274 AN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTH. 



lated on the amount of the chloride, the total is 9()8X lO'' tons. Com- 

 pare this now with the sodium of the ocean calculated as soda, and 

 amounting- to 2,100 XlO'\ and we have a ratio of 1 to 2.2. Had we 

 assumed 0.8 as the missing percentage of potash, allowing such a defi- 

 ciency as exists in the case of the soda to be accounted for by glau- 

 conite and other marine deposits of the land, and estimating that the 

 deficient 0.8 per cent existed now in the sul)()ceanic deposits, we find 

 in the sea and its deposits 79(5 X 10^^ tons. This bears to the soda the 

 ratio of 1 : 2.7, which fairh' well agrees with the ratio obtaining in the 

 alkalies of the rivers. 



From these figures we see that the deficiency indicated b}^ the rocks 

 is quite adequate to justify the supposition that the present 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 nuist have discharged 

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



We maj^ put the matter again in another waj% 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 histor}' 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 past, then a difficulty 

 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 difi'erence 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 denu- 

 dation, then in what manner^ The fact that we can not estimate it in 

 the sediments or in the suboceanic deposits appears legitimately refer- 

 able 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 overbear- 

 ing an objection often urged against the uniform supply of the con- 

 stituents of the rivers. 



This brings us face to face with the question as to where and in what 

 form this missing potash is to be sought. 



