CONGO, formerly known as Zaire, the largest of the rivers of Africa and exceeded in size among the rivers in the world by the Amazon only. The Congo has a length of fully 3,00o m. and a drainage area estimated at I,425,00o sq.m., with a diameter of some 1,40o m. either way. This vast area includes the equatorial basin of Central Africa and much of the surrounding plateaus. West and north the Congo basin is bounded by comparatively narrow bands of higher ground, while east and south the drainage area of the river includes considerable portions of the high plateau of east and south Central Africa. The main drainage of the Congo system is thus north and west, and these two directions dominate the great bow-like sweep of the main stream before it is deflected south on approaching the western highlands, through which it finally forces a way to the Atlantic Ocean. From the high lands of the south and east in which the head streams of the Congo have their origin, the land falls in a succes sion of steps, generally marked by gorges or rapids in the upper courses of the streams. Besides the main stream most of the affluents are navigable for considerable distances ; in all there are over 6,000 m. of navigable water in the Congo basin and 20,000 m. of overhanging wooded banks. On the Congo alone are over 4,000 islands, many of considerable length—some fifty of them are over ten miles long. The volume of water poured into the Atlantic is calculated at I,2oo,o0o cubic ft. or more per second.
The easterly head-streams are regarded gen erally as marking the true course of the parent river. The most remote of these rivers is the Chambezi, which rises (in British territory) on the southern slope of the plateau between lakes Nyasa and Tanganyika at an elevation of about 6,000 feet. The watershed is formed by the crest of the plateau, and is perfectly distinguishable, save at a spot called Ikomba, about half-way between the lakes, where is a swamp which drains to both the Atlantic and the Indian oceans. The Chambezi source is in 9° 6' S., 31 ° 20' E. Its chief tributary, the Karungu, rises in 9° 5o' S., 33 ° 2' E. After the junction of the Karungu and Chambezi the river flows in a south-westerly direction through a fairly fertile country. In its lower course it passes through papyrus marshes, and dividing into several channels, enters the vast swamp which adjoins the southern part of Lake Bangweulu (q.v.). The river, known as the Luapula (Great River), which issues from this swamp is a continuation of the Chambezi. The Luapula on leaving the swamp bends west and then south and approaches the watershed of the Zambezi. The source of its most southern affluent, and therefore the most southern point in the Congo basin, is approximately in 13° 3o' S. Turning north the Luapula precipitates itself down the Mumbatuta (or Mambirima) falls (12° 17' S., 29° 15' E.), the thunder of which can be heard on a still night for 8 or 9 miles. The river, the width of which varies from 25o to 1,200 yd., is almost unnavigable until below the Johnston falls, a series of rapids extending from I I ° Io' to Io" 3o' S. Below the falls the river is navigable by steamer all the way to Lake Mweru—a distance of Ioo miles. Before entering Lake Mweru (q.v.), Ioo m. below the Johnston falls, the Luapula again passes through a swampy region of deltaic character. The river (known now as the Luvua) makes its exit at the north-west corner of the lake, and bending westwards, passes across the zone of the Kebara and Mugila mountains, falling during this interval nearly i,000 feet. In about 6° 45' S., 26° 50' E. it joins the Kamolondo (otherwise Lualaba), the main western branch of the Congo, which, as it flows in a broad level valley at a lower level than the eastern branch, is held by some to be the true head-stream.
