On the Constitution and Mode of Action of Volcanoes, in different Parts of the Earth.

By Alexander Von Humboldt.

Read before the Royal Academy of Sciences of Berlin, Jan. 24, 1823.

No. I.

When we consider the influence which scientific travels into distant regions, and a more extended geographical knowledge, have for some centuries past exerted upon the study of nature, we soon discover how this influence has varied according to the objects of inquiry, which have been, on the one hand, the forms of the organic world, and, on the other, the inanimate formation of the earth;--the knowledge of rocks, their relative ages, and origin.

Different forms of plants and animals enliven the earth in every zone, as well in the plains, where the heat of the atmosphere is determined by the geographical latitude and the different inflexions of the isothermal lines, as where it changes suddenly on the steep declivities of the mountains.

Organic nature gives a peculiar physiognomical character to every zone, which is not the case with the inorganic world where the solid crust of the earth is divested of its vegetable covering.

The same rocks approaching to and receding from each other in groups occur in both hemispheres, from the equator to the poles.

On a distant island, surrounded by strange plants, under a sky where the well-known stars do not shine, the sailor recognises, often with glad surprise, the clayslate which is the common rock of his native country.

This independence of the geognostical relations of places on the present constitution of their climate, does not diminish, but only gives a particular direction to the favourable effect upon the progress of geology and physical geognosy, which is produced by numerous observations made in foreign countries.

Every expedition enriches natural history with new plants, and new genera of animals; at one time they are organic forms ranging themselves with well-known types, and representing to us, in its original perfection, a regularly woven, though often apparently interrupted texture of animated creatures; at another, they are forms which appear to be insolated, as vestiges of genera which have been destroyed, or as surprising members of groups still to be discovered.

Such a variety is not presented by the examination of the solid crust of the earth; it rather reveals to us an agreement, which excites the admiration of the geognost, between the parts of which it is composed, in the superposition of masses of different natures, and in their periodical repetition.

In the chain of the Andes, as well as in the central mountains of Europe, one formation seems, as it were, to occasion the existence of another; masses of the same character assume similar forms: mountains are formed by basalt and dolerite; steep declivities by dolomite, porphyry, and quadersandstein; bell-shaped eminences and high-vaulted domes by vitreous trachyte rich in felspar.

In the most distant zones, larger crystals, as it were by internal evolution out of the more compact texture of the greater mass, aggregate into subordinate beds, and thus frequently announce the vicinity of a new and independent formation.

Thus is the whole inorganic world reflected, more or less clearly, in every mountain of considerable extent; but in order to ascertain completely the most important phenomena respecting the composition, the relative age, and the origin of the different species of rocks, observations from the most distant parts of the earth must be compared together.

Problems which had appeared enigmatical to the geognost in his mother country are solved near the equator.

If distant zones do not furnish new species of rocks, that is to say, unknown arrangements of simple substances, as has already been remarked, they yet teach us how to discover the great laws which are every where the same, and according to which, the different strata of the earth support each other, appear in the form of veins, or are elevated by elastic powers.

We need not be surprised, that notwithstanding the great assistance which our geological information derives from inquiries, having whole countries for their object, an extensive class of phenomena (with which I venture to entertain this assembly,) has been treated, during so long a period, in a confined manner; the points of comparison being more difficult, and, I might say, more troublesome to find.

Whatever we believed we knew, until the end of the last century, respecting the form of volcanoes, and the action of their subterraneous forces, had been derived from two mountains of the south of Italy, from AEtna and from Vesuvius.

The first being more accessible, and having, like all low volcanoes, more frequent eruptions, has served for a type, according to which a whole distant world,--the powerful volcanoes of Mexico, South America, and the Asiatic Islands, has been considered.

Such a method recalls to our remembrance the shepherd of Virgil, who expected his narrow cottage to contain the ideal of the eternal city, imperial Rome.

A careful examination of the whole Mediterranean, and principally of its easterly islands and shores, where mankind first awakened to mental culture, and to noble feelings, might certainly have dispelled such a narrow idea of nature.

Out of the deep bed of the sea, among the Sporades, rocks of trachyte have arisen, like the Azoric island, which has thrice reappeared during three centuries, the intervening periods being almost equal.

