764 A. P. COLEMAN 
Professor Walker’s paper’ and the reports of Dr. Barlow? and the 
present writer on the nickel region;3 so that it will be unnecessary 
to give an elaborate account of the various sections made across the 
edge of the sheet. In general it may be said that where the outcrop 
is broad, as near the Creighton and Murray mines, the norite makes 
up about half of the section; but where the outcrop is narrow, as at 
some parts of the northern range, the basic portion may be nearly 
absent. ‘The micropegmatite forming the upper portion of the 
sheet is more nearly uniform in thickness than the norite beneath 
The ore deposits, consisting chiefly of pyrrhotite with a compara- 
tively small amount of pentlandite, the real nickel-bearing mineral, 
and chalcopyrite, are clearly parts of the eruptive and may be looked 
on as excessively basic phases of the lower edge of the sheet. The 
ore is not continuous around the whole margin, however, but occupies 
especially the lowest points, where the outcrop of the eruptive is wide; 
being largely or entirely absent from narrow parts. 
In crossing a wide outcrop of the eruptive, as at the Creighton or 
the Murray mine on the southern range, one finds on the southeast 
side massive pyrrhotite resting against granite or lower Huronian 
rocks and more or less penetrating them as veinlets, or inclosing frag- 
ments of them. Even the massive ore contains small portions of the 
norite minerals, especially labradorite; and a few feet or yards to 
the northwest the silicates increase in quantity until, when there are 
about equal amounts of silicates and sulphides, the rock may be 
called pyrrhotite-norite. Beyond this the sulphides diminish, until 
within one or two hundred feet there are only blebs of pyrrhotite 
scattered through the norite; and at length norite without sulphides. 
From this point for a mile or two northwest the norite undergoes 
little change, then becomes reddish in color, merging into micro- 
pegmatite, which does not vary greatly till the acid edge is reached. 
On narrow parts of the northern range true norite is almost absent, 
and an intermediate rock containing some quartz, orthoclase, and 
pegmatite forms the bottom of the sheet. 
The norite of the basic edge of the eruptive varies considerably 
t Quarterly Journal of the Geological Society of London, Vol. LIII, pp. 40-46. 
2 Geological Survey of Canada, Vol. XIV, Part H, 1904. 
3 Bureau of Mines, Ontario; Vol. XIV, Part III, 1905. 
