THE ERUPTIVE ROCKS OF NEW ZEALAND. 115 



crystals and grains. Pyrite is rare. Apatite in the felspars and 

 in the ground-mass. 



Occurs as boulders in the Lower Buller at the ferry. Notwith- 

 standing its different appearance, it is closely related to the Mt. 

 William rock. It is a doubtful elvanite ; perhaps it is a rhyolite, 

 but I have seen no rhyolite with a similar ground-mass. 



Gvp.at Barrier Island — Dykes of elvanite with idiomorphic 

 quartz are found cutting the slates and sandstones in Mine Bay, 

 at north part of the island ; but I have no specimens for micro- 

 scopic examination. Hutton, Reports Geol. Explorations, 1868-9, 

 p. 3 ; Cat. Colonial Museum, 1870, p. 112. 





RYOLITB QROUP. 







Trachytic rocks composed of a semi-crystalline or- % itreous 

 ■ound-mass containing porplivritic minerals which are usually 

 lartz* and sanidine with sti.hU «iuantity of some ferro-magnesian 

 licate. The name llliyolite ha^ priority of a year over Liparite. 



No ferro-u 

 Lakn Taupo—A 

 ystals of sanidine 

 ix)und-mass moder 

 •lourless glass dei 



lagnesian silicate, (a) Wit 

 red trachytoid rock witl 

 and smaller quart/es. S.(. 

 ate in quantity and cry^talli 

 rise with h:.'matite gniuul 



h cjuartz 

 1 al.und 

 J. 2-10. 



ant large 



istingo?a 

 colourless 



tTystallitos. The porphyritic minerals are cpiartz, sanidine and 

 plagioclase, and scattered crystals of magjiotite. The sanidine 

 L'rystals go to -3 inch. Th<> ])lagioclase is subordinate to the .^ani- 



■upo ; it 



. may have 



(»0 



fron. Tauhara. 





Luft.hon—K pale 



yellowish-grey vesicular rock . 



v-ith conspit 



^ white 



felspars. 





\-U. Section: (xround-.ii 



a..s abundai 



lourless, 



partly m 



ieroiitic and partlv crystaliiti 



;c (longuliti 



■)U(led 



with mini 



ute n 



licrolites of felsp,-ir, -Ul 



)2o and le: 



ewingH 



uxion, and 



a litth 



•> magnetite. The porpln 



•ritic miner; 



e sanidi 



fiittie !;!' 



agiocU, 



Lse which <'o up to •!.') ii 

 UKl secondary ha-matite 



ich in lengt 



lerc, is 







and limonil 



"lyiiiitt. 





in rh.' 



■ %esicles. An analysis 



by Profess 







I7p.c. 



of silica. On the road from Lvttelt 





r. 11,1,1-, 



t. -li.i 



US. X.Z. Inst., Vol. II., 



p. :)03, ai 









1 Westland, pp. 332and;: 



\:A; Kolenl 



■!.il 



irl.iuh fu, 



.Ml MCI 



•■•ilogie .tc, 1885, p. S, (T 



■rachyte). 



