Southern Tibet : vol.2 / 139 ページ（カラー画像）

0139	Southern Tibet : vol.2
南チベット : vol.2

rovar, he found on his way back that its watershed was almost close to the edge of
Rakas-tal and hardly so much as 100 feet above the level of the lakes.

Along the S.E. shore of Rakas-tal he found a great raised beach, at some 200
or 300 yards from the edge of the water and consisting of granitoid detritus. The
old beach-lines, which I measured in 1907 he calls a series of steps or parallel roads,
situated between the high-water level of the lake and the uppermost of the beaches,
which Strachey found to rise above all in ›a great mound of very remarkable height‹.
He could not help noticing these most strikingly developed features, a consequence,
as he believes, of the violent S.W. winds which blow so regularly in the afternoon,
and constitute thus a permanently dead lee shore.

As to the fluctuations in the level of Rakas-tal, he comes to the following very
clever conclusion worthy of a well-trained observer: ›There is no evidence available
to show whether there is any considerable variation in the level of these lakes from
year to year, or from one season to another; but I think that such variations as
must have taken place to explain the existence of some of these beaches are hardly
compatible with existing conditions, and it is probable that these lakes have been
gradually drying up, as seems to be the case in most of the lakes that have been
observed in other parts of Western Tibet.‹ In the chapters of this work dealing
with my own journey I shall have to return to this question.

He concluded that the Karnali had cut out its deep channel in deposits, con-
tinuous with those of the great plateau and caused by the same agencies. From
his own and his brother's observations he found it certain that Gurla and most of
the highest mountains were chiefly made up of gneiss or mica schist with a com-
paratively small quantity of granite.

Henry Strachey had discovered the source of the Darma Yankti in 1846.
Both at this river and at Gunda Yankti, Richard Strachey came across unmistakable
moraines of old glaciers. The interval between two old moraines was precisely on
the same level as the great plain, or was actually a part of it, and it hence became
evident that the mounds over which he had passed must have been formed along
the rivers, and the agency of glaciers readily suggested itself. He thinks the lake
basins may in the same way have been cut out by glaciers.

The map accompanying this paper is interesting and gives a good idea of the
splendid and, from all points of view, important work of the brothers Strachey (Pl. XII).
It gives the routes of Moorcroft, 1812, Henry Strachey 1846, Richard Strachey
1848, and the route of H. and R. Strachey, 1849. As regards the eastern shore
of the Manasarovar the map is and must be insufficient. Three rivulets enter the

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