Sahara, the great North African desert, lies between the Barbary States (Morocco, Algeria, Tunis, Tripoli) on the N., the Atlantic on the W., and the Nile Valley on the E. Its limits are approximately lat. 16° and 33° N., and long. 17° W. and 33° E., and its area is estimated at 2,500,000 square miles. The N.E. portion, the Libyan Desert, slopes N. towards the Atlantic. It was formerly supposed that the Sahara was the bed of an ancient sea, that it lay below the sea-level, and that it was composed entirely of tracts of sand, the position of which was constantly changing. Recent explorations, however, have shown that the surface is extremely varied and in most parts more or less elevated, rising at one spot to a height of at least 8,000 feet. On the N. it is enclosed by a semicircular range of parallel sand-dunes, extending from Fezzan to the vicinity of Cape Blanco. The central region, S. of Algeria, consists of a tableland of 4,000 feet, called Ahaggar, with mountains of 6,500 feet, on which the snow lies for three months in the year. Still more lofty are the eastern ranges, the altitude of Mount Tusidde, in the Tibboo region, being 8,000 feet above the sea. The mountains in the W. do not exceed 2,000 feet in height. Along the valleys which abound in the mountainous regions lie the beds of ancient rivers, from which water may be obtained at no great distance from the surface. They thus afford pasturage for cattle, sheep, and camels, and are nearly always inhabited. The parts of the Sahara called "hammada" have a level surface covered with masses of granite and other rocks without vegetation of any kind; else~ where there are wide salt marshes from which the water has evaporated, and large tracts are composed entirely of sand or of small round stones~. The oases (q.v.) often extend in a continuous line right across the desert, as, for example, that from Morocco to Cairo through Tafilet, Tuat, and Ghadames. There is a similar line from Mourzouk, in Fezzan, to Lake Tchad and several others which furnish a means of communication between the Soudanese states and the shores of the Mediterranean. The caravan-trade carried on along these routes consists chiefly in the exchange of ivory, gold-dust, ostrich-feathers, gums, spices, and salt for manufactured articles, jewel1ery, etc. Several schemes have been put forward by the French for constructing a railway from the Mediterranean to the fertile regions of the interior. Their purpose is probably political as well as commercial, for they aim at gaining possession of the vast region between Algeria and Tunis and their colonies on the Senegal and the Niger. The agreement between Great Eritain and France drawn up in 1890 leaves them at liberty. to take possession of these lands so far as this country is concerned. After rising much above 100° F. in the day time, the thermometer often falls to freezing-point, or lower, during the night. In most parts of the Sahara rain falls only at intervals of two, three, four, or even five years. Outside the oases the vegetation consists chiefly of coarse grasses, tamarisks, and thorny trees or shrubs, such as the prickly acacia. The antelope, giraffe, and jackals are among the commonest quadrupeds. The salt and dates obtained in the Sahara form important articles of food. The inhabitants are Berbers - viz, Moors towards the coast and Touaricks (Tuaregs) farther inland, Tibboos, a mixed race of Berbers and Negroes, in the region S. of Tripoli and E. of the Touaricks, pure Negroes, Arabs, and Jews. The trade is mainly in the hands of the Touaricks.