GEOLOGY OF CENTRAL SHEN-SI. 309 
more recent date—the Shi-ts’iian formation. North of this area of the 
younger rocks the metamorphosed Paleozoics reappear as closely folded 
schists and limestones. The main road runs nearly parallel to the strike 
of these beds, but crosses them gradually. In the vicinity of Ssi-yen-pa 
the prevailing rock is a silvery sericite-garnet schist spotted with biotite. 
It contains at least one thin member of buff crystalline limestone, which 
is rich in muscovite and has a tendency to cleave readily in parallel slabs 
without regard to the planes of stratification. South of Fan-chan-tan 
hard blue-black siliceous limestone forms a narrows in the valley. Adja- 
cent to it,and probably overlying it, are soft coaly black schists like those 
on the Han river opposite Shi-ts’iian-hién. The limestone is brecciated 
in numerous places, and white veins fill the fractures. It appears to be 
doubled in a closed fold. We consider it an anticline of the Wu-shan 
appearing through the K’ui-chdéu schists. 
North of the black limestone belt the garnetiferous mica-schists and 
buff limestone bed, seen south of it, reappear, and similar schists form 
the surface to the head of the valley. At one bend of the stream, however, 
2 miles, 3 kilometers, north of Fan-chan-tan, we noted a small outcrop of 
much-folded black argillite, and near the divide, on which is situated the 
temple of T’6u-mén-ssi, the black soils observable in the neighboring 
slopes indicate that coaly schists occur extensively. 
Between the pass and Liang-ho the road follows a tributary valley 
which has been excavated along the strike of some dark bluish micaceous 
limestones and mica-schists. The strata are frequently contorted and the 
limestone is sometimes sheared into thin sheets. The hills at Liang-ho 
are composed of spotted biotite-garnet-schists containing several layers 
of limestone a few feet in thickness, which are crystalline gray and buff 
rocks with veins of quartz and abundant spangles of muscovite. Rocks 
of this character continue from Liang-ho northwestward to Ta-ho-pa. In 
this section the mica-schists are probably stratigraphically higher than 
the blue-gray limestone. 
Immediately north of Ta-ho-pa the P’u-ho runs through a narrow 
canyon, which has been cut across the strike of a vertical blue-black quartz 
rock. It is a dense black or banded formation, which we think is the 
silicified limestone above Ssi-yen-pa, except that it is perhaps more thor- 
oughly quartzose. The outcrop appears to be a little more than 2,000 
feet, 600 meters, wide at Ta-ho-pa. ‘To the north of these narrows the 
rocks are soft mica-schists and gneisses, which resemble those at Liang-ho 
and are believed to be the same formation recurring. 
The structure from Fan-chan-tan northward to Ta-ho-pa may be a 
succession of anticlines and synclines, in which the Wu-shan and K’ui- 
