a0 
surface, while locally a few inclusions of Potsdam sandstone 
are present. The nepheline syenite ,which appears in 
isolated outcrops at the surface, widens below to several 
hundred feet. It contains many small rounded fragments 
of Potsdam sandstone which display every stage of absorp- 
tion by the magma. The occurrence appears to have the 
form of a small stock which probably did not extend up- 
wards much farther than the present surface of Mount 
Royal Heights. 
In one of the quarries on the eastern outskirts of the 
city of Montreal, one of the large sheets of tinguaite which 
penetrate the limestone in this district is exposed. In the 
quarries of Morrison & Co., at Delorimier avenue this 
sheet attains a thickness of 25 feet. The Trenton limestone 
forms both the floor and the roof of the sheet, which is 
cut by younger dykes of fourchite, etc. In the quarries 
of Messrs. Rogers & Quick the pipe through which the mag- 
ma rose to supply material for the sheet is seen, as well as 
the sheet itself. The tinguaite of this sheet is very fresh and 
typical. It is rich in nosean and holds also as accessory 
constituents rinkite, lavenite, rosenbuschite, and other 
rare minerals. 
tHE GEOLOGY..OF ST. HELEN ISLAND: 
The western end of this island is underlain by a soft, 
easily disintegrating shale of Utica age. This formation 
overlies the Trenton limestone. The contact of the two 
formations, which follows approximately the north bank 
of the river, is concealed by drift. 
The remainder of the island is composed of a very 
remarkable breccia. This shows no signs of stratification 
and is composed of fragments of rocks of various kinds, 
which are angular, subangular, or partly rounded but not 
waterworn, embedded in a very fine grained greyish 
matrix which weathers to a rusty brown colour. These 
fragments vary in size from microscopic grains to boulders 
twelve and fifteen inches in diameter, and their range in 
age extends from Laurentian to Devonian. The rocks 
represented are red and black shales; hornstone; limestone 
—mainly Trenton; red and grey sandstones—the latter 
probably Potsdam; quartzite; granitic and syenitic gneiss. 
The red shale and red sandstone were considered by Logan 
to be probably of Medina age. 
