness of gray rocks, is very likely the coal zone at 

the top of the Judith Eiver formation. With these two formations 

determined the remainder of the log would follow in sequence as 

indicated above, unless the strata are much disturbed. The considerable thickness of material at the bottom of the well described as 

" soapstone, very soft, porous" very likely absorbed the drilling

1 Personal communication from Brig. Gen. J. F. Morrison, U. S. Army.
. , OIL AND GAS IN NORTH-CENTRAL MONTANA. 73

water rapidly and, it seems probable, is the sandstone of the Eagle. 

True soapstone could not be described as porous and would not take' 

up the drilling water.

The well at the west end of Havre, near the brewery, was drilled 

to a depth of 1,370 feet. Gas was obtained at 900 feet and again 

at the bottom of the hole, but each flow was small. The gas at 

the bottom of the hole gave a closed pressure of 540 pounds after 36 

hours. The well at the east end of Havre, at the race track, is 1,285 

feet deep. It yielded some gas at 885 feet and a larger flow at the 

bottom, which was estimated to b.e less than 1,000,000 feet a day. 

The gas from the lower sand gave a maximum closed pressure of 

540 pounds in 24 hours.

The principal gas well of the Havre Natural Gas Co., brought in 

early in July, 1915, is in the SE. £ sec. 33, T. 33 N., R. 16 E., about 2 

miles northeast of Havre, just south of the Great Northern Eailway. 

This well is on a IOAV terrace overlooking Milk River, in a large area 

in which the bedrock formations are concealed either by the alluvium 

along the river or by the glacial drift on the higher slopes, making 

it impossible to decipher the rock structure in the immediate vicinity 

of the well. However, as indicated by the surrounding exposures, 

it is very probable that the Judith River formation immediately underlies the glacial drift in most of this area. This well is 947 feet 

deep and at the bottom obtained a large flow of gas which was 

roughly estimated, by taking minute pressure readings, to amount 

to 10,000,000 feet in 24 hours. This method of obtaining the openflow volume of a gas well is unreliable, and the figures are therefore 

only approximate. The initial closed pressure of this well in July, 

1915, was about 490 pounds to the square inch. No later readings 

have been obtained.

The rocks encountered in drilling this well were described to the 

writer in a general way by Dr. Wright, of the Havre Natural Gas 

Co. There seems to be little reason to doubt that the drill went 

through part of the Judith River formation, all of the Claggett, and 

part of the Eagle sandstone. The estimated stratigraphic position 

of the first rocks encountered below the glacial drift is about 400 feet 

above the base of the Judith River formation. If the thickness of 

the Claggett shale is taken as 285 feet and that of the Eagle sandstone as 390 feet, the bottom of the hole is about 100 feet from the 

base of the Eagle sandstone and hence is probably in the Virgelle 

sandstone member of the Eagle.

An analysis of the gas from this " gusher" well was kindly furnished by the Havre Natural Gas Co. and is given below, together 

with one of gas from Alberta for comparison. 

43768° Bull. 641 17 6
74 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

Analyses of natural gas from Havre, Mont., and Medicine Hat, Alberta.

[Analysts not known.]

Methane (CH4 ) .....................................................................

Nitrogen (N)......... ..............................................................

Hydrogen sulphide (H2S) ...........................................................

Havre.

0.20

94.80

5.00

100. 00

897

Medicine 

Hat.o

QQ <1Q

.51

100. 00

a Clapp, F. G., and others, op. cit., vol. 1, Table 12.

The analysis in the first column is that of a " dry " gas from which 

little or no gasoline could be extracted by freezing tests and which 

is very similar to that obtained at Medicine Hat, being composed 

chiefly of methane and not containing any of the higher series of 

hydrocarbons. The heating value given is too low for that of a 

natural gas containing 95 per cent of methane, and therefore there 

may be an error either in the determination of heating value or in 

the analysis. A recent analysis of this gas by G. A. Burrell, of the 

Bureau of Mines, gave the following: Heating value, 1,036 British 

thermal units; methane, 97.3 per cent; nitrogen, 2.7 per cent.

A comparison of the results of this large gas well with those 

of the wells drilled at Medicine Hat is of interest because the gas 

obtained at the two localities comes from the same geologic formation. At Medicine Hat, in December, 1913, there were 16 municipal 

wells between 1,000 and 1,300 feet deep, having an open-flow capacity of 43,200,000 cubic feet a day, according to a statement by the 

city engineer. The production of the largest of these wells from 

a 10-inch aperture was 6,000,000 feet a day, but the average yield is 

between 2,000,000 and 3,000,000 feet. There are also in this'field 

several wells, owned by manufacturing companies, concerning which 

data are not available. The development of these gas resources has 

led to a rapid industrial expansion at Medicine Hat.

PROBABLE EXTENSION OF THE FIELD.

The gas pool in the district about Havre will probably have its 

greatest extension in a direction JS. 70°-75° E. This statement can be 

made with considerable certainty, because (1) the single dominant 

uplift in the district has this trend, and (2) the strong flow of gas 

encountered is with little doubt located on or near this uplift. If 

this strong flow should prove to be short-lived the location is probably too far down the flank of the inclined strata present. The territory along the axes of the two Boxelder anticlines and along the 

probable extension of these axes, especially northwestward toward
OIL AND GAS IN" NORTH-CENTRAL MONTANA. 75

Havre, seems to offer the best chance for further extension of the 

field. On the north side of the Meili fault the area of tilted beds 

occupying parts of sees. 27, 28, and 34, T. 33 N., B. 15 E., seems to 

be favorable, with a chance of getting gas at comparatively shallow 

depths. There is also a probability of getting oil and gas in these 

areas by drilling for sands in the lower part of the Colorado shale 

at depths of 2,000 to 3,000 feet, the depth depending on the location 

on the folds.

EXTENT TO WHICH FAULTS HAVE PERMITTED THE ESCAPE OF GAS OR OIL.

