9 



and diorite of Granite Island, showing that here, too, the 

 time-interval between intrusions was small. 



At Green Bay the even-grained granite is definitely- 

 succeeded by the porphyritic type, but it reappears on the 

 coast past Commodore Point and continues for some little 

 distance. 



It is noteworthy that no inclusions of country rock have 

 been found in this even-grained granite. 



lifd (potash) Aplife. — Past Commodore Point the even- 

 grained granite is succeeded by a mass of brick-red coloured 

 aplitic rock which fringes the coast for about 400 yards, round 

 almost to Middleton Beach. This rock is readily distinguished 

 by its characteristic weathering colour and by the close jointing 

 by which the outcrop is intersected. The field relations of the 

 mass could not be made out, but it is probably intrusive 

 towards the even-grained granite. Landward its exten- 

 sion is not very great, and it is soon succeeded by other 

 rocks. The rock is finer grained than the granites but dis- 

 tinctly coarser than the other aplites, and there is a notable 

 absence of ferro-magnesian minerals. 



Greisenised Soda Granophyre. — At the back, or land- 

 ward, side of the red aplite and even-grained granite, and 

 extending up to Middleton Beach, is an outcrop of fine-grained 

 muscovitic rock which microscopical investigation has shown 

 to be a pneumatolytically-altered soda granophyre. Its field 

 relations with regard to the contiguous rocks could not be 

 determined, and inland it soon disappears under a cover of 

 sand. 



Soda Aplite. — Probably very closely related to tlie soda 

 granophyre is a fine-grained soda aplite which occurs as a 

 dyke cutting the granite a little east of Green Bay. . The dyke 

 is only a few feet wide and runs seawards in a more or less 

 meridional direction. Associated with it is a rim of biotite 

 similar to those described below in connection with aplite 

 pipes. The rock is of a cream colour, and towards the edges 

 of the dyke has been contaminated by the granite, acquiring a 

 little biotite and opalescent quartz. 



Minor Potaah Aplites, etc. — Other aplites, characterized 

 by fineness of grain and by the presence of subordinate biotite, 

 are found pretty abundantly at Port Elliot as veins or pipes 

 cutting through the porphyritic and even-grained granites. 

 As a rule the boundaries of the intrusions are quite sharp, but 

 sometimes they are accompanied by a curious segregation rim 

 of biotite. Fig. 3 shows diagrammatically such an occur- 

 rence. There is an aplitic pipe t^a ) with nests of quartz and 

 tourmaline fh): this is surrounded by a zone of the coarser 

 granite (c) with less than the normal proportion of biotite. 



