446 THE PENOKEE IRON-BEARING SERIES. 



was induced before the deposition of" the slates upon them, for it is impossible 

 that rocks could be so profoundly altered and yet the slates of much the 

 same mineral composition in contact with them be unaffected. If they are 

 eruptives the time required for their change frem fresh rocks to extremely 

 foliated, altered ones must have been very great. If tliey are fragment al 

 their metamorphism to completely crystalline rocks must liave taken as 

 great a time. So tluit on either hypothesis they are immensely older tlian 

 the Quartz-slate whicli overlies them, for the rocks of this formation have 

 neither a schistose structure nor a crystalline character. 



West of Potato river, T. 45 N., R. 1 E., Wisconsin, no actual contacts 

 between the Southern Complex and the Penokee rocks are known. At 

 Penokee gap the green schists are found very close to the overlying 

 Cherty limestone. The latter, as usual, dips to the north and strikes 

 appi'oximately east and west. The green schists to the south also have a 

 nearly east and west strike, but their dip is southward. This being the 

 case, the fibers of the gneisses, unless there is here an exceedingly sharp 

 fold of which there is no evidence, abut sharply against the overlying beds, 

 and thus there is here strong, although not conclusive evidence, of uncon- 

 foi'mity. 



At Potato river, fortunatelv, the underhing schists and the overlying 

 Quartz-slate are found in direct contact with each other. Here the Quartz- 

 slate, rising in low cliffs, is exposed throughout its entire thickness upon 

 the east side of the river (Fig. 5). For some distance the green schists 

 to the south are also exposed, and tlie actual contact between the two 

 is seen on the bank at intervals for a vertical distance of 75 feet, while 

 the contact is continuous for the lower 25 or 30 feet. The slates are all of 

 the normal character, dipping to the northward at an angle of about 70" 

 The green schist has no proper dip and strike, and yet it has a strongly 

 schistose character. Its fibers abut almost perpendicularly against the 

 layers of tlie slate, as shown by Fig. (!, rej)roduced from a carefully made 

 drawing on the gromid. So sharj) is the junction line between the two 

 rocks that it can usually l)e located to tlie fraction of an incli, and hand 

 specimens were obtained in part from l)oth formation.s. Tlie .surface of tlie 

 green schist at the beginning of the formation of the conglomex'ate is seen 



