Of these the Lomami is navigable for nearly 650 miles. Rising in the Usamba Plateau, 600 miles east of Lake Moero, it runs almost parallel to the Congo till it joins that stream 150 miles west of Stanley Falls. The Lomami varies in breadth from 60 to 400 yards. In places it has a depth of twenty feet, and it is destined to play an important part in the development of this part of the continent. It was on the Lomami that one of those entrenched camps was established which proved so effective in the expulsion of the Arabs and suppression of the slave trade. The many tributaries of the Lomami, some of which are navigable, make that river the natural base also of commercial operations. The next southern affluent of the Congo is the Lulongo. Rising not far from the valley of the Lomami it flows for several hundred miles in a south-westerly direction and empties into the Congo at Uranga. A northern tributary of the Lulongo is the Lopori. Both of these streams are rendered more important by the fact that, being free from obstruction, they are navigable. They water a beautiful and exceedingly fertile country, some of which is yet unexplored. South of the Lulongo and almost parallel to it is the Ruki. It has two upper courses and rises near the great valley of the Lomami. The Ruki is a wide, open river, nearly six hundred miles in length. It empties into the Congo at Equateurville, and because of its several tributaries it renders a large territory easily accessible. [Illustration: Departure of ss. “Goodwill” from Upoto.] But the largest of all the southern affluents is the Kassai, which ranks in importance next to the Congo itself. The exact course of the Kassai was until recently a matter of considerable speculation. This has now been definitely determined, and the Sankuru, formerly thought by some geographers to be the main course of that river, is now known to be its largest affluent. The Kassai rises nearly one thousand miles south of where it joins the Congo, near the Portuguese possessions in the south-western corner of the Congo State. Its course is north, north-east, and north-west. Navigable from Wissmann Falls, which is situated about midway its length, it forms its junction with the Congo not far above Stanley Pool. Joining the Kassai, near Bokala, is the river Kwango, which, rising in the Portuguese possessions, flows directly northward for several hundred miles. The Sankuru, like so many other of the Congo rivers, rises in the Sambas Plateau. Its course is first due north, then west, and, at its junction with the Kassai, is an imposing stream, almost as deep and broad as the Kassai itself. The Lubefu, a northern tributary of the Sankuru, reaches almost to the valley of the Lomami.