geography]
AFRICA
in the first of the line of islands, rises to over 9000. Towards the extreme west the Futa Jallon highlands form an important diverging point of rivers, but beyond this, as far as the Atlas chain, the elevated rim of the continent is almost wanting. The intervening space between the east and west coast highlands is divided into separate basins by other bands of high ground, one of which runs nearly centrally through North Africa in a line corresponding roughly with the curved axis of the continent as a whole. The best marked of the basins so formed occupies a circular area in West Africa bisected by the equator, once probably the site of an inland sea and now largely covered by recent alluvium. The following table gives the approximate altitudes of the most important features of the continent Table of Altitudes. Mountains— Feet. Lakes (continued)Aiashi (Atlas) . . 14,0001 Kivu . Simen Mountains, AbysTanganyika sinia . . . IS^OO1 Nyasa . Elgon .... 14,200 Mweru Settima . . . 13,390 Bangweulu Kenya .... 17,180 Ngami Kilimanjaro . . 19,4301 Leopold II. Ruwenzori . . . IS^OO Towns, &c.— Rungwe (Nyasa) . . 10,400 Drakensberg . . 11,7001 Constantine (Algeria) Markham, Mashonaland IOjOOO Timbuktu . Cameroon . . -. 13,370 Khartum Addis Abbaba Lakes— Eldoma Ravine Sta. Chad . . . 780 Brit. E. Africa Tsana .... 5750 Tabora Rudolf . . . 1250 Zomba Victoria Nyanza . . 3800 Bulawayo Naivasha . . . 6300 Pretoria Manyara . . . 3300 Bihe . Albert Nyanza . . 2100 Leopoldville Albert Edward . . 3200 [ Stanley Falls Sta
Feet. 4900 2670 1700 2953 3700 2950 1100 2165 800 1263 8000
7240 4130 2948 4469 4462 5500 1115 1470 From the outer margin of the African plateaux a large number of streams run down to the sea with comparatively short courses, while the rivers of the first class River systems. flow for long distances on the interior highlands before breaking through the outer ranges. The main drainage of the continent is to the north and west, or towards the basin of the Atlantic Ocean. The high Basin of lake plateau of East Africa contains the headthe Atlan waters of the Nile and Congo; the former the tic and longest, the latter the largest river of the conMediter= tinent. The southern branch of the Nile receives ranean. its chief supplies from the mountainous region adjoining the Central African trough in the neighbourhood of the equator. Thence streams pour east to the Victoria Nyanza, the largest African lake, and west and north to the Albert Edward and Albert Nyanzas, to the latter of which the effluents of the other two lakes add their waters. Issuing from it the Nile flows north, and between 7° and 10° N. traverses a vast marshy level, during which its course is liable to blocking by floating vegetation. After receiving the Bahr-el-Ghazal from the west and the Sobat, Blue (more correctly, Black) Nile and Atbara from the Abyssinian highlands, it crosses the great desert and enters the Mediterranean by a vast delta. The most remote head-stream of the Congo is the Chambezi, which flows south-west into the marshy Lake Bangweulu, afterwards turning north through Lake Mweru and descending to the forest-clad basin of west equatorial Africa. Traversing this in a majestic northward curve and receiving vast supplies of water from many great tributaries, it finally turns south-west and cuts a way to the Atlantic Ocean through the western highlands. North of the Congo 1
Estimated.
127 basin and separated from it by a broad undulation of the surface is the interior basin of Lake Chad—a flat-shored lake filled principally by the Shari coming from the south-east. West of this is the basin of the Niger, the third river of Africa, which, though flowing to the Atlantic, has its principal source in the far west, and reverses the direction of flow exhibited by the Nile and Congo. An important branch, however—the Benue—comes from the south-east. These four river-basins occupy the greater part of the lower plateaux of North and West Africa, the remainder consisting of arid regions watered only by intermittent streams which do not reach the sea. Of the remaining rivers of the Atlantic basin the Orange, in the extreme south, brings the drainage from the Drakensberg on the opposite side of the continent, while the Kunene, Kwanza, Ogowe, and Sanaga drain the west coast highlands of the southern limb; the Volta, Komoe, Bandama, Gambia, and Senegal those of the western limb. Of the rivers flowing to the Indian Ocean the only one draining any large part of the interior plateaux is the Zambezi, the western branches of which come Basin of from the neighbourhood of the west coast, the Indian Becent explorations have shown that the most Ocean. remote head-stream is the Liba, which, rising midway across the continent, flows west and south before assuming the eastward direction of the lower river. All the largest tributaries, including the Shire, the outflow of Lake Nyasa, flow down the southern slopes of the band of high ground which stretches across the continent in 10° to 12° S. In the south-west the Zambezi system interlaces with that of the Taukhe (or Tioghe), from which it at times receives surplus water. The rest of the water of the Taukhe is lost in a system of swamps and saltpans which formerly centred in Lake Ngami, now dried up. Farther south the Limpopo drains a portion of the interior plateau but breaks through the bounding highlands on the side of the continent nearest its source. The Rovuma, Rufiji, Tana, Juba, and Webi Shebeli principally drain the outer slopes of the East African highlands, the last-named losing itself in the sands in close proximity to the sea. Lastly, between the basins of the Atlantic and Indian Oceans, there is an area of inland drainage along the centre of the East African plateau, directed chiefly into the lakes in the great rift-valley. The largest river is the Omo, which, fed by the rains of the Abyssinian highlands, carries down a large body of water into Lake Rudolf. The latest calculation of the areas of African drainage systems, made by Dr A. Bludau (Petermanns Arefsof Mitteilungen, 43, 1897, pp. 184-6) gives the following drainage general results :— ° systems. Basin of the Atlantic . . 4,070,000 sq. miles. Do. Mediterranean . 1,680,000 ,, Do. Indian Ocean . 2,086,000 Inland drainage area . . 3,452,000 The areas of individual river-basi are :— Congo .... . 1,425,000 sq. miles. Nile .... . 1,082,0002 ,, Niger .... 808,000 Zambezi 513,500 Lake Chad . 394,0002 Orange.... 370,500 Do. (actual drainage area) . . 172,500 _ The area of the Congo basin is greater than that of any other river except the Amazon, while the African inland drainage area is greater than that of any continent but Asia, in which the same area is 4,900,000 sq. miles. The principal African lakes have been alluded to in the description of the East African plateau, but some of the phenomena connected with them may be spoken of more particularly here. As a rule the lakes Lakes. 2
Including waterless tracts naturally belonging to basin.
