[HOWARD] SOME OUTLIERS OF THE MONTEREGIAN HILLS 



83 



The mineralogical composition of the two phases of the intrusive 

 at Ste. Dorothée is as follows: 



Biotite 



Hornblende. 

 Barkevikite . 



Augite 



Titanite. . . . 

 Iron Ore. . . 

 Apatite .... 

 Labradorite . 

 Analcite . . . 



Calcite 



Heulandite. 



a Abundant 



b Subordinate 



c Present 



(x) Also present in irregular patches in the normal type. 



Normal Type. — The normal type consists of phenocrysts of 

 augite, hornblende, barkevikite, and biotite with accessory black 

 iron ore, apatite, and titanite in a groundmass of labradorite and 

 isotropic base. In places there are irregular patches bordered by 

 aegirite-augite, and filled with labradorite, calcite, and an isotropic base. 



Biotite occurs in deep brown idiomorphic individuals with a 

 yellowish brown to very deep brown pleochroism. These attain a 

 length of 0.5 mm. and are practically unaltered, although slight bleach- 

 ing was observed in some individuals, and the ends of crystals cut per- 

 pendicular to the base are irregular, indicating partial resorption. 



Common hornblende is present as perfect crystals up to 0.5 mm. 

 in length. The mineral is yellowish brown in colour, and the pleo- 

 chroism is very light yellowish brown, to brown. 



Barkevikite also occurs as idiomorphic individuals up to 0.5 mm. 

 in length. This was one of the first minerals to crystallize, and is 

 partly enclosed by crystals of the lighter coloured hornblende. Its 

 refractive indices are higher than those of the hornblende, and it is 

 very dark in colour, closely resembling biotite both in colour and in 

 shades of pleochroism. It is readily distinguished from the mica, 

 however, by its crystal outlines. The cleavage in both minerals is 

 greatly masked by the deep colour. 



Augite is by far the most common ferro-magnesian constituent 

 of the rock, and occurs both as large crystals up to 1.0 mm. in diameter 



