[.^AMS A BARLOW] ALKALI SYENITES OF EASTERN ONTARIO SI 



The position of the rock in the Quantitative Classification is accord- 

 ingly as follows : — 



Class 1 Persalane. 



Order 5 Canadare. 



Eang 1 Normarkose. 



Sub-rang 3 Phlegrose. 



It is a question whether the calcite should be considered as an al- 

 teration product or as representing little inclusions of the surrounding 

 limestone, as in the case of the nepheline syenites described below. If, 

 as above, all the lime be considered as belonging to the magma, the rock 

 lies near the line between phlegrose and pulaskose. 



The mode of the rock, that is to say, its actual mineralogical com- 

 position, is found on calculation to be as follows : — 



Quartz 4.20 per cent. 



Orthoclase 37.25 



Albite 45.59 \ 47 26 " 



Anorthite 1.67 / 



Muscovite 4.78 



Biotite 3.93 



Magnetite 1.39 



Apatite 27 



Calcite 1.60 



100.68 



This syenitic phase of the granite passes imperceptibly into the 

 nepheline syenite on either side by the disappearance of the quartz with 

 the concomitant increase of soda feldspar at the expense of the potash 

 feldspars, together with the increase in the proportion of iron-magnesia 

 constituents and the appearance of some nepheline. An albitic phase of 

 the nepheline syenite thus results. This transition is excellently seen 

 on lot 26, con. XII of Monmouth, the transitional rock being rather 

 coarse in grain and dark in colour, having a faint red tinge and show- 

 ing on the weathered surface a little nepheline and in one or two places 

 small crystals of corundum. Eather large grains of magnetite are also 

 scattered through the rock. It has a distinct foliation, due chiefly to 

 the approximately parallel arrangement of the biotite, of which a large 

 amount is present. 



Under the microscope this rock is seen to consist of albite, ortho- 

 clase, microcline and a little microperthite with nepheline, biotite and 

 calcite. As accessory constituents magnetite and apatite are present 

 in the thin sections. A separation by means of Thoulet's solution shows 

 that there is about eighteen times as much albite as potash feldspar ])re- 

 sent in the rock. 



