HILLS WEST OF SNAKE EIVER. 155 



Although the rhyolite lavas of the Park cover and conceal the higher 

 series of strata which formed the flanks of the Teton uplift, subsequent 

 erosion has laid bare a narrow area immediately west of the Snake River 

 meadows in which the Mesozoic beds are exposed. The attitude of the 

 strata shows that they form an anticlinal fold that is one of the lesser 

 flexures of the northern extension of the Teton uplift. This particular fold 

 has a north-south axis, pitching about 5° N., the fold dying away in the 

 region covered by the rhyolite sheet. 



The rocks forming the peak north of Owl Creek, whose summit has an 

 elevation of 1,700 feet above Snake River meadows, have already been 

 noted. East of this peak a low elevation, whose summit is but 7,200 feet, 

 presents excellent exposures of the Triassic and Jurassic series. The basal 

 cherty arenaceous limestones of the Teton formation form the south end of 

 the hill and are cut by the small stream west of it. The summit is covered 

 by the red Teton sandstones, whose detritus is abundant, though good 

 exposures are rare. These sandstones, which are the representatives of the 

 great Red Bed series of Wyoming, consist of lavender-colored, pink, and 

 red sandstones, generally fissile, fine grained, and weathering to sandy 

 clays. On the northern slope of this hill the Teton sandstones are overlain 

 by the gray argillaceous limestones and calcareous shale beds of the Ellis 

 formation, carrying characteristic Jurassic fossils. The strike is N. 70° E., 

 and the clip 40° N. 



Hiiis west of snake River. — North of Berry Creek a long and high ridge extends 

 to the shores of the Grassy Lakes. The eastern flanks of this ridge, extend- 

 ing down to the meadows of Snake River, form benched slopes and a broken, 

 hilly country, in which exposures of the sedimentary rocks are often seen, 

 though the surface is largely covered by drift and is overgrown by vegetation. 

 The Teton formation is exposed at the south end of the ridge, a deep cut 

 eroded in the soft sandstone of this horizon 'continuing the valley of Berry 

 Creek eastward. Above these red sandstones the gray beds of the Ellis 

 formation are seen, forming the 8,500-foot knoll at the south end of the rido-e. 

 This formation presents the same two divisions which are so characteristic 

 a feature of its development in the Gallatin Range. The lower part of the 

 series, the Ellis limestone, consists of thinly bedded, impure, argillaceous, 

 gray limestones and lead-colored calcareous shale, weathering readily and 

 containing an abundance of fossils of characteristic Jurassic types. These 



