368 C. A. SUSSMILCH AND W. G. STONE. 



would according to the quantitative scheme of classification 

 outlined in Iddings' "Igneous Rocks," fall within Division 

 II, Group C, i.e., Quartz-diorites and their equivalent 

 aphanites, to the latter of which he gives the name dacite 

 or dacite-porphyry, the latter being the equivalent of the 

 palseotypal variety quartz-porphyrite. Adopting the 

 scheme in which mode of occurrence has also a bearing 

 on nomenclature, and as outlined in Harker's text book 

 "Petrology for Students," the name quartz-porphyrite 1 is 

 applied. 



(a) Granophyric Quartz-porphyrite (Pink Variety). 



Megascopic Characters.— This rock has a pinkish- 

 brown colour, mottled with dark green, creamy and light 

 yellowish-green patches. It is porphyritic with an aphanitic 

 base of a pinkish-brown colour. The phenocrysts present 

 are chlorite, felspar and quartz. The chlorite is of a dark 

 green colour, dull lustre, and varies considerably in size, 

 reaching 5 mm., the average size being about 2 mm. Occas- 

 ionally harder patches with a fair lustre are noticed, which 

 represent not entirely altered phenocrysts of a ferro- 

 magnesian mineral. Yellowish-green patches of what 

 appears to be epidote are associated with the chlorite and 

 scattered through the groundmass. Quartz occurs very 

 sparingly as phenocrysts which are only noticed here and 

 there with a diameter of about 1 mm. The felspar is pale yel- 

 lowish-green to dull white in colour, and shows evidence 

 of much alteration to kaolin etc. The average size of the 

 crystals is about 2 mm., but ranges up to 4 or 5 mm. The 

 chlorite and felspar phenocrysts appear to be developed in 

 about equal proportions. 



1 Porphyrite as defined by Harker is a rock of hypabyssal type, with 

 intermediate chemical composition and porphyritic structure with a 

 groundmass, and characterised by a soda-lime felspar. 



