400 ZOO-GEOGRAPHICAL NOTES.

therefore, be considered neutral ground, as it were, on which representatives of different zoological regions meet: if we go westwards, the West African type of fauna and flora becomes continually more prominent; if we go eastwards, we meet the well-defined forms of the southern Somal district, and more isolated instances of the forms of the southern half of tropical Kast Africa. It is not necessary for me to point out how exceptionally profitable a thorough exploration of this region would be.

Let us now follow the Bahr-el-Jebel in its farther northern reaches. It flows out of the Albert Lake as a majestic stream, accompanied on either side by mountain ranges running at a ereater or less distance from its margin, and at length approaching close to it in the Madi district, where they confine its bed and give rise to a series of falls and rapids between 3. 40’ and 4° 40’ N. Farther to the north, these mountainchains trend to the west and east, leaving the valley of the river considerably broader and larger. Only solitary mountain groups rise here and there almost abruptly from the level country, until at last, still farther northwards, the endless swamps commence, in which the river, now without banks, is involved up to its confluence with the Bahr-el-Ghazal. In accordance with the character of the mountains, the detritus of which constitutes for the most part the plains beside the river, the soil of the valley is not rich. Sand, often mixed with loam, and red clay impregnated with iron, which covers more elevated parts, are not adapted to develop a particularly luxuriant vegetation. Hence it will be seen that the whole river-valley of the Bahr-el-Jebel, up to the Albert Lake, must be included in the domain of the steppes,—not the sandy steppes of southern Kordofan, nor the extensive savannahs of the eastern Sudan, but wooded steppes, where beautiful forms, such as Tamarindus, Khaya, Odina, Anogeissus, Bassia, and Stereospermum attain to full perfection, and Acacia, Zizyphus, Balanites, Sarcocephalus, Gardenia, &c., are most prominent. The farther we go from the river westwards, the more perceptible does the transformation become, the more striking the resemblance with the sandy plateaux and steppes of the Somal country.

‘The whole Lango district, starting from the eastern frontier of