FROM THE DESERT RANGES TO THE KURUK-TAGH. 489
schneidet in dieselben Furchen ein, aus welchen der Wind den Löss bis zur Kiessohle herab wegbläst and als feinen, trockenen Staub durch die Lüfte führt; auf diese Weise wird die Lössdecke, wo dieselbe durch die Vegetation oder Feuchtigkeit nicht geschützt ist, schrittweise von den Kiesfeldern weggeblasen, bis schliesslich als Reste der einstigen Lössdecke solche Lösshügel zurückbleiben.»*
Exactly the same thing takes place here. These are the jardangs and wind-eroded gulleys of the Desert of Lop, though on a larger scale. They all run parallel to one another, namely from north-east to south-west, and consequently have been subjected to the modelling influence of the same north-east wind that shapes the features of the Desert of Lop. In this desert we found that the differences in level between the top of the jardangs and the bottom of the gulleys was greatest in the north, and that it decreases towards the south, until in the vicinity of the Kara-koschun the surface is virtually level. Here again, in this part of the Desert of Gobi, the difference in elevation between the terraces and the depressions decreases towards the south. In both deserts the shallower gulleys disappear under the drift-sand, which is augmented by the sand particles that the wind sets free and adds to the dunes it forms. The sand would no doubt have accumulated in its present position even though the underlying surface had been a plain, with a uniform slope; but on the other hand the presence of the sand is possibly the cause that these wind-eroded gulleys are not so deep, and that they are most developed in those parts of the desert in which no dunes exist.
The fact that the dimensions of these surface irregularities are so much greater in this more easterly desert than in the Desert of Lop may be thus accounted for. A certain limit is imposed upon their development in the latter desert by the migrations of the Lop-nor, which levels down and smooths away all the irregularities of the surface, whereas in the former desert there have not been any similar inundations to effect a like levelling process.
Fig. 216. CLAY HILLS RUNNING OUT INTO THE DESERT.
But just when these terrace-formations reach their highest altitude in the Desert of Gobi they suddenly come to an end. The left-hand bordering terrace disappears towards the north-west; but from that on the right we diverged more slowly owing to our route running north-east. In the mouth or termination of this long trench there are some solitary detached table-like masses of clay, with small level patches between them overgrown with kamisch and other steppe vegetation. Then, after a short stretch of sterile soil, we came to the kamisch steppe, the reeds being more or less dense, while the ground on which they grow is soft, consisting of sand and
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