ROCKS FROM NORTHERN AND CENTRAL CHINA. 417 
Rocxs OF IGNEOUS ORIGIN. 
The granites associated with the Archean rocks are unquestionably 
much younger than the gneisses and schists, and they may well belong to 
later Algonkian time. Nevertheless it is not possible to separate them 
from the T’ai-shan complex in the region under discussion. ‘They include 
gray biotitic and hornblendic varieties in which the feldspars are usually 
white. The red granites of Shan-tung are not represented here. 
GRANITES. 
Biotitic hornblende granite, No. 77.—Large dikes of this granite traverse 
the ancient gneisses and schists in the small valley west of Féu-p’ing-hién. 
Specimen obtained from such an intrusion 4.5 miles, 7 kilometers, west of 
the city. 
Black crystals of biotite and hornblende embedded in a mass of white 
quartz and feldspar impart a notably speckled aspect to the rock. The 
texture is medium fine and there is no banded structure. 
The feldspars are albite with oligoclase. Hornblende is more abundant 
than biotite and is but little altered. The large flakes of biotite have 
changed in part to chlorite with epidote and zoisite. Magnetite, ilmenite, 
and sphene are clustered about the hornblendes in considerable abundance, 
but are not common in the feldspathic areas. 
The granite bears no marks of deformation. It is probably younger 
than the last epoch of folding in this region. Inasmuch as the upper Algon- 
kian strata near Féu-p’ing lie nearly horizontally upon the Archean, that 
epoch may be assigned with some confidence to the Middle Algonkian, for 
the lower Algonkian rocks of the adjacent Wu-t’ai district are severely 
folded and metamorphosed. 
Biotitic hornblende granite, No. 79.—Very similar to the last and evi- 
dently derived from the same magma. It occurs as a dike 70 feet, 21 meters, 
thick, in the Archean gneisses 4 miles, 6.5 kilometers, west of Féu-p’ing-hién. 
Contrasts in color are less conspicuous in this variety because the 
texture is finer and the dark minerals are more evenly distributed. The 
minerals are much the same in both rocks. In this variety the feldspars 
consist of orthoclase with a zonally built plagioclase of the albite-oligoclase 
group. The dark minerals and accessories require no additional mention. 
Biotite-granite porphyry, No. 67.—Gray granites, represented by Nos. 
67 and 68, occur abundantly in the form of medium-sized dikes in the 
gneisses northeast of T’ang-hién. The rock is quarried by the people and 
used in the manufacture of millstones. This specimen was collected from 
a 2-foot, 0.6-meter, dike at such a quarry 3 miles, 5 kilometers, northeast 
of the city. 
