Volume I Part 24 (1/2)
To explain these great effects of volcanic reactions, and to prove that the group or system of the volcanoes of the West India Islands may sometimes shake the continent, I have cited the Cordillera of the Andes. Geological reasoning can be supported only by the a.n.a.logy of facts which are recent, and consequently well authenticated: and in what other region of the globe could we find greater and more varied volcanic phenomena than in that double chain of mountains heaved up by fire? in that land where nature has covered every mountain and every valley with her marvels? If we consider a burning crater only as an isolated phenomenon, if we be satisfied with merely examining the ma.s.s of stony substances which it has thrown up, the volcanic action at the surface of the globe will appear neither very powerful nor very extensive. But the image of this action becomes enlarged in the mind when we study the relations which link together volcanoes of the same group; for instance, those of Naples and Sicily, of the Canary Islands,* of the Azores, of the Caribbee islands of Mexico, of Guatimala, and of the table-land of Quito; when we examine either the reactions of these different systems of volcanoes on one another, or the distance at which, by subterranean communication, they simultaneously convulse the earth. (I have already observed (Chapter 1.2) that the whole group of the Canary Islands rises, as we may say, above one and the same submarine volcano. Since the sixteenth century, the fire of this volcano has burst forth alternately in Palma, Teneriffe, and Lancerote. Auvergne presents a whole system of volcanoes, the action of which has now ceased; but in the middle of a system of active volcanoes, for instance, in that of Quito, we must not consider as an extinguished volcano a mountain, the crater of which is obstructed, and through which the subterraneous fire has not issued for ages. Etna, the Aeolian Isles, Vesuvius, and Epomeo; the peak of Teyde, Palma, and Lancerote; St. Michael, La Caldiera of Fayal, and Pico; St.
Vincent, St. Lucia, and Guadaloupe; Orizava, Popocatepetl, Jorullo, and La Colima; Bombacho, the volcano of Grenada, Telica, Momotombo, Isalco, and the volcano of Guatimala; Cotopaxi, Tunguragua, Pichincha, Antisana, and Sangai, belong to the same system of burning volcanoes; they are generally ranged in rows, as if they had issued from a crevice, or vein not filled up; and, it is very remarkable, that their position is in some parts in the general direction of the Cordilleras, and in others in a contrary direction.)
The study of volcanoes may be divided into two distinct branches; one, simply mineralogical, is directed to the examination of the stony strata, altered or produced by the action of fire; from the formation of the trachytes or trap-porphyries, of basalts, phonolites, and dolerites, to the most recent lavas: the other branch, less accessible and more neglected, comprehends the physical relations which link volcanoes together, the influence of one volcanic system on another, the connection existing between the action of burning mountains and the commotions which agitate the earth at great distances, and during long intervals, in the same direction. This study cannot progress till the various epochs of simultaneous action, the direction, the extent, and the force of the convulsions are carefully noted; till we have attentively observed their progressive advance to regions which they had not previously reached; and the coincidence between distant volcanic eruptions and those noises which the inhabitants of the Andes very expressively term subterraneous thunders, or roarings.* (* Bramidos y truenos subterraneos.) All these objects are comprehended in the domain of the history of nature.
Though the narrow circle within which all certain traditions are confined, does not present any of those general revolutions which have heaved up the Cordilleras and buried myriads of pelagian animals; yet Nature, acting under our eyes, nevertheless exhibits violent though partial changes, the study of which may throw light on the most remote epochs. In the interior of the earth those mysterious powers exist, the effects of which are manifested at the surface by the production of vapours, of incandescent scoriae, of new volcanic rocks and thermal springs, by the appearance of new islands and mountains, by commotions propagated with the rapidity of an electric shock, finally by those subterranean thunders,*
heard during whole months, without shaking the earth, in regions far distant from active volcanoes. (* In the town of Guanaxuato, in Mexico, these thunders lasted from the 9th of January till the 12th of February, 1784. Guanaxuato is situated forty leagues north of the volcano of Jorullo, and sixty leagues north west of the volcano of Popocatepetl. In places nearer these two volcanoes, three leagues distant from Guanaxuato, the subterranean thunders were not heard. The noise was circ.u.mscribed within a very narrow s.p.a.ce, in the region of a primitive schist, which approaches a transition-schist, containing the richest silver mines of the known world, and on which rest trap-porphyries, slates, and diabasis (grunstein.))
