280 SOILS AND MANUEES 



conditions of their formation have heen determined, it 

 is considered not unlikely that other similar deposits 

 may be discovered elsewhere. 



Formation of the Deposits. The origin of the deposits 

 is attributed to the isolation of bodies of sea-water as a 

 result of changes in the elevation of the land. Thus cut 

 off from the main ocean, the water evaporated and the 

 salts crystallised put. Under these conditions the 

 salts would crystallise in the order of their solu- 

 bilities, gypsum first being the least soluble - 

 then common salt, magnesium sulphate, and lastly, 

 the chlorides of potassium and magnesium. With 

 various intermediate layers they are found practically in 

 that order. Like other rocks, however, they appear to 

 have been subjected to various geological changes since 

 they were first deposited, and different layers and sec- 

 tions have been at various times exposed to the action 

 of the weather. Probably some of the salts were dissolved, 

 and so brought into contact with those in other layers. 

 Eeactions appear to have taken place between them, and 

 secondary deposits, e.g., Schonite, kainite, etc., have 

 been formed. The whole is now covered up with layers 

 of clay, sand and limestone, with rock salt and gypsum 

 sandwiched between them, which have for a long time 

 protected it from further denudation. Below this lies 

 the main deposit in which five principal divisions are 

 generally recognised. Taken from above downwards, 

 these are as follows : 



1. The Carnallite region, containing potash and mag- 

 nesium salts. 



2. The Kieserite region, in which the principal salt 

 is magnesium sulphate. 



3. The Polyhalite region, containing a mixed salt, 

 consisting chiefly of the sulphates of potassium, mag- 

 nesium and calcium. 