The extent to which faults have unsealed any deep-seated sands 

containing gas or oil and have therefore allowed much of their contents to waste is an important problem in the Havre district and 

in all of the area surrounding the Bearpaw Mountains where faults 

are generally prevalent. All the evidence at hand seems to indicate 

that in the soft Cretaceous formations of the Kocky Mountains and 

the Great Plains faulting can at the most only slightly unseal the 

underlying sands. This seems to be especially true of the sands in 

a thick mass of soft marine shale, such as the Colorado shale. In 

Wyoming this is show)n by the fact that many of the producing 

anticlines are faulted, some of them to a considerable extent. In 

the Calgary region, Alberta, a 2,000,000-foot flow of gas obtained 

from an area of much faulted rocks in the disturbed belt 1 adjacent 

to the Rocky Mountains is further proof that gas can accumulate in 

faulted rocks, if the formations are composed of soft materials. The 

well at the west end of Havre, at location No. 2, seems to offer proof 

of this also, for although it is situated close to two faults of considerable throw, it contains gas Avhich had an initial closed pressure 

of 540 pounds to the square inch.

CHANCES OF SUCCESS BY RANDOM DRILLING IN THE MILK RIVER VALLEY.

A successful oil or gas well invariably leads to a popular belief 

that the hydrocarbons are to be found under all lands in the district 

in which it is situated, and that drilling at random locations in that 

district is certain to be successful. In the Milk Eiver valley, throughout which the geologic features remain much the same, five deep 

borings have been put down at random locations three at Havre, 

one at Chinook, and one at Fort Assinniboine. Only one of the five 

was successful, and there is no reason to believe that drilling at haphazard locations will be any more successful over the remainder of 

the area. The only possibility of decreasing this percentage of dry 

holes outside of the proved territory is by a better understanding of

1 Clapp, F. G., and others, op. clt., vol. 2, p. 283.
76 CONTRIBUTION'S TO ECONOMIC GEOLOGY, 1916, PART II.

the lay of the rock strata and its influence on the accumulation of 

oil and gas.

OTHER AREAS OF TILTED AND FOLDED ROCKS NORTH OF THE BEARPAW

MOUNTAINS.

Areas of tilted and folded rocks in the region north of the Bearpaw 

Mountains are shown on Plate VI. Structure similar to that at 

Havre has been noted in at least 11 widely scattered localities. In 

much of the area lying between these faulted tracts the hard rocks 

are covered by glacial till and their structure is therefore not known, 

but it is possible that other anticlines or tilted blocks as extensive as 

those represented on the map are present in the region. However, 

large areas are certainly underlain by rocks that are nearly or 'quite 

horizontal. Outside of the Havre district no developments of oil or 

gas or even indications of these substances have been found in the 

area shown on Plate VI. In the following pages the principal 

features of these areas of tilted beds will be described, beginning with 

the northernmost tier of townships and progressing southward.

T. 37 N., R. 15 E.

On Signal Butte, in the west half of T. 37 N., R. 15 E., an anticline, broken along its crest by faulting, extends in a direction 

approximately N. 25° W. This anticline can be traced very clearly 

for about 2 miles, and there is a possibility that it extends for several 

miles more under the glacial drift. The exposures on the east side of 

Signal Butte are excellent. They show the Judith River formation 

with its coal zone lying near the top, together with 200 feet of the 

underlying beds. The Bearpaw shale appears normally above the 

Judith River formation on either flank of the broken fold. The 

structure is clearly anticlinal that is, the beds dip away on both 

sides from a middle axial line, although there is some displacement 

by faulting along this axis. On the northeast side of the anticline the 

dips close to the fault line range from -10° to 32°. Toward the 

east they flatten rapidly, and about a mile from the fault the strata 

lie nearly horizontal. On the west side the beds do not dip so 

steeply, the average dip being not over 12°, except in a few irregularly disturbed tracts. In the S. -| sec. 20, on the fault cutting the 

crest of the anticline, there is a spring whose surface is covered with 

a thick film of reddish-brown ferric hydroxide. This material should 

not be mistaken for oil. No signs of oil or gas were found in the 

vicinity. A cross fault in the S. ^ sees. 19 and 20, nearly at right 

angles to the trend of the broken anticline, forms the south boundary 

of a block of Judith River beds which are tilted to the northeast at 

angles of 6° to 13°. This tilted block lies in anomalous relations to
. OIL AND GAS IN N6BTH-CENTBAL MONTANA. 77

the faulted anticline just described and covers an area of nearly 4: 

square miles.

T. 36 N., R. 14 E.

In the east half of T. 36 N., E. 14 E., mainly in sees. 11, 14, 22, 

and 23, there is a tilted block of rocks having an average dip of 

about 8°, bounded on the northwest side by a fault. On the whole 

the exposures in this vicinity are not good, the limits of the tilting 

being hidden either by glacial drift or alluvium. The best exposures appear on the northward-facing slope in the N. £ sec. 23. 

Practically all of the Judith River formation is exposed along this 

slope, and there is probably a little Claggett shale at its west end. 

The dips for the greater part of the distance average between- 7° 

and 8°. Near the top of the Judith Eiver there is a local dip of 28°, 

but this flattens to about 9° a short distance farther southeast. The 

Bearpaw shale appears on this slope in normal relations above the 

Judith River beds and is exposed to the southeast across almost all of 

sec. 24. The actual Extent of this tilted block can not be determined, but to judge from the area of the exposed portion it seems safe 

to say that, as indicated on the map, it extends at least 2 miles in a 

northeasterly direction.

T. 35 N., R. 12 E.

In the west half of T. 35 N., R. 12 E., the rocks are uplifted and 

tilted to the southeast by a fault that has a general trend of 

N. 25° W., and extends from Milk River near the southeast corner 

of sec. 14 northwestward for at least 4 miles, crossing sees. 6 and 7 

of the township adjoining on the east. On the northwest side of 

the fault the area is occupied by the Judith River formation, which 

lies approximately horizontal for many miles to the northwest, and 

the beds are undisturbed, even in close proximity to the fault plane. 

