TANGANYIKA (a name said by V. L. Cameron to signify a “mixing-place”), a vast lake in East-Central Africa, the longest freshwater lake in the world, measuring just over 400 m., with a general breadth varying from 30 to 45 m., and an area of about 12,700 sq. m. It lies at an altitude of about 2600 ft. above the sea, and occupies the southern end of the great central rift-valley, which terminates suddenly at its southern point, the line of depression being represented farther south by the more easterly trough of Lakes Nyasa and Rukwa, from which Tanganyika is separated by the Fipa plateau, composed of old granitoid rocks; though even here traces of old valley-walls are said by Dr Kohlschütter to exist. North of Tanganyika the valley is suddenly interrupted by a line of ancient eruptive ridges, which dam back the waters of Lake Kivu (q.v.), but have been recently cut through by the outlet of that lake, the Rusizi, which enters Tanganyika by several mouths at its northern end. The flat plain traversed by the lower Rusizi was evidently once a portion of the lake floor. Tanganyika has been formed by the subsidence of a long narrow tract of country relatively to the surrounding plateaus, which fall to the lake in abrupt cliffs, some thousands of feet high in places. The geological formations thus exposed show that the plateaus are composed of a base of eruptive material, overlaid by enormous deposits of reddish sandstones, conglomerates and quartzites, exposed in parts to a depth of 2000 feet. Besides the plain to the north, a considerable area to the west, near the Lukuga outlet (see below), shows signs of having been once covered by the lake, and it is the opinion of Mr J. E. S. Moore that the sandstone ridges which here bound the trough have been recently elevated, and have been cut through by the Lukuga during the process.

The past history of the lake has long been a disputed question, and Mr Moore's view that it represents an old Jurassic arm of the sea is contested by other writers. This idea originated in the discovery of a jelly-fish, gasteropods, and other organisms of a more or less marine type, and presenting some affinity with forms of Jurassic age. This fauna, to which the term “halolimnic” has been applied, was known to exist from specimens obtained by Mr E. C. Hore and other early travellers, but has been more systematically studied by Mr Moore (during expeditions of 1896 and 1898-99) and Dr W. A. Cunnington (1904-5). Various considerations throw doubt on Mr Moore's theory, especially the almost entire absence of marine fossiliferous beds in the whole of equatorial Africa at a distance from the sea, of any remains of Jurassic faunas which might link the Tanganyika forms with those of undoubted Jurassic age in neighbouring regions. The formation of the existing rift-valley seems in any case to date from Tertiary times only.

Although drinkable, the water of the lake seems at times at least to be very slightly brackish, and it was supposed by some that no outlet existed until, in 1874, Lieutenant Cameron showed that the surplus water was discharged towards the upper Congo by the Lukuga river, about the middle of the west coast. The outlet was further examined in 1876 by Mr (afterwards Sir Henry) Stanley, who found that a bar had formed across the outlet, and it has since been proved that the outflow is intermittent, ceasing almost entirely after a period of scanty rainfall, and becoming again established when the lake-level has been raised by a series of rainy years. About 1880 it was running strongly, but about this time a gradual fall in the lake-level set in, and was continued, with occasional pauses, for some twenty years, the amount being estimated by Wissmann at 2 feet annually. In 1896 Captain H. Ramsay found that a wide level plain, which had before been covered by water, intervened between Ujiji and the lake, but stated that no further sinking had taken place during the two previous years. Near Tembwe Head Mr L. A. Wallace found recent beaches 16 feet above the existing level. The Lukuga was reported blocked by a bar about 1897, but a certain amount of water was found flowing down by Mr Moore in 1899; while in 1901 Mr Codrington found the level 4 or 5 feet higher than in 1900, the outlet having again silted up. A continued rise was also reported in 1907. In any case, the alterations in level appear

to be merely periodic, and due to fluctuations in rainfall, and do not point, as some have supposed, to a secular drying up of the lake.

The lake is fed by a number of rivers and small streams which descend from the surrounding highlands. The Mlagarazi (or Malagarasi), perhaps the largest feeder, derives most of its water from the rainy districts east of the strip of high ground which shuts in the lake on the north-east. The main stream, in fact, has a nearly circular course, rising in 4º 40' S., only some 10 miles from the lake shore and less than 40 miles from its mouth, though its length is at least 220 miles. The other branches of the Mlagarazi, which traverse the somewhat arid granite plateaus between the lake and 33º E., bring comparatively little water to the main stream. In its lower course the river is a rapid stream flowing between steep jungle-clad hills, with one fall of 5 feet, and is of little use for navigation. The various channels of its delta are also obstructed with sand-banks in the dry season. The Rusizi, the next (or perhaps equal) in importance among the feeders of the lake, has already been spoken of. It receives many tributaries from the sides of the rift-valley, and is navigable for canoes. The remaining feeders are of distinctly less importance, the Lofu, which enters in the south-west, being probably the largest.

