144 EEPOKT — 1891. 



ones. Fine crystals and irregular grains of nepheline of large 

 and small size, sometimes several grouped together, are rather 

 numerous, but have suffered more or less through decomposi- 

 tion, as indicated by a light cream-colour, and by their trans- 

 parency being impaired in varying degree even to opaqueness. 

 Some shov/ these features only round the margin and are clear 

 in the centre, others are cream-coloured and opaque through- 

 out. The clear portions are, as a rule, full of cracks, mostly 

 irregular, but sometimes parallel — indicating cleavage — in 

 square or rectangular sections. They also contain an abund- 

 ance of microlitic inclusions and vapour-cavities, in some 

 arranged in zones parallel to their outlines, in others in 

 patches ; but in the majority they form longer and shorter 

 strings running in all directions. Crystals of green augite, 

 singly or in groups, occur also occasionally as inclusions in 

 the larger nephelines. Porphyritic sanidines are scarce in the 

 ground-mass, and generally form Carlsbad twins. Augite of 

 green and purplish-brown colour, and dichroic in green and 

 brownish-yellow, is very abundant in large and small columnar 

 crystals, which are generally impregnated, in varying degree, 

 with grains and dust of iron-ore ; some crystals are rendered 

 quite black-opaque through this impregnation. Larger crystals 

 frequently are purplish-brown in the centre and green around 

 the margin. Olivine occurs rarely in largish grains more or 

 less serpentinised, and with broad black margins of iron-ore. 

 Occasionally several grains are grouped together. Iron-ore is 

 abundantly distributed in larger and smaller grains. Apatite 

 is scarce. 



16. Bell Hill, Dunedin. 



This rock, though greatly resembling in macroscopic charac- 

 ter some of the described rock-samples, turned out to be an 

 " augite-andesite." It is dense and compact, of greenish-grey 

 colour, and very slightly and ininutely porphyritic. The 

 powder gives no gelatinous silica on treatment with HCl. The 

 sections show a dense, irregular network of small plagioclase 

 laths, probably intermixed with some of sanidine, the interstices 

 between being filled with isotropic, rarely devitrified glass. 

 Porphyritically distributed through this ground-mass occur in 

 moderate abundance larger plagioclases, mostly long and stout- 

 columnar and jagged at the ends ; and some showing twinning 

 lamellation according to both the albite and pericline laws ; 

 further augite of greyish-green, light-brown to yellow colour, 

 and very slightly dichroic, in great abundance, in large and 

 small crystals and irregular small grains, generally not much 

 impregnated with grains of iron-ore. This ore is, however, 

 plentifully distributed in larger and smaller grains throughout 

 the ground-mass. Apatite is rather scarce. 



