The Romance of Modern Geology / Describing in simple but exact language the making of the earth with some account of prehistoric animal life

by Edwin Sharpe Grew

In Europe there were large glaciers in the southern mountains and extensive ice-sheets on the southern plains. Radiating from the Scandinavian highlands a succession of great ice-sheets crept forth on the lowlands of Russia, Germany, Denmark, Holland, and Belgium, and crossing the shallow basin of the North Sea touched the shores of Great Britain, where they were met by ice radiating from the mountains of these isles.

From the Alps gigantic glaciers descended to the lowlands in all directions. Then the Rhine glacier moved out far beyond the mountains and joined with the glaciers of Savoy and Dauphiny on the plains of France, while from the Southern Alps glaciers invaded the fertile plains of Italy.

Glaciers of similar size and extent descended into the valleys of the Rhine and Danube. The Pyrenees, some of the higher mountains of the Spanish plateau, the higher mountains of France, the Apennines, the Carpathians, the Balkans, the Urals, all had their ice-sheets. Iceland and the Faroe Islands were buried under ice, and even Corsica had snowfields and glaciers, some of which were not small.

Nearly one half of North America was buried in ice. Strangely enough, it was not the whole northern half, but the north-eastern half that was specially ice-invaded, and, more strangely still, not so much the mountainous portions, though these were affected, as the plains. Alaska was largely free from ice except on or about the mountains: and there was less ice on the western plains than in the valley of the Mississippi. Much the greater part of the four million square miles of ice-field lay on the plains of Canada and in the upper Mississippi valley. The Missouri and Ohio rivers like two great arms embraced the borders of the ice-fields to which they owe their origin.

We do not propose to examine the several theories which have been proposed to account for this extraordinary cold, for none is completely acceptable or accepted, but we may just mention them. Dr. Croll a century ago suggested that the cold may have been due to the alterations in the shape of the earth's orbit, alterations which astronomers tell us take place regularly, though very slowly and at intervals of millions of years. If so, this glacial period was only the last of many glacial periods; the traces of the earlier ones having, however, been for the most part obliterated and destroyed.

Sir Charles Lyell has urged that geographical changes (elevations and subsidences) would of themselves be sufficient to bring about a glacial period, which (he says) would be the result of a great continent being formed round the North Pole while oceanic conditions prevailed at the Equator. Another theory is that the heat given out by the sun is not always equal, being sometimes more (when even polar countries enjoy a warm climate) and sometimes less (when only the equatorial regions are habitable). The objection to this theory is, of course, that we have no proof that our sun is of greatly variable heat. Whatever may have been the cause of the glacial period, we know as a proved fact that a long time ago (as measured by years, although the event itself is among the latest of the many changes recorded in the geological history of the earth) the climate of the British Isles was so intensely cold that the greater part of this country was covered with ice and snow, and we know also that this intense cold was sufficient to change in many respects the habits and appearance of the animals and vegetation of the earth. How much this was the case can be gathered from the fact that in the period which preceded it animals which now live in the tropics roamed in the Arctic circle, and figs and magnolias grew in Greenland.

The last word we shall have to say on the climatic conditions of this period is that the Ice Age had its sub-periods and divisions like all other epochs and in them the ice sometimes retreated, and consequently in parts of the earth where there had been snow and ice, and where there were to be ice and snow again, the wintry conditions retreated (for centuries, perhaps, at a time), and the valleys and plains basked during these intervals in sun and rain and warmth. These epochs are called "inter-glacial epochs."

The life of the regions not much affected by the rigours of snow and ice is gradually being ascertained by geologists now. One of its most marked features was the retreat of the northern and Asiatic animals before the advancing ice towards the warmer tropics and Equator; these animals journeyed back northward again whenever the retreating ice would let them. The great Proboscideans, the Mastodon and the Mammoth were members of this group, and so were the bear, the bison, the musk ox. With these mingled towards the south several types (which were gradually becoming extinct in North America) such as the horse, tapir, llama, and the sabre-tooth cat. A second prominent feature was a southern group in the western hemisphere, consisting of gigantic sloths, armadillos, and water-hogs; and now for the first time the interest of animal life shifts to South America.

"There are many instances," says Sir Edward Ray Lankester in his book on Extinct Animals, "in which small living animals were represented in the past by gigantic forms very close in structure to the little living beasts, but of much greater size. Hence it is concluded that these particular living animals are the reduced and dwindled representatives of a race of primeval monsters. There is some truth in this, as may be seen from the history of the living sloths and armadillos of South America, as compared with the extinct gigantic sloths and armadillos dug up in that country. But it is a great mistake to conclude from this that it is a law of nature that recent animals are all small and insignificant as compared with their representatives in the past. That is simply not true. Recent horses are bigger than extinct ones; recent elephants are much bigger than their earlier elephantine ancestors. There never has been any creature of any kind—mammal, reptile, bird, or fish—in any geological period we know of, so big as some of the existing whales, the Sperm Whale, the great Rorqual, and the whalebone whales.

"It is true that there were enormous reptiles in the past, far larger than any living crocodiles, standing fourteen feet at the loins, and measuring eighty feet from the tip of the snout to the end of the tail; but their bodies did not weigh much more than a big African elephant, and were small compared with whales. So let us be under no illusions as to extinct monsters, and proceed to look at those of South America with simple courage and confidence in our own day."