west the whole way to the Ding-la Range, the folds proved to have been built up with a certain regularity. Every new range had to be crossed in a pass just as the Lunkar Range had been. The rivers were more or less parallel to the Buptsangtsangpo, and each flowed to a salt lake just as the Buptsang-tsangpo. Conclusions could therefore be drawn by analogy, and these conclusions were corroborated by native information. Therefore it could also be regarded as certain that the passes of the great water-parting were situated between the several parallel ranges just as the Samye-la is situated between the Lunkar Range and the Kanchung-gangri. From the south, along the northern bank of the Upper Tsangpo, it is impossible to spread any new light on this part of the system. One only sees an endless series of more or less steep mountain-shoulders and ramifications bordering the valley of the Tsangpo and at intervals cut through by the moderate or small valleys of the tributaries to the Tsangpo. One indeed gets the impression that a continuous range runs along and parallel to the Upper Tsangpo. The drainage area of the Tsa-chu is also unknown, though it seems probable that most of its feeders come from the surroundings of passes of the same geomorphological importance as the Samye-la. Only the eastern feeders of the Tsa-chu take their origin from high snow- and ice-covered crests and peaks, viz., those of the southern Lunkar Range and those of the northern Lunpogangri.
Another question which will have to be cleared up in the future, is the relation between the northern Surla Range and the Bongba-yeke-gangri. It is true that I, on my journey from Poru-tso to Shovo-tso, got the impression of the existence of two parallel ranges. If there are two, the little Surla River which takes its origin from the glaciers to the west and south of the Sur-la-Kemi-la, pierces the Bongbayeke-gangri in the transverse valley by which its water reaches the Poru-tso. But on the other hand, the Bongba-yeke-gangri may as well be a part or a ramification from the main Surla Range, from the northern section of which other ramifications of the same kind may easily fall to the east.
The next crustal fold is of great interest not only on account of its length, which is some 76o km. to Yamdok-tso, but also because it presents a means of connection with the orography of Burrard. From the region west of Tarok-tso it runs from N. W. to S. E. and gradually turns to the right, i. e., N. N.W.—S. S. E. under the name of the Lunkar Range. Near Tarok-tso I crossed it in the pass Lunkar-la, 5570 m. high, and found it here as sharply and well defined as the whole way along its eastern side, where I had seen it from the valley of the Buptsangtsangpo, from Samye-la and from the valley S. E. of it. From 3o° North Lat., or in the region opposite to Samye-la, its stretching becomes N. \V. — S. E., and here are the highest peaks of the range called Lunpo-gangri. From the region where it is pierced by the Chaktak-tsangpo, and where I have seen it from the east, south
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