Between Epidaurus and Troezene, near Methone, the Peloponnesus has a Monte Nuovo, which has been described by Strabo, and seen by Dodwell, higher than the Monte Nuovo of the Campi Phlegraei, near Baia; perhaps higher than the new volcano of Xorullo in the plains of Mexico, which I have found among a thousand basaltic cones, raised out of the earth, and still smoking.

In the basin of the Mediterranean Sea also, the volcanic fire bursts forth, and not only from permanent craters, from insolated mountains which preserve a lasting communication with the interior of the earth, like Stromboli, Vesuvius, and AEtna;--on Ischia, near the Epomaeus, and also, as it would appear from the reports of the ancients, near Chalcis in the Lelantic plains, has lava flowed out of fissures which have suddenly opened.

Besides these phenomena, which have taken place in the period of history within the narrow limits of certain traditions, and which Ritter will collect and explain in his masterly Geography, the shores of the Mediterranean contain abundant remains of more ancient igneous effects.

The south of France shows, in Auvergne, a range of hills, in which bells of trachyte occur alternately with cones of eruption, from which currents of lava have descended.

The Lombardic plain, which forms the innermost bay of the Adriatic Sea, surrounds the trachyte of the Euganean Hills, where domes of granular trachyte, of obsidian, and of pearlstone, rise, which, passing into each other, break through the Jura limestone, but never occur in narrow streams which have flowed.

Similar evidences of former revolutions may be found in many parts of the Grecian continent, and in Asia Minor, countries which will afford the geognost copious subjects for examination, when the light once returns to the land whence it first beamed over the western worldwhen tormented mankind ceases to sink under the savage lethargy of the Ottoman.

I mention the geographical neighbourhood of so many phenomena, in order to prove, that the bed of the Mediterranean, with all its chains of islands, might have afforded to the attentive observer, every thing that has been discovered, in latter periods, under the most varied forms, in South America, on Teneriffe, or on the Aleutian islands, near the polar regions.

There were accumulated objects for observation, but tours into distant regions, and the comparison of large tracts of country within and beyond Europe, were necessary, in order to discover what was common to all these phenomena, and to learn, clearly, their dependence on each other.

On the Constitution and Mode of Action of Volcanoes, in different Parts of the Earth.

By Alexander Von Humboldt.

Read before the Royal Academy of Sciences of Berlin, Jan. 24. 1823.

No. II.

By the usage of language, which often gives stability and respect to the first erroneous views of things, but often, as it were, by instinct, distinguishes the truth, we apply the term volcanic to all eruptions of subterranean and melted matter; to columns of smoke and steam, which rise sporadically out of rocks, as at Colares after the great earthquake at Lisbon; to Salsae, or conical hills of clay which emit mud, asphaltum, and hydrogen, as those near Girgenti, in Sicily, and near Turbaco, in South America; to hot Geyser springs which rise by the pressure of elastic vapours; and, in general, to all violent powers of nature which have their seat deep in the interior of our planets.

In the Spanish main of America, and in the Philippine islands, the inhabitants make a distinction between igneous and aqueous volcanoes, vulcunes de agua y de fuego: they apply the first name to mountains, which, during violent earthquakes, from time to time, eject subterraneous water, and with a dull noise.

Without denying the connexion between the different phenomena just mentioned, it seems advisable to give a distinct language to the physical as well as to the oryctognostic branch of geognosy; and not to apply the term volcano in one instance to a mountain that terminates in a permanent crater; and in another, to every subterranean cause of volcanic phenomena.

In the present state of the earth, the most common form of volcanic eminences is that of isolated cones; such are Vesuvius, AEtna, the Peak of Teneriffe, Tunguragua, and Cotopaxi. I have seen them of every magnitude, from the lowest hills to mountains rising to the height of 17,700 feet above the level of the sea.

Besides these conical mountains, there are other craters, permanently communicating with the interior of the earth, situated upon lengthened craggy ranges of mountains, not always in the middle of their wall-like summits, but towards the end, and near their declivities.

Such is Pichincha which rises between the Pacific Ocean and the town of Quito, and which has become celebrated by Bouguer's earliest formula for the barometer; such also are the volcanoes that rise in the plain de los Pastos, at the elevation of 10,000 feet.

