Chapter 4

[I]See the Epistle of Pliny, jun. to Tacitus.

Dion Cassius relates, that this eruption was so violent, that cinders and sulphurous smoke were driven as far as Rome, and even beyond the Mediterranean into Africa. Heraclea was one of the two towns burned by this first conflagration of Vesuvius, which, in these latter times has been discovered at more than 60 feet deep, the surface above which was become, by length of time, arable land and fit for culture. The relation of the discovery of Heraclea is in the hands of the public, and we can only wish that some person, versed in Natural History, would examine the different matters which compose this soil of 60 feet, attending to their disposition and situation, the alterations they have produced or suffered, the direction they have taken, and the hardness they have acquired.

There is an appearance that Naples is situate on a hollow ground, filled with burning materials, for Vesuvius and Solfatera seem to have interior communications. When Vesuvius casts out lava Solfatera emits flames, and when the one ceases the other is extinguished. The city of Naples is situate nearly between them.

One of the last and most violent eruptions of Mount Vesuvius was in the year 1737.[J]The mountain vomited, by several mouths, large torrents of burning metallic matters, which dispersed themselves over the country, and flowed into the sea. Mons. Montealegre, who communicated this relation to the Academy of Sciences, observed, with horror, one of these rivers of fire, whose length, from the mountain to the sea, was about seven miles, its breadth about 60 feet, its depth 25 or 30 palms, and in bottoms or vallies 120: the matter which flowed was like the scum which issues from the furnace of a forge, &c.[K]

[J]It should be remembered, as noticed by Mr. Smellie, that the original of this work was published by our author in 1749, since when Vesuvius has undergone several eruptions.

[K]See the Hist. Acad. an. 1737.

In Asia, particularly in the islands of the Indian ocean, there are many volcanos; one of the most famous is Mount Albours, near Mount Taurus, eight leagues from Herat; its summit continually smokes, and it frequently throws out flames and burning matter in such quantities that the surrounding country is covered with cinders. In the island of Ternate there is a volcano which throws out matterlike pumice-stones. Some travellers assert that this volcano is most furious at the time of the equinoxes, because certain winds then reign there, which inflame the matter that feeds, and has fed this fire for a number of years.[L]

[L]See Argensola's Travels, vol. 1, page 21.

The island of Ternate is but seven leagues round, and is only the summit of a mountain; it gradually ascends from the shore to the middle of the island, where the volcano rises to a considerable height, to the top of which it is very difficult to attain. Many rills of sweet water descend along the ridge of this mountain, and when the air is calm, and the season mild, this burning gulph is in less agitation than during storms and high winds.[M]This confirms what I have said in a former article, and seems to prove that the fire of volcanos does not proceed from any considerable depth, but from the top, or at least not far distant from the summit of the mountain; for if it was not so, the high winds could not increase their combustion. There are other volcanos in the Malaccas. In one of the Mauritius islands, 70 leagues from the Malaccas, there is a volcano, whose effects are asviolent as those of Mount Ternate. Sorca island, one of the Malaccas, was formerly inhabited. In the middle of this island there is a lofty mountain, with a volcano at the top. In 1693 this volcano vomited bitumen and inflamed matters in such a great quantity as to form a burning lake, and which covered the whole island.[N]

[M]See the Travels of Schuten.

[N]See Phil. Trans. ab. vol. 11 page 391.

At Japan, and in the adjacent islands, there are several volcanos, which emit flames during the night and smoke in the day. At the Philippine islands there are also burning mountains. One of the most famous volcanos of the islands in the Indian ocean, and the most recent, is that near the town of Panarucan, in the island of Java; it opened in 1586, and at the first eruption, it threw out an enormous quantity of sulphur, bitumen, and stones. The same year Mount Gounapi, in the island of Banda, which continued only seventeen years, opened and ejected, with a frightful noise, rocks and matters of every kind. There are also some other volcanos in India, as at Sumatra, and in the north of Asia, but those are not considerable.

In Africa, there is a mountain, or rather a cavern, called Beniguazeval, near Fez, which always emits smoke, and sometimes flames. One of the islands of Cape de Verd, called the Fuogo, is only a large mountain which burns continually; this volcano throws out cinders and stones; and the Portuguese, who have attempted several times to erect habitations in this island, have been constrained to abandon the project through dread of the volcano. The Peak of Teneriffe, considered as one of the highest mountains of the earth, throws out fire, cinders, and large stones; from its top rivulets of melted sulphur flow across the snow, where it forms veins that are distinguishable at a great distance.

