230 WESTWARDS TO LADAK.
which I have mentioned, and they are very sharply demarcated on the south, next the sandy, gravelly plain, with patches of wretched grazing here and there. The northern half on the other hand consists for by far the greater part of a gypsum expanse, with the usual platforms and mounds, such as we always found in the vicinity of lakes that are more or less desiccated. Hence it cannot be doubted that there was once a lake there. Deasy's map even shows a few solitary pools of water still surviving from it. Of these I saw none; but then they may very easily have been hidden amongst the gypsum formations. The greatest difficulty is however to understand the relation which the river bears to this old lake. At Camp CXXIV we just saw the last river bend, but in the course of our further journey north-west down the latitudinal valley we perceived no further sign of any river, nor did we cross over any river-arm or even any dry watercourse, as indeed from Deasy's map we might have expected to do; but then, as I have said, our routes did not coincide. The impression irresistibly borne in upon me was that the river comes from the north, and at Camp CXXIV it turns to the south-south-east. In that case it need not of necessity be intimately connected with the old lake; but it is nevertheless probable that this lake was formerly a sort of »through» lake or marginal lake, which afterwards became cut off from the river. The extensive clay surfaces have conceivably nothing directly to do with the lake, except in so far as they occupy portions of its former floor; but they originated at a far later date and are pretty certainly being increased at the present time. If the Ravur-tsangpo should swell after heavy rains, it may overflow its right bank at this particular spot, covering the clay expanses with a thin layer of water, and dropping there its sediment. This would also help to explain how it is that no higher water-marks are to be detected in the valley, for overflow lakes act as an assured ventilator to keep the lower part of a river within certain bounds. Even then, at the time of our visit, those parts of the river which were next to Camp CXXIV were in places spread out like shallow lacustrine expansions. Finally, it is also very possible, that from time to time the rain-water floods from the southern mountains bring mud and sediment down as far as these level expanses.
IIIF Color HighRes
