CHAMBERLIN— THE AGE OF THE EARTH. 263 



ocean. This salt is thus counted as many times as it is carried back. 

 An endeavor has been made to estimate and make allowance for this 

 by taking the increase of salt solutions near the ocean as a criterion. 

 It has also been recognized that salt solutions are entrapped in the 

 pores of the sediments as they are laid down under the sea, and that 

 when the beds are afterwards raised above the sea-level these solu- 

 tions are drained into the streams and counted again as salts from the 

 land. The amount of duplication involved in this depends on the 

 ability of the rocks to hold salt water mechanically in their pores, and 

 correction has been sought by estimating their porosity and discount- 

 ing for it. Sandstones usually have the highest porosity and lime- 

 stones come next, while shales are relatively close-textured and im- 

 pervious, but still the shales are exceptionally productive. So, also, 

 it has been recognized that beds of rock-salt occur in the stratified 

 series, but these are held to be relatively unimportant. So still fur- 

 ther some particles of the original rock may remain undisintegrated ; 

 so, too, fresh particles may be cut away from exposed rocks by wind 

 blast and widely though sparsely distributed. But when the modify- 

 ing effects of all these have been recognized and discounted, there 

 still remains a serious source of double counting of sodium which we 

 must consider presently. 



4. The ratio of chlorine to sodium is a crucial matter, recognized 

 but not sufficiently emphasized. Inspection of the drainage from 

 regions of igneous rocks shows that the chlorine is relatively low and 

 the sodium relatively high compared with the ratio of these elements 

 in the ocean, which is about 1.8 chlorine to i sodium. The relative 

 deficiency of chlorine in the drainage from the very rocks that are 

 assumed to be the ultimate source of the salt solutions raises a funda- 

 mental issue. 



5. In view of this, let us make our inspection as sweeping as pos- 

 sible. Let us compare the ratio of sodium to chlorine in the ocean 

 with the ratio found in the average igneous rock of the whole " crust." 

 The latest and most authoritative determination of the chemical com- 

 position of the igneous rocks is that of Clarke and Washington, which 

 gives the mean sodium content as 2.83 and that of chlorine as 0.096.^^ 



1^ Frank W. Clarke and Henry S. Washington, U. S. Geol. Surv. and 

 Geophys. Lab., Carnegie Institution of Washington, " The Average Compo- 



PROC. AMER. PHIL. SOC, VOL. LXI, S, DEC. 26, I922. 