In America there are a great number of volcanos, particularly in the mountains of Peru and Mexico; that of Arequipa is one of the most famous; it often causes earthquakes, which are more common in Peru than in any other country in the world. The volcano of Carrappa and that of Malahallo are, according to the report of travellers, the most considerable, next to that of Arequipa; but there are many others in these parts of which we have no exact knowledge. M. Bouguer, in his voyage to Peru,published in the Memoirs of the Academy of the year 1744, mentions two volcanos, called Cotopaxi and Pichincha; the first at some distance from, the other near the town of Quito; he was witness of a conflagration of Botopaxi in 1742, and of the orifice which was made in that mountain; this eruption did no other damage than melting the snow and producing such torrents of water, that in less than three hours inundated a tract of country 18 leagues in extent, and overthrew all they met with in their way.

At Mexico the most considerable volcanos are Popochampeche, and the Popoatepec; it was near this last that Cortes passed in his voyage to Mexico; some of the Spaniards ascended to the top, where they saw the mouth, which was about half a league in circumference. Sulphurous mountains are also met with at Guadaloupe, Tercera, and other islands of the Azores; and, if we were to consider as volcanos all those mountains which smoke, or emit flames, we might reckon more than sixty; we have only spoken of those formidable volcanos, near which no person dares to inhabit.

These volcanos which are in such great numbers in the Cordeliers, as I have formerly said, cause almost continual earthquakes, which preventthe natives from building with stone above one story high, and to construct the upper stories of their houses with reeds and light wood. In these mountains are also many precipices and large vents, the sides of which are black and burnt, as in the precipice of Mount Ararat, in Armenia, which is called the Abyss; these abysses are the mouths of extinguished volcanos.

There was lately an earthquake at Lima, the effects of which were dreadful. The town of Lima and Port Callao were almost entirely swallowed up; but the evil was still greater at Callao. The sea rose and covered every building in that town, drowned all the inhabitants, and left only one single tower remaining. Of twenty-five ships that were in this port, four were carried a league upon land, and the rest were swallowed up by the sea. At Lima, which was a large town, there remains only twenty-seven houses standing; a great number of persons were buried in the ruins, particularly monks and religious persons, as their buildings were higher and constructed of more solid materials than the other houses. This misfortune happened at night, in October 1746; the shock remained fifteen minutes.

There was formerly near the port of Pisca, in Peru, a famous city, situate on the sea shore, which was almost entirely destroyed by an earthquake that happened the 19th of October 1682, for the sea having extended beyond its common bounds, swallowed up this unfortunate place with every person that was in it.

