OF THE DEPENDENT ISLES OF TAIWAN. Oo 



phyritic structure with the phenocrysts of plagioclase and horn- 

 blende. They are much speckled with glittering iron-pyrites 

 (a lirge black spot in Fig. 1), which likely attracted the atten- 

 tion of Mr. Xarita, who had brought back the specimens to 

 Tai-hoku. 



The phenocrystic plagioclase has a tabular form being nearly 

 equidimensional. It has a distinct zonary banding, like the pre- 

 ceding; rock. Contrary symmetrical extinction of about 33° on 

 both sides of the trace of the albite twins shows the plagioclase to 

 be a labradorite of a similar composition as in the rocks, just des- 

 cribed. Hornblende is entirely decomposed (in the right halves 

 of Figs. 1 and 2) into an aggregate of pistacite, chlorite, and 

 calcite-films, which together form the pseudomorph after the 

 hornblende of a prismatic habit with the combination of 010, 

 as ma}^ be conjectured from the original outlines of the now 

 altered mass. The chlorite possesses the normal character, and 

 pleochroic, showing a green shade parallel to the axis of fibres, 

 which corresponds to ';}(. The epidote occurs in tufts and in rugged 

 plates. 



The ground-mass consists of very fine laths, simply twin- 

 ned, and they are arranged in more or less parallel disposition 

 around the phenocrystic felspar. These minute crystals of fels- 

 par swim within the chlorite-lamellœ, mixed with the felspar- 

 microlite, magnetite and the pyrites, the last does not contain 

 any trace of copper. This Apoandesite is no doubt derived from 

 the fi variety of the Hornblende-Andésite, already described, by 

 the pneumatolytic process which caused the impregnation of the 

 pyrites in the rock-mass. 



