国立情報学研究所 - ディジタル・シルクロード・プロジェクト
『東洋文庫所蔵』貴重書デジタルアーカイブ

or 3 miles below Damburachi the river flows through a narrow cut, skirting the
north side of the valley, while the lower terrace rises as a plateau on the south
with an old channel of the Kizil Su on it. Below there it converges with the present
flood-plain and just below Pildona, 6 miles above Hawee, it sinks under. From
there on nearly to Garm, it lies buried in the present flood-plain and the river at
high water swings against the valley sides it scoured during the third erosion cycle.
Just above Garm the lower terrace rises out again and the river enters a channel
that deepens steadily to Obu-garm, the westernmost point of observation, where
this terrace is about 300 feet high as cut into by the present channel, that of
our fourth erosion cycle.

In defining the third stage we inevitably defined the fourth, the channel of
to-day. But some important facts should yet be noted. The present channel
is cut in alluvial gravels all the way, excepting for occasional glimpses of bed-rock
bottom. Obviously, then, the stream had cut down as far as it is now during the
third erosion cycle, which,
however, closed with a re-
filling and valley-widening
to the third stage. The
earth-movements which
wrought its fourth and last
erosion cycle were of such a
nature that about 35 miles
of the valley, that portion
between Garm and Pildona,
was negatively affected,
that is, aggraded instead of
corraded. This would
appear to indicate warping,
and that idea is reinforced
by observations on tribu-
taries. Two large tributa-
ries converge to Hawee,
where they debouch in the
Kizil Su. One comes in
from the west, the other from the north. If the great valley suffered a longi-
tudinal warping, we should expect to find the one from the west rejuvenated, the
one from the north aggrading in sympathy with the main river. This is precisely
the condition at Hawee. One more important fact remains: the Kizil Su has
not yet graded its fourth-cycle channel, excepting over the 35-mile stretch of
relative depression. The present flood-plain is divided into several long stretches
where the river splits into a braided stream. Between these the channel narrows
into short shoots, where it plunges over sills of bed-rock. The fourth erosion
cycle is, therefore, the result of a warped uplift still in process, or so recently
completed that corrasion has not yet attained an even grade.