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Volcanoes: Past and Present
by Edward Hull
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11. GRANOPHYRE.—This term, according to Geikie, embraces the greater portion of the acid volcanic rocks of the Inner Hebrides. They are closely allied to the quartz-porphyries, and vary in texture from a fine felsitic or crystalline-granular quartz-porphyry, in the ground-mass of which porphyritic turbid felspar and quartz may generally be detected, to a granitoid rock of medium grain, in which the component dull felspar and clear quartz can be readily distinguished by the naked eye. Throughout all the varieties of texture there is a strong tendency to the development of minute irregularly-shaped cavities, inside of which quartz or felspar has crystallised out—a feature characteristic of the granites of Arran and of the Mourne Mountains.

12. GRANITE.—A true granite consists of a crystalline-granular rock consisting of quartz, felspar (orthoclase), and mica; the quartz is the paste or ground-mass in which the felspar and mica crystals are enclosed. This is the essential distinction between a granite and a quartz-porphyry or a granophyre. Owing to the presence of highly-heated steam under pressure in the body of the mass when in a molten condition, the quartz has been the last of the minerals to crystallise out, and hence does not itself occur with the crystalline form.

True granite is not a volcanic rock, and its representatives amongst volcanic ejecta are to be found in the granophyres, quartz-porphyries, felsites, trachytes, and rhyolites so abundant in most volcanic countries, and to one or other of these the so-called granites of the Mourne Mountains, of Arran Island, and of Skye are to be referred. Granite is a rock which has been intruded in a molten condition amongst the deep-seated parts of the crust, and has consolidated under great pressure in presence of aqueous vapour and with extreme slowness, resulting in the formation of a rock which is largely crystalline-granular. Its presence at the surface is due to denudation of the masses by which it was originally overspread.



EXPLANATION OF PLATE I.

MAGNIFIED SECTIONS OF VESUVIAN MINERALS.

Fig. 1. Section of leucite crystal from the lava of 1868, with fluid cavities. Mag., 350 diams.

" 2, 3, 4, and 5. Sections of nepheline crystals from the lava of 1767, 1834, and 1854.

" 6. Section of sodalite crystal from the lava of 1794, with belonites and crystals of magnetite enclosed.

" 7, 8, 9. Crystals of leucite with microliths and cavities darkened by magnetite dust; also, containing crystals of magnetite.

" 10. Group of leucite crystals of irregular form from the lava of 1855, congregated around a nucleus of crystals of plagioclase and magnetite.



EXPLANATION OF PLATE II.

MAGNIFIED SECTIONS OF VESUVIAN MINERALS.

Fig. 1. Section of augite crystal from the lava of 1794, with numerous gas cells and delicately banded walls. The interior contains two long prisms, probably of apatite.

" 2. Crystal of augite with banded walls, and indented by leucite crystals, from the lava of 1794. Mag., 40 diams.

" 3, 4, 5. Sections of augite crystals from the lavas of 1794 and 1820.

" 6. Group of augite crystals from the lava of 1835.

" 7. Ditto from the lava of 1822, with encluded mica-flake (a) and portion of the glass paste, or ground-mass, of the rock (b), containing microliths and grains of magnetite.

Fig. 8. Two crystals of olivine from the lava of 1855; they are intersected on one side by the plane of the thin section, and are remarkable for showing lines of gas cells, and bands of growth sometimes cellular. Mag., 40 diams.

" 9. Section of rock-crystal (quartz), with double terminal pyramids, from the lava of 1850.

" 10. Twin crystal of sanidine from the lava of 1858. Mag., 40 diams.

" 11, 12, 13. Sections of plagioclase crystals (probably labradorite) from the lava of 1855. Mag., 100 diams.

" 14. Section of olivine crystal from the lava of 1631—imperfectly formed. Mag., 30 diams.

" 15. Section of mica-flake from the lava of 1822. Mag., 30 diams.



