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



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 97'8 x IC tons of sodium 

 chloride. There are also 16 x 10*^ tons of lithium chloride, and 6-5 x 10*^ tons of 

 ammonium chloride. These quantities include a total of nearly 76 x 10" tons of 

 chlorine. If we assume that the final result as to tlie duration of denudation will 

 not be far from 86 x 10'' years, we arrive at a total deduction of 6536 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 account the quantity of magnesium chloride present in 

 it. This, calculated on the most recent estimate of the mass of the ocean referred 

 to, ante, amounts to 5568 x 10^^ tons, containing 4161 x 10'^, tons of chlorine. 

 The total chlorine in the original ocean is arrived at by adding to 24,155 x 10'^ 

 tons contained in the chloride of sodium, 4161 x 10'" in the magnesium chloride, 

 and subtracting 6536 x 10'- as subsequently introduced. The result is 21,780 x 10'^ 

 tons. 



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 solution of a 

 primitive crust approximating to the present eruptive and igneous constituents of 

 the Earth's crust, 14 per cent, of the chlorine fixed in the salts brought into solu- 

 tion would be united with sodium. This we now find will amount to 3049 x 10" 

 tons, combining with 1972 x 10'" tons of sodium. But we have already seen that 

 to-day there are 15,627 x 10'" tons of sodium in the ocean. The correction is 12'6 

 per cent. This on the period of 99-4 x lO*' years is 12-5 x 10'^ years nearly, which 

 is evidently a subtractive correction, and reduces the estimate of geological time 

 to 86-9 X 10° years. 



This correction is based on the view that the chlorine now in the ocean — ■ 

 or nearly this amount — must originally have been free in the atmosphere and 

 hydrosphere. This is assumed as the only alternative open to us in disposing of 

 this substance. Previous writers have accepted this view. If free it can hardly 

 have been otherwise combined than with hydrogen. The dissociating tempera- 

 ture of HCl is some 500° above that of water ; hence the cldorine would have taken 

 its hydrogen before the formation of water was possible. 



Sterry Hunt has further assumed that sulphur, in the form of acid gas, entered 

 into the composition of the primeval atmosphere. The early high temperature 



