STRATIGRAPHY OF SHAN-TUNG. 47 
intrusion, 100 feet, 30 meters, long and 12 feet, 3.6 meters, thick, which 
consists of a different rock. The phenocrysts are of alkali feldspar and 
hornblende, set in a ground-mass composed of quartz and feldspar; a 
dacite, in the old system of nomenclature. The brown shales were not 
notably metamorphosed at their contact with this porphyry, but the 
planes of cleavage in the shales were observed to be parallel with the 
surface of the laccolite for a distance of about 2 feet. This was brought 
out most clearly near the edges of the intrusion, because there the cleavage 
due to igneous influences was plainly discordant with horizontal planes 
such as are commonly developed by clays during consolidation. 
About half-way between Kau-kia-p’u and Yen-chuang another dacitic 
sill, nearly 100 feet, 30 meters, thick, occupies the contact between the 
lower and the upper members of the Tsi-nan limestone. Even in the 
case of so thick a sheet, the phenomena of contact-metamorphism were 
not prominent. As we approached the Yen-chuang coal-field, with its 
abundant volcanic rocks, we crossed several dikes of buff-brown feldspar- 
porphyry. One mass of this rock, a few yards across, is intruded along 
the fault contact in the north end of Hu-lu-shan butte. Another cuts 
the Kiu-lung and Tsi-nan limestones 2.5 miles, 4 kilometers, southeast of 
Yen-chuang. ‘This dike is 30 to 40 feet, 9 to 12 meters, wide and more than 
a mile in length. Such rocks decompose more rapidly than the limestones 
into which they are intruded, and as weathering proceeds they come to 
occupy cols, swales, and gullies, according to their situation. 
In the alluvial plain north of Tsi-nan-fu several conical hills stand 
out in conspicuous isolation. They are composed of a coarse-grained 
hypersthene-gabbro (norite) of black-green color; the rock contains oliv- 
ine also. The roundish areas of outcrop suggest that the hills may be 
old volcanic necks, but, if so, the ejectamenta of the volcanoes have long 
since been carried away in the degradation of the region, for no tufls or 
lavas are visible there at present. We saw nothing by which we could 
determine the age of the gabbro relative to the Tsi-nan dolomite, which 
forms the hills to the south. 
The only dike of igneous rock found in the limestone hills near Tsi- 
nan-fu occurs near the border of the plain, 2.5 miles, 4 kilometers, west-south- 
west of the city. At first sight it has the appearance of a fine-grained 
pink granite, but upon microscopic examination it proves to be a quartzose 
syenite-porphyry; it has a finely crystalline ground-mass, composed of 
sodic feldspars and quartz, with small phenocrysts of hornblende and feld- 
spars like those of the ground-mass. The composition of this rock is such 
as to indicate that it is not genetically related to the hypersthene-gabbro 
just mentioned. 
