[footnote] *See Berzelius and Wohler, in Poggend., "Annalen", bd. i., s.
221, and bd. xi., s. 146; Gay-Lussac, in the "Annals de Chimie", t. x., xii., p. 422; and Bischof"s "Reasons against the Chemical Theory of Volcanoes", in the English edition of his "Warmelehre", p. 297-309.
If hydrogen were evolved from erupted lava, how great must be the quant.i.ty of the gas disengaged, when, the seat of the volcanic activity being very low, as in the case of the remarkable eruption at the foot of the Skaptar Jokul in Iceland (from the 11th of June to the 3d of August, 1783, described by Mackenzie and Soemund Magnussen), a s.p.a.ce of many square miles was covered by streams of lava, acc.u.mulated to the thickness of several hundred feet! Similar difficulties are opposed to the a.s.sumption of the penetration of the atmospheric air into the crater, or, as it is figuratively expressed, the "inhalation of the earth", when we have regard to the small quant.i.ty of nitrogen emitted. So general, deep-seated, and far-propagated an activity as that of volcanoes, can not a.s.suredly have its source in chemical affinity, or in the mere contact of individual or merely locally distributed substances. Modern geognosy* rather seeks the cause of this activity in the increased temperature with the increase of depth at all degrees of lat.i.tude, in that powerful internal heat which our planet owes to its first solidification, its formation in the regions of s.p.a.ce, and to the spherical contraction of p 237 matter revolving elliptically in a gaseous condition.
[footnote] *[On the various theories that have been advanced in explanation of volcanic action, see Daubeney "On Volcanoes", a work to which we have made continual reference during the preceding pages, as it const.i.tutes the most recent and perfect compendium of all the important facts relating to this subject, and is peculiarly adapted to serve as a source of reference to the "Cosmos", since the learned author in many instances enters into a full exposition of the views advanced by Baron Humboldt. The appendix contains several valuable notes with reference to the most recent works that have appeared on the Continent, on subjects relating to volcanoes; among others, an interesting notice of Professor Bischof"s views "on the origin of the carbonic acid discharged from volcanoes," as enounced in his recently published work, "Lehrbuch der Chemischen und Physikalischen Geologie".] -- Tr.
We have thus mere conjecture and supposition side by side with certain knowledge. A philosophical study of nature strives ever to elevate itself above the narrow requirements of mere natural description, and does not consist, as we have already remarked, in the mere acc.u.mulation of isolated facts. The inquiring and active spirit of man must be suffered to pa.s.s from the present to the past, to conjecture all that can not yet be known with certainty, and still to dwell with pleasure on the ancient myths of geognosy which are presented to us under so many various forms. If we consider volcanoes as irregular intermittent springs, emitting a fluid mixture of oxydized metals, alkalies, and earths, flowing gently and calmy wherever then find a pa.s.sage, or being upheaved by the powerful expansive force of vapors, we are involuntarily led to remember the geognostic visions of Plato, according to which hot springs, as well as all volcanic igneous streams, were eruptions that might be traced back to one generally distributed subterranean cause, "Pyriphlegethon".*
[footnote] *According to Plato"s geognostic views, as developed in the "Phaedo", Pyriphlegethon plays much the same part in relation to the activity of volcanoes that we now ascribe to the augmentation of heat as we descend from the earth"s surface, and to the fused condition of its internal strata. ("Phaedo", ed. Ast, p. 603 and 607; Annot., p. 308 and 817.) "Within the earth, and all around it, are larger and smaller caverns. Water flows there in abundance; also much fire and large streams of fire, and streams of moist mud (some purer and others more filthy), like those in Sicily, consisting of mud and fire, preceding the great eruption. These streams fill all places that fall in the way of their course.
Pyriphlegethon flows forth into an extensive district burning with a fierce fire, where it forms a lake larger than our sea, boiling with water and mud.
