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a paper on earthquakes published in this Magazine, No. 360, we endeavoured to show that they are undeveloped volcanos, the latter being, so to speak, the complement of the former: both earthquakes and volcanos being manifestations of a common subterranean force, but acting under different conditions. For while the latter are caused by the inability of the force to break through overlying rocky matter, when the force is either greater, or the superincumbent strata less impenetrable, gaseous matters find vents at one or more points, and a volcano is produced. Thus, while earthquakes are uncompleted efforts to establish volcanos, volcanos lessen the power and sometimes prevent earthquakes by acting as safety valves for setting free the expansive force exerted by the heated interior of the earth on its external covering or crust.

At all times, volcanic phenomena possess great interest, and, at this period when the volcanos of the old and new world are in a remarkable state of activity, some account of their phenomena as seen by the most recent lights of science, will probably be acceptable.

If earthquakes have always been regarded with awe, volcanos are even more fearful manifestations of the powers attributed in the fabulous mythology of antiquity to the infernal earth-shaking sovereign Ennorigæus.' An examination of a map of the world showing the volcanic and earthquake districts renders it evident that there is an intimate relation between the two classes of phenomena. Both develop themselves mainly along the

The largest proportion of these volcanos are situated in tropical regions, very few more than 30° from the equator. But they are by no means dependent on climate, many in Iceland being on the grandest scale, and others in full blast in the antarctic regions. The loftiest eruptive cones are Sahama in Bolivia, 22,350ft.; and Aconcagua in Chili, 23,004 ft. It is a noteworthy fact with regard to volcanos that the greater number either in islands or on coast-lines near the sea. Indeed the proximity of the ocean seems to be a necessary condition for the manifestation of great volcanic phenomena. The sea water probably finds access to the foci of the subterranean fires, and thereby produces enormous volumes of vapour and occasionally water, which frequently accompanies eruptions on a great scale. It was indeed sug

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gested by Sir H. Davy that if the interior of the earth contains large quantities of the unoxidated metalloids, all the phenomena of volcanos might be occasioned by the penetration of sea water through deep fissures. Though abandoned by its distinguished author, this hypothesis with some important modifications was entertained by the late Dr. Daubeny and other geologists. It is certain that water plays a most important part in volcanic phenomena, elastic vapours supplying the principal motive force of upheavals. Although upwards of 400 volcanos have been noted it is probable that many more exist. For, independently of the fact that a large portion of the earth's subaërial surface has not yet been explored, the far more extensive subaqueous area doubtless contains several volcanic vents which have not yet raised an eruptive orifice visibly above the surface of the ocean. Graham's Island,

which rose out of the sea from a depth of 100 feet in a few days, and attained a height of 200 ft. and a circumference of three miles, is an illustration on a large scale of one of these sea volcanos.

One of the most striking features of volcanos is their remarkable linear distribution. They traverse both hemispheres in a great arched curve, commencing at Terra del Fuego (the land of fire), running up the entire western fringe of that continent, almost to Behring's Straits, crossing the North Pacific through the Aleutian chain of isles, and descending thence southwardly along the peninsula of Kamtschatka, Japan, and the Philippine Islands, to the Moluccas, from which two lines branch, one enclosing Borneo in a semicircular sweep to the west and north, and continuing through Java and Sumatra to the Andaman Islands, and into Burmah, in which last wreath of islands' there are no less than 109 lofty fire-emitting

mountains-the other threading Papua and the Saloman and New Hebrides Islands to New Zealand, whence it seems continued in Victoria Land almost to the South Pole. Thus, not a day passes on our globe without witnessing volcanic phenomena. Heaving volcanos are in full blast throughout Japan; the normal state of that country is indeed that of chronic convulsion, and there is no sign of diminishing vigour in the volcanic centres. The Japanese islands may be said to rest on treacherous ribs of granite which crust over mighty sea of molten lava, and so tremendous is the subterranean force in that region that during the eruptions in 1854, men-of-war at anchor were spun round, and the harbours were scoured out to their

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bottoms. Mr. Scrope, who has made volcanos his special study, distinguishes their phenomena by three general phases:

1. That in which the volcano exists incessantly in outward eruption-phase of permanent eruption.

2. That in which eruptions, rarely of any excessive violence, continue in a comparatime, and alternate with brief intervals of tively tranquil manner for a considerable repose-phase of moderate activity.

3. That in which eruptive paroxysms of intense energy alternate with lengthened periods of complete external inertness— phase of prolonged intermittences.

