RECONNAISSANCE IN CENTRAL TURKESTAN. 20I 
that ill the Wasatch and Uinta ranges there are cases of a descent of 8,000 feet, 
although in the Alai and Tian Shan mountains tlie extreme is only about 4,000. 
In seven Asiatic valleys in which there are still glaciers at the valley head the 
average descent from the foot of the glacier to the foot of the lowest moraine was 
2,150 feet. In four of these cases, where the old moraines lie in sloping valleys and 
the old glaciers were therefore free to descend without obstruction, the average 
descent from present glacier to oldest moraine is 2,550 feet ; in the three other cases 
where the old moraines lie in fiat basins and the glaciers could not descend to lower 
levels, it is 1,600 feet. Similar measures can not be given for the American moun- 
tains, since no glaciers e.xist there to-day, but from the other figures already given 
it is to be inferred that the American measure would be at least twice as great as 
the Asiatic. It is conceivable that this difference in intensit}' between the glaciation 
of Asia and that of the other continents was due to a shifting of the poles; but 
besides being without assignable e.xplauation, this hypothesis becomes complicated 
to an untenable extent when it is made to explain the interglacial epochs also. A 
simpler hypothesis is that during glacial times the sea covered northern Asia and 
rendered the climate more equable, a tlieor>' which has been advanced bv several 
writers. Before this h)pothesis can be adequately tested a great array of facts is 
required not onh- in regard to the old glaciers themselves, but also in regard to 
rainfall and evaporation and in regard to the changes of elevation which the land 
has suffered relative to the sea. 
TERRACES. 
If during the Quaternar\- era there were climatic changes of such magnitude 
and frequency as those demanded in explanation of the old moraines, the changes 
must have left their traces all over the region. vSuch traces can be detected in two 
situations, namely, the terraces of streams and the deposits of lakes. The most 
striking feature of the terraces in the valle)'s of Central Turkestan is their wide dis- 
tribution and uniformity of pattern, without respect to the size or location of the 
stream along which they occur. They were seen in the vallej-s of swift mountain 
torrents and along the sluggish rivers of the plains. They occur not oulv in the 
valleys of tributaries of the Syr Darya (Jaxartes) on the north, and of the Ainu Darja 
(Oxus) on the south, but also along the streams that wither to nothing in the Kash- 
gar basin, whether their source be the Tian Shan plateau to the north or the Alai 
Mountains to the west; and they are found even along the water-courses leading to 
inclosed lakes. They var}- in number from stream to stream as well as in different 
parts of the same stream. At the \-er>- head of a valle\- there is naturally no terrace, 
but as the valley is followed downward, first one terrace appears and then another, 
until in that portion of the valle)- where erosion has been more active the terraces 
reach a maximum both in size and number. Farther dowai-valley they again decrease 
in both respects until finally, far out on the floor of some basin, a single weak ter- 
race dies out entirely as the stream becomes an agent of deposition rather than of 
erosion. 
