Nu 5. 79 



K 2.12 



(Fe,Al)j03 2. 75 



SiO. 11. 67 



202 ANNUAL REPOET SMITHSONIAN INSTITUTION, 19 3 2 



origin and is probably a new contribution to the atmosphere from 

 the interior of the earth. 



The average composition of the dissolved matter in the fresh waters 

 of the globe, as estimated by Clarke, is shown in the subjoined table: 



COz 35. 15 



SO4 12. 14 



CI 5.68 



NO3 .90 



Ca 20. 39 



Mg 3.41 Total 100.00 



The chloridized sodium in the dissolved matter is 3.68 per cent 

 f 5.68 X '^^ ) • The unchloridized is therefore 2.11 per cent ; and on 



\_ u0.40/ 



the assumption that this portion alone represents the sodium newly 

 washed to the ocean each year, the annual increment of sodium to the 

 ocean is 2.735 X 10'' X .0211, or 5.77 X 10^ tons. Dividing this amount 

 into the total oceanic sodium (1.609 X 10^° tons) , we obtain 270,000,000 

 years as the maxinmm estimate of the age of the ocean. Clarke's 

 estimate, after allowing for wind-borne sodium, human contamina- 

 tion, and for disseminated salt of marine origin, in ail amounting to a 

 correction of 10 per cent, is 99,143,000, or in round number 100,000,000 

 years. 



The sodium content of the ocean, according to Clarke (1924, p. 32), 

 has been derived from the decomposition of 84,300,000 cubic miles of 

 average igneous rock containing 2.83 per cent of sodium. In so far 

 as this estimate is based on the sodium content of the average igneous 

 rock, it is approximately accurate, because the amount of sodium in 

 the common rocks that make up the earth's crust does not vary much 

 from Clarke's estimated average; in the two preponderant varieties 

 of igneous rock, granite and basalt, it is 2.41 and 2.31 per cent, respec- 

 tively. If we admit that the sodium in the ocean has been derived 

 from this 84,300,000 cubic miles of igneous rock, we are faced by a 

 great dilemma. For this volume of igneous rock contains only 0.05 

 per cent of chlorine and therefore can have supplied at most 2.82 X 10^* 

 tons of chloririe to the ocean. The chlorine content of the ocean is 

 2.92 X 10^^ tons, however. In other words, only 1 per cent of the 

 chlorine in the ocean can have been supplied by the volume of igneous 

 rock that is estimated to have yielded the sodium. Essentially the 

 same argument was used bj^ Mackie in 1903 in a penetrating analysis 

 of Joly's method of computing the age of the ocean, an analysis to 

 which insufficient attention has been given. 



To account for this enormous discrepancy we may suppose: (1) 

 That much more igneous rock than 84,300,000 cubic miles has been 

 decomposed and that the sodium thus liberated and carried to the 