On the southeast side the beds are tilted to the southeast in an area 

occupying 4 to 5 square miles. The Claggett shale is the lowest 

formation exposed in this area and crops out in a belt that averages 

a quarter of a mile in width adjacent to the fault and is traceable 

as far as the fault is exposed. Southeast of the Claggett outcrop 

is the lower part of the Judith River formation, with a persistent 

thin coal bed at the base in normal relations to the Claggett shale. 

The highest dip (60°) in this tilted block was observed in the 

Claggett shale in sec. 14. The average dip is not over .40°. Northeast of this area, in sees. 12, 6, and 7, the dips in the Claggett shale 

at the same position with reference to the fault do not average more 

than 20° to 25°. In sec. 14 the beds are approximately horizontal 

within three-fourths of a mile of the fault. Farther north the 

distance from the fault to practically horizontal beds is somewhat 

greater, but nowhere is it more than 1 mile.
78 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1016, PAIlT II.

T. 35 N., R. 14 E.

On the upper end of Red Rock Coulee, in T. 35 N., R. 14 E., there 

is a tilted block of strata between two parallel faults extending for 

4 miles in a northeasterly direction. The areas northwest and southeast of the two faults bounding this block are underlain by the 

Bearpaw and Judith River formations, for the most part nearly 

horizontal. Between the faults the rocks are considerably tilted, and 

the steepest dips are on the southeast edge of the block, where dips 

in the Bearpaw shale and in the coal zone in the upper part of the 

Judith River formation range from 35° to 70°. On the northwest 

edge of the block the dips are much less, the observed readings varying from 6° to 14°. The lowest rocks (the upper part of the Claggett shale) are exposed in sec. 30. Southeast of this point the full 

thickness of the Judith River beds is present, followed in the SW. i 

sec. 29 by a small amount of the Bearpaw shale.

T. 35 N., R. 16 E.

In T. 35 N., R. 16 E., near the head of a small coulee tributary to 

Red Rock Coulee, there is an area of tilted beds that strike about 

N. 65° E. These beds dip to the southeast at an average angle of 

about 20°, although readings as high as 37° were observed. The 

lowest beds exposed are those of the Claggett shale, which are followed in normal sequence by the Judith River formation with its 

coal zone at the top, which is well exposed. Southeast of the coal 

outcrops, near the south side of sec. 14, the Judith River beds are 

folded into a shallow syncline that lies on the south edge of the tilted 

block. Beyond this syncline the area is entirely covered with glacial 

drift. The extent of^this tilted block in the direction of the strike 

is very uncertain because of the general cover of glacial drift, which 

makes it impossible to follow the exposures beyond the sides of the 

coulee.

T. 34 N., R. 12 E.

In-the northeastern part of T. 34 N., R. 12 E., on Milk River, 

there is a fault trending about N. 55° E., which is exposed on both 

sides of the river valley and extends an unknown distance under the 

drift to the northeast and southwest. Northwest of this fault, up 

Milk River, the only formation outcropping for many miles is the 

Judith River, which lies nearly horizontal even in close proximity 

to the fault plane. Southeast of the fault for a distance of over a 

mile the strata are tilted to the southeast. The Claggett shale is the 

oldest formation exposed on this side, and overlying it are the Judith 

River beds in normal sequence, with a thin coal bed near their base. 

Within 1,500 feet of the fault the observed dips range from 35° to
OIL AND GAS IN NORTH-CENTRAL MONTANA. 79

60°. Farther away the dips flatten rapidly to 10° and then gradually 

lessen until the strata are nearly horizontal. The exposed rocks involved in this tilting occupy an area of about 3 square miles, but the 

total area may be much greater, including extensions under the cover 

of glacial drift.

T. 34 N., K. 13 E.

In T. 34 N., R. 13 E., there are three tilted blocks identical in form 

and nearly parallel to those in the adjoining townships to the west 

and the northwest, already described. Each block is separated by 

a fault trending northeast from a considerable area of nearly horizontal rocks on the northwest. The northernmost of these tilted 

blocks cuts across Saddle Butte, extending from sees. 18 and 19 to 

sees. 4 and 5. Practically all of the Eagle sandstone is brought up 

by the faulting. This occurrence is noteworthy, as it is the only 

outcrop of the Eagle formation in this part of the Milk River valley. The Eagle is the lowest geologic formation exposed in the area 

covered by Plate VI, and the section given on page 69 was measured at this point. The full thickness of the Claggett shale and 

the lower part of the Judith River formation, with a thin coal 

bed near the base, are also exposed. The dips in the zone occupied 

by the Eagle and Claggett in this faulted area in the first quarter 

of a mile southeast of the fault vary from 45° to 15°. Beyond this 

they rapidly become less, and a mile from the fault the beds lie nearly 

horizontal.

About 3£ miles southeast of the fault just described there is a 

similar fault crossing the Milk River valley and extending from the 

W. | sec. 22 northwestward as far as sec. 1, a distance of a little over 

3 miles. The extent of this fault beneath the glacial drift beyond 

these limits can not be determined. According to Pepperberg,1 the 

Claggett shale is the lowest formation brought to the surface in this 

faulted uplift. The beds on the northwest side of the fault are 

nearly or quite horizontal for several miles to the northwest. On 

the southeast side the dips appear to be irregular, varying from 14° 

to 60°. Farther southeast the beds flatten to a nearly horizontal 

position within a mile of the fault.

Farther down the Milk River valley the Judith River formation, 

lying nearly horizontal, is exposed on both sides of the valley as 

far as the center of sec. 36 and is the only formation exposed in this 

territory. Half a mile above Brown's ranch there is an anticline, 

broken to some extent by faulting, here referred to as the Browns 

Coulee anticline. This anticline trends in a northeasterly direction 

and extends several miles into the township adjoining on the east. 

An account of it is given under the next heading.

1 Unpublished data.
80 CONTRIBUTIONS TO ECONOMIC GEOLOGY; 1916, PART II.

T. 34 N., R. 14 E.

From the west bank of Milk Eiver, in sec. 36, T. 34 N., E. 13 E., 

the Browns Coulee anticline is well exposed, with minor interruptions, for a distance of about 3 miles, as far as the east side of 

Browns Coulee, in sec. 32, T. 34 K, R. 14 E. How much farther 

northeast and southwest it extends under the drift-covered prairies is 

not known. Beginning on Milk River in the southeast corner "of sec. 

