CHAPTER III
.
ARE WE LIVING IN AN EPOCH OF SPECIAL VOLCANIC ACTIVITY?
The question which we are about to discuss in the concluding chapter of this volume is one to which we ought to be able to offer a definite answer. This can only be arrived at by a comparison of the violence and extent of volcanic and seismic phenomena within the period of history with those of pre-historic periods.
At first sight we might be disposed to give to the question an affirmative reply when we remember the eruptions of the last few years, and add to these the volcanic outbursts and earthquake shocks which history records. The cases of the earthquake and eruption in Japan of November, 1891, where in one province alone two thousand people lost their lives and many thousand houses were levelled[1]; that of Krakatoa, in 1883; of Vesuvius, in 1872; and many others of recent date which might be named, added to those which history records;--the recollection of such cases might lead us to conclude that our epoch is one in which the subterranean volcanic forces had broken out with extraordinary energy over the earth's surface. Still, when we come to examine into the cases of recorded eruptions--especially those of great violence--we find that they are limited to very special districts; and even if we extend our retrospect into the later centuries of our era, we shall find that the exceptionally great eruptions have been confined to certain permanently volcanic regions, such as the chain of the Andes, that of the Aleutian, Kurile, Japanese, and Philippine and Sunda Islands, lying for the most part along the remarkable volcanic girdle of the world to which I have referred in a previous page. Add to these the cases of Iceland and the volcanic islands of the Pacific, and we have almost the whole of the very active volcanoes of the world.
Then for the purposes of our inquiry we have to ascertain how these
## active vents of eruption compare, as regards the magnitude of their
operations, with those of the pre-historic and later Tertiary times. But before entering into this question it maybe observed, in the first place, that a large number of the vents of eruption, even along the chain of the earth's volcanic girdle, are dormant or extinct. This observation applies to many of the great cones and domes of the Andes, including Chimborazo and other colossal mountains in Ecuador, Columbia, Chili, Peru, and Mexico. The region between the eastern Rocky Mountains and the western coast of North America was, as we have seen, one over which volcanic eruptions took place on a vast scale in later Tertiary times; but one in which only the after-effects of volcanic action are at present in operation. We have also seen that the chain of volcanoes of Japan and of the Kurile Islands are only active to a slight extent as compared with former times, and the same observation applies to those of New Zealand. Out of 130 volcanoes in the Japanese islands, only 48 are now believed to be active.
Again, if we turn to other districts we have been considering, we find that in the Indian Peninsula, in Arabia, in Syria and the Holy Land, in Persia, in Abyssinia and Asia Minor--regions where volcanic operations were exhibited on a grand scale throughout the Tertiary period, and in some cases almost down into recent times--we are met by similar evidences either of decaying volcanic energy, or of an energy which, as far as surface phenomena are concerned, is a thing of the past. Lastly, turning our attention to the European area, notwithstanding the still
## active condition of Etna, Vesuvius, and a few adjoining islands, we see
in all directions throughout Southern Italy evidences of volcanic operations of a past time,--such as extinct crater-cones, lakes occupying the craters of former volcanoes, and extensive deposits of tuff or streams of lava--all concurring in giving evidence of a period now past, when vulcanicity was widespread over regions where its presence is now never felt except when some earthquake shock, like that of the Riviera, brings home to our minds the fact that the motive force is still beneath our feet, though under restrained conditions as compared with a former period.
Similar conclusions are applicable with even greater force to other parts of the European area. The region of the Lower Rhine and Moselle, of Hungary and the Carpathians, of Central France, of the North of Ireland and the Inner Hebrides, all afford evidence of volcanic operations at a former period on an extensive scale; and the contrast between the present physically silent and peaceful condition of these regions, as regards any outward manifestations of sub-terrestrial forces, compared with those which were formerly prevalent, cannot fail to impress our minds irresistibly with the idea that volcanic energy has well-nigh exhausted itself over these tracts of the earth's surface.
From this general survey of the present condition of the earth's surface, as regards the volcanic operations going on over it, and a comparison with those of a preceding period, we are driven to the conclusion that, however violent and often disastrous are the volcanic and seismic phenomena of the present day, they are restricted to comparatively narrow limits; and that even within these limits the volcanic forces are less powerful than they were in pre-historic times.
