TRAP DYKES. 28g 



the syenite become a dark gneiss. The Esquimaux 

 Islands, which lie off this coast, are composed of this 

 light-colored gneiss. 



Invariably accompanying these rocks is a doleritic 

 trap of a peculiar mineralogical character, occurring in 

 •overflows of a peculiar physiognomy, and upheaved in a 

 ■direction at nearly right angles to that of the Laurentian 

 'dykes, thus following the general northwesterly trend of 

 ■,the Atlantic coast of the peninsula. 



This rock differs from the hard fine-grained trap at 

 Henley Harbor in being coarsely porphyritic. It is 

 (Composed of large crystalline masses of hypersthene and 

 labradorite, this last being of a dark smoky color, and 

 precisely such as described as occurring on Square Island. 

 It seems to follow that this porphyritic trap is the result 

 of the refusion of the anorthosite rock, which must con- 

 sequently underlie this Domino quartzite. This is an 

 argument for the uncpnformable bedding of this gneiss 

 upon the Lower Laurentian gneiss, while this trap-rock 

 is evideintly of the age of the Domino gneiss, which it 

 has somewhat disturbed. The Isle of Ponds is largely 

 composed of these trap hills. Huntington Island is a 

 large mass of trap. Tub Island, as its name betokens, is 

 a peculiar, truncated cone of trap, resembling an inverted 

 tub. These trap overflows extend northward to Cape 

 North, which is a lofty headland of trap capping the 

 gneiss, and thus adding very materially to the elevation 

 «f this, as of all the other numerous gneiss promontories 

 which run out from the main land. Occasionally an 

 island is seen half black and half white, one side being 

 composed of the dark trap-rock, and the other of the 

 light-colored quartzite. Such is " Black and White," a 



