Its average elevation above the sea level is only 600 ft. Although termed a desert, the Kalahari is not, wholly destitute of vegetation; indeed, light grass, an abundance of tuberous plants, and extensive patches of bushes are found in many localities. Rain seldom refreshes any of these arid tracts; but when it does, they are at once carpeted with the richest verdure. - Before the explorations of Dr. Livingstone, southern Africa was believed to be a sterile wilderness, in the equatorial climate of which the existence of an abundant animal or vegetable life was impossible. In 1852, however, Sir Roderick Murchi-son, in an address to the royal geographical society of London, advanced the hypothesis that the whole African interior would prove to be a vast watery plateau of some elevation above the sea, but subtended on the east and west by much higher grounds. This view was based purely on geological reasoning, for at that time absolutely nothing was known of the interior N. of Lake Ngami; it was a blank on the map. Livingstone was then engaged in his first expedition on the Zambesi, and its results triumphantly confirmed the correctness of Murchison's speculations.

A labyrinthine network of rivers extends over the whole table land between the 10th and 20th parallels, so that the natives call the region Linoka-noka, or " rivers upon rivers." S. of the Kalahari desert the Gariep or Orange river is the only considerable stream.

It flows along the northern boundary of the Cape region westward into the Atlantic ocean, but is not navigable in any part of its course, being an impetuous torrent during the rains, and in the dry season little more than a narrow, slow, and shallow current. Of the rivers which flow into the Indian ocean, the Zambesi or Leambye exceeds all others in magnitude and importance; its name signifies "the river," and indicates its preeminence in the native mind. From its origin among the Gilolo hills to its junction with the Chobe river, in lat. 18° 17'S. and lon. 23° 50' E., the general course of the Zambesi is from N. to S., but below this point it flows eastward, making a semicircular bend to the N. on its way to the sea. The area of its drainage basin extends through 10° of latitude and more than 21° of longitude. At the Victoria falls, in lat. 17° 57' S., lon. 26° 6' E., the river narrows from a width of 1,000 yards to a gorge-like channel in the rock about 75 ft. broad, and leaps down a distance of 300 ft., forming one of the most magnificent and beautiful cascades in the world. The rising spray forms a constant cloud above the cataract.

On the upper portion of the Zambesi the adjacent country is low, and villages are built on raised ground to protect the inhabitant against the annual overflow. Further down, the river is a mile wide in many places. It becomes less rapid after descending the falls, and at the commencement of its delta, 300 m. from the Mozambique channel, it is wide and tranquil. The extreme length of the delta and its shallowness except in the main branch render access from the Indian ocean rather difficult. The Limpopo, which reaches the E. coast about midway between Delagoa bay and the tropic of Capricorn, is a river famed among sportsmen for the gigantic game which haunts its banks, but worthless as an avenue to the interior on account of its deficient depth and the shoals at its mouth. The Congo is the southernmost of the great rivers of Africa which descend from the plateau on the Atlantic side. Of its course or character in the interior we have but little authentic information, although it is supposed to be connected with the Kasai, which is said to traverse a country of alternate forest and pasture land. It is navigable in its lower course, where it is 5 m. wide and of great depth; but at the distance of 160 m. from the sea there is a cataract.

The only notable river between this and the delta of the Niger is the Ogowai, which crosses the equator, and enters the sea by the same outlet as the Fernan Yaz. The remarkable facilities which it is altogether probable are furnished by the Niger for direct water communication with the most populous regions of central Africa, render it by far the most important river of the western coast. Precisely where it rises is unknown, but the Bam-barra country, among the Kong mountains in Senegambia, about 1,300 ft. above the sea, has been fixed upon as the most probable locality. Its course from its source to the gulf of Guinea is very tortuous, traversing some 15 degrees of longitude, and an estimated distance of 2,500 m., and making a great bend to the north in the vicinity of Timbuctoo. It is variously known as the Niger, the Quorra, and the Joliba. The river Tchadda, from the heart of Soodan, is the largest tributary; below its embouchure the Niger expands to a great width, the distance from bank to bank sometimes exceeding 6 m. The delta through the innumerable streams of which its waters flow into the bights of Benin and Biafra, is equally famous for its luxuriant vegetation and its deadly climate.

Rising like the Niger in Senegambia, but draining the western declivity of the watershed of that country, the Rio Grande, the Gambia, and the Senegal find their way to the Atlantic through a wall of coast mountains which forms an obstacle to extended inland navigation on these rivers. The Senegal is the largest, and is more than 800 m. in length. Of all African rivers, however, the Nile is at once the most famous and the most wonderful. It is remarkable physically for the unfailing inundation by which a rainless country is annually fertilized; it is remarkable politically for the early and elaborate civilization which has left imperishable monuments along its valley; and it is remarkable geographically for its vast length, which probably exceeds that of any other river, and for the problem concerning its sources, which remained unsolved until the third quarter of the 19th century. The explorations of Baker have fixed the great Albert lake, which lies directly under the equator, as a proximate source, at least; whether a more remote origin exists can only be determined by future geographical research.