ETNA. VESUVIUS. A.D. A.D. 1306. 1329, June 28. 1333. 1408, November 9. 1445. 1446. 1447, September. 1500. 1535, March, till 1537. 1538, 29th September, Formation of the Monte Nuovo, near Puzzuoli. 1566. 1578. 1603, July. Continuance of small 1607. 1610, Feb. eruptions during this interval. 1614, July 2. 1619. 1624. 1631, December 16. 1633, February 22. 1645, November. 1654. 1660, July. 1669, March 8. 1682, December. 1682, August 12. 1688. 1689, March 14. 1694, March to December. (Eruption 1694, March 12, with feeble recuronly of ashes.) rences of action till 1698, 1701, July 2 till 15. 1702, March 8. 1707, May 20, with feeble recurrences of action till August 1707. 1712, Feb. 18, eruption continued till the following year. 1717, June 6, continued as before. 1723, November, beginning of the month. 1727, July 26. 1730, February 27. 1735, October, beginning of the month. 1737, May 14. 1747, September, volcanic action continued for some years. 1751, October 25. 1754, December 2. 1755, March 2. 1759. 1760, December 23. 1766, March 25. 1779, August 3. 1783, August 18. It appears from this Table, that the nearest coincidence between the eruptions of the two volcanos was in 1694 and in 1811, when they occurred within a month of each other; and that on eight several occasions an interval of less than half a year elapsed between them : viz. that of Vesuvius Dec. 2, 1754, was followed by one of Etna on March 2, 1755 ; Vesuvius August 3, 1779, by Etna May 18, 1780 ; Vesuvius October 31, by Etna July 28, 1787; Etna June 1798, by Vesuvius February 1799; again followed by one of Etna in June, same year; Etna March 27, 1809, by Vesuvius December 10, 1809; Vesuvius October 12, 1811, by Etna October 25, 1811; again followed by Vesuvius December 31, same year; Vesuvius May 27, 1819, by Etna November 25, same year. The above-mentioned coincidences do not appear to me sufficiently numerous to warrant the inference, that a connexion subsists between these two igneous vents; nor does such an idea tally with the views of Von Buch, who regards both Etna and Vesuvius as central volcanos, that is, as points of greatest intensity, from which the igneous energy radiates in all directions, as from a centre. It seems to me more probable, that whilst volcanic forces have been, or are in operation on either side of the Apennine chain, from the north of Italy to its very southern extremity, and to the island of Sicily beyond, there are certain transverse lines along which these forces manifest themselves in their greatest intensity, either by their actual phænomena, or by their past effects. Such is the line from Ischia to Vesuvius, the lake Amsanctus and Mount Vultur; that perhaps extending from Latium to the Tremite Islands, which are stated to be volcanic; and lastly, the one running from Mount Etna to the hot springs of Sciacca, thence intersecting the new island thrown up in 1831, and terminating in Pantellaria. Pantellaria. Of this last island Hoffman has presented us with a short account. It is situated at a distance of sixty miles to the south-west of Sciacca, the new island thrown up in 1831 being about midway between it and the coast of Sicily. He distinguishes three kinds of volcanic products: the first a peculiar kind of felspar with a greenish colour and slaty cleavage, which he calls chloric lava; crystals of glassy felspar, and of a black needle-shaped mineral which resembles hornblende, are disseminated through this basis. The second kind of igneous rock is of a glassy character like that found in Lipari, consisting either of pumice in such vast heaps as to form a hill 2000 feet high, or of obsidian, which in some places constitutes lava-streams. Steam issues from many parts of this mountain, and several hot springs gush out from it, which form together a little lake 6000 feet in circumference. The third kind of volcanic product met with consists of lava-streams similar to those of Mount Etna, and therefore altogether different from the pumiceous products before mentioned. They consequently appear to belong to a more recent period, although no record exists as to any eruptions occurring in the island. There appear to be the remnants of an ancient crater of elevation encircling a space of 12 miles, and composed of beds of the trachytic lava and of the pumiceous conglomerate above described. CHAPTER XVI. SARDINIA-SPAIN-PORTUGAL. Sardinia-modern volcanic rocks-consisting of trachyte-obsidian, &c. -Spain-its structure compared with that of Mexico-volcanic rocksin Catalonia-near Carthagena-Cape de Gaieta.-The Colubretes.— Portugal-basaltic rocks near Lisbon.-Indications of volcanos in the Sierra l'Estrella-Cape St. Vincent, &c. BEFORE proceeding to a description of other active volcanos existing in the same quarter of the globe, it may be more convenient to point out those evidences of former igneous action not already described, which have been recognised in parts of Europe situated within the confines of the Mediterranean. First then I may remark, that, according to the researches of M. de la Marmora, the island of Sardinia exhibits evident traces of volcanic eruptions, both of an ancient and a modern date, though not comprised within the limits either of history or tradition. It may be collected from his statement, that the volcanos occur in almost every case in groups of greater or less extent, and that they in general repose on rocks belonging to the most recent order of formations. Parts of these products are of a date posterior to the excavation of the valleys, but others are distinctly recognised as anterior to them. Thus, in the south of the island, between the village of Nurri and the plain called Campidano, the calcareous rocks of the country are capped by a platform of well-characterized lava, which follows the general inclination of the country from east to west. The name given to these platforms is Giarra, and there are several of them, such as the Giarra de Serri, de Gestori, &c. The inclination of the beds, the direction of the cells, and the abundance of the lava which is found alike on the summits of all the calcareous and marly hills of this neighbourhood, lead to the belief that their origin is in all cases the same, or that they belong, to speak more correctly, to one and the same current that proceeded from a crater near Nurri, at an epoch antecedent to the period at which the valleys were excavated. The craters are in great measure effaced, and it is only with hesitation that our author admits that there exist traces of any. In his search he was directed rather by the shape and direction of the cells found in the lavas, than by the actual form of the masses themselves. Among the volcanic formations of this island, the predominant rock is a felspathic (petro-siliceuse) porphyry. It constitutes two-thirds of the lithoide lavas of the country. It occurs in great masses on the two islands already cited; among the mountains of Ales, Bortigali, and the environs of Macomer; forms a large portion of the mountains called Villa Nuova, Monte Leone, and Bosa; and is found at last at Ploaghe, near Osilo and Castel Sardo, where it passes into obsidian. The most remarkable variety which this porphyry presents is a rock of a prismatic form with a fine rosy hue, often ramified with dendrites. It has been observed in the islands of St. Pietro, St. Antioco, and Isola Prima, and affords the only instance of a prismatic structure present amongst the rocks of this quarter. Those portions which are preserved from the action of air and light retain a very bright colour, the lustre of which is relieved by fine ramifications of very large and varied dendrites. The island of St. Antioco is also very rich in pearlstone, which constitutes part of a species of conglomerate or breccia, inclosing likewise other substances, this pearlstone seeming to have been rolled, and occurring in masses from the size of a nut to that of twice or thrice a man's head. It is always accompanied with puzzolana. Obsidian with a conchoidal fracture occurs in the island of St. Peter's, on the summit of Trebina, near Ales, &c., but true pumice has not been met with. Red jasper abounds, especially in the Isle of St. Peter, and in the volcanic rocks of Alghero, Eteri, and Bosa, and basaltic lavas, often scoriform, form the greatest part of Monte St. Lussurgio and of Caglieri. On the eastern flank of the former mountain we observe the lava that flowed from its extinct crater. |