ROCKS FROM NORTHERN AND CENTRAL CHINA. 407 
nent as in the other rock. The dominant feldspar is approximately oligo- 
clase, but there is another variety present which forms more idiomorphic 
crystals and is probably labradorite. For the most part the feldspars are 
unaltered, but, where decay has begun, kaolin and probably albite may be 
detected among the products. 
The pyroxene is a nearly colorless augite. It contains very few inclu- 
sions, and most of them are titanite and feldspars. The mineral occurs in 
short irregular prisms, with corroded edges. Sometimes it appears in the 
form of a fibrous aggregate of little columns which have a tendency toward 
radial or at least divergent arrangement. The alteration of the pyroxene 
has been slight and chlorite seems to be the principal result. 
The interstices between the grains of feldspar and augite are filled with 
a fine-grained cement consisting of minute granules of quartz and feldspar. 
The former is occasionally plainly visible in medium-sized irregular bodies. 
It probably predominates over the feldspar, but occurs in such small grains 
that the two are difficult to discriminate. 
Titanite is abundant in this rock in the form of irregular grains and 
clusters. A much rarer accessory mineral is zircon. A single crystal of 
the latter was seen with a grain of magnetite inclosed in it. 
BASALTS. 
Basalts are among the commonest of the igneous rocks in central Shan- 
tung. They occur as dikes, sheets, and surface flows associated with the 
Carboniferous and related terranes at Yen-chuang, Po-shan, and Wei-hién. 
Porphyritic basalt, No. 54.— This is one of the numerous phases of the 
Post-Carboniferous volcanic rocks in the coal-field of Yen-chuang. Our 
specimen comes from a small dike, about 2.5 feet, 0.75 meter, thick, which 
pierces the tufis and sandy shales of the upper part of the Po-shan series 
about 2 miles, 3 kilometers, northeast of the town. 
A massive blackish rock of dense aphanitic texture thickly studded 
with small phenocrysts of pyroxene, feldspar, and olivine. These pyroxene 
crystals stand out prominently upon the brownish weathered surfaces of 
the rock. 
All of the constituents are comparatively fresh, and of these the olivine 
is as usual the most altered. The prominent minerals of this rock seem 
to have crystallized in the order which is commonly observed in basalts: 
(1) magnetite, (2) olivine, (3) feldspar, (4) pyroxene (Plate LV, Fig. F). 
The magnetite occurs only in small bodies associated with the ground- 
mass or inclosed in the other minerals. 
Olivine occurs in abundant crystals of variable size and shape. The 
only inclusions which it contains are magnetite and a little brown glass. 
Many of the crystals are corroded about the edges, and the cavities thus 
