DEI'AItTJI UNT <>! T11K I N T K It H) It

1!U L LET IN

TIN I TED STATES

GEOLOG 1C AL SIT RVE\r

TST o

T1IK PALEOXOUJ SEC'JT.ION IX THE V.KUMT'V OF 

TI1KKK I'OKKS, .MON'i'AXA

WASH I N (; TON

frOVKHXlMKN'r P K IX-Tl.N(r
LIBRARY CATALOGUE SLIPS.

United States. Department of the interior. (U. S. geological survey). 

Department of the interior \ \ Bulletin | of the | United 

States | geological survey | no. 110 | [Seal of the department] | 

Washington | government printing office | 1893

Second title: United States geological survey | J. W. Powell, 

director | | The | paleozoic section | in the | vicinity of Three 

Forks, Montana | by | Albert Charles Peale | with | petrograpMc 

notes | by | George Perldns Merrill | [Vignette] |

Washington | government printing office 11893

8<>. 66pp. 6 pi.

Peale (Albert Charles).

United States geological survey | J. W. Powell, director | | 

The | paleo/oic section | in the | vicinity of Three Forks, Montana | by | Albert Charles Peale | with | petrographic notes | by | 

George Perkins Merrill | [Vignette] |

Washington | government printing office | 1893

8°. 56pp. flpl.

[UNITED STATES. Department of the interior. (TJ. S. geological survey). 

Bulletin 110.]

United States geological survey | J. W. Powell, director | | 

The | paleozoic section | iu the | vicinity of Three Forks, Montana | by | Albert Charles Peale | with | petrographic notes | by | 

George Perkins Merrill | [Vignette] |

Washington | government printing office | 1893

8°. 56 pp. 6 pi.

[UNITED STATUS. Department of the interior. (V. S. geological survey).
A-DVERTISEMIKNT.

[Bulletin No. 110.]

The publications of the United States Geological Survey are issued in accordance with the statute 

approved March 3, 1879, which declares that 

'' T lie publications of the Geological Survey shall consist of the annual report of operations, geological 

and economic maps illustrating the resources and classification of the lands, and reports upon general 

and economic geology and paleontology. The annual report of operations of the Geological Survey 

shall accompany the annual report of the Secretary of the Interior. All special memoirs aud reports 

of said Survey shall be issued in uniform quarto series if deemed necessary by the Director, but otherwise in ordinary octavos. Three thousand copies of each shall be published for scientific exchanges 

and for sale at the price of publication; and all literary and cartographic materials received in exchange 

shidl be the property of the United States and form a part of the library of the organization; and the 

money resulting from the sale of such publications shall be covered into the Treasury of the United 

States."

On July 7, 1882, the following joint resolution, referring to all Govornnieut publications, was passed 

by Congress:

"That whenever any document or report shall be ordered printed by Congress, there shall be printed, 

11 addition to the number in each'case stated, the 'usual number' (734) of copies for binding and 

distribution among those entitled to receive them."

Except in those cases in which an extra number of any publication has been supplied to the Survey 

by special resolution of Congress or has been ordered by the Secretary of the Interior, this office has 

no copies for gratuitous distribution.

ANNUAL REPORTS.

I. Mrst Annual Report of the United States Geological Survey, by Clarence King. 1880. 8°. 79pp. 

1 map. A preliminary report describing plan of organization and publications.

II. Second Annual Report of the United States Geological Survey, 1880-'81, by J. "W. Powell. 1882. 

8°. Iv, 588 pp. 62 pi. 1 map.

in. Third Annual Report of the United States Geological Survey, 1881-'82, by J. W. Powell. 1883. 

8°. xviii, 564 pp. C7 pi. and maps.

IV. Fourth Annual Report of the United States Geological Survey, 1882-'83, by J. "VV. Powell. 1884. 

8°. xxxii, 473 pp. 85 pi. and maps.

V. Fifth Annual Report of the United States Geological Survey, 1883-'84, by J. W. Powell. 1885. 

8°. xxxvi, 4C9 pp. 58 pi. and maps.

VI. Sixth Annual Report of the United States Geological Survey, 1884-'85, by J. \V. Powell. 1885. 

8°. xxix, 570 pp. 65 pi. and maps.

* VII. Seventh Annual Report of the United States Geological Survey, 1885-'86, by J. W. Powell. 1888. 

8°. xx, 656pp. 71 pi. and maps.

VIII. Eighth Annual Report of the United States Geological Survey, 1886-'87, by J. W. Powell. ^ 889. 

8°. 2 pt. xix, 474, xii pp. 53 pi. and maps; 1 p. 1., 475-1063 pp. 54-76 pi. and maps.

IX. Ninth Annual Report of the United States Geological Survey, 1887-'88, by J. W. Powell, 1889. 

8°. xiii, 717 pp. 88 pi. and maps. 

X. Tenth Annual Report of the United States Geological Survey, 1888-'89, by J. W. Powell. .1.890. 

8°. 2pt. xv, 774pp. 98 pi. and maps; viii, 123 pp.

XI. Eleventh Annual Report of the United States Geological Survey, 1889-'90, by J. W. Powell. 1891. 

8°. 2pt. xv, 757 pp. 66 pi. and maps; ix, 351 pp. 30 pi.

XII. Twelfth Annual Report of the United States Geological Survey, 1890-'91. by J. "W. Powell. 1891. 

8°. 2 pt. xiii, 675 pp. 53 pi. and maps; xviii, 576 pp. 146 pi. and maps.

XIII. Thirteenth Annual Report of the United States Geological Survey, 1891-'92, by J. W. Powell, 

1893. 8°. 3 pt.

MONOGRAPHS.

I. Lalco Bonneville, by Grove Karl Gilbert. 1890. 4°. xx, 438 pp. 5] pi. 1 map. Price $1.50.

II. Tertiary History of the Grand Canon District, with atlas, by Clarence E. Button, Capt. U. S. A. 

1882. 4°. xiv, 264 pp. 42 pi. aud atlas of 24 sheets folio. Price $10.00.

I
II ADVERTISEMENT.

III. Geology of the Corastock Lode and the Washoe District, with atlas, by George F. Beokcr. 1882. 

4°. xv, 422 pp. 7 pi. and atlas of 21 sheets folio. Price $11.00.

IV. Cotnstock Mining and Miners, by Eliot Lord. 1883. 4°. xiv, 451 pp. 3 pi. Price $1.50. 

o V. The Copper-Bearing Kocks of Lake Superior, by Eoland Duer Irving. 1883. 4°. xvi, 464 pp. 

151. 29 pi. aud maps. Price $1.85.

VI. Contributions to the Knowledge of the Older Mesozoic Flora of Virginia, by "William Morris 

Fontaine. 1883. 4°. xi, 144 pp. 541. 54 pi. Price $1.05.

VII. Silver-Lend Deposits of Eureka, Nevada, by Joseph Story Curtis. 1884. 4°. xiii, 200 pp. 16 

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VIII. Paleontology of the Eureka District, by Charles Doolittle Walcott. 1884. 4°. xiii, 298 pp. 

241. 24 pi. Price $1.10.

IX. Brachiopoda and Lamellibranchiata of the Earitan Clays and Greensand Marls of New Jersey, 

byKobertP. Whitfield. 1885. 4°. xx, 338 pp. 35 pi. 1 map. Price $1.15.

X. Dinocerata. A Monograph of an Extinct Order of Gigantic Mammals, by Othniel Charles Marsh. 

188G. 4°. xviii, 243 pp. 561. 56 pi. Price $2.70.

XI. Geological History of Lake Lahontan, a Quaternary Lake of Northwestern Nevada, by Israel 

CookBtissell. 1885. 4°. xiv, 288 pp. 46 pi. and maps. Price $1.75.

XII. Geology and Mining Industry of Leadville, Colorado, with atlas, by Samuel Franklin Emmous. 

18SC. 4°. xxix, 770 pp. 45 pi. and atlas of 35 sheets folio. Price $8.40.

XHL Geology of the Quicksilver Deposits of the Pacific Slope, with atlas, by George F. Becker, 

1888. 4°. xix, 486 pp. 7 pi. and atlas of 14 sheets folio. Price $2.00.

XIV. Fossil Fishes and Fossil Plants of the Triassic Eock.s of New Jersey and the Connecticut Valley, by John S. Newberry. 1888. 4°. xiv, 152pp. 26 pi. Price $1.00.

XV. The Potomac or Younger Mesozoic Flora, by "William Morris Fontaine. 1889. 4°. xiv, 377 

pp. 180 pi. Text and plates bound separately. Price $2.50.

XVI. The Paleozoic Fishes of North America, by John Strong Newberry. 1889. 4°. 310pp. 53 pi. 

Price $1.00.

XVII. The Flora of the Dakota Group, a posthumous work, by Leo Lesquereux. Edited by F. H. 

Knowlton. 1891. 4°. 400pp. 66 pi. Price $1.10.

XVIII. Gasteropoda and Cephalopoda of the Earitan Clays and Greensand Marls of New Jersey, 

byEobertP. Whitfield. 1891. 4°. 402pp. 50 pi. Price $1.00.

XIX. The Penokee'Iron-Bearing Series of Northern "Wisconsin.and Michigan, by Eoland D. Irving 

and C. E. Van Hise. 1892, 4°. xix, 534pp. 37 pi.

XX. Geology of the Eureka District, Nevada, with atlas, by Arnold Hague. 1892. 4°. 419pp. 8 pi. 

In press:

XXI. The Tertiary Ehynchophorous Coleoptera of North America, by Samuel Hubbard Scudder.

XXII. A Manual of Topographic Methods, by Henry Gannett, chief topographer.

XXIII. Geology of the Green Mountains in Massachusetts, by Eaphael Puiupelly, J. E. Wolff, 

T. Nelson Dale, and Bayard T. Putnani. 

In preparation:

 Mollusca and Crustacea of the Miocene Formations of New Jersey, by K. P. "Whitflold.

 Sauropoda, by 0. C. Marsh.

 Stegosauria, by 0. C. Marsh.

 Brontotheridse, by 0. G. Marsh.. " °

 Eeport on the Denver Coal Basin, by S. F. Emmons.

 Eeport on Silver Cliff and Ten-Mile Mining Districts, Colorado, -by S. F. Emmonj.

 The Glacial Lake Agassiz, by Warren Upham.

BULLETINS.

1. On Hypersthene-Andesite and on Triclinic Pyroxene in Augitic Rocks, by Whitman Cross, with a 

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2. Gold and Silver Conversion Tables, giving the coining values of troy ounces of line metal, etc., computed by Albert Williams, jr. 1883. 8°. 8pp. Price 5 cents.

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5. A Dictionary of Altitudes in the United States, compiled by Henry Gannett. 1884. 8°. 325 pp. 

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6. Elevations in the Dominion of Canada, by J. W. Spencer. 1884. 8°. 43 pp. Price 5 cents.

 7. Mapoteca Geologica Americana. A Catalogue of Geological Maps of America (North and South), 

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"8. On Secondary Enlargements of Mineral Fragments in Certain Eocks, by'E.'D. Irving arid'C.B. 

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9. A report of work done in the Washington Laboratory during the fiscal year 1883-'84. F. W. Clarke, 

el) iof chemist. T. M. Chatard, assistant chemist. 1884. 8°. 40.pp. .Price5.centa.
ADVERTISEMENT. . Ill

10. On the Cambrian Faunas of North America. Preliminary studies, by Charles Doolittle Walcott. 

1884. 8°. 74pp. 10])1. Price 5 cents.

11. On the Quaternary and Recent Mollusca of the Great Basin; with Descriptions of New Forms. 

by R. Ells worth Call. Introduced by a sketch of the Quaternary Lakes of the Great Basin, by G. K. 

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12. A Crystallographies Study of the Thiiiolite of Lake Lahontan, by Edward S. Dana. 1884. 8°. 

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 14. The Electrical and Magnetic Properties of the Iron-Carburots, by. Carl Barns and Vincent 

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15. On the Mesozoic and Cenozoic Paleontology of California, by Charles A. White. 1885. 8°. 33pp. 

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16. On the Higher Devonian Faunas of Ontario County, New York, by John M. Clarke. 1885. 8°. 

86 pp. 3 pi. Price 5 cents.

17. On the Development of Crystallization in the Igneous Hocks of Washoe, Nevada, with notes on 

the Geology of the District, by Arnold Hague and Joseph P. Idduigs. 1885. 8°. 44 pp. Price 5 

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18. On Marine Eocene, Fresh-water Miocene, and other Fossil Mollusca of Western North America, 

by Charles A. White. 1885. 8°. 26 pp. 3 pi. Price 5 cents.

19. Notes on the Stratigraphy of California, by George F. Becker. 1885. 8°. 28pp. Price 5 cents.

20. Contributions to the Mineralogy of the Rocky Mountains, by Whitman Cross and W. F. Hillebrand. 1885. 8°. 114pp. 1 pi. Price 10 cents.

21. The Lignites of the Great Sioux Reservation. A Report on the Region between the Grand and 

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22. On New Cretaceous Fossils from California, by Charles A. White, 1885. 8°. 25 pp. 5 pi. 

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23. Observations on the Junction between the Eastern Sandstone'and the Keweenaw Series on Ke« 

wee.naw Point, Lake Superior, by R. D. Irving and T. C. Chamberliu. 1885. 8°. 124 pp. 17 pi. 

Price 15 cents.

24. List of Marine Mollusca, comprising the Quaternary Fossils and recent forms from American 

Localities between Cape Hatteras and Cape Roque, including the Bermudas, by William Healy Ball. 

1885. 8°. 336 pp. Price 25 cents.

25. The Present Technical Condition of the Steel Industry of tlie United States, by Phlueas Barncs. 

885. 8°. 85 pp. Price 10 cents.

26. Copper Smelting, by Henry M. Howe. 1885. 8°. 107 pp. Price 10 cents.

27. Report of work clone in the Division of Chemistry and Physics, mainly during the fiscal year

1884-'85. 1886. 8°. 80pp. Price 10 cents.

28. The Gahbros aud Associated Hornblende Rocks occurring in the neighborhood of Baltimore, 

Md., by George Hunting-ton Williams. 1886. 8°. 78pp. 4 pi. Price 10 cents.

21). On the Fresh-water Invertebrates of the North American Jurassic, by Charles A. White. 1886. 

8°. 41pp. 4 pi. Price 5 cents.

30. Second Contribution to the Studies on the Cambrian Faunas of North America, by Charles Doolittle Walcott. 1886. 8°. .369 pp. 33 pi. Price 25 cents.

31. Systematic Review of our Present Knowledge of Fossil Insects, including Myriapods and Arachnids, by Samuel Hubbard Scudder. 1886. 8°. 128 pp. Price 15 cents.

32. Lists and Analyses of the Mineral Springs of the United States; a Preliminary Study, by Albert 

C. Peale. 188C. 8°. 235 pp. Price 20 cents.

33. Notes on the Geology of Northern California, by J. S. Diller. 1886. 8°. 23 pp. Price 5 cents.

34. On the relation of the Laramio Molluscan Fauna to that of the succeeding Fresh-water Eocene 

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35. Physjcal Properties of the Iron-Carburets, by Carl Barus and Vincent Strouhal. 1886. 8°. 62 

pp. Price 10 cents.

36. Subsidence of Fine Solid Particles in Liquids, by Carl Barus. 1886. 8°. 58 pp. Price 10 cents.

37. Types of the Laramie Flora, by Lester F. Ward. 1887. 8°. 354 pp. 57 pi. Price 25 cents.

38. Peridotite of Elliott County, Kentucky, by J. S. Diller. 1887. 8°. 31 pp. 1 pi. Price 5 cents.

39. The Upper Beaches and Deltas of the Glacial Lake Agassiz, by Warren Uphatn. 1887. 8°. 84 

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40. Changes in River Courses in Washington Territory due to Glaciation, by Bailey Willis. 1887* 

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41. On the Fossil Faunas of the Upper Devonian the Genesee Section, New York, by Henry S-. 

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42. Report of work done in the Division of Chemistry aud Physics, mainly during the tiscal year

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43. Tertiary and Cretaceolis Strata of the Tuscaloosa, Tombigbee, and Alabama Rivers, by Eugene 

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44. Bibliography of North American Geology for 1886, by Nelson H-. -Dartou. 1887. 8°. 35 pp. 

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IV ADVEETISEMENT.

45. The Present Condition of Knowledge of the Geology of Texas, by Kobert T. Hill. 1887. 8°. 94 

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46. Nature and Origin of Deposits of Phosphate of Lime, by B. A. F. Penrose, jr., with an Introduction by N. S. Shaler. 1888. 8°. 143pp. Price 15 cents.

47. Analyses of Waters of the Ycllowstono National Part, with an Account of the Methods of 

Analysis employed, by Frank Austin Gooch and James Edward Whitfield. 1888. 8°. 84pp. Price 

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48. On the Form and Position of the Sea Level, by Koberfc SimpsOn Woodward. 1888. 8°. 88 pp. 

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49. Latitudes and Longitudes of Certain Points in Missouri, Kansas, and New Mexico, by Robert 

Simpson AYoodward. 1889. 8°. 138 pp. Price 1.5 cents.

50. Formulas and Tables to facilitate the Construction and Use of Maps, by Robert Simpson Woodward. 1880. 8°. 124pp. Price 15 cents.

51. On Invertebrate Fossils from the Pacilic Coast, by Charles Abiatbar White. 1889. 8°. 102 pp. 

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52. Subaerial Decay of Bocks and Origin of the Eed Color of Certain Formations, by Israel Cook 

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53. The Geology of Nautucket, by Nathaniel Southgate Shaler. 1889. 8°. 55 pp. 10 pi. Price 10 

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54. On the Thermo-Electric Measurement of High Temperatures, by Carl Barns. 1889. 8^. 313pp. 

inch 1 pi. 11 pi. Price 25 cents.

55. Report of work done in the Division of Chemistry and Physios, mainly during the fiscal year 

1886-'87. Frank Wigirlesworth Clarke, chief chemist. 1889. 8°. 96pp. Price 10 cents.

56. Fossil Wood mid Lignite of the Potomac Formation, by Frank Hall Knowlton. 1889. 8°. 72pp. 

7 pi. Price 10 cents.

57-. A Geological Reconnaissance in Southwestern Kansas, by Robert Hay. 1890. 8°. 49 pp. 2 pi. 

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58. The Glacial Boundary in Western Pennsylvania, Ohio. Kentucky, Indiana, and Illinois, by George 

Frederick Wright, with an introduction by Thomas Chrowder Chamberlin. 1890. 8°. 112 pp. inch 

1 pi. 8 pi. Price 15 cents.

