378 THE CRYSTAL FALLS IRON-BEAHING DISTKICT. 



high ang-les. In attempting to correlate these various beds with those of the 

 south iron belt, Brooks experiences difficulty with the uppermost formation 

 of granite-gneiss and schist. He says: 



The gueiss and granite outcrop above described may be almost regarded as a 

 typical Lauren tian rock in its appearance. If future investigations prove them to be 

 Laurentlan, a very troublesome structural problem would be presented here, as we 

 would have Laurentian rocks conformably overlying beds unmistakably Huronian 



(p. 175). 



As will be seen, this objection which Brooks had anticipated Avas raised 

 by later workers in the area and was explained by Eominger. 



The main points of Brooks's conclusions may briefly be summarized : 



(1) The iron-bearing rocks of the Menominee region occur in two 

 approximately parallel east-and-west belts (the north belt being the Felcli 

 Mountain range and the south belt the Menominee range), separated by a 

 broad granite area which narrows toward the west by the c<:)nvergence of 

 the iron belts. The north-and-south belts were not traced into each other, 

 but their probable connection was inferred from their bending toward each 

 other and from the occurrence of rocks of the iron-bearing series west of 

 the granite area. The equivalence in age of the two belts was inferred from 

 the lithological and stratigraphical similarity exhibited by the great quartz- 

 ite and marble formations, by the probable continuity above referred to, 

 and by the similar relations of these formations to the basement granites. 



(2) The iron-bearing formations of the Felch Mountain range were 

 believed to occur at two horizons. That of Felch Mountain itself in sec. 

 32, T. 42 N., R. 28 W., was held to be a ferruginous phase of the lower 

 quartzite. On the other hand, the exposures of sec. 31, T. 42 N., R. 29 W., 

 were regarded as belonging to a horizon above the lower marble, and as 

 the close equivalent of unimportant lean ores of the Menominee range. 



(8) In geological structure the Felch Mountain area was held to be a 

 northward-dipping monocline. 



(4) As a consequence of this conception of the structure. Major Brooks 

 supposed that there were two marble formations. 



1880. 



Brooks, T. B. The geology of the Menominee iron region, east of the center of 

 Eauge 17 E., Oconto County, Wisconsin. Geology of Wisconsin, 1873-1879, Vol. Ill, 

 published in 1880, Part YIl, pages 429-599. 



