56 RESEARCH IN CHINA. 
green peridotite, consisting of olivine with a little magnetite and pyroxene, 
weathering has long since converted all of the olivine into serpentine. 
As a result of contact metamorphism, the color of the red sandstones, for 
a distance of about 1 foot on either side of the dike, has been altered 
to olive gray; under the microscope we see that the change is due to an 
alteration in the ferruginous cement of the sandstone. 
IN THE YEN-CHUANG DISTRICT. 
The principal outcrop of the Sin-t’ai series is a small triangular area 
east of the W6én-ho, bounded on the south by outcrops of the Po-shan 
series and on the other sides by normal faults. Scattered exposures occur 
west of the river also, but there the alluvium covers most of the surface. 
The succession already described for the Sin-t’ai district coincides 
approximately with that here. The red cross-bedded sandstones lie above 
the coal-measures in an unknown relation, and are in turn overlain by a 
gray shaly and sandy member and red pebbly clays—all lithologically 
similar to the rocks of the Sin-t’ai section. The principal peculiarity of the 
series in this locality is the greater abundance and variety of igneous rocks. 
They consist of basaltic flows and tuffs, and dikes of at least two kinds 
of porphyry. ‘The distribution of the basalts is so irregular that in one 
section which was surveyed across the outcrop they were almost lacking. 
About 2 miles north of Yen-chuang, however, they are interstratified with 
the red sandstone, and become so well developed toward the north as 
to obscure in large measure the gray shales and red clays. This partic- 
ular mass does not extend far to the east. In numerous dikes there are 
pale brown mica-feldspar-porphyry, gray hornblende-syenite-porphyry, and 
a buff-colored porphyry with long acicular crystals of black hornblende. 
The intrusion of these lavas has had only a very slight effect upon the 
country-rock, especially where that rock was sandy. ‘The basaltic erup- 
tions occurred contemporaneously with the deposition of both the Po-shan 
sediments and the lower red beds—a fact which favors the idea that these 
two series are not widely separated in time. The porphyries are at least 
partly of later age, for they were observed cutting across both dikes and 
flows of basalt in each of the two formations. 
IN THE PO-SHAN DISTRICT. 
From Po-shan northward to Chéu-ts’un, and for some miles both east 
and west of the branch railroad, the Sin-t’ai formation occupies the sur- 
face. In our rapid journey along the main road we could only note that 
it consisted of red sandy sediments, which include many tuffs and flows 
and some dikes of greenish lavas, which are probably decayed basalts. 
Northwest of Chi-ch’uan-hién the red sandstone is conglomeratic in certain 
