GEOLOGY OF THE HOUND CREEK DISTRICT OF THE GREAT 

FALLS COAL FIELD, CASCADE COUNTY, MONTANA.

By V. H. BARNETT.

INTRODUCTION.

This paper is based on field work done during the month of September, 1909, by W. R. Calvert and the writer, assisted by J. R. Hoa.^ 

Its objects are to give information regarding the coal resources of the 

Hound Creek district of the Great Falls coal field and to describe the 

geologic formations and the structure relating to the occurrence or 

absence of the coal-bearing rocks. As the work was done primarily

ioo Miles

FIGURE 15. Key map showing location of Hound Creek district, Mont.

for land classification, the determination of the presence or absence 

of the coal was one main purpose.

The Hound Creek district is the southwestern extension of the Great 

Falls coal field, on which a detailed report l has been published. It 

comprises 180 square miles in Cascade County, Mont., and extends

1 Fisher, C. A., Geology of the Great Falls coal field, Mont.: U. S. Geol. Survey Bull. 356,1909.

215
216 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

along both sides of Hound Creek from a point near its mouth on 

Smith River (Deep Creek) to the head of Elk Creek in the foothills of 

the Big Belt Mountains. (See PI. XXII and fig. 15.)

In the course of the field work section corners were found with very 

little difficulty. Plane-table triangulation and mapping with telescopic alidade and stadia rod were also employed, so that a f air degree 

of accuracy was attained. Altitudes were obtained by aneroidbarometer readings based on the assumed altitude of Hound Creek 

bridge, in sec. 24, T. 17 N., R. 2 E.

SURFACE FEATURES.

BELIEF.

The surface of the district is made up of high, rounded hills and 

"broad slopes cut by streams into steep-sided valleys. For the most 

part the area borders a zone of mountain topography, but on the 

north it is adjacent to a more level country. The range of altitide 

is from 3,800 feet near the mouth of Hound Creek to about 7,200 feet 

in the southern part of the district. The average altitude of the 

field is about 5,000 feet, and the greatest difference in any one 

locality is 1,200 feet in three-fourths of a mile in sec. 22, T. 15 N., 

R. 1 E. Most of the streams have cut deep channels into the soft 

shale, and the more resistant limestones and sandstones make the 

valley sides steep and precipitous. The deeper valleys are from 300 

to 500 feet below the level of the bordering plains. Smith River is 

locally known as Deep Creek because it flows through a deep, narrow 

gorge in this part of its course. It crosses the northeast corner of 

the district and empties into Missouri River about 16 miles to the 

northwest. Hound Creek drains the larger part of the area, and its 

numerous mountain tributaries are fed by perennial springs.

CULTURE .

There are few settlements in the Hound Creek district, the population averaging about six families to the township. Adel, the only 

post office, is maintained at a ranch house in the southwestern 

part of the district. The location of ranches is determined by the 

position of readily irrigable land or by proximity of range for stock. 

There is an abundance of water almost everywhere, so that except 

on the higher areas it is not very difficult to procure sufficient water 

for irrigating small tracts.

Wagon roads generally are poor, but two regularly traveled roads 

cross the district from north to south. One is the stage road from 

Great Falls to Milligan post office and the other the main line of travel 

between Adel and Cascade, on Missouri River, 15 miles to the north. 

Other roads connect with these main roads but are difficult to travel 

over even with a light wagon.
CARBON.! FERGUS jJURASSIC _CRETACEOUS

^ ___^__ Uppa-Crei.

O ' 
GEOLOGY OF HOUND CREEK DISTRICT, MONT. 217

An electric power line from Great Falls to Butte has been constructed across this region for the purpose of transmitting power 

from the falls of the Missouri.

GENERAL GEOLOGY.

SEDIMENTARY BOCKS.

The rocks that crop out in the Hound Creek district belong to 

the Carboniferous, Jurassic, and Cretaceous systems, but detailed 

study was confined to- the coal-bearing Kootenai formation (Lower 

Cretaceous). The stratigraphic position, characteristic features, age, 

thickness, and economic importance of the formations are given in 

the accompanying table:

Geologic formations in the Hound Creek district.

System.

Quaternary.

Cretaceous.

Cretaceous (?).

Jurassic.

Carboniferous.

Series.

itpper Cretaceous.

Lower Cretaceous.

Pennsylvanian (?).

Mississippian.

Formation.

Alluvium.o

Colorado shale.

Kootenai formation. 

»

Morrison (?) formation.

Ellis formation.

Quadrant formation.

Madison limestone.

Lithologic character.

Silt, clay, and gravel.

Shale, dark, with beds 

of tough gray sandstone.

Sandstone, gray, and 

shale and clay, red. 

sandy, with local 

beds of white limestone. The sandstone predominates 

in the lower part, but 

the red shale and clay 

constitute most of 

the upper part. Coal 

or shale bed 60 feet 

above base.

Shale, variegated, and 

clay, containing sandstone and limestone 

layers.

Sandstone, tough, drab 

colored, conglomeratic in upper part, 

with some limestone 

underlying it.

Limestone, red, bluish, 

and greenish calcareous shales and clay, 

and a bed of white 

sandstone near top.

Limestone, massive, 

white to gray.

