112 RESEARCH IN CHINA. 



The elevation of the Ts'in-ling-shan is continued toward the west by the 

 Kuen-lung and the Nan-shan, which rise to much greater heights; but the 

 physiographic aspect appears to change. The broad upwarp which, in 

 longitude 108 east, is 100 miles, 160 kilometers, across without a break, is 

 replaced by several ranges separated by valleys and basins. The effects of 

 warping are more complex and are probably accented by faulting. The 

 type is rather that of the Gobi than that of central China. 



Tibet and the Himalayas finally claim attention. 



The Alps of eastern Tibet, the Yung-ling, tower above the lowlands of 

 Ssi'-ch'uan in wonderful grandeur to an extreme altitude of 7,000 meters. 

 We have no definite knowledge of the physiographic aspects of this great 

 mountain face, but in one respect it differs markedly from the southern 

 front of the Himalayas, with which it may naturally be compared. The 

 rivers that drain the Himalayas flow directly across the range, after the 

 manner of consequent streams, which have developed at right angles to the 

 trend and been extended by headwater erosion in consequence of a com- 

 bination of favoring conditions. The rivers of the Tibetan Alps, on the 

 contrary, flow southwest between high ranges, which direct them in courses 

 diagonal to the lines of shortest descent toward the basin of Ssi'-ch'uan. 

 They thus have the character of streams which are consequent upon a 

 folded or faulted surface and take their own way down the axial lines of the 

 major depressions. There is thus reason to regard this slope as being 

 composed of successive upwarps or fault-blocks, which lie en echelon and sink 

 at their southeastern ends to the lowland of Ssi'-ch'uan. The character is 

 expressed in the contours which define the slope north of latitude 30 and 

 about the meridian of 103 east. 



Toward the west and south the great ranges of the Tibetan Alps are 

 bounded apparently by the broad plateau, which is deeply incised by the 

 canyons of the upper Yang-tzi' and the Mekong and their several branches. 

 The parallelism of these great rivers west of the one-hundredth meridian 

 may be an effect of unknown tectonic lines, but it is with equal reason 

 explicable as the growth of autogenous canyons on a uniform slope. The 

 meanders of the Yang-tz'i in latitude 25 north may be attributed to 

 capture across a fault-scarp. 



The western part of the map includes the vast highland of Tibet and 

 its bounding ranges, the Altin-tagh on the north and the Himalayas on the 

 south. The structural character of the plateau is not known, but it appears 

 to be that of a mass which has been forced above a position of equilibrium 

 and which has consequently broken into blocks that have suffered diverse 

 displacements. The depressions are deeply filled with Pliocene and Qua- 

 ternary sediments. 



