SALT WATER AND FRESH. 23 



the ocean, whose vapours have fed them at the source. 

 Thus a circulation, indispensable to the welfare of 

 plants and animals, is maintained over the surface of 

 the globe, either on the earth or through the air. 



There is a marked difference, however, between the 

 water which fertilises the earth and air, and that which 

 remains in the great body of the Ocean. Sea-water, as 

 every one knows, is salt, while what falls from the at- 

 mosphere, and supplies springs and rivers, is destitute 

 of saltness, or fresh. When evaporation of sea-water 

 takes place, the salts dissolved in the sea do not rise in 

 the vapour, but remain behind ; and were the pro- 

 cess continued a sufficient length of time, and were uo 

 fresh water introduced by rivers, the salts would accu- 

 mulate in the waters of the ocean to such a degree that 

 they would at last be deposited in a solid form at the 

 bottom. There would take place, on a vast scale, 

 what occurs in the common method of procuring salt 

 from sea-water, in hot countries, where the water is 

 exposed to the sun in shallow pans until nothing re- 

 mains but a crust of salt. This does not happen to 

 the Ocean, solely because the amount of fresh water 

 which continually returns into it, compensates for what 

 had been withdrawn ; and if there be any deficiency 

 it is of so small an amount as to cause a change in the 

 constitution of the ocean only in a very extended course 

 of ages. We have no evidence to show that any such 

 change has occurred during the historic period; but it 

 is reasonable to think that the change which we know, 

 from the fossil remains of an earlier creation, has come 

 over the marine fauna, may have been connected with 



