90 RESEARCH IN CHINA. 



character, which there extend northeast to southwest, parallel to the 

 structure of the pre-Sinian sediments.* 



To what extent these structures are general in North China is not yet 

 determinable. The Ch'ang-hia district is a very limited area; the folding 

 is moderate and probably local. The folds of the Wu-t'ai district are much 

 more pronounced and occur in a zone of ancient deformation which is mar- 

 ginal to the masses of Mongolia and Ordos. It is traced from northern 

 Chi'-li across Shan-si to Shen-si, a distance of 500 miles, 800 kilometers, and 

 is a structural zone of the first order, which is represented in modern moun- 

 tain systems by notable heights. Southeast of it lies the plateau of eastern 

 Shan-si, which, in the southern part where von Richthofen crossed, presents 

 the Paleozoic in little disturbed strata. It is possible, but not known, that 

 no folds invade its broad area. 



The date of deformation in North China is fixed as not earlier than 

 upper Carboniferous (Pennsylvanian) by the parallelism of strata of that 

 age with the Sinian over wide areas, and as pre-Liassic by the unconformity 

 which was observed by von Richthofen between the Sinian and the Liassic 

 coal-measures of the Ta-tung-fu field in northwest Shan-si. The latter 

 strata are also tilted, probably in consequence of a recurrent movement in 

 Jurassic time. 



As was first pointed out by von Richthofen, the Ts'in-ling-shan, 

 the eastern continuation of the Kuen-lung system, occupies the site of a 

 trough in which Paleozoic sediments accumulated to considerable thickness, 

 if the consensus of opinion regarding the age of the metamorphosed sedi- 

 ments be correct. Its folds embrace the southern margin of the ancient 

 land mass that is now northern Shen-si and Kan-su. The trend of the axes 

 of folding in that part of the range east of longitude 108 is not exactly 

 parallel with the modern height. Von Richthofen's preliminary map, a 

 bold essay on the slight data available to him, was mistaken in this respect. 

 The range trends about north 75 east, and the general axial strike of the 

 structures varies from east-west to north 80 west. Thus the belts of the 

 Archean, Proterozoic, 'and Paleozoic strata in general approach the northern 

 front at an angle and are cut off by the fault, which is the latest tectonic 

 feature. The angle is an acute one, and in the case of the contact of the 

 Proterozoic and Paleozoic south of Ch6u-ch'i-hien, the line trends south of 

 west; but the larger features of the structure diverge from the range and 

 pass under the Wei' valley, where they are faulted down. 



The Ts'in-ling-shan and the mountainous region south of it, through 

 which the Han flows from Han-chung-fu to beyond Hing-an-fu, was the 

 scene of more or less intense metamorphism and intrusion, as well as of 



*Vol. I, chap. v. 



