Section of the Tuff and Slaggy Lava in a place called Vulcanello, Isle of Lipari. The tuff in the west and south of Lipari contains imbedded fragments of obsidian and pumice; but on the south the whole surface of the country is covered with the latter substance, which forms several considerable hills, and extends to the furthest point of the island. Dolomieu* has remarked, that this pumice seems to be derived from the fusion of granite, for not only did he observe in the midst of this substance fragments consisting of quartz, mica, and felspar, but when such fragments were exposed to heat, they were converted into a substance, resembling in its general characters the pumice surrounding it. * Dolomieu sur les Isles de Lipari, p. 67. The pumice of Lipari is found to rest on a bed either of obsidian, or of a semivitreous substance nearly allied to it. Some of the varieties possess a remarkable resemblance to certain products obtained by Mr. Gregory Watt* during the cooling of large quantities of basalt, an incipient crystallization beginning to manifest itself in the midst of the vitreous mass by the appearance of white or lighter coloured spots, which appear to be made up of parts radiating from a common centre. In many of the Lipari obsidians, however, the round spots are composed of concentric laminæ, and are disposed in general in lines, so as to give a resemblance of stratification to the mass. In other cases the whole mass is made up of globules of this kind, which are hollow internally, and sometimes cemented by black obsidian. The obsidian also occurs in a brecciated form; large angular masses of it being held together by a white earthy, looking paste, which is hard and gritty. In other cases the paste has all the appearance of a white enamel, such as is used for china or pottery. It is difficult to know, to what we are to attribute the abundance of pumice in Lipari contrasted with its rarity in other parts of the Mediterranean, for though Dolomieu is disposed to attribute it to the kind of material on which the fire had operated, I am more inclined to the opinion of Humboldt, who considers pumice rather a particular state into which many minerals may be brought, than a separate species; and am therefore obliged to look to the different modes in which the heat was applied for an explanation of the fact. For the formation of pumice it seems requisite, that a considerable disengagement of vapour should have taken place, during the time at which the body acted upon was in a plastic, though not in an altogether fluid, condition. But why this should have occurred at Lipari and among *See Phil. Trans. for 1804. the older volcanic rocks near Naples, rather than at Etna and Vesuvius, still remains unaccounted for. It is also difficult to explain why vitreous lavas, such as obsidians, should be of such common occurrence in Lipari,* for the latter are not, as we should be disposed to consider them, loose ejected masses, which from the great relative extent of their surface, were soon coolled in the atmosphere, and therefore put on a vitreous form, but they constitute extensive beds, which ought, it should seem, to have been subjected to the same laws of congelation as the lavas of other volcanos. The only indications of volcanic action at present exist. ing in Lipari are the hot springs, situated about four miles west of the town. I observed however a rock, which, from the changes it had undergone, seems evidently to have been acted upon by sulphureous exhalations, so that it is probable, that at no very remote period, some of the less equivocal effects of subterranean fire may here have manifested themselves. The antients indeed speak of Lipari as emitting a fiercer fire than Stromboli,+ and Strabo particularly mentions an eruption of mud, attended with smoke and flame, which took place in the sea between Hiera (the Island of Volcano, near Lipari), and Euonymos, now (according to Cluverius) Lisca Bianca.‡ * Is the formation of obsidian at all connected with the presence of boracic acid? This I believe has been conjectured by some Swiss naturalist, but the experiments of Dr. Turner, detailed in the Edinburgh Journal of Science for January, 1826, seem to discountenance such a notion, as he finds that neither the pumice nor obsidian of Lipari appear to contain that substance. + Την δε Λιπαραν και την Θερμισσαν ειρηκαμεν. η δε Στρογγυλη, καλείται μεν από του σχήματος, εστι δε και αυτη διαπυρος, βια μεν φλογος λειπομενη, τω δε φέγγει πλεονεκτουσα. Strabo, lib. vi. May not the comparatively recent origin of the Isle of Lipari be inferred from the sterility ascribed by Cicero to the country; (see Orat. 3. in Verrem) for as it is at present very fertile, its barrenness may have arisen from the circumstance, that sufficient time had not elapsed to cause a suitable decomposition of the masses ejected. Before this occurred, the sea between these two islands rose to an unusual height, and became so warm, that the fish died in numbers sufficient to taint the air.* Strabo indeed adds, that flames have been observed rising from the sea in the neighbourhood of those islands, and Pliny notices the same as happening for several days during the Social War.t Homer seems to allude to something of the same kind in the 12th book of the Odyssey, where Circe relates to Ulysses the dangers he is to undergo near the coast of Sicily; and even the epithet of "floating,” (λwn) which he has applied to the island in which king Eolus reigned, may be supposed to refer to the earthquakes, with, which the country was agitated at a time when the volcanic operations were in greater activity. This may seem far-fetched in a country like our own, happily but little subject to these convulsions of nature; but to an American it might appear an obvious allusion, as Humboldt remarks, that on the coast of Peru earthquakes are so frequent, that we become as much accustomed to the undulations of the ground, as the sailor is to the tossings of * Julius Obsequens, who evidently alludes to the same event, places it in the Consulship of Æmilius Lepidus and Aurelius Orestes, or 125 years before Christ. + Near a century before Christ. Especially in the following lines: Αλλα θ'ομε πινακας τε νεων και σωματα φωτων || Αιολιην δες νησον αφικομεθ' ; ενθα δ' έναιεν μ. 68. VOLCANO. the ship, caused by the motion of the waves.* As however there are no vestiges of any thing like a crater in this island, it is probable that these and similar phænomena were derived for the most part from the Island of Volcano, which is separated from it only by a narrow channel.+ This, which appears at a period antecedent to the Christian era to have been in a state of activity at least equal to that of Stromboli, still emits gaseous exhalations from the interior, as well as from several parts of the external surface, of a crater situated on the highest part of the island. These vapours, acting upon the rock they penetrate, decompose it, and form with its constituents large quantities of alum and other sulphuric salts. * From our infancy, the idea of certain contrasts fixes itself in our minds; water appears to us an element that moves; earth, a motionless and inert mass. These ideas are the effect of daily experience; they are connected with every thing that is transmitted to us by the senses. When a shock is felt, when the earth is shaken on its old foundations, which we had deemed so stable, one instant is sufficient to destroy long illusions. It is like awakening from a dream; but a painful awakening. We feel, that we have been deceived by the apparent calm of nature; we become attentive to the least noise, we mistrust for the first time a soil, on which we had so long placed our feet with confidence, If the shocks be repeated, if they become frequent during successive days, the uncertainty quickly disappears. In 1784 the inhabitants of Mexico were accustomed to hear the thunder roll beneath their feet, as we are to witness it in the region of the clouds. Confidence easily springs up in the human breast, and we end įby accustoming ourselves on the coast of Peru to the undulations of the ground, like the sailors to the tossings of the ship, caused by the motion of the waves. Humboldt's Pers. Narrative, vol. 3. p. 321. + We may collect from the old chronicles, that the last indication of volcanic agency in Lipari took place about the sixth century, for we are told that St. Calogero, the patron of the island, put to flight the Devils, which, like the Typhon of old, inhabited the recesses of the island, and that the latter first took refuge under the mountain from whence the warm springs issue, but being driven from thence repaired to Vulcanello, and finally were chased into the crater of Vulcano. Later writers always speak of the flames of Lipari as extinct. See Dolomieu sur les Iles de Lipari, p. 71. |