CHAPTER IV.
REGION OF THE UPPER NILE TRIBUTARIES.
HE section of the Nilotic basin comprised between Lake Albert and’ the Bahr-el-Ghazal confluence presents a marked contrast to the surrounding land in its abundant waters, its converging streams, extensive marshy tracts, and the general uniformity of its slope. The natural limits of this distinct geographical domain are formed by the course of the Nile and Asua on the east and south-east, and of the Bahrel-Ghazal on the north. In the historic life of the continent the inhabitants of this watery region have also played a separate part. Here lics the chief connecting route between the Nile and Congo basins. The water-parting being marked by no perceptible “divide,” no barrier is presented to the migration of peoples between the two great arteries. Thus the hydrographic parting-line forms no natural limit between ethnical groups, some of which, such as the Niam-Niam, occupy both sides of the slope, while continually encroaching northwards. Through this region of transition must pass the future continental highway from east to west between the Red Sea and the Bight of Benin. It has already been partly opened by Peney, Lejean, Petherick, Piaggia, Schweinfurth, Junker, Bohndorff, and other explorers are eagerly following in their footsteps.
Northwards this region has a natural limit; indicated, however, not by any water-parting, but by the climate, which produces a marked contrast in the aspect of the land, its vegetation, fauna and inhabitants. The latitudinal depression flooded by the waters of the Bahr-el-Arab coincides in a general way with this climatic frontier. South of it the rainfall is sufficiently copious to feed perennial streams, or at all events rivers flowing for six months in the year. But on the north side we have nothing but wadies flushed only during the heavy rains. Hence the great difference presented by the forest vegetation along the right and left banks of the Buhr-el-Arab. On one side we find the baobab, with its huge inflated trunk, on the other the lulu, or butter-tree, in some places covering hundreds of square miles. The large apes never cross the frontier into Kordofan; nor does the elephant venture north of the Bahr-el-Ghazal, where the flocks and herds are also free from the ravages of the tsetse-fly. The southern region belongs to the Negro and his horned cattle, the northern to the horse and camel-breeding Arab.
