IIIFカラー高解像度
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
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| IIIFカラー高解像度 |
| Scientific Results of a Journey in Central Asia, 1899-1902 : vol.3 | |
| 1899-1902年の中央アジア旅行における科学的成果 : vol.3 |
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引用情報
82 MV FIRST JOURNEY IN NORTH-EASTERN TIBET.
and ramifications of the same. The slopes above are furrowed by numerous glacial streams, which cut their way across the belt of sand, for the most part probably underneath the dunes, without in any appreciable way disturbing their position.
Then came a gravelly expanse, barren and level, with smaller dunes, and then another glacier stream, which discharged its reddish brown mud at the place where we were. We made Camp No. XXIII on a slope immediately west of the glaciated mass. The grazing was wretched, little better than hard, dry japkak scrub.
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All day we had no hard rock in sight. At Camp No. XXIII (alt. 4889 m.) the detritus consisted of granite and a species of black diabase, in blocks that seldom measured as much as I cub.foot. As for the bottom of the latitudinal valley, its most conspicuous and noticeable feature is the belt of drift-sand, which stretches, yellow and dreary, around the base of the glaciated mass. With wonderful regularity all these dunes turn their steep leeward sides towards the east. On the northern side of the latitudinal valley there are only rudimentary dunes, and they occur only on the west side of most of the brooks, high up on the slopes above (fig. 66). This again points to the prevalence of a westerly wind, here as throughout the whole of the Tibetan highlands.
The small depressions which contain pools and are inclosed within steep semicircular ramparts of sand bear indeed some slight resemblance to the bajirs of the Desert of Tschertschen and the desert lakes on the right bank of the lower Tarim. Strictly speaking, they are in fact the same phenomenon, namely troughs between the waves in the sandy ocean, which by chance have become filled with water. But there are also great differences : in the first place, these pools are generally surrounded by separate individual dunes, whereas the lakes of the Desert of Tschertschen are surrounded by accumulations of several individual dunes; again, these pools are fed either by springs which gush up from underneath the sand or directly by brooks which have been arrested by the dunes in their eastward progress, whereas the desert lakes are supplied by small canals issuing from a river. The reason that the water gathers into a pool at the base of these circular dunes, and does not force its way through them, is partly the thickening of the encircling rampart with glacial clay and partly the unbroken continuity of the supply that enters the little pool. The eastward advance of the dunes is in no way hindered by these. small sheets of water. But there is a limit to the height to which the surface of such a pool can rise: as soon as the water rises to the level of a permeable layer, it trickles through it, and so resumes its arrested journey, finally emerging as a spring on the windward side of the dune. As the dunes are situated at the west-north-west foot of the glaciated mass and are travelling towards the east, only a very small proportion of the sandy
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Fig. 66.
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