59. The Gabbros and Associated Rocks in Delaware, by Frederick D. Chester. 1890. 8°. 45 pp. 

1 pi. Price 10 cents.

60. Report of work done in the Division oT Chemistry and Physics, mainly during the fiscal year 

1887-'88. F. W. Clarke, chief chemist. 1890. 8°. 174 pp. Price 15 cents.

61. Contributions to the Mineralogy of the Pacilic Coast, by William Harlow Melville and Waldeinar 

Lindgrcn. 1890. 8°. 40pp. 3 pi. Price 5 cents.

62. The Greenstone Schist Areas of the Mcnomiuee and Marquette Regions of Michigan; a contribution to the subject of dynamic metamorphism in eruptive rocks, by George Huntiiigtoii Williams; 

with an introduction by Roland Duer Irving. 1890. 8°. 241 pp. 16 pi. Price 30 cents.

63. A Bibliography of Paleozoic Crustacea from 1698 to 1889, including a list of North American 

species and a systematic arrangement of genera, by Anthony W. Vogdes. 1890. 8°. 177 pp. Price 

15 cents.

64. A report of work done in the Division of Chemistry and Physics, mainly during the fiscal year 

1888-'89. F. W. Clarke, chief chemist. 1890. 8°. 60 pp. Price 10 cents..

65. Stratigraphy of 'the Bituminous Coal Field of Pennsylvania, Ohio, and West Virginia, by Israel 

C. AVhite. 1891. 8°. 212pp. 11 pi. Price 20 cents.

66. On a Group of Volcanic Rocks from the Tewan Mountains, New Mexico, and on the occurrence 

of Primary Quartz in certain Basalts, by Joseph Paxson Iddings. 1890. 8°. 34 pp. Price 5 cents.

67. The Relations of the Traps of the Newark System in the Now Jersey Region, by Nelson Horatio 

Dai'ton. 1890. 8°. 82pp. Price 10 cents.

68. Earthquakes in California in 1889, by James Edward Keoler. 1890. 8°. 25 pp. Price 5 cents.

69. A Classed and Annotated Bibliography of Fossil Insects, by Samuel Hubbard Scudder. 1890. 

8°. 101 pp. Price 15 cents.

70. Report on Astronomical Work of 1889 and 1890, by Robert Simpson Woodward. 1890. 8°. 79pp. 

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71. Index to the Known Fossil Insects of the World, including Myriapods and Arachnids, by Samuel 

Hubbard Scudder. 1891. 8°. 744pp. Price 50 cents.

72. Altitudes between Lake Superior and the Rocky Mountains, by AVarren Upham. 1891. 8°. 

229 pp. Price 20 cents.

73. The Viscosity of Solids, by Carl Barus. 1891. 8°. xii, 139 pp. 6 pi. Price 15 cents.

74. The Minerals of North Carolina, by Frederick Augustus Geuth. 1891. 8°. 119pp. Price 15 

cents. ' »

75. Record of North American Geology for 1887 to 1889, inclusive, by Nelson Horatio Darton. 1891. 

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76. A Dictionary of Altitudes in the United States (second edition), compiled by Henry Gannett, 

chief topographer. 1891. 8°. 393pp. Price 25 cents.

77. The Texan Permian and its Mesozoic Types of Fossils, by Charles A. White. 1891. 8°., 51 pp. 

4 pi. Price 10 cents.
ADVERTISEMENT. V

78. A report of work done in the Division of Chemistry and "Physics, mainly during the fiscal year 

1889-'90. F. W. Clarke, cliiof chemist. 1891. 8°. 131pp. Price 15 cents.

79. A Late Volcanic Eruption in Northern California and its Peculiar Lava, by J. S. Diller. 1891. 8°. 

33pp." 17 pi. Price 10 cents.

80. Correlation papers Devonian and Carboniferous, by Henry Shaler Williams. 1891. 8°. 279 pp. 

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81. Correlation papers Cambrian, by Cluirles Doolittle Walcott. 1891. 8°. .447pp. 3 pi. Price 

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82. Correlation papers Cretaceous, by Charles A. "White. 1391. 8°. 273pp. 3 pi. Price 20 cents.

83. Con-elation papers Eocene, by William .Bullock Clark. 1891. 8°. 173 pp. 2 pi. Price 15 cents.

84. Correlation papers Neocene, by W. H. Dall and G. D. Harris. 1892. 8°. 349 pp. 3 pi. Price 

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85. Correlation papers The Newark System, by Israel Cook Russell. 1892. 8°. 344 pp. J.3 pi. 

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80. Correlation papers Archean and Algonkian, by C. E. Van Hise. 1892. 8°. 549 pp. 12 pi. 

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90. A report of work done in the Division of Chemistry and Physics, mainly during the fiscal year 

1890-'91. F.W. Clarke, chief chemist. 1892. 8°. 77pp. Price 10 cents.

91. Record of North American Geology for 1890, by Nelson Horatio Barton. 1891. 8°. 88 pp. Price 

10 cents.

92. The Compressibility of Liquids, by Carl Barus. 1892. 8°. 96pp. 29 pi. Price 10 cents.

93. Some insects of special interest from Florissant, Colorado, and other points in the Tertiaries of 

Colorado and Utah, by Samuel Hubbard Scuddor. 1892. 8°. 35 pp. 3 pi. Price 5 cents.

94. The Mechanism of Solid Viscosity, by Carl Hams. 1892. "8°. 138pp. Price 15 cents.

95. Earthquakes in California in 1890 and 1891, by Edward Singleton Holden. 1892. 8°. 31 pp. 

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96. The Volume Thermodynamics of Liquids, by Carl Barus. 1892. 8°. 100pp. Price 10 cents.

97. TheMesozoic Echiuodermata of the United States, by William Bullock Clark. 1893. 8°. 207 

pp. 50 pi. Price 20 cents.

98. Flora of the Outlying Carboniferous Basins of Southwestern Missouri,by Bavid White. 1893. 8°. 

139 pp. 5 pi. Price 15 cents.

99. Record of North American Geology for 1891, by Nelson Horatio Barton. 1892. 8°. 73 pp. 

Price 10 cents.

100. Bibliography and Index of the publications of the U. S. Geological Survey, 1879-1892, by Philip 

Crevoliug Warman. 1893. 8°. 495 pp. Price 25 cents.

lift. Insect Fauna of the Rhode Island Coal "Field, by Samuel Hubbard Scudder. 1893. 8°. 27 pp. 

2 pi. Price 5 cents.

103. High Temperature Work in Igneous Fusion and Ebullition, chiefly in relation to pressure, by 

Carl Barus.

104. Glaciation of the Tellowstone Valley north of the Park, by Walter Harvey Weed. 1893. 8°. 

41 pp. 4 pi. Price 5 cents.

105. The Laramie and the overlying Livingston Formation in Montana, by Walter Harvey Weed, 

with Report on Flora, by Frank Hall Ivnowlton. 1893. 8°. 68pp. 6 pi. Price 10 cents.

106. The Colorado Formation and its Invertebrate Fauna, by T. W. Stanton. 1893. 8°. 288 pp. 

45 pi. Price 20 cents.

107. The Trap Dikes of Lake Champlain Valley and the Eastern Adirondacks, by James Furman 

Kern p.

108. A Geological Reconnoissance in Central Washington, by Israel Cook Russell. 1893. 8°. 308pp. 

12 pi. Price 15 cents.

109. The Eruptive and Sedimentary Rocks on Pigeon Point, Minnesota, and their contact phenomena, by William Shirley Bayloy. 1893. 8°. 121pp. 16 pi. Price 15 cents.

110. The Paleozoic Section in the vicinity of Three Forks, Montana, by Albert Charles Pealc. 1893. 

8°. 56pp. 6 pi. Price 10 cents.

In press -. 

102. A Catalogue and Bibliography of North American Mesozoic Invertebrata, by C. B. Boyle.

111. Geology of the Big Stone Gap Coal Field of Virginia and Kentucky, by Marius R. Campbell.

112. Earthquakes in California in 1892, by Charles D. Perrine.

In preparation:

 The Moraines of the Missouri Coteau and their attendant deposits, by James Edward Tocld.

 On the Structure of the Ridge between the Tacouic and the Green Mountain Ranges in Vermont; and On the Structure of Monument Mountain in Great Barringtou, Mass., by T. Nelson Bale.

 A Bibliography of Paleobotany, by David White.

STATISTICAL PAPERS.

Mineral Resources of the United States, 1S82, by Albert Williams, jr. 1883. 8°. xvii, 813 pp. Price 

50 cents,.
VI ADVERTISEMENT.

Mineral .Resources of the United States, 1883 and 1884, l>y Albert Williams, jr. 1885. 8°. xiv, 1010 

pp. Price 60 cents.

Mineral Resources of the United States, 1885.. Division of Mining Statistics and Technology. 1886. 

8°. vii, 576pp. Price 40 cents.

Mineral Kesources of the United States, 1886, by David T. Day. 1887. 8°. viii, 813pp. Price 50 cents.

Mineral Kesources of the United States, 1887, by David T. Day. 1888. 8°. vii, 832 pp."Price 50 cents.

Mineral Resources.of the United States, 1888, by David T. Day. 1890. 8°. vii, 952pp. Price 50 cents.

Mineral Resources orHhe United States, 1889 and 1890, by David T. Day. 1892. 8°. viii, 671 pp. 

Price 50 cents.

Mineral Eesources of the United States, 1891, by David T. Day. 1893. 8°. vii, 630pp. Price 50 cents. 

In preparation :

Mineral Resources of the United States, 1892.

The money received from the sale of these publications is deposited in the Treasury, and the Secretary of the Treasury declines to receive bank checks, drafts, or postage stamps; all remittances, therefore, must be by POSTAL NOTE or MONEY ORDER, made payable to the Chief Clerk of the U. S. Geologica1 

Survey, or in CURRENCY, for the exact amount. Correspondence relating to the publications of the 

Survey should be addressed

To THE DIRECTOR OF THE

UNITED STATES GEOLOGICAL SURVEY,

"WASHINGTON, D. C.

WASHINGTON, D. C., October, 1S9S.
DEPARTMENT OF THE INTERIOR

BULLETIN

OF THE

UNITED STATES

No. 11O

WASHINGTON

GOVERNMENT PRINTING- OFFICE

1893

UNITED STATES GEOLOGICAL SUE VET

J. W. POAVELL, DIKECTOR

THE

PALEOZOIC SECTION

IN THE

YICINITY OF THREE FORKS, MONTANA

ALBEET CHARLES PEALB

WITH

PETROGRAPHIC NOTES

BY

GEOEGE PEEKINS MERRILL

W A SUING-TON

GOVERNMENT FEINTING OFFICE 

1893

CONTENTS.

I'agc.

Introduction................................................................ 9

Structure................................... 1............................... 9

The Three Forks section .................................................... 14

Algonkian .............................................................. 16

Belt formation....................................................... 16

Cambrian............................................................... 20

Flathead formation ................................................ 20

Flathead quartzite.............................................. 20

Flathead shales. ....................i........................... 21

Gallatin formation.................................................. 22

Trilobite limestones............................................. 22

Oholella shales.................................................. 23

Mottled limestones.............................................. 23

Dry Creek shales................................................ 24

Pebbly limestones .............................................. 24

Devono-Silurian ........................................................ 24

Devonian................................................................ 27

Jefferson formation ................................................. 27

Jefferson limestones............................................. 27

Three Forks shales.............................................. 29

Carboniferous .......................................................... 32

Madison formation .J................................................ 33

The laminated limestones....................................... 33

The massive limestones ......................................... 34

The jaspery limestones.......................................... 36

Quadrant formation................................................. 39

The red limestones.................. ............................ 39

The cherty limestones........................................... 41

Eruptive rocks ............................................................. 43

Notes on the petrography of the Paleozoic section in the vicinity of Three

Forks, Montana, by Geo. P. Merrill.................................... 47

Gneissic rocks from the west side of Bridger range, Montana............ 47

Fragmental rocks from the Belt formation............................... 49

Intrusive rocks in the lower part of the Flathead shales................. 49

Intrusive rocks from near Horse Shoe Bend of the Missouri river ........ 54

5

LLUSTRATIONS

Page. 

PLATE I. Geological map of vicinity of Three Forks, Montana ............. 9

II. A. Section across the Madison range between the Madison and

Gallatiu rivers......................................... 12

B. Section across tho south end of Bridger range................ 12

III. A. \

B. > Sections between the Gallatin and Missouri rivers ........... 14

C. )

IV. The Three Forks section ......................................... 16

V. Section along tho north side of the Gallatin river ................ 20

VI. Section north of the Gallatiu river............................... 28

FIG. 1. Paramorphic hornblende ...... *.............................'........ 51

2. Microstructure of syenitic rock . .................................... 53

7

U.S.GEOLOGICAL SURVEY. 

LEGEND

q iPLEISTOCENE.A

n

K

NEOCENE.Bozema

( Dak

Colo

Mon

JURA-TRIAS. Ellis

[ C |cARBONIFEROUS.| ^ I [

f^lHHll r- |»Hl flhre

Dl

 DEVONIAN.

 f

Ab

[Jeffe

{Gall

Flat

ALGONKIAN. Belt f

Diorit

Porp

Aug

Syen

F

IGNEOUS.

.. Coal.

c , __*__ ocale 230,000

Contour Interval 200 feet

Note

The lines AB. CD. & EF. are the lin

shown in Plate HI.

GEOLOGICAL MAP OF VICINITY OF THREE FORKS, MONTANA.

BY

A.C.PE:ALE.
THE PALEOZOIC SECTION IN THE VICINITY OF THREE 

FOKKS, MONTANA,

BY A. C. PEALE.

INTRODUCTION.

The Three Forks sheet of Montana includes the area lying between 

the parallels of 45° and 46°, and extending from longitude 111° to 112°. 

The three forks of the Missouri river unite in the north central portion 

of this area about 5 miles south of the northern line of the map. 1

The area selected for the initial work in the construction of this section was the area adjacent to the three forks of the Missouri river at 

the northern end of the G-allatin valley, and is shown on the accompanying map. (PL i.) This region was the field of reconnaissance 

work for very brief periods in 1871 and 1872, when the writer, with Mr. 

W. H. Holmes, under Dr. Hayden's direction, made a hasty examination of a small part of the area, securing the section published on pages 

172 and 173 of the Sixth Annual Eeport of the U. S. Geological Survey 

of the Territories. The rather complicated structure of the region was 

then recognized, but time did not permit any work except that of the 

most general character, and it was hopped that the future might see the 

work undertaken with a prospect of completing it in more detail. This 

opportunity was presented in 1884, and the object of this paper is to 

describe briefly some of the results of the more detailed reexamination 

then begun.

The first white men to visit the " Three Forks of the Missouri" were 

the members of Lewis and Clarke's expedition in July, 1805, by whom 

the three rivers were given the names of Grallatin, Madison and Jefferson, respectively. No geological work, however, was done until the 

expedition of Eaynolds visited the Three Forks in 1860, when Dr. Hayden made the first geological examination of the area.2 This work was

'This paper was prepared during 1886 and ]887 and completed in the early part of 1888, since which 

time the geological exploration of the entire sheet has been finished. The paper has been revised only 

so far as to make the nomenclature consistent with that adopted for use in the publication of the atlas 

sheet.

2 Geol. Kept, of Explorations of the Yellowstouo and Missouri rivers, Washington, 1867, p. 90.

9
10 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. 110.

naturally more general than the later work of 1871 aiid 1872. The map 

published by the Northern Transcontinental Survey under Prof. Pumpelly' has this area colored geologically, but goes into less detail than 

does the Haydeu map of 187 J, and none of the accompanying text refers 

to it, the explanation of which omission is found in the fact that the 

object of this survey was mainly the discovery of the various coal horizons, and the determination, exploration, and preliminary development 

of the coal fields. In the adjacent region beyond the limits of the Three 

Forks Sheet, on the north and east, considerable detailed geological 

work was done by W. M. Davis 2 and George H. Eldridge,3 while the 

eruptive rocks of the region examined by them have been reported upon 

by Waldemar Lindgren 4 and J. E. Wolff.5

In 1875 Ludlow's expedition passed along the eastern side of the 

Bridger range just beyond the eastern limits of our sheet on the way 

from Fort Logan to Fort Ellis, and Messrs. Griunell and Dana made a 

hasty examination of the east side and summit of the range. Their 

observations are published in Capt. Ludlow's report.6 The region 

examined by them, however, lies mainly east of the mountains on 

the Livingston sheet. Prior to 1884 also, Prof. J. S. Newberry crossed 

the Great Belt mountains from Sulphur springs to Townsend on the 

Missouri river, about 26 miles north of Three Forks. He also crossed 

the Gallatin valley from Bozeman to Gallatin city.7 This completes, 

so far as I am aware, the list of those who have done any geological 

work in or near the region of the Three Forks.

STRUCTURE.

It would be manifestly premature to attempt to deduce from the facts 

observed within the limited area of one topographic sheet of only 3,354 

square miles generalizations affecting the entire Eocky mountain system of Montana, and especially so in view of the fact that the observations noted during hurried trips through various parts of the state 

indicate considerable complication and irregularity in its mountain 

structure. Still there are a few points to which attention may be called 

which seem to be characteristic at least of the immediate area under 

consideration, and may yet possibly be extended to other portions of the 

state.

The most striking feature to be noted is the rather common occurrence of folds in which the strata on one side are inverted so that the

'Keport on the Milling Industries of the United States, vol. xv, Tenth Census.

2 Keport of Tenth Census, vol. xv, p. 697.

3 0p.cit.,p. 739.

«0p.cit.,p.719.

6Neues Jahrb. 1885, i,p. 69, and "Notes on the Petrography of the Crazy Mountains, etc., Heidelberg, 1885."

"Kept, of a Keconnaissance from Carroll, Montana Territory, etc., to the 'Yellowstone National Park 

and return. Washington, 1876, pp. 93-197.

'Notes on the Geology and Botany of the country bordering the Northern Pacific Hail road by Prof. 

J. S. Newberry. From the Annuls of the N.-Y. Acad. of Sci., vol. in, No. 8,1884.
STRUCTURE. 11

beds are bottom side upward. This isoclinal structure was noted in 

the Madison range1 in 1872, when it was illustrated. (This illustration 

is reproduced in A, PI. n.) It was also noted in the range west of 

Eadersburg, 18 or 20 miles north of the Three Forks2 and again in the 

Bridger range, which lies partly on the northeast corner of our sheet 

(see B, PL n). The latter is in its southern extension an overturned 

monocline, complicated by faulting on the west side of the range as we 

trace it to the northward, but as we stand on one of its southern peaks 

where the beds are inverted and look northward, the beds are seen to 

return to their normal condition very much in the way noted in the Elk 

mountains in Colorado by the writer in 1873.3 Still farther along' 

the beds are again overturned, and at the extreme north end of the 

range they are once more in their normal position.