Very few volcanos are in a state of permanent eruption; the most remarkable example is that of Stromboli, which has been in constant activity since Homeric days. The more common condition of volcanos is the intermittent, such as is presented by Vesuvius; the most terrible that coming under the phase of prolonged intermittences and paroxysmal eruptions.

When geological research was in its infancy, volcanic action was generally ascribed to some adventitious union of substances, whose combination resulted in the development of intense heat and vio

lent eruptive action. This hypothesis has long been abandoned by those who have carefully studied volcanos. Nor does the upheaval theory of Humboldt and Von Buch now find supporters. This supposed that some upheaving force raised a portion of the earth's crust in a dome-like shape, and that upon this, volcanic products were cast. Far more probable is the theory propounded by Mr. Darwin, who has had peculiar facilities for observing volcanic phenomena. He maintains that volcanos are caused by subterranean forces, and says in his highly interesting work on coral reefs:

It may be considered as almost established that volcanos are often (not necessarily always) present in those areas where the subterranean motive power has lately forced, or is now forcing outwards the crust of the earth, but that they are invariably absent in those where the surface has lately subsided, or is still subsiding.

Sir C. Lyell conceives that aqueous and igneous agents may be regarded as antagonistic forces labouring incessantly to reduce the inequalities, and he adds:

I have come to the conviction that upheaval has nowhere played such a dominant part in the cone and crater-making process, as to warrant the use of the term Eleva

tion Craters,' instead of cones and craters of eruption. Such a designation, as well

as the theory implied by it, would be alike inappropriate in the case of all the igneous mountains which I have seen, whether in Sicily or in the volcanic district of Naples, central France, or, lastly, Madeira and the Canaries.'

The prodigious quantity of matter ejected from volcanos is amazing. We have only to look at the vast extent and depth of the scoriæ and of lava cast forth by one eruption of magnitude, to realise the formation

1 Principles of Geology.

of cones and craters and the accumulation on volcanic mountains of enormous layers of matter. During the famous eruption of Cotopaxi in 1533, witnessed by the Spaniards under Sebastian de Belelcazar, the plain around the foot of the mountain was strewed through a radius of fifteen miles and more, with great fragments of rock, many of which measured as much as nine feet in diameter; and Humboldt tells us of one rock weighing upwards of 200 tons, as having been launched into the air to a height of several hundred feet during an eruption of this volcano. The force required to produce these results is almost be be wildering to our senses; it may explained however by the power of heat. Bacon long ago cast considerable light on the phenomena of volcanos as connected with heat in his Novum Organum, where he says:

Heat is a motion expansive restrained and acting in its strife upon the smaller particles of bodies. But the expansion is thus modified; for while it expands all ways, it has at the same time an inclination upwards. And the struggle in the particles is modified also; it is not sluggish but hurried and with violence.2

Now, when we bear in mind that a mere scratch on the surface of our globe, which is nearly 8,000 miles in diameter (for so the depth of only one mile must be considered) brings us to a temperature of 105°, we have only to descend in imagination to the still comparatively slight depth of twenty miles to find the earth's crust red-hot, while, if the temperature continues to increase regularly according to the same law, we should come at no very great depth beyond on a liquid sea of fire. But it is probable that

this molten mass is at a greater distance from us than this theory would place it. Astronomical calculations tend to prove that the crust of the earth is at least 800 miles thick, and that the coating of our globe must be extremely solid and rigid to enable our planet to preserve its figure. But the further we remove the seat of the subterranean force from us, the more must we be struck by its great power. Earthquakes are indeed terrific evidence of mysterious dynamic laws; but it is only when the subterranean expansive force breaks through the earth's crust, and after violent earth throes a volcano becomes active, that we obtain a just idea of the forces at work in nature's secret laboratory.

The

A grand example of the tremendous action of this force may be seen in the Monte Nuovo of the Phlegræan fields, which was formed, in September 1538, on the site of the Lucrine Lake, once famous for its oysters. The eruption continued without intermission two days and two nights, and on the third day people climbed to the top of the new hill 440 feet high, and looked into the crater 421 feet deep, within which stones were boiling up. mountain has remained quiescent ever since that period. On the other hand, the volcano of Izalco in Central America rose suddenly to the height of 1,600 feet on February 23, 1770, and has remained since in such constant activity as to serve as a beacon to mariners. The volcano of Tomboro, in Sumbawa, is another amazing evidence of subterranean force. In 1815 it yielded ashes and scoriæ sufficient to form three mountains, each equal in cubic contents

to Mont Blanc, or to cover the whole of Germany with scoria two feet deep.

