Judd, that leucite easily changes into
felspar, and that some ancient igneous rocks which now contain felspar
were originally leucitic, does not seem to be borne out by the above
facts. In such cases the felspar crystals ought to retain the forms of
leucite. See _Volcanoes_, 4th edition, p. 268.

CHAPTER III.

THE LIPARI ISLANDS, STROMBOLI.

(_a._) A brief account of this remarkable group of volcanic islands must
here be given, inasmuch as they seem to be representatives of a stage of
volcanic action in which the igneous forces are gradually losing their
energy. According to Daubeny, the volcanic action in these islands seems
to be developed along two lines, nearly at right angles to each other,
one parallel to that of the Apennines, beginning with Stromboli,
intersecting Panaria, Lipari, and Vulcano; the other extending from
Panaria to Salina, Alicudi, and Felicudi, and again visible in the
volcanic products which make their appearance at Ustica. (See Map, Fig.
11.) The islands lie between the north coast of Sicily and that of
Italy, and from their position seem to connect Etna with Vesuvius; but
this is very problematical, as would appear from the difference of their
lavas. The principal islands are those of Stromboli, Panaria, Lipari,
Vulcano, Salina, Felicudi, and Alicudi. These three last are extinct or
dormant, but Salina contains a crater, rising, according to Daubeny, not
less than 3500 feet above the sea.[1] Vulcano (referred to by Strabo
under the name of Hiera) consists of a crater which constantly emits
large quantities of sulphurous vapours, but was in a state of activity
in the year 1786, when, after frequent earthquake shocks and
subterranean noises, it vomited forth during fifteen days showers of
sand, together with clouds of smoke and flame, altering materially the
shape of the crater from which they proceeded.

[Illustration: LIPARI ISLANDS.
Fig. 11.--Map to show the position of these islands, showing the
branching lines of volcanic action--one parallel to that of the
Apennines, the other stretching westwards at right angles thereto.]

The islands of Lipari are formed of beds of tuff, penetrated by numerous
dykes of lava, from which uprise two or three craters, formed of pumice
and obsidian passing into trachyte. Volcanic operations might have here
been said to be extinct, were it not that their continuance is
manifested by the existence of hot springs and "stufes," or vapour
baths, at St