10 
If any large weathered surface of the anorthosite, 
such as is found in the roches moutonnées anywhere 
within the Morin area, be examined (leaving out of con- 
sideration for the present the arm-like extension and that 
part of the main area adjoining it), it will be noticed that 
the rock, which is coarse-grained and of a deep violet colour, 
has not that regularity of structure which we see in a 
typical granite, but presents a more or less irregular 
structure. This irregularity is sometimes scarcely notice- 
able, but is at other times striking, and is due to con- 
centration of the bisilicates and iron ore in some parts of 
the rock. The portions richer in bisilicates may take the 
form of large irregular-shaped patches occurring at inter- 
vals through the rock, or of many small patches occur- 
ring abundantly in certain parts of the rock which else- 
where is nearly free from them. In some cases these are 
arranged so as to form irregular wavy streaks instead of 
patches. Sometimes these streaks are rudely parallel, 
giving a sort of strike to the rock, but in other places they 
are quite irregular in arrangement. Between these patches 
or streaks rich in bisilicates, and rather badly defined 
against them, are portions of the rock which are very poor 
in or often quite free from bisilicates. The structure is 
well represented in the accompanying photograph of a large 
anorthosite boulder on lot 5 of range IX. of the township of 
Chertsey. Here the iron ore and bisilicates are aggregated 
together in more or less rounded areas of the rock, 
while the remainder of the rock is almost free from iron- 
magnesia constituents. In those portions containing the 
bisilicates and iron ore, these constituents form about one- 
third of the rock, the rest being plagioclase. Large individ- 
uals of plagioclase, irregular in shape and which will be 
referred to again, occur quite abundantly in the parts of 
the rock free from bisilicates, but are very rarely found in 
the patches containing the bisilicates. With the exception 
of the larger individuals of plagioclase, the rock is uniform 
in grain throughout. The portions containing the bisili- 
cates weather more readily than the rest of the rock, and 
thus leave hollows on the weathered surfaces; when the 
patches are elongated, as is usually the case, irregular 
sausage-shaped cavities usually result. In the occurrence 
represented in the photograph, it will be noticed that one 
of the masses rich in bisilicates and much larger than the 
others, forms a rude band across the lower portion of the 
