OF THE DEPENDENT ISLES OF TAIWAIST. 49 



or brown ; but as a whole the interior is fresh. It is the iron- 

 rich variety — hyalosiderite, as is proved by the micro-chemical re- 

 actions, which show only a trace of magnesia. The olivine 

 encloses a large quantity of regular octahedra or elongated 

 crystals of the brown, transparent /»îco^^ïe, mixed with the crystals 

 and dust of magnetite. 



Plagioclase, as a phenocryst, is observed only once in ni}' 

 three slides ; it is long-rectangular in form, with negative crys- 

 tals, filled with a gas. The crystal is multiple-twinned, extin- 

 guishing light symmetrically with the maximum angle of 32°; 

 consequently it is the calcium-labradorite. The augite is rather 

 automorphic, showing, however, a slight corrosion marginally. 

 This character is common to all of the specimens. The crystal 

 occurs in polysynthetic twins ; the colour yellowish-green and non- 

 pleochroic. As usual, it has glass-enclosures with air- pores. 

 Sometimes, the augite is internally and nucleaUy resorbed, leaving 

 an accumlation of grains of the same in its place. The augite 

 is of nearly the same size as the olivine. 



The ground-mass is seen, under the microscope, to make the 

 main bulk of the rock. The micro-phenocrysts of olivine and 

 augite are tlie same in habit as the macro-phenocrysts. The 

 augite is in a few cases fringed with sheleton-crystals. They are 

 inbedded in the plexus of the felspar-laths and clum^^s of mag- 

 netite, rudely showing a fiow structure. The laths are twinned 

 simply or polysynthetically, and in many case hollow, with the 

 very thin external rim, partially or entirely filled up with glass. 

 So far as I am aware^', such skeleton-crystals of felspar seem to 



1) The same skeleton laths are observed_by E. Elich in the Ampbibole-pyroxene An- 

 désite from the Kio Blanco, West Cordillera, Ecuador. Reiss n. Stiibel, ' Eeisen iu^Siid- 

 Amerika, Das Hochgebirge der Eepubik Ecuador, I.; Petrographische Untersuchungen, I. 

 West Cordillère,' S. 163. 