Tanganyika has never been sounded systematically, but the whole configuration of its valley points to its being generally deep, and this has been confirmed by a few actual measurements. Dr Livingstone obtained a depth of 326 fathoms opposite Mount Kabogo, south of Ujiji. Mr Hore often failed to find boftom with a line of 168 fathoms. The French explorer, Victor Giraud, reported 647 metres (about 350 fathoms) off Mrumbi on the west coast, and Moore depths of 200 fathoms and upwards near the south end. The shores fall rapidly as a rule, and there is a marked scarcity of islands, none occurring of any size or at a distance from the coast line. The lake is subject to occasional storms, especially from the south-south-east and south-west, which leave a heavy swell and impede navigation. The cloud and thunder and lightning effects are spoken of as very impressive, and the scenery of the lake and its shores has been much extolled by travellers.

Vegetation is generally luxuriant, and forest clothes portions of the mountain slopes. The lake lies on the dividing line between the floral regions of East and West Africa, and the oil-palm characteristic of the latter is found on its shores. The largest timber tree is the mvule, which attains vast dimensions, its trunk supplying the natives with the dug-out canoes with which they navigate the lake. The more level parts of the shores have a fertile soil and produce a variety of crops, including rice, maize, manioc, sweet potatoes, sugar-cane, &c., &c. The waters dispjay an abundance of animal life, crocodiles and hippopotami occurring in the bays and river mouths, which are also the haunts of water- fowl of many kinds. Fish are also plentiful. Various sections of the Bantu division of the Negro race dwell around the lake, those on the west and south-west showing the most pronounced Negro type, while the tribes on the east exhibit some intermixture with representatives of the Hamitic stock, and (towards the south) some traces of Zulu influence. The surrounding region has been overrun by Arabs and Swahili from the East African coast.

Though rumours of the existence of the lake had previously reached the east coast, Tanganyika was not visited by any European until, in 1858, the famous expedition of Burton and Speke reached the Arab settlement of Ujiji and partially explored the northern portion. Ujiji became famous some years later as the spot where Dr Livingstone was found by Stanley in 1871, after being lost to sight for some time in the centre of the continent. The southern half of the lake was first circumnavigated by Lieutenant V. L. Cameron in 1874, and the whole lake by Stanley in 1876. The mapping of Tanganyika, which long rested on the surveys of Mr E. C. Hore, published in 1882, received considerable modification, about 1899-1900, from the work of Fergusson, Lemaire, Kohlschütter and others, who showed that while the general outline of the coasts had been drawn fairly correctly, the whole central portion, and to a lesser degree the northern, must be shifted a considerable distance to the west. At Mtowa, in 5º 43' S., the amount of shifting of the west coast was about 30 miles. At Ujiji, on the east coast, the longitude was given by Kohlschütter as 29º 40' 2" E. as compared with 30º 4' 30" E. of Cameron, a difference of some 25 miles.

In the partition of Africa among the European Powers, the shores of Tanganyika have been shared by Belgium, Great Britain and Germany, Great Britain holding the southern extremity, Germany the east, and Belgium the west. Stations have been established on the lake by all three Powers, the principal being — German: Bismarckburg in the south and Ujiji in the north; British: Sumbu and Kasakalawe, on Cameron Bay; Belgian: Mtowa or Albertville in 6º S. Missionaries, especially the Catholic “White Fathers,” are also active on its shores. A small steamer, the “Good News,” was placed on the lake by the London Missionary Society in 1884, but afterwards became the property of the African Lakes Corporation; a larger steamer, the “Hedwig von Wissmann,” carrying a quick-firing Krupp gun, was launched in 1900 by a German expedition under Lieutenant Schloifer; and others are owned by the “Tanganyika Concessions” and Katanga companies. The greater part of the trade with Tanganyika is done by the African Lakes Corporation by the Shiré-Nyasa route, but the Germans have opened up overland routes from Dar-es-Salaam.

Authorities. — The narratives of Burton, Livingstone, Cameron and Stanley; E. C. Hore, Lake Tanganyika (London, 1892); J. E. S. Moore, in Geogr. Journal, September 1897 and January 1901; To the Mountains of the Moon (London, 1901); The Tanganyika Problem (London, 1903); L. A. Wallace, Geogr. Journal, June 1899; H. Ramsay, in Verhandl. d. Gesell. für Erdkunde Berlin, No. 7, 1898; H. Glauning and E. Kohlschütter, in Mitt. aus den Deutschen Schutzgebieten, Nos. 1 and 2, 1900; E. Kohlschütter, in Verhandl. 13 Deutsch. Geographentages, 1901; M. Fergusson, in Geol. Mag., August 1901; E. Stromer, in Petermanns Mitteil., December 1901; R. Codrington, in Geogr. Journal, May 1902; W. H. Hudleston, in Transactions Victoria Inst., 1904; also papers on the results of Dr W. A. Cunnington's expedition in Proceedings of the Zoological Society, 1906, &c.; Journal of the Linnean Society, 1907.