rises in this region out of a sort of depression (see fig. 207). From the Upper Astin-tagh the surface slopes gently down towards the south; from the Tschimentagh it slopes gently towards the north, and where the two slopes meet rises the peculiar, but gigantic, upswelling called the Akato-tagh or the White Pass Range. In this way two latitudinal valleys are formed, sloping transversely in opposite directions.
The glen which we then entered has a rather narrow throat, about I oo m. across ; the drainage channel itself is there 5 ni. broad, and I to 2 m. deep, cut through the clay. It clings close to the foot of the left, or eastern, side, consisting only of small and pretty low hills and spurs; so that the jar or erosion terrace is the more developed on the left side (see fig. 208). After emerging from the glen, the watercourse assumes a southerly direction, and at the same time grows broader and shallower, and is soon lost to sight. It is no doubt a rare occurrence for the water that it brings down to reach as far as the Ghas-köl. From the entrance of the glen we had a view of the whole of the little salt lake; but we were unable to say whether it were ice or water that we saw glittering in it, though ice was the more likely, for during the preceding night there had been — 29.6° of frost.
We rode all day up this narrow glen, which had a very gentle ascent, while the bottom of the stream was as hard and as easy as an asphalted street. The only inequalities we encountered were the little low terraces formed by the water grooving runnels in the clay. The glen was like a tunnel, with short, sharp turns; we were seldom able to ride more than 3 min. in the same direction, before a fresh buttress rendered it necessary to take a fresh compass-bearing with a deviation to one side or the other. The surface consisted exclusively of fine yellow clay, moderately hard, its lie being almost horizontal or at 2° towards the S. 5o° W. ; such
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