natural sciences of philadelphia. 167 



July 16. 



Mr. Vaux, Vice-President, in the chair. 



Eight members present. 



The following paper was presented for publication : 



"Descriptions of a new recent species of Glycimeris from Beau- 

 fort, N. C, and of Miocene Shells of North Carolina." By T. A. 

 Conrad. 



July 30. 



Mr. B. A. Hoopes in the chair. 



Six members present. 



On leave being granted, Mr. Tryon read the following commu- 

 nication received by him from Dr. Jos. Leidy. 



ON SOME NEW SPECIES OP FOSSIL MAMMALIA FROM WYOMING. 



Fort Bridger, Uinta Co., Wyoming, 

 July 24th, 1872. 



I arrived at this place on the 15th inst. The country is the 

 most remarkable that I have ever seen. It is an immense basin, 

 the bed of an ancient lake, bounded on the south by the Uinta 

 Mountains, and extending far north to the Wind River Mountains. 

 The deposits of the lake, of the tertiary period, are estimated to 

 be about 8000 feet in thickness. The}^ present the appearance of 

 a succession of terraces or table-lands extending southerly from 

 Green River to the base of the Uintas. The country for the most 

 part is treeless, and, except along the watercourses, nearly a 

 desert. The tertiary deposits consist of strata so little inclined 

 that they appear to be horizontal to the eye. The strata are 

 composed mainly of clays, soft and crumbling or more or less 

 indurated, often mixed with sand. Friable sandstones and in- 

 durated marls, often with abundance of fresh-water shells, also 

 frequently occur. The lands are often isolated Iry broad plains or 

 narrower valleys. These isolated lands are named buttes, and 

 resemble great earthworks or huge railway embankments. Fre- 

 quently their eroded sides give them the appearance of a vast 

 assemblage of Egyptian pyramids flanking the plains above. 

 Such assemblages of earthworks, pyramids, mounds, piles of trun- 

 cated cones, &c, rising from a plain, constitute what are named, 

 in various parts of our great West, "bad lands" or "mauvaises 

 terres." 



As the buttes crumble away under the effect of the weather, the 

 fossils of their strata become exposed to view. 



