50 JoLY — Ati Estimate of the Geological Age of the Earth. 



The missing potash, if we assume the deficiency to be 1 per cent., would 

 amount to 91 x 10" tons. Assume that this is contained in the oceanic pre- 

 cipitates now forming the ocean floor, and add it to the K2O now in solution in 

 the ocean, or, more accurately, what is calculated on the amount of the chloride, 

 the total is 968 x 10" tons. Comj^are this now with the sodium of the ocean 

 calculated as soda, and amounting to 2100 x 10", and we have a ratio of 1 to 2'2. 

 Had we assumed 0*8 as the missing percentage of potash, allowing such a 

 deficiency as exists in the case of the soda to be accounted for by Glauconite and 

 other marine deposits of the land, and estimating that the deficient 0-8 per cent, 

 existed now in the sub-oceanic deposits, we find in the sea and its deposits 

 796 X 10" tons. This bears to the soda the ratio of 1 : 2'7, which fairly well 

 agrees with the ratio obtaining in the alkalies of the rivers. 



From these figures we see that the deficiency indicated by the rocks is quite 

 adequate to justify the supposition that the f resent alkali ratio of the rivers existed in 

 the past. To suppose the river-supply still less in the past is to make the record of 

 the sedimentary rocks still more astray ; or, from another point of view, the record 

 of the sedimentary rocks — if we accept the same data as agreed with the facts 

 with regard to soda alkali — suggest that the rivers of the past must have dis- 

 charged an equal, or even greater, amount of potash than at present. 



AVe may put the matter again in another way, which brings out more clearly 

 the true nature of the evidence : — The ratio of the potash to the soda in the rivers, 

 if preserved throughout the history of denudation, would account for the alkali 

 relations of the primitive and the derived rocks. This is independent of our 

 estimate of Geological Time. The argument is, in fact, mainly directed against any 

 assertion that the relative amounts of the alkalies supplied by the rivers of to-day 

 is at variance with their probable past supplies. 



If this ratio has varied seriously in the long jjast, then a difiiculty not easily 

 surmounted has to be faced. The difficulty may be put thus : — The mean potash 

 percentages of the parent and of the derived rocks are determinable, and the 

 difference represents a certain amount of potash which may be considered, within 

 limits, known. This must have been removed from the parent rocks in some 

 manner. If not by denudation, then in what manner V The fact that we cannot 

 estimate it in the sediments or in the sub-oceanic deposits appears legitimately 

 referable to our ignorance. The assumption that the rivers supplied less potash 

 in the past leaves the revelation of the rocks inexplicable. The assumption is 

 made in order to explain what is really a hypothetical deficiency (that of the 

 potassium in the oceanic reservoir), and renders inexplicable an actual known 

 deficiency (that of the potassium in the rocks). 



The argument thus supports our Uniformitarian views by overbearing an 

 objection often urged against the uniform supply of the constituents of the rivers. 