The area under consideration in this paper was recognized in 1871 

and 1872 as one in which there were several local anticlines and synclines. Our later examinations develop that in the space between the 

G-allatin river and the hills northwest of the head of the Missouri river 

we have four synclincs, two isoclines, and one well-defined anticline. 

The latter begins at the head of the Missouri river with a fold which 

at first has an overturn on the right (i. e., it is an isoclinal fold), but 

within a few miles develops into a normal anticlinal fold, the northwest 

side of which has been cut through by the Missouri river, which occupies a ntonoclinal rift in the Lower Carboniferous and Upper Devonian 

for about 4 miles' from its head, when it cuts across the Carboniferous 

just before it emerges into the broad valley of the Horseshoe bend 

on the northern line of our sheet. A similar inversion was noted in 

1872 4 in one side of the anticlinal fold across which Spring or Rocky 

canyon is cut. It begins as an isocline at the north end, and very soon 

becomes a normal anticline as it is traced southward. Some indications of similar inversions were noted in the uplift west of the Eocky 

canyon uplift, that is in the one which is on a line with the Bridger 

uplift.

In all of the folds observed up to the present time, what may be 

called the plane of the axis dips westward or north westward; that 

is, the steep or overthrown portion is on the west or northwest side of 

the synclinal basin. This is noted even in the beginnings of those 

folds which at first are isoclines, but are in the main normal anticlines. 

The trend of the folds near the Three Forks is about N. 60° E.; in the 

southern portion of Bridger range, where the overturn occurs, the axis 

is N. 15° to"20° E.; in the Eocky canyon uplift it is N. 25° W.; and in 

the Madison range it is approximately north and south. In none of 

the folds which have an east or west direction has any similar inversion

1 Sixtli Ann. Eept. Geol. Survey Territories, p. 104, also p. 84.

2 Sixth Ann. Kept. Geol. Survey Territories, p. 82.

"Seventh Ann. Kept. U. S. Geol. and Geog. Survey of the Territories, p. 256; see also PI. xvn ami 

PI. xvin. 

4Sixth Ann. Kept. Geol. Survey of the Territories, p. 109.-
12 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. IBULL.HO.

been seen. Eeference to the sections in PL in will make clear the structure in the vicinity of the Three Forks. The first section (A) begins 

on the Gallatin river at a point abont 2 miles above the Northern 

Pacific Eailroad bridge, and continues northwest, crossing the Missouri 

river near its head. This section is the only one that crosses to the 

west side of the Missouri, and shows therefore the Cottonwood isocline 

and the Missouri isocline, both of which are well marked, and have been 

traced in a northeasterly direction to the limits of the sheet.

Leaving the Gallatin river on the line of the first section, we cross 

successively the upturned edges of the Belt beds, the Cambrian, Devonian, Carboniferous, and Mesozoic strata, all dipping conformably to 

the northwest at angles of from 8° to 10° in the lower beds, and 20° or 

25° at the top of the Paleozoic and base of the Mesozoic beds, on the 

southeast side of Cottonwood valley. This valley is filled with Cretaceous sandstones and shales with two intrusive sheets. Crossing to the 

northwest side of the valley we find the beds repeated in reverse order, 

the lower portion of the Jura-Trias dipping to the northwest beneath 

the Upper Carboniferous at angles of 50° to 60°. These beds show 

abundantly slickensided surfaces, evidencing the slipping of the beds 

upon each other during their overturning. Crossing next the edges of 

the Carboniferous and Upper Devonian strata, we find the latter standing upon end and after crossing an area in which the beds are parti ally 

concealed by Pliocene lake beds, we come to the upper portions of the 

Devonian dipping to the northwest in their normal position. Proceeding northward on the central portion of the Devonian or DevonoSilurian limestones as exposed here between the two upper Devonian 

outcrops we find very soon that an anticlinal fold develops, in the center of which the Cambrian portion of the section rises to the surface, 

and still farther along erosion has brought to light the Belt beds occupying the axis of the fold. The right or southeastern side of this fold 

is very sharp, the beds for the most part being upon end or inverted, 

as shown in the second section (B, PI. in).

This second section was made on a line parallel to the first, about 5 or 

6 miles farther northeast. It shows the beginning of another synclinal 

fold that of Nixon basin which, as we follow it, merges with that of 

Cottonwood creek. From the middle of this basin an anticline begins 

to rise before the line of the third section, (C), 5 miles farther northeast is reached. This last uplift attains a comparatively slight elevation and soon dies out again to the northeast. The Cottonwood isocline, however, it will be observed, continues through all three sections 

and is equally well marked where the north line of the sheet crosses it, 

as at the lower end of the Cottonwood valley, 10 miles to the southwest.

Returning to the^first section and following it to the head of the Missouri river, we reach the Horseshoe anticline, the axis of which extends 

from near the mouth of the Gallatin to the Horseshoe bend of the Missouri, its direction being alniost parallel to the course of the river.
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 110 PL. II

_...................-- - v...-;;_,.-- ________ ;--,., \ \ A

Section across the Madison Range between the Madison and Gallatin Rivers

Section across the south end of Bridger Range

SECTIONS ACROSS MADISON AND BRIDGER RANGES.
PEALE.] ISOCLINES ISOLATED UPLIFTS. 13

This fold has already been referred to. As we trace it toward the northeast it becomes broader and broader, older and'still older beds rising 

one after the .other until the bend is reached, where the Belt beds are 

exposed in the center, with patches of lake beds resting upon them. 

The three streams forming the Missouri river unite in the Carboniferous 

limestones, and the river flows at first into a canyon-like valley in 

these rocks, which dip from 25° to 30° toward the northwest on both 

sides of the valley.

Very soon, however, the river cuts across into the soft sandstone and 

shales of the Upper Devonian, and the valley becomes somewhat wider. 

Still farther on the channel is cut in a northerly direction diagonally 

across the Carboniferous limestones and a portion of the overlying Mesozoic beds for a mile or two, when it turns abruptly to the south, forming 

the western side of the Horseshoe bend. On the west or northwest 

side of the Missouri we find a synclinal basin filled in part with lake 

beds, resting on the upturned Mesozoic strata. Crossing to the west 

side of this basin we come to a repetition of the Cottonwood isocline, 

the beds here also being inverted, dipping 50° to the northwest, with 

the old,er beds on top. On the east side of the synclinal basin the same 

beds in the regular order of succession dip in the same direction at 

angles of only 25° or 30°. This Missouri isocline has also been traced 

to the northern limits of the map. *

Attention should be called to another point, viz, the isolated character of the uplifts, that* is the existence of folds which are for the most 

part of limited extent, as traced in the direction of their axes. This is 

true eveu within the small area included in the map accompanying this 

paper, where there are at least four anticlines that die out in both 

directions within very short distances.

The fact that over a large portion of Montana the crumpling and 

folding of the strata has resulted in an almost innumerable number of 

ranges was stated in 1871 by Dr. F. V. Hayden. In the report for 

1871, p. 147, he says:

We might say that from longitude 110° to 118°, a distance of over 500 miles, there 

is a range of mountains on an average every 10 to 20 miles. Sometimes the distance 

across the range in a straight line is not more than 5 to 8 miles, while it is seldom 

more than 20 miles. From these statements which* we believe to be correct, the 

reader may form some conception of the vast amount of labor yet to be performed 

to explore, analyze, and locate 011 a suitable scale, these hundreds of ranges of mountains, each one of which is worthy of a name.

He recognized that although due partly to erosion, they were the 

result in the first place of folding or crumpling of the strata, the valleys in most cases being synclinal folds, and the mountains anticlinal. 

The truth of Hayden's observation becomes more and more apparent 

as the country is more and more carefully studied and mapped.

Many of the ridges do not attain the dignity of ranges, and we find 

that inversion of the strata is a more common occurrence than we supposed in 1871, being found in many of the ridges of very low elevation.
14 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. no.

This orographic structure lias given rise to the numerous lake basins 

which, with their peculiar deposits, have been noted by all workers in 

the region as characteristic of the territory. Above these basins, when 

occupied by the old lakes, the higher ridges undoubtedly projected as 

islands. Beyond the limits of the immediate area under consideration 

here, the members of the Northern Transcontinental Survey have recognized and described the various ranges examined by them, as being 

similarly isolated or separated from each other. In addition to what 

may be called the normal type, that is where the ranges show the older 

rocks and are due to folding, Messrs. Davis and Lindgren, in the region 

outlying the main ranges, describe a second type of mountains, where 

the rocks are mainly of Cretaceous age, with little if any disturbance, 

and the mountain structure is due to the fact that the intrusion of dikes 

and the consequent induration and metamorphisni of the surrounding 

beds has preserved them iroin the destructive erosive forces which have 

worn away the softer beds beyond the eruptive areas. 1 This type we 

have not yet found in the mountains and it is probably confined to the 

plains,lying immediately eastward of them.

Still another point to which attention should be called is one. which 

was but vaguely apprehended in 1871 and 1872, and to which reference 

was not made in the reports of those years, viz, the existence of an 

ancie*t pre-Cambrian shore line, which extends in a general westerly 

direction from the Bridger range across the northern part of our area. 

It crosses the Madison and Jefferson rivers probably from 10 to 12 

miles above their mouths. Its eastward and northeastward extension 

beyond the mountains will probably be difficult to trace, but future 

investigation ought to determine approximately its direction to the 

west. All that we can say at present is that all of the area included 

within the limits of the Three Forks sheet south of this line was in 

pre-Cambrian time a part of a continental land mass, the outlines of 

which, with the data now at hand, can be defined only in the most 

general way.

Against this Archean laud mass the sedimentary beds were pushed 

in the process of folding or crumpling, and the result was the series of 

folds already described.

THE THREE FORKS SECTION.

The following system of nomenclature for the Paleozoic section was 

determined upon for the contiguous sheets in Montana, after consultation with the members of Mr. Arnold Hague's division. The names 

given below replace those published on page 131 of the 10th Ann. Eept. 

of the Geological Survey.

' Eept. of 10th Census, Vol. xv, pp. 703-705, and 724,737,
U. 8. GEOLOGICAL SURVEY BULLETIN NO. 110 PL. Ill

'/+ '/Z f/Ki/es

Cottonwoid ,'lsoclinp/ / ,' 

/ ' .'

CottonWo^d Isocl/ne &

' ""] n : /

Lake Beds

Algonkian

. S E.

Missouri Isocline Cottonwood Isocline

SECTIONS BETWEEN THE EAST GALLATIN AND MISSOURI RIVERS.
NOMENCLATURE. 15

Periods. Formations.

i Quadrant formation. Carboniferous ..................... j Madison forraatioJJ.

]>,vonian.........................rr^eeForksshaleS-

( Jefferson formation.

Devono-Silurian .....................

L Gallatin formation. Cambrian....................;.... { Flathead formation.

Algonkiaii? ......................... Belt formation.

The Paleozoic section of the Three Forks region, including the beds 

provisionally assigned to the Algonkian, consists of a series of sedimentary deposits of nearly 10,000 feet thickness, resting upon Archeau 

gneiss. Over 8,000 feet are shown in the Gallatin section (PI. iv), which 

does not, however, reach down to the Archean. A few miles south of 

the region shown on the map (PI. i) this thickness is reduced to a little 

over 3,600 feet by the absence of the Belt formation, as the Flathead 

formation whenever seen there rests unconformably upon the Archean 

gneisses without the interposition of the Belt formation. The section 

of the region to the north, as given by Mr. W. M. Davis, is from. 15,000 

to 20,000 feet, the increased thickness* being due mainly to the greater 

development of the Belt formation (called by him Lower Cambrian 

barren slates). 1

The gneisses of our region can not at present be correlated, even provisionally, Avith the Archean rocks of the east. They are certainly preCambriau, if the Flathead formation is of Lower Cambrian age, for 

included in the loAver strata of the latter at several localities are fragments of gray and red gneiss evidently derived from the underlying 

Archean, and that they are pre-Algonkian is proved by similar occurrences in the Belt formation in the northern portion of our sheet.

Mr. Merrill's notes, appended to this paper, show that the materials 

forming these were without doubt derived from beds similar to those 

now forming the gneissic foothills of the Bridger range. The evidence 

for the reference of the Belt formation to the Algonkian is of a somewhat negative character, and will be noted more particularly when the 

included beds are described on a subsequent page. The entire section 

so far as observed is conformable from the base to the top. There is 

difficulty in attempting to define exactly the lines between the formations, even so far as the greater divisions are concerned, and the correlation necessarily has not been carried any farther, local names beingapplied to the minor divisions. It is a question whether the divisions 

of the geological scale as made in the eastern United States can ever 

be recognized in the strata of the Eocky mountain region.

The characters and strati graphical position of the Flathead quartzite and shales indicate the general subsidence of the country just prior 

to their deposition, a subsideneeAvhich in all probability continued pro1 Tenth Census, vol. xv, p. 097,
16 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. no.

gressively throughout all Paleozoic time, with numerous oscillatious of 

comparatively slight importance.

Between the upper part of the Cambrian limestones and the Devonian horizon above the Jefferson limestones, which we have described 

as the" Three Forks shales, there is a thickness of over 700 feet of beds, 

of which the lower 350 feet have so far yielded no fossils. In the upper 

part meager remains have been found which have a Devonian rather 

than a Silurian fades, while a few indistinct remains occur a little above 

the middle portion. The lithological characters are the same from 

the bottom to the top, showing that the conditions were essentially the 

same throughout, and that the stratigraphic record was probably continuous, and until the paleontological record has been completed for 

this barren interval there remains a doubt as to the age of the lowest 

of these beds. The probabilities are, however, in the opinion of the 

writer, rather in favor of their Devonian age, and they are so described 

under the heading, Jefferson limestones.

x)

ALGONKIAN. 

KELT FORMATION.

The section in the vicinity of the Three Forks begins with a series of 

beds of littoral formation which was in 1884' provisionally called the 

East Gallatin group, so named from the well exposed outcrops occurring along the north side of the East Gallatin river near its junction 

.with the West Gallatin, where a detailed section of 2,300 feet has been 

carefully measured. It consists of an alternation of coarse micaceous 

sandstones and conglomerates, with beds of hard argillaceous slates, 

and bands of thin bedded dark-blue silicious limestones. The latter 

are very hard and some are slightly magnesian.

The following analyses by Mr. Charles Catlett in the laboratory of 

the Survey are of the two typical specimens from the lower portion of 

the measured section.

Iron oxide [Fc2 O3 ] ......."?

Aluminium, oxide [A12 Os] )

Total ......................................

I.

07-85 G-18

2-50

23-50

100-03

II.

59-11

I 1 90

1-92

35-26

98-25

The limestones are developed mainly toward the base of the measured section and occur in bands from 5 to 20 feet in thickness but sometimes reaching nearly 50 feet. Many of the beds are very finely laminated, of a dark blue almost black color in fresh fractures, and showsixth Ann. Kept. U. S. Geol. Survey, p. 50.
U. 6. GEOLOGICAL SURVEY

CARBONIFEROUS.

QUADRANT. 

FORMATION.

MADISON. 

LIMESTONES.

&

S

BULLETIN NO. 110 PL. IV 

=g-.:"r=a'-..~=^v.. -*=J~.

THREE FORKS SHALES

DEVONIAN,

Upper ShctZes. To.ff:-.

JEFFERSON 

LIMESTONES

CAMBRIAN.

GALLAT IN 

FORMATION,

FLAT HEAD 

FORMATION.

FlatheaA S/iales. 29o. /«&.

Quartette. 123. ft

INTftUSIVE SHEET.

ALGONKIAN.

FORMATION.

Conglomerific micaceous Sand/ - 

stones -with fronds ofsi&ceaus 

Limestones and. day shales.

TOTAL

THE THREE FORKS SECTION.
PKALK.J ALGONKIAN. 17

.ing light yellowish brown on weathered surfaces. About half way up 

in the section the limestones change in their appearance. They are 

more compact, not so dark in color, but are still highly silicious and 

layers with peculiar flat round concretions are seen. These concretions 

have been mistaken for fossil turtles by the people living in this part of 

of the Gallatin valley. Some of the concretions are very large, often 

measuring several feet in .diameter and from 0 to 12 inches in thickness, 

but they average about C inches to a foot in diameter with a thickness of only 3 to 4 inches. Sections of them show no peculiarities.

The indurated clay-slates are also most abundant towards the middle 

and base of the measured section, and present a variety of colors yellowish-brown, olive-green, and bluish-black predominating. The beds 

are very fissile, frequently breaking down into fine splintery debris, 

generally of a light color, and with frequent local bands of a bright red 

tint, as though the beds had been subjected to heat. These appear to 

be scattered over the country irregularly, and their weathering gives 

a very bright red debris. The slates are particularly well exposed in 

the bluffs along the west side of Dry creek below its first canyon.

The sandstones are prominent in the upper and lower parts of the 

section, and occur in heavy beds of 5 to 10 and sometimes 20 or 30 feet 

in thickness. They frequently break into cubical blocks with sharp 

edges, which increases their resemblance to eruptive rocks, for which 

they have sometimes been mistaken. As seen in hand specimens, their 

arkose character is evident, and often water-rolled pebbles of considerable size are seen, especially in the coarser beds near the base of the 

section.

The name " bastard granite" has locally been applied to them. Some 

of the layers are slightly calcareous, especially nea.r the base, where 

they are intercalated with numerous thin bands of limestone, and some 

of the lowest sandstones are cut by seams of pure dolomite. The beds 

are generally very coarse and in places strongly conglomeritic. That 

Archean land masses, when they were deposited, existed not far to the 

south is very evident from the general character of the beds, and is 

also proved conclusively when they are compared microscopically with 

the Archean rocks of the adjacent region.

In the Bridger range, where the section is carried lower than on the 

East Gallatin, they contain many pebbles of Archean rocks, and in the 

lowest outcrops there are included angular masses of gneiss, showing 

the immediate proximity of the ancient shore line. There is considerable difference between the various beds so far as structure is concerned, but all are more or less micaceous and occur in massive layers. 

