ORIGIN OF SALINA SALTS 



379 



type. Numerous hopper-shaped cavities formerly occupied by salt 

 crystals occur in the shalier beds. 



When we consider the former extent of the Niagaran strata, 

 from central New York to the Rocky Mountains and from the Ohio 

 or southward to Hudson liay. and its thickness, which in Wisconsin 

 is still over 800 feet, and realize that much of this was worn away 

 during Salina time by the streams flowing- into the Salina basins of 

 New York, Michigan, and Canada West, we can understand that 

 the connate sea water held in these strata was quite sufficient to 



Fig. 70. Map and cross-section of Rhang-el-Melah, a salt dome in Algeria. 

 (After M. Ville.) 



furnish all the salt of the Salina deposits. The intercalated lime- 

 stone and shale layers likewise had their origin in the erosion prod- 

 ucts obtained from these Niagaran formations. The fact that all 

 around the Salina area the Upper Siluric strata rest on Niagaran 

 except where the continental deposits of Salina time intervene, and 

 the further fact that no undoubted marine equivalents of the Salinan 

 are known in North America, greatly strengthen the argument for 

 the wholly continental origin of these salt deposits. 



The Salt Domes. These should be briefly mentioned here, as 

 accumulations of salt in circumscribed areas, often to a thickness of 



