10 



and varying in width from 1 in. up to 18 in. This zone is 

 separated from the normal granite (e) by a narrow band or 

 rim (d) 1 in. to \\ in. wide, very rich in biotite. Along this 

 biptitic rim differential erosion has often produced a little 

 depression or gutter. 



The small nests of quartz and tourmaline are fairly 

 common among the aplites, and appear occasionally in the 

 granites, and even in the syenite of Rosetta Head. 

 Megascopically one of these nests appears as a dense mat of 

 tourmaline needles with a little interstitial felspar, the whole 

 surrounded by a selvage of quartz. Viewed microscopically 

 the tourmaline, strongly pleochroic from light brown to 

 indigo blue, is seen to be replacing felspar, the replacement 



Fig. 3. 



starting along cleavage planes, and the w^hole apparently 

 represents an alteration of aplite by magmatic emanations. 



Of the same general type, though on a larger scale, is a 

 pipe about 4 ft. across, the outer rim being of quartz and 

 biotite with some large felspars, forming a kind of peo^matite. 

 Within this is a zone of quartz, and the centre is occupied by 

 tourmaline. 



Uralitic Dolerite.-r-The uralitic diabase described by Dr. 

 Chewings isC^) from a small pipe cutting through the granites 

 on the eastern side of Green Bay. The outcrop is visible only 

 at low tide, and the author was never fortunate enough to 

 find it uncovered. ' - 



(7) Vide Prof. Howchin. 



