The Birth-Time of the World | Page 2

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
xi
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.
xii
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
xiii
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 the answer. The measurements applied to the little objects render the explanation beyond question. They turn out to be a quite extraordinary record of radioactive energy; a record accumulated since remote geological times, and assuring us, indirectly, of the stability of the chemical elements in general since the beginning of the world. This assurance is, without proof, often assumed in our views on the geological history of the Globe.
Skating is a discourse,