all interior water into the Congo. To the north of the Great Basin stretches the high lands of the unknown countries which form also the watershed of the Shari and the Nile. Eastward stretches the hill country on the west of the Victoria and Albert Nyanza, and on the east of Tanganika, while to the south is the watershed of the Zambesi.
This great circle of hills probably enclosed at one time an immense fresh-water lake, of an area of a million and a half square miles, which at length, overflowing at its weakest point, formed the outlet which we to-day call the Congo River. The immense flood thus released tore out the deep gorge, which is now 1,000 and 1,500 feet below the main level. There are signs in some parts of changes in its course, one notably in the Bundi valley, thirty-five miles from Vivi, which was at one time undoubtedly a channel of the Congo; there are other valleys also presenting that appearance, the levels, entrances, and exits of which would lead one to conclude that such had been the case.
If a transverse section were taken about the middle of the cataract region, there would be first an ascent from the river, almost perpendicular, of from 300 to 500 feet in about one-third of a mile, then a much steadier rise of some 500 to 700 feet in two miles, and then a rise of another 500 to 700 feet in eight miles, with a further steady rise for five miles, so that the actual valley in the cataract region might be estimated roughly at from twenty to thirty miles in breadth. The river itself varies from 300 yards to one-and-a-half or two miles wide at mid-flood; while the difference between the highest water of the rainy season and the lowest in the dry season, varies from forty feet in the worst parts to about three feet on the lower river.
To the geologist the country between the coast and Stanley Pool is best studied along the river. The first low hills approach near to the mouth of the river, which is about seven miles wide, and devoid of a delta; the next step in the plateau occurs at five miles west of Mboma, fifty miles from