The Tanganyika occupies the centre of the length of the African continent, which extends from 32° N. to 33° S. latitude, and it lies on the western extremity of the eastern third of the breadth. Its general direction is parallel to the inner African line of volcanic action drawn from Gondar southwards through the regions about Kilima-ngáo (Kilimanjáro) to Mount Njesa, the eastern wall of the Nyassa Lake. The general formation suggests, as in the case of the Dead Sea, the idea of a volcano of depression—not, like the Nyanza or Ukerewe, a vast reservoir formed by the drainage of mountains. Judging from the eye, the walls of this basin rise in an almost continuous curtain, rarely waving and infracted to 2,000 or 3,000 feet above the water-level. The lower slopes are well wooded: upon the higher summits large trees are said not to grow; the deficiency of soil, and the prevalence of high fierce winds would account for the phenomena. The lay is almost due north and south, and the form a long oval, widening in the central portions and contracting systematically at both extremities. The length of the bed was thus calculated: From Ujiji (in S. lat. 4° 55′) to Uvira (in S. lat. 3° 25′), where the narrowing of the breadth evidences approach to the northern head, was found by exploration a direct distance of 1° 30′ = 90 miles, which, allowing for the interval between Uvira and the river Rusizi, that forms the northernmost limit, may be increased to 100 rectilinear geographical miles. According to the Arab voyagers, who have frequently rounded the lake Ujiji in eight stages from the northern, and twelve from the southern, end of the lake, the extent from Ujiji to the Marungu River, therefore, is roughly computed at 150 miles. The total of length, from Uvira, in S. lat. 30° 25′, to Marungu, in S. lat. 7° 20′, would then be somewhat less than 250 rectilinear geographical miles. About Ujiji the water appears to vary in breadth from 30 to 35 miles, but the serpentine form of the banks, with a succession of serrations and indentations of salient and re-entering angles—some jutting far and irregularly into the bed—render the estimate of average difficult. The Arabs agree in correctly stating, that opposite Ujiji the shortest breadth of the lake is about equal to the channel which divides Zanzibar from the mainland, or between 23 and 24 miles. At Uvira the breadth narrows to eight miles. Assuming, therefore, the total length at 250, and the main breadth at 20, geographical miles, the circumference of the Tanganyika would represent, in round numbers, a total of 550 miles; the superficial area, which seems to vary little, covers about 5,000 square miles; and the drainage from the beginning of the great Central African depression in Unyamwezi, in E. long. 33° 58′, numbers from the eastward about 240 miles.
By B. P. thermometer the altitude of the Tanganyika is 1850 feet above the sea-level, and about 2000 feet below the adjacent plateau of Unyamwezi and the Nyanza, or northern lake. This difference of level, even did not high-hill ranges intervene, would preclude the possibility of that connection between the waters which the Arabs, by a conjecture natural to inexpert geographers, have maintained to the confusion of the learned. The topographical situation of the Tanganyika is thus the centre of a deep synclical depression in the continent, a long narrow trough in the southern spurs of Urundi, which, with its mountain-neighbour Karagwah, situated upon the equator, represents the Inner African portion of the Lunar Mountains. It may be observed that the parallel of the northern extremity of the Tanganyika nearly corresponds with the southern creek of the Nyanza, and that they are separated by an arc of the meridian of about 343 miles.
The water of the Tanganyika appears deliciously sweet and pure after the salt and bitter, the putrid and slimy produce of the wells, pits, and pools on the line of march. The people, however, who drink it willingly when afloat, prefer, when on shore, the little springs which bubble from its banks. They complain that it does not satisfy thirst, and contrast it unfavourably with the waters of its rival the Nyanza: it appears moreover, to corrode metal and leather with exceptional power. The colour of the pure and transparent mass has apparently two normal varieties: a dull sea-green—never, however, verdigris-coloured, as in the shoals of the Zanzibar seas, where the reflected blue of the atmosphere blends with the yellow of the sandy bottom; the other, a clear, soft blue—by day rarely deep and dark, like the ultramarine of the Mediterranean, but resembling the light and milky tints of tropical seas. Under a strong wind the waves soon rise in yeasty lines, foaming up from a turbid greenish surface, and the aspect becomes menacing in the extreme.
It was found impracticable to take soundings of the Tanganyika: the Arabs, however, agreed in asserting that with lines of several fathoms they found bottom only near the shores. The shingly sole shelves rapidly, without steps or overfalls, into blue water. Judging from the eye, the bottom is sandy and profusely strewn with worn pebbles. Reefs and washes were observed near the shores; it is impossible to form an idea of their position or extent, as the crews confine themselves to a few well-known lines, from which they cannot be persuaded to diverge. No shoals or shallows were seen at a distance from the coasts, and though islets are not unfrequent upon the margin, only one was observed or heard of near the centre.
The affluents of this lake are neither sufficiently numerous nor considerable to alter by sedimentary deposit the depth or the shape of the bed. The borders are generally low: a thick fringe of rush and reed, obviating erosion by the element, conceals the watery margin. Where the currents beat, they cut out a short and narrow strip of quartzose sand, profusely strewn with large shingle, gravel, comminuted shells, and marine exuviæ, with a fringe of drift formed by the joint action of wind and wave. Beyond this is a shelving plain—the principal locality for cultivation and settlements. In some parts it is a hard clay conglomerate; in others, a rich red loam, apparently stained with oxide of iron; and in others sandy, but everywhere coated with the thickest vegetation extending up to the background of mountains. The coast is here and there bluff, with miniature cliffs and headlands, whose formation is of sandstone strata tilted, broken, and distorted, or small blocks imbedded in indurated reddish earth. From the water appeared piles of a dark stone resembling angular basalt, and amongst the rock-crevices the people find the float-clay, or mountain meal, with which they decorate their persons and the sterns of their canoes. The uncultivated hill summits produce various cactaceæ; the sides are clothed with giant trees, the mvule, the tamarind, and the bauhinia. On the declines, more precipitous than the Swiss terraces, manioc and cereals grow luxuriantly, whilst the lowest levels are dark with groves of plantains and Guinea-palms.
