The Miocene deposits are not so generally important in the United Kingdom, but in America very valuable fossils have been discovered in these strata. The Pliocene strata extend along the east of Great Britain, where they are denominated “Crag,” as Norfolk Crag, Red Crag, Coralline Crag. Underneath these mammalian remains have been discovered. After the Pliocene we come to the Post-Pliocene, which really closes the long Tertiary period. During these ages the gradual development of created beings apparently reached its height. It was towards the end of the Middle Eocene that the great mountain chain of Europe came into existence, which is connected, as any casual observer may see, with the Himalaya. In fact, the whole chain, from the Thibetian range through India, the Caucasus, Alps, and Pyrenees, is continuous, and formed of the same material (“nummulitic limestone”). There is no doubt that the whole northern hemisphere enjoyed at the commencement of the Tertiary period a warm, not to say tropical, climate, which got colder and colder.
We find the increase of animals and plants more fitted to the requirements of man and our present climate. There are many signs of the successive increase of land in Europe generally, while the contrast the Tertiary period bears to the Secondary is very marked. In the former we have extensive deposits in the waters of wide, open seas; in the latter the depositions were evidently made where dry land, with its accompanying bays and lakes, were extensive and numerous. The former is marine, the latter lacustrine and marine. The seas of the Tertiary period have lately been defined.
Fig. 683.—Megatherium cuvieri (post-Pliocene), S. America.
Sir Charles Lyell, in his “Principles of Geology,” shows us this, and defines the European features at the commencement of the Tertiary epoch. At that time, the British islands, with the exception of the basins of London, the Isle of Wight, and Norfolk, had wholly emerged from the deep. But a third part of France was still under water. Italy consisted only of a long and narrow ridgy peninsula, branching off from the Alps near Savona. Turkey and Greece, south of the Danube, were laid dry; and a tract of land extended from the Vosges, through central Germany, Bohemia, and the north of Hungary, perhaps to the Balkan. But the whole of the north of Europe and Asia, from Holland eastward to central Tartary, and from Saxony and the Carpathians northward to Sweden, Lapland, and the Ural chain, lay beneath the ocean. The same subterranean movements, which have subsequently raised the wide plains of our northern continents above the sea-level, have given great additional elevation to the then existing land. Thus the Alps have certainly acquired an increased height of from two thousand to four thousand feet since the commencement of the Tertiary period. The Pyrenees, whose highest ridge consists of marine calcareous beds, of the age of our chalk and greensand series, while the Tertiary strata at their foot are horizontal, and reach only the height of a few hundred feet above the sea, seem to have been entirely upheaved in the comparatively brief interval between the deposition of the chalk and these Tertiary strata. The Jura, also, owe a great part of their present elevation to convulsions which happened after the deposition of the Tertiary groups. On the other hand, it is possible that some mountain-chains may have been lowered by subsidence, as well as by meteoric degradation, during the same series of ages in this quarter of the globe; and on some points shallows may have been depressed into deep abysses. But, on the whole, everything tends to show that the great predominance of land which now distinguishes the northern hemisphere has been brought about only at a recent period, and Sir Charles holds that the shifting of the continents is sufficient to account for the variations of climate. We have every reason to believe that before the Glacial epoch England and the Continent were united, and during the Glacial period England and North America were joined, viâ Greenland and Ireland. Mr. Dawkins says that England at that time was six hundred feet above its present level. If so—and we cannot question his conclusions—the Channel was then dry.
Fig. 684.—Cervus Megaceros (Megaceros Hibernicus): Irish Elk.—Post-Pliocene.
The “Great Ice Age” then came upon the world. For the information of readers who wish to peruse the whole history of this epoch and its causes, we may add that in Professor Geikie’s most interesting work, they will find full details. We can only refer to it.
The gradual decrease of temperature upon the earth, which was the cause of the Glacial period extending over the north of Europe, has been attributed to the eccentricity of the earth’s orbit; and here astronomy steps in to our assistance. We have read in the chapters on Astronomy, how the movement of the earth, like a top near the end of its “spin,” causes the “precession of the equinoxes,” and in connection with this phenomenon the earth’s orbit becomes more and more circular at certain periods of thousands of years, and goes away from the sun. We therefore receive the light and heat at a greater angle. Consequently, less heat is received, and ice is formed, as at the North and South Poles at present.