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GEOLOGICAL SURVEY OF CANADA. 
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Area of Much-altered Huronian Rocks lying South of the Intrusive Granitic 
» Mass of the North-west Angle. ive 
55. This detached area of Huronian is comparatively small; its gr 
est diameter, which lies nearly east and west, may be stated as about ei 
miles, and its width at about four. So far as could be ascertained a, [ 
examination of the islands which fill this narrow part of the lake, the me 
northern and western edges of the area are bounded by intrusive rock, 
A 
and the eastern passes in the manner already described into the Laurentian; 
but, as the southern edge is only defined by the margin of the belt of | 
islands, and the falling away of the rock surface below the waters of the — 
lake, it may possibly extend much further in this direction. Indeed, con- 
sidering the close manner in which the form of the lake accommodates — 
itself to the areas occupied by the softer rock formations, itis not improbable | 
that much of the southern part of its basin may have been excavated in 
” 
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Huronian rocks softer than those now treated of, which have assumed au; 
altered character from their proximity to the granitic mass. 
56. The rock first found on leaving those of the Laurentian series, and 
belonging to the eastern end of the area now in question, isa dull-green 
soft hornblendic slate, separating into rather thin lamine, often brownish 
in colour along the division planes, and where weathered. It includes, in 
some places, more or less lenticular masses of grey rock resembling 
gneiss in appearance, which may have been intruded parallel to the 
stratification planes, but is more probably bedded, and formed of material 
differently affected by metamorphism. A short distance west of this, the 
rocks assume a vertical attitude, with a strike of about N. 80° HE. 
Quartzites of greyish colours preponderate, and are associated with a rock 
resembling diorite, but which may possibly be a much altered sedi- 
ment. The quartzite shows many joints running in all directions, and in 
some places is so cut up by them as to render it difficult to break off a 
clean-faced specimen. The joints are sometimes slickensided and gener-— 
ally rusty. West of this, at about six miles east of the northern end of 
Flag Island, the strata dip N. 27° E., < 70°, the rock being a soft, very | 
finely laminated micaceous schist of a grey colour; the mica in which is ee 
black. It is intersected in one place by a well defined dyke of diorite, 
not of great width, but with a fixed direction of S. 40° EB. Forabout = 
a mile south-west of this, the rock, where seen, is a thinly bedded 
grey gneiss, imperfectly crystallized. It was found to have at three 
points where observations were taken, the following attitudes:—N. 8° 

