STRUCTURAL GEOLOGY. 49 



Extent of the Animikie.] 



are intimately associated with the large amounts of the rock muscovadyte which is 

 not known to occur in connection with the Animikie and its ores, but which, in 

 several places, has been observed to be derived from the Keewatin by metamorphism. 

 Therefore, it appears that the Animikie is lost under and in the gabbro at a short 

 distance from Gunflint lake, and reappears, with its own characters, only affected 

 by contact metamorphism, on the west of the west side of the gabbro southwestward 

 fi-oni Birch lake, and thence continues along the south side of the Giant's range, 

 constituting the Mesabi Iron range* to Pokegama falls. Its extension south of the 

 belt of iron mines, on the western Mesabi range, is unknown, owing to the heavy 

 mantle of drift, but it is well known that the black slates of the Animikie overlie 

 the iron ore horizon all along the mining belt. 



What becomes of the Animikie, after its disappearance in and under the gabbro, 

 has been one of the interesting geological problems of the survey. From preliminary 

 field examinations it was stated by the writer, twenty years ago (1878), that the sedi- 

 mentary rocks at various places along the shore of lake Superior, and notably on 

 Pigeon point, at the Great Palisades and at Beaver bay, had been converted into 

 crystalline rocks, and had been fused by contact with the basic igneous rocks. Nearly 

 every year from fchat time to this has contributed in the progress of the survey to 

 the verification and the extension of that truth. It has already been applied in the 

 discussion of the Archean and its igneous rocks. In the Taconic are some of the 

 most evident facts and the most convincing transformations tending to this result. 

 They are recorded in some of the annual reports and in occasional papers, and are 

 systematically summarized where they occur in some of the special chapters of this 

 report. Therefore, at this place, in tracing out the extension of the Animikie, it may 

 be assumed that, in general, the strike of the red rock shows the strike of the Ani- 

 mikie. But as there is reason to assume that the mass of the gabbro moved superfi- 

 cially toward the south, it is necessary to allow that the fused products of its intru- 

 sion partook in that movement. Indeed, it is certain that, in several instances, the 

 red rock formed lava flows which reached the latitude of the present shore line of 

 lake Superior; and toward the western limit of the gabbro where it seems to have 

 flowed farther as a great mass than toward the east, so the red rock is further 

 displaced from the locus of its origin. It is not known that this red rock flow has no 

 interruptions in surface extension from Lake county westward to Duluth, but it is 

 highly probable that, with occasional variations and mutual overlapping with the 

 cotemporary diabasic flows from the gabbro, its general continuity could be seen if 

 the forest and the drift could be removed. It is seen at many places, as at Baptism 



*It is the opinion of Dr. Grant that the Animikie continues, under disguised conditions, as formerly supposed, and as 

 represented in the annual reports and in some of the chapters devoted to the Mesabi Iron range, all along the northern border of 

 the gabbro. Facts mentioned by him in the chapter on the Akeley Lake plate are indicative of the Animikir age of the iron at 

 Akeley lake, and that locality might be excepted from the hypothesis above expressed. 



