326 THE MAEQUETTE IKON-BEAEING DISTEICT. 



autoclastic, having been rent from the slate in the tbkling. In these phases 

 the rock approaches a breccia, but the breccias occur only adjacent to the 

 contact plane between the slate and graywacke. 



Area east of Teal Lake — East of Teal Lake, in sees. 31, 32, 33, and 34 (Atlas 

 Sheets XXX and XXXIII), there are again very large exposures of slate 

 and graywacke, but these need not be especially described, as in all par- 

 ticulars they are similar to the central mass of slate and graywacke of the 

 Siamo Hills. 



In the southern part of sec. 35 (Atlas Sheet XXXIII), about three- 

 fourths of a mile southeast of Eagle Mills, are numerous exposures of slate 

 and graywacke, which are in most respects similar to those of the Siamo 

 Hills. At one place the slates are sharply folded into a minor anticline, 

 which plunges to the west at an angle of 15°. At the middle of the ledge 

 is a band of reibungsbreccia, about 4 or 5 feet broad, composed mainly 

 of cemented slate fragments, but containing areas of quartz and ferruginous 

 chert. These latter are apparently secondarj-. Iron oxide is one of the 

 abundant cementing materials, and many of the slate fragments are heavily 

 imjiregnated with this material. 



Eastern area. — Tlic ucxt important cxposures are at the east end of the 

 great westward-plunging syncline in sec. 31, T. 48 N., R. 25 W., in sec. 

 1, T. 47 N., R. 26 W., and in sec. 6, T. 47 N., R. 25 W. (Atlas Sheets 

 XXXVI and XXXVII). Here, at the bottom of the formation, especially 

 in sees. 1 and G, the slate and graywackes are very ferruginous, and the}' 

 contain considerable belts of material which approaches very closeh' to a 

 ferruginous chert. In some cases, for narrow zones, this chert is in all 

 respects similar to the ferruginous chert of the Negaunee formation. As 

 in the previous localities, the bands of pure chert or ferruginous chert are 

 minutely interlaminated with belts which are largely fragmental. The 

 unusual abundance and persistence of the ferruginous slates at this locality- 

 have alread}^ been explained as due to the fact that they are at the Ijottom 

 of a westward-plunging syncline and rest upon a quartzite; that is, thev 

 are at a ]ilace where there has been extensive readjustment between the 

 two formations, and also where percolating waters would be converged. 

 In passing to higher horizons these ferruginous slates grade into the 

 ordinary slates and graywackes of the formation. 



