rchipelago as composed of tuff which has
evidently flowed like mud, and yet on consolidating has preserved an
inclination of twenty and even thirty degrees. The tuff does not fold in
continuous sheets round the hills as would have happened if they had
been formed by the upheaval of horizontal layers. The author describes
the composition of the tuff as very similar to that of Monte Nuovo, and
the high angles at which the beds slope, both those which have flowed
and those which have fallen in the form of ashes, entirely removes the
difficulty supposed by M. Dufranoy to exist in regard to the slope of
Monte Nuovo, where it exceeds an angle of 18 degrees. to 20
degrees.[512] Mr. Dana, also, in his account of the Sandwich
Islands,[513] shows that in the "cinder cones" of that region, the
strata have an original inclination of between 35 degrees and 40
degrees, while in the "tufa cones" formed near the sea, the beds slope
at about an angle of 30 degrees. The same naturalist also observed in
the Samoan or Navigator Islands in Polynesia, that fragments of fresh
coral had been thrown up together with volcanic matter to the height of
200 feet above the level of the sea in cones of tufa.[514]

I shall again revert to the doctrine of the origin of volcanic cones by
upheaval, when speaking of Vesuvius, Etna, and Santorin, and shall now
merely add, that, in 1538, the whole coast, from Monte Nuovo to beyond
Puzzuoli, was upraised to the height of many feet above the bed of the
Mediterranean, and has since retained the greater part of the elevation
then acquired. The proofs of these remarkable changes of level will be
considered at length when the phenomena of the temple of Serapis are
described.[515]

_Volcanoes of the Phlegraean Fields._--Immediately adjoining Monte Nuovo
is the larger volcanic cone of Monte Barbaro (2, fig. 43, p. 367), the
"Gaurus inanis" of Juvenal--an appellation given to it probably from its
deep circular crater, which is about a mile in diameter. Large as is
this cone, it was probably produced by a single eruption; and it does
not, perhaps, exceed in magnitude some of the largest of those formed in
Ischia, within the historical era. It is composed chiefly of indurated
tufa like Monte Nuovo, stratified conformably to its conical surface.
This hill was once very celebrated for its wines, and is still covered
with vineyards; but when the vine is not in leaf it has a sterile
appearance, and, late in the year, when