Southern Tibet : vol.7 / 698 ページ（カラー画像）

0698	Southern Tibet : vol.7
南チベット : vol.7

From old moraines he concludes that the basin was once or twice filled with
ice, while later lacustrine deposits are due to less severe changes of climate in
more recent times. Although the old outlet is evident as well as the supposed dam
which he found to be a large fan of 1500 feet in radius, having its lowest point
90 feet above the lake, Huntington cannot accept the view of Drew. According to
Huntington, this water-parting fan does not appear to have been the cause of the
formation of the lake; on the contrary, it rather appears to have been able to grow
up because the former stream from the Panggong region ceased to flow. He points
to the fact that the permanent stream just above Muglib has had no difficulty in
keeping open the broad channel through fans as large as that at the divide. One
of the smallest tributaries would not be able to dam the main stream. Neither are
there any traces of a moraine that has dammed the valley. The dam theory is
therefore untenable. The only alternative Huntington is able to find is that the
Panggong-tso basin is closed by a rock-lip, behind which the basin may have
been glacially eroded. There seemed to be nothing against this theory, for Huntington
found abundant signs of glacial action, a fact that of late years has been often
corroborated, especially in the Kara-korum. The authors of A Manual of the
Geology of India also speak of the evidence of a former great extension of
the Himalayan glaciers.¹ They mention glaciers which formerly were 15 miles
in length, and now have dwindled to only one mile. Some glaciers once reached
to below 2000 feet above the sea. Regarding the extension of the presumed
Panggong glacier Huntington says: »The glacier did not come to an end at the rock-
lip, as might be expected, but continued on for 20 or 30 miles as a comparatively
narrow tongue giving rise to the U-shape of the outlet valley . . . . If the Pangong
basin is due to glacial erosion, it is necessary to explain why in what once was
a single uniform valley the part above the lip has been widened ten times as much
as the part below, and deepened correspondingly.»
When travelling along the Tso-nyak, Tso-ngombo and Panggong-tso, December
1901, I also got the impression that the basin of this long series of lakes was
excavated by glacier action. But as the most extended and compact region of glaciation
was situated in the gigantic mountains to the north-west of the Panggong depression,
where the greatest portion of the precipitation was caught, and formed enormous
ice-fields, I thought that the old Panggong glacier, perhaps fed from several ice-fields,
was directed from the moist parts of the mountains in the north-west to the dry
plateau regions in the east. I wrote: »The impression rose in my mind, that the
elongated depression in which the lakes lie, and which orographically really is a
latitudinal valley, once served as the pathway for a big and massive glacier, which

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