GEOLOGY. 
29 
Thian Shan must have greatly subsided, and the wider the valleys, the more effectively 
was the extent of subsidence felt. To support this idea by an observation, I may notice 
that north of Chung-terek, at the base of the Koktan range, the Artysh beds have entirely 
disappeared in the depth, and the gravel beds overlying them dip partially under the 
Trias limestone,—a state of things which cannot be explained by denudation, but only by 
subsidence and consequent overturning of the older beds above the younger ones. A similar 
state of things is to be observed on the Terek range, where the young tertiary limestone- 
conglomerate is in some places of contact overlain by the much older dolomite. Now, if the 
broad valley of the Kasbghar plain sank first, and gradually lowest, as it in all probability 
did, we find a more ready explanation of the large quantities of loose gravel pouring into 
it and accumulating at the base of the Artysh range. 
The sinking in of the volcanic centre north-west of Chakmak first appears to have 
drained off the former head of the Aksai river, making it the head of the Toyanda instead; 
and to the north of the Terek ridge it was most probably the cause of the origin of the 
Chadyr-kul. The subsidence of the country followed in the south, making it possible for the 
united Suyok and Toyanda rivers to force their passage right across the Koktan range, 
strengthen the Artysh river, cut with facility through the Artysh range, and join the Kashghar 
Daria. While thus indicating the course of the comparatively recent geological history of 
the ground, it must be, however, kept in mind that this change in the system of drainage 
had no essential effect upon the direction of the hill ranges. This, dating from much older 
times, was mainly an east-westerly one, following the strike of the rocks which compose the 
whole mountain system. 
