GEOLOGIC HISTORY. 439 



Archeaii acid intrusives, the granites of Trout, Basswood, Burntside, and 

 Saganaga lakes and connecting areas. The main masses of these granites 

 are vast batholiths, froni which there are innumerable offshoots. These 

 intrusions cut the Ely greenstone most intricately, but all of the granites — 

 for example, the granite of Saganaga Lake — have not been found in such 

 relations to the Soudan formation. It is believed, however, that this age 

 relationship exists and that it is only owing to absence of the Soudan 

 formation in good development near the g'ranite of Saganaga Lake that 

 dikes of the granite have not been found in it. This may, therefoi'e, 

 antedate the Soudan formation and really be of early Archean age, although 

 if this were the case it is thought probable that the disturbances attending 

 its intrusion would have raised the Ely greenstone above the sea at various 

 places in the Vermilion district, and thus would have resulted in the 

 formation of thick mechanical sediments below the Soudan formation. It is 

 therefore thought to be more probable that the granite is contemporaneous 

 with the others, and is later than the Soudan formation. 



The Ely greenstone, the mechanical sediments preceding' the Soudan 

 jaspers, the Soudan jaspers themselves, and the intrusive rocks following 

 the Soudan constitute the Archean rocks. 



Probably contemporaneous with these great intrusions of igneous rock 

 were the powerful orogenic movements following Archean time. These 

 movements probably raised the entire Vermilion district above the sea. 

 They certainly folded the rocks into mountain masses of enormous extent 

 and exceeding complexity, so that the Vermilion district, which up to the 

 present time had been a sea area, was now a land area. No sooner was the 

 district raised above the sea than the epigene forces attacked the land and 

 the process of degradation began. This was very long continued, and land 

 and sea erosion cut deeply into the previous formation. For large parts of 

 the district it removed the entire Soudan formation ; in places it cut away 

 the Ely greenstone, exposing the underlying intrusive granite. 



Attending the granitic intrusions, the orogenic movements, and the 

 erosion were the metamorphic changes in the rocks. Dependent upon the 

 granite intrusion r was the deep-seated alteration of the Ely greenstone, 

 resulting in the production of amphibole- schists and amphibole-gneisses. 

 Adjacent to the granite masses the more superficial agents of metamorphism, 

 and especially those of weathering, greatly changed the carbonate of the 



