SINO-MONGOLIAN FRONTIER 
The slopes facing the plain (i.e. eastward) are 
in the form of a steep and rugged escarpment, 
formed, possibly, by extensive erosions, but more 
probably by a fault running roughly north and 
south, with the downthrow on the east. This 
theory may be supported by the fact that the 
strata, which are very marked, dip to the west at 
varying angles. Slight folding is also noticeable. 
After passing westward through the Hu-t’o 
series for a short distance, one encounters typical 
Sinian limestones, which are next replaced by 
sandstones of the Shansi coal measures. Here, 
at a point just before Ching-hsing Hsien is reached, 
a good quality of bituminous coal is extensively 
mined by the Ching Hsing Mining Company. 
Immediately west of Ching-hsing Hsien, mas- 
sive limestone mountains are again encountered, 
suggesting the existence of another fault, especially 
as the eastern slopes again present rugged escarp- 
ments, and the strata still dip tothe west. As far 
as could be judged from the train, this limestone 
extends all the way to the P’ing-ting Chou district. 
This does not agree exactly with Richthofen’s 
map, which gives alternating outcrops of limestone 
and coal measures, but it must be remembered 
that the railway line follows the valley bottoms, 
it was described and named “ Untersinisch ’ by Richthofen. 
This was subsequently divided from the Sinian system by 
the members of the Carnegie Expedition, 1904, who discovered 
the unconformity between the two systems. 
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