Thickness 

(feet).

2-25

6250

400-500

200±

100±

300±

6150+

Economic features.

Forms irrigable fertile tracts.

Contains sandstone 

which is resistant 

to weather and 

covers fields with 

loose slabs.

Contains locally a 

bed of coal.

Contains limestone 

suitable for building stone.

Contains sandstone 

and limestone probably suitable for 

building stone.

Contains limestone 

probably suitable 

for a flux or for a 

building stone.

Contains abundance 

of limestone probably suitable for 

building stone.

a Alluvial deposits in the Hound Creek district occupy small tracts in valleys. 

6 Exposed.

43768° Bull. 641 17 15
218 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PAET II.

CARBONIFEROUS SYSTEM. 

MISSISSIPPIAN SERIES.

Madison limestone. Only the upper 150 feet of the Madison limestone is exposed in this field. It crops out in the gorge of Smith. 

River, in the northeastern part of the district, and is the gorge-forming rock along that river for a number of miles above this area. It is 

also the most prominent sedimentary rock along the west slope of the 

Little Belt Mountains.

Weed l ascribes a thickness of 1,000 feet to the Madison and divides 

it into three members at the bottom the Paine shale, consisting Of 

gray thin-bedded shaly limestones; in the middle the light-colored 

Woodhurst limestone, whose beds are separated by thin argillaceous 

layers; and at the top the massive Castle limestone.

No special study was made of the Madison in connection with the 

work in the Hound Creek district, and no fossils were obtained from 

it, but collections made by Fisher 2 in 1906 in the Great Falls field, 

and by Calvert 3 in 1907 in the Lewistown coal field were determined 

by George H. Girty to be of Mississippian age.

PENNSYLVANIA^ (1) SERIES.

Quadrant formation. The Madison limestone is overlain by the 

Quadrant formation. The lower'two-thirds of this formation consists 

principally of red, bluish, and greenish calcareous or dolomitic shale 

with irregular bands of limestone. This shale rests upon the Madison 

limestone, and the change in lithology is so abrupt, from the Madison 

beds, laid down in a deep quiet sea, to the Quadrant beds, laid down 

in shallow water, that an unconformity is suggested, but no stratigraphic evidence regarding it has been obtained. The upper part of 

the Quadrant consists mainly of bluish compact massive or thinbedded limestone. The formation received its name from Quadrant 

Mountain, in the Yellowstone Park, where it is well developed.

The thickness of the Quadrant formation, according to Weed, 

ranges from 230 feet on Sixteenmile Creek, in the southwestern part 

of the Little Belt Mountains quadrangle, to 1,400 feet on Judith 

River, in the northeastern part of the quadrangle. Calvert 4 found 

it ranging in thickness from 425 feet to about 750 feet in the Lewistown coal field, and Fisher 5 noted its absence from the section at a, 

few localities in the southern part of the Great Falls field, where, 

according to his statement, the Ellis formation lies unconformably 

upon the Madison limestone. At one locality in the Great Falls

» Weed, W. H., U. S. Geol. Survey Geol. Atlas, Little Belt Mountains folio (No. 56), 1899.

2 Fisher, C. A., Geology of the Great Falls coal field, Mont.: U.S. Geol. Survey Bull. 356,1909.

3 Calvert, W. R., Geology of the Lewistown coal field, Mont.: U. S. Geol. Survey Bull..390,1909..

< Idem, pp. 15-17.

6 Fisher, C. A., op. cit., p. 25.
GEOLOGY OF HOUND CREEK DISTRICT, MONT. 219

field (in sec. 34, T. 17 N., R. 3 E.) W. R. Calvert and the writer found 

about 190 feet of the Quadrant formation exposed. At this place a 

section was measured through the Quadrant formation, and fossils 

were founo^near the top and in the overlying- Ellis formation. The 

fossils from bed 1 of the section (see below) were determined by T. W. 

Stanton to be Ostrea strigilecula White and Camptonectes sp., both 

Jurassic forms, whereas those from bed 3 of the section were found 

by George H. Girty to contain a single species which he determined 

to be Myalina arkansana and which he assigns to the Quadrant. The 

Quadrant-Ellis contact therefore must be concealed in bed 2 of the 

section, so that the thickness of the Quadrant formation at this place 

can not be more than 196 feet and may be 25 or 30 feet less.

Section of Quadrant formation on Smith River, in sec. 34, T. 17 N., R. 8 E.

1. Limestone, massive, irregular bedded (Ellis). Feet.

2. Covered (Quadrant-Ellis contact).............................. 36

 3. Limestone, thin bedded, and shale, with few fossils............. 15

4. Limestone, bedded and massive, argillaceous, with irregular layers 

of chert................................................... 11

5. Shale, greenish, and thin beds of limestone................'..... 103

6. Sandstone, white, saccharoidal................................. 4

7. Partly covered; red shale where exposed elsewhere............. 27

196

The quadrant formation is variable not only in thickness but also 

in character. Generally the lower half is more shaly than the upper 

half, but red, blue, and green shales and clays occur at many levels 

and are replaced laterally by limestone beds.

No especial study was made of the Quadrant in the Hound Creek 

district, so that but few fossils were collected. Those obtained from 

the upper part of the formation are listed below as determined by 

George H. Girty.

