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SECTION IV.

Volcanoes of the Isle of Bourbon.

THE face of the Isle of BOURBON or REUNION is peculiarly volcanic, and studded with masses of basaltic columns, of various forms and directions. M. Bory has given an interesting and picturesque description of these, in his "Voyage dans les quatres principales Isles des Mers d'Afrique," printed at Paris 1804, in 3 vols. 8vo. The principal summit of the volcano is allowed to retain the appellation of Mascarenhas, after the name of the Portuguese admiral by whom the island was first discovered. "The small hill,” says M. Bory, "at the basis of which we were now arrived, after so much fatigue, is about a hundred and sixty feet in height. It did not appear to us truncated, and we soon climbed it, though the sides be very steep, so as to form with the horizon an angle of more than eighty degrees. They are composed of little currents of glassy scoriæ, spongy, very light and brittle, and exteriorly of a brown colour, with metallic or red reflections from the pores. This volcanic substance is easily broken with the fingers, and reduced to brilliant dust, which resembles aventurine. From the top of the Piton we perceived, on the right and the left, parts of the circumference of two immense craters, which induced us to call this the central hill. The access of this central hill is nearly perpendicular; and on the summit is a round hole about forty fathoms in diameter, and eighty feet in depth. The bottom of this crater was filled with fragments of greyish lava, piled without any order, while the sides were very thin and much scorified on the outside; and were not covered with any sort of varnish, nor with that lava in tears or drops, which in general clothe the other vents. They are formed of confused fragments of different hard and grey lavas, compact, or porous. From some rents there arose light vapours, leaving yellow traces of sublimated sulphur, on the spots exposed to their contact. At one place, where a projecting rock formed a cornice, stopping for a while one of these cords of vapour, it was dissolved in drops of water to a considerable quantity.

"In general a very false idea is formed of volcanoes, and many works which pretend to describe them, paint them very different from what they are. If we believe many travellers, on the brink of a

crater, the eye cannot without terror penetrate the vast depth. As, before I had seen volcanoes, I was persuaded that their chief focus was not their summit, and that the substances which they eject were conveyed from a great depth, I believed that the vents of a burning mountain were immeasurable precipices. I had not yet reflected that when an eruption happens lava must remain in the interior of the crater, forming a solid bottom when the volcano ceased to burn, and which is broken by the following eruptions.

"Meanwhile we asked each other whence the sulphureous vapours could proceed, which annoyed us from time to time, and sought to guess what could produce the noise we heard, when one of our company, who had advanced towards the left, stopped short with strong signs of terror. On hearing his inarticulate cries, I imagined that he must see some extraordinary object, which he could not find words to express. The negroes around him stood petrified. I advanced, and at the sight of a wonderful spectacle very difficult to describe, I was seized with amazement in my turn, and could not explain my sensations. At our feet, from the bottom of an elliptic abyss formed like a tunnel of vast extent, and of which the sides of burnt lava threatened a speedy ruin, issued two contiguous gerbes, or perpendicular sponts, like a Chinese tree in artificial fire-works; but here the fiery matter seemed like tumultuous waves, darted to the height of more than a hundred twenty feet, dashing against each other with a bloody light, in spite of the splendour of an unclouded sun.

"One of these fiery spouts was perpendicular, while the other somewhat oblique seemed at intervals to diminish or increase. Rocks not yet melted, in sharp fragments, distinguishable on the purple of the burning waves by their deep black hue, were pushed with violence from amidst the melted matter in which they had passed from the cavities of the mountain, and fell with great noise, describing a long parabola. A continual noise, resembling that of a vast cataract, accompanied this majestic scene, which filled the soul at once with terror and admiration."

The account of several eruptions of this grand volcano is also interesting. The lava sometimes give indications of containing mineral alkali. In the eruption of 1800, the lava fell in three torrents into a ravine, about eighty feet in depth, forming a horrible cascade, the middle, or hottest torrent being, by the account communicated to M. Bory, as fluid as water, while the two others seemed to have the consistence of honey. When the lava joined

the sea, the scene was tremendous, but there is no hint of any appearance of basaltic columns. The spouts of fire often produce the phenomenon of cords of lava, twisted in different directions.

[Phil. Trans. Cook. De Borda. Glas. Bory.]

CHAP. XV.

AMERICAN VOLCANOES.

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SECTION I.

Volcanoes of Mexico.

E shall now proceed to a brief notice of the chief volcanoes of the American continent, and shall commence with the northern side of the isthmus.

The very singular territory of Mexico, or New Spain, contains numerous volcanoes of a powerful and extraordinary character. Not fewer than twenty-one are laid down on the maps, from that of Soconusco, in the north, to that of Vara in the south. They are all in the south western coast; and after a considerable interval, reemerge towards the eastern coast in the vicinity of the city of Mexico. The principal are those of Orizava, Popacatepec, Iztaccihuath, Ilascala, Tentzon, Toloccam, and above all Jorullo, or Xurullo.

