412 RESEARCH IN CHINA. 
edges of the section of quartz are sometimes cavernous and the pits thus 
formed are filled with the material of the ground-mass. Inclusions of the 
same character in the body of the crystals are also not infrequent. These 
corroded edges are much more characteristic of the quartz than of the feld- 
spar, although the latter also show the same peculiarity in some cases. 
Minute specks arranged in roughly parallel streaks are included in many 
of the quartz crystals. It is hardly possible that these are of a secondary 
nature, as they are said to be found in such metamorphosed rocks as the 
gneisses. Larger crystal inclusions are by no means common; they com- 
prise grains of zircon, magnetite, and little olive-green tourmalines. A 
few of the quartzes in the porphyry exhibit the rhombic cleavage which 
is so rarely seen in sections of this mineral. Such crystals are traversed 
by zigzag cracks in two systems which make an angle of about 78° with 
each other. 
These two systems are approximately parallel to the outlines of rhom- 
bic sections. This is so rare a characteristic of quartz that it is likely to 
mislead the observer at first glance into thinking that the mineral is ortho- 
clase. The index of refraction, however, and in this case also the absence of 
alteration products, is amply sufficient to correct the error as soon as the 
crystals are more closely examined. 
The ground-mass is composed of densely crowded irregular grains 
of feldspar and quartz. The feldspar seems to predominate in quantity 
over the quartz. Certain striated grains which have a low index of refrac- 
tion indicate the presence of sodic plagioclase; but orthoclase is much the 
more abundant feldspar. 
The less common components of the ground-mass are biotite, zircon, 
and magnetite, together with the reddish alteration products of the last. 
The iron ore occurs in rather numerous grains of variable size and shape, 
but distinctive forms are often seen among them. Formerly small flakes 
of biotite were not infrequent in the rock, but they have been almost wholly 
altered to fibrous aggregates of yellow delessite (?). The red and ocher- 
colored iron oxides, which have been derived in large measure from the 
alteration of magnetite, occur in small irregular blotches or are disseminated 
in thread-like stringers. The reddish hue of the rock-mass is undoubtedly 
due to the presence of these secondary ferruginous materials. 
The absence of these visible effects of mechanical deformation such as 
granulation, microscopic shear-planes, strain-shadows, etc., indicate that 
the rock has never been subjected to the heavy stresses of the zone of 
anamorphism. Evidently this is part of an intrusion which crystallized 
at no great depth and whose subsequent history has been without notable 
events. 
