NOTES ON A GRANITE CONTACT ZONE. — McINTOSH. 247 



the minerals enumerated above being largely recrystallisation 

 products. Originally, the rock was probabh^ a carbonaceous 

 clay slate or shale. The grains and shreds all lie for the most 

 part with their long axis in the same direction — that of the 

 slaty cleavage. The re-crystallization is doubtless the result 

 of pressure through a long period of time, and is itself the 

 cause of the cleavage, normal to the pressure. This occured 

 during the long time in which the folding was going on, which 

 is evidenced in the present attitude of the rock and was prior 

 to the intrusion of the granite. The proportion of the 

 minerals of the ''base" varies in the sections examined, in 

 some sericite is more abundant, in 'others quartz, while in 

 others there is more carbonaceous material. This difference 

 is probably due to constituent varieties of the original ])eds. 

 Pyrite is abundant in some laminae, in others almost absent. 

 Recrystallisation was probabh' completed before the 

 contact metamorphism began. The first change brought 

 about by the granitic intrusion was likely the production of a 

 clear, brownish biotite in shreds and irregular crystals. 

 Cleavage lines are rarely pronounced and inclusions are rare. 

 Associated, and sometimes intergrown with it, is a colourless, 

 slightly pleochroic mineral with rather high refraction, 

 probably phlogoplte. The biotite flakes are set at various 

 angles to the cleavage planes and were, therefore, not affected 

 by the pressure. It also occurs as inclusions in minerals to be 

 described further on, which fixes its position in the time scale 

 of metamorphism. 



The spots so characteristic of the slate are found to be 

 fibrous, ovoid and irregular patches of partially decomposed 

 cordierite (Fig. 1). Unaltered portions occur at and about 

 the centre of the patch, while the edges consist of a yellowish 

 chloritic substance. The refractive index and double refrac- 

 tion are low. A faint bluish pleochroism is observable in one 

 or two places. The crystal outline, which can be seen only 

 between crossed nicols is mostly prismatic with occasionally 



