water was thirty fathoms in depth. At the same time the cliff's of St. Michael were shattered by an earthquake. This island, which was called Sabrina, from the ship of Capt. Tillard, rose 200 feet above the water, but soon after disappeared being composed almost entirely of ashes and einders. We have already noticed the Aleutian islands, as the theatre of volcanic action. In the year 1806, a new island, which still remains, and consists of solid rock, about four miles in circumference, was thrown up from the bottom of the sea; and in 1814, another of the same character, but much larger, being 3000 feet in height, was added to the same group. We might enumerate many other islands formed by volcanic agency did our limits permit, but we hasten to consider next the volcanoes of South America. In noticing the great chain of mountains which runs along the western coast of America, we alluded to the five volcanic vents in about the parallel of the City of Mexico, arranged in a line at right angles nearly to the general direction of the mountainous chain. One of these volcanoes, that of Jorullo, is particularly remarkable, being the product of an eruption which occurred in 1759, and lasted about nine months. The volcanoes of Tuxtla, Orizava, and Popocatapetl, are on the eastern side of Mexico, the latter is continually burning, but seldom emits anything more than smoke and ashes. At the west of the city, are the volcanoes of Colima, and Jorullo, the former about 9000 feet in height, and emitting smoke and ashes; between the city and this volcano lies the plain of Jorullo, in which a crater was formed in 1759. In that year according to Humboldt, who has minutely described the phenomena, in the month of June, a subterranean noise was heard in the district of Jorullo; hollow sounds of the most frightful nature, which were accompanied by frequent earthquakes, succeeded each other for from forty to fifty days; causing great terror to the inhabitants of that district. From the beginning of September everything seemed to announce the complete reestablishment of tranquility, when, in the night of the 28th and 29th, the horrible subterranean noise recommenced. The affrighted Indians fled to the mountains, soon a tract of ground, from three to four square miles in extent, began to swell like waves ERUPTION OF JORULLO. 255 of the sea, and finally rose up in the shape of a bladder, then opened, and fragments of burning rocks accompanied with flames, were thrown to an immense height. The rivers Cuitimba and San Pedro, which watered this plain, formerly cultivated with fields of cane and indigo, precipitated themselves into the burning chasms. Hundreds of small cones from three to ten feet high, called by the natives hornitos issued from the smoking plain, and six large volcanic cones were formed, the smallest three hundred feet high, and the largest, which is the present volcano of Jorullo, 1600 feet in height. It is continually burning, or rather now sending forth sulphureous gasses, and has thrown up from its north side immense masses of basaltic lava, with fragments of granitic rocks. Below we give an outline of this celebrated vol This canic mountain, a is the summit of Jorulle, b c inclined plane, sloping at an angle of 6° from the base of the cones. eruption occurred at a distance of 150 miles from the sea-coast, and is somewhat remarkable on this account, all other active volcanoes being near the sea. The eruptions of mud, however, and balls of decomposed basalt, and especially strata of clay, seem to indicate that subterraneous water had no small share in producing this phenomenon. Humboldt visited the country more than forty years after the eruption, and found the elevated mass of the former plain, shown by the slope b c in the preceding outline sketch, still hot enough in some of the fissures at a depth of a few inches, to light a cigar. The hornitos have now ceased to emit steam, or smoke, and the central volcano is itself almost extinct, the plain and slope of the mountain is covered with a luxurious vegetation, and the memory of the former terrific convulsions seems almost forgotten. We have now given an account of the most celebrated volca noes, and the effects produced by their eruptions. When we bear in mind that during the earlier periods of the earth's existence, volcanic action was much more general and severe than at present, we will be at no loss for a sufficient cause to produce most of the upheavings, and contortions of strata, observed on our globe. In some parts of the world, whole districts are composed of extinct volcanoes, which even yet have not wholly ceased to emit deleterious gasses, and the traces of their former and powerful action are seen in every country. We have not discussed at all, the causes which produce volcanic eruptions; these are not yet satisfactorily determined; and a great diversity of opinion still exists among philosophers. It will be seen upon referring to the diagram, (page 178), that the comparative height of the loftiest mountains, is but as a minute grain of sand on a large globe, and that such slight changes from the general level of the surface may be produced by causes comparatively small. IGNEOUS CAUSES OF CHANGE. 257 CHAPTER VIII. Earthquakes. "Of chance or change, oh! let not man complain ; For from the imperial dome, to where the swain All feel the assault of fortune's fickle gale. Art, empire, earth itself, are doom'd; Earthquakes have raised to heaven the humble vale; And gulfs the mountains' mighty mass entomb'd; And where the Atlantic rolls, wide continents have bloom'd." Beattie. In the present chapter we shall briefly describe some of those remarkable convulsions which from time to time have caused the crust of the earth to heave like the waves of the ocean, and to gape open in many places, suddenly engulphing cities and their inhabitants, or deluging whole tracts of country by the upheaved waters. These phenomena, which are supposed to be caused by immense evolutions of steam, and other vapors, or gasses, under an intense pressure, which is only relieved by a volcanic eruption, or an opening of the earth, constitute the most terrible warnings, which reminds us of the instability of all things. The evidences of mighty change which the philosopher sees in each upheaved hill of granite, and dike of trap, or in the formation of contorted strata may read to him a lesson, which, if rightly understood, will teach him to look far from his present abode, for the unchangable world; but the careless observer, who builds his cottage on the side of a volcanic cone, and feeds his flocks within its crater, needs the awful sound of subterranean thunder, and the rocking of the plain, to convince him that the neglected traditions of former calamities, were not all a fiction. There is something startling in the idea that our earth, or rather its crust, is perhaps but a few hundred miles in thickness, or in other words, that our globe is a hollow ball of no very great dimensions. It is a well established proposition that, under influence of the attraction of gravitation, a body, or a mass of matter, placed any where within a hollow globe, as at a or b, (see the diagram below), will remain at rest wherever it may be situated. Hence, whether the interior of the hollow globe be molten or not, the mass will not be displaced, or in other words, it will have no tendency to move, unless operated upon by other force than the attraction of gravitation. The name earthquake has been given to those convulsions of supposed igneous origin, which cause the surface of the earth to heave, or undulate, producing rents, and generally precursing the eruption of some volcano. The region of violent earthquakes, is generally the site of some active volcano, and the paroxysms of an earthquake, are generally relieved by a volcanic eruption. Thus, during the earthquake which overturned Lima in 1746, and which was one of the most terrible which has been recorded, four volcanoes opened in one night, and the agitation of the earth ceased. The phenomena attending earthquakes are various, sometimes there is but a slight undulatory movement, barely sufficient to cause the lighter articles upon the surface to change places. Persons unacquainted with the phenomena of earthquakes, suppose themselves seized with a sudden giddiness. Of'ten the first shocks are of this light character, then gradually be |