36, its axis trends N. 65° E., passing a few rods south of the east quarter corner of the section. Continuing northeastward it crosses the 

north branch of Browns Coulee about TOO feet north of the center 

of sec. 31. In the main branch of Browns Coulee, in the NW. £ 

sec. 32, the crest of this fold is broken by a fault of relatively small 

throw, the dark shale of the Claggett abutting against a massive 

brown sandstone at the base of the Judith River formation, but the 

essential anticlinal nature of the structure, the strata dipping in opposite directions from a medial line, still prevails. The Claggett 

shale, according to Pepperberg,1 is the lowest geologic formation exposed on the Browns Coulee anticline. The observed dips on the 

north limb of the fold range from 20° to 55° within half a mile of 

the axis; on the south limb the recorded dips range from 10° to 50°. 

The north limb is somewhat the more steeply tilted of the two. The 

total distance in a direction transverse to the axis of this anticline 

between the beds lying nearly horizontal on the north and those in 

the same attitude on the south is about If miles.

TILTED AND FOLDED KOCKS NORTH OF CHINOOK. 

T. 34 N., R. 19 E.

On Lodge Creek, in the southwestern part of T. 34 N., R. 19 E., 

the Claggett and Judith River formations are tilted about 25° S. 

in an area covering parts of sees. 19, 20, 29, and 30 and probably extending a short distance into the township adjoining on the west. 

The fault that produced this tilting crosses the river valley near the 

south quarter corner of sec. 19 and trends N. 1T° E. There are no 

exposures on Battle Creek, where this fault, if extended, would cross 

the valley. The prevailing cover of till and glacial drift makes it 

impossible to determine how far the tilting continues.

In the southeastern part of this township there is an anticline 

whose axis trends northwest. It is very poorly exposed and seems 

to merge into a fault, which becomes prominent in the township to 

the south. The most definite indications of this fold are in the 

vicinity of the southwest corner of sec. 23, where the axis trends N. 

30° W. and is outlined by opposite dips appearing on both sides of 

the valley of Dry Fork Creek. The fold is probably closely compressed. The observed dips on the east limb range from 20° to T5°

1 Unpublished data.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 81

and those on the west limb from 4° to 30°. In the S. £ sec. 35 there 

is a fault in the position that would be occupied by the anticlinal fold 

above mentioned if it were extended. This fault, however, trends 

more nearly north and causes the Judith River beds, dipping 11° 

W., to abut against the BearpaAv shale.

T. 33 N., R. 19 E.

On Battle Creek, in the northeastern part of T. 33 N., R. 19 E., 

there is a fault trending nearly north, which seems to merge into the 

axes of the small anticlines at each end of it. For the greater part 

of the distance along this fault the Judith River formation, which 

is the lowest geologic formation exposed, abuts against the Bearpaw shale, the Judith River beds appearing mainly on the west 

side of the. fault and the Bearpaw shale on the east. The dips 

within a few hundred feet on either side of the fault appear to be 

very steep, the observed readings, according to Pepperberg,1 being 

as high as 65°, but the dips lessen both east and west of the fault 

line, and at a distance of one-half to three-fourths of a mile the 

beds lie approximately horizontal. On the east side of the fault 

the beds dip to the east at angles between 60° and 3°, according to 

the distance from the fault line, making the structure in effect anticlinal that is, the beds dip in opposite directions from a medial line.

The only drilling operation in this part of the Milk River valley 

whose record is available was undertaken at Chinook in July, 1890. 

The well was drilled to a depth of 960 feet 2 by the town of Chinook 

in an attempt to develop artesian water. At the bottom of the 

bore, in a 6-foot stratum of blue clay, gas and petroleum were reported. Water was encountered at several horizons, of which the 

lowest, at 540 and 620 feet, yielded salt water. The log of this well 

is as follows:

Log of well at Chinook, Mont.

[Elevation, 2,404 feet.]

Probable formation.

Glacial drift.

Claggett shale or Colorado

shale (?).

Driller's description of the rock.

Loam and sand. ...........................

Stone bowlders... . ........................

Stiff clay. .................................

Sandstone. ................................

Blue clay... ...............................

Blue clay, interspersed with thin strata 

of lime and sandstone, soft mud. 

Blue clay. .................................

Contents.

Water.......

TJVotfir

Saltwater...

troleum.

Thickness.

Feet. 

112

12

96

2

318

li

78*

330

6

Depth.

Feet. 

112

124

220

222

540

541J

620

950

956

1 Unpublished data.

2 Nettleton, E. S., Final report on artesian and underflow investigation to the Secretary 

of Agriculture : 52d Cong., 1st sess., S. Ex. Doc. 41, pt. 2, pp. 72-73, 1892.
82 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

T. 33 N., R. 20 E.

On Coal Creek, in the west half of T. 33 N., R. 20 E., there is a 

fault whose trace makes a curved outline that can be followed, except for several minor interruptions by drift and alluvium, for 

about 3 miles across sees. 3, 10, and 14. According to Pepperberg,1 

the Bearpaw shale is present over most of the northern part of 

this township, but the Judith Kiver formation, the lowest exposed, 

is brought to the surface along the southwest side of the fault. The 

observed dips in these beds, which are tilted to the southwest, range 

from 3° to 20°. The exposures are poor, and the distance to which 

the tilting of the strata extends southwestward was not determined, 

but it is probably as much as three-fourths of a mile.

AREA OF TILTED AND FOLDED ROCKS SOUTH OF THE BEARPAW

MOUNTAINS.

GENERAL FEATURES.

In the vicinity of Missouri River south of the Bearpaw Mountains 

there are many areas of tilted and folded rocks similar to those near 

Havre, already described. On Plate VII the largest and least 

disturbed of these areas of folded and faulted rocks, comprising 

18 separate structural features, each of which may be of importance 

as a reservoir of oil and gas, are outlined. A considerable portion 

of the area lying north of Missouri River has not been examined 

geologically, but there are doubtless similar structural features in 

these unsurveyed townships. Escapes of gas or seeps of oil have 

not been recorded in any par.t of the region along Missouri River, 

nor are the records of any deep borings available.

