224 THE DESERT OF LOP.
They are built up of a more reddish variety of clay; but even in their case also the horizontal position is extraordinarily distinct. It is in the east that they are chiefly developed, and I have no doubt that in that direction they are connected with the deeply excavated jardangs we travelled through in February 1901.
On the accompanying illustration (fig. i 38) the uppermost layer is indicated by the widespaced dotted lines, the middle layer by dotted lines placed closer together, while the white portions represent the bottom layer. In this part of the desert, it may in general be said, that approximately one-half of the area is occupied by gullies, the other half by the usual jardangs, or the middle layer, upon which the topmost layer rests as upon a pediment. You can sometimes ride for long distances beside one and the same clay ridge, that is in the same unbroken gully ; but generally these parallel elevations are interrupted at short intervals. Our line of march was entirely determined by their direction towards the south-south-west, and it was very seldom that we encountered any low threshold that required to be crossed over. From the top of one of the i s m. high clay eminences, we were able to make out the gullies running to an immense distance towards the south-south-west; but, on the other hand, there was no sand. In the bottom of one gully we noticed patches of sand an inch thick, but nowhere were there even the beginnings of a dune-formation.
Fig. 137. A 15 M. HIGH CLAY EMINENCE OR HIGHEST STOREY OF JARDANG.
Only once did we see any old kamisch stubble. I have already observed, that in the northern part of the Desert of Lop the vegetation, i. e. old, dead forest, decreases in quantity from west to east precisely in the same way as it does in the Kara-koschun. In the latter locality the last poplars are found at Tschigelik-uj, and south and east of that point there are none but young and tender trees, and even
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