328 J. S. Lee—An Outline of Chinese Geology. 
the chemical composition of the pre-Cambrian rocks signifies 
certain physical conditions of the sea in which they were formed in 
such a way as it does in the case of post-Cambrian deposits, then we 
may take the fact that the Nankou Formation changes its lithological 
character from argillaceous to calcareous towards its upper part 
in the area of Chi-li and Shan-si, as being indicative of a persistent 
lowering of the sea-floor. Nevertheless, in western Shan-tung, apart 
from the occasional presence of a few thin beds of a flinty limestone, 
which may be doubtfully regarded as the latest stage of the Nankou 
Formation, we know no rocks equivalent to the Nankou System of 
Chi-li. What are supposed to be the representatives of the Wutai 
System there are schists and quartzites which nowhere attain a 
great thickness, and are frequently absent. These facts converge 
to show that practically during the whole of the Nankou period 
western Shan-tung was subjected to subaerial denudation. The 
Tsing-ling area is likewise reported to be free from sediment 
belonging to the Nankou System. 
The continued subsidence of the sea-floor in Chi-li and Shan-si 
appears to have been accompanied by a gradual and uniform 
elevation of the neighbouring lands, enabling the eroding agencies 
to reduce north-east China to a vast peneplain of mature type. 
Elsewhere towards the close of the Nankou period the tranquil 
sedimentation was, however, punctuated by local earth movements. 
In the Tsing-ling area this movement may have reached to the 
magnitude of an orogenic upheaval. Igneous magma again intruded 
itself at several localities in northern China. They are essentially 
of basic composition, and relatively insignificant in number. 
THE SINIAN OR CAMBRO-ORDOVICIAN. 
The term Sinian was first introduced by Pumpelly for expressing 
a system of north-east folds in Eastern Asia.t Richthofen during his 
exploration found a group of rocks, chiefly composed of limestones, 
spreading over large areas in north-east China where the Sinian 
folds prevail. He then termed the rocks the Sinian (Sinisch) 
Formation. The discovery of a “ primordial fauna’’ *in the middle 
part of this mighty sequence of racks led Richthofen to believe that 
the top of the Sinian chronologically extended into the Ordovician, 
and its base reached down, in some cases, to the pre-Cambrian. 
An unconformity of great magnitude was subsequently discovered 
by Willis and Blackwelder within the Sinian System of Richthofen. 
The plane of the unconformity lies directly below a series of red 
shale and sandstone. They therefore found it desirable to shift the 
lower boundary of the Sinian System on to the plane of the said 
unconformity. The lower part of Richthofen’s Sinian System, 
namely, the series of strata lying underneath the fossiliferous red 
1 Pumpelly, ‘‘ Geological Researches in China, Japan, and Mongolia”’: 
Smithsonian Contributions, vol. xv, p. 67. 
2 Dames, China, vol. iv, pp. 1-33. 