They are very similar in color, dark greenish gray, steel-gray, and. 

rusty brown tints prevailing. Seen from a distance, these sandstones 

resemble outcrops of eruptive rocks, owing partly to their somber appearance and partly to their mode of weathering; in fact, when first 

seen in 1860, they were so mistaken in the following description: 

8046 Bull. 110 2
18 PALEOZOIC SECTION NEAR THREE PORKS, MONTANA. [BULL. no.

Beneatll are a series of thin strata of dark steel-gray micaceous sandstone, sometimes becoming a fine aggregation of water-worn pebbles, and dark brown clayslate, gradually passing down into what appears to be a true eruptive rock with 

vertical seams of white quartz running through it. 1

The formation occurs in bluffs along the Gallatiu for a distance of 5 

miles, and also makes up the mass of the foothills on the western side 

of the Bridger range from Spring hill northward, reaching in the latter place a thickness of at least 6,000 feet. It is also characteristically 

exposed in the canyon of the Jefferson river, 14 or 15 miles above its 

mouth, where the upper sandstones and conglomerates are seen in massive beds of dark green color.

In the Big Belt range, north of the limits of the Three Forks sheet, 

Mr. W. M. Davis, in two sections, found a series of from 10,000 to 

12,000 feet of beds, which from his description undoubtedly belong to 

this group. 2 He refers to them as " a vast series of Lower Cambrian 

barren slates.3

The same beds are described by Prof. Newberry,4 who says: " There is 

little doubt that this is the same formation as that seen beneath 

the Potsdam in Little Cottonwood canyon near Salt Lake city, and in 

the canyon of the Colorado, a formation considered Cambrian by King, 

Powell, and Walcott, and which has yielded the latter a few fossils, 

but is universally barren and disappointing." He also refers to their 

absence in the Beltxmountains, farther to the east, ajid says they are 

absent "for the same reason that the ' Georgia slates' do not underlie the Potsdam in the Adirondacks, viz, because the Potsdam is a.sheet 

of sea-beach, produced by a widespread, almost continental, depression 

of the land, or general elevation of the sea level, which carried the 

shore line inland beyond the areas where the Cambrian rocks had accumulated."

Nowhere in the Gallatin valley have we as yet seen this group in 

immediate superposition upon the Archean, although we have reason 

to think that the line of junction is nearly reached at the base of the 

section, as seen in the Bridger range. A great fault in the canyon of 

the Jefferson, by which the Paleozoic'limestones and the overlying Mesozoic beds are thrown down against this formation, prevents our seeing 

the junction at that locality, while the overlapping lake beds and alluvial deposits of the Gallatiu valley conceal the line of junction within 

the limits included in the accompanying map (PI. i).

As to the age of this formation we have no paleontological evidence 

to offer, as careful search in the beds for fossils during several seasons 

has been unsuccessful. Hayden, in 1860, in 1871, and in 1872, was in1 Exploration of the Yeilowstono and Missouri rivers, p. 91.

2 .Report on the Mining Industries of the United States, vol. xv, Tenth Census, pp. 701, 702.

3 Ibid., p. 697.

4 Op. cit.,pp. 249, 250.
ALGONKIAN. 19

dined to regard them as representing- a portion of the Potsdam sandstone. 1

In 1885 they were doubtfully referred to the Middle Cambrian;2 in 

1872 the writer suggested the possibility of their Huroniaii age,3, and 

as already noted, Da vis and Newberry both refer to them as Lower 

Cambrian.

All that can be said with certainty is thnt they are post-Archean and 

probably pre-Cambrian, as they are made up largely of Archean debris 

and lie below beds containing Cambrian fossils. So far as observed, no 

well-defined unconformity between them and the overlying Flathead 

quartzite has been seen; but there is certainly an unconformity by subsidence, which is not always well shown and might easily be overlooked. 

There is no doubt that after the Belt formation was deposited there 

was an orographic movement by which the Archean area of nearly the 

entire region represented on our map south of the G-allatin and Three 

Forks was submerged just prior to the beginning of the Cambrian before the Flathead quartzite was deposited. Whether this movement 

occurred immediately after the laying down of the Belt- beds or after 

an interval is of course the question to be decided, and the decision 

can not be positively reached with the meager data now at hand. I 

am inclined to think that the subsidence of the Archean continent (or 

possibly islands) began with the first accumulation of the sediments 

that formed the lower portion of these beds and was coincident with 

their deposition throughout the entire period. It may have been succeeded by an emergence of the land area for a brief period, but the 

probability is that the interruption to the downward movement, if it 

occurred, was slight. Next the widespread pre-Cambrian subsidence 

preceding the formation of the Flathead quartzite took place, and the 

Cambrian sea covered large areas that had thitherto been above the sea 

level. There is a marked difference in the character of the, beds of the 

two groups. Little, if any, induration is seen in the Flathead formation, 

while the Belt beds are so altered in most cases as to resemble closely 

the metamorphic crystalline rocks which underlie them, and from the 

breaking down of which they were derived.4 Notwithstanding the 

metamorphism there is no mistaking their sedimentary character.

We have, therefore, a nonfossiliferous group of clastic beds, sometimes slightly metamorphosed, which lie between the Archean gneisses 

and a belt of quartzite, above which are beds with Middle Cambrian 

fossils. From its stratigraphical position, this group could be only of 

Lower Cambrian or of Algonkian age.

The possibility that Lower Cambrian fossils may yet be found in the 

quartzite at the base of the Flathead formation; the absence of organic

1 Exploration oftlio Yollowstone and Missouri rivers, p. 01, PreliminaryReport of the U. S. Geological Survey of Montana, p. 140; Gth AumialReportjoftrie U. S. Geological Survey of the Territory, p. 72,

2 Seventh Ann. Kept. U. S. Geological Survey, p. 80.

3 Sixth Annual Report of the U. S, Geological Survey of the Territories, p. 174.

4 See Mr. Mprrill's notes appended to this paper.
20 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL.HO.

remains in the Belt formation; the metamorphosed condition of the 

latter, and the existence of the unconformity between the quartzite 

and the beds below lead us to refer the latter, for the present at least, 

to the Algonkian.

CAMBRIAN.

The Cambrian rocks of our section are divisible into two portions, 

differentiated from each other by their lithological characters, the lower 

being mainly arenaceous and the upper calcareous. They will be 

described under the names of the Flathead formation and the G-allatin 

formation. The former may be subdivided into the Flathead quartzite 

and the Flathead shales, while the Gallatin formation will be described 

under the following subdivisions: The trilobite limestones, the obolella 

shales, the mottled limestones, the Dry creek shales, and the pebbly 

limestones.

As the collections of fossils have been only partially examined, no 

attempt will be made to draw with precision the lines separating the 

Lower Cambrian from the Middle Cambrian, nor the latter from the 

Upper Cambrian. The Flathead quartzite in the main probably represents the Lower Cambrian or its upper portion, and the trilobite limestones are very likely of Middle Cambrian age, while the mottled 

limestones with the overlying beds should doubtless be referred to the 

Upper Cambrian. It is altogether possible, however, that the pebbly 

limestones, or a portion of them, may eventually have to be taken from 

the Cambrian and considered as belonging to the Silurian.

FLATHEAD FORMATION.

Flathead qiiartzite. Besting upon the Belt formation in the Three 

Forks area is the remarkably persistent quartzite or sandstone, 

which has "long been recognized in the Rocky mountain region as 

lying in most cases at the base of the Paleozoic section, and which 

has been almost universally referred to as the equivalent of the Potsdam sandstone. It is usually quartzitic, and in the Gallatin valley is 

composed of siliceous grains of considerable uniformity in size, cemented by a siliceous matrix. In some localities there are interlaminated beds of reddish or reddish-brown sandstones in which the cementing material is partly an iron oxide. These sandstone sometimes have 

sufficient development to furnish a good building stone, and they 

have been utilized and quarries have been opened at several places in 

the valley, the one at the south end near Salesville, on the West Gallatin river, being the oldest. Owing to the hardness of the beds as exposed in most localities this quartzite is conspicuous topographically, 

and serves admirably as a reference horizon in making detailed sections in this region. In the illustration in PI. v it is well shown, outlining the double fold in the beds that outcrop on the north side of the 

Gallatin and East Gallatin rivers.
U. S; GEOLOGICAL SURVEY BULLETIN NO. 110 PL. V

GalJatin formation Fiathead formation

CAMBRIAN

Belt Mountain formation Flat head formation Belt Mountain formation

ALGONKIAN ALGONKIAN

SECTION ALONG THE NORTH SIDE OF THE GALLATIN RIVER. 

a. a,a. Bridger Range. 6. Fiathead Pass. c,c. Dry Creek Valley.
PEALE.J CAMBRIAN FLATHEAD FORMATION. 21

From the comparatively small thickness of the basal quartzite, it 

being only about 125 feet, and the fact that it is usually inclined at a 

considerable angle, the area occupied by it is relatively small, and if 

separately colored upon the map it would be represented by little 

more than a line of color.

Although the Flathead quartzite in the southern portion of the 

Bridger range and south of the Jefferson Valley rests immediately 

upon Archean schists or gneisses without the interposition of the Belt 

beds, it presents exactly the same litiiological characters as in the region of the Three Forks, where the latter are well developed. Its 

thickness, however, is somewhat less. An interesting fact in connection with its outcrops seen north of the East Gallatin is the occurrence 

of several dip faults in it where the quartzite is apparently thrown 

down in blocks, and wherever these blocks occur there is found an 

intrusive sheet lying immediately above the quartzite or separated 

from it in a few cases by a narrow belt of shales. These sheets are 

apparently absent at every place where the beds are in their normal 

position. The faults will be referred to again under the head of " Eruptive rocks, 1 ' where this intrusive sheet is described in detail.

In view of the fact that no fossils have been found in the quartzite, 

and that those from the beds above have been only cursorily examined, 

it is impossible to designate with exactness its position in the geological scale. From the preliminary examination of the fossils of the 

Cambrian and Devonian portions of the section Mr. Walcott has no 

doubt that this region belongs to the same geologic province as do the 

Paleozoic rocks of the " Eureka district," and if we attempt to correlate the two sections this quartzite should be at least provisionally correlated with the Prospect mountain quartzite, which he considers to be 

of Lower Cambrian age.

Flathead shales. AboVe the quartzite, separated from it in several 

places, as already indicated, by a layer of eruptive rock, follows a series 

of rather shaly beds, which, owing to their generally soft character, 

form one of the deepest of the ravines met with in crossing the country 

at right angles to the strike of the beds. These shaly beds attain a 

thickness of about 200 feet, and seem to be transitional in their lithological characters. The detailed sections show them to be made up of 

beds in which the arenaceous element largely predominates in the lower 

portion near the quartzite, but gradually becoming more and inors 

calcareous as we ascend towards the base of the massive limestones 

that lie next above. There are thin beds of glauconitic limestone interlaminated with- the shales, and several of these bauds have 'been 

found to be fossiliferous. They are frequently micaceous on the surfaces and contain green grains of what is apparently glauconite. The 

general color of the beds is green, due in all probability to the occurrence of this mineral. Towards the base there are beds of very dark 

reddish brown and green sandstone that are slightly calcareous and
22 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. 110.

highly fossiliferous in the bottom layer. The shales seen at the top, 

immediately below the limestones, are greenish and purplish, with very 

thin bands of sandstone and glaueouitic limestone in equally thin layers. They are sandy, and separate into laminae of only an inch or two 

in thickness, with green micaceous surfaces. The area occupied by the 

shales is coincident with that of the underlying quartzite.

The weathering of the beds results in their concealment in most 

places, but they form characteristic ravines which can be traced without difficulty abovt the quartzite from the beginning of the fold at the 

Gallatin to the crossing of Dry creek, the zone or belt occupied by 

them widening or narrowing, as shown upon the map, according to the 

effect of the erosive forces upon the overlying limestones.

The Flathead shales are fossiliferous at about three horizons, the first 

near the base, the second a little below the middle part, and the third 

near the top. The collections have not been specifically determined, 

but there is apparently no difference in the specimens from the different horizons. The following genera were identified:

Lingulella.

Hyolithes.

Ptychoparia.

An exact reference of these shales ca'n not, therefore, be made at 

present. So far as lithological characters go, they seem to be transitional between the Flathead quartzite and the trilobite limestone, but 

where the line between the Lower and Middle Cambrian should be 

drawn if they are in part of Lower Cambrian age it is at present impossible to say.

GALLATIN FORMATION.

The lower limit of the Gallatin formation has been drawn at the base 

of the first well defined limestone (trilobite limestone). The shales 

that immediately follow the latter attain a greater thickness than do 

the limestones or their underlying shales, but they are more calcareous 

than arenaceous, while in the Flathead shales the latter character is 

predominant. There are three belts of limestone and two of shaly 

beds, the upper one of the latter being comparatively thin.

Trilolite limestones. Immediately following the fine green sandy 

shales that lie at the top of the beds described as the FJathead shales 

are thin bedded limestones dark gray in color, breaking into lamime of 

an inch or two in thickness. These lamince are highly fossiliferous 

wherever they have been examined, and at several localities have at 

the ^ottom a few thin bands of greenish shales containing concretions 

which are full of trilobite remains. The very lowest limestone is about 

3 feet in thickness, followed by 6 inches of shale and then 7 feet more 

of limestone, above which are found dark blue lami"ated limestones 

breaking into lamina) 2 or 3 inches thick. The total thickness of 

the trilobite limestones is about 120 feet. The central portions are 

massively bedded, while the upper part becomes more and more lami-
WSALB.] CAMBRIAN GALLATIN FORMATION. 23

ililted, pebbly layers also being found at the top. In the latter a few 

indistinct remains of trilobites were found. . These limestones are very persistent and form a low bluff back of 

the sharp ridge formed by the Flathead quartzite, from which they are 

separated by the shaly interval already described. They are characteristically fossiliferous, especially at the base, as already indicated.

The list of fossils identified by Prof. F. B. Meek from the collections 

of 1871 (made mostly by the writer) has been revised by Mr. Walcott 

after comparison with the collections made in 1884, and the following 

list is the result:

Lingulella sp. ? Agnostus bidens.

Kntorgina sculptilis. Ptychoparia gallutinensis.

Acrotreta gemma. Oleuoides serratus.

Hyolithes gregaria. Bathyuriscus? liaydeni.

Of this Mr. Walcott says: "The facies of the above group of species correlates the horizon at which they occur with that of the Middle 

Cambrian zone of the Nevada and British Columbia sections. There 

is not, to my knowledge," he says, " such a, grouping of genera and 

species at any known Upper Cambrian horizon."

The collections examined by Prof. Meek and revised by Mr. Walcott 

came from only three or four localities in all, while the collections made 

since then are much larger, and represent the same horizons from at 

least a dozen localities. The later collections have not yet been thoroughly examined, but when they are the list of species will undoubtedly 

be greatly enlarged.

Obolella shales. For a space of 280 feet above the trilobite limestones 

the outcrops are very obscure in most places, owing to the soft character of the shales, whose erosion has caused the formation of deep ravines 

parallel to the strike of the beds. Such exposures as have been seen, 

however, leave no doubt that the entire space is occupied by shaly 

beds, which are mostly calcareous. There are a few thin bands of limestone and several calcareous sandy beds with micaceous surfaces in 

the central portion of the outcrops. The lower beds are covered from 

the breaking down of the shales above, and the upper beds are concealed by the yellowish debris washed down from the overlying lime- 

 stones. Very tine, rather dark greenish shales prevail in the lower 

part, while the upper beds are very much lighter in colpr. The only 

organic remains found were from the middle of the series, and they consist solely of undetermined species of Obolella, from which the shales 

nave been provisionally named the Obolella shales.

Mottled limestones. The trilobite limestones and overlying Obolella 

shales are followed by massive-bedded limestones that form one of the 

characteristic topographical features of the area under consideration. 

They weather into the first high and prominent bluff face that is 

met with after leaving the Flathead quartzite. These beds are well 

shown in PI. v where the mottled limestones come to the river's
24 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL.UO.

edge in the extreme left of the illustration, and can thence be readily 

traced, forming the line of bluffs back of the ridge of Gallatin quartzite 

which is seen in the central portion of the picture. The name mottled 

has been applied to these limestones from the mottling of yellowish 

and dark spots observed in the central portion of the beds. This 

mottling, however, is not peculiar to them. It occurs also in a slight 

degree in the trilobite limestones and in some of the Jefferson limestones. The total thickness is about 260 feet. The lower 20 or 25 

feet consists of laminated beds, generally of a light gray or brownish 

color; some of the layers are glauconitic and oolitic and contain 

remains of trilobites (Ptychopariaf) and hyolithes.

The mottled portions are light bluish gray and massively bedded, 

gradually becoming more and more laminated as we approach the top, 

where they are again glauconitic and pebbly, with numerous fragments 

of fossils, mostly trilobites. None of the collections from these beds 

have been studied by the paleontologist, but the facies is apparently 

not very different from that of the trilobite limestones. Until more 

specific determinations are made it can not be stated whether these 

beds are referable to the Upper Cambrian or to the Middle Cambrian.

Dry creek shales. An interval of shales or shaly calcareous sandstones follows the glaucouitic and pebbly layers that cap the mottled 

limestones. The outcrops are naturally obscure in most localities, and 

the best exposure noted was found on Dry creek, where the total thickness is about 30 feet. Here they consist of brownish yellow, red, and 

pink sandstones, saccharoidal in structure, breaking into thin laminae, 

with streaks and seams of calcite. So far as examined they are nonfossiliferous.

Pebbly limestones. Passing up from the narrow belt of the shales just 

described we find a series of light colored laminated limestones, which 

reach a thickness of 145 feet. .They are in bands of 4, 6, or 8 inches to 

a foot, and are pebbly from top to bottom, although the lower bands are 

the coarsest, and contain glauconite abundantly. The pebbles are of 

limestone, and reach a diameter of an inch or two. At the base the beds 

are yellowish brown in color and are somewhat thicker, and generally 

crowded with the remains of trilobites and small shells. As we ascend 

in the beds they become more and more compact, and are mainly dovecolored limestones, with many trilobite fragments in the central portion, 

although the latter are not so numerous or so distinct as at the base. 

These upper beds are not glauconitic. The upper 25 feet are much 

darker in color, more crystalline in structure, probably somewhat siliceous, and gradually approach so closely the general characters of the 

overlying black limestones that it is difficult to draw a definite line of 

separation between them. Dark bluish layers began to alternate with 

the lighter-colored ones as we ascend, and the line for the top of the 

Cambrian has been arbitrarily drawn at the base of the lowest crystalline black limestone, 20 feet above the last fossiliferous horizon of the
i

)

PEALE.] DEVONO-SILURIAN. 25

pebbly limestones. The remains collected here are very fragmentary, 

and, although they are referred to the Cambrian, they are undoubtedly 

on or near the. border line between the Cambrian and the Silurian.

As just noted, three horizons are fossiliferous in these limestones: 

the base, the middle part, and the top.

The lowest fossiliferous band contains innumerable fragments of trilobites crowded in the rock, with shells and pebbles.

