Copper Mlniii'i in Miimesofd ILiU. lur^ 



piivju-r- uiidistingnishable froii these, are se^n in the Cujirifcrons^ 

 serie.'i ol Lake Superior, there associated with dark basic igneouj- 

 rocks, the nature of which is not disputed. 



If these fossils be taken as guides — and they are the only ones 

 that have ever been found in these rocks — the age of the red 

 (juartzites of Minnesota seems to be the same as the so-called lower 

 Potsdam, or St. Johns' group, and they at the same time indicate 

 that the Cupriferous series of Lake Superior belongs to the same 

 age. 



( )ctober 0, 1 SSr). 



\ UKIEF HISTOUY OF COPPER .MINTING IX -MfXXESOTl. — C. H '. HalL 



1. 



The Cri'HLFEFioi s KocKs. The copper-bearing rocks in Min- 

 nesota are those comprised in the so-called Keweenaw formation or 

 group of rocks. There are only one or two localities at present 

 known where attempts at copper mining have been made, which are 

 not referred to that group of rocks, and these attempts will be 

 mentioned farther on. 



The Keweenawan rocks, frequently called the Cupriferous se- 

 ries, enter the state in its northeastern corner, a little to the west 

 of Grand Portage bay, Lake Superior, and are continuous along- 

 the north shore of the lake to and beyond Duluth. Passing away 

 from the lake shore, which by the way forms the southern and 

 southeastern boundary of this northwestern Cupriferous, and we 

 also see the noi'thern and northwestern border passing from Grand 

 Portage in an aluiost due west course for fifty miles, and then 

 (piite likely in a very regular curve to the southwest, closing in on 

 the soutlieastern boundary just mentioned, to the west of Du- 

 luth, doubtless not far from Fond du Lac* 



Another area of the Keweenawan in Minnesota lies along the 

 eastern border of the state, entering it from Wisconsin, and ex- 

 posed along the Kettle, Snake and St. Croix rivers, and in the vicin- 

 ity of Taylors Falls southward from these first two named streams. 



*This portion of the state, owing to the ditHculty of access on account of 

 almost impenetra1)!e forests, has not yet been explored. 



