(B) AFRICA - GEOGRAPHY (cont'd)
(b) The Northern Lower Land of Africa. The Sahara.
The Sahara has often been pictured as a monotonous and immense expanse of sand; but nothing could be more erroneous, as the greatest variety exists in the physical configuration of its surface, as well as in its geological features. Our knowledge is as yet too scanty to enable us to trace its features in every part. On the north, this great desert is fringed with extensive table-lands, which in some places rise abruptly from the Mediterranean, as the great plateau of Barbary, extending through Marocco, Algeria, and Tunis, and the table-land of Barca, elevated 1500 feet, and gradually descending towards the Delta of the Nile. This elevated ground is succeeded to the south by a depressed region, which extends from the Great Syrtis or Gulf of Sidra, in a general direction as far as Middle Egypt, and comprises the oases of Augila and Siwah. So greatly depressed in this region, that the level of the oasis of Siwah is 100 feet, and in one place (Bajrein) even 167 feet below the level of the sea, the western portions of this country, between the oases of Augila and Siwah, explored in 1869 by the traveller Rohlfs, were found to be everwhere from 100 to 150 feet beneath the level of the Mediterranean; and De Lesseps, in conducting a survey from the Egyptian side, found the eastern part to be much beneath the level of the Nile. Here then must be one of the greatest areas of depression in the land of the globe, comparable with that which surrounds the Caspian Sea. This depressed region is again followed by a table-land of considerable extent and width, extending from the Gulf of Kabes in a southerly direction, along the Tripoline shores, and probably traversing, in the same direction, the Libyan Desert, and reaching as far as the Nile, near the first cataract. Its north-western part, as far as Sokna, consists of the Hamadah, a stony, dreary, and extensive table-land, of froms 1500 to 2000 feet high, "which seems to be like a broad belt intercepting the progress of commerce, civilization, and conquest, from the shores of the Mediterranean to Central Africa." Near Sokna this plateau breaks up and forms what are called the Jebel-es-Soda, or Black Mountains, a most picturesque group of cliffs; and again, on the route from Murzuk to Egypt, it also breaks into huge cliffs, and bears the name of El-Harouj. The whole of the central portion of the Northern Sahara, as far south as the plateau of Air or Asben, is occupied by similar bare table-lands, with lower areas of sand dunes between. Numerous wadys, the only inhabited parts of the country, intersect the slopes of these plateaux. The country of Ahaggar, between 23° and 29° B. lat., and 5° E. long., appears to from the central elevation from which the greater of these dry water-courses radiate; from it a series of long wadys-one of them, the wady Rharis or Igharghar, being about 600, miles in length-run northward towards a depressed country which lies inland from the Gulf of Cabes, and contains several salt lagoons, covered with a few feet of water in winter, but dried up in summer, and lying considerably below the Mediterranean level. Other wadys radiate west and south-west from Ahaggar to the unknown region of the Sahara, which lies between this and the northern bend of the Niger. The most truly desert region of the Sahara is an irregular belt of shifting sand dunes, the "Erg" or "Areg," which stretches from the lagoons above referred to near the Mediterranean coast south-westward to near the river Senegal and the atlantic, in an unbroken chain for upwards of 2000 miles, and having an average width of perhaps 200 miles. In this sand belt the wadys of the inward slope of the plateau of Barbary terminate, excepting the Wady saura, which crosses the Erg to the important oasis of Tuat, near the centre of its southern border, and the Wady Draa, turns to the Atlantic coast. From Wady Draa a great plain extends along the western shore as far as the river Senegal, and probably continues as such to the east towards Timbuktu, and thence to Lake Chad. Thus it appears that the western half of the Sahara is surrounded by a broad belt of pains and depressions, the central parts being formed by extensive table-lands, with occasional mountain knots, such as that which forms the fertile kingdom of Air and Asben, the culminating points of which are from 4000 to 5000 feet high.
The eastern portion of the Sahara appears to have nearly the same general elevation as the western half, and near its centre several fertile mountain regions, comparable with that of Asben, are known. Such is the mountainous country of Borgu, north-east of the kingdoms which surround Lake Chad, and Tibesti, north of it, in the centre of the Tibbu district, recently explored by Dr Nachtigal, who found rich vegetation and abundant animal life in the valleys of this mountain group.
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Africa - Table of Contents