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National Institute of Informatics - Digital Silk Road Project
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| IIIF Color HighRes |
| Scientific Results of a Journey in Central Asia, 1899-1902 : vol.4 |
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Citation Information
HYPSOMETRY AND RELIEF OF THE TIBETAN PLATEAU.
585
discussed above and the mean altitudes in the known parts of western Tibet which are restricted to internal drainage. In the former we have a mean pass-altitude of 5 189 m., counting from Arka-tagh I to Tschang VII. For the twenty intervening latitudinal valleys we obtain a mean altitude of 49 to m., and this we may take as the altitude of the fundamental base or socle of this part of Tibet. Generally speaking therefore, this base lies too m. higher than the summit of Mont Blanc. Hence the difference in altitude between it and the mean pass-altitude amounts to only 279 m. From this it is evident, that the relative altitude of the mountain-ranges on the Tibetan plateau is very unimportant, and it is easy to understand why some travellers designate these crests as »hills►, notwithstanding that they reach altitudes of 5,500 m. above the level of the sea. If we suppose that the real crest-altitude rises as far above the pass-altitude as this last rises above the base-altitude of the plateau, the mean altitude of the crests would be about 5470 m., or in round numbers 5500 m. Individual parts of these crests reach up to 6000 m., and an occasional peak to 7000 m., although of these there exists no great number. I very much doubt whether any peak in this part of Tibet attains an elevation of 8000 m., though Bonvalot gives this as the altitude of the Dupleix range; for it is probable that within this peculiar denudation region there exists a superior denudation limit above which no single summit has been able to lift itself within the present geological epoch.
Let us now endeavour to ascertain what are the hypsometrical relations between eastern and western Tibet; and first we will examine the results arrived at by the five most distinguished travellers who have explored the internal-drainage area of western Tibet. When we come to calculate the mean pass-altitude we are however often in doubt. With the English travellers the word »pass» can in most cases indicate nothing more than cross-thresholds in the latitudinal valleys, the altitudes of which are extremely small, often less than the altitude of an adjacent camp. Consequently their maps yield only very few passes of the first magnitude. It is only in Dutreuil de Rhins that passes of that category are fairly numerous (14) and distinctly marked as such. But the figures which we get for the mean altitude of the socle or base are all the more reliable, for each of these travellers naturally preferred to encamp in the bottom of the valleys as frequently as possible. The result of my inquiry is as follows.
From Bower's map I have extracted four passes giving a mean altitude of 5502 m. and twelve altitudes for the base, giving a mean of 5312 m. From De Rhins's map I get fourteen passes, giving 5448 m., and thirty-five base measurements, giving 5139 m. Wellby supplies two passes, with 5587 m.; and twenty-nine base measurements, which give 5139 m. From Deasy I obtain two passes, with 5412 m. and fifty-seven base altitudes, resulting in a mean of 5005 m. Rawling furnishes two passes and twenty base data, with means of 5587 and 5183 m. respectively. The result is set forth more clearly in the subjoined table: —
Bower.
| De Rhins. | Wellby. | Deasy. | Rawling. |
| 5448 | 5587 | 5412 | 5587 |
| 5139 | 5139 | 5005 | 5183 |
| 309 | 448 | 407 | 404 |
| Pass-altitude . . . | 5502 |
| Base-altitude . . . | 5 312 |
| Difference | 190 |
74
He d i n, 7ourney in Central Asia. IV.
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