584 THE HYPSOMETRICAL RELATIONS OF THE TARIN BASIN.
the loftiest pass in the eastern Kuruk-tagh! I am however willing to concede that there are higher points in the Kuruk-tagh than those I touched; but the figures I
have given above show clearly how insignificant the mountain-system is, and how little it is entitled to be delineated in the pronounced way in which it is indicated on our maps.
The second half of my journey through the Kuruk-tagh system brings to light a very remarkable and interesting phenomenon in hypsometry. During the stage of 17th February (see above pp. 113 ff.) we crossed over an unmistakable depression, containing in part schor, in part clay desert, with jardangs modelled with extraordinary sharpness of outline and reaching 4 to 6 m. in altitude. This depression stretches towards the north-north-east through the gap that exists there in the Kuruktagh, and • appeared to continue towards the south-south-west, though after that it almost certainly inclines towards the south-west, and becomes merged in the old bed of the Lop-nor. Nevertheless it is probable, if one may judge from the Chinese maps, that this depression is separated from the depression of Lop by a threshold, and that it was already dry at the time when Lôu-lan flourished. In this depression I took altitudinal measurements at two places, namely 797 and 792 m. respectively. Continuing south-westwards along the base of the Kuruk-tagh until we strike the part of the 1900 route which lies north of Lôu-lan, we find there two other altitudinal measurements, taken on 27th March, namely 777 and 78 i m. respectively. Now as these observations were taken in different years, it would be a strange coincidence if it were simply chance which gave rise to such a close resemblance in these altitudes, especially as the two pairs of altitudes were taken in an unmistakable elongated depression or gully. Moreover in two places beside the lowest Kuruk-darja we found an altitude of 81 o m., that is exactly in the situation in which the Chinese map puts its three small lakes. Dr. Ekholm's first calculation for the altitude of Lôu-lan was 807 m.; but this, thanks to our surveyed line, we were subsequently able to correct to 818 m. Yet even when we increase by II the four data quoted above, and so make them 8o8 m. and 803 m. for the north-eastern depression, and 788 m. and 792 m. for the depression north of the proper Lop-nor, we must nevertheless acknowledge, that the indications still point to the existence here of an elongated depression deeper than any other part of East Turkestan, a depression the continuation of which to the west-north-west is plainly prescribed by the position of the Kuruk-darja. Pos-
. sibly a portion of the Lop-nor ran, even in the Lôu-lan epoch, into this northernmost depression, although it is most probable that it was separated from it (see Pl. 4o). On Pl. 59 I have not ventured to take this depression into account, for even though its existence is undoubted, we possess too few points of certainty to be able to determine its boundaries. The line GH on Pl. 41 is however drawn from this absolutely deepest depression of the Desert of Lop to the shore of the Kara-koschun. The mean of the four altitudes quoted above is 798 m., while the altitude of Karakoschun is 816 m. Hence over a distance of 87 km. the desert here rises 18 m. from north to south — precisely the same relation that we obtained west of the line we surveyed.
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