The middle beds have two fossiliferous lines separated by only a few 

feet, and from both collections were obtained. They contain apparently 

the same forms as those identified from the lowest layer.

In the latter Mr. Walcott has recognized:

Leptsena melita. Triplesia calcifera. 

Ophilita sp ? Ptyclioparia sp ?

Of the forms specifically indentified he says: " In the Eureka district 

section they occur in the Cambrian and pass into the base of the Ordovician." It is possible, therefore, that these beds may eventually have 

to be taken from the Cambrian and referred to the Silurian (Ordovi 

cian).

DEVONO-SILURIAN.

The pebbly limestones just described, and referred to the top of the 

Cambrian, pass gradually and almost imperceptibly into a series of 

black crystalline limestones, which for about 700 feet have as yet yielded 

no paleontological evidence that is conclusive as to their age. The 

lower 350 feet of the beds are barren of all remains so far as we have 

examined them, but careful search in other localities may be rewarded 

by the finding of fossils which are as likely to prove the Silurian age 

of the lowest beds as to determine their reference to the Devonian. 

The pebbly limestones have every indication of being on or near the 

border line between the Cambrian and the Silurian, and there is a possibility of a part of the beds being Silurian. A part of the beds 

above may also have to be so referred eventually. They will all, 

however, be described under the head of Devonian, inasmuch as the 

very meager remains found in the middle portion have more the aspect 

of the Devonian than of the Silurian.

The evidence for the presence of Silurian beds in the Eocky mountains is still very meager, and may be briefly detailed as follows:

In 1871 Dr. Hayden obtained from limestones above the Potsdam in 

Box Elder canyon, Utah, a specimen of Halysites catemdaria (catenulatusf). !

From the finding of this fossil in Utah and the occurrence of Upper 

Silurian fossils in the Nevada section the 100 to 200 feet of the Ute limestone in the Wasatch section is referred by King to the Upper Silurian.2

'Seepp. 15 and 373, Hayden Eeport for 1871. (In vol. 1, Systematic Geology, U. S. Gnol.Exploration of the 40th Parallel, p. 178, the finding of this fossil is credited to Prof. F. W. Bradley, who was 

not with the Hayden Expedition of 1871.) 

2 Vol. 1, U. S. Geol. Exploration 40th Parallel, pp. 180, 181.
26 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [DOLL.IIO.

Iii 1872 Prof. Theo. B. Comstoek 1 referred the beds immediately overlying the Potsdam sandstone in the Wind river mountains to the Niagara group from the presence of Halysites catenulatits and other corals 

of the genera Cyatliopliyllum and Zaphrentis, with a specimen of an 

Orthoceras and a poorly preserved brachiopod resembling Pentamerus 

(galeatusf).

A series of limestones in Colorado, occupying the same stratigraphical position in relation to the Potsdam, has also been referred to the 

Silurian.2 -

In Mr. Hague's Eureka section of Nevada3 there is a considerable development of Silurian with a characteristic fauna in the lower portion 

and some imperfect corals of the genus Halysites in the upper part. 

Mr. Walcott also refers to the occurrence of Halysites catenulatus at 

the same horizon in the White Pine district. (See p. 4 of Paleontology 

of the Eureka district.) Although these latter are not in the Eocky 

mountain region, they are mentioned here because a large number of 

the species in the collections from the upper part of the Devonian of 

our section are identical with species occurring in the Upper Devonian 

of the Eureka section, and the Cambrian of the Gallatiu section also 

bears a general resemblance to that of the Eureka section.

Mr. R. G. McConnell,4 of the Canadian Geological Survey, in his general section of the formations examined by him in the vicinity of the 

51st parallel recognizes the Silurian horizon in a series of beds 1,300 feet 

thick, which he calls the " halysites beds." 5

Neither Dana and Grinnell,6 nor the members of the Northern Transcontinental 7 Survey obtained any fossils from these beds in the region 

north and northeast of our area^»

In view of the fact that there is no apparent break in the continuity 

of the beds from the top of the Cambrian to the top of the crystalline 

limestones, just above which the Devonian fossils occur in great abundance, I have given them throughout the name "Jefferson limestones," 

simply referring to the fact that the lower portion may be of Silurian 

age, drawing at present only an arbitrary line, dividing them below 

from the pebbly limestones in the hope that future careful search may 

reveal evidence that will establish their age positively.

It is probable that the more we know of the organic remains of these 

beds the more difficult will it be to draw the lines of separation between 

them, for the lithological characters are the same throughout and there 

is little doubt that the sedimentation was continuous, and if there wereany changes in the character of the fauna they probably occurred

1 Reconnaissance of ~N. W. Wyoming, Jones, 1873, p. 112.

2 Geology and Mining Industry of the Leadville Eegion. 188G, p. 60.

3 Third An. Rep. of the TJ. S. Geological Survey, pp. 253,260, et seq.

4 Report on the Geol. Structure of a portion of the Rocky Mountains, etc., 1887, p. 15 D.

6 Report on the Geol. Structure of a portion of the Rocky Mountains, etc., 1887, p. 21 D. 

6 Report of a reconnaissance from Carroll, Montana, to Yellowstone Park and return, Ludlow 1876, 

p.122.

7 Davis's report on Mining Industries of U. S., vol. xv, 10th Census, p. 697.
DEVONIAN. 27

gradually, so we need not be surprised if we find a mingling1 of Silurian 

and Devonian forms of life on the border line. 1

DEVONIAN.

JEFFERSON FORMATION.

As just intimated, it is impossible to define exactly the base of the 

Devonian, but provisionally the entire thickness of the Jefferson limestones is so referred. It includes three fossiliferous horizons, although 

the fragments from the lower'two are so poor that practically only the 

upper one is worthy of mention.

Above the Jefferson limestones are two belts of shales, mostly argillaceous and calcareous, separated from each other by a band of limestone. The upper belt of shales is highly fossiliferous, and from its 

organic remains the first identification of the Devonian in this region 

was made. The divisions of the Devonian will, therefore, be described 

below, under two heads, viz: a. The Jefferson limestone, and I, the 

Three Forks shales.

Although the collections of the Hayden survey from this region in 

1871 and 1872 contained genera common to both the Carboniferous and 

Devonian, as determined by Prof. F. B. Meek,2 the specimens were all 

from the limestones that overlie the Upper Devonian shales, and, as 

will be shown subsequently, were of Lower Carboniferous age.

From the upper shales that lie above the Jefferson limestones the 

writer obtained in 18843 a collection of fossils which were identified by 

Mr. Walcott as proving a well-marked Devonian fauna horizon. This 

was the first positive identification of that horizon in Montana, and in 

1885 another fossiliferous horizon, 40 to 75 feet lower down, afforded a 

meager collection of Devonian forms.

Jefferson limestones. Above the pebbly limestones which were referred 

provisionally to the upper part of'the Cambrian we have beds resembling at first the pebbly limestones, but gradually becoming more crystalline and darker, so dark indeed, as a whole, that in our field notes they 

are usually designated as the "black limestones."

They are well developed in the hills a mile or two north of the East 

Gallatin river and on the main Gallatin above the G-allatin bridge of 

the Northern Pacific railroad, as shown to the right in the illustration, 

(PL vi). Here the river cuts across the ends of the beds almost at 

right angles to the strike. They are also well exposed in the hills on 

bo.th sides of the Missouri just below the junction of the Three Forks

'Since writing above I am, informed by Mr. Walcott that lie has received a collection of LowerSflurian (Ordovician) fossils from th BlacTt hills. He lias also identified the Trenton fauna among name 

of the collections of Mr. Ermnons from Colorado, and has recognized in collections jriade in the 

mountains eastward forms which indicate the probable eqnlvalent of the Pogonip limestones of tlie 

Eureka and Nevada section.

a ]laydeu's (ith Ann. Kept. TJ. S.Geol. Survey, p. 432. (A part of these collections were made by the 

 writer, who unpacked all of them, and in certain that none of them came from the Devonian horizons 

since found and collected from.)

3 Scieuce, vol. V, March 27, 1885, p. 249.
28 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BOLL. 110.

and on both sides of the Jefferson a few miles above its mouth. They 

have been designated the Three Forks limestones because they are so 

well shown at many localities near the Three Forks. 

Although there is considerable difference in detail between the limestones as noted at different localities, still there is a general resemblance between them and they are not easily mistaken. In the Bridger 

range they consist of an alternation of dark, almost black, beds, and 

lighter, mud-colored beds at the top, with a brecciated limestome at 

the very summit of the series. On the Gallatiu the beds are generally 

darker than in the Bridger range, but otherwise the general appearance is the same. They are.brown and blackish in color, and microgranular in structure, due to their being very crystalline, and occur in 

alternations of rather massive beds of the very dark limestones, from 

10 to 15 feet in thickness, with lighter colored, more laminated limestones in layers of 2 feet to 5 or G feet each. At some of the localities 

there are indications of light colored sandy beds near the top, but the 

dark limestones generally prevail to the very top. On the south side 

of the Jefferson the upper and lower portions of the series are considerably lighter in color, the very black limestones being restricted to a 

central zone of several hundred feet. The lower portions here are 

drab-colored crystalline limestones with considerable yellow jasper distributed through them, while the upper part of the section, although 

generally much obscured, consists of light colored limestones of rather 

irregular structure.

On the North Boulder, still farther west, the black limestones are 

more intense in. color, but so far as the structure and general appearance is concerned they are identical with those on the G-allatin. The 

brecciated beds of the Bridger range have as yet not been seen at any 

of these more western localities.

The following analyses were made, in the laboratory of the Survey by 

Mr. Charles Catlett. I is a brownish-black limestone from north of 

the East Gallatin, and II is a very black limestone from the west side 

of the North Boulder valley.

I.

54-54

43-63

 22

 34

mined.

98-73

11.

54-54

42-62

 40

1-78

luined.

99-34

The specimens analyzed are from localities more than 30 miles apart, 

and it will be seen that the limestones are remarkably alike, their composition being that of normal dolomite.
U. S. GEOLOGICAL SURVEY BULLETIN NO. 110 PL. VI

Bndger Limestones Three Forks Sfia/es 

(in Devonian ffaismej.

Three Forte Limestones

SECTION NORTH OF GALLATIN RIVER. 

East of Gallatin Bridge of N. P. R. R.
TKALE.] DEVONIAN. - 29

As previously indicated, only the upper portion of the limestones 

have yielded any recognizable fossils. From one locality about 30 feet 

below the top of the limestones a few fossils were obtained, and among 

them Mr. Walcott has identified the following:

Spirifera disjuncta. Smitliia ? sp. undetermined. 

Chouetes macrostriata. Orthis, sp. undetermined.

Three Forks shales. Back of the Jefferson limestones, which generally dip at angles of 20° to 30° there is usually found a deep ravine 

beyond which the Carboniferous limestones rise with steep bluff faces. 

This ravine is due to the interval of shaly beds which lie between the 

two belts of limestone. For purposes of description the shales may be 

divided into the Lower and Upper Shales. They are separated by a 

band of limestone 15 to 20 feet thick which is grayish brown in color, 

generally very compact and close grained, sometimes micro-granular 

with streaks of calcite, and upon weathering gives a yellow debris. 

The structure appears to be irregular. A qualitative analysis by Mr. 

E. L. Howard in the Survey laboratory proves that it is argillaceous 

and contains strontia in appreciable quantity.

The Lower shales. No good continuous exposure has been seen of 

the entire 50 feet of shales below the limestone just described, as they 

occur so low down in the ravines that they are generally covered with 

the material from above, or if not so concealed, the breaking down of 

their own beds and the intermediate limestone has obscured them with 

an orange-colored debris which is quite brilliant at a number of localities, and generally serves to indicate their position. The beds are, so 

far as known, reddish and brownish yellow calcareous and argillaceous 

shales. No fossils have been obtained from them or from the overlying 

limestones.

The Upper shales. Immediately above the thin band of limestone 

occur the shales referred to several times as containing a fauna characteristically Devonian. They begin at the bottom with about 30 feet 

of tine green argillaceous shales which are generally so soft as to be 

broken down and largely concealed under their own debris. In some 

places these shales are purplish and at others black. In their upper 

part are bands of black or purplish calcareous and argillaceous limestones which are also very soft and shaly, and these beds pass gradually up into dark bluish drab, almost black, limestones, which are highly 

argillaceous and are succeeded by limestones with greenish surfaces 

on their thin bands. They are very irregular in structure, greenish 

gray in color, and contain numerous nodules or concretions which are 

generally filled with fossils. They break into small angular pieces for 

the most part, and the fossils are finely preserved. These greenish 

gray argillaceous limestones become somewhat arenaceous at the top, 

and contain strontia in small quantity. They have a total thickness of 

about 45 feet, and contain fossils at five or six different levels, but as 

there is no apparent difference in the fossils from them, they are not
30 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. IBULL.HO.

separated in the lists. The shales are capped by a yellow, laminated 

sandstone which is usually about 25 feet thick. This sandstone gives 

frequently an orange-yellow colored debris which indicates the position 

of the beds when they are covered, which is often the case. The lower 

part of this sandstone is slightly inagnesian and the cementing material is calcareous. A qualitative examination shows the presence of 

strontia as in the beds just below. Near the Horseshoe bend of the 

Missouri a detailed section shows just below the sandstone a band of 

coal black slate about 5 feet thick, which has misled prospectors, who 

at one locality have sunk a shaft in it for 60 feet in hopes of findingcoal. 1 It is followed by 10 feet of gray limestone crowded with fossils. 

Below are the green shales with bands of limestones fossiliferous in 

many layers. The very knvest beds are also highly argillaceous and 

full of fossils.2

The base of the Upper yellow sandstone at nearly all the localities 

examined contains a few fossils, among which Rliynclionella tethys, Billings [?], occurs most frequently.

The total thickness of the section is about 135 feet. The description 

just given has reference to the region north of the Gallatin and East 

Gallatin rivers. When followed eastward into the Bridger range, the 

beds appear to be somewhat more arenaceous, while to the west on 

the north side of the Jefferson, they are more calcareous, especially 

in the layers that are fossiliferous. South of the Jefferson on Antelope 

creek at the same horizon, below the yellow sandstones, are very hard 

black shales, almost slates, in which a shaft has been sunk to the depth 

of some 20 feet, and a coal claim has been located, although no coal has 

been, found. The slate is coal black in color and has evidently misled the prospectors, as in the locality already noted between Gallatin 

station and the Horseshoe bend of the Missouri. At the latter place, 

however, the beds are not so hard. As they are inclined wherever 

they have been examined, their soft character is the cause of their erosion into one of the most conspicuous ravines of the area under consideration. This persistent topographic feature indicates their position 

wherever the section is crossed, even when the outcrops are concealed 

by the d6bris of the beds overlying them.° In PL vi this ravine occupies the center of the illustration., and at this locality has been named 

Devonian ravine. The beds here are highly fossiliferous, and the first 

fossils found were obtained from the eastward or northeastward continuation of this ravine, 2 or 3 miles from the river. Although so characteristic a feature on the north side of the Gallatin and along the Jefferson river, in the region a few miles farther north, it appears to have

1 In the JeiFerson Valley, jnst below the canon above the station of Sappington, coal is found at 

this horizon with nodules of limestone in it containing Devonian fossils, some of the species being 

identical with those found on the Gallatin and at Horseshoe bend of the Missouri.

2 The fossils from Horseshoe bend have not been studied as yet and therefore they are not included 

in the lists that follow, although there is not the least doubt that many of the same forms occur in 

these collections that were found in the others.
DEVONIAN. 31

escaped the notice of the geologists connected with the Northern 

Transcontinental Survey, who have included the entire series of limestones between the Cambrian and the Mesozoic under the head of the 

great series of mountain limestones 1 . In 1871 and 1872 the Hayden 

survey also included the Devonian as now outlined, and the overlying 

Carboniferous, all under the head of the Carboniferous. The beds just 

described were not recognized, mainly on account of the rapidity with 

which the work had to be carried on, and partly from their obscure 

outcrops, and if any stray fossils from this horizon were obtained (which 

is extremely doubtful), they were referred to in the descriptions as 

coming from the lower Carboniferous limestones, which lie immediately 

above.

The collections of 1884 were obtained at a point about 4 miles northwest of the mouth of the East G-allatin river, and about the same distance northeast of the Northern Pacific Eailroad bridge crossing the 

main Gallatin. Among them, the folloM'ing were identified by Mr. C. 

D. Walcott:

Discina lodensis, Hall [?] Rliynchonellatetliys, Billings.

Streptorhj'iiclius cbemnugensis, Conrad. Atrypa reticularis, Linnarsou.

Ortbis vannxerui [?] Hall [?] Ambocielia;imbonata,Courad.

Cbonetcs mncronata, Hall. Atbyris birsnta, Hall.

Prodnctnslachryinosusvar. limns, Conrad. Atliyris sp. [.?]

Productns speciosns. Aviculopeeten.

Spirifera disjnucta, Sowerby. Grammysia, three sp.

Spirifera engelmanni, Meek. Morliomorpha.

Rbyncbonella pugna, Martin. Nucnla.

Rhynclionella sinuata, Hall. Schizodns.

Of the twenty-two species enumerated in the list, Mr. Walcott says 

"twelve are identical with species occurring in the Upper Devonian 

of the Eureka district, Nevada; of the others, two are Upper Devovonian species in New York State.'7 2 The remaining forms are lamellibranchs belonging to five genera, and the species closely resemble those 

of the Lower Carboniferous of the Eureka district. The collections 

made from the same horizon in 1885,1886, and 1887, have added to the 

number, and the list now includes thirty-nine species, as follows:

Fenestella, sp. nndet. Productus lacbrymosa var?

Discina lodeusis. stigmatus.

Orthis vannxemi. Spirifera disjnncta.

Streptorb.yncb.ns chemim- Spirifera engelmanni.

gensis. Syringothyris cuspidata.

Strophomena rhomboidalis. Atrypa reticularis.

Stropbodouta, sp. ? Ambocoelia uinbonata.

Cbonetes filistriata. Atbyris snblamellosa.

Chouetes mncronata. Atbyris, sp. ?

Prodnctns speciosns. Atbyris birsuta.

Prodnctus laclirymosa var. Ebyncbonella [Stenocblinia. isma] tctbys.

1 Report ou the mining imlustrios of the U. S., vol. XV, 10th census, pp. 079, 701, etc. 

s Sciouce, vol. V, 1285, p. 249.
32 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. no.

Rliynchonella [L] sinaata. Nucula.

Rhynchonella pugna. Grammysia, threo species.

Rhynclionella inetallica. Schizodus.

Rhynchonella horsfordi. Ortlioceras [annulatcd speRhynchonella [Leiorynciras] cies].

laura. Orthoceras, sp. undet.

