ROCKS FROM NORTHERN AND CENTRAL CHINA. 367 
anamorphism.* ‘Titanite, in the usual wedge-shaped crystals, and irregular 
magnetites are frequently associated with the seams of biotite and horn- 
blende. Idiomorphic prisms of apatite, and, rarely also, of zircon, are 
distributed through the rock. 
Biotitic hornblende gneiss, No. 29.—This is a local phase of the gray 
gneiss, which is intermediate between Nos. 28 and 30, though most resem- 
bling the latter. It is finer grained than No. 30, and biotite is not as import- 
ant a mineral as in that variety. Locality: T’ai-shan, a few meters above 
the rock last described (30). 
This differs from No. 30 chiefly in its finer texture and larger proportion 
of hornblende. The dark and light bands are parallel and not wavy. 
The essential minerals in this gneiss are orthoclase, albite, quartz, 
and hornblende, while the less common constituents are zircon, pyrite, 
titanite, rutile, ilmenite, biotite, zoisite, epidote, and allanite. The crys- 
tals are arranged in layers, some of which are rich in hornblende, while 
others contain little besides quartz and feldspar. Taking this into account 
and noting the general absence of strain-shadows, shear-zones, etc., we 
must conclude that the rock has undergone complete recrystallization. 
Since this variety is much like No. 30 on the one hand and No. 28 on the 
other, it will suffice to point out only one or two features which are of 
especial interest. 
Where lime-soda feldspars are present, one of the commonest alteration 
products is saussurite, a mixture of zoisite with various other minerals. 
Here we have abundant little prisms of zoisite inclosed in alkali feldspars 
and often associated with epidote. Manifestly, they could not be derived 
alone from minerals so poor in calcium. It is noteworthy in this case 
that the little crystals are most numerous in proximity to hornblende 
crystals and particularly to those in which alteration has evidently begun. 
Probably the hornblende has furnished a part of the material for the zoisite 
and epidote. The alteration of hornblende to biotite is well shown in this 
slide. The mica penetrates the hornblende like a parasitic growth and is 
surrounded by a bleached area in which the amphibole is colorless. Simul- 
taneously with the biotite epidote is formed, and later the biotite may 
be changed in part or entirely to chlorite. 
Two of the rarer minerals deserve mention in this connection. In 
most of the Chinese rocks which contain it, allanite is inclosed in epidote. 
Here, however, it occurs in zoisite. The titanite is brownish in color 
and in many cases it has inclusions of a deep brown color, which appear 
to be rutile. 
* Van Hise: A Treatise on Metamorphism, p. 288. 
