296 THE VEKMILION IRON-BEARINGS DISTRICT. 



of Soudan. Being near tlie base of the formation, the slates here contain 

 small amounts of conglomerate and graywacke. 



More interesting than these common phases are the slates which occur 

 in the southern portion of the area, and which have been subjected to 

 metamorphic action to such an extent that they have been transformed 

 into mica- and amphibole-schists. Excellent opportunities for the study 

 of these metamorphosed sediments are afforded by exposures near Pike 

 River. The best places for such study, however, are in the cuts along 

 the Duluth and Iron Range Railroad between Embarrass and Tower, 

 and especially in those between East Two Rivers and milepost 92. On 

 these exposures the sedimentary character of the rocks is clearly shown by 

 sedimentary banding, false bedding, the presence of large bluish fragmental 

 quartz eyes which stud some of the beds, and in the vicinity of milepost 

 92 by the fact that exactly similar sediments are there interbedded with the 

 Ogishke conglomerate, into which the slates grade. Some of the sediments 

 have been so extremely metamorphosed, however, that but for their field 

 relations it would be impossible to recognize them with absolute confidence 

 as derived from sediments. It should be noted that the sediments at these 

 exposures are cut by granite dikes, and that the change in the sediments 

 from normal slates to mica- and amphibole-schists coincides with the 

 ap23earance of the dikes. The metamorphism of the rocks increases south- 

 ward along the railroad, in which direction the dikes become more numerous 

 as one approaches the large granite areas on the Giants range, from which 

 the dikes are presumed to be offshoots. Winchell," who has noted the 

 metamorphism of the graywacke and the slates to mica-schists south and 

 west of Tower, attributes this metamorphism to the Griants Range granite, 

 but classes these sediments in his Keewatin division. The sedimentary 

 banding, which still shows very plainly, even at places where the rocks 

 have been metamorphosed to mica-schists, is evidently indicative of a differ- 

 ence in original mineralogic, and hence chemical, composition. In spite of 

 the metamorphism these original differences have continued to exist, and 

 hence the sedimentary banding is retained. 



«Geol. and Nat. Hist. Survey of Minnesota, Final Kept., Vol. IV, 1899, p. 254, and PI. LXVII 

 and LXXXVI. 



