22 



kind of interpenetration multiple twinning, and sometimes to 

 an actual intimate parallel intergrowth of two multiple- 

 twinned individuals. 



While traces of biotite are occasionally visible in the slide, 

 the original mineral has been almost entirely converted into a 

 very pale green, faintly pleochroic chloritic mineral with a 

 double refraction a shade stronger than that of quartz. It is 

 uniaxial and positive. These optical characters do not agree 

 with those of any of the usual rock-forming chlorites. The 

 mineral is found both as inclusions in the phenocrysts and 

 squeezed in between the felspar crystals. 



Abundant minute red-brown pleochoric prisms of rutile 

 are either enclosed in the chlorite or strung out and aggre- 

 gated along the boundaries of felspars. Indeed this abund- 

 ance of rutile is one of the characteristic features of the rock. 



A few crystals of zircon with green pleochroic haloes are 

 embedded in the chlorite, also a little apatite. Quartz is 

 present very sparingly as irregular inclusions in the pheno- 

 crysts, but does not occur otherwise. 



The rock mass has been subjected to considerable 

 pressure, resulting in undulose extinction, bending of 

 the chlorite, and in fracture and dislocation of the 

 felspars, with considerable granulation, many patches 

 of the rock being rendered quite microgranular. It is 

 interesting to note how much more this essentially felspathic 

 rock has suffered than the granites. It might be thought that 

 the collapse of the rock took place as a result of the decrease 

 in volume consequent on the change from biotite to chlorite, 

 but that this has not been so is proved by the fact that the 

 altered country rock, in which the biotite has been chloritized, 

 is extremely compact and free from all traces of cataclasis. 



A slide cut from a non-porphyritic specimen of the rock 

 shows a much greater proportion of mica (chlorite), and 

 among this there is some muscovite. The chlorite is sometimes 

 so arranged as to give a rosette or 'fan-shaped effect. Quartz 

 is more abundant than in the previous specimen ; it is quite 

 clear, is interstitially disposed, and though showing some 

 undulose extinction is not granulated. Rutile is very abund- 

 ant, though rather sporadically distributed. Apatite and 

 zircon are distinctly more abundant than in the previous 

 slide. 



Fresh specimens of the rock were very hard to get, but 

 one which was fairly fresh was analysed. This particular 

 specimen was somewhat porphyritic and the ferro-magnesian 

 constituents were subordinate. Microscopically chlorite was 

 often seen to be associated with quartz in the little stringers 



