_Naosaurus_, The, 230 Neandarthal man, 285 Nebulæ, 92 Negroes, Nature's reason for the dark pigmentation of, 116 Neolithic Age, The, 287 Neptune, 119 New Chum Mine, Temperature of, 83 New Madrid, Earthquake at, 140 Niagara Falls, The work of the, 52 Nile, The Delta of the, 20 Nineveh, 45 North America, Ice in, 76 North Garden Gully Mine, Temperature of, 83 North Sea, The, how it was formed, 19 North Sea, Ice in the, 75 Ocean deposits, 61; life, 114 Oceanic Era, The, 101 Old Red Sandstone, 212 Oolite, 66, 238 Ordovician Period, Life in the, 204; surface of the earth in the, 206; insect life in the, 206; fish in the, 207; the Trilobite, 207 Ordovician rocks, 202 _Oreopithecus_, The, 268 Organisms, Multicellular and Unicellular, 111 Orion, 92 _Ostracoderm_ group, The, 215 Ostrich, The, 260 Oxygen, The action of, 47 Palæolithic Age, The, 287 _Palæomastodon_, The, 261 Palæozoic Period, The, 199 Palæozoic Alps, The, 219 _Pareiasaurus_, The, 232 Parsons, Hon. Charles, on the difficulties of deep boring, 79 "Pea-grit," 238 Peak Cavern in Derbyshire, 195 Pearl-oyster, The, 210 Peat-water, The action of, 48 Pelée, Mount, 86, 108; the obelisk, 184 Permian or Dyas formation, 227 Peroxide of Iron, 40 Perseids, 99 _Pharorachus_, The, 251 _Pithecanthropos erectus_, 285 Planetismals or Meteorites, 99 Plant life in the Silurian Period, 210 Plants, Era of the first, 103 Pleiades, The, 91 Pleistocene Period, The, 269 _Plesiosaurus_, The, 234, 239 Pliny on the upheaval of land, 192 Pliocene Period, The, 257 Po, Sediment deposited by the River, 20 Polyps, Coral, 65 "Pot-holes" in Yorkshire, 195 Pre-Cambrian, 201 Pressure, of air, 80; of the ocean, 190 Pressure and weight of rocks, 85; astounding effects of, 134 Pribylof Islands, 164 _Proboscideans_, The, 273 _Proterozoic era_, The 130 Pteraspes, The, 215 _Pterichthyds_, The, 215 _Pterodactyls_, 242 _Pterosaurs_, The, 255 Quartzite, 200 Quaternary Period, The, 199 Quebec, Collapse of the bridge of, 25 Rag-stone, 238 Rain, The influence of, 47 Rainfall on the British Isles, 128 Raised Beaches, 151 Red clay deposit in the ocean, 61 Red Sandstone Formation, 212 Reptiles and Amphibians of the Triassic Period, 232; of the Jurassic Period, 237 Reptiles in the Carboniferous Period, 229 Rhinoceros, The, 265 Rhizopods, The, 224 Rhætic beds, 237 Rivers and Streams in the Silurian Age, 209 River Terraces, 55 Rivers, Work done by, 20; records left by, 50 Rocks, how they are made, 79; igneous and sedimentary, 104, 129; "foliated," 200 Rocks, Pressure and weight of, 85 Roestone, 238 Romney Marsh, 60 Rorqual, The, 275 Royal Commission on Sea Erosion, 19