The Kamolondo is formed by the junction of several streams having their source on the northern slope of the south-central plateau as it dips towards the equatorial basin. The streams flowing south from it belong to the Zambezi basin, but the water shed is not everywhere clearly defined. There is, however, no connection between the Zambezi and Congo systems. The Lualaba, also known as Nzilo, which is the main stream of the Kamolondo, rises at an altitude of 4,70o ft., in 26° 40' E., just north of 12° S. East of the Lualaba—between it and the Luapula—rises the river Lufira. With many windings the Lualaba and Lufira pursue a generally northerly direction, passing through the Mitumba range in deep gorges, their course being broken by rapids for 40 or 50 miles. Below Konde rapids in 9° 20' S. the Lualaba is, how ever, free from obstructions. (Just above the last of the series of rapids it is joined by the Lubudi, a considerable river and the westernmost of the Kamolondo affluents.) Between the rapids named and
40' S. its valley is studded with a chain of small lakes and backwaters. In the rainy season the whole region be comes a marsh; various grasses, especially papyrus, form floating islands, and the conditions generally recall the sudd region of the Nile. In about 8° 20' S. the Lualaba and Lufira unite in one of these marshy lakes—Kisale—through which there is a navi gable channel. The region watered by these western head-streams of the Congo includes Katanga and other districts, which are among the most valuable parts of the Belgian Congo. For prac tical purposes navigation down stream begins at Bukama, in about 9° 50' N., the Lualaba there being some 30o yd. wide and
ft. deep. Bukama is in railway connection with Cape Town and with the lower Kasai.
After the junction of the Luapula (Luvua) and the Lualaba (Kamolondo) the united stream, known as the Lualaba or Lualaba-Congo, and here over half a mile wide, pursues a north-north-west course towards the equator. The Dia rapids, some 30o m. below the Konde rapids, are the first obstruction to navigation encountered. A mile or two lower down the Lualaba passes through a narrow gorge called the Porte d'En f er. From this point to as far north as 3 ° 10' S. the course of the river is interrupted by falls and rapids. In this part of its course the Congo becomes a majestic river, often over a mile wide, with flat wooded banks. Between the junction of the two main upper branches, about 1,70o ft. above the sea, and the first of the Stanley falls (1,52o ft.), the fall of the river is less than 200 ft., in a distance of Soo m. Of the tributaries it receives in this section the Lukuga connects Lake Tanganyika with the Congo system (see TANGANYIKA).
Stanley falls, which mark the termination of the upper Congo, begin a few miles south of the equator. At this point the river forsakes the northerly course it has been pursuing and sweeps westward through the great equatorial basin. The falls consist of seven cataracts extending along a curve of the river for nearly 6o miles. They are not of great height— the total fall is about 200 ft.—but they effectually prevent navi gation between the waters above and those below except by canoes. The first five cataracts are near together; only 9 m. separate the first from the fifth. The sixth cataract is 22 m. lower down, and the seventh, the most formidable of all, is 26 m. below the sixth. The fall, divided into two portions by an islet, is 800 yd. wide. The channel is narrowed at the foot of the fall to some 45o yd. by an island close to the left bank; on the right bank is the island of Wane Rusari (2 m. long by a m. broad), separated from the mainland by a channel 3o yd. wide. The fall is only about 1 o ft.; but the enormous mass of water, and the narrow limits to which it is suddenly contracted, make it much more imposing than many a far loftier cataract.
Below Stanley falls the Congo is un broken by rapids for g8o m., and is navigable throughout this distance all the year round. The river here makes a bold north westerly curve, attaining its most northerly point (2° 13' 5o" N.) at 2 2 ° 13' E., and reaches the equator again after a course of 63o m. from the falls—the distance in a direct line being 472 miles. For another 25o m. the river flows south-westerly, until at Stanley pool the limit of inland navigation is reached. For the greater part of this section the Congo presents a lacustrine char acter. Immediately below the falls the river, from i to 1 m. broad, flows between low hills, which on the south give place to a swampy region, the river-bank marked by a ridge of clay and gravel. After receiving the waters of the Aruwimi-13o m. below the falls—the Congo broadens out to 4 or 5 m. ; its banks, densely wooded, are uniformly low, and the surface of the water is studded with alluvial islands and innumerable sandbanks. The velocity of the current decreases as the waters spread out, though there is always a channel from 41 to 5 ft. deep. About ioo m. below the Aruwimi confluence the Loika or Itimbiri joins the main stream from the north, the Congo narrowing considerably here, owing, it is supposed, to the matter deposited by the Loika. At two or three other places lower down, the river is contracted to 21 or 2 m.. as a result of a slight elevation in the ground, but for a distance of 50o m. no real hill is met with.
