old tracks were just as dark as the ground itself, and the little depressions were filled with gravel, lying loose in them, whereas the fresh tracks were lighter, owing to the disappearance of the stones into the soft material underneath, and it is only when this last is blown away that they come to light again.
Fig. 56. EFFECTS OF REFRACTION.
The lower saj is furrowed by innumerable watercourses of all sizes, with hard clay bottoms. At one spot, where the Kuruk-darja hugs the base of the lower saj, we observed the termination of a pretty big gully coming out of the Kuruktagh. To the north of this, behind the nearest shoulder of the mountains, there is said to be a spring called Muchlaj-bulaghi, or Muchlaj's Spring, after thé Mongol who, some forty years ago, is reputed to have discovered it. West of the same lies the spring of Kak-su, and the low-lying mountainous parts around this are known as Kök-tagh. At the close of the day's march the two saj terraces appeared to melt together without there being any step-like transition between them. Most of the fresh-water rivulets which come down towards the Kuruk-darja, and no doubt once discharged into it, now turn aside towards the east; that is they are deflected towards the south-east. The Kuruk-darja was frequently visible from the saj, owing to its distinctly marked terraces showing at the bends, as well as owing to its dead forest. But in certain places its bed disappeared; no doubt this was where it formerly traversed shallow lakes.
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