The History of the European Fauna

by R. F. Scharff

The Seal of the Caspian (Phoca caspica) is closely allied to the Arctic Seal, and its presence alone in that sea indicates that at no very distant date—at any rate since pliocene times—a closer connection with the Arctic Ocean existed than at present.

I am sure it will be readily granted that there is zoological evidence for the belief of such a connection or union between the two great seas. However, it may be urged that owing to the presence of an ice-sheet in Northern Europe during the Glacial period, such a connection must either have been pre-glacial or have existed after that period. But the connection must have occurred at a time when the Caspian extended far to the north—when indeed the so-called post-tertiary Caspian deposits were laid down ([Fig. 17]). Since the boulder-clay which covers the plain of Northern Russia is assumed to be the ground-moraine of the great northern ice-sheet, we might expect to find that the Caspian deposits were not contemporaneous with it. Curiously enough, it has been shown by Mr. Sjögren that all observations have pointed to the fact that these two deposits do not overlie one another, but occur side by side, and are therefore contemporaneous. This seems to warrant our belief, that while the boulder-clay was being laid down in Northern Europe, the Aralo-Caspian Sea had some communication with the White Sea.

Fig. 17.—Map of European Russia (after Karpinski). The faintly dotted parts indicate the areas covered by boulder-clay, the strongly dotted ones those exhibiting Aralo-Caspian and other post-pliocene deposits.

The boulder-clay of Northern Continental Europe, as already stated, is now generally recognised to be the product of a huge ice-sheet which invaded the lowlands of Continental Europe from the Scandinavian mountains. Though Alpine glaciers at the present day produce little or no ground moraine, these ancient larger ice-sheets, or "mers de glace," are believed to have deposited immense layers of mud containing scratched and polished stones. Many of the latter have been carried great distances from their source of origin. The Scandinavian ice-sheet is supposed to have advanced as far south as the line indicated on the map, after which it gradually retreated. On this point, however, as in almost every detail connected with the Glacial period, geologists are at variance. Professor James Geikie maintains, that there were no less than four Glacial periods, separated from one another by milder inter-glacial phases. On the Continent the view of two Glacial and one inter-glacial period is, I think, more generally adopted. Professor Geikie's four periods seem to me to have originated in a desire to correlate the British pleistocene deposits with the continental ones, and at the same time to retain the old view of the inter-glacial position of the Forest-Bed. The two theories agree in so far as that in both the glacial conditions culminate in a maximum glaciation, followed by a more temperate phase of climate, with consequent retreat of the ice-sheets, and finally by a renewed advance of the glaciers.

We are told that there is not the slightest doubt about it that a marked but gradual decrease of temperature took place all over Europe either during the beginning of the Pleistocene or towards the end of the Pliocene Epoch.

We might reasonably suppose, then, that a similar climatic effect was produced in Siberia, in consequence of which the fauna would have been obliged to retreat from the extreme northern latitudes southward. No doubt great efforts would have been made by the members of the Siberian fauna—at any rate by those possessing strong power of locomotion—to extend their range in other directions. But we have no evidence that a migration from Siberia came to Eastern Europe at that time. It seems, therefore, as if the barrier referred to by Brandt, Köppen, Boyd Dawkins, and others (p. 222), had existed at this time. This would have effectually prevented an overflow of the fauna from Siberia. Only in deposits later than the lower continental boulder-clay do we find traces of a Siberian migration. The time of maximum glaciation had then passed away; the great glacier which was believed to have invaded the lowlands of Northern Europe had again retreated, before the Siberian mammals made their appearance in Germany.

It has been stated above (p. [226]) that while the Russian boulder-clay was being laid down, the Aralo-Caspian probably had some communication with the White Sea.

But how can this view be reconciled with the existence of a huge mer de glace in the northern plains of Russia? The existence of the ice-sheet has been conjured up in order to explain the presence of the boulder-clay. But not long ago a very different interpretation of the origin of this clay was given; and one, I may say, which explains the history of the Siberian and the European fauna in a more satisfactory manner than is done by the ice-sheet hypothesis. It is that the boulder-clay is not the product of land-ice, but has been deposited by a sea with floating icebergs. Thus the latter hypothesis does not deny the existence of glaciers, but allows the mud to be deposited on the floor of a turbid sea, instead of beneath an immense mer de glace. I need hardly mention that this view, which was formerly universally accepted by geologists, is now scouted by almost every authority, both British and Continental. I should scarcely venture the attempt to revive old memories and stir up again long forgotten controversies, were it not for the fact that many new points have arisen in the course of the above inquiries, which appear to me so very difficult to explain by the land-ice hypothesis, while they are comparatively easy to understand when we adopt the old theory of the marine origin of the boulder-clay. But a few geologists even at the present day, while believing in the land-ice theory, recognise that the marine hypothesis should have some consideration shown to it. I need only remind glacialists of the work recently published by Professor Bonney. "The singular mixture," he remarks (p. 280), "and apparent crossing of the paths of boulders, as already stated, are less difficult to explain on the hypothesis of distribution by floating ice than on that of transport by land-ice, because, in the former case, though the drift of winds and currents would be generally in one direction, both might be varied at particular seasons. So far as concerns the distribution and thickness of the glacial deposits, there is not much to choose between either hypothesis; but on that of land-ice it is extremely difficult to explain the intercalation of perfectly stratified sands and gravels and of boulder-clay, as well as the not infrequent signs of bedding in the latter."