basins. Westwards rise the volcanic heights of Tasili, at whose foot winds the Aghelåd, or "Passage," followed by the main caravan route from Rhât to Ghadames, and continued northwards by the Wadies Titerhsîn and Ighargharen, the latter a tributary of the Igharghar. To the east stands the almost inaccessible schist and sandstone Akakus range, which in a whole generation has scarcely been Fig. 25. — Rhât.
scaled by more than two or three venturesome Tuareg mountaineers. At its northern extremity this rugged chain is skirted by the path leading to Fezzan, which through the arid Tanezzuft valley reaches the Murzuk plateuu by the Rhallé pass and the stony Taita wastes.
Southwards the Rhât valley rises gradually in the direction of a hill about 4,000 feet high, which marks the northern verge of the Sahara. Here, amid huge blocks and pillars of sandstone, and within sight of granitic domes and pyramids, ends the long narrow defile, where the traders have established their chief depôt between Ghadames and the Sudan. Barth, who has named this section of the waterparting the "Adzjar Uplands," identifies them with the Jebel Tantana of mediæval Arab writers.
Rhất stands on a slight eminence at the north-west foot of a rocky hill. Within the ramparts it is almost geometrically divided into six quarters by streets terminating at as many gates. The houses are in the same style, but generally smaller and less numerous, than those of Ghadames. Within the enclosures the population scarcely exceeds four thousand; but outside are a number of villages, and in the intervening space is held the annual fair, on which the prosperity of the plain largely depends. The surrounding plain is here and there dotted over with clumps of palms and other trees; but the oasis nowhere presents the continuous stretches of verdure seen at Ghadames. Yet it would be easy to extend the area of culti-