EXPLANATION OF PLATE III.

MAGNIFIED SECTIONS OF VOLCANIC ROCKS.

1. Diorite dyke, traversing Assynt limestone, North Highlands.

2. Basalt from upper beds, near Giant's Causeway, County Antrim.

3. Hornblende-hypersthene-augite Andesite, from Pichupichu, Andes.

4. Augite-Andesite from Pichupichu, Andes.

5. Olivine dolerite, with hornblende and biotite, Madagascar.

6. Leucite basalt, with mellilite, Capo di Bove, Italy.



EXPLANATION OF PLATE IV.

MAGNIFIED SECTIONS OF VOLCANIC ROCKS.

1. Vesuvian lava, glass paste with numerous crystals of leucite; others of augite and nepheline porphyritically developed; also small grains of magnetite.

2. Vesuvian lava, glass paste with numerous crystals of leucite; others of olivine, hornblende, and sanidine, porphyritically developed; small grains of magnetite.

3. Trachyte from Hungary; felsitic paste with crystals of hornblende and sanidine, and a little magnetite.

4. Gabbro, from Carlingford Hill, Ireland, consisting of anorthite, augite, a little olivine, and magnetite.

5. Dolerite, from old volcanic neck, Scalot Hill, near Lame, consisting of labradorite, augite, olivine, and magnetite.

6. Dolerite, Ballintoy, County Antrim, showing ophetic structure, consisting of augite, labradorite, and magnetite.

[1] Mr. S. Allport has discovered this in the rock called the "Wolf Rock" off the coast of Cornwall. The most important work on basalt is that by F. Zirkel, Unters. ueber mikros. Zusammensetzung und Structur der Basaltgesteine. Bonn (1870).

[2] Zirkel, Die mikroskopische Beschaffenheit der Mineralien und Gesteine, p. 153. Leipsig (1873).

[3] Zirkel, Petrog., i. 578; B. von Cotta, p. 178 (Eng. Trans.).



INDEX.



INDEX.

Abyssinian table-lands, 190 et seq.

Albano, Lake, 89

America, volcanic regions of North, 136 et seq.; of Western, 144

Andes, 18, 27, 227, 254

Andesite, 263

Antrim, 154 et seq.

Arabia, dormant volcanoes of, 126-135

Arabian desert, 134

Archibald, C. D., 213

Arizona, volcanoes of, 137

Argyll, Duke of, 173

Ascension, 36

Ashangi, volcanic series of, 192

Atmospheric effects of Krakatoa eruption, 213-214

Auckland district, volcanoes of, 147

Auvergne, volcanic regions of, 14, 16, 92 et seq.

Azores, 32

Ball, Sir R. S., 242, 244

Basalt, 260

Blanford, W. T., 188, 189

Bonneville, Lake, 141-142

British Isles, Tertiary volcanic districts of, 154 et seq., 227; pre-Tertiary volcanic districts of, 196 et seq.

Buch, L. von, 6, 11, 24

California, volcanoes of, 140

Callirrhoe, springs of, 133

Canyon, the Grand, 138

Cantal, volcanoes of the, 99-101

Cape Colony, Basalts of, 194

Charleston earthquake, 218, 222, 224

Chambers, G. F., 246

Charnwood Forest, 198

Chimborazo, 18

Clermont, vale of, 96-97

Clinkstone, 263

Cordilleras of Quito, 25

Cotopaxi, 16-18, 24, 26

Crater-cones, Lava, 19

Crateriform cones, 13

Craterless domes, 15

Dana, Prof. J. D., 19, 39, 249

Darwin, 28, 30

Darwin, Prof. G. H., 9, 231

Daubeny, 7, 61, 69

Davison, C., 9, 231

Davy, Sir H., 11

Deccan trap-series, 187 et seq.

