westerly course for 240 miles, during which it is joined by its largest affluents. From the east come the deep Lu-Longo with its Ba-Ringa (Lopori) tributary, the Ikalemba, and the Ruki (Bo-Ruki or "Black River"), all ascended by Grenfell to the head of their navigation. But however copious these affluents, they are all exceeded by the mighty U-Banghi, which comes from the north, probably collecting all the waters of the vast semicircle of plateaux, highlands, and water-partings stretching from the sources of the Shari to those of the White Nile in the Niam-Niam territory. Here it is also perhaps joined by the Nana, rising on
the same uplands as the Benue, and by the outflow from the liva, or "lake" in a pre-eminent sense, which has been heard of by so many explorers, but has never yet been visited. According to Von Francois, the mean discharge of the U-Banghi is 260,000 cubic feet per second, which however seems an exaggerated estimate to M. Ponel, who resided eleven months at Nkunjia, on its lower course. The navigation is first interrupted over 800 miles from its mouth by the Zongo Falls, which even at high water arrested van Gelé's expedition in 1886, although surmounted two years previously by Grenfell.
