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 |
| Southern Tibet : vol.7 | |
| 南チベット : vol.7 |
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引用情報
GEOLOGICAL OBSERVATIONS OF DR. THOMSON.
20I
western Transhimalaya with the Ladak Range. The tract between this southern range and his Kwen-lun he believes to be made up of a number of isolated lake-basins.
Across the southern range MOORCROFT and TREBECK went to Panggong-tso, and from their narrative Thomson understands that the lake basin »had originally an outlet at its north-west extremity, discharging itself along the valley of Tanktse into the Shayok». With this single exception »every part of this country must be viewed as terra incognita» .
Thomson regards Western Tibet as »a highly mountainous country, lying on both sides of the river Indus, with its longer axis directed like that river from southeast to north-west. It is bounded on the north-east by the Kouenlun chain of mountains, by which it is separated from the basin of Yarkand.» I In these words Thomson emphazises his conviction that the Kara-korum System (his Kwen-lun) is bounding the Tibetan highlands towards Eastern Turkestan.
The height of the mountains of Western Tibet he describes as being pretty much the same. Therefore the valleys are much deeper in the lower courses of the rivers than near their sources, where the mountains are apparently much lower and more rounded. In this he is also correct. In almost all valleys he thought he could recognize unmistakable proofs that they had formerly been occupied by glaciers at much lower levels than at present. He also thought the snow-line went much lower down formerly than now.
His geological observations he summarizes thus: the greater part of Tibet consists of plutonic and metamorphic rocks; granite occurs in great abundance; the stratified rocks strike in a direction which varies between N. W.—S. E. and N. N. W.
S. S. E., and he says: »It is not a little remarkable that a belt twenty miles wide in the direction of this line of strike, drawn from Iskardo to the Niti Pass, would cover every place south of the Indus in which limestone has been observed in Tibet .... Of course the limestone of Nubra and the Karakoram on the one hand, and of Kashmir on the other, cannot in any way be connected with this line.»
On his small sketchmap, Pl. XLV, Thomson has a legend »Probable Glaciers» in the neighbourhood of the place where the Remo glacier is now known to exist. But he does not regard these probable glaciers as the source of the Shayok which he places at the head of the eastern tributary. Both on THOMSON'S and on WALKER'S maps the Chang-chenmo is shown, after the survey of HENRY STRACHEY. The range with the Kara-korum Pass he calls Mustagh or Kouenlun Mountains, and just north of the pass is a river which »joins the Yarkand river» . Pl. XLVI is the northern half of the map illustrating Thomson's journey.
It is not exaggerated to say that Dr. Thomson's journey is one of the most important and successful ever undertaken against the secrets of the highest mountain-land of the earth.
I Ibidem, p. 46 5.
26. VII.
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