iding 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.

14

entirely different method of approaching the question of the
Earth's age (which shall be presently referred to), it has been
contended that it is too low. It is even asserted that it is from
nine to fourteen times too low. We have then to consider whether
such an enormous error can enter into the method. The
measurements involved cannot be seriously impugned. Corrections
for possible errors applied to the quantities entering into this
method have been considered by various writers. My own original
corrections have been generally confirmed. I think the only point
left open for discussion is the principle of uniformitarianism
involved in this method and in the methods previously discussed.

In order to appreciate the force of the evidence for uniformity
in the geological history of the Earth, it is, of course,
necessary to possess some ac