Having here allowed our camels a little feeding, we entered upon gravelly soil with projecting blocks of granite, and then went on ascending through a succession of small plains and valleys, till we reached Erazar-n-Gébi, among the splendid vegetation of which we first observed the abísga, or _Capparis sodata_, called siwák or lirák by the Arabs, an important bush, the currant-like fruit of which is not only eaten fresh, but also dried, and laid up in store, while the root affords that excellent remedy for the teeth which the Mohammedans, in imitation of their prophet, use to a great extent. The root, moreover, at least on the shores of the Tsád, by the process of burning, affords a substitute for salt. It is the most characteristic bush or tree of the whole region of transition between the desert and the fertile regions of Central Africa, between the twentieth and the fifteenth degree of northern latitude; and in the course of my travels I saw it nowhere of such size as on the northern bank of the Isa or Niger, between Timbúktu and Gágho, the whole ground which this once splendid and rich capital of the Songhay Empire occupied being at present covered and marked out by this celebrated bush. As for the camels, they like very well to feed for a short time upon its fresh leaves, if they have some other herb to mix with it; but eaten alone it soon becomes too bitter for them. In this valley the little berries were not yet ripe; but further on they were ripening, and afforded a slight but refreshing addition to our food. Leaving the pleasant valley of Gébi by a small opening bordered with large blocks of granite, while peaks of considerable elevation were seen towering over the nearer cliffs, we entered another large valley, called Tághajít, but not quite so rich in vegetation, and encamped here, on an open space, a little after noon. The valley is important as being the first in the frontier region of Aïr or Asben where there is a fixed settlement—a small village of leathern tents, inhabited by people of the tribe of Fade-ang, who preserve a certain independence of the Kél-owí, while they acknowledge the supremacy of the Sultan of Ágades, a state of things of which I shall have occasion to say more in another place. CHAPTER XIII. INHABITED BUT DANGEROUS FRONTIER REGION.