All these differently formed summits consist of trachyte, or trapporphyry, a granular rock, full of cracks and fissures, and composed of glassy felspar and hornblende, but often containing in addition, augite, mica, laminar felspar, and quartz.

Where the evidence of the first eruption, and where the first scaffolding, I might say, has been entirely preserved, the isolated conical hills are surrounded by a high wall of rocks forming a circus, consisting of superposed strata; such walls, or annular surrounding masses, are called craters of elevation; of these very important phenomena, Leopold von Buch, the first geognost of our times, from whose works I have taken several views contained in this paper, read a remarkable account, five years ago.

The volcanoes which communicate with the atmosphere by means of craters, and the conical hills of basalt and bellshaped trachytic hills without craters, the latter either low like Sarcouy, or high like Chimborazo, form different groups.

A geographical comparison shows, in one place, small Archipelagi, or, as it were, classed systems of mountains, either with craters and currents of lava, as in the Canaries and Azores, or devoid of craters and real currents of lava in the Euganeans, and the Siebengebirge near Bonn; or it shows, in other places, single and double chains of volcanoes, connected with each other, and forming tracts of many hundred miles in length, which are either parallel to the direction of the mountains, as in Guatimala, Peru, and Java, or in directions perpendicular to their axis, as in the land of the Aztekes, where none but volcanic trachyte-mountains attain the limits of eternal snow, and those, probably, have been thrust out of a fissure nearly 500 miles in length, which divides the whole continent, from the Pacific Ocean to the Atlantic.

This aggregation of volcanoes either in single round groups, or in double ranges, affords the most determinate proof that volcanic effects do not depend upon slight causes existing near the surface of the earth, but that they are great and deeply founded phenomena.

The whole eastern part of the American continent, which is poor in metals, is at present without craters, without trachyte, probably even without basalt.

All the volcanoes are situated in the part opposite to Asia, in the meridian line of the Andes chain, 1800 geographical miles long; the whole of the elevated district of Quito is nothing but a single volcanic hearth, the summits of which are Pichincha, Cotopaxi, and Tunguragua.

The volcanic fire now bursts from one, and then from another of these apertures, which we are accustomed to consider as separate volcanoes.

The progressive motion of the fire here, in the space of three centuries, turned from north to south.

The earthquakes with which this part of the world is so terribly visited, furnish remarkable evidences of the existence of subterraneous communication, not only between countries without volcanoes, as was known long ago, but even between craters which are far distant from each other.

Thus the volcano of Pasto, situated to the east of the river Guaytara, uninterruptedly vomited a high column of smoke, during the three months of the year 1797; and this column disappeared at the very moment, when, at the distance of nearly 300 miles, the great earthquake of Riobamba and the mud eruption of the Moya, killed from 30,000 to 40,000 Indians.

The sudden appearance of the Azoric island Sabrina, on the 30th of January, 1811, was the forerunner of those dreadful shocks, which, further to the west, shook, almost uninterruptedly, from the month of May, 1811, to that of June, 1813, first the Antilles, afterwards the plains of the Ohio and the Mississippi, and at last the opposite coast of Venezuela.

Thirty days after the complete destruction of the town of Caraccas, the eruption of the volcano of St. Vincent in the neighbouring Antilles took place; at the same moment when this explosion happened, on the 30th of April, 1811, a subterranean noise was heard throughout a country of 2200 geographical square miles, or 47,900 English square miles, in extent.

The inhabitants near the Apure, where it is joined by the Rio Nula, as well as those of the most distant part of the coast, compared this noise to that of artillery.

From where the Rio Nula falls into the Apure, through which river I came into the Orinoco, to the volcano of St. Vincent, the distance, in a direct line, is 731 English miles.

The noise just alluded to, which certainly was not communicated through the air, must, therefore, have had a deep internal cause.

Its intensity on the coast of the Antillic sea was scarcely greater than in the interior of the country.

It would be useless to augment the number of examples, but for the purpose of recalling to memory a phenomenon which has become historically interesting to Europe, I will mention the earthquake at Lisbon.

