passing northward into desert. At the head of the Gulf of Guinea are the Kamerun Mountains, more than 13,000 feet high. Further westward along the coast of Upper Guinea there are mountains, but of no great height, the supposed “Kong Range” of old geographies having been proved non-existent. The highest peaks of the hinterland of Sierra Leone and the Mandingo Mountains do not exceed 3,500 feet, except in the Peak of Komono (4600 feet). The coast of Senegal is flat; that more southerly, except in Liberia, swampy; all the rivers, and especially the Niger, form extensive deltas.
The region of arid waste lands called the Sahara lies between the Sudan on the south and the Atlas Mountains and the Egyptian coast on the north. It is a part of an arid belt extending eastward to Baluchistan, the entire area measuring about 4,000,000 square miles. Of this area at least two-thirds lies west of Suez, and is known in general as the Sahara. It is all an elevated plain, into which many valleys have been eroded by the ancient drainage systems which are now the only marked topographical features of the region. The whole area may, therefore, be divided into certain regions, limited by natural features. First, the so-called Arabian or Nubian Desert; the area between the Nile, the only living river that crosses the arid zone, and the Red Sea. This is marked in its southern portion by the continuation of the volcanic uplands of Abyssinia, which lessen in height toward the north, but border the Red Sea in a line of jagged mountains, many of which exceed 4000 feet, and one, Soturba, reaches 6900 feet. In the south is the great rift of the Wady Mahall, probably an ancient Nile channel; and in Lower Egypt are the rifts occupied by the Khargeh, Dakhel, and others, forming a line of notable oases. West of the Nile rises the desolate plateau of the Libyan Desert, which covers the whole region from central Darfur to the Mediterranean (long. 18° to 30° E.), excepting the few oases above mentioned. Its general altitude varies from about 1500 feet in the south to 500 on the Mediterranean, where it breaks down in hills. A line of elevations extending northwestward from the Marra Mountains in Darfur to the Algerian Atlas forms a sort of boundary to the Libyan Desert, and makes possible the thinly inhabited oasis regions of Tibesti and Murzuk. Further west there are wadies, or dried-up river valleys, of which one, with numerous branches, is traceable from the Tropic of Cancer north to the “shotts” or swampy lakes which occupy the large, low plain (in places below sea-level) west of the Gulf of Cabes. It is believed that within 2500 years this valley was occupied by a flowing river, but now only a few pools and springs exist through the dry season. West of this more broken region between Algeria and Lake Chad there stretches an enormous space of waterless waste land, with shifting sand dunes, broken by lines of rugged and naked elevations having a general northeast and southwest direction. This waste extends to the Atlantic coast all the way from about lat. 18° to 28° N., that is, from the hills of Senegal to the western extremity of the Atlas. The elevation of the Sahara throughout the greater part of its extent exceeds 1000 feet, diminishing gradually from the south toward the north in the Libyan Desert, and from its centre in the western half of the desert toward the Lake Chad Basin and the Niger, and toward the coast of Tunis and Tripoli. Only very small and irregular areas along the northern border are below the level of the Mediterranean.
The elevated district called the Atlas Region, with its littoral margin along the Atlantic Ocean and Mediterranean Sea, is a part of the great Alpine system of Europe, to which it is linked by the mountains of Spain and the Pyrenees. Unlike other African mountains, the Atlas have a folded structure and an Alpine character, and present many parallel zones. These ranges extend in a nearly straight line from Cape Nun, on the Atlantic, northeast to the headlands of Tunis, where they are broken through by the narrows of the Mediterranean. Along the Mediterranean coast the elevations are volcanic, and descend very abruptly. Toward the interior, irregular ranges form a long line of heights of Paleozoic rocks, which is sometimes called the Tell Atlas; but this is more prominent in Algeria than in Morocco, where the seaward side is a rough plateau. The Atlas stretches over a distance of about 1400 miles, and attains its greatest elevation in the western portion, where it rises to a height of nearly 15,000 feet.
Geology. The geological structure of Africa has been studied only in bare outline, but its broad features may be said to exhibit great simplicity and uniformity. The entire lower limb, with the Sudan and the western portion of the Sahara Desert, has a basal complex of crystalline rocks supporting sediments of Paleozoic and Mesozoic age. Strata of more recent deposition, with but one exception (Lower Egypt), occur only along the sea coast and the rivers. The greater part of the land surface, therefore, was formed in early geological times, and has remained above sea-level during succeeding periods. Owing to this uniformity, Africa cannot be divided upon a strictly geological basis into more or less distinct units; such a division, however, has been made from a combined geological and geographical standpoint, separating the entire area into three provinces. The first of these comprises South Africa, Madagascar, and a huge portion of Central Africa, which at one time was united with lower India by an easterly land extension through the area now occupied by the Indian Ocean; the second includes the Sahara Desert and Egypt, and is a continuation of Arabia and Syria; the third comprises the Atlas Mountains, and is really a part of the Eurasian continent and of the great system of upheaval that is represented in Europe by the Alps and the Apennines.
The most ancient rocks found in South Africa are granites, gneisses, and schists, which lie below all fossil-bearing rocks, and may, therefore, be classed as Archæan. Above these are tilted and eroded beds of sandstones and slates, which form the rampart along the southern extremities of Cape Colony, and extend around to the west and north, spreading out over large areas in Namaqualand, Griqualand, Rhodesia, and regions to the north, and which have special economical importance, as they include within their limits the rich gold deposits of the Transvaal. These rocks are mostly of Paleozoic age. Higher up in the series are the Kimberley shales and the Karoo formation of sandstones and slates, which attain great development in British South Africa. No remains of a sea fauna have been found in the Karoo beds, but they are rich in ampliihian and reptilian fossils that bear a striking simi-
