TRANSACTIONS OF SECTION C. 137 



and general appearance with some varieties of the latter, it is 

 evidently a " phonolite,"' and specifically a " nepheline- 

 phonolite " (Boricky), or " nephelinitoid phonolite" (Kosen- 

 busch) . 



Descriptions of Thin Slides of Eock-samples from 

 Various Parts of the District.* 



1. Galder's Quarry, North-east Valley, about One Mile north- 

 cast of Dunedin. 



Bock. — Light greenish-grey, very close-grained and com- 

 pact ; not porphyritic. Gives a large amount of gelatinous 

 silica on treatment with cold HCl. 



Sections. — Clear ground-mass of allotriomorphic nepheline, 

 densely filled with generally very long, lath-shaped micro- 

 crystals and microlites of sanidine, intermixed in no great 

 abundance with such of plagioclase, all arranged in pronounced 

 fluidal structure. Idiomorphic nephelines scarce, and mostly 

 hidden beneath and between the feldspar laths. Transparency 

 of these minerals more or less impaired through brown colora- 

 tion by ferric hydrate. Green augite, idiomorphic and in 

 irregular grains, tolerably abundant, but partly converted into 

 chloritic matter, partly and more frequently filled with dusty 

 black iron-ore, which also abundantly occurs in the crevices 

 between the feldspar laths. Solid grains of iron-ore also 

 abundant. 



2. North Quarry, behind the Boys' High School, Dunedin. 



Bock. — Very dark greenish-grey, nearly black ; very fine- 

 grained, and slightly porphyritic. Gives a large amount of 

 gelatinous silica with HCL 



Sections. — Allotriomorphic nepheline ground-mass, inter- 

 mixed with microlites of sanidine and pale-green -coloured 

 augite (probably a?girine). Greenish and brown-coloured augite 

 in sometimes large columnar crystals, idiomorphic nephelines, 

 and sanidines, the latter often in Carlsbad twins, are frequent. 

 Black iron-ore, in larger and smaller grains, abundant ; often 

 densely impregnating augite crystals, and forming dark zones 

 around their margins; also scattered and in zonal arrangement 

 within large sanidine crystals. Olivine and brown hornblende 

 scarce, and both having generally broad black margins of dusty 

 iron-ore. Apatite rather rare. 



3. Top of Main Peak, Mount Cargill (2,292ft. high). 

 Bock. — Dark greenish-grey, and very slightly porphyritic. 

 Gives a large amount of gelatinous silica on treatment with 

 HCl. 



* Of each rock-sample, at least two, — of some, four or five slides, — 

 have been submitted to microscopic examination. 



