492 REPOET UNITED STATES GEOLOGICAL SURVEY. 



tion of tlie Snake Eiver Eange is occupied Tby a miicli disturbed belt, in 

 wliich rocks of the age of the Triassic and Jurassic take a prominent 

 part. Their x)osition in that part of the range visited is upon the south- 

 west flank of a faulted anticlinal, the beds dipping into a rather wide 

 depression intervening- between the two Carboniferous belts on the north- 

 east and southwest borders of the range, and which is filled with softer 

 and more recent deposits, probably of the early Cenozoic. But to the 

 southeast, in the neighborhood of the upper entrance to the Grand Caiion, 

 apparently corresponding- deposits are thrown into a series of sharp folds, 

 as indicated by the observations on this region recorded by Professor 

 Bradley. Only at the southern extremity have strata of Mesozoic age 

 been detected in the Teton Eange, where a remnant remains on the west- 

 ern flank descending into the valley of West Teton Pass Creek. But on 

 the northern and southwestern flanks of the Gros Ventre Mountains a 

 fine exhibition of these rocks is met with. Indeed, m the northern de- 

 clivity of the range, to the east, Dr. Hayden, in 1860, discovered repre- 

 sentative formations pertaming to all three of the Mesozoic periods, viz, 

 Triassic, Jurassic, and Cretaceous. The same series of formations, at 

 least the "red beds" of the Trias atid probable Jurassic deposits, have 

 been upraised on the flanks of the Buffalo Fork uplift, which thej^ doubt- 

 less encomi)ass in a belt of variable width. Professor Bradley notes a 

 limited belt of probable Triassic sandstones and red beds in the northern 

 extremity of the mountain ridge between Buffalo Fork and the main 

 Snake Eiver north of Jackson's Basin. 



The rocks of this era in the region under consideration represent its 

 three periods, a generalized section of which is given below: 



General section of Mesozoic formations in the Teton district. 



Sandstones, limestones, arenaceous marls, and indurated clays, nnderlaid by drab or 

 ash-colored laminated marls and fine sandstone, "with lignitic horizons; 300 feet and 

 more. Dr. Hayden. 



Limestones, indurated calcareous shales, variegated clays, and sandstones; 1,000 to 

 2,500 feet. 



Deep-red arenaceous shales, -with drah clays, thin limestone layers, and heavy beds of 

 red, sometimes buff, sandstones; l,C0O feet and less, to 2,500 fieet or more. 



TEIASSIC. 



The "red bed" or Triassic series is well developed in most parts of 

 the district where the strata of this period have been brought to view 

 by ui^heaval and denudation. But, largely owing to the prevalence of 

 siialy matter in their composition, at only few localities are they at all 

 well exposed. In the southwest it would ai>pear doubtful whether these 

 deposits attain anything like their normal development, at least under 

 the typical lithological phases which so uniformly distinguish the hori- 

 zon to the east. In the vicinity of Fort Hall a heavy series of supra- 

 Carboniferous and infra-Jurassic siliceous and calcareous deposits con- 

 stitute a large share of the strata making up the divide ridge betAveen 

 Eoss Fork and the Blackfoot, northeast of Mount Putnam, the relative 

 position of which corresponds to that of the Trias. But if we are to 