From thence it moves in circles round the earth, turbid and muddy." This stream of molten earth and mud is so much the general cause of volcanic phenomena, that Plato expressly adds, "thus is Pyriphlegethon const.i.tuted, from which also the streams of fire ([Greek words]), wherever they reach the earth ([Greek words]), inflate such parts (detached fragments)." Volcanic scoriae and lava streams are therefore portions of Pyriphlegethon itself, portions of the subterranean molten and ever-undulating ma.s.s. That {Greek words] are lava streams, and not, as Schneider, Pa.s.sow, and Schleiermacher will have it, "fire-vomiting mountains," is clear enough from many pa.s.sages, some of which have been collected by Ukert ("Geogr. der Griechen und Romer", th. ii., s. 200): [Greek word] is the volcanic phenomenon in reference to its most striking characteristic, the lava stream. Hence the expression, the [Greek word] of Aetna. Aristot. "Mirab. Ausc.", t. ii., p. 833; sect. 38, Bekker; Thucyd., iii., 116; Theophrast., "De Lap"., 22, p. 427, Schneider; Diod., v., 6, and xiv., 59, where are the remarkable words, "Many places near the sea, in the neighborhood of Aetna, were leveled to the ground, [Greek words];" Strabo, vi., p. 269; xiii., p. 268, and where there is a notice of the celebrated burning mud of the Lelantine plains, in Euboea, i., p. 58, Casaub.; and Appian, "De Bello Civili", v., 114. The blame which Aristotle throws on the geognostical fantasies of the Phaedo ("Meteor.", ii., 2, 19) is especially applied to the sources of the rivers flowing over the earth"s surface. The distinct statement of Plato, that "in Sicily eruptions of wet mud precede the glowing (lava) stream," is very remarkable.
Observations on Aetna could not have led to such a statement, unless pumice and ashes, formed into a mud-like ma.s.s by admixture with melted snow and water, during the volcano-electric storm in the crater of eruption, were mistaken for ejected mud. It is more probable that Plato"s streams of moist mud ([Greek words]) originated in a faint recollection of the salses (mud volcanoes) of Agrigentum, which, as I have already mentioned, eject argillaceous mud with a loud noise. It is much to be regretted, in reference to this subject, that the work of Theophrastus [Greek words] "On the Volcanic Stream in Sicily", to which Diog. Laert., v., 49, refers, has not come down to us.
p 238 The different volcanoes over the earth"s surface, when they are considered independently of all climatic differences, are acutely and characteristically cla.s.sified as central and linear volcanoes. Under the first name are comprised those which const.i.tute the central point of many active mouths of eruption, distributed almost regularly in all directions; under the second, those lying at some little distance from one another, forming, as it were, chimneys or vents along an extended fissure. Linear volcanoes again admit of further subdivision, namely, those which rise like separate conical islands from the bottom of the sea, being generally parallel with a chain of primitive mountains, whose foot they appear to indicate, and those volcanic chains which are elevated on the highest ridges of these mountain chains, of which they form the summits.*
[footnote] *Leopold von Buch, "Physikal. Beschreib. der Canarischen Inseln", s. 326-407. I doubt if we can agree with the ingenious Charles Darwin ("Geological Observations on Volcanic Islands", 1844, p. 127) in regarding central volcanoes in general as volcanic chains of small extent on parallel fissures. Friedrich Hoffman believes that in the group of the Lipari Islands, which he has so admirably described, and in which two eruption fissures intersect near Panaria, he has found an intermediate link between the two princ.i.p.al modes in which volcanoes appear, namely, the central volcanoes and volcanic chains of Von Buch (Poggendorf, "Annalen der Physik", bd. xxvi., s. 81-88).
The Peak of Teneriffe, for instance, is a central volcano, being the central point of the volcanic group to which the eruption of Palma and Landerote may be referred. The long, rampart-like chain of the Andes, which is sometimes single, and sometimes divided into two or three parallel branches, connected by various transverse ridges, presents, from the south of Chili to the northwest coast of America, one of the grandest instances of a continental volcanic chain. The proxiimity of p 239 active volcanoes is always manifested in the chain of the Andes by the appearance of certain rocks (as dolerite, melaphyre, trachyte, andesite, and dioritic porphyry), which divide the so-called primitive rocks, the transition slates and sandstones, and the stratified formations. the constant recurrence of this phenomenon convinced me long since that these sporadic rocks were the seat of volcanic phenomena, and were connected with volcanic eruptions. At the foot of the grand Tunguragua, near Penipe, on the banks of the Rio Puela, I first distinctly observed mica slate resting on granite, broken through by a volcanic rock.
In the volcanic chain of the New Continent, the separate volcanoes are occasionally, when near together in mutual dependence upon one another; and it is even seen that the volcanic activity for centuries together has moved on in one and the same direction, as for instance, from north to south in the province of Quito.*
[footnote] (Humboldt, "Geognost. Beobach, uber die Vulkane des Hochlandes von Quito", in Poggend., "Annal. der Physik", bd. xliv., s. 194.
The focus of the volcanic action lies below the whole of the highlands of this province; the only channels of communication with the atmosphere are, however, those mountains which we designate by special names, as the mountains of Pichincha, Cotopaxi, and Tunguragua, and which, from their grouping, elevation, and form, const.i.tute the grandest and most picturesque spectacle to be found in any volcanic district of an equally limited extent.
