364 RESEARCH IN CHINA. 
medium, and as it has a low index of refraction, the natural inference is 
that the material is rock-glass. Under a high-power objective, however, 
the ground-mass is seen to be more or less granular, the individual grains 
being obviously birefringent. One of the minerals appears to be quartz. 
This matrix shows, though somewhat indistinctly, flowage and even 
microperlitic structures. Although the perlitic fracturing is far from 
being prominent, it can be seen in the thin sections at several points. 
Grouped in certain areas, which are more obviously crystalline than others, 
there are a few rounded bodies which appear to be altered spherulites. 
They are now opaque white in color and probably represent altered feld- 
spar microlites arranged in rosettes. 
The flowage of the viscous lava, previous to its solidification, is shown 
in two ways. In the first place, some of the phenocrysts have been frac- 
tured and the broken pieces dragged apart by the matrix. Most of the 
micas have been sharply bent and dislocated, and in some cases there 
are planes of movement in the adjacent ground-mass, corresponding to 
the fractures in the biotite. There are also winding streaks, like micro- 
scopic shear-zones, which bend out around such phenocrysts as they 
encounter, but are otherwise approximately parallel. In some cases the 
crystals seem to have been rotated between the unequally gliding layers 
The phenocrysts consist principally of quartz and orthoclase, with albite, 
biotite, and a few accessory minerals in smaller grains. Crystal faces are 
frequently well developed in all of these. The quartz is clear and almost 
free from inclusions. The orthoclase is also clear and is so fresh that it is 
often difficult to distinguish it from the quartz. Some of the crystals, how- 
ever, exhibit cleavage cracks along which the processes of weathering have 
begun to change the feldspar into its usual decomposition products. ‘The 
orthoclase crystals are frequently Carlsbad twins. The striated albite 
occurs, for the most part, in smaller crystals than the orthoclase and has 
progressed farther in decay. The alteration is most prominent around the 
edges, and it is therefore common for the albite crystals to possess narrow 
cloudy borders. Biotite is quite infrequent, but occurs in irregular plates. 
Magnetite occurs in medium-sized crystals which are partly altered to ferric 
oxides. Zircon and brown tourmaline are also present. 
Associated with the phenocrysts there are small angular bits of a 
material much like the ground-mass. They have curved edges and are 
often elongated and stringy, like fragments of pumice. Certain small 
bodies of chalcedony apparently fill cavities which existed in the rock 
after it had finally hardened. The slide also reveals certain foreign bodies 
of irregular shape embedded in the mass. One of these is a bit of flint, 
and another appears to be glassy basalt containing numerous little laths 
