INTRODUCTORY. 157 



This extension of the investigation begun in the Sierra Nevada has fur- 

 nislied us with interesting resuhs, in a great measure corroborating those 

 obtained on the Pacific slope of tlie continent. Tliat the diminution of 

 the rivers flowing down the western slope of the Sierra could be so fully 

 proved, was due to the peculiar facilities offered by the extremely numerous 

 and extensive mining operations carried on in and about the former chan- 

 nels of these "buried rivers," as thev have sometimes been called; and 

 although the same kind of proof could not be furnished bearing on the dimi- 

 nution of the precipitation in portions of the continent adjacent to Cali- 

 fornia, a large body of focts was brought forward showing that an extensive 

 area of country west of the Rocky Mountain range was formerly covered 

 by water, in the form of lakes, which lakes have either disappeared alto- 

 gether, or become greatly diminished in area, this diminution having taken 

 place during the Tertiary' epoch, and having been continued almost if not 

 quite up to the present time, thus indicating important physical changes — 

 either climatic or orographic, or both together — as marking the Tertiary 

 and Recent periods over a vast area of territory, outside of the State of Cali- 

 fornia, as well as within it. The difference between the I'esults arrived at in 

 the Sierra Nevada and those obtained in the region between the Sierra and 

 the Rocky Mountain range was chiefly this : that in the former case we 

 had proof of a diminution of precipitation independent of any orographic 

 changes ; while, in the latter, the phenomena were more complicated, oro- 

 graphic changes being not .so easily disentangled from climatic ones. 



In regard to the period of the extension of the glaciers over the crest 

 of the range of the Sierra Nevada at a period subsequent to that of former 

 increased precipitation, we found, on examination, as detailed in the first 

 chapter of the present volume, that a precisely similar condition of things 

 took place all over the Cordilleras, north of a certain latitude. The highest 

 portions of the Rocky Mountains and the very highest summits of the loftiest 

 ranges of the Great Basin were, at a very recent geological period, covered 

 by snow, from which were formed glaciers rivalling in magnitude those 

 of the Sierra itself And as in the last-mentioned range, so in those farther 

 east, only the most diminished representatives of the ancient glaciers re- 

 main ; although the peculiar markings and other proofs of their former much 

 greater extension are preserved in such freshness as to lead to the belief 

 that they are of extremely recent formation. 



All of what has been stated, in regard both to the former glaciation and 



