AGE OF GYPSUM OF CENTRAL IOWA 74 1 



Manifestly the lake is disposing of the calcium as fast as it is 

 received. Deposits of tufa occur on the old Bonneville, Inter- 

 mediate, and Provo shore lines, on their weather faces, and a few 

 feet below their crests. It is absent in sheltered bays and most 

 abundant on points that were especially exposed to wave action. 

 Calcareous oolitic sands are now forming along certain parts of 

 the shore of Salt Lake "between the delta of the Jordan and 

 Black Rock, where it constitutes the material of a beach, and is 

 drifted shoreward in dunes."' Of the three important fresh- 

 water tributaries of Great Salt Lake, the water of Utah Lake is 

 characterized by sulphate of lime, over 60 per cent, of the total 

 solids held in solution by it consisting of this salt, while the 

 waters of Bear River and City Creek are characterized by car- 

 bonate of lime.^ The deposits of tufa and oolite alone may 

 account for the absence of calcium carbonate from the water of 

 the Great Salt Lake, yet it is possible that both the calcium car- 

 bonate and sulphate are precipitated in the ordinary manner by 

 evaporation. Yet the fact that the calcium carbonate is, at least 

 in a measure, taken from the water by the aeration due to wave 

 action and deposited on the shores as tufa and oolite is interest- 

 ing and, taken with other conditions, may account for deposits of 

 pure gypsum from waters which contain a certain amount of lime 

 carbonate. 



Basins which are in some degree co?inected with the ocean may 

 next be considered. The Bessarabian coast of the Black Sea 

 furnishes an example of salt deposits in bays slightly connected 

 with the open sea and fed from the landward side by rivers. 

 From the Danube to the Dnieper the rivers before emptying into 

 the ocean expand into lakes which are separated from the sea by 

 natural dams. Under ordinary circumstances the water flows 

 into the sea through an opening in the dam, while during storms 

 the water of the sea enters the lakes. Three of these lakes 

 become partially dry every surfimer and deposit salt which in 

 places amount to a layer a foot thick. 3 This salt is used for 

 commercial purposes. The calcium sulphate of the river water 

 and of the sea water which is driven in during storms must also 

 be deposited, but the quantity, being small, readily escapes notice. 



'^ Ibid., p. 169. "Ibid., p. 207. 3 BisCHOF, c/. cit.. Vol. I, p. 392. 



