36 ROYAL SOCIETY OF CANADA 



off in solution by the magmatic waters contained in the invading magma 

 and given off by it as it solidified. 



On the weathered surface of the syenite, the limestone fragments, 

 which in many places are tliickly scattered through the rock, are dissolved 

 away, leaving little pits and cavities into which the individuals of the 

 nepheline and other constituents of the rock project, often with rude 

 crystallographic forms. 



The intrusion has a marked foliation or gneissic structure, and is 

 irregular in composition, consisting of a series of thick bands or schlieren 

 running parallel to one another and to the strike of the surrounding lime- 

 stones. Some of these schlieren are very highly feldspathic and hold but 

 little nepheline. Much of the rock, however, is rich in nepheline. while 

 in some of it, nepheline replaces the feldspar almost entirely. Bands as 

 much as six feet in width can be found, which consist almost exclusively 

 of nepheline. Usually those streaks which are rich in nepheline are 

 also rich in hornblende, often with red garnet as an accessory constituent. 

 Elsewhere the rock consists of nepheline and albite. In the latter variety 

 small individuals of white mica sometimes occur which exactly resemble 

 the crystals of this mineral which in other parts of the area are formed 

 by the alteration of corundum. 



The highly feldspathic type which resembles those already described 

 does not require further mention, but three tpyical varieties of the rock 

 in which nepheline is more abundant were selected for study. 



Nepheline Syenite — Town^ship of Monmouth — Lot 11, Con. VIII. 



(First variety). 



This is a variety rich in hornblende. It is coarse in grain, dark in 

 colour, and possesses a distinct gneissic structure. 



Under the microscope it is seen to consist of nepheline, albite, horn- 

 blende and calcite, with a small amount of apatite as an accessory con- 

 stituent. These minerals, with tlie exception of the apatite, are all in 

 large individuals, and like most of the nepheline syenites of this area, 

 have a peculiar structure whicii approaches an allotrimorphic struc- 

 ture in character. None of the minerals have good crystalline 

 forms, but all have a tendency to occur with more or less 

 rounded outlines and to come against one another in curved lines. In- 

 clusions of one mineral in another arc common, no definite order of 

 succession can be observed in the crystallization, and the structure in 

 some respects approaches the ''mosaic" structure ^een in the metamor- 

 phic rocks when a complete recrystallization has taken place. 



The nepheline is considerably altered to a very fine grained turbid 

 aggregate resembling kaolin, but in places it is quite fresh and shows 



