482 Geological Society. 



river Hunter, occurs in the Lower Coal-measures, which are above 

 the Lower Marine beds with Trilobites, below which again are nu- 

 merous fossiliferous beds before the porphyry is reached ; and (2) 

 that the Cannel belongs to beds in which Glossopteris occurs, and 

 therefore may be a slight additional evidence of their antiquity, as 

 it is an analogue of the "Bog Head" Cannel of Scotland. 



3. " Remarks on the Copper mines of the State of Michigan." 

 By H. Bauerman, Esq., F.G.S. 



The author described briefly the different conditions under which 

 native copper is found in the trappean belt of the Upper Peninsula 

 of Michigan, on Lake Superior. The district in question is a 

 narrow strip of ground about 1 40 miles long, and from 2 to 6 miles 

 in breadth, made up of alternations of compact and vesicular traps, 

 with subordinate beds of columnar and crystalline greenstones, con- 

 formably interbedded with sandstones and conglomerates. Three 

 different classes of deposits are known, — namely, transverse or fissure 

 lodes in the northern district ; cupriferous amygdaloids and conglo- 

 merates following the strike, in the central or Portage district ; and 

 irregular concretionary lodes, also parallel to the bedding, in the 

 southern or Antonagon district. In the fissure-veins copper occurs 

 either spotted through the vein-stuff, or concentrated in compara- 

 tively smooth plates, or lenticular masses, of all sizes up to 500 

 tons. In the Antonagon lodes the masses are also large, but of 

 much more irregular forms. In the Portage district, on the other 

 hand, only small masses are found, the great production of the mines 

 of this region being derived from the finely divided spots and grains 

 interspersed through the amygdaloids and conglomerates. 



After giving details of the phenomena observed in the lodes of 

 particular mines, and a list of the principal alternations of minerals, 

 chiefly zeolites with quartz, native copper, and calcite, the latter 

 mineral being both newer and older than the copper, the author 

 proceeded to notice the various hypotheses that may be framed for 

 elucidating the occurrence of native copper in the Lake Superior 

 traps. Two principal sources were indicated — the first on the sup- 

 position that protoxide of copper may have originally formed part of 

 the felspathic component of the trap, or that the same rock may 

 have contained sulphuretted compounds of copper mechanically in- 

 termixed ; while according to the second view the overlying sand- 

 stones may have contained small quantities of copper-bearing 

 minerals, in a similar manner to the Kupferschiefer and other Per- 

 mian and Triassic rocks in Europe. Supposing the trappean rocks 

 to have been percolated by solutions carrying the products of the 

 alteration of such minerals, it was suggested that the reduction to 

 the metallic state was mainly produced by the action of substances 

 containing protoxides of iron, which by higher oxidation have given 

 rise to the dark-red colour and the earthy ochreous substances found 

 in the vein-matter. The causes producing the metalliferous de- 

 posits in the trap were stated to have evidently acted throughout 

 the whole system ; and the absence of copper from the compact beds 

 is probably rather due to the absence of cavities fit for the reception 

 of such masses, than to any difference in chemical composition. 



