 Chapter 24 Part 2 of Principles of Geology. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. Principles of Geology by Charles Lyell. Chapter 24 Part 2. Vesuvian Lavas. The Lavas of Soma are characterized by containing disseminated crystals of lucite, called by the French, alfigen, a mineral said to be very rare in the modern Lavas of Vesuvius, which are in general much more scouracious and less crystalline than those of Soma. At the fortress near Tore del Greco, a section is exposed 15 feet in height of a current which ran into the sea, and it evinces, especially in the lower part, a decided tendency to divide into rude columns. A still more striking example may be seen to the west of Tore del Anunziata, near Fortes Casatto, where the mass is laid open to the depth of 20 feet. In both these cases, however, the rock may rather be said to be divided into numerous perpendicular fissures than to be prismatic, although the same picturesque effect is produced. In the lava currents of central France, those of the vivaree in particular, the uppermost portion, often 40 feet or more in thickness, is an amorphous mass passing downwards into lava irregularly prismatic, and under this there is a foundation of regular and vertical columns. But these Lavas are often 100 feet or more in thickness. We can scarcely expect to discover the same phenomenon in the shallow currents of Vesuvius, where the lowest part has cooled more rapidly, although it may be looked for in modern streams in Iceland, which exceed even those of ancient France in volume. Mr. Scrope mentions that, in the cliffs encircling the modern crater of Vesuvius, he saw many currents offering a columnar division, and some almost as regularly prismatic as any ranges of the older basalts, and he adds that, in some, the spheroidal-concretionary structure on a large scale was equally conspicuous. Brislac also informs us that, in the salacious lava of 1737, which contains augite, lucite, and crystals of felspar, he found very regular prisms in Aquari, near Tore del Greco, an observation confirmed by modern authorities. Effects of Decomposition on Lavas The decomposition of some of the felspathic lavas either by simple weathering or by gaseous emanations converts them from a hard to a soft clay-y state so that they no longer retain the smallest resemblance to rocks cooled down from a state of fusion. The exhalations of sulphurated hydrogen and muriatic acid, which are disengaged continually from the sulfatata, also produce curious changes on the trachite of that nearly extinct volcano. The rock is bleached and becomes porous, fissile, and honeycombed, till at length it crumbles into a white, salacious powder. Numerous globular concretions, composed of concentric laminate, are also formed by the same vapors in this decomposed rock. Vesuvian Minerals A great variety of minerals are found in the lavas of Vesuvius and Soma. Augite, Lucite, felspar, mica, olivine, and sulfur are most abundant. It is an extraordinary fact that in an area of three square miles round Vesuvius, a greater number of simple minerals have been found than in any spot of the same dimensions on the surface of the globe. Augite enumerated only 380 species of simple minerals as known to him, and no less than 82 had been found on Vesuvius and in the tufts on the flanks of Soma before the end of the year 1828. Many of these are peculiar to that locality. Some mineralogists have conjectured that the greater part of these were not of Vesuvian origin, but thrown up in fragments from some older formation, through which the gaseous explosions burst. But none of the older rocks in Italy or elsewhere contain such an assemblage of mineral products, and the hypothesis seems to have been prompted by a disinclination to admit that in times so recent in the Earth's history the laboratory of nature could have been so prolific in the creation of new and rare compounds. Had Vesuvius been a volcano of high antiquity, formed when nature, wantoned as in her prime and played at will her virgin fancies, it would have been readily admitted that these, or a much greater variety of substances, had been sublimed in the crevices of lava just as several new earthy and metallic compounds are known to have been produced by fumaroles since the eruption of 1822. Mass Enveloping Herculaneum and Pompeii In addition to the ejections which fall on the cone and that much greater mass which finds its way gradually to the neighboring sea, there is a third portion, often of no inconsiderable thickness, composed of alluviums spread over the valleys and planes at small distances from the volcano. Aqueous vapors are evolved copiously from volcanic craters during eruptions and often for a long time subsequently to the discharge of scoriae and lava. These vapors are condensed in the cold atmosphere surrounding the high volcanic peak and heavy rains are thus caused. The floods thus occasioned sweep along the impalpable dust and light scoriae till a current of mud is produced which is called, in Campania, lava d'aqua and is often more dreaded than an igneous stream, lava de fuoco, from the greater velocity with which it moves. So late as the 27th of October 1822 one of these alluviums descended the cone of Vesuvius and after over spreading much cultivated soil flowed suddenly into the villages of St. Sebastian and Massa where, filling the streets and interior of some of the houses it suffocated seven persons. It will therefore happen very frequently that towards the base of a volcanic cone alternations will be found of lava, alluvium and showers of ashes. To which of these two latter divisions the mass enveloping Herculaneum and Pompeii should be referred has been a question of the keenest controversy but the discussion might have been shortened if the combatants had reflected that whether volcanic sand and ashes were conveyed to the towns by running water or through the air during an eruption the interior of buildings so long as the roofs remain entire together with all underground vaults and cellars could be filled only by an alluvium. We learn from history that a heavy shower of sand pumice and lapilli sufficiently great to render Pompeii and Herculaneum uninhabitable fell for eight successive days and nights in the year 79 accompanied by violent rains. We ought therefore to find a very close resemblance between the strata covering these towns and those composing the minor cones of the flagrayan fields accumulated rapidly like Montenuovo during a continued shower of ejected matter with this difference however that the strata incumbent on the cities would be horizontal whereas those on the cones are highly inclined and that large angular fragments of rock which are thrown out near the vent would be wanting at a distance where small lapilli only can be found. Accordingly with these exceptions no identity can be more perfect than the form and distribution of the matter at the base of Montenuovo as laid open by the encroaching sea and the appearance of the beds superimposed on Pompeii. That city is covered with numerous alternations of different horizontal beds of tough and lapilli for the most part thin and subdivided into very fine layers. I observed the following section near the amphitheater in November 1828 descending series. Black sparkling sand from the eruption of 1822 containing minute regularly formed crystals of algite and tourmaline two and one-half inches. Vegetable mold three feet brown incoherent tough full of piezolytic globules in layers from half an inch to three inches in thickness one foot six inches small scoriae and white lapilli three inches brown earthy tough with numerous piezolytic globules nine inches brown earthy tough with lapilli divided into layers four feet layer of whitish lapilli one inch gray solid tough three inches pumice and white lapilli three inches total ten feet three and one-half inches Many of the ashes in these beds are vitrified and harsh to the touch. Crystals of lusite both fresh and farinaceous have been found intermixed. The depth of the bed of ashes above the houses is variable but seldom exceeds twelve or fourteen feet and it is said that the higher part of the amphitheater always projected above the surface. Though if this were the case it seems inexplicable that the city should never have been discovered till the year seventeen fifty. It will be observed in the above section that two of the brown half-consolidated toughs are filled with small piezolytic globules. This circumstance is not alluded to in the animated controversy which the Royal Academy of Naples maintained with one of their members, Signor Lippi, as to the origin of the strata incumbent on Pompeii. The mode of aggregation of these globules has been fully explained by Mr. Scrope who saw them formed in great numbers in 1822 by rain falling during the eruption on fine volcanic sand and sometimes also produced like hail in the air by the mutual attraction of the minutest particles of fine damp sand. Their occurrence, therefore, agrees remarkably well with the account of heavy rain and showers of sand and ashes recorded in history. Lippi entitled his work, Fu il fuocco o l'acqua che sotterò Pompeii ed ercolano and he contended that neither were the two cities destroyed in the year seventy-nine nor by a volcanic eruption but purely by the agency of water charged with transported matter. His letters wherein he endeavored to dispense as far as possible with igneous agency even at the foot of the volcano were dedicated with great propriety to Werner and afford an amusing illustration of the polemic style in which geological writers of that day indulged themselves. His arguments were partly of an historical nature derived from the silence of contemporary historians respecting the fate of the cities which, as we have already stated, is most remarkable and partly drawn from physical proofs. He pointed out with great clearness the resemblance of the two-facious matter in the vaults and cellars at Herculaneum and Pompeii to aqueous alluviums and its distinctness from ejections which had fallen through the air. Nothing he observes but moist pasty matter could have received the impression of a woman's breast which was found in a vault at Pompeii or have given the cast of a statue discovered in the theatre at Herculaneum. It was objected to him that the heat of the tough in Herculaneum and Pompeii was proved by the carbonization of the timber, corn, papyrus rolls and other vegetable substances they are discovered but Lippi replied with truth that the papyri would have been burnt up if they had come in contact with fire and that their being only carbonized was a clear demonstration of their having been enveloped like fossil wood in a sediment deposited from water. The academicians in their report on his pamphlet assert that when the amphitheater was first cleared out the matter was arranged on the steps in a succession of concave layers accommodating themselves to the interior form of the building just as snow would lie if it had fallen there. This observation is highly interesting and points to the difference between the stratification of ashes in an open building and of mud derived from the same in the interior of edifices and cellars. Nor ought we to call the allegation in question because it could not be substantiated at the time of the controversy after the matter had been all removed although Lippi took advantage of this removal and met the argument of his antagonists by requiring them to prove the fact. There is decisive evidence that no stream of lava has ever reached Pompeii since it was first built although the foundations of the town stand upon the old leucitic lava of Soma several streams of which, with tough interposed had been cut through in excavations. Infusorial beds covering Pompeii A most singular and unexpected discovery has been recently made, 1844-5 by Professor Ehrenberg respecting the remote origin of many of the layers of ashes and pumice