JoLY — An Estimate of the Geological Age of the Earth. 



29 



are jjrincipal rivers of the world — arrives at the following estimate of the dissolved 

 materials in tons per cubic mile of river water : — 



762587 



He further estimates that the total volume discharged by the rivers into the 

 ocean is 6524 cubic miles per annum. 



Taking 32-40 per cent, of the sodium sulphate, 27-06 per cent, of the sodium 

 nitrate, and 39-32 per cent, of the sodium chloride as sodium, we obtain a total 

 mass of sodium of 24,106 tons per cubic mile; and multiplying this number 

 by the number of cubic miles of river water annually discharged into the ocean, 

 we find that this amounts to 157,267,544 tons. 



The quotient of 14,151 x 10'- divided by 15,727 x 10* is very nearly 90 x 10". 



From these data then tlie period of time required to supply its present amount 

 of sodium to the ocean by rivers possessing the average approximate compositions 

 of the existing rivers would be ninety millions of years. 



The foregoing figures admit of amendment as the result of a more recent 

 estimate of the volume of the ocean by Sir John Murray.* He estimates the 

 volume as 323,800,000 cubic miles, very closely Taking the weight of a cubic 

 mile of sea- water as 43 x 10* tons, this affords a mass in tons of 1-392 x 10^* or 

 a mass 5-3 j^er cent, nearly, in excess of that previously assumed; which of course 

 raises the figures obtained for geological time in years by a corresponding amount. 

 Thus, on this more carefully estimated basis the period of geological denudation 

 becomes 94*8 x 10*^ years nearly. 



But this number admits of still further amendment on another and perhaps 

 more complete estimate of the oceanic area. Prof. Hermann Wagnerf reconsiders 

 Sir John Murray's estimate just quoted, and arrives at the result that the whole 



* Scottish Geographical Magazine, 1888, p. 1. f Scottish Geological Magazine, 1895, p. 185. 



