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Digital Archive of Toyo Bunko Rare Books

of the Āltin-tāgh glacis. ¹⁰ It is apparently in this bay that the depression reaches its
deepest point, and here it may be supposed in earlier geological times to have received also
the drainage from the terminal basin of the Su-lo-ho which adjoins eastward. Down the
southern side of this valley and beyond along the clearly marked southern shore-line of the
ancient sea, leads the difficult desert track from Tun-huang to Lop, graphically described by
Marco Polo and still used by rare caravans during the few winter months when it is
practicable. ¹¹

Before leaving the Tārim basin for regions further east a brief account may conve-
niently be given here of the small but geographically very interesting
Turfān depression. basin of Turfān north of the Lop depression, to which a good deal of
our survey work was devoted in 1914-15. Quite detached from the
Tārim basin it shares so many of its physical characteristics that it appears like a small scale
reproduction of it. As Sheet No. 28 shows, it is enclosed in the north by a rugged snowy
portion of the T'ien-shan, rising to peaks over 14,000 feet in height, by an outlying range of
the same in the west, and by utterly barren hills and plateaus of the Kuruk-tāgh in the south
and east. Within these limits it contains a succession of well-defined zones exactly corre-
sponding to the gravel glacis, the belts of cultivation and desert vegetation, and the dune-covered
areas of the Tārim basin.

The terminal sea-bed of the latter has also its pendant in the narrow salt lake, for the
most part dry, ¹² stretching along the south-eastern edge of the basin.
Character and depth of Into its lowest portion at the time of the summer floods gathers
Turfān depression. whatever drainage from the mountains escapes evaporation. To the
east of it we have a miniature edition as it were of the Taklamakān in the plateau-like area
covered by high ridges of dunes known as Kum-tāgh, the 'Sand Hills'. ¹³ Its position seems
to be determined by the direction of the prevailing winds which as a result of 'aspiration'
sweep down from the cooler region in the north-west when the great heat of the spring and
summer causes the air to rise from the lower parts of the basin. A very remarkable feature
of the Turfān basin is the depth of its terminal depression. Along the lake-bed above
mentioned it descends to a level which according to our mercurial barometer observations lies
in places close on 1,000 feet below the sea, while most of the principal oases lie also about
or below sea-level. ¹⁴

To the very high summer temperatures resulting from this low position may be
attributed, at least partly, the peculiar conditions affecting the water
Irrigation in Turfān supply of the basin and in consequence the cultivation in its oases. ¹⁵
oases.
The streams which carry down the melting snows of the T'ien-shan in
the spring and summer lose most of their water on the descent over the bare glacis of gravel.
A portion of the water absorbed in the ground, it is true, comes to light again, like the kara-su
of the Khotan region, in marshy springs at the northern foot of the low and utterly arid hill
range stretching across the middle of the basin from east to west and dividing its cultivable
area into two unequal belts. ¹⁶

But this water supply, too, would permit of irrigation only over very limited ground
were it not at the present time supplemented on a big scale by means
Kāréz irrigation. of sub-terraneous channels or 'Kārézes' which catch the subsoil water
beneath the gravel slopes and carry it, protected from evaporation, over
considerable distances to ground otherwise hopelessly sterile but under irrigation extremely
fertile. The use of Kārézes is unknown elsewhere throughout Chinese Turkistān, and in the
Turfān district, too, it can apparently not be traced further back than the 18th century. Yet