116 RESEARCH IN CHINA. 
gneiss, indicating that the T’ai-shan complex occurs not many miles away. 
As in the district about Wu-t’ai-shan, the quartzites and schists in this 
locality are inclined toward the north; they lie unconformably beneath 
Cambrian shales and limestones, and are completely covered by them on 
the north (see Fig. 46). 
GROUPING AND CORRELATION OF WU-T’AI STRATA. 
Three groups distinguished.—An inspection of the varied sequence of 
schists, gneisses, and other rocks in the T’ai-shan-ho section (Plate XVIII) 
will readily suggest that the interpretation of the Wu-t’ai system is both 
complex and difficult. Most of the strata have had their original compo- 
nents and structures obliterated by metamorphism. They have been 
intensely folded, and are interrupted by igneous rocks of several gener- 
ations. In our brief reconnaissance, we did not succeed in unraveling the 
complexities of the stratigraphy and structure, but the facts observed 
enable us to add materially to previous knowledge of the region and to 
suggest explanations for many of the phenomena which must engage the 
attention of future students of the region. 
The portion of the Wu-t’ai rocks exposed along our route seems to be 
divisible, on a lithologic basis, into three distinct groups, which we have 
named after appropriate geographic positions: 1. Shi-tsui group; 2. Nan-t’ai 
group; 3. Si-t’ai group. 
The first group, Shi-tsui, comprises gray schists and gneisses with 
thick layers of quartzite. They occupy the eastern end of the T’ai-shan-ho 
section (Plate XVIII, beds 2-20). The Nan-t’ai group is characterized 
by dark quartzites and marble with subordinate schists. They are best 
exposed in the T’ai-shan-ho valley above Shang-ho-miau, and with them 
we have classed tentatively the white marble and schistose strata, which 
have been described as the Shang-ho-miau section, and which lie south of 
the typical Nan-t’ai sequence, separated from it by an overthrust. The 
third or Si-t’ai group consists largely of green schists, and includes the 
schistose clastics of coarse texture (Plate XVIII, beds 28-32). It forms 
the great mass of the main ridge of the Wu-t’ai-shan. 
In the preceding pages the strata which constitute these three groups 
have been described as we observed them in the section on the T’ai- 
shan-ho. We now proceed to consider each group as a stratified sequence 
with the other groups. While not positive that we have correctly ascer- 
tained the true order of succession, we nevertheless begin with what we 
consider the oldest of the three. 
Shi-tsut_ group.—The rocks which are assigned to this group are those 
which are described in the Shi-tsui section, We include in the group the 
