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consequences than an alteration in the disposition of land and water. Mr. Hopkins suggested several hypotheses to account for glacial periods, attributing them either to a variation in the intensity of solar radiation, or to the possibility that the sun in its motion through space may have recently passed from a colder into a warmer region; but Sir John Lubbock,1 who has passed all the various hypotheses of modern writers under review, points out that these theories are untenable, because the formation of glaciers requires an alternation of heat and cold. Another hypothesis suggested by Mr. Hopkins, and for which he claims something approaching an ascertained fact, is an alteration in, or rather the absence of, the Gulf Stream, which, he says, would lower the January temperature of Western Europe ten degrees, while a cold current from the north would make a further difference of three or four degrees; and this, Mr. Hopkins asserts, must follow the submergence of North America. But Sir John Lubbock shows that this also would necessitate an immense time, for “if when the gravels and loëss of the Somme and the Seine were being deposited, the Gulf Stream was passing up what is now the valley of the Mississippi, then it follows that the formation of the loëss in that valley and its delta, an accumulation which Sir Charles Lyell has shown would require a period of about 100,000 years, would be subsequent to the excavation of the Somme valley, and to the presence of man in Western Europe." 2

But the hypothesis which next to that of Mr. Croll has been received with most favour in the scientific world, is that which attributes the evidences of glaciation in Central Europe to a change in the position of the earth's axis. This solution of the grand geological problem had suggested itself to my mind many years ago; but upon its first proposition by Mr. Hopkins, or some other scientist, it was scouted as impossible, improbable, and absurd. Like many other theories, however, and some great truths, it has outlived the 2 Ibid. p. 393.

1 Pre-historic Times.

period of ridicule, and has made for itself disciples among the foremost men of science not only in Great Britain, but on the Continent. Sir John Lubbock writes on this subject as follows—

"The possibility of such a change has been denied by many astronomers. My father, the late Sir J. W. Lubbock, on the contrary, has maintained that it would necessarily follow from upheavals and depressions of the earth's surface, if only they were of sufficient magnitude. The same view has recently been taken by other mathematicians. This suggestion, however, involves immense geographical changes, and would therefore necessarily have required an enormous lapse of time."

Dr. John Evans, in his presidential address to the Geological Section at the British Association meeting in Dublin, in 1878, spoke thus

"The general opinion of physicists, as to the possibility of a change in the position of the earth's axis, has recently undergone modifications somewhat analogous in character to those which, in the opinion of some geologists, the position of the axis has itself undergone. Instead of a fixed dogma as to the impossibility of change, we find a divergence of mathematical opinion, and variations of the pole differing in extent, allowed by different mathematicians who have of late gone into the question, as, for instance, the Rev. J. F. Twisden, Mr. George Darwin, Professor Haughton, the Rev. E. Hill, and Sir William Thompson. All agree in the theoretical possibility of a change in the geographical position of the earth's axis of rotation being affected by a redistribution of matter on the surface, but they do not appear to be all in accord as to the extent of such changes. Mr. Twisden, for instance, arrives at the conclusion that the elevation of a belt, twenty degrees in width, such as that which I suggested in my presidential address to the Geological Society in 1876, would displace the axis by about ten miles only; while Professor Haughton maintains that the elevation of two such continents as Europe and Asia would displace it

by about sixty-nine miles; and Sir W. Thompson has not only admitted, but asserted as highly probable, that the poles may have been in ancient times very far from their present geographical position, and may have gradually shifted through ten, twenty, thirty, forty, or more degrees, without at any time any perceptible sudden disturbance of either land or water."1

Dr. Evans then goes on to express his own opinion that the earth cannot be as solid and rigid as many suppose it to be, and that sufficient regard has not been paid to the effect of the readjustment of the large fluid area of the globe, nor to the possibility of internal as well as external changes in affecting the distribution and readjustment of matter. In truth this assumed rigidity appears to be contradicted by many well-ascertained facts. Mr. Waters, F.G.S., has calculated the changes traceable in the level of land and sea in Italy and Sicily, and estimated the movement of the pole which would result therefrom; and when we take into consideration the vast elevations and subsidences which have undoubtedly occurred, and are still slowly in progress, it appears to me impossible to doubt that the earth's axis has been gradually shifted, and is still constantly shifting, probably in one given direction, but possibly in a curve, although the yearly motion is too small to be appreciable, and this motion of the axis, added to Mr. Croll's theory, will, I believe, eventually be found to give the true cause of the so-called Great Ice Age.

