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 Kashghar 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. 



