958 
Oak, evergreen, fossil forms of, 855, 866 
Oak, fossil forms of, 803, 838, 855, 866, 
871, 875 
Obolella, 650*, 652 
Obolus, 660 
Obsidian, 140; alteration of by volcanic 
vapours, 235 
‘ Ocean (see Sea) 
Oceanic islands, voleanic nature of, 32 
Odontopteris, 726, 752 
Odontopteryx, 840 
Odontornithes, 811 
Oeningen Stage, 867 
CEnocarpus, 846 
Oesel Group, 688 
Ogygia, 655, 664, 665* 
Ohio River, ratio of discharge to rainfall, 
361 
Oil-regions of Pennsylvania, 236, 351 
Oil-shale, 172, 740, 799 
Oil-springs, 351 
Oldhamia, 650*, 657 
Oldhaven Beds, 845 
Old Red Sandstone System, 693, 706; 
conglomerates of, 157 ; volcanic rocks in, 
7138, 715; possible glacial detritus in, 716 
Oleandrideum, 772, 828 
Olenellus, 660 
Olenidian rocks, 652 
Olenus, 649*, 651, 664 
Olenus-schists, 658 
Oligocene, 836, 854 
Oligoclase, 72 
Oliva, 840, 865 
Olivine, 77, 81; ejected bombs of, 207; 
alteration of, 353 
Olivine-enstatite rock, 151 
Olivine-rocks, 151 
Omphacite, 77 ~ 
Omphyma, 664, 677* 
Onchus, 666 
Onondago Salt Group, 692 
Onychodus, 705 
Oolite as a kind of limestone, 1138 
Oolite, Great, 792; Inferior, 791 
Oolites, Lower or Bath, 790; Oxford, 793 ; 
Upper, 794 
Oolitic structure, 113, 175; 
469 
Oolitic System (see Jurassic) 
Ooze, 167; diatom, 461; 
469; radiolarian, 469 
Opacite, 108 
Opal, 66 
Ophiderpeton, 733, T54 
Ophileta, 666 
Oplioglypha, 789 
Ophitic structure, 131 
Opossum, fossil, 868 
Oppellia (Ammonites), 784 
Orbicula, 659 
Orbitolina, 804 
Orbitolitenkalk, 829 
Orbitolites, 850 
in Coral reefs, 
foraminiferal, 
INDEX. 
Ore deposits, 589 . 
Oreodonts of American Miocene — 
869 
Oreopithecus, 864 
Ores, 592; deposition of with organisms, 
757 
Organic acids, sources of, 347, 452; action — 
of, 174, 453, 463, 470; pass into carbon 
dioxide, 453 
Organic agency in elimination of silicates, 
152 
Organic matter in rain, 330; 
in spring water, 347, 348 
Organic remains (see Fossils) 
Organic structures in rocks, 106 
Organically derived rocks, 102, 106, 165 
Organisms, relative persistence of, 611 
Original minerals, 61 
Oriskany Formation, 692 
Orkney Islands, no raised beaches among, 
19 
Ormoxylon, 708 
Ornithotarsus, 811 
Orozoe, 664 
Orthis, 651*, 665, 667, 669*, 696, 723 
Orthisina, 660 
Orthoceras, 651*, 666, 667*, 679%, 698, 724, 
725*, 753, 764 
Orthoceratites as type-fossils, 615 
Orthoclase, 70 
Orthoclase-porphyry, 138 
Orthoclase-rocks, 130, 131 
Orthonota, 665, 679* 
Orthoptera, early forms of, 710, 732 
Ortonia, 664, 723 
“‘Osar”’ (Kames or Eskers), 892 
Osborne or St. Helen’s Beds, 857 
Osmunda, 849, 858 
Osteolepis, 709*, 710 
Ostia, alluvial erowth at, 390 
Ostrea, 777*, 778*, 805, 806*, 844, 854*, 
855, 862 
Ostrich, fossil, 880 
Otodus, 807, 840, 842* 
Otopteris, 786 
Otozamites, 761, 772 
Otter, fossil, 864, 874, 876 
Ottrelite Slate, 122 
Outcrop, 511 
Overlap, 495, 599 
Ovis, 880 
Ox, fossil forms of, 872, 880 
Oxford Clay, 793 
Oxford Oolites (Oxfordian), 793 
Oxidation by rain, 331, 339 
Oxus River, change of course of, 324 
Oxygen in earth’s crust, 57 
Oxyrhina, 807, 876 
Ozone, 31 
in soil, 339; 
Pachycormus, 790 
Pachyderms, reign of, 856 
Pachynolophus, 840 
Pachyphyllun, 772 
