INDEX. 



499 



I. Page. 



Iceland, volcanica of 75 



Iddings, J. P.,oii magmatic diflerentiation 105 



ou micropoikilitic texture 84 



on origin of igneous rocks 265 



referred to 95 



Illinois Steel Co. (See Toungstown mine.) 



Ilmenite altering to rutile 202,239 



altering to spheue 239 



included in biotite 216 



included in bronzite 238 



included in chlorite 216 



included in hornblende 236,246 



including epidote 444 



including quartz 444 



of basic dikes 47 



of Bone Lake schist 151 



of chlorite schist 442 



of gabbro and norite 236,238,239 



of Hemlock schist 444 



of metadolerite 202 



of picrite-porphyry 216 



of sedimentary inclusions in granite 197 



Instruments, magnetic, use of, described 341-344 



luterrange exploration 439, 443 



Intersertal texture in metabasalt 98, 99, 104 



Intrusives described 187-265, 469-470, 482-485 



age of 188,189 



correlation of 189 



effect on magnetic observations 371, 372 



in Archean x viii, 38, 45-49 



in Felch ilouhtain range 426 



in Hemlock formation 77 



in Huronian xsiii, 190 



in Mansfield slate 63,64,204-211,413 



in Sturgeon Kirer tongue, described 469-470,482-485 



in Upper Huronian 164,174,175,190 



influence on topography 54, 333 



metamorphism of Mansfield slate, described. -204-211, 413 



relations to Cambrian 188 



use of term 187 



Intrusive series, related, described 221-265 



composition of 263-265 



crystallization of minerals of 262 



relative age of rocks of 265 



textures of 262 



Intrusives, unrelated, described 190-221 



Iron-bearing formation described xs, 415-423, 446-450 



correlation of 20,330 



intruded by granite 381 



magnetic observations in 338,339 



near Crystal Falls, succession in 379,180 



of relch Mountain range 378 



described 415-423 



distribution 377 



Kominger on 381-383 



of Penokee district, located by magnetic work .. 24 



of Upper Huronian 168 



relations to marble 376 



relations to volcanics of Penokee series xxi 



{See Groveland formation. Iron-ore deposits.) 

 Iron carbonate. {See Siderite.) 



Iron County 11 



Iron Mountain 385 



slates of, correlation with Mansfield schist.- 413 



Iron ore, analyses of 69 



by Brooks, referred to ^. 19 



Page. 



Iron ore, composition of. 181 



from siderite 70, 71, 184 



from eruptive rock 134 



origin of 70,71,184 



Credner on 71 



Irving on ....- 70,71,130 



Spurron 422 



VauHiseon 39,70,71,130,168 



Iron ore deposits associated with intrusives 1 83 



comparison with ore deposits of adjacent dis- 

 tricts 180-181 



concentration of, at Mansfield mine 72 



conditions favorable for, Van Hise on 72 



discovered at Crystal Falls 175 



discovered at Florence 175 



explorations for 12,330 



of Aniasa area 175, 177 



of Armenia mine, description of 183 



of Crystal Falls area 178,186 



productiou of ore from, table of op. 186 



of Crystal Falls district, compared with Mo- 

 nominee iron ores 19 



table of production from op. 186 



of Columbia mine described 182 



of Dunn mine described 182 



of Great '^''estern mine described 182 



of Felch Mountain range, Burt on 375 



of Hemlock mine 177 



of Mansfield formation 27,62 



described '. 65-73 



of Mansfield mine 63 



described 67-70 



of Paint River district. Brooks on 18 



of Paint Eiver mine 183 



of Peshakumme Falls 375 



of sec. 20, T. 45 N., K. 33 W 176 



of sec.34, T.46N.,E. 33'U'' 176 



of Upper Huronian 28, 166 



described 175-186 



distribution of, described 176-180 



history of 175 



methods of mining in, described 184-185 



origin of, described 183-184 



prospecting in 185 



relations to adjacent rocks, described 182-183 



size of, described 184 



sketch of occurrence of 182 



table of shipments from op. 186 



relations to clay slate 63 



search in Bone Lake schists 151 



shipments from Crystal Falls area, table of op. 186 



Iron oxide altering to sphene 212 



from feldspar 42, 92 



included in chlorite 218 



included in feldspar 151,234 



included in hornblende 47, 215, 251 



included in quartz 419 



included in siderite 133 



of acid lavas 89.91 



of amygdules 124 



of biotite-granite 192 



of Bone Lake schists 151 



of conglomerate 64 



of dolomite 53 



of gabbro and norite 239 



of Groveland formation 417,419,449 



