ORIGIN AND COMPOSITION OF SOILS 27 



form of carbonate, potassium forms one of the 

 chief ingredients of hard-wood ashes, and in this 

 form of combination is especially valuable for 

 fertilizing purposes ; potash salts, being extremely 

 soluble, are likely to be held long in solution. 

 Some of them are recovered in animal and vege- 

 table life, but the great mass of potash carried 

 into the sea still remains unaccounted for. The 

 recovery of waste of potash is chiefly secured by 

 the isolation of sea waters containing large quan- 

 tities of this salt and their subsequent evapora- 

 tion. Such isolation of sea waters takes place by 

 means of geological changes in the level of the land 

 and sea. In the raising of an area above the 

 water level, there is almost certain to be an 

 enclosure, of greater or less extent, of the sea 

 water in the form of a lake. This enclosure may 

 be complete or only partial, the enclosed water 

 area being still in communication with the main 

 body of the sea by means of small estuaries. If 

 this body of water be exposed to rapid evapora- 

 tion as was doubtless the case in past geological 

 ages, there will be a continual influx of that 

 evaporated. The waters may thus become more 

 and more charged with saline constituents. Finally 

 a point is reached in the evaporation when the 

 less soluble of the saline constituents begin to be 

 deposited. In this way the various formations 

 of mineral deposits, produced by the drying up of 

 enclosed waters takes place. 



Sodium is never found free in nature, but its 



