462 THE MAMMALIA OF THE UINTA FORMATION. 



Part I. 



BY AYILLTAM B. SCOTT 

 GEOLOGICAL AND FAUNAL RELATIONS OF THE UINTA FORMATION. 



While the palaeontological relations of the various series of Eocene deposits in 

 the upper Green Eiver valley are, for the most part, quite clear, the stratigraphical 

 relations are as yet hut imperfectly known, and leave many questions still open. Dr. 

 White (iJ^o. 18, p. 35) believes that the entire series is conformably deposited : " In 

 the great region now drained by the Green river, there are three well-marked groups 

 of strata, that come in their order above the Laramie group, and which all agree in 

 referring to the Tertiary period. These are the Wasatch, Green River and Bridger 

 groups, named in ascending order. The Wasatch group is the lowest of a series 

 of three fi-esh-water Tertiary groups, all of which are intimately connected, not 

 only by an evident continuity of sedimentation throughout, but also by the pass- 

 age of a portion of the molluscan si^ecies from one group up into the next above. 

 Not only were the three groups, aggregating more than a mile in thickness, evidently 

 produc(!d by a continuous sedimentation, but it seems equally evident that it was 

 likewise uninterrupted between the Laramie and Wasatch epochs, although there 

 was then a change from brackish to fresh waters and a consequent change of all the 

 species of invertebrates inhabiting these waters." 



King, on the other hand (N^o. G, p. 353 et seq.), adduces evidence to show, not 

 only that the Wasatch and Laramie are very clearly separated by unconformities, but 

 that the three Eocene series are likewise divided by lack of conformity with each 

 other. 



Pala^ontologically the arrangement of the series is less obscure, though if we 

 accept White's view of a continuous sedimentation from the Laramie to the Bridger 

 we shall meet with very formidable dillicuUies. Thus no place is left for the very 

 peculiar and primitive fauna of the Pucrco group, which is not at all represented in 

 the noi'thern basin ; the same reasoning will apply to the transition fauna of the 

 Wind River group, a formation estimated as being 1000 feet or more in thickness 

 (St. John, No. 12, p. 200), bui so far as is yet known confined to the Wind River 

 valley. To assume that the I*uerco is contemporaneous with the Wasatch, the Wind 

 River with the Bridger, and the beds of the Bridger basin with those of the Washakie 



