INDEX. 



Sandstone of Keweenaw Point, age of, 108; 

 belongs to the Quebec group, 93, 97 ; 

 Calciferous age of, 93, 94 ; Cambrian age 

 of, 90 ; cause of absence of fossils in, 85 ; 

 of Chazy age, 94 ; of " New Red " age, 

 79, 80, 81, '89, 90,93, 97; of "Old Red" 

 age, 77, 80 ; origin of, 82 ; of Permian 

 age, 94; of Potsdam age, 82, 91, 93, 

 103, 104, 107; pre- Potsdam age of, 83. 



Sandstone, Western, of same age as the 

 traps, 121, 122. 



Schist, composed of basaltic detritus, 37 ; 

 contortion of stratification planes of, 67 ; 

 garnet-bearing, of Republic Mountain, 47 ; 

 granite intrusive in, 55 ; Iluronian age 

 of, 14, 24, 52 ; lamination cut by iron 

 ore, 31 ; miqroscopic study of, 36, 37, 47, 

 48, 53, 58 ; mineralogically like diorite, 

 37 ; passage of magnesian, into dioritic 

 rocks, 20 ; its relation to the iron ore, 31 ; 

 sedimentary origin of, 26, 48 ; uplifted 

 by granite, 53 ; welded to granite, 53. 



Schoolcraft, H. R., falsification of original 

 documents in his " Summary Narrative " 

 of 1854, 10, 11; his views in regard 

 to the copper region of Lake Superior, 

 76. 



Schoolhouse Mine, conglomerate at, 30 ; 

 dike of jasper at, 30. 



Sedimentary origin of eruptive and ciystal- 

 line rocks, 11, 12, 14, 15; of the iron 

 ore, 6, 14, 15. 



Sedimentary rocks, rapid deposition of, 118. 



Selwyn, A. R. C, on the Huronian age of 

 the copper-bearing rocks, 106. 



Serpentine, an alteration form of pcridotitc, 

 61, 66 ; an alteration product of olivine, 

 42 ; on the formation of, 75 ; microscopic 

 study of, from Isbpeming, 65, 66 ; net- 

 work structure of, 61 ; origin of, 64, 65 ; 

 of Presque Isle, 60-65. 



Shale, i-aindrop impressions, ripple-marks, 

 and mud-flows in, 121. 



Shelden and Columbian Mine, character of 

 copper deposit at, 129. 



Silica, eruptive with hematite, 33. 



Silver, its union with copper, 79, 81, 105, 

 106, 109. 



Spherulitic structure, produced by alteration, 

 113, 119, 120. 



Stone cavities in feldspar, 42 ; formed from 

 devitrified base, 42 ; in quartz, 56. 



Sweet, E. T., unconformability of Lauren- 

 tian and Huronian, 24. 



Tachylite, altered form of, 44. 

 Talc, in ottrelite schist, 45. 

 Teal Lake, diorite of, 41 ; lamination of 

 schist at, 41 ; quartzite of, 9. 



Thermal waters, action of, 49, 50, 51, 116, 

 117, 123, 124, 125, 126. 



Titanite, in granite, 56. 



Torch Lake, sandstone quarry at, 117. 



Tourmaline, in eclogite, 48 ; crystals in 

 diorite, 45 ; in ottrelite schist, 45 ; pres- 

 ence of, in iron region, 75 ; in radiating 

 groups of crystals in quartz, 45. 



Trachyte, microscopic study of, 113, 114, 

 117, 120; pebbles of, 113. 



Trap, action on the sandstone, 86-88, 101- 

 103 ; age relative to Eastern sandstone, 

 108 ; amygdaloidal and scoriaceous on 

 upper surface, 110; characters and rela- 

 tions of, 104, 109-113, 118, 128; denu- 

 dation of, before sandstone was deposited, 

 113 ; evidence that they are lava flows, 

 127, 128 ; pseudo-stratification of, 86 ; 

 sends tongues into the "ash-bed," 113; 

 tongues of, extending into sandstone, 

 110; metamorphic sedimentary origin 

 of, 91. 



Triassic age of copper -bearing rocks, 97. 



Trichites in quartz, 59, 120. 



Unconformability, based on foliation and 

 lamination, 71 ; not proof of distinct age, 

 31. 



Vapor cavities in quartz, 39. 



Veins, filling of, 124, 129: of iron ore, 29; 



valuations of, 129 ; width of, 124. 

 Veins fissure, formation of, on Keweenaw 



Point, 123. 

 Vein material, derived from the traps, 123. 

 Veinstones, character of best forms, 130. 

 Viridite, replacing augite, 42 ; replacing 



base, 37. 

 Volcanic action, earlier than Tertiary times, 



119 ; gradual increase and diminution of, 



122. 

 Volcanic origin of the copper-bearing rocks, 



where shown, 131 ; of copper veins, 80. 



Warwick, Rhode Island, masonite of, 45. 



Washington jNline, rocks of, 43, 44, 45. 



Washington Mine (new), dikes of ore at, 36. 



Washington Mine (old), relations of iron 

 ore and actinolite schist, 35. 



Water, action of percolating, 123, 129. 



Whitney, J. D., alternations in formation of 

 zeolites, 95 ; chemical analysis of Presque 

 Isle serpentine, 14, 62, 65 ; " Metallic 

 Wealth of the United States," 90 ; igneous 

 origin of iron ore, 7, 10; on the iron dis- 

 trict, 7. 



Whittlesey, C, copper-bearing rock contin- 

 uous with, but below, the sandstone, 94 ; 

 eruptive origin of granite, 24 ; Huronian 



