242 E. B. BRANSON THICK GYPSUM AND SALT DEPOSITS 



2. The evaporation causing the precipitation of gypsum lies between 

 .19 and .095, the original volume of sea-water, and the only other salt 

 precipitated at that stage is CaCOg, which amounts to less than '.] per 

 cent of the whole. 



3. The absence of salt is accounted for by the precipitation being in- 

 terrupted before the salt stage is reached, either by freshening from the 

 inflow from rivers, by increase in rainfall, or by the filling of the outer 

 basins with sediments so that the overflow exceeds that necessary to bal- 

 ance the evaporation from the inner basins. 



4. The absence of sedimentary impurities is explained by the rapid 

 accmnulation of the deposits and by their having no inflowing streams 

 bearing sediments. 



5. The absence of fossils is due to tlie waters being so highly concen- 

 trated that life had ceased to exist in them before gypsum began to be 

 deposited. 'J'he percentage of salt in the water when the first precipita- 

 tion of gypsum occurred was four-fifths tluit in the waters of the Great 

 Salt l^ake at the present time and greater than in tlie Great Salt I.ake 

 when the first analyses were made. 



All difficulties mentioned on the second page of this article in explain- 

 ing thick deposits of almost pure salt are met by the hypothesis : 



1. The de])th of water is ample, even in relatively shallow basins. 



'2 and 3. The gypsum was precipitated out before salt deposition be- 

 gan and when the waters occupied much wider areas, and was relatively 

 unimportant below the salt or might be entirely lacking, as explained on 

 page 232. 



4. Fossils would 1)e absent in the >;ilt jind in tlie sediments associated 

 with it for the same reasons as, with the uvpsutn. 



