8 
about Montagne Noire in the township of Archambault. 
On the whole, this anorthosite area is rather more rugged 
than that underlain by the surrounding gneiss. 
As will be seen on consulting the accompanying map, 
the gneissic series through which this anorthosite has been 
intruded, is, so to speak, closely wrapped around the 
anorthosite mass, its strike for the most part following the | 
sinuosities and curves of the contact. The most notable 
exception to this is along a portion of the southern bound- 
ary where the band of white crystalling limestone inter- 
stratified with the gneiss is seen to be cut out off by the an- 
orthosite. The foliation of the gneiss is thus evidently ,in 
part at least, a secondary structure, induced by great 
pressure subsequent to the intrusion of the anorthosite. 
This pressure has affected the anorthosite as well, for the 
anorthosite, especially near the contact on the eastern side, 
possesses a distinct foliation coinciding in direction with 
that of the gneiss. 
At a number of places near the limits of the area, 
especially about the dividing line between the rear ranges 
of Wexford and Chertsey, near the road to St. Donat, 
very large masses of orthoclase gneiss occur inclosed in the 
anorthosite ,and afford additional proof, if any be required, 
of the intrusive character of the latter. 
COMPOSITION OF THE MORIN ANORTHOSITE. 
The anorthosite throughout the area is pretty uniform 
in composition, the chief variations being due to a somewhat 
uneven distribution of the constituent minerals in the 
schlieren which are in places developed in the rock. The 
most noteworthy exception is the greater preponderance. 
of the iron-magnesia constituents in the extreme north- 
west corner of the area in consequence of which the an- 
orthosite passes over into a gabbro. 
Plagioclase, augite, hypersthene and ilmenite are by far 
the most important constituents. Hornblende occurs in 
a few places, more especially near the contact with the 
surrounding gneiss. Garnet, apatite, zircon and other 
minerals are occasionally found as accessory constituents. 
The plagioclase has been found in every case where it 
has been examined to be labradorite and throughout the 
area, except where the rock has been granulated by the 
