SURVEYING THE DESERT. 23 5
desert lakes we discovered in 1900, but of whose connection with the Kara-koschun we as yet had no knowledge. What I wanted to ascertain was the general relations of level which obtain in the desert, the difference of elevation between the country around Lôu-lan and the Kara-koschun, and how far the existence of a northern depression admitted of demonstration. I knew there was a southern depression; the water in the Kara-koschun was proof of it. In a word, I wanted to learn whether the contours would warrant the solution of the Lop-nor problem which Baron von Richthofen had offered. His view was, as is well known, that the Kara-koschun cannot be identical with the Lop-nor, but that the basin of the latter must lie to the north of the Kara-koschun. Even without a survey, I had been able to prove that von Richthofen is right, when I discovered that the Kuruk-darja formerly emptied itself into a lake, the existence of which was best proved by the occurrence of millions of mollusc-shells. As far back as 1896 I put forward the suggestion, that the Desert of Lop as a whole must be practically horizontal, that is to say, the differences of elevation within its area could not amount to more than a few meters. Accordingly a survey-line drawn through the desert would settle the point, and put an end to the controversy which was first started by von Richthofen and Prschevalskij, and continued by Kosloff and myself. If the result of the survey was to show a gentle slope southwards from Lôu-lan, the probability would be, that the Karakoschun formerly extended as far north as Lôu-lan, and thus covered the whole of the Desert of Lop; that the existing Kara-koschun is only a fragment of the historical lake of Lop-nor; and that Prschevalskij, Kosloff, and others are quite justified in calling that lake Lop-nor. On the other hand, if the survey disclosed a depression existing north of the Kara-koschun, it would prove not only the possibility, but also the probability, of the lake having existed formerly in the northern part of the Desert of Lop.
I now proceed to describe the actual survey itself and the results it yielded day by day, as well as the general appearance of the desert in this its eastern part, and then, when I have all the material before me, I will pass on to an analysis of the results of the survey as a whole.
Owing to the advanced season of the year, and for other practical reasons, I was not able to retrace my steps from the Kara-koschun northwards to the point of departure, so as to obtain a second series of readings by which to control the first. It is of course very desirable that that should be done, for without it the work cannot lay claim to be strictly scientific. It would indeed not be impossible to take the levels of the Desert of Lop, but it would be attended with difficulties, which it was not consistent with my plans that I should attempt to overcome. For that purpose two or three corresponding bases would have been necessary, e. g. one at Jaka-jardang-bulak, another at the lowest oasis of Altmisch-bulak, and a third at the Kara-koschun. It would also have demanded a triple supply of provisions and ice, and camels in proportion; and above all it would have been indispensably essential to select a more favourable season than the middle of March. Accordingly the only choice open to me was to make a single line of traverse across the desert, and endeavour as far as possible to eliminate the sources of error. My levelling-telescope and staff might be regarded as being in perfect order, and the accuracy
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