Schizophoria? sp.

Derbya kaskaskiensis. 

Myalina arkansana.

Productus semireticulatus. 

Productus pileiformis. 

Productus sp.

Mr. Girty states that the above forms "would not of themselves 

afford very satisfactory evidence for exact age determinations, but 

they seem to agree with more extensive collections from the same 

formation made by W. R. Calvert and me, which show that the 

fauna is very closely related to that of the interval of the Moorefield, 

Batesville, and Fayetteville formations of the Arkansas section, 

which have generally been regarded as upper Mississippian." He 

says, however, that there is a possibility that the rocks may prove 

to be of early Pennsylvania!! (Pottsville) age. In areas to the south 

and southwest the Quadrant formation has yielded Pennsylvania!!
220 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

fossils. In the absence of conclusive fossil evidence, the beds belonging to the Quadrant formation in this area are doubtfully assigned 

to the Pennsylvanian series.

JURASSIC SYSTEM.

Ellis formation. Resting unconformably upon the Quadrant is the 

Ellis formation, made up of compact impure limestone and dullcolored sandstone. It has been described by Weed/ Fisher,2 and 

Calvert.3

The formation crops out in a narrow zone over a large part of the 

east side of the district and along the slopes bordering many of the 

streams, where the resistant beds of the formation have formed 

escarpments in many places. The Ellis, wherever observed in this 

area, lies unconformably on the Quadrant formation.

The Ellis formation is almost as variable in thickness and lithology 

as the Quadrant. Where the full section is present the lowest part 

usually consists of compact limestone from 15 to 25 feet thick, and in 

places is separated from the upper part by a bed of calcareous shale. 

The upper member is usually a sandstone from 50 to 75 feet thick 

which is compact and locally conglomeratic in the lower part, but 

thin-bedded or even shaly toward the top.

The fossils collected from this formation, a list of which follows, 

have been determined by T. W Stanton to belong to the Ellis formation (Jurassic)'.

Astarte sp. 

Camptonectes sp. 

Cyprina? sp. 

Gervillia? sp.

Ostrea strigilecula White. 

Rhynchonella gnathophora Meek? 

Trigonia ep. 

Undetermined small pelecypods.

Mytilus sp.

CRETACEOUS (?) SYSTEM.

Morrison (?) formation. The strata here tentatively assigned to 

the Morrison formation (named by Eldridge 4 from the town of Morrison, near Denver, Colo.), consist of alternating beds of shale, sandstone, and argillaceous limestone. They rest conformably on the 

underlying Ellis formation and are overlain with apparent conformity3 

by the Kootenai, though the line of contact between the two formations is not well defined, and the similarity of their beds, both in color 

and in lithology, makes it difficult to define the limits. In the Hound

1 Weed, W. H., and Pirsson, L. V., Geology and mineral resources of the Judith Mountains of Montana: 

U. S. Geol. Survey Eighteenth Ann. Kept., pt. 3, pp. 476-480,1898. Weed, W. H., U. S. Geol. Survey 

Geol. Atlas, Little Belt Mountains folio (No. 56), 1899.

« Fisher, C. A., op. cit., pp. 27-28.

s Calvert, W. R., op. cit., pp. 19-22.

4 Emmons, S. F., Cross, Whitman, and Eldridge, G. H., Geology of the Denver Basin in Colorado: U. S. 

Geol.Survey Mon. 27, p. 60,1896.
GEOLOGY OP HOUND CREEK DISTRICT, MONT. 221

Creek district few good exposures of the Morrison (?) formation occur. 

The following section was measured in this district:

Section of Morrison (?) formation in the NE. \ sec. 34, T. 16 N., R. 3 E.

Kootenai formation. FeetSandstone, hard, drab, shaly...................................... 12

Clay, soft, green; contains some sandstone concretions............. 17

Sandstone, hard, brown to pink, calcareous........................ 6

Shale, soft, pink to red, alternating with bands of sandy and calcareous shale from 2 inches to 24 inches thick........................ 115

Ellis formation. 

150

Fisher l mapped the beds overlying the Ellis formation as Morrison because of their similarity to that formation in Colorado and 

Wyoming and also because they contain vertebrate fossils. This 

was the first recognition of the Morrison in Montana, although 

Weed and Pirsson,2 in speaking of the beds above the Ellis formation 

say that "it is possible they may be equivalent to the Upper Jurassic 3 

(Morrison formation) recognized in Colorado." Vertebrate fossils 

found in them by Fisher were provisionally identified by C. W. Gilmore as beiifg of Jurassic age. Calvert 4 has also mapped the Morrison in the Lewistown coal field, and the meager fossil evidence 

obtained in that field seems to point toward the Jurassic age of the 

beds, but until more evidence is at hand the age of the Morrison can 

not be known with certainty. Although search was made at every 

opportunity, no fossils were obtained during the present work, and 

so this paper can add nothing toward the solution of the problem.

CRETACEOUS SYSTEM. 

LOWER CRETACEOUS SERIES.

Kootenai formation, The term Kootenai, derived from the name 

of a tribe of Indians in the Canadian Rockies, was proposed by Dawson 5 in 1885 for beds that occur in that part of Canada, consisting of 

sandstone interbedded with shale and shaly sandstone, in which 

there are in places layers of conglomerate and a zone of coal beds.