On the southern curve of the horseshoe bend are found the largest islands of the Congo—Esumba, 3o m. long, and Nsumba, 5o m. long, and over 5 m. across at its broadest part. At this point the river from bank to bank is 9 m. wide. Opposite Nsumba, the Mongala, a northern affluent, enters the main stream, whilst lower down (just north of the equator) the Lulanga, Ikelemba and Ruki rivers, southern tributaries, mingle their black waters with the dark current of the Congo. Thirty miles south of the equator the river is joined by the Ubangi (q.v.), its greatest northern affluent. Here the Congo is fully 8 m. wide. Opposite the Ubangi confluence is the mouth of a narrow channel, some Io m. long, which connects the Congo with Lake Ntomba, a sheet of water about 23 m. long by 8 to 12 broad. In flood time the water flows from the Congo into the lake. Immediately below ferruginous conglomerate hills of slight eminence reduce the river to a width of less than 2 m., and in comparatively close succession are two or three other narrows. With these exceptions the Congo continues at a width of 5 to 6 m. until at 2° 36' S. it abruptly contracts, being confined between steep faced hills.
This stretch of the river, known as the "Chenal," is 125 m. long and is free from islands, though long reefs jut into the stream. Its width here varies from 2 M. to less than r mile. About 4o m. after the Chenal is entered the Kasai (q.v.), coming from the south, empties its brick-coloured waters at right angles into the Congo through a chasm in the hills 70o yd. wide. The confluence is known as the Kwa mouth. The Chenal ends in the lake-like expansion of Stanley pool, 20 m. long by 14 broad. The middle of the pool is occupied by an island (Bamu) and numerous sand banks. The banks offer considerable variety in character. On the north bank are the Dover cliffs, so named by H. M. Stanley from their white and glistening appearance, produced, however, not by chalk but by silver sand. On the south side stands the great red cliff of Kallina Point (about 5o ft. high). Round the point rushes a strong current 71 knots an hour, difficult to stem even for a steamer. On the northern bank of the river at the western end of the pool is Brazzaville, the capital of French Equatorial Africa. South of the pool, hills, low but steep, reappear, and 4 m. lower down begin the cataracts which cut off the middle Congo from the sea. Some 30o yd. above the first of these cataracts is Leopoldville, the capital of the Belgian Congo Colony, connected with the lower river at Matadi by railway. At Stanley pool the elevation of the river above the sea is about 800 ft., a fall of over 50o ft. in the 98o m. from Stanley falls. The velocity of the stream in the middle Congo varies considerably. At the Aruwimi confluence the rate is from 30o to 3 5o ft. a minute; in the broader stretches lower down the current is not more than zoo ft. a minute. Through the Chenal the pace is greatly accelerated, and as it flows out of Stanley pool the current is not less than 600 ft. a minute.
The cataracts below Stanley pool are caused by the river forcing its way through the mountains which run parallel to the western coast of the continent. About 3o main rapids are distinguished, and in 215 m. the river falls 800 feet. The highlands (known as the Serro do Crystal) consist df two mountain zones with an intermediate zone of lower elevation. The passage of this intermediate zone is marked by a fairly navigable stretch of river extending from Manyanga to Isangila, a distance of 7o m. The last rapid is a little above Matddi, whence the river is navigable for large vessels to the sea, a distance of about 85 miles. At Matadi the river widens out into an estuary with many mangrove-bordered creeks and forest-clad islands of a deltaic character. This estuary is traversed by a deep canon, in which soundings of goo ft. have been obtained. The mouth of the river is in 6° S. and I 2° 20' E. The cafion or gully is con tinued into the open sea for over ioo m., with depths as much as 4,000 ft. below the general level of the sea floor. Just below Matadi, where the width of the river is about half a mile, depths of 276 and 36o ft. have been found, the current here running at from 4 to 8 knots, according to the season; while the difference in level between high and low water is 2o-25 feet. The difference is caused by the rainy or dry seasons, of which there are two each during the year. In the middle Congo May and November are the times of greatest flood; in the lower river the floods are somewhat later. At Stanley pool the maximum rise of water is about 15 ft. The tides are 'felt as far as Boma, 49 m. from the mouth of the river, but the rise is there less than a foot; while at the mouth it is 6 ft. The cafion above mentioned is occupied by salt water, which is nearly motionless. Above it the fresh water runs with increasing velocity, but decreasing depth, so that just within the mouth of the river it is only a few feet deep.
