243 



upon the edges of the laminae of the green azoic slates. The quartz 

 beds of the Montreal and Bad Rivers are far below the Potsdam, and 

 are schistose. Iron enters into the composition of the silicious forma- 

 tion No. 4, while the quartzite of the Brule is pure silex. 



For the purpose of more fully exhibiting the difference between the 

 azoic slates on the waters of the Menominee and the systems repre- 

 sented above, I insert some analyses made in 1858. 



In both systems the oxide of iron is an universal constituent, but 

 with one exception in the azoic rocks it is in the form of protoxide. 

 Tbis exception Is in a surface specimen, and may be the result of 

 higher oxidation by exposure. Silex Is the principal substance in the 

 slates of both systems as well as In the compact portions. On the 

 Menominee, It ranges from 52| to 92 per cent. ; on the Montreal, 

 56 to 93. As the silex decreases, the iron increases, these being the 

 principal ingredients. The azoic slates are much more aluminous 

 than those of the Bad River region. Both carry the elements of 

 hornblende In limited quantities, and might for that reason be called 

 hornblende rocks, but this term conveys no hint of their origin or 

 chronology, and is, therefore, without any other than a mineraloglcal 

 significance. 



The Menominee system Is both laminated and lamellar, with occa- 

 sionally a silky lustre, and a magnesian feel and aspect. The slates of 

 the Montreal are laminated, but rough to the touch, and have a silicious 

 aspect. In this region the laminae conform to the uplift In strike, and 

 In their dip conform to the stratification. It is different on the waters; 

 of the Menominee. There the ridges or local uphfts and the bearing 

 of the slates are at various angles, and the dip of the laminated por- 

 tions is various and Irregular. The uplifts have the character of cor- 

 rugations, resulting from lateral pressure, and if, as It seems Is now 

 pretty well established, lateral pressure gives rise to lamellae and flat- 

 tened spangles, it is fair to presume such to have been the origin 

 of the uplifts. On the shore of Lake Superior the whole country has 

 been moved, together and with great regularity. The entire series 

 has either been lifted in mass by one movement or by successive up- 

 lifts that were parallel in direction, and about equal in amount. This 

 applies to the Ontonagon, Portage Lake and Point Keweenaw por- 

 tion as well as that of the Montreal and Bad Rivers. If the Potsdam 

 should hereafter be discovered in the swamp region south of the 

 Penokle Mountains, It would throw light upon the age of these rocks. 

 Formation 2 of the above section In Its upper portion, is contempora- 

 neous with the Potsdam. The azoic slates of the southerly water- 

 shed are more ancient. Are the black slates of formations 3 and 4 

 contemporaneous with the green slates of the Menominee ? Are 

 either or both of them metamorphic ? Can we assign them a position, 

 in the Canadian system ? 



