264 THE VERMILION IRON-BEARING DISTRICT. 



a uumber of granite and granite-porphyry dikes which, since they are of 

 practically the same petrographic character as the large mass and show the 

 same relationship to the adjacent rocks that this mass shows to similar rocks 

 adjacent to it, are presumed to be offshoots from this large mass, or at least 

 to have come from the same deep-seated mass of magma from which it 

 came. 



JExposures. — The exposures are fairly numerous where the large mass 

 of granite occurs, but over a portion of the area underlain by this there 

 is a large amount of fallen timber, which helps to conceal the rocks and 

 renders the area exceedingly difficult of access. 



PETROGRAPHIC CHARACTERS. 



On fresh fracture this granite is dark gray in color, though at times 

 it has a reddish tinge. On weathered surfaces it usually becomes grayish. 

 It is of medium grain, and is sometimes developed as a granite-porphyry 

 in which the feldspar and quartz phenocrysts can be easily seen lying in 

 the dark-gray fine-grained groundmass. The granite-porphyry facies bears 

 a very strong resemblance to the porphyries of Vermilion Lake, as well as 

 to the porphyritic facies of the granite of Saganaga Lake. These rocks 

 show only the ordinary characters of granites, and a brief description of 

 them will suffice. The constituents are the usual ones — quartz, orthoclase, 

 plagioclase feldspar so altered that no individuals suitable for close deter- 

 minations of character could be foimd, a little brown mica, and magnetite. 

 In the porphyry the feldspar is the most prominent phenocryst, occurring 

 in both larger and more numerous individuals than the rounded quartz 

 phenocrysts associated with it. The feldspar shows fairly good crystal con- 

 tours, though sometimes the crystals are rounded. In the porphyries the 

 groundmass in which the phenocrysts lie is a fine-grained aggregate of feld- 

 spar, quartz, calcite, epidote, zoisite, rutile, chlorite, biotite, sericite, and 

 pyrite, all in small individuals. Most of these are of secondary origin, yet 

 some of the quartz and feldspar, and possibly some of the biotite may be 

 primary, although not recognizable as such. 



RELATIONS TO ADJACENT FORMATIONS. 



In immediate proximity to the main mass of this granite are the Ely 



greenstone of the Archean and sedimentaries of Lower Huronian age only. 



Eelation to Archean. — In the vicinity of the granite the Archean green- 



