THE OCEAN 173 



the sea not less than 300,000,000,000,000,000 

 tons of calcium carbonate, which they have 

 temporarily utilized as structural material. 

 Whether this estimate be correct or not, the 

 process is certainly the cause of the most 

 considerable change wrought by life upon the 

 face of the earth. 



The relative quantities of the several saline 

 constituents of the ocean are hardly at all 

 subject to variation. Chlorine, for example, 

 makes up never less than 55.21 per cent and 

 never more than 55.34 per cent of all the dis- 

 solved inorganic substances, so that the total 

 salinity may be readily estimated with consid- 

 erable accuracy by titration of the chlorides. 

 Such constancy is due to the elaborate mixing 

 of the waters resulting from ocean currents. 

 There can be no doubt, however, that the 

 relative amounts of the different acids and 

 bases have slowly but steadily changed during 

 the progress of geological evolution. Many 

 substances, like calcium carbonate, have been 

 steadily removed, a few, like sodium chloride, 

 have steadily accumulated without loss. 



The total salinity of the ocean, as stated 

 above, is subject to slight variation. Along 

 the North American coast, in the polar cur- 

 rent, upon the coast of Norway, and toward 

 the south of South America, the concentration 



