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 [geography A F R I C A. of comparatively recent date, which runs from east to west the north-east with (6) the East African plateau, with parallel to the northern coast. This range—the Atlas— probably a slightly greater average elevation, and marked by some distinct features. It is formed by a widening North and belongs to the European system both in its out of the eastern axis of high ground, which becomes South direction and in its constituent formations. Africa. Archaean rocks play quite a subordinate part, subdivided into a number of zones running north and while a regular series of stratified formations, from palaeo- south and consisting in turn of ranges, tablelands, and zoic to tertiary, most of which have equally experienced depressions. A wide area of granite and gneiss runs the effects of folding, constitute the greater part of the down the centre, forming in part a rolling plain, while range. Of these the mesozoic—particularly the cretaceous the more elevated ridges are composed chiefly of schists, —cover the largest area, while tertiary strata occur chiefly quartzites, and stratified rocks. The most striking feature in narrow bands near the coast. The eastern half of North is the existence of two great lines of depression, due Africa contains large expanses both of tertiary formations largely to the subsidence of whole segments of the earth’s and of cretaceous. The extreme south of the continent is crust, the lowest parts of which are occupied by vast lakes. marked by the large extent of mesozoic formations (trias, Towards the south the two lines converge and we find only one great valley (occupied by Lake Nyasa), the &,c.), in addition to older rocks. The mean elevation of Africa has been variously esti- southern part of which is less distinctly due to rifting mated at from 1962 feet (Heiderich) to 2133 (Wagner), and subsidence than the rest of the system. Farther and may thus be considered to approximate north the western depression, sometimes known as the ReIief ' closely to 2000 feet, which is roughly the eleva- Central African trough, is occupied for more than half its tion of both North and South America, but is considerably length by water, forming the four lakes of Tanganyika, less than that of Asia (3117 feet). In contrast with the Kivu, Albert Edward, and Albert, the first - named other continents it is marked by the comparatively small over 400 miles long and the longest fresh-water lake in area both of very high and of very low ground, lowlands the world. Associated with these great valleys are a under 600 feet occupying an unusually small part of the number of volcanic peaks, the greatest of which occur on surface; while not only are the highest elevations inferior a meridional line east of the eastern trough. The eastern to those of Asia and South America, but the area of land, depression, known as the East African trough or rift-valley, over 10,000 feet, is also quite insignificant, being repre- contains much smaller lakes, many of them brackish and sented almost entirely by individual peaks and mountain without outlet, the only one comparable to those of the ranges. Moderately elevated tablelands are thus the western trough being Lake Rudolf, or Basso Norok. characteristic feature of the continent, though the surface Towards the northern end are Kilimanjaro—with its two of these is broken by higher peaks and ridges. As a peaks Kibo and Mawenzi, the former (according to Dr. general rule, the greater elevations lie to the east and Hans Meyer’s latest measurement) 19,430 feet, and probsouth, while a progressive diminution in altitude towards ably the culminating point of the whole continent—and the west and north is observable. Apart from the low- Kenya (17,180 feet). Hardly less important is the lands and the Atlas range, the continent may be divided Ruwenzori range (probably over 18,000 feet), which into two regions of higher and lower plateaux, the lies east of the western trough. Other volcanic peaks dividing line (somewhat concave to the north-west) running rise from the floor of the valleys, Kirunga, north of Lake from the middle of the Red Sea to about 6 S. on the Kivu, being still partially active, (c) The third division west coast. We thus obtain the following four main of the higher region of Africa is formed by the Abyssinian divisions of the continent:—(1) The coastal plains—often highlands, a rugged mass of mountains forming the largest fringed seawards by mangrove swamps—never stretching continuous area of its altitude in the whole continent, far from the coast, except on the lower courses of streams. little of its surface falling below 5000 feet, while the Recent alluvial flats are found chiefly in the delta of the summits reach heights of 15,000 to 16,000 feet. This more important rivers. Elsewhere the coast lowlands block of country lies just off the line of the great East merely form the lowest steps of the system of terraces African trough, the northern continuation of which passes which constitutes the ascent to the inner plateaux. (2) along its eastern escarpment as it runs up to join the Red The Atlas range, which, orographically as geologically, is Sea. There is, however, in the centre a circular basin distinct from the rest of the continent, being unconnected occupied by Lake Tsana. The basis of the region is a with any other area of high ground, but divided off on the mass of ancient crystalline rocks which have been furrowed south by a depressed area in places below sea-level. (3) by deep valleys under the influence of denudation. They The high southern and eastern plateaux, rarely falling are surmounted, especially towards the south, by a large below a height of 2000 feet, and having a mean elevation area of newer volcanic rocks, which have once covered the of about 3500. (4) The north and west African plains, surface in continuous sheets, while the north-western bordered and traversed by bands of higher ground, but margin is overlaid by sedimentary strata of Jurassic age. The lower north-western half of Africa, though the generally below 2000 feet. The two last divisions may be again subdivided. Thus greater part of its area is below 2000 feet, is traversed the high plateaux include :—(a) The South African plateau by bands of higher ground which run off from as far as about 12° S., bounded on all sides by the higher lands to the south. Both in the east Higher bands of high ground which fall steeply to the and west the bordering highlands are continued pa ' coasts. On this account South Africa has a as strips of plateau parallel to the coast, the Abyssinian general resemblance to an inverted saucer. The bounding mountains being continued northwards along the Red Sea ridges belong, as a rule, to the crystalline axes of the coast by a series of ridges reaching in places a height of continent, but in the south-east, where they attain their 7000 feet. In the west the zone of high land is broader maximum elevation in the Drakensberg range, the ancient but somewhat lower. The most mountainous districts lie rocks are overlaid by extensive beds of permian and trias. inland from the head of the Gulf of Guinea (Adamawa, &c.), Quite in the south the plateau rim is formed by three where heights of 6000 to 8000 feet are reached. Exactly parallel steps with level ground between them. In the at the head of the gulf the great peak of the Cameroon, north the interior basin is demarcated merely by a strip on a line of volcanic action continued by the islands to of plateau somewhat more elevated than the rest of the the south-west, has a height, according to the measuresurface. The South African plateau is connected towards ments of Dr. Breuss, of 13,370 feet, while Clarence Peak, 126