Southern Tibet : vol.7 / 691 ページ（カラー画像）

0691	Southern Tibet : vol.7
南チベット : vol.7

0691

Southern Tibet : vol.7

南チベット : vol.7

enormous block of mountain folds which originally constituted the Himalaya (incl.
Transhimalaya), the mighty valleys of the Gartok-Indus, the Satlej and the Tsangpo
along the latitudinal axis of the system were chiefly formed by erosion of running
water. Only by these valleys was the Transhimalaya separated from the Himalaya.
Hennig, however, does not deny the possibility that these valleys were originally
and partly traced as fold-troughs or were due to other orogenetic causes, and that
the rivers then had only to continue to cut out the depressions. However, from
geological facts Dr. Hennig regards the valleys separating Transhimalaya from Hima-
laya as erosive valleys and not as tectonic or merely orogenetic valleys.¹

In Hennig's opinion the comparatively even lake depression north of Trans-
himalaya, as a rule consists of the same sedimentary and eruptive formations as
Transhimalaya itself. It it consequently not to be regarded as a depression formed
by denudation as in the case of the depression south of Transhimalaya. He thinks
that the depression including Tengri-nor, Dangra-yum-tso, Nganglaring-tso, etc., is a
folding-trough of the same nature as those separating other mountain systems of Tibet
to the north of the Transhimalaya.

Hennig has thus proved that also the post-eruptive Oligocene and Pliocene
sandstone formations have taken part in the folding procedure of the Transhimalaya;
consequently the folding activity of the mountain system continued to the end of
the Tertiary epoch. Therefore the folds of the Transhimalaya are as young as those
of the Tibetan plateau-land, a fact that is not at all interfered with by the different
stretching of the Transhimalayan ranges.

The same process has been explained by H. H. HAYDEN in the following words²:
»Until a comparatively recent date in the geological time-scale — the middle Tertiary
epoch — all the northern part of what is now the Himalaya, and probably the whole
of Tibet were covered by a great sea, in which deposition of sediment had continued
for a vast period. At length, owing to forces the origin of which we can at present
only conjecture, a period of crust-movement set in and the floor of the Tibetan sea
began gradually to rise and to be thrown into a series of long parallel wave-like folds.

»As the crests of the earth-waves rose from the waters of the sea, they were
eroded by rain and weather, and the rising land became broken and irregular: drainage
basins were carved out of its flanks and a river system, composed of 'transverse'
valleys, was gradually developed. As elevation continued, the troughs of the folds
emerged and a series of 'longitudinal' valleys was established at right angles to the
transverse valleys and parallel to the longitudinal axes of the folds. From a combination

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