26 THE ROYAL SOCIETY OF CANADA 



Varieties 



Garnet-norite. — A variety which differs from the main type is one 

 containing garnet. The garnet is of the andradite variety with no 

 crystal outHnes and crossed by numerous irregular fractures. The 

 garnet-bearing variety is most abundant in the border zones near the 

 intruded dark coloured gneisses. 



Pyrite-norite. — Another variety of norite is one containing iron ore 

 in abundance. In all the sections studied, magnetite and pyrite occur 

 in varying amounts, and in places in the field considerable quantities 

 of pyrite were found disseminated throughout the rock. One specimen 

 seen by the writer, but not found in place, consists of a fine-grained 

 rock, thickly dotted with crystals of yellow pyrite. The pyrite- 

 bearing zones seem to have no definite relation to the borders of the 

 norite intrusions, but were scattered irregularly through them. 



Quartz-norite. — A dyke of quartz-norite was found cutting 

 granite-gneiss, nine miles east of Fond du Lac. Though it is thirty 

 miles from the main norite intrusions at the eastern end of lake 

 Athabaska, it is considered as being genetically related to them. 

 The rock is fine-grained, even granular, and dark grey in colour. It 

 contains large crystals of feldspar, which give it a porphyritic character 

 in places. 



In thin section the following minerals are found : iron ore, apatite, 

 zircon, tourmaline, garnet, biotite, amphibole, hypersthene, plagio- 

 clase and quartz. 



The iron ore consists of magnetite and pyrite in irregular masses. 

 Zircon is represented by a few small crystals. Apatite occurs as small 

 prismoids, as broken rod-like crystals, and as irregular-shaped masses. 

 Tourmaline is represented by a single crystal in the section. It is 

 highly pleochroic in shades from pale violet to deep blue. Garnet is 

 present as small round grains, and as larger broken masses crossed in 

 all directions by fractures. 



The biotite is a very deep brown variety, highly pleochroic, and 

 contains abundant iron ore along its borders, and its cleavage planes, 

 and also in small bunches scattered irregularly through it. The 

 amphibole is of the tremolite variety, and is practically colourless. 

 In places it presents a fibrous appearance. Much more abundant 

 than the amphibole is an orthorhombic pyroxene which is slightly 

 pleochroic, hence to be classed as hypersthene. It contains inclusions 

 of quartz. 



