Page:The New International Encyclopædia 1st ed. v. 01.djvu/223

AFRICA. where it joins the great eastern highland, is a broad plateau 750 miles wide from north to south and 1500 miles from west to east, with a general elevation of 3000 to 6000 feet. This forms the divide between the Ngami and Zambezi basins on the south and the Congo waters on the north, and has its highest points on the west end in the plateau of Bihe (Lovili Mountains, 7800 feet), and at the eastern end in the plateau mountain of Chitane (6500 feet) near Nyassa Lake. Toward the south it slopes gradually to the Ngami and Zambezi basins, and toward the north it falls more abruptly to the Congo region. Near the eastern end are two lakes, Moero or Meru (3000 feet), and Bangweolo (3700 feet), that drain into the Upper Congo River.

Stretching northward from the Zambezi River to the Red Sea is that great eastern highland which attains its most extensive development just south of the equator in the region about the Victoria Nyanza. Through a large part of its extent this highland maintains an elevation of over 5000 feet, which in Abyssinia rises over considerable areas to heights of six, eight, and ten thousand feet. The main highland extends northward nearly to Suakin, and a narrow, interrupted spur reaches eastward from lakes Abba and Zuway to the apox of the Somali Peninsula, with peaks declining in height from Mount Mulata (9840 feet) to Godobb (4875 feet) at Cape Guardafui. The surface of this eastern highland is traversed longitudinally by a great system of so-called rift-valleys that constitute the most important feature of East African topography, and with which is associated a system of great lakes. These rift-valleys mark the course of parallel cracks in the earth's crust, between which the surface has sunk for thousands of feet, forming narrow, elongated depressions, or broad cañons, with precipitous walls that rise to the broken edges of the high-level plateau. In these rift-valleys lie the majority of the great African lakes, most of which, consequently, are of elongated form. The longest of these rifts has its northern end in Palestine, in the Jordan and Dead Sea valleys; it forms the Red Sea Basin southward to the Straits of Bab-el-Mandeb, where it is joined by a broader rift that comes from the east, forms the Gulf of Aden, and continues southwestward through French Somaliland and the Galla country into British East Africa to lakes Stephanie and Rudolf. At this point the rift-valley divides. One branch continues southward to beyond Lake Manyara, and another trends westward from Lake Rudolf to Lake Albert, and then southward to Lake Shirwa at the southern end of the eastern highland. In addition to these great rift-valleys there are many smaller fracture lines throughout the entire highlands that exercise considerable control over the smaller drainage features.

In the vicinity of the rifts are found the highest mountains, and in general the courses of the great rifts mark the location of volcanic peaks. The massive, snow-topped Ruwenzori Range, with its central peak rising to 16,600 feet, is among the most important of African mountain ranges, and it appears to be largely of volcanic or laccolitic origin. South of Lake Albert Edward, on the eastern side of the western rift-valley, is a group of volcanic mountains, some of which are active, culminating in Mount Kirunga (4350 feet). The most extensive volcanic district, however, lies along the eastern rift-valley and on the Abyssinian highland. Kilimanjaro (19,720 feet) and Kenia (17,200 feet), two isolated, snow-clad, volcanic peaks, rise from the eastern margin of this rift-valley near its southern termination. About the southern half of Lake Rudolf is a series of volcanic peaks, where several active cones rise 2000 feet above the plains, the best known of which is Teleki. Several very high mountains lie between Lake Rudolf and the Victoria Nyanza, the highest of which is Mount Elgon (14,030 feet). The Abyssinian highland is topped by massive fields of ancient lava, from which rise extinct volcanic peaks to heights of about 15,000 feet (Mounts Dashan, Abba-Yared, etc.). A few active volcanoes occur on the northeastern slopes of Abyssinia, near the shore of the Red Sea, where a chain of mountains presents summits of 9000 to 10,000 feet.

The great topographical feature of West Central Africa is the Congo Basin, equaling in area the basin of the Mississippi, and stretching from lat. 12° S. to lat. 6° N., and from long. 33° to about 16° E., where it narrows into the restricted valley by which the river makes its way through the coastal mountains to the Atlantic Ocean. The whole of this area is an elevated plain, sloping gradually from all sides toward the middle west, where the vast outlet debouches, in lat. 6° S. It presents no elevated regions worthy of mention, except about the borders. The southeast watershed is not high, nor is that on the south, which separates the Congo waters from those flowing into Lake Ngami or collected by the Zambezi. North of Lake Tanganyika the high mountains form a lofty watershed between the northeastern sources of the Congo and the sources of the Nile, and a line of hills sweeps around to the westward in the southern Sudan, and are continued to the lofty Jebel-el-Marra, in Darfur, whose slopes contribute the remotest northern waters of the Congo. The high ranges of Adamawa and the coast mountains separate its more westerly northern tributaries from the Ogowe and other coastal rivers. The mountains which separate the Congo Basin from the coast are rather the broken eroded margin of the continental plateau than true mountains, and few if any peaks exceed 5000 feet in height.

The topographical division of Sudan covers the equatorial area between the watershed of the Congo and the Sahara Desert, from the headwaters of the Bahr-el-Ghazal, a tributary of the Nile, to the mountains of the coast—that is, the drainage basins of Lake Chad and of the Niger. The basin of Lake Chad is an inclosed area almost in the centre of the continent, its southern margin being removed but a few hundred miles from the head of the Gulf of Guinea. The lake itself has no outlet, and lies about 900 feet above the sea. The eastern border of this basin is separated from the Nile waters by a line of highlands which continue northward across the desert, and which culminate in Darfur in the Marra Mountains, rising some 7000 feet above the plain, and forming a watershed for eastern Sudan. The western border of the Chad Basin is formed by rocky plateaus, which constitute a divide between this and the Niger Basin; and a uniform plain, diversified by rocky hills, stretches westward to the coast mountains. Large portions of the Chad Basin are dry and open, while other extensive areas are forested or swampy,