Experience shows us, in many instances, that the extremities of such groups of volcanic chains are connected together by subterranean communications; and this fact reminds us of the ancient and true expression made use of by Seneca,* that the igneous mountain is only the issue of the more deeply-seated volcanic forces.
[footnote] *Seneca, while he speaks very clearly regarding the problematical sinking of Aetna, says in his 79th letter, "Though this might happen, not because the mountain"s height is lowered, but because the fires are weakened, and do not blaze out with their former vehemence; and for which reason it is that such vast clouds of smoke are not seen in the day-time. Yet neither of these seem incredible, for the mountain may possibly be consumed by being daily devoured, and the fire not be so large as formerly, since it is not self-generated here, but is kindled in the distant bowels of the earth, and there rages, being fed with continual fuel, not with that of the mountain, through which it only makes its pa.s.sage."
The subterranean communication, "by galleries," between the volcanoes of Sicily, Lipari, Pithecusa (Ischia), and Vesuvius, "of the last of which we may conjecture that it formerly burned and presented a fiery circle," seems fully understood by Strabl (lib. i., p. 247 and 248). He terms the whole district "sub-igneous."
In the Mexican highlands a mutual dependence is p 240 also observed to exist among the volcanic mountains Orizaba, Popocatepel, Jorullo, and Colima; and I have shown* that they all lie in one direction between 18 degrees 59" and 19 degrees 12" north lat.i.tude, and are situated in a transverse fissure running from sea to sea.
[footnote] *Humboldt, "Essai Politique sur la Nouv. Espagne", t. ii., p.
173-175.
The volcano of Jorullo broke forth on the 29th of September, 1759, exactly in this direction, and over the same transverse fissure, being elevated to a height of 1604 feet above the level of the surrounding plain. The mountain only once emitted an eruption of lava, in the same manner as is recorded of Mount Epomeo in Ischia, in the year 1302. But although Jorullo, which is eighty miles from any active volcano, is in the strict sense of the word a new mountain, it must not be compared with Monte Nuovo, near Puzzuolo, which first appeared on the 19th of September, 1538, and is rather to be cla.s.sed among craters of elevation. I believe that I have furnished a more natural explanation of the eruption of the Mexican volcano, in comparing its appearance to the elevation of the Hill of Methone, now Methana, in the peninsula of Troezene. The description given by Strabo and Pausanias of this elevation, led one of the Roman poets, most celebrated for his richness of fancy, to develop views which agree in a remarkable manner with the theory of modern geognosy. "Near Troezene is a tumulus, steep and devoid of trees, once a plain, now a mountain. The vapors inclosed in dark caverns in vain seek a pa.s.sage by which they may escape. The heavier earth, inflated by the force of the compressed vapors, expands like a bladder filled with air, or like a goat-skin. The ground has remained thus inflated, and the high projecting eminence has been solidified by time into a naked rock."
Thus picturesquely, and, as a.n.a.logous phenomena justify us in believing, thus truly has Ovid described that great natural phenomenon which occurred 282 years before our era, and consequently, 45 years bfore the volcanic separation of Thera (Santorino) and Therasia, between Troezene and Epidaurus, on the same spot where Russegger has found veins of trachyte.*
[footnote] *Ovid"s description of the eruption of Methone ("Metam.", xv., p. 226-306): "Near Troezene stands a hill, exposed in air To winter winds, of leafy shadows bare: This once was level ground; but (strange to tell) Th" included vapors, that in caverns dwell, Laboring with colic pangs, and close confined, In vain sought issue for the rumbling wind: Yet still they heaved for vent, and heaving still, Enlarged the concave and shot up the hill, As breath extends a bladder, or the skins Of goats are blown t"inclose the h.o.a.rded wines; The mountain yet retains a mountain"s face, And gathered rubbish heads the hollow s.p.a.ce."
"Dryden"s Translation".
[footnote continues]
This description of a dome-shaped elevation on the continent is of great importance in a geognostical point of view, and coincides to a remarkable degree with Aristotle"s account ("Meteor.", ii., 89, 17-19) of the upheaval of islands of eruption: "The heaving of the earth does not cease till the wind [(Greek word)] which occasions the shocks has made its escape into the crust of the earth. It is not long ago since this actually happened at Heraclea in Pontus, and a similar event formerly occurred at Hiera, one of the Aeolian Islands. A portion of the earth swelled up, and with loud noise rose into the form of a hill, till the mighty urging blast [(Greek word)]
found an outlet, and ejected sparks and ashes which covered the neighborhood of Lipari, and even extended to several Italian cities." In this description, the vesicular distension of the earth"s crust (a stage at which many trachytic mountains have remained) is very well distinguished from the eruption itself. Strabo, lib. i., p. 59 (Casaubon), likewise describes the phenomenon as it occurred at Methone: near the town, in the Bay of Hermione, there arose a flaming eruption; a fiery mountain, seven (?) stadia in height, was then thrown up, which during the day was inaccessible from its heat and sulphureous stench, but at night evolved an agreeable odor (?) , and was so hot that the sea boiled for a distance of five stadia, and was turbid for full twenty stadia, and also was filled with detached ma.s.ses of rock. Regarding the present mineralogical character of the peninsula of Methana, see Fiedler, "Reise durch Griechenland", th. i., s. 257-263.
