300 MINERALS AND GEOLOGY 



Keweenian series are very generally amygdaloidal (see page 182). 

 Both series are traversed by numerous trappean and dioritic dykes 

 (often distinctly porphyritic) in which a transverse columnar struc- 

 ture, as first pointed out by Sir William Logan, is very conspicuous. 

 Both series also are interpenetrated by mineral veins carrying native 

 silver, silver-glance, galena, zinc blende, copper-pyrites, and other 

 ores, some of which are more or lass auriferous. These are referred 

 to below. 



The Animikie formation extends from Pigeon River eastward 

 across the Kaministiquia and around the shore of Thunder Bay to a 

 little beyond Thunder Cape. The Keweenian formation stretches 

 from this point around Black Bay (on the west shore of which it 

 abuts against a large mass of granite), and across Nepigon Bay, St. 

 Ignace and adjacent islands ; and it occupies also a broad area on 

 the south, west and north sides of Lake Nepigon. Michipicoten 

 Island with its cupreous greenstone dykes, and one or two headlands 

 on the east shore of Lake Superior, likewise belong to this series. 



Superficial Deposits : Over the floor of crystalline rocks by which 

 this vast region is essentially underlaid, Drift clays and boulders, and 

 Post-Glacial clays and sands, with other recent accumulations, are 

 spread in many places. Glacial furrows and striae also are seen in 

 numerous localities. The prevalent direction of the strise is decidedly 

 towards the south-west, although some run nearly south, others east 

 of south, and others, again, almost east and west. Where commonly 

 seen two or more sets of strise occur together and thus intersect each 

 other. Drift clays are seen in many of the river channels, and 

 boulders are of very general distribution. The latter are accumu- 

 lated in some places in long ridges or morains at the opening of 

 valleys or along the lower slopes of hills. Whilst many of these 

 boulders are of essentially local origin and thus consist on the north 

 shore of Lake Huron of jasper-conglomerate, quartzite, and other 

 Huronian rocks, and of Laurentian and Copper-Bearing rocks about 

 Lake Superior examples of limestone boulders, containing Middle 

 or Upper Silurian and Devonian fossils, occur in places throughout 

 the region. These latter must have come generally from the northern 

 country which lies beyond the height of land and extends north-east- 

 erly to Hudson's Bay. The Post-Glacial deposits of the district con- 

 sist in their lower beds of stratified clays and sands, referred by the 