Demavend, Mount, 24

Diabase, 262

Diorite, 261

Dolerite, 261

Domite, 263

Dore, volcanoes of Mont, 100-101

Doughty, C. M., 127

Durocher, 232

Dutton, Capt. C. E., 9, 220, 222

Dykes in Ireland, 169-170

Earthquakes, 217 et seq.

Errigal, 10

Etna, 14, 61 et seq., 229

Fingal's Cave, 185

Forbes, D., 27

France, extinct volcanoes of, 92 et seq.

Gabbro, 261

Gardner, J. S., 156

Geikie, Sir A., 8, 29, 143, 156, 160, 169, 172, 176, 177, 196

Giant's Causeway, 165-166

Granite, 264

Granophyre, 264; of Mull, 174

Green, Prof. A. H., 194

Hatch, Dr., 260

Haughton, Prof., 68

Hauran, volcanoes of the, 22, 129

Haute Loire, volcanic districts of, 101-105

Hawaii, volcanoes of, 39, 249, 251

Hecla, 32

Herschel, Sir J., 244

Hibbert, Dr. S., 6, 114, 124

Hochstetter, F. von, 147

Hopkins, 171, 217

Hull, Dr. E. G., 110

Humboldt, A. von, 20, 25

Hutton, James, 5

Iceland, volcanoes of, 30-32

Ireland, volcanic Tertiary rocks of, 154 et seq.

Jaulan, 129

Johnston-Lavis, 52

Jordan valley, 126 et seq., 226

Jorullo, 24

Judd, Prof., 8, 68, 69, 71, 172, 178, 208

Krakatoa, eruption of, 206 et seq.

Kurile Islands, volcanoes of, 28

Laacher See, 121-123

Lampophyre, 262

Lancerote, 34

Lasaulx, Prof. von, 68

Lavas, relative density of, 232-234

Lima in 1746, earthquake of, 222

Lipari Islands, volcanoes of, 69 et seq.

Lisbon, earthquake of, 221

Lister, J. J., 38

Lunar volcanoes, 236 et seq.

Lyell, Sir C., 30, 62, 78, 217

Mackowen, Col., 74

Magdala, volcanic series of, 192-193

Mallet, R., 9, 217

Mauna Loa, 19, 39, 249

Mica-trap, 262

Milne, Prof., 28, 218, 253

Moab, volcanic regions of, 132

Moon, volcanoes of, 236 et seq.

Monte Nuovo, 85

Mull, 172 et seq.

Neapolitan group of volcanoes, 28

New Zealand, volcanoes of, 146

Obsidian, 264

Ocean waves of seismic origin, 208, 220

O'Reilly, Prof., 9, 219

Orizaba, 21

Ovid, 3

Pacific, volcanic islands of, 37

Palestine, dormant volcanoes of, 126-135

Palmieri, Prof., 55

Pantelleria, 74

Phlegraean fields, 85

Phonolite, 263

Pitchstone, 264

Pliny, 2, 4

Porphyrite, 262

Powell, Major, 138

Pre-Tertiary volcanic rocks, 187 et seq.; of British Isles, 196 et seq.

Puy de Dome, 105-110

Pythagoreans on volcanoes, 2-3

Quito, Cordilleras of, 25

Rangitoto, 19, 149

Reyer, Dr. E., 17

Rhine valley, volcanoes of, 113 et seq.

Rhyolite, 263

Riviera in 1887, earthquake of, 219

Rocca Monfina, 80

Roderberg, 119, 120

Rome, 88-89

Rosenbusch, H., 260

Roto Mahana, 151

Ruapahu, 151

Russell, Hon. Rollo, 213

Rutley, F., 260

St. Helena, 37

San Francisco, Mount, 138

Santorin, 76-83

Schehallion, 10

Schumacher, 127

Scotland, volcanic districts of, 172 et seq.

Scrope, Poulett, 5, 73, 93, 98

Scuir of Eigg, 180-184

Seismic phenomena, special, 201 et seq., 217 et seq.

