BRIDGE R EOCENE. 247 



summit. On the face of Turtle Bluffs, so called from the great quantity 

 of fossil remains of this animal which have been weathered out of the beds 

 of its slopes, the calcareous beds are easily distinguished. One of them is 

 almost entirely made up of remains of Planorhis spectabilis. An analysis of 

 a green calcareous marl from these bluffs, made by Mr. B. E. Brewster, 

 gave : 



Silica - ! 31.28 31.45 



Alumina. 1.83 1.58 



Ferric oxide - 0.22 0.21 



Lime 34.20 3418 



Magnesia 0.11 0.08 



Soda 0.18 0.28 



Potassa : 0.33 0.33 



Carbonic acid 26.79 26.82 



Water 464 4.64 



99.58 99.57 



To the south of Henry's Fork, on the immediate flanks of the Uinta 

 Mountains, which are largely covered by forest growth, the Tertiary beds are 

 mostly disintegrated and concealed beneath the svn'face accumulations, and 

 their actual contact with the upturned Carboniferous strata was not observed. 

 That this line was deeply covered by the deposits of the Wyoming Con- 

 glomerate is rendered probable by the great thickness of these beds now 

 existing on Mount Corson, where it amounts to nearly 1 , 000 feet. In the same 

 way in the higher bench-ridges to the westward, the presence of Tertiaries is 

 rather indicated by their shape than actual observation of the beds, the slopes 

 of the ravines being covered by gravel, and the canon-bottoms, toward the 

 head, containing large accumulations of moraine-material. A considerable 

 extent of the Wyoming Conglomerate is found on the surface of the flat 

 ridge between Black's Fork and Bear River, called Concrete Plateau. On 

 the northern edge of the plateau, it is exposed in a thickness of 100 to 200 

 feet, and consists of a white conglomerate made up of pebbles of white and 

 red quartzite, and sometimes Carboniferous limestone in a calcareous cement. 



