486 AGRICULTURAL, ANALYSIS 



in which the potash exists in plants, when engaged in investiga- 

 tion of fertilizers. It is chiefly found in combination with or- 

 ganic and phosphoric acids, and on ignition will appear as phos- 

 phate or carbonate in the ash. 



POTASH IN MINERAL DEPOSITS 



415. Occurrence and History. The generally accepted the- 

 ories of the manner in which potash has been collected into de- 

 posits suited to use as a fertilizer are described below. 



The most extensive potash deposits known are those in the 

 neighborhood of Stassfurt, in Germany. The following descrip- 

 tion probably represents the method of formation of these de- 

 posits : 98 



The Stassfurt salt and potash deposits had their origin, thou- 

 sands of years ago, in a sea or ocean, the waters of which grad- 

 ually receded, leaving near the coast, lakes which still retained 

 communication with the great ocean by means of small channels. 

 In that part of Europe the climate was then tropical, and the 

 waters of these lakes rapidly evaporated, but were constantly re- 

 plenished through these small channels connecting them with 

 the main body. Decade after decade this continued, until by 

 evaporation and crystallization the various salts present in the 

 sea water were deposited in solid form. The less soluble material, 

 such as sulfate of lime or "anhydrite," solidified first and formed 

 the lowest stratum. Then came common rock salt, with a slowly 

 thickening layer which ultimately reached 3000 feet, and is esti- 

 mated to have been 13,000 years in formation. This rock salt 

 deposit is interspersed with lamellar deposits of "anhydrite," 

 which gradually diminish towards the top and are finally re- 

 placed by the mineral "polyhalit," which is composed of sul- 

 fate of lime, sulfate of potash, and sulfate of magnesia. The 

 situation in which this polyhalit predominates is called the 

 "polyhalit region," and after it comes the "kieserit region," in 

 which, between the rock salt strata, kieserit (sulfate of mag- 

 nesia) is embedded. Above the kieserit lies the "potash region," 

 consisting mainly of deposits of carnallit, a mineral compound 

 96 Potash, Published by the German Kali Syndicate, 1906. 



