72 Y. KIKUCHI 



The direction of extinction can be measured in thicker plate«, 

 in which there is a distinct effect upon the polarised ray. On the 

 face M, the direction of extinction makes -40° with the edge P : M. 

 Thus there seems to be much probability that the ' Rhombic 

 lamelke' are Anorthite. 



All of these glassy rocks contain more or less well-defined crystals 

 of Rhombic Pyroxene, but it is in the more glassy modifications found 

 in patches among these rocks that the well-detined crystals of this 

 mineral are developed at the expense of the light-green coloured 

 filiform Augite. Such modifications have been found so far on the 

 coasts of Tatsumiura and Miyanoura in Chichijima. The specimen 

 obtained from Tatsumiura presents a dirty brownish green colour, 

 resulting from the alteration of the dark glass- into a product resemb- 

 ling ' Palagonite,' in which green translucent crystals of Rhombic 

 Pyroxene may be picked out. The specimen from Miyanoura also 

 presents a similar character, but the degree of alteration is much less, 

 the vesicular cavities being chiefly lined with Zeolites.* Microscop- 

 ically examined, the glass transmits ;i faint greyish green colour. The 

 glass would correspond to the ' Sideromelane ' in Tachylyte. The 

 fissures and cavities are filled up with a palagonitic matter, which 

 transmit a sulphur-yellow colour in thin sections. 



The palagonitic alteration- product above mentioned is of a dirty 

 green colour, and is made up of fibrous microcrystalline aggregates, 

 showing a weak double refraction. When it is found filling up 

 round pores, the periphery is often radially fibrous, so that an 

 aersrreo'ate polarization exhibiting a dark cross is observed between 

 crossed Niçois. Before the blowpipe, the glassy portion swells up to 

 a great bulk and easily fuses, due to the large amount of water it 



* One of these Zeolites is Stilbite, in combination of the faces, oP (001), a>Pdb (0101, 

 oo P 5c (100), P* (101), 2P (221) ; another is Cltabasite, with characteristic striatums on. the 

 rhombohedral face. There are also some fibrous crystals of an uncertain Zeolite. 



