Page:Africa by Élisée Reclus, Volume 3.djvu/231

which are flooded or decomposed into secondary islets by the tides, which here rise 13 or 14 feet. Thus at low water Cagnabac forms continuous land with Porcosand Gumbana, while Gallinhas, Formosa, Ponta, Corbelha become attached to the neighbouring lands. The archipelago, the navigation of which is rendered extremely dangerous by the strong currents and shifting character of the channels, terminates southward in the isolated Alcatraz, or "Pelican" rock, round which hover dense clouds of aquatic birds. Fig. 77. — Bissagos Archipelago Orango, or Harang, largest member of the group, is mostly sandy, with a scant vegetation, whereas the others are generally covered with tall palms and gigantic baobabs, which from a distance seem to grow right out of the water. All the islands are low, and disposed in the direction from north-west to south-east parallel with the mainland. Belcher and the other early explorers described the group as volcanic, but the rocks supposed by them to be eruptive were probably ferruginous clays, analogous to those on the West African seaboard. The islands, mere fragments of the old coast, consist of the same formations and present identical features. Whether through erosion or slow subsidence, the sea has encroached on the land, converting peninsulas into islands, islands into reefs and banks, the lower reaches of the rivers into estuaries, and these into marine inlets. During these secular transformations numerous animal and vegetable species have had to adapt themselves to the slowly changing environment. Such is the hippopotamus, elsewhere rarely seen far from freshwater streams, but which Belcher met on the south-west coast of Cagnabac (Kanabak), over 30 miles from the coast rivers.