45° 



ARTHUR SEVAN 



The thickness of the individual formations and their main character- 

 istics are shown in Table I. Many of the thickness values have 



TABLE I 



Formations in the Beahtooth Mountains and Adjacent Great Plains 



Age 



Formation 



Approxi- 

 mate 

 Thickness 



Dominant Characteristics 



Quaternary . 

 Tertiary .... 

 Tertiary (?). 



Tertiary (?) 



and 

 Cretaceous . . 



Cretaceous. 



Comanchean. . . . 



Comanchean and 

 Jurassic (?) 

 Jurassic 



Triassic 



Permian (?) . . . 

 Penn. and Miss. 

 Mississippian. . . 



Devonian. . 

 Ordovician . 



Cambrian.. 



Fort Union 

 (Lance (?) in 

 lower part) 



Livingston 



Montana group: 

 Bearpaw 



Judith River 



Claggett 



Eagle 



Colorado 



Kootenai 

 Morrison 

 Ellis 



Chugwater 

 Phosphorial 

 Quadrant J 

 Madison 



fThreeforks 

 [Jefferson 

 Bighorn 

 [Gallatin 



[Flathead 



Pre-Cambrian . . 

 (Archean?). 



Feet 



? 



? 



8,soo 



3,000- 

 5,000 



I2S 



375 



435 



200-300 



2,000- 

 3 , 700* 



300-500 



150 



350-450 



0-700 

 400 



100 



42s 

 435 

 400 



400 



Glacial drift, stream gravels, talus, and landslides 



Andesitic breccias and lavas 



Yellowish sandstone and shale with several beds of 

 workable coal; contains leaves and fresh-water 

 shells 



Brownish and greenish andesitic sandstone and 

 shale, with a thick member of andesitic agglomer- 

 ate; lower beds are leaf-bearing 



Dark-gray clayey shale with scattered concretions 

 and a few thin sandstones; marine invertebrate 

 fossils 



Soft, gray to yellowish sandstone and sandy shale with 

 some lignitic beds; fresh- and brackish-water shells 



Gray sandstone and sandy shale; marine and brackish- 

 water invertebrates 



Gray to white sandstone, thin- to massive-bedded, 

 with sandy and carbonaceous shale; contains 

 workable coal; marine fossils in lower part 



Dark-gray clayey shale with some intercalated sand- 

 stone and scattered calcareous concretions; marine 

 fossils 



Buff coarse-grained to conglomeratic sandstone, and 

 purple to maroon shale 



Dark -gray to greenish-gray sandstone and shale 



Greenish and reddish sandy shale, gray sandstone, and 

 gray limestone; becomes sandy limestone to north- 

 west; abundant marine fossils 



Red sandstone and shale with beds of gypsum 



Gray quartzite and sandstone, chert, reddish shale, 

 and impure limestone; marine fossils 



Light- to dark-gray, blue-gray and brown limestone in 

 thin to thick beds; chert nodules locally; abundant 

 marine fossils 



Dark-gray, thin-bedded limestone alternating with 

 dark shale; marine fossils locally 



Light- to dark-gray and brown fetid dolomite; com- 

 monly thin-bedded; marine fossils locally 



Light-gray to buflf cliff-making dolomite alternating 

 with thin beds; few marine fossils 



Interbedded limestone and shale, flat-pebble con- 

 glomerate, glauconitic and oolitic beds; marine fos- 

 sils, as trilobites 



Shale, thin sandstone, and thin limestone; basal 

 conglomerate locally 



Mainly granite, granite-gneiss, and mica schist; 

 basic gneiss locally 



* This thickness is doubtfully assigned to the Colorado near Livingston by W. R. Calvert, U.S. Geol. 

 Survey Bull. 471, 1912, p. 387- 



been obtained from the publications to which reference is made in 

 the footnotes.^ 



I The data for the Montana group in this area have been obtained largely from 

 C. A. Fisher, "Southern Extension of the Kootenai and Montana Coal-Bearing Forma- 

 tions in Northern Montana," Econ. Geol., Ill (1908), pp. 93-96. 



