139 



[Cope. 



Contributions to the History of the Vertebrata of the Lower Eocene of 

 Wyoming and New Mexico, made during ISSl. By E. D. Cope. 



{Read before the American Philosophical Society, Dec. 16, 18S1. ) 



I. The Fauna op the Wasatch Beds of the Basin of the Big 

 Horn River. 



The basin of the Big Horn river contains the most nortlicrn area of tlie 

 deposits of the Wasatch or Suessonian epoch known. In order to ascer- 

 tain whether tlie fiiuna it contains difiers in any way from that I discov- 

 ered in the corresponding beds of New Mexico in 1874, I sent, during the 

 past season, an expedition, under the direction of J. L. Wortman, already 

 known from his successful exploration of the Wind River basin in 1880. 

 The present paper gives a review of tlie results of the season's work, pre- 

 faced by an account of the geology furnished by Mr. Wortman. The 

 species herein described are being engraved for the fourth volume of Dr. 

 Hayden's report of the United States Geological Survey of the Territories, 

 now passing through the press. 



1. The Geology of the Big-Horn Basin, by Jacob L. Wortman. 



As early as 1859 Dr. Hayden described in detail the Tertiary sediment 

 occupying the upper drainage basin of the Big-Horn river, which he deter- 

 mined as belonging to the lower Eocene formation, and applied the name 

 Wind River group, from its being exposed along the Wind river, a name 

 given to the upper portion of the Big-Horn. From an extensive collec- 

 tion of vertebrate fossils made by the writer at this horizon, during the 

 summer of last year. Prof. E. D. Cope, for whom the collection was made, 

 has, in a bulletin, U. S. Geol. Surv. Terrs., F. V. Hayden, Vol. vi. No. 

 1, 1881, confirmed this determination, and discussed at length the faunal 

 relations they bear both to the Bridger and Wasatch beds respectively. 

 The conclusions reached are, that this series is intermediate to a certain 

 degree, containing genera hitherto regarded as peculiar to each. This 

 upper basin covers quite an extensive area, and is bounded upon every 

 side by lofty mountains. The Owl Creek mountains, which afforded a 

 barrier to the waters of this Eocene lake on the north, has subsequently 

 been cleft by the Big-Horn, leaving a deep and rough canon, thi'ough 

 which it now flows in its course north to the Yellowstone. After passing 

 the Owl Creek mountains it emerges into a second or lower basin, com- 

 monly called the Big-Horn basin proper. This one covers a much larger 

 area than the upper, and like it is walled in by mountain ranges, 

 and filled with a mass of sedimentary rock which is also referable to the 

 lower Eocene series. 



During the summer of the present year the writer has been engaged in 

 further exploration of this interesting region, which resulted in the col- 

 lection of a large number of extinct vertebrates, obtained exclusively from 

 the lower Eocene horizon of the Big-Horn, and which have all been sub- 



PROC. AMER. PHILOS. SOC. XX. 111. R. PRINTED MARCH 11. 1882. 



