160 THE VERMILION IRON-BEARING DISTRICT. 



under". The rocks that were first inckided under this term can be shown 

 to be to a lai'ge extent formed by metamorphism from the Ely green- 

 stones as above described. The remaining portion has been formed by 

 metamorjjhism of sediments of Lower Huronian age, as described in 

 Chapter IV. Should Lawson's name Coutchiching be applied to the 

 amphibole- and mica-schists lying between the granites of the district and 

 the rocks that have been intruded by the granite, we should have included 

 under this term two series of rocks which, though possessing the same 

 schistose characters, are demonstrably of different age, both as regards 

 their initial period of formation and their period of metamorphism. 

 The use of the name Coutchiching is not warranted in connection with the 

 rocks of the Vermilion district of Minnesota, and Lawson's insistence ^ on the 

 presence of a series of rocks in this district comparable to his supposed 

 Coutchiching series is explaiiaable only as due to his imfamiliarity with the 

 district. 



The character of the metamorphism involved in the change of the 

 greenstone of the Archean from a massive rock to a predominant!}' schistose 

 rock of a different mineralogic character migdit be made a matter of question 

 by some who wish to classify metamorphic rocks into those produced by 

 contact action and those produced by regional metamorphism. The agents, 

 however, in both cases are the same. They are heat, jJressure, and water, 

 and whether these agents owe their activity to the intrusion of an igneous 

 mass of rock or to orogenic movement is merely a matter of detail. In 

 the present instance the field relations of the greenstones to the metamor- 

 phic rocks and the granite show that the metamorphism of the greenstones 

 accomj^anied the intrusion of the granite. Hence, as this was the prime 

 agent in their production, they have been classed under contact metamor- 

 phic pi'oducts. Yet while these schistose rocks may well have been pro- 

 duced by the intrusion of igneous masses that caused recrystallization of 

 their already partially altered original minerals, nevertheless essentially the 

 same chemical constituents are present in them now as were present in 

 them formerly. The rocks have merely been recrystallized under pressure. 



oGeol. and Nat. Hist. Survey of Minnesota, Final Rept., Vol. IV, 1899, pp. 14 and 15. 

 6Geol. and Nat. Hist. Survey of Minnesota, by N. H. Winchell; Final Rept., Vol. IV. Review 

 by A. C. Lawson, Am. Jour. Sci., 4th series, Vol. IX, 1900, p. 151. 



