multitude of facts which point to that conclusion."[726] And when we
reflect on the dates of the principal oscillations of level, and the
volcanic history of the country before described (chap. 23), we seem to
discover a connection between each era of upheaval and a local
development of volcanic heat, and again between each era of depression
and the local quiescence or dormant condition of the subterranean
igneous causes. Thus for example, before the Christian era, when so many
vents were in frequent eruption in Ischia, and when Avernus and other
points in the Phlegraean Fields were celebrated for their volcanic aspect
and character, the ground on which the temple stood was several feet
above water. Vesuvius was then regarded as a spent volcano; but when,
after the Christian era, the fires of that mountain were rekindled,
scarcely a single outburst was ever witnessed in Ischia, or around the
Bay of Baiae. Then the temple was sinking. Vesuvius, at a subsequent
period, became nearly dormant for five centuries preceding the great
outbreak of 1631 (see p. 374), and in that interval the Solfatara was in
eruption A. D. 1198, Ischia in 1302, and Monte Nuovo was formed in 1538.
Then the foundations on which the temple stood were rising again.
Lastly, Vesuvius once more became a most active vent, and has been so
ever since, and during the same lapse of time the area of the temple, so
far as we know any thing of its history, has been subsiding.

These phenomena would agree well with the hypothesis, that when the
subterranean heat is on the increase, and when lava is forming without
obtaining an easy vent, like that afforded by a great habitual chimney,
such as Vesuvius, the incumbent surface is uplifted; but when the heated
rocks below are cooling and contracting, and sheets of lava are slowly
consolidating and diminishing in volume, then the incumbent land
subsides.

Signor Niccolini, when he ascertained in 1838 that the relative levels
of the floor of the temple and of the sea were slowly changing from year
to year, embraced the opinion that it was the sea which was rising. But
Signor Capocci successfully controverted this view, appealing to many
appearances which attest the local character of the movements of the
adjoining country, besides the historical fact that in 1538, when the
sea retired permanently 200 yards from the ancient shore at Puzzuoli,
there was no simultaneous retreat of the waters from Naples,
Castelamare, a