48 



of muscovite are seen to flash against the dark background 

 here and there, recalling the appearance of a dark micaceous 

 shale broken along the lamination. 



Under the microscope no traces of schistosity are to be 

 seen. The rock consists for the most part of angular grains 

 of quartz with much fine-grained biotite, a fair sprinkling of 

 tiny muscovit-e crystals, grains of dusty plagioclase, and a 

 little magnetite and apatite. The grainsize is very fine, that 

 of quartz being not more than '2 mm. 



The only definitely autogenic minerals are the micas, 

 and the structure is blastopsammitic. 



(2) INCLUSIONS IN THE PORPHYRITIC GRANITE. 



The metamorphism effected by the granite is not revealed 

 in many places; at Rosetta Head the dominant alterations 

 have evidently been due to the syenite, and it is only in the 

 inclusions of country rock that one can see what transform- 

 ations have been produced by the granite. A specimen from 

 one of these inclusions on the east side of Granite Island 

 is a fine-textured and fairly even-grained mosaic of quartz, 

 felspar, and biotite, with a little residual apatite and iron 

 ore. Some of the felspar is probably relict, but for the most 

 part it is recrystallized, and a noteworthy feature is the 

 presence of quite a considerable amount of clear untwinned 

 orthoclase. This mineral has not been noted in any of the 

 rocks away from the intrusions, and while in the present 

 instance it may represent the recrystallization of an original 

 constituent, it is more likely to have been introduced from 

 the igneous magma, especially as it appears to bear an inter- 

 stitial relatioiiship to the other minerals of the rock. 



A specimen obtained from another inclusion in the 

 granite forming the breakwater at Granite Island shows faint 

 traces of the original lamination in hand specimen. Micro- 

 scopically it is composed of autogenic quartz and biotite (with 

 a little muscovite) with a good deal of relict plagioclase and 

 a little apatite and zircon. Tliis rock, like the previous one, 

 contains a certain amount of clear untwinned orthoclase, 

 evidently autogenic. 



There is a large dark-coloured mass of country rock em- 

 bedded in the granite on the coast at Port Elliot near the dyke 

 of soda aplite. It is, like the others, massive, and in its degree 

 of metamorphism is only a stage farther advanced than the 

 micaceous quartzites some distance inland. The grainsize is 

 fairly fine but very uneven, and the rock contains much 

 angular relict quartz and plagioclase. Autogenic biotite and 

 subordinate muscovite occur, and a fair sprinkling of iron 

 ore with some apatite. A good deal of recrystallization has 