FAULTED AREAS IN" THE VICINITY OF VIRGELLE.

In T. 26 N., Rs. 11 to 13 E., in the vicinity of Virgelle, there are 

four areas of tilted rocks in which the Colorado shale is the lowest 

formation exposed. The westernmost of these tilted blocks is produced by a fault that crosses sees. 16, 17, and 18, T. 26 N., R. 11 E., 

extending from the west side of Missouri River along the coulee 

that enters the river near the center of sec. 16. This fault, according 

to E. R. Lloyd,1 trends N. 65° W., and is best exposed along the 

sides of the coulee in sees. 17 and 18. The Colorado shale is exposed 

southwest of the fault, where it dips to the southwest at low angles 

for half a mile to a mile beyond the fault line. On the fault line the 

lower shales of the Colorado- have been carried upward against the 

Virgelle sandstone and the uppermost beds of the Colorado. The 

beds on the northeast side of the fault lie for the most part nearly

1 Unpublished data.
U. 8. GEOLOGICAL SURVEY BULLETIN 641 PLATE VI

SASKATCHEWAN

.MONTANA.

HILL

Cotton wood"

SECTION OF FORMATIONS

Bearpaw shale 

Judith River formation

Claggett shale

Eagle sandstone

Virgelle sandstone member

=-=^ -Colorado shale

EXPLANATION

Area in which Judith River formation is 

lowest formation exposed in the uplift

Area in which Claggett shale is lowest 

formation exposed in the uplift

Area in which Eagle sandstone is lowest 

formation exposed in the uplift

Axis of anticline

Tilted fault block'witfi 

direction of dip

R._14_E, R. 15 E. R. 16 E. R. 17 E. R. 18 E. R. 19 E. R, 2O E. R. 21 E.

Gas well 

 *- Small flow of gas

Show of oil and gds 

_. _ o 5 "10 Miles

SKETCH MAP SHOWING TILTED AND FOLDED STRUCTURES NORTH OF THE BEARPAW MOUNTAINS, MONT.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 83

horizontal. A second fault, nearly parallel with this one, and the 

largest of those present in the vicinity of Virgelle, extends from a 

point near the center of sec. 20, T. 26 N., R. 12 E., northAvestward 

to a point near the south quarter corner of sec. 4, T. 26 N., R. 11 E"., 

a distance of about 6 miles. This fault is well exposed in sec. 24 of 

the latter township, on the south bank of the Missouri. Here beds 

of the Colorado shale that dip as much as 43° abut against nearly 

horizontal beds of the Colorado shale, but the inclined beds flatten 

to nearly horizontal within about three-fourths of a mile. To the 

northwest the trend of this fault follows Missouri River very closely, 

but the fault is covered by the alluvium along that stream as far as 

the W. $ sec. 10. From sec. 10 to its northeastern extremity the fault 

is again well exposed and has a trend identical with that noted in 

sec. 24. A tilted block on the southwest, composed of Colorado shale, 

abuts against nearly horizontal Virgelle sandstone and the upper 

beds of the Colorado shale on the northeast. .This fault can be 

traced for about 2 miles, into the township on the east, to a point 

where it is concealed under the cover of glacial drift. The trend 

changes to nearly east, as shown by the exposures near the center of 

sec. 20, T. 26 N., R. 12 E.

In the north half of T. 26 N., R. 12 E., about 4 miles northwest 

of Virgelle, tilted rocks lie on the west side of a fault trending N. 40° 

E., which crosses Missouri River in the W. -| sec. 3 and extends 

northeastward beyond the river for a short distance to a point where 

it is concealed by glacial drift. The dips near this fault are comparatively steep, but they flatten rapidly, and within a mile of the fault 

plane the beds lie horizontal.

The fourth area of tilted rock in the vicinity of Virgelle occupies 

a part of the west half of T. 26 N., R. 13 E., near the lower end 

of Lone Tree Coulee. The fault, which has uptilted the beds in 

this locality, trends nearly west across sees. 17 and 18 of this township and is cut at several points by dikes of igneous rock. On the 

north side of the fault the beds are tilted northward at angles ranging from 23° to 60°, the steeper dips being near the fault, and the 

area of tilted rocks extends about a mile from the fault line. The 

Colorado shale, the lowest formation exposed, is overlain by the Eagle 

sandstone and Claggett shale in normal succession. On the south side 

of the fault the beds lie nearly horizontal, except in the S. % sec. 

17, where exposures in the Claggett shale on Lone Tree Coulee show 

a small anticline with dips of 3° on the west limb and 4° on the east 

and an axial trend approximately due north. This anticlinal axis 

probably meets the fault mentioned above near the, center of sec. 

17. Its southward extent is not known because of the prevailing 

cover of glacial drift.
84 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 19l6, PART EL

FAULTED AREAS ALONG MISSOURI RIVER BETWEEN EAGLE CREEK AND

ARROW RIVER.

In the west half of T. 25 N., R. 13 E., and in the township adjoining on the south, there are two nearly parallel faults trending about 

N. 30° W. The northern fault can be traced continuously, except 

for several interruptions caused by the cover of glacial drift, from 

sec. 7 to the west bank of the Missouri in sec. 28. The tilted beds, 

which occupy an area extending about three-fourths of a mile southeastward from the fault line, show dips that for the whole area may 

average about 15°. The Colorado shale is the lowest geologic formation exposed and is overlain in normal succession to the southwest 

by the Eagle sandstone and the Claggett formation. The second of 

the two faults in this township crosses the NE. £ sec. 31 in a direction about N. 50° W. As in the faulted rocks lying immediately to 

the north, the Colorado shale is the lowest formation exposed in the 

tilted block southwest of this fault. The fault reaches the west 

bank of the Missouri in the NE. | sec. 4, T. 24 N., E, 13 E., where 

it finally disappears under the alluvium on the sides of the river. 

