140 THE BOGTSANG-TSANGPO.
granulated or knotty, overgrown with low grass and perforated by innumerable rabbits' holes. The northern ridge, as may be seen on the panorama from Camp LXXXII, is more continuous and has very steep rocky slopes. A little transverse valley pierces them, opening to the N. 7° W. on the last-mentioned panorama. The scree of gravel and débris at the base of the southern mountains reaches the vicinity of the river, and one of them, with hard harren ground of fine gravel, projects farther than the rest and is crossed by our road. The plain part of the valley may be one mile, or a little more, broad. At intervals we touch the south-going bends of the river. The ice-sheet of the river is concave and broken up at the banks, proving that the volume of water decreases gradually during the winter. In 190I I had found much more water in the Bogisang-isang-po, but then the season was earlier or in the first days of October. The river is almost entirely fed by springs, which get completely frozen as soon as the severe cold sets in. It is the rains of late summer that again brings life into the springs, and they are very numerous in the valley of this river. The Bogisang-tsang-po may be regarded as a recipient of the water of innumerable springs. After rains it receives direct affluents. Some springs do not freeze even during the coldest part of the winter and if they are not too far from the river, their water reaches its bed. Probably some water keeps running during the whole winter under the ice-sheet. Now the volume was only about
1 cub. m. a second at Camp LXXXII, but increases slowly down the course on account of new tributaries. East of this camp we passed a spring the brook of which did not freeze until some 5o m. below its beginning. It formed a pool covered with ice, but from there continued to the river. The right erosion terrace is always clearly visible, though sometimes rather low; at Camp LXXXII, for instance, only
2 m. Farther on, at a new bend of the river, a little partly open brook goes out to the river which here is open for about I 00 m. along the right bank, though only to a breadth of 1 m.
Then we cross the plain at some distance from the river which disappears from sight. But sometimes we ride over old abandoned beds, some of them dry, others containing ice-sheets, but no water. On account of the levelness of the ground, the river seems from time to time to change its bed. The river sticks to the northern side of the valley which is due chiefly to the screes from the southern mountains. Between their base and the base of the northern mountains the profile of the valley here forms a straight horizontal line. In this plain part of the valley the ground consists of clay and alluvium without a single stone.
Camp LXXXIII was pitched at a branch of the Bogisang-tsangpo which seemed to be cut off from the main river with the running water. The latter probably turns to the N. E. just at the eastern base of the Palu-loma mountain group. The panorama, 99A and 99B , Tab. 17, was sketched from Camp LXXXIII. To the
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