ii. 11, 18, 24, 36;

Permian, 57, 58; Tertiary, 194, 197, 202, 204, 211, 222 Tyrol, Triassic eruptive rocks of, i. 29 Tyrone, Old Red Sandstone of, i. 314

Ulster, Old Red Sandstone volcanic rocks of, i. 314 Ultra-basic rocks, i. 14, 118, 377, 417 Unconformability, deceptive case of, i. 163 Urgneiss, i. 110 Uriconian volcanic rocks, i. 129 Ussher, Mr. W. A. E., i. 260, 262; ii. 35, 95 Utah, laccolites of, i. 86; volcanic regions of, ii. 115, 267

Valleys, tendency of vents to appear in, i. 272, 368, 376; ii. 61, 65, 96 Vapours, action of volcanic, i. 13, 15, 16, 17, 31, 57, 72, 78, 97, 99, 180, 289, 426 Variolitic structure, i. 21, 206, 235 Veins, intrusive, i. 66, 77, 79, 98, 426, 429; ii. 311, 313, 400, 410, 432, 437 Velay, volcanic rocks of, i. 26, 27, 29, 60; ii. 271, 373, 375 Vents, volcanic, i. 53; ground-plans of, 54; size of, 55; filled with non-volcanic detritus, 57; ejected crystals found in, 62; agglomerates of, 62; ii. 13, 28, 47, 61, 69, 276, 280, 284, 288, 289; stratification in, i. 63; ii. 80; metamorphism in, i. 67, 71; metamorphism of rocks around, 72, 349, 350, 352, 399, 404, 432; ii. 76, 272, 280; connection of, with geological structure-lines, i. 68; occurrence of, in lines and in groups, 69; double and multiple, 69; possible indications of length of activity of, 72; inward dip of strata around, 73, 352; ii. 76, 295; stages in history of, i. 74; tendency of, to rise in lines of valley, 272, 368, 376; ii. 61, 65, 96, 468; criteria for the relative ages of, 270; connection of, with later eruptive bosses, 280, 384, 399, 400 ---- Silurian, i. 209, 214, 234; Old Red Sandstone, 272, 287, 298, 305, 323, 328, 337; Carboniferous, 394, 399, 400, 404, 406, 424, 465; ii. 13, 28, 47; Permian, 61, 69; Tertiary, 202, 270, 294, 400 Vesicular structure of lavas, i. 15; ii. 187 Vesuvius, denudation of, i. 3; as an active volcano, 4; as a type of volcano, 10, 39, 53, 100; ii. 108, 115, 261, 266 Vicary, Mr. W., ii. 95 Vogesite, i. 277, 293 Volcanello Island, i. 70 Volcanic action, permanent traces of, i. 4; of present time elucidates that of the past, 5; submarine, 5; transient effects of, 8; chief factors in, 10; explosive energy of, 13, 99; uniformity of, in geological time, 13, ii. 470; metamorphism by, i. 67, 71; underground phases of, 77; proofs of gradual quiescence of, 155, 157, 166; connected with subsidence, 295, 297; ii. 205, 444, 463, 470; repetition of, in the same region, i. 368, 375, 377; ii. 42, 69, 94, 467; developed along continental borders, 466; persistence of, in Britain, i. 7; ii. 466; connection of, with lines of geological structure, 468; connection of, with terrestrial disturbance, 469; gradual decline of, during Palæozoic time, 471; quiescence of, during Mesozoic time, 472 Volcanic cycles, i. 27, 92 ---- products, general characters of, i. 14; persistent uniformity of, 30, 46; thickest mass of, in Britain, 229 (_see_ Agglomerate, Lava, Tuff) Volcano, Island of, i. 4, 24 Volcanoes, their influence on mythology, i. 1, 2; denudation of, 3; number of extinct, 4; ancient, of Britain, 6; influence on scenery, 8, 100, 102; defined, 10; types of, 10, 39; ii. 471; determination of relative dates of, i. 46; their geographical condition in old times, how ascertained, 48; parasitic, 69; contemporaneous denudation of, 73, 100; connected with granite, 89; incompleted, 86, 93, 99 Vom Rath, G., ii. 474

Wacke, i. 157 Walcott, Mr., i. 30 Wales, pre-Cambrian rocks of, i. 126, 142; early geological work in, 142; Cambrian volcanoes of, 145, 159; volcanic scenery of, 176; Silurian volcanoes of, 176, 202, 205, 207, 218, 219; Old Red Sandstone of, 257, 259 Waller, Mr. T. H., i. 171, 278 Ward, J. C., i. 227, 228, 229, 230, 231, 233, 234, 235, 236, 237; ii. 23 Warwickshire, Cambrian rocks of, i. 137, 171 Waterford, volcanic region of, i. 247 Watts, Mr. W. W., i. 131, 132, 135, 137, 189, 190, 191, 243, 276, 278, 336, 347, 417, 421, 423; ii. 40, 42, 43, 45, 57, 96, 184, 204, 224, 272, 424, 425 Weaver, T., i. 238 Wenlock group, i. 175; volcanic rocks of, 552 Wernerian School, ii. 109 West Lothian, volcanic rocks of, i. 47, 55, 415, 433, 437 Whin Sill of England, i. 83, 85, 97, 449; ii. 2 Whitehurst, J., ii. 9, 109 White trap, i. 96, 426, 449, 456; ii. 65, 87, 103, 165, 252 Williams, Mr. G. J., i. 179, 185, 186, 188 Williamson, W. C., i. 392 Wilson, Mr. J. S. Grant, i. 148, 149, 153, 276, 344, 375, 379, 380;