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 Galloway, 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, 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. CALIFORNIA. duced by a series of eruptions proceeding from several ori fices, and joined together by the masses subsequently ejected. It is time however to proceed to consider the volcanos of the Continent of America, our acquaintance with which is exclusively due to the labours of a single individual, the celebrated Alexander de Humboldt. It is much to be regretted that, owing to the surprising variety of subjects which he has undertaken to investigate, it has been impossible for him hitherto to do more, than present the world with fragments and glimpes as it were of that information with respect to the geology of the New World, which it is to be hoped he will one day unfold to us. Beginning with the Peninsula of California, we may reckon three volcanos, supposed to be at present in activity Mount Saint Elia, Mount del Buen Tiempo, and Volcano de las Virgines. Of these, however, little is known except their names, although the mountain of St. Elia ranks among the highest in the globe, being, according to Perouse, 12,672, and according to the Spanish navigators, who measured it in 1791 by precise means, no less than 17,875 feet above the level of the sea. In Mexico appears to commence the great chain of volcanic mountains, which extends with little interruption from the 24th deg. of N. to the 2d deg. of S. lat. The most northern point in this country in which any signs of volcanic action are known to occur, is near the town of Durango, in lat. 24. long. 104, where there is a groupe of rocks covered with scoriæ, called La Breña, which rise up in the midst of a level plain. The latter consist of basaltic amygdaloid, and on the summit of one of the neighbouring mountains a regular crater was discovered. No active volcanos however are to be met with until we MEXICO. reach the parallel of the city of Mexico itself, and here. almost in the same line occur five, so placed that they appear to de derived from a fissure traversing Mexico from west to east, in a direction perpendicular to that of the great mountain chain, which, extending from north-west to south-east, constitutes the great table land of the American Continent. It is interesting to remark, that if the same parallel line, which connects the active volcanos of Mexico, be prolonged in a westernly direction, it would traverse the groupe of islands called the Isles of Revillagigedo, which there may be reason to consider volcanic from the pumice found amongst them.* The most eastern of these, that of Tuxtla, is situated a few miles to the north west of Veracruz. It had a considerable eruption in 1793, the ashes from which were carried as far as Perote, a distance of 57 leagues. In the same province, but farther to the west occur, the volcano of Orizaba, the height of which is 17,300 feet, and the peak of Popocatepetl, 300 feet higher, the loftiest eminence in New Spain. The latter is continually burning,t though for several centuries it has thrown nothing up from the crater but smoke and ashes. On the western side of the city of Mexico, are the volcanos of Jorullo and Colima. The elevation of the latter is estimated at about 9000 feet. It frequently throws up smoke and ashes, but has not been known to eject lava. The volcano of Jorullo, situated between Colima and the town of Mexico, is of much more modern date than the rest, and the great catastrophe which attended its first appearance, is perhaps, (says Humboldt) one of the most extraordinary physical revolutions in the annals of the history of our planet.‡ * See the map of Mexico, which accompanies this volume. + Mr. Bullock has called in question this statement of Humboldt's, but a still more recent traveller, Mr. Stapleton, has confirmed it. Bull. des Sci. for September, 1825. Nouvelle Espagne, y. 218. Fol. Ed. MEXICO. Geology points out parts of the ocean near the Azores, in the Egean Sea, and to the south of Iceland, (?) where, at recent epoques, within the last 2000 years, small volcanic islands have risen above the surface of the water; but it gives us no example of the formation, from the centre of a thousand burning cones, of a mountain of scoriæ and ashes 1695 feet in height, comparing it only with the level of the adjoining plains, in the interior of a continent, 36 leagues distant from the coast, and more than 42 leagues from every other active volcano. A vast plain extends from the hills of Aguasarco nearly to the villages of Teipa and Pelatlan, both equally celebrated for their fine plantations of Cotton. Between the Picachos del Mortero, the Cerros de las Cuevas, and de Cuiche, this plain is only from 2400 to 2600 feet above the level of the sea. In the middle of a tract of ground in which porphyry with a greenstone base predominates, basaltic cones appear, the summits of which are crowned with vegetation, and form a singular contrast with the aridity of the plain, which has been laid waste by volcanos. Till the middle of the last century, fields covered with sugar-cane and indigo occupied the extent of ground between the two brooks called Cuitimba and San Pedro. They were bounded by basaltic mountains, the structure of which seems to indicate, that all this country, at a very remote period, had been already several times convulsed by volcanos. These fields, watered by artificial means, belonged to the farm of Don Pedro di Jorullo, and were among the most fertile in the country. In the month of June, 1759, a subterraneous noise was heard. Hollow sounds of the most alarming nature were accompanied by frequent earthquakes, which succeeded each other for from fifty to sixty days, to the great consternation of the inhabitants of the farm. From the beginning of September every thing seemed to announce the complete Y |