enveloping Pompeii. They are, he says, in great part of organic and freshwater origin consisting of the siliceous cases of microscopic infusoria. What is still more surprising this fact proves to be by no means an isolated or solitary example of an intimate relation between organic life and the results of volcanic activity. On the Rhine several beds of tough and pumiceous conglomerate resembling the mass incumbent upon Pompeii and closely connected with extinct volcanoes are now ascertained to be made up to a great extent of the siliceous cases of infusoria or diatomacea invisible to the naked eye and often half-fused. No less than ninety-four distinct species have already been detected in one mass of this kind more than one hundred fifty feet thick at Hoxmer on the left bank of the Rhine near the Locker Sea. Some of these rainish infusorial accumulations appear to have fallen in showers others to have been poured out of lake craters in the form of mud as in the Brawl Valley. In Mexico, Peru, the Isle of France and several other volcanic regions analogous phenomena have been observed and everywhere the species of infusoria belong to fresh water and terrestrial genera except in the case of the Patagonian pumiceous tufts specimens of which brought home by Mr. Darwin are found to contain the remains of marine animal cules. In various kinds of pumice ejected by volcanoes the microscope has revealed to Professor Ehrenberg the silicious cases of infusoria often half obliterated by the action of heat and the fine dust thrown out into the air during eruptions is sometimes referable to these most minute organic substances brought up from considerable depths and sometimes mingled with small particles of vegetable matter. In what manner did the solid coverings of these most minute plants and animal cules which can only originate and increase at the surface of the earth sink down and penetrate into subterranean cavities so as to be ejected from the volcanic orifices? We have of late years become familiar with the fact in the process of boring artesian wells that the seeds of plants the remains of insects and even small fish with other organic bodies are carried in an uninjured state by the underground circulation of waters to the depth of many hundred feet. With still greater facility in a volcanic region we may conjecture that water and mud full of invisible infusoria may be sucked down from time to time into subterranean rents and hollows in cavernous lava which has been permeated by gases or in rocks dislocated by earthquakes. It often happens that a lake which has endured for centuries in a volcanic crater disappears suddenly on the approach of a new eruption. Violent shocks agitate the surrounding region and ponds, rivers and wells are dried up. Large cavities far below may thus become filled with fenn mud chiefly composed of the more indestructible and silicious portions of infusoria destined perhaps to be one day ejected in a fragmentary or half-fused state yet without the obliteration of all traces of organic structure. Herculaneum It was remarked that no lava has flowed over the site of Pompeii since that city was built but with herculaneum the case is different. Although the substance which fills the interior of the houses and the vaults must have been introduced in a state of mud like that found in similar situations in Pompeii. Yet the super-incumbent mass differs wholly in composition and thickness. Herculaneum was situated several miles nearer to the volcano and has therefore been always more exposed to be covered not only by showers of ashes but by alluviums and streams of lava. Accordingly masses of both have accumulated on each other above the city to a depth of nowhere less than seventy and in many places of one hundred twelve feet. The tuft which envelops the buildings consists of comminuted volcanic ashes mixed with pumice. A mask embedded in this matrix has left a cast the sharpness of which was compared by Hamilton to those in plaster of Paris nor was the mask in the least degree scorched as if it had been embedded in heated matter. This tuft is porous and when first excavated is soft and easily worked but acquires a considerable degree of induration on exposure to the air. Above this lowest stratum is placed according to Hamilton the matter of six eruptions each separated from the other by veins of good soil. In these soils Lepi states that he collected a considerable number of land shells an observation which is no doubt correct for many snails burrow in soft soils and some Italian species descend when they hibernate to the depth of five feet and more from the surface. Delatore also informs us that there is in one part of this superimposed mass a bed of true salacious lava lava de pietra dura and as no such current is believed to have flowed till near one thousand years after the destruction of Herculaneum we must conclude that the origin of a large part of the covering of Herculaneum was long subsequent to the first enumation of the place. That city as well as Pompeii was a seaport. Herculaneum is still very near the shore but attractive land a mile in length intervenes between the borders of the Bay of Naples and Pompeii. In both cases the gain of land is due to the filling up of the bed of the sea with volcanic matter and not to elevation by earthquakes for there has been no change in the relative level of land and sea. Pompeii stood on a slight eminence composed of the lavas of the ancient Vesuvius and flights of steps led down to the water's edge. The lower most of these steps are said to be still on an exact level with the sea. Condition and contents of the buried cities After these observations on the nature of the strata enveloping and surrounding the cities we may proceed to consider their internal condition and contents so far at least as they offer facts of geological interest Notwithstanding the much greater depth at which Herculaneum was buried it was discovered before Pompeii by the accidental circumstance of a well-being sunk in 1713 which came right down upon the theater where the statues of Hercules and Cleopatra were soon found. Whether this city or Pompeii both of them founded by Greek colonies was the more considerable is not yet determined but both are mentioned by ancient authors as among the seven most flourishing cities in Campania. The walls of Pompeii were three miles in circumference but we have as yet no certain knowledge of the dimensions of Herculaneum. In the latter place the theater alone is open for inspection. The Forum, Temple of Jupiter and other buildings having been filled up with rubbish as the workmen proceeded owing to the difficulty of removing it from so great a depth below ground. Even the theater is only seen by torchlight and the most interesting information perhaps which the geologist obtains there is the continual formation of stalactite in the galleries cut through the tough for there is a constant percolation of water charged with carbonate of lime mixed with a small portion of Magnesia. Such mineral waters must in the course of time create great changes in many rocks especially in Lavas the pores of which they may fill with calcareous spar so as to convert them into amygdaloids. Some geologists therefore are unreasonable when they expect that volcanic rocks of remote eras should accord precisely with those of modern date since it is obvious that many of those produced in our own time will not long retain the same aspect and internal composition. Both at Herculaneum and Pompeii temples have been found with inscriptions commemorating the rebuilding of the edifices after they had been thrown down by an earthquake. This earthquake happened in the reign of Nero sixteen years before the cities were overwhelmed. In Pompeii one fourth of which is now laid open to the day both the public and private buildings bear testimony to the catastrophe. The walls are rent and in many places traversed by fissures still open. Columns are lying on the ground only half-hewn from huge blocks of travertine and the temple for which they were designed is seen half-repared. In some few places pavement had sunk in but in general it was undisturbed consisting of large irregular flags of lava joined neatly together in which the carriage wheels have often worn ruts an inch and a half deep. In the wider streets the ruts are numerous and irregular. In the narrower there are only two one on each side which are very conspicuous. It is impossible not to look with some interest even on these ruts which were worn by chariot wheels more than seventeen centuries ago and independently of their antiquity it is remarkable to see such deep incisions so continuous in a stone of great hardness. End of Chapter 24 Part 2 Recording by Linda Johnson Chapter 24 Part 3 of Principles of Geology This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer please visit LibriVox.org Principles of Geology by Charles Lyle Chapter 24 Volcanic District of Naples Part 3 Small Number of Skeletons A very small number of skeletons have been discovered in either city and it is clear that most of the inhabitants not only found time to escape but also to carry with them the principal part of their valuable effects. In the barracks at Pompeii were the skeletons of two soldiers chained to the stocks and in the vaults of a country house in the suburbs were the skeletons of 17 persons who appeared to have fled there to escape from the shower of ashes. They were found enclosed in an injurated tuff and in this matrix was preserved a perfect cast of a woman perhaps the mistress of the house with an infant in her arms. Although her form was imprinted on the rock nothing but the bones remained. To these a chain of gold was suspended and on the fingers of the skeletons were rings with jewels. Against the sides of the same vault was ranged a long line of earthen amphorae. The writings scribbled by the soldiers on the walls of their barracks and the names of the owners of each house written over the doors are still perfectly legible. The colors of fresco paintings on the stuccoed walls in the interior of buildings are almost as vivid as if they were just finished. There are public fountains decorated with shells laid out in patterns in the same fashion as those now seen in the town of Naples. And in the room of a painter who was perhaps a naturalist a large collection of shells was found comprising a great variety of Mediterranean species and as good a state of preservation as if they had remained for the same number of years in a museum. A comparison of these remains with those found so generally in a fossil state would not assist us in obtaining the least insight into the time required to produce a certain degree of decomposition or mineralization. For although under favorable circumstances much greater alteration might doubtless have been brought about in a shorter period yet the example before us shows that an inhumation of 17 centuries may sometimes affect nothing towards the reduction of shells to the state in which fossils are usually found. The wooden beams in the houses at Herculaneum are black on the exterior but when cleft open they appear to be almost in the state of ordinary wood and the progress made by the whole mass towards the state of lignite is scarcely appreciable. Some animal and vegetable substances of more perishable kinds have of course suffered much change and decay yet the state of preservation of these is truly remarkable. Fishing nets are very abundant in both cities often quite entire and their number at Pompeii is the more interesting from the sea being now as we stated a mile distant. Linen has been found at Herculaneum with the texture well-defined and in a fruterer's shop in that city were discovered vessels full of almonds, chestnuts, walnuts and fruit of the carubiere all distinctly recognizable from their shape. A loaf also still retaining its form was found in a baker's shop with his name stamped upon it. On the