136 RESEARCH IN CHINA. 
PALEOZOIC. 
By ELiotT BLACKWELDER. 
PRE-SINIAN UNCONFORMITY. 
Out of the thirteen instances in which Sinian rocks were found in con- 
tact with older systems, four were fault contacts and the rest were visible 
erosion unconformities. Among the latter, the rocks which underlie the 
Sinian were in four cases the T’ai-shan complex, in two cases the Wu-t’ai 
schists, and in two cases the Hu-t’o system. Five of these exposures, 
each of which presents distinctive features, are here described. 
About 7 miles, 11 kilometers, southeast of Hin-chéu, in the north slope 
of the mountain, the red granite of the T’ai-shan complex lies upon the 
upturned edges of the Sinian strata on a gently sloping overthrust plane 
(Fig. 31). Below the fault, however, the Lower Cambrian sediments rest 
undisturbed upon the eroded and weathered surface of the granite. The 
basal layer of the Cambrian shales consists of a few inches of coarse arkose 
sand, composed of the red feldspars and blue-gray quartzes derived from 
the granite. This sandstone is followed as usual by the red shales. 
Another excellent exposure of the unconformity appears in the slopes 
of a valley 3 miles, 5 kilometers, south of Yau-t’6u in Shan-si (Fig. 46). 
On the west side of the valley the Cambrian red shales lie upon the 
eroded edges of white quartzite, embedded in dusky biotite-schists. In 
the opposite slope the contact is upon purplish biotite-schists. There is a 
close similarity between these schists and certain members of the Wu-t’ai 
system southeast of Shi-tsui. The ancient surface at this point is nearly 
plane and the rocks are deeply weathered. A greenstone dike, which had 
penetrated the schists in Pre-Sinian time, is squarely cut off at the uncon- 
formity. Contrary to the usual composition of the Cambrian shales, 
the basal portion here is composed of 15 feet, 4.5 meters, of coarse sand- 
stone and conglomerate. ‘The constituents of the pebbles are banded chert 
and white, red, and black quartzites, all of which rocks have been found in 
the Wu-t’ai and Hu-t’o systems. 
At Yen-t’ou north of Wu-t’ai-shan, the cliffs of the O-shui canyon ex- 
pose the Sinian limestones and shales lying in marked discordance on the 
green Si-t’ai schists (Lower Algonkian). (Plate XIX and Fig. 34.) The 
schists are weathered and brownish at the contact, and the basal member 
of the Cambrian is a thin conglomerate of quartz pebbles. Red sandy 
strata overlie the conglomerate and are in turn followed by red shales, all 
belonging to the Man-t’o formation. 
In the fourth example the Cambrian rests upon the Hu-t’o strata, 
thus proving the Pre-Paleozoic age of the latter. The older rocks consist 
