waters across the continent. Some old maps represent the latter as rising in the same lake as the eastern Nile, whereas its main source lies, not in the centre of Africa, but at Mount Loma, on the slope of the Rokelle Mountains, in the vicinity of the west coast. A space of at least 2,700 miles thus intervenes between the farthest headstreams of both rivers, while the nearest affluents are still separated by a distance of some 720 miles. The Niger in fact belongs to a region wholly different from that of the Nile in the form and disposition of its plateaux. On the other side of the hills where it takes its rise, the Congo, Rio Grande, Gambia, and several other streams flow to independent estuaries on the west coast, while farther north the Senegal, rising on the same slope as the Niger, sweeps round the hills, forcing its way to the Atlantic through a series of rocky gorges and rapids.
North of the Senegal no large river reaches the coast, and for a space of 4,800 miles from the bar of Saint Louis to the Nile delta nothing is met except a few wadies or small streams, such as the Draa, in the south of Morocco, the Moluya, Shelif, Mejerda, flowing to the Mediterranean. The Congo alone probably discharges as much water as all the other African rivers together. Next to it rank the Niger and Zambezi, the Nile in this respect taking only the fourth place.
Of the inland basins either constantly or intermittently closed, the most important are Lakes Tsad in the north, and Makarakara-Ngami in the south, both lying at nearly equal distance from the middle Congo, and thus presenting a symmetrical disposition on either side of the equator. Tsad, much the largest of the two, is also situated in the northern or largest section of the continent, the extent of both thus corresponding with that of the surrounding regions draining to the oceans. But here all further analogy ceases, at least if it be true that Tsad has always been a closed basin; for the Ngami reservoirs certainly communicated at some former geological epoch with the Limpopo and Zambezi.
Besides these central depressions, each section of the continent has its deserts, strewn with secondary basins and oases, whose waters lose themselves in the surrounding sands. Altogether the area of inland drainage is estimated by Chavanne at nearly 3,000,000 square miles, of which 560,000, or less than a fifth, lie south of
the equator. Amongst the northern tracts without any outflow there are some depressions which at present lie below sea-level. These are probably the remains of straits and inlets formerly belonging to the Mediterranean and Red Sea. The largest are those which seem to form a continuation of the Tunisian Gulf of Cabes (Syrtis Minor), south of Algeria, which formerly received the discharge of the now dried up Igharghar, a river 780 miles long, and consequently longer than the
Closed hydrographic basins of the African continent:—
Sq. Miles. Basin of the Tsad, including Ihe Fedé 730,000 ""Igharghar 330,000 Other basins and waterless spaces 1,345,000
Basin of Lake Ngami 314,000 Other basins and waterless spaces 257,000