ROCKS FROM NORTHERN AND CENTRAL CHINA. 4II 
alteration to amorphous dark clay-like products has made considerable 
progress. 
Throughout the rock iron ores are abundant in the form of grains, 
shapely crystals, and micaceous flakes. They are coffee-brown in all cases 
where the sections are sufficiently thin to render the mineral translucent. 
The numerous quadratic grains suggest an isometric mineral. Although 
magnetite may be present it is probable that this opaque mineral is prin- 
cipally chromite, for in rocks of this character chromite has usually been 
found to be a common constituent. 
EASTERN SHAN-TUNG. 
This comprises the wedge of mountainous land, known as the Shan- 
tung peninsula, which lies to the northeast of the new German railroad. 
The explorations of von Richthofen have shown us that the rocks of the 
area are mainly igneous and metamorphic, and are probably Pre-Cambrian 
in age.* Of this district we made no study, and our only opportunity to 
observe the rocks which occur there was afforded by a few hours’ sojourn 
in the city of Tsing-tau. 
PRE-CAMBRIAN. 
The only rock observed is a reddish quartz porphyry which appears 
to be the prevalent rock around the city of Tsing-tau. 
Rocxs OF IGNEOUS ORIGIN. 
Pink rhyolite porphyry, No. 56.—This porphyry is exposed at the shore 
of the harbor in the principal business district of the city of Tsing-tau. 
The associations and relationships of the rock are entirely unknown to us, 
although it is evident that the porphyry has been intruded into other rocks 
of greater age which doubtless occur in the vicinity of the city. Specimen 
obtained in front of the Hotel Prince Heinrich. 
Numerous small phenocrysts of quartz and feldspar are embedded in 
a pink or flesh-colored ground-mass of aphanitic texture. The feldspar 
crystals average larger than the quartz and yet they rarely exceed 2 or 3 
millimeters in breadth. This is an intrusive rock, which presents none 
of the peculiar structures and textures which frequently characterize 
rhyolites that have been extruded upon the surface. 
The feldspar of the rock is orthoclase, but it is now very largely altered 
to grayish kaolin with scattered flakes of muscovite. Inclusions of a 
primary nature are quite rare. 
Quartz occurs in sharply defined crystals which present rhombic, 
trigonal, and rounded forms. On account of corrosion by the magma the 
* China, vol. U, pp. 212-219, and atlas map. 