If we consult historians and travellers, we shall find relations of many earthquakes and eruptions of volcanos, whose effects have been as terrible as those we have just mentioned. Pesidonius, whom Strabo quotes in his first book, relates, that a city in Phœnicia, near Sidon, was swallowed up by an earthquake, with the neighbouring territory, and even two thirds of Sidon; this effect was not so sudden but that many of the inhabitants had time to avoid it by flight. This shock extended throughout all Syria, and as far as the Cyclade islands, and into Eubœa, where the fountains of Arethusa suddenly stopped, and did not reappear for many days after, and then by many new springs remote from the old ones; that this earthquake did not cease from shaking the island, sometimes in one part and sometimes in another, until the earth opened in the valley of Lepanta, and ejected a great quantity oflava and other inflamed matters. Pliny, in his first book, chap. 84, relates, that in the reign of Tiberius an earthquake happened which overthrew twelve towns in Asia: and in his second book he mentions a prodigy caused by an earthquake. St. Augustin records, that by a great earthquake there were towns overthrown in Lybia. In the time of Trajan, the town of Antioch, and a great part of the adjacent country were swallowed up by an earthquake; and in the time of Justinian, in 528, it was a second time destroyed by the same cause, with upwards of 40,000 of its inhabitants. Sixty years after, in the time of St. Gregory, it felt the effects of a third earthquake, when 60,000 of its inhabitants perished. In the time of Saladin, in 1182, most of the towns of Syria and Judea were destroyed by the same calamity. In Calabria and Apulia, there have been more earthquakes than in any other part of Europe. In the time of Pope Pius II. all the churches and palaces of Naples were overthrown, and above 30,000 of its inhabitants killed; the remainder were obliged to live in tents till houses were built. In 1629, there were earthquakes in Apulia, which destroyed 7000 persons, and in 1638, the townof St. Euphemia was swallowed up, and there remains only a stinking lake in its place. Ragusa and Smyrna, at the same time, were also almost destroyed. There was an earthquake in 1692, which extended into England, Holland, Flanders, Germany, and France; it was chiefly felt on the sea coasts and near large rivers; it shook at least 2600 square leagues; it lasted only two minutes, and the motion was more considerable on mountains than in vallies.[O]On the 10th of July, 1688, there was an earthquake at Smyrna, which began by a motion from west to east; the castle was at first overthrown, its four walls being divided and sunk six feet in the sea; this castle stood upon an isthmus, but is at present a real island, about 100 paces distant from the land. The walls from east to west are fallen down, those from north to south are yet standing; the city, which is ten miles from the castle, was destroyed shortly after; in many places the earth opened, and subterraneous noises were heard; five or six shocks were felt as night came on, the last continued only half a minute; the ships in the roads were shaken; the ground of the town was lowered about two feet; notabove a quarter of the town withstood the shock, and those principally the houses which stood on rocks; from 15 to 20,000 persons are computed to have been buried under the ruins.[P]In 1695, an earthquake was felt at Bologna, in Italy, and it was remarked as a particular circumstance, that the water was much troubled a day before.[Q][R]

[O]See Ray's Discourses, page 272.

[P]See the Hist. of the Acad. des Sciences, anno 1688.

[Q]Ibid. anno 1696.

[R]See the Voyages of Mandelso.

At Tercera there happened an earthquake on the 4th of May, 1614, which overthrew in the town of Angra eleven churches and nine chapels, besides private houses; and in the town of Praya it was so terrible, that scarcely an house was left standing. On the 16th of June 1628, there was an earthquake in the island of St. Michael, the effects of which was so great, that in a place where the sea was more than 150 fathoms deep an island was thrown up more than a league and a half long, and upwards of 60 fathoms high. Another happened in 1691, in the island of St. Michael, which began the 6th of July, and lasted till the 12th of the following month: Tercera and Fayal were agitated the next morning with so much violence, that they appeared to move; butthese frightful shocks returned there only four times, whereas at St. Michael they did not cease a moment for several days. The islanders quitted their houses, which they saw fall before their eyes, and remained all the time in the fields exposed to the injuries of the weather. The whole town of Villa Franca was overthrown to its very foundation, and most of the inhabitants buried under its ruins. In many parts the plains rose into hills, and in others, mountains were flattened into vallies. A spring of water issued from the earth, which flowed for four days, and then ceased all on a sudden. The air and sea, still more agitated, resounded with a noise which might have been taken for the roaring of a number of wild animals. Many persons died with the fright; the ships in the harbour suffered dangerous shocks, and those which were at anchor, or under sail at 20 leagues distant from the islands, received great damage. Earthquakes are frequent in the Azores, and about twenty years before a mountain in St. Michael was overturned by one of them.[S]

[S]Hist. of Voyages.

In Manilla, in the month of September, 1627, an earthquake levelled one of the twomountains called Carvallos, in the province of Cagayon; in 1645, one third of the town was destroyed by a like accident, and 300 persons perished. The succeeding year it experienced another; and the ancient Indians say they were more terrible formerly, which was the reason they build their houses only of wood; a custom still continued, and which the Spaniards follow.[T]

[T]See le Voyage de Gemelli Careri, page 120.

"The quantity of volcanos in this island confirms that assertion; because at certain times they vomit forth flames, shake the earth, and perform all the effects Pliny attributes to those of Vesuvius; that is, they change the beds of rivers, drive back the adjacent sea, fill with cinders the neighbouring plains, and throw out stones to great distances, with reports louder than those of cannons.

