38 NOETH-WEST AFRICA. The Black Mountains, the highest range in south Tripolitana, follow the normal direction from east to west, while describing a slight curve with its convex side facing northwards. It is divided into two sections of different aspect by a broad breach, or as Duveyrier describes it, "a continuous series of ravines," traver8e<l by the caravan route between Murzuk and the Jofra oasis. The very names given to each of these sections of the range — Soda Sherkiyah and Soda Gharbiyah — indicate their respective positions east and west of this commercial highway. The Soda Sherkiyah, or " Eastern Soda," stands at but a slight elevation above the limestone plateau ; whereas the " Western Soda " attains considerable altitudes, the Kalb-Warkau, onn of its summits, having a height of 3,000 feet, according to some authorities. At its western extremity, where it merges in the great stony hamada known as the Hamada-el-IIomra, or *' Red Plateau," the Xaber-ol- Jrug, another of its peaks, is even said to be 4,330 feet high. According to Rohlfs, who, however, was unable to take any accurate measurements in the Jebel-es-Soda, there are also in the eastern section of the system other crests reaching an altitude of 5,000 feet. The statement of Ilornomann, that the Jebel-es-Soda is to a large extent of volcanic origin, has been fully confirmed by Duveyrier, who has brought back fragments of a basaltic lava, which the geologist Descloizeaux regards as coming very probably from an ancient submarine eruption. Various spurs branch off northwards from the main range, sinking gradually down to the low-lying coastlands. Several other projections have also become completely isolated from the rest of the s^'stem. Such, for instance, are those running towards the Jofra oasis, where they rise from 650 to 880 feet above the wady, which has itself a mean elevation of about 650 feet above the sea. The liokhmani, one of these isolated groups, is clothed with palm groves half way up its sides. North of the oasis the plain is dominated by the Jebel-Tar, a mountain mass completely distinct from the Soda range, and consisting of tertiary formations which contain thick fossiliferous beds. But its moderate elevation, not exceeding 1,330 feet, is not sufficient to arrest the moisture-bearing clouds, so that on the slopes of the Jebel-Tar nothing is found except springs of bitter water. In memory of the explorer Nachtigal, who has done such excellent work in the Sahara and Sudan, his friend Rohlfs has given to the culminating point of the Tar system the appellation of Jebel Bulbul, or " Mount Niglitingale " (Nachtigal). West and north-west of the Jebel-es-Soda stretches the interminable " Red riuteau," whose superficial area is estimated at some 40,000 square miles. From north to south, where it was traversed by Barth in 1850, between Tripoli and Muzurk, it is over 120 miles long, while extending through the Tinghert plateau for 420 miles east and west to the south of the Ghadames oases and of the region of Algerian dunes. This namada-el-TIomra is of all the African •' hamadas" the hamada in a superlative sense — the " burnt" region which, owing to the absence of water, is most dreaded by caravans. On the edge of the cliff leading to it, each wayfarer religiously casts a stone on the busajfar, or " father of the journey," a <;airn or