p 241 Santorino is the most important of all the "islands of eruption" belonging to volcanic chains.*
[footnote] *[I am indebted to the kindness of Professor E. Forbes for the following interesting account of the island of Santorino, and the adjacent islands of Neokaimeni and Microkaimeni. "The aspect of the bay is that of a great crater filled with water, Thera and Therasia forming its walls, and the other islands being after-productions in its center. We sounded with 250 fathoms of line in the middle of the bay, between Therasia and the main islands, but got no bottom. Both these islands appear to be similarly formed of successive strata of volcanic ashes, which, being of the most vivid and variegated colors, present a striking contrast to the black and cindery aspect of the central isles. Neokaimeni, the last-formed island, is a great heap of obsidian and scoriae. So, also, is the greater ma.s.s, Microkaimeni, which rises up in a conical form, and has a cavity or crater.
On one side of this island, however, a section is exposed, and cliffs of fine pumiceous ash appear stratified in the greater islands. In the main island, the volcanic strata abut against the limestone ma.s.s of Mount St.
Elias in such a way as to lead to the inference that they were deposited in a sea bottom in which the present mountain rose as a submarine ma.s.s of rock.
The people at Santorino a.s.sured us that subterranean noises are not unfrequently heard, especially during calms and south winds, when they say the water of parts of the bay becomes the color of sulphur. My own impression is, that this group of islands, const.i.tutes a crater of elevation, of which the outer ones are the remains of the walls, while the central group are of later origin, and consist partly of upheaved sea bottoms and partly of erupted matter -- erupted, however, beneath the surface of the water."] -- Tr.
It combines within itself p 242 the history of all islands of elevation. For upward of 2000 years, as far as history and tradition certify, it would appear as if nature were striving to form a volcano in the midst of the crater of elevation."*
[footnote] *Leop. von Buch, "Physik. Beschr. der Canar. Inseln", s.
356-358, and particularly the French translation of this excellent work, p.
402; and his memoir in Poggendorf"s "Annalen", bd. x.x.xviii., s. 183. A submarine island has quite recently made its appearance within the crater of Santorino. In 1810 it was still fifteen fathoms below the surface of the sea, but in 1830 it had risen to within three or four. It rises steeply like a great cone, from the bottom of the sea, and the continuous activity of the submarine crater is obvious from the circ.u.mstance that sulphurous acid vapors are mixed with the sea water, in the eastern bay of Neokaimeni, in the same manner as at Vromolimni, near Methana. Coppered ships lie at anchor in the bay in order to get their bottoms cleaned and polished by this natural (volcanic) process. (Virlet, in the "Bulletin de la Societe Geologique de France", t. iii., p. 109, and Fiedler "Reise durch Griechenland", th. ii., s. 469 and 584.)
Similar insular elevations, and almost always at regular intervals of 80 or 90 years,* have been manifested in the island of St. Michael, in the Azores; but in this case the bottom of the sea has not been elevated at exactly the same parts.**
[footnote] *Appearance of a new island near St. Miguel, one of the Azores, 11th of June, 1638, 31st of December, 1719, 13th of June, 1811.
[footnote] **[My esteemed friend, Dr. Webster, professor of Chemistry and Mineralogy at Harvard College, Cambridge, Ma.s.sachusetts, U. S., in his "Description of the Island of St. Michael, etc.", Boston, 1822, gives an interesting account of the sudden appearance of the island named Sabrina which was about a mile in circ.u.mference, and two or three hundred feet above the level of the ocean. After continuing for some weeks, it sank into the sea. Dr. Webster describes the whole of the island of St. Michael as volcanic, and containing a number of conical hills of trachyte, several of which have craters, and appear at some former time to have been the openings of volcanoes. The hot springs which abound in the island are impregnated with sulphureted hydrogen and carbonic acid gases, appearing to attest the existence of volcanic action.] -- Tr.
