THE KErUBLlC TJtOL'Gn. 529 



In tliiii sections the various phases of this member are seen to be 

 emineutl}- (TystaHine. The vitreous varieties consis-t mainly of interlocking 

 areas of (quartz, within and between which are plates of light and dark 

 mica and, less often, of chlorite. Magnetite and garnet are more rarely seen, 

 and nearly complete the list of contained minerals. In the more schistose 

 varieties the mica is more abundant, and occurs in long plates which have 

 a parallel i)hysical orientation. In none of the many slides that have been 

 studied do any feldspar grains appear, nor has a trace been detected of 

 the outlines of original rolled grains. These have been obliterated in the 

 course of the profound changes tlu-ough which the rock has passed since its 

 deposition, and the feldspar of the original granitic ddbris is now doubtless 

 represented by the light micas and secondary quartz. 



In many cases the larger structures of the original rock have survived. 

 Faint color banding and alternations in texture and composition parallel to 

 the original deposition planes are often seen, and in one locality a beautiful 

 false bedding can be distinctly recognized. 



THE NEGAUNEE FORMATION. 



The iron-bearing formation is not generally exposed in the Republic 

 area, except at the extreme southeastern end of the syncline, where mag- 

 nificent outcrops extend from the old Kloman mine in the SW. ^ sec. 6, 

 T. 46 N., R. 29 W., almost entirely around the horseshoe, through a large 

 part of sec. 7 (Atlas Sheet XI). Within this area of nearly a square mile, 

 which comprises Republic ]\Iountain, there are small portions only of the 

 interval between the Ajibik quartzite beneath and the Goodi-ich quartzite 

 above that are not somewhere represented by outcrops. The rock of the 

 iron formation has maiiy phases, but consists essentially of finely crystalline 

 quartz, a pale-green radiating am^hibole which has been determined to be 

 griinerite, and the iron oxides. Within this area the iron-bearing member 

 has been divided by intrusive masses of diorite mainly parallel with the 

 stratification planes, and near the contacts with these it frequently carries 

 large amounts of red garnet. The three chief constituents of this rock 

 are not always present. Two, or even one, may predominate to the par- 

 tial or nearly entire exclusion of the rest. So the rock is found in certain 



MON xxviii 34 



