OF THE DEPEXDENT ISLES OF TAIWAX. 35 



grains of augite, all of a liolei-hvown colour, besides the grains 

 of olivine, and the laths of the multiple-twinned plagioclase, the 

 octahedra and dust of magnetite, and ilmenite. The texture of 

 the rock is crystalline and typically granulitlc. In a coarse 

 variety, the idioinorphic augite with hour-glass structure forms 

 stellar aggregates, and these aggregates closely resemble ihe 

 glome roporphyri tic phenocryst. 



B. THE TYPE OF THE IDDIXGSrTE-BEARIXG BASALT. 

 {PI. I, Figs. 4, 5 and 6; PI, II, Fl<j. 1.) 



Megascopically this type is greyish-black Anamesitic-looking, 

 and finely uniform-granular, owing to the nearly equal size and 

 form of the laths of plagioclase which predominates quantitatively 

 over the other components. 



The characteristic features of this group are firstly, the pre- 

 sence of large phenocrysts of olivine which is more or less iddingsi- 

 tized ; secondly, the majority of the augite is xeuomorphic or 

 granuhn-, and of small size, and these grains are grouped together 

 inteisertal! v Avith the devitrified irlass between the laths of 

 plagioclase. The structure is typically intersertal. The promi- 

 nent characters distinguish this group from the rest of the Basalts. 

 This type is represented in my slides from the Pescadores by 

 three specimens, one from Kippai, and two from Hôko, one of 

 which was struck off at the locality Tai-san ;^' according to 

 Y. Saito, it forms the uppermost flow there. The same may 

 be said of the specimen from Kippai, since the youngest 



1) ^^^'cUl) Sç-SA î0îffl- '^Jie rock efleive;ces witli ticid. The microscope discloses the 

 fact tliat tlie radinlly arranged fibies of calcite fill up the j^olygonal spaces between other 



components, showing bars which correspond to the position of crossed niçois. 



