60 REPORT — 1851. 



forms. These are succeeded by chloritic and partially talcose slates, which become 

 interstratified with obscure conglomerates with a slaty base, and upon them rest 

 unconformably bluish slates, with intermingled bands of chert and limestone towards 

 the bottom, and a thick and extensive overflow of greenstone trap at the top. Re- 

 posing on these are white sandstones, which pass by an alternation of colours into 

 red sandstones and conglomerates, often with jasper pebbles, and these are repeated 

 after the occurrence of an uncertain amount of reddish limestone of an argillaceous 

 quality. The sandstones and conglomerates become interstratified with amygda- 

 loidal trap layers, and an enormous amount of volcanic overflow divided into beds 

 crowns the summit. The sandstones are often argillaceous, and display ripple-mark 

 and crack casts on their surfaces, while the concentric curves of flow sometimes 

 characterize those of the trap. Innumerable dykes cut up the sedimentary and vol- 

 canic beds, and both the dykes and the overflows are almost universally marked by 

 a transverse columnar structure. The thickness of the whole from the base of the 

 blue slates cannot be less than 1 2,000 feet, and the whole formation is intersected by 

 copper lodes of different characters in different places, which run in directions both 

 with and transverse to the strike. 



On the north shore of Lake Huron the granite is succeeded by a formation con- 

 sisting of white, often vitreous sandstone or quartz rock of great thickness, some- 

 times passing into a beautiful jasper conglomerate, and alternating with great beds 

 of slate and bands of conglomerate with a slaty base, both being interstratified with 

 thick masses of greenstone. A persistent band of limestone of about 150 feet in 

 thickness and interstratified with thin cherty layers, occupies a place in the series, 

 probably somewhere about the middle. The surfaces of the sandstone often exhibit 

 ripple-mark, and the total thickness of all the members of the formation may be about 

 10,000 feet. Different intrusive rocks intersect those of stratification, and as related 

 to one another, they display a succession of events in the history of the formation. 

 There is of course a set of dykes — greenstone no doubt — cutting the sedimentary rocks 

 and giving origin to the greenstone overflows. It is difficult however to identify 

 these ; but another set of greenstone dykes are seen cutting both the sedimentary 

 and igneous strata ; intrusive granite, sometimes occupying considerable areas, thrusts 

 these antecedents aside, sending forth dykes of its own order, intersecting all and 

 reaching to considerable distances from the nuclei ; and then another set of green- 

 stone dykes cuts through the intrusive granite, its dykes, and all that previous causes 

 had placed. Evidences of disturbances and dislocations accompany all these suc- 

 cessive intrusions, those connected with the granite being the most violent. But 

 there is in addition another set of disturbances of still posterior date, and it is to 

 these that is due the presence of those metalliferous veins which give the countiy its 

 value as a mineral region. 



In respect to the age of the Huron cupriferous formation, the evidence afforded by 

 the facts collected by my friend and associate, Mr. Murray (published in our Report 

 of Progress for 1847-48), on the Grand Manitoulin, La Cloche, Snake, Thessalon, 

 Sulphur, and other islands, points ranging along a line of 90 miles out in front of 

 the coast, is clear, satisfactory and indisputably conclusive. On these islands, the 

 Potsdam sandstone, the Trenton limestone, the Utica slates, and the Loraine shales, 

 successive formations in the lowest fossiliferous group of North America, were each, 

 in one place or another, found in exposures denuded of all vegetation, resting in un- 

 conformable repose, in a nearly horizontal position, upon the tilted beds and undu- 

 lating surface of the quartz rock and its accompanying strata, filling up valleys, over- 

 topping mountains, and concealing every vestige of dykes and copper veins ; and it 

 would appear that some of these mountains have required the accumulation of the 

 whole thickness of the lowest three and part of the fourth fossiliferous deposit, equal 

 to about 700 feet, to bury their summits. 



The chief difference in the copper-bearing rocks of Lakes Huron and Superior 

 seems to be the great amount of amygdaloidal trap present among the latter, and 

 of white quartz rock or sandstone among the former. But on the Cauadian side of 

 Lake Superior there are considerable areas without amygdaloid, while white sand- 

 stones are present in others, as on the south side of Thunder Bay, though not in the 

 same vast amount, or the same state of vitrification as those of Huron. But not- 

 withstanding these differences, there are such strong points of resemblance in the 



