SINO-MONGOLIAN FRONTIER 
colour. This colour on the exposed surface is 
changed, through weathering, to a dark brown.. 
Typical crystals of felspar occur throughout the 
mass. In the specimens gathered the crystals 
had undergone considerable decomposition. 
At a place called Hsi-tien-tzi the valley takes 
a bend eastward, at right angles to its original 
course, while a wide but waterless valley enters 
it from the north. This is called Ching-kou, 
while the main valley, which has a good per- 
manent stream, is now called Ch’ing Ho. 
The trachyte continues all the way to Kao- 
chia-yin-tzti, just beyond which place it ends. 
Here it is of a lighter colour, the weathered sur- 
face being of a bright brick red, while the new 
fracture shows the rock itself to be of a light 
mauve-grey. The white crystals of felspar are 
also much larger and more noticeable than in the 
outcrops nearer Kalgan. Where they are exposed 
at the surface, these crystals rapidly disintegrate 
and are washed away, leaving the surface rock full 
of holes, which gives it something the appearance of 
a rock charged with air-bubbles. 
Beyond Kao-chia-yin-tzt, still working east- 
ward, we found metamorphic (chiefly gneiss) 
rocks, alternating with plutonic (granite), the 
former predominating. 
Both the metamorphic and plutonic rocks are 
seamed with stringers, leads and ledges of quartz 
(probably auriferous). 
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