106 NORTH- WEST AFRICA. South of the central Tunisian plateaux the uplands diminish in height, and are interrupted by broad valleys, and limited eastwards by e^xtensive plains, where have been collected the brackish waters of the sebkhas. But beyond these depressions the Sahel, or "seaboard," which advances in a semicircle seawards between the Gulfs of Hammamat and Cabes, merges in a rugged plateau which is terminated by vast plains and sharp headlands. West of the sebkhas, southern Tunis preserves its hilly aspect, mountains here following continuously as far as the great depression of the shotts which forms the natural boundary between Mauritania and the Sahara. Nearly all these ridges are disposed normally from south-west to north-east, in the same direction as the section of the coast of the Lesser Syrtis lying between Cabes and Sfakes. Here rises the remarkable Jebel-bu-Hodma, commanding the saline waters of the Manzuna or En-Nuail scbkha, north-west of the Gulf of Cabes. Its peaks, over 4,300 feet high, rise majestically above a broad region of arid steppes, and in its gorges are still visible the galleries of the old Eoman mines, where auriferous ore has been discovered by Fuchs. Farther west, in the neighbourhood of Gafsa, stands the Jebel Arbet, from whose summit (3,660 feet) a panoramic view is afforded of the surrounding plains, high- lands, seas, oases, and sandy wastes. These uplands are limited southwards by an abrupt ravine, through which will run the future railway from Constantino to Cabes. But beyond this gorge the plateau again develops a series of terraces gradually falling towards the Faraun sebkha. South of the low-lying region of the sebkhas are seen a few hills, the advanced spurs of the range which is continued south-eastwards through the Metmata and Urgharama highlands in the direction of the Jebels Nefuza and Yefren belonging to the Tripolitan system. From the summit of the narrow Urghamma crests are at once visible the Mediterranean and the great desert. They are separated by steppelands from the dunes and rocky heights of the seaboard. IIydrographic System. The Tunisian hydrographic system is readily explained by the relief of the land. Along the " ironbound coast " stretching from Cape Roux to the Ras-el- Abiod there is no space for anything beyond small torrents descending from the neighbouring hills ; but farther east, notwithstanding the slight local rainfall, rivers of considerable size have been developed, thanks to the broad depressions here occurring between the ranges and on the plateaux of Mauritania. Notwithstanding its Wed-el-Kebir, or " Great River," better known under the name of the Wed Ahmor, the northern slope of Tunisia does not boast of a single stream exceeding 60 miles in length. The most copious is the Wed-el-Tin, which discharges into the Eshkol or Eskel basin, whose level and salinity vary greatly according to the abundance of the rainfall and evaporation. It has a meatt depth of from 2 to 6 or 7 feet, and the reefs abounding in the fossil carcUum ediile show that it was at one time a salt or brackish reservoir, probably a marine inlet