In proportion as equinoctial America shall increase in culture and population, and the system of volcanoes of the central table-land of Mexico, of the Caribbee Islands, of Popayan, of los Pastos, and Quito, shall be more attentively observed, the connection of eruptions and of earthquakes, which precede and sometimes accompany those eruptions, will be more generally recognized. The volcanoes just mentioned, particularly those of the Andes, which rise above the enormous height of two thousand five hundred toises, present great advantages for observation. The periods of their eruptions are singularly regular. They remain thirty or forty years without emitting scoriae, ashes, or even vapours. I could not perceive the smallest trace of smoke on the summit of Tunguragua or Cotopaxi. A gust of vapour issuing from the crater of Mount Vesuvius scarcely attracts the attention of the inhabitants of Naples, accustomed to the movements of that little volcano, which throws out scoriae sometimes during two or three years successively. Thence it becomes difficult to judge whether the emission of scoriae may have been more frequent at the time when an earthquake has been felt in the Apennines. On the ridge of the Cordilleras everything a.s.sumes a more decided character. An eruption of ashes, which lasts only a few minutes, is often followed by a calm of ten years. In such circ.u.mstances it is easy to mark the periods, and to observe the coincidence of phenomena.
If, as there appears to be little reason to doubt, that the destruction of c.u.mana in 1797, and of Caracas in 1812, indicate the influence of the volcanoes of the West India Islands* on the commotions felt on the coasts of Terra Firma, it may be desirable, before we close this chapter, to take a cursory view of this Mediterranean archipelago.
(* The following is the series of the phenomena:--
27th of September, 1796. Eruption in the West India Islands.
(Volcano of Guadaloupe).
November, 1796. The volcano of Pas...o...b..gan to emit smoke.
14th of December, 1796. Destruction of c.u.mana.
4th of February, 1797. Destruction of Riobamba.
30th of January, 1811. Appearance of Sabrina Island, in the Azores.
The island enlarged very considerably on the 15th of June, 1811.
May, 1811. Commencement of the earthquakes in the island of St.
Vincent, which lasted till May 1812.
16th of December, 1811. Commencement of the commotions in the valley of the Mississippi and the Ohio, which lasted till 1813.
December, 1811. Earthquake at Caracas.
26th of March, 1811. Destruction of Caracas. Earthquakes, which continued till 1813.
30th of April, 1811. Eruption of the volcano in St. Vincent; and the same day subterranean noises at Caracas, and on the banks of the Apure.)
The volcanic islands form one-fifth of that great arc extending from the coast of Paria to the peninsula of Florida. Running from south to north, they close the Caribbean Sea on the eastern side, while the greater West India Islands appear like the remains of a group of primitive mountains, the summit of which seems to have been between Cape Abacou, Point Morant, and the Copper Mountains, in that part where the islands of St. Domingo, Cuba, and Jamaica, are nearest to each other. Considering the basin of the Atlantic as an immense valley* which separates the two continents, and where, from 20 degrees south to 30 degrees north, the salient angles (Brazil and Senegambia) correspond to the receding angles (the gulf of Guinea and the Caribbean Sea), we are led to think that the latter sea owes its formation to the action of currents, which, like the current of rotation now existing, have flowed from east to west; and have given the southern coast of Porto Rico, St. Domingo, and the island of Cuba their uniform configuration. (* The valley is narrowest (300 leagues) between Cape St. Roque and Sierra Leone.
