( 405 ) 



The dmphibole, which abundantly occurs, forms blunt needles, no! 

 exceeding' a length of 1 mm.: c == green, t> =.- greyish green and a = 

 greyish yellow, in which i^> b ^> a, bul : and j «Idler only insignificantly. 

 Now and then m zonal structure comes to the trend, which is perceptible 

 especially in some sections perpendicular to the axis of elongation. In this 

 case there is seen parallel to the crystal-circumference a zone, showing 

 the colours a = blue greyish green or dark greyish green, b = brown 

 greyish green, c = light greyish green. The idiomorphic crystals have 

 often been so strongly affected by resorption, thai the groundmass 

 penetrates into them with deep windings. The resorption-border is 

 formed by an exceedingly dense fell-like tissue of fine microliter, 

 becoming larger here and there, in some places even exceeding the 

 feldspar-laths of the groundmass in size and which can then with 

 certainty be recognised as a rhombic pyroxene. Mixed with them we 

 find magnetite and strongly double-refracting grains, which have 

 probably to be taken for augite. The resorption-border is not everywhere 

 distinctly developed, in some crystals it seems even to be wanting 

 partially. An explanation of this might be given by the supposition 

 that the rock, even after the resorption-period, has been raised with 

 violence, by which movement the components of the resorption- 

 border were in some places swept away from the phenocrvst. This 

 conception is positively backed by the observation that the border 

 often passes cloudlike into the groundmass, while the bigger needles 

 pretty generally by transversal cracks are broken into pieces, which 

 have lost their mutual orientation. But besides the components of 

 the first generation show mechanical deformations, which have come 

 about before the solidification of the glass-base and in all probability 

 after the resorption-period. The feldspar shows irregular fissures and 

 rents, along which pieces of broken twin-lamellae have sometimes 

 moved with respect to each other and which are Idled with glass 

 of the groundmass as soon as the fragments through a mutual trans- 

 position are no longer closely united. 



By irregular cracks perpendicular to the axis of elongation, the ninphi- 

 bole too is nearly always broken into fragments, which are often 

 tolerably far carried away from each other ; not rarely also opened 

 wide along the cleavage directions. Also here the gaping rents are 

 tilled with glass and stress is to be laid upon the fact that this 

 glass is nearly always entirely free from the resorption-products, 

 which show themselves along the original crystal-boundaries. This 

 proves that those rents were opened at an epoch when the resorp- 

 tion-period was all but over, a conclusion \\ Inch is wholly in accord- 

 ance with the above fact dial the needles themselves, forming die 



