Innermost Asia : vol.1 / 432 ページ（白黒高解像度画像）

0432	Innermost Asia : vol.1
極奥アジア : vol.1

tion of the ground in the Bēsh-toghrak valley. For this purpose I had instructed the Surveyor
before our start from Mīrān to carry a continuous series of levels with the Zeiss levelling instrument
provided on Sir Sidney Burrard's recommendation, from north of Kum-kuduk to the first dry
lake basin crossed by the route eastward of Bēsh-toghrak.

Line of
levels. My instructions were that this line of levels should, as far as practicable, be carried along the
lowest ground of the depression separating the foot of the hill range on the north from that of the
chain of high sand ridges on the south. But Muḥammad Yāqūb, soon after starting from Kum-
kuduk, encountered the great belt of hard salt crust which here marks the eastern arm of the dried-
up ancient salt sea, and recognizing the formidable obstacle it presents to prolonged work, decided
to commence his levelling on the sandy scrub-covered ground which edges the salt-encrusted
belt on the north. Starting from his Camp XCVIII a little to the east of the meridian of Kum-kuduk
(Map No. 32. D. 4), his line of measured levels, as marked by the route line past his Camps XCIX–
CII, kept first near the northern edge of the salt-encrusted ground and farther on approached closer
to the middle of the valley. Owing to a misapprehension, which however does not affect the result,
it crossed the valley to the Bēsh-toghrak wells, before it was finally brought with a north-easterly
curve to the ' basin with wet sand ' shown in Map No. 35. B. 3. The total length of the line over
which the series of levels was measured was 59 miles, 6 furlongs, a constant distance of 600 feet
being maintained between each pair of the 526 stations.

Datum
point at
Bēsh-
toghrak. The result of this operation is recorded graphically in the sectional drawing of the levelled
ground which is reproduced as Appendix C of my Memoir on Maps of Chinese Turkistan and
Kansu. In this the height of Bēsh-toghrak (Camp CII), 2,340 feet, as shown in Map No. 35. B. 3,
has been adopted as the datum point. This height was derived, at the time of compiling the
1 : 500,000 map, from the mean value of the observations made in 1907 and 1914, and in view
of the considerable discordance between the two it can lay no claim to any close approach to
accuracy.¹³

Continuous
descent of
valley
bottom. But this in no way affects the very definite proof which the levelling chart affords of the gradual
and continuous descent of the valley bottom from the dry lake basin east of Bēsh-toghrak to the
salt-encrusted ancient sea-bed north of Kum-kuduk. The starting-point of the levelled line at the
latter point is shown to lie 250 feet below the former, and the descending slope to be a gentle but
steady one, with an average fall of about 4·2 feet per mile. Such occasional small breaks in the
continuity of the downward slope as the chart indicates nowhere exceed 5 feet, and are such as
inevitably occur owing to slight inequalities of the ground wherever levels are measured in a more
or less straight line and not along the actual course of the surface drainage.

Geographi-
cal interest
of levelling. In view of the uncertainties besetting all height observations made only by aneroid or hypso-
meter and the impossibility of judging slopes on ground which appears as flat to the eye as does
the salt-encrusted bed of the ancient Lop Sea and of its eastern extension into the Bēsh-toghrak
valley, the conclusive evidence supplied by the above levelling claims special importance. It
proves that the whole of the valley belongs to the drainage area of the Lop basin. The geographical
interest attaching to this fact will become clearer in the light of what I have to record below regard-

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