AN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTH. 271 



This restored to the original mass of 91Xl(»^" 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. 

 We 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 valual)le 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 exceptional results on weathering, an incompletely recorded 

 basalt, and a soapstone, his examples give the following results: 



Granite (p. 209) 

 Gneiss (p. 215) . 

 Syenite (p. 216) 

 Diabase (p. 221) 

 Diabase (p. 222) 

 Basalt (p. 223) . 

 Diorite (p. 225). 



Mean 



56.3 



This indicates tfiat 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 re- 

 moved in solution formed but 38 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 dia- 

 base 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 Na.,0 in the crust i.s represented 

 by 1.4:7 per cent in the sediment. From these figures we can calcu- 

 late the amounts of this constituent lost and saved. To efl'ect this 

 accurately we must suppose some one constituent to pass over without 

 loss from the one rock to the other and use its percentage as a stand- 



' Treatise on Rocks, Rock Weathering, and Soils, Macmillan, 1897. 



