An OtfTLiNE OF fHE GtEOLOGY OF ONl'A&iO. 687 



Hiii''cmian belt of Thunder Bay ; and the gold-bearing veins of the 

 Lake Shebandowan country. 



The strata known conventionally as the Upper Copper-bearing 

 rocks of Lake Superior, overlie the Huronian formation in some 

 places, and rest directly on Laurentian rocks in others. They belong 

 to three series : a lower series, composed mostly of dark slates, beds 

 of chert, and greenish-grey sandstones, with interstratified beds of 

 trap or hardened volcanic mud * a middle or second series, consisting 

 chiefly of red and white marls and calcareous sandstones, also with in- 

 terstratified belts of trap or volcanic mud ; and a third division, consist^ 

 ing of an enormous overflow of trap, resting uncomformably on both the 

 lower ser'ies. The first or lowermost division occurs along the coast 

 between Pigeon River and the eastern extremity of Thunder Bay, and 

 is capped by the third division or so-called crowning overflow of trap 

 in many places, as, more especially, at the bold promontory of Thun- 

 der Cape, at McKay's, Mountain, on Pie Island, and elsewhere, 

 The red and white marl and sandstone series occurs principally be- 

 tween Thunder Cape and Kepigon Bay, and is also capped by masses 

 of trap belonging to the crowning overflow. It appears alsO to oc^ 

 cur at othef points on the north-east and eastern shores of the lake< 

 Both the first and second divisions are penetrated by qiiartz veins 

 Carrying various metallic matters, as native silver, silver glance, ga- 

 lena, zinc blende, nickel ore, copper ore, etc. The Silver Islet, Thun- 

 der Bay, Trowbridge, Dilncan or Shuniah, Jarvig Island, Spar Island^ 

 and other mineral locations lie on the lowermost series j whilst the 

 Korth Shore, Cariboo, Enterprise or Black Bay, Silver Lake, and 

 other locations, belong to the second division. The age of these 

 t-ocks is still a subject of controversy. By some observers they ard 

 regarded as Triassic, a view based chiefly on mineral aspect. Sir 

 William Logan, on the other hand, stoutly maintains their Lower 

 Silurian age, regarding them most probably as equivalents of the 

 Potsdam and Calciferous formations of eastern localities, or, at leasts 

 as occupying a lower geological horizon than that of the Chazy for- 

 mation; and the weight of evidence at present is certainly in. favour 

 of this view. Certain sandstone beds, commonly known as the Ste. 

 Marie sandstones, are seen at points east of St. Mary's Biver, (as on 

 the Island of Campement d'Ours, etc.,) to underlie fossiliferous lime- 

 stones of the Trenton (or Black- Biver) formation ; and these same 

 Sandstones at points on the eastern side of Lake Superior overli€5 



