2 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



by a long period of desiccation, and was followed by a second dry epoch, 

 during which the valleys of Nevada were even more completely desert 

 than at present. During the second flood stage the lake rose higher than 

 at the time of the first high water, and then evaporated to complete desic- 

 cation. The present lakes of the basin are of comjiaratively recent date, 

 and are nearly fresh, for the reason that the salts deposited when the Quater- 

 nary lake evaporated were buried or absorbed by the clays and marls that 

 occupy the bottom of the basin. 



As Lake Lahontan did not overflow, it became the receptacle for all 

 the mineral matter supplied by tributary streams and springs both in sus- 

 pension and in solution. The former was deposited as lacustral sediments 

 and the latter as calcareous tufa, or formed desiccation products when 

 the lake evaporated. 



The introductory chapter indicates the position of the field of study, 

 and contains a sketch of the Great Basin, as the explorer finds it to-day, of 

 which the desiccated bed of Lake Lahontan forms a part; also a brief 

 notice of previous explorations, and an account of what was known of Lake 

 Lahontan before the present study Avas begun. Eoutes of travel and areas 

 surveyed are indicated on Plate IL 



Chapter II (on the genesis of Lake Lahontan) contains a summary of 

 the facts which show that the lake filled a compound orographic basin, 

 resulting from the tilting of faulted beds. A desci-iption is given of the 

 character of the irregular area whose drainage the lake received, together 

 with an account of the outline and area of the basin which held the ancient 

 lake. 



The question of outlet is discussed in detail, the conclusion being that 

 the lake did not overflow (page 32). 



Chapter III (on the phj^siography of the Lahontan Basin) contains a 

 description of the region as it exists at the present time. The most distinct- 

 ive characteristics of the valleys and mountains are briefly noticed; an 

 account of the existing rivers is given, including measurements of volume, 

 chemical composition, etc. The present springs of the basin are also 

 desci'ibed and analyses of the watcns of a few of them presented. These 

 analyses are believed to represent aj)pn>.\iiiiately the character of the tribu- 



