THE SUDBURY LACCOLITHIC SHEET 765 
from point to point even along the broader parts of the range, but it 
will be sufficient for our purpose to describe the characters of an 
average fresh example. It should be remarked that fresh norite 
is oftenest found close to large ore bodies and may be shotted with 
particles of ore. On the southern range the rock is dark gray, coarse- 
grained, with blebs of bluish quartz and large flakes of biotite. On 
the northern range it is lighter gray, but does not differ in composi- 
tion. 
In thin sections the rock is found to contain labradorite to the 
extent of at least one-half—often more—hypersthene about a quarter, 
and smaller amounts of monoclinic pyroxene, hornblende, and _bio- 
tite, with quartz, titaniferous magnetite, apatite, and often sulphides 
as accessory minerals. The labradorite is usually very fresh, pale 
brown from dusty inclusions on the southern range, and clear on the 
northern, with hypidiomorphic forms, sometimes platy. ‘The hyper- 
sthene forms rough prisms with good pleochroism, but without scale- 
like inclusions. The monoclinic pyroxene seems closely related to 
the hypersthene in appearance, is pleochroic, but has a small or fairly 
large extinction angle. One is tempted to think of the hypersthene 
as merely augite with the extinction angle reduced to zero. 
Of the minor minerals hornblende occurs mostly as secondary 
rims about the pyroxenes, while quartz forms small wedges between 
the feldspars, and occasionally has pegmatitic intergrowths with 
feldspar. i 
The typical rock just described is not found everywhere, since 
usually the ferromagnesian minerals are completely changed to 
bastite or hornblende accounting for the older designation of the 
rock as diorite. 
At the Creighton mine the norite contains notable amounts of 
quartz, orthoclase, and microcline, partly intergrown as micropeg- 
matite, but this is unusual. The country rock at this point is gneiss, 
in general free from micropegmatite, but sometimes showing a rim 
of coarse pegmatite against the norite, suggesting that the basic 
magma has interacted with the neighboring rock, perhaps absorbing 
part of it. 
Thin sections of the pyrrhotite-norite found adjoining the ore 
bodies are often surprisingly fresh, in several of the two dozen slices 
