THE STASSFURT SALTS 373 



ther fact that anhydrite is the first deposit and not gypsum, as would 

 be the case for evaporating sea water. The second series of deposits 

 above the mother hquor salts again begins with anhydrite instead 

 of gypsum. Walther (65) regards these deposits as due to evapora- 

 tion of a shallow late Permic or Zechstein sea, entirely cut off from 

 the ocean, and surrounded by a country changing gradually from 

 pluvial to desert conditions. This old sea extended from the Urals 

 in Russia, on the east, over North Germany, and the region of the 

 North Sea to the center of England. On the south its boundary 

 was partly formed by the Bohemian mass, and the old Vindelician 

 and Armorican Mountain chains, the former in the region of the 

 present Danube plain, the latter extending through France, Belgium, 

 South England, and Ireland. In the north, and on the southeast, 

 the separation was caused by the development of extensive broad 

 marsh lands. During the gradual evaporation of this sea, the salt 

 deposits accumulated in the deeper areas of the basin, where to-day 

 they cover scarcely the fiftieth part of the original area of the salt 

 sea. As partial areas were laid bare the salt deposited there was 

 again dissolved by the streams and carried to the pools which still 

 existed, and thus the concentration became more and more pro- 

 nounced. Under the influence of changing temperature and mois- 

 ture with the change of seasons, the nature of the precipitate varied, 

 and thus the salt beds are separated at regular intervals by layers of 

 anhydrite or polyhalite, forming the annual rings. Their number 

 suggests that the deposition of the Stassfurt salt occupied a period 

 of about 10,000 years. Erdmann (16) holds that the amount of an- 

 hydrite in the deposits is too great to be derived solely from the 

 drying up of this sea, and he therefore supposes that additional 

 amounts of calcium sulphate were brought into it by the streams 

 from the surrounding regions. 



According to Van't Hoff and Weigert (54 :ii4o) anhydrite forms 

 from gypsum in sodium chloride solutions at 30° C. (+86° F.), 

 while in the sea water this transformation takes place at 25° C. 

 {-\-77° F.). At ordinary temperatures, according to Vater, calcium 

 sulphate crystallizes from a saturated solution of salt in the form of 

 gypsum. Such high temperatures are not to be found in water of 

 bays still in connection with the sea, especially in the present latitude 

 of the Stassfurt salt deposit, unless indeed the temperature of the 

 whole earth was higher. The Red Sea, which to-day has the highest 

 temperature of any mediterranean, has a bottom temperature of 

 21.5° C, its mean temperature being 22.69° C. The Persian Gulf, 

 on the other hand, has a mean temperature of 24°, owing to its 

 greater shallowness (see Chapter IV). Where influx of cooler 



