( $99 ) 



Crystals, partly in consequence of differences in the velocity of crystal- 

 lization in nol equivalenl directions, by which planes (by preference 

 (010)) broaden latnellarly to far beyond the original boundary ribs, 

 partly by ;i dense accumulation of glass-inclusions with negative 

 crystal-forms, which at bottom is connected with the same pheno- 

 menon. These glass-inclusions press the feldspar-substance together 

 into narrow little laths with two main directions and which combine 

 into a very complicated meandrous pattern, while also the crystal- 

 circumference assumes an irregular indented shape. The glass, how- 

 ever, also forms irregular notch-like or claviform inclusions and is 

 neither in colour, nor in the nature of the microlites to he distin- 

 guished from the glass of the groundmass. 



The amphibole occurs in fresh little columns and crystal-fragments ; 

 the corrosion of the crystals by the magma at the effusion has not 

 given rise to the origin of a proper reeorption-border, bul has con- 

 fined itself to rounding the crystals and largely accumulating tin 1 

 magnetile-globulites of the groundmass along their periphery. The 

 dichroism moves between darkgrey -green // the c-axis and greenish 

 grey -yellow perpendicularly here to; with regard to the axis of elon- 

 gation an extinction of 15° was measured. Parallel to (100) and (001) 

 we sometimes find a narrow I win-lamella linked between. Besides 

 the good prismatic cleavage a system of rough cracks shows itself 

 perpendicularly to the r-axis. Quartz is wanting. 



The groundmass consists principally of colourless glass in which 

 excellent idiomorphic lathshaped or tabular feldspars, the former often 

 with fine skeleton-forms and exhibiting a tluidal texture, come to 

 the front. Al bite-lamellae and feeble zonal structure are general, glass- 

 inclusions much less frequent than in the phenocrysts ; on the other 

 hand the crystals contain many microlites of magnetite and bronzite. 

 Those two last minerals take an important place among the secretions 

 of the base. The magnetite, which on the ground of the chemical 

 analysis seems to contain Ti0 2 , may, according to the size, be broughl 

 to two distinctly separated generations. The intratelluric magnetite 

 (average crystaldiameter 15 n) forms excellent octahedrons, which 

 occur both in the groundmass and in the phenocrysts. In the ground- 

 mass the magnetite crystals are found partly isolated, partly in aggre- 

 gates and then often grown together to dendritic markings. Thai the 

 on an average 10 X smaller magnetite-crystals and globuliles, occur- 

 ring by the side of those mentioned above, did not crystallize until 

 the effusion-period, is proved by their accumulation at the circum- 

 ference of the corroded ainphihole-siibstanee. The bronzite forms ;i 

 pretty compact tissue of' slender needles, which generally show an 



