JAMAICA: is a pit which throws up asphaltum, together, as it is said, with violent explosions, smoke and flames. Almost in the same parallel, and also in the sea, but to the west of the island (near Punta de la Brea, south of the port of Naparaimo) is a similar vent. At the south-west extremity of the island, between Point Icacos and the Rio Erin, are small cones, which appear to have some analogy with the volcanos of Air and Mud, which occur at Turbaco in New Grenada, and are described by Humboldt. It is possible, that the whole of these phænomena may be analogous to those of Macaluba, and of the Lago Naftia in Sicily, which, though they appear to shew some kind of affinity to volcanos from their frequent occurrence in the vicinity of rocks derived from such operations, can hardly be viewed without more sufficient evidence as originating from the same deep-seated cause, to which the latter are commonly referred. Respecting Jamaica, I am spared the necessity of collect ing any details, by the promised appearance of a volume of the Geological Transactions, which will contain the memoir lately read by my friend Mr. De la Beche, on the physical structure of that part of the world. Relative to a small extinct volcano which he discovered in one corner of the island, I have his permission for extract* ing the following particulars : "In that part of Jamaica," says Mr. De la Beche, "which I examined, I observed rocks of a volcanic character only at the Black Hill, which is situated between Lennox, Low Layton, and the sea; this hill, when viewed from the neighbourhood of Buff Bay, has a somewhat conical appearance, and rises above the low hills that extend towards Savanna Point; the hill however, when approached, is seen to be no cone, notwithstanding its effect at a distance. JAMAICA. "The rock, of which the Black Hill is composed, is greyish green and hard, gives out an earthy smell when breathed upon, and may be described in general terms as a volcanic amygdaloid, the cells, with which it abounds, being mostly filled; those however which have been exposed to the weather are frequently empty, as are also those within a few inches from the surface. The interior of the empty cells is often incrusted with a little oxide of iron, while those that are full, and which convert the rock into an amygdaloid, contain chalcedony, calc-spar, &c." Of the physical structure of Cuba, nothing appears to be known; so that it is rather from analogy than from any thing else, that I have ventured to refer this island to the same class as Jamaica. Even to the remaining two a similar remark may in a degree apply; for St. Domingo has been too little explored by naturalists, to allow of our collecting any thing definite with regard to its constitution-we know only that it is extremely subject to earthquakes. Cortes, in his Memoir on the Antilles, before referred to, speaks of Porto Rico as containing antient volcanic, as well as primitive rocks, but he does not enter into any details. Of the second class of islands, which consist exclusively of volcanic rocks, the following is a summary, commencing with the most southern. 1. Grenada, an extinct crater filled with water; boiling springs; basalts between St. George and Goave: 2. St. Vincent, an active volcano, called Le Souffrier, the loftiest mountain in the chain which runs through the island. It first threw out lavas in 1718, but its most tremendous eruption was in 1812, when there issued from the mountain so dreadful a torrent of lava, and such clouds of ashes, as nearly covered the island, and injured the soil in a manner which it has never yet recovered. The total ruin of the city of Caraccas preceded this explosion by thirty-five days, and violent oscillations of the ground were felt, both in the islands, and on the coasts of Terra Firma.* 3. St. Lucia contains a very active Solfatara, from 12 to 14 hundred feet in height. Besides a considerable condensation of sulphur given out from the crevices, jets of hot water likewise take place, which fill periodically certain small basins, like the Geysers of Iceland. 4. Martinique can hardly be said to belong to this class, for limestone is seen resting upon the volcanic products. The latter however constitutes the fundamental rock throughout the whole island, and forms three principal hills called Vauclin, the Paps of Carbet consisting of felspathic lava, which are the most elevated summits in the whole of this series of islands, and Montagne Pelèe. Between the first and second of these is found in a neck of land a tract composed of ancient basalts, called La Roche Carrée. Hot springs at Prêcheur and Lameutin. 5. Dominica is completely composed of volcanic matter, but the action is extinct. 6. Guadeloupe may be divided into two parts, according to its physical structure. The first, properly called Guadeloupe, consists entirely of volcanic rocks, and therefore belongs to this division of our subject; the second, named Grande Terre, is calcareous, consisting of a shelly limestone, covered by a bed of clay, Humboldt's Pers. Narr. vol. 4. and containing rolled masses of lava. The volcanic part of the island contains fourteen antient craters, and one in a state of present activity. The eruption of 1797 took place from an elevation of 4800 feet. Pumice, ashes, and clouds of sulphureous vapours were then ejected. The particulars are given in the report made to the French Government on the state of the volcano in 1797 by Mons. Amie. 7. Montserrat—a Solfatara; fine porphyritic lavas, with large crystals of felspar and hornblende, near Gallo way, often much decomposed by the sulphureous exhalations.* 8. Nevis a Solfatara. 9. St. Christopher's-a Solfatara at Mount Misery. 10. St. Eustachia-the crater of an extinguished volcano, surrounded by pumice. The 3rd class comprehends the islands of Margarita, Desirade, Curaçoa, Bonaire, and in general all the islands of low elevation; they consist entirely of limestone of very recent formation. The 4th class, partly composed of volcanic products, and partly of shelly limestone, comprises the Islands of Antigua, St. Barthelemi, St. Martin, and St. Thomas. Antigua is stated by Dr. Nugent+ to be composed, on the north and east, of a very recent calcareous formation, corresponding with that of Guadaloupe, in which an admixture of marine and freshwater shells is found; subordinate to this rock on its southern limit, we find extensive masses of coarse chert, full of casts of shells, chiefly cerithia. It is 'sometimes intermixed with marl. * Dr. Nugent. Geological Transactions, vol. 1. + Geological Transactions, vol. 1. new series. Beneath these beds occurs an extensive series of stratified rocks, which Dr. Nugent has chosen to call claystone conglomerate, but which seems from his description to be a sort of trachytic breccia. The rock has generally an argillaceous basis, with minute crystals of felspar imbedded, and a remarkably green tinge from the numerous spots of green earth intermixed. Its brecciated character is derived from the fragments of silicified wood, chert, agate, jasper, porphyry, lava, and other substances imbedded. The silicified woods are particularly abundant. Respecting the remaining islands, I possess no information that can be relied on, and it is much to be wished, that some Geologist, in imitation of what has been done by Humboldt on the American Continent, and by Von Buch in the Canaries, would present us with a detailed account of the physical structure generally of the Antilles. The process, by which these islands, according to Moreau de Jonnes, are in many instances formed, is sufficiently curious; first a submarine eruption raises from the bottom of the sea masses of volcanic products, which, as they do not rise above the surface of the water, but form a shoal a short way below its surface, serve as a foundation on which the Madreporites and other marine animals can commence their superstructure. Hence those beds of recent coralline limestone, seen covering the volcanic matter in many of the islands.* It may also be observed, that such as exhibit traces of the recent action of fire, are all situated in a line on the western boundary of the range, from N. latitude 12 to 18, and W. long. 61 to 63. Whatever indications of the kind occur farther to the west belong to eruptions of an older date. Humboldt remarks,t that we must not suppose each island the product of a single volcano, but rather to be pro Humboldt's Pers. Narr. vol. 4. p. 42.-See also Chamisso in Kotzebue's Voyage of Discovery. + Personal Narrative, vol. 4. |