506 THE START FOR TUN-HUANG CH. XLV
favoured by an unusual calmness of the air, and was of interest as introducing me to certain characteristic features of the southern shore of that ancient lake bed along which the greater part of our journey was to lead. Already on setting up the plane-table in the morning on one of the tamarisk cones, I noticed beds of reeds forming a belt to the north, and beyond them as far as the eye could reach a bare level plain of whitish colour, evidently encrusted with ' Shor ' or salt efflorescence. We saw this quite clearly when after about two miles' march to the north-east the route began to skirt an unmistakable old lake shore marked by a steep fall northward of the low gravel-covered plateau over which we were moving. The route, now taking a more easterly trend, seemed to keep closely to this ancient shore line, but to cut off its sinuosities. In one place it crossed a former bay where the flat of the old lake basin was broken by curious isolated clay terraces up to thirty feet high, which looked as if carved out by erosion. Was it the action of wind alone or had water and wind been successively at work here ? I had plenty of occasions to ask myself this question thereafter.
Farther on, a stretch of tamarisk cones appeared again on our left, a clear sign that life-giving moisture was being still received at least periodically by the subsoil. The explanation soon appeared when about the middle of the march we crossed a succession of dry flood channels marking the course of the Lachin stream. It was said to bring down occasional floods from rain or melting snows in the barren high mountains of which the outer spurs were dimly visible to the south. But there was no vegetation by its side where we crossed it, only a narrow belt of drift sand and then once more the same monotonous gravel Sai we had skirted all the way from Donglik.
It was getting dark when we found ourselves on the edge of this morne low plateau with the route descending to the foot of the steep clay cliffs, forty to sixty feet high, in which it falls off to the dried-up lake bed. The old bank above us made a good guide as we moved on to cover the last five or six miles of our march. In the moonlight I could see a narrow strip of reed-beds hugging the shore line,
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