9 
action of pressure, this labradorite is filled with an infinite 
number of minute schillerization inclusions, which give 
to it a deep violet or nearly black colour, so that the massive 
anorthosite is always very dark. 
Augite, while present in much smaller quantity than the 
plagioclase, is, next to it, the most abundant constituent 
of the rock. Rhombic pyroxene (hypersthene) is present, 
however, in nearly, ifnot quite, equal amount. Both mine- 
rals occur in grains of a pale green colour and of irregular 
shape. The hornblende, when found, occurs in individuals of 
a similar shape in intimate association with the pyroxenes 
and frequently forms a border around the pyroxenes. 
It is usually green, but is sometimes brown. Garnet 
very seldom occurs as a constituent of the normal an- 
orthosite but is often found near its contact with the sur- 
rounding gneiss. It has a pale pinkish colour and is 
often intimately associated with grains of iron ore. 
In nearly every section of anorthosite, some grains of 
an opaque black iron ore are seen. Those portions of the 
anorthosite rich in iron ore are very restricted in extent and 
they fade away into the normal anorthosite of the area 
which, as above mentioned, is very poor in iron ore. 
The other constituents of the anorthosite are found 
but occasionally and are present in such small amount 
that they do not merit any especial mention. 
STRUCTURE OF THE MORIN ANORTHOSITE. 
The macroscopic structure of these anorthosites, as 
well as that of most of the crystalline rocks forming the 
Laurentian system, is best studied on the great glaciated 
surfaces of the roches moutonnées, which protrude through 
the drift in all directions. On a freshly fractured surface, 
or even on a smoothly glaciated surface which has been 
protected from the weather, the structure is not clearly 
seen; but, when the glaciated surface has been exposed 
during the interval which has elapsed since the disappear- 
ance of the ice, to the etching action of the weather, the 
structure of the rock is brought out in a wonderfully clear 
and striking manner. Such weathered surfaces, moreover 
are often square yards in extent and enable the structure of 
considerable masses of the rock to be determined and the 
relations of different structures to one another to be clearly 
seen. 
