42 
The sphene is abundant in small but perfect wedge- 
shaped individuals. It sometimes shows a rather remark- 
able decomposition into calcite traversed by little needles 
of rutile. 
The garnet is of dark reddish brown colour and occurs 
in individuals often of considerable size but of very irregular 
shape, and which hold numerous inclusions of nosean and 
orthoclase. 
THE DYKE ROCKs. 
The greater part of the district about Mount Royal is 
covered by drift of varying thickness. There is scarcely 
a place, however, in the area, where the drift is absent, 
that the underlying strata are not seen to be cut by dykes 
consanguineous in character with the rocks forming the 
intrusive mass of the mountain. Similar dykes, though 
in smaller number, cut the rocks of the mountain itself. 
About 375 of these dykes and sheets have been observed 
on the Island of Montreal, and evidently a very much 
greater number are covered by the drift. The dykes 
range from a mere film to six feet (1-8 m.) or more in 
width. They are especially abundant on the slopes of 
Mount Royal about Westmount reservoir, in Outremont, 
in the area now covered by the waters of the Lower Reser- 
voir (adjacent to the grounds of McGill University and 
formerly known as the Reservoir Extension), and along 
the harbour front. Dykes are also excellently exposed 
at the Mile End quarries, the Corporation quarry, Maison- 
neuve and elsewhere. 
Unfortunately the rocks composing these dykes are, 
in almost all cases, considerably altered, and it is rare to 
find one which is entirely free from decomposition products. 
In many cases the alteration has progressed so far that it 
is impossible to determine the precise character of the 
original rock. As a rule, the dykes at Outremont ate 
fresher than those of Westmount or from the Reservoir 
Extension. 
The following types of dyke rocks are represented :— 
Bostonite Monchiquite 
Aplite Fourchite 
Nepheline aplite Camptonite 
Tinguaite Alnoite 
Analcite dykes. 
