260 AN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTH. 



the sea itself. It enters into the composition of rain water in districts 

 bordering- or near the sea. It would appear that farther inland it 

 is an inappreciable constituent of rain water. At Rothamstead the 

 average of 71 analyses afforded 0.33 of chlorides in 100,000. At Lands 

 End this rose to 21.8 in 100,000. On the west and east coasts of Scot- 

 land it is 1.19 and 1.26, respectively, per 100,000. In London it is 

 0.12, and in Ootacamund, India, it is only 0.01 per 100,000 parts, ^ 

 the latter town being some 300 miles from the coast, in south India. 

 The amount in British rivers free from pollution is 1 in 100,000; and 

 evidently, as these represent a concentration to one-third of the rain- 

 fall, this amount would be accounted for b}^ the chlorine carried from 

 the sea. 



This is not the case with the great rivers of the world. Many of 

 these must derive their chlorides from the rocks by solvent denuda- 

 tion.^ Some deduction should, however, be made for the supply 

 referable to the sea. A deduction of 10 per cent is probably sufficient; 

 it is a correction on a correction. This need be applied to the sodium 

 chloride only, reducing it from 16,657 tons per cubic mile to 15,000 

 tons, in round numbers; and, multiplying by the number of cubic miles 

 of river discharge, the total annual supply to the ocean is 07.8X10*' 

 tons of sodium chloride. There are also 16 X 10" tons of lithium chloride, 

 and 6.5X10* tons of ammonium chloride. These quantities include 

 a total of nearly 76x10® tons of chlorine. If we assume that the final 

 result as to the duration of denudation will not be far from 86x10'* 

 years, we arrive at a total deduction of 6,536 X 10^" tons as a correction 

 on the amount of chlorine contained in the sodium chloride of the 

 ocean. 



On the other hand, however, an estimate of the total quantity of 

 chlorine in the ocean must take into a'ccount the quantity of magne- 

 sium chloride present in it. This, calculated on the most recent esti- 

 mate of the mass of the ocean (referred to cmte) amounts to 5,568 X 10^'^ 

 tons, containing 1,161 X 10^^ tons of chlorine. The total chlorine in 

 the original ocean is arrived at by adding to 21,155 X 10^' tons, contained 

 in the chloride of sodium, 4,161X10^*^ in the magnesium chloride, and 

 subtracting 6,536x10'', as subsequently introduced. The result is 

 21,780 XlO'Uons. 



We can now apply these figures to correct the original estimate of 

 geological time, which assumed that all the sodium in the ocean had 

 been delivered by the rivers. 



According to the results obtained by considering the effects of solu- 

 tion of a primitive crust approximating to the present eruptive and 



1 Thorp's Dictionary of Applied Chemistry; article, "Water." 



''See Bischof's Chemical Geology, Chap. VII, Vol. I, English edition, 1854. 



Bischof thinks the rivers can carry back to the sea only very little from the l)eds of 



rock salt (p. 111). 



