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also be added the pumice, sand, and ashes, scattered not only over the whole island, but to a distance of 300 miles round, in such abundance as to destroy the fisheries in the neighbouring sea. With these additions it would amount, we may believe, to fifty or sixty thousand millions of cubic yards, exceeding the solid contents of Hecla, which, if six miles in diameter at the base, and 1700 yards high, would contain nearly fifty thousand millions (49,537,270,000) of cubic yards. This is probably larger than any individual mass of the older igneous rocks known to exist." This one discharge of this volcano, if spread over the coal fields of Great Britain, would cover them with a coating of basaltic rock twenty feet thick, or accumulated together upon the site of London, the product would be a mountain rivalling the Peak of Teneriffe.

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Besides the deposition of horizontal beds of ejected matter, the bulging up of the surface in the form of cones and hills of considerable elevation and diameter, on the flanks of volcanic mountains, or on plains subject to volcanic action, is a common instance of change wrought by the mighty disturbing force exerted.. Thus the entire volcano of Jorullo arose out of a plain to the west of Mexico, to the height of 1680 feet, the surrounding district, through an area of three or four miles, being swelled up like a bladder, studded with cones of inferior size. The formation of Monte Nuovo in the neighbourhood of Naples, and of Monte Rossi upon the side of Etna, are instances of similar phenoExtensive subsidences also frequently attend volcanic eruptions. The greater part of the Papandayang, on the western extremity of Java-one of the largest volcanic mountains of the island-was swallowed up in the year 1772. On the night of this event, the inhabitants on the declivities and at the foot of the mountain were alarmed by the appearance of a luminous cloud, which seemed to envelop the higher regions; but before they could retire from the vicinity, the mass began to give way, and disappeared with a tremendous noise in the earth. An extent of ground belonging to the mountain itself and the environs, fifteen miles long and six broad, subsided by this convulsion. The formation of cracks and fissures is another feature of change effected by volcanic agency. In 1669, in the plain of St. Lio, upon the side of Etna, a fissure six feet broad and of unknown depth opened with a loud crash, traversing a length of twelve miles, and emitting a vivid light, indicating the presence of incandescent lava. Five other parallel fissures also opened, extending a considerable way; and the same effect has been often produced by the paroxysmal excitement of Vesuvius. The external appearance of active volcanic mountains is thus in a state of striking instability; and in not a few instances great changes may be traced, both of form, elevation, and magnitude. Though the altitude of Etna may not have materially varied during the last 2000 years, yet the cone has repeatedly fallen in, and been reproduced. It was 320 feet high in the year 1444, but fell in during the earthquake of 1537; and, after reproduction, the cone lost so much of its height in 1693, that, from several places in Val Demone, it ceased to be visible where it had been seen. The summit of Vesuvius, about a quarter of a century ago, was a rough and rocky plain, covered with blocks of lava and scoriæ, and cut by numerous fissures, from which clouds of vapour were evolved. These were all removed by the violent eruptions of October 1822; and a vast elliptical chasm was formed, three miles in circumference, three quarters of a mile in the longest diameter, and about two thousand feet deep. Upwards of eight hundred feet of the ancient cone were carried away, which reduced the height of the mountain from 4000 to 3200 feet. But whatever changes may have transpired within the period embraced by the records of history, they are utterly insignificant to those anterior to that date, of which the geological appearance of Etna exhibits indisputable evidence. All the most conspicuous of its eighty lateral cones are older than the era at which authentic history commences, and bear witness to violent catastrophes in the hoar antiquity of time; and as one in three eruptions is supposed to

take place from the summit as every eruption from the flanks does not produce a cone and as great intervals of rest occur between successive explosions, in some instances amounting to a century, the mere superficies of Etna develops a series of changes which carry us back to a vastly remote date.