Its extent southeastward along the opposite side of the river is not 

known, that area not having been examined, but the trend of the 

fault is so closely in alignment with that of the extensive fault 

crossing the west half of T. 23 N., R. 14 E., that they are probably 

parts of a single fault.

In the west half of T. 25 N., E. 14 E., there is an area of strata 

tilted to the northeast along a fault mapped by Bowen,1 trending 

about N. 50° W. These upturned rocks occur in a large area in 

which the Claggett shale is the principal formation. The Eagle 

sandstone, the lowest formation exposed, has been carried upward 

and lodged against the Claggett shale lying southwest of the fault. 

This fault is in many places concealed by the usual cover of glacial 

drift, but the best exposures are on Spring Creek in sees. 19 and 29. 

Where this fault crosses Eagle Creek, near the southwest corner of 

sec. 18, it turns to a direction N. 20° W. The area occupied by the 

tilted strata, so far as the exposures indicate, includes about 4 square 

miles.

In the west half of T. 23 N., E. 14 E., and the townships adjacent 

on the northwest, west, and south, there is a fault over 12 miles long. 

In places this- fault produces an anticline, as the dips are in opposite directions on the two sides of the fault line. Most of the tilted 

beds, however, lie on the southwest side of the fault. The rocks 

affected by this long and somewhat irregular fault show at a number of points where it crosses the watercourses. The northwest end 

of the fault is best exposed where it crosses Missouri River, in the

»U. S. Geol. Survey Bull. 541, pi. 21, 1914,
OIL AND GAS IN NORTH-CENTRAL MONTANA. 85

S. £ sec. 25, T. 24 N., R. 13 E. Here an area of tilted Colorado shale 

overlain by the Eagle and Claggett formations is exposed southwest 

of the fault, which trends S. 30° E. It next appears, with approximately the same trend, along the watercourses in the W. £ sec. 1, 

T. 23 N., R. 13 E., where the Colorado shale dips both to the southeast and the southwest from the fault line. From this locality the 

beds are covered by glacial drift as far as the crossing of the next 

coulee, in the W. $ sec. 7, T. 23 N., R. 14 E. In the coulee at this 

point the Colorado shale and the entire succession of formations 

above it are again well exposed. Farther southeast the fault, trending about S. 20° E., is still readily traceable by means of the numerous exposures in the drainage ways to the south side of T. 23 N., 

R. 14 E., crossing Flat Creek Pass in the N. ^ sec. 33. It continues 

southwestwai'd as far as sec. 15, T. 22 N., R. 14 E., crossing the main 

valley of Flat Creek in sec. 10. At this point there is a considerable 

area of tilted rocks on the southwest side of the fault, and the average dip in the more steeply tilted beds is about 15°, but this gradually 

flattens and the beds are nearly horizontal about three-fourths of a 

mile to the southwest. At its southeast extremity, in sec. 15, this 

fault becomes very irregular, being lost in an area of much broken 

and disturbed rocks in sees. 13, 14, 23, and 24.

Near the west line of T. 23 N., R. 14 E., there is a well-developed 

fault that has a slightly curving trend but extends in a general 

northerly direction. In sees. 13 and 24 this fault appeal's along the 

west side of Missouri River, where the Colorado shale abuts against 

the Virgelle sandstone and the upper members of the Eagle formation. The tilted (Strata, in which some petroleum or gas may have 

accumulated, lie east of this fault line, occupying a considerable 

part of the alluvium-covered areas along Missouri River. To the 

south the fault is much concealed by glacial drift, but in the N. \ 

sec. 36 it is again well exposed, trending in a northeasterly direction 

across the valley of Flat Creek. The tilted strata here also lie on 

the east side of the fault, the Colorado shale and Eagle sandstone 

being carried against the Eagle sandstone and Claggett shale on the 

west side. The dips are between 15° and 20° in the steeper beds, 

but they flatten to approximately horizontal a mile or so east of the 

fault line.

TILTED ROCKS OF LOWER PART OF JUDITH RIVER.

In the north half of T. 22 N., R. 16 E., there is an extensive fault 

cutting across the township with a trend about N. 65°-W. Southwest of this fault there is a tilted block which is the largest of those 

in the region along the Missouri River described in this report. 

The tilted beds are best exposed along Judith River is sees. 10, 11,
86 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART H.

14, and 15. At this locality the Colorado shale is the lowest formation exposed and is succeeded to the southwest by the Eagle and 

Claggett formations, and part of the Judith River, in normal succession. The tilted beds extend southwestward from the fault line 

for a distance of about 2 miles. In the S. -J sec. 15 they are cut by 

a small fault trending in a northeasterly direction, which probably 

meets the main fault near the west line of sec. 12. Along Missouri 

River near the north line of sees. 5 and 6, the main fault crosses 

Missouri River, bringing up the Colorado shale and the overlying 

formations. At this locality the area of tilted strata extends to the 

southwest about 1£ miles from the fault line.

From sec. 6, T. 21 N"., R. 16 E., a fault whose trace makes a 

slightly curved line extends eastward for a distance of over 12 miles 

into the townships adjoining on the east. On the north side of the 

fault there are tilted beds dipping about 8° N. The best exposures 

of these tilted rocks are^along Judith River in the S. | sec. 2, T. 21 N., 

R. 16 E. Here the upper part of the Colorado shale, overlain by 

the Eagle sandstone and the Claggett formation, are brought against 

shale in the lower part of the Colorado. In T. 21 N., R. 17 E., this 

fault extends in a slightly curved line southeastward through sees. 

7, 8, and 16. In the N. \ sec. 22 it is broken by several cross faults, 

but its extension continues eastward, makes a sharp curve toward 

the south, and extends northeastward about 1 mile into T. 21 N., 

R. 18 E., nearly to the northeast corner of sec. 19. The beds on the 

north side of this fault dip northward at an average rate of about 7°.

TILTED ROCKS ON DOG CREEK.

