STRATIGRAPHY OF CHI-LI AND SHAN-SI. 147 
covering of loess south of these hills. It has doubtless been brought up 
behind the limestones by the great normal fault of the Ki-chéu-shan. 
The unfamiliar gray limestone continues westward from the Shi-ling 
pass an unknown distance. In the north base of these hills red shales 
appear beneath the loess, indicating that the overthrust of Algonkian on 
Cambrian persists several miles west of the pass. 
PRE-SHAN-SIAN UNCONFORMITY. 
In Chi-li and Shan-si.—The obscure but definite unconformity at 
the base of the coal-measures in Shan-tung has already been described. 
In Chi-li the relations are almost exactly the same. 
At Ning-shan there are several 
exposures which show this unconfor- 
mity clearly. The upper layers of the 
Sinian limestone are buff and siliceous 
from prolonged weathering, and the sur- 
face buried beneath the coal-measures 
is covered with a coarse breccia of 
decayed limestone rubble. The inte- 
Fic. 41 (Willis).—T’ién-hua, Shan-si, atlas sheet aac ae ae ee oe fegalh 
CI. Shale at the base of the Shan-si series cavities, which indent the upper layers 
in joint crevices and solution cavitiesin Ki- of the limestone, is rounded and coated 
Soy inns ong, with incrustations of silica and calcite. 
In these cavities, and filling the chinks in the breccia, lie shales of various 
colors, which are identical and continuous upward with the basal shales 
of the Shan-si formation. Since the shales coincide in bedding with the 
underlying limestones, the unconformity is not easy to recognize. 
In the T’ién-hua district, Shan-si, numerous canyons expose the coal- 
measures and the adjacent limestones in many places, and the contact 
is opened by diggings for pottery clays, which are yellow and black and 
contain decomposed cherts. The clayey shales lie in joint crevices in the 
limestone, and also in solution cavities along weak layers under more 
massive ones, as if interbedded (see Fig. 41). 
At a contact immediately above the limestone in the southern part 
of the field Willis observed the sequence of consolidated tufa, shale, and 
bog-iron ore indicated in Fig. 42. The contact with the limestone was 
not exposed, but occurs just below the bottom of the section on the left. 
Relations similar to those noted in the T’ién-hua field were observed 
in the Yau-t’6u district, at the base of the Shan-si system. 
The gap between the Sinian and the coal-measures represents much, 
if not all, of the long lapse of time from the Middle Ordovician far into 

