HONEYMAN ON THE METAMORPHISM OF ROCKS. 



igneous rock is a patch of Lower Carboniferous conglomerate. 

 This is divided in all directions by the trap which sometimes passes 

 into it like veins. This arrang-ement is well seen below the mill 

 dam. The consequence of this conjunction is that, conglomerate, 

 generally loose in structure and yielding, is made intensely hard 

 and resisting, forming a very rugged passage for the water below 

 the mill dam, and a very great obstruction to the road maker. 

 Here we have metamorphism of conglomerate by igneous action. 

 Following the exposures of this trap westward we reach it where it 

 comes in contact with the Upper Arisaig Series. This series is 

 rendered metamorphic generally in the third degree, by what we 

 call regional metamorphism. Here the trap forms a great dyke, 

 dark and rugged ; it is continued for about a mile, and for about 

 half a mile it is interrupted, or passes under the sea; it reappears 

 on the shore and continues until it nearly reaches the Frenchman's 

 barn ; it disappears and rises in the sea immediately north of the 

 barn ; it disappears, reappears to the east of Arisaig Pier, is inter- 

 rupted, and then largely exposed, forming a great proportion of 

 the break water of Arisaig Pier and Harbour. 



This trap is generally homogeneous, sometimes porphyritic, fre- 

 quently amygdaloidal, where decomposed vesicular. The crystals 

 of the porphyritic are felspar, — the amygdala are calcite, — one 

 cavity is filled with an agate. I found this in the trap at Doctor's 

 Brook, some years ago, when dw^elling among these rocks for the 

 purpose of studying them. It thus appears that this trap is poor 

 in minerals and very dissimilar to the traps of later age, e.g.^ of 

 Blomidon and Five Islands. On the north this trap is bounded by 

 the sea ; on the south of the trap we have the Arisaig Middle and 

 Upper Silurian Series. Passing along the line of junction of the 

 trap and overlying sedimentary rocks, which form the lowest part 

 of the Upper Arisaig Series, or A. the possible equivalent of the 

 Oneida conglomerate, we find on the east side of the Arisaig Pier, 

 opposite the break of the trap already noticed, low banks of the 

 third degree ; they are in marked contrast with the other parts of 

 the same band, and the overlying strata. Higher in the series we 

 have the slates, having cleavage and other characteristics of the degree 

 of metamorphism indicated. To the east of the arenaceous shales is 



