Davis — Bearing of Physiography upon Suess' Theories. 267 



ingly undulating, so that laterally swinging rivers can have 

 had little share in its production : the only exception to this 

 rule was in the immediate neighborhood of the Irtysh river, 

 whose lateral swinging may have there been effective. The 

 rocks were crystallines or disordered sedimentaries, and the 

 gently undulating surface was evidently the result of long con- 

 tinued subaerial erosion. Here and there mountains rose ; 

 some of them seemed to be residual masses, as they had undu- 

 lating skylines ; others seemed as clearly to be isolated blocks 

 of the peneplain, as they possessed uplands of remarkably 

 even form. The conclusion thus grew upon me that the whole 

 region, mountains and steppes alike, had once, been greatly 

 worn down, although it probably retained strong monadnocks 

 here and there ; and that the mountain ranges which we see 

 to-day had been afterwards uplifted in blocks of greater or less 

 extent ; the residual eminences of the former cycle presumably 

 form the loftiest peaks that rise above the present highlands. 



This conclusion was strengthened on receiving the report of 

 my companion, Mr. Ellsworth Huntington, who had turned 

 southward from Issik-kul and crossed the Tian Shan to Kash- 

 gar. He found large plateau-like highlands of deformed 

 structure and moderate relief surmounted by occasional higher 

 eminences, monadnock-like, and deeply dissected by steep- 

 sided valleys, and he was thus convinced that these highland 

 areas had gained their altitude relative to sea level in compara- 

 tively recent time, after prolonged erosion : he describes the 

 Tian Shan, where he crossed it, as " potentially but not actu- 

 ally mountainous." Farther eastward, however, the domi- 

 nating mass of Tengri-khan is actually mountainous in a high 

 degree : it may be provisionally regarded as a reelevated sur- 

 viving mountain group of the former cycle. On looking over 

 the reports of other observers after my return home, several 

 brief descriptions of the plateau-like aspect of the Tian Shan 

 highlands were found ; but the only account which interprets 

 their meaning is by Friedrichsen, a pupil of Richthofen's, who 

 visited the region in 1902, and who is now docent in geography 

 at Gottingen : his articles unfortunately came to my notice 

 only after my return from Turkestan. He recognizes the 

 even highland which he saw southeast of Issik-kul to be a 

 formerly lower-lying Denudationsflache, now displaced and 

 exposed to revived erosion, but thinks it may have been worn 

 down with respect to a local baselevel in a relatively enclosed 

 basin (Petermann's Mitteilungen, xlix, 1903, 136), and hesi- 

 tates to express an opinion as to the area over which correlated 

 peneplains once extended. 



In view of these interpretations, it seems inadmissible to 

 follow Mushketof and Suess in regarding the Tian Shan as a 



