36 THE PENOKEE IRON-BEARING SERIES. 



on Black river. If \vc suppose this iron to liavi- beuu mostly ])recipitate(I as a car- 

 bonate, then we niiglit expect it would he more generally dittused through the rocks 

 of certain eixichs than those materials derived from the cT'osion of adjacent coasts. 



There is evidently hut one hyi)othesis which will reconcile these facts, whi(;li is, 

 that the granitoid formation in questiou is of the Ilurouian period, and probably the 

 youngest member, which series are here nonconfornmhly overlaid by the Copper-bear- 

 ing rocks. I coiu'.eive that this view is supported by the observations ia the Menom- 

 inee region above recorded, and suppose this Peiiokie granitoid fornuition may be the 

 equivalent of granitic bed XX of the Huronian series as developed in that region. 

 On this hypothesis it is possible that the valley dividing the Pcnokie range proper 

 from the granitoid licit may be underlaid by a soft slate, the equivalent of the micace- 

 ous schist, bed XIX. (Pp. 207-:iOS.) 



We are not in accord with Brt)oks as to the view.s liere expressed. We 

 can not aUow that tlie granite of the Menominee is Huronian at all, inasmuch 

 as we think it plainly belongs to the older or gneissic series; nor can we 

 agree with the statements of Brooks as to the granites north of the Penokee 

 range. As to the Menominee granite, we do not now need to present any 

 arguments in defense of our belief As to the Penokee granites, we may 

 merely repeat the substance of what one of us has already said in several 

 ]nd)lications, viz, (1) that the belt of "granite, syenite, and hornblende rocks" 

 outlined by Whittlesey really has no existence; (2) that the granites occur- 

 ring in the vicinity of Bad river, and north of the Penokee range, lie in no 

 continuous belt, but are veins and masses intersecting the gabbros at the 

 base of the Copper-bearing series, and the micaceous quartzites at the sum- 

 mit of the Iron-bearing series; (3) that these granites are manifestly but a 

 phase of the intrusive reddish, granitic porphyries which mark this liorizon 

 both north and south of lake Superior; (4) that being so manifestly intru- 

 sive, there is nothing like bedding about these granites; (5) that the 

 "wedging out" to the eastward, which Brooks speaks of as characteristic of 

 his supposed granite belt, is really a characteristic of a great gabbro area 

 here occurring, and not of a granite area; (6) that this gabbro mass does 

 traverse the Huronian beds in a most noticeable nianner, in places even 

 ctittiug them out at the surface altogether; and (7) that at the southern 

 margin of this gabbro, or along its contact with the Iron-bearing slates, it 

 is plainly involved with and intrusive in those slates, as the granite is in 

 both gabbro and slates. 



