414 RESEARCH IN CHINA. 
Greenish chlorite gneiss, No. 80.—Another phase of the gneisses, found 
in close proximity to the rock last described. Its origin is wholly indeter- 
minate. 
The color of this rock is dark greenish-gray from the association of 
chlorite pseudomorphs with quartz and feldspar. The banding and texture 
are both rather fine. 
The specimen is badly altered and is therefore not a true representa- 
tive of the fresh rock. Quartz, feldspar, hornblende, biotite, and pyrite 
are the essential minerals of the rock. Of these the first is, of course, 
unchanged, while the second is clouded with kaolinitic products and the 
rest have been changed almost entirely to hydrous minerals characteristic 
of the belt of cementation. 
The feldspars (orthoclase with less oligoclase) predominate over the 
quartz. Biotite and hornblende were formerly the most abundant minerals. 
Both have since been replaced by chlorite. The hornblende may still be 
seen in isolated bits inclosed in the chlorite; but the mica is recognized 
only by the forms of its chloritic pseudomorphs. The pyrite has likewise 
suffered extensive alteration to limonite. 
The basic composition of the hornblende-biotite gneiss suggests that 
it may have been derived from an igneous mass of basaltic character. 
Pale-brown hornblende gneiss, No. 71.—A very prevalent phase of the 
Archean gneisses in the vicinity of T’ang-hién. It is there associated with 
sericite schists, amphibolites, mica schists, and white marble. Although 
its origin can not now be determined, both its relations with the marble 
and its somewhat unusual composition are consistent with derivation from 
a sedimentary rock. The specimen comes from the hill, 2 miles, 3 kilo- 
meters west of Chuang-li (= stratum h in Fig. 12, Part I). 
The gneiss is hard, compact, and of light color. The individual bands 
are ill-defined and yet the parallel structure is plain in the hand-specimen. 
The abundant minerals are orthoclase, quartz, albite, and green hornblende. 
Subordinate varieties include red garnet, epidote (with allanite), ilmenite, 
titanite, and zircon. 
A large part of the rock possesses a granitoid texture, but it has been 
heavily deformed along certain sinuous planes, resulting in the production of 
shear-zones. In the granitoid portion the feldspars and quartz are not 
greatly distorted and other minerals rarely occur. The shear-zones are loci 
of granulation. The quartz and feldspar have been sliced and mashed into 
long streaks consisting of granules and lenticular shreds. Minerals adjacent 
to the shear-zones, when not actually broken up, show tension-cracks, bent 
lamine (Plate LVI, Fig. A), and strong undulatory extinction. The darker 
and rarer minerals are closely associated with these shear-zones and thus 
