OF THE DEPENDENT ISLES OF TAIWAN. 37 



the liouf-glass structure is faintly indicated in some individuals. 

 In the coarse, felspar-rich .«specimen, the iron-ore is piesent only 

 in small quantity [PL I, Fig. 6), but comparatively large, lamel- 

 lar and flat with glittering bluish lustre on ihc perfect cleavage- 

 surface. It looks rather more like ilnienite than magnetite. Stiff!, 

 slender (r/;K////e- need les, sometimes \Yith a bi'own canal traversing 

 the whole length, are particularly abundant, being scattered 

 through the whole mass. 



In the dark fine specimens {PL I, Figs. 4 and ~)\ small 

 regular crystals of inagneliie are plentiful, and in these slides, 

 I found abundantly the small laths of twinned plagioclase, which 

 lesolve at the ends into slightly diverging columns {PL I, Fig. o), 

 and these may be easily mistaken for those of apatite, if needles are 

 found detached from the waist. Optical properties aie not in- 

 dependtly shown in them, on account of their extreme thinness- 

 Similar bodies are noticed by H. S. Washington in the sanidine 

 of some Ischian Trachytes and named by him heraunoid.^^ 

 He and also Lehmann'-' attribute the splittings and ramifications 

 from the main crystal to the existence of internal tensions in 

 felspar, but the cause of the existence of such tensions remains 

 to be solved. 



The glass together with the augile fill up the poly synthetic 

 space left by the laths of j^h^gioclase. The glass-base is coloured 

 bottle-green, sometimes dirty brown, and devitrified in various 

 ways. It consists of polarizing scaly aggregates of vermiform, 

 spherulitic, or, irregular shapes. Sometimes fascicular and 

 radiating needles, which are colourless and biréfringent, are 

 imbedded, in the green base as a product of devitrification. The 



1) 'On some Ischian Trachyte.' Journ. Anier. Sei., May, 1896, p. 3S0. 

 2j ' Molecularphysik,' I, 1888, S. 378. 



