80 DYNAMICAL GEOLOGY. 



also got its salt from the rocks. The salts of I ho sea 

 are the accumulated leachings of all Geological times. 



Deposits in Saline Lakes. We have seen that saline 

 lakes occur only in dry climates. Furthermore, the cli- 

 mate of the regions where they occur has heen for a long 

 time, and still is, growing drier. The lakes have been, 

 and are still, drying up, and many have entirely dried 

 away. In the Basin region i. e., the desert region be- 

 tween the Wahsatch and Sierra ranges there are hun- 

 dreds of such dried-up lakes. Now, from the time the 

 point of saturation is reached until the lake is dried up, 

 deposits of some kind must occur. These, of course, vary 

 with the composition of the water, but the simplest are 

 those formed by the drying up of an isolated body of sea 

 water. What will take place in such a case is known by 

 the artificial evaporation of sea water in the manufacture 

 of salt. No deposit at all takes place until nine tenths of 

 the water is evaporated. Then, as the point of saturation 

 for salt is approached, first gypsum is deposited ; after the 

 whole of the gypsum is deposited, the common salt begins 

 to deposit, and continues until nearly all is crystallized, 

 and a dense mother liquor, or bittern, is left, containing 

 the more soluble matters, especially magnesium chloride 

 and sulphate. 



In Nature the process is the same, except that it is 

 complicated by mechanical deposits of silt (sand and 

 clay). Until the point of saturation is reached, only 

 mechanical deposits of silt take place, as in fresh lakes. 

 Then gypsum will begin to deposit, but not continuously. 

 In all such dry countries, all the rain that falls at all, falls 

 in a few months of each year. The deposit of gypsum 

 will alternate with mechanical deposits of mud or silt. 

 The chemical deposits of gypsum will represent the dry 

 season, and the mechanical deposits of silt the season of 

 rains. When all the gypsum is exhausted, the common 

 salt will begin to deposit, and this will alternate in the 



