Commercial Resources of Lake Superior. 61 



only concurred in the same effects ; shaping and elevating the ad- 

 jacent lands. 



In after-geological times important modifications arose in the form 

 of the lake. Promontories were pushed out, and islands raised up 

 by successive outbursts and overflows of trap from separate fissures 

 of great length — those for example of Keweenaw, Thunder Moun- 

 tain, and Isle Royale — all intercalcated with conglomerates, formed 

 in agitated seas between eruptions ; — at different and most probably 

 distant times, judging from the fact that some of the conglomerates 

 are altogether trappose, while others abound in granite and other 

 boulders. 



We thus obtain the general order of all these events, and little 

 more ; but the knowledge is worth having. From the position of 

 the uplifted mural cliffs, we see that the upheaving impulse came 

 from the south-east. 



Drift. — The groovings and strise are almost always northerly here. 

 New proofs are daily accumulating to shew more decisively the 

 northerly origin of the foreign drift of Lake Superior. One of these 

 is the fact that the limestone boulders on the north shore are upper 

 Silurian,* and derived from the large calcareous basins some hundreds 

 of miles north of Lake Superior : from whence Dr B. had brought 

 characteristic fossils. Another is found in the occurrence of boul- 

 ders of iron ore, in heaps, on the north side of certain cliffs, but 

 which are absent on the south side — the original site of the ore 

 being to the north of the cliffs, and near Lake Superior. 



A Sketch was exhibited of a Wisconsin prairie, dotted with northern 

 blocks dropped from icebergs. — From Dr D. Owen. 



III. Commercial Resources. 



Agriculture will only be carried on in parts of the south shore. 

 Large quantities of white fish and of furs are annually exported. 



The chief staple of Lake Superior is native copper. For ages 

 before the appearance of Europeans in America, this metal was sup- 

 plied from hence to the Indian nations far and near. The tumuli 

 of the Mississippi, &c, contain the identical copper of this lake. 

 Traces of ancient mining in Keweenaw, Ontonagon, and Isle Royale, 

 are abundant, in the form of deep pits (a ladder in one), rubbish, 

 stone mauls, hammers, wedges, and chisels of hardened copper. In 

 a native excavation, near the river Ontonagon, with trees five hundred 

 years old growing over it, lately lay a mass of pure copper 81 tons 

 in weight, partly fused and resting on skids of black oak. 



Modern explorers have hitherto only found two centres of metallic 

 riches on the south coast, — that of Keweenaw and of Ontonagon. 

 In the first are the valuable mines of the Cliff, North American, 



* Containing Pentamerus, Spirifer, Leptaena (alternata) atrypa, various 

 corals, minute trilobites, orthocerae, and some cytherinae. 



