CHAPTER VIII. 
STRUCTURAL GEOLOGY OF THE WU-T’AI DISTRICT. 
By BatiLey WILLIS. 
ENUMERATION OF DISTINCT STRUCTURES. 
The following paragraphs contain a summarized statement of the 
general structure peculiar to each of the great series of rocks of the Wu’tai 
district. 
STRUCTURE OF THE T’AI-SHAN COMPLEX. 
Banding and contortion.—The T’ai-shan complex, which constitutes 
the basement of all other series of rocks observed in Chi-li and Shan-si, 
consists of gneisses and schists, which exhibit the internal structures due 
to metamorphism, igneous injection, and compression. ‘They are minutely 
cleaved, are to a great extent composed of mineral particles arranged with 
longer axes parallel to the cleavage, and are banded in layers a few inches to 
a few feet thick, likewise parallel to the cleavage. ‘The banding and nearly 
horizontal jointing give to mountain slopes and summits the forms which 
suggest stratified rocks (Fig. A, Plate XVII). The attitude of the banding 
frequently approaches horizontality, but steep dips and sharp contortions 
on a small scale are common. By exhaustive surveys, larger structures 
may be traced among the different varieties of gneiss and schist, but they 
could not be worked out in a reconnaissance. 
STRUCTURE OF THE PRE-CAMBRIAN SEDIMENTS. 
Schistosity and folding of the Wu-t’ai schists.—The great mass of the 
Wu-t’ai-shan is composed of schists, which have a general northwesterly 
dip. This is the attitude of the original bedding of the quartzites, marbles, 
and altered clayey rocks, and is also that of the schistosity. The mass 
is essentially isoclinal, and in general the dip is 70° to 80°, though occa- 
sionally as low as 30°. All of the rocks are highly altered, and the general 
development of mica-schists indicates that they recrystallized under great 
pressure. 
The internal structure of the sedimentary masses involves both folds 
and overthrusts, and we have felt justified in drawing inferences regarding 
their occurrence in the section we observed on the T’ai-shan-ho. We 
recognize, however, that the inference based on only one section is liable 
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