174 EXPLORATIONS IN TURKESTAN. 
well covered with grass and by contrast seem fertile. The niountaiiis on the 
southern border of the basin reach a height of from 15,000 to 17,000 feet and have 
been carved into truly Alpine forms by numerous large glaciers. Another basin is 
that of the Ak Sai and Chadir Kul (Tent Lake), where glaciation has played a rela- 
tively small part. The ridge south of this basin forms the Chinese border and 
has already been described. The valleys descending thence to the Kashgar basin 
are of the .same nature as those on the north slope of the plateau toward Issik Kul. 
They are cut in somewhat softer strata, however, and hence are wider, and for the 
same reason the interstreani areas are more dissected into sharp hills. Vegetation 
is almost absent because of the dryness of the climate, and the older contorted 
limestones and slates stand naked in black and gray, while the later strata are bright 
with red, pink, and green. 
Chadir Kul. — The lake of Chadir Kul, at the head of the Ak Sai l)asin, near the 
southern side of the Tian Shan plateau, is a small sheet of water about 16 miles long 
by 6 wide. It is in the midst of a barren, mountain-girt plain, and does not over- 
flow, in spite of the snowy heights that surround it and of a drainage area which, 
according to the Russian maps, is five times as large as the lake itself This has not 
always been the case, however. The plain of Chadir Kul is composed largely of fine 
silt which could hardly have been deposited by aggrading streams so near their moun- 
tainous headwater area, but which might easily have been deposited in a lake. In 
one place a cut some 15 feet deep along the side of a brook discloses iine silt full of 
sphagnum, on which rests a little gravel. The lake formerly had an outlet at the 
head of the Ak Sai basin, where the plain contracts to a distinct channel about a 
third of a mile wide, bounded on either side by a terrace 40 or 50 feet high. Across 
the mouth of this outlet lies a little ridge of sand and gravel 10 or 15 feet high, 
apparently an abandoned and dissected beach. It does not e.xteird quite to the 
northern terrace, being separated from it by an open gap of 200 or 300 feet. Appar- 
ently the outlet was first stable long enough to allow the cutting of the broad 
valley and the terraces on either side. Then a change of some sort caused the 
building of a beach and the partial closing of the otitlet, through which, however, a 
stream still ran for a time before another change caused the lake to retire to its pres- 
ent level. Around Chadir Kul itself nothing was seen to show what these changes 
were and why they occurred. From the evidence of other places, which will be 
discussed later, the changes seem referable to alternate expansions and contrac- 
tions of the lake under the influence of glacial epochs and inter-glacial epochs. 
The outlet of the lake is later than at least one epoch of glacial action, for while 
the terrace on the south side of the broad channel is composed of ordinary gravel, 
the other terrace consists partly of moraine stuff full of bowlders of schistose slate 
ranging up to 3 or 4 feet in diameter. This must have come from the valleys just 
to the north, where there are other moraines, and it ma>- have blocked the outlet 
and caused the lake to expand. The lake as a whole, however, seems to be due to 
a slight swell or bulge in the basin floor between the Ak Sai basin and its contin- 
uation in that of Chadir Kul. 
