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
『東洋文庫所蔵』貴重書デジタルアーカイブ

Terminal basin of Etsin-gol.

Limitation of alluvial deposits on Etsin-gol.

Sand ridges east of Umne-gol.

434 THE ETSIN-GOL DELTA AND THE RUINS OF KHARA-KHOTO [Chap. XIII

the Sokho-nôr into the western main course of the Ümne-gol, was no longer found running by Lâl Singh. It had obviously dried up meanwhile and thus failed to keep the water of the basin fresh, as it did previously. A comparison of the two surveys also brings out the fact that the extent of the Gashun-nôr, the western and main terminal lake, had shrunk in an exactly corresponding measure, its width from east to west appearing reduced from about twenty to fourteen miles. With regard to the relation between the two lakes it deserves to be specially noted that Lai Singh's height observations, like those of M. Kaznakov, show the Sokho-nôr as lying appreciably higher than the Gashun-nôr.5 The fact that the Etsin-gol terminates in two separate, and in 1914 quite independent, lakes has its distinct interest, because it furnishes a close parallel to what we had occasion to point out above as regards the relation between the Su-lo-ho and the Hua-hai-tzû basin on the one hand and the bifurcation at an earlier period of the terminal Su-lo-ho towards the Lop sea-bed on the other.6

The survey of this interesting ground in'the terminal basin of the Etsin-gol had to be carried out by Lai Singh alone, while I myself was kept busy by archaeological work at the Khara-khoto site. Having to my regret been unable from lack of time to visit this ground in person farther north than Dashoba, I must be content with a few brief remarks suggested by a comparison of the available topographical data with those noted in the Lop and Su-lo-ho basins. Apart from the bifurcation already referred to, the Etsin-gol terminal basin shares with that of the Su-lo-ho two surface features, not less noteworthy because they are of a quasi-negative character. One is the absence of any very large salt-encrusted areas, and the other the very limited effect that wind-erosion is able to assert on the present surface of the ground, in spite of the violent winds that sweep over both basins during great parts of the year.

I believe that the explanation in each case may be sought in the comparatively rapid fall of both the Su-lo-ho and the Etsin-gol in their terminal courses. This has necessarily greatly limited the ground liable to periodic inundation and consequent salt-incrustation. At the same time it has also limited the extent of alluvial clay deposits upon which wind-erosion can best work its force when desiccation sets in and leaves them unprotected by vegetation. Along the Ümne-gol branch the fall of the river-bed between Camp 156, some three miles above Tâwun-tora, and the Gashunnôr, a distance of about 44 miles, amounts to fully 57o feet, and it is just the same over the corresponding distance between Camp 150 (Map No. 45. B. 1) and the Gashun-nôr. The belts to which the several river branches have carried their alluvium at different periods are not very wide and are still receiving enough moisture, whether from floods or subterranean drainage, to maintain vegetation and thus receive protection from wind-erosion. The same protection is afforded by the very nature of their surface to the stretches of gravel ` Sai ' which separate these belts and are found right down to the vicinity of the terminal lakes. Hence the marked rareness of Yârdangs in the Etsin-gol basin, and the scarcely noticeable effect that wind-erosion has had upon its ruins.

Yet the strength and frequency of the winds that blow down into the Etsin-gol basin, mainly, as we learned by trying experience, from the west and north-west, have left their landmark in the shape of big ridges of dunes to the east of the Ümne-gol. As the maps (Nos. 44. c. 4; 45. c. 1) show, this accumulation of sand ridges reaches a height of 200 feet to the south of the Sokho-nôr, and stretches for a total length of over twenty miles. We have in it the exact counterpart of the high ridges of drift-sand which rise to the west and south-west of the terminal lake-bed of the Su-lo-ho

5 According to M. Kaznakov's observations the Sokhonôr at the level seen by him lies about a hundred feet higher than the Gashun-nôr. LA1 Singh's readings, with an aneroid

that kept a remarkably good record, make the former lie about two hundred feet higher. 6 See above, pp. 386 sqq.