12 VERTEBRATA OF THE TERTIARY. 



northern base of the Uinta Mountains to the latitude of the mouth of the 

 Big Sandy River nortliward. In this area it reaches a depth, according- 

 to King,* of 2,000 or 2,500 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 1,200 feetf 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. J Dr. 

 Peale found it near the Gunnison River, as he discovered vertebrae of Pap- 

 pichthys, a genus which belongs to this horizon only ; but he did not dis- 

 tinguish it from the underlying formations, so that I do not know its thick- 

 ness at that point. South of this locality it is unknown. 



As already pointed out, this period is especially characterized by a 

 peculiar and rich vertebrate fauna. 



THE XJINTA. 



Resting directly, but by unconformity of sequence, upon all the Tertiary and Cre- 

 taceous groups in the region surrounding the eastern end of the Uinta ^lountaia range 

 is another Tertiary group, that has received the name of " Uinta Group" from Mr. King, 

 and "Brown's Park Group" from Major Powell. § It is possible that this group was 

 deposited continuously, at least in part, with the Bridger Group, but at the places where 

 the junction between the two groups has been seen in this region there is an evident 

 unconformity, both by displacement and erosion. 



The group consists of fine and coarse sandstones, with frequent layers of gravel, 

 and occasionally both cherty and calcareous layers occur. The sandstones are some- 

 times firm and regularly bedded, and sometimes soft and partaking of the character of 

 bad-land material. The color varies from gray to dull reddish-brown, the former pre- 

 vailing north of the Uinta Mountains and the latter south of them. 



The only invertebrate fossils that are kuown to have been discovered in the strata 

 of this group are some specimens of a Pliysa, very like a recent species. Therefore, 

 invertebrate paleontologj' has fimiished no evidence of its assumed Tertiary age and 

 lacustrine conditions of its deposition. Its fresh-water origin, however, seems unques- 

 tionable, because of its intra-continental position, its limited extent, and the fact that 

 none but freshwater deposits are known in this part of the continent that are of later 

 date than the close of the Laramie period. 



To these remarks of Dr. White I add, that several species of vertebrata 

 have been obtained from this formation by Professor Marsh, who has deter- 



• Gool. Explor. Fortiith Pnrallpl, ii, p. 245. 



t Aiiniml Hi-iiort U.S.Geol. Siirv. Ivm., 1873 (1874), pp. 436-437. 

 I Anniiiil R<>port, 187(), p. :it). 



♦ Anuoal Report U. 8. Geol. Siir>-. Terra., 1874, pp. 157, 158. 



