SINO-MONGOLIAN FRONTIER 
basalt of a dark grey colour, not unlike that en- 
countered in Shansi, while in the valley leading 
up to it various kinds of rock, all igneous, were 
noticed. Amongst others, we gathered specimens 
of a red-brown porphyry containing numerous 
elongated: air-holes, besides distinct crystals of 
felspar and quartz. Specimens of metamorphosed 
felspar, of light grey basalt, and of a peculiar 
yellow sandstone, were also gathered. The pre- 
dominating rock throughout, however, was found 
to be basalt, and, nearer to Kalgan, trachyte. 
Except in the hills and on the ridges of the 
Plateau, the thick grass-covered surface soil pre- 
vented our noting the nature of the sublying 
rock, but an examination of the outcrops in the 
hills showed that basalt greatly predominated, 
while dykes of granite occurred here and there. 
As -we approached Lama Miao the granite in- 
creased in proportion till it seemed, sometimes, 
as if dykes of basalt crossed the general mass of 
granite. Usually, however, the higher ridges 
were found to be of granite, while wherever the 
sublying rock in the lower slopes and valleys was 
visible it usually turned out to be basalt. At a 
place named Oola Hutaga some gneiss was noticed, 
but here also the hills were chiefly of granite and 
volcanic rock. 
At Tabool we noticed some wide veins of quartz 
running north and south through metamorphic 
and granitic rocks. This quartz was not noticed 
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