CONGO rising on the southern limits of the Congo basin, between 11° and 12° S.—combine to form the Kamolondo, the valley of which contains many small lakes and backwaters. The Nzilo and Lufira pass through the Mitumba Mountains in deep gorges, their courses being broken by rapids for distances of 40 to 50 miles. The Upper Congo or Lualaba.—During its northerly course to the Equator, the united stream of the Congo— after breaking through the ridge of the Bambara Hills in another series of rapids in 4-|°—3-^° S.—becomes a majestic river, often over a mile wide, with fiat wooded banks, the only real impediment to navigation between 4^° and the Stanley Falls being the rapids near Nyangwe in 3° 55', and at Ukassa in 3° 15'. Between the junction of the two main upper branches (about 1700 feet above the sea) and the first of the Stanley Falls (1520 feet) the fall of the river is less than 200 feet, in a distance of 500 miles. During the whole of this section the Lualaba receives most of its tributaries from the east. Of these, the Lukuga, the outflow from Lake Tanganyika, has been followed throughout its whole length, and has been found to be broken by rapids, falling 1000 feet during its course of some 300 miles. Farther north the streams which drain the forest region between 4° S. and the Equator have been only partially explored, the Elila or Lira, the Urindi, and the Lowa being the most important. Their sources lie on an upland region west of the Central African rift valley. The Urindi in its middle course has a general width of 60 to 100 yards, but the Lowa is larger, receiving two important affluents, the Ozo and Luvuto, both from the north. Its lower course is very tortuous. The Middle Congo.—After passing the Stanley Falls,— 7 in number besides minor rapids, with a total fall of some 200 feet,—the Congo enters, at an altitude of some 1320 feet, the great alluvial plain of West Equatorial Africa, assuming a westerly direction, and also changing its character. This section of the river, navigable for a distance of at least 1000 miles, may be designated the Middle Congo. Gradually widening out and becoming strewn with low alluvial islands, it forms great lacustrine expansions, sometimes (as, e.g., in 21° and 22° 30' E.) 16-20 miles wide, but is from time to time contracted by the approach of high ground on either side. The islands, like the banks, which appear to be often raised above the level of the surrounding country, are forest-clad, but are inundated at high water. In 22^° E. the river reaches its most northern point (about 2° 12' 1ST. on the north bank), beyond which its course gradually bends south, and in 2° 45' S., on approaching the western continental highlands, it again contracts to a width of a mile and under, remaining, however, unbroken by rapids until after passing the lakelike expansion of Stanley Pool. Here its elevation above the sea is just over 1000 feet. Northern Tributaries.—Of the right bank tributaries of the Middle Congo, the Chopo and Lindi, which enter by one mouth in about 25° 4' E., are little known. Their basins do not extend to the Outer Congo watershed, but the next feeder, the great Aruwimi, was found by Stanley to rise, as the Ituri, in close proximity to Albert Nyanza, flowing generally from east to west. It is formed of many branches, including the Nepoko from the north, and its upper basin extends over 2^° of latitude. The upper river, to about 27° E., is much broken by rapids, but apart from those of Yambuya in 25°, which form the limit of navigation from the mouth, the lower section is generally navigable. The Aruwimi flows almost entirely through the great equatorial forest, which here seems to reach its maximum density. The next tributary, the Rubi, rises in about 26° E., and flowing generally west, joins the Congo by two mouths, 22° 40'-50'. Within the bend of the
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Ubangi, the greatest northern tributary, the Mongalla or Dua flows in a somewhat similar curve (on a smaller scale) from beyond 23° E. The identity of the Ubangi with the Welle of Schweinfurth was finally proved by Yangele in 1888, and its upper basin has since been explored by French and Belgian officers. Next to the Welle (principal tributary Bomokandi, from the south), its largest upper branch is the Mbomu, which, rising in 27° 12' E., 4° 50' S., on the confines of the Bahr-el-Ghazal region, itself receives two large streams, the Shinko and Bali, from the north. The junction of the Welle and Mbomu is in 22° 37' E., and a short distance farther west the Kotto, coming from beyond 8° N., on the borders of Darfur, and forming the most northerly extension of the Congo basin, enters the united stream on the right bank. The remaining tributaries (still mostly coming in on the right bank) are smaller, but the Kemo, which joins the Ubangi near its most northern point (5° 8' N.), is of some importance as offering water-communication within a short distance of the Shari basin. The Upper Ubangi is broken in many places by rapids, between which are navigable stretches in which the river is often (especially west of 25°) wide and strewn with islands. The Zongo series of rapids near the great bend of the Ubangi, do not form an insuperable obstruction at all states of the river, but navigation is quite blocked by the Mokwangu Falls in 23° 5' E. (10 feet), by the rapids of Goie (the worst on the upper river) in 25°, and by those of Panga in 26° 40'. A little below the mouth of the Ubangi, the Sanga, a large stream flowing from north to south, enters the Congo. Its lower course is tortuous, as it flows across level, often swampy, plains; but though comparatively narrow, it is navigable for a long distance. The main northern branch rises in southern Adamawa in about 7° N., while an almost equally large western branch, the Ngoko, rises in the German territory of Cameroon (probably in about 12° 10' E.), traversing a vast tract of uninhabited forest. It is navigable to about 13° 40' E. The Likuala, Licona, and Alima, which all join the Congo within 30 miles of the mouth of the Sanga, are much smaller streams. The Licona is still almost unexplored. Southern Tributaries.—The first of the southern tributaries of the Middle Congo, the Boloko or Lubilash of Grenfell, which enters in 24° 17' E., has been proved to be identical with the Lomami of Cameron, rising in nearly 9° S., and thus flowing through more than nine degrees of latitude. Its course is generally parallel to the Upper Congo, which it approaches within 40 miles between 2° and 3* S. It is comparatively narrow and tortuous, but deep, with a strong current, and is hardly broken by rapids north of 4-|° S. About 3° S. it traverses a region of swamps, which may have given rise to reports of a great lake in this locality. Below the mouth of the Lomami there is a long stretch with no southern tributary, as the great plain within the Congo bend is drained by streams flowing from east to west parallel to the main river. The northern branch of the Lulonga, which enters in 0° 40' N., approaches the latter within 20 miles in its upper course. The main branch of the Ruki, which enters just north of the Equator, and the Lukenye or Lukeni, the northern unit of the great Kasai system, have their sources between 24 and 25° E. in the vicinity of the Lomami swamp above alluded to. These streams have tortuous courses, for the most part not broken by rapids, flowing across a level country once occupied by a lake, of which the present Lake Leopold II., connected with the lower course of the Lukenye, is the scanty remnant. Its shores are low and inundated in the rains, so that its outline is very ill-defined. Besides the Lukenye, the chief units of the Kasai system all flow north in parallel courses before acquiring the east to west
