ABSENCE OF MOLLUSKS IN SALINE LAKES. 243 



In the experiments that have been made in reference to the influence 

 of saline waters on the Hfe and growth of fresh water moUusks, the eifect 

 of common salt (sodium chloride) has principally been considered. The 

 lakes of Nevada, however, are characterized by the presence of alkaline 

 carbonates, which it is believed have a more decidedly deleterious effect on 

 the life and growth of fresh water mollusks than common salt. This con- 

 sideration lends still greater weight to the conclusion that the waters of the 

 former lake were not highly charged with mineral matter during the time 

 the fossil-bearing sediments and tufas were formed. 



The condition of several of the enclosed lakes of the Great Basin at 

 the present time, however, indicates that a very moderate degree of salinity 

 and alkalinity is perhaps' favorable to the growth of fresh water mollusks. 

 Franklin, Ruby and Humboldt lakes are all more highly charged with salts 

 than is the case with ordinary lakes and streams (the total of solids in solu- 

 tion, however, not exceeding a small fraction of 1 per cent.) but have an 

 abundant molluscan fauna. The inference is that a decided althouoh indefi- 

 nite degree of salinity is requisite to produce depauperation. In the more 

 strongly saline and alkaline lakes, of which Mono, Abert and Great Salt 

 Lake are examples, careful search has been made for living mollusks but 

 none haive been found. These lakes are believed to be entirely destitute 

 of both molluscan and piscine life. 



As Lake Lahontan never overflowed, it is safe to conclude that its 

 waters at all times must have been less pure than those of ordinary lakes 

 with outlet. The depauperation of its fossils and their variation in size at 

 various horizons, are thus correlated with known saline and alkaline condi- 

 tions, which also varied with fluctuations of lake level. We conclude, 

 therefore, that at least one cause of the depauperation of the mollusks now 

 found fossil was the chemical composition of the waters they inhabited. 



In reference to the evidence furnished by the Lahontan fossils as to 

 the climate of the Quaternary, a conclusion seems impossible at this stage 

 of the investigation, for the reason that a sufficient cause for the observed 

 variation and depauperation of the shells has been found in the chemical 

 character of the waters in which they lived. If we postulate a cold Quater- 

 nary climate, the logical sequence would be a depauperation of the fresh- 



