396 RESEARCH IN CHINA. 
The plagioclase in the phenocrysts belongs to the oligoclase-andesine 
series. Many of the crystals are zonally built, and in these the peripheral 
portions are albite. An unusual feature of many of these plagioclases 
is the absence or indefinite character of the twinning lamelle; in the case 
of such crystals the index of refraction furnished almost the only means 
of distinguishing them from orthoclase. The alteration of the feldspar 
to kaolin has made considerable progress especially along the edges of the 
crystals. 
The hornblende seems to have preceded the feldspars in time of crys- 
tallization. In this specimen the mineral is almost wholly changed to 
green chlorite, calcite, and iron ores, with a little quartz. So complete 
is this change that the identification of the hornblende rests principally 
on the characteristic crystal forms of the pseudomorphs. During the 
weathering of the hornblende the magnetite gathers along the cracks and 
edges of the crystals, or, in association with calcite and quartz, it forms 
clusters of grains in the interior of the hornblende bodies. 
The biotite is also entirely decayed into chlorite, calcite, etc., and is 
now recognizable only by its tabular and hexagonal forms and the peculiar 
cleavage, both of which characteristics the pseudomorphs still preserve. 
During the alteration to chlorite numerous bits of iron ores, little prisms of 
rutile, and other minerals, have separated out of the biotite in the form of 
inclusions. The forms of some of these minute bodies are strongly sugges- 
tive of another titanium mineral—anatase. From the relations of the 
calcite to the chlorite it appears that the former has resulted from the 
decomposition of the latter—a well-known reaction in the belt of weather- 
ing. The expansion of volume which takes place in consequence of this 
production of calcite has caused the bending and crushing of the chlorite 
fibers adjacent to the lenticular bodies of the carbonate. 
Both magnetite and ilmenite occur as primary constituents of the rock, 
the ilmenite showing considerable alteration to leucoxene. 
SYENITIC PORPHYRIES. 
Altered syenite porphyry, No. 16.—This hornblende porphyry was found 
in the form of intrusive sheets in the lower part of the Cambrian shales, 
east of the village of Ch’ang-hia. Usually there are several sills at different 
horizons in the shales. In no case did the adjacent sediments show prom- 
inently the effects of contact metamorphism by the intrusion. 
A greenish-gray aphanitic rock through which are distributed decayed 
phenocrysts. Many of these crystals are very long and plainly show the 
diamond-shaped cross-sections characteristic of minerals of the hornblende 
group. The rock is obviously much altered. Small laths of feldspar, 
