The Fort Union Formation of Montana and Adjacent Areas

Home , Bull Mountains, Fort Union Formation, Horn Mountains, Lance Formation, Wasatch Formation

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5-15-1948 The orF t Union Formation of Montana and Adjacent Areas Charles Christman

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Recommended Citation Christman, Charles, "The orF t Union Formation of Montana and Adjacent Areas" (1948). Bachelors Theses and Reports, 1928 - 1970. 268. http://digitalcommons.mtech.edu/bach_theses/268

This Bachelors Thesis is brought to you for free and open access by the Student Scholarship at Digital Commons @ Montana Tech. It has been accepted for inclusion in Bachelors Theses and Reports, 1928 - 1970 by an authorized administrator of Digital Commons @ Montana Tech. For more information, please contact [email protected]. --THE FORT trmon 1roRrv:ATION -OF MON~~TA ~ ADJAC~~ AREaS

by Charles Christman

A thesis submitted to the Departme~t of Geology ir partial fulfillment of the requireme~ts for the Degree of Bachelor of Science i~ Geological E~g1~eer1~g

Montana School of Mines Butte, Montana May 15, 1948 THE ~ UNION FORMATION OF

MONTANA ~ ADJACENT AREAS

by Charles Christman

A thesis submitted to the Department of Geology in partial fulfillment of the requirements for the Degree of Bachelor of Science in Geological Engineering

19713

Montana SoIwo.1.of Mines But te, Montana May 15, 1948

) COl\1TEN"TS :ta.ge

Introduction • • • • • • • • • • • • • • • • • • • • 1 Fort Unior. Stratigraphy. • • • • • • • • • • • • • 3 Members. • • • • • • • • • • • • • • • • • • 3 Lebo Shale. • • • • • • • • • • • • 3 River. • 4 Tongue • • • • • • • ·, • • Kingsbury Conglomerate. • • • • • • • 4 Serrt Lne L Butte. ·.. • • • • • • • • • 5 Ludlow and Ca'nnonball 0 • • • • • • • 5

Equivalent Formations. • 0 • • • • • • • • • 7 ConditioY'ls of Deposition • • • • • • • • • • 8 Lithology of the Sediments • • • • • • • • • 9 General Stratigraphy of the Area • • • • • • 12

Discussion of the Isopach Map. • • • • • • • 13 Economic Geology • • • • • • • • • • • • • • 15 Coal. • • • • • • • • • • • • • • • • 15 Clay. • • • • • • • • • • • • • • • • 16

Water • • • • • • • • o • 0 • • • • • 16 Oil and Gas • • • o • • • • • • • • • 17

o • o • 17 Summary o • • • • • • • • • • • • • • • • • Bibliography • • • • • • • • • • • • • • • • • • • • 19 ILWsTRATIONS

Plate l--~~p showing outcrop area of the Opposite

Fort Union formation in Mon.tana • • • • Page 2 Plate 2--NAP showing drainage pattern in Opposite Eastern. Montana a"d Northern Wyomi~g. • Fage 16 Plate 3--Modified Isopach Map of the Inside Fort Union Formation in Montana Back

and Adjace!'1tAreas •••••••• 0 • Cover

Fig. l---Correlation chart of Upper Cretaceous

and Tertiary Formations •• • • • • • • • Fage 6 --THE FORT ~ITON FORMATION -OF MO!l.TTANA m. ADJ ACll.'t\TT AREAS

by Charles Christman

INTRODUCTION The Fort Union formation is one of the most important and best known geologic formations of the northern Great Plains, and is found lying almost horizontal at the surface over large areas in this region. (See Plate I). With the Fort Union and the associated Wasatch formation the conformable series of sediments stops, and the formations representing the later history of the region are surficial deposits of limited extent laid down during favorable inter-erosional periods. The Cypress EllIs gravels and the Flaxville gravels which cap a series of plateaus upon eroded surfaces of the Fbrt Union, lance and Bearpaw formations are typical of these later deposits in Montana. Almost the entire eastern half of Montana is underlain by beds of good lignite and coal, and about 90% of the total tonnage of these fuels is found in the Fort Union formation, making it by far the most important coal bearing horizon in this region. The only known locality where Fort Union rocks in Montana do not contain important workable coal is in Teton County in the northwest part of the State where only a few very thin and scattered coal

