REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1903 95 



In such a case, however, the deposit would be of a comparatively 

 small thickness, since it would contain only the materials which 

 were dissolved in the waters of the inland seas. The great 

 deposits of gypsum and rock salt have undoubtedly been formed 

 in some bay where there has been a continuous or intermittent 

 influx of water containing gypsum and salt. An instructive 

 example of such a deposit and chemically the most complete one 

 in the world, is that of Stassfurt, Germany. 



Its lower principal mass consists of rock salt, which is divided 

 by thin parallel layers of anhydrite into beds from 2 to 5 inches 

 in thickness. Upon it rests a stratum, 200 feet thick, of impure 

 rock salt mingled with easily soluble compounds such as chlorid 

 of magnesium, which is divided by thin layers of polyhalite.' 

 Upon this is a stratum 180 feet thick, in which rock salt and 

 sulfates, principally kieserite" (sulfate of magnesia), occur in 

 alternate layers, some of which are a foot thick. The upper- 

 most bed, about 135 feet thick, is composed of a succession of 

 reddish layers of rock salt and salts of magnesium and potas- 

 sium (kainite,^ kieserite, carnallite* and tachhydrite^) in addi- 

 tion to which are also masses of snow-white boracite.^ The 

 boundaries between these four principal divisions are not exact, 

 and the change from one to the other is gradual. 



(2) Thermal springs. In regions where geysers and thermal 

 springs are abundant, in some cases the water contains sulfur- 

 ous acid, which becoming oxidized, changes to sulfuric acid, 

 and this acting on the carbonates, changes them to sulfates. 

 In this way dolomite may be changed so as to form gypsum and 

 epsomite. 



(3) Volcanic agencies. Near some of the volcanos, particu- 

 larly at Girgenti, in Sicily, gypsum, aragonite, sulfur and celes- 



' Polyhalite, 2 Ca SO,, Mg SO,, K, SO, + 2 H^ O. 



* Kieserite, Mg SO* -1- H2 O. 



' Kainite, Mg SO,, K 01 + 3 H3 O. 



* Carnallite, K 01, Mg CI2 + 6 H2 O. 



' Tachhydrite, Ca CI2, 2 Mg CI2 + 12 H2 O. 



* Boracite, 2 Mgs Bg O15, Mg CL. 



