22 Y. KIKTJCHI 



OZZ 



that a longitudinal section meets the three twin individuals in dis- 

 similar positions with regard to the optical plane. The different fibres 

 have their maximum of darkness under crossed Niçois, when they 

 are parallel and at right angles to the direction of the longer side. 



The outer portion is generally homogeneous, and in those parts 

 where the section falls at right angles to the optical plane, i. e., par- 

 allel to the face (010), an axial image may be observed under a conver- 

 gent polarized ray. The image reacts positive by the mica plate, and 

 the distance between the two rings is wider apart than in the case of 

 the cross section. 



The arrangement of Enclosures is different in the inner and the 

 outer portions. These enclosures are mostly chains of black car- 

 bonaceous particles. Under the microscope, however, we find very 

 fine platy enclosures. Sometimes these platy enclosures are visible 

 to the naked eye, and consist of a black lustrous mineral like 

 Graphite, giving a decided reaction for manganese. In some cases 

 Iron -pyrites is found also in the form of elongated plates. In 

 the outer portion, these enclosures are set parallel to the macropina- 

 coidal face of each twin individual, causing a radial arrangement in 

 the transverse section, as shown by the thicker lines in Figure 1. 



In the inner portion they are always arranged longitudinally, 

 parallel to the direction of the longer side. Neither the pleochroic 

 halos nor the needle-like inclusions, which have been described as 

 very characteristic of some Cordierite, have ever been observed ac- 

 companying these enclosures. 



The boundaries of twinning, and of the inner and the outer por- 

 tions are formed as we have stated, of black coaly particles. As- 

 sociated with the carbonaceous matter are found numerous irregular 

 grains transmitting a very pale pinkish colour, reminding us of 

 Andalusite-grains. Besides these, there are often found very small 



