OF THE DEPENDENT ISLES OF TAIWAN. 41 



on account of their vivid colours of polarisation in contrast with 

 the grey tint of the hypersthene in the interior. Pleocliroism is 

 scarcely perceptible. Traces of a few rough cleavages run 

 through the hypersthene lengthwise, and as in the case of the 

 plagioclase, it is trasversed with many fissures. The hypers- 

 thene is of intratelluric origin, and has the general aspect of its 

 having been worn out caustically and frittered, and the peri- 

 pheral accumulation of augite, already referred to, seems to have 

 some genetic relation with the act of degeneration. 



Large, monoclinic augite sometimes makes its appearance in 

 company with the hypersthene and plagioclase, forming local 

 patches of secretional origin, wiili the hyperitic structure. 



The ground-mass, which constitutes the main bulk of 

 the rock, consists of laths of plagioclase and grains of the 

 frittered and corroded augite, together with rugged clumps 

 of magnetite. The relation of the first two components cannot 

 be told in a few words. In one instance, the mutual relation 

 is such that we could almost say it is ophitic ; in another, it 

 is intersertal in company with a little remnant of brown glass, 

 while in the third, no such arrangement could be discovered, 

 but a simple aggregate of felspar and grains of augite, there- 

 by calling forth the structure which is termed graniditic. The 

 augites of both generations are of yelloivish broivn and not violet- 

 brown. 



Shingly tridymite fills up polygonal spaces, and the loose 

 brushes or tufts of either plagioclase or apatite are thrown 

 through the whole mass. A doubtful iddingsite {PL I, Fig. 3) 

 was once o1)served, and some rocks are calcareous too. The 

 stratigraphie position of this type is not known to me. It may 

 be the lava of either the first or the second flow. 



