CHAPTER XII. 
STRATIGRAPHY OF THE MIDDLE YANG-TZI PROVINCE. 
By Eviot BLACKWELDER. 

This chapter and the one on structure, which follows, relate to what 
may be called the province of the middle Yang-tzi, the geologic features 
which characterize the region being typically developed along the water- 
shed of that great river in its middle section, below the junctions of its 
principal headwaters and above the lower course in its vast flood-plain; 
that is, between Chung-king, and I-chang (Plate 1). We saw the eastern 
portion of this province only. The western limit lies along the Tibetan 
plateaus west of the Red Basin of Ssi-ch’uan. On the south the boundary 
is indefinite, but on the north there is a distinct line between this belt of 
Paleozoic strata, which are not metamorphosed, and a similarly extensive 
zone, in which rocks of the same era are metamorphosed. 
We entered the province of the middle Yang-tzi at Chén-p’ing-hién, 
Shen-si, a point on the northern limit (atlas sheet d 6); proceeded south 
to the Yang-tzi at Wu-shan-hién; and thence followed the river to I-chang. 
The route is given on Plate VII, and details of topography and geology 
are shown on atlas sheets d 6 and d 7. 
The accompanying columnar section, Fig. 59, gives the sequence of 
strata for that part of the province which we saw. It is probable that 
certain relations may differ in other parts of the province, particularly 
those which characterize the Middle Paleozoic and Permo-Mesozoic. ‘The 
meager representation of the Silurian, Devonian, and Lower Carboniferous 
appears to develop to a fuller record further west, along the route followed 
by von Richthofen,* and his section of Post-Carboniferous rocks is much 
thicker than anything we saw. 
PRE-CAMBRIAN, 
HUANG-LING GRANITE-GNEISS. 
A granite exposed above Huang-ling-miau on the Yang-tzi is the 
only Pre-Cambrian formation known in place in the middle Yang-tzi 
province. The river cuts through a broad anticline, exposing in succes- 
sion each of the Paleozoic systems, and in the flat dome of the fold finally 
lays bare the foundation beneath the sediments. The fundamental rock 

* China, vol. U1, p. 598. 265 
