The prevailing opinion seems to be that most of the important gypsum deposits of the world have been formed under “salt-pan” conditions. This opinion is held, even though many persons have pointed out the difficulties which the theory involves.
The classical illustration of the “salt-pan” theory for gypsum deposits is found in certain nearly detached basins at the eastern end of the Caspian Sea and elsewhere. Conditions in these basins, however, in at least one important particular, differ from those that characterize gypsum deposits. Myriads of organisms are drawn into the basin from the Caspian Sea and perish in its denser brine. Gypsum deposits, on the other hand, are generally devoid of fossils. To avoid this difficulty, certain students of the problem have postulated a second, or inner, basin in which the brine reaches the gypsum-depositing stage. According to this conception, the . . .