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 Limpopo. Other cavities below sea-level follow in succession between the Great Syrtia and the Nile south of the plateau of Cyrenaica. At the foot of the Abysinian highlands on the Red Sea coast are also found deep troughs, the surface waters of which have sunk to a level far below that of the neighbouring inlets. In the southern section of the continent such maritime depressions do not occur.

Africa is as poorly furnished with a complement of islands aa it is with large inlets and orographic systems. In their submarine relief those in the Mediterranean belong rather to Europe than to this continent. Crete is connected with Asia Minor and with Greece; Sicily, Corsica, and Sardinia with Italy; the Balearic group by a submarine bank with the coast of Valentia; Jerba alone and a few islets in the Gulf of Cabes and along the Mauritanian shores form parts of the northern seaboard. On the Atlantic side little occurs beyond some rocks and low-lying banks, such as the Bissagos or Bishlas Archipelago, which a slight alluvial deposit or upheaval of the land would suffice to connect with the continent. The more distant groups of Madeira and Porto Santo, the Canaries and Cape Verde Islands, are of volcanic origin, and separated from the mainland by abysses over 3,000 feet in depth. Of igneous formation are also the islets in the Gulf of Guinea, Annabom, Saint Thomas, Prince, Fernando-Po, which form a chain of volcanoes all more recent than the neighbouring mainland.

The small groups in the Red Sea are mere coral reefs dominated here and there by a few volcanic peaks. Even in the Indian Ocean the only real African island is Socotra, the "spear-head" of the peninsula at present terminating at Cape Gardafui, and farther south Pemba, Zanzibar, and Mafia, disposed parallel with the coast. The Comoro Group is of volcanic origin, and Madagascar too far removed from Mozambique to be regarded as a dependency of the continent. Its nearest headland is 180 miles distant, and even this space is doubled for ordinary craft by the velocity of the intervening marine currents. Its flora and fauna also show that this great island belongs to a distinct geological domain. Geoffrey de Saint-Hilaire looked on it as a world apart, and most subsequent zoologists have regarded it as a fragment of "Lemuria," a vanished continent, which also embraced the granite groups of the Seychelles and Rodriguez as well as Ceylon and the Maldives, and may have even reached as far as Celebes in the Eastern Archipelago.

Above all the great divisions of the globe, Africa is distinguished by the general regularity of its climatic phenomena, a circumstance due to its massive form and to its equatorial position. In the region approaching nearest to the northern or southern lines of the equinoxes, rain falls throughout the year, thanks to the opposing trade winds, which by neutralising each other often preserve the stillness