infrequently occupied by marshes and lagoons, fed by springs that gush out at the foot of the mountains. It would require only a very slight rise of the existing level of the lake for it to flood this flat moist strip of ground. And that it really does flood it sometimes appears evident from the fact, that several of the marginal lagoons are encircled by rings of white salt. The mountain-range which we had immediately on our left consisted of the usual schists, and the ground was covered with their detritus, although intermingled with pieces of tuff. Dunes of fine sand had gathered at a projecting promontory. One brook, rather bigger in size, was fenced in on the left by an eroded terrace 3 m. high. From that point we perceived C, and D,, summits of the Arka-tagh, almost due east. On the southern shore of the lake are relatively low ridges, and behind them rises the great snowy
mass of the southern range.
Similar conditions obtain on the northern shore of the eastern part of the lake. The mountains slope gently down towards it, and the lake is shallow. Here too we found various small saltwater lagoons, together with a strip of salt, several meters broad, close along the shore. This is of course a clear proof, that the lake level does oscillate at different seasons of the year. In another place however we perceived amongst the loose gravel very distinctly marked beach-lines, which belong to quite a different category. One of these was 2 I, 2 m., the other 3 '/2 m., above the existing level of the lake. It is however impossible to tell what is the range of volume of the lake between maximum and minimum; but it is probable that in July, when the snows are melting fastest, the water will be higher and the lake bigger than in the beginning of September, and that the saltwater lagoons, which are now cut off from the lake, will then in any case be entirely under water. More particularly the river which enters the lake from the west will at that season ( July) carry down very considerable quantities of water. But on the other hand it would of course be absurd to suppose, that the beach-line at 3 I/2 m., which I have just mentioned, is a mark of the range of the oscillations within the course of a single year. It is more reasonable to regard them as old beach-lines, mementos of a time when the lake had a more extensive area than it has now, and when, it is fair to assume, the precipitation was more abundant. It is pure accident, that the beach-lines remain so distinct just at that particular spot, while in other places they have been broken down; for some reason or other they happen to have been better protected. Generally speaking, it was very seldom that I had an opportunity of establishing the existence of beach-lines in this North Tibetan latitudinal valley. The basins that the lakes fill are so flat and shallow, and the beach-lines are demarcated with so little distinctness, that as a rule they seldom have any opportunity to leave behind them either distinguishable marks or abrasion terraces. The lakes in the central, southern, and western parts of Tibet are very different in character; for they frequently possess steep shores, so that the beat of the surf is able to concentrate its energy upon a line and does not dissipate it over a surface as in the
lakes of Northern Tibet.
Camp XXII stood at the same altitude as the lake, namely 4947 m. Close beside the former a pier-like projection shot out into the lake for about 2 km., pointing towards the east and terminating in a point. It was only a few meters
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