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THE ULTIMATE SOURCE 



present in the earth, is rock salt itself. Sodic chloride does 

 not enter appreciably into the composition of the solid crust 

 of the earth at all, except where it is found as a separate and 

 distinct formation, known as rock salt. 



If, in the earliest ages of our planet, before its substance 

 had been differentiated into dry land and water, sodic chloride 

 was diffused through its mass, we should expect that in the 

 gradual denudation of the earth's surface, which followed in 

 later ages, the sodic chloride and more soluble salts would be 

 dissolved and retained in solution, whilst the less soluble matters 

 would be deposited. This is almost exactly what we find to 

 be the case. The sea is a great reservoir of sodic chloride 

 and all the salts more soluble than it ; and the land is 

 composed of rocks for the most part sedimentary and little 

 soluble, whilst there is no salt worth considering in it, except 

 rock salt, which is a distinct and peculiar formation. 



The most important question we have consequently to 

 consider at the outset, is, the source of rock salt. Has it been 

 deposited from the sea, or has it been ejected from the 

 molten bowels of the earth, or can it have come into existence 

 in any other way ? These are problems upon which philoso- 

 phers are not yet agreed. Their solution will depend a good 

 deal upon the information obtainable from an examination 

 of the age, extent, formation, and origin of rock salt, which 

 will now be considered. 



(reologists are wont to consider the strata which form the 

 earth's crust, as the tablets of time, written at successive epochs, 

 on different materials, and stamped with different characters, the 

 characters that happened to exist at the period that the tablets 

 were formed. If we unfold the strata and examine the tablets, 

 we find that they are superimposed, one on top of the other, 

 not very regularly now, since earthquakes have upheaved 

 them and denudation has blotted them out in parts, but 

 sufficiently so to render it a moral certainty that they had been 



