The discoveries of Livingstone, Burton, Speke, Grant, and Baker, seem to confirm the theory put forward by Sir Roderick Murchison, that the central portion of South Africa is a large and elevated basin, abounding in immense plains, in fertile lands, besprinkled with numerous lakes fed by a thousand currents descending from the lofty mountains that surrounded it. The rains, says Morin, cause these lakes to overflow, and their waters, prevailing over every obstacle, break through the barrier of the high lands, and descend into the lower levels in a series of cataracts, to make their way eventually towards the ocean. Livingstone has proved the truth of this felicitous induction as far as the Zambesi is concerned. The Nile also issues from the lofty table-lands through deep and rocky ravines. The great reservoir of the mysterious Egyptian river, the _N'yanza Spekii_, may be accepted as the final confirmation of Sir Roderick's theory, and the conspicuous feature of the African people. The southern extremity of this lake stretches as far as the watershed between North and South Africa. Starting from the same viewpoint, Speke concludes that another great lake will be found under the Equator, to the west of the Tanganyika and the N'yanza Victoria. This will be the reservoir of the Congo. To establish this fact will be to solve the last problem of the hydrographic system of Africa.[86] The western region of the African equatorial zone has been but superficially explored, and in this direction numerous hypotheses remain to be verified. Lake Tchad, situated in Central Nigritia, between Bornou on the west and the south-west, and the Kanem to the north and east, was discovered in 1823 by Major Denham, and explored by Dr. Barth in 1852. The latter traveller grows eloquent in his description of the delicious perspective which he had supposed it would offer to the gaze. He met with numerous slaves on their way to cut grass for the horses. But instead of a lake, an immense treeless plain stretched as far as the eye could reach. The herbage became fresher and greener, thicker and taller; a marshy bottom, describing a curve which projected here and receded there, embarrassed his progress more and more; and after a useless and prolonged struggle to escape from the quagmire, seeking in vain on the horizon some mirror-like surface, he retraced his steps, dabbling in the slimy water, and consoling himself with the reflection that at least he had seen some traces of the "liquid element." But the scene was strangely different when, in the winter of 1854-55, more than one-half of the Ngornou was destroyed by the inundation; and to the south of that town lay a deep sea, swallowing up the whole plain even to the village of Koukiya! The lower stratum of the soil, composed of limestone, appeared to have given way in the preceding year, and had lowered the shore of the lake several yards; hence the inundation. But apart from