The middle part of the Tertiary period appears, in fact, to have been one of extraordinary volcanic activity, whether we regard the wide area over which this activity manifested itself, or the results as shown by the great amount of the erupted materials. Many of the still active volcanic chains, or groups, probably had their first beginnings at the period referred to; but in the majority of cases the eruptive forces have become dormant or extinct. With the exception of the lavas of the Indian-Peninsular area, which appear, at least partially, to belong to the close of the Cretaceous epoch, the specially volcanic period may be considered to extend from the beginning of the Miocene down to the close of the Pliocene stage. During the Eocene stage, volcanic energy appears to have been to a great degree dormant; but plutonic energy was gathering strength for the great effort of the Miocene epoch, when the volcanic forces broke out with extraordinary violence over Europe, the British Isles, and other regions, and continued to develop throughout the succeeding Pliocene epoch, until the whole globe was surrounded by a girdle of fire.
* * * * *
The reply, therefore, to the question with which we set out is very plain; and is to the effect that the present epoch is one of comparatively low volcanic activity. The further question suggests itself, whether the volcanic phenomena of the middle Tertiary period bear any comparison with those of past geological times. This, though a question of great interest, is one which is far too large to be discussed here; and it is doubtful if we have materials available upon which to base a conclusion. But it may be stated with some confidence, in general terms, that the history of the earth appears to show that, throughout all geological time, our world has been the theatre of intermittent geological activity, periods of rest succeeding those of
## action; and if we are to draw a conclusion regarding the present and
future, it would be that, owing to the lower rate of secular cooling of the crust, volcanic action ought to become less powerful as the world grows older.
[1] Admirably illustrated in Prof. J. Milne's recently published work, _The Great Earthquake of Japan, 1891_.
APPENDIX.
A BRIEF ACCOUNT OF THE PRINCIPAL VARIETIES OF VOLCANIC ROCKS.
The text-books on this subject are so numerous and accessible, that a very brief account of the volcanic rocks is all that need be given here for the purposes of reference by readers not familiar with petrological details.
Let it be observed, in the first place, that there is no hard and fast line between the varieties of igneous and volcanic rocks. In this as in other parts of creation--_natura nil facit per saltum_; there are gradations from one variety to the other. At the same time a systematic arrangement is not only desirable, but necessary; and the most important basis of arrangement is that founded on the proportion of _silica_ (or quartz) in the various rocks, as first demonstrated by Durocher and Bunsen, who showed that silica plays the same part in the inorganic kingdom that carbon does in the organic. Upon this hypothesis, which is a very useful one to work with, these authors separated all igneous and volcanic rocks into two classes, viz., the Basic and the Acid; the former containing from 45-58 per cent., the latter 62-78 per cent. of that mineral. But there are a few intermediate varieties which serve to bridge over the space between the Basic and Acid Groups. The following is a generalised arrangement of the most important rocks under the above heads:--
_Tabular View of Chief Igneous and Volcanic Rocks._
BASIC GROUP.
1. Basalt and Dolerite. 2. Gabbro. 3. Diorite. 4. Diabase and Melaphyre. 5. Porphyrite.
INTERMEDIATE GROUP.
6. Syenite. 7. Mica-trap, or Lampophyre. 8. Andesite.
ACID GROUP.
9. Trachyte, Domite, and Phonolite. 10. Rhyolite and Obsidian. 11. Granophyre. 12. Granite.
In the above grouping, and in the following definitions, I have not been able to follow any special authority. But the most serviceable text-books are those of Mr. Frank Rutley, _Study of Rocks_, and Dr. Hatch, _Petrology_; also H. Rosenbusch, _Mikroskopische Physiographie der Mineralien_, and F. Zirkel's _Untersuchungen über mikroskopische Structur der Basaltgesteine_. We shall consider these in the order above indicated:--
1. BASALT.--The most extensively distributed of all volcanic rocks. It is a dense, dark rock of high specific gravity (2.4-2.8), consisting of plagioclase felspar (Labradorite or anorthite), augite, and titano-ferrite (titaniferous magnetite). Olivine is often present; and when abundant the rock is called "olivine-basalt." In the older rocks, basalt has often undergone decomposition into melaphyre; and amongst the metamorphic rocks it has been changed into diorite or hornblende rock; the augite having been converted into hornblende.
