52 RESEARCH IN CHINA. 
The Yen-chuang field is characterized by abundant volcanic rocks of 
various kinds, occurring in the forms of dikes, sills, surface flows, and tuffs. 
Although the source of this material was not definitely located, it is thought 
that an irregular area of massive dolerites and pyroxene andesites, casually 
noted about 4 miles, 6.5 kilometers, southeast of the town, may repre- 
sent the throat of the ancient volcano. In the immediate vicinity of this 
mass the Tsi-nan dolomite is metamorphosed into siliceous hornstones. 
The lava flows in the coal-measures themselves are basaltic and are now 
greatly weathered. They alternate with fine-grained greenish tufis, yellow 
shales, and sandstones. The dikes and sills are composed not only of 
olivine basalt, but of brown and green hornblende-syenite-porphyries and 
buffish feldspar-porphyries. The largest dike of the latter seen was 70 feet, 
21 meters, across, but most of the intrusions are relatively thin. As the 
coal-measures at Yen-chuang are exposed continuously for a distance of 
a mile or more, measured along the dip, and lie at an inclination which is 
rarely less than 25° and sometimes more than 40°, the total thickness of 
the formation, including the volcanics which are part of it, may exceed 
2,000 feet, 600 meters. 
Fossils from Po-shan formation.—The shales have yielded no fossils 
except the macerated remains of plants, and of these the majority are 
too imperfect for identification. Animal fossils were found at only two 
points, viz, near Yen-chuang in black limestone, and a few miles northwest 
of Sin-t’ai-hién. In the former locality a block of limestone was found 
in the material excavated from a shallow mine shaft, and its source could 
not be ascertained; there can be no doubt, however, that the stratum is 
within 100 feet, 30 meters, of the base of the Po-shan formation. Among 
the fossils contained in this block, Girty has found: 
Chonetes sp. Squamularia (cf. Squamularta perplexa) 
Marginifera sp. Cleiothyris? sp. 
This fauna indicates that the formation is of Upper Carboniferous 
(Pennsylvanian) age. A few other forms were discovered in pebbles 
of Post-Carboniferous conglomerate (W6n-ho formation) near Ts’ai-kia- 
chuang. The species were preserved in chert nodules, which obviously 
had been derived from outcrops of Carboniferous limestone in the same 
region. Among the forms here found are: 
Clavulina (2) sp. Chonetes sp. 
Fustlina sp. Dielasma (2) sp. 
Zaphrentis (2) sp. Phillipsia sp. 
Archeocidaris sp. Bythocypris (2) sp. 
The material was too scanty and too poorly preserved to permit of 
accurate identification. 
