106 RESEARCH IN CHINA. 
in the basal complex. In the first occurrence noted the gneiss is in con- 
tact with the magnetic quartzite of the Shi-tsui group, while in the latter 
it lies adjacent to the arkose quartzite, which appears to be one of the 
lowest members of the sedimentary sequence. In both cases the banding 
of the gneiss is parallel to that in the schistose sedimentaries, as if gneiss, 
schists, and quartzites were all in parallel stratigraphic sequence. It is 
more probable, however, that the banding of the rocks is parallel because 
it has been produced simultaneously by forces which affected both gneiss 
and sedimentaries. 
The rock consists almost entirely of medium-grained augen-gneiss 
in which the colors range from deep purplish-gray through pinkish-gray 
to black-and-white. The mineral constituents observable in the hand 
specimens are mainly quartz, white and pink feldspars, and lustrous sepia- 
colored biotite. The texture of the rock is unusually even, and varies but 
slightly from point to point. The so-called ‘“‘augen’’ are lenses of quartz 
and feldspar, averaging 1 centimeter in length, with a breadth of about 
half as much. In marked contrast to the T’ai-shan gneisses, this rock is 
very homogeneous; there is little variation in its character in the section 
on the T’ai-shan-ho, which is continuous for 3 miles, 5 kilometers. Veins 
of quartz and pegmatite and also igneous dikes are comparatively rare. 
Most of the last are evidently intrusions of more recent date than the 
metamorphism; in addition the gneiss contains a few thin bodies of 
serpentine and greenstone schists, which appear to be ancient intrusives 
now thoroughly metamorphosed. 
This homogeneity of composition, and the broad extent of the mass 
exposed, incline us to the hypothesis that the augen-gneiss is a metamor- 
phosed intrusive granitic rock,—perhaps a porphyritic granite. ‘That we 
did not find dikes or other offshoots from the gneiss penetrating the strata 
at the contacts with the quartzite-bearing series, at several different local- 
ities, may be due to later metamorphism which has obscured the contact 
phenomena. The contacts appeared to be sharp and clean; they probably 
represent planes of shearing. 
The idea that the gneiss may be a portion of the T’ai-shan complex, 
lying beneath the Wu-t’ai schists in an overturned anticline, is rendered 
doubtful by the fact that the quartzites which bound it on the south are not 
repeated on its northern edge. An overthrust on each side of the gneiss 
would explain the relations, but the structure is regarded as less probable 
than that of intrusion. 
Pei-t'av gneiss.—Another gneiss of undetermined relationships forms 
the summit and upper slopes of Pei-t’ai-shan, the highest peak of the region. 