-1- Plate 1

S ASK A T 0 HEW A N B. C. ALB E R T A

,,0 Havre

e Conrad

o Lewlstown

o Harlowt

°Butte G o oColumbus

, it!' t '

nnie OUTC RO P AREA 0 F THE F '1'. U N ION F 0 R- MATION IN MONTANA

IDAHO WYOMING MONTANA SCHOOL OF MINES 1948

20 /0 0 2" 4J btl ~o~le in Miles! seams occur. In order that the depth of potential oil bearing horizons may be accurately predicted it is important to the petroleum geologist to have an estimate of the thickness of the strata to be penetrated. The construction of the modified isopach map of the Fort Union formation was ehosen as the subject for an undergraduate thesis largely as an aid in making these predictions. HOwever, in this report the writer has speculated on the original thicknesses of this formation as shown on the accompany- ing iso pach , The area under consideration includes all the state of Montana, the northern part of Vfyoming and the western half of North Dakotao The information upon which the iSOPach map is based was obtained from various reports of State and Federal surveys and from articles in tech- nical journals. In construction of the isopach map, no account was taken of the irregularities in thickness caused by erosion and therefore the map must be considered as so modified. The suggestions and help offered by Dr. E. S. Ferry of the Department of Geology of Montana School of Mines have greatly aided the writer in preparing this report, and the writer wishes to express his gratitude and appre- Ciation.

-2- ,i I

l!URT UNION STRATIGRAPHY

The Fort Union formation receives its name from a former military post on the Missouri River near Buford, North Dakota, about three miles from the Montana state line. It was originally described by Meek and Hayden in 18tH who stated that it "occupies the country around Fbrt Union extending north into the British possessions to unknown distances; also, southward to Ft. Clark". MOre of the surface of eastern and central Montana is underlain by Fort Union strata than by any other formation and it covers approximately 25,000 square miles, or about one-quarter of the p1l;in's ar-ea of the State, and eighteen counties of eastern and oentra1 Montana have rooks of the Fbrt Union formation within their boundaries. The main deposit is found in the eastern part of the State, but it also overlies about 1,200 square miles in central Montana in the area known as the Bull Mountains in Musselshell and Rosebud Counties and also is found in smaller amounts in Carbon and Sweet Grass Counties.

Members Lebo Shale:

This member was first described by R. W. Stone, from its occurence in the vicinity of the Orazy Mountains and the name "Lebo Andesitic member of the Fort Union formation" was first used by stone and Calvert in 1910. How-

-3- ever the Lebo shale member is described in preliminary reports by Woolsey who referred to the member as "Beds on Dean Creek" and by Richards who referred to the Lebo as "eomber- colored beds ft 0 It is typically developed on Lebo Creek, Montana, northeast of the Crazy Mountains and consists of a tongue of andesitic rocks resembling the Livingston formation and the Lennep·sandstone. Tongue River: The Tongue .River member contains the chief coal bearing rocks in Montana and in some localities, as for example south of Roundup, as many as twenty-six differ- ent coal beds have been mapped within it. It is well exposed along the Tongue River between Carneyville, V'lyoming,and Brandenberg, Montana, and derives its name from this river. Good exposures may also be found a- long the Yellowstone River between Glendive, Montana and BUford, Jorth Dakota, and in the Missouri River Val- ley above Fort Clark, North Dakota. Kingsbury Conglomerate: The Kingsbury conglomerate member is one of the . , lesser divisions of the Fort Union formation and is fOund only in a limited area in northern Wyoming. It takes its name from Kingsbury Ridge, a prominent topo- graphic feature about six miles southwest of Buffalo and is one of the most conspicuous and prominently exposed rock divisions in the Buffalo region.

