VI 



INDEX. 



Irving, R. D., on the copper-bearing rocks, 

 104 ; on Keweenawan granite, 7 1 ; rela- 

 tions of trap and sandstone, 104 ; unity 

 of foliation and stratiiication, 25. 



Ishpemiug, Michigan, contact of diorite and 

 schist, 41 ; gneiss south of, 55 ; iron ore 

 of, 30, 31 ; quartzite of, 59; red granite 

 south of, 56 ; serpentine of, 65, 66 ; 

 " soft hematite " mines of, 49, 50. 



Isle Royale, geological structure of, 86, 87. 



Isle Royale Lode, thermal water action on, 

 124. 



Jackson, C. T., the copper mines of Lake 

 Superior probably not of permanent value, 

 81 ; copper and silver, of igneous origin, 

 81, 85, 86; copper veins valuable only in 

 the amygdaloid, 86 ; on the deposition of 

 the copper, 90 ; on drift agencies in early 

 geological times, 85 ; on the formation of 

 the zeolites, 91 ; on the geology of Ke- 

 weenaw Point, 80-82 ; the igneous origin 

 of calcite veins, 90 ; " New Red " age of 

 sandstone of Lake Superior, 80, 85 ; the 

 New Red sandstone of Upper Silurian age, 

 89 ; origin of amygdaloid sandstone and 

 conglomerate, 84, 85 ; on the origin of 

 the " ash-bed," 91 ; various opinions in 

 regard to the age of the sandstone, 84, 

 89, 93. 



Jackson Mine, diabase of, 43 ; intrusion of 

 iron ore in schist, 31; jasper of, 33; 

 " soft hemrtite " at, 32, 51. 



Jasper, associations of, 29 ; brecciated struc- 

 ture of, 32 ; not coincident with lamina- 

 tion of schist, 31 ; cutting schist, 33 ; 

 a deep-sea deposit, 25 ; dikes of, 30, 32 ; 

 eruptive nature of, 35, 67 ; fluidal struc- 

 ture in, 33 ; fragments in quartzite, 59 ; 

 interlaminations with iron ore, 29 ; lim- 

 its between it and the ore, 33 ; micro- 

 scopic study of, 33, 34, 44 ; at Negaunee, 

 31, 32 ; relation to diorite, 51, 52 ; up- 

 lift of, 51, 52. 



Jaspilite, proposal and definition of the tei-m, 

 75, 76. 



Joint planes, no proof of stratification, 28 ; 

 taken for bedding planes, 117. 



Julien, A. A., dikes near Marquette, 36 ; 

 doubts the presence of diabase in iron re- 

 gion, 45. 



Junction line between diorite and schist, 40, 

 41. 



Kaolin, pseudomorphs after feldspar, 43 ; at 

 Salisbury and McComber Mines, 50, 51. 



Keweenaw Bay, dip of sandstone, 88. 



Keweenaw Point, copper deposits mined on, 

 128, 129; geological structure of, 76, 77, 



78, 79, 80, 81, 82, 83, 86, 87, 96, 97. 



116, 127. 

 Keweenawan Series, numerous geological 



ages in, 118. 

 Keweenawan System, no basis for, 72, 



13L 

 Keweenian Group, name first used by Hunt, 



99. 

 Keystone Mine, magnetite dike at, 36. 

 Kimball, J. P., on origin of iron ore, 16 ; on 



the structure of the iron district, 15, 16. 

 Koch, Fr. C. L., on metamorphic rocks, II ; 



description of iron region, 11. 



Lake Angeline Mine, diorite of, 42. 



Lake Gogebic, copper-bearing rocks near, 

 98. 



Lake Huron, azoic rocks of, confounded by 

 Logan with Keweenaw Point traps, 90. 



Lake Superior Mine, greenish quartz rock of, 

 49 ; iron ore and jasper at, 30 ; microscopic 

 study of the jasper of, 33 ; oven-shaped 

 structure in, 51. 



Lake Superior Region, methods of observa- 

 tion in, 27, 28, 73 ; rocks of mixed 

 eruptive and sedimentary origin, 27- 



Lamination, of jasper, 30 ; not proof of sedi- 

 mentation, 28 ; of Picnic Point eruptive 

 granite, 55 ; of the schists, 67, 68 ; of 

 schist between dikes, 41 ; of schist cut by 

 iron ore, 31. 



Laumontite, red feldspar mistaken for, 121.- 



Laurentian, conformable with Huronian, 25 ; 

 contact with Huronian not seen, 24, 25 ; 

 doubtful basis of, 72 ; a name first applied 

 to post -Tertiary deposits by Desor, 7 ; 

 younger than the Huronian, 22, 24. 



Laurentian age, of the granite, 14, 15, 17; 

 of the iron ore, 13. 



Laurentian granite, eruptive in Huronian, 

 70. 



Laurentian rocks, in iron district, 24 ; un- 

 conformable with Huronian, 22, 24; 

 younger than the Huronian, 22. 



Lava, scoriaceous form of, preserved, 113. 



Lava flow at Presque Isle, 9, 10. 



Lava flows, mining of old, 124. 



Lavas, geological age of, determined litho- 

 logically, 72. 



Lesley, J. P., errors made in quoting the 

 " Metallic Wealth of United States," 12, 

 13 ; opposes the igneous origin of any 

 iron ore, 12. 



" Leucoxene," alteration product after iron 

 ores, 37. 



Lherzolite of Presque Isle, 60-65. 



Lighthouse Point, diorite of, 23. 



Literature of the geology of Lake Superior, 

 132-157. 