Proceeding toward the north along the Coasts of the New Continent, from its pyramidal extremity, or the Straits of Magellan, we imagine we recognise the effects of a repulsion directed first toward the north-east, then toward the north-west, and finally again to the north-east.) This supposition of an oceanic irruption has been the source of two other hypotheses on the origin of the smaller West India Islands. Some geologists admit that the uninterrupted chain of islands from Trinidad to Florida exhibits the remains of an ancient chain of mountains. They connect this chain sometimes with the granite of French Guiana, sometimes with the calcareous mountains of Pari. Others, struck with the difference of geological const.i.tution between the primitive mountains of the Greater and the volcanic cones of the Lesser Antilles, consider the latter as having risen from the bottom of the sea.
If we recollect that volcanic upheavings, when they take place through elongated crevices, usually take a straight direction, we shall find it difficult to judge from the disposition of the craters alone, whether the volcanoes have belonged to the same chain, or have always been isolated. Supposing an irruption of the ocean to take place either into the eastern part of the island of Java* (* Raffles, History of Java, 1817, pages 23-28. The princ.i.p.al line of the volcanoes of Java, on a distance of 160 leagues, runs from west to east, through the mountains of Gagak, Gede, Tankuban-Prahu, Ungarang Merapi, Lawu, Wilis, Arjuna, Dasar, and Tashem.) or into the Cordilleras of Guatimala and Nicaragua, where so many burning mountains form but one chain, that chain would be divided into several islands, and would perfectly resemble the Caribbean Archipelago. The union of primitive formations and volcanic rocks in the same range of mountain is not extraordinary; it is very distinctly seen in my geological sections of the Cordillera of the Andes. The trachytes and basalts of Popayan are separated from the system of the volcanoes of Quito by the mica-slates of Almaguer; the volcanoes of Quito from the trachytes of a.s.suay by the gneiss of Condorasta and Guasunto. There does not exist a real chain of mountains running south-east and north-west from Oyapoc to the mouths of the Orinoco, and of which the smaller West India Islands might be a northern prolongation. The granites of Guiana, as well as the hornblende-slates, which I saw near Angostura, on the banks of the Lower Orinoco, belong to the mountains of Pacaraimo and of Parime, stretching from west to east, * (From the cataracts of Atures towards the Essequibo River. This chain of Pacaraimo divides the waters of the Carony from those of the Rio Parime, or Rio de Aguas Blancas.) in the interior of the continent, and not in a direction parallel with the coast, between the mouths of the river Amazon and the Orinoco. But though we find no chain of mountains at the north-east extremity of Terra Firma, having the same direction as the archipelago of the smaller West India Islands, it does not therefore follow that the volcanic mountains of the archipelago may not have belonged originally to the continent, and formed a part of the littoral chain of Caracas and c.u.mana.* (* Among many such examples which the structure of the globe displays, we shall mention only the inflexion at a right angle formed by the Higher Alps towards the maritime Alps, in Europe; and the Belour-Tagh, which joins transversely the Mouz-Tagh and the Himalaya, in Asia. Amid the prejudices which impede the progress of mineralogical geography, we may reckon, 1st, the supposition of a perfect uniformity of direction in the chains of mountains; 2nd, the hypothesis of the continuity of all chains; 3rd, the supposition that the highest summits determine the direction of a central chain; 4th, the idea that, in all places where great rivers take rise, we may suppose the existence of great tablelands, or very high mountains.)
