Vlll 



INDEX. 



Ncwberiy, J. S., on the origin of iron ores, 

 23, 24. 



iNorian, in Eastern Massachusetts, 72 ; erup- 

 tive basaltip (ccabbro) forms, 73. 



North Island, diabase and diorite of, 39. 



Nova Scotia, trap of, 81. 



Olivine, action of magma on, 40 ; altera- 

 tion of, 42, 61 ; in diabase, 40, 42, 43, 

 45 ; foreign in basalt, 119 ; greenish 

 pseudomorphs of, 61 ; in peridot ite, 60, 

 61 ; presence of, in iron region, 75 ; pseu- 

 domorphs after, 36. 



Ontonagon district, structure of, 104, 105. 



Ontonagon lliver, origin of copper of, 76 ; 

 sandstone on west fork of, 100. 



Organic matter, precipitation of the copper 

 by, 92, 95, 109, 130. 



Orthoc'lase, secondary origin of, 37. 



Osceola Mine, microscopic study of pebbles 

 from, 119. 



Ottrelite, microscopic characters of, 45. 



Ottrclite schist, formation of, 36, 75 ; mi- 

 croscopic study of, 45 ; production of, 45. 



Ovifak, Disko, iron-bearing basalt of, 13. 



Owen, D. D., on the age of the sandstone, 

 84, 90. 



Owl Creek Vein, mass copper of, 130. 



Palaeozoic age of rocks of Eastern Massa- 

 chusetts, 72. 



Palmer Mine, eniptive character of jasper 

 at, 32. 



Peck, Samuel, credited with first discovery 

 of iron ore in the iron district, 4. 



Pendill Mine, geological structure of, 51. 



Penokee Gap, unconformability of Huronian 

 and Laurentian at, 25 ; Iluronian and 

 Laurentian at, 24. 



Peridotite, alteration of, 61-66 ; contact 

 with sandstone, 2, 3 ; eruptive origin of, 

 64 ; place of, in lithological nomenclature, 

 65 ; of Ishpemiug, 65, 66 ; of Presque 

 Isle, 2, 3, 42, 60-65, 75 ; microscopic 

 study of, from Presque Isle, 60-62 ; re- 

 lations of, to sandstone at Presque Isle, 

 10. 



Pei-mian age of copper-bearing rocks, 97. 



Pethcrick j\Iine, "ash-bed" at, 112. 



Phoenix (old) Mine, "ash-bed" at, 112; 

 diabase of, 111 ; a fissure vein, 129. 



Picnic Island, diorites of, 23, 39. 



Picnic Point, granite of, 39, 55, 56 ; micro- 

 scopic study of rocks of, 39, 40 ; rocks of, 

 39, 40, 74. 



Pittsburg and Lake Superior Mine, micro- 

 scopic section of iron ore intrusive in 

 quartzite, 32. 



Plagioclase, cutting augite, 42. 



Plasticity of iron ore, jasper, and chlorite 

 schist, 67. 



Porcupine Mountains, geological structure 

 of, 76, 77, 84. 



Porodite, use of the term, 60. 



Porphyry, formation of, 84. 



Portage Lake, copper deposits of, 94 ; dip 

 of sandstone at, 82 ; melaphyr at, 94 ; old 

 lava flows mined at, 124 ; trap at, 86. 



Portage Lake district, copper deposits mined 

 in, 128, 129; no fissure veins in, 124; 

 " slates " of, 121. 



Porter's Island, 80. 



Potsdam age, of all Lake Superior rocks, 

 12 ; of iron region, 26 ; of Keweenaw 

 Point sandstone, 82, 84, 87, 90, 103, 

 104. 



Potsdam sandstone, source of materials in, 

 60 ; microscopic study of, 60. 



Prehnite, igneous origin of, 80. 



Presque Isle, dolomite of, 3; forming an 

 island in the Potsdam Sea, 23 ; geologi- 

 cal structure of, 2, 3, 9, 10, 23, 60 ; peri- 

 dotite of, 75 ; peridotite and serpentine of, 

 60-65. 



Pseudo-amvgdaloidal structure, origin of, 

 100, loi, 123, 129, 130. 



Pseudomorphs after olivine, 36. 



Pseudo-stratification, 28. 



Pumpelly, R., on alteration of basaltic rocks, 

 105 ; on black inclusions in garnet, 47 ; 

 copper-bearing traps, diabases, and mela- 

 phyrs, 105 ; on the deposition of the cop- 

 per by protoxide of iron, 97 ; derivation of 

 copper from sandstone, 126, 127 ; geo- 

 logical report on the copper district, 100; 

 pre-Potsdam age of copper-bearing rocks, 

 99; "specular slate ore," pseudomorph 

 after chlorite schist, 20. 



Pyrite, in felsite, 38. 



QuAKTZ, bearing fluid and vapor cavities, 

 38, 39, 114, 117, 119; containing double 

 pyramidal inclusions, 120 ; crystals in 

 sandstone with unworn facets, 117; de- 

 vitrification form of, 33 ; fluid inclu- 

 sions in, 43, 44, 45, 55 ; foreign, in 

 rhyolite and felsite, 119 ; grains formed 

 by fissuring of a silicious mass, 53, 54 ; 

 heat action on, 33 ; inclusions in, 44, 

 54-59 ; microlites in, 38 ; prismatic 

 structure of surrounding ring, 48 ; sec- 

 ondary origin of, 33, 36, 37, 38, 39, 47, 

 113, 114, 117, 119, 120; stone cavities 

 in, 38, 119, 120; structure of, in felsite, 

 118, 119; with unworn facets iu sand- 

 stone, 60 ; water-deposited, 63. 



Quartz Porphyry, rhyolitic character of, 119. 

 See Felsite. 



