INTERESTING LOCxVLITlES OF AJIBIK QUARTZITE. 313 



Republic and Southwest tongues. TllO ratliei' llUUSUal pllHSeS of tllC A)il)ik 



quartzite occurring- in tlie southwestern part of the area, along the Republic 

 and Southwest tongues, are described in the general description (pp. 287, 

 289, 293) and in Chapter VI, upon the Republic trough. Near Republic 

 occurs one of the best basal conglomerates in contact with the Archean in 

 the district. Also the coarse quartzite just above this conglomerate is wortliy 

 of mention. It is gray, massive, crystalline-looking, and appears in hand 

 specimen to contain griinerite. When examined in thin section it is found 

 to be composed mainly of coarsely crystalline, interlocking' quartz. The 

 particles show undulatory extinction, but no granulation. Some of them 

 have a roundish appearance, but no distinct cores are observable. Between 

 these grains and included in some of them are clusters of griinerite, garnet, 

 chlorite, and magnetite crystals. Some of the garnet crystals are so large 

 as to inclose a number of grains of quartz. The griinerite in radiating 

 blades penetrates the quartz grains in all directions. Appai-ently the clilo- 

 rite is a secondary product, which has developed in part from the garnet 

 and in part from the griinerite. The relations of these minerals, and par- 

 ticularly the griinerite, to the quartz strongly suggest that the rock has 

 lai'gely recrystallized. 



Sees. 29 and 30, T. 48 N., R. 27 w. — More tliau a mile north of the main northern 

 belt of the Ajibik quartzite is an isolated quartzite ridge about a half mile 

 long, bounded on the north by peridotite and on tlie south by the Kitelii 

 schist. The rock strikes northeast-southwest and dips to the southeast 

 at an angle of 25°. This ridge in places is conglomeratic. Botli the 

 quartzite and quartzite-conglomerate are similar macroscopically and 

 microscopically to the rocks west of Teal Lake, and are placed with the 

 Ajibik formation on lithological grounds. The exceptional position of the 

 area is probably due either to overfolding or to faulting. 



SECTION v.— THE SIAMO SLATE. 



The Siamo slate is so called because abundant exposures occur between 

 the Ajibik quartzite and the Negaunee formation on the Siamo Hills, just 

 south of the west part of Teal Lake (Atlas Sheet XXVII), and because the 

 most typical rock of the formation is a slate, although locally it passes into 

 a graywacke, or into a rock approaching a quartzite. 



