210 PETROLOGY OF ROCK COLLECTIONS 



Accompanying these granites are frequent dyke rocks, including granite porphyrites, 

 aplites, pegmatites, and lamprophyres. 



In regard to the metamorphic action of the granites upon the intruded rocks, little 

 exact information is available. It is more than likely, however, that the majority 

 of the schists and gneisses, so abundantly represented in our collections, originated in 

 connection with the intrusion of the granites. 



It seems sufficiently clear at least that the great marble and calc-silicate belt owes 

 its present condition to the influence of these intrusions upon original limestones. 



THE PINK GRANITES 



Chiefest and best known is the coarse-grained pink granite typically developed at Cape 

 Irizar. The outcrop there protrudes from the ice over a length of half a mile or more. 



Other examples were met with in the Ferrar Glacier locality and at intervals along 

 the coast. Dr. Prior has described this and allied granites occuring in situ at the 

 Ferrar Glacier,* and at Cape Adare.f Professor David, Mr. Smeeth, and Mr. Schofield 

 have described granite erratics collected by Mr. Borchgrevick at Cape Adare.J 



The textures vary somewhat in the different outcrops. At Cape Irizar the Shap 

 Fell type is general, whilst certain of the specimens from the Ferrar Glacier are textured 

 like the Rapakiwi granite. Very similar granites are met with intruding the Cambrian 

 sediments of South Australia ; e.g. at Murray Bridge and Granite Island. 



The pink coloration is due to the prevailing tint of the abundant orthoclase felspars. 

 The depth of colour is affected somewhat by exposure, for the outcrops are generally 

 pinker than freshly broken faces. The tinting is by no means evenly distributed, but 

 even in small exposures varies from a deep red to practically white. At Cape Irizar 

 a fracture zone in the granite, up which a lamprophyric magma ascended, has assumed 

 a deep red colour, due, obviously, to secondary causes. In general the deeper coloured 

 the rock the greater is the content of accessory minerals. 



All the pink granites are hornblendic ; with the hornblende is usually some biotite 

 also. In this way they differ from the grey granites, which contain but little or no 

 hornblende. 



Hornblende-Biotite Granite ; Cape Irizar. (Plate I, Fig. 4) 



Most conspicuous in the hand-specimen are abundant porphyritic rectangular pink 

 orthoclase crystals twinned after the Carlsbad law : these are embedded in an even 

 granular base containing a little orthoclase, much plagioclase, abundance of quartz 

 blebs, conspicuous hornblendes, and a varying quantity of biotite. The chief variants 

 are the hornblende and biotite. In particular parts of the outcrop the one may increase 

 in quantity almost to the exclusion of the other. 



Microscopic Characters. (Figs. 4 and 5, Plate III . ) The texture is porphyritic granular. 

 Large idiomorphic orthoclases distributed through a hypidiomorphic granular base con- 

 sisting of plagioclase, orthoclase, quartz, hornblende, mica, and accessory minerals. 



Quartz in subangular grains often showing strain effects. The usual inclusions are 

 present. It is a later crystallisation than the plagioclase, and appears to have ac- 

 companied the latest phase of orthoclase separation. Orthoclase. Present in two forms. 

 The porphyritic individuals measure up to 2 5 cm. diameter and are twinned after the 

 Carlsbad law. Idiomorphic plagioclases are often included in them. The small 

 orthoclases in the ground-mass and certain additions to the porphyritic individuals 



* Loc. cit. p. 125. 



t '"Southern Cross' Collections," Brit. Mus. Nat. Hist, publication, 1902, p. 322. 



% Proc. Roy. Soc. N.S.W., vol. xxix, p. 481 (1895). 