A careful investigation and comparison of statements leads to the belief that the Tanganyika receives and absorbs the whole river-system—the net-work of streams, nullahs, and torrents—of that portion of the Central African depression whose water-shed converges towards the great reservoir. Geographers will doubt that such a mass, situated at so considerable an altitude, can maintain its level without an effluent. Moreover, the freshness of the water would, under normal circumstances, argue the escape of saline matter washed down by the influents from the area of drainage. But may not the Tanganyika, situated, like the Dead Sea, as a reservoir for supplying with humidity the winds which have parted with their moisture in the barren and arid regions of the south, maintain its general level by the exact balance of supply and evaporation? And may not the saline particles deposited in its waters be wanting in some constituent which renders them evident to the taste? One point concerning the versant has been proved by these pages, namely, that the Tanganyika cannot be drained eastward by rents in a subtending mountain ridge, as was supposed by Dr. Livingstone from an indiscriminately applied analogy with the ancient head-basin of the Zambezi. Dr. Livingstone (chap. xxiv. xxvi. et passim) informs his readers, from report of the Arabs, that the Tanganyika is a large shallow body of water; in fact, the residuum of a mass anciently much more extensive. This, however, is not and cannot be the case. In theorising upon the eastern versant and drainage of the Tanganyika, Dr. Livingstone seems to have been misled by having observed that the vast inland sea of geological ages, of which Lake Ngami and its neighbour Kumadau are now the principal remains, had been desiccated by cracks and fissures, caused in the subtending soils by earthquakes and sudden upheavals, which thus opened for the waters an exit into the Indian Ocean. This may have happened to the Nyassa, or Southern Lake; it must not, however, be generalized and extended to the Nyanza and the Tanganyika.
As in Zanzibar, there is little variety of temperature upon the Tanganyika. The violent easterly gales, which, pouring down from the cold heights of Usagara, acquire impetus sufficient to carry the current over Ugogo, Unyamwezi, and Uvinza, are here less distinctly defined. The periodical winds over the Lake—regular, but not permanent—are the south-east and the south-west, which also bring up the foulest weather. The land and sea breezes are felt almost as distinctly as upon the shores of the Indian Ocean. The breath of the morning, called by the Arabs El Barad, or the zephyr, sets in from the north. During the day are light variable breezes, which often subside, when the weather is not stormy, into calms. In the evenings a gentle afflatus comes up from the waters. Throughout the dry season the Lake becomes a wind-trap, and a heavy ground sea rolls towards the shore. In the rains there is less sea, but accidents occur from sudden and violent storms. The mountainous breakers of Arab and African informants were not seen; in fact, with a depth of three feet from ridge to dell, a wave would swamp the largest laden canoe. Wind-currents are common. Within a few hours a stream will be traversed, setting strongly to the east, and crossed by a southerly or south-westerly current. High gales, in certain localities where the waves set upon a flush, flat shore, drive the waters fifteen to twenty feet beyond the usual mark. This circumstance may partly explain the Arab’s belief in a regular Madd wa Jarr—ebb and flow—which Eastern travellers always declare to have observed upon the Tanganyika and Nyassa Lakes, and which Mr. Anderson believes to exist in the little Ngami. A mass of water so large must be, to a certain extent, subject to tidal influences; but the narrowness of the bed from east to west would render their effect almost unobservable. Mr. Francis Galton referred me for the explanation of this phenomenon to a paper ‘On the Seiches of Lakes,’ by Colonel J. R. Jackson, F.R.G.S., published in the ‘Journal of the R. G. S.,’ vol. iii. of 1833, in which the learned author refers the ebb and flow of the waters of Lake Leman, or of Geneva (and of the lakes of Zurich, Annecy, and Constance), to “an unequal pressure of the atmosphere on different parts of the lake at the same time; that is, to the simultaneous effect of columns of air of different weight or different elasticity, arising from temporary variations of temperature, or from mechanical causes.”
The scenery and the navigation of the Tanganyika have been illustrated in the last chapter. Remains only a succinct account of the physical and ethnological features of its Periplus, carefully collected from authorities on the spot.
According to the Wajiji, from their country to the Runangwa or Marungu River, which enters the Lake at the southern point, there are twelve stages; this Periplus numbers 120 khambi or stations, at most of which, however, provisions are not procurable. An extended list of fifty-three principal points was given by the guides; it is omitted, as it contains nothing beyond mere names. There are, however, sixteen tribes and districts which claim attention: of these, Ukaranga and Ujiji have already been described.
The kingdom of Urundi, which lies north of Ujiji, has a sea-face of about fifty miles; a low strip of exceeding fertility, backed at short distances by a band of high green hill. This region, rising from the Lake in a north-easterly direction, culminates into the equatorial mass of highlands which, under the name of Karagwah, forms the western spinal prolongation of the Lunar Mountains. The residence of the Mwami, or chief sultan Mwezi, is near the headstream of the Kitangure (Kitangule), or River of Karagwah, which rises at a place distant six days’ march (sixty miles), and bearing north-east from, the Tanganyika. His settlement, according to the Arabs, is of considerable extent; the huts are built of rattan, and lions abound in the vicinity.