1912.] CLARKE— SOME GEOCHEMICAL STATISTICS. 229 



surface of the continents would be lowered by solvent erosion alone, 

 to the extent of one foot in 32,833 years. In some areas the rate is 

 much more rapid, in others it is slower ; but the average is as close 

 as can be computed with the data now in hand. Its uncertainty may 

 be as great as ten per cent., or perhaps even greater. The chief 

 uncertainty is due to our lack of precise knowledge concerning the 

 greater African and Asiatic rivers. 



From the ratio between fluviatile and marine sodium the age of 

 the ocean can be calculated. The ocean contains 14,611 X 10^^ 

 metric tons of sodium, and the rivers contribute 175,040,000 tons 

 annually. Hence, if the ocean were originally fresh, its entire con- 

 tent of sodium would be supplied by the rivers in 83,472,000 years. 

 This form of calculation was first applied by Joly,^" whose work is 

 well known ; and has since been discussed by Sollas^^ and also by 

 myself in the memoir already cited. The quotient thus obtained, 

 however, is subject to various corrections, which have been con- 

 sidered by the authors named above, and which operate in opposite 

 directions. Whether they compensate or not it is impossible to say. 

 The calculation, so far, assumes a uniform rate of supply since the 

 surface of the earth took on its present form, and that assumption 

 has been well criticized by Becker.^* He shows that in all probability 

 the rate is diminishing, for the reason that the exposure of fresh 

 rocks, of unleached material, is constantly growing less and less, and 

 the true age of the earth since stability was established, lies between 

 55 and 70 millions of years. The higher of these values appears to 

 be the more probable. If, however, the ocean were primitively 

 saline, the quotient representing its age would be still smaller. 



Sodium tends to accumulate in the ocean, while the other saline 

 radicles added to it are more or less precipitated as solid deposits on 

 its floor. Calcium and magnesium are removed as carbonates, silica 

 goes to build the skeletons of radiolarians, diatoms, and so forth ; 

 potassium is taken to produce glauconite, etc. These deposits or 

 sediments cover vast areas to an unknown thickness, but their 



"^Trails. Roy. Soc. Dublin (2), Vol. 7, p. 23; Rep. British Assoc. Adv. 

 Sci., 1900, p. 369. 



" Quar. Journ. Geol. Soc, Vol. 65, p. xli. 

 " Smithsonian Misc. Coll., Vol. 56, No. 6. 