The volcano of Orizaba, or as Clavigero writes it, Pojauhtecatl, began to send forth smoke in 1545, and continued its emissions for twenty years, when it ceased, and has not since renewed them. This celebrated mountain lies sixty miles to the south-east of the city of Mexico, not far from the road to Vera Cruz. According to D'Auteroche, it is the loftiest in the Spanish territory; and according to Gage, as high as the highest of the Alps. Its summit is visible from the capital, and is covered with perpetual snow, yet its sides are adorned with forests of large cedars, pines, and other valuable and picturesque trees.

The detached mountains, called by the Mexicans Popacatapec and Iztaccihuatl, but by the Spaniards Sierra Nevada [the Snowy ridge] in the neighbourhood of each other, lie also to the south-east of Mexico, at about thirty miles distant. The crater of the former,

Clavigero makes more than half a mile wide; but though active formerly, it has not emitted flames of late. In the last century, however, it still continued to emit flames and ashes, the last of which overspread the country to a considerable extent. Iztaccihuath appears to have been exhausted for a longer period than the pre. ceding. Both these mountains, like Orizava, have their summits covered with perpetual snow, in such quantities as to supply the metropolis and the adjacent country for forty miles round, as an article of luxury to the wealthy.

All the others we have enumerated have been quiescent, perhaps immemorially, except Jorullo, which is the most singular of the whole; and whose history, therefore, we shall give more at large from the very interesting account of it, lately published by M. Humboldt.

"The grand catastrophe," says he, " in which this volcanic mountain issued from the earth, and by which the face of a considerable extent of ground was totally altered, was perhaps one of the most extensive physical changes, that the history of our globe exhibits. Geology points out spots in the ocean, where, within the last two years, volcanic islets have arisen above the surface of the sea, as near the Azores, in the Archipelago, and on the south of Iceland : but it records no instance of a mountain of scoriæ and ashes, 517 met. [563 yards] above the old level of the neighbouring plains, suddenly formed in the centre of a thousand small burning cones, thirtysix leagues from the shore, and forty-two leagues from any other volcano. This phænomenon remained unknown to the mineralogists and natural philosophers of Europe, though it took place but fifty years ago, and within six days journey of the capital of Mexico.

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Decending from the central flat towards the coasts of the Pacific ocean, a vast plain extends from the hills of Aguasarco to the villages of Toipa, and Patatlan, equally celebrated for their fine cotton plantations. Between the picachos del Mortero and the cerras de las Cuevas and de Cuiche, this plain is only from 750 to 800 met. [820 to 880 yards] above the level of the sea. Basaltic hills rise in the midst of a country, in which porphyry with base of green-stone predominates. Their summits are crowned with oaks always in verdure, and the foliage of laurels and olives intermingled with dwarf fan palms. This beautiful vegetation forms a singular contrast with the arid plain, which has been laid waste by volcanic fire.

To the middle of the eighteenth century fields of sugar-canes and indigo extended between two rivulets, called Cuitimba and San Pedro. They were skirted by basaltic mountains, the structure of which seems to indicate, that all the country, in remote periods, has several times experienced the violent action of volcanoes. These fields, irrigated by art, belonged to the estate of San Pedro de Jorullo, or Xorullo, one of the largest and most valuable in the country. In the month of June, 1759, fearful rumbling noises were accompanied with frequent shocks of an earthquake, which succeeded each other at intervals for fifty or sixty days, and threw the inhabitants of the estate into the greatest consternation. From the beginning of the month of September, every thing seemed perfectly quiet, when in the night of the 28th of that month a terrible subterranean noise was heard anew. The frightened Indians fled to the mountains of Aguasarco. A space of three or four square miles, known by the name of Majpays, rose in the shape of a bladder. The boundaries of this rising are still distinguishable in the ruptured strata. The Malpays towards the edge is only 12 met. [13 yards] above the former level of the plain, called las playas de Jorullo; but the convexity of the ground increases progressively towards the centre, till it reaches the height of 160 met. [175 yards.]

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They who witnessed this grand catastrophe from the top of Aguasarco assert, that they saw flames issue out of the ground for the space of more than half a league square; that fragments of red hot rocks were thrown to a prodigious height; and that through a thick cloud of ashes, illumined by the volcanic fire, and resembling a stormy sea, the softened crust of the earth was seen to swell up. The rivers of Cuitimba and San Pedro then precipitated themselves into the burning crevices. The decomposition of the water contributed to reanimate the flames, which were perceptible at the city of Pascuoro, though standing on a very wide plain 1400 met. [1530 yards] above the level of the playas de Jorullo. Eruptions of mud, particularly of the strata of clay including decomposed nodules of basaltes with concentric layers, seem to prove, that subterranean waters had no small part in this extraordinary revolution. Thousands of small cones, only two or three yards high, which the Indians call ovens, issued from the raised dome of the Malpays. Though the heat of these volcanic ovens has diminished greatly within these

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