26 FROM CENTRAL TIBET TO LADAK.
and oldest is the most powerfully developed. It might indeed have been expected that this, just because of its greater edge, would have been obliterated, or at any rate more broken down than the others; but on the other hand it dates from a time when the lake covered an incomparably greater area than it does now, and when consequently the force of the waves was immensely more powerful and violent. The medium-sized gravel of which the ramparts consist will also offer stubborn resistance to the atmospheric agencies. If we suppose the surface of the lake raised to the level of the highest rampart, which I estimated at 5o m., it
Fig. 18. WESTERN EXTREMITY OF THE ESCARPMENT-RANGE OF THE PENINSULA.
would inundate all the adjacent low-lying country, and especially the whole of the lower part of the broad valley in which flows the lower Satschu-tsangpo. Even Camp LXXII, although 24 km. distant from the existing lake and only a few meters above its surface, must then have lain in a considerable hollow, and above it the lake must moreover have sent out a large bay to the north and north-east. Indeed the whole of the alluvial region below this camp must have been under water even at the time when the lowest strand-rampart was formed. For this reason alone it would be idle to search for traces of former beach-lines. And even though beach-lines had been left behind by the lake as it slowly retreated, they would have been unable to maintain themselves for long in the loose clay which we found so seriously attacked in the gulleys close beside the river, especially considering that the rain is powerful enough to obliterate every trace. At the time the lake rose to the level of the highest rampart, the great peninsula which I have mentioned would be connected with the mainland by only an extremely narrow isthmus; while at an even earlier period it would be entirely cut off from it. Indeed it is possible to conceive of a time when the escarpment-range of the peninsula and the little detached sand-
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