RECONNAISSANCE IN CENTRAL TURKESTAN. 193 
floor of the latter is half a mile wide and verj' flat where it is not cuinl)ered bv the 
third moraine. Main- of the smaller \alle\s tributarj- to this one are themselves 
glacial in form and open in the sides of the main valley at heights of 300 or 400 
feet, in true hanging-valley arrangement. These features are due to the work of 
the glaciers of the first and second epochs, and their freshness as compared with 
the weathering of the moraines is a good witness to the great influence of solid 
rock as contrasted with rock waste in preserving physiographic fonns. About 
6 miles below the junction of the Juuka and Jnkuchak streams, which unite at the 
end of the third moraine to form the Yak Tash, the valley loses its glacial form 
and broadens into a basin 5 or 6 miles wide and 8 or 10 miles long. In this lies the 
second moraine, forming a great horseshoe. It .still retains much of morainal 
form and has ninnerous undrained basins, many of them filled with ponds. On 
account of its breadth and flatness, it has suffered less erosion than has its steeper and 
narrower successor. The Yak Tash River flows through it in numerous braided 
channels, which wander freeh' over a gravel flood-plain a mile or two broad. 
So far the moraines of the Yak Tash lie in a linear series like those of all the 
other valleys that we have considered. The relation of the first and second moraines 
is qtiite different. South of the Yak Tash 3 or 4 miles the character of the countn,- 
changes quite abruptly as one passes from the second moraine to the first. On the 
north is the second moraine, a flat country studded here and there with bowlders 
and pitted with numerous little holes and irregular depressions. It is very clearly 
a moraine, for although the slopes are ever>'where well graded, the drainage is 
irregular and by no means completely established. A belt of country south of this 
is 100 or 200 feet higher and has a thoroughly established drainage system, to 
which every part is tributary; the main river has cut a valley several miles wide 
through this belt. There is not a sign of kettle-holes or other glacial topography 
and at first sight there is no sign of moraine ; here and there, however, large bowl- 
ders of slate or oftener of granite from 3 to 6 feet in diameter rise out of the smooth, 
fine soil, and smaller, angular bits of rock of various kinds are scattered about on 
the surface. These lie largely on hill tops, where they can have been brought onlv 
by glaciers, and are therefore to be regarded as belonging to an ancient moraine. 
The branch and main valleys are 200 or even 300 feet deep, and are cut through 
the moraine into an underlying deposit of soft silt. Apparently a glacier flowed 
into this basin .soon after a great deposition of silt had taken place, and becau.se of 
the flatness of the district the ice spread out broadly and deposited an extensive 
morainic sheet 10 to 50 feet deep. A period of subaerial erosion ensued, during 
which the ice retired long enough and far enough to allow. the submature dissection 
of the moraine and of the underlying silts, and to allow the river to cut a valley 5 
or 6 miles wide through both deposits. The ice nuist have stood nnich farther 
upstream during this epoch of erosion, and at its close must have again advanced to 
deposit the second moraine in the valley that had been eroded in the first moraine. 
(5) Afora/ius of the k'ait Si/ ^ r7//<_)'.— In the Kan vSu \'alley all five of the 
old moraines can be detected in addition to the modern one, but the first and second 
are not w'ell differentiated and do not need to be considered. The third moraine 
lies at an elevation of about 9,0100 feet in the triangle between the two main branches 
