It was three o’clock when we arrived at the Marárraba[91], the “half- way” between Ghát and Aïr, a place regarded with a kind of religious awe by the natives, who in passing place each a stone upon the mighty granite blocks which mark the spot. To our left we had irregular rocky ground, with a few elevations rising to greater height, and ahead a very remarkable granite crest, sometimes rising, at others descending, with its slopes enveloped in sand up to the very top. This ridge, which is called Giféngwetáng, and which looks very much like an artificial wall erected between the dry desert and the more favoured region of the tropics, we crossed further on through an opening like a saddle, and among sand-hills where the slaves of our companions ran about to pick up and collect the few tufts of herbage that were scattered over the surface, in order to furnish a fresh mouthful to the poor wearied animals. At four o’clock the sand-hills ceased, and were succeeded by a wide pebbly plain, on which, after six miles travelling, we encamped. Our encampment was by no means a quiet one; and to any one who paid due attention to the character and disposition of the people, serious indications of a storm, which was gathering over us, became visible. Mohammed Bóro, who had so often given vent to his feelings of revenge for the neglect with which he had been treated, was all fire and fury; and stirring up the whole encampment, he summoned all the people to a council, having, as he said, received intelligence that a large party of Hogár was coming to Asïu. Not having paid much attention to the report about Sídi Jáfel’s expedition, I became anxious when made aware of the man’s fury; for I knew the motives which actuated him. [Sidenote: Friday, August 16th.] We started early. Gravelly and pebbly grounds succeeded each other, the principal formation being granite; but when, after a march of about thirteen miles, we passed the narrow sandy spur of a considerable ridge approaching our left, a fine species of white marble became visible. We then passed a rugged district, of peculiar and desolate appearance, called Ibéllakang, and crossed a ridge of gneiss covered with gravel. Here, while a thunder-storm was rising in the east, our caravan, to our great regret, divided, the Tinýlkum turning off towards the east, in order, as we were told, to look for a little herbage among the sand- hills. Meanwhile thick, heavy clouds, which had been discharging a great quantity of rain towards the east, broke over us at a quarter past four o’clock in the afternoon, when we were just in the act of crossing another rocky crest covered with gravel. A violent sand-storm, followed by heavy rain, which was driven along by a furious gale, soon threw the caravan into the utmost confusion, and made all observation impossible; but fortunately it did not last long.