-4- Sentinel Butte:

The Sentinel Butte shale mem~er derives its name. from Senti"e1 Butte, North Dakota, where it is ty1;>ica11y exposed. It resembles the Hell Creek member of the Lance formation, but is found above the Tongue River member of the Fort Union formation. This member is characterized by extel'1sivebeds of bentonite and bentonitic clays and does not contain nearly as many coal seams within it as the underlying Tongue River member. At Sentinel Butte, the member is 500 feet thick. How- ever, in North Dakota the Sentinel Butte member is considered to be the lower unit of the Wasatch formation in this State (Ref. 32, p. 1414). LUdlow and Cannonball: The Cannonball and Ludlow members are interfingering con.temporan.eous sediments of Fort Union and Lance times. The Cannonball member becomes gradually thinner towards the west and is not round as far west as the Montana- Dakota state line. It consists of greenish marine sa"'dsto1'lesand dark gray shales and attains a thickness of 300 feet. The Cannonball member is typically exposed in the bluffs of the Cannonball river in Morton County, North Dakota and numerous round concretion.s connnonly known as "cannonballs U which accumulate upon' weathered surfaces of the member probably account for this member's name. TowardS the west the Cannonball merges into, and

-5- overlies the non-marine Indlow member. The Ludlow member derives its name from its type locality, Ludlow, South Dakota, and here consists of 350 feet of loosely consolidated butf and cream-colored calcareous sandstone and shale with interbedded lignite (Ref. 26, p. 528). The numerous beds of lignite dis- tinguish the ludlow from the Cannon.ball and the member contains the majority 01" the lignite of South Dakota. The Ludlo,,,varies in thickness from 40 teet near Breien., North Dakota, to 250 feet near Marmarth, North Dakota (Ref. 32, p. 1417).

Period Epoch Forma- E.Central Mont.-Dak. N.E.Wyo. tion &, S.E.Mont. state Line , , , , , t , Eocene,' Wasatoh, Wasatch , Wasatch ,Wasatch , , , , t , ,. , , , , Sen.tin.el Sentinel ,Kingsbury , , , Butte Butte ,conglom. , t , , , ~ , ttl Pal- , Fort , , , ori ,, .p eocene, Union , , , ~ , , Tongue , TO'l1gue ,Tongue , , Q). , , , River , River ,River, , E-i , ,. , , , , ~! , , , , , , , , Lebo , Lebo ,lebo' , , , Lud-, , , low , , , • , , Tullock , .p , , , , Tullock ,Tul- , Q) 1"G~l- rance ~ , an t , ,lock , 0 , , , ll Creek , Hell Creek , , Hr , p• , , , , , , , Colgate SS ,

Fig. 1 Correlation chart of Upper Cretaceous and Tertiary formations. Equivalent Formations In most localities the Fort Union formation which is lowermost Tertiary or Paleocene in age, constitutes the Upper few hundred feet of the sedimentary series, and only in a few scattered districts are younger rocks found above the Fort Union. In the southeastern corner of Montana small areas of chalk-like clays and sands of the White River formation are found deposited on top of the Fort Union and in northeastern Montana the Flaxville gravel which is composed of gravel, clay, volcanic ash and mud, is found capping a series of plateaus upon e- roded surfaces of the Fort Union and other formations. Near the Wyoming state line southeast of Billings the Wasatch formation overlies the Fort Union. The Lebo strata in eastern Montana are the stratagraphic equivalent of the upper part of the Livingston formation, which at the type locality Livingston, Montana, is in excess of 1400 feet in thickness and represents nearly the whole of the Montan.a group, the Lanoe fonnation and the lower part of the Fbrt Union. Other stratagraphic equivalents of the Fort Union formation are: the Ludlow formation in northeastenn Wyoming, eastern Montana and western North Dakota, the Reece formation in the Cooke City-Gardiner region, the SPhinx Oonglomerate near Ennis, Montana, the Torregon formation in Mexioo, and the Thanetion formation in Western

