1 882.] Central Region of the United States. 187 



ceous, and rather thin beds of conglomerate are not uncommon. 

 The colors that predominate are greenish-gray and brownish- 

 green, with frequent ash-colored beds. The peculiar condition of 

 hardness of most of the strata, render it one of the formations 

 which most generally present the bad-land scenery ; it permits 

 the erosive action of the elements without general breaking 

 down, great numbers of fragments of the strata remaining in 

 spaces between the lines of destructive action. The result is the 

 extraordinary scenery of Black's Fork, Church Buttes and Mam- 

 moth Buttes, of which mention has been made in various recent 

 publications. 



The distribution of the Bridger formation is limited, and is, so 

 far as I am aware, restricted to three areas, whose mutual connec- 

 tion is as yet uncertain. Its principal mass is in the Bridger 

 basin, which extends from the northern base of the Uinta moun- 

 tains to the latitude of the mouth of the Big Sandy river north- 

 ward. In this area it reaches a depth, according to King, of 

 2000 or 2500 feet. A second district is also in Wyoming, and 

 lies east of Green river, between Bitter creek and the northern 

 boundary of Colorado, in what is called by King the Washakie 

 basin. The depth of the formation there reaches 1200 feet. 1 The 

 third region is in Western Colorado, where it loses much of its 

 importance. Dr. C. A. White found it only 100 feet in thickness 

 near the White river. 2 Dr. Peale found it near the Gunnison 

 river, as he discovered vertebrae of Pappichthys, a genus which 

 belongs to this horizon only; but he did not distinguish it from 

 the underlying formations, so that I do not know its thickness at 

 that point. South of this locality it is unknown. 



As pointed out by Leidy, this period is especially characterized 

 by a peculiar and rich vertebrate fauna. This is of truly Eocene 

 character, as I first showed, but it is distinguished from the 

 Wasatch by various subordinate peculiarities. These are the 

 presence of Dinocerata, and of the leading Perissodactyle genera, 

 PalcBosyops and Hyrachyus, together with the absence of many 

 types, as Coryphodon, Tceniodonta, etc. 



" Resting directly, but by unconformity of sequence, upon all 

 the Tertiary and Cretaceous groups in the region surrounding the 

 1 Annual Report U. S. Geol. Surv. Terrs., 1873 (1874), PP- 436-437- 

 8 Annual Report, 1876, p. 36. 

 Annual Report U. S. Geol. Surv. Terrs., 1874, pp. 157. 158. 



