_SALINA, section in_, 132, fig. 53 Sandwich Islands, lavas of, 125 San Sebastiano, destruction of, 26 _San Stephano, section in_, 131, fig. 50 Santorin, 42 _Sarcoui, Grand Puy of_, 126, fig. 44 Sciarra del fuoco, 13 Scoria, how formed, 68, 70 Scoria-cones, altered by acid gas, 155 -- breached, 156 -- characters of, 153 -- preservation of, 155 -- red colour of, 154 _Scoria-cone in Vesuvius_, 122, fig. 39 _Scoria-cone near Auckland, N. Z._, 1656, fig. 66 Schmidt, referred to, 153 Schreibersite, 314 Scrope, Mr. Poulett, cited, 5, 69, 106, 135, 198, 205, 212, 238, 289 Sea of Azof, mud-volcanoes of, 182 Secchi, Father, cited, 362 Shiant Isles, 105 Silica, presence in lavas, 47 Silicates in lavas, 47 Silicon, proportion in lavas, 47 Siliceous sinter, deposits of, 220 Silver, spitting of, 355 Silvestri, Professor, cited, 230 Similarity of lavas of different ages, 260 _Sinter-cones, forms of_, 183, fig. 79 Skye, dissected volcano of, 144 Slags, compared with lavas, 46 Smith, Lawrence, cited, 320 Smoke, appearance of, due to steam, 2 Snowdon, 274 _Solar prominences_, 364-366, figs. 92, 93, 94 Solfatara of Naples, 214 Solfatara-stage of volcanoes, 215 Somma, 133 -- crater-ring of, 83 Sorby, Mr. H. C., referred to, 59, 252 Spallanzani, early researches of, 4 -- observations on Stromboli, 8 -- cited, 39, 367 Specific gravities of lavas, 49 -- -- of glassy and crystalline rocks, 59 Spectroscope in vulcanology, 41 Spectrum-analysis, results of, 311 Specular-iron, deposited on lava-streams, 110 Sperenberg, boring of, 341 _Sphærulites_, 54, _Frontispiece_ Sporadosiderites, 316 Stability of crust of globe, 326 Staffa, Isle of, 106 Steenstrup, cited, 319 Steam-engine compared to volcano, 8 Steam, emitted by lava of Vesuvius, 27 Sternberg, referred to, 113 St. Kilda, 181 Stokes, Professor, 65 St. Paul, Island of, 180 Stromboli, 42, 158 -- apertures at bottom of crater, 15 -- appearances in crater of, 16 -- -- at night, 10 -- compared with Vesuvius, 23 -- crater of, 13 -- dependence of eruptions on atmospheric conditions, 34 -- eruption of, 14, fig. 4 -- general features of, 11 -- map of, 11, fig. 2 -- observations by Spallanzani, 8 -- resemblance to flashing light, 10 -- _section of_, 13, fig. 8 -- soundings around, 12 -- vapour-cloud above, 9 -- violent eruptions of, 23 Strombolian stage, 23 Stufas, nature of, 217 Submarine volcanoes, 179 Subterranean forces, beneficial effects of, 303 Subsidence in centre of volcanoes, 165 Sulphur, absorption of water by molten, 356 -- deposited on lava-streams, 110 -- how formed at volcanoes, 18 -- not the cause of volcanic outbursts, 18 _Surfaces of lava-streams_, 97-99, figs. 22, 23 _Sun-spots_, 361-363, figs. 89, 90, 91 Syenite, 59 Syssiderites, 316 Szabo, Professor, cited, 199