6 
INTRODUCTION. 
GENERAL STATEMENT CONCERNING THE ANORTHOSITE 
INTRUSIONS OF THE CANADIAN SHIELD. 
The Laurentian shield, or great Northern Protaxis of 
the continent of North America has an area of rather 
over 2,000,000 square miles (5,000,000 square kilometres) 
and lies almost entirely within the bounds of the Dominion 
of Canada. : 
As is well known, it consists of rocks of pre-Cambrian 
age, the greater part being made up of the gneisses of the 
Laurentian System. 
Penetrating these rocks of Laurentian age, more espec- 
lally along the border of the eastern portion of the Pro- 
taxis, there are great intrusions of anorthosite. These are 
typical plutonic intrusions, often of vast dimensions, that 
which occurs about the head waters of the River Saguenay 
having an area of not less than 5,800 square miles (13,500 
square kilometres). It was from these anorthosite areas 
in Labrador that the minerals labradorite and hypersthene 
were first obtained and sent to Europe by the Moravian 
missionaries. 
The greater number of these anorthosite intrusions 
are situated in very wild and inacessible districts, but one 
of them, the Morin anorthosite intrusion, can be reached 
with comparative ease, and the present excursion has 
been arranged with a view to enabling the members of 
the Congress to obtain an idea of the chief characteristics 
of this great anorthosite area. The various anorthosite 
bodies resemble one another closely in character, although 
in some of them certain phenomena are especially accent- 
uated; thus, in the Labrador area to which reference has 
been made, the beautifully iridescent variety of labra- 
dorite (‘‘Labrador Feldspar’’) is abundant. This occurs 
less abundantly in the other areas, and in the Morin area 
is scarcely ever found. The Morin anorthosite area can, 
be taken however, as a typical representative of the great 
anorthosite intrusions of Canada. 
The anorthosite may be considered as a variety of 
gabbro in which plagioclase (‘‘anorthose’’) preponderates 
so largely that the other components sink to the rank of 
accessory constituents. It may be said that usually they 