However limited the field of active volcanic operation, and local the effects of the enormous fires that occasionally flare up, and perpetually smoke, large tracts of country furnish unquestionable proof of having formerly been scenes where "fire ran along upon the ground," though no record exists of such explosions but that written by the eruptive force upon the face of the territory subject to its ravages. The Roman plain is one of these districts. Nowhere east of the Appenines, or in the central range, is any trace discoverable of volcanic eruptions, except along a line drawn eastwards from Campania to Horace's Mount Vultura conical hill of lava and tuff, from whose sides issue carbonic acid and sulphuretted hydrogen. But a great part of the Campagna of Rome is, in one sense or another, a volcanic formation, a fact which illustrates some of the traditions of the Eternal City. Westphal and Hoffmann have minutely examined the geology of the Roman plain, from whose memoirs upon the subject the following account of the changes that have transpired is condensed. At a time when the sea washed the sides of the Sabine and Volscian mountains, and the plain lay deep beneath the waters of the ocean, it was thrown into disorder by the breaking out of numerous volcanoes. One of the principal centres of disturbance was at the northern extremity in the Ciminian Hills, where a chain of volcanic heights now appear, among which Monte Soriano has an elevation of 4000 feet above the level of the sea, and is covered with currents of trachytic lava. The Alban Mount was another centre in the southern quarter, from which a great stream of lava may be traced for rather more than eight miles, ending near the tomb of Cecilia Metella, and was largely used by the old Romans as material for paving their roads. Both centres discharged a prodigious quantity of ashes and scoriæ, which by long deposition beneath the waters became agglutinated into the earthy rock called tuff, of which several varieties are frequent in large masses about Rome. The catacombs are excavated in the "tufa granulare," a soft, dark-coloured, granular sort, which furnishes the Roman cement of commerce. In the "tufa lithoides"-a more compact rock-the cavities were quarried, which were afterwards the prisons of the Capitol. The Seven Hills are composed of these volcanic products, resting upon marine alluvial deposits. In that of the Capitol, upon a bed of sand and clay- the uppermost marine formation there is granular tufa ten feet in thickness, and about a hundred feet of lithoid tuff over it, rising to the summit. The Palatine, Viminal, Quirinal, and Pincian hills are chiefly composed of granular tuff, which appears mixed with the lithoid in the Esquiline, Cælian, and Aventine. For a long period after the volcanoes began to play, the sea must have rested upon the plain, to allow of the formation of these tufaceous beds beneath its waters, derived from the ashes and scoriæ, and now overlying the alluvial marine strata. At length the fires died away; the waves withdrew, through the land rising suddenly or by degrees; a series of lakes remained, gradually drained by the Tiber and the Anio as they scooped out their channels; the Latins came down from the Appenines; and Rome arose to become for a season the mistress of the world. Of these physical changes we have an enduring memorial graven, as with a pen of iron, upon the Campagna. Its lava currents, its tufaceous masses, and its crateriform mountains, proclaim the occurrence here of unwritten catastrophes.

Equally significant are the appearances presented by a district in the southern part of Central France, more than forty miles in length and twenty in breadth, which was formerly comprised in the provinces of Auvergne and Languedoc. Here are found unquestionable evidences of long-extinguished subterranean fires, in more than two hundred

