The accompanying drawings made by Sir William Hamilton enable us to understand the nature of the changes which have been continually taking place at the summit of Vesuvius. The drawing [fig. 14] shows the appearance presented by the crater in the year 1756.
Fig. 15.—The Summit of Vesuvius in 1767. (From an original drawing.
VESUVIUS IN MODERN TIMES.
At this time we see that inside the crater a series of cones had been built up one within the other from which lava issued, filling the bottom of the crater and finding its way through a breach in its walls, down the side of the cone. It is evident that the ejected materials falling on the sides of the innermost cone would tend to enlarge the latter till its sides became confluent with the cone surrounding it, and if this action went on long enough, the crater would be entirely filled up and a perfect cone with only a small aperture at the top would be produced. But from time to time, grand and paroxysmal outbursts have occurred at Vesuvius, which have truncated the cone, and sometimes formed great, cup-shaped cavities, reaching almost to its base, like that shown in [fig. 13].
In 1767 the crater of Vesuvius, as shown in [fig. 15], contained a single small cone in a state of constant spasmodic outburst, like that of Stromboli.
Fig. 16.—Summit of Vesuvius in 1848.
In 1843, we find that the crater of Vesuvius contained three such small cones arranged in a line along its bottom as depicted in [fig. 16].
These drawings of the summit of Vesuvius give a fair notion of the changes which have been continually going on there during the whole of the historical period. Ever and anon a grand outburst, like that of 1822, has produced a vast and deep crater such as is represented in [fig. 13], and then a long continuance of quiet and regular ejections has built up within the crater small cones like those shown in figs. [14], [15] and [16], till at last the great crater has been completely filled up, and the cone reconstructed.