408 RESEARCH IN CHINA. 
formed have been filled with the material of the ground-mass. Black 
‘reaction rims’’ of magnetite surround almost all of the olivines, whether 
they are decayed or fresh. It thus appears that such rims are not due to 
a subsequent alteration of the olivine, but to reaction with the magma while 
it was still somewhat fluid. The alteration of the olivine to a yellowish or 
greenish serpentine has made some progress; although some of the smaller 
crystals have been completely altered, the majority have been affected only 
along the numerous cracks. 
The feldspars are zonally built and are therefore of varying composition. 
A study of the extinction angles by the Michel-Lévy method indicates 
that the average is a labradorite having approximately the composition 
Ab,An,. In these feldspars distinct crystal forms and Carlsbad twins 
are usually well developed. Although inclusions of magnetite and bits of 
the ground-mass occur in the feldspars they are not prominent. In some 
cases minute inclusions are arranged in belts which are parallel to the zonary 
shells of which the feldspars are composed: it is inferred from this that 
the growth of such crystals was not continuous, but that it was arrested 
and subsequently continued after an interval. The alteration of the feld- 
spars in this rock is insignificant. 
The pyroxene is a pale-green augite without perceptible pleochroism. 
The crystals are entirely fresh, but usually present a dusty appearance as 
if they contained inclusions too small to be distinguished. The visible 
inclusions consist of magnetite, feldspar, apatite, and glass, with olivine 
only in rare instances. The bits of glass are either clear or brownish in 
color and contain abundant specks of magnetite. The augites are usually 
bounded by distinct crystal faces, but in many cases these regular outlines 
are interrupted by cavities produced by the corrosion of the magma. 
The base of the ground-mass is nearly isotropic, but a higher power 
and the selenite plate show that it is not glassy. In this there are embedded 
bits of feldspars, pyroxene, and magnetite, which vary from good-sized 
crystals down to the vanishing point of visibility. In certain places these 
small crystals are so abundant that the rock appears to be almost com- 
pletely, if minutely, granular. The feldspar crystals are much stouter 
and more irregular than is usual in basaltic rocks.* 
Porphyritic basalt, No. 57.—This is the basalt mentioned by von Richt- 
hofent as being the first which he encountered in his travels in China. 
Judging from the glassy character of the rock and the suggestions of pitted 
surfaces which were preserved on the weathered exteriors, it is part of an 
extrusive lava flow. ‘The exposure is about 3 miles, 5 kilometers, southeast 
* For a basalt with feldspar microlites of the usual character, see No. 57. 
{ China, vol. 11, page 201. 
