GEOLOGY OF CENTRAL SHEN-SI. 311 
with which they are, nevertheless, in all probability correctly correlated. 
Beyond a general correlation we can not go, as we did not observe any 
distinctive horizons which we can now recognize. 
To distinguish this series, which we can identify only as Paleozoic 
and which may correspond to more or less of the Han system, we may 
call it the Hei-shui system after the river of that name, which crosses it 
west of our route. 
The structure of the Hei-shui system is probably not very intricate, 
if one had a key to the stratigraphic sequence, but there are large areas 
of monotonous slates, which exhibit numerous folds. Under the condi- 
tions of our journey the structure eluded us except in its larger features. 
The following is quoted from Willis’s notes written at Chang-k’6u-shi, 
after ascending the canyon: 
Although the rocks are continuously exposed from Siau-wang-kién to Chang-k’éu- 
shi no definite section was obtained, as the strata present great similarity throughout 
considerable thicknesses, and are repeated by obscure but numerous folds and possibly 
by thrusts. In general the strike of the series varies from N. 80° E. to S. 55° E. At Siau- 
wang-kién the dip is northward, as low as 30°. In about 2 miles it changes to southward 
over an anticlinal axis and continues so for about 3 miles, becoming vertical. Again 
northward and also flat dips come in. Where well exposed, the strata exhibit isoclinal 
folds overturned southward. About 2 miles below Chang-k’6u-shi gray limestone appears 
accompanied by black slate and apparently beneath the argillite and quartzite. It is 
much silicified and exhibits tension crevices, which weather out as cavities. Slaty cleavage 
is highly developed in the black calcareous argillites accompanying the limestone. Flesh- 
colored and greenish quartzites form a conspicuous member of the series apparently above, 
but closely related to, the limestone. 
The structure thus interpreted is expressed graphically, and neces- 
sarily more definitely than we know, in the section, geologic sheet a 2. 
The actual folds are no doubt more intricate. On an anticlinal axis 2.5 
miles, 4 kilometers, south of Lung-t’an-ssi, which is an eastern extension 
of the anticline near Siau-wang-kién, the lowest beds immediately beneath 
greenish slates are quartzite above conglomerate of quartz pebbles in 
quartzite; and large masses of similar conglomerate and blocks of crystal- 
line white marble were seen 4.5 miles, 7 kilometers, southeast of Lung- 
t’an-ssi, on the trail from Mu-tzi-p’ing. These appear to be the lowest 
beds occurring in this district. The slates are lithologically like the Sin- 
t’an (Middle Paleozoic) and the marbles may correspond with those seen 
in the northern section, presently to be described; if so, they are probably 
Cambro-Ordovician. 
A plausible statement of the structure according to these lithologic 
identifications is that an anticlinorium, which along the anticline of 
Siau-wang-kién brings up earlier Paleozoic strata, is succeeded on the 
