ding the formation
of volcanic cones by elevation or upheaval. The works dealing with the
volcanic phenomena of Central and Southern Italy are also written with
the object, in part at least, of illustrating and supporting the same
theoretical views; with these we have to deal in the next chapter.

5. Dr. Charles Daubeny, F.R.S., _Description of Active and Extinct
Volcanoes, of Earthquakes, and of Thermal Springs, with remarks on the
causes of these phenomena, the character of their respective products,
and their influence on the past and present condition of the globe_ (2nd
edition, 1848). In this work the author gives detailed descriptions of
almost all the known volcanic districts of the globe, and defends what
is called "the chemical theory of volcanic action"--a theory at one time
held by Sir Humphrey Davy.

6. Wolfgang Sartorius von Waltershausen, _Der Aetna_. This work possesses
a melancholy interest from the fact that its distinguished author did
not live to see its publication. Von Waltershausen, having spent several
years in making an elaborate survey of Etna, produced an atlas
containing numerous detailed maps, views, and drawings of this mountain
and its surroundings, which were published at Weimar by Engelmann in
1858. A description in MS. to accompany the atlas was also prepared, but
before it was printed, the author died, on the 16th October 1876. The
MS. having been put into the hands of the late Professor Arnold von
Lasaulx by the publisher of the atlas, it was subsequently brought out
under the care of this distinguished petrologist, who was so fully
fitted for an undertaking of this kind.

7. Sir Charles Lyell in his _Principles of Geology_[10] devotes several
chapters to the consideration of volcanic phenomena, in which, being in
harmony with the views of his friend, Poulett Scrope, he combats the
"elevation theory" of Von Buch, as applied to the formation of volcanic
mountains, holding that they are built up of ashes, stones, and scoriae
blown out of the throat of the volcano and piled around the orifice in a
conical form. Together with these materials are sheets of lava extruded
in a molten condition from the sides or throat of the crater itself.

8. Professor J. W. Judd, F.R.S., in his able work entitled, _Volcanoes:
What they are, and what they teach_,[11] has furnished the student of
vulcanicity with a very complete manual of a general character on the
subject. The author, having extensive per