OF COMMON SALT, 



145 



But there is also much internal evidence in rock salt 

 formations that they were formed from the sea by deposition, 

 Eock salt deposits are described as lenticular, that is to say, 

 the greatest depth of the salt is found in the centre, and as the 

 edge is approached the deposit thins out and diminishes, 

 The same description applies to most natural basins, whether 

 lakes or seas. If rock salt were of aqueous origin and formed 

 from marine basins, the deposit would have the shape of the 

 basin, below, whilst plain above ; it would form a plano- 

 convex lens, thick in the centre, and thinning out to the 

 circumference ; convex below, and plane at the surface, such 

 in fact as we find it. Here is another strong presumption 

 in favor of its marine origin. 



But rock salt is also a stratified rock. When undisturbed, 

 it is found in horizontal beds, and these beds are often 

 interleaved and separated by others of clearly aqueous origin, 

 as gypsum beds, sandstone, limestone, marl, &c, Stratifica- 

 tion is admitted to be one of the most distinctive marks of the 

 aqueous origin of a rock formation, and this stratification, 

 in alternate layers with sedimentary rocks, is almost conclu- 

 sive proof that rock salt itself is sedimentary. 



Although rock salt deposits are by no means fossiliferous, 

 still bivalve and other marine shells, casts of fish, &c, are not 

 wanting in most deposits to testify to their marine origin, 

 In the Cis-Inclus salt range, the oldest known, shells of one 

 genus of mollusca have been found. A block of rock salt 

 from the Wieliczka mine — the youngest mine of rock salt and 

 about the finest in the world — on being examined by Professor 

 Philippi, was found to contain 5 zoophytes, 1 echinus, 1 

 serpula, 7 conchifers, 8 univalves, 3 crustaceans, and a 

 cirithium identical with one now living in the Mediterranean. 

 Such instances might be multiplied. 



Again, certain other salts of peculiar significance, as calcic 

 sulphate, are almost invariably found associated with common 



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