CHAPTER XII.
WESTERN SAHARA.
EST of the transverse depression which extends from the southern limits of the province of Oran southwards to the Niger, and which throughout its entire length is probably occupied by the dried-up bed of the Messaura, the Suhara nowhere presents any prominent mountain ranges constituting a distinct physical region. Throughout its whole extent this vast tract, comprising a superficial area of over 800,000 square miles, presents nothing but an everlasting succession of dunes, depressions, slightly elevated hamadas, rocky ridges or low ranges scarcely anywhere exceeding 1,600 feet above sea-level. To the whole of this western section of the Sahara, which nevertheless has a breadth of over 600 miles, the inhabitants of the Wed Saura basin apply the general designation of Sahel, or "coastland," as if it were a mere inland extension of Atlantic seaboard.
The northern division of this Saharian region is mainly occupied with low plateaux or level tracts and dunes, the hills forming unimportant groups, lost, as it were, like islets in the midst of a boundless sea of sands. South of the Wed Draa the caravan routes running in the direction of Timbuktu at first traverse nothing but hamadas with a mean elevation of from 1,250 to 1,300 feet, and separated from each other by river gorges, all inclined towards the west. The surface of the plateaux consists almost everywhere of paleozoic formations underlying more recent rocks, which by erosion have been cut up into the appearance of towers, crenellated walls, and other fantastic forms. Some of the serirs are paved, as it were, with a mosaic floor consisting of myriads of little quartz, agate, opal, and chalcedony pebbles.
The Iguidi Dunes — Juf — Adrar.
South of these plateaux stretches, like a marine inlet, the great erg of Iguidi, which is disposed in the direction of the Atlas range, that is, from south-west to north-east, and which begins in sight of Twat, on the left side of the Wed Saura basin. At the point where the traveller, Lenz, crossed the chain of dunes east of the famous Bel-Abbas well, the general movement of the sands lies in the direction from north-west to south-east. Such, at least, appears to be the trend, judging the Atlas range, that is, from south-west to south-east. Such at least appears to be the trend judging
