THE REGIONS SURVEYED [Chap. II
For the western and higher portion of this mountain rampart which rises to peaks of over 23, 000 feet, the Sheets Nos. 6, 9,10,14, 15 afford ample cartographical materials. To the east of the Keriya river the character of the chain overlooking the Tarim basin does not change; but its width is reduced and the elevated Tibetan plateaus approach it closer from the south. Throughout the whole length of the chain the foot of its northern slopes is formed by a glacis of piedmont gravel, attaining in parts a width of 40 miles and more, and everywhere utterly sterile.
On the north the basin of the Tarim is enclosed by the great Tien-shan chain. In the west it meets the meridional range above mentioned near the Alai and the
mien-shah range. headwaters of the Kashgar river. Thence it stretches away unbroken to
its north-easternmost corner near Korla where the Konche-darya, fed by the Baghrash lake, enters the plains (Sheets No. 24., 25). North of Ak-su, the T'ien-shan attains its culminating point in the great peak of Tengri-khan (Sheet No. 11). Thence eastwards a branch of the main chain, gradually diminishing in height, forms the enclosing wall of the basin. To the west of Ak-su a series of outlying lower ranges intervenes between the main chain and the plains (Sheets No. 4, 5, 7).
While our surveys show this portion of the northern rim in some detail, east of Ak-su they were confined mainly to the southern slopes of the range immediately overlooking the basin (Sheets No. 16, 17, 20, 21). Nevertheless they suffice to bring out certain characteristic differences between this northern mountain border and the K'un-lun. Among them I may mention the much smaller width, or complete absence, of the gravel glacis at the foot of the Tien-shan, and the less arid character of the main range as demonstrated by the presence of conifer forest in a number of valleys on its southern slopes. r Both these facts bear evidence to the influence asserted by the far moister climatic conditions which prevail north of the Tien-shan.
Beyond Korla the desert uplands of the Kuruk-tagh, the `Dry Mountains', take the place of the Tien-shan as the border of the Tarim basin both to the
Desert ranges of north and north-east. The character of this barren succession of much-
decayed parallel ranges with wide gravel-filled valleys and drainageless basins between them, is adequately illustrated by the surveys embodied in Sheets No. 25, 28, 29, 32. What scanty moisture ever reaches the southern slopes of the Kuruk-tagh and escapes evaporation on its wide gravel glacis, descends in wide flood-beds to the Konche-daryâ and its ancient continuation eastwards, the Kuruk-darya or 'Dry River', which once carried its waters to the Lou-lan area. The aridity of the Kuruk-tàgh steadily increases eastwards until at about longitude 91° even the rare salt springs, which rendered its exploration possible, are no longer encountered.
Within the Tarim basin enclosed by the mountain barriers briefly described above, we may conveniently distinguish four main regions. By far the
Central desert of largest, and perhaps the best defined, comprises the huge central area
drift-sand. b ~ P P ~ p~ huge
bare drift-sand desert, popularly known as the Taklamakàn. Its borders to the west, north, and east are roughly determined by the belts of vegetation accompanying the Tiznaf, the Yarkand and the Tarim rivers, the last being the name generally given to the Yarkand-daryâ after receiving the rivers of Kashgar, Ak-su and Khotan. The dune-covered area has outliers beyond these riverine borders in a number of places. But only two of these, both at the extreme ends of the central area, are sufficiently large to deserve here special mention. In the west we have the moving sands of Ordampàdshah stretching from the vicinity of Yangi-hissar to the left bank of the Yarkand river