The most usual appearance of the crater, when in comparative repose, is that of a vast circular or oval hollow basin, with nearly perpendicular walls, broken in their continuity, every here and there, by large projecting dykes, formed by the injection of more recent lavas into fissures rent in those which had previously become consolidated. Below the perpendicular walls is a rapid slope, composed of fine ashes or sand, descending to the floor of the crater, which is, for the most part, nearly flat. It is much rent by fissures, which during the night are seen to glow with a ruddy glare, emanating from the hot materials beneath, and giving to the floor the appearance of being overspread with a fiery tissue, like a spider's web. From the bottom there usually rise one or two small craters of eruption, whence continually issue sulphurous fumes, and which, at pretty regular intervals, discharge showers of stones heated to whiteness. The exterior of the cone is composed entirely of loose cinders, ashes, and stones, so that the ascent is very laborious. The region of the mountain beneath the cone presents no difficulties, and that part of the ascent may be performed on donkeys or mules. The view from the top is magnificent. The contrast between the desolate aspect of the interior of the crater, and the smiling prospect which may be seen from its edge, has been well compared to looking out of Tartarus into Paradise. Near Puzzuoli, in the Bay of Baiæ, and not far from Monte Nuovo, stand the ruins of the Temple of Serapis, so interesting to geologists. These remains, consisting chiefly of the shafts of three marble columns, still erect, though with a slight inclination sea-ward, afford distinct proofs, confirmed by other phenomena in the neighbourhood, that, since the beginning of the Christian era, the level of the coast in relation to that of the sea has changed twice--the land having first sunk and been then raised again, each time to the extent of upwards of 20 feet. The evidence of the submergence of the pillars consists mainly of a zone commencing at the height of about 12 feet above their pedestals, and extending 9 feet upwards, in which are numerous perforations, made by a marine bivalve mollusc. The upraising again of the ground on which the temple stands, to nearly its original height, appears to have occurred about the time of the formation of Monte Nuovo. CHAPTER IV. Mount Etna--Its Appearance and Height-Ancient Eruptions-Pindar's Allusion--Virgil's Description--Subordinate Cones and Craters--Caverns--Val del Bove--Formation of Monti Rossi--Eruption of 1852--Whirlwinds--Lava Torrents--Cascades of Lava--Description of Crater --Empedocles--Enceladus--Craters of 1865-Cyclopean Isles--Homer's Legend-Volcanic Origin--Other Basaltic Groups