The Birth-Time of the World | Page 8

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.
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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 acquaintance with geological science. Some of the most eminent
geologists, among whom Lyell and Geikie[1] may be mentioned, have
upheld the doctrine of uniformity. It must here suffice to dwell upon a
few points having special reference to the matter under discussion.
The mere extent of the land surface does not, within limits, affect the
question of the rate of denudation. This arises from the fact that the rain
supply is quite insufficient to denude the whole existing land surface.
About 30 per cent. of it does not, in fact, drain to the
[1] See especially Geikie's Address to Sect. C., Brit. Assoc. Rep., 1399.
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ocean. If the continents become invaded by a great transgression of the
ocean, this "rainless" area diminishes: and the denuded area advances
inwards without diminution. If the ocean recedes from the present
strand lines, the "rainless" area advances outwards, but, the rain supply
being sensibly constant, no change in the river supply of salts is to be
expected.
Age-long submergence of the entire land, or of any very large
proportion of what now exists, is negatived by the continuous sequence
of vast areas of sediment in every geologic age from the earliest times.
Now sediment-receiving areas always are but a small fraction of those
exposed areas whence the sediments are supplied.[1] Hence in the
continuous records of the sediments we have assurance of the
continuous exposure of the continents above the ocean surface. The
doctrine of the permanency of the continents has in its main features
been accepted by the most eminent authorities. As to the actual amount
of land which was exposed during past times to denudative effects, no
data exist to show it was very different from what is now exposed. It
has been estimated that the average area of the North American
continent over geologic time was about eight-tenths of its existing
area.[2] Restorations of other continents, so far as they have been
attempted, would not
[1] On the strength of the Mississippi measurements about 1 to 18
(Magee, _Am. Jour. of Sc._, 1892, p. 188).
[2] Schuchert, _Bull. Geol. Soc. Am._, vol. xx., 1910.
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suggest any more serious divergency one way or the other.
That climate in the oceans and upon the land was throughout much as it
is now, the continuous chain of teeming life and the sensitive
temperature limits of protoplasmic existence are sufficient evidence.[1]
The influence at once of climate and of elevation of the land may be
appraised at their true value by the ascertained facts of solvent
denudation, as the following table shows.

Tonnes removed in Mean elevation. solution per square Metres. mile
per annum. North America - 79 700 South America - 50 650 Europe -
100 300 Asia - 84 950 Africa - 44 650
In this table the estimated number of tonnes of matter in solution,
which for every square mile of area the rivers convey to the ocean in
one year, is given in the first column. These results are compiled by
Clarke from a very large number of analyses of river waters. The
second column of the table gives the mean heights in metres above sea
level of the several continents, as cited by Arrhenius.[2]
Of all the denudation results given in the table, those relating to North
America and to Europe are far the
[1] See also Poulton, Address