and now form depressions encircling the kamisch-fields. We have already seen, that the deeper parts of the numerous kamisch-lakes which I have described, such as the Kara-koschun and Kara-köl, are free from reeds; indeed reeds seldom grow in greater depths of water than 2 m. The vertical section shown in fig. 63 is such as may generally be found in these lakes, with kamisch growing upon the sand-banks and elevated parts of the lake-bottoms. Imagine a basin of this character to become dry, and the wind to have free play across its surface, it is easy to see that the kamisch-grown ridges will be protected against its erosive energy, while the deeper parts of the basin between will be still farther deepened by it. This is what has happened with regard to the kamisch-fields in the Lop-nor, as well as in several other instances that we shall encounter lower down. These kamisch-fields grew either on the shores of the former lake or in the shallower parts of its basin, whereas the adjacent areas, which are free from kamisch-stubble, correspond to the deeper parts of the lake.
Fig. 63. KAMISCH IN A LAKE.
Here I may reasonably observe — although we shall later on have more convincing proofs of it — that the kötäk is always found on the tops of the jardangs, clay ridges, and elevated parts of the desert, never in the gullies and hollows, unless, and exceptionally, it has fallen into them in consequence of its having been undermined by the wind, or is, as in the Kuruk-darja (see fig. 55), really drift-wood of a very aged character that lies half buried in their bottom. Thus here again it is the ancient vegetation, and its roots, which have enhanced the power of resistance of the clay desert, and prescribed where the jardangs should be left. Had the poplar in fig. 64 stood upon perfectly level ground, and there died in consequence of the withdrawal of moisture, then the loose, dry layers, not bound together by vegetation, and situated at the side of it, would be gradually deported by the wind, until at length the poplar would be left upon a base of varying height. But then, owing to the consstancy with which the wind blows from one direction, the leeward side of the base or pedestal just mentioned affords a certain amount of shelter to the ridge behind it, and this, being relatively undisturbed by the wind, eventually forms a jardang. Still this protection will not extend very far, and finally those parts of the jardang which are destitute of roots, will be destroyed. The result is something like the tamarisk-mound, except that this last is invariably characterised by its regular, rounded shape.
We pitched Camp No. XII in an absolutely sterile spot, in the vicinity of a depression about 5o m. broad, 2 m. deep, and a couple of hundred meters long, lying exactly parallel to the wind-eroded gullies. Had it not been bordered on both sides by dead toghrak forest, pretty thick, with the trees both standing and lying on the ground, it might have been taken for an unusual expansion of one of these gullies. Its form betrays however that it is an old river-bed, evidently a short connecting
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