398 RESEARCH IN CHINA. 
The rock is pinkish-gray, finely crystalline, and includes a few scattered 
phenocrysts of plagioclase and hornblende. The greater part of the mass 
consists of closely packed, irregular grains of feldspar with a subordinate 
amount of quartz. The less common primary minerals are pyroxene, 
magnetite, sphene, and apatite. 
Orthoclase is the commonest of the feldspars. It occurs in irregular 
crystals which are partially altered. The plagioclases are rich in soda and 
some of the crystals are zonally built, having basic oligoclase in the center 
with peripheral shells of albite. The only large phenocryst occurring in 
the section is oligoclase. On the whole, therefore, the alkali feldspars 
predominate. 
Although quartz is decidedly a subordinate mineral in this rock it is 
rather common in the form of small interstitial grains. 
The amphibole is a pale-green, slightly pleochroic hornblende, which 
occurs in irregular crystals. It is now partly altered to greenish chlorite 
which is easily confused with the remaining hornblende, except when 
crossed nicols are used. In addition to the chlorite there are other alter- 
ation products such as iron ores and calcite, with a little epidote. It is not 
unlikely that the calcite is partly a product of subsequent changes in the 
chlorite. In several cases the hornblende incloses areas of colorless 
pyroxene. ‘The character of the latter is much obscured by specks of iron 
ores and alteration products. 
Altered quartz-syemte porphyry, No. 13.—The rock occurs as a rather 
thick intrusive sheet in soft shales and thin limestones of the Man-t’o for- 
mation (Cambrian) on the southeast slope of the Man-t’o butte. This is a 
phase of the hornblende porphyries which are common in the basal shales 
of the Cambrian series, in the region of Ch’ang-hia. Most of these intru- 
sions have an abundance of plainly visible hornblende needles lying in an 
aphanitic ground-mass. The outcrops are so deeply weathered that in 
most cases we were unable to secure coherent specimens. 
A dull greenish-gray finely crystalline rock, weathering to a brownish 
color onexteriors. Phenocrysts are ordinarily not noticeable, but moderate- 
sized crystals of hornblende, with a very few much larger ones of quartz, 
are scattered here and there. This rock does not differ widely from the 
quartz syenite (3). Quartz is somewhat less abundant, there are no traces 
of pyroxene, and lime-bearing feldspars are not present in noteworthy 
amount. Most of the feldspars appear to be albite with considerable ortho- 
clase. Although the feldspars are only partially altered to kaolin, sericite, 
etc., the hornblendes are so completely decayed that it would hardly be 
possible to identify this mineral if it occurred in allotriomorphic masses. 
Fortunately there are in this slide numerous sharp rhombic and prismatic 
sections which are unmistakable. In some cases the sites of the horn- 
