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to invade the country of the reindeer. All the remains of fossil hippopotamus in this country which I have seen, with two exceptions, belong to adults, and it is very probable that that animal seldom or never bred in our country. The mammoth has purposely been omitted in this analysis of the evidence afforded by the mammalia as to the climate, because it happens to be one of the few creatures which were able to live under very different climatal conditions, being found alike in the volcanic ash in which Rome is built, the frozen marshes of Siberia, and in the morasses of the Southern States.

Nor does this evidence as to the Pleistocene climate stand alone. The contorted gravels, and the angular state of the pebbles of which they are often composed, are, as Mr. Prestwich infers, explicable only on the theory of ice having been formed in our rivers in larger quantities than at the present day: the one being the result of the grounding of large masses of ice, and the other of their melting away, and consequently dropping their burden of pebbles. The large plateaux of brick earths are also probably deposited by floods, caused, like those of Siberia and North America, by the sudden melting of the winter snow.

This consideration of a Pleistocene climate leads necessarily to the difficult problem of the relation of the Pleistocene mammalia to the period of intense cold, the Glacial period; and before this can be discussed, I must define exactly what I mean by the term. At the close of the Pleiocene period the temperature of northern and central Europe became lowered to such a degree that it became almost Arctic in character, and those complex phenomena were manifested which we know as glacial. And the latter indicate geographical changes of enormous magnitude. The researches of many eminent observers prove, that at the commencement of the Glacial period an enormous sheet of ice, like that under which Greenland now lies buried, extended from the hills of Scandinavia over North Germany, the North Sea, Scotland, Ireland, Cumbria, and the hilly districts of England, at least as far south as the valley of the Thames. The land then, most probably, as Professor Ramsay and Sir Charles Lyell believe, stood higher than it does now. Then to this succeeded a period of depression, during which the mountains of Wales were submerged to a height of at least 1,300 ft.; and the waves of the sea washed out of the pre-existing glacier detritus the shingle and sand, termed the middie drift,' of the North of England and of Scotland and Ireland.* Then the land was re-elevated above the

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* I have to acknowledge the kind assistance of Professor Hull, F.R.S., Mr. Kinahan, and the Rev. M. H. Close, in this portion of the subject.

waves, and a second period of glaciers set in, traces of which occur abundantly in Wales, Scotland, Ireland, and even as far south as Dauphiné and Auvergne. They were, however, of far less extent than those which preceded them, occupying isolated areas instead of forming one continuous icy covering to the country. Such as this is a brief résumé of the glacial phenomena: 1. As the pleiocene temperature was lowered, the glaciers crept down from the tops of the mountains, until at last they formed one continuous ice sheet, moving resistlessly over the smaller hills and valleys to the lower grounds, and the first glacier period set in. 2. Then followed the period of depression beneath the sea. 3. And, lastly, on the land re-emerging from the sea, the second glacier period set in. The climate during the marine depression must obviously have been milder than that of either of the glacier periods, because of the moderating effect of the presence of a stretch of sea.

What is the precise relation of the Pleistocene mammals to these two glacier periods? Did they invade northern and central Europe during the first or the second, before or after, the marine submergence indicated by the "middle drift?" We might expect, à priori, that as the temperature became lowered the northern mammalia would gradually invade the region occupied before by the pleiocene forms, and that the reindeer and the mammoth would gradually supplant the Cervus ardens and the Elephas meridionalis. Traces of such an occupation would necessarily be very rare, since they would be exposed to the grinding action both of the advancing glacial sheet, and also subsequently to that of the waves on the littoral zone during the depression and re-elevation of the land. At the time also that the greater part of Great Britain was buried under an ice sheet, they could not have occupied that region, although they may have been, and most probably were, living in the districts further to the south, which were not covered by ice. The labours, however, of Dr. Bryce and others proved that one at least of the characteristic Pleistocene mammalia-the mammoth as well as the reindeer -lived in Scotland before the deposit of the lower boulderclay; while Mr. Jamieson has pointed out that they could not have occupied that area at the same time as the ice, and therefore must be referred to a still earlier date.* The teeth and bones discovered in the ancient land surface at Selsea also very probably indicate that the mammoth lived in Sussex

For account of these discoveries, see "Trans. Geol. Soc. Glasgow," vol. i. part 2; "Quart. Geol. Journ.," vol. xxi. pp. 161 et seq. and pp. 204 et seq. I am also indebted to Mr. James Geikie for valuable information on the subject.

before the glacial submergence, although they were never admitted by Dr. Falconer to be of the same age as the remains of Elephas antiquus from the same preglacial horizon. On a careful examination of the whole evidence, I am compelled to believe, with Mr. Godwin-Austen and Mr. Prestwich, that the à priori argument that Pleistocene mammalia occupied Great Britain before the first glacier period to be fully borne out by the few incontestable proofs that have been brought forward of the remains being found in preglacial deposits. And the scanty evidence on the point is just what might be expected from the rare accidents under which the bones in superficial deposits could have withstood the grinding of the ice sheet and the subsequent erosive action of the waves on the coastline. This view seems to me to be more likely to be true than that which I have hitherto maintained, that the Pleistocene mammalia arrived here after the marine submergence, and to which I had been led partly by the doubts of Dr. Falconer as to the age of the mammoth at Selsea, and partly from my own doubts whether the clays under and on which the animal was found in Scotland belonged to the first or to the second period of glacier extension; while, on the other hand, the postglacial range of the Pleistocene mammalia in central and eastern England was clearly proved in many cases.