-7- Europe. Conditions of Deposition Sedimentation in the Rocky Mountain region was continuous and uninterrupted from the beginning of Cretaceous Lance to and through the Tertiary Fort Union, and consequently the beds of the Fort Union formation frequently closely resemble those of the underlying Lance formation (Refo 21, p. 33l). Nearly all the beds of the Fort Union formation are continental deposits consisting of shale and fine- grain sandstone, occasionally alternating in some areas with thin beds of calcareous sandstone that may be fos- sil-bearing. The formation has resulted from sediments derived from the erosion of the Rocky Mountains and deposited on a coastal plain by rivers flowing a- way from the Rocky MOuntain region. Changing conditions of deposition were prevalent during Fort Union time and occasionally swamps favorable to the accumulation of vegetable matter were formed. Sooner or later, however, these swamps were buried by sand, mud and silt, and new swamps formed elsewhere. These variable conditions led to the deposition of beds that are very irregular in their distribution and extent, just as one might e-xpect of river deposits on a flood plain.

-8- Lithology of the Sediments As a whole, the Fort Union formation consists of a variable thickness of yellowish, grayish sand and sandstone, interbedded with gray clays, shales and coal • .A noticeable feature of the formation is the very irregular character of the beds, which often change abruptly in a horizontal direction. Clastic deposits predomi- nate, but at several places in the upper portion of the formation thin beds of non-marine, buff limestone, one to three feet in thickness, occur. The limestone is generally fine in texture resembling lithographic limestone and consequently preserves excellent impressions of leaves of plants of the formation period. Fort Union beds contain a flora of over four hundred species and a fauna comprising both vertebrates and inverte- brates, however, vertebrate fossils are rarely found. Leaves from deciduous broad-leaved trees very similar to present existing species are the most common forms met with.

Generally the rocks of the Fort Union formation are classified into two divisons:· the lower gray beds known as the Lebo shale member, and the upper yellow beds which are known as the Tongue River member. How- eVer, two other members, the Kin.gsbury Conglomerate and the Sentinel Butte member are also recognized. The Lebo shale member consists of dark grey, br-own and black shale with occasional beds of light gray and

-9- yellow sandstone and is often bentonitic. In the west, the member grades into the Livingston formation which is composed of andesitic detridal and tuffaceous material. In these western exposures, the member is generally referred to as the Lebo andesitic member of the Fort Union rormat ton , The presence of this andesitic or volcanic material in the Lebo is still evident as far east as Forsyth, l~ntana, but in it's eastern exposures, the member consists principally of dark clays and shales and is appropriately called the Lebo shale member within these eastern areas. Some of the beds, especially those composed of sandstonel are fairly resistent and tend to form rimrocks; but the member as a whole is soft and suffers rapid erosion. In some areas, the Lebo is characterized by beds that carry brown ttironstone" concretions in great abundance. They are composed essentially of iron carbonate but upon weathering are converted into brown iron oxide. These nodules, which range in size from one-quarter inch up to one foot in diameter, when released by the weathering of the enclosing shale, slump down and give the surface a "coffee grain" appearance. In some areas, the Lebo member is strikingly dif- ferent from the strata above and below and it is easily

distinguished from these sedimentso It is a mapable

-10- unit, and is commonly shown on geologic maps. In other areas, however, nhe Lebo grades upwards into \ a transition zone of sandy shale and is separated \ . only with difficulty from the overlY1ng Tongue River member. In western North Dakota this transitional phase may be designated as the Ludlow lignite member. The beds of the Tongue River member consist largely of impure arkosic sandstone. In places, they are interbedded with gray to black shale and with numerous thick coal seams. Generally, the sandstones are loosely cemented with clay, so that the beds weather readily. Occasionally, however, the sandstones are so firmly cemented that massive layers may resist erosion and form ridges and escarpments. Porosity in the sandstone differs with the amount of cementation and_with the purity of the sand. In some very impure sands, porosity may be less than eight per cent, whereas in some ~ure sandstones it may reach thirty per cent. An average porosity would probably be between fifteen and twenty per cent. As stated before, a few thin beds of limestone also occur in this member. Near Buffalo, Wyoming, the Kingsbury Conglomerate is Considered as a member of the Fort Union formation. The Conglomerate is composed of water-rounded gravel and boulders derived from older sedimentary rocks of the adjacent mountains and includes some granite derived

