Southern Tibet : vol.7 / 452 ページ（カラー画像）

0452	Southern Tibet : vol.7
南チベット : vol.7

294

In 1869 Drew went across the plateaux to the eastern branch of the Kara-kash
partly following JOHNSON'S, partly CAYLEY'S footsteps. He gives a good description
of the »Southern Watershed», which is situated north of Chang-chenmo. Here he
crossed a pass 19,500 feet high. He is right in saying that the passes in this tract
are not much below the general level of the ridge. The rock he found to be shale,
with interstratifications of sandstone. From its northern side the small streams go
to the salt lake farther east. Still farther north is Lingzi-tang, separated by the
Lokzhung Mountains from the northern plains, which he calls the Kwen-lun Plains.
The average height of Lingzi-tang he calculates at 17,200 feet, very well in accor-
dance with HENDERSON'S 17,300. West of Lingzi-tang there are »bolder hills and
even snowy peaks; in these there is a gap, to follow which would lead one down
to the River Shayok». But he does not say that this is in reality the Kara-korum
Mountains.

He found that the Lingzi-tang forms an isolated drainage basin. The whole
ground has been deposited in a lake, a fact which had already been proved by
JOHNSON. Drew found no means of ascertaining the depth of the deposits, and
could follow them to 20 feet only, in the deep parts of the basin. At the margin,
along the foot of the Lokzhung Range, he saw how the light-coloured flat of hard
clay ends with a marked boundary against ground sloping about 2° upwards.

North-west of Tsothang he found complete beaches, — parallel curved shingle-
banks, partly cemented by carbonate of lime dissolved from the stones themselves,
which are of limestone. Such beaches were seen up to 150 feet above the flat plain.
There has thus been a lake, the shore of which went along the edge of the Lokzhung
Mountains, and there are evidences of a still higher water-level. Some margin-marks
were also seen along the southern edge of the basin.

In the Lokzhung Range which is crossed by the path from Tsotang to Thaldat,
different ridges are of different rock. There is an older encrinitic limestone, ferruginous
sandstone, and above that a limestone containing Hippurites, unconformably on the
older limestone; other portions of a light-coloured limestone or crystalline marble,
make conspicuous white rocks.

His Kwen-lun Plains are situated between the Lokzhung and Kwen-lun Moun-
tains 16,000 feet high. The upper plateau is in parts covered with fragments of a
brown calcareous cake an inch or less in thickness.

He discerns between HAYWARD'S Kara-kash the real source, and the eastern
Kara-kash. The latter river is bounded immediately on the north by the main Kwen-
lun chain, on the south by a nearly parallel line of mountains of slate and shale;
otherwise he makes the Kwen-lun chiefly granitic.

North of Thaldat he also found shingle-beaches up to 80 or 100 feet above
the plain. And after a very careful and interesting analysis of the materials and

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