When leucite or nepheline replaces plagioclase, the rock becomes a leucite-basalt,[1] or nepheline-basalt. Some basalts have a glass paste, or "ground-mass," in which the minerals are enclosed.
The lava of Vesuvius may be regarded as a variety of basalt in which leucite replaces plagioclase, although this latter mineral is also present. Zirkel calls it "Sanidin-leucitgestein," as both the macroscopic and microscopic structure reveal the presence of leucite, sanidine, plagioclase, nephiline, augite, mica, olivine, apatite, and magnetite.[2]
_Dolerite_ does not differ essentially from basalt in composition or structure, but is a largely crystalline-granular variety, occurring more abundantly than basalt amongst the more ancient rocks, and the different minerals are distinctly visible to the naked eye.
A remarkable variety of this rock occurs at Slieve Gullion in Ireland, in which mica is so abundant as to constitute the rock a "micaceous dolerite."
2. GABBRO.--A rather wide group of volcanic rocks with variable composition. Essentially it is a crystalline-granular compound of plagioclase, generally Labradorite and diallage. Sometimes the pyroxenic mineral becomes hypersthene, giving rise to _hypersthene-gabbro_; or when hornblende is present, to _hornblende-gabbro_; when olivine, to _olivine-gabbro_. Magnetite is always present.
These rocks occur in the Carlingford district in Ireland, in the Lizard district of Cornwall, the Inner Hebrides (Mull, Skye, etc.) of Scotland, and in Saxony.
3. DIORITE.--A crystalline-granular compound of plagioclase and hornblende with magnetite. When quartz is present it becomes (according to the usual British acceptation) a _syenite_; but this view is gradually giving place to the German definition of syenite, which is a compound of orthoclase and hornblende; and it may be better to denominate the variety as _quartz-diorite_. The diorites are abundant as sheets and dykes amongst the older palæozoic and metamorphic rocks, and are sometimes exceedingly rich in magnetite. Mica, epidote, and chlorite are also present as accessories.
The rock occurs in North Wales, Charnwood Forest, Wicklow, Galway, and Donegal, and the Highlands of Scotland. There can be little doubt that amongst the metamorphic rocks of Galway, Mayo, and Donegal the great beds of (often columnar) diorite were originally augitic lavas, which have since undergone transformation.
4. DIABASE.--It is very doubtful if "Diabase" ought to be regarded as a distinct species of igneous rock, as it seems to be simply an altered variety of basalt or dolerite, in which chlorite, a secondary alteration-product, has been developed by the decomposition of the pyroxene or olivine of the original rock. It is a convenient name for use in the field when doubt occurs as to the real nature of an igneous rock. Melaphyre is a name given to the very dark varieties of altered augitic lavas, rich in magnetite and chlorite.
5. PORPHYRITE (or quartzless porphyry).--A basic variety of felstone-porphyry, consisting of a felspathic base with distinct crystals of felspar, with which there may be others of hornblende, mica, or augite. The colour is generally red or purple, and it weathers into red clay, in contrast to the highly acid or silicated felsites which weather into whitish sand.
6. SYENITE.--As stated above, this name has been variously applied. Its derivation is from Syene (Assouan) in Egypt, and the granitic rocks of that district were called "syenites," under the supposition (now known to be erroneous) that they differ from ordinary granites in that they were supposed to be composed of quartz, felspar, and hornblende, instead of quartz, felspar, and mica. From this it arose that syenite was regarded as a variety of granite in which the mica is replaced by hornblende, and this has generally been the British view of the question. But the German definition is applied to an entirely different rock, belonging to the felstone family; and according to this classification syenite consists of a crystalline-granular compound of orthoclase and hornblende, in which quartz may or may not be present. From this it will be seen that, according to Zirkel, syenite is essentially distinct from diorite in the species of its felspar.[3] It seems desirable to adopt the German view; and as regards diorites containing quartz as an accessory, to apply to them the name of _quartz-diorite_, as stated above, the name syenite as used by British geologists having arisen from a misconception.
