194 The Tertiary Formations, etc. [March, 



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. 1 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 one or two 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 

 California the formation is chiefly gravel, and reaches a depth, in 



Fiu. H. — Sand hills, Northwestern Nebraska, from Hayden. 



some localities, of several hundred feet. Here, as has been proven 

 by Whitney, it contains human remains, associated with Masto- 

 don, Equns, Auchenia, etc. I have obtained Mylodon from the 



Traces of this fauna are found over the Eastern United States, 

 and occur in deposits in the caverns excavated in the Lower Silu- 

 rian and Carboniferous limestones, wherever the conditions are 

 suitable. This deposit is a red or orange calcareous mud, varied 

 with strata of stalagmite and gypsum. Remains of the fauna are 

 found in clay deposits along several of the Atlantic rivers, as the 

 Delaware and Potomac. 

 'See American Naturalist, 1878, p. 125. 