At the same time with this, on the 1st of November, 1755, not only were the Swiss lakes, and the sea on the Swedish shores violently agitated, but even in the easternly Antilles, around Martinque, Antigua, and Barbadoes, where the tide never exceeds 28 inches, it suddenly rose to 20 feet.

All these phenomena prove, that the subterranean powers act either dynamically, by producing tension and vibration, as in earthquakes; or chemically, by producing or altering substances, as in volcanoes.

They prove, likewise, that these powers do not act from superficial causes, from the exterior crust of the earth; but from deeply-seated causes, from the interior of our planet; extending their simultaneous effects to the most distant parts of the earth, through fissures and empty veins.

On the Constitution and Mode of Action of Volcanoes, in different Parts of the Earth.

By Alexander Von Humboldt.

Read before the Royal Academy of Sciences of Berlin. Jan. 24. 1823.

No. III.

The more different the structure of volcanoes; that is to say, of those raised masses which surround the canal through which the melted substances proceed from the interior of the earth to its surface, the more important is it to become thoroughly acquainted with that structure by exact measurement.

The interest attached to this measurement, which has been a particular object of my examination in another part of the world, is heightened by the consideration, that that which is to be measured is a variable magnitude.

The physiognomy of nature consists in the change of phenomena tending to connect the present with the past.

In order to ascertain a periodical return, or the laws of progressive natural changes in general, certain fixed points are necessary; and observations carefully made at stated periods, may serve for numerical comparison.

Had the mean temperature of the atmosphere in different latitudes been observed for a few thousand years, and the mean height of the barometer at the level of the sea, we might now know in what proportion the heat of different climates has increased, or diminished, and whether the height of the atmosphere has undergone any changes.

Similar points for comparison are required, for the variation and the declination of the magnetic needle, and for the intensity of the electromagnetic power, upon which two excellent philosophers of this Academy have thrown so much light. If it be a praiseworthy undertaking of learned societies to inquire assiduously into the changes of temperature undergone by the globe, into those which take place in the pressure of the atmosphere, and in the magnetic variation,--it is the duty of a travelling geognost, in ascertaining the inequality of the earth's surface, to consider, principally, the variable height of the volcanoes.

What I formerly attempted on the mountains of Mexico, on the Toluca Nauhiampatepetl and Xorullo, and in the Andes of Quito, on the Pichincha, I have found opportunity, since my return to Europe, to repeat at different periods on Vesuvius.

Saussure measured this mountain in 1773, at the time when both sides of the crater, the south-eastern and north-western, appeared to be of equal altitude; he found their height to be 609 toises (3894 feet) above the level of the sea.

The eruption of 1794 occasioned a fall on the south side, which even the unaccustomed eye discovers at a great distance.

In 1805, I measured Vesuvius three times, in conjunction with M. von Buch, and M. Gay-Lussac; we found the elevation of the northern edge, opposite to Monte Somma, la Rocca del Palo, to be exactly the same as Saussure had before determined it; the southern edge we found 71 toises (454 feet) lower than it was in 1773; the total height of the volcano on the side opposite Torre del Greco (towards which side the fire seems to have acted the most powerfully, during the last 30 years,) had diminished one-ninth part.

The cone of ashes on Vesuvius bears the proportion of one-third to the height of the whole mountain, that on Pichincha is as 1 to 10, and that on the Peak of Teneriffe as 1 to 22; Vesuvius has, therefore, the largest cone of ashes in proportion, because, probably, as a low volcano, it has acted principally through its summit.

A few months ago, I succeeded not only in repeating my former measurements on Vesuvius, but also in ascertaining the elevation of all the edges of the crater.

This work, perhaps, deserves some consideration, for the periods at which it was executed include those of the great eruptions from 1805 to 1822, and it is, perhaps, the only admeasurement yet published of any volcano which may be compared in all its parts.

It proves that the edges of the craters, not only where they evidently consist of trachyte, as in the volcanoes of the Andes, but likewise every where else, are much more constant phenomena than has hitherto been believed.

Simple angles of elevation ascertained from the same points are more proper for these examinations than barometrical and trigonometrical measurement.

According to my last determination, the north-western edge of the crater of Vesuvius has not changed its form in the least since Saussure's time, a period of 49 years.

The south-eastern edge towards Bosche tre Case, which became about 450 feet lower in 1794, has sunk very little since that time.

