432 MK. J. PARKIBTSON ON AN INTRUSION OP GRANITE [Aug. 1 899, 



streaks and veins mingled with the more normal rock. A difference- 

 in general appearance, the porphyritic felspars, and the presence of 

 fragments distinguish the former. The clear outlines which usually 

 characterize the inclusions of such rocks are frequently softened 

 and almost lost, and are replaced by fine-grained patches, 2 or 3 

 inches in diameter, containing much quartz, and speckled thickly 

 or thinly with the dark minerals. Here and there in these a 

 cloud-like streak indicates less complete dissolution. These patches 

 pass gradually away into the coarser rock beyond. Here the large 

 felspars come in, and occasionally the dark minerals are also larger. 

 The texture of some of the better defined veins is much more 

 uniform, owing to the fact that the ferromagnesian minerals are evenly 

 disseminated, and more in keeping in their characters with the other 

 constituents. A thin section shows how close has been the welding ; 

 a preponderance of mica and hornblende on one side, with rather 

 large felspars, a tendency to a granophyric structure on the other, 

 constitute the only differences. It is to be understood that these 

 changes in the state of the ferromagnesian minerals are local only. 

 The presence of porphyritic felspars in the rock which has done the 

 mixing, coupled with their absence in the brick-red granite, which 

 moreover contains no inclusions, — these conditions point to an early 

 intrusion differing somewhat from that which came after. 



The evidence at hand suggests that the granite-magma was in- 

 truded in an order somewhat as follows : — The earliest intrusion^ 

 characterized by the presence of porphyritic felspars, brecciated the 

 diabase, carrying away fragments, some of which were softened and 

 permeated by acid material, in greater or less degree. Injections 

 often less porphyritic followed, still further softening fragments 

 already partially dissolved, and completing the work of mixing 

 begun at an earlier period. Here would arise a type of rock in 

 which the dark minerals would show no sign of their foreign origin. 

 Finally would come the non-porphyritic, granophyric, brick-red 

 granite, following the lines taken by the earlier intrusions, scarcely, 

 if ever, itself brecciating the diabase, but carrying on with it in its 

 course the badly-mixed more basic mass, loaded with fragments, 

 which had preceded it. This last intrusion, probably viscous, would 

 be interstreaked with its predecessors, without the diffusion into 

 itself of the basic material which the latter had acquired. 



Tongues of the brick-red granite would be thrust into the earlier 

 rock, and the onward movement of the whole might at times detach 

 and isolate these, making them appear as fragments included in the 

 more basic rock. 



II. The Granite. 



The porphyritic granite which probably formed the first intrusion 

 is not seen at Sorel Point, except with the accompaniment of basic 

 material, the foreign origin of which can scarcely be doubted. At 

 La Houle, however, 300 or 400 yards to the east, a porphyritic 

 granite, differing in several respects from the brick-red granite of 

 the adjacent headland, is seen clearly cutting the basic rock. 