-11- from the core of the range. The conglomeratic strata aregen,erally thick and massive and are interbedded with finer-grained uniformly-bedded layers of sandstone and shale, greenish gray in color. This member is considered as a delta or alluvial fan deposit and is found only within a very limited area. Above the Tongue River member in western North Dakota, there is a bed of dark hued sandy shale and clay- ey sandstone which upon weathering forms an adobe soil. This member is named the Sentinel Butte shale member and is limited mainly to western North Dakota, though a few isolated occurrences have been reported in Montana. General Stratigraphy of the Area

The Fort Union formation covers a vast area east of the Rocky Mountains, stretching from Vlryomingto the Arctic Ocean and the valley of the McKenzie River and including several Canadian provinces, much of western North Dakota, eastern and central Montana, northwestern South Dakota and northern Wyoming. Naturally, in such a large area of terrestrial sediments one would expect to find an infinite variety of topographical expressions. A brief resume of the Fort Union area in Montana follows. The Fort Union region in eastern Montana and western North Dakota is a broad plain of nearly horizontal rocks, characterized by an extensive "bad land" topography a-

-12- long the larger streamso A very conspicuous feature of the region is the red hills, benches, ridges and buttes that have been heated by burning coal beds. This heat has been intense enough to burn the overlying clays to a red or salmon pink color, and in many places to completely fuse them to slaglike masses. The beds of clinkers formed by the burning coal may attain a thickness of forty feet in some areas and can often be traced for long distances.

Discussion of Isopach Map The iso:pa.chmap of the Fort Union formatioTl shows generally a progressive thinning of strata toward the easto This condition might well be expected, as the Fort UTlion sediments were, in all probability, derived from the Rocky Mountains on the west and deposited on a piedmont plain by eastward flowing rivers. However, a more careful inspectlon of the isopach map reveals several outstanding features. First, there are two centers of major uplift which tend to disrupt and complicat.e this general pattern of thinnil1g towards the easto The Sweet Grass arch in north central Montana, and the Black HiJ!ls uplift in South Dakota are two posi- tive areas where no Fort Union strata are found, It is Possible, or even probable, that the Fort Union formation was Once continuous over these areas and now has been re-

-13- moved by erosion. If this were the case, it would place the age of these two uplifts as post Paleocen •• However, at present definite data are lacking which would confirm or deny this hypotheses, and until further geological evidence regarding the age of these uplifts is brought to light, it may be presumed that the Fort Union formation was never deposited in these areas. Such is not the case, however, in Wyoming where the isopach map has been constructed to show deposition· of FOrt Union sediments across the area of the Big Horn and Pryor Mountains. Of course, today this formation has been completely removed by erosion in this area, but there is good reason to believe that it was once quite thick.

As evidence, the fact that Fort Union strata bend Upward at angles of twenty and thirty degrees on the flanks of these mountains would show that this formation was involved in the folding, and is therefore older than the Uplift. Second, the isopach map reveals a thickness distribution pattern that otherwise is extremely difficult to aocount for with an easterly drainage from the moun~ tains to the west. The distribution of these sediments is logically explained by postulating a drainage pattern northeast into HUdson Bay during Fort Union time. That this has been the case, is supported by the present drainage pat-

-14- tern of the Tongue, Little Big HOrn, Fowder, Little Missouri, Big Horn and Yellowstone Rivers, all flowing in a northeasterly direction. (See Plate 2). Of course, with the coming of Pleistocene glaciation, the no.,rtherncourses of these and other rivers were altered to the present pattern. The deep canyons formed by the Little Big Horn, Big HOrn and Tongue Rivers in the Big Horn and Pryor mountain ranges of Montana, and the Owl Creek Mountains of Wyoming give evidence that these are all antecedent streams, and therefore the drainage pattern that existed during Fort Union time in this region was essentially the same as now, but had its outlet to the northeast.

