94 NEW YORK STATE MUSEUM 



(1) Gredner's theory. The beds of rock salt and gypsum which 

 occur in the earth's crust have been produced by direct separation 

 from sea water or from the water of inland seas in which chlorid 

 of sodium was the principal substance held in solution. In quiet 

 bodies of salt water, the stronger brine formed at the surface by 

 evaporation sinks to the bottom and accumulates there, so that 

 a concentration of the salt takes place from the surface toward 

 the bottom. In open seas full of currents, such a concentration 

 can not occur, for, on the one hand, in consequence of the cur- 

 rents, there is a constant mingling of the stronger and weaker 

 solutions of salt, and, on the other, the rivers replace the evap- 

 orated water, but in inland seas, specially those into which but 

 little river water flows, the saturated solution of salt sinks to 

 the bottom, from which rock salt crystallizes out and by continual 

 accumulation, a layer of salt is formed. In periods of excessive 

 rainfall, when the tributary streams are muddy, beds of saliferous 

 clay rre deposited, while, on the other hand, in periods of drouth, 

 when no mud is borne by the streams and more water is evap- 

 orated than is contributed by the streams, deposits of pure rock 

 salt are formed. If the water of a bay in which such process of 

 evaporation and deposition is going on, contains sulfate of lime, 

 a deposit of gypsum is formed before the separation of the salt 

 begins, because the water becomes saturated with gypsum sooner 

 than with salt. In consequence, beds of rock salt are frequently 

 found overlying beds of gypsum and anhydrite. With a new 

 influx of sea water, the water of the bay becomes less saturated 

 with the saline materials, and the deposition is interrupted, anid, 

 in case this interruption occurs before the salt has been deposited, 

 we may have a layer of gypsum overlain by layers of saliferous 

 clay, or in some cases, limestone. 



By the drying up of an inland sea originally containing salts 

 in solution, the first substance to separate from the water would 

 be gypsum, then layers of rock salt containing some impurities, 

 after which pure rock salt would be deposited, and on top would 

 be found a layer of the more easily soluble sulfates and chlorids. 



