Page:A Treatise on Geology, volume 2.djvu/231

 CHAP. IX. the encampment of Spartacus; and only obscure tradition or uncertain inference raised the conjecture that this smiling tract was based on subterranean fire. If the passage of Lucretius (vi. 748.) has any reference to Vesuvius, the only symptoms of activity of heat were sulphureous exhalations, such as might rise many centuries after the volcano had sunk to rest, such as now rise in the Solfatara, and have risen, with little difference, for 1600 years! (See Dr. Daubeny on Volcanos, p. 166. first edition.)

The great eruption of A.D. 79 was followed by six others, at long intervals, averaging 164 years, till 1036, when, for the first time, the flowing of lava is mentioned, the previous eruptions being of ashes and lapilli. Three eruptions are on record between 1036 and 1306. Vesuvius has never, since the first outbreak on record, been at rest for so long a period as between 1306 and 1631, between which epochs only one slight revival of action happened in 1500. Throughout this period Etna was in a state of unusual activity, as if the rival craters of Sicily and Campania were connected to the same subterranean channels. Before the eruption of 1631, the crater of Vesuvius was a pasture for cattle, its sides were covered with brushwood, in which wild boars sheltered. The old surface was all blown into the air, and seven streams of lava poured at once from the crater, committing enormous destruction. Since that time the mountain can hardly be said to have been ever tranquil, and the frequency of eruptions appears to have progressively augmented to the present time. In the seventeenth century, the intervals between the outbreaks of Vesuvius are, on an average, twenty years; in the eighteenth, five years; and since 1800, two years.

Etna has experienced, within the reach of history, sufficient variations of volcanic energy to justify the use made of its changes in the Pythagorean philosophy.