At the mouth of Dog Creek, about 2 miles east of Judith post 

office, there is a thrust fault extending in a northerly direction, which 

crosses Dog Creek in the NE. \ sec. 6, T. 22 K, R. 17 E. West of 

this fault, which extends to and probably crosses Missouri River, 

there is an area of about 2 square miles of tilted beds which dip 

to the west. In this area the Colorado shale, overlain by the full 

thickness of the Eagle and a part of the Claggett shale, is carried 

upward against the lower part of the Claggett formation. The 

dips near the fault plane vary between 6° and 12°. About half a mile 

west of the fault they become steeper, averaging between 20° and 30°, 

and still farther west the beds flatten and approach a horizontal 

attitude within 1 mile of the trace of the fault.

In the north half of T. 21 N., R. 18 E., is a fault that extends 

across the township with a trend about N. 60° W. and brings a considerable block of tilted rocks, in which the Claggett shale is the 

lowest formation exposed, against nearly horizontal Judith River 

beds. This fault crosses very near the northeast corner of sec. 6 and 

extends about 4 miles northwestward from this point, into T. 22 N.,
OIL AND GAS IN NOBTH-CENTEAL MONTANA. 87

E. 17 E. On the southeast it holds this trend to and beyond 

Dog Creek, in sec. 10, and is well exposed in the badlands along 

the creek. The tilted strata lie southwest of this fault and have an 

average dip of about 15°. Nearly horizontal beds are present within 

about 1£ miles southwest of the fault line.

A fault that is probably a continuation of the fault last described 

extends due east from, a point near the northwest corner of sec. 18, 

T. 21 N., E. 19 E., for a distance of nearly 4 miles. On the south 

side of this fault there is a considerable area of tilted and slightly 

folded strata, in which the upper half of the Judith Eiver is the 

lowest formation exposed and is overlain normally by the Bearpaw 

shale to the south. These tilted beds are carried upward against 

nearly horizontal Bearpaw shale on the north side of the fault. A 

well-defined anticline in the tilted area on the south side of the fault 

was noted in sees. 17 and 18. Its axis passes through the center of 

sec. 18, with a trend about N. 75° E., and extends into the N. -| sec. 17, 

where the trend changes to nearly east. On the north limb of the 

anticline the rocks dip between 7° and 35°, and the steeper dips 

occur close to the fault line. On the south limb the dips vary between 6° and 12°. East of this fold, in an area of tilted strata lying 

south of the fault, the ground is much broken by short faults trending nearly at right angles to the principal break. The strata in this 

area are irregularly folded or bent but generally lie at low angles, 

the dips rarely exceeding 10°. In the S. % sec. 17 there is a minor 

fault which ca^ be traced for about a mile in^a direction nearly due 

east and which offsets the coal zone in the upper part of the Judith 

Eiver formation.

! In the northeastern part of T. 21 N., E. 19 E., there are two faults 

lying nearly at right angles to each other, both of which have 

brought up the Judith Eiver beds in an area in which the Bearpaw 

shale is the predominating formation. The longer of these faults 

crosses sees. 1, 2, and 12 in a direction about N. 60° W. On its northeast side'the Judith Eiver beds, overlain by the Bearpaw shale in 

normal succession, are tilted at angles varying between 40° and 50° 

within a quarter of a mile of the fault, but farther northeast the dip 

of the beds is less, and within 1 mile of the trace of the fault they 

are nearly horizontal. Southwest of the fault the Bearpaw shale, 

lying practically horizontal, occupies a considerable area. The other 

fault in the northeastern part of the township crosses sec. 13 in a 

direction about N. 50° E. and joins the fault just described in the 

SW. J sec. 7, T. 21 N., E. 20 E. On the southeast side of this fault 

there is an area of titled upper Judith Eiver and lower Bearpaw 

beds, which dip at angles ranging from 20° adjacent to the fault to 

10° within 2,000 feet. This fault crosses Cutbank Creek about 1,500 

feet north of the center of sec. 13 and is there well exposed, but to the
88 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II. ,

southeast it can not be traced more than a few hundred yards and 

probably dies out before reaching the west line of sec. 13. In the 

SE. | sec. 13 the strata in the tilted block are folded into a shallow 

syncline, the south limb of which is near the south line of the section. 

The axis of this syncline trends northeast, nearly parallel to the 

fault.

AREA OF COLORADO SHALE EXTENDING FROM A POINT NEAR 

GREAT FALLS TO THE SWEETGRASS HILLS.

GENERAL FEATURES.

The results of six deep borings (see locations on the map, PL IV) 

are available for the area extending across the outcrop of the Colorado shale from Great Falls to the Sweetgrass Hills. None of these 

borings were successful, although five report showings of gas or oil, 

or both. These wells, located regardless of the structure, seem to 

show that a fair percentage of success can not be obtained by random 

drilling in the large area occupied by the Sweetgrass arch. Two of 

the wells are near the center of the arch, and seem to prove that this 

broad uplift as a whole has not caused the accumulation of oil or gas 

along its crest. However, if local folds are present within the 

broader uplift, they may have served as reservoirs for oil or gas.

The Bow Island gas field,1 60 miles north of the Canadian boundary, is near the northwestward extension of the Sweetgrass arch, its 

exact position probably being a little to the east of the crest of the 

arch. The details of the structure in the vicinity of the Bow Island 

field have never been published, but it is not improbable that the 

field is located on a local fold within the arch. The first well in this 

field was drilled about 1908. By 1914 sixteen wells had been completed, spaced about 1 mile apart over an area of about 15 square 

miles. The total production from these wells in 1914 was 75,000,000 

cubic feet a day, and the gas was distributed from a 16-inch pipe 

line, for 160 miles, supplying Lethbridge, Calgary, and intermediate 

towns.

DRILLING NEAR THE SWEETGRASS HILLS.

Several wells have been drilled within the last few years in the 

vicinity of the West Butte of the Sweetgrass Hills. These wells are 

a,bout 3 miles northeast of the oil seep in the Colorado shale, described on page . They were put down in a flat plain, much covered by glacial drift, and are not known to have been located with reference to local structure of any description. The general dip in the 

vicinity, as shown by a few scattered outcrops of the Virgelle sandstone, is northward at a low angle. The deepest of these wells was

1 Clapp, F. G., and others, op. cit., pp. 276-277,
U.S. GEOLOGICAL SURVEY BULLETIN 641 PLATE VII

R.8 E. R. 9 E. R. 1O E. R. 11 E. R. 12 E. R. 17 E. R. 18 E. R. 19 E. R. 20 E.

