SINO-MONGOLIAN FRONTIER 



rocks, consisting chiefly of light buff-coloured 

 granite. This formation continues to well beyond 

 the crest of the ridge, till the mountains give 

 place to a wide plain — the valley of the Ta-sha 

 Ho, which joins the Ta-yang Ho a little to the 

 south. 



Crossing this plain in a north-westerly direc- 

 tion, a second range is encountered, which runs 

 from east-north-east to west-south-west, and 

 consists, as far as can be judged from the train, 

 of limestone formation (probably Ta-yang lime- 

 stone). 



Near Hsia-hua-yiian, where the Ta-yang Ho 

 cuts through this range in a narrow and deep 

 valley, the sedimentary rocks become rather 

 complicated. Coal-bearing sandstone and shale 

 strata lie underneath the limestone, an uncon- 

 formity between the two formations being dis- 

 tinctly discernible. This can only be explained 

 by the existence of an overfold or overthrust. 

 The coal-bearing strata are more or less horizontal 

 and somewhat folded, while the limestone shows 

 perpendicular or very sharply dipping strata. 



North-west of Hsia-hua-yiian, for a considerable 

 distance, horizontal strata of purple shale and 

 sandstone occur. These next give place to lime- 

 stone, which extends to within six miles of Kalgan, 

 when it is replaced by the volcanic rocks of the 

 Kalgan district. In our rambles through the 

 hills round this town we found porphyry, chiefly 



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