INDEX. 



V 



lizLiig out oP ,innl(cn iiingmas, 09 ; erup- 

 tive wiili silina., 08; fi]ins of surround itiLi; 

 Tiiagncfitc and {jjarnet, 48 ; forining a dike, 

 30 ; sccondaiy origin oC, 30, 48. 



Hematite, "soft," at Jaekson Mine, 33; 

 composition of, 51 ; couditions of forma- 

 tion, 50 ; not bug-iron oi'e, 51 ; origin of, 

 10, 20, 25, 70; origin and eliarueters of, 

 -49-52; probable deposit near Lake Ange- 

 liuc Mine, 50. 



riodge, James T., origin of copper and sil- 

 ver veins, 84. 



Home Mine, sandstone and ore at, 32; jas- 

 per dikes at, 33. 



Hornblende, alteration ol', 114, 117, 120; 

 ulteration produrt afier augite, 37, 39, 42, 

 46; altered to clilorile and biotite, 50 ; 

 foreign in andesite, 119 ; secondary origin 

 of, 30, 37; pseudomorphs after fragments 

 of, 38. 



Hougbton, D., liis views in regard to tbe 

 geology of tbe copper region, 77-Sl ; 

 geology of iron district, 2, 3 ; geology of 

 Presqne Isle, 2, 3, 63 ; variability of liis 

 views, 108. 



ITouuliton, Micbigan, conglomerate west of, 



121. 



Hubbard, B., on tbe geological structure of 



Iveweenaw Point, 83; on tbe geology of 

 tbe iron district, 3, 4 ; on metaniorpliisni, 

 5 ; on tbe Porcupine Wounlains, 83, 84 ; 

 traps eruptive In sandstone, 83. 



Hunibobll;, Mi(diigan, granite intrnsive in 

 schist, 57 ; 1be rocks and ore of, 35, 30. 



Hungarian Palls, sandstone at, 113. 



Hunt, T. S., his erroneous observations in 

 Eastern Massacliuseits, 72 ; bis views in 

 regard to tlie copper region of Lake Supe- 

 rior, 93, 94, 99, 105; beniatiie a proof 

 of presence of organic matter, 14; liis 

 views in regard to the iron region, 13, 

 19, 24; indefinitcupss of Ids staicmcuts, 

 109; objects to decomposition theory 

 of origin of "soft hematites," 51; not 

 personally acquainted with the iron dis- 

 trict, 40; on tlic Presque Isle serpen- 

 tine, 03 ; on the sedimentary origin of 

 greenstones, 25. 



Huronian and Laurentian in iron region, 



36. 



ITuroniau, conformable with Laurentian, 35; 



contact with Laurentian not observed, 24, 



25 ; according to Hunt, equivalent of tbe 



Cambrian, 13; eru])tive granite in, 55; 



including rocks of two distinct ages, 31 ; 



relation to Laureulian, 70, 71 ; younger 



than the Laurentian, 23, 24. 

 Huronian age, according to Bigsby, distinct 



from the Cambrian, 14; of iron district, 



13, 14, 15, 17; of Prcsquc Isle serpen- 

 tine, 03, 64. 

 Huronian rocks in iron region, 34 ; uncon- 

 I'oruuible with the Laurentian, 23. 



Lndians, tbe customs of, 93 ; use of copper 

 by, 93. 



Iro]i a2;e of geoloCT, 9. 



Iron district, country rocks of, 28, 39 ; 

 eruptive rocks of, 40 ; geological stiaic- 

 ture of, 75 ; iustorical discussion of, 1- 

 30; Huronian age of, 13, 14, 15, 17; 

 jasper and iron ore of, 38-30; not visited 

 by C. T. Jackson, 0;. object of the in- 

 vestigation of, 37; sea-beaches in, 31; 

 summary of geological views on, 20, 27. 



Iron ore, breaking tlirough schist, 31 ; chem- 

 ical and metaUurgieal ohjcetious to erup- 

 tive OTgin of, 08,09; has tbe color and 

 streak of hematite, but is magnetic, 33; 

 cutting schist, 31 ; a deep-sea deposit, 35; 

 its deposition considered due to tbe pres- 

 ence of organic nmiier, 14 ; dikes of, 30, 

 33 ; difficulty in, mining, 31 ; history of 

 its discovery, 8.4, 18; eruptive eb.arac- 

 ters of, 33 ; eruptive origin of, 27, 67 ; 

 form of eru])tion, 68 ; form of masses of, 

 29; Huronian age of, 14, 15, 17; inter- 

 laminations of, with jasper, 39 ; igneous 

 origin of, 7, 9, 10; not inicrstratified 

 with schists, 07; intrusive character of, 

 35 ; at Ishpenung, 30 31 ; junction of, 

 with clilorile schist, 30 ; the Laurentian 

 age of, 13 ; limits between it and tlie jas- 

 per, 33 ; magnetic in contact with dikes, 

 43 ; magnetic state induced by secondary 

 causes, 34; manner of intrusion, 35; in 

 Marquette district, 6, 7, 14, 15; in Me- 

 nomonec region, 3, G, 7 ; in metamorphic 

 rocks, 7; originally magnetite, 17; nii- 

 eroscopie study of, intrusive in quarfzite, 

 33 ; at Negaunce, 31, 33 ; in octabedrous, 

 33 ; origin of, 13, 13 ; its origin a matter 

 of economic im])ortanee, 39 ; the oritjinal 

 state of, 33, 34; plasticiiy of, 21,^07; 

 according to EJvot, of Potsdam age, 91 ; 

 proof of its intrusive character, 07 ; its 

 relations to (he country rock, 30-36; re- 

 lation to schist, 31 ; secondary deposition 

 of, 33 ; sedimentary origin of, maintained 

 bv various geoloijisls, 0, 13, 14, 15, 17, 18, 

 30, 31, 33, 24, 25, 37 ; not in veins, 19, 

 39 ; wedge-shaped nnisses of, 31, 33. 



Iron, oxides of, their action in reduction of 

 tbe copper, 90, 93, 93, 97 ; precipitation 

 of copper by, 130. 



Iron, tbe protoxide of, an agent in the depo- 

 sition of copper in veins, 90. 



Iron, titaiiiferous, decomposition of, 48. 





