Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/273

Rh FEATURES.] A F E, I C A 251 edge is the great water-parting of the continent, and the streams which form tho Orange river flow down its inward slope. There is no break in the continuance of the edge where it passes round from the Drakenberg to form the inmost and highest of the alternate ridges and terraces of the Cape Colony. It is now named in successive parts outliern from east to west the Storm Berge, the Zuur Berg, Schnee dge of the Bcrge, Nieuwe-veld, and Rogge-veld, the last-named por- lateau. t | on ^ Q ec jg e turning northward with the bend of the western coast. Its greatest height within the Cape Colony is in Compass Berg, the summit of the Schnee Berge, 8500 feet above the sea, The outer terraces of the Cape Colony, in which two chief ridges may be traced, lie closer together, and much nearer the coast; between these and the inmost or chief edge is the dry elevated region known as the Great Karroo. Their elevation is also very considerable, though they are broken through by lines of drainage sloping from the chief edge ; the part of the middle ridge, which is named the Little Zwarte Berge, attains 7G28 feet, and several points in both are upwards of GOOO feet above the sea. Table Mountain, a well-known and flat-topped mass of granite overhanging Cape Town, 3550 feet high, is the nucleus of the peninsula which extends south to form the Cape of Good Hope, but is altogether separated from the mountain ridges of the colony. restern The western edge of the great African plateau is generally !go of the lower than the eastern, since the whole slope of the continent .nk uu. j g more or less from the great heights on its eastern side, towards the west, but it is also clearly traceable, and of great height throughout. Rounding the Avestern side of the Cape Colony, the three ridges above noticed run together, and decrease somewhat in elevation as the mouth of the Orange river is approached. Their elevation at the point of union in Little Namaqua Land is still veiy considerable ; and here Mount Welcome attains 5130 feet, and Vogelklip, to north of it, 4343 feet above the sea. Beyond the Orange river in Namaqua and Damara Lands, the western edge continues in one or more terraces parallel to the coast. Mount Omatako, in the latter country, rises to 8800 feet. Northward, through Benguela and Angola, a more broken series of ridges and terraces mark the descent from the interior plateau, and the great Congo river breaks through to the coast-land at the place where it forms the cataracts of the narrow gorge of Yellala. Sierra Complicla is the name given by the Portuguese to that part of the western edge which runs between the Congo and the rapids of the lower Ogowai river on the equator. On the plateau edge at the southern side of. this river, Du Chaillu has made known a mountain of 12,000 feet in elevation; and the furthest point which has been reached on the Ogowai was in the vicinity of high mountains. Passing the Ogowai, and following the coast of the Bight of Biafra, the edge is now known as the Sierra do Crystal. The Camaroon mountains, at the head of the gulf, form a high peninsula of volcanic mountains, rising to 13,700 feet; but are isolated from the plateau lands, and belong rather to the remarkable line of volcanic heights which shows itself in the islands of Fernando Po, Prince s Island, St Thomas, and Annobon, stretching away into the ocean in the direction of St Helena. From the Sierra do Crystal the plateau edge inclines towards the lower course of the river Niger to a point above its delta, and below the confluence of the Benue, and then turns abruptly to the east. The heights which skirt the northern coast-land of the Gulf of Guinea, and which stretch as far as the head- waters of the Senegal and Gambia, and in the inner slope of which the Niger also has its sources, may be considered as an extension from the great plateau. But they are of smaller general elevation; and that best known part of the ridge, which has the name of the Kong Mountains, is apparently not higher than from 2000 to 3000 feet. The northern edge of the great African plateau is almost Norti c unknown ; but there are evidences that it runs eastward Cll -S e - between the 4th and 8th parallels of N. latitude, to a point P lateai at which it is well known, and where the Nile falls over its slope, forming the succession of rapids above Gondokoro. The character of the upper Benue river is that of a mountain- born river; and Mounts Alantika, 10,000 feet high, and. Mindif, GOOO feet, which rise to southward of Lake Chad, seem to be the outliers of the plateau edge in which the Benue has its sources. Beyond the Nile the margin of the plateau curves northward, to form the inner slope of the Abyssinian table-land. The general elevation of the surface of the great African plateau, the limits of which have now been traced, may be taken at from 3000 to 4000 feet above the sea; but its surface presents very great undulations, from tho depressions which are occupied by some of the great lakes, to the high mountains which rise above its average level. The most prominent of these interior masses yet known Height are the Blue Mountains, discovered by Baker, rising from i 11 the i the western shore of the Albert Lake to a height of per- terioro haps 10,000 feet, and which are believed to extend south- p a ward to unite with the Balegga Mountains, made known by Livingstone in his journey of 1871, north-west of Lake Tanganyika; these again are believed to join with the mountains which rise midway between the Victoria, the Albert Nyanza, and the Tanganyika, dividing the drainage to these vast lakes, and rising here in Mount M fumbiro to upwards of 10,000 feet. Another great central line of heights which also had an important part in directing the water-shed of the interior of South Africa, runs from the north of the Nyassa Lake, where it is named the Lobisa plateau, through the Muchinga Mountains, which separate the drainage of the Lualaba and its lakes from that of the Zarnbeze basin, westward to the heights in the far interior of Angola, known as the Mossamba Mountains, and from which rivers flow in all directions. The plateau of Barbary, in the north of the continent, Plateai beyond the lower land of the Sahara, is a distinct and B:rbar separate high land, stretching from Cape Bon, on the Medi terranean coast opposite Sicily, in a south-westerly direction to the Atlantic coast, through Tunis, Algeria, and Marocco. The eastern portion of it in Algeria and Tunis rises in a broad plateau from 2000 to 3000 feet in general height, with outer heights, enclosing an elevated steppe, at a distance of about 100 miles apart. On the west, where it enters Marocco, these outer ridges draw together and form the high ranges of the Atlas Mountains, rising to a much greater elevation, and attaining 11,400 feet in the summit named Mount Miltsin. The African continent, as far as it has yet been explored, seems to be the portion of the globe least disturbed by volcanic action. The known active volcanoes in the con tinent are those of the Camaroon Mountains, on the coast of the Gulf of Guinea in the west, and the Artali volcano in the depressed region of the salt desert which lies be tween the Abyssinian plateau and the Red Sea. This latter volcano is probably a part of the system with which the volcanic island of Jebel Tur, in the Red Sea, near the same latitude, is connected. One other active volcano only Greater is known by report, the Njemsi volcano, in the country &quot;,^s K between Mount Kenia and the Victoria Lake. Shocks features of earthquake appear to be almost unknown in any part of the continent. It has been pointed out by the late Sir Roderick Murchison that the older rocks which are known to circle round the continent, unquestionably in cluded an interior marshy or lacustrine country, and that the present centre zone of waters, whether lakes, rivers, or marshes, extending from Lake Chad to Lake Ngami, are but the great modern residual phenomena of those