420 THE CHEMISTRY OF CREATION. 



evaporation from the surface of the sea ; the 

 area of the latter, compared with that of the 

 land, being very great, necessarily so, perhaps, 

 to furnish the requisite extent of evaporating 

 surface. This water is, as is well known, per- 

 fectly fresh and pure, the saline constituents of 

 the ocean having no sensible degree of volatility 

 at the temperature at which the vapour has 

 been raised. No sooner, however, does it reach 

 the earth, than it becomes contaminated with 

 soluble substances which it meets while flowing 

 on the surface of the ground, or percolating 

 beneath. It is thus that the waters of springs 

 and rivers invariably contain a greater or less 

 amount of alkaline and earthy salts, which all 

 eventually find their way into the sea, and there 

 remain, since there is no channel for their re- 

 turn. The saline condition of sea-water is but 

 an exaggeration of that of ordinary lakes and 

 rivers ; the materials are the same, and of ne- 

 cessity so ; the ocean being, in fact, the great 

 depository of all the soluble substances which, 

 during many ages, have been separated by a 

 process of washing from the land. The case of 

 the sea is but a magnified representation of 

 what occurs in every lake into which rivers 

 flow, but from which there is no outlet except 

 by evaporation. Such a lake is invariably a salt 

 lake ; it is impossible that it can be otherwise ; 