The island which Captain Tillard named "Sabrina", appeared unfortunately at a time (the 30th of January, 1811) when the political relations of the maritime nations of Western Europe prevented that attention being bestowed upon the subject by scientific inst.i.tutions which was afterward directed to the sudden appearance (the 2d of July, 1831), and the speedy destruction of the igneous island of Ferdinandea in the Sicilian Sea, between the limestone sh.o.r.es of Sciacca and the purely volcanic island of Pantellaria.*
[footnote] *Prevost, in the Bulletin de la Societe Geologique, t. iii., p.
34; Friedrich Hoffman, "Hinterla.s.sene Werke." bd. ii., s. 451-456.
p 243 The geographical distribution of the volcanoes which have been in a state of activity during historical times, the great number of insular and littoral volcanic mountains, and the occasional, although ephemeral, eruptions in the bottom of the sea, early led to the belief that volcanic activity was connected with the neighborhood of the sea, and was dependent upon it for its continuance. "For many hundred years," says Justinian, or rather Trogus Pompeius, whom he follows,* "Aetna and the Aeolian Islands have been burning, and how could this have continued so long if the fire had not been fed by the p 244 neighboring sea?"**
[footnote] *"Accedunt vicini et perpetui Aetnae montis ignes et insularum Aeolidum, veluti ipsis undis alatur incendium; neque enim aliter durare tot seculis tantus ignis potuisset, nisi humoris nutrimentis aleretur."
(Justin, "Hist. Philipp.", iv., i.) The volcanic theory with which the physical description of Sicily here begins is extremely intricate. Deep fissured; violent motion of the waves of the sea, which, as they strike together, draw down the air (the wind) for the maintenance of the fire: such are the elements of the theory of Trogus. Since he seems from Pliny (xi., 52) to have been a physiognomist, we may presume that his numerous lost works were not confined to history alone. The opinion that air is forced into the interior of the earth, there to act on the vocanic furnaces, was connected by the ancients with the supposed influence of winds from different quarters on the intensity of the fires burning in tna, Hiera, and Stromboli. (See the remarkable pa.s.sage in Strabo, liv. vi., Aetna.) The mountain island of Stromboli (Strongyle) was regarded therefore, as the dwelling-place of Aeolus, "the regulator of the winds," in consequence of the sailors foretelling the weather from the activity of the volcanic eruptions of this island. The connection between the eruption of a small volcano with the state of the barometer and the direction of the wind is still generally recognized (Leop. von Buch, "Descr. Phys. des Iles Canaries", p. 334; Hoffmann, in Poggend., "Annalen", bd. xxvi., s. viii), although our present knowledge of volcanic phenomena, and the slight changes of atmospheric pressure accompanying our winds, do not enable us to offer any satisfactory explanation of the fact. Bembo, who during his youth was brought up in Sicily by Greek refugees, gave an agreeable narrative of his wanderings, and in his "Aetna Dialogus" (written in the middle of the sixteenth century) advances the theory of the penetration of sea water to the very center of the volcanic action, and of the necessity of the proximity of the sea to active volcanoes. In ascending Aetna the following question was proposed: "Explaina potius n.o.bis quae petimus, ea incendia unde oriantur et orta quomodo perdurent. In omni tellure nuspiam majores fistulae aut meatus ampliores sunt quam in locis, quae vel mari vicina sunt, vel a mari protinus alluntur: mare erodit illa facillime pergitque in viscera terrae. Itaque c.u.m in aliena regna sibi viam faciat, ventis etiam facit; ex quo fit, ut loca quaeque maritima maxime terrae motibus subjecta sint, parum mediterranea. Habes quum in sulfuris venas venti furentes inciderint, unde incendia oriantur tn tuae. Vides, quae mare in radicibus habeat, quae sulfurea sit, quae cavernosa, quae a mari aliquando perforata ventos admiscrit Aestuantes, per quos idonea flammae materies incenderetur."
[footnote] **[Although extinct volcanoes seem by no means confined to the neighborhood of the present seas, being often scattered over the most inland portions of our existing continents, yet it will appear that, at the time at which they were in an active state, the greater part were in the neighborhood either of the sea, or of the extensive salt or fresh water lakes, which existed at that period over much of what is now dry land. This may be seen either by referring to Dr. Boue"s map of Europe, or to that published by Mr. Lyell in the recent edition of his "Principles of Geology"
(1847), from both of which it will become apparent that, at a comparatively recent epoch, those parts of France, of Germany, of Hungary, and of Italy, which afford evidences of volcanic action now extinct, were covered by the ocean. Daubeney "On Volcanoes", p. 605.] -- Tr.