Indeed, the evidences, so far as they have been examined, appear to warrant the conclusion that the region of the western Tian-shan, from Lake Issyk-kul southwards, was in great part the scene of probably five successive glacial periods, each being less severe than the period which immediately preceded it.
After great suffering Hsiian Tsang reached Igu, the seat of a Turkish principality, and pursued his way along the southern foot of the T'ian-shan, which he crossed by a glacier pass (vividly described) in the longitude of Lake Issyk-kul.
From Issyk-kul there is a sharp rise of6000-9000ft.
This last is continued without a break past the western end of Issyk-kul, being directly prolonged by the Alexander Mountains, although parted from them by the gorge of Buam or Bom, through which the Issyk-kul probably once drained.
It forms the barrier between the Issyk-kul and Balkash lakes, the elevation of which is about 5000 ft.