442 THE VERMILION IRON-BEARING DISTRICT. 



Lower Huroniaii series became transformed to slates. The sediments 

 near the Giants Range and Snowbank granites were transformed to 

 schists and gneisses. From the iron carbonates of the Agawa forma- 

 tion ferruginous slates and ferruginous cherts were formed, although 

 this process by no means neared completion. It appears that following 

 Lower Huronian time, as in inter -Archean-Htironian time, igneous intru- 

 sions, orogenic movements, erosion, and metamorphism were largely 

 contemporary, or at least overlapping, and that they were largely the result 

 of the same causes; that is to say, there was a time of the readjustment of 

 the earth's crust where before there had been a time of sedimentation. 

 These earth movements resulted in folding and in vulcanism, and conse- 

 quent upon this were erosion, and dependent upon all this was metamor- 

 phism, both deep seated and surface. 



Following the unconformity above Lower Huronian time the Vermilion 

 district was again depressed and the Upper Huronian (Animikie) series 

 was deposited above the upturned rocks of Archean and Lower Huronian 

 age. Only a small area in the eastei'n part of the Vermilion district is 

 covered by the Upper Huronian sediments, and we have little data in this 

 district for determining the history of this time. The basal formation of 

 the Upper Huronian in the Vermilion distiict is the Gunflint formation, 

 whose character is such as to indicate that it was deposited in relatively 

 deep water or a protected area of the sea. Southwest of the Vermilion 

 district in the Mesabi district a conglomerate occurs at the base of the 

 Upper Huronian below the Biwabik formation which is correlative with the 

 Gunflint formation of the Vermilion district. We thus conclude that while 

 the Upper Huronian sea advanced, conglomerates were formed to the west, 

 but that in the Vermilion district the conditions were not favorable for the 

 production of this kind of rock. Over the Gunflint formation was then 

 deposited possibly 10,000 and more feet of Rove slates and graywackes. 

 These rocks presumably covered the entire Vermilion district and probably 

 extended far northward beyond the district, but all evidence of such 

 extension has been removed by erosion. 



Following the period of deposition of the Upper Huronian there came 

 an upheaval succeeded by a long period of extensive erosion. This erosion 

 removed great thicknesses of the overlying Upper Huronian rocks and in 

 some cases the entire thickness, and having cut through the Upper 



