84 THE ROYAL SOCIETY OF CANADA 



and also as a host of smaller lath-like individuals usually about 0.1 

 by 0.3 mm. The mineral is the titanium-bearing variety and has a 

 slight purplish tinge. It is slightly pleochroic, ranging from colour- 

 less to light purplish grey in colour. Some individuals have a tendency 

 to irregular outlines indicating a slight amount of resorption. 



Titanite is a very abundant constituent, almost equalling the 

 ferro-magnesian minerals, with the exception of augite, in amount 

 and occurs in regular rhombic crystals up to 0.3 mm. in length. It is 

 practically colourless and non-pleochroic. 



Black iron ore occurs as irregular grains, and consists of magne- 

 tite or ilmenite with small amounts of pyrite. Some of this iron ore 

 appears to be secondary, and as some of the biotite apd augite have 

 been resorbed, the iron ore may have been derived from these minerals. 



Apatite is present in minor amounts as minute laths. 



The above minerals represent the phenocrysts in the principal 

 variety; the irregular patches containing aegirite-augite, and the 

 pegmatitic phase will be considered separately. 



The groundmass consists principally of labradorite between 

 Abi Aui and Abg Ans, and an isotropic mineral. 



Labradorite is almost universally twinned according to the Carls- 

 bad law, but the albite twinning is less perfectly developed, and is 

 lacking in the greater part of the feldspar present. The last stage in 

 the solidification of the magma is marked by the formation of an 

 amorphous colourless mineral. This isotropic mineral has a refrac- 

 tive index below that of Canada balsam, and it may be analcite or a 

 glass of very low refractive index. 



Calcite is present in the groundmass to a very small extent, but 

 is more frequently associated with the irregular patches referred to 

 above. While the groundmass is as a rule interstitial, there are some 

 small patches, several millimetres in diameter, which are composed 

 entirely of bytownite, calcite, and an isotropic base, in addition to 

 aegirite-augite, and a zeolite (heulandite) ; these minerals do not 

 appear ■ Isewhere in the rock. 



Two varieties of these patches are found in the normal phase of 

 the intrusive. In the one case, there is a tendency to regular rounded 

 outlines with small crystals of aegirite-augite around the borders, 

 while the centres are filled with bytownite, heulandite, calcite, and 

 the isotropic base. The other variety is simply an irregular jumble 

 of microcrystalline augite, aegirite-augite, and calcite with an iso- 

 tropic centre in which regular crystals of calcite 0.05 mm. in diameter 

 occur. These aggregates are frequently surrounded by iron ore. 



