AGE OF GYPSUM OF CENTRAL IOWA 739 



large masses of water are carried into the Dead Sea, and the saline solution 

 thereby diluted, while at the same time the evaporation is but slight, no 

 common salt is deposited. During the ensuing warmer months the chemical 

 deposition of common salt and carbonate of lime take place. Should the 

 stream become turbid at this season in consequence of continued rain, deposits 

 are formed which contain a less amount of common salt. In this way there 

 must arise a constant alternation of different irregular layers of greater or 

 less thickness. All these layers must contain gypsum, since in a water which 

 contains so much chloride of magnesium as is present in the Dead Sea, 

 gypsum, as we shall subsequently see, is dissolved with difficulty, as is also 

 shown by the small proportion in which this salt exists in that sea. 



Lake Elton, a brine pool of the Russian steppes, may once 

 have had an oceanic connection. If this is true, the calcium 

 carbonate and gypsum of the original sea water have been 

 deposited, for the water now contains but small quantities of 

 lime salts, but chlorides of sodium and magnesium with sulphide 

 of magnesium are present in abundance.^ Bischof describes 

 the lake as follows : 



The Elton lake, whose greatest diameter is 20 and its smallest 16 versts, 

 lies 19 feet below the level of the ocean. It has flat banks and may be 

 waded through almost anywhere. On its margins and upon its bed there is 

 almost everywhere crystalline salt. This forms layers from one to two inches 

 in thickness which are separated from one another by layers of mud and 

 earth. The streams which empty into it are eight in number. They all 

 contain more or less salt, and consequently carry supplies of this substance 

 into the lake. The most considerable among them is the Charisacha, which 

 is also the only one which continues to flow during the whole year. In the 

 loamy soil which surrounds the lake numerous small crystals of gypsum are 

 imbedded. 



A deposit of salt is formed in this lake every summer. In 

 the winter and spring the water is diluted by the rivers which 

 are then copious, and a layer of silt, probably carrying some 

 gypsum, is formed. The decrease or complete disappearance of 

 CaSO^ from the water of Lake Elton into which it is being 

 constantly conveyed by the Charisacha River, the waters of which 

 have been analyzed, shows that the gypsum goes down with the 

 salt. 



Great Salt Lake in Utah furnishes an excellent example of 

 salt deposits in a lake without oceanic connections. The present 

 ' Analysis by Gobel, quoted by Bischof, loc. ciL, p. 404. 



