Southern Tibet : vol.7 / 695 ページ（カラー画像）

0695	Southern Tibet : vol.7
南チベット : vol.7

Further Oswald observes that the Transhimalayan arcs exhibit a sharper
curvature than the arc of the Himalaya taken as a whole. »It will also be noticed
that the orientation of the Transhimalaya arcs has more in common with that of
the Great Himalaya on the south side of the Brahmaputran trough than with the
latitudinal alignment of the ranges of Tibet; that the convexity of the arcs decreases
from north to south, and that structurally Transhimalaya must be regarded as part
of the Himalayan system.¹ Its mountain-folds must also have been formed at a date
anterior to those of the Tibetan-plateau.» As quoted above, Hennig has proved that
the formation must have been simultaneous.

Some 25 years before Prof. Hennig had adopted the view of the erosive for-
mation of the great latitudinal valley separating the Transhimalaya from the Himalaya,
the same opinion was clearly set forth in the Manual of the Geology of India by
H. B. MEDLICOTT and W. T. BLANFORD, which in 1893 was again published by
R. D. OLDHAM.² According to them the forms of the hills and their intervening
valleys are due to the action of rain and rivers and to frost. The sources of the
Himalayan rivers are situated north of the line of highest peaks, and this zone of
special upheaval is crossed by the deep valleys of the river. »These valleys are
due to subaerial erosion and are entirely produced by the action of rain and rivers.»
In the very beginning of the upheaval of the Himalayas a pair of latitudinal valleys
was established along the northern face of the system. The drainage from these
valleys escaped round the extremities of the upheaval. All the water north of the
present line of highest peaks escaped through this pair of latitudinal valleys. »As
the mountains were upheaved the gradients of the rivers flowing directly to their
southern margin became steeper than those of the longitudinal valleys north of the
main range, the erosive power of the streams increased, and they were able to cut
back through the line of maximum upheaval and rob part of the drainage which
originally flowed east and west to the gorges of the Indus, Sutlej, and Sanpo.» The
slopes of the valleys to the south of the passes thus became much steeper than
those of the northern. The erosion of the southern valleys therefore became more
rapid, and in course of time the water-parting gradually progressed northwards.

According to Oldham, differential earth movements show that the Himalayan
system is still in a state of strain, and he naturally concludes that this strain is due
to the compression which originally caused the elevation of the Himalayan folds. If
it be true that this compression and upheaval is still going on, the gradual desiccation
of the Tibetan lakes also becomes quite natural. »There are no data available regarding
the rate at which this is taking place, but the fact that some have dried completely

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

引用情報

OCR読み取り結果

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

引用情報

OCR読み取り結果

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