696 R. C. ALLEN AND L. P. BARRETT 



top layer of heavily bedded quartzite 50 feet thick. The basal 

 horizon is a conglomerate from i to 10 feet thick. East of this 

 township the massive upper quartzite is generally persistent, but 

 the lower horizons grade irregularly into micaceous and hornblendic 

 schists toward the contact with the intrusive Presque Isle granite 

 in which, so far as we have determined, the base of the Palms is 

 involved. The former correlation of the metamorphosed lower 

 horizons of the Palms formation with the Keewatin is based on 

 early field studies and has unfortunately been carried without 

 revision into later work. 



The Ironwood formation. — The iron-bearing member overlies 

 abruptly but conformably the heavy upper quartzite of the Palms 

 formation, A thin basal layer is in some places finely detrital. 



The Tyler slate, which overlies the Ironwood formation west of 

 Sunday Lake, is abruptly cut out at the great Wakefield over- 

 thrust and does not appear on the east end of the range. From 

 Wakefield east to section 16, T. 47 N., R. 44 W., the Ironwood 

 formation is overlain by the Keweenawan series, and beyond this 

 locality with the Copps group, by which it is trunkated and cut out 

 in the N.W. ^ of section 22, T. 47 N., R. 43 W. 



Except where altered by intrusives, to which further reference 

 will be made, the Ironwood formation is made up of ferruginous 

 chert and slate, iron ore, cherty iron carbonate, and interbedded 

 black and gray slate. In T. 47 N., R. 44 W., it is split, 200 feet 

 above its base, by a great graywacke-slate member about 500 feet 

 thick, which is identical in character with the slate forming the 

 so-called "secondary foot wall" of the Brotherton, Sunday Lake, 

 and Castile mines at Wakefield and is apparently at the same 

 stratigraphic horizon. The inclusion of this slate member for a 

 distance of not less than six miles east of Sunday Lake gives the 

 Ironwood formation a maximum thickness of 1,300 to 1,400 feet.^ 



' Further observation west of Sunday Lake in both Michigan and Wisconsin 

 indicates that the base of the Ironwood is conglomeratic throughout almost its 

 entire extent. An intra-formational conglomerate and quartzite, first observed by 

 geologists of the Oliver Iron Mining Company, occurs in the Pabst mine at Ironwood, 

 a little less than 500 feet vertically above the Palms quartzite. A similar conglom- 

 erate has been observed at about the same horizon by W. O. Hotchkiss, state geolo- 

 gist of Wisconsin, in some of the mines on the Wisconsin end of the range. So far 



