THE EEUPTIYE EOCKS OF NEW ZEALAND. 129 



Section : Composed of plagioclase, hornblende, enstatite and 

 magnetite. The plagioclase is in small crystals, from -025 

 to -05 in length, and well twinned. It forms more than half the 

 rock. The hornblende is allotriomorphie, green, slightly pleochroic 

 clianging from yellow-green to brown-green ; go up to about -06 

 or -10 m length. Polarization colours not so bright a^ in the 

 oiistatite Tlie enstatite is allotriomorphie, and fornib inter growths 

 NMth tlie hornblende. Yellow-green in ordinary light, pleochroic, 

 (li.inunng from led to ))luibli-green. Polarization colouis \ery 

 bnlhant , buboi-dinate to the hornblende. The magnetite is not 

 .ibunclant, it is in masses or in crystaK Hutton, Geology of 

 Ot.iiro, p. 41 (Syenite); Hamilton, Trans. X.Z. Inst., Vol. xix., p. 

 4:)2 , Park, Ilept. Geol. Expl. 1887-8, p. 72. 



AUGITE DiORITE. 



Mt. Charh^, npor Ilerherf, Otaqo — A rather coarsely grained 

 light grey rock, composed of plagioclase, augitc and titaniferous 

 iron w Inch is largely decomposed to leucoxene. S G. 2 73. Section : 

 Textui-e ophitic in places. The felspar is chiefly in broad laths 

 from -02 x -015 to -07 x -03, but occasionally in square plates. 

 Tlie autrite is in crystals from -02 to -04 in length, of a pale 

 brow nisli-yellow colour. Secondary minerals are leucoxene and a 

 linlr pyIlte^. Hutton, Geology of Otago (Oamaru formation) p. 

 •>0 . McKay, Kepoi-ts Geol Explorations, 1876-7, p. Go. 

 PORPHYRITE QROUP. 



Micro-granitic compounds of plagioclase withbiotite, hornblende 



iitic crystals of minoi-ak similar to those forming the gi-ound m.i-,-,. 



HOKXRLEVDK PoRPHYRITE. 



f'^^'f Hill, So7ifIihin<{ — A dark greenish-grey, compact rock, 

 ^^ U h crystals, of black hornblende S G. 2-20. Section : Ground- 

 "1 1^^ abundant, mici-ogranitic, formed of felspar grains, hornblende 

 'kI chlorite, the cr-ystaK ranging between -003 and -007 in length 

 )orr)hvritiu minerals are hornblende and 







lt^■t•ed, but plagioclase is generally recognisable. Tli 

 ^ P-irtly idiomorphic and goe^ up to '-06 in diame 

 •"•vvn colour. Therv is also some magnetite. Chi 