Two years later Newberry 8 correlated the coal-bearing beds of the 

Great Falls region with Dawson's Kootenai formation of the Canadian 

Rockies. The question of the age of the Kootenai and the application 

of the term in the Great Falls and Lewistown coal fields is fully discussed in the bulletins by Fisher and Calvert, already cited.

1 Fisher, C. A., op. cit., pp. 28-30.

2 Weed, W. H., and Pirsson, L. V., op. cit., p. 480.

3 The Morrison formation is now classed by the United States Geological Survey as Cretaceous (?).

* Calvert, W. R., op. cit., pp. 22-24.

6 Dawson, G. M., Roy. Soc. Canada Trans., vol. 3, sec. 4, p. 2,1885.

6 Newberry, J. S., School of Mines Quart., vol. 8, No. 4, p. 327,1887.
222 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

The Kootenai of this area overlies the Morrison (?) formation with 

apparent conformity, and the beds of the two are lithologically similar. 

There is, however, a predominance of red shale in the Kootenai and 

fewer beds of limestone than in the underlying formation. Measurement of the thickness of the Kootenai was rendered impracticable by 

the fact that the full section is not exposed in any one locality in the 

area. It is believed, however, that there is little variation in thickness from about 500 feet as measured by Fisher in the Great Falls field.

The formation is composed of red, blue, and gray shales and clays 

alternating with beds of-sandstone and in the lower portion with thin 

beds of impure limestone. A coal bed is also present locally. The most 

prominent of the sandstone beds occurs about 60 feet above the base 

of the formation and is about 20 feet thick. This is the thickest bed 

of sandstone in the formation, and to its hardness is due much of the 

bench land as well as many of the loose rock slabs scattered over the 

surface. The coal bed, wherever present, occurs either immediately 

below or within 6 or 8 feet of the base of this sandstone. The beds 

below the coal zone consist of about 60 feet of alternating red and blue 

shales and thin beds of sandstone and impure limestone. The beds 

above the massive sandstone overlying the coal zone are composed 

of red, blue, and gray shales and clays alternating with gray sandstone. 

The red color predominates in the upper part of the formation and 

continues up to the base of the overlying Colorado shale. No discordance of dips at the top of the Kootenai was observed. The Kootenai occupies a broad bench in the north-central part of the district 

and borders Hound Creek on the west, extending to the southwestern 

part of the area. It is also present in isolated areas in the eastern part 

of the district. In the mountains bordering the district on the southwest the Kootenai formation is present, but it is complexly faulted 

and occupies only a small portion of the surface.

With the exception of one small collection 'of ferns which were too 

fragile to bear transportation and which were obtained from a carbonaceous shale near the coal, no fossils were found in the Kootenai of 

this district, but in the Great Falls field an abundant flora of Lower 

Cretaceous age was found by Newberry,1 who used the fossil plants 

in correlating the Kootenai of this field with that of the Canadian area, 

and also by Fisher.2 In the Lewistown field, farther east, Calvert 3 

observed that fossils in the Kootenai are not abundant, and the same 

thing is true of the area under discussion.

UPPER CRETACEOUS SERIES.

Colorado shale. The Colorado shale, the highest formation present 

in the Hound Creek district, overlies the Kootenai formation and is

1 Newberry, J. S., op. cit., p. 327.

2 Fisher, C. A., op. cit., pp. 33-35.

3 Calvert, W. K., op. cit., pp. 28-29.
GEOLOGY OF HOUND CREEK DISTRICT, MONT. 223

300 or 400 feet thick. It is composed of alternating beds of dark 

clay and shale with interbedded pale-yellow shaly sandstone. The 

base of the Colorado is marked by a heavy sandstone from 15 to 30 

feet thick that is distinguishable from the sandstone of the Kootenai 

formation by its pale-yellowish color and finer texture; in fact,, this 

color is fairly constant for all the sandstones of the Colorado in the 

region. The Colorado shale probably represents part of the beds 

originally described by Meek and Hayden as the Fort Benton shale. 

That term was derived from the name of a town on Missouri River 

about 40 miles below Great Falls, but the stratigraphic limits of the 

formation (now called Benton shale) are based largely on a section 

along Missouri River in northern Nebraska, where the Benton shale 

rests upon the Dakota sandstone and is overlain by theNiobrara limestone. The Niobrara is not separable in this region, and consequently the group term Colorado is used, Benton not being appropriate.

The exposures of the Colorado shale in this district are so poor that 

fossils were obtained at but one locality, in the bed of West Hound 

Creek, in the NW. J sec. 11, T. 15 N. ; R. 1 E. These fossils as determined by T. W. Stanton are Anchura sp., Inoceramus labiatus Schlotheim, and Lingula spv all referred by him to the Benton.

QUATERNARY SYSTEM.

No attempt was made in the Hound'Creek district to map Quaternary deposits, for they are confined entirely to narrow beds of gravel 

along the streams and to very small alluvial deposits.

IGNEOUS BOCKS.

