THE MAMMALIA OF THE UINTA FORMATION. 463 



basin, Avould involve very complicated hypotheses of barriers and mij^rations for 

 wliich there is no present evidence. The fauna of the Wind River deposits has been 

 shown by Cope (No. 1) to be intermediate betAveen the "Wasatch and the Bridger, 

 mingling types which elsewhere are found only in one or other of these formations 

 with some forms peculiar to itself Thus such typically Wasatch genera as Coryph- 

 odon, Phenacodus, Didymictis, Calamodon and E$thonyx are associated with equally 

 typical Biidger genera, Palceosyops, Lamhdotheriwn, Mkicis and Microsyop^, while the 

 earliest and smallest known member of the Dinocerata, Bathyopsis, is confined to 

 these deposits. Thus the Wind River formation occupies the same intermediate 

 position between the Wasatch and Bridger palreontologically as does the Green River 

 stratigraphically. One is therefore led to infer with Cope (No. 2, p. 453) that the 

 Green River and Wind liiver are parts of the same formation, though the entire 

 absence of mammalian fossils from the former renders this determination somewhat 

 uncertain. It may perhaps be objected to tTiis view that in South westei-n Wyoming 

 the Bridger beds lie conformably upon the Wasatch. This conformity is, however, 

 not improbably deceptive, for the following reasons : (1) King states (No. 6, p. 380) 

 that he has observed unconformities between the Wasatch and Green River beds. 

 "In the region east of the Wasatch a large amount of the Vermilion Ci'eek [Wa- 

 satch] series was left in a nearly horizontal position and the sediments there sank 

 quietly through deep water upon an appi'oximately level bottom, accumulating in 

 strata nearly conformable with the underlying Vermilion Creek rocks. From the 

 manner in which tlie rocks of the Green River group abut westward against the Ver- 

 milion beds, it is evident that there was in the region included between the Wasatch 

 and Uinta a highland lifted above the lake of the Green River period." (2) The 

 direct contact between the Wasatch and Bridger strata at the west of the Bridger 

 basin takes place by the latter bed's overlappiiir/ the Green River and thus reaching 

 the Wasatch. If we assume that the Green River shales represent a distinct series, 

 this oveilap can be explained only by supposing either that these beds had been 

 swept away from the western part of the basin before the deposition of the liridger 

 series, oi', what is much more probable, that a series of disturbances first contracted 

 and then expanded the waters of the lake. (3) It is im[)03sible to account for the 

 faunal differences between the Wind River and tlie Wasatch on the one hand and the 

 Bri<lger on the other on geographical grounds alone, as this area is encompassed 

 ]>()tli on the north and the south by typical Wasatch beds. 



The balance of evidence would thus seem to point to the conclusion that the 

 Wind River beds are to be regarded as forming the base of tiic Bridger scries, and 

 this view has the further advantage, thai the Bridger, thus deliued, is characterized 



