98 B. KOTO 



black, owing to an enormous accumulation of graphite-particles, 

 rhombobedra of garnet, tourmaline-crystals, actinolite-prisms with the 

 combination of ooP, coP à, and other colourless grains and micro- 

 crystals of an undeterminable nature, together with opaque iron-oxide. 



On igniting a thin slice, graphite (possibly identical with the 

 Grapliitoid of Snuer^^ ov Inostranzetf's sliuugite)-^ is partly removed 

 from the felspar-substance, although a dark centre remains as before. 

 A closer inspection with higher powers discloses, besides amorphous 

 coaly dust, some minute inclosures of air and liquid, the latter with 

 movable bubbles. These inclosures are arrano-ed more or less in 

 stripes, and appear under weak powers as black dots. It is their 

 presence that chiefly causes the opacity of the felspar as in the 

 minerals of the h any ne group. 



As to the arrangement of the black dust, the fine particles are 

 disposed in the most fantastic manner, thereby producing at the centre 

 a cyclonal, at the margin a fluxional-structure, as shown inßg. 7. PL II. 

 Dr. A. Sauer^) has described a similar arrangement of interposition in 

 a felspar contained in the felsparphyllite from Plane, Saxony ; but 

 there the interposed mineral is rutile instead of coaly dust. This 

 peculiar structure has evidently arisen from the squeezing accom- 

 panying the movements of the crystals during their formation. Herr 

 Dr. Sauer is rather disposed to think that the structure as of a 

 primary nature, arguing in support of this view that the periphery 

 of the felspar is perfectly pure and free from inclosures of foreign 

 substances, and moreover that the suture of twinning-lamellœ passes 

 straightforward throughout the whole section of crystals irrespective 



1) Zeitschrift d. d. geol. Gesselschaft, XXXVII Band, 1885, p. 441. 



2) Neues Jahrbuch f. Min. u. Geol. etc. 1880. I Band, p. 97. 



3) N. J. f. Min. etc. 1881, I Band, p. 2.32. 'Kutil als mikroskopischen Gemengtheil in 

 der Gneiss — und, Glimmerschieferformation, sowie als Thonschiefernädelchen in der 

 Phyllitformation. 



