RELATIONS OF THE RIVER CIIU TO ISSIK KUL. II3 
evident, then, that the maintenance of the lake shore at A in a lake without outlet 
involves an extremely improbable correlation of two independent processes — a 
balancing- or tilting of the region and an external climatic change. Hence a lake 
in which the shoreline remains nearly fixed at A, while it sinks to D (E) and rises 
to G (H), must in all probability be unlike the lake here postulated ; that is, it must 
be provided with an outlet, instead of being without one. 
It is plain enough that an ov-erflowing lake will keep its shoreline fixed at the 
outlet, however much it may change elsewhere on account of a tilting of its basin. 
Hence there can be no cjuestion that the recent valley erosion and valley drowning 
around Issik Kul are Ix'tter accounted for by the example of a lake with, and not 
without, an outlet; and it therefore seems reasonable to conclude that the present 
relations of the Cliu to Issik Kul is exceptional, and tliat the river lias generally 
flowed into and out from the lake. Under such conditions it may well be that the 
overflowing river was a comparatively small one ; and it is possible that the heavy 
valley deposits, now dissected, in the Chu Valley for the first 20 miles west of Issik 
Kul were accumulated there at a time when the river was too weak to sweep them 
away, as well as because of the block faulting of the neighboring ranges, as 
suggested in an earlier section. Indeed, there is a point about 5 miles west of Issik 
Kul where the fans from the range on the north would close the outlet valley, or 
raise its floor 100 or 150 feet o\'er the present lake, if their slope were continued 
forward from their now dissected mass ; and it may be that when these fans were 
formed Issik Kul temporarily had no overflow. 
We are thus led to think that Issik Kul has generally had a water supply 
sufficient to cause overflow during the snbrecent time of the erosion and the 
drowning of the valleys in its surrounding slopes of piedmont waste, and that the 
Chu has frequentl}- or usually been an aflSuent of the lake ; also, that the fall of the 
lake from its 25-foot shoreline to its present level ma}- be explained, in good part 
at least, by the diversion of the Chu past the west end of the lake, as well as by 
climatic change. It might be possible, by means of soundings, to extend the time 
to which these inferences apply, so as to include the earlier period in which the 
piedmont slopes and the eastern plain were aggraded. 
It is, on the other hand, probable that the outlet of the lake may often have 
been of so small a volume that it ceased to overflow during arid epochs of secular 
duration, as well as during dry seasons. It is quite possible that the present era of 
desiccation may be of the former character, and in this connection it is noteworthy 
that, according to Schwarz, the level of Issik Kul was lowered b)- 2 meters from 
1867 to 1877 (1900, 581). It should not, however, be forgotten that the inferences 
here offered are tentative. The history of the lake is evidently too complicated to 
be deciphered in a week's visit to part of its shores. It is a most inviting field for 
further study, and all the more so when its relation to human settlement is 
considered, as will appear in a later section. 
