ClIL. 



porphyritic 



earthy fracture. Section 

 abundant, consisting of a colourless or pale 



with innumerable crystallites, and chloritic infiltrations. The 



linerals are quartz and sanidine with some plagioclase, 



nd biotite. Pseudomorps of chlorite after hornblende 



and hiotite. Pyrite occurs in all, sometimes in great abundance. 



Hutton, Quart. Journ. Geol. Soc. of London, Vol. XLiii., p. 184. 



These rocks were thrown out from the Okaro craters during the 



eruption in 1886. They exhibit very interesting examples of 



; remarkably like the changes that have taken place in 



2 I 



the auriferous ro 



cks at the Thames. 



At Okaro the 



rocks are 



rhyolites, while 



it the Thames they 



are andesites, I 



ut in both 



cases the ferro-magnesian silicates hav 



e been changed ir 



to chlorite 



have^fken ^""^ 



jeen produced. At 



Okaro these cha 



nges must 





near the surface. 







^Thnml^Dis'tric 



t—A compact pale grey rock. S.G. 2-6 



2. Section: 



Felsitic, shewing 



a mosaic, and contair 



ing small angula 



fragments 



of quartz and cry 





red abundantly t 



iroughout. 



The quartz conta 



l!^lce^o!!Sy^l^ 



glass inclusions 



^ithatixed 



bubble, t;eiierall\ 



it lias only clouds and sheets of minut 



e gas pore>. 



There a.v also pi 



t<;h('s of a colourle.ss 



irregularly tibro 



"andoce'at 



with aggregate j 



.larization and rathe 



r brilliant colours 





ionally witli gret 



uish inclusions. C 







ground-mass and 



occasionally in larger 



masses which we 



•eprobal-Iy 



once felspars. 











erous branching vei 





>elow high- 



water mark, a little south of Waioha 



iga Creek. It appears to be 



a Chlorite Rhyo 

 removed. 



ite from which mo 



St of the chlorit 



has been 





OBSIDIAN GROUP. 





Lithoid or stony obsidian with crystallitic texture. 



f,\tNlrr Dnn-ns, A.^iJihiir/oH Co. — Compact rocks of various colours 

 red, })urple, pale green, or grey, often mottled, and with sub-con- 

 choidal fracture. S.G. 2 23 to 2-35 Section : Crystallitic, longu- 

 litic, with scattered fel.spar microlites, sometimes shewing Huxion, 

 and often with opaque white specks of leucoxene or kaolin. 



These rocks are identical with the ground-mass of the stony 

 rhyolites, or liparit«s. The late Sir Julius von Haast told me that 

 he had sent specimens to Vienna many years ago, and that they 



