CHAPTER XIII. 
STRUCTURAL GEOLOGY OF THE MIDDLE YANG-TZI PROVINCE. 
By BaILeEy WILLIS. 
DEFINITION OF THE PROVINCE, 
The geologic province of the Yang-tzi river, as it is here defined, is 
a region within which strata of Paleozoic and Mesozoic age are folded 
in apparent conformity, without notable metamorphism; and which pre- 
sents structures of the Appalachian type. Its limits are only partially 
known; the eastern boundary, at which the strata sink beneath the allu- 
vium of the Great Plain of China, crosses the Yang-tzi at I-chang. The 
northern boundary is a transition zone between the Yang-tzi province 
and the metamorphic province of the Han watershed, which we crossed 
at Chén-p’ing-hién, whence it extends east by south past Chu-shan-hién, 
Hu-pei, and west by north, south of Han-chung-fu, Shen-si. Toward 
the west it extends beneath the red beds of the basin of Ssi-ch’uan and is 
continued in the ranges which trend north and south along the eastern 
borders of Tibet. Its limits south of the Yang-tzi are not determined. 
Referring the reader to the preceding chapter by Blackwelder, for 
discussion of our observations on stratigraphy I take up the description 
of structure at I-chang, and follow the sequence of folds up the Yang- 
tzi to Wu-shan-hién and thence up the Ta-ning-ho, and northward across 
the Ki-sin-ling range to Chén-p’ing-hién. At the latter place the discus- 
sion joins that of the metamorphic rocks of the Han watershed. The 
length of the section across the strike is about 50 miles, 80 kilometers, on 
the Yang-tzi and 464 miles, 75 kilometers, up the Ta-ning-ho and beyond 
to Chén-p’ing-hién. 
YANG-TZi SECTION: I-CHANG TO WU-SHAN-HIEN,. 
DETAILS OF THE YANG-TZI SECTION. 
Northwest of I-chang the mountains rise from the plain in a long 
slope to a range of striking peaks. The slope is the bared dip plane of 
the Wu-shan (Carboniferous) limestone; the crest is the upturned edge 
of the limestone. The dip is 10° to 15° southeast. In contrast to the 
dead level plain which stretches far to the eastward, this mountain front, 
which is probably 4,000 feet, 1,200 meters, or more in height, is surprisingly 
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