112 THE SOIL SOLUTION 



sium and magnesium. Calcium is also present, appearing in deep 

 deposits as anhydride, and at the surface as gypsum. 



From the results of this work it is possible to predict the 

 order in which the different salts or minerals will separate 

 from the evaporating solution. At ordinary temperature 

 (25 C) the first salt to be deposited from the dilute solution 

 is gypsum (CaSO 4 .2H 2 O) followed by halite or sodium chloride 

 (NaCl) in quantity. Sodium chloride continues to separate at 

 all higher concentrations. Next will be deposited kainite 

 (MgSO 4 KC1.3H 2 O). At the concentration then reached, the 

 stable sulphate of calcium is anhydride (CaSO 4 ), which con- 

 tinues to separate from solution as desiccation proceeds. Con- 

 sequently, if the gypsum previously deposited is yet in con- 

 tact with the solution, it tends to be transformed to anhydrite 

 and at all higher concentrations the deposition of anhydrite may 

 be expected. As evaporation proceeds a point is reached where 

 kainite and kieserite (MgSO 4 .H 2 O) separate. Further evapora- 

 tion brings a concentration at which kieserite and carnallite 

 (MgCl 2 .KC1.6H 2 O) are precipitated, and as the process pro- 

 ceeds, finally the point is reached where kieserite, carnallite and 

 bischofite (MgCl 2 .6H 2 O) all three separate with sodium chloride. 

 The final products separating at a higher temperature, 83 C., 

 are the same four solids, sodium chloride, kieserite, carnallite 

 and bischofite. 1 The alternate layers of anhydrite and sodium 

 chloride noticeable in some desiccated sea beds is probably the 

 result of alterations in temperature, anhydrite being less soluble, 



*It will be interesting to compare with the above the following brief 

 description of the Stassfurt salt deposits, taken from Ries's Economic 

 Geology of the United States (1905), p. 127. "At the bottom is the 

 main bed of rock salt which is broken up into layers 2-5 inches thick 

 by layers of anhydrite. Above this come 200 feet of rock salt, with 



which are mixed layers of magnesium chloride and polyhalite Resting 



on this is 180 feet of rock salt, with alternating layers of sulphates 

 chiefly kieserite, the sulphate of magnesia. These layers are about I foot 

 thick. Lastly, and uppermost, is a 135-foot bed consisting of a series 



of reddish layers of rock salts ef magnesia and potassium, kainite 



kieserite carnallite tachhydrite as well as masses of snow-white 



boracite." 



