Turfàn basin with special interest, as briefly mentioned above (p. 48) is the great depth below sea-level to which it descends in its lowest portion around the Aidin-köl marsh. It may hence be specially noted that the heights or depressions recorded in the map for the following places are derived from observations made with a mercurial barometer:
Kara-khöja, Camp 242 (house of Beg, near N.E. corner of ruined town ; C. 3), —110 ft.
Kara-khôja, Camp 242 (in Bezel.; C. 3),
Yàr-mahalla, Camp 243 (house of Russian Ak-sakàl; C. 3), 250 ft.
Sai-kàrez, Deghar, Camp 275 (D. 3),
Tuz-kan, Camp 276 (near east end of dry lake-shore ; D. 3), — 940 ft.
Plane-table station, N.W. of Camp 276 (on dry lake-shore; D. 3),-980 ft.
Camp 277, (on edge of gravel Sai ; C. 3),-860 ft.
Fixing S.W. of Camp 277 (on gravel Sai; C. 3),-720 ft.
Camp 279, N. of Bejàn-tura (by bed of dry stream ; C. 3), — 780 ft.
Bejàn-tura, Camp 282 (foot of ruined tower; C. 3), — 910 ft.
Turfàn, Yangi-shahr, Camp 280 (C. 3), — 80 ft.
The approximate datum-line and contours below sea-level, at approximate intervals of 250 feet, have been shown by broken lines of greyish-green.
Other heights shown in this sheet are mostly derived from aneroid observations, checked in the case of those taken in 191415 by R. B. Lel Singh with reference to readings at mercurial barometer stations.
The assumed snow-line was fixed at a level of 12,500 feet with regard to the conditions observed on crossing the pass above Pa-no-p`a (B.1) on October 23, 1914.
As already observed above in Chap. x (p. 35) the Turfàn basin reproduces on a
Astronomically observed latitudes.
small scale most of the physical features characteristic of the different zones of the Teem basin. Thus below the rugged Tien-shan main range in the north, rising with part of its crest above the snow-line, we find a wide and utterly barren gravel glacis (B-D. 2). The underground drainage, caught by means of kdrèzes at its foot and at that of a low but rugged outer hill-range which traverses the basin from east to west, supplies most of the irrigation for the richly cultivated tracts scattered north and south of that transverse hill-range.
Between and below these oases extends a belt of scrub-covered and for the most part sandy ground right down to the long-stretched narrow lake-bed, mostly dry and salt-encrusted, which occupies the deepest part of the basin. This descends near the eastern end of the lake-bed to a level close on 1000 feet below sea-level. To the east of these rises a dune-covered expanse, the Kum-tàgh, like a miniature Taklamakàn. In the south there lies the ascent, over a gravel glacis and a succession of arid plateaus, to the northernmost of the Kuruk-tàgh ranges.
The northern end of the sheet shows the slopes of the Tien-shan which descend, forest-clothed at elevations from about 6000 to 9000 feet and receiving ample water, towards the plateaus and open plains of Dzungaria. Extensive cultivatiOn dependent on rainfall only is found on these northern slopes, evidence of the great climatic divide formed by the Tien-shan range.
The historical importance of the Turfàn depression, especially during the early Turkish (Uigur) domination, is attested by a large number of ruins within or close to the cultivated tracts. For a brief account of the visits paid to these in 1907, see Desert Cathay, ii. pp. 353 sqq.; Serindia, iii. pp. 1159 sqq. A short summary of my prolonged labours in the district during 191415 is given in Geograpk. Journal, 1916, xlviii. pp. 202 sqq.