ROCKS FROM NORTHERN AND CENTRAL CHINA. 375 
The feldspars are represented chiefly by orthoclase and microcline, with 
numerous crystals of albite. Although the feldspars appear a trifle dusty 
in the thin section, they have suffered very little alteration. 
The epidote is scattered indiscriminately in the form of grains or prisms 
with distinct terminations. Many of these are bordered with ocherous 
deposits of limonite, which is evidently a decomposition product. Chlorite 
occurs in greenish plates as a pseudomorph after biotite, and also in little 
clusters of roughly parallel quadratic plates, associated with epidote and 
titaniferous iron ore. ‘The presence of titanium is inferred from the fact 
that borders of leucoxene surround many of these black crystals. 
Of the accessory minerals allanite is occasionally found as deep brown 
prisms inclosed in epidote. There is a surprising dearth of apatite, rutile, 
and other rarer constituents generally present in granites. 
This rock plainly shows the effects of mechanical deformation. The 
quartz and feldspar grains have, in many instances, been fractured, and 
granulation is prevalent everywhere in the slide. The recrystallization of 
a portion of the granulated material has produced the so-called mortar 
of fresh quartz and feldspars surrounding the original grains. All three of 
the varieties of feldspars are represented in this recrystallized cement, but 
microcline is particularly characteristic of such situations. Some of the 
original feldspars have been fractured and the fragments have been either 
shifted or in other cases actually pulled apart. Fissures developed in 
this way have been subsequently filled with a granular cement of quartz 
and feldspar with which are frequently associated grains of epidote. 
Another effect of strain is seen in the bent laminz of some of the albites. 
As would be expected both quartz and feldspar show undulatory extinction 
strongly. 
The original ferro-magnesian mineral of this acid granite was biotite, 
and in addition there may have been others. The mica is now represented 
only by chloritic pseudomorphs, and the epidote may have been derived 
from the same source. 
In this granite a large portion of the substance has been rearranged 
in fresh crystals and even in new minerals. The changes happen to be of 
a kind not particularly conducive to the development of gneissic banding or 
schistosity, and hence the rock is massive and uniform in color. 
Dark biotite gramte, No. 31.—This is one of the most characteristic 
rocks in the slopes of the T’ai-shan, but it was not observed elsewhere in the 
province. It appears to have been intruded into the ancient schists and 
gneisses, but whether it is older or younger than the red granites was not 
determined. It was extensively used in the construction of the great 
stairway which was built during the T’ang dynasty. Specimen taken at 
