176 JOURNEY TO CENTRAL AFRICA.

On the second morning we passed through a gorge in the black hills, and entered a region called El Biban, or " The Gates." Here the mountains, though still grouped in the same disorder, were more open and gave room to plains of sand sev eral miles in length. The narrow openings, through which the road passes from one plain to another, gave rise to the name.

The mountains are higher than on the Nile, and present the most wonderful configurations — towers, fortresses, walls, pyramids, temples in ruin, of an inky blackness near at hand, but tinged of a deep, glowing violet hue in the distance. Towards noon I saw a mirage — a lake in which the broken peaks were reflected with great distinctness. One of the Nubians who was with us, pointed out a spot where he was obliged to climb the rocks, the previous summer, to avoid being drowned. During the heavy tropical rains which sometimes fall here, the hundreds of pyramidal hills pour down such floods that the sand cannot immediately drink them up, and the valleys are turned into lakes. The man described the roaring of the waters, down the clefts of the rocks, as something terrible. In summer the passage of the Desert is much more arduous than in winter, and many men and camels perish. The road was strewn with bones and carcasses, and I frequently counted twenty dead camels within a stone's throw. The stone-heaps which are seen on all the spurs of the hills, as landmarks for caravans, have become useless, since one could find his way by the bones in the sand. My guide, who was a great believer in afrites and devils, said that formerly many persons lost the way and perished from thirst, all of which was the work of evil spirits.

My next camp was in the midst of a high circular plain