Tst.AxDs. In connection with the regularity of the coast line, it is of interest to note the small number of islands adjacent to this conti nent, and also the small proportion of these that have any physical relations with the mainland.
Aladagasear, off the eastern coast, is the only large island near the continent: it was at a dis tant period of geological time an integral part of the mainland. hut it is now separated from it by the Mozambique Channel, which appears to be a rift valley analogous to that of the Red Sea. The Seychelles, the islands in the vicinity of Zanzibar (Mafia, Zanzibar, and Pemba), and Socotra, off the apex of the Somali Peninsula, may be considered as fragments of the conti nental mass, while many of the small islands along the east coast, including those in the Red Sea, are of volcanic and coral reef origin, and rise apparently from submerged portions of the continental plateau. On the Mediterranean coast the islands of Djerba and Kerkinah in the Gulf of Cabes were formerly united to the main land. and in past geological times even the island of Sicily was part of a chain of folded moun tains that extended from the Tunisian highlands no•theastwardly across the Mediterranean Sea.
Of the western extension, the Madeira, Canary. and Cape Verde archipelagoes are of volcanic origin, and appear to lie on the outer submerged slope of the continent. perhaps marking lines of folding and fracture that are extended under the ocean level. The Bissagos group, thirty in number, lying a short distance south of Cape Verde, are small fragments of the mainland. From the Bissagos group, the coast is free from islands as far as the head of the Bight of Biafra, where four volcanic islands. Fernando Po, Prince, St. Thomas, and Annobon, extend in a southwest ward direction from Mount Ka merun on the coast. Southward from this point the coast has but few islands, and these of small size, all the way to the Cape of Good Hope; and this same condition, in even more marked degree, is con tinued along the eastern coast for 2500 miles to the island of Mafia. The small extent of Africa's island territory is expressed by its proportion to the mainland area, which is as 1 to 4S.