374 PRINCIPLES OF STRATIGRAPHY 



ocean water is prevented, however, the temperature of the entire 

 body may easily rise to the required degree. When the deeper 

 layers had become a concentrated brine the successive influxes of 

 calcium sulphate, probably during the rainy period when the streams 

 brought this mineral in solution from the surrounding country, were, 

 on passing through these layers of brine, deposited directly as anhy- 

 drite, in alternate layers with the salt deposits. That these influxes 

 of calcium sulphate were not due to successive ingressions of the 

 open sea is shown by the utter lack of marine organic remains in 

 these strata. In this manner were formed the 3,000 or more layers 

 of anhydrite which divide the older rock salt. With the progress of 

 concentration, the supernatant solution became a bittern rich in mag- 

 nesium salts, whereupon the calcium sulphate united with these salts, 

 forming polyhalite (2CaS(:)4.MgS04.K,SO,.2H.O). The polyhalite 

 stratum of Stassfurt is essentially a bed of rock salt, containing, 

 with other impurities, from 6 to 7 per cent, of polyhalite. With 

 further concentration of the mother liquor, kieserite (MgSO^.HoO) 

 was deposited, this requiring a temperature above 72° C. for its dep- 

 osition. The zone named after it contains about 17% of this min- 

 eral, together with 13 of carnallite, 3 of bischofite, 2 of anhydrite, 

 and 65 of rock salt. At this stage polyhalite was no longer de- 

 posited. 



The final step in the concentration of the mother liquor produced 

 the carnallite zone. The average composition of this zone is 55 

 per cent, of carnallite, 25 of rock salt, 16 of kieserite, and 4 of 

 various other minerals. The carnallite (KMgCL.6H20) was formed 

 from the chlorides which had hitherto remained in solution, and it 

 represents the more or less complete drying up of the bittern lake. 

 The protecting layer of clay must have been formed by winds, for 

 water would have caused a resolution of the carnallite. 



The reestablishment of the conditions of deposition, first for anhy- 

 drite and later for rock salt, which produced the "younger succes- 

 sion," suggests a renewed invasion of the sea. This is negatived, 

 however, by the absence of organic remains either in the salt clay 

 or in the succeeding anhydrite. This younger series may, therefore, 

 be wholly of continental origin, the anhydrite and salt being both 

 derived from connate waters. 



The change to a dry climate over the region of North Germany 

 is understood when we take into consideration the fact that at the 

 beginning of Permic time the Armorican Mountain chain began to 

 rise, extending from the region of what is now central France north- 

 westward to the present Irish Isle. This placed a barrier directly 

 across the path of the prevailing Westerlies, which then were ap- 



