At this city he was detained by various circumstances until the 8th of September, and during this period was enabled to make numerous inquiries into the history of the country, civil and natural, together with the manners, customs, religions, and character of its inhabitants. But when the day of departure arrived, he proceeded with indescribable pleasure on his journey, having the Nile on his right-hand, and the Bahr-el-Abiad, or White River, which he never approached, on the left. On the 21st he again crossed the Nile, and after travelling along its banks for several days, took a long leave of its stream, and plunged into the vast desert of Nubia. The soil here consisted of fixed gravel, of a very disagreeable whitish colour, mixed with small pieces of white marble and pebbles like alabaster, and wholly bare of trees. As they proceeded, indeed, a few patches of coarse grass, with small groves of acacia, met and refreshed the eye. On the 14th of November they halted in a small hollow, called Waadi-el-Halboub, and “were here at once surprised and terrified,” says Bruce, “by a sight surely one of the most magnificent in the world. In that vast expanse of desert, from west and to north-west of us we saw a number of prodigious pillars of sand, at different distances, at times moving with great celerity, at others stalking on with a majestic slowness. At intervals we thought they were coming in a very few minutes to overwhelm us, and small quantities of sand did actually more than once reach us. Again they would retreat, so as to be almost out of sight, their tops reaching to the very clouds. There the tops often separated from the bodies; and these, once disjoined, dispersed in the air, and did not appear more. Sometimes they were broken near the middle, as if struck with a large cannon-shot. About noon they began to advance with considerable swiftness upon us, the wind being very strong at north. Eleven of them ranged alongside of us about the distance of three miles. The greatest diameter of the largest appeared to me at that distance as if it would measure ten feet. They retired from us with a wind at S.E., leaving an impression upon my mind to which I can give no name, though surely one ingredient in it was fear, with a considerable deal of wonder and astonishment. It was in vain to think of flying: the swiftest horse or fastest sailing ship could be of no use to carry us out of this danger, and the full persuasion of this riveted me as if to the spot where I stood.”