Southern Tibet : vol.7 / 533 ページ（白黒高解像度画像）

0533	Southern Tibet : vol.7
南チベット : vol.7

South of, and more or less parallel with this, comes the Ladákh range, which may
be regarded as commencing near the junction of the Sháyak and Indus rivers and running
thence south-eastwards along the north side of the Indus valley. This range, which has
a most marked individuality both geographically and geologically, is breached by the
Indus at about 150 miles from its north-westerly termination in 79° of east longitude.
The range continues as far as Hanle, forming there the south, instead of the north, side
of the Indus valley, but its further continuation is imperfectly known.
The Zanskar range appears to owe its existence quite as much to the accident that
it forms the watershed between the Indus and Chenáb drainage, and has consequently been
less denuded than the regions on the north and south, as to any special elevation it has
undergone.
The outermost of the principal ranges is the Pir Panjal-Dháoladhár Range.
I have to return to the following important passage, already quoted in Vol. III:
Nothing definite can be said of the south-easterly continuation of the range. The
Pir Panjál, Dháoladhár and Zanskar ranges may be regarded as coalescing and becoming
continuous with the great range of snowy peaks, while the Ladákh and Karakoram ranges
coalesce to continue as the range of mountains which runs north of the great longitudinal
valley of the upper Indus, Sutlej, and Sanpo rivers. It may, however, well be doubted
whether either of these ranges has a real continuity along the whole length of the Himá-
layas and it is altogether more probable that, whether we regard them structurally or
according to the accidents of the existing contour of the ground, they consist of a series
of comparatively short ranges overlapping each other at their extremities. The final
classification of the minor ranges of the great Himálayan system of mountains must wait
for a more detailed geological and geographical knowledge than is at present available.
Though it is impossible to give any definite idea of the detailed orography of the
Himálayas it is possible to divide the mountains into orographical regions sufficiently
distinct from each other, even if their exact boundaries are somewhat indefinite. The
innermost of these is the upland of Tibet, characterized by great elevation and a dry
climate with its concomitant of very extensive accumulations of detritus in the valleys.
All the principal rivers draining from the Himálayas have their sources to the
north of the line of highest peaks. They cross this zone of special upheaval in
deep valleys.
Oldham regards it as probable that the first effect of the commencement of the
upheaval of the Himálayas was to establish a pair of longitudinal valleys along its northern
face, whose drainage escaped round the extremities of the upheaval, and that in the first
instance the whole of the drainage north of what is now the line of highest peaks, escaped
by these rivers. 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.
From the maps of northern Kumáun and Garhwál and from the accounts of
travellers he gathers that the slopes on the southern side of the passes are much
steeper than on the northern: »the erosion of these slopes would consequently be
more rapid, and as it progressed the watershed would gradually be forced northwards.»

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