70 SOILS. 



region now supplies the demand of the entire world, both for 

 industrial and agricultural purposes. 



The cheapening of potash as a fertilizer has rendered pos- 

 sible the profitable cultivation of large areas of land which 

 were naturally too poor in that substance for ordinary cul- 

 tures; and has likewise rendered possible the restoration to 

 general culture of lands that had ceased to produce adequately, 

 on account of the depletion caused by long-continued cropping. 

 It has likewise served to intensify agricultural production 

 wherever desired; and between this supply and that of phos- 

 phoric acid from the phosphorites (see above), and the dis- 

 covery of the nitrogen-absorbing power of leguminous plants, 

 which can be used for green-manuring, farmers have been 

 enabled to dispense, in many regions, with the production and 

 use of stable-manure, which until then had been considered an 

 indispensable adjunct to agriculture everywhere. Even 

 within the last fifty years it was proclaimed by high authority 

 in Germany that stable-manure constituted, as it were, the 

 farmer's raw material, from which he manufactured the var- 

 ious products of the field through the intervention of the 

 plant-producing power of the soil. 



Origin of the Potash Deposits. The manner in which this accumu- 

 lation of potash salts has been formed deserves explanation. It is 

 abundantly evident that nearly all deposits of rock-salt thus far known 

 have been formed by the evaporation of sea-water at times when bays 

 or arms of the sea were cut off from open communication with the 

 ocean. The composition of sea-water has already been given and 

 discussed (chap. 2, p. 26) ; and by the slow evaporation of sea-water on 

 a small scale we can quite successfully imitate the phenomena observed 

 in natural rock-salt deposits. When sea-water is heated a slight deposit 

 of lime carbonate (usually containing a little ferric oxid and silica) is 

 soon formed ; and a corresponding thin deposit of ferruginous limestone 

 is commonly found at the base of rock-salt-bearing deposits. Next 

 above this we almost invariably find a deposit of gypsum, sometimes of 

 great thickness ; in the artificial evaporation of sea-water the same thing 

 occurs so soon as the brine has reached a certain degree of concen- 

 tration. It constitutes the major portion of the " panstone " of salt- 

 boilers. Next above follows a deposit of rock-salt, at base somewhat 

 mixed with gypsum ; its thickness varies greatly according to circum- 

 stances. Above it lie the potash salts. 



