126 THE VERMILION IRON-BEARING DISTRICT. 



character. It is the object of the paper to give in outline an account of the 

 phenomena seen on these rocks. An outline of the local geology is given. 

 The rocks range from Archean, through the Lower Huronian (or Keewatin) 

 and Upper Huronian (or Animikie), to the Keweenawan. The Animikie of 

 this area is subdivided from the base up into an iron-bearing member, a black- 

 slate member, and a graywacke-slate member. The Keweenawan is rep- 

 resented by the gabbro, which has metamorphosed the Gunflint iron-bearing 

 beds, and the graywacke and black slate members of Upper Huronian age. 



The metamorphism of the black-slate and graywacke-slate members is 

 relatively insignificant, and consists of the more or less complete recrystal- 

 lization of the rocks, which are now made up of granitic aggregates of 

 quartz, feldspar, biotite, muscovite, and occasionally cordierite. 



The most complete recrystallization and the most interesting phe- 

 nomena are shown in the metamorphosed iron-bearing beds. 



The original rock is regarded as a glauconitic greensand in which there 

 is more or less iron carbonate. This has been altered to a quartz-magnetite- 

 amphibole-slate, the amphibole being in the form of actinolite, griinerite, 

 cummingtonite, and hornblende. This has been profoundly changed by 

 the gabbro, and is now a coarse-grained aggregate of quartz, magnetite, 

 olivine (which is frequently fayalite), hypersthene, augite, hornblende, and 

 occasionally griinerite and cummingtonite. These rocks, like the rocks 

 from which they are derived, are beautifully banded, the separate bands 

 being composed of quartz, or of magnetite, or of silicates, or of a mixture of 

 any two or more of the minerals. 



Satisfactory reasons are given showing that these rocks are a part 

 of the Animikie (Upper Huronian) and not a border facies of the gabbro, as 

 has been thought to be the case by some. 



The gabbro is in contact with very diverse strata of the Keewatin, and 

 the resulting metamorphic rocks differ greatly. Biotite and hypersthene 

 are prominent in these contact rocks. 



The Archean consists of granites and greenstones. The granites have 

 not been affected by the gabbro in a noticeable way at least. The green- 

 stones have been affected in such a way as to reproduce the minerals 

 of the original rocks from which the greenstones were derived. Com- 

 monly a granular product is found which is quite similar in appearance to 

 a gabbro. 



