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
A THEORY OF BURRARD.
Ij
Jr 1 3 3
outflows from the interior hydrographic systems and capture them, emptying the lake basins one after another. The interior peripheric rivers, such as the Sachutsangpo, Tagrak-tsangpo, Targo-tsangpo, Buptsang-tsangpo and others, would take part in the fight for the water-parting, and the lakes whose affluents they are would grow considerably and enter into communication with one another until they, as well as those to the north, found outlets to the ocean.
To return to the long feeder of the Indus which before the beginning of the arid period would have flowed from the heights of the Tang-la and through the present basins of Selling-tso and Panggong-tso, this theory does not seem to be more audacious than another, regarding the Tsangpo, and described by BURRARD as follows I :
»The remarkable feature of the Brahmaputra in Tibet is the tendency of its feeders to flow in a direction opposite to that of the trunk river. If but one feeder had been observed to take a course contrary to that of the river, the phenomenon might have been attributed to some local topographical peculiarity; but where all the principal affluents of a long section of the river are found to follow the same contrary course, it becomes evident that the Brahmaputra must at no distant time have flowed from east to west in Tibet, and that its tributaries were developed during that period of its history — .... in our opinion the evidence furnished by its feeders is conclusive; the Brahmaputra formerly flowed through Tibet from east to west. It is not possible to express an opinion at present as to where it escaped through the Himalaya : it may have flowed over the Photu Pass and through the defile of the Kali Gandak; it may have passed through the basin of the Karnali, and it may have followed the present Himalayan course of either the Satlej or the Indus; arguments can be adduced to show that each of these hypotheses is worthy of future investigation, but with our present knowledge no conclusion can be reached.»
The curious fact that the tributaries take a course contrary to the great river is true only for the section from Shigatse to the point where the Brahmaputra begins to pierce the Himalaya. Above Shigatse and to the source of the Tsang-po, the abnormal course of a tributary must be regarded as exceptional. All the uppermost feeders have a quite natural course in relation to the trunk river, and so have the Gyang-chu, the Tsa-chu, the Chaktak-tsangpo, the Raga-tsangpo, the Rung-chu, and the Mü-chu; the latter, however, coming in under a right angle. The fact that the Photu-la, my Kore-la, the extraordinary low depression in the Ladak Range, is only 2 50 feet higher than the Brahmaputra supports, according to Burrard, the evidence that the river once escaped from Tibet along the present course of the Kali Gandak, the immensely deep gorge of which cannot have been eroded by its present river.
I A Sketch, p. 155.
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