7. MICA-TRAP (LAMPOPHYRE).--A rock, allied to the felstone family, in which mica is an abundant and essential constituent, thus consisting of plagioclase and mica, with a little magnetite. Quartz may be an accessory. This rock occurs amongst the Lower Silurian strata of Ireland, Cumberland, and the South of Scotland; it is not volcanic in the ordinary acceptation of that term. The term _lampophyre_ was introduced by Gümbel in describing the mica-traps of Fichtelgebirge.
8. ANDESITE.--This is a dark-coloured, compact or vesicular, semi-vitreous group of volcanic rocks, composed essentially of a glassy plagioclase felspar, and a ferro-magnesian constituent enclosed in a glassy base. According to the nature of the ferro-magnesian constituent, the group may be divided into _hornblende-andesite_, _biotite-andesite_, and _augite-andesite_. Quartz is sometimes present, and when this mineral becomes an essential it gives rise to a variety called _quartz-andesite_ or _dacite_.
These rocks are the principal constituents of the lavas of the Andes, and the name was first applied to them by Leopold von Buch; but their representatives also occur in the British Isles, Germany, and elsewhere. Dacite is the lava of Krakatoa and some of the volcanoes of Japan.
9, 10. TRACHYTE and DOMITE, etc.--These names include very numerous varieties of highly silicated volcanic rock, and in their general form consist of a white felsitic paste with distinct crystals of sanidine, together with plagioclase, augite, biotite, hornblende, and accessories. When crystalline grains or blebs of quartz occur, we have a quartz-trachyte; when tridymite is abundant, as in the trachyte of Co. Antrim, we have "tridymite-trachyte."
The trachytes occupy a position between the pitchstone lavas on the one hand, and the andesites and granophyres on the other.
(_b._) _Domite_ is the name applied to the trachytic rocks of the Auvergne district and the Puy de Dôme particularly. They do not contain free quartz, though they are highly acid rocks, containing sometimes as much as 68 per cent. of silica.
(_c._) _Phonolite (Clinkstone)_ is a trachytic rock, composed essentially of sanidine, nepheline, and augite or hornblende. It is usually of a greenish colour, hard and compact, so as to ring under the hammer; hence the name. The Wolf Rock is composed of phonolite, and it occurs largely in Auvergne.
(_d._) _Rhyolites_ are closely connected with the _quartz-trachytes_, but present a marked fluidal, spherulitic, or perlitic structure. They consist of a trachytic ground-mass in which grains or crystals of quartz and sanidine, with other accessory minerals, are imbedded. They occur amongst the volcanic rocks of the British Isles, Hungary, and the Lipari Islands, from which the name _Liparite_ has been derived.
(_e._) _Obsidian (Pitchstone)._--This is a vitreous, highly acid rock, which has become a volcanic glass in consequence of rapid cooling, distinct minerals not having had time to form. It has a conchoidal fracture, various shades of colour from grey to black; and under the microscope is seen to contain crystallites or microliths, often beautifully arranged in stellate or feathery groups. Spherulitic structure is not infrequent; and occasionally a few crystals of sanidine, augite, or hornblende are to be seen imbedded in the glassy ground-mass. The rock occurs in dykes and veins in the Western Isles of Scotland, in Antrim, and on the borders of the Mourne Mountains, near Newry, in Ireland.
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.
[Illustration: Plate I.]
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.
[Illustration: Plate II.]
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.
[Illustration: Plate III.]
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.
[Illustration: Plate IV.]
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. über 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
Callirrhoë, springs of, 133
Cañon, 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
Haurân, 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._
Jaulân, 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
Phlegræan 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 Dôme, 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 Ahmâr, 131
Tell el Akkasheh, 131
Tell el Farras, 131
Tell Abû en Nedâ, 130
Tell Abû Nedîr, 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 Brühl 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
Yarmûk, valley of the, 129, 131
Yellowstone Park, 145
Zirkel, F., 260
Zöllner, 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