GRABEN Otf SHAN-SI. IO9 



our own account of the others in volume i, except with reference to the 

 most northwestern, for which Loczy may be consulted.* 



The zone of these basins, comprising an arc which surrounds Mongolia 

 and Ordos on the southeast and which is more than 1,500 miles, 2,400 kilo- 

 meters long, is a downwarp with reference to the mountain regions that 

 adjoin it. It is related to the heights southeast and south of it by warped 

 surfaces, which are, however, faulted throughout considerable stretches, 

 producing great scarps several thousand feet high that face inward toward 

 central Asia. The ascent toward the northwest or north is generally by 

 long, gently inclined slopes, but locally by more steeply tilted surfaces, and 

 occasionally by a fault. The O-shan fault in central Shan-si, which defines 

 the Fon-ho graben on the west, is the only one which has been definitely 

 recognized on that side. 



In its internal displacements the zone of depression is not simple. The 

 basins lie en echelon and are separated by moderate upwarps that traverse 

 the zone diagonally or directly as the case may be. The dividing ridges 

 may be enumerated as follows: the Man-t'o-shan, separating the basins of 

 Ta-tung-fu and Hin-chou; the Shi'-ling, south of the latter; the Si-yau-ling 

 and Si-sin-ling in central Shan-si, between the T'ai-yiian-fu and P'ing-yang- 

 fu basins; and the lesser upwarp dividing the Fon-ho from the salt lake 

 basin in southern Shan-si. These details of warping are characterized by 

 the youthful features of the Fon-ho epoch, namely, the mantle of Huang-t'u 

 formation not yet removed, the relation to antecedent streams, and the 

 characteristic deep gorges. 



This zone is one of the major structure lines of the continent, which is 

 recognized in modern displacements by relatively slight elevation above sea. 

 It agrees in general trend with the directions of folding of pre-Cambrian as 

 well as of Permo-Mesozoic deformation. It was apparently the littoral of 

 pre-Cambrian seas, a strip bordering the downwarps in which the Wu-t'ai 

 and Hu-t'o sediments accumulated to great thickness; but after they were 

 folded it became part of the land across which the Sinian sea transgressed 

 and over which Carboniferous continental deposits more or less generally 

 accumulated. During the long quiescence of the continent it does not 

 appear to have been a distinctive line; in the Permo-Mesozoic disturbance 

 it was folded; and in the recent extraordinary diastrophism it has again 

 become manifest in marked differences of elevation. 



Mongolia lies northwest of the basins of Shan-si and north of the 

 depression of Shen-si and Kan-su. It is a region throughout which separate 

 ranges rise from great expanses of Pliocene and Quaternary desert waste, a 

 region in which the evidences of structure and of physiographic development 



* Reise des Grafen Szechenyi, vol. i, p. 499 et seq. 



