Southern Tibet : vol.7 / 747 ページ（カラー画像）

0747	Southern Tibet : vol.7
南チベット : vol.7

From east to west the first four of these lakes show an increasing altitude.
In the region of Lakes XIV, XIII and XII, a rise of ground seems to have taken
place. The difference in altitude between the lowest and the highest lake in the
series is no less than 474 m. The altitudes of the two easternmost lakes directly
indicate the affinity of this valley for the upper feeders of the Yang-tse River. The
relative altitudes of the thresholds situated between the lakes is very small, viz.
between Lake XIX and Lake XVIII, 5085 m., between Lake XVIII and Lake XVI,
5099 m., between Lake XVI and Lake XV, 5116, thus increasing in altitude from
east to west, whereas the threshold between Lake IV and Lake II is only 5026 m.
From Lake XVIII and westwards the valley may be said to be very level, 220 m.
being the greatest difference in altitude between a lake and a threshold.

The valley just described is a very regular and typical depression between
two gigantic folds, the Arka-tagh and the Koko-shili. Lac de Corbeaux and Lac
de l'Antilope de de Rhins clearly indicate its western prolongation. Then follows an
extensive area of terra incognita. It may be regarded as pretty certain — by con-
clusions of analogy — that the latitudinal valley continues through the whole of this
region, is nearly parallel with the valley of Wellby, and is in uninterrupted connection
with the valley of the Antelope-plain, with the itineraries of WELLBY, DEASY, RAWLING
and myself, and still farther west with the latitudinal valley of Yeshil-köl, Lighten
Lake, the Aksai-chin Lake and the Salt marsh of 4663 m. The lakes of this
enormous valley are fed from the snow fields and glaciers on the very high and mighty
range of Kwen-lun—Arka-tagh. It is surprising that such considerable rivers as the
Yurun-kash, Keriya-darya and Cherchen-darya take their origin from the northern
side of this range which faces the desert, whereas only small brooks flow to the
lakes along its southern side which ought to catch the greatest amount of the moisture
brought hither by the southern winds.

It is of course impossible to tell, with any degree of certainty, how the drainage
of this great latitudinal valley was arranged at an epoch where the whole of Tibet
drained off to the ocean and to the Tarim basin. Very likely, however, the whole
eastern part of the valley, from the region of Lac de l'Antilope and including all
my lakes of 1896, drained to the Di-chu, King-sha-kyang, and Yang-tse; and the
western part, from Yeshil-köl or Lighten Lake, to the Kara-kash. As to the precipitation
falling in the yet unknown part of the great valley, it may have found its way out
either to the west or the east, or, providing that it possessed the same force as the
Kara-kash to break through the Kwen-lun in transverse valleys, — to the Tolan-khoja,
Bostan-toghrak or Kara-muran.

An interesting problem which can only be slightly discussed in this connection
is the question of the struggle between the rivers and the sand dunes of the Takla-
makan Desert during the epoch of abundant precipitation in Tibet. If we consider

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