490 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



Apparently the same set of limestone and siliceous strata prevails in 

 the Gros Ventre and Bnffalo Fork Mountains, but time did not permit 

 of more detail examinations beyond recognizing their general similarity to 

 synchronous deposits in other parts of the district. 



Permo-Carhoniferous.- — The discovery of Permian or Permo-Carbon- 

 iferous horizons in the Eocky Mountain region, and in the great jjlateau 

 to the west, was announced now several years since, and their occurrence 

 in this more northern quarter is no more than might have been antici- 

 pated, however interesting the fact. 



As already mentioned, in the low divide next east of Mount Putnam 

 occurs a rather heavy ledge of limestone, overlj-ing white and buff sand- 

 stones and arenaceous shaly deposits, which was found to contain a 

 meagre fauna resembling, so far as the imperfect preservation of the 

 specimens enables the determination of their generic and specific affini- 

 ties, forms prevalent in Permo-Carboniferous horizons. These consist 

 of a little coral, like Stenopora or Ghcetetes, a small Fleurophortis (?), a 

 medium-sized ScMzodus (?), and an obscure shell, which may belong to 

 Athyris. The stratum in which the above fossils occur is overlaid l)y a 

 heavy series of generally buff-gray, sometimes reddish, hard sandstones, 

 with intercalated thin layers of limestone, in which no fossils were de- 

 tected ; and this is in turn succeeded by Jurassic beds containing char- 

 acteristic fossils. The deijosit holding the above-mentioned fossils would, 

 therefore, on stratigraphical grounds alone, be referred to the Ui)per Car- 

 boniferous, while the apparent affinities of the fossils themselves strongly 

 favors their reference to the latest epoch of the period. 



The narrow belt of Palaeozoic that fringes the northeastern flank of 

 the Caribou Eange, at one place between Pall and Pyramid Creeks, re- 

 veals an interesting exposure of the uppermost horizons of the Carbon- 

 iferous. We here meet with associations of fossils, Pleurophonis and 

 other Lamellibranchiate shells, which possess a peculiarly Permo-Car- 

 boniferous facies. The beds containing the fossils belong to a heavy 

 series of limestones and sandstones several hundred feet in thickness, 

 and which somewhat contrast with equivalent horizons in other parts 

 of the district, as will be aj^parent from a comparison of the sections of 

 these beds to which reference has been made in preceding chapters on 

 local geology ; but this may be due to the particularly clear exposm^e of 

 the strata at the present locality, while elsewhere, with rare exceptions, 

 they are much obscured by detrital accumulations in the surface. These 

 Permo-Carboniferous deposits abrujitly cease in a heavy bed of lime- 

 stone, upon which rest the Triassic "red-beds;" while below they were 

 preceded by limestones containing fossils which have been referred to 

 the age of the Upper Coal Measures. 



The northeastern belt in the Snake Eiver Eange exhibits another com- 

 paratively clear exposure of these deposits, where the stratigraphic de- 

 tails of their occurrence are varied to some extent, while paleontologi- 

 cally they offer the same distinctive features which characterize the hori- 

 zon at other localities. But in this quarter, as in the Caribou Eange, 

 the uppermost deposit consists of a heavy bed of limestone, containing 

 a small Pleiirophorus-lilie shell, and IJngiila, and which is immediately 

 overlaid by the tyi)ical "red beds." The section in the vicinity of Sta- 

 tion XL presents a fair view of the relative position of these deposits, 

 which may include a thickness of 500 to 800 feet. In the Teton Moimt- 

 ains and eastern i)ortion of the district it is not improbable similar de- 

 posits will be found to occur, although none were observed in that quar- 

 ter the past season. 



