ROCKS FROM NORTHERN AND CENTRAL CHINA. 453 
Spotted mica schist, No. 115.—This spotted schist forms a stratum of 
considerable thickness interbedded between gneissic quartzite (No. 114) 
and black slates and limestones (No. 113), in the valley of the Han river 
near Shi-ts’tian-hién. There can be little doubt that the horizon is approxi- 
mately the same as that from which Nos. 118 and 123 were collected. 
These spotted silky schists are especially characteristic of the schists which, 
it is thought, represent the Triassic. In general appearance the rocks do 
not differ widely from those which have been called the ‘‘knotenschiefer”’ 
by Rosenbusch;* but they are sedimentary rocks which have been altered 
under conditions of great pressure deep in the earth, while the true ‘‘knoten- 
schiefer’’ are found in the contact-zones surrounding large igneous intru- 
sions. Specimen collected in the lateral ravine on the west bank of the 
Han river, 1 mile, 1.6 kilometers, below Shi-ts’tian-hién. 
This rock is silvery-gray in color and is distinguished by the presence 
of numerous small knots of black micas which impart to the rock a char- 
acteristic spotted appearance. Although the cleavage is distinct it is by 
no means as facile as is the parting in most mica schists. On this account 
it is possible to secure hand-specimens which, on account of their banded 
appearance, might be classed as gneisses rather than as schists. In gen- 
eral the rock is very similar to No. 123 and also No. 118, but it appears to 
represent a more advanced stage of metamorphism than either of them. 
In addition to the brown knots of biotite, the surface is frequently sprinkled 
with black, needle-shaped bodies; but these prove, on examination of the 
thin slice, to be merely sections of biotite crystals which are not parallel 
to the schistosity. 
The minerals and structures in this variety are very much the same 
as in Nos. 118 and 123, except that staurolite was not detected. A trans- 
verse section shows that the minerals have a strongly marked parallel 
arrangement. Notonly are the micas oriented alike, but even the quartz 
grains, in many instances, are somewhat rectangular and elongated in the 
direction of schistosity.T 
Micas in this slide are olive-green in color rather than reddish-brown, 
as in the other two varieties above mentioned. The larger flakes, which 
have grown without regard to the schistosity and subsequent to the pro- 
duction of that structure (Plate LVII, Fig. F), are ragged in outline and 
include numerous crystals of quartz, magnetite, apatite, and zircon. In 
most cases the mica flakes are comparatively fresh, but in some an altera- 
* Physiographie der Mineralien, 11, 88-92. 
} For an illustration of this texture see Diller: Educational Series of Rock Specimens, U. S. Geol. 
Surv. Bull. 150, Plate x~11; and Van Hise: A Treatise on Metamorphism, U. S. Geol. Surv. Monograph 
xLvu, Plate x1, c; and G. §. A. Bull. 1, Plate v, Fig. 2. 
