GABBRO, 59 Gardiner's river, travertine terraces of, 185 Gases emitted from volcanoes, 40 -- -- volcanic vents, 212-216 Geanticlinals, formation of, 297 Gems, formation of, 147 -- mode of occurrence, 148 Geological continuity, doctrine of, 247 Geosynclinals, formation of, 294 Geysers, formation of, 217 -- intermittent action of, 218 -- of Colorado, 184, 217 -- of Iceland, 184, 217 Giant's Causeway, 108 Gilbert, Mr. G. K., cited, 208 Girgenti, mud-volcanoes of, 182 Glass, formed by fusion of lavas, 52 Glasses, composed of certain silicates, 58 Glassy base, 57 Goethe, cited, 112 _Graham Isle_, 178, 179, fig. 78 Graham, cited, 345 Grand Sarcoui, Auvergne, 161 Granite, 59 Granite of Secondary and Tertiary ages, 254 Granitic rocks, position beneath volcanoes, 145 Great earth movements, nature of, 286 Great volcanic bands of the globe, 232-234 Grenelle, boring of, 341 Greystones, 49 Groundmass of lavas, 52 Grotto del Cane, 215 Guevo Upas, Java, 215 Guiscardi, Professor, referred to, 45 _Gustavila, crater-lake of_, 172, fig. 72 HAMILTON, Sir W., researches of, 4, 75, 84 -- -- observations on Vesuvius, 80 Hannay, Mr., referred to, 147 Hartley, Mr. Noel, referred to, 65 Hawaii, volcanoes of, 100, 125 -- -- lava-masses of, 159 -- -- volcanic eruptions at different levels, 327 Hebrides, volcanoes of, 271 Henry, Dr., cited, 355 Henry Mountains, Southern Utah, 208 Hephæstus, forge of, 3 Hochstetter, cited, 135, 356 Holosiderites, 315 Hopkins, Mr., cited, 349 Hot springs, numbers of, 219 Humboldt, researches of, 4 Hungary, lavas of, 96, 103 -- volcanoes of, 126, 201 -- deep wells of, 341 _Hverfjall, Iceland_, 178, fig. 77 Hydro-electric machine of Sir W. Armstrong, 29 Hypothesis, value of, 331-333 ICE under lava of Vesuvius in 1872, and of Etna, 110 Iceland, volcanic dust of, carried to Norway, 72 Indian Ocean, volcanoes in, 229 _Insel Ferdinandez_, 178, 179, fig. 78 Intermediate lavas, 48 Intervals between Eruptions, 33 Ireland, north-east of, 103 _Iron in Ovifak-basalts_, 319, fig. 87 Iron, seething of, 356 -- of Ovifak, terrestrial origin of, 320 Ischia, eruption in 1301, 164 -- _crater-lake of Bagno in_, 172, fig. 71 -- _plan of_, 163, fig. 64 -- _parasitic cones in_, 164, fig. 65 Island of Bourbon, 93 _Isle Julie_, 178, 179, fig. 78 Isogeotherms, 359 JANSSEN, referred to, 42 Joint-structures in lava, 104-110 _KAMMERBÜHL_, 112-114, fig. 33 -- _section of_, 114, fig. 34 -- _section in side of_, 118, fig. 36 Kant, nebular hypothesis of, 352 Kilauea, volcano of, 71, 138 -- crater of, 181 King, Mr. Clarence, cited, 301