"In 1646, a mountain in the island of Machian split by an earthquake, with a dreadful noise; from this opening issued a number of flames, which destroyed several plantations with the inhabitants and all that was therein. In the year 1685, this prodigious crack was to be seen, and probably is still apparent; it is called the path of Machian, because it descends fromthe top to the bottom, like a road hollowed out, but which at a distance appears like a path."[U]

[U]See the Hist. of the Conquest of the Malaccas, vol. ii. p. 318.

The history of the French Academy mentions in the following terms, the earthquakes that took place in 1702 and 1703. "The earthquakes began in Italy in October 1702, and continued, till July 1703; the country which suffered the most by them, and where they began, is the town of Norcia, with its dependencies under the ecclesiastical government, and the province of Abruzzo, which are situated at the foot of the Apennines on the south side.

"They were often accompanied with terrible noises in the air, which also were heard without any dreadful effects, when the sky was serene. The earthquake which happened on the 2d of February 1703, was the most violent; it was accompanied, at least at Rome, with a great serenity of sky and calmness in the air. It lasted at Rome half a minute, and at Aquila the capital of Abruzzo three hours. It destroyed the whole town of Aquila, buried 5000 persons under the ruins, and made great havock in the environs. The vibration of the earth, accordingto the observations made by the lamps in the churches, was from south to north.

"It opened two places from whence issued a great quantity of stones, which entirely covered it and rendered it barren; after the stones they threw out water above the height of the trees; this lasted half an hour, and inundated the adjacent fields. The water was whitish, like soap suds, and had not any remarkable taste.

"A mountain near Sigillo, a city twenty-two miles distant from Aquila, had on its summit a very large plain surrounded with rocks like a wall. The earthquake of the 2d of February, changed this plain into a gulph of unequal breadth, whose greatest diameter is twenty-five fathoms and the least twenty; the depth of it has not been discovered, although a line 300 fathoms has been let down in it. At the time this opening was made, flames were seen to issue out, and afterwards a great smoke which lasted three days with some interruptions.

"At Genoa on the 1st and 2d of July 1703, there were two slight earthquakes, the last was felt only by the people on the pier: at the same time the sea in the port sunk six feet, and remained so a quarter of an hour.

"The sulphurous water in the road from Rome to Tivoli it diminished two feet and a half, both in the bason and in the canal. In many places of the plain, called Testine, the springs and rivulets, which formed morasses, are all dried up. The waters of the lake called l'Enfer is also lowered three feet. In place of the ancient springs new ones have appeared at above a league distance, so that possibly they are the same waters which have changed direction[V].

[V]Anno 1704, page 10.

"The same earthquake which, in 1538, formed Monti di Cinere, near Pozzoli, filled lake Lucrin with stones, earth and cinders, so that this lake is now a marshy ground.[W]

[W]See Ray's Discourses, page 12.

"There are earthquakes also felt at some distance at sea, says Mr. Shaw; in 1774, being on board the Gazella, an Algerine vessel, mounting 50 guns, three violent shocks were felt one after the other, as if every time a weight of 20 or 30 tons had been thrown on the ballast. This happened on a part of the Mediterranean that was more than 200 fathom deep. He relates also, that others had felt earthquakes much more considerable inother parts, and one among the rest at 40 leagues west from Lisbon."[X]

[X]See Shaw's Travels.

Schouten, speaking of an earthquake in the Malacca islands, says, that the mountains were shaken, and the vessels at anchor in 30 or 40 fathoms water were shook, as if they had struck against rocks or banks. "Experience, continues he, teaches us every day that the same happens in the open sea, where no bottom is to be met with, and that ships are tossed to and fro by earthquakes, even where the sea is tranquil."

Gentil, in his voyage round the world, speaks of earthquakes in the following terms: "I have, says he, made some remarks on these earthquakes; first, that half an hour before the earth is agitated every animal is struck with fear; horses snort, break their fastenings, and fly from the stable; dogs bark; birds, as if stupified, fly into houses for safety; and rats and mice quit their holes. Secondly, that vessels at anchor are so violently agitated, that every part of them seems as if going to pieces, the cannons force themselves loose, and the masts break in several places. These facts I should scarcely have given credit to if manyunanimous testimonies had not convinced me. I know the bottom of the sea is a continuation of the land, and that if one is agitated it will communicate to the other; but I could not conceive how every part of a vessel, floating in a fluid, should be affected in the same manner as if she was on the earth: it appeared to me that her motion should have been such as she experiences in a storm; besides, in the circumstance which I speak of, the surface of the sea was smooth, and there was no wind. Thirdly, that if the cavern of the earth, where this subterraneous fire is contained, has a direction from north to south, and if the buildings of an adjacent town are in a parallel line with it, all the houses are overthrown, whereas if this vein or cavern executes its effects by the breadth of the town, the devastation of the earthquake, is much less considerable."[Y]

[Y]See Gentil's Voyages, vol. I. page 172, &c.

