THE SUBMERGED LANDS OF EUROPE
This map and section show how the Continental shelf of Europe runs out to the Atlantic, and how enormous is the area now submerged in the comparatively shallow water of the North Sea, the Irish Sea, and the Channel.
In Central Europe the climatic conditions can have been only slightly different. During the middle Tertiary Period palms grew in Switzerland; and even at the end of the Tertiary Period, as it was slowly passing into the Drift Era, the climate in Central Europe was still warmer than now, being much like that of Northern Italy, and its protected west coast the Riviera. There was also a rich flora, partly evergreen, and a fauna adapted to such mild surroundings. Even in the oldest (Preglacial) strata, and again in the middle (Interglacial) strata of the Central European drift, there was still an abundant plant-growth requiring a temperate climate, at any rate not more severe than Central Europe possesses at the present day. Our chief forest trees grew even then—the pine, fir, larch, and yew, and also the oak, maple, birch, hazel, etc. On the other hand, Northern and Alpine forms are absent among the plants. The same holds good of the animal world, which was certainly much farther removed than the plant world from the conditions prevailing now. The gigantic forms—the elephant, rhinoceros, and hippopotamus—appear particularly strange to us, as also the large beasts of prey—the hyena, lion, etc. But besides these, and the giant deer with its powerful antlers, and two large bovine species—the bison and the urus—there were also the majority of the present wild animals of Central and Northern Europe that were originally natives—as the horse, stag, roe, wild boar, and beaver, with the smaller rodents and insectivora, and the wolf, fox, lynx, and bears, of which last the cave-bear was far larger than the present brown bear, and even than the Polar and grizzly bears.
We have sure proofs that through a decrease in the yearly temperature a glacial period set in over Europe, North Asia, and North America, burying vast areas under a sheet of ice, of the effect and extent of which Northern Greenland, with its ground-relief veiled in inland ice, can give us an idea.
The immediate consequence of this total climatic change was an essential change in the fauna. Forms that were not suited to the deteriorated climate, that could neither stand it nor adapt themselves to it, were first compelled to retire, and then were exterminated. This fate befell the hippopotamuses, and also one of the two elephant species, Elephas antiquus, with its dwarf breeds in Sicily and Malta, probably thus developed by this retreat; then the rhinoceros-like Elasmotherium, a species of beaver; the Trogontherium, and the powerful cat Machairodus or Trucifelis, which still lived in England, France, and Liguria during the Drift Period. Other animals, like the lion and hyena, withdrew to more southerly regions, not affected by the increasing cold and more remote from its effects.
The Older Drift Animals
On the other hand, according to Von Zittel’s description, an immigration of cold-loving land animals took place, which at the present day live either in the Far North or on the wild Asiatic steppes, or in the high mountain ranges. These new immigrants mixed with the surviving forms of the older drift fauna. The latter lived, as we have seen, by no means in a warm climate, but only in a temperate “northerly” one, even in the warmer periods of the epoch. So we can understand that many of this older animal community were well able to adapt themselves to colder climatic conditions, and among them two of the large Drift pachydermata, the elephant and rhinoceros, whose kin we now find only in the warmest climes. But a thick woolly coat made these two Drift animals well fitted to defy a raw climate—namely, the woolly-haired mammoth, Elephas primigenius, one of the two Drift species of elephants of Europe, and the woolly-haired rhinoceros, Rhinoceros antiquitatis. A second species of rhinoceros, Rhinoceros merckii, was also preserved, and maintained its region of distribution. The horse was now more largely distributed, and inhabited the plains in herds; but, above all, the reindeer immigrated along with other animals that now belong only to Far Northern and Arctic regions, and pastured in large herds at the edges of the glaciers. With the reindeer, although less frequent, was the musk-ox of the Far North, besides many other cold-loving species, such as the lemming, snow-mouse, glutton, ermine, and Arctic fox. Many of the animal forms that were very frequent then, in the Drift Period, appear now in Central Europe only as Alpine dwellers, living on the borders of eternal snow, such as the ibex, chamois, marmot, and Alpine hare.
The Animal Invasion of Europe
Of special importance for our main question is the great invasion of Europe by Central Asiatic animals; immigrants direct from the Asiatic steppes pushed westward “as in a migration of nations,” among them the wild ass, saiga antelope, bobac, Asiatic porcupine, zizel, jumping mouse, whistling hare, and musk shrew-mouse. According as the glaciers and inland ice grew or shrank, the animals of the glacial period advanced more or less far to the North or retired more to the South, extending or reducing their range of distribution. The Glacial Period was no invariable climatic phenomenon. It is perfectly certain that a first Glacial Period with a low yearly temperature, under the influence of which the ice-masses, with their moraines, advanced a long way from the North and from the high mountains, so that in Germany, for instance, only a comparatively narrow strip remained free and habitable for higher forms of life between the two opposing rivers of ice—was succeeded by at least one period of warmer climate, and that certainly not a short one. The mean yearly temperature had increased so much that the ice-masses melted to a considerable extent, and had to retire far to the North and into the high valleys of the Alps. In this warmer Interglacial Period, as it is called, the Drift animals advanced far to the North, especially the mammoth, which, with the exception of the greater part of Scandinavia and Finland (districts which remained covered with ice during the Interglacial Period), is distributed throughout the drift strata of the whole of Europe and North Africa, and as far as Lake Baikal and the Caspian Sea in Northern Asia. Even the older Drift fauna, so far as it had not yet died out or retired, returned to its old habitats, so that the Interglacial fauna of Central Europe appear very similar to the Preglacial fauna. A long-sustained decrease of temperature led once more to the growth of the ice, which in this second Glacial Period almost reconquered the territory it had won at first.