counter of an apothecary was a box of pills converted into a fine earthy substance and by the side of it a small cylindrical roll evidently prepared to be cut into pills. By the side of these was a jar containing medicinal herbs. In 1827 moist olives were found in a square glass case and caviar or row of a fish in a state of wonderful preservation. An examination of these curious condiments has been published by Covelli of Naples and they are preserved hermetically sealed in a museum there. Papyri. There is a marked difference in the condition and appearance of the animal and vegetable substances found at Pompeii and Herculaneum. Those of Pompeii being penetrated by a gray, pulverulent tuft those in Herculaneum seeming to have been first enveloped by a paste which consolidated round them and then allowed them to become slowly carbonized. Some of the rolls of papyrus at Pompeii still retain their form but the writing and indeed almost all the vegetable matter appear to have vanished and to have been replaced by volcanic tuft somewhat pulverulent. At Herculaneum the earthy matter has scarcely ever penetrated and the vegetable substance of the papyrus has become a thin, fryable black matter almost resembling in appearance the tinder which remains when stiff paper has been burnt in which the letters may still be sometimes traced. The small bundles of papyri composed of five or six rolls tied up together had sometimes lain horizontally and were pressed in that direction but sometimes they had been placed in a vertical position. Small tickets were attached to each bundle to which the title of the work was inscribed. In one case only have the sheets been found with writing on both sides of the pages. So numerous are the obliterations and corrections that many must have been the original manuscripts. The variety of handwriting is quite extraordinary. Nearly all are written in Greek but there are a few in Latin. They were almost all found in a suburban villa in the library of one private individual and the titles of 400 of those least injured which have been read are found to be unimportant works but all entirely new chiefly relating to music, rhetoric and cookery. There are two volumes of Epicurus on nature and the others are mostly bywriters of the same school only one fragment having been discovered by an opponent of the Epicurian system, Chrysopis. In one of the manuscripts which was in the hands of the interpreters when I visited the museum in 1828 the author indulges in the speculation that all the Homeric personages were allegorical that Agamemnon was the aether Achilles the sun Helen the earth Paris the air Hector the moon et cetera. Probability of future discoveries of manuscripts. In the opinion of some antiquaries not one hundredth part of the city has yet been explored and the quarters hitherto cleared out at a great expense are those where there was the least probability of discovering manuscripts. As Italy could already boast her splendid Roman amphitheaters and Greek temples it was a matter of secondary interest to add to their number those in the dark and dripping galleries of Herculaneum and having so many of the masterpieces of ancient art we could have dispensed with the inferior busts and statues which could alone have been expected to reward our researches in the ruins of a provincial town. But from the moment that it was ascertained that rolls of papyrus preserved in this city could still be deciphered every exertion ought to have been steadily and exclusively directed towards the discovery of other libraries. Private dwelling should have been searched before so much labor and expense were consumed in examining public edifices. A small portion of that zeal and enlightened spirit which prompted the late French and Tuscan expedition to Egypt might long air this in a country near her home have snatched from oblivion some of the lost works of the Augustan age or of eminent Greek historians and philosophers. A single roll of papyrus might have disclosed more matter of intense interest than all that was ever written in hieroglyphics. Stabii besides the cities already mentioned Stabii a small town about six miles from Vesuvius and near the site of the modern Castel Amare C. Map of volcanic district of Naples was overwhelmed during the eruption of 79. Pliny mentions that when his uncle was there he was obliged to make his escape so great was the quantity of falling stones and ashes. In the ruins of this place a few skeletons have been found buried in volcanic ejections together with some antiquities of no great value and rolls of papyrus which like those of Pompeii were illegible. Torre del Greco overflowed by lava. Of the towns Hitherto mentioned Herculaneum alone has been overflowed by a stream of melted matter but this did not as we have seen enter or injure the buildings which were previously enveloped or covered over with tuff but burning torrents have often taken their course through the streets of Torre del Greco and consumed or enclosed a large portion of the town in solid rock. It seems probable that a destruction of 3,000 of its inhabitants in 1631 which some accounts attribute to boiling water was principally due to one of those alluvial floods which we before mentioned. But in 1737 the lava itself flowed through the eastern side of the town and afterwards reached the sea and in 1794 another current rolling over the western side filled the streets and houses and killed more than 400 persons. The main street is now quarried through this lava which supplied building stones for new houses erected where others had been annihilated. The church was half buried in a rocky mass but the upper portion served as the foundation of a new edifice. The number of the population at present is estimated at 15,000 and a satisfactory answer may readily be returned to those who inquire how the inhabitants can be so inattentive to the voice of time and the warnings of nature as to rebuild their dwellings on a spot so often devastated. No neighboring site unoccupied by a town or which would not be equally insecure combines the same advantages of proximity to the capital, to the sea and to the rich lands on the flanks of Vesuvius. If the present population were exiled they would immediately be replaced by another for the same reason that the Marama of Tuscany and the Campania di Roma will never be depopulated although the malaria fever commits more havoc in a few years than the Vesuvian Lavas in as many centuries. The district around Naples supplies one amongst innumerable examples that those regions where the surface is most frequently renewed and where the renovation is accompanied at different intervals of time by partial destruction of animal and vegetable life may nevertheless be amongst the most habitable and delightful on our globe. I have already made a similar remark when speaking of tracks where aqueous causes are now most active and the observation applies as well to parts of the surface which are the abode of aquatic animals as to those which support terrestrial species. The sloping sides of Vesuvius give nourishment to a vigorous and healthy population of about 80,000 souls and the surrounding hills and plains together with several of the adjoining isles owe the fertility of their soil to matter ejected by prior eruptions. Had the fundamental limestone of the Apennines remain uncovered throughout the whole area the country could not have sustained a twentieth part of its present inhabitants. This will be apparent to every geologist who has marked the change in the agricultural character of the soil the moment he has passed the utmost boundary of the volcanic ejections. As when, for example, at the distance of about seven miles from Vesuvius he leaves the plain and ascends to the cleavity of the Sorrentine Hills. Yet favored as this region has been by nature from time immemorial the signs of the changes imprinted on it during the period that it has served as the habitation of man may appear in after ages to indicate a series of unparalleled disasters. Let us suppose that at some future time the Mediterranean should form a gulf of the Great Ocean and that the waves and tidal current should encroach on the shores of Campania as it now advances upon the eastern coast of England. The geologist will then behold the towns already buried and many more which will evidently be entombed hereafter laid open in the steep cliffs where he will discover buildings superimposed above each other with thick intervening strata of tuft or lava some unscathed by fire like those of Herculaneum and Pompeii others half melted down as in Tare Del Greco and many shattered and thrown about in strange confusion as in Tripragola beneath Montnuovo. Among the ruins will be seen skeletons of men and impressions of the human form stamped in solid rocks of tuft nor will the signs of earthquakes be wanting the pavement of part of the Domitian Way and the temple of the Nymphs submerged at high tide will be uncovered at low water the columns remaining erect and uninjured. Other temples which had once sunk down like that of Serapis will be found to have been upraised again by subsequent movements if they who study these phenomena and speculate on their causes assume that there were periods when the laws of nature or the whole course of natural events differed greatly from those observed in their own time they will scarcely hesitate to refer the wonderful monuments in question to those primeval ages. When they consider the numerous proofs of reiterated catastrophes to which the region was subject they may perhaps commiserate the unhappy fate of beings condemned to inhabit a planet during its nascent and chaotic state and feel grateful that their favoured race has escaped such scenes of anarchy and misrule. Yet what was the real condition of Campania during those years of dire convulsion? Quote, a climate where heaven's breath smells sweet and wooingly a vigorous and luxuriant nature unparalleled in its productions a coast which was once the fairy land of poets and the favoured retreat of great men even the tyrants of the creation loved this alluring region spared it adorned it lived in it died in it unquote foresight Italy volume two the inhabitants indeed have enjoyed no immunity from the calamities which are the lot of mankind but the principal evils which they have suffered must be attributed to moral not to physical causes to disastrous events over which man might have exercised a control rather than to the inevitable catastrophes which result from subterranean agency when Spartacus encamped his army of ten thousand gladiators in the old extinct crater of Vesuvius the volcano was more justly a subject of terror to Campania than it has ever been since the rekindling of its fires end of chapter 24 chapter 25 part one of principles of geology this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org recording by Amy Koenig principles of geology by Charles Lyle section 57 chapter 25 Aetna external physiognomy of Aetna lateral cones their successive obliteration early eruptions Montirossi in 1669 towns overflowed by lava part of Catania overflowed mode of advance of a current of lava subterranean caverns marine strata at base of Aetna Valdalbove not an ancient crater its scenery form, composition and origin of the dikes linear direction of cones formed in 1811 and 1819 lavas and breaches flood produced by the melting of snow by lava glacier covered by a lava stream Valdalbove how formed structure and origin of the cone of Aetna whether the inclined sheets of lava were originally horizontal antiquity of Aetna whether signs of deluvial waves are observable on Aetna external physiognomy of Aetna after Vesuvius our most authentic records relate to Aetna which rises near the sea in solitary grandeur to the height of nearly 11,000 feet footnote in 1815 Captain Smythe ascertained trigonometrically that the height of Aetna was 10,874 feet the Catanians disappointed that