246 



GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



the walls of tlie Trnckee Cafinn. At the base of the layer of dendritic tufa 

 exposed along the Humboldt and Truckee rivers this fossil occni-s in pro- 

 fusion, frequently intermingled with the shells of Pninpliohix. ( )n the bor- 

 ders of the Carson Desert the cases of Cypris have been accumulated by 

 the wind in such quantities as to form small drifts resembling sand dunes. 

 What specific name this fossil may bear has not been determined, but spe- 

 cies with which it is evidently closely related are known to live in both fresh 

 and salt water. Its value, therefore, as indicating the nature of its environ- 

 ment in Lake Lahontan is indefinite. 



Fid. 32. — L.arvfil c.iaes of a f nddis fly encased in litUoid tufa. 



At a single locality, the larval cases of a caddis fly were obtained, 

 which were coated over and partially imbedded in lithoid tufa (Fig. 32). 

 This fossil is very similar to the larval cases of the caddis fly now found 

 abundantly in streams and lakes, and, so far as the evidence goes, indicates 

 that the waters in which the fossils were formed were not intensely alkaline 

 or saline. 



The worm-like larval cases of a fly occur in the tufa about the Soda 

 Lakes near Ragtown, Init these are evidently of ((uite recent date and cannot 

 be considered as Lahontan fossils. 



The fossil from the Lahontnn basin that will probably be considered 

 b}' both geologists and archaeologists as of the greatest interest, is a spear- 



