ROCKS FROM NORTHERN AND CENTRAL CHINA. 441 
About three-quarters of the rock is composed of quartz and alkali 
feldspars. The darker minerals are biotite and hornblende in about equal 
amounts, with smaller quantities of titanite, iron ores, etc. There are also 
the usual little grains and prisms of zircon, apatite, and rutile. 
The quartz appears in rather large irregular crystals which have very 
few inclusions aside from a few zircons. 
The feldspars consist of orthoclase and microcline with a subordinate 
amount of plagioclase. The latter is mostly oligoclase, but some of the 
crystals show a zonal structure and appear to consist of nuclei which have 
a composition approximate to labradorite, surrounded by concentric shells 
which are more sodic in composition. The plagioclases contain many 
secondary inclusions of sericite, grains of epidote and zoisite, and possibly 
kaolin. Certain irregular plagioclases show a micropegmatitic intergrowth 
with quartz, indicating that the two minerals were contemporaneous in 
crystallization. 
In general the ferro-magnesian minerals are closely grouped in separate 
clusters. The hornblende occurs in fresh irregular crystals which are closely 
packed together with the biotite. The pleochroism varies in general from 
pale greenish-yellow to light emerald-green and dark olive-green. Inclu- 
sions in the hornblende are neither numerous nor distinctive. Along its 
edges and cleavage cracks the mineral has undergone alteration into chlo- 
rite and yellowish fibrous aggregates, with epidote and probably other 
minerals. Many edges, however, show almost no alteration. 
The large scales of biotite, although usually irregular, are sometimes 
decidedly hexagonal in outline. The color is a rich brown, but without 
any reddish tinge. Inclusions of apatite, iron ores, and rutile are abundant 
and there are also little zircons which are surrounded by dark halos. The 
process of alteration of the biotite to chlorite is fairly well advanced, and 
is accompanied by the formation of some epidote. In some of the flakes 
the edges and cracks have been bleached to a brownish-yellow color, prob- 
ably by the removal of some of the iron. 
Of the rarer minerals represented in the Ts’in-ling granite, apatite is 
found in small lath-shaped prisms, some of which have a pale bluish-green 
color while others have brownish centers. As usual the apatite was one 
of the first minerals to crystallize. Zircon is rather abundant in minute 
grains and regular prisms. Rutile occurs in a similar fashion, but is rare. 
The rock is a typical biotite-hornblende granite, which is but little 
metamorphosed. Considerable evidence of mechanical deformation is 
shown by the quartzes, 7. e., strain-shadows and minute fracture-zones are 
prominent throughout the rock. Along contacts certain crystals have been 
granulated and the material partially recrystallized into a quartz mosaic, 
