862 NORTH-WEST AFRICA. A similar glacial origin is attributed to the undulations on the great plateaux stretching east of the Atlas along the axis of the orographic system in the province of Oran. A portion of this plateau is filled by the shott or sebkha of Tigri, which is strewn with a reddish argillaceous* deposit. This shott does not form a single basin, but is divided into several secondary depressions standing at different levels between the altitudes of 3,700 and 3,800 feet. The greatest contrast is presented by the two slopes of the Avlas. The declivity exposed to the moist clouds of the Atlantic is covered here and there with verdure, and in some places, especially towards its northern extremity, clothed with magnificent forests. But the opposite side, facing the desert, is both much steeper and more arid, presenting the aspect of bare rocky surfaces burnt by the parching winds coming up from the sands. Yet the southern escarpments are almost evervwhere protected from these winds by a lower parallel chain, usually designated by the name of the Little Atlas, or Anti- Atlas. The Little Atlas and Bani Ranges. In its western section, south of the Wed Sus, the Anti-Atlas, seen by Ball and Hooker from the summit of the Jebel Tiza, seemed to have an elevation of about 10,000 feet. But Rohlfs, who crossed it on his journey from Tarudant to Tafilelt, gives it a mean altitude of not more than 5,000 feet, or about half that of the Great Atlas. Towards the east it is known to the natives by the name of the Jebel Shagherun. A broad and apparently perfectly level zone separates the Little Atlas from another ridge running parallel with the main axis of the system. The Bani, as this ridge is called, rises little more than 500 or 600 feet above the surrounding plains, with a thickness of about a mile from base to base. The Bani. which is destitute of lateral chains or spurs, is said to begin near Tamagurt, on the Draa, and to run north of that river almost in a straight line for a distance of nearly 360 miles to the Atlantic. It is pierced at intervals by khenegs, or defiles, usually very narrow, above which five or six streams converge in a single channel, through which the waters of the Little Atlas find their way to the Draa. One of these khenegs is regarded by the Berbers as the cradle of their race, and here they assemble every year to offer sacrifices, followed by feasts and dancing. Throughout its entire course the bare rocky mass of the Bani range consists of a sandstone, charred in appearance, and covered with a bright black incrustation. This sandstone is probably of Devonian origin, like the blackish sandstones of the Central Sahara, and like them it is sometimes polished, sometimes striated or grooved, effects due to the incessant action of the sands. Between the Bani and the Draa Valley occur here and there certain rocky protuberances, to which the natives give the name of " snakes," from their serpentine appearance when seen from a distance. Like the Bani, they are all disposed in the normal direction of the Atlas systjpm, from south-west to north-e^st.
