174 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



directly beneath the Teton beds, but nothing- similar to the compact siliceous 

 deposits which characterize the Quadrant quartzites in the Gallatin Range 

 has been observed. 



Overlying the Teton beds come the drab limestone, marl, and fine 

 sandstone which mark the Ellis formation, everywhere defined by Jurassic 

 fauna. Fine-grained sandstones which form the uppermost beds of the 

 Ellis formation pass gradually into a coarser and more compact series 

 of sandstones, which here represent the Dakota beds. These in turn are 

 followed by impure sandstones and black shales of the Colorado forma- 

 tion, and these again by the Montana. The latter have already been referred 

 to in describing the geological features north of Huckleberry Mountain. 

 This entire mass of uplifted sediments dips to the south, forming a part of 

 the general syncline which constitutes the Wildcat Peak and Huckleberry 

 Mountain orographic block. About 5 miles east of Lewis River the phys- 

 ical features of the canyon wall change. The Madison limestone, dipping 

 eastward, dies out, and the Mesozoic strata, which to the west are seen only 

 high up on the cliffs, turn and pitch down the mountain slope toward the 

 river. The Mesozoic strata are much faulted and crumpled, and lie inclined 

 at varying angles. Overlying the Madison limestone the Teton red beds 

 incline to the southeast, but the dip soon changes, and the beds which make 

 up the long ridge stretching down to the river dip for the most part to the 

 southwest. 



Both the Teton and Ellis formations are exposed along the south side 

 of the river, but neither the Dakota nor Colorado have been recognized 

 along the river bank. Good exposures are few. The Dakota conglomerate 

 is not characteristically developed, and the slopes for 200 feet above the 

 river are largely covered by glacial drift. On the ridge south of the river 

 and Avest of Coulter Peak, where the Ellis beds are well exposed, dipping 

 at a low angle to the southwest, the drab limestone has furnished Ostrea 

 strigilecula, Camptonectes, and Rhynchonella myrina. Several hundred feet 

 higher up the ridge, in the arenaceous limestone passing into sandstone, the 

 same species were obtained, together with R. gnathophora, and at still 

 another locality on the ridge the beds yielded GryphcEa planoconvexa. As 

 regards the relative position of the horizons furnishing these species nothing 

 definite can be stated. Still higher up the ridge the coarse sandstones 

 assigned to the Dakota formation are well exposed, and above the Dakota 