There are no crystalline rocks in the Hound Creek area except 

along the west and southwest sides. The high ridges bordering the 

area for nearly its entire length along the west side are hills of igneous 

rocks. Radiating from this igneous mass are numerous dikes and 

sills, most of which are small and composed of basic rocks. Little 

time was given to the study of these rocks, however, for they lie 

mostly outside of the area occupied by the coal-bearing formation.

The Colorado shale, through which the dikes cut, is not extensively 

altered. Alteration is confined usually to a few inches on each side 

of the dikes and is noticeable along a zone a few feet thick in contact 

with some of the igneous masses.

Specimens were collected from a few of the dikes and sills, and 

examined by E. S. Larsen, who describes them below.

Specimen 5, trachydolerite. From a dike cutting the Colorado shale 

in sec. 31, T. 15 N., R. 1 E. The dike is about 2$ feet thick and is 

traceable for about half a mile.
224 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

In the hand specimen this rock is dense and dark green. The numerous darkgreen augite crystals, some of which are a centimeter in length, break out cleanly 

from the matrix. Small lenses of white fibrous natrolite occur. Analcite is present 

in rounded grains. The groundmass is finely crystalline and shows numerous cleavage 

faces of feldspar. The thin section reveals rather abundant phenocrysts of augite, 

feldspar, and analcite in a holocrystalline groundmass. This groundmass consists of 

feldspar laths, biotite, augite, and altered olivine. Accessory apatite and iron ore 

and secondary natrolite, calcite, and chlorite are present. The feldspar phenocrysts 

are labradorite and bytownite, and nearly all of them have a rather broad border of 

orthoclase; those of the groundmass are mainly orthoclase, though they likewise have 

a core of labradorite. The plagioclase core of the feldspar is always much altered, 

but the border is fresh. The analcite is probably primary and occurs as poorly developed crystals, many of which are pierced by orthoclase laths. The olivine is altered 

to a green pleochroic mineral with the optical properties of iddingsite. The rock is of 

rather basic character and is rich in the femic minerals and the alkalies. It belongs, 

to the trachydolerites of Bosenbusch.

Specimen 8. From a dike about 5 feet wide in the bed of West 

Hound Creek, in sec. 11, T. 15 N., R. 1 E.

This specimen is a dense dark-green rock with abundant large euhedral crystals of 

pyroxene and some small crystals of feldspar in an aphanitic groundmass. Microscopic examination shows that the rock is porphyritic and contains numerous large 

crystals of pyroxene, now replaced by calcite and chlorite, and about an equal amount 

of labradorite in a fine-textured altered groundmass, which consists of minute feldspar 

laths with nearly parallel extinction, abundant grains of iron ore, and secondary 

calcLte, chlorite, etc. The groundmass probably consisted originally in the main of 

alkali feldspar, augite, iron ore, and glass. The rock is very similar to that represented by specimen No. 5, although it is finer textured and more altered. It should 

probably also be called a trachydolerite.

Specimen 4, soda syenite porphyry. From the largest dike in the 

Hound Creek area. The dike occurs in sec. 2, T. 15 N., R. 1 E., and 

is about 6.0 feet thick. It forms a prominent ridge wall about threefourths of a mile long and from 20 to 60 feet high.

This is a dense, rather light gray rock, which has scattered phenocrysts of hornblende 

and feldspar in a very fine textured groundmass. The thin section shows a few phenocrysts of oligoclase-albite and still fewer of a greenish amphibole in a groundmasa 

which consists largely of stout prisms of albite and oligoclase with some orthoclase 

and pyroxene and a very little interstitial quartz. Apatite and iron occur as accessory 

minerals. The amphibole has an extinction angle (approximately Z A c) on the cleavage 

face of 18° and a maximum index of refraction of about 1.70. It is probably an alkali 

variety. The pyroxene occurs in small grains. It is pale green and faintly pleochroic. 

The extinction angle could be measured only approximately, but the measurement 

gave as a maximum value ZA c=28°. The texture of the groundmass might be called 

coarsely trachytic. The rock is fairly fresh, though the feldspars are dusted with 

alteration products and large parts of the femic minerals are changed to a brown 

chloritic material. The texture is rather coarsely porphyritic and the rock is a soda 

syenite porphyry.

Specimen 6, syenite. From a sill a few feet thick that crops out in 

the east bank of Hound Creek in sec. 19, T. 14 N., R. 1 E.:

This specimen is a rather light green fine even-grained rock. It consists largely of 

orthoclase, but there ie considerable altered augite and biotite, some plagioclase, and
GEOLOGY OF HOUND CREEK DISTRICT, MONT. 225

a little quartz. Long needles of apatite are prominent; titanite and iron ore are 

sparingly present; secondary calcite, chlorite, and uralite are rather abundant. The 

plagioclase occurs as the core of the orthoclase crystals. The orthoclase is probably a 

variety rich in soda, as it has a maximum index of refraction of about 1.53. The 

texture is hypidiomorphic granular and the composition is that of a syenite.

STRUCTURE. 

MAJOR FEATURES. *

The availability and extent of coal in any field are directly related 

to the structure. Since the period when the coal-bearing beds were 

deposited in this region there has been, first, the deposition of several 

hundred feet of Upper Cretaceous strata, then an epoch of mountain 

building which resulted in the uplift of the Little Belt and Big Belt 

mountains and elevated the area above the sea. During or after 

this epoch intrusions of igneous rocks occurred, and possibly at the 

same time the faulting and folding of the Hound Creek district was 

begun. Then followed the degradation of the land to the present 

surface. All these factors have contributed to produce the present 

structure of the rocks.