In opposing the objections of some celebrated naturalists, I am far from maintaining the ancient contiguity of all the smaller West India Islands. I am rather inclined to consider them as islands heaved up by fire, and ranged in that regular line, of which we find striking examples in so many volcanic hills in Auvergne, in Mexico, and in Peru. The geological const.i.tution of the Archipelago appears, from the little we know respecting it, to be very similar to that of the Azores and the Canary Islands. Primitive formations are nowhere seen above ground; we find only what belongs unquestionably to volcanoes: feldspar-lava, dolerite, basalt, conglomerated scoriae, tufa, and pumice-stone. Among the limestone formations we must distinguish those which are essentially subordinate to volcanic tufas* from those which appear to be the work of madrepores and other zoophytes. (* We have noticed some of the above, following Von Buch, at Lancerote, and at Fortaventura, in the system of the Canary Islands. Among the smaller islands of the West Indies, the following islets are entirely calcareous, according to M. Cortes: Mariegalante, La Desirade, the Grande Terre of Guadaloupe, and the Grenadillas. According to the observations of that naturalist, Curacoa and Buenos Ayres present only calcareous formations. M. Cortes divides the West India Islands into, 1st, those containing at once primitive, secondary, and volcanic formations, like the greater islands; 2nd, those entirely calcareous, (or at least so considered) as Mariegalante and Curacoa; 3rd, those at once volcanic and calcareous, as Antigua, St. Bartholomew, St. Martin, and St. Thomas; 4th, those which have volcanic rocks only, as St. Vincent, St. Lucia, and St. Eustache.) The latter, according to M. Moreau de Jonnes, seem to lie on shoals of a volcanic nature. Those mountains, which present traces of the action of fire more or less recent, and some of which reach nearly nine hundred toises of elevation, are all situated on the western skirt of the smaller West India Islands.* (* Journal des Mines, tome 3 page 59. In order to exhibit in one point of view the whole system of the volcanoes of the smaller West India Islands, I will here trace the direction of the islands from south to north.--Grenada, an ancient crater, filled with water; boiling springs; basalts between St. George and Goave.--St. Vincent, a burning volcano.--St. Lucia, a very active solfatara, named Oualibou, two or three hundred toises high; jets of hot water, by which small basins are periodically filled.--Martinique, three great extinguished volcanoes; Vauclin, the Paps of Carbet, which are perhaps the most elevated summits of the smaller islands, and Montagne Pelee. (The height of this last mountain is probably 800 toises; according to Leblond it is 670 toises; according to Dupuget, 736 toises. Between Vauclin and the feldspar-lavas of the Paps of Carbet is found, as M. Moreau de Jonnes a.s.serts, in a neck of land, a region of early basalt called La Roche Carree). Thermal waters of Precheur and Lameutin.--Dominica, completely volcanic.--Guadaloupe, an active volcano, the height of which, according to Leboucher, is 799 toises; according to Amie, 850 toises.--Montserrat, a solfatara; fine porphyritic lavas with large crystals of feldspar and hornblende near Galloway, according to Mr.
Nugent.--Nevis, a solfatara.--St. Christopher's, a solfatara at Mount Misery.--St. Eustache, a crater of an extinguished volcano, surrounded by pumice-stone. (Trinidad, which is traversed by a chain of primitive slate, appears to have anciently formed a part of the littoral chain of c.u.mana, and not of the system of the mountains of the Caribbee Islands.)) Each island is not the effect of one single heaving-up: most of them appear to consist of isolated ma.s.ses which have been progressively united together. The matter has not been emitted from one crater, but from several; so that a single island of small extent contains a whole system of volcanoes, regions purely basaltic, and others covered with recent lavas. The volcanoes still burning are those of St. Vincent, St.
Lucia, and Guadaloupe. The first threw out lava in 1718 and 1812; in the second there is a continual formation of sulphur by the condensation of vapours, which issue from the crevices of an ancient crater. The last eruption of the volcano of Guadaloupe took place in 1797. The Solfatara of St. Christopher's was still burning in 1692. At Martinique, Vauclin, Montagne Pelee, and the crater surrounded by the five Paps of Carbet, must be considered as three extinguished volcanoes. The effects of thunder have been often confounded in that place with subterranean fire. No good observation has confirmed the supposed eruption of the 22nd of January, 1792. The group of volcanoes in the Caribbee Islands resembles that of the volcanoes of Quito and Los Pastos; craters with which the subterranean fire does not appear to communicate are ranged on the same line with burning craters, and alternate with them.
Notwithstanding the intimate connection manifested in the action of the volcanoes of the smaller West India Islands and the earthquakes of Terra Firma, it often happens that shocks felt in the volcanic archipelago are not propagated to the island of Trinidad, or to the coasts of Caracas and c.u.mana. This phenomenon is in no way surprising: even in the Caribbees the commotions are often confined to one place. The great eruption of the volcano in St. Vincent's did not occasion an earthquake at Martinique or Guadaloupe. Loud explosions were heard there as well as at Venezuela, but the ground was not convulsed.