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Digital Archive of Toyo Bunko Rare Books

ever that the attempt, if it is to succeed—on foot, of course, not by aeroplane—will have to be made
from the latter point. For the traveller starting from the Khotan river, the foot of the Mazār-tāgh
would afford relatively easy going for the first twenty miles, if not farther. Slight as the elevation
of the Khotan Mazār-tāgh is, as far as Lāl Singh reconnoitred it in 1908, it would yet give a fair
chance of sighting any isolated rock islands which might be found to continue its direction farther
on. After crossing some further sixty miles of difficult ground, the crest of the Chok-tāgh would
be sighted and offer safe guidance for the rest of the desert crossing. January or February would
probably be the best season for good visibility as well as for the transport of water in the form of ice.

Survival of
desert range
on Khotan
river. And here I may in conclusion offer a few conjectural observations of geological interest. It
is evidently deserving of notice that the north-west and the south-east ends of the ancient hill range
that may be assumed to have once diagonally crossed the great basin now covered by the sands
of the Taklamakān, both survive in the immediate vicinity of large rivers. The fact cannot be
due to mere chance, and its explanation is not far to seek. It is clear that the large river beds, and
still more the broad belts of vegetation that moisture must always have maintained along them,
would inevitably make the accumulations of drift-sand less heavy, and consequently their corrosive
effect when in movement less great, on that side which, in respect of the prevailing wind direction,
would lie under the lee of the river beds. Now all the surface features due to wind-erosion that I
have observed, from the Lop desert to the fragments of the old transverse range about Marāl-bāshi,
conclusively prove the prevailing direction of the winds at work in the Tārim basin to have always
lain from NE. or ENE. to SW. or WSW. Keeping this fact in view, it is easy to realize from the
map that the Khotan river flowing approximately from south to north could afford that protection
only to such portions of the old hill range as lay near to the west of it. Thus the survival of the
Mazār-tāgh, to a distance as actually traced of some fourteen miles from the river's left bank, is
fully accounted for.

Protection
afforded by
riverine
belts. Turning to the area where the range is adjoined by the Yārkand river we find conditions some-
what different. Here the general bearing of the river's course is approximately from S. 243° W.
to N. 63° E., or roughly WSW. to ENE., and thus approximately the same as the prevailing
wind direction. If account is taken of the width of the riverine belts of vegetation—and owing
to the close vicinity of the Kāshgar river delta it is particularly great on the left or northern bank
of the Yārkand river—it is evident that the hills near either side of the Yārkand-daryā must
receive some protection from corroding drift-sand ; but this would necessarily be more effective
on the left bank, where the vegetation belt is greatly increased by the added moisture from the
end of the Kāshgar river. The map shows us topographical facts in close agreement with this
theoretical assumption ; the high and relatively broad massif of the Marāl-bāshi Mazār-tāgh lies
near the left bank, and the distinctly lower and more attenuated ridges of Chok-tāgh and Kum-tāgh
lie on the right. It is further fully in keeping with the above theory that we find the detached ridges
to the north and north-east of the Marāl-bāshi Mazār-tāgh sinking lower and lower the farther
away they lie from the protection of the riverine belts of the Kāshgar-daryā. Thus the Bēl-tāgh
is distinctly lower and more eroded than the Ōkur-mazār-tāgh of which it is a prolongation (Map
No. 8. A, B. 1), and the Lāl-tāgh lower than the hills near Tumshuk. A probable explanation is thus
found for the almost total effacement of the ancient range where its line approaches at right angles
the outermost T'ien-shan or Kelpin-tāgh, presumably of geologically later origin ; here the small
Shikarwai knoll (Map No. 8. A. 1) appears to form its only remnant.

Persistence
of factors
affecting
desert
formations. These observations are offered with all the reserve which my want of systematic geological
training necessarily imposes. But it may at least be claimed for them that they are consistent
with that method, the application of which, as a safe guide to the genetic history of present desert