| OCR Text |
Show ..... DESCRIPTION OF THE PL~TES AND MAP. FRONTISPIECE. View of part of the Valley del Bove, on the East side of the great Cone of Etna. THIS valley is a cavity of immense depth, commencing at a short distance below the summit of Etna, and descending through that zone of the mountain where lateral eruptions are frequent. The general dip of the volcanic beds in the precipices surrounding this valley is towards the sea, but exceptions occur where lateral cones have been buried in the manner described in the first volume (p. 363). The stupendous precipices surrounding this great amphitheatre vary from 600 to nearly 3000 feet in height, and they are traversed on all sides by innumerable vertical walls or dikes of compact lava, which cut through the sloping beds of lava, sand, and scorire, of which the great cone is formed. These dikes, which will be described in the next volume, seem all to have been produced by ancient lateral eruptions on the flanks of Etna. The causes which have produced this great depression in the otherwise symmetrical cone of the volcano will be discussed in the third volume, and we shall merely state here, that we consider the conformation of the rocky barrier encircling the cavity, as entirely at variance with an hypothesis recently proposed, that the hollow was a crater of eruption from whence the scorire of the surrounding heights have proceeded. We have introduced two colours into the plate, the grey to express that part of the mountain which may have been formed before the origin of the " Val del Bove," the red to indicate the part which has resulted from eruptions subsequent to the |
