ROCKS FROM NORTHERN AND CENTRAL CHINA. 423 
probable that they represent bits of clastic limestone in the original con- 
glomerate. 
To summarize the foregoing statements it may be said that the rock 
was formerly a conglomerate of quartz and quartzite pebbles set in a sandy 
clay cement. Under anamorphic conditions, new micaceous minerals have 
developed, shearing has occurred, and the matrix is now schistose. Some 
of the pebbles have been distorted and crushed, but the large bodies of 
quartz are scarcely deformed. 
Quartzite from schist conglomerate, No. 155.—In the pass across the Wu- 
t’ai-shan 17 miles, 27 kilometers, north of Tung-yti-chén, the green schist 
conglomerate of the Si-t’ai group contains large pebbles of quartzite. The 
present specimen is a fragment of a pebble which was more than a foot 
long. It is particularly interesting as evidence of the great durability of 
pure quartzite, for although it is obviously older than the ancient schist in 
which it is inclosed, nevertheless its own coustitutien and structure show 
only moderate alterations. 
A hard greenish-gray quartzite, indistinctly streaked with darker bands 
which represent stratification and cross-bedding in the original sandstone. 
The dark bands weather more rapidly than the lighter ones because they 
contain iron minerals which are more soluble than the quartz. The rock is 
of rather fine texture, visibly granular, and not vitreous. 
The original sand-grains of pure quartz were well rounded and cemented 
with subsequent quartzose material. ‘Their edges are now rough, however, 
and the distinction between sand and cement rests chiefly on the forms of 
the grains. This condition has probably been produced by the recrystal- 
lization of the cement and the peripheral portions of the sand-grains. 
Shreds of green chlorite which may have been derived from the clay con- 
stituents of the rock impart the greenish tinge to the quartzite. The other 
minerals present are iron ores with a little rutile. 
PSAMMITES, 
Arkose quartzite, No.82.—This quartzite is regarded as being one of the 
lowest members of the Shi-tsui group of the Wu-t’ai system. It is exposed 
in the mountains southeast of Shi-tsui and is associated with mica schists, 
brown quartzites, and amphibolites. The present specimen was taken 
near the base of stratum d in Fig. 20. 
A light-reddish rock composed of glassy quartz and a nearly equal 
amount of red feldspar. The texture is coarse and crystalline rather than 
granular, and the isolated specimen might easily be mistaken for a binary 
granite (alaskite). 
Internally the rock shows abundant evidence of severe deformation, 
but it has not yet lost its identity as an arkose. The original sand-grains 
