144 Tibet and Turkestan
also a Tarim affluent. We found nothing coming in—all going out. We crossed, or passed near, the headwaters of the Amou Daria (Oxus), the Syr Dana (Jaxartes), whose waters go to the great Russian lake, the Aral Sea, so-called. Then proceeding on the long lines, drawn north-east, then east around Mongolia, we could cross or see the sources of the Irtysh, the Yenisee, the Lena — all the tribe of Siberian streams that seek the Arctic Ocean.]
We may now give meaning to the long circumferential inspection—an airy journey of seven thousand four hundred miles. It is evident that we are dealing with great plateaus, one much lower than the other. The Mongolia-Turkestan region has an average elevation of about three thousand five hundred feet. The Turkestan region, separately considered, and with which we are most concerned, is at once a plateau and a depression, since it lies much lower than the mountains surrounding it. This characteristic is not so marked in the Mongolian region, as the Gobi desert area is in a sort of great terrace-form, stepping up to the surrounding mountains eastward. The Tibetan plateau, in all its northern (much the larger) area, is approximately at
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sixteen thousand feet elevation. The great valley, toward which the slope is more gradual from the north than from the south, varies from thirteen thousand to eleven thousand feet elevation ; Lhasa is between eleven and twelve thousand ; Gyangtse, Leh, and indeed all the other considerable towns in similar region are at about the same elevation.
The whole of the three great regions we have
IIIFカラー高解像度
