496 A. AY. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



ing for the distribution of these organisms, our last excuse for regarding 

 the Shawangunk conglomerate as a marine deposit falls to the ground. 



The origin of salt deposits. — I have elsewhere 92 discussed at some 

 length the origin of salt deposits and will merely summarize the chief 

 points in this connection. 



The ultimate source of the salt is probably in all cases the sea, but the 

 method of abstraction from sea-water varies, while a relative dryness of 

 climate seems to be a necessary requisite. The known methods of separa- 

 tion are (1) complete evaporation, (2) deposition according to the bar 

 theory, and (3) the desert theory of separation. Eegarding the first 

 theory — that is, the evaporation of water of an extensive basin and the 

 concentration of the salt in a small area — I have shown that : 



"Several facts are to be considered in this method of salt deposition 

 as forming crucial test points for the application of this theory to the 

 elucidation of the origin of an older salt deposit. These are : 



"First. Complete evaporation of sea-water furnishes a normal succes- 

 sion of deposits, beginning with gypsum, followed by the sodium chloride 

 and ending with the potash salts. These latter might under circum- 

 stances be removed under the influence of desert conditions by the winds. 



"Second. Later deposits should be separated from the first by layers of 

 detrital sediment, for it is inconceivable that a flooding of a desert area 

 by the sea should be unaccompanied by a great spread of clastic material 

 over the entire area flooded. 



"Third. With the incursion of the sea into this area, the life of the 

 outer oceans will also enter the inclosed sea to exist for a while, until the 

 connection is broken and evaporation again renders the waters too saline 

 for the existence of these organisms. ! Long before evaporation has pro- 

 ceeded far enough to deposit the salt, these organisms are killed off and 

 their preservable remains become embedded in the clastic strata forming 

 at the bottom of the inclosed basin. Thus the dividing clastic layers 

 would also be fossiliferous. 



"Fourth. The sea being near enough to flood the basin at intervals, 

 contemporaneous marine deposits, carrying the remains of the normal 

 marine fauna, which also characterizes the clastic beds between the salt 

 layers, are formed within a comparatively short distance of the salt de- 

 posits." 



92 A. W. Grabau : The origin of salt deposits, with special reference to the Siluric salt 

 deposits of North America. Bull. 57, Mining and Metallurgical Society of America, Feb., 

 1913. See also Principles of Stratigraphy, chapter ix, where the whole question of 

 modern salt deposits and the various themes of origin are discussed and illustrations 

 cited. 