Rhynchonella, sp. ? Goniatites, sp.?

Aviculopecten. ScMzodus orbicnlaris.

Aviculopecten, sp. undet. Conularia. 

Hodiomorpha.

Of the twenty-three forms specifically determined, thirteen occur in 

the Upper Devonian of the Eureka section, and seven in the Lower 

Devonian of the same, while two are common to both. Four are found 

in the Lower Carboniferous of the Eureka district. Of the remainder, 

at present only generically determined, as Mr. Walcott says, " Five 

have a close resemblance to species of the Eureka Carboniferous," and 

all the genera are found in the Devonian.

There is a faint possibility that when the localities are added to and 

larger collections are made, these beds may be relegated to the lower 

part of the Carboniferous, but at present the preponderance of evidence seems to be in favor of the Devonian. They are certainly near 

the border line and there is no reason Avhy a mingling of forms from 

the two horizons should not be a common occurrence throughout our 

region, not only at this line, but at all the others which lie so close to 

the division lines between the formations.

CARBONIFEROUS.

The carboniferous rocks, although considerably reduced in this section from the thickness originally given them in the Montana Eocky 

Mountains by Eayden and others, are still conspicuous and uniformly 

well developed on the borders of the Gallatin valley, and especially so 

in the northern portion, in the vicinity of Three Forks, where there are 

above the Three Forks shales about 1,600 feet of beds (mainly limestone) which probably are all referable to this period. It is impossible 

to divide the beds into Lower, Middle, and Upper Carboniferous, as the 

fossils collected up to the present time do not present sufficient evidence 

to warrant such a subdivision, although two divisions can be made, 

based partly on the paleontological evidence, but mainly upon lithological and stratigraphical grounds.

The Carboniferous, therefore, is described in this paper under two 

heads, viz, the Madison formation and the Quadrant formation. The 

former are well exposed in the central portions of the Bridger range on 

the east, and in the area adjacent to the Three Forks on the west, as 

well as at the head of the Missouri river at Gallatin city, and wherever 

examined has been found highly fossiliferous. The canyon of the 

Jefferson river presents one of the best and most fossiliferous sections 

of the upper beds.

In the region immediately adjacent to the Three Forks, both the
PEALE.] CARBONIFEROUS. 33

Madison and Quadrant formations are equally characteristic, not only 

in the exposures, but also in the contained fauna, and from top to bottom the sections present the same general characters as are seen elsewhere. The beds consist of bluish gray or drab limestones compact or 

ime grained and even bedded, sometimes in massive beds and often 

laminated, partly pure limestones, partly cherty, and in the upper part 

passing into quartzitic beds that can scarcely be distinguished from the 

quartzites that we have taken as the base of the Mesozoic (Jura-Trias).

For purposes of description the following subdivisions maybe made. 

Beginning at the base the Madison formation is divided into Laminated 

limestones, Massive limestones, Jaspery limestones; and the Quadrant 

formation is divided into Eed limestones and Cherty limestones.

Paleoutologically, the Madison formation appears to be of Lower 

Carboniferous age, and some of the fossils from the lower portion have 

naturally a Devonian facies. The lowest beds of the Eed limestones 

have so far yielded a comparatively meager fauna which does not positively determine its horizon, but which might be Middle or even Upper 

Carboniferous, while the upper portion of the Cherty limestones up to 

this time have given only a linguloid shell and an undetermined species 

of Athyris. However, the collections from the lower horizons indicate 

the Upper Carboniferous age of the greater part at least of the Cherty 

limestones, and possibly also of the Eed limestones, and renders doubtful, therefore, the separation of any portion to which the name of Middle Carboniferous can be applied.

MADISON FORMATION.

The Laminated limestones. Immediately overlying the yellow sandy 

beds of the Upper Devonian, dark colored, compact, and fine-grained 

limestones are found occurring in laminated beds. Indistinct fossils 

are seen on the weathered surfaces of some of these lower layers, and 

among them an undetermined species of Fenestella is always found. 

The rather even bedded limestones continue with little or no change in 

appearance for about 170 feet in vertical distance, when they pass 

gradually into bluish gray Laminated limestones, some bands of which 

weather yellowish on the surfaces. These are about 85 feet in thickness, then follow a"bout 70 feet of Laminated limestones very much the 

same as those just below, except that they are rather lighter in color, 

especially on the weathered surfaces. An analysis of a specimen from 

the base, collected in the Bridger range was made by Mr. Catlett with 

the following result:

Carbonate of lime (CaC03 ) .................. ....................... 88-50

Carbonate of magnesium (MgCOa) .................................. -95

Iron oxide (FejO;j ) ........) . 

Aluminium oxide (Al^Oa).. )

Insoluble (Silica) .............................................'...... 9-98

Alkalies, undetermined .............................................

Total......................................................... 99-81

8046 Bull. 110 3
34 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. 110.

The lowest fossils from the laminated limestones were obtained south 

of the Jefferson river, between Willow and Antelope creeks. There 

have been identified among them the following:

Productus elegans. Lophophylluni, sp. nutlet. 

Productus, sp. ? Strophomeiia rhomboidalis. 

Chonetes, ? Spirifera centronata. 

Aviculopecten, sp. undet. Retzia radialis. 

Rhynchonella, sp. undet.

Mr. Walcott, who examined them, says " the facies is more Devonian 

than Carboniferous." In the upper portions of the laminated limestones 

the following fossils were obtained from the beds east of the Gallatin 

bridge, where the best section was made.

Lophophyllum f sp. Spirifera centronata.

Productus longispinus. Spirifera rockymontana.

Productus semireticnlatus. Chonetes granulifera.

Productus nebrascensis. Rhynchonella, sp. undet.

Productus cora. Terebratula, sp. undet.

Streptorynchus crenistria. Platyceras, sp. undet.

In the upper part of the beds south of the Jefferson, 10 or 12 miles 

west of Three Forks, the following were collected:

Zaphrentis, sp. undet. Spirifera crenistria.

Fenestella, sp. undet. Spirifera, sp. undet.

Streptorynchns crenistria. Retzia radialis.

Strophomena rhoniboidalis. Athyris, sp. undet.

The Massive limestones. Light bluish gray limestones in rather massive layers cbme next above, and in the upper layers which are still 

more massively bedded, a series of fossils is found, among which the 

following have been identified by Mr. Walcott:

Zaphrentis, sp undet. Terebratula bovidens.

Productus cora. Bellerophon, sp. undet.

Streptorynchus crenistria. Retzia radialis.

Chonetes granulifera. Euoniphalus, sp. undet.

Spirifera centronata. Mnrchisonia, sp ?.

Spirifera rockymontana. Phillipsia, sp.? 

Spirifera (Martinia) setigera. Athyris, sp?

At about this same horizon, farther east, or about halfway between 

the .Gallatin river and Dry creek, the following forms were obtained:

Orthis resupinata. Rhynchonella, sp. undet. 

Strophomena rhomboidalis. Lithostrotian, sp?. 

Spirifera centronata.

In the bluffs on the east side of the Missouri river at the mouth of 

the Gallatin the following were collected:

Prodnctus seruireticulatus. Spirifera centronata.

Prbductus, sp? Spirifera (Martinia) liueata.

Streptorynchus crenistria. Retzia radialis.

Chonetes granulifera. Rhyuchonella, sp?

Syringothyris cnspidata, Phillipsia peroccidens.
CARBONIFEROUS. 35

A locality 8 miles west of the Three Forks, about 2 miles nortii of the 

Jefferson river, yielded the following:

Productus speciosus. Orthis impressa? 

Procluctus lachryinosa var. Orthis, sp. unclet. 

Productus cora? Euomphalus, sp. undet. 

Chonetes granulifera. Murchisonia, sp. undet. 

Streptorynchus crenistria. Retzia radialis? 

Spirifera ceutronata.

The following occur south of the Jefferson river about 10 miles 

southwest of the last locality, and represent about the same horizon, 

coming from three localities:

Productus cora. - Atliyris sublaniellosa.

Productus nebrasceusis. Athyris, sp. undet.

Productus semireticulatus. Streptoryuchus creuistria.

Productus, sp. uiidet. Terebratula hastata.

Chonetes granulifera. Terebratula, sp. undet.

Rhynchiuella, sp. undet. Strophodonta, sp. undet.

Spirifera centronata. Orthis resupinata.

Spirifera striata. Orthis, sp. undet.

Athyris lamellosa. Fenestella, sp. undet.

From four localities on the Bridger range the following forms were 

obtained:

Zaphrentis, sp. uudet. Fenestella, sp. undet.

Syriugopora, sp. undet. Productus cora.

Cyathophyllum, sp. uudet. Productus, sp. undet.

Streptorynchus crenistria. Chonetes granulifera.

Strophodonta, sp. undet. Athyris sublainellosa.

Spirifera centronata. Retzia radialis.

Spirifera (Martinia) lineata. Platyceras, sp. undet.

Rhynchonella metallica. Lophophyllum, sp. undet.

Rhynchonella, sp. uudet. Micheliua, sp. undet.

Terebratula, sp. undet. Phillipsia, sp. undet. 

Euomphalns) sp. undet.

In Cherry creek canyon southwest of the Gallatin valley, about 25 

miles south of the Gallatin bridge locality, the same horizon has yielded 

the following:

Orthis, sp. undet. Retzia radialis.

Productus cora. Rhynchonella. sp. ?

Productus semireticulatus. Rhynchonella (compare R. metallica).

Productus longispiuus. Euomphalus, sp. undet.

Productus, sp. undet. Phillipsia, sp. undet.

Streptorynchus crenistria. Atliyris, sp. undet.

Chonetes grauulifera. Terebratula,0 sp. undet.

Spirifera rockymontana. Platyceras, sp. undet.

Spirifera centronata.

The last two lists may represent also a part of the laminated limestones, as the section could not be very accurately measured at these 

localities. About 20 miles east of the last locality, and 12 to 15 miles
36 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. no.

south of the Bridger range, at two localities on Middle creek and Cottonwood creek, the folio wing forms occur:

Zaplirentis, sp. undet. Prodnctus cora. 

Spirifera centrouata. Prodnctus, sp. undet. 

Spirifera, ep. undet. Lophophyllum? 

Athyris, sp.uudet. Strep tpxyuchus crenistria. 

Fenestella, sp. undet. Chonetes granulifera. 

Productus nebarscensis.

These come from iieaf theliue between the massive beds and the Jaspery limestones that lie above and may belong in part to both, as it is 

difficult to draw a very sharp line between them, that will be the 

same at all localities. At one place the Massive limestones maybe much 

thinner and the Laminated limestones thicker, and at still another locality the conditions may be reversed. Usually they are pretty nearly 

evenly divided as to thickness, the laminated portion being above 325 

feet and the more massive portion 350 feet.

An analysis of one of the limestones from these beds shows them to 

be rather pure limestones. The following is the analysis by Mr. Catlett:

Carbonate of lime, (CaC03 ).......................................... 91-96

Carbonate of magnesia, (MgCOa) .................................... 1-35

Iron oxide (FejO^)

Aluminium oxide (A1203 )

Insoluble (silica) .................................................. 5'99

Alkalis ............................................................ undet.

Total ......................................................... 99-88

The Jaspery limestones. Eeturning to the section near the Gallatin 

we find that the upper portion of the massive bedded limestones to 

which we have applied the name Jaspery limestones^ shows a thickness 

of between 500 and 600 feet. These limestones become more and more 

massive as we ascend in them, and are somewhat magnesian and also 

highly siliceous, as the following analysis by Mr. Catlett shows:

Carbonate of lime (CaC03 ) .......................................... 32-28

Carbonate of magnesium (MgCOs) ................................... 13-91

Iron oxide (Fe^Oa) ) .OQ

Aluminium oxide A12 03 ) )

Insoluble (silica).................................................... 50-74

Alkalis............................................................. undet.

Total ......................................................... 97-23

Seams of jasper intersect the beds irregularly. Usually this jasper 

is yellow, but some of the beds contain black, olive-gray, and red varieties. In one place near the west end of the Gallatin bridge the yellow jasper occurs in masses of 6, 8, or even 10 feet thickness. It is so 

abundantly distributed in them that Jaspery d6bris is scattered over 

the surface wherever the limestones are exposed.

The upper 300 or 400 feet of the Madison formation consists of somewhat lighter colored limestones (generally yellowish white and light drab)
CARBONIFEROUS. 37

but still massively bedded. They are all somewhat cherty and jaspery, 

and chert nodules are frequently found arranged in lines parallel to the 

bedding. Many of the beds have geodic cavities, lined with chalcedony 

and drusy quartz. Near the base of the series in the Gallatin section 

the following fossils were collected from a flinty limestone in which the 

specimens were very poorly preserved:

Spirifera centrouata. . Rhynchonella, sp. undet.

Spirifera, sp. undet. Athyris hirsuta.

Rliynchouella horsfordi. ' Streptorynclius crenistria.

A little higher in the series at another locality the following forms 

occur in two layers, separated by a distance of about 30 feet, in a fine 

grained, bluish limestone, which passes down into flinty and jaspery 

layers. The fossils in the lower layer are very indistinctly preserved.

Orthis, gp. Spirifera ceutronata. 

Productus cora. Athyris, sp. ? 

Streptorynchus crenistria.

The highest fossiliferous horizon that we noted in the Madison limestones was in a small gully on the south side of the Jefferson valley, 

below the mouth of Antelope creek, where the stratigraphic relations 

are somewhat obscure. The limestones from which they were collected 

were, however, estimated to be about 100 feet below the red limestones, and yielded the following forms:

Productus cora. Chonetes granulifera.

Productus seuiireticulatus, var. Pleurotoinaria.

Myalina. Retzia radialia.

Euomphalus. Undetermined species of Lamellibrauchs.

Combining the collections of the upper part of the limestones from, 

all the other localities bordering the Gallatiu valley we get the following list, which represents five localities, and may include a few specimens from the purer limestones that lie just below:

Zaphrentis, sp. ? undet. Spirifera striata.

Terebratula, sp. undet. Spirifera (Martinia) pinguis. f

Strophoruena rhomboidalis. ' Discing sp. undet.

Streptorynchus crenistria. Orthis resupiuata.

Productus speciosus. Orthis sp. undet.

Productns seniireticulatus. Athyris rossyi.

Productus sp. undet. Athyris snblamellosa.

Chonetes granulifera. Athyris lamellosa. ?

Spirifera centronata. Athyris, sp. undet.

Spirifera disjuncta. ? Fenestella, sp. undet.

In comparing the collections from the three portions of the limestones, viz, the base, the middle, and the upper part, we find that about 

twenty-one species occur in the lower portion, arid of these there are 

only two that have not been collected from the middle and upper portion, viz: Productus elegans and an undetermined species of Aviculopecten. Five species are common to all the horizons, among them 

Chonetes granulitera, Spirifera centronata, and 8treptorynchus crenistria.
38 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. no.

From the upper portion the list includes twenty-five species, only five 

of which were not obtained from the middle part. Of these two, viz, 

Spirifera disjuncta ? and Ehynchonella horsfordi, occur in the Devonian 

of the Eureka section, and two, Athyris hirsuta and Terebratula hastata, 

are found in the lower Carboniferous of the same section. It will be 

seen, therefore, that with the material in our collections at present it 

is impossible to draw any decisive lines of separation in these limestones, based upon paleontological grounds. The following is the full 

list of forms as identified by Mr. Walcott, from a preliminary examination of the collections:

Zaphrentis, sp. unclet. 

Syringopora, sp. undet. 

Cyathophyllum, sp undet. 

LophophyJlum, sp. undet. 

Lithostrotion, sp. undet. 

Micheliua, sp. undet. 

Feuestella, sp. undet. 

Disciua, sp. undet. 

Chonetes granulifera. 

Chonetes, sp.? 

Productus cora. 

Productus elegaus. 

Productus lachrymosa, var. 

Productus lougispinus. 

Productns nebrascensis. 

Productus semireticulatus. 

Productus speciosus. 

Productus sp. ? 

Productus sp. undet. 

Productus sp. undet. 

Stropliomena rhomboidalis. 

Strophodonta, sp. undet. 

Streptorynchus crenistria 

Orthis resupinata. 

OrtMs impressa. 

Or this sp. undet. 

Spirifera rockymontana. 

Spirifera centronata. ° 

Spirifera striata. 

Spirifera disjuncta. ?

Spirifera (Martinia) pinguis. 

Spirifera, ps. undet. 

Spirifera (Martinia.) setigera. 

.Spirifera (Martinia) liueata. 

Syringothyris cuspidata. 

Ret/ia radialis. 

Athyris rossyi. 

Athyris birsuta. 

Athyris lamellosa. 

Athyris sublamellosa. 

Athyris sp. ? 

Athyris sp. undet. 

Rhynchonella horsfordi. 

Rhynchonella metallica. 

Rhynchouella sp. undet. 

Rhynchonella sp. ? 

Rhynchouella sp. ? 

Terebratula hastata. 

Terebratula bovidens. 

Terebratula sp. undet. 

Aviculopecten, sp. uudet. 

Myalina, sp. uudet. 

Platyceras, sp. uudet. 

Euomphalus, sp. undet. 

Pleurotomaria, sp. undet. 

Bellerophon, sp. undet. 

]\'urchisonia, sp.? 

Phillipsia peroccidens. ? 

Phillipsia, sp. ? 

Phillipsia, sp. undet.

Of Streptorynchus crenistria, which ranges from the base to the top 

of the Madison formation, Mr. Walcott says, "it is essentially the form 

usually identified as 8. chemungensis in the Devonian." Including this 

form we have the following list common to both the Three Forks shales 

and the Madison formation:

Streptorynchus crenisl^ria (or chemungensis). 

Productus lachrymosa var. - 

Productus speciosus. 

Strophomena rhomboidalis. 

Syringothyris cuspidata.

Spirifera disjuncta. 

Athyris sublamellosa. 

Athyris hirsuta. 

Rhynchonella metallica. 

Rhynchouella horsfordi.

Of these Productus speciosus, Spirifera disjuncta, and Athyris sub-
I-EALE.I CARBONIFEROUS. 39

lamellosa are also found in the middle or upper part of the limestones. 

Comparing the list with that of the Eureka section, we find twelve are 

identical with species in the Devonian of that section, seventeen occur 

in the Lower Carboniferous, and seven in the Upper Carboniferous. 

The latter are as follows:

Productus cora or pnitteuiauus. Spirifera rockyinontana. 

Productus longispiuus. Retzia radialis. 

Productus uebrascensis. Terebratula bovideus. 

Productus semireticulatus.

Of these, all but the last one are common to both the Upper and 

Lower Carboniferous in the Eureka district.

