Joty—An Estimate of the Geological Age of the Earth. 49 
also, possess an appreciable percentage of alkalies, which has been left out of 
account in the foregoing estimate of the soda contents of the sedimentaries. 
VI.—The Potash of the Rivers. 
The matters referred to in the last section lead to the consideration of an 
objection—which may be urged against the present thesis—on the inconsistent 
relations of the alkalies, as estimated in the rivers and in the ocean, an objection 
which has led to the inference that the river-discharge of to-day must be different 
in its chemical nature from what it was in the past. We hope to show that this 
conclusion is arrived at without consideration of the whole facts, and that in truth 
the record of the rocks is best to be explained by assuming that this river supply 
was maintained in the past. 
The potassium in the ocean, on the most reliable estimate of the mass of the 
latter, amounts to 565 x 10”, tons; converted to K,O, this becomes 683 x 10” tons. 
The mass of Na,O in the sea is 21x 10" tons. This is a ratio of 1 to 31 nearly. 
On the other hand, the annual river-discharge of K,O is 7:3 x 10’, and the 
soda-discharge about 21 x 10’, or a ratio of about 1 to 2°8. We must then 
suppose that the rivers are now supplying more potash relatively to soda than 
formerly, or that some process of abstraction of the potash from the ocean is in 
continual progress. Before considering the last alternative, we will examine the 
first to determine if such an explanation will clear away the difficulty. 
A deficiency merely due to the river-supply having increased in recent periods 
should not interfere with effecting such a restoration of the potash percentage of 
the sedimentary detrital rocks as we effected in the case of the soda. Let us see 
if we can effect such a restoration. We take the most probable estimate of the 
sedimentary rocks and that most favourable to the restoration. 
This afforded 64 x 10" tons of detrital rock, and 91 x 10" tons as the mass of 
the parent rock. The potash percentage obtained from Rosenbusch’s tables of 
sedimentary rocks amounted to 2°49. Hence we find 1°594 x 10" tons of K,O 
in the detrital rocks, and adding 663 x 10” tons contained in the sea we get 
1:66 x 10%. This, on the total mass of 91 x 10", is 1°82 per cent. But from 
Clarke’s estimate of the chemical composition of the original crust this should be 
2°83, or about 1 per cent. of the potash is missing. On this same estimate of the 
sedimentary rocks the soda percentage comes out correct within 0°4 per cent., and 
for that we have the great deposits of Rock Salt as a partial set off. 
It is apparent, therefore, that the actual amount in the ocean disagrees with 
the indications of the rocks, and in the same direction—that of deficiency—as it does 
with the indications of the rivers. 
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