Page:Africa by Élisée Reclus, Volume 3.djvu/412

 844 WEST AFRICA. south the twin-crested Mendif, which at a distance seem white, but which are said to be really blackish, probably basaltic, the white appearance being due to a deposit of guano from the myriads of birds whirling round these heights. Towards the west the incline is very slight from the plains of Bornu to the divide separating them from the oceanic basin. The absolute height of the hills does not exceed 2,000 feet, except in the isolated Mount Fika, visible in all direc- tions for several days' march. In the extreme north the limits of the Tsad basin are indicated less by the relief than by the climate, although some chains of sand- hills, escarpments of the plateau, and a few rocky eminences vary the monotony of the steppe zone intermediate between the forest regions and the Saharian wastes. Lake Tsad. Although the streams flowing westwards from the Marrah range belong to the Tsad system, it seems probable that none of them, except on rare occasions, actually reach the lake or its great tributary, the Sbari. The Wady Azum and its various affluents form a permanent watercourse only during the kharif, or rainy season, and even then the slight general incline and the intervening eminences cause the sluggish current to expand in shallow meres, soon carried off by evaporation. The Batha, which rises in the Tirdze hills, flows south-west and west to the Fitri depression, alternately a morass and a lake, according to the abundance of the rainfall. In the language of the riverain populations who preceded the present Kanuri masters of the land, Tsad (Tsade, Chad, Chade), had the sense of " great body of water," and the term Kolo (Kula), applied to this vast flooded depression by the Yedina islanders, appears to have the same meaning. Burckhardt was the first to describe it with some approach to accuracy. All Arab traders, accepting the assumed identity of the Timbuktu, Bornu, and Egyptian waters, regarded Lake Tsad either as a common reservoir of all the African " Niles," or the inland sea of a great central plateau, whence the rivers escaped in all directions to the periphery of the continent. Since Denham, the 'first European who reached the lake, which he named "Waterloo," accurate surveys have shown that, on the contrary, it occupies one of the lowest regions in Africa, standing, according to Vogel and Nachtigal, not more than 850 or 900 feet above sea-leVel, while its hydrographic function is limited to collecting the surrounding waters in a completely landlocked basin. Its actual extent cannot yet be even approxim'ately estimated, the sources and headwaters of its chief affluent, the Shari, being still unknown. Nachtigal's tentative calculation of 11,000 square miles for the lake alone is reduced by Rohlfs to 4,500 for the dry, and raised to 22,000 for the wet season. But although thus rivalling in extent some of the other great lakes of the Old and New Worlds, Tsad cannot compare with them in the depth or volume of its waters. According to the natives the greatest depth -between the shore near Kuka and the Shari mouth, is only " the height of two men," and the island of Seyorum, 12 miles off the coast, may be reached on horseback. In the deepest parts sur-