282 ß ^<^Tö. 



hedra of magnetite, and a little epidote. 



Through the preponderance of feldspar of the second generation, 

 the rock becomes dioritic in appearance with somewhat large crystals 

 of fibrous hornblende as porphyritic crystals often arranged in stellar 

 aggregates. Some of the fibrous amphibole contains cores of mujite, 

 from which it may be inferred that the hornblende of uralitic habitus 

 has been derived from the augite. 



3) The thinl modification is black and fine-granular, and a dark 

 magnesian bisilicate glitters through it by reflected light. .Examined 

 with high powers, it is a panidiomorphic-crystalline aggregate ol lath- 

 shaped feldspar, and prismatic hornblende, together with biotite and 

 epidote. The feldspar is simple-twinned, rarely polysynthetic, and 

 more or less kaolinized and dirty, being full of muscovite, w^ith the 

 secondary epidote at the centre ; zonings are rarely developed. The 

 hornblende is prismatic in habitus with the clinopinacoid present, so far 

 as may be judged from the outlines of imperfect basal sections. It is 

 pleochroic; c = dark- brown with a slight tinge of violet, 6= brown, 

 a = light-yellow ; absorption, c = ß > ct. Forms of the hornblende are 

 never perfect, but ragged and tattered, as if it were, the resorption- 

 residue of larger individuals. This supposition is, moreover, strength- 

 ened l)y a beautiful emerald-green colouring of the peripheral portion 

 which is materiall)' connected with the brown core ; the former has 

 surely resulted from alteration ot the original amphibole. At first sight, 

 the hornblende appears like augite, for which it may be easily taken. 

 It seems to me that the present amphibole is likely to be one of the 

 sodium-bearing varieties, as otherwise the formation of the bluish- 

 green margins can not be explained. 



A dirty green biotite is irregularly scattered through the whole 

 mass, and the dark colour of the rock is due mainly to the presence of 

 this component. Titaniferous iron is sparingly present with highly 



