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 90 miles broad, to the Asiatic mainland. Even this isthmus itself is an old marine and fluvial basin—Mediterranean alluvium in the north, a deposit of the Red Sea in the south; between these two marine zones an ancient Nilotic delta, which, to judge from the allied faunas, probably at one time communicated with the Jordan. But although the Isthmus of Suez had no existence in Tertiary times, there were other stretches of land connecting Egypt with Cyprus and Syria; for nowhere else in the periphery of the globe are there found contiguous marine inlets presenting such differences in their fauna as do those of Suez and Gaza.

But if the waters of the Indian Ocean have remained completely distinct from those of the Mediterranean since the Eocene epoch, with the exception perhaps of a shallow channel flooded in Quaternary times, the intervening barrier has at last been removed by the hand of man. Thanks to his industry, the two seas henceforth mingle their waters in the inland basin of Lake Timsah, and the circumnavigation of Africa is open to the largest vessels afloat. Compared with this southern continent, whose contour is so clearly defined, the two other divisions of the Old World seem to merge in one continental mass. Certainly the depression skirting the Ural range from the Gulf of Ob to the Caspian, and the Manich isthmus between the Caspian and Euxine, cannot be regarded as such sharp geographical parting lines as the marine channel now flowing between Suez and Port Said.

But however clearly severed at present from the rest of the Eastern hemisphere, Africa is not so entirely distinct from Europe and Asia as might at first sight be supposed. Parts of its seaboard were even formerly connected directly with the regions beyond the Mediterranean, and there was a time when the Atlas Mountains effected a junction across the present Strait of Gibraltar with the parallel Sierra Nevada range. Even down to the close of the Pliocene epoch, Tunisia was still united with Sicily and Italy through a broad zone, of which the only surviving fragments are the little Maltese group of islets. Greece also merged southwards in boundless plains watered by streams whose banks were frequented by the elephant and hippopotamus.

Although now detached from Spain and Italy, North-west Africa is still in its geology, natural history, and climate essentially a Mediterranean land, forming with the opposite European seaboard a distinct physical region. Along both coasts the same fossils occur on the old rocks, while similar floras and faunas are now in possession of the soil. The Mauritanian coastlands differ far more from Nigretia, from which they are separated by the Sahara, than they do from Provence, and as already remarked by Sallust, North Africa is physically a part of Europe. Eastwards also the Ethiopian shore of the Red Sea belongs to the same formations as the opposite coast of Arabia, and a general resemblance characterises the climate, natural productions, and inhabitants on either side of Bab-el-Mandeb.

In its massive outlines Africa presents the same monotonous appearance as the two other southern divisions of the globe—South America and Australia. It is even less indented than the corresponding section of the New World; nor is it supplemented, like Australia, by a vast region of archipelagoes and islands, scattered over