CHAPTER VIII. 



-QUATERNARY CLIMATE. 



In preceding chapters we have considered the pliysical, chemical, and 

 biological histories of Lake Lahontan, as determined from facts gleaned 

 here and there in its now empty basin. In each of these chapters reference 

 has been made to the climatic conditions on which these vaiious elements 

 of history depended. In the present chapter it will be our aim to review 

 the evidence afforded by the records of the ancient lake which have a bear- 

 ing on the determination of the climatic conditions that j^ermitted of Its 

 existence. 



The investigations of naturalists have shown that the fauna and flora 

 of a region are expressions of its climatic condition. To the geologist, tlie 

 physiography of a counti'y reflects, with nearly equal clearness, the eftects 

 of that resultant of a plexus of independent meteoric forces, designated by 

 the term climate. Each year, as the seasons succeed each other, the geo- 

 logical changes, that are ever active, although so slowly and so silently 

 that manv times they escape observation, may be correlated with the ele- 

 ments of climate on which they are most closely dependent. Of the atmos- 

 pheric forces at work, on every hand, in remodeling the earth's suiface, 

 those dependent upon humidity and temperature are the most obvious. 

 These vary in intensity with the seasons, and at times their independent 

 workings may be observed. Throughout the geological ages these same 

 invisible agents of the air have never ceased to woi'k changes on the earth, 

 at times surrounding it with warmth, beauty, and life, and again, as the 

 aeons passed on, blotting out the fair ])Icture themselves had drawn, and 

 replacing it with cold, desolation, and death. • 



The general effects of climate are so well known that one may predict 

 the results pi'oduced by its various elements on the aspect of a given region. 



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