OCCURRENCE AND HISTORY 487 



of chlorids of potash and magnesia. The carnallit deposit is 

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

 crude potash salts and that from which are manufactured most 

 of the concentrated articles, including muriate of potash. 



Overlying this region is a layer of impervious clay which acts 

 as a water-tight roof to protect and preserve the very soluble 

 potash and magnesia salts, which, had it not been for the pro- 

 tection 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 thick- 

 ness of anhydrite, and still above this is a second salt deposit, 

 piobably formed under more recent climatic and atmospheric 

 influences or possibly by chemical changes resulting in dissolv- 

 ing and subsequent precipitation of the compounds. 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 perpendicular distance from the lowest to the upper sur- 

 face of the Stassfurt salt deposits is about 5000 feet (a little less 

 than a mile), while the horizontal extent of the bed is from the 

 Harz Mountains to the Elbe River in one direction, and from 

 the city of Magdeburg to the town of Bernburg in the other. 



According to Fuchs and de Launay the saline formation near 

 Stassfurt is situated at the bottom of a vast triassic deposit sur- 

 rounding Magdeburg." The quantity of sea water which was 

 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 a long time, to produce this result. 



These authors, therefore, admit that all the theories so far ad- 

 vanced to explain the magnitude of these deposits are attended 

 with certain difficulties. What, for instance, could have caused 

 a temperature of 100 ? The most reasonable source of this high 

 temperature must be sought for in the violent chemical action 

 produced by the double decompositions of such vast quantities 

 99 Trait^ des Giles mineraux, 1893, 1 : 429. 



