Since the date of the appearance of the last editions of Scrope's works, inquiry and speculation concerning the nature and origin of volcanoes have been alike active, and many of the problems which were discussed by him, now present themselves under aspects entirely new and different from those in which he was accustomed to regard them. No one was ever more ready to welcome original views or to submit to having long-cherished principles exposed to the ordeal of free criticism than was Scrope; and few men retained to so advanced an age the power of subjecting novel theories to the test of a rigorous comparison with ascertained facts.

But this eminent geologist was not content with the devotion of his own time and energies to the advancement of his favourite science, for as increasing age and growing infirmities rendered travel and personal research impossible, he found a new source of pleasure in seeking out the younger workers in those fields of inquiry which he had so long and successfully cultivated, and in furthering their efforts by his judicious advice and kindly aid. Among the chosen disciples of this distinguished man, who will ever be regarded as one of the chief pioneers of geological thought, I had the good fortune to be numbered, and when he committed to me the task of preparing a popular exposition of the present condition of our knowledge on volcanoes, I felt that I had been greatly honoured.

In order to keep the work within the prescribed limits, and to avoid unnecessary repetitions, I have confined myself to the examination of such selected examples of volcanoes as could be shown to be really typical of all the various classes which exist upon the globe; and I have endeavoured from the study of these to deduce those general laws which appear to govern volcanic action. But it has, at the same time, been my aim to approach the question from a somewhat new standpoint, and to give an account of those investigations which have in recent times thrown so much fresh light upon the whole problem. In this way I have been led to dwell at some length upon subjects which might not at first sight appear to be germane to the question under discussion;—such as the characters of lavas revealed to us by microscopic examination; the nature and movements of the liquids enclosed in the crystals of igneous rocks; the relations of minerals occurring in some volcanic products to those found in meteorites; the nature and origin of the remarkable iron-masses found at Ovifak in Greenland; and the indications which have been discovered of analogies between the composition and dynamics of our earth and those of other members of the family of worlds to which it belongs. While not evading the discussion of theoretical questions, I have endeavoured to keep such discussions in strict subordination to that presentation of the results attained by observation and experiment, which constitutes the principal object of the work.

The woodcuts which illustrate the volume are in some cases prepared from photographs, and I am indebted to Mr. Cooper for the skill with which he has carried out my wishes concerning their reproduction. Others among the engravings are copies of sketches which I made in Italy, Hungary, Bohemia, and other volcanic districts. The whole of the wood-blocks employed by Mr. Poulett Scrope in his work on Volcanoes were placed at my disposal before his death, and such of them as were useful for my purpose I have freely employed. To Captain S. P. Oliver, R.A., I am obliged for a beautiful drawing made in the Island of Bourbon, and to Mr. Norman Lockyer and his publishers, Messrs. Macmillan & Co., for the use of several wood-blocks illustrating sun-spots and solar prominences.

J. W. J.

London: May 1881.

CONTENTS.

CHAPTER I.
PAGE
INTRODUCTORY: NATURE OF THE ENQUIRY
[1]
CHAPTER II.
THE NATURE OF VOLCANIC ACTION
[7]
CHAPTER III.
THE PRODUCTS OF VOLCANIC ACTION
[39]
CHAPTER IV.
THE DISTRIBUTION OF THE MATERIALS EJECTED FROM VOLCANIC VENTS
[67]
CHAPTER V.
THE INTERNAL STRUCTURE OF VOLCANIC MOUNTAINS
[112]
CHAPTER VI.
THE VARIOUS STRUCTURES BUILT UP AROUND VOLCANIC VENTS
[161]
CHAPTER VII.
THE SUCCESSION OF OPERATIONS TAKING PLACE AT VOLCANIC CENTRES
[186]
CHAPTER VIII.
THE DISTRIBUTION OF VOLCANOES UPON THE SURFACE OF THE GLOBE
[224]
CHAPTER IX.
VOLCANIC ACTION AT DIFFERENT PERIODS OF THE EARTH'S HISTORY
[247]
CHAPTER X.
THE PART PLAYED BY VOLCANOES IN THE ECONOMY OF NATURE
[281]
CHAPTER XI.
WHAT VOLCANOES TEACH US CONCERNING THE NATURE OF THE EARTH'S INTERIOR
[307]
CHAPTER XII.
THE ATTEMPTS WHICH HAVE BEEN MADE TO EXPLAIN THE CAUSES OF VOLCANIC ACTION
[331]
INDEX
[371]

ILLUSTRATIONS.

