506 AGRICULTURAL, ANALYSIS 



The southern states, it is seen, use more than twice as much 

 potash as the northern, and this is due chiefly to the application 

 of this plant food to the cotton and sugar cane crops. 



437. Changes in Potash Salts in Situ. The deposits of potash 

 salts are not all found at the present in the same condi- 

 tion in which they were first deposited from the natural brines. 

 The layers of salt have been subjected to the usual upheavals 

 and subsidences peculiar to geological history. The layers of 

 salt were thus tilted and the edges often brought to the surface. 

 Here they were exposed to solution, and the dissolved brine 

 afterwards separated its crystallizable salts in new combinations. 

 For instance, kieserit and the potassium chlorid of the carnallit 

 were first dissolved and there was left a salt compound chiefly of 

 potassium and sodium chlorids sylvinit. In some cases there was a 

 mutual reaction between the magnesium sulfate and the potassium 

 chlorid and the magnesium potassium sulfate, schonit, was thus 

 produced. This salt is also prepared at the mines artificially. 

 The most important of these secondary products however, from 

 the agricultural standpoint, is kainit. This salt arose by the 

 bringing together of potassium sulfate, magnesium sulfate, and 

 magnesium chlorid, and was formed everywhere about the borders 

 of the layers of carnallit wherever water could work upon them. 

 In quantity the kainit, as might be supposed, is far less than the 

 carnallit, the latter existing in immense deposits. There is, how- 

 ever, quite enough of it to satisfy all the demands of agriculture 

 for an indefinite time. In fact for many purposes the carnallit 

 can take the place of kainit without detriment to the growing 

 crops. The relative positions and quantities of the layers of 

 mineral matters in the potash mines, and the depth in meters at 

 which they are found is shown in Fig. 43. 7 



438. Theory of Deposition of Potash Salts. The conditions 

 which obtained in the evolution of the earth's crust upon which 

 the deposition of soluble salts depends, are of great interest to ag- 

 riculture in so far as the laying down of the stores of phosphoric 

 acid, nitrates and potash are concerned. Deposits of phosphoric 



Maercker, Die Kalidiingung, 2nd Edition, 1893 : 3. 



