RECONNAISSANCE IN CENTRAL TURKESTAN. 
173 
the Jukuchak pass, is full of old moraines spread in a broad, uneven sheet and inclos- 
ing numerous lifeless ponds and lakes. In other basins the moraines have not 
advanced so far and the streams have cut slight terraces in the gravel silt or the Ter- 
tiary strata which lie on the floor of the depressions and fonn the plains. Such in 
general are the basins and ridges of the most typical portion of the Tian Shan plateau. 
In the very center of the plateau is a valley of erosion of quite a different char- 
acter. South of Chakur Korum pass the Kara Kul River, one of the main branches 
of the Narin, flows in a young valley 1,000 or 2,000 feet deep, with a narrow 
bottom and steep walls like those which characterize the valleys on the north .slope 
of the plateau. The road descends from the pass to the river by a narrow side 
valley with walls a thousand or more feet high, and in some places perpendicular 
Fig. 125. — Scene in the Yak Tash Basin, in the northern part of the Tian Shan plateau, looking 
northwest. In the foreground the basin-floor is covered with a flat moraine holding numerous 
ponds : beyond are smooth-topped mountains cut by glacial valleys. 
for several himdred feet. Near its mouth, where the flood-plain widens a little, the 
valley is suddenly blocked by a barrier nearly 200 feet high, lying directly across 
the path of the stream. This barrier is the moraine of a little glacier tenninating 
far up on the precipitous side of the valley. The moraine is so porous that the stream 
flows directly through it with no apparent check, although the gra\-el flood-plain 
above the barrier is broader than below. 
Among the elevated basins of the Tian Shan plateau one of the largest is 
that of the Mudirum Su. Its upper portion is a desert of old morainic waste 
unrelieved by vegetation ; the lower portion is also full of moraines, but they are 