Economic Geology -Coal About ninety per cent of .the total amount of lignite and coal found in Montana occurs in the Fort Union formation, and practically everywhere in eastern Montana and western North Dakota this formation contain beds of good lignite. The lignite grades from the ordinary brown and black, easily slacking varieties to the dark- er, heavier sUbbituminous varieties of coal. The beds range in thickness from an inch and less to forty feet or more, and beds eight and ten feet thick are common. MOst of the seams are nearly horizontal, and in numer- ours places are not deeply buried, and are suitable for

-15- stripping methods of mining. The coal beds are present trom top to bottom of the formation, and are not confin- ed to any particular horizon or horizons. Montana has a reserve of 340,000,000,000 short tons of lignite and subbituminous coal in the Fort Union tormation. Glal

OVer a large area in southwestern North Dakota, the Fort Union formation contains beds of white, very pure plastic clays suitable for manufaoture of oeramic products. These clay beds lie about 600 feet above the .base of the Fort Union and :attain a maximum thickness of 150 feet. Elsewhere good clay deposits are rarely found in the Fort Union formation. \fater

Wells penetrating sandstone and coal beds of the Fort Union formation, it not located too 'near the out- orop, nearly always yield, water. The quality is variable, and the mineral content often reaches prohibi- tive values, especially in water comi~g'from the Lebo member. Water found in the coal seams is usually rel- atively pure, however. Since, in most loc~lities the Fort Union tormation constitutes the upper few hundred feet of the sedimentary series, few flowing wells are I found in the formation. The Tongue River member with its large number of sandstone beds constitutes a good reservoir for water. The sandstone water is usually mineralized however,

-16- but few wells yield poor water. Shallow wells, seldom exceeding 300 feet in depth, usually obtain adequate supplies for domestic use. The Lebo member is a poor source of water. Though some springs occur, much of the water is highly mineralized, especially with iron, and is therefore unfit for domestic purposes. Oil and Gas The Fort Union formation is not known to be a reservoir for commercial amounts of either gas or oil. The formation is of interest to the oil and gas industry only in that it is at the surface throughout most of eastern Montana and western North Dakota, and test wells penetrating to deeper and more favorable horizons must pass through the Fort Union formation.

Sumnary Overlying the Lance formation of uppermost Creta- ceous age is the Fort Union formation of Paleocene age. Since this formation is the youngest of the sedimentary series common throughout the area studied, it occurs almost entirely in great structural basins, and only where uplift has taken place, or where rivers have cut deep valleys, has it been removed by erosion. The formation, which is composed almost entirely of continental clastic deposits, has resulted from· the deposition of sediments

-17- on a coastal plain by northeastward flowing rivers. It covers a vast area stretching from central Wyoming on the south to Alaska on the north, and from central Montana on the west to Opheim, North Dakota on the east. Attention is called to the probable decrease in thickness in a northeastward direction, as shown by the modified isopach map, and also to the postalated drainage during Fort Union time northeastward toward HUdson Bay. The Fort Union formation everywhere contains numerous beds of lignite or subbituminous coal, and has 90 per cent of MOntana's 380,000,000,000 tons of coal within its formational boundaries. Besides carrying the principal lignite beds of the region, the formation also contains scattered beds of shale and clay suitable for the manufacture of brick and other clay products. No oil or gas has been found in the Fort Union formation, and the possibility that some will be found in it in the fUture is slight.

-18- BIBLIOGRAPHY

1. Baker, A. A., The Northward Extension of Sheridan Coal Field, mntana; U. S. Geol. Survey Bull. 806 B,

1929, p , 15-67. 2. Barnum-Brown, Cretacious-Eocene Correlation in New Mexico, Wyo., Mont., Alberta; Bull. of the Geo.

