200 EXPLORATIONS IN TURKESTAN. 
COMPARISON OI" OLACIATIOX OK ASIA WITH THAT Ol" AMURICA AND IvUKorK. 
When the glacial history of Asia is comparefl with tliat of Aiueiica and Europe 
there is found to be an essential agreement of the main facts. In all three conti- 
nents there seem to have been cold glacial and warm interglacial epochs. American 
geologists usually recognize three advances of the ice, while many European geol- 
ogists recognize a larger number, and in Asia, as we ha\e seen, there seem to liaVe 
been five. In so far as these facts agree, they indicate that the cause of the glacial 
period must have been of widespread influence, since it has produced similar effects 
in many parts of the northern hemisphere. The present discrepancy in the number 
of glacial epochs detected in different regions may yet be reconciled ; but there is 
another discrepancy which can not as yet be explained. It has been already .stated 
that the glaciatioii of Central Asia was much less severe than that of Europe and 
America. A specific comparison will make this clearer. The onh- European 
mountains that are at all comparable in height to the Alai and the Tian Shan 
ranges are the Alps; but the Alps lie so much farther north than the Tian Shan 
and in a region of so much greater precijiitation that a direct comparison as to 
glaciatioii can not be made between them. In .\inerica, however, the Uinta and 
Wasatch ranges, although somewhat lower than the Asiatic ranges, are in other 
respects very similar to them. In both cases the mountains lie at a latitude of 
from 40° to 42° N., in the center of a continent far from the .sea, and therefore in a 
region of slight rainfall. Close by are extensive desert plains, along the border of 
which are numerous piedmont villages dependent entirely on irrigation by moun- 
tain streams. The Asiatic mountains are higher than the American ranges above 
named by an average of fully 3,000 feet ; they seem also to have at present a greater 
precipitation, if we may draw such a conclusion from the number of summer storms, 
the height of the snowline, the number of perennial streams, and the amount of 
vegetation. From these considerations it is clear that if during the glacial period 
there was an equal climatic change in both countries the Asiatic glaciers ought to 
have descended lower than the American ; but this was not the case. Let us com- 
pare the figures in the two regions. 
In order to avoid all po.ssibility of exaggerating the unlikeness between the 
Asiatic and the i.\merican ranges, let us .say that the average lower limit of perma- 
nent snow is 13,000 feet in both cases, although in America it is above this, and in 
Asia decidedly below. Let us also suppose that the greater height of the Asiatic 
mountains had no effect on the descent of their more protected northern glaciers. 
Even with these concessions we find that the Uinta Mountains weie covered by 
glaciers which locally merged into something of an ice sheet near their western 
end, while those of the Alai and Tian .Shan were all confined to the valleys. The 
average descent of the ice in the twenty-four valle\'s listed in Table III, from 
the assumed snow-line of 13,000 feet, places the base of the lowest old moraine at 
9,740 feet f while in the Uinta and Wa,satch mountains the average altitude of the 
moraines on the northern slops is 8,055 ^^^^ ^'^^^ on the southern slope 7,033 feet, 
as determined by Dr. W. W. Atwood. If we compare the extreme jjoints to which 
the lowest glaciers descended below the present snow line in either region it apj^ears 