If in the description of great eruptions, in the public papers, the completely changed form of Vesuvius has frequently been mentioned, if this opinion often seems to be corroborated by the picturesque views of the mountain made at Naples, the cause of this mistake may be found in the circumstance, that the outlines of the edges of the crater have been confounded with those of the cone of eruption which is accidentally formed in the middle of the crater, upon a bottom that has been raised by vapours.

Such a cone of eruption, consisting of rapilli and slags loosely heaped together, has become visible over the south-eastern edge of the crater, since 1816 and 1818.

The eruption of February, 1822, had so much increased it that it had become from 70 to 80 feet higher than the north-eastern edge of the crater, Rocca del Palo.

This remarkable cone, which, at Naples, they were accustomed to consider as the true summit of Vesuvius, fell in with a tremendous noise, during the eruption of the 22d of October, so that the bottom of the crater, which had been uninterruptedly accessible from the year 1811, now lies 850 English feet beneath the northern edge, and about 213 feet deeper than the southern edge of the volcano.

The variable form and relative situation of the crater of eruption, the opening of which must not be taken for the real crater of the volcano, as frequently has been done, gives, at different times, a peculiar physiognomy to Vesuvius; and the historiographer of that volcano, from the mere outline of the summit, and the relative height of the northern or southern side of the mountain, as it is drawn in Hackert's Views in the palace Portici, would guess the year in which the artist made the sketch of his picture.

In the night between the 23d and 24th of October, one day after the fall of the cone of slags 400 feet in height, when small but numerous currents of lava had already flowed, the fiery eruption of ashes and rapilli began.

It continued uninterruptedly for twelve days, but was most violent during the first four.

During this time the detonations in the interior of the volcano were so violent, that the mere concussion of the air (no earthquake had been observed) caused the roofs to burst in the palace of Portici.

In the surrounding villages of Resina, Torre del Greco, Torre del Annonciata, and Bosche tre Case, an interesting phenomenon was observed; the atmosphere was so thickly filled with ashes, that the most intense darkness overspread the whole country for several hours in the middle of the day.

The people walked in the streets with lanterns, as is often done at Quito when Pichincha is in eruption.

The flight of the inhabitants was never more general; currents of lava were less feared than a fall of ashes, a phenomenon which was unknown there with such violence, and in consequence of the relations respecting the destruction of Herculaneum, Pompeii, and Stabiae, filled the minds of the people with frightful images.

The hot steam which rose from the crater during the eruption and passed into the atmosphere, formed on cooling a thick mass of clouds, around the column of ashes and fire, 9000 feet in height.

This sudden condensation of steam, and, as Gay-Lussac has shown, the very formation of the clouds, increases the electric tension.

Lightnings burst forth in all directions from the column of ashes, and the rolling thunder might clearly be distinguished from the interior noise of the volcano.

At no former eruption had the play of electric charges been so surprising.

On the morning of the 26th of October, a singular account was circulated, that a current of boiling water had issued from the crater, and rushed down from the cone of ashes.

Monticelli, the zealous and learned observer of the volcano, soon discerned that the rumour had been occasioned by an optical deception.

The supposed current of water was nothing but a dry mass of ashes, which flowed down, like quicksand, from a fissure in the superior edge of the crater.

A drought, which had completely desolated the fields, preceded the eruption, but the volcanic thunderstorm occasioned, towards its termination, a very heavy and continued rain.

Such a phenomenon characterizes the conclusion of an eruption in every zone. On account of the cone of ashes being generally covered with clouds during this time, and likewise because the torrents of rain are heaviest in its neighbourhood, currents of mud flow down on all sides.

The affrighted peasant considers it to be water which has risen from the interior of the crater, and the deceived geognost conceives that he recognises in it either sea-water, or mud-like volcanic productions, which are called eruptions boueses, or, as the old French systematic writers termed them, products of a fiery-aqueous liquefaction.

On the Constitution and Mode of Action of Volcanoes, in different Parts of the Earth.

By Alexander Von Humboldt.

Read before the Royal Academy of Sciences of Berlin. Jan. 24. 1823.

No. IV.

