| | on the same slope was quartzite, with a dip of 8o° N.; just beyond the first col the same crystalline schist was visible, dipping 68° towards the S. 58° W. The lake lies 4,572 m. above the level of the sea. Thus in the region around the two salt lakes we had been moving 200 to 300 m. lower than usual on the Tibetan highlands. At the time when the lakes lay 133 m. higher than they do now, this region did not possess in so conspicuous a degree the character of a depression. Once or twice subsequently we came across circumstances that are in every respect the same. And indeed it is evident a priori that so it must be, for it is only in the depressions of the highlands that salt lakes occur, and they gather into the lowest part of each self-contained drainage-basin. But in proportion as the salt lakes dry up, the more pronounced becomes the character of the actual depression. When your aneroids and your boiling-point thermometers continue for the whole of one day's march or longer to indicate a constant downward inclination of the surface, you have every reason to expect a fresh salt lake. On 22nd October we made a very short stage towards the north-west, along the foot of the southern mountains and in part across the gypsum area. We only covered a distance of 4.4 km., and then came to good grazing, better, according to our Tibetans, than any we should find for several days to come. Having gone clown from the brook to the foot of the mountain, we then had close on our right in part a barren marsh, in part some other small pools, covered with strong ice, that would bear, and containing water that was almost fresh. These pools hardly seemed however to have any connection with the spring-fed brook, but rather to be fed by independent springs, which emerge within them, and out of them the water proceeds to the marsh and the lake. It is only at the foot of the mountains that any grass grows; otherwise the bottom of the glen is white and sterile. The pools and lagoons which I have mentioned are often bordered on one or more sides by vertical terraces of gypsum; but these generally belong to insular platforms with level tops. When you look at them from a low point au niveau with their surface, their superficial contours melt together into a perfectly straight line. Between them you see the usual gypsum mounds, indicating the places in the gypsum deposits in which erosion has advanced farthest. These mounds are seldom 3 m. high. On the other hand I can hardly say that there is any increase in the height of the mounds to be observed from east to west: the mounds in the west, which have been exposed to wind and weather for a longer period, and consequently ought to be more severely attacked and modelled out by erosion, are not apparently any higher than those in the east, which were exposed at a later period; for even though erosion does deepen them at the bottom, the wind planes them away on the top at an equivalent rate, and the result is, that no perceptible difference of elevation can be detected between those in the east and those in the west. After travelling for a couple of kilometers across this extraordinary gypsum formation, we approached a little brook coming from the west, and making its way across that area towards the western shore of the lake, though it does not appear to be able to reach it, but dwindles away amongst the gypsum elevations. A little below the point where it ceases, we observed one or two rivulets trickling from the westernmost of the marshes, and they no doubt derive water from this brook after | | | |
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