466 THE MAMMALIA OF THE UINTA FOKMATION, 



Washakie at the top, and in regarding the Dinocerata as the group characteristic of 

 the entire epoch. It is interesting to note that where the fauna of the "Washakie 

 basin departs from that of the Bridger basin, it does so in the way of resemblance to 

 the Uinta. 



The geology of the Uinta formation is even more impeifectly known than that 

 of the earlier formations. Dr. White says of it (ISTo. 18, p. 37): " Resting directly, 

 but by unconformity of sequence, upon all the Tertiary or Cretaceous groups in the 

 region surrounding the eastern end of the Uinta Mountain range, is another Tertiary 

 group that has received the name of 'Uinta Gi'oup' from Mr. King, and 'Brown's 

 Park Group' from Prof Powell. It is jwssible 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, Ijoth l)y displacement and erosion." Dr. White has also informed us 

 (orally) that the moliusca of these beds are strikingly different from those of the 

 earlier Eocene. The Uinta deposits are composed of sandstones and clays much 

 like those of the Bridger in appearance. They are of no great thickness and are best 

 developed in the valley of the White Rivci-, a tributary of the Gieen, in eastern 

 Utah and Western Colorado. The mammalian fauna of the Uinta formation, while 

 very distinctly of more modern character than that of the Bridger, is nevertheless 

 quite closely allied with it, more especially with that of the Washakie subdivision, 

 and it should he further remembered that this fauna has as yet been only very par- 

 tially explored, and we may therefore expect that future discoveries will fill up many 

 of the gaps still existing. 



The more extended study of this fauna confirms the generally accepted view 

 that the Uinta group should be placed at the summit of the Eocene, forming the 

 transition to the White River Miocene, with which it has many affinities. The most 

 striking and obvious difference fi'om the Bridger fauna consists in the absence of 

 the great Dinocerata so characteristic of this series, of which no trace has yet been 

 found, nor is it likely that they will be discovered in the future. If present at all, this 

 group must have formed but a rare and unimportant factor in the assemblage of 

 Uinta mammals. Another Bridger type of which no member has been discovered in 

 the Uinta (with a possible exception hereafter to be mentioned) is that of the Tillo- 

 dontia, which seem to have finally disappeared, unless, as some have supposed, we 

 are to look for their successors in the Edentata. The smaller mammals are very 

 much more scantily repi-esented than in the Bridger, though some of this difterence is 

 perhaps due to conditions of preservation, as indeed the Uinta fossils are scantici- and 

 less well preserved than in the immediately preceding or succeeding epochs. A simi- 



