PETKOCiKAPHICAL CHAKACTEE OF AJIBIK QUARTZITE. 293 



the Negauuee formation is jasper, the change takes phice by the dying out 

 of fragniental quartz and the appearance of hematite, magnetite, and finely 

 crystalhne quartz; where the overlying formation is griinerite-magnetite- 

 schist, the minerals wliich appear are magnetite, griinerite, and often garnet. 

 Occasionally the intermediate i)liase is a ferruginous slate, like the transi- 

 tion horizon of the Siamo and Negaunee formations. In the southwest 

 part of the area — that is, in the Republic and Southwest tongues — the folding" 

 and consequent mashing were so severe as to transform the Ajibik quartzite 

 formation into a completely crystalline schist. Even the pure quartzitic 

 phases now show no distinctly fragniental grains of quartz, l)ut consist 

 mainh' of coarsely crystalline interlocking quartz, in wliich are small 

 amounts of griinerite, garnet, chlorite, l^iotite, and muscovite. In some cases 

 the chlorite developed from the griinerite and garnet. While the quartz 

 grains show undulatory extinction and fracturing, the dynamic effects are 

 not so great as would be expected, and the appearance of the section 

 strongly suggests that the rock was largely recrystallized. Where the 

 sandstones were less pure there developed from tliem coarse-grained, 

 typical biotite-schists, muscovite-schists, and chlorite-schists, often garnet- 

 iferous. In these rocks we have a somewhat uniformh' granular quartzose 

 background, through which developed the biotite, muscovite, and chlorite. 

 There is a tendency for the micaceous minerals to be concentrated into lay- 

 ers, the less micaceous zones perhaps correspcmding to the original, more 

 quartzitic laminae. Occasionally the quartzose bands have a distinct oval 

 or lenticular character, as if each represented a greatly mashed and granu- 

 lated quartz pebble. The mica bends around these areas, joining at their 

 ends, thus presenting a mesh-like appearance, but differing from a mesh in 

 that the leaflets of mica do not intersect. In some of the slides the biotite, 

 muscovite, and chlorite are all in large blades with a parallel arrangement- 

 In other cases the sericite is in part in innumerable minute leaflets. In 

 certain of the chlorite-schists the chlorite leaflets are minutely puckered by 

 the folding in some places, and in other places the stress has been relieved 

 by minute faulting- diagonal to the schistosity. Thus we have a cleavage 

 in one direction parallel to the schistosity and a fissility diagonal to this. 

 By a dying out of the micaceous element and the appearance of griinerite 



