CHAPTER V.

EUROPEAN EXTINCT OR DORMANT VOLCANOES.

We are naturally led on from a consideration of the active volcanoes of
Europe to that of volcanoes which are either dormant or extinct in the
same region. Such are to be found in Italy, Central France, both banks
of the Rhine and Moselle, the Westerwald, Vogelsgebirge, and other
districts of Germany; in Hungary, Styria, and the borders of the Grecian
archipelago. But the subject is too large to be treated here in detail;
and I propose to confine my observations to some selected cases which
are to be found in Southern Italy, Central France, and the Rhenish
districts, where the volcanic features are of so recent an age as to
preserve their outward form and structure almost intact.

(_a._) _Southern Italy._--Extinct volcanoes and volcanic rocks occupy
considerable tracts between the western flanks of the Apennines and the
Mediterranean coast in the Neapolitan and Roman States, forming the
remarkable group of the Phlegraean fields (Campi Phlegraei), with the
adjoining islands of Ischia, Procida, Nisida, Vandolena, Ponza, and
Palmarola; at Melfi and Avellino. All the region around Rome extending
along the western slopes of the Apennines from Velletri to Orvieto,
together with Mount Annato in Tuscany, is formed of volcanic material,
and the same may be said of a large part of the island of Sardinia. From
these districts I shall select some points which seem to be of special
interest.

_Monte Nuovo and the Phlegraean Fields._--The tract of which this
celebrated district forms a part lies as it were in a bay of the
Apennine limestone of Jurassic age. The floor of this bay is composed of
puzzolana, a name given to beds of volcanic tuff of great thickness, and
rising into considerable hills in the vicinity of the city of Naples,
such as that of St. Elmo. Its composition is peculiar, as it is chiefly
formed of small pieces of pumice, obsidian, and trachyte, in beds
alternating with loam, ferriferous sand, and fragments of limestone. It
is evidently of marine formation, as Sir William Hamilton, Professor
Pilla, and others have detected sea-shells therein, of the genera
_Ostraea_, _Cardium_, _Pecten_ and _Pectunculus_, _Buccinum_, etc. It is
generally of a greyish colour, and sometimes sufficiently firm to be
used as a building stone. The Roman Campagna is largely formed of
similar materials, which were deposited at a time when the districts in
question were submerged, and m