474 NORTH-WEST AFRICA. line between Cape Berbas and Cape Blanc. The coast itself is here formed of slightly elevated cliffs, also containing many fossil shells belonging for the most part to species which still survive in the surrounding waters. North of Adrar Settuf stretch the vast plains of Tiris, forming a kind of granite floor pierced here and there by sharp rocks, " which serve as observatories for men and moufflons." The sand which is formed by the decomposition of the granite supports an aromatic vegetation affording excellent pasturage for camels. Rivers of the Western Sahara. The neighbourhood of the sea and of the zone of regular tropical rains secures for the Western Sahara a sufficient quantity of water to prevent this region from being entirely destitute, if not of a fully developed hydrographic system, at least of some intermittent streams and watercourses. South of the Wed Draa, which receives a considerable number of lateral affluents, another torrent drains in the direction of the Atlantic, terminating in a large mouth between the cliffs, which has been named the Boca Grande by the fishermen from the Canary Islands frequenting this coast. This is the Wed Shibica of the Arabs, and here probably stood the ancient Spanish settlement of Santa-Cruz de Mar-Pequeiia. At this point Mackenzie proposed to begin cutting the canal which was to convey the Atlantic Ocean across the intermediate waterparting into the imaginary depression of the Juf, and thus flood the Sahara. About 180 or 200 miles from the sea there certainly exists a watershed running parallel with the coast, whence the rain waters flow in one direction through independent channels seawards, in the other descend towards the south-east. In this direction they disappear beneath the Iguidi dunes, beyond which they again come to the surface in the form of springs and little gucltas, that is to say, small meres and saline basins. South of the Boca Grande, the only river valley of any great extent is the Sakiet-el-Homra, or " Red Watercourse," which has sometimes been designated as the official limit of Marocco, although really lying some 300 miles beyond the true frontier of the empire. The Adrar heights themselves also possess an independent hydrographic system, although certainly of very limited extent. The chain of hills skirting the east side of this group of eminences sends down supplies sufficient to feed two rivers, both of which flow in the direction from north-east to south-west, that is, parallel with the main axis of Adrar. The northern stream comes to an end in a depression where its waters spread out and evaporate ; yet it seems to be continued by the southern stream, both having their origin in the same valley. This watercourse, on whose banks are concentrated nearly all the inhabitants of Adrar, escapes from the region of highlands, ultimately losing itself in a marsh lying farther south in the desert. The Atlantic Seaboard. The coast, which is broken at intervals to admit a passage for the inland streams between its cliffs and dunes, is one of the most dangerous in the whole of
