52 THE OCEAN 



being richer in sulphates and the brine richer 

 in chlorides. 



Of the elements in solution in sea-water, 

 sodium and chlorine seem to be the only 

 ones that are scarcely withdrawn at all, 

 apart from a small quantity deposited in 

 shallow evaporating pans along the shores 

 of the land-surfaces, and they may therefore 

 have been uniformly on the increase since the 

 beginning of geological time. This fact has 

 been made use of in attempts to estimate the 

 age of the earth, and J. Joly has calculated 

 that to supply the total oceanic content of 

 sodium by the discharge of rivers must have 

 required a period of 90 to 100 millions of years. 



Salinity of Sea-Water. — It has been found 

 by numerous analyses that the composition 

 of sea-water salts remains the same in all 

 parts of the ocean and at all depths — ^that is to 

 say, the actual ratio of bases and acids remains 

 quite constant. The waters associated with 

 the muds and oozes on the floor of the ocean 

 and the waters of coasts, estuaries, and frozen 

 seas, show slight variations in the individual 

 constituent salts, but in the open ocean, away 

 from contact with the shore and the bottom, 

 the composition of the salts in sea-water 

 remains practically constant, while the 

 concentration varies. 



The salinity or saltness of sea-water is 