In countries subject to earthquakes, when a new volcano breaks out earthquakes cease, and are only felt in the violent eruptions of the volcano, as is observed in the island of St. Christopher.[Z]

[Z]See Abridgement of Phil. Trans. vol. XI. page 302.

The enormous ravages produced by earthquakes have made some naturalists think that mountains and other inequalities of the surface of the globe were only the effects of subterraneous fires, and that all the irregularities must be attributed to the violent shocks which they have produced. This, for example, is the opinion of Mr. Ray; he imagines that all mountains have been formed by earthquakes, or the explosion of volcanos, as Monti di Cinere, the new island near Santorini, &c. but he has not considered that the slight elevations formed by the eruption of a volcano, or by the action of an earthquake, are not internally composed of horizontal strata, as all other mountains are; for by digging in the Monti di Cinere we meet with calcined stones, cinders, burnt earths, metallic dross, pumice-stones, &c. all mixed and confounded like a heap. Besides, if earthquakes and subterraneous fires had produced the great mountains of the earth, as the Cordeliers, Mount Taurus, the Alps, &c. the prodigious force necessary to raise these enormous masses might, at the same time, have destroyed a great part of the surface of the globe; and earthquakes, requisite to produce such effects, must have been of inconceivableviolence, since the most famous of which history makes mention have not had sufficient power to form a single mountain; for example, in the time of Valentian I. an earthquake happened, which was felt throughout all the known world;[AA]and yet not a mountain was thrown up by it.

[AA]As Ammianus Marcellinus relates, lib. 26. cap. 14.

It is nevertheless certain, that although we might be able to find an earthquake sufficiently powerful to throw up the highest mountains, it would not be sufficient to disorder the rest of the globe.

For supposing that the chain of the highest mountains which cross South America from the Magellanic lands to New Grenada, and the Gulph of Darien, had been produced by an earthquake, and then let us see by calculations the effect of this explosion. This chain of mountains is near 1700 leagues in length, and commonly 40 in breadth, comprehending the Sieras, which are not so lofty as the Andes. The surface therefore is 68,000 square leagues; I suppose the thickness of the matter displaced by the earthquake to be about one league, that is, the height of these mountainstaken from the top to the caverns, which according to this hypothesis must support them, is one league, then I say, the power of an explosion must have raised a quantity of earth equal to 68,000 cubical leagues to a league in height. Now the action being equal to the re-action, this explosion must have communicated the same motion to the rest of the globe. The whole globe consists of 12,310,523,801 cubical leagues, from which subtracting 68,000, there remains 12,310,455,801 cubical leagues, the quantity of which motion will be equal to that of 68,000 cubical leagues raised one league; from whence we perceive that the force which will have been great enough to elevate 68,000 cubical leagues would not have displaced the whole globe a single inch.

There would therefore be no absolute impossibility in the supposition that mountains have been raised by earthquakes, if their internal composition as well as their external form were not evident proofs of their being the work of the sea. Their internal parts are composed of regular and parallel strata, intermingled with shells, and their external consists of a figure whose angles are every where correspondent: is it credible thenthat this uniform composition and regular form should have been produced by irregular shocks and sudden explosions?

But as this opinion has prevailed among some philosophers, and as the nature and effects of earthquakes are not well understood, it may possibly be pertinent to hazard a few ideas with a view of explaining those intricate subjects.

