the diagram, with the same vertical height, should be pulled out 1 oo times in the horizontal to give the real relations.
It shows that the Drugub, the Shayok and the Indus, between Drugub and Skardo, fall 1527 m. in a distance of about 300 km., 1. e. as 1 :196; and that the upper Indus, from Lungkung to a point on the Indus between Leh and Tikse, falls 965 m, in a distance of about i 8o km., 1. e. as 1 :186. In both cases the fall of the rivers is therefore about the same. But above Drugub and Lungkung the parallelism ceases completely, and it is here that the upheaval, the rise of the crust, has taken place. From the Panggong threshold to Drugub, a distance of 38 km., the valley falls 455 m., or at a rate of 1: 83; from Demchok to Lungkung, a distance of 7o km., the upper Indus valley falls only 95 m. or at a rate of 1:737. In these sections the fall of the Drugub river is therefore nearly ten times as steep as the upper Indus.
In the next sections to the east we find that the threshold is at an absolute altitude of 4329 m., and the eastern shore of Tso-nyak at 4317 m. ; between both is the lake series, 155 km. in length and with a maximum depth of 47,5 m. Here the valley is thus practically level. At Hlagar (my Camp CCXLVI) the altitude is 4672 m., at Demchok 4274 m. ; in a distance of 211 km. the Singi-kamba therefore falls 398 m., or as 1:53o.
If now in connection with a continued mountain-folding activity a pressure from below should raise the crust at Demchok as the arrow shows, the result would be exactly the same as in the Panggong case. From Demchok to Hlagar the Indus and the Singi-kamba would be dammed up and changed into an exceedingly long and narrow lake which, as the little sketch map shows, would have exactly the same form as the Panggong Lakes and become perfectly parallel with them, that is to say, its uppermost basins would run from S. E. to N. W., its middle basins nearly from east to west, and its westernmost portion from S. E. to N. W. Just as the westernmost part of Panggong-tso has a tectonic continuation to the S. E. in the valley Tsake-la-Chushul, so the westernmost part of the lake above Demchok has a tectonic prolongation in the Gartang-Indus valley. There can hardly be conceived a more striking proof of the correctness of Oldham's theory, viz., that the PanggongLakes have been formed by a damming up of the valley by means of a rise of the ground in the region where the threshold separates the lakes from the Drugub river and Shayok system.
If the desiccation continues for any length of time the Panggong Lakes will dwindle, the connection between Tso-ngombo and Panggong-tso will be cut off, and the Tso-ngombo also will become salt. The same will be the fate of Rakas-tal and Manasarovar, and finally the small salt lakes will disappear. But precipitation is subject to periodical changes. If a moist period should obtain in the interior of Asia, the
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