ANALYTICAL ABSTRACTS. 45 I 



the iron is believed to have been chemical and mechanical oceanic deposits, 

 which have simply concentrated in the present situation, perhaps from rocks 

 now completely removed by erosion. The water which brought in the iron 

 ore to supply the place of the silica taken away in solution followed the natural 

 drainage courses, either the drainage slopes or else the joints. The Giant's 

 Range is regarded as having been uplifted at the time of the gabbro outflows, 

 arid to have been caused by them. 



Commejtts. — The succession of the Mesabi range is almost identical with 

 that given by the reviewer for the Penokee-Gogebic district. At the base of 

 the Penokee series constituting the basement complex are granite, syenite, 

 and various green schists. These correspond to Nos. 6 and 7 of the Mesabi. 

 Resting unconformably upon this basement complex is the quartz slate mem- 

 ber, consisting largely of quartzite, corresponding to Winchell's No. 5. Rest- 

 ing conformably on the quartzite is the iron-bearing member, which has two 

 main horizons, the lower carrying the ore bodies, and the other free from ore 

 bodies. This iron-bearing formation of non-fragmental origin consists of 

 cherts, slates, and jaspers, all more or less ferruginous. It evidently corres- 

 ponds exactly to Winchell's Nos. 3 and 4, his " taconyte " being a new name 

 proposed for ferruginous chert, or what the miners call " soft ore jasper." 

 Overlying the iron-bearing member is the upper slate member, which is iden- 

 tical in character with Winchell's Animikie black slates. Unconformably 

 upon the black slates is the Keweenawan series, which, in the Eenokee area, 

 has different characters in different places, but to which Winchell's No. i 

 gabbro belongs. There thus appears to be absolute identity as to succession, 

 and also the structural breaks occur in' precisely the same horizons in the 

 Penokee and Mesabi districts. The facts given as to the iron ores, apart from 

 theory, correspond in nearly every respect with the occurrences in the Penokee 

 district. The differences are that the basement impervious formation in the 

 Mesabi range is not a dike rock, but the pitching quartzite alone. The source 

 of the iron ore is said to be an oceanic deposit, but while the presence of iron 

 carbonate is asserted, it is denied that it can be assumed that it has been 

 present in sufficient quantity to furnish ore beds. The cherty iron car- 

 bonate of the Gogebic range, the source of the ore, was a water deposited 

 sediment. 



The presence of three like unconformable series in the Penokee and 

 Mesabi districts, the identical succession of the iron-bearing series, the 

 remarkable similarity of the rocks of each of the corresponding formations, 

 and the nearly identical history of the ore-deposits, is a remarkable instance 

 of like conditions prevailing simultaneously in a geological basin throughout 

 a wide area. 



