[1] Trans.  R.D.S., 1899.  A paper by Edmund Halley, the astronomer, in the Philosophical Transactions of the Royal Society for 1715, contains a suggestion for finding the age of the world by the following procedure.  He proposes to make observations on the saltness of the seas and ocean at intervals of one or more centuries, and from the increment of saltness arrive at their age.  The measurements, as a matter of fact, are impracticable.  The salinity would only gain (if all remained in solution) one millionth part in Too years; and, of course, the continuous rejection of salts by the ocean would invalidate the method.  The last objection also invalidates the calculation by T. Mellard Reade (Proc.  Liverpool Geol.  Soc., 1876) of a minor limit to the age by the calcium sulphate in the ocean.  Both papers were quite unknown to me when working out my method.  Halley’s paper was, I think, only brought to light in 1908.

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by all the rivers of the world is found to be probably not far from 175 million tonnes.[1] Dividing this into the mass of oceanic sodium we get the age as 80.7 millions of years.  Certain corrections have to be applied to this figure which result in raising it to a little over 90 millions of years.  Sollas, as the result of a careful review of the data, gets the age as between 80 and 150 millions of years.  My own result[2] was between 80 and 90 millions of years; but I subsequently found that upon certain extreme assumptions a maximum age might be arrived at of 105 millions of years.[3] Clarke regards the 80.7 millions of years as certainly a maximum in the light of certain calculations by Becker.[4]

The order of magnitude of these results cannot be shaken unless on the assumption that there is something entirely misleading in the existing rate of solvent denudation.  On the strength of the results of another and

[1] F. W. Clarke, A Preliminary Study of Chemical Denudation (Smithsonian Miscellaneous Collections, 1910).

[2] Loc. cit.

[3] “The Circulation of Salt and Geological Time” (Geol.  Mag., 1901, p. 350).

[4] Becker (loc. cit.), assuming that the exposed igneous and archaean rocks alone are responsible for the supply of sodium to the ocean, arrives at 74 millions of years as the geological age.  This matter was discussed by me formerly (Trans.  R.D.S., 1899, pp. 54 et seq.).  The assumption made is, I believe, inadmissible.  It is not supported by river analyses, or by the chemical character of residual soils from sedimentary rocks.  There may be some convergence in the rate of solvent denudation, but—­as I think on the evidence—­in our time unimportant.

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