[ADAMS * BAHLOw] ALKALI SYENITES OF EASTERN ONTARIO 1 1 



feet foliated structure which in many places presents an actual schistose 

 development, the strike of which conforms to that of the adjacent country 

 rock. The foliation has all the characters of an original structure. 

 They vary in texture from medium to coarse grained, while the peg- 

 matitic phases sometimes present nepheline and plagioclase individuals 

 as much as a yard in diameter. 



The rock is, as a rule, remarkably fresh and unaltered. Evidences of 

 pressure even in the most pronouncedly foliated or schistose varieties 

 are extremely rare. In occasional instances, however, some of the feld- 

 spars show strain shadows and curved or slightly dislocated twinning 

 lamellae. Sections of the rock comprising the narrow part of the hand, 

 crossing the Monck road in Faraday township, show quite pronounced 

 granulation and cataclastic structure. 



The relations of the constituent minerals, especially the feldspa- 

 thoid species, do not indicate the same regular and definite order of 

 succession which is seen in most of the rocks which have crystallized from 

 a molten magma. In general, however, it may be stated that after the 

 cr}^stallization of such minerals as apatite, zircon, sphene, corundum 

 and magnetite, individuals of which usually possess rather good crystal 

 outlines, the hornblende and biotite were formed. Both of these last 

 mentioned minerals, and especially the hornblende, exhibit many sharp 

 and distinct crystallographic boundaries. Plagioclase came next in 

 order, while the remaining interspaces were filled either with potash 

 feldspars when present, or with nepheline. So' far as the texture of the 

 rock is concerned, in the great majority of instances nepheline ap- 

 parently plays the same part as quartz in an ordinary granite. Garnet, 

 which is a verv' frequent and often abundant accessory constituent, is 

 distinctly later than all of these constituents. Sodalite and cancrinite 

 are also' distinctly later, filling cracks and fissures. 



On the other hand many grave exceptions to this general order of 

 crystallization have laeen noticed, such as the inclusion of roimded in- 

 dividuals of nepheline and microcline in the plagioclase, and of plagio- 

 clase and nepheline in the hornblende. Again albite is frequently found 

 forming poikilitic intergrowths with hornblende, such included in- 

 dividuals of albite often having direct connection and more or less dis- 

 tinct optical continuity with certain mantles or borders which sometimes 

 surround the hornblende, separating individuals of this mineral from 

 the other constituents of the rock. There is moreover undoubted evi- 

 dence of very pronounced magmatic corrosion, due apparently to pro- 

 gressive changes in the physical constitution and composition of the 

 magma. 



