Southern Tibet : vol.7 / 768 ページ（カラー画像）

0768	Southern Tibet : vol.7
南チベット : vol.7

slightly interrupted by the low threshold of Nima-lung-la (4920 m.), the open plain
of Bongba-Kebyang, and finally the valley of Buptsang-tsangpo the whole way to
30° North Lat. In its present state this valley is no doubt chiefly a work of erosion,
but its relation to the ranges on both sides makes it likely that the valley originally
was pressed down and forced to sink. The rest of the sculpture has been achieved
by erosion. The same may be said of the deep valley going down from the S. E.
side of Samye-la (5527 m.), and which may be regarded as the continuation of the
long depression north of the pass. The valley of the lower course of the Chaktak-
tsangpo is a direct continuation of this long depression which practically cuts the
whole Transhimalaya into a western and an eastern part, the latter again being cut
by a third meridional line of sunken ground.

As to our first transverse line, with Rakas-tal to its west and Manasarovar to its
east, its nature is more difficult to explain. We have here a fine example of Burrard's
law that »the several parallel ranges of the Himalaya and Tibet tend to culminate
in sympathy with each other». The strong stresses from east and west which have
forced the folds to culminate on one meridional line, may also have forced the crust
on both sides to sink down, forming the two depressions which gradually have been
filled with water. Burrard also observes the fact that very often the passage of a
river across a range occurs near the highest part of it. He tries to explain this
phenomemon of contrast in different ways, one of which seems very well to suit the
ordinary combination of high mountains in the immediate vicinity of deep lake de-
pressions, the latter being a general occurence in Tibet. His hypothesis is the following:
»It may be that, as one portion of the earth's crust becomes elevated to a great
height, an adjacent portion becomes depressed, in accordance with the theory of
isostasy.» This seems to have been the case with the meridional line of the Kailas,
the isthmus, and Gurla-mandata, as this transverse fold has a sunken part of the
crust at each side. Though the general morphology at Tengri-nor is very different,
the same rule occurs here.

We have seen that the Kailas Range could be traced the whole way to Surnge-
la, and very likely it continues E. S. E. to the north of Gunchu-tso and Maryum-la.

Directing now our attention to the Transhimalaya, we first meet the N. W. —
S. E. running range of Ding-la which probably reaches the Tsangpo in the vicinity
of Tangyung (5760 m.). In its N. W. part I crossed this range at Chargo-ding-la
(5885 m.). It may be that the range continues to the N. W. from the pass and that
it is in connection with the Pundit's Nakchel-gangri and Nakchel-la, and perhaps with
one of my passes near the source of the Indus; for instance Dam-tarngo-la, (4991 m.),
or even Lamo-latse-la (5426 m.). Its length would thus be about 210 km.

Proceeding eastwards we come across a small range to which the two mountains
of Lavar-naglep and Gang-chen seem to belong. This range is only 100 km. in length.

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