260 THE PENOKEE IRON-BEAEING SERIES. 



derived is a siliceous iron carbonate l)earing calcium and maonesium. In 

 this case tlie silica had but to unite with these bases to produce the actino- 

 lite; like solutions in the limestones liad only to linite with the bases there 

 present to produce tremolite. 



SECTION III.— THE ANIMIKIE IRON-BEARING SERIES. 



Before leaving this pai-t of the subject it is necessary to make some 

 allusion to like formations in other parts of the lake Su])erior country. 

 The Animikie and Vermilion lake series of northeastern Minnesota and 

 Ontario, the i\larquette and Felcli mountain series of Michigan, and the 

 Menominee series of ]\Iichigau and Wisconsin, all contain large develop- 

 ments of rocks which in their characters are almost exact reproductions 

 of the iron-formation rocks in the Penokee series. In each of the disti'icts 

 mentioned all the types and most of the varieties described in the latter 

 series are quite widely found. Cherty iron carbonate is not extensively 

 known in some of them, but in one is more largely developed than in the 

 Penokee series itself, while in the most folded and altered series men- 

 tioned tliis I'ock typically occurs, as is shown by PI. xxiv, Figs. 3 and 4 

 A oeiieral condensed account of the iron formations and ore bodies of these 

 various districts, including the Iron-bearing rocks of the Penokee series, has 

 l)een })ublislied by us.' While a c(tntinued study has made some modifi- 

 cations of detail necessary, the main conclusion of the papers lias been 

 rendered more certain; i. e., that the many phases of peculiar rocks asso- 

 ciated with the iron ores in these various districts have been derived mainly 

 from a clavey or cherty iron carbonate. In the first i)aper refeired to an 

 exception was taken in the case of some of the coarser grained actiuolitic 

 slates which are foundin the Marquette country, "as to whose relations to 

 the other ferruginous materials we feel now unwilling to s[)eak." Later 

 investigations make it not improbable that some of these rocks have been 

 derived from eruptives; but the origin of this class of rocks has not yet 



' R. D. Irving: Origin of tho Ferniginonn Schists and Irim Ores of tlic Lake Snpi-rior Region; 

 Am. Jour. Sci., 3(1 series, vol. xxxil, 188t), iij). 255-272 C. R. Van Hise: The Iron Ores of the Mar- 

 (|uetti' DiKtrict of Michigan; Am. .)onr. Sei., .3(1 series, vol. .XLiii, 1892, jip. 110-132. C. R. Van Hise: 

 Tlie Iron Ores of the Lake .Superior Region; Trans. Wisconsin Acad, of Sci., Arts, and Letters, vol. 

 VIII, 18!I2, lip. 219-228. 



