386 f. a. wilder the origin of gypsum 



Difficulties of generally accepted Theory 



Theories that seek to explain extensive deposits of gypsum as the direct 

 result of the evaporation of brines in natural liasins are quite involved. 

 They require the nice adjustment of a numl^er of factors, and at best they 

 fail to wholly explain how thick beds of practically pure mineral can be 

 formed free from lime carbonate and silt and devoid of fossils. 



No extensive beds of practically pure gypsum due to the evaporation 

 of sea-water are known to be in process of formation. Gypsiferous beds 

 due to the evaporation of saline waters are forming in a great many 

 localities, but the gypsum is present, either as scattered crystals in mud 

 or as thin streaks with other salts. On the other hand, extensive beds of 

 practically pure gypsum are today being fomied by other agencies. 



In 1910 P. L. Hess^ grouped gypsum deposits in four classes. His 

 arrangement of these classes deserves notice : 



1. Efflorescent deposits. 



2. Periodic lake deposits. 



3. Interbedded deposits. 



4. Veins. 



The text of the bulletin gives the impression that "efflorescent deposits" 

 is purposely placed first. Apparently he arrived at this arrangement and 

 classification because his studies were made in California and" included 

 large arid areas where interesting gypsum deposits occur. 



E. W. Stone, whose bulletin on "Gypsum deposits of the United 

 States" ^ is just from the press, adopts a similar classification for gypsum 

 deposits derived from solutions. He further adds deposits produced by 

 alteration and deposits produced by disintegration and mechanical reac- 

 cumulation. 



Although these classifications reduce the emphasis laid on deposits due 

 to direct evaporation of brines, the evidence seems to show that extensive 

 deposits of gypsum of this sort are extremely rare, if, indeed, they exist 

 at all. 



The Lime Carbonate Problem 



In the first place, the difficulties growing out of the presence of lime 

 carbonate in sea-water are greater than is generally realized. Prof. Julius 

 Stieglitz, in an interesting discussion of the relations of equilibrium be- 



2 F. L. Hess : A reconnaissance of tlie gypsum deposits of California. IT. S. Geol. Sur- 

 vey Bulletin 413, 1910. 



3 Gypsum deposits of Ibe United States. U. S. Geol. Survey Bulletin 607, 1920. 



