530 A STRANGE OLD LAKE BED CH. XLVIII
of those readings showed the height of Besh-toghrak camp as 262o feet above sea-level.
This was a distinct confirmation of the slight but steady
rise of level I thought I had observed during the last two marches, and to me the geographical interest of this observation was great. The depression in which we were moving since Achchik-kuduk had gradually narrowed into a regular valley descending from the north-east. The ease with which water was reached along its bottom by digging wells, and equally also the appearance of the high banks of clay edging it, suggested that this valley might once, and that within the present geological period, have served to carry surface drainage down to the ancient
Lop-nor lake bed we had traced as far as Achchik-kuduk. But from where could this have come in sufficient quantity to erode such a valley ? Not from the utterly barren Kuruk-tagh hills north, which, as our clinometrical readings showed, in the so far visible chain rose nowhere above circ. 4200 feet, and nowhere disclosed the debouchure of any important side valley. Nor from the high range of the Altin-tagh, a hundred miles or so away to the south, with its scanty drainage running at right angles to the direction of our valley, and lost long before reaching it on the huge gravel glacis and amidst the big drift-sand ridges of the Kum-tagh.
Naturally my thoughts turned eastward, up the direction from which the valley seemed to trend to Beshtoghrak. I knew that two large snow-fed rivers, the Su-lo Ho and the Tang Ho, united north of Tunhuang, and after flowing for a short distance to the west were supposed to end their course in the Khara-nor lake. The latter was to be looked for some eighty miles to the east of Besh-toghrak, judging from the Russian map embodying Roborowsky's and Kozloff's reliable surveys. A series of isolated small lakes and marshes shown there west of the Khara-nor, and thus in our direction, seemed to tempt the conjectural explanation that they might be connected somehow with a far more ancient line of drainage towards our valley and the dried-up Lop-nor lake bed. But Colonel Kozloff's manifestly careful route
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