these regions we could not count upon finding water every day; indeed it would be almost perilous to travel through these high desert regions without a guide.
Almost the whole of the stage, 28 km. towards the N. 83° W., was across the bottom of an old lake, of which nothing now survives except the gypsum deposits. Sometimes the surface is perfectly level and vividly white; sometimes it is shaped into tabular masses and terraces, 4. to 5 m. high at the most; sometimes, again, these irregularities are very much lower, and locally are interrupted by hard, yellow, muddy clay, which had recently been under water, in part as level as a floor, in part furrowed by brooks and rivulets; and sometimes the surface was schor-like, slightly moist or cracked. Occasionally, though it was not very often, we would pass a little patch of yellow grass, the blades few and far between. The unusual feature about this gypsum formation was however that it was in places quite full of the white shells of the same little molluscs that we had also observed beside the Naktsong-tso. Here however they were extraordinarily common, sometimes as thick as in the Desert of Lop. Farther on the ground consisted of fine, dry powdery dust, with a thin scattering of small gravel, though only on the surface, where it lay as if swimming in water. One or two decimeters below the sur-
face there was no gravel; nevertheless what lay on the top was sufficient to impart a darker grey tint to the ground. The kulan paths and the tracks of single kulans, like the trail of our caravan, showed up therefore as lighter-coloured lines and dots against the darker background, for the gravel was there covered over with the disturbed dust. The frozen pools in the middle of the depression still continued to resemble a winding river-bed as we followed them towards the north-west. The Tibetans declared, that they were neither springs nor river, nor lake, but a lztma, or what the Mongols call a namaga, or »open pool». These accumulations of water do of course originate from springs, which gush out in the lowest trough of the depression and collect in those parts of the former lake that are deepest. The water was perfectly fresh, nothwithstanding that it lay over barren ground in a self-contained drainage-area; the ice was thick. The largest sheets of water were situated at the point in our route where we changed our direction from north-west to west. The pool was however only a couple of hundred meters long and barely r oo m. broad. The ice that covered it was the purest and most beautiful blue imaginable, nor is that in any way surprising, seeing that the water is perfectly still and limpid, the immediate surroundings a vivid white, and the sky as reflected on the ice a turquoise blue. Generally these long, narrow accumulations of water are framed about with fairly steep terraces, like the scarped terraces of a river-bed. The last pool too, which had not the slightest indication of a marsh round it, possessed fresh water. From this we may conclude, that this water is at times in motion. Farther east, at Camp CXXXII, it emerges into the light of day
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