SAHARA, SAHRA, or the Great Desert, is a country of immense extent, which occupies the central parts of Northern Africa. Its western extremity is washed by the Atlantic, along which it exteuds from Cape Nun, 28° 46' N. lat., to the mouth of the river Senegal, 17° N. lat. From the shores of the Atlantic it extends eastward nearly across the continent of Africa, being separated from the Red Sea only by the valley of the Nile and the rocky country which lies between that river and the Red Sea. The valley of the Nile constitutes the eastern boundary of the Sahara. The western edge of that valley occurs between 30° and 32° E. long., and as the African shore along the western boundary of the Desert is between 11° and 17° W. loug., the Sahara extends from east to west, on an average, through 44 degrees of longitude, or about 2000 miles. The northern and southern bound aries are very imperfectly known. The Atlas constitutes the northeru boundary of the Sahara from Cape Nun on the west to 10° E. long. on the east. From this meridian as far east as the valley of the Nile (30° E. long.), a stony and broken country extends between the Sahara and the Mediterranean, comprehending the countries belonging to Tripoli, including Barca and the stony desert which lies between Berea and Egypt. This rocky region terminates in the desert near 20° E. long., and on the east of it the Sahara appears to extend to the shores of the Mediterranean. This northern branch of the Sahara has pro bably an average width of about 100 miles. On the shores of the Gulf of Sidra in the Mediterranean it occupies the space between Geria and liaen-Agan.
The southern boundary of the Sahara is best known towards the Atlantic, where it extends to the vicinity of the Senegal River, and between 15' and 4° W. long. approaches the parallel of 15° N. lat. Farther east the ri ver Joliba, or Quorm [Nra Ea], constitutes the dividing line between the Desert and Soodan as fares the meridian of Greenwich, so that Soodan advances to 17' N. lat., near Timbuctoo. Between that place and the Lake Tailed the boundary line probably lies near 14° N. lat., and this parallel may also be considered as dividing the Sahara from Eastern Soodan as far as the frontier of Dar-Fur, near 23° E. long. Farther east it lies between 16° and 17° N. We may therefore suppose that on an average the Sahara extends from north to south over 14 degrees of latitude, or 960 miles. The area of the Sahara, within these limits, occupies more than 2,500,000 square miles.
The Sahara is a desert, but it is not, as is commonly supposed, covered in Re whole extent by a fine and loose sand. There are tracts of considerable extent, the surface of which is covered with a thick layer of fine and loose sand, and with low sandy hills ; but it would seem that the greater part of this immense country consists of a firm soil, in many parts composed of indurated sand, in others of sand stone. The surface of other tracts consists of rocks, especially granite,
frequently mixed with quartz. A very few tracts of small extent are found covered with bushes and coarse grass. This general sterility is chiefly owing to the dryness of the atmosphere. The Sahara is situated in that part of the globe which separates the region of the winter rains from those of the summer rains, and it does not participate in either of them. In the greatest part of this extensive region a drop of rain never falls to refresh the arid soil ; and in those districts which approach the countries which have abundant rains, only a few showers occur in August and September, and even these not every year. This want of rain renders the whole region unfit for any kind of cultivation, but not uninhabitable, as the lower depressions contain a few wells, in the vicinity of which the soil is covered with grass and hushes, that afford pasture to camels, goats, and sheep. These animals supply subsistence to the nomadic tribes, who wander about in this boundless waste. Travellers who cross this region are exposed to many dangers, both from the nature of the country and from the character of Its inhabit ants. Though the camels occasionally find some shrubs or grass to satisfy their hunger, no provisions can be got along the whole route, which exceeds 1000 miles in length. The traveller must carry every thing with him. The wells of drinkable water occur only at a distance of ten days' journey from one another, and sometimes the distance is still greater. The traveller in the desert must therefore provide him self with as much water as is required for his consumption until ho reaches the next well; and if the season is drier and hotter than usual, the well is dried up, and he runs imminent risk of perishing of thirst. If he loses his way in the wilderness certain death awaits him from hunger and thirst. In those tracts which are covered with fine loose sand the whirlwind. often blow with great force, and raise a large portion of the sand to a considerable height, and deposit it again at some distance. Such pillars of sand have buried many cafiles. The inhabitants of the desert lead a wandering life, and, like all no madic tribes, are always ready to attack the traveller, to deprive him of his goody and to reduce him to slavery. In spite of all these dangers the Sahara is annually traversed by sevetal milling, which carry on the commerce between Soodau and the countries on the shores of the Mediterranean.