But whatever view may be held as to the arrival of the Pleistocene mammalia in Britain during the lowering of the temperature which immediately preceded the first glacier period, an examination of the accompanying map (Pl. LXXVIII.) will prove that they were in full occupation of the low country at the time that the higher lands and certain other regions were occupied by the ice during the second glacier period. The dotted areas are those in which the Pleistocene mammalia have been found in Scotland, Ireland, Wales, and England, Northern France and Belgium, and which occur equally in the bed of the North Sea and in the British Channel; while those areas which are left plain on the map are those which are full of the most fresh-looking traces of ice action, old moraines, glacial striæ, and the like, which have a direct relation to the existing valleys.

The absence of these animals from those areas must have been caused by the existence of some barrier to their migration; and the hypothesis that this was the presence of ice alone satisfies all the conditions of the case. It accounts both for the exceedingly modern aspect of the glacial phenomena, and for the irregular distribution of the animals. We may

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* The authorities for the distribution of the mammalia are to be found in my Essay published in "Quart. Geol. Journ.," May 1869.

therefore be tolerably certain that the Pleistocene mammalia lived here at the same time that the glaciers still covered large areas in Great Britain and Ireland.

The consideration of the Pleistocene climate is also intimately connected with the former extension of NorthWestern Europe into the Atlantic; for the extremes of temperature implied by the mixed character of the former can only be satisfied by the view that Great Britain was not an island, but an integral portion of a continent. In the following map, which is based on that drawn by Dr. Petermann and published by Dr. Stieler, I have followed Sir H. de la Beche and Sir Charles Lyell in taking the 100-fathom line as representing the coast, the time from which the soundings deepen seawards so quickly in every direction, that the line of 200 fathoms would include an area which is but slightly larger. As evidence of this coast line, Mr. Godwin-Austen has brought forward the littoral shells, the shingle, and the line of rocks which are found near the embouchment of what may be called the river of the English Channel. And that this river is no myth is proved by the discovery of the Unio pictorum, in from 50 to 100 fathoms water, by Captain White, at the same point.

To complete this very brief sketch of the physiography of Pleistocene Britain, I have inserted the rivers, and have traced them by the soundings to their mouths in the Pleistocene sea. A glance at the map will show the relation of the present rivers to those great arteries to which they once contributed their waters. It is obvious that the great valleys of the English Channel and the North Sea, and probably that of the British Channel, would afford free scope for the migration of the Pleistocene mammalia from France and Germany to our country, and that of the Irish Channel to Ireland. And it is by no means remarkable that the paleolithic savages who lived on the banks of the Somme or the Seine, or in the caves of Belgium, should have left like traces of their presence in the south and the east of England. Had they merely occupied one side only of what must have been to them a most valuable hunting-ground, and not sometimes have crossed over to the other, we should have cause to wonder at their caprice.

EXPLANATION OF PLATE LXXVIII.

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Dotted Areas those in which Pleistocene mammalia have been found. = the extension of land to the 100-fathom line.

Lined

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Figures = fathoms.

398

STAR STREAMS AND STAR SPRAYS.

BY RICHARD A. PROCTOR, B.A., F.R.A.S., AUTHOR OF 66 OTHER WORLDS," "THE SUN," "LIGHT SCIENCE," &c. &c.

THE

HE stellar heavens present us with a problem of vast difficulty-the problem of determining the laws according to which those myriads of orbs which the unaided eyes can see, or which the telescope reveals, are distributed throughout space. We can determine the laws of stellar distribution so far as they relate to the imaginary concave of the heavens. We could form a globe upon which millions of stars might be indicated; or, better, we might mark these millions of stars upon the interior surface of a hollow globe; and thus, so far as the apparent laws of stellar arrangement are concerned, we might actually render the eye cognisant of all which even the most powerful telescopes can reveal. But when this had been accomplished, we should have made but a short step towards the determination of the manner according to which the stars are distributed throughout space. We should have placed all the stars which the telescope reveals upon a spherical surface, whereas we know that they lie in reality on no such surface, but some at distances much vaster than the distances which separate us from others. We know that if we have to deal with a sphere of stars at all, it is a sphere full of stars, and not a spherical surface covered with stars, that we have to consider. But, in truth, we know that the space containing all the stars revealed by powerful telescopes may not even approach the form of a sphere; and that within that space the stars may be distributed in the most irregular manner-here crowded most densely, here sparsely scattered, and throughout enormous regions mayhap altogether wanting; in some places arranged into clustering aggregations, in others in streams, and elsewhere in fantastic convolutions or reticulations; while, for aught that has yet been shown, the whole stellar region may be occupied more or less richly with a variety of forms of matter other than stars or suns, and even differing perhaps from any forms of matter with which we are acquainted.

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