366 PRINCIPLES OF STRATIGRAPHY 



of accumulation of ancient deposits of this type, and hence to fur- 

 nish a clue to the physiographic characters of the region at the 

 time of such deposition. In general, we may divide the deposits of 

 salts into those abstracted from the hydrosphere, either directly de- 

 posited from the water or secondarily redeposited after leaching, and 

 those of chemical origin, i. e., formed by reactions of salts with each 

 other. 



Sources of Sodium Chloride. 



Marine. Practically all deposits of sodium chloride may 

 be traced back to the ocean water as their original source. 

 Direct deposition by evaporation and concentration of sea water 

 is, however, not the only mode of origin of such salts, al- 

 though many authors, following Ochsenius, have so regarded it. 

 The bar theory has already been discussed, and its application to 

 the origin of many saline deposits has been indicated. It has been 

 shown that such deposition can take place only in arid regions, 

 where evaporation concentrates the sea water within a nearly cut-off 

 basin, to the extent required for the deposition of the salts, and 

 holds it at such a state by removing a quantity of water equal to 

 that brought by the feeding current from the sea. In order that 

 such a feeding may be accomplished, it is necessary that the salt- 

 depositing bay be in the vicinity of a constant source of supply, i. e., 

 the ocean or an inland saline sea of vast dimensions, like the Cas- 

 pian. In such an ocean or inland sea, deposits of clastic and or- 

 ganic character would accumulate, so that for every great salt de- 

 posit formed in the neighborhood of the sea by concentration of 

 sea water, there should be a corresponding fossiliferous series of 

 normal marine type of sediments. Furthermore, as shown by the 

 deposits in the Bitter Lakes of Suez, and the Karabugas Gulf, the 

 deposits formed within the natural salt pan will be highly fossilifer- 

 ous, full of the remains of the organisms of the contemporaneous 

 sea from which the supply of salt water was derived. These two 

 criteria are the most significant, and when they fail, as in the case 

 of the salt deposits of the Mid-Siluric (Salinan) of North America, 

 these deposits cannot be regarded as the results of direct evapora- 

 tion of sea water. (Grabau-19.) 



Leaching of Salt from Older Formations and Its Segregation. 

 Extensive salt deposits may form by the leaching of the salt of an 

 older saliferous formation and its redeposition within a drainless 

 basin by concentration through evaporation. That such salt deposits 

 are now going on is believed to be the case in a number of regions. 