The earth has undergone great changes on its surface; we find at considerable depths, holes, caverns, subterraneous rivulets, and void places, which sometimes communicate by chinks, &c. There are two kinds of caverns; the first are those produced by the action of subterraneous fires and volcanos; the action of this fire uplifts, burns, and throws out to a distance the matters that are above, and at the same time divides and deranges those which are on the sides, and thus produces caverns, grottos, and irregular holes, but which however is only effected in the environs of volcanos; and these kinds of caverns are more rare than those produced by water. We have already observed that the different strata which compose the terrestrial globe are all interrupted by perpendicular fissures: the waters which fall onthe surface descend through them; collect when stopped by clay, and form springs and rivulets; by their natural propensities they seek out cavities or small vacancies, and always incline to open a passage till they find a vent, carrying along with them sand, gravel, and other matters they can divide and dissolve; by degrees, in the internal part of the earth they form small trenches; and at last issue forth in the form of springs, either at the surface of the earth, or bottom of the sea; the matters which they carry along with them, leave caverns whose extent may be very considerable, the origin of which is quite different from those produced by volcanos or earthquakes.

There are two kinds of earthquakes, the one caused by the action of subterraneous fires, and the explosion of volcanos which are only felt at small distances at the time of eruptions: when the matters which form subterraneous fires ferment, heat, and inflame, the fire makes an effort on every side to get out, and if it does not find a natural vent, it raises the earth above and forces itself a passage by throwing it out; such is the beginning of a volcano whose effects and continuation are in proportion to the quantity of inflammable matters they contain. Ifthe quantity of matters is not considerable, an earthquake may ensue, without a volcano being formed. The air rarefied by the subterraneous fire may also escape through small vents, and in this case there will be only a shock without any eruption or volcano. But when the inflamed matter is in great quantities and confined by solid and compressed bodies, then a commotion and volcano is certain to ensue; but all these commotions form only the first kind of earthquakes, and can only shake a small space of ground. A violent eruption of Ætna will cause, for example, an earthquake throughout the whole island of Sicily; but it will never extend to the distance of three or four hundred leagues. When any new mouth bursts out in Vesuvius, there are earthquakes at Naples, and in the neighbourhood of the volcano; but these earthquakes never shake the Alps, nor extend into France, or other countries remote from Vesuvius. Therefore earthquakes produced by volcanos, are limited to a small space, are properly but the effects of the re-action of the fire; and they shake the earth, as the explosion of a powder magazine produces a shock perceptible at many leagues distance.

But there is another kind of earthquake very different in its effects, and perhaps equally so in its cause; such are felt at great distances, and shake a long course of ground, without any new volcano, or eruption in the old ones appearing. We have instances of earthquakes being felt at the same time in England, France, Germany, and even in Hungary; these earthquakes always extend more in length than breadth; they shake a zone of ground with greater or less violence in different places, and are almost always accompanied with a rumbling noise like that of a coach rolling over the stones with rapidity.

With respect to the causes of this kind of earthquake, it must be remembered that the explosion of all inflammable matters produces, like gunpowder, a great quantity of air; that this air by the heat is in a state of very great rarefaction, and that by its state of compression in the bowels of the earth, it must produce very violent effects. Let us suppose, that at a depth of one or two hundred fathoms, pyrites and other sulphurous matters are collected in great quantities, and that by the fermentation produced by the filtration of the water, or other causes, they inflame; what must happen? Firstthese matters are not placed in horizontal layers, as are the ancient strata, which have been formed by the sediment of the waters; on the contrary, they are formed in perpendicular fissures, in caverns, and in other places where the water can penetrate. Inflaming, they produce a quantity of air, the spring of which being compressed in a small space, like that of a cavern, will not only shake the ground directly above, but will seek out for passages by which it may escape. The roads which offer themselves are caverns and trenches, formed by subterraneous rivulets: into these the rarefied air will precipitate with violence, form in them a strong wind, the noise of which will be heard at the surface, accompanied with shocks of the earth, &c. this subterraneous wind, produced by the fire, will extend as far as the subterraneous cavities, and cause an agitation more or less violent as it is distant from the vent, and finds the passages of a larger or lesser extent: this motion being made longitudinal, the shock will be the same, and the earthquake be felt through a long zone of ground. This air will not produce any eruption, or volcano, because it will find sufficient space to expand, or rather because it will have found vents, and issue forth in formof wind and vapour. Even should it not be allowed that there exist internal passages, by which the air and vapours can pass, it may be conceived that in the place where the first explosion is made, the ground being lifted up to a considerable height, that the most adjoining to this spot must divide and split in an horizontal manner by the force of its motion; and by this means passages communicating one with the other may be opened to great distances; and this explanation agrees with every phenomena. It is not at the same moment or hour that an earthquake is felt in two distant places. Neither fire nor eruption attend those earthquakes which are heard at a distance, and the noise always marks the progressive motion of this subterraneous wind. This theory is confirmed by two other facts; it is well known that mines exhale unhealthy air and suffocating vapours, independent of the wind produced by the current of water: it is also known that there are holes, abysses and deep lakes in the earth, which produce winds, as the lake Boleslaw, in Bohemia, which we have already spoken of.