AvS a whole, therefore, the Madison limestones have the aspect of the 

Lower Carboniferous, to which they must be, at least provisionally, referred.

QUADRANT FOKMATION.

After the deposition of the Madison formation there was a marked 

change in the character of the sediments, due mainly to the prevalence 

of shallower seas. At one locality north of the Gallatin we find at the 

base of the formation, below the red limestones, a conglomerate limestone, and the lower beds are everywhere quite arenaceous. They are 

also magnesian, although no true dolomites are found. These conditions, 

as already seen, were foreshadowed in the upper part of the Madison 

limestones. Some of the beds are also somewhat argillaceous, but the 

arenaceous character prevails at the base, with limestones developing 

more and more towards the middle, the beds then becoming gradually 

more siliceous until the section ends with quartzites predominating 

Qualitative analyses show that the lower beds contain strontia in 

quite appreciable quantities. There is more lithological variation in 

this portion of the section when different localities are compared titan 

iu any other. The remarks already made apply particularly to the 

Gallatiu, or Three Forks, section. In the Bridger range not only is 

there a difference in the character of the beds, but the section is also 

much thinner, while on the Jefferson the upper beds are less siliceous 

and the fossils more abundant. The Quadrant formation has been 

divided into the Bed limestones and the Cherty limestones. The line of 

separation is a shifting one when different localities are compared with 

each other.

The Red limestones. Conformably overlying the Madison formation 

is a series of beds which, although presenting considerable variation 

in detail, are still easily recognized from their bright, red color at the 

base, their shaly structure and their softness, which causes them to 

yield readily to denuding influences. Their red color, which is particularly brilliant in their debris, renders them conspicuous in most localities. Their general character is that of limestones, although it is 

frequently difficult to determine from hand specimens whether they 

should be called arenaceous limestones or calcareous sandstones. In
40 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. no.

 the Three Forks the base of the section shows red and greenish mottled 

magnesian limestones, with irregular structured gray or grayish blue 

limestones immediately beneath them. Occupying as they do in every 

case the bottom of a ravine of greater or less depth, they are generally 

concealed and in many places can be traced only by the red debris. A 

brecciated limestone appears to lie sometimes at the base and at one 

locality a limestone conglomerate was found. This occurs in irregular 

layers, the whole thickness being only ab.out 1 foot. The pebbles are 

small, mostly of light gray or yellowish color. There are a few rounded 

siliceous grains as seen under the microscope, and cherty pebbles are 

evident to the unaided vision. The small grains are found mainly in 

the cementing material, which is calcareous, and red in color. This 

conglomerate passes into rather coarse arenaceous beds, which are followed by the limestones which here are dark purplish red, the greenish mottled limestones not showing at this locality. The latter are 

best seen in the hills near the Gallatin bridge, where they occur with 

fine grained red limestones, and they may be entirely wanting at the 

other locality. A few of the pebbles in the conglomerate look as 

though they might have been derived from the bright red limestones. 

A specimen of the limestone from the latter horizon has been analyzed 

by Mr. Charles Catlett in the laboratory of the Survey, with the following result:

<?

Insoluble (silica) ................................................... 25 -24

Calcium carbonate (CaCo:! )......................................... 40-21

Magnesium carbonate (MgCog)...................................... 25-25

Alumina ajid iron (A^OsFe^) ...................................... 5-30

Alkalies............................................................ unclet.

Total....................................../,.'................ 96-00

The total thickness of these beds is about 50 feet. In the Bridger 

range they occur as two red streaks, largely argillaceous, separated 

from each other by a band of reddish gray compact limestone. They 

are only a few feet each in thickness and have compact limestones both 

abo0ve and below. Near the mouth of the Jefferson canyon the lower 

red limestones are very much the same as on the Gallatin. Yellow 

limestones occur at the top and the debris resembles yellow ochre. 

Qualitative analyses show them to be argillaceous, and as at many 

other localities they contain strontia.

Near the Gallatin bridge the bright red limestones are followed by 

about 120 feet of purplish gray and bluish limestones with narrow 

bands of red. There is considerable chert irreguarly scattered throughout them, and the upper part of the beds are very compact. Many are 

blue and grayish in color, but frequently purplish bands come in between the others. These upper beds are fossiliferous at two horizons, 

one at the top and the other with very indistinct fragments a little 

above the middle portion.
I'lCALli.) CARBONIFEROUS. 41

From the former the following were collected:

Productus lougispinus. Productus seraireticulatus. 

Productus nebrascensis. Productus sp.? 

Productus cora. . Discina, sp.?

The fossils already referred to as coming from the red limestones at 

the base are as follows:

Streptorynchus crenistria. Clionetes granulifera. 

Productus cora.

In the Bridger range the following were identified from the red

streaks:

Strep.torynclfus crenistria. Clionetes granulifera. 

Prodnctus cora.

Near the mouth of the Jefferson canyon the red limestones at the 

base are probably somewhat less than 100 feet in thickness, and are 

separated from the limestone above by about 20 feet of quartzite. 

These upper limestones are not purplish or reddish, as it is in the Gallatin section, but begiu with a yellowish limestone which is finely conglomeritic, and contains numerous fragments of fossils at the base. 

Among them. Mr. Walcott recognizes the following, viz:

Chonetes grauulifera. Spirifera cainerata. 

Streptoryuchus crenistria. Orthis sp. ?

This conglomerate bears a close resemblance to the conglomerates 

already described as occurring in the red limestones north of the G-allatin river. These beds become more crystalline as we pass upwards, 

and 30 feet above the fossils we find 5 feet of limestones that are crystalline at the base and argillaceous at the top. They are somewhat 

laminated and have fossils at the base. Among them the following 

have been identified:

Zaphreutis sp. ? Orthis pecosi.

Clionetes granulifera. Orthis resupinata.

Productus longispinus? Spiriferina cristata.

Productus sp. ? Phillipsia sp. ?

Five feet above these the following were found:

Productus seniircticulatus var. Spirifera camerata. 

Orthis pecosi. Athyris subtilita.

Then follow 50 feet more of limestones, which are generally light 

gray and quite compact, .especially at the top, where they are also fossiliferous. They contain Productus cora in great abundance, and associated with it Streptorynchus crenistria, and an undetermined species 

of Phillipsia. Qualitative analyses prove these to be rather pure 

limestones.

The Cherty limestones. In the Three Forks section we have separated from the red limestones about 150 feet of beds in which thin bedded cherty limestones alternate with quartzite layers, the former being 

'most numerous in the lower part and the latter predominating at the 

top of the series, which is capped by the prominent bed of quartzite 

which has been provisionally taken as the base of the Mesozoic. The
42 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL. HO.

lower portion of the series consists mainly of gray laminated limestones 

with a pinkish tinge on weathered surfaces. After 25 or 30 feet of 

these beds a layer of about 2 feet of hard gray limestones is seen, above 

which we find a light colored pink or white magnesiau limestone, very 

fine grained and compact, with fossils, among which' the following are 

are most numerous, Productus cora especially being very abundant:

Streptorynchus crenistria. Euornphalus (S.) subrugosus? 

Productus cora. Euomplialus (small species)..

Above this belt the limestones for about 30 feet are very much the 

same as below, compact gray limestones alternating with purplish mottled limestones, and in most localities a few quartzitic bauds come in. 

The limestones are all more or less siliceous. About 12 to 15 feet above 

the fossils last enumerated the following occur:

Chonetes granulifera. Productus cora. 

P.roductus longispinus. Orthis pecosi. 

Athyris, sp. ?

From the same horizon near the South Boulder, south of the Jefferson river, the following were'obtained:

Chouetes granulifera. Productus (like young shells of P. giganteus). 

Productus cora. Athyris, sp. ?

At the locality where the limestone conglomerate \vas seen the following were collected in the limestones from 75 to 100 feet above the 

conglomerate. They came from three layers separated from each other 

about 5 feet, respectively, but showing no specific differences:

Chonetes grauulifera. Orthis resupinata?

Productus cora. Spirifera camerata.

Productus semireticulatus. Spiriferina cristata.

Streptorynchus creuistria. Athyris, sp. ?

These are probably from the base of the Cherty limestones or possibly from, the upper part of the Bed limestones. 1 am inclined to correlate, them Avith the former.

The upper 100 or 120 feet of the Cherty limestones so far have yielded 

no fossils beyond an indistinct linguloid shell and an indeterminable species of athyris, which were found near the lower part. The line at the 

top has been arbitrarily drawn at the base of the Mesozoic quartzite, 

which forms everywhere throughout the region a characteristic topographic feature very useful as a reference line when the beds have to be 

mapped.

Beginning at the top of the section, below this quartzite, a series of 

thin bedded quartzites and cherty beds with flinty limestones continue 

downward for more than 100 feet, with the quartzite layers largely predominating. These beds in places show cherty masses or rolls of about 

an inch in diameter which penetrate the beds at right angles to the 

plane of deposition. Below these beds limestones, which are sometimes 

crysfcalline and generally very cherfcy, make up the most of the section. 

Chalcedonic geodic cavities are numerous, as are also cherty nodules.
PEALE.] ERUPTIVE EOCKS. 43

In several layers the latter are several inches in diameter and frequently 

oval in shape, and are arranged in layers parallel with the bedding. 

Many of the beds are also conglomeritic. They are altogether most 

unpromising beds for the finding of fossils, and up to the present, as 

already noted, they have yielded nothing to determine their exact place 

in the scale.

Combining all the fossils that have been identified from the Quadrant 

formation we get the following list. It must be remembered that their 

examination by Mr. Walcott has been only preliminary, and that when 

the collections are more carefully studied the list will undoubtedly be

considerably enlarged: .

Zaphrentis, sp. ? Orthis resupinata.

Discina, sp. ? Orthis, sp. ?

Chonetes granulifera. Spirii'era camefata.

Productns longispinus. Spiriferina cristata.

Productus nebrascensis. Athyris subtiliia.

Productus cora. Athyris, sp.?

Productus semireticulatus. (Undetermined species of lamellibranchiata.)

Productus, sp.? Euomphalus (S.) subrugosus?

Streptorynchus crenistria. Euomplialus, sp?

Orthis pecosi. Pliillipsia, sp?

Of the twelve forms specifically determined seven were also identified in the collections from the Madison formation, and only one, Strep- 

 torynclms crenistria (chemungensisf), passes down into the Three Forks 

shales (Upper Devonian).

Comparing with the Eureka section we find that one (Orthis pecosi) 

is found only in the Upper Carboniferous of that section, and seven are 

common, to both the Upper and Lower Carboniferous, and two run 

down into the Devonian.

There is an absence of most of the forms so conspicuous in the Madison formation, and there is little doubt but that careful study in the 

future will confirm the reference of these beds to the Upper Carboniferous, a reference now made largely upon stratigraphical evidence.

ERUPTIVE ROCKS.

The only eruptive rocks noted in the section described in this paper 

are found in the Flathead shales, and they may be divided into two 

groups, according to locality: First, the two rocks described by Mr. Merrill as a trachytic or syenitic rock overlain by a dark aphanitic rock 

from the hills north of the East Gallatin river, and, secondly, the 

intrusive sheet near the Horseshoe bend of the Missouri.

The former locality was noted first in 1884 and revisited in 188G. The 

rocks outcrop in the ravines resulting from the weathering of the soft 

sandy shales which lie immediately above the hard sandstones and 

quartzitcs lying at the base of the Ofallatin sjindstones. The rock itself 

has presented no more resistance to the erosive forces than have the 

overlying shales. In most cases it presumably rests immediately upon
44 PALEOZOIC SECTION NEAR THREE FORKS, MONTANA. [BULL- no.'

the quart/ite, a few bauds of shales only occasionally coming in below 

it. It therefore occupies the bottom of the ravine and consequently 

the lower contact is obscured; in fact, throughout the entire 6 miles 

of observed outcrop careful search has not revealed the actual contact 

between it and the underlying quartzite.

The total thickness of the rock in the best exposure examined is 

about 45 feet. Beginning at the top we find in contact with the overlying indurated sandy shales a very compact black rock, tough and 

hard to break. It is usually about 6 inches in thickness but increases 

to 12 inches and frequently thins out to only 3 or 4 inches. . It is de 

scribed by Mf. Merrill as aphauitic, but even the freshest specimens 

obtained after considerable labor show a great deal of alteration, and 

the relations to the underlying rocks are still obscure. Below it for 

about 10 feet is a layer of decomposed rock weathering into a greenish 

d6bris with seams of a pink rock of about an inch in thickness, which 

resembles in general appearance the syenitic (?) rock forming the main 

portion of the outcrop. The harder portions of this pink rock also 

occur somewhat like seams or very irregular veins of from 1 foot to 3 or 

4 feet in thickness, the decomposed material surrounding them having 

apparently the same composition as the harder portion. At the bottom 

of the outcrop, however, the rock again resembles that underlying the 

aphanitic rock at the top. It is a very soft, badly decomposed rock, 

with a dark greenish debris. Neither this nor the upper belt yielded 

anything hard enough to make sections for microscopic study.

As noted on a previous page, these intrusive rocks are found in connection with several dip-faults. Three were observed, and the one in 

which the relations are best shown is at a locality north of the East 

Grallatin river, a few miles above its mouth, where the basal quartzites 

of the Flathead formation are found in characteristic outcrops on the 

right of a ravine in a prominent ridge, the end of which abuts against 

the shales and upper part of the intrusive sheet, which is exposed on 

the left side of the ravine in the lower part of a bluff. Opposite this, 

and below the ridge just referred to, the eruptive rock abuts against 

the micaceous sandstones of the Belt formation, which lie below the 

first-mentioned outcrop of the basal quartzites. The fault, therefore, 

is practically at right angles to the strike of the beds, and lies in the 

ravine formed by a small stream flowing along its line, the downthrow 

being on the left or west side. The horizontal displacement was estimated at about 300 feet, the throw being from 100 to 150 feet. The dip 

of the beds on the side of the downthrow is 20° and on the opposite side 

it is from 25° to 30°.

The ends of the beds in the narrow belt of shales lying belor^ the 

erupted mass curve to the south close to the line of faulting, while 

on the opposite or east side of the fault a very slight turning to the 

north was observed in the ends of the Belt formation. In the overlying limestones no trace of the fault could be found. In the fault on
ERUPTIVE EOCKS. 45

Dry creek, which was the most eastern one noted, the line 01 disturbance cuts across all of the beds from the Cambrian to the upper part 

of the Carboniferous limestones, where the latter pass out of sight 

beneath the overlying lake beds, which also conceal the fault line.

Following the Flathead shales to the most western fault, we find 

the exposures so obscured that the relations could not be definitely 

determined, but so far as we could see no faulting occurs in the overlying limestones.

From the stratigraphic position of these rocks we can infer only that 

they are of post-Cambrian age, for they have not as yet been found in 

rocks of later age in our district. A few miles farther to the northwest, in the Cretaceous section, certain peculiar eruptive rocks occur, 

in one of which the preliminary examination suggests that eventually 

some relationship between the two occurrences may be determined. 

There is a possibility that the faulting may have occurred subsequent 

to the uplifting and folding of the beds, and also after a certain amount 

of erosion had been effected. If so, it would indicate a post-Cretaceous 

or perhaps even a late Tertiary age for this intrusion. Whether there 

Avas one intrusion or whether the two rocks were erupted at different 

times will probably be determined only when the decomposed material underlying the upper aphanitic rock can be traced into a more 

solid mass that has not undergone such complete alteration. The two, 

although always occurring together, are, as already stated, entirely 

distinct in their structure, and Mr. Merrill is unable to trace any connection between them.

The intrusive sheet in the Flathead shales near Horseshoe bend of 

the Missouri, according to Mr. Merrill, has no connection with this 

rock, although it suggests certain relations with another intruded rock 

found in the Cretaceous rocks of Nixon basin of Cottonwood valley, 

which may possibly be a connecting link between the two. These suggestions at present, however, are too vague for further remarks here.

NOTES ON THE PETROGRAPHY OF THE PALEOZOIC SECTION 

IN THE VICINITY OF THREE FORKS, MONTANA.

BY GrEo. P. MEREILL.

The rocks described in. the following notes comprise (1) specimens 

collected by Dr. Peale from the Archean outcrops exposed along the 

western face of the Bridger mountains between. Bridger creek and 

Spring hill5 (2) for comparison with tlie former, from which they were 

evidently derived, specimens of fragmental rocks from the Belt group, 

as shown along the north side of the Bast Gallatin river and in the foothills of the Bridger range between Spring hill and Flathead rjass; (3) 

specimens from an .intrusive sheet in the lower part of the Flathead 

shales about a mile north of the East Gallatin river, and equidistant 

from Hillsdale and the mouth of the river. In the summer of 1886 the 

writer visited this locality, and thus had an opportunity to observe the 

field relations of these rocks. (4) Three specimens of an intrusive sheet 

from the base of an exposure of the Flathead shales near the Horse 

Shoe bend of the Missouri river.

GNEISSIC ROCKS FROM THE WEST SIDE OF BRIDGER RANGE,

MONTANA.

No. 232. Moutli of Bostivick canyon. The rock is a highly quartzosegneiss, or possibly a quartzite, but with so pronounced a cataclase 

structure that there was felt at first some doubt regarding its true 

nature. In most cases the individual quartz granules are separated 

from one another by a comparatively wide zone of triturated material 

almost as fine as dust and stained reddish by infiltrated iron oxides. 

The only original constituents now recognizable are these shattered 

quartzes, feldspars, if such existed, having been completely crushed and 

kaolinized. The abundant segregations of hematite along the lines of 

crushing give the rock a reddish hue.

No. 233. Bostwiclt canyon. This rock consists essentially of a bright 

green dichroic hornblende, occurring in broad plates quite devoid of 

crystal outlines, but with deep rounded embayrnents, which, together 

with the interspaces, are occupied by badly kaolinized feldspars. The

.47
48 NOTES ON PETROGRAPHY. [BULL. lio.

kaolini^ation has in most cases gone so far that the true nature of the 

feldspars is almost unrecognizable. In a few instances traces of twin 

strite indicate a triclinic variety. The only other constituent worthy 

of note occurs, but rarely, and in the form of pale greenish, almost colorless, rounded crystals with faint pleochroisin, and which show on basal 

sections nearly rectangular cleavages and on longitudinal sections 

give extinction angles as high as 40°. It is presumably a monoclihic 

pyroxene.

No. 234. Between Brldger and Lyman creeks. This rock differs radically from either of the above. It is evidently a gneiss very poor in 

iron-magnesian silicates, but consisting essentially of quartz and potash feldspars with an abundant besprinkling of a plagioclastic variety. 

