4oo 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 

 East 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 

 greater or less distance from its margin, and at length ap- 

 proaching 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 mountain- 

 chains trend to the west and east, leaving the valley of the 

 river considerably broader and larger. Only solitary moun- 

 tain 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 resem- 

 blance with the sandjr plateaux and steppes of the Somal country. 

 The whole Lango district, starting from the eastern frontier of 



