The Birth-Time of the World | Page 2

GLACIER JOINING THE
GREAT ALETSCH GLACIER. GLACIERS OF THE
LAUTERBRUNNEN THAL - to face p. 285
PLATE XXVIII. PERCHED BLOCK ON THE ALETSCH GLACIER.
GRANITE ERRATIC NEAR ROUNDWOOD, CO. WICKLOW;
NOW BROKEN UP AND REMOVED - to face p. 286
And Fifteen Illustrations in the Text.
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PREFACE
Tins volume contains twelve essays written at various times during
recent years. Many of them are studies contributed to Scientific
Reviews or delivered as popular lectures. Some are expositions of
views the scientific basis of which may be regarded as established.
Others--the greater number--may be described as attempting the
solution of problems which cannot be approached by direct
observation.
The essay on The Birth-time of the World is based on a lecture
delivered before the Royal Dublin Society. The subject has attracted
much attention within recent years. The age of the Earth is, indeed, of
primary importance in our conception of the longevity of planetary
systems. The essay deals with the evidence, derived from the
investigation of purely terrestrial phenomena, as to the period which
has elapsed since the ocean condensed upon the Earth's surface. Dr.
Decker's recent addition to the subject appeared too late for inclusion in
it. He finds that the movements (termed isostatic) which geologists
recognise as taking place deep in the Earth's crust, indicate an age of

the same order of magnitude
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as that which is inferred from the statistics of denudative history.[1]
The subject of Denudation naturally arises from the first essay. In
thinking over the method of finding the age of the ocean by the
accumulation of sodium therein, I perceived so long ago as 1899, when
my first paper was published, that this method afforded a means of
ascertaining the grand total of denudative work effected on the Earth's
surface since the beginning of geological time; the resulting knowledge
in no way involving any assumption as to the duration of the period
comprising the denudative actions. This idea has been elaborated in
various publications since then, both by myself and by others.
"Denudation," while including a survey of the subject generally, is
mainly a popular account of this method and its results. It closes with a
reference to the fascinating problems presented by the inner nature of
sedimentation: a branch of science to which I endeavoured to
contribute some years ago.
Mountain Genesis first brings in the subject of the geological
intervention of radioactivity. There can, I believe, be no doubt as to the
influence of transforming elements upon the developments of the
surface features of the Earth; and, if I am right, this source of thermal
energy is mainly responsible for that local accumulation of wrinkling
which we term mountain chains. The
[1] Bull. Geol. Soc. America, vol. xxvi, March 1915.
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paper on Alpine Structure is a reprint from "Radioactivity and
Geology," which for the sake of completeness is here included. It is
directed to the elucidation of a detail of mountain genesis: a detail
which enters into recent theories of Alpine development. The weakness
of the theory of the "horst" is manifest, however, in many of its other
applications; if not, indeed, in all.

The foregoing essays on the physical influences affecting the surface
features of the Earth are accompanied by one entitled _The Abundance
of Life._ This originated amidst the overwhelming presentation of life
which confronts us in the Swiss Alps. The subject is sufficiently
inspiring. Can no fundamental reason be given for the urgency and
aggressiveness of life? Vitality is an ever-extending phenomenon. It is
plain that the great principles which have been enunciated in
explanation of the origin of species do not really touch the problem. In
the essay--which is an early one (1890)--the explanation of the whole
great matter is sought--and as I believe found--in the attitude of the
organism towards energy external to it; an attitude which results in its
evasion of the retardative and dissipatory effects which prevail in
lifeless dynamic systems of all kinds.
_Other Minds than Ours_? attempts a solution of the vexed question of
the origin of the Martian "canals." The essay is an abridgment of two
popular lectures on the subject. I had previously written an account of
my views which carried the enquiry as far as it was in
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my power to go. This paper appeared in the "Transactions of the Royal
Dublin Society, 1897." The theory put forward is a purely physical one,
and, if justified, the view that intelligent beings exist in Mars derives no
support from his visible surface features; but is, in fact, confronted with
fresh difficulties.
Pleochroic Haloes is a popular exposition of an inconspicuous but very
beautiful phenomenon of the rocks. Minute darkened spheres--a
microscopic detail--appear everywhere in certain of the rock minerals.
What are they? The discoveries of recent radioactive research--chiefly
due to Rutherford--give