ROCKS FROM NORTHERN AND CENTRAL CHINA. 363 
The granite possesses a speckled appearance because smoky quartz 
and black biotite are embedded in white feldspars. The quartz and 
feldspar together appear to form more than 80 per cent of the mass. The 
feldspars are orthoclase with a subordinate amount of oligoclase. Both are 
slightly altered. In addition to the olive-brown biotite there area few 
grains of titaniferous magnetite bordered in some cases by sphene. 
The granite has not been greatly strained. Undulatory extinction of 
the crystals and occasional loci of granulation are the only evident results. 
Flesh-colored aplite, No. 59.—The rock is used as railroad ballast near 
Shi-san-ch’an and is obtained from a quarry southwest of the granite. 
A dense lithoidal rock of light color minutely speckled with black. 
It consists of finely granular quartz and alkali feldspar intimately mingled 
and of uniform texture. The black specks noted in the large prove to be 
minute bits of iron oxides. There are no phenocrysts. 
The mass shows no marks of alteration and it is believed to be an 
unaltered igneous rock of highly siliceous composition. 
PEKING BASIN. 
This area includes the embayment of fluvial plain in which Peking 
is situated. No systematic petrological work was attempted in this area, 
and the rocks of the region are represented in our collection by only one 
specimen. 
Rocks OF IGNEOUS ORIGIN. 
Greenish aporhyolite, No. 156.—The aporhyolite occurs in an isolated 
ridge surrounded by alluvium about 4 miles, 6.5 kilometers, southwest 
of Chang-p’ing-chéu, or 20 miles, 32 kilometers, northwest of Peking 
itself. Its relations were not observed, but judging from the reports of 
earlier explorers,* this is one of the volcanic rocks which are associated 
with the post-Sinian sediments north and west of Peking. 
A fresh-looking greenish lava with a dense stony ground-mass, through 
which are scattered abundant phenocrysts of glassy and smoky quartz, 
together with reddish feldspar and biotite. A few of the feldspar crystals 
attain a breadth of nearly 4 inch, but the majority are much smaller. In 
the hand-specimen one fails to see any suggestion of banding, perlitic parting, 
or other textural peculiarities which are common among the rhyolites. 
In the thin section the stony ground-mass appears cloudy grayish- 
brown in ordinary light. Between crossed nicols it behaves as an isotropic 
* Von Richthofen mentions the occurrence of volcanic flows and agglomerate near Chang-p’ing-chou, 
but describes the rock as carmine-red and containing white feldspar phenocrysts. (China, vol. 1, pp. 
316-321.) Pumpelly appears not to have visited this locality, but he described ‘greenish felsitic 
porphyries” which he observed at Ching-t’ai (which is not far to the west of Chang-p’ing-chou) in the 
form of dikes cutting Sinian limestones. (Smithsonian Contributions to Knowledge, vol. xv, p. 13.) 
