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

that the western lake freezes one month earlier than the eastern, then the former is
very likely shallower than the latter. More difficult it would be to understand why
the Rakas-tal should break up about 15 days earlier than the Manasarovar, which is
also said to be the case. If it be true it may depend upon some local wind, which is
not unlikely; during my stay at the lakes at least the Rakas-tal was usually exposed
to very strong winds at the same time as the neighbouring lake enjoyed calm
weather. And it may be the same in the spring.

As regards the soundings only a few words are necessary. The accompanying
map (of my Atlas) will show how they are distributed over the lake. On the line
from Camp 212 to a point a little south of Camp 213 we find two maxima, 65m. in
the eastern half, and 81.8 in the western. Between the two is a minimum of 55.4m
opposite the mouth of the Tage-tsangpo, which, during an earlier epoch, may have
carried down so much solid stuff into the lake that the distances between the isobaths
have gradually grown greater, and the lake shallower in this part. No such convexi-
ties of the isobaths can be noticed outside of the mouth of the Samo-tsangpo. Only
outside the Gyuma-chu is the lake comparatively shallow. The fact that the depo-
sits of Tage-tsangpo influence the isobaths almost to the very middle of the lake
affords us a new proof of the correctness of the Chinese view, namely, that the Tage-
tsangpo is the source of the Satlej, and not, for instance, the Samo-tsangpo or any
other river falling into the Manasarovar.

Along this line 28 soundings were made at fairly equal distances; the average
depth being 59.8m.

On the line between Camp 212 and 214 the same arrangement may be noticed,
although less developed. For the maxima are here 60.3 and 57.5m., and the
minimum between them 55.2m. Along this line 20 soundings were made, the
average depth being 52.7m.

On the line between Camp 212 and Chiu-gompa there are again two clearly
developed maxima, 55.4 and 49.8m., with a minimum of 33m. between them. The
Gyuma-chu cannot be responsible for the course of the isobaths on this line, for the
minimum is far east of the mouth of that river. There are 19 soundings and the
average depth is 44.4m. Comparing the three lines we get a value of the rate by
which the lake becomes shallower from south to north, namely, 59.8m., 52.7m.,
and 44.4m.

As compared with these principal lines of soundings, the others are less im-
portant and chiefly serve the purpose of completing the isobathic map of the lake.
The two S.E.—N.W. lines in the south-western part of the lake cross not far from the
deepest depression and have the maxima of 77 and 76m. resp. The two short
lines from the southern shore, ending at depths of 63.5 and 56.2 resp. prove that
the southernmost part of the lake goes down fairly steeply to the deepest depres-
sion, which *a priori* was likely from the appearance of the Gurla fans. The two
lines directed southwards from Camp 220 and 222 at the northern shore clearly show