Soco of Amer., Vol. 25, 1914, pp. 335-380. 3. Baur, C. M., Lignite in the Vicinity of Plentywood and Scobey, Sheridan County, Montana; U. S. Geol. Sur. Bull. 541, 1914, pp. 293-315. 4. Baur, C. M., The Ekalaka Lignite Field, Southeastern Mont.; U. S. Geolo Sur. Bull. 751 f, 1925, p. 231-267. 5. Beekly, A. L., The Culbertson Lignite Field, Valley County, MOntana; U. S. Geol. Sur. Bull. 471, 1912,

pp. 319-358.

60 Bowen, C. F., Gradation from Continental to Marine Conditions of Deposition in Central Montana during Eagle and Judith River Epochs; U. S. Geol. Sur. Prof. Raper 125, 1921, pp. 11-21. 7. Calvert, W. R., The Livingston and Trail Creek Coal Fields, Rark, Gallatin and Sweet Grass Counties, Montana; U. S. Geol. Sur. Bull. 471, 1912, pp. 384-405.

8. Calvert, w. R., Geology of Certain Lignite Fields in Eastern Montana; U. S. Geol. Sur. Bull. 471, 1910,

pp. 187-201.

-19- 9. Calvert, W. R., and others, Geology of the Standing Rock and Cheyenne River Indian Reservati.ons, N. and S. Dakota; U. S. Geol. Sur. Bull. 575, 1914. 10. Collier, A. J. and Smith, C. D., The Miles City Coal Field, Montana; U. S. Geol. Sur. Bull. 341, 1909, p. 36-61. 11. Collier, A. J., The Scobey Lignite Field, Valley, Daniels and Sheridan Counties, Montana; U. S. Geol.

Sur. Bull. 751 e, 1925, pp. 152-230. 12. Darton, N. H., Geology of the Big Horn Mountains; U. S. Geol. Sur. Prof. Raper 51, 1906. 13. Dobbin, C. E., MQntana Cool Fields, U. S. Bur. of Mines, Tech. Raper 520, 1932. 14. Dobbin, C. E., The Forsyth Coal Field, Rosebud, Treasure and Big ~rn Counties, Montana, U. S. Geol. Sur. Bull 812 a, 1930, pp. 1-55. 15. Gale, H. S. and Wegemann, C. H., The Buffalo Coal Fleld, Wyo. U. S. Geol. Sur. Bull. 381, 1908,

pp. 137-169. 16. Hancock, E. T., Geology and Oil and Gas Prospects of the Lake Basin Field, Montana; U. S. Geol. Sur. Bull. 691, 1918, pp. 101-147. 17. Hancock, E. T., Geology and Oil and Gas Prospects of the Huntley Field, Montana, U. S. Geol. Sur. Bull. 711,

1919, pp. 105-148.

-20-

MONTANA sc=oot O~ 1'1fJ":':3LmRAR1' BUTTE lB. Hancock, E. T., The New Salem Lignite Field, Morton County, N. Dak.; U. S. Geol. Sur. Bull. 726, 1922, pp. 1-39. 19. Herald, F. A., The Terry Lignite Field, Custer County, Montana; U. S. Geol. Sur. Bull. 471, 1912, pp. 227- 270. 20. Herald, F. A., The Williston Lignite Field, Williams County, N. Dak.; U. S. Geol. Sur. Bull. 531, 1913, pp. 91-157. 21. Knowlton, F. H. Cretaceous-Tert iary Boundary in. the Rocky MOuntain Region; Bull. of the Geol. Soc. of America, Vol. 25, 1914, pp. 325-340. 22. Leonard, A. G., The Cretaceous-Tertiary Formations of Western N. Dak. and Eastern MOntana; Journal of Geol., Vol. 19, 1911, pp. 507-547. 23. Leonard, A. G. and Smith, C. D., The Sentinel Butte Lignite Field, N. Dak. and Mont.; U. So Geol. Sur. Bull. 341, 1909, pp. 15-35. 24. Leonard, A. G. a~d Smith, C. D., The Coal Fields of' Dawson, Rosebud and Custer Counties, Montana; U. S. Geo1. Sur. Bull. 316, 1907, pp. 194-211. 25. IJ.oyd, E. R., The Cannonball River Lignite Field, Mort.on, Adams and Hett'inger Counties, N. Daks : U. S. Geo1. Sur. Bull. 541, 1912, pp. 243-291. 26. Lloyd, E. R. and Hares, C. J., The Cannonball Marine Member of the Lance Formation of N. and S. Dak. and

