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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, and to have been caused by them.

Comments.—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 member, consisting largely of quartzite, corresponding to Winchell's No. 5. Resting 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. The iron-bearing formation of non-fragmental origin consists of cherts, slates, and jaspers, all more or less ferruginous. It evidently corresponds 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 identical in character with Winchell's Animikie black slates. Unconformably upon the black slates is the Keweenawan series, which, in the Penokee area, has different characters in different places, but to which Winchell's No. 1 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 carbonate 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.