6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



AGE FEOM SODIUM ACCUMULATION 

 The Data 



For comparison with the results of radioactive studies age determina- 

 tions from chemical denudation have an advantage over those from re- 

 frigeration, because decomposition of the rocks is only remotely affected 

 by thermal action and radioactivity. Mr. Joly's method of finding the 

 age of the ocean consists substantially in dividing the total sodium con- 

 tent of the ocean by the amount of sodium annually poured into it by the 

 the rivers. The result is corrected for wind-borne sodium and marine 

 denudation. I cannot agree tluit this quotient is the required age, but 

 before discussing that matter it is essential to ascertain as nearly as 

 possible the numerator and the denominator of Mr. Joly's ratio. 



Mr. Clarke's new discussion has already been referred to and he has 

 been kind enough to furnish me with the following data. The total 

 sodium content of the ocean is 14,130 X 10^- metric tons. The annual 

 uncorrected sodium increment escaping from the rivers is 175 X 10" tons. 

 The river-borne unchloridized sodium is 62.57 X 10** tons. The amount 

 of average igneous rock needed to supply the total sodium of the ocean is 

 48.225 X 10** cubic miles, while the amount of rock necessary to supply 

 both this and the sodium retained as silicates (mostly feldspars) in the 

 sedimentaries would occupy 77.570 X 10" cubic miles. This would make 

 a shell 2,050 feet tliick enveloping the globe. These figures I shall accept. 



The Sodium Increment. 



To the order of accuracy required for the purposes of this paper there 

 is little difficulty in finding a correction for wind-borne sodium. The 

 normal distribution of chlorine throughout New England and New York 

 has been studied in considerable detail and the results are stated in Mr. 

 Daniel D. Jackson's paper on this subject/ Nearly all of the normal 

 chlorine of this region is due to wind-borne sea-salt and I find by examina- 

 tion of typical cross-sections of the chlorine charts that the total chlorine 

 is fairly represented by supposing the coastal value of six parts per million 

 to be constant for 20 miles inland and there to vanish.^ The waters ex- 

 amined for normal chlorine were by preference surface waters, and since 

 the region has a rainfall of 45 inches with no excessive evaporation, it 

 seemed probable that if the rain from appropriate rain gauges had been 

 bottled periodically, the collected precipitation would show substantially 



^ Jackson, D. D., The normal distribution of chlorine in the natural waters of New York and 

 New England: Water-Supply Paper U. S. Geol. Suri'ey, No. 144, 1905. 



" The means employed was to plot a typical cross-section, adapt to the observed points a logarith- 

 mic curve, and take its area from the shore to a distance theoretically infinite. The section 

 selected as representative passed through Rye, N. H., and bore N. 65 W. The method is capable 

 of much elaboration. 