-21-

19713 Its Bearing on the Lance-laramie Problem; Jour. of Geol., Vol. 23, pp. 523-547. 27. Parker, F. W., The Richey-Lambert Coal Field, Rich- land and Dawson Count i_es, Mon.tana; U. S. Geo 1. Sur. Bull. 847 c, 1936, pp. 121-174. 28. Fierce, W. G., The Roseb~d Coal Field, Rosebud and Custer Counties, Montana; U. S. Geo1. Bull. 847 b, 1936, pp. 43-120. 29. Rogers, G. S., and Wallace, Lee, The Tullock Creek Coal Field; U. S. Geol. Sur. Bull. 749, 1923. 30. Rogers, G. S. and Wallace, Lee, The Little Sheep Mountain. Coal Field, Dawson, Custer and Rosebud Counties, Montana; U. S. Geol. Sur. Bull. 531, 1913, pp. 159-227. 31. Rogers, G. S. and Wa11aoe, Lee, Geology and Coal Resources of the Area Southwest of Custer, Yellow- stone and Big Horn Counties, Mont.; U. S. Geo1. Sur. Bull. 541, 1914, pp. 316-328. 32. Seager, O. A. Et.A1., Stratigraphy of N. Dak.; Bull. of the Am. As. of Pet. Geologists, Vol. 26, No.8, Aug., 1942, pp. 1414. 33. Stanton, T. W., Boundary Between Creta.ceous and Tertiary in N. America as Indicated by Stratigraphy and Invertibrate Faunas; Bull. of the Geol. Soc. ·of America, Vol. 25, 1914, pp. 341-354. 34. Stebinger, Eugene, The Sidney Lignite Field, Dawson

-22- County, Mont.; U. S. Geol. Sur. Bull. 471" 1912 ,.. pp. 284-318. 35. Stebinger, Eugene, The Coal Fields of MOntI; Trans. of the A. I. M. E., Bull. 81, 1913, pp. 2329-2359. 35. Stone,H. W., and Lupton, C. T., The Powder River Coal Field, Wyo. Adjacent to the Burlington Railroad; U. S. Geol. Sur. Bull. 381, 1910, pp. 115-136. 37. Stone, R. W., and Calvert, W. R., Stratigraphic Relations of the Livingston Formation, Montana; Economic Geology, Vol. 5, 1910, pp. 551-557, 552-569, 741-754. 38. Taff,. J. A., The Sheridan Coal Field, Wyo. U. S. Geol. Sur. Bull. 341, 1909, pp. 123-150. 39. Thom Jr., W. T., and Dobbin, C. E., The Boplar- Wolf Point Lignite Field, Rich,and, McCone and Garfield Counties, MOnt.; U. S. GeQl. Sur. Bull. 40. Thom Jr., W. T., and Dobbin, C. E., Stratigraphy of Cretaceous-Eocene Transition Beds in Eastern MOnta~a and the Dakotas; Bull. of the Geol. Soc. of Amer., Vol. 35, Sept. 30, 1924, pp. 481-505. 41. Wegemann, C. H., The Sussex Coal Field, Johnson, Natrona and Converse Counties, Wyo.; U. S. Geol. Sur. Bull. 471, 1912, pp. 441-471. 42. Winchester, D. E., and Others, the Lignite Field of Northwestern South Dakota; U. S. Geo1. Sur. Bu1. 527, 1916.

-23- 43. Woodruff, E. G., The Red lodge Coal Field, Mont. U. S. Geol. Sur. Bull. 341, 1909, pp. 92-107. 44. Woolsey, F. H., and others, The Bull Mountain Coal Field, Musse1lshell and Yellowstone qounties, Mont.; U. S. Geo1. Sur. Bull, 847, 1917.

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