All this being considered, I do not see how it can be imagined that earthquakes produce mountains, since the cause itself of these earthquakesare mineral and sulphurous matters, which are generally found only in perpendicular clefts of mountains and other cavities of the earth; the greatest number of which have been produced by the operation of water; since this matter by inflaming produces only a momentary explosion and a violent wind which follows the subterraneous roads of the water: since the duration of the earthquakes at the surface of the earth is so short that their cause can only be explosion and not a durable fire: and in short, since these earthquakes, which extend to a considerable distance, very far from raising chains of mountains, do not produce the smallest hills throughout their whole extent.

Earthquakes are, in fact, most frequent in places near volcanos, as in Sicily and Naples, but it is known, by observations, that the most violent earthquakes happen in the time of the greatest eruptions of volcanos; that they are very limited, and cannot produce a chain of mountains.

It has been sometimes observed, that the matters thrown out of Mount Ætna, after laying for many years and afterwards moistened with the rain, have rekindled and thrown outflames with such violent explosions as even to produce a slight shock.

In a furious eruption of Ætna in 1669, which began the 11th of March, the summit of the mountains sunk considerably;[AB]which proves the fire of this volcano comes rather from the top than from the bottom of the mountain. Borelli is of the same opinion, and says, "That the fire of volcanos does not proceed from the centre, nor from the foot of the mountain, but that it issues from the summit, and flames kindle but at a small depth."[AC]

[AB]See Trans. Phil. Abridged, Vol. II. page 387.

[AC]Borelli, De incendiis Montis Etnae.

Mount Vesuvius in its eruptions, has thrown out great quantities of boiling water. Mr. Ray, who thinks that the volcanean fire proceeds from a great depth, says, that it is the water of the sea which communicates by subterraneous passages with the foot of the mountain; he gives, as a proof of it, the dryness of the summit of Vesuvius, and the agitation of the sea at the time of these eruptions, which sometimes retreats from the coasts, and leaves the Bay of Naples almost dry. But, if these facts are true, they do not prove, in a solid manner, that the volcanean fire proceeds from a great depth; for the waterwhich is thrown out is certainly rain water, which penetrates through the fissure, and collects in the cavities of the mountains. Rills and rivulets flow from those containing volcanos as well as other lofty mountains, and as they are hollow, and have been more shaken, it is not astonishing that the water collects in their caverns in their internal part, and that these waters are thrown out in the time of eruptions with other matters. With respect to the motion of the sea, it proceeds solely from the shock communicated to the waters by the explosion, which causes them to advance or retreat according to different circumstances.

The matters which volcanos generally throw out, come forth in the form of a torrent of melted minerals, which inundates all the environs of those mountains; these rivers of liquified matters extend to considerable distances, and in cooling form horizontal or inclined strata, which for position are like the strata formed by the sediment left by the waters: but it is very easy to distinguish the one from the other. First, because strata of lava are not throughout of an equal thickness: secondly, because they contain only matters which have evidently been calcined, vitrified, or melted;and thirdly, because they do not extend to any great distance. As there are a great number of volcanos at Peru, and as the foot of most of the mountains of the Cordeliers is covered with matters thrown out by eruptions, it is not astonishing that marine shells are not met with there, as they must have been calcined and destroyed by the fire; but I am persuaded, if we dig in argilaceous earth, which, according to M. Bourguet, is the common earth of the valley of Quito, shells would be found there, as they are in other places, at least where the ground is not covered, like that at the foot of the mountains, with matters thrown out of a volcano.

It has often been asked, why volcanos are all met with at the top of mountains? I think I have partly given a satisfactory answer to this question in the preceding article, but I have thought it necessary not to finish this without farther explaining what I have said on this subject.