The area considered in this report lies between the north ends of 

the Big Belt and Little Belt mountains and extends from the flanks 

of the latter range on the east to the base of the former on the west. 

The strata lie in a low monocline dipping away from the mountains 

toward the northwest. This monocline is broken in many places by 

faults and folds, and though the beds dip locally in almost any direction, the average dip is about 4° or 5° NW., but as the plains country 

is approached the dips flatten.

The Little Belt Mountains constitute a broad, flat-topped anticline 

of sedimentary rocks cut up into smaller ridges by subsequent erosion. The steeply dipping sides of this anticline form the slopes of 

the mountain range, and the more gently dipping beds extending out 

from it toward the west are the bench lands of the Hound Creek district. There are few faults and local folds associated with the Little 

Belt Mountains anticline.

From the complexity of the structure along the northeast border 

of the Big Belt Mountains, where faults are very numerous and where 

igneous rocks have in many places been thrust up through Paleozoic beds, the formation of these mountains was apparently accompanied by more complex disturbances than in the Little Belt 

Mountains. The beds of the Hound Creek area, though more 

faulted, also dip away from the Big Belt Mountains. The number and 

magnitude of faults increase toward the mountains, which suggests 

that the faults are directly related to the disturbances connected 

with mountain .building.
226 CONTRIBUTIONS TO ECONOMIC GEOLOGY-, 1916, PART II.

FOLDS.

In the Hound Creek district there are several small folds of the 

strata which are parallel to one another and to the faults of the field, 

and which strike northwest. Perhaps the most prominent anticline is in the extreme southwestern part of the district. Here the 

folding was so sharp that a thrust fault resulted, in which the beds 

on each side dip away from the fault zone. Although the fault hue 

was not actually observed, it is known to be present because the 

Kootenai formation and the Colorado shale are almost in contact with 

the Quadrant formation. In the valley of Elk Creek, in sec. 34, 

T. 14 N., R. 1 E., the anticline is less sharp and seems to pitch and 

die out, but from this place eastward the beds are covered, so that 

it was impossible to decipher the structure in detail. North of the 

fault above referred to and forming a rather broad valley is a syncline, the axis of which enters this district in the SE. | NE. J sec. 

25, T. 14 N., R. 1 E., and extends westward through sees. 25 and 26, 

where it bends toward the northwest and trends in a nearly direct 

line to the boundary of the district near the SW. J sec. 6, T. 14 N., 

R. 1 E. At the east side of the district this syncline is very narrow 

and pitches westward. It becomes broader toward the west until 

it is about 4 miles across at the west side of the field. The greater 

part of the surface rock included in this syncline is the Colorado shale, 

which is bordered on either side by the Kootenai. The beds dip 

irregularly toward the axis of the syncline at angles varying from 

a very slight amount to 50° or 60°.

At the east edge of the district, in the NE. J sec. 34, T. 16 N., R. 

3 E., an anticline is exposed where it crosses a north-south ridge. 

The fold could not be traced beyond the ridge, but rather strong 

local dips toward the north were observed in the NW. \ sec. 34, and 

the beds to the south, in sec. 5, T. 15 N., R. 3 E., dip 15°-35° S., so 

that the broad valley of Clark Creek in sees. 28, 29, 32, and 33 is 

believed to be in part at least an anticlinal valley.

In sees. 11 and 12, T. 16 N., R. 1 E., there is an anticline which 

seems to replace a fault from the southeast. This anticline is 

observable for less than a mile in a northwesterly direction. It 

brings the Kootenai formation to the surface in an outcrop which is 

entirely surrounded by the Colorado shale in such a way that an 

elongated dome is suggested. The exposures are so incomplete that 

the structure could not be determined with certainty.

A syncline on the south side of the fault in T. 16 N., R. 2 E., 

extends from the SE. | sec. 35 to Hound Creek in sec. 27. It pitches 

northwestward parallel to the fault and not more than a mile distant. 

The dips on the two sides of the syncline range from nearly horizontal 

to 20° or 30.°
GEOLOGY OF HOUND CEEEK DISTRICT, MONT. 227 

FAULTS.

The Hound Creek district is much faulted, particularly in the 

southwestern part. The principal faults are of the overthrust type, 

normal faults being confined principally to those of lesser throw. 

Faulting has brought the hard rocks of the Quadrant and Ellis formations to the surface in places, and from their greater resistance to 

weathering escarpments have been formed.

Carter ranch fault. A fault enters T. 16 N., R. 2 E., in sec. 36 and 

leaves it in sec. 7. It crosses Hound Creek near Carter ranch, in 

sec. 21, and for this reason is termed the Carter ranch fault. The 

fault curves to the west and dies out near the township line, on the 

west side of sec. 7. This fault displaces the beds about 700 feet at 

the place of its maximum throw, in sees. 26 and 27, where the Quadrant is brought up against the Kootenai along the south side of the 

fault line. Partly on account of the westerly dip and partly because 

of the difference in amount of throw, which has produced a stronger 

westerly dip on the south side, the fault has offset the KootenaiColorado contact about 3 miles. On the north side of the fault this 

contact is in the valley wall on the west side of Hound Creek in sec. 

