CHAPTER VII. 



RfiSUMli; OF THE HISTORY OF LAKE LAHONTAN. 



The history of the fluctuations of the Quaternary lake of northwestern 

 Nevada is recorded in various ways, as has been described in the last three 

 chapters, which treat it from the physical, chemical, and biological stand- 

 points; in the present chapter it is our purpose to present briefly the con- 

 clusions based upon these various lines of evidence. The phenomena 

 observed have great diversity of character, but when interpreted in terms of 

 geological history, they support and supplement each other in sucli a way 

 that the conclusions drawn are believed to be well sustained. Moreover, 

 the facts observed in the Bonneville basin and in more than a score of desert 

 valleys throughout the northern half of the Great Basin which contained 

 contemporary water-bodies, harmonize with the interpretation of the La- 

 hontan record here presented. 



The fact that all the minor basins in the arid regions of the Far West 

 are filled to a depth of many hundreds of feet with alluvium and lacustral 

 sediments, together with the occurrence of the beach lines of the Quaternary 

 lakes on the surface of the vast alluvial cones, leads to the conclusion that 

 all these basins were barren deserts before the rise of the Quaternary lakes. 

 The pre-Lahontan condition of northwestern Nevada nuist have closely 

 resembled its present charaot.er, but at times it was probably completely 

 desiccated. 



The change of climate admitting of the existence and gradual expan- 

 sion of lakes in the various valleys throughout the Great Basin caused a 

 number of those situated in northwestern Nevada to rise sufficiently to unite 

 and form a single irregular water-body 8,922 square miles in area. This 



