BQUUS BEDS. 19 



The material of the Ticholeptus horizon is a more or less finable argil- 

 laceous sand ; not so coarse and gritty as the Procamelus bed, nor so cal- 

 careo-argillaceous as the White River. 



The Procamelus bed is extensively distributed. It is found in Kansas, 

 Nebraska, Colorado, New Mexico, Utah, Nevada, and Oregon. 



THE EQUUS BEDS. 



I can give little information respecting the depth and stratigraphy 

 of the beds of this period as they occur on the plains west of the Missis- 

 sippi River, for although sections of them as they occur in Nebraska and 

 elsewhere have doubtless been published by authors, their paleontological 

 status has not been determined for the localities described. My own 

 knowledge of the deposits is based on localities in California and Oregon. 

 In Nebraska they have probably been confounded with the Loup Fork, 

 beds. They represent the latest of all the Tertiary lakes, and include a 

 fauna which consists of a mixture of extinct and living species, with a few 

 extinct genera. • 



I have received fossils of this age from Idaho, Washington, Oregon, 

 and California. The most important locality in Central Oregon is from 

 thirty to forty miles east of Silver Lake.* The depth of the formation is 

 unknown, but it is probably not great. It consists, first, of loose sand 

 above, which is moved and piled into dunes by the wind; second, of a 

 soft clay bed a few inches in thickness ; third, by a bed of sand of 1 or 

 2 feet in depth ; then a bed of clay mixed with sand of unknown depth. 

 The middle bed of sand is fossiliferous. In Northern and Middle Califor- 

 nia the formation is chiefly gravel, and reaches a depth in some localities 

 of several hundred feet. Here, as has been proven by Whitney, it con- 

 tains human remains, associated with Mastodon, Equus, Auchenia, etc. I 

 have obtained Mylodon from the same gravel. 



Traces of this fauna are found over the eastern United States, and 

 occur in deposits in the caverns excavated in the Lower Silurian and Car- 

 boniferous limestones, wherever the conditions are suitable. This deposit 

 is a red or orange calcareous mud, varied with strata of stalagmite and 



* See American Naturalist, 1878, p. 125. 



