238 E. B. BRANSOK THICK GYPSfM AND SALT DEPOSITS 



salt, with about 2^ per cent impurities, as listed above, will be deposited 

 in 1,500 3^eaTS, if the basin is deep enough to receive so miic]i. 



The loss from the larger basin would be 6 inches per year and, replac- 

 ing this with fresh water at the rate of 6 inches per year, its concentra- 

 tion would be only three-fourths as great at the end of 1,500 years, and 

 the total amount of salt carried in by the waters would be seven-eighths 

 as much as though the same concentration had been maintained. This 

 correction has been applied to the computation in the preceding para- 

 graph. 



The Example of the Caspian Sea 



The Caspian Sea and its Gulf of Karaboghaz furnish conditions analo- 

 gous to those postulated save in the solutions. The area of the Caspian 

 is about 169,000 square miles and of tbe Gulf of Karal)oghaz 7,100 sqTuire 

 miles. The gulf is separated from the main sea by a narrow sand-bar 

 pierced by a strait, 1^ miles long and 115 to 170 yards wide, through 

 which a current flows continuously into the gulf at the rate of 11/^ to 5 

 miles per lionr. and there is no cojiipensating outflow. The evaporation 

 from the gulf is 3.2 feet per year.''' 



If the gulf were deep enough to accommodate large amounts of water 

 and the incoming waters from the Caspian had already deposited most 

 of their gypsum, great deposits of salt would be formed. 



The Salina Salt 



Schuchert's map of the Salina Sea shows it covering an area of a little 

 mure than 220,000 square miles and the salt and gypsum deposits extend- 

 ing over about 12,000 square miles. If this sea were 900 feet deep and 

 evaporated to one-third the area and ono-tliird the depth, it would leave 

 about 73,000 square miles of inland lakes witli a depth of 300 feet and a 

 concentration nine times as great as in the original sea. ■ Fov convenience 

 in computation, it is assumed that the concentration was ten times tliat 

 of the original sea-water. Assume that the drainage from the surround- 

 ing region practically all came into 60,000 square miles of the lakes and 

 these overflowed to supply the loss from evaporation of the other 13,000 

 square miles of lakes. If the rate of evaporation was 5 feet per year, the 

 rainfall over the inland seas 1 foot, the overflow foirr-fifths of 1 foot, and 

 the run-off over the drainage basin 8 inelies, tlie area of tbe drainage 

 basin must have ])een al)out 360.000 s(|u;ii'(' miles, in .-idditiii;! td tbe area 

 of the lakes, to supply the necessarv water. 'I'his is ;i little less tlinii oiie- 



Bncyclopedia Britauuica, 19\'2. 



