266 Davis — Bearing of Physiography upon Suess* Theories. 



the Bural-bas-tau, in the neighborhood of Son-kul (lake), 

 attracted my attention. Its plateau-like surface was heavily 

 snow-covered at an altitude of 12,000 or 13,000 feet or more ; 

 its northern flank was deeply gashed with deep ravines head- 

 ing in glacial cirques ; the rocks exposed in the cirque walls 

 and in the sharp aretes between the ravines seemed to be 

 massive crystallines, but as my observations were made with 

 a field-glass at a distance of ten or fifteen miles, this point will 

 not be insisted upon. Yet in any case there was no indication 

 of horizontal structure, with reference to which the even high- 

 land surface might have been determined. I have published 

 a brief account of the range in Appalachia (x, 1904, 277-284). 

 There is no question in my mind that the plateau-like mountain 

 top is a displaced fragment of a peneplain, and hence that its 

 present highland surface is the work of erosion at a compara- 

 tively moderate height above baselevel of an earlier time. * 



Other ranges in the Tian Shan system exhibit similar dis- 

 placed or tilted blocks of a peneplain, though none of them that 

 I saw are so remarkable in this respect as the Bural-bas-tau, 

 whose highland combines the features of exceptional smooth- 

 ness, great altitude, and unusually good preservation. The 

 Alexander range, west of Issik-kul, seemed to be a tilted 

 block, with a gentle slope to the south independent of structure, 

 and an abrupt descent to the north. The western end of the 

 Kungei Ala-tau, north of Issik-kul, was of plateau-like form. 

 It is noteworthy that when the even highland of the western 

 part of this range is projected eastward, it seems to rise above 

 the serrate summits of the rest of the range. The same is true 

 regarding the westward prolongation of the highland in the 

 Bural-bas-tau. Both these examples therefore suggest that 

 certain ranges of Alpine form, in which the sharp peaks now 

 give no indication of having been carved from a flat-topped 

 mass, may nevertheless have had precisely such an origin. It 

 is also to be noted that in these cases the relation of the ser- 

 rate peaks to the even highland is not such as to suggest that 

 the former are recarved residuals that once rose above and 

 more or less completely surrounded the latter. Other exam- 

 ples of ranges that indicate former peneplanation are described 

 in my part of Professor Pumpelly's forthcoming report. All 

 these ranges seemed to be isolated and dissected blocks of a 

 broken peneplain. 



Between Yiernyi and Semipalatinsk (northeastern Turkestan 

 and southern Siberia), I crossed many miles of rolling steppe 

 of small relief and of moderate altitude above sea-level. Parts 

 of this extended surface came nearer to the realization of a 

 low-lying peneplain than anything that had previously come 

 under my observation, yet even there the surface was prevail- 



