286 THE MARQUETTE IllOX-BEAliING DISTRICT. 



fragmental rock occupies the valleys and the j^rauite the elevations. These 

 valleys open out to the west and close to the east, the granite thus forming 

 amphitheaters about the quartzite. This is due to the fact that the south- 

 dipping isoclinal folds have a steep westward pitch. As a result of this 

 complex folding, an island of granite appears surrounded by the Ajibik 

 quartzite in sec. 30, and another island of granite occurs within the 8iamo 

 slate above tlie quartzite in sec. 31. Consequently, the north-south subor- 

 dinate rolls are of sufficient size to form at the anticlines islands of granite 

 within the sedimentary rocks. 



Running southeast between the Archean area of sec. 23 and the 

 Archean area of sec. 22, T. 47 N., R. 26 W. (Atlas Sheet XXXV), is a 

 northwestward-plunging syncline of the quartzite, making an arm project- 

 ing from the main area. This belt may extend farther than map]>ed and 

 connect with the belt to the south. 



With the exception of a single swing about the Archean .anticline in 

 sec. 30, T. 47 N., R. 2G W. (Atlas Sheet XXXII), the southern belt of 

 Cj^uartzite has a general northward dip away from the Archean and under 

 the iron formation. The exposures in sees. 27 and 28, T. 47 N., R 27 W. 

 (Atlas Sheets XXVI and XXIX), when cursorily examined, appear to have 

 a uniform northward dip, Ijut when examined closely the upper members 

 of the formation, which are here slates, are found to be pressed into a sharp 

 set of overfolds with northern dips. These folds are not horizontal, but 

 plunge steeply (PI. XXXV, fig. 1). Acompanying these minor rolls are, 

 doubtless, major rolls. This is indicated by the fact that interstratified with 

 the .slate are apparently three belts of amygdaloid; but as the rocks of these 

 belts are all exactly alike, and as amygdaloid is absent elsewhere in the for- 

 mation, it is more than probable that this is the same lava flow, reduplicated 

 by the northward-dipping overfolds. In the Republic tongue and in the 

 tongue to the west the Ajibik quartzite is in a closely compressed syncline. 



PETROGRAPHICAL CHARACTER. 



Macroscopicai. — Tlic Ajibik quartzite has two main areas — a western one, 

 in which it rests directly upon the Archean, and an eastern one, in which 

 it is underlain by the Wewe slate (Atlas Sheet IV). This difference is fully 