Here, as in No. 232, a cataclase structure has been developed, though 

in a less pronounced degree. A portion of the feldspar is evidently 

orthoclase, but a much larger portion shows the beautiful basket-work 

structure of inicrocline. The plagioclases are repeatedly twinned in 

very thin bands, some of the sections showing not less than 40 striae 

on face not over 1 mm. in diameter. The most striking feature of the 

rock is the amount of distortion through mechanical agencies exhibited 

by some of the feldspars. In many instances twinning bands show a 

wavy structure throughout their entire length. In others the crystals, 

besides having suffered faulting and slight displacement (as shown by 

the twinning bauds), are often distorted and crimped in a very interesting manner.

No. 235. Bosticiclc canyon. This is also a gneiss, but has suffered 

less from mechanical agencies than has the last. As seen under the 

microscope it consists of 'abundant plates of clear, fresh plagioclase 

nonstriated feldspars, which may be orthoclase, clear colorless quartzes, 

and occasional shreds of brown mica.

No. 236. Limestone canyon, near Spring Mil. This is a highly micaceous gneiss. The thin section shows very abundant small and irregular scales of deep brownish red strongly dichroic mica, comparatively 

large plates of a plagioclase feldspar, orthoclase, finely granular quartz, 

and occasional small and very irregular garnets. In a few instances 

were noticed foliae of a colorless biaxial mica with the brilliant iridescent polarization colors of muscovite. The feldspars are, as a rule, 

badly kaolinized.

No. 237. Locality as above. This is also a highly micaceous gneiss, 

showing under the microscope the same very irregular foli»3 of deep 

reddish brown strongly dichroic mica and occasional garnets and iron 

ores interspersed with quartz granules and badly kaolinized feldspars 

as does No. 236. The garnets are, in the section, of a pale wine color 

and devoid of crystal outlines; the iron ores are apparently magnetite. 

The quartzes contain but few fluid inclusions, and these are of small 

size. The feldspar is in part at least a triclinic variety, but in most 

cases is so badly kaolinized that the twinning bands are quite obscured,
MERRIU,] FRAGMENTAL AND INTKUSIYE ROCKS. 49

i

FRAGMENTAL ROCKS FROM THE BELT FORMATION.

JVo. 224. Clastic rode, from section north of East Gallatin. This con-. 

sists of abundant clear, fresh, and sharply angular fragments of quartz 

and feldspar, interspersed with calcite shreds of mica and a plentiful 

besprinkling of iron oxides. The feldspars, which' are very clear and 

fresh appearing, are in part orthoclase (or microcline) and in part a 

plagioclase variety. The cementing constituent is by ordinary light 

very light greenish, chloritic in appearance, and, betAveen crossed nicols, 

it remains almost wholly dark during an entire revolution of the stage.

Both as regards the mineral character and their relative conditions 

of purity and freshness, this rock resembles very closely No. 234 of the 

gneiss series, from which it was evidently derived.

Nos. 226 and 227. Locality same as above. These are both similar to 

224. No essential differences.

No. 228. Canyon in Bridger range, south of Flathead pass. This 

rock is evidently of the same origin as the above (Nos. 224, 22G, and 

227), but has undergone a certain amount of metamorphism, and may 

be said to stand intermediate between a truly fragmental and a crystalline jock, The mineral fragments, and especially the quartzes, 

have undergone a process of secondary enlargement, and are surrounded by a narrow and very irregular zone of the same substance, 

which merges gradually into the material of the cement. The interstitial or cementing constituent itself is largely chloritic, and remains 

perfectly dark, or polarizes in bluish colors between crossed nicols. In 

places the section shows a crystalline granular structure such as is 

characteristic of the gneisses and schists; other portions show a fragmental structure. As a whole the section resembles that of a clastic 

rock which has undergone a certain amount of metamorphism more 

than a crystalline rock that has suffered through mechanical agencies. 

The rock has the same mineral composition as Nos. 224, 226, and 227. 

The grains, however, too closely interlock and by too irregular borders 

to permit one to consider it a product of sedimentation only.

No. 229 from the same locality as 228, and No. 230 from the limestone 

canyon just north of Spring Hill, are similar.

INTRUSIVE ROCKS IN THE LOWER PART OF THE FLATHEAD

SHALES.

NORTH OF THE EAST QALLATIN RlfER.

The rocks described below outcrop at the base of the sandy shales

that lie just above the basal quartzite of the Flathead formation as

exposed in the hills about 1 mile north of the East Gallatin river.

They have .been traced eastward about 3 miles from the most west8046 Bull. 110 4
50 NOTES ON PETROGRAPHY. [BULL. 110.

cm exposure when they pass beneath the lake beds, but show again 

where the Flathead shales cross Dry creek 3 miles farther to the 

northwest. In all these outcrops they hold the same relation to each 

other. The upper rock is usually from 6 inches to a foot in thickness, 

but sometimes thins out to even less than 6 inches. It lies in close 

contact with the shales, is dark gray, nearly black, in color, tough, flue 

grained, and compact, and shows to the unaided eye only occasional 

small black crystals evidently belonging to a mineral of the, pyroxene 

group, and numerous small reddish amygdules. This is succeeded by 

and seems to pass gradually into a zone of decomposed material which 

carries numerous scales of black mica and which is traversed in a direction parallel with the sheets by several veins from 1 to 2 inches in width 

of a light pinkish feldspar. The lower or underlying rock, which also 

seems to pass into this zone of decomposed material, appears to the 

unaided eye as a holocrystalline mass composed essentially of elongated 

light pink feldspars and abundant small, often radiating, foliae of black 

inica. The microscopic and chemical properties of this rock are given 

below. Although the upper and lower rocks belong apparently to two 

quite distinct types their constant association, even when in sheets but 

a few inches thick, is somewhat confusing. Geologically they appear 

as one and the same body; from a petrographic standpoint they differ 

radically. It is useless to speculate on their possible relationships 

until further outcrops are fouud,-or until, by digging or blasting, the 

nature of the intermediate zone of decompo.sed material is made appai1 -, 

ent. The total thickness of the eruptive sheet or sheets is about 45 

feet.

The Upper Rock. Macroscopically this is a very tough aphanitic 

rock, hard, dark gray, and nearly black, bearing abundant small pseudoamygdules of a dull red or yellowish green color and with rarely a black 

porphyritic mineral sufficiently developed to suggest a member of the 

pyroxene or amphibole group. In the thin section the rock was found 

so completely altered that it was only after repeated sections had been 

cut from samples from various portions of the outcrops that anything 

like a satisfactory idea of its original nature.could be learned. Sections of the freshest samples obtainable show under the microscope a 

nearly colorless devitrifled base impregnated with innumerable small, 

sometimes mere dust-like particles of opacite and elongated yellowish mica-like needles, in places so abundant as to form a truly feltlike groundmass. Scattered thickly throughout this groundinass are 

numerous pseudo-amygdules of calcite, chloritic and ferruginous substances, and occasional badly shattered, imperfect, and greatly decomposed augites.

The amygdules are due wholly to the decomposition of porphyritic 

augites and olivines, as can be determined by occasional still quite 

perfect crystal outlines in the least decomposed portions of the rock,
MERRILL.] INTRUSIVE ROCKS. 51

and are in no case true gas cavities niled with, secondary minerals. In 

a few instances the outlines of these cavities were such, as to suggest 

that the decomposed mineral may have been a feldspar, but this can 

not be determined for a certainty. Sections from the more highly 

altered portions of the rock exhibit interesting changes. The groundmass here, as above, consists of the colorless base so filled with mica (?) 

needles as to be almost felsitic, but the porphyritic augites are replaced 

wholly by light greenish blue, faintly dichroic, somewhat fibrous hornblendes. Although optically these secondary forms are undoubted 

hornblendes, giving maximum extinctions on clinopinacoidal section of 

15°, their outlines, when sufficiently perfect for measurement, are still in 

part at least those of augite. In a number of cases the prism outlines on 

cross sections were measured with results varying from 87° to 90°. 

The cleavage in such cases was somewhat imperfectly developed, but 

I was able to obtain measurements of the obtuse angle varying from 

123° to 125-5°, which is perhaps as close as can be expected in sections

FIG. 1. Paramorphic hornblende.

cut at haphazard. The above features I have endeavored to bring out 

iu the accompanying figure.

Although the hjornblendes are so plainly paramorphic, I have found 

in no case traces of an augitic nucleus, the change being in all cases 

complete. (Fig. 1.)

Chemical analysis of a rock so highly altered can be regarded as 

merely suggestive. The following results were obtained by Mr. Eakins 

on a sample in which the augitic alteration just described was complete:
.')2 NOTES ON PETKOGRAPHY. [BULL.IIO.

Si0.2 ........................................................ 49 -47

Ti02 ......................................................... -21

Al,0.j ....................................................... 12 -15

Cr-zOi ....................................................... Trace.

Fe^O,,....................................................... 1-93

FeO ........................................................ 4-07

MnO..................... .................................... 0-10

BaO ........................................................ 0-03

CaO ........................................................ 9-30

MgO....................... ................................ 10-86

K2 0 ........................................................ 2 -42

Na^O........................................................ 2-08

H.,0 ........................................................ 4-14

P2 05 ........................................................ 0-37

CO.......................................................... 3-31

The association of tliis rock with, that next to be described is peculiar and needs further investigation.

The Lower Eook. In the hand specimen this rock appears to the 

unaided eye as a holocrystalline mass of pink lath-shaped feldspars 

interspersed with very numerous, long, slender, and at times radiating, 

needle-like folia of black mica. As seen under the microscope the 

structure is quite simple, consisting of a holocrystalline aggregate of 

badly kaolinized sanidins, lath-shaped plagioclases, scales of mica, 

scattering granules of iron oxide, apatite needles, and in the interspaces, secondary calcite, plagioclase and rarely quartz. The most 

interesting feature of the rock is the almost constant intergrowth of 

the sanidins with plagioclase, the effect being in the section as if 

each crystal of plagioclase was set in a frame of orthoclase. Unfortunately in the samples at hand both feldspars are so badly decomposed that their optical properties are greatly obscured. The plagioclase alteration gives rise to innumerable minute flecks of a silvery 

white mica, and in many cases the twin structures have become entirely obscured; the potash feldspar has become brown, muddy, and 

opaque, resembling the orthoclase of many granite rocks, and at times 

acts scarcely at all upon polarized light. The effect of this is that 

when the section is examined by a low power and between crossed 

nicols the plagioclases appear surrounded by a dark irregular border 

of varying width. (See Fig. 2.)

That this border is not an individualized base, which it at times 

closely resembles, is shown by still evident cleavage lines and its indistinct optical properties. Such sections as show two sets of cleavage 

lines cutting one another at right angles give their maximum extinctions parallel with these lines and show the optic axes lying in a plane 

parallel with the cleavage most pronounced. Other sections traversed 

by but a single series of parallel lines give extinctions varying from 

Oto9. All the characteristics seem to indicate that the mineral is a 

normal monocliuic potash feldspar. A similar parallel intergrowth is 

mentioned by "Eoseubnsch"* as occurring in the trachyte of Mount

* " Mik. Physiographic" (1885), p. 513.
INTRUSIVE ROCKS. 53

Dore, Auvergne. The mica of the rock occurs only in very irregular 

shreds and is apparently normal biotite. The small plagioclase in the 

interspaces are judged to be secondary both by the position relative to 

the other constituents and by their perfectly fresh and unaltered appearFIG. 2. Microstructure of syenitic rock.

ance. No truly amorphous ground mass was anywhere observed. A 

partial analysis of as fresh a sample of the rock as could be obtained 

yielded Mr. Chatard results as follows: Silica, 58-88; potash, 518; 

soda, 3-40. The rock is therefore of a trachytic or perhaps a syenitic 

type.

The intermediate zone of decomposed material mentioned above was 

observed traversed at intervals of a couple of feet by veins from one to 

two inches in width, composed of a light pinkish feldspathic material. 

Examined under the microscope these veins were found to consist of a 

portion not over a centimeter in width, made up largely of clear pinkish 

nonstriated feldspars. This was bounded on either side by a zone consisting of feldspars and brown mica as in the underlying rock, though 

here the feldspars in no case showed the plagioclase intergrowths, and 

they were, moreover, much less decomposed. These veins would seem 

to have been injected along lines of rift at the time the lower rock was 

erupted. The inicrostructure of the rock as described above I have 

endeavored to bring out in Fig. 2, in which the clear portions with 

twinning bauds represent the plagioclase and the dotted portions sanidin.1

1 Since the above was written these same rocks have been found near Antelope creek in a much 

better state of development and presentation.
54 NOTES ON PETROGRAPHY. [BULL. HO.

INTRUSIVE ROCKS FROM NEAR THE HORSESHOE BEND OF THE

MISSOURI RIVER.

These are massive kolocrystalline rocks, consisting of a feldspathic 

grouudmass, through which are strewn abundant small shreds of 

brown mica and scattering granular aggregates of a nearly colorless 

(in.the section) monoclinic pyroxene. The feldspars are in lath-shaped 

forms, and in large part a plagioclase variety, though sundry unstriated 

forms may prove to be sanidins. All are greatly muddied through decomposition. Augitic and micaceous alteration has given rise to abundant flecks of a greenish and yellowish chlorite.

There is no evident connection between this rock and either of those 

described above.
INDEX.

Paga 

Algonkian ........._..--........--.------ 15,16

Analyses of Algonkian limes tones .......; - 16

Of Carboniferous limestones......... 33,36

Of Devonian limestones .............. 28

By Eakins.........-.----..-..-..-...-- 52

Analysis of Red limestone................ 40

Archean................................... 15

Landof .......... v.................... 1*

Bastard granite........................... 17

Belt formation---------...-- ----15,16,19,44

Fragmental rocks from............... 49

Big Fleet range ........................... 18

Bostwick canyon, gneissic rocks from.. 47,48 

Bridger range.. ..'..10,11,14,17,18,21,28,40,47,49

Building stone ............................ 20

Cambrian.................................. 20

Slates of.............,.......-------.-. 15

Carboniferous............................. 32

Fossils of.............34.35,36,37,38,41,42, 43

Catlett, Charles, Analyses by........16,28,33,40

Cherty limestones of Quadrant formation .................................. 41

Coal in Devonian.......................... 30

Comstock, Theo. B........................ 26

Concretions ............................... 17

Cotton wood isocline . ......._.....-. 12

Dana and Grlnnell cited......... ..:... 26

Davis, W. M., cited........................ 10,14

On Cambrian Slates .................. 15,18

Devonian ._... ..........--....-..- . 27

Coal from.............................. 30

Devono-Silurian .......................... 25

Dip faults.................................. 21,41

Dry Creek..............................22,24,45

Slates at................................ 24

Eakins, Analysis by ...................... 52

EastGallatin group...................... 16

East Gallatin river ...........16,20,27,30,43,49

Eldridge, Geo. H., cited .................. 10

Elk mountains, Colorado................. 11

Eruptive rocks............................ 43

Eureka district, comparison with .......21,25,

26, 32,38,43 

Faults ...................................18,21,41

Flathead formation....................... 15,20

Flathead pass............................. 49

Flatheadquartzite........................ 20,21

Flathead shales........................... 21,45

Intrusive rocks in .................... 49

Page. 

Fossils of Cherty limestones ............. ' 42

Of Flathead shales .................... 22

Ot Jefferson limestones .............'.. 29

Of Madison limestones .... . ...34,35,36,37

Of Pebbly limestones ................. 25

Of Quadrant formation ............... 43

Of Red limestones..................... 41

Of Cambrian....----..............22,23,24,25

Of Carboniferous .34,35,36,37,38,39,41.42,43 

Of Devonian........................... 29,31

Of Trilobite limestones............... 23

Gallatin formation.......___.._.._....._... 22

Gallatin river......................9,12,20,28,30

Gallatin valley..........................10,18,20

Geological folds in Montana ............. 10

Glauconite...._.____..:.._.._._.......... 24

Gneiss..................................... 15

Gneissic rocks of Bostwick canyon ...... 47,48

OfLimestone canyon.................. 48

Hague, Arnold, cited ..................... 14,26

Hayden, F. V., cited .... ................. 9,18

On Silurian...._.....__.__.._.....__... 25

On structure of Montana............. 13

Hayden Survey ........................... 27

Holmes, W. H., cited...................... 9

Horseshoe bend of Missouri........... 13,30,43

intrusive rocks from..._............ 54

Horseshoe isocline........._............ 12

Intrusive rocks in Flathead shales ...... 49

Inversion of strata........................ 11

Isoclinal structure.............._...... 11

Jaspery limestones of Carboniferous.... 36

Jefferson formation..................._ 27

Jefferson limestones..._........_..... 27

Jefferson river .._........ .....:_.._____ 9,14

Jefferson valley _._.__..._.._...'.....__.... 21

King,Clarence, cited......... ............ 25

Lake basins of Montana.................. 14

Laminated limestone of Carboniferous.. 33 

Lewis and Clarke's expedition ......._ 9

Limestone canyon, gneissic rocks from.. 48 

Lindgren, Waldemar..................... 10,14

Ludlow's expedition...................... 10

Madison formation ....................... 33

Madisonrange............................ 11

Madison river......_...__............ 9,14

Massive limestones of Carboniferous.... 34

McConnell, R. G ,.on Silurian in Canada. 26 

Meek, F. B., cited ......................... 23,27

55
56 INDEX.

Page. 

Merrill, Geo. P.,cited.................15,43,44,45

Notes on petrography................. 47

Missouri isocline.......................... 11

Montana, geological folds in............. 10

Montana Mountain ranges............... 13

Mottled limestones ....................... 23

Mountain ranges in Montana _......... 13

Newberry, J. S., cited..................... 10

On Cambrian Slates _. _........... lg

1 Northern Transcontinental Survey .. 10,14,26 

Obolellashales............................ 23

Paleozoic section, nomenclature of.. _. 14 

Pebbly limestones.. ................ 24

Petrography, notes on by Geo. P. Merrill 47 

Pre-Cambrian orographic movements... 19 

Quadrant formation.....__.._........ 39

Eaynold's expedition..................... 9

Red limestones of Quadrant formation.. 39 

Rocky canyon............................. 11

Rocky Mountain structure in Montana.. 10 

Salesville quarry......................... 20

Sectionof Algonkian..................... 17

Shoreline, pre-Cambrian.._........... 14

Siliceous concretions..................... 17

Silurian, evidence of, in Rocky mountains ..<.................................. 25

Three Forks of the Missouri......9,11,12,16,21

Three Forks section ...................... 14

Three Forks shales........................ 16.29

Trilobite limestones ............_....... 22

Types of mountain structure ............ 14

Walcott, C. D., cited ..21,23,25,26,27,32,34,38,43 

Wolff, J. E., cited......................... 10