336 MINERALS AND GEOLOGY 



NORTHERN ARCHAEAN DISTRICT. 



This is essentially a region of ancient crystalline strata rocky and 

 mountainous in character : an eastward extension i f the Laurentian 

 district of Ontario, but with certain special features of its own. It 

 comprises the wide expanse of territory lying between the Ottawa 

 River and Labrador, with the exception of a comparatively narrow 

 strip of country (occupied by Lower Palaeozoic formations), extend- 

 ing along the St. Lawrence from near the junction of the two great 

 rivers to a point a short distance below the city of Quebec. It is 

 traversed by the Lauren, tide Mountains, proper, which form within 

 it several broken ranges curving roughly parallel with the course of 

 the St. Lawrence. The more southern of these gradually approach 

 the river, and run closely adjacent to it along the lower part of its 

 course. The average height of the Laurentides generally, is from 

 about 1,200 to 1,500 feet, but at one or two points they reach an 

 altitude of over 2,000 feet above the sea. Numerous rivers rise 

 among them. Some of the more important comprise : the Riviere 

 du Moine, the Gattineau, the Riviere du Lievre, the Riviere Rouge, 

 and the Riviere du Norcl, flowing into the Ottawa ; and the 1'Assomp- 

 tion, Chicot, St. Maurice, Batiscan, Ste. Anne (Portneuf), Jacques 

 Cartier, Montmorenci, Ste. Anne (Montmoreiici), Murray, Saguenay, 

 Moisie, and other eastern rivers, flowing into the St. Lawrence. 

 The rocks of this Archaean area consist for the greater part of 

 typical Laurentian gneiss (composed of quartz and orthoclase, with 

 associated mica or hornblende) interbedded with quartzites and bands 

 of crystalline limestone and iron ore. These Laurentian strata, as a 

 rire, are more or less strongly tilted and corrugated, or otherwise 

 disturbed. They are also traversed very generally by granitic or 

 syenitic veins, and are broken through in places (more especially in 

 Wentworth, Chatham, and Grenville on the Lower ^Ottawa) by 

 enormous masses of eruptive syenite and greenstone. The crystalline 

 limestones very commonly contain diopside or light-coloured pyrox- 

 ene, phlogopite, zircon, sphene, and other crystallized silicates, with 

 scales of graphite, and grains and crystals of fluor-apatite. The 

 latter mineral also occurs in workable quantities, associated mostly 

 with pyroxene, phlogopite mica, calcite, and scapolite, in broad veins 

 which cut the gneissoid strata transversely especially in the townships 



