STRUCTURAL GEOLOGY OF THE WU-T’AI DISTRICT. 159 
in the areas colored to correspond with the lower argillites. Along its 
southeastern margin the synclinorium is cut off by an overthrust, which 
constitutes the contact with the Cambrian. 
STRUCTURE OF THE PALEOZOICS. 
Shallow synclines and sharp anticlines.—The Paleozoic strata consist 
of a thin formation of shales at the base, a very thick and massive limestone 
sequence, and a relatively thin succession of coal-bearing sandstones and 
shales at the top. They constitute a very rigid strut, which is separated 
from the structurally distinct Pre-Cambrian rocks by the easily disturbed 
layer of Lower Cambrian shale. They were, therefore, capable of retain- 
ing a simple attitude over wide areas, and of moving easily upon their 
foundation. 
The structures which the Paleozoic strata exhibit correspond with 
these indications. The broader areas are gentle, shallow synclines, which 
in this district are barely deep enough to retain small areas of the Car- 
boniferous rocks. Associated with these synclines are sharp anticlinal 
folds, which frequently have vertical dips and include a keel of the Lower 
Cambrian shale. These anticlines are localized in consequence of the ease 
with which the mass moved upon its foundation, and a corresponding effect 
is found in certain overthrust faults, by which the massive portion of the 
Ki-chéu limestone comes to lie upon various older strata. 
STATEMENT OF OBSERVATIONS. 
Occurrences east of Téu-ts’un.—iIn the high mountains east of the 
Shi-t’ou-ho basin, 7 miles, 11 kilometers, east of Tou-ts’un, we first came 
upon Paleozoic strata in Shan-si. We there found the characteristic Lower 
Cambrian red shale and Middle Cambrian oolitic limestone, overturned 
in the northwestern limb of the syncline, as represented in Figs. 35 and 36. 
The northwestern boundary was marked by a zone of brecciated chert 
and buff limestone, later recognized as belonging to the Hu-t’o system 
and overthrust upon the Cambrian. The northeastern end of the syncline 
was traced by the occurrence of the red shales as seen from the ridge, but 
we were unable to extend our observations by descending the wild canyon 
in the mountains further east. As our route up the T’ai-shan-ho, across 
Pre-Cambrian schists, was but 5 or 6 miles, 8 or 10 kilometers, northeast 
of the great synclinorium in which the Paleozoic strata lie, it is evident 
that the latter do not extend far in that direction. The rising pitch of 
the axis carries them out to the mountain summits. 
The canyon of the Shi-t’ou-ho, southeast of Téu-ts’un, exposes the 
section shown in Fig. 37. At its northwestern end limestone and quartzite 
