54 



H. I. JENSEN. 



These tliree minerals occur in the form of corroded pheno- 

 crysts and are in some rocks coexistent in equal abundance 

 whilst in other rocks one of them may be practically 

 absent. 



(3) The hornblende is a light yellowish-green variety 

 with extinction angles of usually between 0° and 15°, 

 but sometimes as high as 29°. It is only feebly pleochroic 

 and is distinguishable from the augite only by its cleavage 

 and lower extinction angle. It is probably uralitic, 

 secondary after augite. 



(4) A greenish coloured bronzite of feeble pleochroism 

 is invariably present and is distinguished from the horn- 

 blende by its weak double refraction, its form and its 

 cleavage. In colour and pleochroism there is no percep- 

 tible difference between these minerals. There are small 

 crystals of a second generation of both the hornblende and 

 bronzite. The hornblende phenocrysts commenced to 

 crystallise earlier and attain a greater size than those of 

 the rhombic pyroxene. 



(5) Fayalite of red colour, having the outline of olivine, 

 occurs in two of my specimens. Dr. Woolnough informs 

 me that the deep colour of this mineral is due to secondary 

 heating. The colour is so deep that double refraction is 

 completely obscured. 



(6) Magnetite in steel-blue opaque grains. 



(7) Ilmenite and brownish titaniferous magnetite are also 

 present in some sections. Leucoxene occurs occasionally 

 as a decomposed product. 



(8) Copper iron pyrites and chalcocite are present in 

 small idiomorphic grains and aggregates of grains. 



(9) Decomposition products especially from the decay of 

 felspars occur. 



(10) Opal and tridymite occur especially in vesicular 

 varieties. 



