[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.
13
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
archæan 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.