ii. 293;

points to earliest eruptions of a vent, ii. 76 Nordenskjöld, Mr. O., i. 120 North Berwick Law, i. 371, 373, 403 North, Mr. Barker, ii. 244 Norway, eruptive rocks of, i. 28 Nuneaton, i. 171

Obsidian, i. 18, 19; ii. 370 Ochil Hills, i. 274, 276, 277, 279, 281, 286, 287, 288, 293, 303, 308, 311 Oil-shales of the Lothians, i. 361, 362, 462 O'Kelly, J., i. 349; ii. 49 Oldham, T., ii. 299 Old Red Sandstone, lines of vents in, i. 69; granite protrusions of, 236, 272, 277, 290, 337; of County Waterford, 251; distribution in Britain, 257; an exceptional stratigraphical type, 258; conditions of its deposit, 259, 263, 297; original scenery of, 265; vegetation of, 265; isolation of the water-basins of, shown by fossil evidence, 265; classification of, 260; history of the investigation of, 268; volcanic centres in, 271; nature of volcanic products in, 273; structure of lavas and tuffs of, 281; volcanoes of, 259, 263, 294, 303, 323, 325, 337, 341, 343, 346, 348, 352; subdivisions of, 297; thickest conglomerates of, 301; composition of conglomerates of, 302, 315, 341; unconformabilities in, 267, 328, 333; Upper division of, 348, 375, 383; ii. 42 Olenellus-zone, i. 112, 130, 132, 140, 144 Olenus-zone, i. 144 Olivine, i. 154, 418, 420; ii. 58, 135 Omagh, i. 315 Ophitic structure, i. 21, 417; ii. 136, 184, 274 ---- type of dolerite, i. 418, 421 Oregon, crater lake in, i. 58 Orkney Isles, i. 271, 344, 350; ii. 121 Orthoclase, ejected crystals of, ii. 79 Orthophyre, i. 273, 276, 277, 308 Osann, A., ii. 191 Oyenhausen, C. von, ii. 112, 280, 333, 340, 367, 372, 381

Palæopicrite, i. 261 Palæozoic systems, i. 139; volcanic rocks resemble modern, i. 30 Palagonite, i. 33, 61, 151, 180, 246, 422, 423; ii. 44, 46, 57, 223 Paradoxides-zone, i. 144 Paramorphism, i. 249 Peach, Mr. B. N., i. 114, 128, 147, 168, 191, 192, 195, 196, 197, 198, 199, 200, 216, 240, 277-294, 307, 308, 329, 331, 344, 345, 369, 375, 425, 426, 476; ii. 133, 145 Pebidian, i. 145 Pegmatite, i. 20, 119, 127, 418, 449; ii. 5, 368, 437 Pembrokeshire, volcanic rocks of, i. 145, 159, 205 Penmaen-mawr, i. 209, 215 Pennant, T., ii. 109 Pennine chain, ii. 8 Pentland Hills, volcanic series of the, i. 102, 269, 273, 276, 279, 281, 285, 287, 289, 291, 311, 317 Perlite, i. 130 Perlitic structure, i. 19, 196, 199, 206, 211, 216, 232, 274 Permian system, geographical conditions accompanying the deposition of,