60 ' JVeiw Publications. [Jan., 



Our business, however, now is, to state facts and leave conjec- 

 ture to others. On this subject our facts are derived partly from 

 oral communications, and partly from the published reports of 

 those who have been employed as mineral surveyors in the cop- 

 per region. Two of these reports are before us, and we 

 have selected Capt. Bayfield's general observations for the pur- 

 pose of making this communication more complete on the geolo- 

 gy of the region which forms the subject of the essay. 



Dr. Jackson states that the earliest accounts of the existence of 

 metals on the south shore of Lake Superior, date as far back as 

 1760. Since then many persons have partially explored those 

 shores, with greater or less success. Masses of native copper 

 have from time to time been discovered, but the most accurate 

 explorer of this region was Henry R. Schoolcraft, who published 

 an account of it in the third volume of Silliman's Journal. 



Among those, however, who have examined the region of 

 the northern lakes, Capt. Bayfield has probably explored a much 

 greater space than any other individual. Lake Superior, accord- 

 ing to his observations, is placed in an oval basin or depression, 

 and is surrounded by hills, whose average height does not exceed 

 700 ft. ; even the highest do not rise over 2000 ft. above the lake, 

 whose surface is about 623 feet above, and its extreme depth 

 about the same number of feet below the tidal waters of the At- 

 lantic ocean. These hills or mountainous tracts are composed of 

 various granitic aggregates, in which horneblende is often a pro- 

 minent element. These compounds often pass into sienite and 

 greenstone, by the diminution of quartz, mica and feldspar, and 

 the increase of horneblende. The general direction or strike of 

 these formations is north-east. Basaltic dykes of enormous 

 width traverse these formations, and range up the hills for miles. 

 In addition to these rocks he describes various trap and amygda- 

 loidal rocks, which occur on both sides oLthe lake, but are more 

 fully developed upon its northern shore. 



The minerals of the granitic rocks are schorl, garnet, amethyst, 

 rock-crystal, epidote, purple fluor spar, chlorite and green earth, 

 calcareous spar, specular iron, barytes, iron pyrites, and copper 



