for in spring this region is presumably subject to the predominance also of the east-northeast wind, and then the dunes turn their leeward faces in the opposite direction. This is the reason why there exists no regular uniform relief, but instead a chaos of dunes, nowhere interrupted by bajir-depressions. It is close in under the mountains that the dunes exhibit especially fantastic shapes, the result of the divergent effects produced upon the direction of the wind by the projecting, irregular flanks of the mountains.
Quite naturally too the watercourse is most distinct and most sharply outlined close to the mountains, where the sand is swept cleanest away; and as we advanced towards the north the channel became increasingly less distinct, while at the same time the sand obtruded into its bed in the form of small transverse tongues or thresholds. Whenever it rains amongst these mountains, the resulting torrent must be extraordinarily turbid, seeing that it is forced to concentrate all its erosive energy within that narrow rocky gateway, out of which it must therefore sweep every particle of transportable material. But in proportion as the torrent advances farther and farther away from the foot of the mountains, it gradually loses a great part of its water, which is absorbed by the thirsty clay and sand, so that its volume continually diminishes. The torrents from even slight rains get down to, and out through, the rocky gateway, but it is only the heavier showers which propel them into the desert beyond.
The saksaul bushes still continued to appear singly at the sides of the watercourse, often half buried in the sand, and many of them were already dead. Here too there occurs a dry desert plant known as schaft. The corners and angles were often full of portions of dry plants, blown there by the wind. The signs of wild-camel, which were extraordinarily numerous in the desert-range, had by this entirely ceased. The animals no doubt fight shy of such a narrow passage-way, where they are unable to see all around them, and consequently are more liable to be surprised. And the same thing is true of the tracks of antelopes; for they too were plentiful in the mountains, but were absent down here. On one slope we observed a small pyramid of stones, though it was impossible to make out whether it had been put together by human hands or whether it owed its existence to pure chance. In two or three places there were blocks of granite and quartzite, .a cubic foot big, lying on the surface of the sand. Even so small an obstacle is avoided by the sand, otherwise these blocks would have been covered up with it. Strange to say however, there were no annular accumulations of sand round them, the consequence no doubt of changing winds and wind-eddies. The stones lay as if they had been placed where they were by a gentle hand. This recalls the endeavour of glacial ice to free itself from the solid materials that chance to get entangled in its mass.The observation applies however only to those slopes of the dunes which are exposed to the wind, for any object lying on the leeward side is of course bound to be buried under the sand.
Then the sand grows lower and lower, and the edges of the clay project more and more, while at the same time the country becomes more open. The nearest dunes appear to be little more than to m. high; but farther on there are pyramidal dune-accumulations, which, to judge by the eye, attain altitudes of 6o and even 8o m. At the same time the watercourse makes a decided turn towards the north-west, and then runs in an almost straight line, without even the slightest bend. Here there was an abundance of saksaul bushes.
IIIFカラー高解像度
