236 HONE YM AN ON THE METAMORPHISM OF KOCKS. 



the Silurian strata ; outcropping on the southern bend of West 

 Branch of Doctor's Brook in several places, bringing up in its 

 course the same strata, with the addition of overlying Upper Silu- 

 rian strata, giving them all a northerly dip. It outcrops on the 

 elevated ground where the track turns to the north ; this is nearly 

 south of Arisaig Pier. From this onward its course is obscured. 

 Its influence is manifest from the continuation of the elevated ground 

 — south of the ravine in which Arisaig Brook flows, which is evi- 

 dently the eflfect of the elevation of the Silurian obscured strata. 

 When we reach the end of the ravine from which a branch of Mill 

 Brook now flows, the trap is seen to outcrop to the south of 

 MacAra's Brook, the eastern extremity of the Upper Arisaig Series. 

 This series is thus bounded on all sides by trap. 



Returning to Malignant Brook, we find the trap of the Sugar 

 Loaf Series, the red metamorphosed strata of the Upper Silurian 

 of the Mountain Series on the south. This is^the southern part of 

 a band which is found undivided, southof the Upper Arisaig Series, 

 but is divided into three parts by the trap, on the east side of 

 the mountain part of the East Branch of Doctor's Brook. On the 

 west side of this part of the tract this trap is largely exposed ; here 

 it is associated with a dark brown porphyritic rock which underlies 

 the Lower Carboniferous patch already referred to. It then runs 

 to the south of the red band, being often exposed in its course, 

 and then appears to terminate in a fine exposure on the side of the 

 West Branch of Doctor's Brook, south of Arisaig Pier. 



The lower part of this mountain series or Middle Silurian meta- 

 morphic, is bounded by and underlaid by the syenite of McNeal's 

 mountain, which rises to 1010 feet above the sea level. The dior- 

 ite of Mackintosh's on the top of East Branch Doctor's Brook, and 

 the syenites which lie in the rear of McDonald's mountain, south of 

 the Frenchman's barn, and in the table land south of Arisaig Pier. 



You will have observed that the trap besides being the agent in 

 local metamorphism, has also been a great intruder and disturber 

 of the Upper Silurian and Lower Carboniferous rocks of this locality. 

 These have been tilted and altered and elevated by its force in a 

 manner singular and perplexing. The two insulated patches of 



