246 NOTES ON A GRANITE CONTACT ZONE. — ^MclNTOSH. 



section of this area, is the intruded rock, a black slate with a 

 general easterly-westerly strike, and a south dip of 65° in 

 the north which gradually decreases as: the trough of the 

 Dartmouth Synclinal is approached. 



The original mineral composition of the slate beds varied 

 somewhat. This is evident in the difference now seen in the 

 rock; some are carbonaceous, others siliceous, while almost 

 all the rock contains pyrite in varying proportions. This 

 slate forms a. part of the Upper Division of the Gold-Bearing 

 series. The Halifax and South Western railroad passes 

 through the area, and the numerous cuttings afforded means 

 of easily obtaining material for examination. Samples of the 

 slate were taken at intervals along the railroad from the point 

 where it crosses the Dutch Village Road up to the contact with 

 the igneous rock. Within this belt, metamorphism is excel- 

 lently well shown. Even at the edge of the area, the furthest 

 point from the nearest surface contact, metamorphic altera- 

 tion is evidenced by the spotted appearance of the slate. 

 Beyond this, doubtless, the rock is also altered, the zone 

 being wider than the extent studied. Additional work 

 could be done in tracing the result of the metamorphism from 

 this point back into the unaltered slate. All through the 

 contact zone the slate has a spotted appearance easily recog- 

 nized, while as the granite is neared, long slender well-formed 

 crystals are seen in the rock. The presence of these crystals 

 from the cleavage faces of which the light is reflected, serves 

 easily to distinguish it from the less altered spotted slate. 



Microscopic examinations of the sections reveal a marked 

 similarity between this granite contact and those more or less 

 celebrated ones described from the Barr-Andlau of the 

 Vosges Mountains, the Lake District of England, and else- 

 where. The "base" of the slate, which is fine textured, is 

 composed of sericite, minute grains of quartz and feldspars, 

 graphite and other black carbonaceous particles. Probably 

 very little, if any, of the original detrital material is present, 



