172 THE FITNESS OF THE ENVIRONMENT 



are dissolved about 0.019 gram of silver and 

 about 0.006 gram of gold, amounts which 

 correspond to 0.0000019 per cent and 

 0.0000006 per cent, respectively. 



It has been calculated that 166,000,000 

 years have been required for the streams to 

 carry into the sea the sodium chloride which 

 is now present. The calcium carbonate of 

 the rivers would however suffice to supply 

 the present amount of that substance in 500,- 

 000 years. Accordingly, the present store of 

 the latter substance represents but a very 

 small fraction of what has passed through the 

 ocean, and as a result of the intervention of 

 life has finally been deposited as sedimentary 

 limestone. Since the formation of the ocean, 

 if present conditions correspond with the past, 

 water must have carried to the dwellers of 



ently of one another. Thus the composition of sea water is 

 stated as follows : — 



Sodium chloride, NaCl . . 

 Magnesium chloride, MgCl 2 . 

 Magnesium sulphate, MgSO* 

 Calcium sulphate, CaS0 4 

 Potassium sulphate, K2SO4 . 

 Calcium carbonate, CaC03 . 

 Magnesium bromide, MgBr 2 



Relative 

 Amount 



77.758 

 10.878 

 4.737 

 3.600 

 2.465 

 0.345 

 0.217 



