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



47 



The mass of 64 x 10^" tons contains 940 x 10" tons of NaaO. Adding the 

 amount in the ocean (21 x IC tons), we obtain 30'4 x 10'^ tons. This restored to 

 the original mass of 91 x 10'^ tons gives a percentage of 3'34. 



It may be independently shown that the soda ratio of the original rock to that 

 of the sedimentaries supports the view that 30 per cent, must have been about the 

 loss, by solution, of the original rock. Wo assume that the sedimentaries are 

 derived from an original rock, such as Clarke arrived at, but we assume no more. 



To see this, we have to refer again to Mr. Merrill's valuable book,* which gives 

 a useful collection of analyses of rocks and their derived soils. 



Omitting a few cases, i. e. a Phonolite containing a soda-zeolite giving excep- 

 tional results on weathering, an incompletely recorded Basalt, and a Soapstone, 

 his examples give the following results : — 



This indicates that, if at this stage of weathering, these soils were removed, 

 redeposited, and reconsolidated, the mass of the parent rock would have been 

 correctly estimated, on the basis that the mass removed in solution formed but 

 thirty-eight per cent, of the original rock. At this stage of weathering we see 

 that 69 '7 per cent, of the original soda was removed. 



If we assume that the loss of the soda bears to the loss of the entire rock a 

 constant ratio — and with the exception of the first quoted Diabase this appears 

 supported by the individual examples — we can apply to the mean analysis of the 

 sedimentaries on the one hand, and to that of the mean original crust on the other, 

 to arrive at a rough estimate of the loss of entire rock by solution in the process 

 of formation of the former. 



We find that [ante) 3"61 per cent, of Na20 in the crust is represented by 1-47 

 per cent, in the sediment. From these figures we can calculate the amounts of 

 this constituent lost and saved. To effect this accurately we must suppose some 



* " Treatise on Eocks, Eock "Weatheriug, and Soils.' 



TKANS. EOT. DUB. SOC, N.S. TOL. VII., PART HI. 



Macmillan, 1897. 