When the summits of volcanoes (as is generally the case in the chain of the Andes,) extend into the region of eternal snow, or even to double the height of AEtna, the melted snow renders the inundations amazingly frequent and destructive.

They are phenomena meteorologically connected with volcanic eruptions, and are multifariously modified by the altitude of the mountains, the extent of their summits covered with eternal snow, and the calefaction of the sides of the cone of ashes; but they should never be considered as real volcanic phenomena.

Subterranean lakes, in connexion with alpine rivers, are formed both on the slopes and at the foot of the mountains.

When the earthquakes which precede every eruption in the chain of the Andes, shake with mighty force the entire mass of the volcano, the subterranean vaults are opened, and emit, at the same time, water, fishes, and tufa-mud.

This is the singular phenomenon that furnishes the pimelodes cyclopum, which the inhabitants of the high lands of Quito call prenadilla, and which was described by me soon after my return.

When the summit of the mountain Carguairazo, to the north of Chimborazo, and 18,000 feet high, fell, in the night between the 19 and 20th of June, 1698, the surrounding fields, to the extent of about 43 English square miles, were covered with mud and fishes.

The fever which raged in the town of Ibarra, seven years before, had been ascribed to a simular eruption of fishes from the volcano Imbaburu. I recur to these facts, because they throw some light on the difference between the eruption of ashes, and that of mud-like masses of tufa and trass, which contain wood, coal, and shells.

The quantity of ashes ejected by Vesuvius in the late eruptions like all other things which are connected with great and appalling phenomena, has been enormously exaggerated in the public papers; and two Neapolitan chemists, Vincenzo Pepe, and Giuseppe di Nobili, have affirmed, that they contain gold and silver, notwithstanding the contradiction of Monticelli and Covelli.

According to my examination, the stratum of ashes which had fallen in twelve days, towards Bosche tre Case, on the slope of the cone, where rapilli were mixed with it, was only three feet in thickness, and in the plain, it did not exceed from 15 to 18 inches.

Measurements of this kind must not be made in places where the ashes have been drifted by wind, like snow, or sand, nor in those where they have been accumulated by water.

The times are past in which we sought only for the marvellous in volcanic phenomena, and, like Ctesias, made the ashes of AEtna fly to the Indian peninsula.

Some of the Mexican gold and silver mines are certainly in trachytic porphyry, but in the ashes of Vesuvius which I collected, and which, at my desire, have been analyzed by Henry Rose, of Berlin, an excellent chemist, no traces of either metal could be discovered.

However great may be the discrepancy between the results that I have here given, but which agree with Monticelli's more exact observations, and those which have been circulated during several months past, yet the eruption of ashes from Vesuvius, from the 24th to the 28th of October, still remains the most remarkable of which we have any certain account since the death of the elder Pliny.

Its quantity perhaps was three times as great as that of all the ashes, collectively, which have been observed to fall, during the time in which volcanic phenomena have been attentively considered.

A stratum of from 15 to 18 inches in thickness, seems at first view unimportant, if compared to the mass with which we find Pompeii to be covered; but without speaking of the torrents and inundations which certainly may have increased this mass for centuries, without renewing the violent dispute concerning the cause of the destruction of the Campanian towns, which have been carried on with so much skepticism on the other side of the Alps, it may be affirmed that the eruptions of one and the same volcano at distant periods can by no means be compared with respect to their intensity.

All conclusions founded on analogy are insufficient, when the question is about quantitative proportions,--the quantity of ashes and lava, the height of the column of smoke, or the violence of the detonation.

From the geographical description of Strabo, and from an opinion of Vitruvius concerning the volcanic origin of pumice, we see that until the year in which Vespasian died, that is to say, until the eruption which overwhelmed Pompeii, Vesuvius was more like an extinguished volcane than a solfataro.

When after long rest the subterranean powers suddenly open new passages, and again break through beds of primitive rocks and of trachyte, effects must necessarily take place, for which all the phenomena subsequently observed do not afford any standard of comparison.

It may be clearly seen from the wellknown letter in which the younger Pliny announces the death of his uncle to Tacitus, that the recommencement of the eruptions, I might say, the awakening of the dormant volcano, began with an eruption of ashes.

