SURVEYING THE DESERT. 239
At first I aimed for the south-east, so that we had to cross over these innumerable jardangs at right angles; and this we were able to do travelling on foot, although it was very tiring work. On the other hand this conformation was very favourable for levelling, owing to its raising no hindrance in our path, the instruments being placed on the top of these natural walls. Thus in the northern part of the desert our line of traverse ran along the summits of the jardangs, not in the wind-excavated gullies; indeed it would not have been possible to carry it along these last, because their depth was generally somewhere about 2 m. Farther south, after the jardangs came to an end, and the survey-line ran along the level ground, the traverse naturally was taken at a lower level, in such a way that the deep gullies which occur between the jardangs farther north nowhere appear in the profile of the levelled line. This however is of no consequence. I would only remark, that between the successive stations of the traverse there were hollows and gullies which sometimes lay as much as 3 to 4 m. below the general level. The annexed illustration is therefore merely a rough sketch; as an actual fact the distance between the telescope and the staff was twenty-five times the height of the staff, so that between the two there were generally from 10 to zo wind-excavated gullies.
In the vicinity of one broad trench (i85 m. across) that we crossed over, there were some small detached dunes. The sand was however by this reduced to a minimum, occurring only in thin layers under the shelter of the jardangs. Mounds crowned by dead tamarisks were very few and far between, though they did still crop up at intervals. Along certain stretches there was an utter absence of vegetation; possibly these were the parts of the former lake that were too deep to allow of the kamisch growing in them. Towards the close of the day's march the jardangs ceased entirely in two or three places; the almost perfectly level surface was here strewn with fine dust intermingled with crystals of gypsum.
Upon reaching Camp No. CLX we observed the utmost care in marking the point where we stopped for the day, as indeed we did at each subsequent camp. After marking it distinctly, we protected the spot by inverting a box over it.
The result of the first day's survey was a drop of 0.197 m., which, strictly speaking, is of no significance; for had we placed our last staff on the top of one of the adjacent jardangs, the result would have been a rise of one or two meters; whilst, on the other hand, if we had placed it in the bottom of the channel-like depression on the southern edge of which we were encamped, there would have been an equivalent drop. One fact however was even 1 thus early quite evident, namely the extraordinary flatness of the desert.
Iltdin, Tourney in Central Asia. II. 31
IIIFカラー高解像度
