AN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTH. 253 



Sir John ^Iiirray/ as the result of the analyses of nineteen rivers — 

 many of which are principal rivers of the world — arrives at the follow- 

 ing estimate of the dissolved materials in tons per cubic mile of river 

 water: 



Tons. 



CaCOg 326, 710 



MgCOs 112, 870 



CaSO, 34, 361 



CagP^Os 2, 913 



Na2Sb4 31, 805 



K2SO, 20, 358 



NaNOs 26, 800 



NaCl 16, 657 



LiCl - 2, 462 



NH,C1 1,030 



SiOa .■ - 74, 577 



Fe^Os 13, 006 



AI2O3 14, 315 



IMn^Og ■ 5, 703 



Organic matter 79, 020 



762, 587 



He further estimates that the total volume discharged by the rivers 

 into the ocean is 6,52-i cubic miles per annum. 



Taking 32. -iO 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 

 multiplj'ing this number by the number of cubic miles of river water 

 annually discharged into the ocean, we find that this amounts to 

 157,267,54^: tons. 



The quotient of 14,151 X 10'' divided by 15,727 X 10* is very nearly 

 90 X l(f. 



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 mil- 

 lions 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 afi'ords a 

 mass in tons of 1.392 X 10'*, or a mass 5.3 per cent, nearh^, in excess 

 of that previously assumed, which of course raises the figures obtained 

 for geological time in years bj^ 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 anothei' and 

 perhaps more complete estimate of the oceanic area. Prof. Hermaiui 



^Scottish Geographical Magazine, 1887, p. 76. Ubid., 1888, p. 1. 



