SUMMARY OF PAL^ONTOLOGICAL EVIDENCE. 249 



Canon where fossils were found in the medial gravels, it is probable that the 

 strata are in part a flood plain deposit, accumulated when the lake was 

 below that horizon. 



SUMMARY. 



The evidence derived from organic remains indicates that Lake 

 Lahontan throughout its higher stages was never a strong saline and 

 alkaline solution. Even during the abundant precipitation of dendritic tufa 

 the lake was inhabited by mollusks in great numbers, and was probably 

 also the home of Teleost fishes of large size. During the thinolitic stage, 

 when its waters were greatly concentrated by evaporation, the absence of 

 fossils indicates that it was uninhabited by either fishes or mollusks. 



The life history of the lake, as we know it at present, cannot be con- 

 sidered as affording definite information in reference to the character of the 

 climate during the Quaternary. The reason is that any change in the 

 molluscan life that might be due to climatic oscillations, is complicated and 

 masked by the effects produced by variations in the chemical composition 

 of the waters. 



When other basins in the same region are explored, especially those 

 which found outlet, the character of their moUusean fossils may lead to 

 positive conclusions in this direction, for in such instances the influence of 

 an abnormal chemical condition of the waters on the growth of mollusks 

 would be eliminated. 



