318 



II. General Description. 

 The granite mass occupies an area of approximately 2 

 square miles, and forms a length of coastline of 5^ miles. In 

 plan the outcrop is roughly triangular, in shape approaching 

 a right-angled triangle, with the coastline forming the two 

 sides of the right angle. 



Along the sea coast, the granite ends sharply up against 

 dark-coloured quartzites, which macroscopically suffer little 

 or no change; nor does there appear to be a border or contact 

 zone to the granite, for this retains the mineralogical and 

 textural characteristics of the main mass. 



The intrusive nature of the mass is well shown by the 

 manner in which the granite cuts across the strike of the 

 quartzites and by the presence of rifted blocks of the quartzite 

 (accidental xenoliths), which are developed near the contact 

 and are obviously derived from the country rock. 



At the northern sea coast contact with the country rock, 

 small aplitic veins proceed into the micaceous quartzites, 

 which are here striking north-east with a south-easterly dip 

 at 64°. The rifted blocks maintain proximity to the contact 

 surface. At the southern sea coast termination of the granite 

 xenoliths are less numerous and are generally small. The 

 quartzites here have the same north-east and south-west 

 strike, but dip south-east at 74° to 80°. 



In the granite, near the junction, occur quartz geodes 

 lined and filled with tourmaline. Associated with the granite 

 occur a series of aplitic and pegmatitic dykes, which are 

 clearly younger than the main mass of granite, for they are 

 seen to cut across and intersect it. These intrusions bear a 

 close relationship to the granite, and form a highly interesting 

 series. 



The main occurrences are listed below : — 



(i.) A large elliptical (in cross section) mass of grey 



aplite is developed behind Barn Bluff. 

 (ii.) A smaller mass occurs on the sea coast, south of 



Cannon Hill. This is a pink aplite. 

 (Hi. J Minor dykes of a white pegmatite occur at the 

 northern side of Barn Bluff at the head of the first 

 gully south of the lighthouse, and veins both north 

 and south of Pink Bay. These latter veins have 

 the trend for the most part of the joint planes of 

 the granite. 



In the main mass of granite segregations are sporadically 

 distributed. These are generally ovoid and finer-textured 

 patches (cognate xenoliths). Some show a slightly darker 

 colour than the general colour of the normal granite. 



