SINO-MONGOLIAN FRONTIER 
schist, with veins of quartz running through it, 
abruptly replace the sedimentary rocks. Ascend- 
ing the steep pass, first a broad vein of dark 
basalt containing a high percentage of iron is 
encountered: subsequently two high ridges 
formed by a massive dyke of granite are crossed. 
The metamorphic rocks, which are not very 
extensive, may owe their existence to the granite, 
as, judging from the stratigraphy of the district, 
it seems probable that the granite is an intrusion 
of later date than the limestone and coal 
measures. 
On the western descent the outcrops show the 
same rocks as on the east (i.e. granite and schist). 
These, however, are soon replaced by Ki-ch’ou 
limestone of an equal height with that east of 
the passes, with a slight north-westerly dip. 
As may be expected, this gradually gives place 
to the carboniferous series (Shansi formation) 
once more. Soon the Fén Ho is reached (at 
Tsing-lo Hsien), crossing the valley of which, 
we still find the sandstone and shales of the 
Shansi formation. The strata here, however, 
are now horizontal for a short distance, sub- 
sequently dipping more and more sharply to 
the south-east, till they are almost perpendicular. 
They are suddenly replaced by almost per- 
pendicular strata of limestone (Ki-ch’ou). These 
form a high ridge, with a dip slope on the south- 
south-east of at least 80°, and a very steep escarp- 
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