SALT LAKES AND SALINAS 359 



gons buckled up on the edges and became saucer-shaped. By count- 

 less repetitions of this process, or of something analogous to it, the 

 entire lake-bed Ijecame a mass of i)entagons with ragged, blistered 

 edges." (Huntington-28:-'5i'-j.) In the salt of this plain Hunt- 

 ington found "a half-buried plover, dead for centuries — ever since 

 the time when the bottom of the lake was still soft." Aside from 

 this, and from a few deeply buried roots of some reeds, Huntington 

 found no signs of life for nearly a hundred miles of his journey 

 in this region. 



In the African deserts salinas are equally characteristic. Those 

 of the Bilma and Kalala oases in the Sahara supply much of Central 

 Africa with salt. A new crust of salt several inches thick forms 

 over these lakes in a few days after the harvesting of the preceding 

 salt crop. 



Salt deposited by Katwee Lake north of Albert Edward Nyanza 

 Lake in Central Africa contains 81.7% NaCl, 5.32% NaoSO^, 

 8.43% K,SO„ 2.46% NaXO,, 0.15% Fe,0„ and 0.82% H.O. In 

 the Kalahari, salinas are a characteristic feature. (Passarge-43.) 



Calcium sulphate in the form of gypsum or anhydrite is, as 

 we have seen, a frequent accompaniment of the deposits of sodium 

 chloride in the cut-off lagoons of the sea and in normal salt lakes. 

 Gypsum of undoubted marine origin has been found on some small 

 coral islands in the Pacific, where it constitutes a residue formed by 

 the evaporation of lagoons, and may reach a thickness of 2 feet. 

 Gypsum may also be deposited by concentrated lake water, as in 

 the case of Lake Chichen-Kanab in Yucatan. Gypsum likewise 

 forms on an extensive scale in the playas or sebchas of desert 

 regions. At Fillmore, Utah, such a deposit covers an area of 2 

 square miles and has been opened to a depth of 6 feet without 

 reaching bottom. (Russell-48 :6'^.) In general it accumulates in 

 the center of the basin in the form of gypsum, rendering the bot- 

 tom and sides of the basin impervious and so forming a foundation 

 on which the salt may accumulate, above which, in turn, is formed 

 the impervious cover of anhydrite. Such deposits in desert regions 

 are often of considerable thickness. The great depression of the 

 Ued Rir, which merges from the south into the Schott Mel Rir, 

 carries a flooring of gypsum which extends at least to a depth of 

 50 meters, and beneath which is often a great accumulation of 

 water under strong hydrostatic pressure. Piercing of one of these 

 gypsum floors in South Tunis in 1885, at a depth of 90 m., dis- 

 covered a well of water which rushed up with such force as to hurl 

 blocks weighing 12 kgm. into the air. (Ochsenius-41 -.jS.) 



In many sections the salinity is not sufficient to produce solid 