Sections of igneous rocks illustrating the passage from the glassy to the crystalline structureFrontispiece
Fig.Page
1.Stromboli, viewed from the north-west, April 1874to face p. [10]
2.Map of the Island of Stromboli[11]
3.Section through the Island of Stromboli from north-west to south-east[13]
4.The crater of Stromboli as viewed from the side of the Sciarra during an eruption on the morning of April 24, 1874.[14]
5.Vesuvius in eruption, as seen from Naples, April 26, 1872. (From a photograph)to face p. [24]
6.View of Vulcano, with Vulcanello in the foreground—taken from the south end of the Island of Lipari[43]
7.Minute cavities, containing liquids, in the crystals of rocks. (After Zirkel)to face p. [60]
8.Minute liquid-cavity in a crystal, with a moving bubble. (After Hartley)[63]
9.Cavity in crystal, containing carbonic-acid gas at a temperature of 86° F., and passing from the liquid to the gaseous condition. (After Hartley)[64]
10.Monte Nuovo (440 ft high) on the shores of the Bay of Naples. (After Scrope)[76]
11.Map of the district around Naples, showing Monte Nuovo and the surrounding volcanoes of older date[78]
12.Outlines of the summit of Vesuvius during the eruption of 1767. (After Sir W. Hamilton) to face p. [80]
13.Crater of Vesuvius formed during the eruption of 1822 (After Scrope)[82]
14.Crater of Vesuvius in 1756, from a drawing made on the spot. (After Sir W. Hamilton)[84]
15.The summit of Vesuvius in 1767, from an original drawing. (After Sir W, Hamilton)[85]
16.Summit of Vesuvius in 1843[86]
17.Outlines of Vesuvius, showing its form at different periods of its history[87]
18.Cascade of lava tumbling over a cliff in the Island of Bourbon. (After Capt. S. P. Oliver, R.A.)[93]
19.Lava-stream (obsidian) in the Island of Vulcano, showing the imperfect liquidity of the mass[95]
20.Interior of a rhyolitic lava-stream in the Island of Lipari, showing broad, sigmoidal folds, produced by the slow movements of the mass[96]
21.Interior of a rhyolitic lava-stream in the Island of Lipari, showing the complicated crumplings and puckerings, produced by the slow movements of the mass[96]
22.Vesuvian lava-stream of 1858, exhibiting the peculiar 'ropy' surfaces of slowly-moving currents. (From a photograph)to face p. [98]
23.Vesuvian lava-stream of 1872, exhibiting the rough cindery surfaces characteristic of rapidly flowing currents. (From a photograph)to face p. [96]
24.Concentric folds on mass of cooled lava. (After Heaphy)[100]
25.Mass of cooled lava formed over a spiracle on the slopes of Hawaii. (After Dana)[100]
26.Group of small cones thrown up on the Vesuvian lava-current of 1855. (After Schmidt)[101]
27.Natural section of a lava-stream in the Island of Vulcano, showing the compact central portion and the scoriaceous upper and under surfaces[104]
28.Section of a lava-stream exposed on the side of the river Ardèche, in the south-west of France. (After Scrope)[106]
29.Portion of a basaltic column from the Giant's Causeway, exhibiting both the ball-and-socket and the tenon-and-mortise structure [107]
30.Vein of green pitchstone at Chiaja di Luna, in the Island of Ponza, breaking up into regular columns and into spherical masses with a concentric series of joints. (After Scrope)[108]
31.Illustration of the 'perlitic structure' in glassy rocks[109]
32.Transverse section of a lava-stream[111]
33.The Kammerbühl, or Kammerberg, Bohemia (as seen from the south-west)[113]
34.Section of the Kammerbühl in Bohemia[114]
35.Natural section of a volcanic cone in the Island of Vulcano[116]
36.Section in the side of the Kammerbühl, Bohemia[118]
37.Experimental illustration of the mode of formation of volcanic cones, composed of fragmental materials[120]
38.Natural section of a tuff-cone, forming the Cape of Misenum, and exhibiting the peculiar internal arrangement, characteristic of volcanoes composed of fragmentary materials. (After Scrope)[121]
39.Section of a small scoria-cone formed within the crater of Vesuvius in the year 1835, illustrating the filling up of the central vent of the cone by subsequent ejections. (After Abich)[122]
40.Volcanic cones composed of scoriæ, and breached on one side by the outflow of lava-currents. (After Scrope)[128]
41.Campo Bianco, in the Island of Lipari. A pumice-cone breached by the outflow of an obsidian lava-streamto face p. [124]
42.Volcanic cones in Auvergne, which have suffered to some extent from atmospheric denudation. (After Scrope)[124]
43.Experimental illustration of the mode of formation of volcanic cones composed of viscid lavas. (After Reyer)[126]
44.The Grand Puy of Sarcoui, composed of trachyte, rising between two breached scoria-cones (Auvergne). (After Scrope)[126]
45.Volcanic cone (Mamelon) composed of very viscid lava (Island of Bourbon). (After Bory de St. Vincent) [127]
