Joty—An Estimate of the Geological Age of the Earth. 29 
are principal rivers of the world—arrives at the following estimate of the dissolved 
materials in tons per cubic mile of river water :—- 
Tons. 
CaCOs, : ; : , 826710 
WiGO,, 6 we eo BURG 
CaSO,, eS 13.611 
Ca;P.0,, : : 0 ; 2918 
NEES ORME Uy PILE FRY. 31805 
K,S0,, : Seen20358 
NaNO, 0 6 : . ~ 26800 
NaCl, ee e166 5,7 
Lil, ee eG 
NH,Cl, Mi hetote sfavebe iyi 31030 
Si0,, ; : : Aouad 
Fe,0s, Thal ita) slestit 213006 
Al,0,, : ; s . 14815 
Mn,0,, 5 j ‘ j 5708 
Organic matter, . : . 79020 
762587 
He further estimates that the total volume discharged by the rivers into the 
ocean 1s 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 the 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 per 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 Wagnert reconsiders 
Sir John Murray’s estimate just quoted, and arrives at the result that the whole 
* Scottish Geographical Magazine, 1888, p. 1. } Scottish Geological Magazine, 1895, p. 185. 
