
32 B. N. A. BOUNDARY COMMISSION. 
granitic outburst, these must have suffered intense metamorphism, and 
had this been superimposed on that which is seen to effect the Laurentian 
rocks in eeneMil, they would have assumed a very different aspect from 
that they now have. They differ, however, from the altered Huronian on 
the north side of the granite, in the absence, so far as observed, of rocks 
clearly representing altered conglomerates, so common there. 
Intrusive Granitic Mass of the North-west Angle and Vicinity. 
60. This intrusion may be considered as roughly separating the Huron- 
ian series of the northern part of the lake, from the Laurentian of the south ; 
but cuts off the area of much altered Huronian rocks, just described, from 
the rest. Its general form, so far as I have been able to define it, is that 
of the letter Y, the bifurcation taking place westward, and the northern 
branch passing almost directly up the North-west Angle Inlet, while the 
southern curves southward toward Flag Island. In the fork of the Y an 
area of sedimentary rocks is caught up, which appears, like those lying 
to the south and north, to be highly altered Huronian, but may also 
include some beds of the Laurentian. 
61. The multitude of large and small islands separated by narrow and 
tortuous channels, which fill the lake opposite the’ North-west Angle 
Inlet, are due to the superior hardness of this mass, and its surrounding 
altered rocks; and it very probably, as suggested by Dr. Bigsby, runs 
eastward and constitutes the backbone of the promontory, which so con- 
stricts this part of the lake. Its most western visible extension is seen at 
McKay’s Island, a rounded half-submerged hill, which stands boldly out: 
from the low swampy ground of the northern shore of the Inlet, some 
seven miles east of the government landing, and about cight miles from 
the Laurentian rock already described as existing at the Reference 
Monument not far from that place. The granite is moderately coarse, and 
greyish-red in colour. It has scattered through it irregular masses of 
greyish fine-grained hornblendic rock, which is softer and weathers away 
into hollows, and probably represents included fragments of surrounding 
strata. Many segregation veins of coarse-grained reddish felspar with 
quartz, occur, with a general course nearly east and west. They run 
very straight in some places, but do not exceed a foot in width. Eastward 
from McKay’s Island, on the north shore of the Inlet, several points 
show a granite similar to that there represented, grey in colour, and 
often holding segregations of red felspar and quartz. 