The same circumstance was observed at Xorullo, in Sept. 1759, when the new volcano, breaking through beds of syenite and trachyte, suddenly arose in the plain.

The peasants fled, because they found in their huts, ashes that had been ejected from the fissures of the earth, which was burst in every place.

Every partial eruption, in the periodical general eruptions of volcanoes, terminates with a shower of ashes.

There is a passage in Pliny's letter, which shows, that the dry ashes which had fallen from the air had already attained a height of from four to five feet, in the commencement of the eruption, and without the effect of accumulation by water.

"The court which led to his [uncle's] apartment," he says, "being now almost filled with ashes and pumice, would have been impossible for him, if he had continued there any longer, to have made his way out."

In the narrow space of a court, the wind could not have had any great effect in accumulating the ashes.

I have ventured to interrupt my comparative view of volcanoes by observations solely on Vesuvius, partly on account of the great interest which the last eruption has excited, and partly because every great fall of ashes almost involuntarily reminds us of the classic ground of Pompeii and Herculaneum.

We have hitherto considered the form and the effects of those volcanoes which are in permanent communication with the interior of the earth, by means of a crater Their summits are raised masses of trachyte and lava, intersected by numerous veins; the duration of their effects causes us to believe that they have a very stable and undisturbed structure.

They posess, I may say, a more individual character, which remains the same during long periods.

Neighbouring mountains often furnish completely different products, leucite-lava, and felsparlava; obsidian, with pumice, and basaltic masses containing olivine.

They belong to the newer phenomena of the earth, pass generally through all the strata of secondary rocks, and their eruptions and currents of lava are of later origin than our valleys.

Their life, if I may use that expression, depends upon the manner and duration of their connexion with the interior of the earth.

They often rest for centuries, suddenly take fire again, and terminate as solfataras, which emit steam, gases, and acids.

Sometimes, as on the Peak of Teneriffe, their summit has already become such a depository of reproduced sulphur, while mighty currents of lava flow from the sides of the mountain, like the basalt below, and above, where the pressure is less, like obsidian with pumice.

On the Constitution and Mode of Action of Volcanoes, in different Parts of the Earth.

By Alexander Von Humboldt.

Read before the Royal Academy of Sciences of Berlin. Jan. 24. 1823.

No. V.

Independently of these with permanent craters, volcanic phenomena of another kind exist, which have been observed less frequently, but are principally interesting in geognosy, and remind us of the primitive world; that is to say, of the earliest revolutions of our earth.

Mountains of trachyte suddenly open, eject lava and ashes, and close again, perhaps, for ever; thus was it with the mighty Antisana; and thus with the Epomaeus, in Ischia, in 1302.

Such an eruption sometimes takes place even in the plain as in the high lands of Quito; in Iceland, far from Hecla; and in Euboea, in the Lelantic fields.

Many of the islands which have been raised up are owing to these temporary phenomena.

In these cases the communication with the interior of the earth is not permanent, and the effect ceases as soon as the fissure, which is the communicating channel, is closed again.

The veins of basalt, dolerite, and porphyry, which, in different parts of the world, pass through every formation; and those of syenite, augite-porphyry, and amygdaloid, which are characteristic of the newest strata of the transition formation, and of the oldest rocks of the secondary strata, have probably been formed in a similar manner.

In the first age of our planet, the yet liquid substances penetrated through the crust of the earth, which was every where intersected by fissures, and assumed the form of granular rocks, either in veins, or spreading over and expanding themselves in strata.

The rocks strictly volcanic which the primitive ages have afforded us, have not flowed in currents like the lava of our insulated conical hills; the same mixture of augite, titaniferous iron, glassy felspar, and hornblende, may have existed at different periods, but at one time it may have approached nearer to basalt, and at others to trachyte; the chemical substances may have combined in a crystalline form, in distinct proportions, as we are taught by M. Mitscherlich's new and important labours, and by the analogy of artificial products of fire: we find that substances similarly formed have arrived at the surface of the earth in very different ways; they have either been merely raised, or protruded by temporary fissures through the older strata; that is to say, through the already oxidized surface of the earth; or they have flowed, as currents of lava, from conical hills with a permanent crater.

By confounding such different phenomena together, the geognosy of volcanoes is carried back to that darkness from which a great number of comparative observations are beginning to extricate it.

