402 RESEARCH IN CHINA. 
refraction. In spite of the fact that the crystals are more or less altered, 
there can be but little doubt that they are orthoclase. Small grains and 
short prisms of colorless augite are rather numerous in this ground-mass. 
Some of these pyroxenes have undergone alteration along their borders, 
resulting in the formation of epidote and a brownish or yellowish product 
of unknown composition. 
Hornblende-syentte porphyry, No. 53.—This is one of the commonest 
porphyries associated with the Permo-Carboniferous strata in the region 
about Yen-chuang. It occurs in dikes varying from 5 to nearly 100 feet 
in thickness, having in the thicker dikes a somewhat coarser texture. 
Its relations to the other igneous rocks in the district are not known. 
Specimen collected from a 12-foot dike in sandstones and greenish tufls 
of the Po-shan series (Carboniferous), 2 miles northeast of Yen-chuang. 
A rather fine-grained porphyry in which the ground-mass is of a lav- 
ender-gray color. This is thickly set with small phenocrysts of pink feld- 
spar and weathered hornblende. The usual pinkish tinge of the rock, as 
a whole, is seen to be due to the abundance of these feldspars. 
The rock is composed of potash-soda feldspars and a subordinate 
amount of hornblende and biotite with the usual accessory minerals: 
iron ores, titanite, apatite, and zircon. 
The most abundant phenocrysts are idiomorphic feldspars which, 
upon closer inspection, are found to be of two kinds. By far the larger 
number are striated, have a low index of refraction and moderate extinction 
angles; these are evidently albite. They are now almost completely altered 
into micaceous kaolin and clay. A few of these phenocrysts, however, 
are apparently orthoclase; they are of course unstriated and they are also 
much less altered than the albite. 
The first of the important minerals to crystallize seems to have been 
the hornblende—a rather light-green amphibole which occurs in smaller 
crystals than the feldspars. In the process of alteration the hornblendes 
are changing to a yellowish-brown serpentinous material associated with 
specks of iron ores, especially along cracks and borders. Included crystals 
of apatite, zircon, and magnetite are rather common. 
The original biotite is now very badly decayed, though it may still 
be recognized not only by remaining bits of the mineral itself, but by the 
characteristic cleavage and forms which are preserved by the pseudomorphs 
of iron ores and gray opaque decomposition products by which it is replaced. 
The ground-mass is made up very largely of rounded or subangular 
grains of feldspar of nearly uniform size. In this part of the rock the 
ratio between the two varieties of feldspar is almost reversed, the ortho- 
clase greatly predominating over the striated feldspar. The whole mass is 
