STRATIGRAPHY OF CHI-LI AND SHAN-SI. 129 
in the Hu-t’o because it has no resemblance to any member of the Sinian 
system, and is comparable in some of its features to certain layers in the 
Tung-yu limestones. 
INTRUSIONS IN THE Hv-T’o SYSTEM. 
Igneous rocks do not occur frequently in the Hu-t’o system in this 
region. The most common are dikes of dark greenstone, which are now 
partly schistose. ‘The gray slates southeast of Liu-yiian are penetrated 
by a few dikes of greenish hornblende-porphyry and greenstone. Three 
miles, 5 kilometers, south of Wu-t’ai-hién a single greenstone dike cuts 
the reddish argillites and limestone. Other similar intrusions, too deeply 
decayed to be identified specifically, are associated with the Hu-t’o strata 
south of Tung-yii and along the front of the Ki-chéu-shan. 
GROUPING AND CORRELATION WITHIN THE Hvu-T’0o SYSTEM. 
As already stated, the order of strata of the Hu-t’o system, as now 
understood by us, is deduced from an interpretation of the structure in the 
typical district. We have there a body of folded Pre-Cambrian strata, 
bounded on the southeast by a fault, along which they are overthrust on 
the Cambrian, and on the northeast and north by the older Wu-t’ai schists. 
According to the strikes and dips of this folded series, the pitch of the axes 
is toward the southwest. The folds sink in that direction and the synclines 
become deeper. The general structure may be regarded as consisting of 
two wide synclinoria, divided by an overthrust (geologic atlas sheet C I). 
According to this interpretation of structure, strata about the mar- 
gins of the synclinoria should be the older and strata in the central zones 
should be the younger. In a general way our observations indicate that 
there is a difference between the strata appearing in the general positions 
thus opposed. In the more northeasterly sections, soft slates associated 
with characteristic thin beds of limestone and quartzite prevail, and hills 
having a synclinal structure are capped by flinty gray limestones; whereas, 
toward the southeast, similar but thicker limestones associated with quartz- 
ite and thin beds of argillaceous rocks occur. On this basis we distinguish 
between an older and a younger group, namely the Téu-ts’un slates below 
and the Tung-yii limestones above. The lowest of the Tdou-ts’un slates 
seen are supposed to be the beds of quartzite and conglomerate east of 
Liu-yiian, near the Wu-t’ai rocks and next the overthrust east of Tung-yii. 
The more massive limestone beds of the upper Tung-yti occur southwest 
of Wu-t’ai-hién adjacent to the Sinian limestones, and are with difficulty 
distinguished from the latter at a distance. 
We are not able to give complete sections of either of these groups, 
or to point out a plane of demarkation between them. In view of the 
folding of the Hu-t’o system, it may be difficult to establish complete 
sections, even with detailed surveys, especially as the outcrops are limited 
