Southern Tibet : vol.7 / 716 ページ（白黒高解像度画像）

0716	Southern Tibet : vol.7
南チベット : vol.7

0716

Southern Tibet : vol.7

南チベット : vol.7

CHAPTER LVIII.

THE OLD DRAINAGE OF THE SELLING-TSO —
PANGGONG-TSO DEPRESSION.

We now turn to the period preceding the lacustrine epoch of the Panggong
valley. Everybody who has travelled in the mountain valleys of the Indus and its
tributaries will have noticed the enormous terraces raising their naked and sometimes
nearly perpendicular walls on the banks of the rivers. In the first Chapter of Vol. IV
of this work I briefly mention some of them, and in the same volume I have a
few photos giving an idea of their appearance. Opposite p. 16 there is a photo
from the Chang-chenmo valley at Pamsal showing, on the right side of the river,
a fluviatile terrace 50 m. high or more with sharply marked horizontal layers of
shingle-and-gravel, sand and clay. The photo opposite p. 20 shows another part of the
same erosion terrace a short distance above Pamsal, where it is cut through by a
northern tributary. At p. 22 and p. 24 are photos from Gogra showing another
example of well developed river terraces. And finally Pan. III in the same volume
gives an excellent view of the Chang-chenmo terrace. A look at this panorama is quite
sufficient to tell us what has taken place at an earlier epoch in this valley. The
present river would hardly have had strength enough to cut down its bed with such
enormous energy. Only the powerful river that flowed down the valley in post-glacial
time could have been able to bring about such a result.

Regarding the river that is most interesting to us, viz., the little Drugub tributary
of the Shayok, the lower part of the old Panggong river, I made the following
annotation at my first visit, in 1901: At the actual elbow, where the valley changes
its direction (to S. W. between Muglib and Tanksi), we observed, at a good 100 m.
above its bottom, some especially well-defined terraces, interrupted at only a couple
of places by fissures and gravelly screes. During the period in which this valley
served as the outlet conduit of the Panggong-tso, and when the volume of water
that streamed down it was immense in comparison with that which it now carries,
the valley was excavated with great energy, the effect being such as nobody would

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