ents of this kind
are described by Mr. Dana as having been caused, during a late eruption,
in one of the volcanic domes of the Sandwich Islands. They remained open
at various heights on the slopes of the great cone, running in different
directions, and demonstrate the possibility of future junctions of
slightly inclined lava-streams with perpendicular walls of lava.

To me, therefore, it appears far more easy to explain the uniform
thickness and parallelism of so many lavas and beds of fragmentary
matter seen in the Val del Bove, by supposing them to have issued
successively out of one or more higher vents near the summit of a great
dome, than to imagine them to have proceeded from lateral dikes or rents
opening in a level plain. In the Sandwich Islands, we have examples of
volcanic domes 15,000 feet high, produced by successive outpourings from
vents at or near the summit. One of these, Mount Loa, has a slope in all
directions of 6 degrees 30 minutes; another, Mount Kea, a mean
inclination of 7 degrees 46 minutes. That their lavas may occasionally
consolidate on slopes of 25 degrees, and even more, and still preserve
considerable solidity of texture, has been already stated; see above, p.
383.

We know not how large a quantity of modern lava may have been poured
into the bottom of the Val del Bove, yet we perceive that eruptions
breaking forth near the centre of Etna have already made some progress
in filling up this great hollow. Even within the memory of persons now
living, the rocks of Musara and Capra have, as before stated, lost much
of their height and picturesque grandeur by the piling up of recent
lavas round their base (see fig. 51, p. 408), and the great chasm has
intercepted many streams which would otherwise have deluged the fertile
region below, as has happened on the side of Catania. The volcanic
forces are now laboring, therefore, to repair the breach which
subsidence has caused on one side of the great cone; and unless their
energy should decline, or a new sinking take place, they may in time
efface this inequality. In that event, the restored portion will always
be unconformable to the more ancient part, yet it will consist, like it,
of alternating beds of lava, scoriae;, and conglomerates, which, with all
their irregularities, will have a general slope from the centre and
summit of Etna towards the sea.

I shall conclude, then, by remarking that I conceive the general
inclination of the alternating