The last snow-covered mountains are no longer visible. In this respect these central parts of Tibet are very unlike the eastern regions of the plateau-land I had previously travelled through and where high mountain groups with eternal snow and glaciers are occasionally seen. The view to the south from the pass was not easy to make out; it looked like a series of different ranges stretching east and west, one beyond the other.
On the Yumrang-lopchangs Pass, a cairn was erected. The road was quite distinct, though it seemed not to be very much frequented by travellers. In the valley going south from the pass, there are, however, many old and new fireplaces, though there is now not a drop of water nor any ice. At seasons when travellers pass there must be water from springs which become dry in the autumn. The red range of limestone and conglomerate that was called Mukpo-malung- (or Mog-bo) by some Tibetans, and has a rather rocky and wild crest, stretches east and west and is pierced by the valley. The latter opens out into a great tectonic valley running N. E.—S. W. Its N. E. part seems to be closed by mostly rounded hills, where only here and there living rock crops out ; it forms a self-contained basin or flat depression bounded to the north by the Mukpo-malung- Range, and to the south by a double range of moderate size. The central part of the depression is occupied by a little salt lake with some open water and surrounded by an extensive bed of calcareous sinter and greenish white deposits, forming a labyrinth of furrows and ridges of the same kind as at Rinek-chulsan and reminding one of the yardangs of the Lop Desert. The lake is oblong from N. 68° E. to S. 68° W. In its N. E. prolongation, there is another little salt pool, also surrounded by the same white bed of deposits. The little lake was called Loma yäsung, and its absolute altitude was 4,713 ni. The depression is, therefore, comparatively low and surrounded by mountains on all sides. From the point where the pass valley goes out into the depression, Pan. 84, Tab. 14, was sketched showing the series of mountains and hills bounding the depression to the east ; to the S. 2 7 ° E. the lake Loma yäsung- is visible.
The tectonic valley, the N. E. part of which is formed by this depression, continues S. S. W., but here becomes much narrower and is occupied by the little brook called Niring-isangpo, according to the description previously given by the Tibetans. Between the point where we first reached the brook and the basin of Loma yäsung, there is, obviously, somewhere a flat threshold.
From the foot of Mukpo-ralung we marched S. S. W. along the base of a
series of well-marked and steep hills cut through by several small deep-cut transverse valleys with gravelly beds. At the point where we came nearest to the lake we were about 4o m. above its surface, and could clearly see how all the erosion furrows gathered at the little lake. When our direction becomes S. W. we have to our right a series of small rugged rocks and cliffs consisting of much weathered greyish red quartz-amphibol-diorite-porphyrite.
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