146 EXPLORATIONS IN TURKESTAN. 
FORM OF THE GREAT ALAI VALLEY, 
THE VALLEY ITSELF. 
Although the dimensions of the Alai Valley have already been given, a repeti- 
tion seems necessary. It is, except for the flood plains of streams, a smooth, grass- 
covered plain about 75 miles long, averaging 12 miles in width, and broken by 
transverse undulations where moraines project from the principal side valleys. It 
has a longitudinal pitch from 10,500 feet at the pass on the east to 3,200 feet at 
Darak Kurgan on the west end, and a transverse inclination of about one-half a 
degree alongside streams from its southern to its northern border. The Kizil Su, 
or trunk stream, thus flows close to the northern border. 
Very few of the side streams coming down from the Trans-Alai, or southern 
border, reach the Kizil Su, except in high flood. On July 14 we followed the flood 
plain of the Kizil-Art dar>-a, which is one of the larger streams, from Bor Daba to the 
Kizil Su. Although there had been three days of rainy weather, all the channels of 
this stream were dry at 15 versts down from Bor Daba. The lower portions of the 
flood plains of larger streams from the Trans-Alai are often several versts in width 
and generally of clean gravel, with certain strips grown over with loess, and rising 
in the middle to a considerable height above the surrounding plain. These observa- 
tions, together with the extensive distributary s)-stems as seen on the map, are good 
evidence of delta accumulation. In the eastern half of the valley the Kizil Su itself 
is a sluggish stream and incapable of transporting more than a very small propor- 
tion of the immense amount of waste supplied by the Alai Valley tributaries. This 
is shown l:)y the splitting of the stream over long stretches and absence of any 
permanent channel cut down below the surrounding plain. 
We have seen that, in the past, great accumulations of moraine were brought 
into the Alai Valley, that since the Kurumdi, or later glacial epoch, great depths of 
moraine of that advance have been l:)uried by later waste, and that the valley is now 
rapidly filling up with alluvium. A general glance at the valley as a whole would 
show that it has the character of a fonnerly deep \'alle)' now much filled up with 
waste. The ledges flanking the mountains on both sides of the valley slope 
sharply into alluvial and glacial deposits. It wotdd be interesting to know how long 
this valley has been filling up, what proportion, if any, of this filling took place 
before the Alai glacial epoch, what proixyrtion between the Alai and Kurumdi epochs, 
how much since the Kurumdi epoch, and how far down it would be to bedrock in 
a cross-section. Much light might be thrown on these questions in exposures of 
the gorge at the outlet to the valley. It seems highly probable that the valley has 
suffered from morainal blocking. This might explain the existence of the gorge 
that drains it as a drop-over from the high zone of morainal blocking and consequent 
alluvial accumulations into lower regions unaffected by glacial action. 
SIDE TRIBUTARIES. 
The side valleys emptying into the Alai Valley from the Trans-Alai range have 
already been described in paragraphs on glacial geology. It was shown that there had 
been a lowering of baselevel of those streams from the south and consequent cutting 
