RECONNAISSANCE IN CENTRAL TURKESTAN. 21 5 
By the end of the Tertiar>' era erosion and deposition had so far lowered the 
mountains and filled the basins that the countr>' was in a stage of late maturity or 
even of old age. Considerable warping had taken place during the preceding 
period, and perhaps was still going on, but the rate was so slow that even the 
languid erosion of late maturity was able to keep pace with it. At the beginning 
of the Quaternary era, however, there was a revival of internal activity which 
manifested itself chiefly along the lines of movement of earlier times. Warping 
and .some faulting then took place so rapidly and so recently that the forms to which 
they gave rise still dominate the topography, and the effects of erosion are chiefly 
noticeable in the young valleys. By these movements Central Turkestan was 
divided into its present physiographic provinces. One province, the Tian Shan 
plateau, is essentially a broad, flattened arch, on the top of which a number of 
minor warpings give rise to lofty plateau-like ridges surrounding elevated basins. 
A second province, the Alai Mountains, is a similar arch, except that it is narrower 
and lacks the minor comigations on the top. Both of these provinces are char- 
acterized by very precipitous young valleys, between which are tilted and well- 
preserved portions of the Tertiary penepJain. The two other provinces are basins, 
those of Kashgar and Fergana, the flat floors of which have for ages been regions 
of deposition. In the Fergana basin deposition has for the present ceased, but in 
the Kashgar basin it is still progressing actively. 
The recent geological history of Central Asia has been controlled b\- a series 
of climatic oscillations between conditions of relative warmth to those of relative 
frigidity. Evidence of these changes is found in phenomena of three distinct types 
associated with the headwaters, the tnmks, and the lower ends of the rivers. In 
the high mountains many headwater streams flow from glaciers which in ancient 
times were much expanded so as to deposit moraines at considerable distances down 
the valleys. The moraines show that the ice advanced five times during as many 
glacial epochs, and that between the advances there were epochs of retreat which 
must have been almost as warm as the present, if not wanner. The moraines 
further/ show that the glacial epochs steadily decreased in intensity- from first to last, 
and, although less clearly, that the interglacial epochs correspondingly decreased in 
length. Along'their middle course the streams, almost without exception, flow in 
terraced valleys. The only adequate explanation for these seems to be a series of 
decreasing climatic oscillations from cold epochs on the one hand, when increased 
weathering overloaded the streams and caused them to aggrade and broaden their 
\alleys, to warm epochs on the other hand, when the streams cut narrow canyons 
in the bottoms of the previously formed flood-jilains, thus jiroducing terraces. The 
number of the terraces does not agree precisely with the number of the old 
moraines, but the disagreement is easily explicable by a simple expansion of tlie 
theory of climatic changes so that it shall include a series of increasingly severe 
glacial epochs preceding the epochs of the decreasing series. In other respects the 
agreement of the terraces and the moraines seems \-er\' close. The fonner as \\cll 
as the latter indicate not only that there were oscillations from one extreme of 
climate to the other, but lliat in intensity as well as in length each succeeding 
period was less than its predecessor, for the terraces decrease steadily in breadth and 
