330 THE TSCHERTSCHEN DESERT.
stationary than that which falls in the barren depressions. However the vegetation does not give us any information as to the velocity with which the sand-waves move. Owing to the insignificant role which it plays in this respect, it may be left out of account altogether, for it is much too thin and starved to check the windward flank of the dune-wave in its progress westwards: the utmost it can do, supposing it to be sufficiently dense at any spot, is to retard a little one or the other promontories or spurs of the main mass. So far as I observed, the kamisch grows only on the evel floor of the bajirs. It does not grow amongst the lowest dunes on the windward side of the dune-accumulations; no doubt the ground-water is there too far from the surface. On the east side of the bajirs such vegetation as exists is smothered by the advance of the steep leeward flank and by the avalanches of sand which pour down over it. The westward advance of the dune-waves, and. consequently also of the bajir depressions, takes place much more slowly than the vegetation is able to spread itself over the floor of the bajir. Though strip after strip is thus overwhelmed by the sand, fresh strips are at the same time set free from the superincumbent sand on the west, so that in its outward appearance the bajir really suffers no essential change. In fact, the depression itself travels westwards, and as it advances, its soil, and the vegetation which may chance to cover the same, are steadily renewed as time goes on.
On the 2 8th December, after the thermometer had dropped to — 21° C. during the night, there was a violent wind from the east, apparently an unusual quarter for it to come from at this season of the year. The sky was clouded, and the atmosphere full of dust and sand, and we never once caught a glimpse of the sun. The wind continued all the morning, and in fact all day. Owing to the thickness of the atmosphere it is easy to deceive yourself as to distance. You fancy that the bajir you are dipping down into is long, and looks promising; but before you have gone very far along it you see the southern threshold looming out through the haze. The masses of sand immediately in front of you look like distant mountain-chains and the pyramidal dunes like gigantic mountain-peaks, and yet they are in reality quite close at hand. I do not know whether the weather in this desert is always what it was that winter, but to us it was in the highest degree repugnant, and weighed oppressively upon our senses. Do what we would, and in very despite of the sure knowledge that we were only so and so many miles from the edge of the desert, a feeling of strange uneasiness would keep creeping over us, and we kept fancying we were being led hopelessly astray deeper and deeper into the heart of that most inhospitable region. Our spirits were depressed by the continuous twilight which prevailed; it was as though we were travelling in a region which the sun's rays never reach, as though we were travelling through the wintry landscape of the eternal shades.
After traversing the rest of bajir No. 31 we again entered upon the heavy sand, leaving on our left a small fragmentary bajir. The next bajir in our course, No. 32, was exactly like its predecessors, neither better nor worse. Towards its northern end it had two or three small dunes, towards its southern a short stretch of level, but barren, soil, while everywhere else it was clothed with sparse fields of kamisch. The immediately following threshold was very difficult, and long, and it took us a considerable time to climb to the top of it. The individual dunes of which
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