their mountain had lost nearly 2,000 feet of the height assigned to it by Recupero refused to acquiesce in the decision afterwards in 1824 Sir J. Herschel not being aware of Captain Smythe's conclusions determined by careful barometrical measurement that the height was 10,872 and a half feet this singular agreement of results so differently obtained was spoken of by Herschel as a happy accident but Dr. Woliston remarked that it was one of those accidents which would not have happened to two fools and footnote the base of the cone is almost circular and 87 English miles in circumference but if we include the whole district over which its lavas extend the circuit is probably twice that extent divided into three regions the cone is divided by nature into three distinct zones called the fertile the woody and the desert regions the first of these comprising the delightful country around the skirts of the mountain is well cultivated, thickly inhabited and covered with olives, vines, corn, fruit trees and aromatic herbs higher up the woody region encircles the mountain an extensive forest six or seven miles in width affording pastureage for numerous flocks the trees are a various species, the chestnut, oak and pine being most luxuriant while in some tracts are groves of cork and beech above the forest is the desert region, a waste of black lava and scoriae where on a kind of plane rises a cone of eruption to the height of about 1100 feet from which sulfurous vapors are continually evolved cones produced by lateral eruption the most grand and original feature in the physiognomy of Etna is the multitude of minor cones which are distributed over its flanks and which are most abundant in the woody region these, although they appear but trifling irregularities when viewed from a distance as subordinate parts of so imposing and colossal a mountain would nevertheless be deemed hills of considerable altitude in almost any other region without enumerating numerous montaquils of ashes thrown out at different points there are about 80 of these secondary volcanoes of considerable dimensions 52 on the west and north and 27 on the east side of Etna one of the largest called Monte Menardo near Bronte is upwards of 700 feet in height and a double hill near Nicolosi called Monte Rossi formed in 1669 is 450 feet high and the base two miles in circumference so that it somewhat exceeds in size Monte Nuovo before described yet it ranks only as a cone of the second magnitude amongst those produced by the lateral eruptions of Etna on looking down from the lower borders of the desert region these volcanoes present us with one of the most delightful and characteristic scenes in Europe they afford every variety of height and size and are arranged in beautiful and picturesque groups however uniformly may appear when seen from the sea or the plains below nothing can be more diversified than their shape when we look from above into their craters one side of which is generally broken down there are indeed few objects in nature more picturesque than a wooded volcanic crater the cones situated in the higher parts of the forest zone are chiefly closed with lofty pines while those at a lower elevation are adorned with chestnuts, oaks, beech and home successive obliteration of these cones the history of the eruptions of Etna, imperfect and interrupted as it is affords us nevertheless much insight into the manner in which the whole mountain has successively attained its present magnitude and internal structure the principal cone has more than once fallen in and been reproduced in 1444 it was 320 feet high and fell in after the earthquakes of 1537 in the year 1693 when a violent earthquake shook the whole of Sicily and killed 60,000 persons the cone lost so much of its height, says Bacone that it could not be seen from several places in Valdemone from which it was before visible the greater number of eruptions happen either from the great crater or from lateral openings in the desert region when hills are thrown up in the middle zone and project beyond the general level they gradually lose their height during subsequent eruptions for when lava runs down from the upper parts of the mountain and encounters any of these hills the stream is divided and flows round them so as to elevate the gently sloping grounds from which they rise in this manner a deduction is often made at once of 20 or 30 feet or even more from their height thus one of the minor cones called Monte Pelusa was diminished in altitude by a great lava stream which encircled it in 1444 and another current has recently taken the same course yet this hill still remains four or five hundred feet high there is a cone called Monte Nucila near Nicolosi round the base of which several successive currents have flowed and showers of ashes have fallen since the time of history till it lasts during an eruption in 1536 the surrounding plain was so raised that the top of the cone alone was left projecting above the general level Monte Nero situated above the grotta del Capre was in 1766 almost submerged by a current and Monte Capriolo afforded in the year 1669 a curious example of one of the last stages of obliteration for a lava stream descending on a high ridge which had been built up by the continued superposition of successive lavas flowed directly into the crater and nearly filled it the lava therefore of each new lateral cone tends to detract from the relative height of lower cones above their base so that the flanks of Etna sloping with a gentle inclination enveloping succession a great multitude of minor volcanoes while new ones spring up from time to time early eruptions of Etna Etna appears to have been in activity from the earliest times of tradition for Diodorus Siculus mentions an eruption which caused a district to be deserted by the Sicani before the Trojan War Thucydides informs us that in the sixth year of the Peloponnesian War or in the spring of the year 425 BC a lava stream ravaged the environs of Catania and this he says was the third eruption which had happened in Sicily since the colonization of that island by the Greeks the second of the three eruptions alluded to by the historian took place in the year 475 BC and was that so poetically described by Pindar two years afterwards in his first Pythian Ode Chion Durania Suneche Nifoes Etna Panates Chionos Ocseas Tithena in these and the seven verses which follow a graphic description is given of Etna such as it appeared five centuries before the Christian era and such as it has been seen when an eruption in modern times the poet is only making a passing allusion to the Sicilian volcano as the mountain under which Tithes lay buried yet by a few touches of his master hand every striking feature of the scene has been faithfully portrayed we are told of the snowy Etna the pillar of heaven the nurse of everlasting frost in whose deep caverns lie concealed the fountains of unapproachable fire a stream of eddying smoke by day a bright and ruddy flame by night and burning rocks rolled down with loud uproar into the sea eruption of 1669 Monte Rossi formed the great eruption which happened in the year 1669 is the first which claims particular attention an earthquake had leveled to the ground all the houses in Nicolosi a town situated near the lower margin of the witty region about 20 miles from the summit of Etna and 10 from the sea at Catania two gulfs then open near that town from whence sand and scoriae were thrown up in such quantity that in the course of three or four months a double cone was formed called Monte Rossi about 450 feet high but the most extraordinary phenomenon occurred at the commencement of the convulsion in the plain of San Leo a fisher six feet broad and of unknown depth opened with a loud crash and ran in a somewhat tortuous course to within a mile of the summit of Etna its direction was from north to south and its length 12 miles it emitted a most vivid light five other parallel fissures of considerable length afterwards opened one after the other and emitted smoke and gave out bellowing sounds which were heard at the distance of 40 miles this case seems to present the geologists with an illustration of the manner in which those continuous dykes of vertical porphyry were formed which are seen to traverse some of the older Lavas of Etna for the light emitted from the great rent of San Leo appears to indicate that the fisher was filled to a certain height with incandescent lava probably to the height of an orifice not far distant from Monte Rossi which at that time opened and poured out a lava current when the melted matter in such a rent has cooled it must become a solid wall or dyke intersecting the older rocks of which the mountain is composed similar rents have been observed during subsequent eruptions as in 1832 when they ran in all directions from the center of the volcano it has been justly remarked by Monsieur Elie de Beaumont that such star-shaped fractures may indicate a slight upheaval of the whole of Etna they may be the signs of the stretching of the mass which may thus be raised gradually by a force from below the lava current of 1669 before alluded to soon reached in its course a minor cone called Montpilierre at the base of which it entered a subterranean grotto communicating with a suite of those caverns which are so common in the lava's vetna here it appears to have melted down some of the vaulted foundations of the hill so that the whole of that cone became slightly depressed and traversed by numerous open fishers part of Catania destroyed the lava after overflowing 14 towns and villages some having a population of between 3 and 4000 inhabitants arrived at length at the walls of Catania these have been purposely raised to protect the city but the burning flood accumulated till it rose to the top of the rampart which was 60 feet in height and then it fell in a fiery cascade and overwhelmed part of the city the wall however was not thrown down but was discovered long afterwards by excavations made in the rock by the Prince of Biscari so that the traveler may now see the solid lava curling over the top of the rampart as if still in the very act of falling this great current performed the first 13 miles of its course in 20 days or at the rate of 162 feet per hour but required 23 days for the last two miles giving a velocity of only 22 feet per hour and we learn from Dolomue that the stream moved during part of its course at the rate of 1500 feet an hour and in others it took several days to cover a few yards when it entered the sea it was still 600 yards broad and 40 feet deep it covered some territories in the environs of Catania which had never before been visited by the lavas of Etna while moving on its surface was in general a mass of solid rock and its motive advancing as is usual with lava streams was by the occasional fishering of the solid walls a gentleman of Catania named Papa Lardo desiring to secure the city from the approach of the threatening torrent went out with a party of 50 men whom he addressed in skins to protect them from the heat and armed with iron crows and hooks they broke open one of the solid walls which flanked the current near Bel Passo and immediately fourth issued a rivulet of melted matter which took the direction of paterno but the inhabitants of that town being alarmed for their safety took up arms and put a stop to farther operations as another illustration of the solidity of the walls of an advancing lava stream I may mention an adventure related by Recupero who in 1766 had ascended a small hill formed of ancient volcanic matter to behold the slow and gradual approach of a fiery current two miles and a half broad when suddenly two small threads of liquid matter issuing from a crevice detached themselves from the main stream and ran rapidly towards the hill he and his guide had just time to escape when they saw the hill which was 50 feet in height surrounded and in a quarter of an hour melted