320 THE CAJfADIAN NATURALIST. [Vol. vii. 



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angles of 50° — 70°, and where the Huronian come in contact 

 with the sandstones above mentioned, there is the same sudden 

 alteration in dip as between these same sandstones and the 

 copper-bearing rocks on the Keweenah promontory. Hence, one 

 would infer that the traps and conglomerates of the upper-bearing 

 series come next in age to the underlying Huronian schists, and 

 that subsequently to their upheaval were deposited the sandstones 

 whose horizontality has not been broken by any disturbing force. 

 The sandstones are generally attributed to the lower Silurian 

 system. 



Copper explorations on the Keweenah promontory have been 

 made at innumerable spots over a distance of 100 miles along 

 the strike of the beds, between the Point and Lake Agogibic, 

 but the mines which have proved productive are confined to 

 three districts, viz., Keweenah Point or Eagle River, Portage 

 Lake, and Onontagon. 



On the Point, the copper-bearing rocks attain their greatest 

 lateral development, and beds of conglomerate, melaphyre, and 

 compact sandstone, with the same dip and strike, stretch from 

 shore to shore. Thence, as they curve round in a south-westerly 

 direction, the range diminishes in width. Some of the first 

 mines opened were on the west coast of the promontory, where, 

 for nearly 30 miles' members of the copper-bearing series form 

 the shore wall. 



Here the most productive group of mines is on a system of 

 fissure veins, which cut the rocks of the northern range at right 

 angles to their strike. The Cliff Mine, the first of the lake 

 mines to pay a dividend, and which, from first to last, has dis- 

 tributed nearly $2,280,000 among its shareholders, is on a vein 

 which, though not generally wide, was often filled with mass 

 I copper. The copper was associated with quartz, cnlc-spar, and 

 I other vein-stones. The contents of the fissure exhibited a banded 

 I structure, and were influenced markedly by the country rock. In 

 I this district, likewise, copper was mined from a bed of amygda- 

 I loidal trap, here known as the asli hed, and work was also done 

 I on conglomerate beds ; but, if we except Copper Falls and the 

 I Phenix Mines, the operations on the fissure veins alone have 

 been financially successful. 



While the Cliff Mine near the point of the promontory was 

 the first to prove that the native copper is more than a mineral- 

 ogical curiosity, the Minnesota, near the south western end of 



