47 



Granite Island and Port Elliot, and a few specimens of these 

 are described below. 



Tlie rocks in the neighbourhood of the contact often 

 exhibit well-marked schistosity. Whether this was developed 

 as a result of magmatic pressure or by dynamic metamorphism 

 before the intrusion is not quit-e clear. The micaceous quartz- 

 ites some distance inland, although partially recrystallized, 

 show no signs of schistosity; but this may be due to the 

 quartzite being a "competent" rock, and successfully resisting 

 the stresses of the regional metamorphism, which was able to 

 convert the more aluminous sediments into schistose rocks. 



On the whole it is probable that the schistosity as we see 

 it now was produced originally by regional forces, and that 

 the force of intrusion of the magma accentuated the effect 

 to some extent. The inclusions of country rock in the 

 granite comprise massive types, sometimes showing well- 

 marked lamination, and distinctly schistose types as well, 

 one in particular from Rosetta Head possessing strong 

 schistosity at an angle of about 37° to the original bedding. 



(1) MICACEOUS QUARTZITES AWAY FROM THE INTRUSIONS. 



About two miles in from the coast at the back of Rosetta 

 Head the prevailing rock is massive, micaceous looking, and 

 almost black in colour, with uneven fracture and with no 

 traces of schistosity. In thin section it is seen to be blasto- 

 psammitic in structure and of fine but very uneven grainsize. 

 Quartz and felspar together constitute about 85 per cent, of 

 the rock, the former somewhat in excess, the remainder of 

 the rock being mainly biotite, with subordinate muscovite 

 and a little ilmenite, apatite, and zircon. 



Irregular and angular grains of quartz and of kaolinized 

 plagioclase (with a refraction exceeding that of Canada 

 Balsam) up to '6 mm. are set in a much finer-grained paste 

 of quartz, felspar, and mica. While the larger quartz and 

 felspar are clearly relict, there are traces of incipient alteration 

 in some of the plagioclase, and a certain amount of recrystal- 

 lization of the light-coloured minerals of the paste has 

 occurred, the mica, too, being of course autogenic. The rock 

 was originally a highly impure grit, and may be called a 

 micaceous felspathic quartzite. 



Another specimen, collected about one mile inland, shows 

 very similar characters in thin section, though in hand 

 specimen it is of a lighter-grey colour. 



A third example, collected from half a mile along the 

 east-west road running inland from just north of Rosetta 

 Head, is likewise a dense dark-grey rock with little or no 

 trace of schistosity, except that on a certain fracture flakes 



