818 N. H. WINCHELL ORIGIK OF LAKE SUPERIOR IRON ORES 



eruptive origiii was attributed to larger masses of irregular shapes occu- 

 pying preexisting depressions, or inclosed between strata that had been 

 folded over them, or running in long dikelike lines across or among the 

 associated strata. Thus igneous action, with its immediate products, was 

 the primary agent. It is curious that Whitney, who was at that date an 

 assayer and chemist rather than geologist, and whose reputation and 

 skill placed him, in the judgment of the foremost authorities of his time, 

 in the forefront of his j^rofession, should liave been willing to adopt a 

 theory that violated so many of the principles of chemical science. The 

 chemical impossibilities of this hypothesis have been shown amply in a 

 former publication,- and the geological difficulties Avhich it encounters 

 are entailed in part by the erroneous fundamental chemical assumptions, 

 and yet chiefly by insufficient and incorrect field observations. The errors 

 of structural geology into which these pioneers fell, though numerous 

 and sometimes vast, can be excused in the light of the newness of the 

 problems and the inchoate ideas of Archean geology which were then 

 prevalent. There was a profound non-appreciation of the importance of 

 careful field studies, and of detailed description of the facts as they exist. 



It is not intended here to discuss this hypothesis. It is necessary, 

 however, in justice to Whitney, to give him credit for the origination of 

 the primary idea of igneous forces and igneous rocks as the first cause 

 of the ores of the region, whatever may have been the steps he trod to 

 reach it, and whatever may have been the geological and chemical history 

 that succeeded in order to get the oxides of iron into the condition in 

 which we now find them. He appealed to sedimentation in a very limited 

 way. He rightly rejected the idea of the sedimentary origin of the 

 banding seen in massive jaspery ores on the tops of the conspicuous 

 knobs, and rightly accepted it in the case of certain so-called "metamor- 

 phic strata," where the beds are of various widths, but with a conform- 

 able range and dip ; and wherever some conglomeratic beds were found to 

 be so interstratified, though containing traveled fragments of ore, they 

 were believed to be in the same formation with the ore, and to have been 

 formed by convulsive outbreaks of volcanism which broke the preexisting 

 strata and furnished fragmental debris amenable to contemporary violent 

 sedimentary distribution. 



As there are two great fundamental causes for the origination of rocks, 

 namely, igneous action and sedimentation, so, to a large extent, theories 

 of the iron ore have oscillated from igneous eruption to aqueous sedimen- 

 tation, since iron ore is one of the important components of the rocks of 

 the earth's crust — not important because of its relative bulk, but because 

 of its economic value and its wide distribution. 



*The iron ores of Minnesota. Bulletin VI of the Minnesota Geological Survey, 1891. 



