JoLY — An Estimate of the Geological Age of the Earth. 49 



also, possess an aj^preciable iDercentage of alkalies, whicli has been left out of 

 account in the foreg'oino: 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 K2O, this becomes 683 x 10'- tons. 

 The mass of NajO in the sea is 21 x 10" tons. This is a ratio of 1 to 31 nearly. 



On the other hand, the annual river- discharge of K2O is 7'3 x 10', and tho 

 soda-discharge about 21 x 10', or a ratio of about 1 to 2-8. We must then 

 sujDpose that the rivers are now sujDplying 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 lO"' 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 KjO 

 in the detrital rocks, and adding 663 x 10'- tons contained in the sea we get 

 1-66 X lO"'. 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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