l82 EXPLORATIONS IN TURKESTAN. 
THE QUATERNARY PERIOD. 
Ill our survey of Central Turkestan we have found tluit its geological history 
was long characterized by a remarkable unit>'. The geological series is uniform in 
the main, though not in detail. Much of the country- in late Tertiary time was 
reduced to tlie stage of mature or old topography ; and now, after broad deforma- 
tion, the basins continue to be aggraded plains, and even the mountains retain 
much of their Tertiary maturity, although exhibiting marked results of revived 
erosion. When the country- was divided into strongly marked provinces by the 
Quaternary defonnatioii, a considerable diversity was introduced between the 
mountains or plateaus on the one hand and the basins on the other. Both the pre- 
Quaternarv uiiitv and the Ouaternar)- diversity were due largely to internal causes — 
to tectonic movements or to lack of movement. In the remainder of this report 
I shall consider a series of changes of a different character, which seem to have 
nothing to do with movements of depression or elevation, but appear to depend 
upon external controls. The changes now considered were climatic and seem 
to have affected all parts of the country at the same time, although in different 
ways. As the changes continued to take place through a large part of Quaternary 
time, they furui.sh the basis for a definite time-scale of wide application. They 
involve a series of oscillations between glacial and interglacial epochs. The plan 
of study outlined by Professor Davis at the beginning of our work in Turkestan 
directed attention to the evidence of possible climatic changes shown (i) in ancient 
moraines; (2) in terraces, especially along streams flowing from moraines; (3) in 
lakes and lake deposits ; and (4) in deltas and flood plains of streams which do not 
reach the sea. In examining evidence of the first three classes it was found not 
onlv that climatic changes have occurred, but that there has been a series of changes 
of decreasing se\erity ; it has, however, not yet been possible to correlate exactly 
the changes shown by one class of evidence with those shown b}' another. In the 
fourth class there should also be indication of climatic changes if the facts elsewhere 
olxserved have been rightly interpreted, but as yet this cla.ss of evidence has not 
been detected. 
GLACIATION. 
DISTRIBUTION OF GLACIERS AND AMODNT OF EROSION. 
During the two months' journey from Issik Kul to Marghilan a considerable 
number of glaciers, possibly fifty, were seen among mountains ranging from 
14,000 to 18,000 feet in height. Most of the glaciers were small and ended close 
to the ba.se of their cirques. The largest was that of Khoja Ishken* in the Alai 
Mountains, close to the Bokharan boundar}-, at the head of one of the innumerable 
Kok Sus or Blue rivers. It is a small example of the vallej* type of glaciers com- 
monly associated with the Alps. Its length, so far as can be judged from very 
incomplete maps, is 5 or 6 miles. None of the glaciers descend to a low elevation, 
*0n the Russian map, scale 10 versts to the inch, this is called the Adramova glacier, but as the 
Kirgphiz in the neighborhood use the name Khoja Ishken, I have adopted the latter. 
