On the 26th of July the caravan again set out. On the 29th they commenced their ascent to the greatest elevation of the desert, four thousand feet above the sea. The path winding along through loose blocks of stone, the precipitous ascent proved very difficult. Several loads were thrown off the camels, and the boat frequently came in contact with the rocks. It is indeed the wildest and most rugged region of the whole desert. At one place the road meandered in a remarkable way, sometimes reduced to a narrow crevice between curiously-terraced buttresses of rocks. Two hours were occupied in descending. At the bottom was a _wady_ between steep, precipitous cliffs looking almost like walls erected by the hand of man. They were more than a thousand feet high, with a pond of rainwater at the bottom. The valley is called Aegeri. They had now to pass a region of sand-hills. During their passage the mirage set before their eyes beautiful sheets of water, which quickly disappeared as they approached. Desolate as the country appears, large herds of wild oxen rove over it. Though the men tried to catch some of them, they were unsuccessful, as the animal, sluggish as it seems, rapidly climbs the rocks and is soon lost to sight. The travellers, having now entered the tropics, expected to reach pleasanter regions than they had hitherto passed through. Their guides, however, were leading them further to the west than they wished, their great desire being to reach Negroland as soon as possible. On the 18th of August they were quietly pursuing their road, when one of their party was seen running up behind them, swinging his musket over his head and crying: "Lads, our enemy has come!" Alarm was spread through the caravan: everyone seized his arms, and those who were riding jumped from their camels. The man reported that a number of Tawarek, mounted on camels, had been seen rapidly approaching, with the evident intention of attacking the caravan. A warlike spirit prevailed, and all, the doctor thought, would fight valiantly. Freebooting parties, however, do not attack openly. They first introduce themselves in a peaceable way, when, having disturbed the little unity which exists in most caravans, they gradually throw off the mask. After some time they came to the conclusion that it was not likely that they would be attacked by daylight. They, therefore, sent off a body of archers to gain information from a small caravan which was coming from Soudan, consisting of a few Tebus, ten camels, and about forty slaves. The unfortunate Tebus were soon afterwards attacked by a fierce tribe, the Haddanara, who, disappointed at getting nothing from the English expedition, murdered the whole of them and carried off their camels and slaves.