CHOUTEAU

.COUNTY

SECTION OF FORMATIONS

~^^ Bearpaw shale

il_--.- Judith River formation

g -Claggett shale

sandstone 

Virgelle sandstone member

= -Colorado shale

EXPLANATION

Area in which Judith River formation is 

lowest formation exposed inthe uplift

Area in which Claggett shale is lowest 

formation exposed in the uplift

Area in which Eagle sandstone is lowest 

formation exposed in the uplift

Area in which Colorado shale is lowest 

formation exposed inthe uplift

Axis of anticline

\ Tilted fault block with 

J direction of dip

10 Miles

SKETCH MAP SHOWING TILTED AND FOLDED STRUCTURES SOUTH OF THE ^EARPAW MOUNTAINS, MONT.
OIL AND GAS IN NORTH-CENTRAL MONTANA. 89

drilled to a depth of 2,670 feet, nearly to the base of the Kootenai, 

and obtained small flows of gas at two horizons. According to W. A. 

English, of the United States Geological Survey, the seep on "West 

Butte probably comes from the 50-foot member of the sandstone that 

is reported to contain water, whose base in this well is at a depth of 

1,640 feet. A log of the well, furnished by E. C. Galbraith, of the 

General Land Office, is as follows:

Log of well in sec. 4, T- 37 N., R. 2 E., a few yards south of the international

boundary.

[Elevation, 3,675 feet (barometric).]

Probable formation.

Glacial drift.

Colorado shale.

1

Driller's description of the rock.

Black sandy shale.. . ......................

Gray shale.... ............................

Contents.

Water.......

Water.......

ter.

Thickness.

Feel. 

65

f)A K

970

qin

50

20

70

25

45

5

10

20

40

180

70

68

1S2

20

150

170

Depth.

Feet.

sm

i 9sn

1,590

1,6'10

1,665

1 7ie;

i 7r»n

1,805

1,810

1,820

1,840

1

QQA

9 ftfift

2

1QA

2

1QQ

2,330

2

oef\

9 f^nn

2,670

A second hole was put down about a quarter of a mile southeast of 

the well just described and passed through the same strata. According to C. H. Jennings, who superintended the drilling of this well, 

shows of oil were encountered at about 960 and 1,660 feet, and small 

flows of gas at 1,300,1,535, and 1,810 feet.

DRILLING NEAR KEVIN, TOOLE COUNTY.

A boring in search of oil was made about 8 miles southwest of 

Kevin, Toole County, on the James Miller ranch. It went to a depth 

of 1,755 feet, passing through part of the Colorado shale and all of 

the Kootenai formation, and probably entering the Jurassic. This 

well is in the midst of a large area of horizontal rocks, as shown by 

exposures in the vicinity and also by the lay of the Virgelle sandstone in the prominent escarpment to the west and north. This well 

was therefore drilled in an unfavorable structure position. Small 

43768° Bull. 641 17 7
90 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

flows of gas, however, were encountered at three horizons. The log 

of the well, furnished hy H. C. Price, of Great Falls, Mont., is as 

follows:

Log of well at the James Miller ranch, in the NW. I sec. 25, T. 84 N., R. 4 W.

[Elevation, 3,360 feet.]

Probable formation.

Colorado shale.

Driller's description of the rock.

Sand. ......................................

Sand. .....................................

Light shale.... . ...........................

Light shale. ...............................

Shell......................................

Sand......................................

Sand. .....................................

Light shale... . ............................

Hard sand ................................

Hard shell ................................

Hard sand ................................

Yellow shale. .............................

Gritty sand ...............................

Hard shell ................................

Black shale ...............................

Hard shell1 . ...............................

Lime rock. ................................

Black shale ...............................

Contents.

water.

Gas.........

flow.

Thickness.

Feet. 

40

120

2

153

5

100

10

30

10

ISO

70

10

40

80

100

90

20

5

30

15

35

45

5

25

5

70

» 60

30

10

60

40

10

40

50

50

. 5

20

5

50

25

Depth.

Feet. 

40

160

162

315

320

420

Jlfl

460

470

650

720

73(1

770

850

950

1,045

1,005

1,070

1,100

1,115

1 1 <^(\

i iQ1;

1,200

1,225

1,230

1,300

1,360

1,390

1,400

1,460

1,500

1,510

1,550

i AM

1,650

1,655

1,675

1,680

1,730

1,755

DEEP BORINGS IN CHOUTEAU COUNTY.

About 10 miles southeast of Collins a prospect hole for oil and gas, 

known as the Banatyne well, was driven to a depth of 1,500 feet 

and obtained a small flow of gas at one horizon. The log for 1,240 

feet of this bore, passing through the Colorado shale and into the 

Kootenai formation, is given below. This well is near the crest of 

the Sweetgrass arch, if that structure extends this far south of Teton 

River. Nothing is known of the local structure, and it is probable 

that the rocks are much concealed by glacial drift.
OIL AND GAS IN NOETH-CENTEAL MONTANA. 91 

Log of Banatyne well, 10 miles southeast of Coiling.

Probable formation.

Kootenai formation.

Driller's description of the rock.

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

Sand. .....................................

Contents.

and gas.

Saltwater...

Thickness.

I'eel. 

74

206

5

73

7

11^

9 

96

175

90

10

20

509<"»

65

Oft

30

40

40

Depth.

Feet. 

74

280

358

365

500

509 

605

780

870

880

900

950

975

1.040

1,130

1,160

1,200

1,240

Small flows of gas are also reported from two deep wells in the 

northeastern part of Chouteau County. One of these, 15 miles northwest of Fort Benton, obtained gas in the Colorado shale at a depth 

of 300 feet. The other gas well is 10 miles north of Virgelle and 

was drilled to a depth of 800 feet. Details of the structure in the 

vicinity of these borings are not known.