Shasta, Mount, 140

Siebengebirge, 116-120

Skye, 177-179

Sleamish, 168

Smyth, Piazzi, 33

Snake River, volcanoes of, 142

Staffa, 185-186

Strabo on volcanoes, 3

Stromboli, 71-73

Sumatra, volcanic action in, 226

Syenite, 262

Symes, R. G., 167

Syria, earthquakes in, 219

Taupo Lake, 150

Taylor, Mount, 138

Tell el Ahmar, 131

Tell el Akkasheh, 131

Tell el Farras, 131

Tell Abu en Neda, 130

Tell Abu Nedir, 129

Templepatrick, quarry at, 160

Teneriffe, 33

Tertiary period, volcanic activity of, 255

Thucydides, 2

Tonga Islands, volcanoes of, 38

Tongariro, 151

Trachyte, 263

Trass of Bruehl Valley, 123-125

Tristan da Cunha, 37

Tristram, Canon, 127, 131

Utah, volcanoes of, 137

Verbeek, R. D. M., 202

Vesuvius, 4, 14, 41-60, 67, 229

Volcanoes, historic notices of, 1-5; form, structure, and composition of, 10-19; lines and groups of active, 20-29; of mid-ocean, 30-40; extinct or dormant, 84 et seq.; special volcanic and seismic phenomena, 201 et seq.; the ultimate cause of volcanic action, 225 et seq.; whether we are living in an epoch of special volcanic activity, 253-256; brief account of volcanic rocks, 259-265

Vulcanists, 5

Vulcano, 69, 71

Wallace, A. R., 81

Waltershausen, W. S. von, 7, 61

Wellington, Mount, 149

Wharton, Capt., 212

Whymper, E., 18

Yarmuk, valley of the, 129, 131

Yellowstone Park, 145

Zirkel, F., 260

Zoellner, 240

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Transcriber's note:

Changed 'Kilarrea' to 'Kilauea' on page 19: Mauna Loa and Kilarrea.

Changed 'Kilanea' to 'Kilauea' on page 39: Kilanea, 4158 feet.

Made punctuation (semi-colons) consistent in caption to figure 16.

Changed 'Brionde' to 'Brioude' on page 94: till at Brionde it becomes.

Changed 'occuping' to 'occupying' on page 96: occuping a hollow.

Changed 'Rodesberg' to 'Roderberg' on page 118: old extinct volcano of Rodesberg.

Changed 'Wolkenberg' to 'Wolkenburg' on page 118: and that of the Wolkenberg.

Left the reference to Jeremiah, l. 25. in footnote to Part III Chapter I, although Jeremiah, li. 25. seems more appropriate.

Changed 'fumarols' to 'fumaroles' on page 137: fumarols give evidence.

Removed extra comma on page 153: of the present, epoch.

Changed 'columnal' to 'columnar' on page 176: the columnal structure.

Changed 'groves' to 'grooves' on page 183: the groves and scorings.

Changed 'Angust' to 'August' on page 212: the 27th of Angust.

Changed 'mikroskopischen' to 'mikroskopische' on page 260: ueber mikroskopischen Structur.

Changed 'become' to 'becomes' on page 260: the rock become a leucite-basalt.

Left inconsistent spellings of 'Baalbec' and 'Baalbeck'; 'Harrat' and 'Harrat'; 'metres' and 'metres'; 'pitchstone' and 'pitch-stone'; 'prehistoric' and 'pre-historic'; 'Rhone' and 'Rhone'; 'sub-aerial', 'subaerial' and 'subaerial'; 'tableland' and 'table-land'.

Greek words were replaced with their transliterations: 'meson pyr' and 'Peri kosmou'.

The oe-ligature was expanded to the two separate characters: 'Euboea' and 'Boeotia'.

Left the list numbering as is at the beginning of Chapter II of Part IV, even though the list begins at item c, as if it continues the list which began in the previous chapter.

THE END

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