A TIBETAN SALT LAKE. III
appear to be more than a few kilometers. The difference of level between them is wonderfully little. The velocity of 0.846 m. in the second prevailed for only a very short distance in the narrow passage; above and below it the velocity was slight. And the same thing was no doubt true of the rest of the way up to the upper lake. I dare say the difference of level did not at that time exceed a couple of decimeters.
The upper lake is fed by the voluminous glacier brooks that flow down from the glaciated mass V, that is to say the whole of the region round about our two Camps XXVIII and XXIX. The large stream into which these brooks gather enters the lake on the north. Streams of thaw-water from other snowy mountains, which we saw to the west of that glaciated mass, likewise eventually make their way down into the same lake, and I have no doubt it also receives another considerable river from the west. On the other hand it does not appear to receive any noteworthy affluent from the south. All this water gathers into the stream that enters the salt lake, this being the deepest depression and collecting basin of the entire region. How large this self-contained basin of internal drainage is, it is impossible to say; but probably it is one of the largest in Tibet. The river at any rate was the largest I measured during that excursion, and indeed it was only exceeded in size by one other river out of all those that I subsequently crossed over in Tibet proper.
We might infer a priori that the area of the salt lake is great, when we know that its mean depth is only 1.6 m., and that it at the same time receives 43 cub.m. per second. Moreover it may safely be assumed that this is not the only inflow into the lake; for even though we did not see any conspicuons snow-field towards the east, nevertheless all the thaw-water in that direction must flow down into a main stream, which traverses the eastward continuation of the latitudinal valley, and it too
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