150 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



extending southward from the Upper Geyser Basin and the Yellowstone 

 Lake to the southern limit of the Park, and the wagon trail from the Mormon 

 settlements of the Falls River Basin to the great natural meadows of Jack- 

 son Lake, make the region readily accessible. 



sedimentary series. — The sedimentary rocks begin with the Middle Cambrian, 

 which rests directly upon the crystalline schists. The Sheridan quartzite 

 has not been found in this vicinity, nor have any beds resembling the Algon- 

 kian been noticed in the area mapped as Archean. The Paleozoic includes 

 beds of Silurian and Devonian age, whose character and relations appear to 

 be the same as those of like age in the Gallatin Mountains. The Carboniferous 

 series presents no features different from those noted in the northern ranges. 

 The Juratrias, on the contrary, presents a far greater development than in the 

 Gallatin Range, and its typical member, the Teton sandstone, forms bright 

 red outcrops that are especially prominent features of the scenery wherever 

 exposed. The Ellis limestones appear in full development and include the 

 impure, shaly, fossiliferous beds which contain an abundant marine fauna, 

 and the overlying littoral deposit whose character varies from a conglomer- 

 ate or coarse sandstone with comminuted shells to a pure crystalline lime- 

 stone. The Cretaceous, as noted in Chapter V, in the description of the 

 region lying east of the one here described, is essentially a series of sand- 

 stones in which the usual subdivisions are not readily recognizable. The 

 Dakota has been mapped by the occurrences of the basal conglomerate, and 

 the Colorado has been delimited by the upper belt of dark shales that occurs 

 in the sandstones. The Montana group is represented by coarse yellow 

 sandstone, containing numerous fossils. The Laramie has not been found 

 in the exposures of this locality, but is probably buried beneath the rhyolite 

 flows of Pitchstone Plateau. The most northern extension of the Teton 

 Range is a small outlying area of sedimentary rocks which have been 

 upturned by the dacite-porphyry that forms the summit of the Birch Hills, 

 8 miles north of Survey Peak. The structure of the Teton region shows 

 that it is the end of an anticlinal uplift, modified by faults parallel to the 

 axis of the fold; thus, in Forellen Peak the crystalline schists have been 

 faulted against Carboniferous beds, a small area of the Flathead quartzite 

 remaining attached to the gneissic mass. To the west, in the amphitheater 

 at the head of Conant Creek, Cretaceous shales have been faulted against 

 volcanic rocks. 