The peaks or points of mountains were formerly covered with sand and earth, which the rain gradually washes along with it into the vallies, and has left only the rocks and stone, which forms the nucleus of the mountain.This being left bare will have been still worn by the injuries of the air, the frost will have loosened the large and small parts, which of course have rolled to the bottom. The rocks, at the base of the summit, being left bare, and no longer supported by the earth which surrounded them, will have given way a little, and by dividing one from the other formed small intervals. This separation of the lower rocks could not be made without communicating a greater motion to the upper. By this means the nucleus of the mountain would be divided into an infinity of perpendicular clefts, from the summit to the base of the lower rocks; the rain will have penetrated into all these clefts, and loosened, in the inside of the mountain, all the mineral parts and other matters that it could carry away or dissolve; they will have formed pyrites and other combustible matters, and when by length of time these matters were accumulated in great quantities, they fermented, and by inflaming produced explosions and other effects of volcanos; perhaps likewise, within the mountains, there were masses of these mineral matters already formed before the rain could penetrate therein; in that case, as soon as holes and clefts weremade, which gave passages to the water and air, these matters inflamed and formed a volcano. None of these motions could be made in plains, since all is at rest and nothing can be displaced. It is not therefore surprising that volcanos are found only in high mountains.

When coal-mines are opened, which are generally met with in argile earth, at a great depth, it sometimes happens that the mineral substances have taken fire: there are even mines of coal in Scotland, Flanders, &c. which have burnt for a number of years. The admission of the air suffices to produce this effect; but these fires produce only slight explosions, and do not form volcanos, because all being solid and full in these places, fire cannot be excited like that of volcanos, in which there are cavities and void places where the air penetrates, which must necessarily extend the conflagration and augment the action of the fire, so as to produce the terrible effects we have just described.

ARTICLE XVII.

OF NEW ISLANDS, CAVERNS, PERPENDICULAR CLEFTS, &C. &C.

New islands are formed either suddenly by the action of subterraneous fires, or gently by the deposit of the sediment of waters. Ancient historians and modern travellers relate facts on this subject which put it beyond all kind of doubt. Seneca assures us, that in his time the island Therasia appeared suddenly in the sea, to the astonishment of many mariners who beheld it. Pliny relates, that formerly thirteen islands in the Mediterranean sprung at the same instant out of the sea, and that Rhodes and Delos are the principal of them: it appears, from him, as well as Ammianus Marcellinus, Philo, and others, that these thirteen islands were not produced by an earthquake,nor by any subterraneous explosion, but that they were formerly hid under the water, which lowering left them uncovered. Delos had the name of Pelagia given to it, from having formerly belonged to the sea. Whether the origin of these thirteen islands is to be attributed to the action of subterraneous fires, or to some other cause which might occasion a sinking of the water in the Mediterranean, is uncertain. But Pliny relates, that the island Hiera, near Therasia, had been formed of ferruginous masses, and earth thrown from the bottom of the sea; and in chapter 89, he speaks of other islands formed in the like manner; but on this subject we have more clear and certain facts of later date.

On the 23d of May 1707, at the sun's rising, there was seen, at some little distance from the island of Therasia, or Santorini, something like a floating rock in the sea; some persons, to satisfy their curiosity, went towards it, and found it a shoal which had issued from the bottom of the sea; it increased under their feet, and they brought with them the pumice-stone and oysters, which the rock still had attached to its surface. There was a slight earthquake at Santorini two days before thisshoal appeared: it increased considerably till the 14th of June, it was then half a mile round, and from 20 to 30 feet high; the earth was white, and a little argilaceous; after that the sea became more and more troubled; vapours arose which infected the island Santorini; and on the 16th of July several rocks were seen to issue at one time from the bottom of the sea, and unite into one solid body. This was accompanied with a dismal noise, which continued upwards of two months. Flames issued from the new island, which kept increasing in circumference and height, and the violent explosions frequently threw large stones to more than seven miles distance. The island Santorini itself was deemed among the ancients as a modern production, and in 726, 1427, and 1573, it increased in size, and small islands were formed near it.[AD]The same volcano, which in the time of Seneca formed the island of Santorini, in that of Pliny produced Hiera or Volcanella, and in our time the shoal above-mentioned.

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