GEOLOGY OF CENTRAL SHEN-SI. 301 
Chon-p’ing-hién to Hing-an-ju.—Chén-p'ing-hién (lat. 31° 49’, long. 
109° 34’, atlas sheet d 6) is near the southern margin of the district of 
that regional metamorphism which characterizes the Han system. From 
the limestones which occur from 0.5 to 3.5 miles, 1 to 6 kilometers, south 
of the town, we collected Cambrian fossils, and we have no doubt that the 
shales which appear on the north as well as on the south of the limestone 
anticline are the Middle Paleozoic Sin-t’an shales. Following the Nan- 
kiang northward from Chén-p’ing-hién, we first cross dull olive-green and 
gray argillites. These argillites have been subjected to sufficient dynamic 
action to crush and shear them in many places and even to develop an 
imperfect slaty cleavage. They have been intruded by a number of thick 
gabbro dikes. 
Three miles below Chén-p’ing-hién the Nan-kiang receives a large 
tributary from the west. On the south side of this stream the black 
limestones and slates, similar to the Wu-shan limestone on the Yang-tzi, 
overlie the green argillites and continue in closed recumbent and con- 
torted folds to Ku-niu-tu and beyond. The rocks are very dark argilla- 
ceous and frequently bituminous limestones interbedded with gray slates 
and pyritic black slate, which locally contain thin coal-seams. 
Two or 3 miles, 5 kilometers, north of Ku-niu-tu greenish slates 
reappear. They resemble in color and in general composition the 
green argillite near Chén-p’ing-hién, differing from that formation chiefly 
in the more prominent development of slaty cleavage. The rock is a 
moderately hard olive-green slate, which is well but not regularly cleaved. 
The original bedding is indicated by specimens which show planes of strat- 
ification at angles of about 25° to the slaty cleavage. The slate is intruded 
by irregular bodies of gabbro, some of which are several hundred feet in 
width. The contact between gabbro and slate is sharp, and the latter 
has been locally altered by the intrusion to a chlorite-hornfels. It is 
probable that these slates are a reappearance of the Sin-t’an shale. 
The structure of the belt between Chén-p’ing-hién and the green slates 
north of Ku-niu-tu is apparently that of a syncline, whose northern limb 
is overturned southward. Our observations of dip have been used in 
making up the forms shown in the northern end of the section, Fig. 62, 
and also on the geologic atlas sheet d 6. The dips are gentle and to the 
north throughout; but there are axes of minor anticlines and synclines, 
especially noticeable in gray limestone near the base of the Wu-shan forma- 
tion north of Shi-chai-ho, and also in black slaty limestone near Ku-niu-tu. 
Certain observed folds near Ku-niu-tu are shown in Figs. 63, 64, and 65. 
Two miles, 3 kilometers, south of Pai-kiu-hia the green slates of the 
Sin-t’an are succeeded by black limestone and slate, through which the 