down into the burning mass so as to flow on with it but it must not be supposed that this complete fusion of rocky matter coming in contact with lava is of universal or even common occurrence it probably happens when fresh portions of incandescent matter come successively in contact with fusible materials in many of the dykes which intersect the tufts and lavas of Aetna there is scarcely any perceptible alteration affected by heat on the edges of the horizontal beds in contact with the vertical and more crystalline mass on the side of Montpellier one of the towns overflowed in the great eruption above described an excavation was made in 1704 and by immense labor the workmen reached at the depth of 35 feet the gate of the principal church where there were three statues held in high veneration one of these together with a bell some money and other articles were extracted in a good state of preservation from beneath a great arch formed by the lava it seems very extraordinary that any works of art not encased with tufts like those in Herculaneum should have escaped fusion and hollow spaces left open in this lava current which was so hot at Catania eight years after it entered the town that it was impossible to hold the hand in some of the crevices subterranean caverns on it mention was made of the entrance of a lava stream into a subterranean grotto whereby the foundations of a hill were partially undermined such underground passages are among the most curious features on it and appear to have been produced by the hardening of the lava during the escape of great volumes of elastic fluids which are often discharged for many days in succession after the crisis of the eruption is over near Nicolosi not far from Monte Rossi one of these great openings may be seen called the Forza della Palomba 625 feet in circumference and its mouth and 78 deep after reaching the bottom of this we enter another dark cavity and then others in succession sometimes descending precipices by means of ladders at length the vaults terminate in a great gallery 90 feet long and from 15 to 50 broad beyond which there is still a passage never yet explored so that the extent of these caverns remains unknown the walls and roofs of these great vaults are composed of rough and bristling scoriae of the most fantastic forms Marine strata at base of Etna if we skirt the fertile region at the base of Etna on its southern and eastern sides we behold marine strata of clay sand at volcanic tuff cropping out from beneath the modern lavas the marine fossil shells occurring in these strata are all of them or nearly all identical with species now inhabiting the Mediterranean and as they appear at the height of from 600 to 800 feet above the sea near Catania they clearly prove that there has been in this region as in other parts of Sicily farther to the south an upward movement of the ancient bed of the sea it is fair therefore to infer that the whole mountain with the exception of those parts which are of very modern origin has participated in this upheaval if we view Etna from the south we see the marine deposits above alluded to forming a low line of hills or a steep inland slope or cliff as in the annex drawing taken from the limestone platform of Primozole figure 47 it should be observed however in reference to this view that the height of the volcanic cone is 10 times greater than the hills at its base although it appears less elevated because the summit of the cone is 10 or 12 times more distant from the plain of Catania than is Lakodia the mountain is in general of a very symmetrical form a flattened cone broken on its eastern side by a deep valley called the Valdilbove or in the provincial dialect of the peasants Valdibue for here the herdsmen in reducta valemugientium prospectat errantes gregeis Dr. Buckland was I believe the first English geologist to examine this valley with attention and I'm indebted to him for having described it to me before I visited Sicily is more worthy of attention than any single spot in that island or perhaps in Europe the Valdilbove commences near the summer of Etna and descending into the woody region is farther continued on one side by a second and narrower valley called the Valdicalana below this another named the Valdi Santo Giacomo begins a long narrow ravine which has prolonged to the neighborhood of Zafarana on the confines of the fertile region these natural incisions in the side of the volcano are of such depth that they exposed to view a great part of the structure of the entire mass which in the Valdilbove is laid open to the depth of from 3,000 to about 4,000 feet from the summit of Etna the geologist thus enjoys an opportunity of ascertaining how far the internal conformation of the cone corresponds with what he might have anticipated as the result of that motive increase which has been witnessed during the historical era end of chapter 25 part 1 Chapter 25 Part 2 of Principles of Geology this is a LibriVox recording all LibriVox recordings are in the public domain for more information or to volunteer please visit LibriVox.org Recording by Amy Canick Principles of Geology by Charles Lyle Section 58 Description of Plate 3 The accompanying view is part of a panoramic sketch which I made in November 1828 and may assist the reader in comprehending some topographical details to be alluded to in the sequel although it can convey no idea of the picturesque grandeur of the scene The great lava currents of 1819 and 1811 are seen pouring down from the higher parts of the valley overrunning the forests of the Great Plain and rising up in the foreground on the left with a rugged surface on which many hillocks and depressions appear which is often characterized as a lava current immediately after its consolidation The small cone number 7 was formed in 1811 and was still smoking when I saw it in 1828 The other small volcano to the left from which vapor is issuing was I believe one of those formed in 1819 The following are the names of some of the other points indicated in the sketch 1. Montanmola 2. Torredo Philosopher 3. Highest Cone 4. Lepra 5. Finocchio 6. Capra 7. Cone of 1811 8. Sima de la Sino 9. Musara 10. Zuccolaro 11. Roca di Calana Description of Plate 4 The second view represents the same valley as seen from above or looking directly down the Val del Bove from the summit of the principal crater formed in 1819 I am unable to point out the precise spot which this crater would occupy in the view represented in Plate 3 but I can see that it would appear in the face of the great precipice near which the smoke issuing from the cone number 7 is made to terminate There are many ledges of rock on the face of that precipice where eruptions have occurred The circular form of the Val del Bove is well shown in this view, Plate 4 To the right and left are the lofty precipices which form the southern and northern sides of the great valley and which are intersected by dykes projecting in the manner afterwards to be described In the distance appears the fertile region of Etna extending like a great plain along the sea coast The spots particularly referred to in the Plate are the following A. Cape Spark de Vento in Italy of which the outline is seen in the distance B. The Promontory of Taormino on the Sicilian coast C. The River Alcantra D. The Small Village of Riposto F. The Town of Aci Reale G. Cyclopean Islands are for Alione in the Bay of Trezza H. The Great Harbor of Syracuse K. The Lake of Lentini I. The City of Catania near which has marked the course of the lava which flowed from the Monte Rossi in 1669 and destroyed part of the city L. To the left of the view is the crater of 1811 which is also shown at number 7 in Plate 3 M. Rock of Musara also seen at number 9 in Plate 3 I. Valley of Calanna The Val del Bove is of truly magnificent dimensions a vast amphitheater 4 or 5 miles in diameter surrounded by nearly vertical precipices varying from 1,000 to above 3,000 feet in height the loftiest being at the upper end and the height gradually diminishing on both sides The feature which first strikes the geologist as distinguishing the boundary cliffs of this valley is the prodigious multitude of vertical dykes which are seen in all directions traversing the volcanic beds The circular form of this great chasm and the occurrence of these countless dykes are so forcibly recalled to my mind the phenomena of the Atrio del Cavallo on Vesuvius that I at first imagine that I had entered a vast crater on a scale as far exceeding that of Soma as Etna surpasses Vesuvius in magnitude but I was soon undeceived when I had attentively explored the different sides of the great amphitheater in order to satisfy myself whether the semicircular wall of the Val del Bove had ever formed the boundary of a crater and the aquaversal dip which is so beautifully exhibited in the escarpment of Soma Had the supposed analogy between Soma and the Val del Bove held true the tufts and lavas at the head of the valley would have dipped to the west those on the north side toward the north and those on the southern side to the south but such I did not find to be the inclination of the beds they all dipped towards the sea or nearly east as in the valleys of Santo Giacomo and Calana below Scenery of the Val del Bove Let the reader picture to himself a large amphitheater five miles in diameter and surrounded on three sides by precipices from 2,000 to 3,000 feet in height If he has beheld that most picturesque scene in the chain of the Pyrenees, the celebrated Cirque of Gavarni he may form some conception of the magnificent circle of precipitous rocks which enclose on three sides the great plain of the Val del Bove This plain has been deluged by repeated streams of lava and although it appears almost level when viewed from a distance it is in fact more uneven than the surface of the most tempestuous sea Besides the minor irregularities of the lava the valley is in one part interrupted by a ridge of rocks two of which, Musara and Capra, are very prominent it can hardly be said that they like giants stand to sentinel enchanted land for although like the Trossaks and the Highlands of Scotland they are of gigantic dimensions and appear almost isolated as seen from many points yet the stern and severe grandeur of the scenery which they adorn is not such as would be selected by a poet for a veil of enchantment the character of the scene would accord far better with Milton's picture of the infernal world and if we imagine ourselves to be hold in motion in the darkness of the night one of those fiery currents which have so often traversed the great valley we may well recall Yandere plain for lorn and wild the seat of desolation void of light, save what the glimmering of these livid flames casts pale and dreadful the face of the precipice is already mentioned is broken in the most picturesque manner by the vertical walls of lava which traverse them these masses visually stand out in relief are exceedingly diversified in form and of immense altitude in the autumn their black outline may often be seen relieved by clouds of fleecy vapor which settle behind them and do not disperse until midday continuing to fill the valley while the sun is shining on every other part of Sicily and on the higher regions of Etna as soon as the vapours begin to rise the changes of scene are varied in the highest degree different rocks being unveiled and hidden by turns and the summit of Etna often breaking through the clouds for a moment with its dazzling snows and being then as suddenly withdrawn from the view an unusual silence prevails for there are no torrents dashing from the rocks nor any movement of running water in this valley such as may almost invariably be heard in mountainous regions every drop of water that falls from the heavens or flows from the melting ice and snow is instantly absorbed by the poorest lava and such as the dearth of springs that the herdsmen is compelled to supply his flocks during the