Page:Aspects of nature in different lands and different climates; with scientific elucidations (IA b29329668 0002).pdf/235

 at different epochs, in which the different parts of the examination are all truly comparable with each other. We learn from it that the margins of craters are a phenomenon of far more permanent character than had been previously inferred from passing 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 vapours. Such a cone of eruption, consisting of loosely heaped-up rapilli and scoriæ, 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