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 Tia-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 UHsia-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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