hot season from stores of snow laid up in hollows of the mountain during winter the strips of green herbage and forest land which of here and there escaped the burning lavas served by contrast to heighten the desolation of the scene when I visited the valley nine years after the eruption of 1819 I saw hundreds of trees or rather the white skeletons of trees on the borders of the black lava their trunks and branches being all leafless and deprived of their bark by the scorching heat emitted from the melted rock an image recalling those beautiful lines as when heaven's fire hath scathed the forest oaks or mountain pines with singed top their stately growth the bear stands on the blasted heath form, composition, and origin of the dykes but without indulging the imagination any longer in descriptions of scenery I may observe that the dykes before mentioned form unquestionably the most interesting geological phenomenon in the Val-galbove some of these are composed of trachite others of compact blue basalt with olivine they vary in breadth from two to twenty feet and upwards and usually project from the face of the cliffs as represented in the annex drawing figure 49 they consist of harder materials than the strata which they traverse and therefore waste away less rapidly under the influence of that repeated congelation and thawing to which the rocks in this zone of Etna are exposed the dykes are for the most part vertical but sometimes they run in a tortuous course through the tafs and breaches as represented in figure 50 in the escarpment of Soma where similar walls of lava cut through alternating beds of sand and scoria a coating of coal black rock approaching in its nature and appearance to pitch stone is seen at the contact of the dyke with the intersected beds I did not observe such parting layers at the junction of the Etnian dykes which I examined but they may perhaps be discoverable the geographical position of these dykes is most interesting as they are very numerous near the head of the Val-galbove where the cones of 1811 and 1819 were thrown up as also in that zone of the mountain where lateral eruptions are frequent whereas in the valley of Kalana which is below that parallel and in a region where lateral eruptions are extremely rare scarcely any dykes are seen and none whatever is still lower in the valley of Santo Jacomo this is precisely what we might have expected if we consider the vertical fissures now filled with rock to have been the feeders of lateral cones or in other words the channels which gave passage to the lava currents and scoriae that have issued from vents in the forest zone in other parts of Etna there may be numerous dykes at as low a level as the valley of Kalana because the line of lateral eruptions is not everywhere at the same height above the sea but in the section above alluded to there appeared to me an obvious connection between the frequency of dykes and of lateral eruptions some fissures may have been filled from above but I did not see any which by terminating downwards gave proof of such an origin almost all the isolated masses in the Valdilbove such as Capra, Musara and others are traversed by dykes and they perhaps have partly owed their preservation to that circumstance if at least the action of occasional floods has been one of the destroying causes in the Valdilbove for there is nothing which affords so much protection to a massive strata against the undermining action of running water as a perpendicular dyke of hard rock in the accompanying drawing figure 51 the flowing of the lavas of 1811 and 1819 between the rocks Finocchio, Capra and Musara is represented the height of the two last mentioned isolated masses has been much diminished by the elevation of their base caused by these currents they may perhaps be the remnants of lateral cones which existed before the Valdilbove was formed and may hereafter be once more buried by the lavas that are now accumulating in the valley from no point of view are the dykes more conspicuous than from the summit of the highest cone of Etna and of some of them is given in the annex drawing figure 52 Eruption of 1811 I have alluded to the streams of lava which were poured forth in 1811 and 1819 Gemellato, who witnessed these eruptions informs us that the great crater in 1811 first testified by its loud detonations that a column of lava had ascended to near the summit of the mountain a violent shock was then felt and the stream broke out from the side of the cone at no great distance from its apex Shortly after this had ceased to flow a second stream burst forth in another opening considerably below the first then a third still lower and so on till seven different issues had been thus successively formed all lying upon the same straight line it has been supposed that this line was a perpendicular rent in the internal framework of the mountain which rent was probably not produced at one shock but prolonged successively downwards by the lateral pressure an intense heat of the internal column of lava as it subsided by gradual discharge through each vent Eruption of 1819 In 1819 three large mouths or caverns opened very near those which were formed in the eruptions of 1811 from which flames, red-hot cinders and sand were thrown up with loud explosions A few minutes afterwards another mouth opened below from which flames and smoke issued and finally a fifth lower still once a torrent of lava flowed which spread itself with great velocity over the deep and broad valley called Val del Bove This stream flowed two miles in the first 24 hours and nearly as far in the succeeding day and night The three original mouths that length united into one large crater and sent forth lava, as did the inferior apertures so that an enormous torrent poured down the Val del Bove When it arrived at a vast and almost perpendicular precipice at the head of the valley of Calana it poured over in a cascade and being hardened in its descent made an inconceivable crash as it was dashed against the bottom So immense was the column of dust raised by the abrasion of the two-facious hill over which the hardened mass descended that the Catanians were in great alarm supposing a new eruption to have burst out in the woody region exceeding in violence that near the summit of Etna Motive advance of the lava Of the cones thrown up during this eruption not more than two were of sufficient magnitude to be numbered among those 80 which were before described as adorning the flanks of Etna The surface of the lava which deluged the Val del Bove consists of rocky and angular blocks tossed together in the utmost disorder Nothing can be more rugged or more unlike the smooth and even superficies which those who are unacquainted with volcanic countries may have pictured to themselves in a massive matter which had consolidated from a liquid state Mr. Scrope observed this current in the year 1819 slowly advancing down a considerable slope at the rate of about a yard and hour nine months after its emission The lower stratum being arrested by the resistance of the ground the upper or central part gradually protruded itself and being unsupported fell down This in its turn was covered by a mass of more liquid lava which swelled over it from above The current had all the appearance of a huge heap of rough and large cinders rolling over and over upon itself with no propulsion for behind The contraction of the crust as it solidified and the friction of the score form cakes against one another produced a crackling sound Within the crevices a dull red heat might be seen by night and vapor issuing in considerable quantity was visible by day It was stated that when the lava of 1819 arrived at the head of the valley of Calana after flowing down the Val del Bove it descended in a cascade Like many previous currents of lava which have flowed down successively from the higher regions of Etna was churned by a great promontory projecting from the southern side of the Val del Bove This promontory consists of the hills called Zocallaro and Calana and of a ridge of inferior height which connects them See figure 53 It happened in 1811 in 1819 that the flows of lava overtopped the ridge intervening so that they fell in a cascade over a lofty precipice and began to fill up the valley of Calana Other portions of the same lava current flowed around the promontory and they exhibit one of the peculiar characteristics of such streams namely that of becoming solid externally even while yet in motion Instead of thinning out gradually at their edges their sides may often be compared to two rocky walls which are sometimes inclined at an angle of between 30 and 40 degrees When such streams are turned from their course by projecting rock they move right onwards in a new direction and in the valley of Calana a considerable space has thus been left between the steep sides of the lavas so deflected and the precipitous escarpment of Zocallaro which bounds the plain Lavas and breaches In regard to the volcanic masses which are intersected by dykes in the Val del Bove they consist in great part of grey stone lavas of an intermediate character between basalt and trachite and partly of porphyritic lava resembling trachite but to which that name cannot according to von Buch and G. Rose be in strictness applied because the felspar belongs to the variety called Labradorite There is great similarity in the composition of the ancient and modern lavas of Etna both consisting of felspar augite, olivine, and tight niferous iron The alternating breaches are made up of scoriae sand and angular blocks of lava Many of these fragments may have been thrown out by volcanic explosions which falling on the hardened surface of moving lava currents may have been carried to a considerable distance It may also happen that when lava advances very slowly in the manner of the flow of 1819 the angular mass is resulting from the frequent breaking of the mass as it rolls over upon itself may produce these breaches It is at least certain that the upper portion of the lava currents of 1811 and 1819 now consist of angular masses to the depths of many yards Dabouisson has compared the surface of one of the ancient lavas of Avernia to that of a river suddenly frozen over by the stoppage of immense fragments of drift ice a description perfectly applicable to these modern Etnian flows The thickness of the separate beds of conglomerate or breccia which are seen in the same vertical section is often extremely different varying from 3 to nearly 50 feet observed in the hill of Kalana End of Chapter 25 Part 2 Recording by Amy Koenig Chapter 59 Part 3 of Principles of Geology This is a LibriVox recording All LibriVox recordings are in the public domain For more information or to volunteer please visit LibriVox.org Principles of Geology By Charles Lyle Etna Eruptions, structure and antiquity of the cone Flood produced by the melting of snow by lava It is possible that some of the breccias or conglomerates may be referred to aqueous causes as great floods occasionally swept on the flanks of Etna when eruptions take place in winter and when the snows are melted by lava It is true that running water in general exerts no power on Etna, the rain which falls being immediately imbibed by the porous lava. So that, fast as is the extent of the mountain, it feeds only a few small rivulets and these even are dry throughout the greater portion of the year. The enormous rounded boulders therefore of felspar porphyry and basalt, a line of which can be traced from the sea from near Giardini by Mascali in Zalfarana to the Valdel Bovi would offer a perplexing problem to the geologist if history had not preserved the memorials of a tremendous flood which happened in this district in the year 1755. It appears that two streams of lava flowed in that year on the second of March from the highest crater. They were immediately precipitated upon an enormous mass of snow which then covered the whole mountain and