112 KANSAS ACADEMY OF SCIENCE, 



DEPOSITION OF GYPSUM FROM BODIES OF SALT WATER. 



The most generally accepted theory of origin of the large deposits 

 of gypsum and salt has been the evaporation of salt-water lakes, bays, 

 and seas, cut off from the main ocean. This theory has been given 

 for the Iowa, New York and Kansas deposits in the reports on salt 

 and gypsum in those states. In the Kansas report the writer en- 

 deavored to picture the history of the changes resulting in the de- 

 position of gypsum in a bay whose waters retreated to the southwest 

 in Permian time. 



Examples of these changes can be found in the salt lakes, ocean 

 gulfs and bordering seas at the present day. In southern Europe are 

 excellent examples of the evaporation of salt lakes ; and in this country 

 the best examples are to be seen in the Great Salt Lake and neighbor- 

 ing salt lakes of Utah and Nevada. 



Lake Bonneville, in the Quaternary geological time, covered an 

 area of 19,750 square miles, with a depth of 1050 feet, and its waters 

 were fresh. Through evaporation, its level was lowered below the 

 place of outlet at the north, and its waters in course of time became 

 more and more saline. This evaporation has continued until the 

 present remnant, Salt Lake, has less than 2400 square miles of area, 

 with an extreme depth of fifty feet, and its waters almost a concen- 

 trated brine, with specific gravity of 1.1. The total amount of salts 

 in this lake water is 15 per cent., of which 11.8 per cent, is common 

 salt (sodium chloride). 



The waters of the Dead Sea afford another example of concentrated 

 brine due to evaporation. In this water there is 26 per cent, of salts, 

 but differing in composition from the American lake. There is only 

 3.6 per cent, of common salt and over 15 per cent, of magnesium 

 chloride, as compared with 1.5 per cent, in Great Salt Lake. The 

 amount of gypsum (lime sulfate) in the two basins is nearly the 

 same, 0.086 per cent. Geikie, in his text-book (page 383), gives the 

 chemical composition of these waters as follows : 



Great Salt Lake. Dead Sea, 



Chlorideof sodium (common salt) 11.8628 3.6372 



Chloride of magnesium 1.4908 15.9774 



Chloride of calcium 4.7197 



Chloride of potassium 0.0862 0.8379 



Bromide of magnesium 0.8157 



Sulfate of lime ( gypsum ) 0.0858 0.0889 



Sulfate of potassium 5363 



Sulfate of magnesium 0.9321 



Water 85.0060 73.9232 



100. 100. 



Ocean water, according to the analyses of the "Challenger" reports, 

 contains 3.5 per cent, of mineral salts, of which three-fourths is com- 



