OCR Text |
Show OF VOLCANOS, 385 observations, and this not only where (as in the Peak of Teneriffe, and in all the volcanos of the chain of the Andes) they are visibly composed of trachyte, but also elsewhere. According to my last determinations, the north-west edge of Vesuvius has, perhaps, not altered at all since the time of Saussure, an interval of 49 years ; and the south-eastern side, on the side towards Bosche Tre Case, which, in 1794, had become 400 French (426 English) feet lower, has since then hardly altered 10 toises (60 French or 64 English feet.) If the public journals, in describing great eruptions, often state the shape of Vesuvius to have undergone an entire change, and if these assertions appear to be confirmed by picturesque views sketched at Naples, the cause of the error consists in the outlines of the margin of the crater having been confounded with those of the cones of eruption, accidentally formed in the middle of the crater, on its floor or bottom, which has been upheaved by vapors. Such a cone of eruption, consisting of loosely heaped-up rapilli and scorire, had in the course of the years 1816--1818 gradually risen so as to be seen above the south-eastern margin of the crater; and the eruption of the month of February, 1822, augmented it so much, that it even became from 100 to 110 (about 107 to 117 English) feet higher than the north-western margin of the crater (the Rocca del Palo). This remarkable cone, which it had become customary in Naples to regard as the true summit of the mountain, fell in, with a dreadful noise in the last eruption, on the night of the 22d of October (1822): so that the floor of the crater, which had been constantly accessible since 1811, is now 750 (almost 800 English) feet lower than the northern, and 200 (213 English) feet lower than the southern edge of the volcano. Variations in the form and relative position of the cones of eruption-the openings of which ought not to be confounded, as they often are, with the crater of the volcano itself-give to Vesuvius at different epochs a different appearance, which would enable a person well acquainted with the history of the volcano, on a mere inspection of Hackert's paintings in the palace of Portici, to tell from the outlines of the summit, according as the northern or the southern side of the mountain is represented as the 33 |