was extremely deep near the summit. The sudden melting of this frozen mass by a fire retorrent three miles in length produced a frightful inundation which devastated the sides of the mountain for eight miles in length and afterwards covered the lower flanks of Etna where they were less steep together with the plains near the sea with great deposits of sand, sory and blocks of lava. Many absurd stories circulated in Sicily respecting this event such as that the water was boiling and that it was vomited from the highest crater that it was as salt as the sea and full of marine shells but these were mere inventions to which Rup Caparo, although he relates them as tales of the mountaineers seems to have attached rather too much importance. Floods of considerable violence have also been produced on Etna by the fall of heavy rains aided probably by the melting of snow. By this cause alone in 1761 60 of the inhabitants of Accattina were killed and many of their houses swept away. Glacier covered by a lava stream a remarkable discovery was made on Etna in 1828 of a great mass of ice preserved for many years perhaps for centuries from melting by the singular accident of a current of red hot lava having flowed over it. The following are the facts and attestations of a phenomenon which must at first sight appear of so paradoxical a character. The extraordinary heat experienced in the south of Europe during the summer and autumn of 1828 caused the supplies of snow and ice which had been preserved in the spring of that year for the use of adjoining parts of Sicily and the island of Malta to fail entirely. Great distress was consequently felt for want of a commodity regarded in those countries as one of the necessaries of life rather than an article of luxury and the abundance of which contributes in some of the larger cities to the celebratory of the water and in general health of the community. The magistrates of Accattina Senor M. Gemallaro in the hope that his local knowledge of Atna might enable him to point out some crevice or natural grotto on the mountain where drift snow was still preserved nor were they disappointed for he had long suspected that a small mass of perennial ice at the foot of the highest cone was part of a large and continuous glacier covered by lava current. Having procured a large body of man, he quarried into this ice and proved the superposition of the lava for several hundred yards so as completely to satisfy himself that nothing but the subsequent flowing of the lava over the ice could account for the position of the glacier. Unfortunately for the geologist the ice was so extremely hard and the excavation so expensive that there is no probability of the operations being renewed. On the first of December 1828 I visited this spot which is on the southeast side of the cone and not far above the Casa Inglise but the fresh snow had already nearly filled up the new opening so that it had only the appearance of the mouth of a grotto. I do not however question the accuracy of the conclusion of Senor Gemallaro who being well acquainted with all the appearances of drift snow in the fissures and cavities of Etna had recognized even before the late excavations the peculiarity of the position of the ice in this locality. We may suppose that at the commencement of the eruption a deep mass of drift snow had been covered by volcanic sand showered down upon it before the descent of the lava. A dense stratum of this fine dust mixed with scurry is well known to be extremely bad conductor of heat and the shepherds in the higher regions of Etna are accustomed to provide water for their flocks during summer by screwing a layer of volcanic sand a few inches thick over the snow which effectually prevents the heat of the sun from penetrating. Suppose the mass of snow to have been preserved from liquefaction until the lower part of the lava had consolidated we may then readily conceive that a glacier protected at the height of 10,000 feet above the level of the sea would endure as long as the snow was of Mont Blanc unless melted by volcanic heat from below. When I visited the great crater in the beginning of winter, December 1st, 1828 I found the crevices in the interior encrusted with thick ice and in some cases hot vapors were actually streaming out between the masses of ice and the rugged and steep crater. After the discovery of Senor Jimmlero it would not be surprising to find in the cones of the Icelandic volcanoes which are covered for the most part with perpetual snow, repeated alternations of lava streams and glaciers. We have indeed Lieutenant Kendall's authority for the fact that Deception Island in New South Shetland latitude 62 degrees 55 minutes south is principally composed of alternate layers of volcanic ashes and ice. Origin of the Velal Bovi It is recorded as will be stated in the history of earthquakes Chapter 29 that in the year 1772 a great subsidence took place on Papandayan the largest volcano in the island of Java, an extent of ground 15 miles in length and 6 in breadth covered by no less than 40 villages was engulfed and the cone lost 4,000 feet of its height. In like manner the summit of Carguera Azul, one of the loftiest of the Andes of Cuito fell in on the 19th July 1698 and another mountain of still greater altitude in the same chain called Capac Arú a short time before the conquest of America by the Spaniards It will also be seen in the next chapter that so late as a year 1822 during a violent earthquake and volcanic eruption in Java one side of the mountain called Galangun which was covered by a dense forest became an enormous gulf in the form of a semi-circle. The new cavity was about midway between the summit and the plane and surrounded by steep rocks. Now we might imagine a similar event or a series of substances to have formally occurred on the eastern side of Etna although such catastrophes have not been witnessed in modern times or only on a very trifling scale. A narrow ravine about a mile long 20 feet wide and from 20 to 36 in depth has been formed within the historical era on the flanks of the volcano near the town of Mascalucia in a small circular tract called a cisterna near the summit sank down in the year of 1792 to the depth of about 40 feet and left on all sides of the chasm a vertical section of the beds exactly resembling those which are seen in the precipices of the Valdal Bovi at some remote periods therefore we might suppose more extensive portions of the mountain to have fallen in during great earthquakes. But we ought not to exclude entirely from our speculations another possible agency by which the great cavity may in part at least have been excavated namely the denuding action of the sea. Whether its waves may once have had access to the great valley before the ancient portion of Etna was appealed to its present elevation is a question which will naturally present itself to every meteorologist. Marine shells have been traced to a height of 800 feet above the base of Etna and would doubtless be seen to ascend much higher were not the structure of the lower region of the mountain concealed by floods of lava. We cannot ascertain to what extent a change in the relative level of land and sea may have been carried in this spot but we know that some of the of no ancient date reach a height of 3000 feet and the marine deposits on the flanks of Etna full of recent species of shells may ascend to equal or greater heights. The narrow valley of Kalana leading out of Valdalbovi and that of San Giacomo lower down have much the appearance of ravines swept out by aqueous action. Structure and origin of the cone of Etna. Our data for framing a correct theory of the manner in which the cone of Etna has acquired its present dimensions and internal structure are very imperfect because it is on the eastern side only in the Valdalbovi above described that we see a deep section exposed. Even here we obtained no insight into the interior composition of the mountain beyond a depth of between 3000 feet below the base of the highest cone which has been several times destroyed and renewed. The precipices seen at the head of the Valdalbovi in the escarpment called the Sierra del Solvisio exhibit merely the same series of alternating labids and brashias which descending with a general dip towards the sea form the boundary cliffs of all the other parts of the Valdalbovi If then we estimate the height of Etna at about 11,000 feet we may say that we know from actual observation less than one half of its component materials assuming it to extend downwards to the level of the sea namely first the highest cone which is about 1000 feet above its base and secondly the alternations of lava, tough and volcanic brashia which constitute the rocks between the cisterna near the base of the upper cone and the foot of the precipices at the head of the Valdalbovi at the lowest point to which the vertical section extends there are no signs of any approach to a termination of the purely volcanic mass which may perhaps penetrate many thousands of feet further downwards there is indeed a rock called Raka Giannacola near the foot of the Great Escarpment which consists of a large mass between 150 and 200 feet wide not divided into beds and almost resembling granite in that structure although agreeing very closely in mineral composition with the lavas of Etna in general this mass may doubtless be taken as a representative of those crystalline or plutonic formations which would be met with evidence if we could descend to greater depths in the direction of the central axis of the molten for a great body of geological evidence leads us to conclude that rocks of this class result from the consolidation under great pressure of melted matter which has risen up and filled rents and chasms such for example as may communicate with the principal and minor vents of eruption in a volcano like Etna but if we speculate on the nature of the formation which the lava may have pierced in its way upwards we may fairly presume that a portion of these consist of marine tertiary rocks like those of the neighboring Valdinoto or those which skirt the borders of the Etnian cone on its southern and eastern sides Etna may in fact have been at first an insular volcano raising its summit slightly above the level of the sea but we have no grounds for concluding that any of the beds exposed in the deep section of the Valdalbovi have formed a part of such a marine accumulation on the contrary all the usual signs of subacquias origin are wanting and even if we believe the foundations of the mountain to have been laid in the sea we could not expect this portion to be made visible in sections which only proceed downwards from the summit through one half the thickness of the mountain especially as the highest points attained by the tertiary strata in other parts of Sicily very rarely exceed 3000 feet above the sea on the eastern and southern base of Etna a marine deposit already alluded to is traced up to the height of 800 or 1000 feet before it becomes concealed beneath the covering of modern lavas which is continually extending its limits during successive eruptions and prevents us from ascertaining how much higher the marine strata may ascend as the embedded shells belong almost entirely to species now inhabiting the Mediterranean it is evident that there has been here an upheaval of the region at the base of Etna it is fair therefore to infer that the volcanic nucleus of the mountain partly perhaps of submarine and partly of sub aerial origin participated in this movement and was carried up bodily now in proportion as a cone gains height by such a movement combined with accumulative effects of eruptions throwing out matter successively from one or more central vents the hydrostatic pressure of the column of lava augments with their increasing height until the time arrives when the flanks of the cone can no longer resist the increased pressure and from that period they