Page:Africa by Élisée Reclus, Volume 2.djvu/39





THE AUJILA OASES.

ROM the crest of the Jebel Akhdar the land falls southwards, not ina gradual slope, but rather through a succession of terraces, or terraced plains intersected by wadies, whose beds were excavated by the running waters at a time when the climate was more humid than at present. But besides the traces of ancient rivers, here may also be seen those of a marine inlet, which may be regarded as the natural limit of the land of Barka in the direction of the Libyan desert. West of the Siwah and Faredgha oases, both studded with "bitter lakes," which were also old arms of the sea, the valley probably still continues at a lower level than that of the Mediterranean. The ground is here covered by myriads of shells of the oyster, I I wikt:pecten|pecten I I, urchin, and other marine fossils. The old level of the plain eroded by the waters is here and there indicated by isolated eminences surrounded by sand.

This depression, known to the Arabs by the name of Gerdoba, is interrupted by the high dunes of Rhat. But if the preliminary measurements taken by Rohlfs and his associates can be trusted, it begins again farther west under the form of a winding wady, which is connected with the oases of Jalo and Aujila. The level of these depressions varies, according to Rohlfs, from 100 to 170 feet below the sea. East of the group of onses the broadest valley, known specially as the "wady," presents a general direction from south to north and north-west, probably merging in the Bir Rassam, another marine bed, which Rohlfs found to be from 330 to 350 feet below the Great Syrtis. Here the ground is abundantly strewn with fossil plants, especially palms and the mastic, forming extensive "petrified forests" like those of Egypt.

At the point where the Bir Rassam depression was crossed by the German traveller, it turns north-westwards, probably to form a junction near its old mouth with the Wady Fareg, another dried-up basin which, according to the Arabs, is a five days' journey long. Its mouth, now closed by dunes or, perhaps, rocky hills, is indicated by the Ain Kebrit, a place nearly 120 miles south of Benghazi. The Wady Fareg is usually regarded as the line of demarcation between the habitable lands and the desert. Travellers for the first time ascending the southern escarpment are expected to treat their companions to the "feast of