THE SELLING-TSO AND THE JAGJU-RAPGA.
the most part filled with soft disintegrated material, and indeed they do exhibit the same character as the numerous sandstone ridges which we found in the lowest part of the Satschu-tsangpo. But they are also instances of the effects of erosion. In general the Jagju-rapga has a fairly insignificant fall, and the difference in altitude between the Tschargut-tso and the Selling-tso cannot amount to more than half a dozen meters.* The velocity is, it is true, rather high, but as a rule the current flows silently and without breaking into cataracts. It is only at the two thresholds — and possibly there may be several others like them higher up — that the velocity is increased, the erosive power of the current being intensified to its greatest conceivable limit; hence the threshold must keep travelling backwards up the stream in the direction of the Tschargut-tso. But that they also constitute a proof of the contraction in area of the Selling-tso is clear enough, when it is borne in mind, that in case the lake were to drop yet one or two meters more, there would inevitably come into existence, at the foot of the lowest threshold, either a series of cataracts or a new threshold Nvith a new cataract at some ridge of hard rock across the river.
Fig. 25. FISHING IN THE JAGJU-RAPGA.
Close to the camp I measured the volume of the Jagju-rapga, or Sellingtsangpo as some of the Tibetans also called it. Its breadth was 36.4 m. ; its mean depth, 0.56 m. ; mean velocity, 1.269 m. ; and volume, 25.9 cub.m. per second. In consequence of the fact which I have pointed out above, namely the part played by the Tschargut-tso, and in a still higher degree by the Addan-tso, which lies farther to the west and possesses an extensive drainage-area, we may take it that this volume of 26 cub.m. is fairly constant, and subject to only minimal variations during the
* In the Meteorological Section the altitude of the Tschargut-tso is given as 4607 instead of 4617 nI.
Ile (lin, 7t urnes' in Central Asia. II'. 5
IIIF Color HighRes