21, T. 16 N., R. 2 E., but on the south side it is in sec. 12, T. 16 N., 

R. 1 E., over 4 miles farther west. The strata dip in general away 

from the fault at angles of 70° to 90° on the upthrown side but less 

steeply on the downthrown side. This fault, like the other great 

faults farther southwest, is probably of the thrust type, although the 

evidence along the fault plane is not conclusive. However, as it is 

parallel to others which are known to be thrusts, and as it also seems 

to have resulted from a broken fold, it is believed to be a thrust 

fault.

Green ranch faults. Two faults cross East Fork of Hound Creek 

just above the Green ranch. They are best exposed in the valley 

walls, where they are about a quarter of a mile apart, but they 

converge on the hill about half a mile northwest of Hound Creek. 

They continue roughly parallel in a southeasterly direction. The 

northern one dies out in Crooked Creek valley near the west side 

of sec. 12, T. 14 N., R. 1 E., and the other extends to the southeast 

border of the district in sec. 19, T. 14 N., R. 2 E. Although the 

fault line is not exposed farther northwest than the top of the hill 

near the township line, the fault continues in this direction as much 

as 2 miles and forms the escarpment south of Adel. These are thrust 

faults, in which the fault plane dips southwest, toward the upthrow. 

In the hillside on the north bank of Hound Creek limestone of the 

Quadrant formation is thrust up over sandstone of the Colorado. 

The succession of beds as exposed here is Kootenai and Colorado 

below (downstream from the east fault); Quadrant, Ellis, Morrison( ?),
228 COiSfTRIfctmON-S TO ECONOMIC GEOLOGY, 1916, PART II.

and Kootenai between the two faults; and Quadrant, Ellis, Morrison (?), 

Kootenai, and Colorado west of the upper fault. Between the two 

faults Quadrant, Ellis, Morrison (?), and Kootenai occur in narrow 

zones and dip southwest at an angle of about 40°. The maximum 

displacement of beds by these faults occurs in sec. 3, T. 14 N., R. 1 E., 

and is probably about 1,000 feet. The offset of the Kootehai-Colorado 

contact is nearly 4 miles from sec. 3, T. 14 N., R. 1 E., to sec. 30, 

T. 15 N., R. 1 E. The dips on both sides of these faults are southwest 

and range from 5° or 6° to 40° or 50°.

Crooked Creek fault. The Crooked Creek fault is best developed 

in sec. 24, T. 14 N., R. 1 E. It enters the Hound Creek area at the east 

side of the section on Crooked Creek, strikes in a northwesterly direction, and dies out gradually within about 2 miles. It is apparently 

a thrust fault, as the Quadrant-EUis contact on its south side is brought 

up against the Kootenai. The maximum throw is about 400 feet, and 

the base of the Kootenai formation is offset about 2 miles.

Faults near Elk Greek. Fault near the Northern Pacific coal 

prospect, in sec. 15, strikes in a northwesterly direction. For about 

half a mile on each side of Elk Creek this fault is very prominent, but 

beyond this stretch it can not be made out. The beds on the north 

side of the break dip at a low angle southward into the fault; those 

on the south side dip 40°-74° S. The fault plane dips at a high angle 

to the south. The fault is normal and has a downthrow of about 150 

feet to the south, which brings the base of the Morrison (?) against 

the Quadrant.

Near the head of Elk Creek, in sees. 3 and 4, T. 13 N., R. 1 E., are 

two parallel faults about a quarter of a mile apart. These are both 

thrust faults which strike in an easterly direction and dip about 60° S. 

The fault planes are parallel to the bedding planes and the throw on 

both planes has brought the Quadrant against the Kootenai. These 

faults extend about half a mile on each side of Elk Creek, being 

terminated by an igneous mass on the east and merging into more 

complex faults on the west.

ECONOMIC GEOLOGY.

BE SOURCES.

Coal is present locally in the area under discussion, and there is an 

abundance of sandstone in the Ellis, Kootenai, and Colorado formations and of limestone in the Quadrant and Madison formations, which 

might be used for building. It is probable that calcareous shale, 

with the proper proportions of lime and clay to make Portland cement, 

could be found in the Quadrant. No metallic minerals are known to 

occur in the Hound Creek district.
GEOLOGY OF HOUND CREEK DISTRICT, MONT. 229

THE COAL. 

' OCCURRENCE.

Coal occurs locally in this district in a zone about 60 feet above the 

base of the Kootenai formation in close association with a thick bed 

of sandstone. The work of the United States Geological Survey in the 

Great Falls coal field in 1906 and in the Lewistown field in 1907 has 

shown that coal does not occur regularly throughout the region, the 

coal zone being in places either occupied by a very thin seam embedded in carbonaceous shale or entirely replaced by shale. This irregularity was found also in the Hound Creek district.

