NO. 5 STUDY OF CHEMICAL DEXUDATIOX — CLARKE 15 



The foregoing calculations, so far as geologic time is concerned, imply 

 the assumption that rivers add sodium to the sea at an average uniform 

 rate, slight accelerations being offset by small temporary retardations. 

 This subject is to be discussed by Mr. G. F. Becker; but one phase of it 

 demands consideration here. The present rate of discharge has been has- 

 tened during modern times by human agency, and that acceleration may 

 be important to take into account. The sewage of cities, the refuse of 

 chemical manufactures, etc., is poured into the ocean, and so disturbs the 

 rate of accumulation of sodium quite perceptibly. The change due to 

 chemical industries, so far as it is measurable, is wholly modern, and that 

 due to human excretions is limited to the time since man first appeared 

 upon the earth. Its exact magnitude, of course, cannot be determined; 

 but its order seems to be measurable, as follows : 



According to the best estimates, about 14,500,000 metric tons of com- 

 mon salt are annually produced, equivalent to 5,700,000 tons of sodium. 

 If all of that was annually returned to the ocean, it would amount to a 

 correction of about 3.25 per cent, on the total addition of sodium to the 

 sea. The fact that much of it came directly or indirectly from the ocean 

 in the first place is immaterial to the present discussion ; the rate of dis- 

 charge is affected. All of this sodium, however, is not returned ; much of 

 it is permanently fixed in manufactured articles. The total may be larger, 

 because of other additions, excretory in great part, which cannot be esti- 

 mated ; but we may assume, nevertheless, a maximum of 3 per cent, as the 

 correction to be applied. Allowing 7 per cent., as already determined, to 

 cyclic or wind-borne sodium, and 1 per cent, to disseminated salt of m^arine 

 origin, the total correction is 11 per cent. This reduces the 175,040,000 

 tons of river sodium to 155,785,600 tons, and the quotient representing 

 crude geologic time becomes 90,700,000 years. 



The corrections so far considered are all in one direction, and increase, 

 by a roughly evaluated amount, the apparent age of the ocean. Other 

 corrections, whose magnitudes are more uncertain, tend to compensate the 

 former gi'oup. The ocean may have contained primitive sodium, over and 

 above that since contributed by rivers. It receives some sodium from the 

 decomposition of rocks by marine erosion, which is estimated by Joly 

 to be a correction of less than 6 per cent, and more than 3 per cent, on the 

 value assigned to geologic time. Sodium is also derived from volcanic 

 ejectamenta, from "juvenile" waters, and possibly from submarine rivers 

 and springs. The last possibility has been considered by SoUas," but 

 no numerical correction can be devised for it. These four sources of 

 sodium in the sea may be grouped togetlier as non-fluviatile, and reduce 

 the numerator of the fraction which gives the age of the ocean. Whether 



' Presidential address, Quar. Journ. Geol. Soc, May, 1909. 