cones, craters, volcanic hills and mountains, which have discharged their red-hot streams of lava, and showers of ashes, at some former period of the history of the globe, the antiquity of which, the application of thousands of years will go but a little way to measure. This district has been attentively examined by Mr. Bakewell and Mr. Poulett Scrope, whose memoirs upon it are full of interesting and striking facts to the physical inquirer. It was not till the year 1751 that the existence of this volcanic region was known, when M. Guettard and a companion naturalist, returning from Vesuvius, stopped to botanise upon the mountains in Auvergne, and were surprised at the resemblance they bore to the Italian volcano, and at the similarity of the lavas and minerals in both. The valley of Clermont exhibits a series of fresh-water limestone strata upon a substratum of granite, which appear in the surrounding hills interposed between the granite and volcanic rocks; but, ascending towards the west, all traces of the limestone disappear, and the volcanic rocks rest immediately upon an elevated granitic plain. From this plain a number of conical and dome-shaped mountains rise, the highest of which the Puy de Dome celebrated by the barometrical experiments of Pascal, ascends 3451 feet above the town of Clermont, and 4797 feet above the level of the sea. Some of the mountains preserve the forms of well-defined craters, from which currents of lava may be traced descending into the present valleys. The crater of the Puy de Pariou, 3800 feet above the level of the sea, is as perfect as that of any recent volcano, and from it, or from the flanks of the mountain, a lava current has streamed, now lying upon the plain, from thirty to sixty feet thick, covered with scoria and basaltic lava. All the accompaniments of volcanic action, with the exception of the phenomenon of an actual eruption, are found in Auvergne in as perfect a manner as at Etna and Vesuvius, in the Lipari Islands and Iceland; and the interposition of stratified formations among the volcanic products show different and distinct periods separating the eruptions from each other. The lavas have been cut by the action of rivers, which have not only exposed the columnar basalt which now forms the precipitous walls of their channels, but have eaten their way into the granitic rock beneath, these excavations having of course been executed subsequent to the eruptions which poured the fiery floods into the valleys. "Yet when did these fires burn? When took place this amazing combination of volcanic eruptions and their terrible accompaniments? How long ago was the last of them? And by what interval of time could we ascend, from that last, to the earlier eruptions, and to the earliest of the astounding number?" It is certain that we must go by several thousands of years at least to arrive at the era of the last disturbance.

The general history of Europe contains no record of any volcanic eruption in Auvergne, nor does any thing occur in any rhyme or legend of the monkish chroniclers from which it might be inferred. Some, indeed, have deemed it not improbable that in a thinly inhabited country like that of the mountain parts of this province, the volcanoes might have been in action after the fall of the western empire, without being noticed or known by the historians of the barbarous ages, when men were too earnestly engaged in destroying each other, or in providing for their own safety, to bestow much thought on natural phenomena. But this supposition will not bear examination, for monastic pens were busy enough at the time in question; and to surmise the occurrence of such physical convulsions in the heart of Gaul, without the rumour of them gaining a wide circulation, and long surviving in the traditions of the locality, is obviously extravagant. Going farther back, we find Cæsar encamped at Gerzovia in this very district during his Gallic wars; yet, though his Commentaries show that he surveyed the country with a careful eye, he mentions no volcanic outbreaks, nor records any tradition picked up in the neighbourhood of such events having formerly occurred. But the water-worn lavas conduct us much farther back into the past. It requires a long period for the action of a river to cut

into a hard rock to any extent; yet the beds of basalt in the district have in several places been corroded by the streams to the depth of from 150 to 160 feet, and the underlying granite rocks have been penetrated. The production of effects of this magnitude, by a cause which is so slow in its operation, requires an amount of time, in comparison with which the historic period is a trifling span; and hence it follows that the volcanic fires which discharged the liquid masses of these various lavas belong to an era incalculably remote. "Such analogies," says Dr. Smith, "as may be inferred by comparative examinations of the condition of Etna, Vesuvius, and other active volcanoes, carry us to the contemplation of a period which runs back, not to the age of Noah merely, but immeasurably beyond the date of the creation of man, and his contemporary plants and animals." The geological state of Auvergne, in several respects to which we have not adverted, fully warrants the use of this language. Another important and interesting inquiry has been proposed,— Whether the volcanic fires that once raged in this district are absolutely extinct, or have periods of returning activity at distant intervals of time? In reply, it can only be stated, that at Guadaloupe, in Teneriffe, the Azores, and the Grecian archipelago, volcanic eruptions have been renewed after a cessation of from one to four centuries. Vesuvius also, for four centuries, from the twelfth to the sixteenth, was in a state of repose, so that a forest of chestnut trees was growing in the crater prior to the great outbreak of 1531; but previous to the first recorded instance of its activity in 79, it had certainly been idle for at least seven or eight hundred years, and perhaps for a much longer period. These intervals are however so short when compared with that which has intervened since Auvergne began to repose, that obviously they supply no data upon which a conjecture of renewed disturbance can be built. There are springs of hot water in the district, as Mount d'Or and Vichy, where the temperature is from 120° to 125°, which indicate a subterranean source of heat: yet, apart from the extant memorials of volcanic action, nothing can be inferred from the indication, as it is common to localities where those memorials are not found.

