WE ENCOUNTER A SAND-STORM. 411 On the third day we left the plain and entered on a region of black, stony ridges, with grass and thorns in the long hollows between them. The sky was so clear that the moon (in her last quarter) was visible until nearly noon. About ten o'clock, from one Of the porphyry hills, I caught sight of Djebel Attshan, or the Mountain of Thirst, which crosses the middle of the Beyooda. It was in the north and north-west, apparently about thirty miles distant. During the morning I saw four beautiful gazelles, not more than a stone's throw distant. One of them was lame, which induced me to believe that I could catch it. I got down from my camel and crept stealthily to the crest of the ridge, but when I looked down the other side, no gazelle was to be seen. Half a dozen nar row gullies branched away among the loose mounds of stones, and further search would have been useless.

At noon we reached another and different region. The grass and thorns disappeared, and the swells of black gravel gave place to long drifts of bright yellow sand which extended on all sides as far as the eye could reach. We toiled on, over drift after drift, but there was still the same dreary yellow waste, whitening in the distance under the glare of the sun. At first, the air was so tremulous with the radiated heat, that the whole landscape glittered and wavered like the sea, and the brain became giddy from gazing on its unsteady lines. But as the wind began to blow more violently, this disappeared. The sky then became obscured nearly to the zenith, with a dull purple haze, arising from the myriads of fine grains of sand with which the air was filled. The sun became invisible, although there were no clouds in the sky, and we seemed to be journeying under a firmament of rusty copper. The drifts