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 |
| Overland to India : vol.2 | |
| インドへの陸路 : vol.2 |
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引用情報
244 OVERLAND TO INDIA CHAP.
When we, then, find in Eastern Iran sand on the southern
sides of enclosed basins we may hence conclude that r
northerly winds predominate. On A. Buchan's wind maps of the world we find the following prevailing winds given
January . . NW. or N. July . . . N. or NW.
February . . N. or NW. August . . NW.
March . . N. September . . NNW.
April • . NW October . . NW.
May • . NW. November . . NW.
June . N. December . . N.
Accordingly, winds from the northern 'quadrant prevail throughout the year in Eastern Persia, and therefore all doubt is removed as to the cause of the driftsand's distribution. As regards the great Kevir in particular, it is hardly possible to entertain any other conception but that the belt of blown sand on the southern margin is fed by material from the weathered hills on the northern boundary of the salt desert, as well as by the sand which forms so large a constituent part of the Kevir soil. This, however, is only attacked by the wind during the dry season, for when the Kevir is wet the wind is completely powerless. The prevailing winds may be assumed to have been the same as at present for endless ages past. Weathered material for the maintenance of the sandy deserts has not been wanting. It is the third factor, the configuration of the country, which determines the extent of the sandy area.
Over level plains, where there are no obstacles, the dunes move on and are succeeded by new sand formation. Such is the case in the Kizil-kum, Kara-kum, Takla-makan, and Rigistan. Where hills stand to the south of the sand-belt they offer resistance and set bounds to the extension of the desert. This is the case in all the depressions of Eastern Persia. The crescent-shaped sand-belt on the southern margin of the basin is constantly fed by fresh blown sand carried thither by the wind over the level floor of the basin. But as much sand is carried away to contribute in other places farther south to the progressive filling up of
1 Report of the Scientific ,Results of Me Voyage of H. M.S. " Challenger," 1873.76, vol. ii.
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