316 RESEARCH IN CHINA. 
while others have recrystallized into amphibolites. None of them, how- 
ever, are schistose, with the exception of the greenstone and aplite west 
of Shi-ts’tian-hién. Like the granites, they pierce the strata of the Han 
system, and it is not improbable that they date from the epoch of defor- 
mation, which appears to have taken place in the Mesozoic. 
A few dikes, which were observed associated with the Ts’in-ling schists 
at Hei-shui-k’6u, may well be older than any of the igneous rocks previously 
mentioned, as they are thoroughly metamorphosed. 
LATE MESOZOIC. 
SHI-TS’UAN SANDSTONE. 
The Shi-ts’iian sandstone consists of conglomerate and reddish arkose 
sandstone. It was seen only in the vicinity of Shi-ts’itian on the Han river, 
where it is exposed in an open lowland bordered by mountains of Paleozoic 
strata (see Plate XLIV). The prevailing rock is a firm coarse-grained 
sandstone, composed of heterogeneous materials. It contains seams of 
conglomerates, which become more numerous downward and finally pre- 
dominate at the base of the formation. The pebbles range up to 12 inches, 
30 centimeters, in diameter, and consist chiefly of dark limestones and 
schists derived from the Han system. ‘The strata are not folded, but are 
gently tilted toward the west and southwest. Cross-bedding, inclined at 
angles of about 20° toward the west, is very prominent in the sandy por- 
tions, which have the character of a delta deposit, the cross-bedding being 
more regular and persistent inits dips than it usually is among the worked 
and reworked accumulations of river flood-plains, or in subaerial deposits. 
The distribution of the mass in the river valley probably does not signify 
that it was deposited by the existing river; it is more likely that the valley 
has developed on the soft sandstone. The southern margin is straight 
like a normal fault, and we therefore regard the mass as a down-faulted 
block. It is possible that the faulting produced a depression, in which 
the sandstone gathered as the wash of streams on the tilted slope. We 
observed a thickness of 320 feet, 97 meters, but the actual thickness of 
the formation may be much greater. 
Although the contact at the base of this sandstone and conglomerate 
was not observed, the fragments of the Han river rocks included in the 
formation prove beyond question that the contact is unconformable. ‘The 
sandstone was evidently deposited at a period later than the folding, 
metamorphism, and igneous activity, which have so conspicuously affected 
the strata of the Han system. 
