188 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 



Section 2.— CHEMICAL DEPOSITS OF LAKE LAHONTAN. 



In commencing the study of the chemical precipitates of Lake Lahon- 

 tan, we have for our guidance the fact that the rivers now entering the 

 basin flow through the same channels that they occupied during the Qua- 

 ternary, and that many of the springs which rose in the bottom of the 

 former lake are still active. The salts contributed to the former lake were, 

 therefore, of essentially the same nature as those now being earned into 

 the basin. From these data and a knowledge of the composition of the 

 present lakes of the basin, it is evident that at least the general chemistry 

 of the waters of the former lake may be inferred. Providing that no salts 

 were deposited in the basin during an smtecedent period of desiccation, it 

 is evident from the character of the inflowing waters, that during its first 

 rise Lake Lahontan was a fresh- water lake, with about the normal per- 

 centage of calcium carbonate but i-icher in sodium salts than is common 

 with ordinary lakes in regions where stratified rocks abound. We need 

 to qualify this statemeiit, perhaps, for the reason that the lake rose slowly, 

 owing to a gradual change from arid to more humid conditions, and be- 

 came somewhat concentrated dui-ing its gradual increase. At the time of 

 its first maximum it must have been somewhat more highly charged with 

 mineral matter than is usually present in lakes with outlet. Should a 

 climatic change take place which would allow Pyramid Lake to expand at 

 such a rate that at the end of a hundred years, for example, it would be 

 900 feet deep, i. e., refill the Lahontan basin, it would form a fresh-water 

 lake in which the chemist could detect a somewhat greater percentage of 

 saline matter than occurs in the Laurentian lakes; but to the taste it would 

 appear as fresh as ordinary river waters. Such, we conceive, was the 

 nature of Lake Lahontan at its first rise. 



From our knowledge of the chemistry of natural waters we should 

 expect that calcium carbonate would be the first ^n'ecipitate formed as the 

 waters of Lake Laiiontan were concentrated, and should evaporation and 

 precipitation balance each other for a considerable time, an immense de- 

 posit of this salt would bu accumulated. If loss and supply were balanced 