It is obvious that, supposing the earth to have retained its present form from a remote period, and the poles to have gradually circulated round the world, that those places over which the poles have passed would not only have experienced a long glacial period, but would also have become more or less submerged, in consequence of the flattening of the Polar region, and more or less elevated as they again approached the equator, with a corresponding variation of climate, and one completed revolution, or it may be one completed

1 Proceedings of British Association, 1878.

circle, not round the world, but round a given centre, would of necessity result in two glacial epochs, probably of varying intensity, in accordance with the eccentricity of the earth's orbit at the time. Various recent investigations seem to confirm the truth of this theory. Humboldt long ago noted the north-westerly trend of all mountain ranges, and the same has been remarked by Captain Stokes in the southern hemisphere. Linnæus saw the changes of ocean-level, and marked its encroachments by a stone, which is now 340 feet nearer to the sea.1 În railways running north and south in America, a singular creeping of the rails southwards has been observed, the western rail always creeping faster than the eastern; and lately, which is perhaps the most significant fact of all, observations have been made at St. Petersburg which show a diminution of latitude there, and also at Greenwich, Washington, Paris, Milan, Rome, Naples, and Konigsberg. Another curious fact which has attracted much attention of late is, that recent Arctic explorations have proved incontestably that a mild semi-tropical climate once existed within the Arctic circle, for not only have coal and coral been found in the most northerly lands discovered, but the fossil flora of these lands is found to include plants semi-tropical in character, and which could not thrive and produce seeds with the amount of light now received in those regions, even if they could. by change of habit have borne a considerable increase of cold.

The Arctic regions indeed would seem to be now passing through their first glacial epoch, for Professor Nordenskjold gives as the result of his geological observations in the Polar regions, that he has never seen in Spitzbergen or Greenland, in mountains 1000 or 1500 feet high, sections of which are exposed quite free from snow or vegetation, any trace of boulders even as large as a child's head, in strata prior to the middle of the Tertiary, that is, in the later Miocene, although the rocks thus exposed include all formations from the

1 British Lyceum, Nov. 1870.

Silurian to the Tertiary, and an extent of over one thousand miles,1

Comparing this with the testimony of geologists as to the traces of glaciation in Europe, North America, India, and South Africa, at different epochs from Silurian to Tertiary times, it would seem more reasonable to imagine that the poles are being constantly but very slowly shifted, according to a law at present unknown, causing glacial epochs of varying extent and intensity (probably in accordance with Mr. Croll's theory) within a certain zone, but leaving portions of the earth's surface to enjoy a temperate rising to a tropical climate rather than to suppose a glacial epoch or rather several glacial epochs, and extending to within a few degrees of the tropics in both hemispheres, and yet not reaching the north pole, which would appear at that time to have enjoyed a semi-tropical climate.2

;

Speculations on the Great Ice Age would seem to have little to do with anthropology; but, as will presently appear, the subject has an important bearing upon the antiquity of the human race, for it cannot be doubted that the traces of man in Britain date back to a period which, if it did not precede, certainly followed close upon, that epoch; and if we accept the theory and the chronology of Mr. Croll, the date of man's appearance in these islands, remote as it is, may thus be roughly estimated; but as no one has yet suggested that the genus homo originated in Britain, he must of necessity have been some time in existence before he found his way to these distant and at that time inhospitable

3

1 Wallace's Island Life, p. 18.

2 The theory of the shifting of the earth's axis appears to be still favoured by geologists, for Mr. Green, in his address to the Geological Section of the British Association at Leeds this year (1890), says" At a gathering where several of our best English geologists were present, the question of the cause of changes of climate was under discussion. The explanation which found most favour was a change of the position of the axis of rotation within the earth itself."

Croll and Geikie assign 80,000 years as the close of the glacial epoch on astronomical grounds.

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