Just north of the Hound Creek district, on both sides of Hound 

Creek, in T. 17 N., R. 2 E., and along McMullin Creek, in T. 17 N., 

,R. 3 E., there is a coal bed averaging about 4 feet in thickness, and 

two mines are in operation in sec. 24, T. 17 N., R. 2 E., where about 

2,000 tons is taken out annually for local consumption. These 

mines are described by Fisher 1 under the heading "Smith River 

mines." It is believed that the coal pinches out within a short 

distance south of these mines, for in a prospect along McMullin 

Creek, in the SW. i sec. 31, T. 17 N., R. 3 E., the coal changes from a 

bed 3 feet thick at the entrance of the prospect to a thin film in the 

face of the entry, and in the NW. £ sec. 6, T. 16 N., R. 3 E., the 

sandstone immediately above the coal zone shows prominent crossbedding, giving evidence of shore conditions and strong currents. 

Only carbonaceous shale could be found at the coal horizon along 

the west side of Hound Creek in T. 15N.,R.2E., and in the southern 

part of T. 16 N., R. 2 E. The only coal observed more than 6 or 8 

inches in thickness occurs in two prospects on Elk Creek.

In the area along Elk Creek the Northern Pacific Railway Co. 

prospected for coal in 1905, but most of the openings have since 

caved. That this company found no coal which it considered of 

economic value is indicated by the fact that the land was offered 

for sale as agricultural land. There are two prospects which were open 

at the time the field examination was made, however, one in sec. 15, 

T. 14 N., R0 1 E., and the other in sec. 3, T. 13 N., R. 1 E. The one 

in sec. 15 was open 40 feet down a dip of 47° S. The following section 

was measured here:

Section of coal bed in sec. If, T. 14 N., R. 1 E.

Ft. in. 

Shale..................................................... 2 4

Coal, fair quality...................................... 1 9

Shale, carbonaceous....................................... 2 8

Coal, very impure..................................... 6 10

Shale, carbonaceous. 

13 7

i Fisher, C. A., op. cit., pp. 66-67.
230 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1916, PART II.

East of this prospect the coal bed approaches a fault and increases 

in dip until an angle of 74° is reached. Then for a short distance the 

coal bed is cut out, but it reappears and the heavy sandstone above 

it is traceable around the synclinal trough in sec. 25.

Near the head of Elk Creek, in sec. 3, T. 13 N., R. 1 E., there are 

two prospects, one on each side of the stream. The one on the west 

side was full of water at the time of visit and so could not be entered, 

but the one on the east side was open for a distance of about 60 feet, 

and the coal was found to be 7 feet 6 inches thick with roof and floor 

not exposed. The coal is much crushed, however, and dips 61° S. 

The coal undoubtedly terminates on the east at the igneous mass 

in sec. 2. West of the prospect the structure is very complex and 

the rocks are largely covered to the foot of a mesa of igneous rock. 

Whether the coal is present south and west of this place the writer, 

was not able to learn, but the heavy sandstone that comes near the 

coal horizon was observed at two or three places high in the hills.

CHARACTER..

No samples for analysis were taken in the Hound Creek district, 

because only weathered coal could be obtained. However, a sample 

was taken by the writer from the Gibson mine, on Hound Creek, 

just north of the area, and according to the Pishel mortar test 1 

some of it possesses coking properties but other pieces do not.

The mortar test was. worked out by Pishel while engaged in the 

study of the physical properties of coal in the United States Geological Survey. He found that coals known to possess coking qualities 

adhered to the sides of the mortar and to the pestle on being pulverized, whereas noncoking coals adhered very slightly or not at all. 

Sufficient experiments have not yet been made to prove that this test 

is absolutely reliable, yet it is probably more certain than the ordinary 

field method of testing in a pit.

Fisher 2 states that "Certain benches of the coal of the Great Falls 

field possess coking properties. Formerly a number of coke ovens 

were operated by the Anaconda Copper Mining Co. at Belt. The 

separation of coking from noncoking coal, however, was too expensive to render the work profitable, and they were abandoned."

As the sample above referred to was obtained in the ordinary manner, by making a cut entirely across the bed, the fact that some pieces 

of this sample show coking properties and other pieces do not would 

indicate that the coal bed here, as in the Belt district, contains benches 

which might be coked. Samples collected by Fisher 3 in 1906 from

i Pishel, M. A., A practical test for coking coals: Econ. Geology, vol. 3, No. 4, pp. 265-275, June-July, 1908. 

a Fisher, C. A., op. cit., pp. 80-81. 

3 Idem, p. 80.
GEOLOGY OF HOUND GREEK DISTRICT, MONT. 231

mines near the mouth of Hound Creek show the coal to average about 

10,500 British thermal units, and from the analysis and physical 

properties he states that the coal is medium-grade bituminous.

 FUTURE DEVELOPMENT.

.It is highly improbable that the Hound Creek district will ever be 

an important coal-mining center because the coal probably does not 

occur in sufficient quantity and is too impure to justify the establishment of a plant to mine coal for shipment, even if transportation 

facilities were available. At present the nearest railroad is the 

Helena-Great Falls branch of the Great Northern Railway, which is 

about 20 miles to the northwest. The known amount of coal will 

certainly not warrant the extension of the Great Northern Railway 

into the Hound Creek district on that account alone, and the other 

resources of the district are too meager to bring about in the near 

future a betterment of transportation facilities. Development of the 

coal, therefore, will probably be dependent on purely local demand.