44 



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



We ma}^ now refer to a similar table of the sedimentaries : still deriving our 

 figures as averages calculated from Rosenbusch's work : — 



We may observe further that the averages afforded by the valuable collection 

 of analysis of American rocks, compiled by Messrs. Clarke & Hillebrand, will 

 be found to confirm these results.* 



For the original crust, Clarke's alkali ratio works out — 



and Rosenbusch's, 



Ka,0 

 K,0 



1-29 



1'22 

 ~Y'' 



On the other hand Rosenbusch's sedimentary rocks show that 



Na,0 



0-59 

 ~1~ 



When it is remembered that, age by age, those sediments were being 

 deposited, some directly from the parent igneous rocks, and others by denudation 

 of former sediments, the great importance to the present hypothesis of this broad 

 difference in the alkali ratios, and in the absolute amounts of sodium and potash 

 in the original and derived rocks, must be evident. 



If now the inference is right that the missing alkalies were supplied to the ocean, 

 we should expect to find on a rough approximation of the bulk of sedimentaries, 

 and hence of the original rocks giving rise to them, that such a mass of parent 

 rock would be adequate to supply the sodium in the ocean. And this is actually 

 the case ; we find, in fact, that the estimated amount of sedimentary strata would. 



* U. S. Geol. Survey. Bulletin No. 148, 1897. 



