154 THE DESICCATION OF AFRICA. 



rivers, the Lomami and the Lualaba, further east, have not 

 been tapped by the westwards-flowing river, but continue 

 their northward course for another three hundred miles, till 

 the Aruwimi River, flowing west, cuts them off; this is the 

 second section. The third section is the Ubangui-Welle 

 River, which flows west from the mountains about Albert 

 Nyanza, and then turns south. All the water poured forth by 

 these great rivers ponds up against the coastal rampart and 

 forms the Stanley Pool, from which it flows over a series of 

 cateracts to the sea. On the northern bank of the Ubangui 

 River rise the tributaries flowing into Lake Chad; the Gribingi 

 and Fufa Rivers actually rise some seventy miles north of 

 the Ubangui. The watershed between the Gribingi and the 

 Ubangui is about 400 feet high above the Ubangui stream- 

 level. Just at the bend of the Ubangui the Tomi River has 

 a course similar to that of the Black Volta; it rises in the 

 hills, about fifty miles north of the Ubangui, flows north 

 towards Lake Chad, and then makes a complete semicircle 

 and flows south into the Ubangui. This shows that the 

 rivers are more vigorous on the south of the divide than on 

 the north. The opening of the poort through the coastal 

 rampart, to let through the waters of the Congo, is fairly 

 recent, but it has allowed the rivers to scour their valleys 

 very considerably, and a scour of 400 feet is not a very 

 large one to assume. In Cape Colon}', in the Eastern 

 Province and the Transkei we see valleys which have cut deep, 

 narrow canyons four times as deep. Raise the level of the 

 rock barrier at Stanley Pool and the whole water-system behind 

 will be checked ; if the elevation be sufficient the whole drainage 

 of the Congo would pour into Lake Chad- The following are 

 the heights above sea-level: — 



In the bend of the Ubangui, Zongo 

 In the bend of the Ubangui, Banzyville... 

 Mean-mouth of Tomi River (about) 

 Highest point in the Ubangui-Gribingi 



divide 

 Stanley Pool 



In other words, it requires an elevation of 485 feet at the 

 mouth of the Tomi River to empty the Ubangui River into 

 Lake Chad, and an elevation of 897 feet at Stanley Pool to 

 empty the whole of the Congo waters into Lake Chad. There 

 is a poort in the Zwartberg Mountains, in Cape Colony, 

 called Meiring's Poort, in which the mountains rise to 7,000 

 feet above sea-level, while the level of the river is 1,000-1,200 

 feet, giving a depth of a river-cut gorge of 5,800-6,000 feet. 

 Throughout the coastal mountains of Cape Colony there are 

 similar poorts cut by the rivers since the Cretaceous period, 