But even more tremendous is the volcano of Mauna Loa, a huge domed-shaped mountain in Hawaii, nearly 14,000 feet above the sea, formed chiefly by the repeated outflows of a highly liquid lava boiling up and cascading over the lips of a central vent at its summit. The phenomena of this volcano are on the most stupendous scale. The highest crater, which is circular, 8,000 feet in diameter, and 830 feet deep, is frequently filled by the welling up of the lava from the vents at its bottom. During one of the latest eruptions the lava stream extended sixty-five miles, and averaged four miles in width, and twelve feet in depth. Its discharge was accompanied by columns of fire, scoriæ of filamentous lava (called Pele's hair), and dense vapour which towered over the crater to the height of 800 feet for twenty days, darkening the sun and obscuring every object a few yards distant; while from the surface of the lava currents, clouds of steam rolled upwards. On this occasion it is calculated that within ten months 15,400,000,000 cubic feet of molten matter were blown out of the crater, and that the lava overflowed an area of 200,000 acres in the same period of time. The lava in this gigantic crater rarely remains long at the same level. It sometimes rises to the lip of the crater, at other times sinks entirely out of sight. The subsidence leaves irregular shelves or ledges around the walls of the crater. The eruption in 1840 of Kilawea, fifteen miles from Mauna Loa, was if possible, more appalling.

The wonderful crater of this volcano is of an irregular elliptical figure, seven miles round, and 1,430 feet deep. It became full in the latter part of 1839 of boiling lava more or less crusted over, and suddenly in 1840 the tremendous caldron was emptied by means of lateral vents. A lava stream four miles wide and thirty miles in length was formed in seventy hours, and for the space of fourteen days it plunged in a vast fiery cataract one mile wide over a precipice fifty feet in height into the sea, where it formed three islands, and killed immense numbers of fish.

Vast, however, as is this crater, it is but a tiny cup compared to those craters with which the moon's surface is crowded. The crater of Copernicus is forty-five miles in diameter, and its depth, according to computations made by aid of the most powerful modern telescopes, is no less than 11,300 feet, while the height of the wall above the general surface of the moon is 2,650 feet. The tremendous energy of the eruptive forces which created such a volcano as this, staggers our senses, and those who have enjoyed a good telescopic survey of this lunar phenomenon doubtless well remember its unearthly grandeur. It is very remarkable, too, how greatly certain areas on the moon's surface resemble terrestrial volcanic regions. The lunar mountain Gassendi is very similar to the extinct volcanic district of Auvergne, and there is even a greater resemblance between the volcanic region of Vesuvius and the Phlegræan fields, and the Mount Maurolycus, with its numerous adjoining craters. The moon indeed, at least as respects the hemisphere which alone we are able to contemplate, presents the appearance of a burnt-out globe once imbued with volcanic life and an intense outward activity, probably with seas and an atmosphere now dried up and ex

tinct. Strange that this orb of whose brilliance poets so sweetly sing, and whose reflected light is the charm of our nights should in reality be a burnt-out globe. Thinking thus, may we not imagine that if our world should not be destroyed in the manner pointed out by the new meteoric theory of the sun's heat, but become a dead planet, it may too, like the moon, shine brillantly to other worlds, the inhabi tants of which will perhaps gaze curiously on the craters and ridges

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the bones, so to speak-of our globe, and speculate on what manner of people once lived upon it.

The recent eruption of Leon may be cited as a strong instance of the apparently undiminished power of subterranean force. The phenomena commenced on November 27, 1867, by a series of explosions which shook the earth throughout a large area. The volcano then discharged vast quantities of black sand, and a column of flame and smoke which appeared from Leon to be sprinkled by meteor-like spots, rose to a height of 3,000 feet. These spots proved to be rocks from four to five feet in diameter. The discharge of sand continued until the morning of November 30, and was of such density that the surrounding country to a distance of above fifty miles from the volcano was covered by it. The forest for leagues around the volcano is represented as being scarred and maimed by the swift falling showers of keen edged sand and stones, and for half a mile from the cone trees are levelled with the ground. The volcano was prodigiously active for sixteen days, and now in its repose is a most instructive field for the geologist. Indeed no volcanic region presents a more interesting study than the plain of Leon. Twenty volcanic cones may be seen from the town, and the entire country rises up, as it were, in terrible evidence of what Nature