The question has often been asked, What is it that burns in volcanoes?

What was it that excited the heat by which earths and metals were melted?

Modern chemistry answers, that the substances which melt are the metals of the earths and alkalies.

The solid crust of the earth, already oxidized, separated the surrounding air with its oxygen, from the combustible unoxidized substances of the interior of our planet.

The observations which have been made in mines and caves in every zone, and which, in conjunction with M. Arago, I have collected in a particular paper, demonstrate that the heat of the mass of the earth is yet much greater than the mean temperature of the atmosphere at the same place.

Such a remarkable and almost generally proved fact, is closely connected with those which are proved by volcanic phenomena.

Laplace has even gone so far as to endeavour to calculate the depth at which the body of the earth may be considered to be a melted mass.

Whatever doubts may be entertained, notwithstanding the veneration due to so great a name, with respect to the numerical certainty of such a calculation, thus much remains probable; that all volcanic phenomena originate in a very simple cause, in a permanent or in a variable communication between the interior and the exterior of our planet.

The pressure of elastic vapour forces the melted substances upwards through deep fissures while they are undergoing oxidation; volcanoes, if I may so speak, are intermitting springs of the earth; the liquid mixtures of metals, alkalies, and earths, which on cooling become currents of lava, flow quietly when they are raised, and find a vent.

The ancients imagined, according to Plato's Phaedon, that all volcanic currents of fire flowed in a similar way, from the Periphlegeton.

It may be permitted me, perhaps, to add to these considerations one which is still more hazardous.

In this interior heat of the earth, indicated by experiments with the thermometer, and by observations on volcanoes, the cause, perhaps, may be found, of one of the most wonderful phenomena which the examination of fossils presents to us.

Tropical forms of animals, arboriform ferns, palms, and bamboo-like plants, lie interred in the cold north.

The primitive world every where shows a distribution of organic forms at variance with the then existing nature of the climate.

In order to solve this important problem, several hypotheses have been invented; as the neighbourhood of a comet, the altered inclination of the ecliptic, the increased intensity of the solar light.

Neither of these has been sufficient to satisfy at once the astronomer, the natural philosopher, and the geognost.

For my part, I leave the axis of the earth unaltered, as well as the light of the solar disc, by the spots on which, a celebrated astronomer has explained both the fertility and the unfruitfulness of the fields; but I believe, that in every planet, independently of its relation to a central body, and of its astronomical situation, various causes exist of the production of heat; oxidation, precipitation, and a change in the capacity of bodies; by increase of electromagnetic charge, by the opening of a communication between the interior and the exterior part of the earth.

Where the deeply cleft crust of the earth in the primitive world radiated heat from its fissures, whole countries, perhaps, could produce for centuries, palms and aborescent ferns, and sustain all the animals of the torrid zone.

According to this view, to which I have already alluded in a work just published, "Essai Geognostique sur le Gissement des Roches dans les deux Hemispheres, the temperature of volcanoes would be that of the interior of the earth itself, and the same cause which now occasions such dreadful destruction, would once have occasioned, on the newly oxidated crust of the earth, upon the deeply cleft strata of rocks, the most luxuriant growth of plants in every zone.

Even if any one should be inclined to suppose, in order to explain the marvellous distribution of tropical forms in their ancient graves, that shaggy animals of the elephant tribe now imbedded in icebergs, were once peculiar to a northern climate, and that similar forms belonging to the same primary types, like lions and lynxes, could live in very different climates, such an explanation could not, however, be extended to the products of vegetation.

For reasons which the physiology of plants explains, palms, and arboriform monocoty ledones cannot sustain the northern cold, and in the geological problem we here speak of, it seems difficult to me to separate plants and animals.

The same explanation must be applied to both.

Towards the end of this paper, I have combined uncertain hypothetical suppositions with facts collected from the most different parts of the world.

The philosophical knowledge of nature rises above a mere description of nature.

It does not consist in a sterile aggregation of isolated observations.

It may sometimes be allowed, therefore, to the curious and ever-active mind of man, to look back upon the past, to imagine what cannot be clearly known, and to amuse himself with the ancient, and, under many forms, returning mysteries of geogony.