The Old World Eocene has a very different development from that of North America, the eastern continents not assuming their present outlines till much later. At the close of the Cretaceous period extensive geographical changes had taken place in Europe, consisting chiefly in the retreat of the sea from wide areas which it had occupied in the Cretaceous. This was especially the case in Russia, northern Germany, and France, and southern England, and in place of the great gulf which had occupied these regions (see p. 712) were found only scattered bodies of fresh and brackish water in which the Paleocene deposits were laid down. At a later time the sea again advanced over part of these areas, which explains the general unconformity between the Cretaceous and Tertiary strata. In southern Europe the Mediterranean regained the great expansion which it had partly lost in the latter part of the Cretaceous, extending far over northern Africa, where nearly the whole continent north of the equator was submerged in the early Eocene sea, and transgressing over southern Europe. A long, narrow arm of this sea extended from southern France, past the north side of the future Alps and Carpathians, into western Asia. Another narrow sea, or strait, extended down the east side of the Ural Mountains, from the Arctic Ocean to the expanded Mediterranean, completely cutting off Europe from Asia. This complete severance of Europe from Asia necessitates an independent land connection of the former with North America to explain the community of terrestrial animals and plants between these continents.

From Asia Minor the Mediterranean extended across Persia and Turkistan, northern India, Borneo, and Java, to the Pacific, separating the southern peninsulas from the Asiatic mainland. There was thus a continuous sea around the earth, everywhere separating the southern continents from the northern, though transient connections between them may have been es-tablished.

In the Alpine and north African regions were accumulated thick masses of limestone, largely composed of the gigantic foraminiferal shells called Nummulites, a hard massive limestone which reaches a thickness of several thousands of feet. Closely associated with the Nummulitic facies of the Eocene is the Flysch, an extremely thick mass of sandstones and shales, which occurs in the Alps and Apennines, the Carpathians and Balkan Peninsula, the Caucasus, Asia Minor, and southern Asia generally. In the Alpine region the Flysch contains enormous erratic blocks of granite, gneiss, etc., which appear to have come from southern Bohemia, and which have been interpreted as due to transportation by glaciers. This interpretation has not, however, been established. In northern Europe no such widely spread formations occur. After the Eocene had continued for some time, a marine basin, the Anglo-Gallic, was formed over southern England, northern France, and Belgium, which contains a succession of alternating marine, brackish, and fresh-water strata.

This basin is classic ground, for in it were made the studies of Cuvier and Brongniart, which led to the recognition of the Tertiary as a distinct system and founded the science of Palaeontology.

On the west coast of Africa the sea encroached in a' narrow belt. The correlations of the early Tertiary rocks of Australia and New Zealand are still the subject of debate, but there seems to be little doubt that the Eocene is present. In South America the Eocene of Patagonia consists of a series of continental deposits containing a highly interesting succession of mammals. These grow more and more divergent from the mammals of the northern continents.

The Eocene thus had broad seas where now is land, and continents now connected were then separated by straits and sounds. On the other hand, there were then land bridges joining land areas which are now far apart. Some of these land bridges may be reconstructed with much confidence, while others are more or less probable. America was connected with Asia across what is now Bering's Sea, and also with Europe, probably by an extension of Greenland and Iceland. The Antarctic continent apparently had a much greater extension than it has now, and seems to have been joined with both Australia and South America. It is quite possible that Africa was more or less directly connected with the same land mass. If this be true, then in Eocene times the northern continents, Europe and Asia, were joined in the Arctic latitudes by way of North America, while South America, Africa, and Australia radiated in three great lines from the South Pole. Between the two series of continents, northern and southern, swept the transverse seas, of which the Mediterranean and Caribbean are remnants.

Climate

The Eocene climate, especially as inferred from the plants, was warmer than that of the Paleocene. In England, for example, the temperate flora of the latter epoch was followed by one of subtropical character, and in North America the subtropical zone extended much farther north than in recent times.