THE WASTE AND CONSERVATION OF PLANT FOOD. 233 



Tlie most exteusive deposits of potash known are those in the neigh- 

 borhood of Stassfurt, in Germany, The following description i^robably 

 represents the method of formation of these deposits:^ 



''The Stassfurt salt and potash deposits had their origin thousands 

 of years ago, in a sea or ocean, the waters of which gradually 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 still tropical, and the waters of these lakes rapidly 

 evaporated, but were constantly re])leuished through these small clian- 

 nels 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 de]30sited in solid form. The less soluble 

 material, such as sulphate of lime or 'anhydrite,' solidilied first and 

 formed the lowest stratum. Tlien came common rock salt with a slowly 

 thickening layer which ultimatelj^ reached 3,000 feet, and is estimated 

 to have been thirteen thousand years in formation. This rock-salt 

 de])osit is interspersed with lamellar deposits of 'anhydrite,' which 

 gradually diminish toward the toj) and are finally replaced by the 

 mineral ' polyhalite,' which is composed of sulphate of lime, sulphate of 

 potash, and sulphate of magnesia. The situation in which this polyha- 

 lite predominates is called the 'polyhalite region' and after it comes the 

 'kieserite region,' in which, between the rock-salt strata, kieserite (sul- 

 phate of magnesia) is embedded, xVbove the kieserite lies the 'potash 

 region,' consisting mainly of deposits of carnallite, a mineral comjwund 

 of muriate of potash and chloride of magnesia. The carnallite deposit 

 is from 50 to 130 feet thick and yields the most important of the crude 

 l)<)tash salts and that from which are manufactured most of the concen- 

 trated articles, including inuriate (»f potash. 



"Overlyiilg this region is a layer of impervious clay which acts as a 

 water-tight roof to protect and preserve the very soluble ])otash and 

 magnesia salts which, had it not been for the very protection of this 

 overlying stratum, would have been long ages ago washed away and 

 lost by the action of the water percolating from above. Above this 

 clay roof is a stratum of varying thickness of anhydrite (sulphate of 

 lime), and still above this a second salt dei)Osit, probably formed under 

 more recent climatic and atmospheric influences or possibly by chemical 

 changes in dissolving and subsequent precipitation. This salt deposit 

 contains 98 per cent (often more) of pure salt, a degree of purity rarely 

 elsewhere found. Finally, above this are strata of gypsum, tenacious 

 clay, sand, and limestone, which crop out at the surface. 



"The perijendicular distance from the lowest to the upper surface of 

 the Stassfurt salt deposits is about r),0(K) feet (a little less than a mile), 

 while the horizontal extent of the bed is from the Harz Mountains to 

 the Elbe Eiver in one direction, and from the city of Magdeburg to the 

 town of Bernburg in the Other." 



According to Fuchs and De Launy'^ the saline formation near Stass- 

 furt is situated at the bottom of a vast Triassic deposit surrounding 

 the city of Magdeburg. The quantity of sea water which evaporated 

 to produce saline deposits of more than 500 meters in thickness must 

 have been enormous and the rate of evaporation great. It appears 

 that a temperature of 100^ would have been quite necessary, acting 

 for ai long time, to produce this result. 



iPotasli, Columbian Exposition, German Kali Works, pages 3, 4. 

 2 Gltes Miu^raus, page 429, 



