Page:Africa by Élisée Reclus, Volume 2.djvu/55

 pyramid of propitiation raised from century to century by successive generations of travellers.

Herbage, brushwood, and living things are rare in this desolate waste, which is avoided by the very birds, that fear to wing their way across solitudes more formidable than the seas themselves. Nevertheless camels find here and there a little nourishment in the scanty vegetation offered by a few depressions along the track across the plateau. Barth even came upon some stunted palms in one of these hollows, where the water collected after the rare storms soon evaporates leaving nothing in its place except a thin saline efflorescence. In many places channels have been formed by the wadies, although the running waters have not been sufficiently copious to excavate a complete river bed in the rock, so that beyond the last basin of erosion the depression is again closed.

The plateau is on the whole remarkably level and uniform, free alike from stones and sand. In altitude it varies scarcely more than 100 feet, from 1,500 to 1,650, the highest point along the route followed by Barth being 1,700 feet, and indicated at a distance by a heap of stones. At first sight the surface of the ground might seem to be formed of basaltic slabs, so black and parched is its appearance. But it really consists of sandstone layers overlain with clay and gypsum, and still more frequently with marls, limestone, and silicious strata, in which numerous fossil shells have been collected.

Southwards the ground falls through a succession of terraces and cliffs scored with deep ravines. The limit of the northern desert is marked by the copious Hassi wells and other springs, which ooze up from a depth of 7G0 feet below the plateau. South of this point begins the region of oases inhabited by the Hamatic (Berber) communities. The observer asks in amazement how the Roman armies, possessing no camels like the caravans of our days, were able to traverse the Red Hamdda, as stated by the old writers, and as attested by the richly sculptured tombs occurring at intervals along the line of march, and especially on the crests or summits commanding extensive views of the country. Some of these sepulchral monuments, the sânem of the Arabs, are graceful little shrines, whose correct style shows that the architects and sculptors of these remote regions scarcely yielded in artistic taste to those of the mother country.

In modern times the direct route over the hamâda was first explored by Barth, Overweg, and Richardson, other European travellers having followed the more easterly road across the Jebel-es- Soda. There can be little doubt that during the last two thousand years the whole region has gradually become drier, and thus would be explained the relatively easier access to the interior formerly afforded by the western route, præter caput saxi, "by the head of the rock." North-eastwards the Red Plateau, furrowed by numerous wadies, is broken into narrow promontories, which are again cut up into secondary headlands. Some of these segments of the great rocky tableland have even been completely detached from the hani&da, thus forming small distinct ridges limited on either side by watercourses. Such are the Kaf Mugelad, the Jebel Ehadamia, and the Jebel