46.Another Mamelon in the Island of Bourbon, with a crater at its summit. (After Bory de St. Vincent)[127]
47.Cliff-section in the Island of Madeira, showing how a composite volcano is built up of lava-streams, beds of scoriæ, and dykes. (After Lyell)[125]
48.Section seen at the cascade, Bains du Mont Dore. (After Scrope)[130]
49.Section in the Island of Ventotienne, showing a great stream of andesitic lava overlying stratified tuffs. (After Scrope)[130]
50.Cliff on the south side of the Island of San Stephano[131]
51.The headland of Monte della Guardia, in the Island of Ponza[131]
52.Western side of the same headland, as seen from the north side of Luna Bay[132]
53.Sea-cliff at Il Capo, the north-east point of Salina, showing stratified agglomerates traversed by numerous dykes, the whole being unconformably overlaid by stratified, aqueous deposits[137]
54.Section observed in the Val del Bove, Etna, showing a basaltic dyke, from the upper part of which a lava-current has flowed[138]
55.Basaltic dykes projecting from masses of stratified scoriæ in the sides of the Val del Bove, Etna[134]
56.Sheets of igneous rock (basalt) intruded between beds of sandstone, clay, and limestone (Island of Skye)[137]
57.Plan of the dissected volcano of Mull in the Inner Hebridesto face p. [142]
58.Section of the volcano of Mull along the line A B " [142]
59.Summit of the volcano of Monte Sant' Angelo, in Lipari, exhibiting a crater with walls worn down by denudation[158]
60.Outlines of lava-cones[160]
61.Diagram illustrating the formation of parasitic cones along lines of fissure formed on the flanks of a great volcanic mountain[162]
62.Outline of Etna, as seen from Catania [162]
63.Outline of Etna, as seen from the Val del Bronte[163]
64.Plan of the volcano forming the Island of Ischia[163]
65.A primary parasitic cone, with a secondary one at its base—Ischia[164]
66.Scoria-cone near Auckland, New Zealand, with a lava-current flowing from it. (After Heaphy)[165]
67.Section of rocks below the ancient triassic volcano of Predazzo in the Tyrol[165]
68.Cotopaxi, as seen from a distance of ninety miles. (After Humboldt)[168]
69.Citlaltepetl, or the Pic d'Orizaba, in Mexico, as seen from the Forest of Xalapa. (After Humboldt)[169]
70.Lac Paven, in the Auvergne. (After Scrope)[171]
71.The crater-lake called Lago del Bagno, in Ischia, converted into a harbour[172]
72.Lake of Gustavila, in Mexico. (After Humboldt)[172]
73.Peak of Teneriffe, surrounded by great crater-rings. (After Piazzi-Smyth)[175]
74.The volcano of Bourbon, rising in the midst of a crater-ring four miles in diameter. (After Bory de St. Vincent)[176]
75.The volcano of Bourbon, as seen from another point of view, with three concentric crater-rings encircling its base. (After Bory de St. Vincent)[176]
76.Vesuvius as seen from Sorrento, half encircled by the crater-ring of Somma[177]
77.Outlines of various volcanoes illustrating the different relations of the craters to conesto face p. [178]
78.Island thrown up In the Mediterranean Sea in July and August, 1831. (After the Prince de Joinville)[179]
79.Sinter-cones surrounding the orifices of geysers[183]
80.Diagram illustrating the mode of formation of travertine- and sinter-terraces on the sides of a hill of tuff[185]
81.Map of the volcanic group of the Lipari Islands, illustrating the position of the lines of fissure upon which the volcanoes have been built up [192]
82.The Puy de Pariou, in the Auvergne, illustrating the shifting of eruption along a line of fissures[193]
83.Ideal section of the Puy de Pariou[194]
84.Fissure formed on the flanks of Etna during the emotion of 1865. (After Silvestri)[194]
85.Plan of the Island of Vulcano, based on the map of the Italian Government[196]
86.Vulcanello, with its three craters[197]
87.Section of basalt from Ovifak, Greenland, with particles of metallic iron diffused through its mass[319]
88.Diagram illustrating the relations between the terrestrial and the extra-terrestrial rocksto face p. [322]
89.A group of sun-spots. (After Secchi)[362]
90.A sun-spot, showing the great masses of incandescent vapour rising or falling within it. (After Secchi)[363]
91.The edge of a sun-spot, showing a portion of the prominent masses of incandescent gas (A) which detached itself at B and floated into the midst of the cavity. (After Norman Lockyer)[363]
92.Drawing of a solar prominence made by Mr. Norman Lockyer, March 14, 1869, at 11 h. 5 m. A.M.[364]
93.The same object, as seen at 11 h. 15 m. on the same day. (After Norman Lockyer)[365]
94.Drawings of a solar prominence at four different periods on September 7, 1871. (After Young)[366]
95.A group of Lunar craters (Maurolycus, Barocius, &c.), the largest being more than sixty miles in diameter[368]