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 cellules, acquires a marshy taste and becomes unwholesome. But all this refuse is swept away or destroyed by the first floods from the Abyssinian rivers, which thus restore to the Nile water its excellent properties.

The "Gazelle," which joins the main stream in the No basin, is a "bahr," that is, a considerable river, flowing from the west, and during the floods bringing sufficient water to sweep away the temporary obstructions. In its channel are collected a hundred other rivers, whose numbers and copiousness form a striking contrast to the poverty or total absence of running waters characteristic of the Nile basin farther north. Altogether the affluents of the great river are distributed

Fig. 13.—

very irregularly, thus illustrating, as it were, the discrepancies of the climate. In the region of the plateaux the Victoria Nyanza and Somerset Nile receive feeders both from east and west, for the rainfall is here sufficiently heavy to cause watercourses to converge from all directions in the great lacustrine reservoir. But north of the Albert Nyanza the affluents occur alternately now on one now on the other bank of the Nile. In the section of its course terminating in the No lagoons it receives contributions only from the west, and farther, north only from the Abyssinian highlands lying to the east. Then for a distance of 1,500 miles no more permanent tributaries reach its banks either from the right or the left. Even during the rainy season the gorges opening on its valley send