ROCKS FROM NORTHERN AND CENTRAL CHINA. 413 
WESTERN CHI-LI. 
Our geologic studies in Chi-li were confined almost entirely to the 
mountains immediately west of Pau-ting-fu. The area surveyed is repre- 
sented on the atlas sheets E Ito GI. In this belt gneissic rocks of the 
T’ai-shan complex (Archean) lie at the surface over a wide area. ‘There 
are also limited outcrops of the Ta-yang (Upper Algonkian), Sinian, and 
Shan-si systems. 
T’AI-SHAN COMPLEX (ARCHEAN). 
Gneisses, schists, granites, porphyries, and a few other rocks are the 
constituents of the Archean of eastern China. Much of the mass has been 
metamorphosed past recognition and with present methods we are unable 
to ascertain the origin of many of the rocks. A large part is, however, 
clearly composed of igneous intrusives, some of which are moderately 
metamorphosed. In one instance only we observed unquestionable sedi- 
mentary rocks in the Archean, but there is some evidence suggestive of 
a similar origin for various gneisses and schists which are now classed 
as doubtful. The facts from China are of particular interest at present 
because the Archean has been held until recently to consist entirely of 
metamorphosed igneous material.* 
Rocks OF DOUBTFUL ORIGIN. 
GNEISSES AND SCHISTS. 
Flesh-colored biotite gneiss, No. 81.—A member of the metamorphic 
complex of the Féu-p’ing region. The geologic relations of the gneiss are 
not known, but its composition suggests that it is a severely metamorphosed 
granite. Our specimen is from the roadside 3 miles, 5 kilometers, south- 
east of Li-yiian-p’u. 
The mass of the gneiss is pinkish-white, but dark seams of mica mod- 
ify the color. It has a granular texture with poorly developed cleavage. 
The light-colored minerals are chiefly quartz, orthoclase, and micro- 
cline, with a little oligoclase; while the prevalent dark mineral is biotite. 
The absence of iron ores is noteworthy. The banding, which is distinct 
in the specimen, is not so obvious in the slide. 
No trace of the original constituents of the rock now remains visible; 
all have recrystallized. Moderate deformation subsequently is evidenced 
by strain-shadows, cracks, and local granulated edges. The feldspars have 
tension-cracks and microcline structure which are believed to be strain 
phenomena. Weathering has partly reduced the feldspars to kaolin and 
has converted many of the biotite flakes into green chlorite. 

* Sedimentary rocks have been reported in recent years from the Archean (basement-complex) rocks 
of United States, Canada, and Europe. A summary of these occurrences appears in Bulletin of the U.S. 
Geological Survey, Van Hise and Leith: Correlation papers, Archean and Algonkian 
