Nepheline Syenite in Ontario. — Miller. 183 
shown that nepheline as a rock constituent occurs widely 
distributed in the Archaean districts of the Province. These 
rocks are of ecomonic interest from the fact that the corun- 
dum deposits, which have given rise to an important indus- 
try in the eastern part of the Province during the last three 
or four years, belong to the same series. 
Hand specimens of the Sturgeon lake boulders show the 
rock to be light gray in color, and medium to coarse-grained 
in structure. The minerals that can be made out with the 
naked eye are feldspar, nepheline, black mica, magnetite, 
apatite and pyrite. 
Feldspar is the most abundant mineral in the rock and ap- 
pears to be, so far as can be determined without the use of 
the microscope, all of the alkali variety. Carlsbad twinning 
is shown by some of the individuals which exhibit a tendency 
to take on a crystal outline, being set in a ground mass of 
nepheline. 
Nepheline is the most abundant constituent after the 
feldspar. On a weathered surface, which is, however, not 
characteristic of all the specimens, the nepheline has become 
stained a light brown, while the feldspar is to all appearance 
unaltered. The latter mineral here makes up approximately 
two-thirds of the mass of the rock, and the former one-third. 
Black mica is, after nepheline, present in the greatest 
proportion. In one specimen there is considerable apatite. 
This mineral shows a tendency to associate itself with the 
mica. 
The magnetite is present in subordinate amounts. One 
octahedral crystal, which has a diameter about two-thirds 
that of a pea, reminds one of the occurrence of this mineral 
in the nepheline syenite of Hastings county. 
One or two cubes of pyrite are present in the specimens. 
They have diameters of about the same length as that of the 
magnetite crystal just mentioned. 
As is well known, nepheline rocks show a great tendency 
to exhibit variety of grain and mineralogical composition in 
comparatively small parts of the same mass, or even in a 
single hand specimen. It is therefore difficult to give a clear 
idea of the characteristics of a mass of this rock by describing 
a few thin sections. 
