ands
ejected from Hecla have been wafted thither by the winds.

Besides the continuous spaces of subterranean disturbance, of which we
have merely sketched the outline, there are other disconnected volcanic
groups, of which several will be mentioned hereafter.

_Lines of active and extinct Volcanoes not to be confounded._--We must
always be careful to distinguish between lines of extinct and active
volcanoes, even where they appear to run in the same direction; for
ancient and modern systems may interfere with each other. Already,
indeed, we have proof that this is the case; so that it is not by
geographical position, but by reference to the species of organic beings
alone, whether aquatic or terrestrial, whose remains occur in beds
interstratified with lavas, that we can clearly distinguish the relative
age of volcanoes of which no eruptions are recorded. Had Southern Italy
been known to civilized nations for as short a period as America, we
should have had no record of eruptions in Ischia; yet we might have
assured ourselves that the lavas of that isle had flowed since the
Mediterranean was inhabited by the species of testacea now living in the
Neapolitan seas. With this assurance, it would not have been rash to
include the numerous vents of that island in the modern volcanic group
of Campania.

On similar grounds we may infer, without much hesitation, that the
eruptions of Etna, and the modern earthquakes of Calabria, are a
continuation of that action which, at a somewhat earlier period,
produced the submarine lavas of the Val di Noto in Sicily. But on the
other hand, the lavas of the Euganean hills and the Vicentin, although
not wholly beyond the range of earthquakes in Northern Italy, must not
be confounded with any existing volcanic system; for when they flowed,
the seas were inhabited by animals almost all of them distinct from
those now known to live, whether in the Mediterranean or other parts of
the globe.

CHAPTER XXIII.

VOLCANIC DISTRICT OF NAPLES.

History of the volcanic eruptions in the district round
Naples--Early convulsions in the island of Ischia--Numerous cones
thrown up there--Lake Avernus--The Solfatara--Renewal of the
eruptions of Vesuvius, A.D. 79--Pliny's description of the
phenomena--His silence respecting the destruction of Herculaneum and
Pompeii--Subsequent history of Vesuvius--Lava discharged in Ischia
in 1302--Pause in the eruptions of Vesuvius--M