ON THE PYROXENITES OF THE GRENVILLE SERIES 

 IN OTTAWA COUNTY, CANADA. 



The pyroxenic rocks associated with the apatite deposits, and by 

 Hunt' called pyroxenites, constitute an important feature of the 

 Grenville series over considerable areas north of the Ottawa River in 

 Canada. There has been a wide divergence of views as to their 

 origin, some regarding them as metamorposed sediments, while others 

 consider them to be of igneous origin. The observations of the writer 

 support the latter view. They were made in the vicinity of High 

 Rock, an apatite mine, situated on the right bank of the Du Lievre 

 River about twenty-one miles above Buckingham and forty miles 

 north of Ottawa. The openings here cover about six hundred acres 

 in all on the tops of the hills which rise to a height of seven hundred 

 feet above the level of the river. The longer axes of the hills trend 

 south 40° east parallel with the strike of the rocks of the region. The 

 apatite occurs in veins or pockets in the pyroxenite or along the con- 

 tact of the pyroxenite with dikes of syenite which cut it in various 

 directions. As described by the writer,^ this dike rock varies from 

 a course-grained syenite to a rather fine-grained gneiss. As an inter- 

 mediate stage there occurs at a number of places, both on the surface 

 and associated with the apatite in the diggings, a peculiar spheroidal 

 phase of the syenite, called "leopard rock," which is considered due 

 to dynamic processes. 



The pyroxenites usually occur in parallel bands intercalated in 

 the quartzites, though they sometimes cut across the bedding of the 

 latter. Fig. 2 represents the relations of these rocks as seen at one 

 locahty on the hill. The pyroxenite bands, which have the appear- 

 ance of an intrusion in the quartzite, have suffered breaking and 

 stretching, while quartzitic material has taken possession of the spaces 

 between the disrupted blocks. Still better are these relations shown 

 in Fig. 3. At this locality the pyroxenite appears in the main to have 



' Geology of Canada, 1866, p. 185; Chemical and Geological Essays, p. 208. 

 ^ Bulletin of the Geological Society of America, Vol. VII, pp. 95-134. 



316 



