32 ROYAL SOCIETY OF CANADA 



The transition between the syenitic phase of the granite and the 

 nepheline syenite is also well seen at the southern end of lot 15, con. 

 VIII of Monmouth. The nepheline syenite here, has a schlicren struc- 

 ture, caused by a variation in the relative amount of the constituent 

 minerals in the different streaks. Some of these schlieren consist of red 

 syenite and others are intermediate in composition between the red 

 syenite and the nepheline syenite. There is thus represented in these 

 schlieren a complete transition from the red syenite to the normal white 

 or gray nepheline syenite. 



The nepheline syenite which forms the border of the mass, has a 

 distinctly foliated structure and is coarse in grain. It is white to dark 

 gray in colour, according to the proportion of the iron-magnesia con- 

 stituents which it contains. In a few places, as, for instance, on lot 23, 

 con. XI, it is pale pinlcish, owing to the presence of a pink geiseckite- 

 like alteration product of the nepheline. The rock is by no means uni- 

 form in composition, but usually possesses a rudely banded or schlieren 

 structure which conforms to the direction of the foliation, the different 

 schlieren being marked by a variation of the relative percentage of the 

 several minerals present. Thus, in some schlieren, the rock will be rich 

 in nepheline, while, in the adjacent ones, the nepheline will almost or 

 entirely disappear; again, there may be a variation in the relative pro- 

 portion of the iron-magnesia constituents, which will give rise to a 

 change in character. As a place where the rock is locally very rich in 

 nepheline, lot 24, con. XII, may be cited, the nepheline rock here in 

 some places containing much magnetite m large grains scattered through 

 it. These respective schlieren or bands are usually of considerable 

 dimensions, being several feet to many yards in width, and, of course, 

 are not sharply defined, hut fade away into one another, although rather 

 abruptly. Occasionally the grain of the rock will suddenly become much 

 coarser, the rock passing into a pegmatitic faciès, this being most com- 

 mon in those places where nepheline is abundant. 



A detailed study was made of a variety of the nepheline syenite 

 rich in albite and poor in nepheline, which occurs on lot 16, con. IX of 

 Monmouth, and forms part of this belt of nepheline syenite surrounding 

 the granite. It was collected on the east side of the road between 

 McCue lake and Hotspur, about one third of the way south of the north- 

 ern limit of the ])and. Tlie rock is coarse in grain and possesses a 

 distinct foliation. 



Under the microscope it is seen to possess a hypidomorphic structure 

 and to consist of the following minerals : — Albite, microcline, microper- 

 thite, nepheline, lepidomelane, magnetite and calcito. In some few 

 schlieren a dark green hornblende (probably hastingsite) replaces a 

 portion of the biotite. Albite and lepidomelane arc the chief con- 



