﻿Iron Ores of the Lake Superior region. 257 



three or four years served to convince me, not only that the ore 

 and banded jasper-schists of the region are derived from a 

 deposit of some sort, of sedimentary origin, but that several 

 other forms of ferruginous rocks — viz : various schists composed 

 of magnetite and quartz ; of magnetite, hematite and quartz ; 

 of magnetite, actinolite and quartz ; of magnetite, actinolite, 

 quartz and carbon ; of magnetite, actinolite, garnet and quartz ; 

 and also various cherty (the silica partly chalcedonic) ferrugin- 

 ous rocks banded with magnetite — must have had a common 

 origin with the ordinary ore and jasper, since all are intimately 

 associated parts of one continuous belt, which was traced at the 

 time a distance of forty miles or more. None of the writers on 

 the present subject seem to have appreciated that any explana- 

 tion of the origin of the iron ores must include also, not only 

 the jaspery schists, which are particular associates of the ore in 

 the Marquette region, but also the long list of ferruginous rocks 

 -above named ; though Julien appears to have covered the 

 relatively unimportant garnetiferous rocks with his mechanical 

 sedimentation theory. 



The foregoing paragraphs present the condition of the ques 

 tion as it stood in my mind at the beginning, in 1883, of the 

 investigations in the Lake Superior region of which I now 

 have charge. I was strongly impressed with the inadequacy of 

 any theory of an eruptive origin for any of these materials; 

 but, while realizing that the true theory must begin with sedi- 

 mentation, I had no more definite conception than this, all the 

 explanations that had been advanced seeming unsatisfactory, or 

 at least insufficiently supported. In what follows I draw on 

 the results of my later studies, which have been extended 

 in the years since the early summer of 1883, over all the areas 

 in the Lake Superior country in which the ferruginous rocks 

 occur; during which time also several hundred thin sections of 

 the various ferruginous rocks have been made and studied in 

 detail. In this microscopic work I have had the constant 

 assistance of Professor C. R. Van Hise, who has prepared a full 

 description of each section examined. Many theories during 

 this time have presented themselves to me and my assistants, 

 but none have been held heretofore more than very loosely, 

 each to be set aside in turn as new and destructive facts were 

 gathered. 



Early in the study, however, it became evident enough — since 

 as already intimated, some of the beds of ferruginous material 

 have yielded fra^^uients which have entered into the compo- 

 sition of the immediately overlying fragmental deposits, form- 

 ing part of the same series — that any satisfactory explanation 

 must provide for the fact that these materials reached their 



