246 THE DESERT OF LOP.
consists of 'clay, • the outline of the lake is • exceptionally denticulated, with creeks and
bays running out towards the north-east, but where it consists of schor the shore-line is straight. If the northern depression were now to be filled.with water, its northern shore-line would in all probability resemble in this respect the shore-line of the existing lake, that is, it would exhibit a deeply denticulated outline on the north and north-east, but on the south, i. e. in the existing schor region, a more evenly rounded outline.
The annexed section of the line of survey shows clearly, that the ground is leveller in the schor desert than in the clay desert, and that the differences of elevation are there extremely unimportant, in fact they are such as only become evident in a survey. To the eye, as indeed to any ordinary instrument, there is of course no perceptible difference at all. This state of things can only have been caused by water. The lake which once existed here was remarkable for its shallowness and uniformity of depth, just as the Sate-köl of the Kara-koschun is now. The sediment was laid down in uniform layers; but after the lake disappeared, and its bed dried up, and after the saliferous bottom mud hardened into schor, certain processes of expansion must have taken place in the thin crust, resulting in the swellings and ridges alluded to. Had those processes been processes of contraction, the result would have been a series of cracks or crevices; but it is precisely these swellings that are the characteristic feature. In some places one may hear the surface slightly crackling, pointing apparently to alterations brought about by changes of temperature.
In consequence of these swellings in the schor desert its horizon-line assumes a serrated and ragged outline. You imagine that what you are looking at is row upon row of withered tamarisks or toghraks, whereas it is nothing more than the upturned edges of the sheets of schor.
On the i 5th of March, the weather being fine and the ground favourable, we covered fully 16,239 m., travelling south-south-west, the descent in that distance being 0.304 m.; from this it is to be inferred, that we had crossed the threshold or »watershed» which in that meridian separates the two depressions of the desert the one from the other. The whole of the day's march led across schor of the same appearance as that hitherto described, except that the ridges and crests were rather lower. But there was one thing which we had not had the day before, namely old river-beds, most of them occurring towards the end of the day, and directed towards the N. 64° E. They resembled the arms of an old delta, an embouchure region where the Tarim or some part of it once emptied itself into a lake. The breadth 'varied from 4 to 20 m., and the depth from I `/2 to 2 1/2 m. The bottom was covered with fine dust or a thin coating of sand; and here again there were vast quantities of Limnæa shells. In the last bed, beside which we encamped, they were so numerous that they crunched under our feet as we walked about amongst them. It is hardly possible to conceive that these shells were transported thither by either water or wind; they must be actually in situ. But elsewhere in the schor desert we found- no mollusc-shells.
About half-way we passed some small depressions, which were not river-beds; but, although just as sharply outlined and just as distinctly cut, they were lake-basins,
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