468 RESEARCH IN CHINA. 
glacial origin. None of these rocks have been metamorphosed to any 
noteworthy degree—taking the word ‘‘metamorphism” in its prevalent 
and restricted sense. They have undergone only such changes as take 
place at moderate depths, 7. e., cementation, advance in crystallization 
and weathering. 
ROCKS OF SEDIMENTARY ORIGIN. 
PSAMMITES. 
Reddish sandstone, No. 150.—This sandstone is the basal member of 
the Paleozoic system at Nan-t’ou on the Yang-tzi. The specimen was 
taken about 50 feet, 15 meters, above the unconformable contact with the 
underlying granitic rock. 
A dull reddish-brown rock of medium grain. The color and texture 
are nearly uniform. Although somewhat friable, the rock is well cemented 
and relatively hard. 
The subangular and closely packed grains consist very largely of 
quartz. In addition there are several varieties of feldspars, iron ores, 
flints, etc., amounting to perhaps 15 per cent of the rock. These fragments 
are joined together partly by a filling of clay, but even more by quartz, 
which has been brought in and deposited upon the sand-grains, the material 
thus added having the same crystallographic orientation as the original 
grain. These secondary borders are sometimes very broad. ‘The clay- 
like filling appears as a brightly polarizing fibrous mass which is so fine- 
grained that the components are not distinguishable; probably it consists 
of kaolin, sericite, and perhaps talc discolored by iron oxides. 
The sandstone has suffered but little change except the cementation 
just alluded to. ‘ Aside from strain-shadows in some of the grains, no 
effects of compression are noticeable. 
Pink sandstone, No. 149.—This is merely another phase of the same 
sandstone as No. 150, which it resembles closely in both texture and solid- 
ity. It differs chiefly in containing much less ferruginous matter, and on 
this account its color is much lighter. In this specimen bits of muscovite 
and hornblende may be seen with the unaided eye. 
Greenish quartzite, No. 144.—A very thin local layer near the top of 
the green shales of the Sin-t’an formation. The rocks of the vicinity are 
folded, but have not been subjected to great compression and are, there- 
fore, relatively little altered. 
Specimen collected in the canyon 2 miles, 3 kilometers, north of 
Ta-ning-hién, Ssi-ch’tian. 
A dense fine-grained quartzite, which fractures conchoidally. The 
color is a uniform dull olive-gray, and the weathered surfaces are ocherous 
brown. 
