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AFRICA 165 reached the snow line, and who describes its lower slopes as covered with forests of gigantic trees, above which are rich growths of heath and pasture. About 200 m. further N. Mt. Kenia also rises into the region of perpetual snow, its altitude being estimated at 17,000 ft. A continuous chain is believed to connect this range with Abyssinia. The Abyssinian system of mountains comprises numerous lofty summits clustered in groups on the elevated plateau which separates the Nile basin from the E. African coast. This table land sinks abruptly to the lowlands on the edge of the Red sea, but descends by much gentler gradations on its W. slope. The dividing ridge of the watershed averages 8,000 ft. in height; on the north it is considerably lower, while it ascends to 11,000 ft. on the south. There are said to be peaks over 15,000 ft. high in the Simen range, and in other parts of the country there are known to be many higher than 12,000 ft. Africa has long been regarded as distinctively and pre- eminently the country of deserts. The Sahara extends over almost all the northern portion of the continent between lat. 15 and 30 N". With an average width of 1,000 m., and an ex- treme length of "3,000 m., it stretches from the Nile to the Atlantic, and from the southern slopes of the Atlas to Soodan, covering an area which exceeds that of the Mediterranean, and with a surface in some places below the level of that sea. The southern limits of this vast land of desolation have never been continuously traced by Europeans, and our knowledge of its track- less wastes is confined to the ancient lines of caravan travel across them. The surface is made up of shifting sand, rough gravel, and barren rock, variously distributed, and occa- sionally traversed by low chains of bare hills. Extensive plains of salt also occur. Through- out this sterile region rain is almost unknown, and the heat is terrific. At the equinoctial seasons the easterly wind, which blows during three fourths of the year, rises at times to a gale, and causes the terrific sand storms by which caravans have so frequently been over- whelmed. The western portion of the Sahara, called Sahel, is the wildest and most desolate ; in the eastern portion, to a part of which the name Libyan desert is applied, are numerous oases. These differ greatly in extent, but all contain springs, rich grass, and date palms. Many of them are depressions below the sur- face of the surrounding desert. Some consist of little more than a well of fresh water, a clump of trees, and a spot of verdure ; others cover many miles of fertile country. The more important are : the Great Oasis, or oasis of Thebes, 120 m. long and about 5 m. wide; the Lesser Oasis, smaller but similar in outline ; the oasis of Darfoor, constituting the monarchy of a sultan; the oasis of Siwah, in which are the ruins of the famous temple of Jupiter Ammon ; and the oasis of Fezzan, with the town of Moorzook as its capital. All of these except the last are situated in a furrow-like depression, parallel to the Nile, intersecting the Libyan desert in its gradual descent toward the Med- iterranean. The dreaded wind known as the simoom is a terrible scourge of the desert and the neighboring countries. It is due to the high temperature, sometimes 200 F., attained by the surface sand of the desert under the in- fluence of the vertical rays of the sun pouring down upon it through an intensely dry atmos- phere. The furnace-like wind to which this gives rise is rendered still more terrible by the particles of burning sand with which it is im- pregnated and which tinge the atmosphere with the reddish hue characteristic of the si- moom. Burkhardt in 1813 recorded 122 F. m the shade during the prevalence of this pes- tilential blast, and 114 was observed in 1861 by Sir Samuel Baker. Many other winds of the same class blow from the desert; among them the parching sirocco, which sweeps from northern Africa over Sicily, southern Italy, and Syria ; the khamsin, which blows in Egypt for 50 days between the end of April and the sum- mer solstice; the harmattan, which prevails at regular intervals between November and February throughout Senegambia and Guinea, coming from the western Sahara; and the withering N. W. wind which occasionally visits Natal and the Cape. The great desert of south- ern Africa is the Kalahari, extending from the Orange river on the south to the 20th parallel of S. latitude, and from the pastoral Narnaqua district on the west to a strip of pasture land which is believed to border the inland slope of the Quatlamba mountains. Its average eleva- tion above the sea level is only 600 ft. Al- though 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 impossi- ble. In 1852, however, Sir Roderick Murchi- son, in an address to the royal geographical so- ciety 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 expe- dition on the Zambesi, and its results triumph- antly 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 riv- ers." S. of the Kalahari desert the Gariep or Orange river is the only considerable stream.