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A third site, displaying remarkable monuments of volcanic combustion in past ages, may be briefly noticed. This is the region of ancient Sardis and Philadelphia, in the west of Asia Minor, which Strabo has called "the burnt," KarakɛKavμέvη. Cones of scoriæ of different ages, lava-flowings forming plateaux upon the summits of isolated hills, and lava currents worn through by the action of running water, are here the monuments of successive eruptions, between which long intervals have occurred, the last of which cannot have transpired for at least three thousand years, otherwise history would have preserved some record of it. Mr. Hamilton has sketched some of the principal features of the Catecucaumene, or burnt-up region of the geographer, as seen from a neighbouring ridge. Beginning with the north, on our extreme right was the barren termination of the ridge on which we stood; to the west of which a black and dome-shaped hill of scoriæ and ashes rose about 500 feet above the plain. This was the Karedevlit, or Black Inkstand, the volcano of Koula-so near to us that none of the effects of its wild and rugged character were lost, and so steep that to ascend its slope of cinders appeared impossible. In front of us a black and rugged stream of lava extended from right to left, the surface of which, broken up into a thousand forms, looked like the breakers of a sea converted into stone amidst the fury of a gale, and forming, as it issued from the base of the cone, a striking contrast with the rich plain through which it seemed to flow. Beyond, to the N. W., were other volcanic cones, which, from their smooth and cultivated appearance, the vineyards reaching to their summits, must have belonged to a much older period. Further to the left was the town of Koula itself, with its tall and graceful minarets rising above the lava, on the southern point of which it has been built." The Karedevlit referred to, and two other cones, answer precisely to the three funnels, rpɛiç púoai,

spoken of by Strabo as distinguishing the geography of Lydia, about forty stadia, or five miles, apart; but we may infer the inaction of the volcanoes in his time, and for a long period before, or otherwise the fact would have been known and recorded. From the foot of each of the cones, a flood of rugged black vesicular lava has streamed, encircling their bases, and flowing down the inclined face of the country towards the bed of the Hermus. In the same region there are upwards of thirty other cones, of a more ancient date than the preceding, as their surfaces show a long course of smoothing from atmospheric influence

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and aqueous action, whereas the dark and cindery sides of the former are rough and undecomposed. From the silence of history, the age of thirty centuries is at least due to the more recent cones, and a greater antiquity belongs to the rest. Thus the Catecucaumene bears silent testimony to physical changes in the remote past, and yet it proclaims the uniformity of those causes of disturbance to which our planet for ages has been subject.

The action of earthquakes, to which we now glance, is a far more potent cause of change in the condition of the terrestrial superficies than that of volcanoes, and far more tremendous to the human race, affecting those level sites upon which they congregate, and often transpiring without a warning. The volcano generally gives preparatory signals of an eruption, by denser columns of smoke issuing from the crater, and loud rumbling sounds proceeding from the interior; its immediate effects are commonly confined either to the mountain itself, or to a scanty area around it: but in the case of an earthquake, the suddenness of the crisis, the extent of its influence, and the nature of the event-the very ground rocking beneath the feet of its inhabitants-render the visitation the most formidable physical source of peril with which our species have to contend. Both phenomena have unquestionably a common origin, and hence in countries where active volcanoes exist, the people are in expectation of an earthquake, if the former, which operate as a kind of safety-valve, remain long in complete repose. The Creoles of South America distinguish two kinds of earthquakes by the terms tremblores and terremotos. The tremblores are slight tremors of the ground, which effect no derangement of the surface, are in some districts of daily occurrence, and transpire with perfect security to

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