182 GEOLOGICAL HESTORY OF LAKE LAHONTAN. 



the general area by an elevation of the land. This hypothesis has been 

 mostly abandoned, however, as one lake after another has been studied, 

 until at the present time it is difficult, if not impossible, to point to a single 

 lake, excepting perhaps the Caspian, having such a history. The origin of 

 the salt lagoons found on so many shores is not here included, as their mode 

 of formation is too obvious to admit of their being confounded with inland 

 seas. 



SUCCESSION OF SALTS DEPOSITED UPON ETAPORATION. 



As already seen, inclosed lakes are constantly receiving additions from 

 streams, springs, and rain, but do not overflow, their influx being counter- 

 balanced by evaporation. This assures us tliat their percentage of saline 

 matter must increase. This process continuing, a point is eventually reached 

 when the waters are saturated with one or more of the more abundant 

 salts and precipitation commences. Very simple experiments suffice to 

 prove that waters of complex composition, when subject to slow evapora- 

 tion, do not deposit their salts in a homogeneous mass, but in successive 

 layers or strata of varying composition. As the order in which different 

 salts are deposited varies with the composition of the waters, it is safe to 

 say that in no two lakes is the succession of saline deposits formed on 

 evaporation apt to be identical. Disregarding for the present the reactions 

 of the various salts upon each other, it is evident that in the evaporation of 

 natural brines the order in whidi the contained salts will be deposited is 

 inversely as the order of their solubility. For example, a salt that requires 

 a large amount of water for its solution, or, in other words, is sparingly 

 soluble, will reach its point of saturation and commence to crystallize out, 

 as evaporation progresses, previous to the deposition of a more soluble salt. 

 To illusti'ate, it has been found that calcium carbonate requires about 10,000 

 times its weight of water, saturated with carbon dioxide, for its solution, 

 while calcium chloride is very deliquescent and dissolves in nearly its own 

 weight of water. In inclosed lakes to which streams are contributing these 

 salts in equal quantities, and in which evaporation equals or exceeds the 

 supply of fresh water, it is evident that the calcium carbonate would reach 

 its point of saturation and commence to separate long before the waters had 



