Iron Ore Ranges of Minnesota. 



Differences of Geographic Location. 



45 



In order that this great difference in the stratigraphlc relat 

 of the great iron-bearing formations may be fairly understood I will 



illustrate it by a few lantern views. 



(1) Northern Minnesota, showing the areas of the Kewe. 

 wan and Taconic, and of the Archaean; also the geographic positions 

 of the Vermilion and Mesabi iron ranges. This vi.-w is taken from 

 the Collections of the Minnesota Historical Society, Vol. VIII. paper 

 read January 21, 1895. The rocks of the Vermilion range ei 

 westwardly a great distance. The indication on the map shows only 

 where they have been seen, and especially where they have been 

 known to carry more or less ore like that at Soudan. These rocks 

 are not simple, but complex, and yet they have some general char- 

 acters in all areas in which they are uniform, and by which they can 

 always be distinguished from the rocks of the Mesabi range. For 

 our present purposes these are the only formations which it is nec- 

 essary to consider — two great non-conformable formations separated 

 by what has been called by Lawson "the great eparchaean interval." 



(2) A section of the rocks extending from Soudan near Ver- 

 milion lake, southward under lake Superior to the Penokee range 

 at Penokee gap, showing the dip of the different formations. Here 

 are the Archean rocks at Tower, or Soudan, standing vertical, dis- 

 appearing under the rocks of the Mesabi range and reappearing on 

 the south side of the lake still maintaining their vertical attitude 

 It is these rocks that hold the ores of the Vermilion range. Over- 

 lying these vertical strata are the gently dipping strata that carry 

 the Mesabi ores, and above them are the trap rocks, gabbro, sand- 

 stones and shales that compose the great Keweenawan formation 

 which on Keweenaw point are famed for the metallic copper which 

 they have furnished. The Mesabi rocks and the copper-bearing rocks 

 agree essentially in dip, and are closely related in age. This dia- 

 gram is taken from the sixth bulletin of the Minnesota survey, "The 

 Iron Ores of Minnesota," published before the great working of the 

 Mesabi range and cotemporary with the first discovery of merchant- 

 able ore on that range. This non-conformity extends, so far as has 

 been observed, throughout the whole Lake Superior region, all over 

 Canada and New York and New England. This remarkable fact has 

 great significance, nothing less than the date of separation between 

 two great world epochs. 



3. Structure of the Vermilion Range Rocks. 



If we inquire now how these formations can be distinguished, 

 we enter upon the actual problems that confront the geologist, both 

 in the field and in the laboratory. It is not possible to give the de- 

 tailed differences nor the steps by which these differences have 

 been determined. Suffice it to state that the main result was 

 ed after long field examination and mapping, and after minute 

 examination of the mineralogic characters. Before arriving at that 

 stage in the research where we were qualified to give reliably the 

 conclusions of our labor, we had spent 21 rears on the inv. 

 tion, and had minutely examined 1000 microscopic thin secttol 

 rocks gathered in the course of the survey. What I shall give you 

 will be the merest skeleton, and will embrace onl most 



tangible features. If you wish for more detail you may exam in*' the 



