betrayed that displacements were taking place even then, and ridges and cracks showed in places near the shores (fig. 175).
It may be said as a rule that this string of lakes grows increasingly deeper towards the west. The eastern basin of the lake lies in a flat, open valley and is clearly very shallow; towards the western extremity we found later on that the depth amounts to 48 m. This difference is of course caused first of all by the original shape of the valley, but is also due to the subsequent progressive filling up with sedimentary matter. It is in the eastern lake-basin that the greatest quantity of solid material is deposited; consequently it fills up the fastest, and is now therefore the shallowest. By the time the water reaches the basin which has Bal on its northern shore
it is clarifièd and pure after passing through the upper basins. As is evident from its colour, the Bal lake is considerably deeper than those above it. All the same these lakes receive direct contributories out of the numerous side-glens, and consequently they too are being filled with sediment, though of course at an extremely slow rate. For instance, the fourth lake, which is very small, looks as if it would soon be completely filled by the river that issues out of the big transverse glen on the south. Thus there are two factors contributing to blot out the Tso-ngombo and Panggong-tso entirely from the face of the earth — (I) the progressive sedimentation or filling up of the lake depressions with solid material, and (2) the climatic changes, caused by the decreasing rainfall, changes which, as we had abundant opportunities for observing, are taking place in the lake depressions all over the interior of Tibet. Farther on we shall also discover all too evident proofs that these lakes in western Tibet are likewise contracting.
All day it had proved impossible to cross over the water to the opposite shore, for the channels were everywhere deep-cut and the ice did not bear.
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