8o EXPLORATIONS IN TURKESTAN. 
ORIGIN OF THE EXISTING RANGES OF THE TIAN SHAN. 
When the features here described from Son Kul to Seniipalatinsk are con- 
sidered in a broad way, they suggest many reflections of interest in theoretical 
geolog}-. The extended occurrence of surfaces of small relief, indifferent to the 
rock stnictures which they tnincate, implies a long cycle of uninterrupted degra- 
dation, continued past late maturity, even to old age. The earlier form of the 
eroded region may well have been motmtainous ; witness the steep-dipping or 
vertical strata seen at various points, as well as the occurrence at the surface of 
rocks whose origin nuist have been deep-seated, like granites. The agency of 
erosion was not the sea, of whose presence in modern geological time the region 
gives no indication ; nor was it the lateral swinging of rivers, as Philippson (1898) 
has supposed for the plains of central European Russia, for the eroded surface fre- 
quently possesses a minor relief that is inconsistent with such a process of planation. 
The various processes of subaerial erosion, of which the swinging river is but one, 
best explain the widespread peneplanation here obser\-ed. 
Although the peneplain was not observed by any means continiiously from 
Son Kul to Seniipalatinsk, there is good ground for thinking that it once stretched 
as an almost continuous lowland, interrupted only by residual ranges, over all 
this distance, and indeed over still greater distances ; for it is not reasonable to 
believe that a cycle of erosion which sufficed to develop a peneplain even on granitic 
rocks should find other rocks resistant enough to maintain a great relief, unless, 
indeed, tiplift came to aid resistance. There is, however, no direct evidence of 
uplift during the cycle of peneplanation. Where great relief occurs in the region 
to-day, it is accompanied b}- the suggestion of uplift after peneplanation — or, at 
least, after a ver}- late mature stage of erosion — had already- been reached. Witness 
the peaks of the Dongus-tau below the westward prolongation of the highland 
surface of the Bural-bas-tau, or the peaks of the central Kungei Ala-tan below the 
eastward prolongation of the even crest in the western part of the same range. If 
certain ranges do not to-day present such evidence of a former c3-cle of erosion, it 
is more consistent with the general features of the region and with the general 
principles of mountain sculpture to suppose that they have lost the e\-idence than 
that they have never had it. 
This conclusion, based on my own observations, is strongh- supported b)' the 
observations made independently by Mr. Huntington and presented in the report 
on his Kashgar journey. He describes large highland areas of the Tian Shan 
between Issik Kul and Kashgar as broadly uplifted peneplains, here and there 
bearing subdued mountains, the whole being in process of revived erosion. He 
therefore names the region " the Tian Shan plateau." It is, as he happily phrases it, 
not actually but only potentially mountainous. Previous observers hsLxe recognized 
the plateau-like highlands of the Tian Shan, but most of them do not seem to have 
recognized their meaning. Roborovsky, reporting on an expedition led by Piev- 
tsoff" in 1889, briefly describes a high plateau, between Issik Kul and the Tarim 
basin, called the Syrt, 100 miles wide, and at an altitude of 10,000 or 11,000 feet. 
" Scattered over it are separate mountain groups and ridges, running east and west" 
(1890, 23). St Ives, who crossed this region later, says that it is an immense 
