PEALE.l DESCKIPTIVE GEOLOGY — SALT EIVER EANGE. 547 



its head opposite Sickle Creek, and flows directly north, in a canon-like 

 valley, which is on the line of what would be the fault, if extended. 

 Opposite the pass the crest of the range is the edge of a monoclinal 

 fold, or what appears to be a monoclinal, for at this point there may 

 be an obscure anticlinal, of which the upper members of the eastern 

 half are removed. The western members present a bluff face about 400 

 to 600 feet high, in which is the following general section, beginning at 

 the base : 



Section No. 13. 



1. Black shales. 



2. Massive limestones. 



3. Interlaminatecl limestones and sliales ; some of tlie latter are probably arenaceous. 



4. Reddish limestones and shales. 



5. Interlaminated limestones and shales, like those of No. 3, but probably more arena- 



ceous. 



At the base of layer I^o. 2 occurs Productus multistriatus. It is 

 this layer that preserves the fold just east of the range. East of this 

 the upper bed appears to be a quartzite, and below it occur the fossils 

 found at Yirginia Peak. The fold is gentlest and broadest just south of 

 Sickle Creek. On Station 56 the beds are steeper in their dip than at 

 the pass. The following fossils were obtained in the beds of the section 

 just given, occurring in layers 3 and 5 : 



Aviculopecten pealei, n. sp. 

 GervilUa, sp. ? 



These are identical with species obtained from near Station 66, which 

 have been identified as Lower Trias. 



At the bend of Glacier Creek as we look north, the quartzites that 

 cap the ridge running south from Yirginia Peak apx)ear to abut against 

 the limestones of the main range, which are here folded into a very 

 sharp anticlinal. The creek cuts directly across this fold. The dip of 

 the quartzites east of the anticling;! is about 30<3 towards the west. The 

 eastern side of the anticlinal dips eastward 80^. As we approach the 

 centre of the fold, this angle diminishes to 75°. On the west side the 

 dip rapidly diminishes to 25°, and the creek soon crosses a rather broad 

 synclinal. The rocks are massive limestones, some containing fragments 

 of zaplirentis. Before leaving the canon the stream crosses another an- 

 ticlinal that is shari^er than the first. The western members of this 

 fold pass under the valley of Salt Eiver. The section in the accompany- 

 ing figure gives the structure of the range at this point. It represents 

 a sharp fold at the east with the beds dragged rather than faulted. The 

 latter was not actually observed at any point near here, and a fold was 

 noted at several places. This, however, was the only point at which the 

 range was crossed. Two stations were made in it, one to the south of 

 Glacier Creek and the other north of it. 



Station 57 is located about eight miles north of Glacier Creek, just 

 above the north line of our district. To reach the station fi?om Salt 

 Eiver Valley, we cross the upturned edges of massive blue limestones 

 that form a rather gentle fold along the western side of the range. On 

 Station 57 the beds are almost horizontal, dipping slightly to westward 

 or rather somewhat south of west, as the trend here is west of north. 

 This is, therefore, the west side of the same antichnal noted on Glacier 

 Creek, near Salt Eiver Yalley. Here, however, it is much broader. 



According to Professor Bradley (Eeport United States Geological Sur- 

 vey for 1872, p. 269) the valley of Snake Eiver, below the mouth of Salt 

 Eiver, is located by an anticlinal fold. This is probably the northern 



