460 RESEARCH IN CHINA. 
required for the production of the tremolite associated with it; the augite, 
therefore, seems to be inadequate as a source for the supply of lime required 
to form the zoisite. Furthermore, rocks which are rich in augite and the 
titanium minerals usually contain calcic feldspars rather than the alkaline 
varieties. It is suggested, therefore, that the present feldspars of this 
gabbro have been derived from calcic plagioclase. Becke* describes the 
alteration of plagioclase plus orthoclase into albite, zoisite, quartz, and 
muscovite. Without orthoclase we should have no muscovite and hence 
a condition similar to that observed in the present rock. 
Brown hornblende is of rare occurrence and is altered for the most part 
into chlorite, zoisite, and iron ores. It seems to have been reddish-brown 
originally, but with the exception of a few lingering spots the mineral has 
become bleached during the earlier stages of alteration and appears nearly 
colorless. This bleaching almost destroys the pleochroism, but it does not 
seriously affect the birefringence; under crossed nicols, therefore, the brown 
and bleached areas are not easily distinguished.t 
Although ilmenite and pyrite are both common, the former is much 
the more abundant. Titanite frequently forms borders surrounding the 
ilmenite and also occurs in irregular masses of relatively large size; most of 
the ilmenite is now altered to the gray powdery form of titanite known as 
leucoxene. 
It is unnecessary to make further mention of any of the secondary 
minerals except the zoisite. This appears in the form of irregular grains 
or short crystals which are either distributed separately or in clusters 
throughout the rock. Very frequently crystals are embedded in masses of 
chlorite. Many of the zoisites possess a brownish or dusty aspect which 
is due to the presence of excessively minute inclusions. 
Augite syente, No. 142.—Inasmuch as this specimen was taken from 
the extreme periphery of the intrusion, it is probably not typical of the 
igneous rock. Although it now has the composition of a true syenite, it 
is not improbable that it was derived by magmatic differentiation from a 
more basic rock like the gabbro last described (No. 137). 
Specimen collected from debris in the great landslide of 1901, 4 miles, 
6.5 kilometers, south of Pai-kiu-hia. 
Our specimen shows the contact of a syenite with the green shales 
which have been transformed by the intrusion into a soft, dense, chlorite 
rock. The intrusive itself is a moderately fine-grained greenish-gray rock 
of even texture and without porphyritic crystals. The feldspars and the 
darker minerals are fairly well contrasted, so that the rock has a finely 

* Neues Jahrbuch fiir Mineralogie, etc., vol. 1, 1896, p. 182. 
} Similar bleaching of the hornblende has been described by Williams, from the greenstones of Michigan 
(U.S. Geol. Surv. Bull. 62, pp. 79 and 126), 
