TRANS-HIMALAYA AND TIBET 43 



its south-westerly extension along the Surkh Ab valley) the 

 line of the western fracture of the uptilted Pamir block. 



Just as the uptilted blocks of the Armenian border-ranges 

 show evidence, by means of the river-courses, of having been 

 planed down prior to the differential movements which have 

 raised them to their present position, so in like manner Prof. 

 W. M. Davis^ and Mr. Ellsworth Huntington have independently 

 come to the conclusion that not only the Tian Shan mountains 

 but also the Pamir plateau had been worn down to a fairly 

 uniform surface after their principal folding had occurred ; and 

 that they owe their present irregular surface more to subse- 

 quent differential uplift than to denudation. " Even in the lofty 

 Pamir there are certain ranges where the snowy peaks are 

 mostly truncated as though by the old pene-plain, in spite of the 

 fact that they are from 15,000 to 20,000 ft. high." 



To return to the Trans-Himalaya — all its characteristics 

 point to the inference that here we have to deal with a block of 

 ancient rocks, which indeed had been thrown into folds at a long 

 distant epoch, but at the time of the folding of the Tibetan 

 plateau had lost all their original plasticity and could only yield 

 to the mountain-making forces by becoming first of all fractured 

 and then uptilted. These earth-movements are probably still in 

 progress ; at any rate this surmise receives some support from 

 the observation by Dr. Sven Hedin ^ that whilst at Selipuk, in 

 the Rartee plain (which, according to my interpretation, lies on 

 the actual northern line of fracture of the Trans-Himalayan 

 block) he was shaken by an earthquake, the only one he ever 

 experienced during his journeyings in Tibet. 



Although the Tibetan plateau is traversed, in the first place, 

 by latitudinal mountain-folds, which are to be regarded 

 essentially as the expanding branches or fan-like virgation of 

 the Karakoram ranges, yet in all probability Tibet consists, in 

 its present condition, of a succession of uptilted and depressed 

 blocks of resistant strata, no longer capable of being folded, just 

 as 1 have shown {op. cit) to be the case in the plateau of 

 Armenia. The innumerable lakes still scattered over its surface, 

 although many more have completely dried up, lend support to 



' Explorations in Tufkestan, with an Account of the Basin of Eastern Persia 

 and Sistan. Expedition of the Carnegie Institution of Washington in 1903 under 

 the direction of Raphael Pumpelly, pp. ']'^^ 80, 168. Washington, 1905. 



' Op, cit. ii. p. 399, 



