76 THE ROYAL SOCIETY OF CANADA 



Large idiomorphic augite crystals are abundant and are usually 

 associated with the apatite as larger grains enclosing the hexagonal 

 plates and long laths of the latter mineral. Augite, unlike olivine, is 

 perfectly fresh and is greenish grey in colour, with a dark green to 

 purplish grey pleochroism. It is, therefore, the titanium-bearing 

 variety and thus, titaniferous augite is probably the source of the 

 ilmenite and perovskite of the main intrusion. 



Light brown biotite is an abundant constituent and exhibits 

 strain shadows, indicating motion in the magma after partial crystal- 

 lization. A light green mica, probably phlogopite, is also present, 

 although in smaller quantities. 



The groundmass consists of a granular aggregate of indeterminate 

 character which has been largely altered to calcite, and grains of 

 calcite are common throughout the rock. 



Black iron ore is not so abundant as in the main intrusion where 

 it is probably of secondary origin, and has apparently been dçsrived 

 from the olivine. The sulphides, pyrite and pyrrhotite, are abundant 

 locally, although some sections contain very little of either mineral. 



Just how much of the calcite is due to inclusions of the Grenville 

 limestone and how much to weathering cannot be determined, but 

 doubtless both have contributed a share of the carbonate present. 



This exposure lies between the main intrusive and the dyke 

 associated with the breccias and appears to be largely composed of 

 the ferro-magnesian constituents of the magma, while the dyke is 

 slightly more acid, and the paste of the breccia is apparently com- 

 posed of the final products of crystallization. Therefore, it appears 

 probable that in the surging of the magma during the formation of 

 the breccia, the constituents which were the first to crystallize settled 

 toward the parent mass. 



In other words, the paste of the breccias, the dykes closely 

 associated with the breccias, and outlying occurrences such as the 

 one described immediately above, are not only associated in position, 

 but are also differentiation products of the original magma. The 

 earlier phenocrysts settled towards the main intrusive during the 

 period while the still fluid acid part of the magma was brecciating the 

 country rock through which it welled. 



Eastern Dyke and Breccia.— A mile to the east of the Monastery 

 is a breccia which is described by Harvie. Between this breccia and 

 the Monastery on the small hill in rear of the buildings is a dyke 

 about two feet in width cutting the Grenville limestones and quartzites. 



This dyke is essentially the same as that described above from 

 near the Monastery gates, except that olivine is much less abundant. 