The river at its mouth between Banana Point on the north and Sharks Point on the south is over 7 m. across. Banana Point (which grows no bananas) is the end of a long sandy peninsula, its highest spot not more than 6 ft. above high water; Sharks Point is bolder and shaped somewhat like a reaping-hook with the point turned inward, thus enfolding Diegos bay. The current of the river is perceptible fully 3o m. out to sea, the brown waters of the Congo being distinguishable from the blue of the ocean.
Of the many affluents of the middle river the Ubangi on the north and the Kasai on the south, with their tributary streams, are noticed separately. Other notable affluents which join the river on its right bank include the Lindi, which enters the Congo about 15 m. below Stanley falls in 25° 4' E. and is navigable from its mouth for over ioo m., and the great Aruwimi, which rises, as the Ituri, in close proximity to Albert Nyanza, flowing generally from east to west. The Aruwimi is formed of many branches and its upper basin extends over 21° of latitude. The river flows almost entirely through the great equatorial forest, which here seems to reach its maximum density. Its confluence with the Congo is in I° If N., 23° 38' E., and it is navigable for 90 m., up to the Yambuya rapids. The Loika, Itimbri or Lubi river, rises in about 26° E., and joins the Congo by two mouths, 22° 35'-46' E. The Loika is navigable as far as the Lubi falls, a distance of so miles. The Mongala, which drains the country between the Loika to the east and the Ubangi to the west, rises in about 3° N., 23° 20' E., and flows in a somewhat similar curve (on a smaller scale) to that of the Ubangi. The Mongala is navigable for over 3oo m. The Mongala confluence is in I° 53' N., 19° 49' E. Below the Ubangi confluence the Sanga, in I° 12' S., 16° 53' E., joins the Congo. The Sanga rises in the north-west verge of the Congo basin and flows in a general north to south direction. The main northern branch rises in southern Adamawa in about 7° N., i5° E. An almost equally large western branch, the Dscha (or Ngoko), rises about 3° N., 131° E., and in its course traverses a vast tract of dense forest. The Sanga is navigable by steamers as far as the south-east corner of the Cameroons, a distance of approximately 35o miles. The Likuala and Alima, which join the Congo within 3o m. of the mouth of the Sanga, are much smaller streams.
The first of the southern tributaries of the middle Congo, the Lomami, enters the main stream in o° 46' N., 24° 16' E. It has a length of over 7oo m., rising in nearly 9° S. It flows south to north, the greater part of its course being parallel to and from 4o to 15o m. west df the upper Congo. For the last 200 M. it is navigable by steamers. 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 in the same direction as the middle Congo- east to west. The Lulanga (or Lulongo), about 400 m. long, enters in o° 4o' N., 18° 16' E. The main branch of the Ruki or Juapa, which enters a little north of the equator in 18° 21' E., has its rise between 24° and 25° E. and about 3° S., in the swampy region traversed by the Lomami. It is about 600 m. long and has two large southern tributaries. A few miles above the Ruki confluence the Ikelemba (some i5o m. in length) joins the Congo. The Lulanga, Ikelemba and Ruki, and their sub-streams, have between them over i,000 m. of navigable waters. No rapids intercept their course.
