INDEX 
491 
Troctolite, ii. 332 
Tuffs, i. 31 ; association of, 33 ; composition of, 
34 ; alternations of, 34, 61 ; blending of, with 
non-volcanic sediment, 35, 437 ; fossiliferous, 
36 ; without lava, 36 ; necks of, 58 ; relation 
of, to lavas, 61 ; metiiinorphisni of, ii. 224 
pre-Cambrian, i. 125, 135 ; Cambrian, 147, 
161, 155, 163, 165, 167 ; Silurian, 178, 189, 
190, 195, 205, 209, 212, 213, 222, 224, 22'9, 
232, 211, 245, 246, 254, 255 ; Devonian, 262 ; 
Old Red Sandstone, 279, 281, 289, 337, 339, 
351 ; Carboniferous, 381, 384, 387, 399, 422, 
427, 429, 432, 436, 466; 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 
Unconformabilitv, deceptive case of, i. 163 
Crgneiss, i. 110 
Uriconian volcanic rocks, i. 129 
Ussher, Mr. W. A. E,, i. 260, 262; ii. 35, 95 
Utah, laecolites 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, 
81, 57, 72, 78, 97, 99, 180, 289, 426 
Variolitie structure, i. 21, 206, 235 
Veins, intrusive, i. 66, 77, 79, 98, 426, 429 ; ii. 
811, 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 ; agglomer- 
ates of, 62 ; ii. 13, 28, 47, 61, 69, 276, 2S0, 
284, 288, 289 ; stratification in, i. 63 ; ii. -SO ; 
metamorphism in, i. 67, 71 ; metamorphism 
of rocks around, 72, 349, 350, 352, 399, 404, 
432 ; ii. 76, 272, 280 ; connection of, with geo- 
logical 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 clip of strata around, 73, 
352 ; ii. 76, 295 ; stages in history of, i. 74 ; 
tendency of, to vise 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 Sand- 
stone, 272, 287, 298, 305, 328, 328, 337 ; Car- 
boniferous, 394, 899, 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. IV., 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, 166 ; persistence of, in Britain, i. 
7 ; ii. 466 : connection of, with lines of 
geological . structure, 168 ; connection of, 
with terrestrial disturbance, 469 ; gradual 
decline of, during Palieozoic time, 471 ; qui- 
escence of, during Mesozoic time, 472 
Volcanic cycles, i. 27, 92 
■ products, general characters of, i. 14 ; per- 
sistent uniformity of, 30, 46 ; thickest mass 
of, in Britain, 229 (sec 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 011 scenery, 
8, 100, 1.02; 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; contem- 
poraneous denudation of, 73, 100 ; connected 
with granite, S9 ; iueompleted, 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, 46, 57, 96, 184, 204, 224, 
272, 424, 425 
Weaver, T., i. 238 
Wenloek 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, S5, 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 ; ii. 137, 164 
Wilson, Mr. A., ii. 49 
Winch, N. T„ ii. 118, 147 
Witliam, H. T. M., ii. 113, 238 
Wood, N., ii. 113 
Woods, Mr. EL, i. 204 
Woodward, Dr. Henry, ii. 449 
Woodward, Mr. IE. B. , ii. 32,435, 453 
Worcestershire, latest eruptive rocks of, ii. 
101 
Worth, Mr. R. N., ii. 99 
Wrekin, i. 130 
Wright, J. R., ii. 102 
