422 RESEARCH IN CHINA. 
WU-T’AI SYSTEM. 
The rocks of this system are referred to the early Algonkian. They 
comprise a great variety of mica schists and gneisses, garnet schists, 
chlorite schists, quartzites, marble, schistose conglomerates, arkoses, etc. 
Through these metamorphosed sediments igneous masses of several ages 
have been intruded, and some of them have since been metamorphosed. 
They include granite, augen-gneiss (probably Post-Wu-t’ai), hornblende 
schists, quartz porphyries, etc. Some of these dikes are older than the 
Hu-t’o series, while some are later and may even be Post-Paleozoic. 
Rocks OF SEDIMENTARY ORIGIN. 
PSEPHITES. 
Green schistose conglomerate, No.97.—Layers of conglomerate are prom- 
inent in the greenish schists at several points in the Wu-t’ai range. The 
present specimen was taken from such a layer in the canyon below Wu-t’ai- 
shan village (Plate XVIII, stratum No. 30). ‘This formation is regarded 
as the base of the Si-t’ai green schist group. 
A thoroughly schistose greenish rock in which numerous pebbles of 
quartz, quartzite, and granite are embedded. The less refractory inclu- 
sions have been visibly elongated in the direction of cleavage, but some of 
the pure quartz pebbles retain their original forms. 
The matrix is a heterogeneous mixture of particles, great and small, of 
quartz, feldspar, calcite, iron ores, and pale micas. The mica flakes are 
roughly parallel and the mass is traversed by many wavy shear-zones, all 
of which coincide with the schistosity. The visible grains of quartz and 
feldspar are often set in eye-spots avoided by the shear-zones, and are 
therefore to be regarded as sand-grains older than the schistosity. Other 
granules have been produced by the peripheral granulation of the pebbles 
under heavy stresses. 
The cryptocrystalline brightly polarizing aggregate which forms the 
base of the ground-mass is composed largely of micaceous minerals such 
as sericite, kaolin, and chlorite. Some of this probably represents original 
clay material partly metamorphosed, but another portion is intimately 
associated with granulated edges of feldspars and is to be regarded as an 
anamorphic product of the alteration of that mineral. 
The origin of the calcite bodies is not entirely clear. The mineral is 
not common in schists and is probably not produced in the zone of anamor- 
phism. A part may have developed since the rock emerged from that zone, 
but the relations of many of the calcite bodies proves that they were present 
during the deformation of the mass. Many of them are inclosed in eye- 
spots which are avoided by the little shear-zones in the matrix. It is 