Unlike the Nile there are no classic associations with the Congo. A single mention made of the Zaire by Camoens in the Lusiads exhausts its connection with literature (up to the beginning of the i9th century), other than in little known and semi-fabulous accounts of the ancient kingdom of Congo. The mouth of the river was discovered by Diogo Cdo or Cam either in 1482 or 1483. To mark the discovery and to claim the land for the Portuguese crown he erected a marble pillar on what is now called Sharks Point. Hence the river was first called Rio de Padrao (Pillar river). It soon, however, became known as Zaire (q.v.), a corruption of a native word meaning "river," and subse quently as the Congo. In the three centuries succeeding Diogo Cao's discovery strangely little was done to explore the river though various European firms established "factories" in the estu ary, trading in slaves and other commodities. At length the British Admiralty took action, and in 1816 despatched Captain J. K. Tuckey, R.N., at the head of a well-equipped mission. The expedition was prompted by the suggestion that the Congo was identical with the Niger. Captain Tuckey reached the Congo on July 6, 1816, and managed to push up stream as far as Isangila, beyond the lowest series of rapids; but sickness broke out, the commander and 16 other Europeans died and the expedition had to return. Captain Tuckey and several of his companions are buried on Prince's island, just above Boma, the point where the Congo widens into an estuary. For 6o years, though two or three attempts were made no other European reached even as far as Isangila. Lieutenant W. Grandy, R.N., who was sent from England in 1872 to the relief of David Livingstone, started from Ambriz, south of the Congo estuary, and, after many vicis situdes, reached, late in 1873, a point on the Congo below the cataracts. The death of Livingstone was soon afterwards re ported; and in April 1874, just as Grandy was prepared to ascend the river, letters of recall brought the expedition to a close.
It was by working down from its source that the riddle of the Congo was solved. In 1868 David Livingstone traced the course of the Chambezi to Lake Bangweulu. In March 1871 he reached the town of Nyangwe on the Lualaba, and died (1873) whilst endeavouring to trace the head-streams of that river, which he believed to be the Nile. "I have no fancy," he once said, "to be made into 'black man's pot' for the sake of the Congo." But by 1872 geographers were able to affirm, from Livingstone's own reports, that the great river system he had explored must belong to the Congo and not to the Nile. Actual proof was lacking, and of the course of the main river there was absolute ignorance. In Oct. 1876, H. M. Stanley arrived at Nyangwe from Zanzibar and from that point navigated the river over 1600 m. to Isangila— "Tuckey's Furthest"—reached in July 1877, thus demonstrating the identity of the Lualaba with the Zaire of the Portuguese. Stanley's great journey marked an epoch in the history of Africa, politically and commercially as well as geographically. Of the travellers who followed Stanley none did more to add to the exact knowledge of the main river and Its greatest tributaries than the Rev. George Grenfell (1849-1906) of the Baptist Mis sionary Society, while the Aruwimi was partly explored by Stanley in 1887 in his last expedition in Africa. The detailed sur vey of the river system was mainly done by Belgian officers, notably by Captains A. Delacommune and C. Lemaire. In 1913 Captain R. Walker, R.E., showed that the Luapula did not issue from Lake Bangweulu, as had been supposed, but was a direct continuation of the Chambezi. Alongside all the non-navigable reaches of the river railways have been built (see BELGIAN CONGO).
y. Narrative of an Expedition to explore the river Zaire (1818) ; H. M. Stanley, Through the Dark Continent (1878) ; George Grenfell, Map of the River Congo, with Memorandum (1902) ; Sir H. H. Johnston, George Grenfell and the Congo (2 vols., 1908) ; C. Lemaire, Mission scientifique du Ka-Tanga (Brussels, 1901 o8) ; 17 memoirs; E. A. Steel, "Zambezi-Congo Watershed" Geog. Jnl. (Sept. 1917) . (F. R. C.)
