IO2 RESEARCH IN CHINA. 



plateaus of the world. But we need not rest upon mere inference. Davis 

 has described the summit character of the various ranges of the Tien-shan.* 

 He says: 



Certain observations made in the central and northern ranges [of the Tien-shan] near 

 lakes Son-kul and Issak-kul, and on the steppes that border the mountains on the north, 

 led to the belief that the region had been very generally worn down to moderate or small 

 relief since the time of greater deformation, which probably occurred in the Mesozoic age ; 

 that large areas of subdued or extinguished mountain structures are still to be seen in 

 the low ranges and in the steppes north of the Hi river, and that the present relief of 

 many of the higher Tieii-shan ranges is the result of a somewhat disorderly uplift and of a 

 more or less complete dissection of dislocated parts of the worn-down region. Mr. Hunt- 

 ington's report shows the application of these conclusions to a large part of the central and 

 southern Tin-shan. 



We have no direct evidence of the age of this peneplain, which is now 

 elevated to altitudes approaching 14,000 feet, 4,200 meters, but the perfec- 

 tion of the profile of the Bural-bas-tau and other ranges sketched by Davis 

 suggest that they have not long been exposed in their present altitude. 

 And when we consult the geologic section of the adjacent region of western 

 Turkestan, we find no record earlier than the middle Tertiary of volumi- 

 nous deposition, such as the mountains are capable of yielding. 



The descriptions of Mongolia and northern Tibet give the physiog- 

 rapher no reason to expect that an ancient topographic surface may there 

 survive. Much of the region is buried beneath Pliocene and Quaternary 

 sediments, and the deeply sunken surface of the hard rocks is hidden from 

 view. The mountain ranges which rise above the sands have been sharply 

 sculptured and appear to be the skeletonized edges of warped and tilted 

 blocks. While it is possible that Davis's observations of the Tien-shan 

 may be repeated elsewhere in the Kuen-lung or the Nan-shan, it is more 

 probable that our own experience in the southeastern extension of these 

 ranges, the Ts'in-ling-shan, will be paralleled, and that the observer will be 

 able to recognize nothing older than a mature surface of late Tertiary date. 



When we consider that physiographic studies have been applied to the 

 interpretation of the features of Asia only within the last three years, it 

 arouses some surprise to find so much evidence of a surviving peneplain; 

 but that evidence appears to deserve frank recognition in view of the series 

 of events leading up to the early Tertiary, the stratigraphic record of the 

 Cretaceous and Tertiary, and the character of plateaus and plains of denu- 

 dation which so much of the land presents, even at high altitudes. 



It is, however, improbable that an entire continent of such extent as 

 Asia should be completely peneplained. In America the peneplanation 

 of the Cretaceous period failed to reduce the Unaka mountains of North 



* Explorations in Turkestan, Carnegie Institution of Washington Publication No. 26, p. 72. 



