Southern Tibet : vol.7 / 692 ページ（カラー画像）

0692	Southern Tibet : vol.7
南チベット : vol.7

of the concurrent processes of elevation and erosion, the existing mountain systems
of the Himalaya and Tibet have been slowly evolved.» He adds that the great series
of parallel plications in Asia are supposed to have been caused by a horizontal thrust
from the north.» It is important to remember this view, for the arrangement of the
Transhimalayan folds cannot be explained merely as a result of a horizontal thrust
from north to south.

A few quotations from Dr. Felix Oswald's above-mentioned article will be of
interest in this connection. Regarding the mountain-folding and formation of lakes he says¹:

»Although the Tibetan plateau is traversed, in the first place, by latitudinal
mountain folds, which are to be regarded essentially as the expanding branches or
fan-like virgation of the Karakoram ranges, yet in all probability Tibet consists, in
its present condition, of a succession of uptilted and depressed blocks of resistant
strata, no longer capable of being folded, just as I have shown to be the case in
the plateau of Armenia. The innumerable lakes still scattered over its surface,
although many more have completely dried up, lend support to this view, for their
origin is now explained by local uplift of the beds of the rivers which originally
traversed the region. Hence, if the rate of elevation exceed that of the erosion
of the river, the stream would be unable to keep its channel open and consequently
a lake would be formed. In other words, local elevation has enhanced the erosive
power of the river below and diminished it above the line of uplift! However, in
some cases at any rate, a river has been able to keep pace with the local uplift in
the plateau region.» Here he mentions my observation that the Bogtsang-tsangpo
at some places sharply turns to cut through a rocky crest, whereas it would seem
much easier to flow on along the open latitudinal valley. The same phenomenon was
observed by Oswald in the valley of the Murad or Eastern Euphrates, and Burrard
describes the curious way in which the Indus thrice pierces the Ladak Range.

In opposition to Prof. Hennig he regards the Tsangpo valley as a sunken
trench and not as a valley formed by river erosion: »As a corollary to the explanation
which I offer of the Transhimalayan system, it follows that the natural continuation
of the parallel ranges of the block lies now sunk beneath the Brahmaputra valley,
at the base of the great fault-scarp, to which the river flows in parallel alignment.
Accordingly this valley must be of the nature of a rift-valley or sunken trench,
especially since the opposite (southern) wall of the valley lies parallel to the northern
wall and in like manner possesses an average height of 23,000 feet . . . . The
sacred lakes Manasarovar and Rakas-tal lie centrally in a glacial trough in this
W. N.W.-E. S. E. rift-valley, which occupies the site of a relative depression between
uptilted mountain blocks.»

国立情報学研究所 - ディジタル・シルクロード・プロジェクト
『東洋文庫所蔵』貴重書デジタルアーカイブ

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国立情報学研究所 - ディジタル・シルクロード・プロジェクト 『東洋文庫所蔵』貴重書デジタルアーカイブ

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国立情報学研究所 - ディジタル・シルクロード・プロジェクト
『東洋文庫所蔵』貴重書デジタルアーカイブ