give way more readily lateral outbursts becoming more frequent hence independently of any local expansion of the fractured volcanic mass those general causes by which the modern tertiary strata of a great part of Sicily have been raised to the height of several thousand feet above their original level would tend naturally to render the discharge of lava in scurry from a summit of Etna less copious and the lateral discharge greater if then a conical or dome shaped mass of volcanic materials was accumulated to the height of four thousand or perhaps seven thousand feet before the upward movement began or what is much more probable during the continuance of the upward movement that ancient mass would not be buried under the products of the newer eruptions because these last would then be poured out chiefly at a lower level since I visited Etna in 1828 M. D. Beaumont has published a most valuable memoir on the structure and origin of that mountain which he examined in 1834 and an excellent description of it also appeared in the poshumous work of Hoffman in M. D. Beaumont's essay in which he has explained his views with uncommon perspicuity and talent he maintains that all the alternating stony and fragmentary beds more than three thousand feet thick which are exposed in the Veldel Bovi were formed originally on a surface so nearly flat that the slope never exceeded three degrees from this horizontal position they were at length heaved up suddenly to Unsocu into a great mountain to which no important additions have since been made prior to this upthrow a platform is supposed to have existed above the level of the sea in which various fissures open and from these melted matter was poured forth again and again which spread itself around in thin sheets of uniform thickness from the same rinse issued showers of scurry and fragmentary matter which were spread out as to form equally uniform and horizontal beds intervening between the sheets of lava but although by the continued repetition of these operations a vast pile of volcanic matter four thousand feet or more in thickness was built up precisely in that region where Etna now rises and to which nothing similar has produced elsewhere in Sicily still we are told that Etna was not yet a mountain no hypothetical diagram has been given to help us to conceive how this great mass of materials of super marine origin could have been disposed of in horizontal beds so as not to constitute an eminence towering far above the rest of Sicily but it is assumed that a powerful force far below at length burst suddenly through the horizontal formation uplifted it to a considerable height and caused the beds to be in many places highly inclined this elevatory forest was not all expended on a single central point as Van Bush has imagined in the case of Palma Teneriff or Soma but rather followed for a short distance a linear direction among other objections that may be advanced against the theory above proposed I may mention first that the increasing number of dykes as we approach the head of the Veldel Bovi or the middle of Etna and the great thickness of lava scurry and conglomerates in that region imply that the great center of eruption was always where it now is or nearly at the same point and there must therefore have been a tendency from the beginning to a conical or dome shaped arrangement in the ejected materials secondly were we to admit a great number of separate points of eruption scattered over a plane or platform there must have been a great number of cones thrown up over these different vents and these hills some of which would probably be as lofty as those now seen on the flanks of Etna or from 300 to 750 feet in height would break the continuity of the sheets of lava while they would become gradually enveloped by them the ejected materials more over would slope at a high angle on the sides of these cones and where they fell on the surrounding plane would form strata thicker near the base of each cone then at a distance what then are the facts it will be asked to account for which this has been the case of original horizontality followed by a single and sudden effort of upheaval which gave to their beds the present slope has been invented M. de Montt observes that in the boundary precipices of the Vald El Bovi sheets of lava and intercalated beds of cinders mixed with polarulent and fragmentary matter evidently cast out during eruptions varying from 15 degrees to 27 degrees it is impossible he says that the lobbies could have flowed originally on planes so steeply inclined for streams which descend a slope even of 10 degrees form narrow stripes and never acquire such a compact texture their thickness more over always inconsiderable varies with every variation of steepness in the declivity down the slope whereas in several parts of the Vald El Bovi the sheets of lava are continuous for great distances in spite of their steep inclination and are often compact and perfectly parallel one to the other even where there are more than 100 beds of interpolated fragmentary matter the intersecting dykes also terminate upwards in many instances at different elevations and blend or as M. de Montt terms it, articulate with sheets of lava which they meet at right angles it is therefore assumed that such dykes were the feeders of the streams of lava with which they unite and they are supposed to prove that the platform on the surface of which the melted matter was poured out was at first so flat that the fluid mass spread freely and equally in every direction and not towards one point only of the compass as would happen if it had descended the sloping sides of a cone. This argument is ingeniously and plainly put in the following terms Had the melted matter poured down an inclined plane after issuing from a rent the sheet of lava would after consolidation have formed an elbow with the dyke like the upper bar of the letter F instead of extending itself on both sides like that of a T It is also contended that a series of sheets of lava formed on a conical or dome shaped mountain would have been more numerous at points far less from the central axes since every dyke which had been a source of a lava stream must have poured its contents downwards and never upwards In reference to the facts here stated I may mention that the dykes which I saw in the Valdelbovi were either vertical or made almost all of them a near approach to the perpendicular which could not have been the case had they been the feeders of horizontal beds of lava and had they consequently joined them originally at right angles for then the dykes ought subsequently to have acquired a considerable slope like the beds which they intersect I may also urge another objection to the views above set forth namely that had the dykes been linear vents or orifices of eruption we must suppose the inter stratified scurry and lapoli as well as the lavas to have come out of them and in that case the irregular heaping of fragmentary matter around the vents would as before hinted have disturbed that uniform thickness and parallelism of the beds which M. de Beaumont describes if however some of the sheets of lava joined the dykes in such a manner as to imply that they were in a melted state simultaneously with the contents of the fissures a point not easily ascertained where the precipices are for the most part inaccessible the fact may admit of a different interpretation from the proposed by the French geologists. Rents like those before alluded to which open in the plain of South Leo in 1669 filled below with incandescent lava may have lain in the way of currents of melted matter descending from higher openings in that case the matter of the current would have flowed into the fissures and mixed with the lava at its bottom numerous open rinse of this kind are described by Mr. Donna as having been caused during a lady ruption in one of the volcanic domes of the Sandwich Islands they remained open at various heights on the slopes of the Great Cone running in different directions and demonstrate the possibilities of future junctions of slightly inclined lava streams with perpendicular walls of lava to me therefore it appears far more easy to explain the uniform thickness and parallelism of so many lavas and beds of fragmentary matter seen in the Vald El Bovi by supposing them to have issued successively out of one or more higher vents near the summit of a Great Dome than to imagine them to have proceeded from lateral dykes or rents opening in a level plain. In the Sandwich Islands we have examples of volcanic domes 15,000 feet high produced by successive outpourings from vents at or near the summit one of these, Mount Lao has a slope in all directions of 6 degrees 30 minutes another, Mount Kia a mean inclination of 7 degrees 46 minutes that their lavas may occasionally consolidate on slopes of 25 degrees and even more and still preserve considerable solidity of texture has been already stated. We know not how large a quantity of modern lava may have been poured into the bottom of the Vald El Bovi yet we perceive that eruptions breaking forth near the center of Aetna have already made some progress in filling up this great hollow. Even within the memory of persons now living the rocks of Masura and Capra have as before stated lost much of their height and picturesque grandeur by the piling up of recent lavas around their base and the great chasm has intercepted many streams which would otherwise have deluged the fertile region below as has happened on the side of Katania the volcanic forces are now laboring therefore to repair the breach which subsidence has caused on one side of the great cone and unless their energy should or a new sinking take place they may in time efface this inequality. In that event the restored portion will always be unconformable to the more ancient part yet it will consist like it of alternating beds of lava scurry and conglomerates which with all their irregularities will have a general slope from the center and summit of Aetna towards the sea. I shall conclude then thinking that I conceive the general inclination of the alternating stony and fragmentary beds of the Veldalbo V from the axis of Aetna towards its circumference or base and the greater thickness of the volcanic pile as we approach the central parts of the mountain to be due to the preponderance of eruptions from that center. These gave rise from the first to a dome shaped mass which has ever since been increasing the height and area being fractured again and again by the expansive force of vapors and the several parts made to cohere together more firmly after the solidification of the lava with which every open fissure and chasm has been filled. At the same time the cone may have gained a portion of its height by the elevatory effect of such dislocating movements and the sheets of lava are greater in others a less inclination than that which at first belong to them. But had the mountain been due solely or even principally to upheaval its structure would have resembled that which geologists have so often recognized in dome shaped hills or certain elevated regions which all consider as having been thrust up by a force from below. In this case there is often a cavity at the summit due partly to the fracture of the upraised rocks but still more to aqueous denudation as they rose out of the sea. The central cavity or valley exposes to view the subjacent formation and the incumbent mass dips away on all sides from the axis but has no tendency to thin out near the base of the dome whereas at this point it alternates and allows the fundamental rock to appear at the surface. The more ordinary case is represented of a great hollow or crater at the summit of the volcanic cone but instead of this we have seen that in the case of etna there is a deep lateral depression called Valdela bovi the upper part of which approaches near the central axis and the origin of which ends of section 59 part 3.