318 
THE UKOI.OGIST. 
Bronte, 
Tlio cliaiige of dip in the iiifevior, medial, and uppermost beds of 
the Giannicohi, and the convergence of the greenstone-dikes towards 
the Ti'ifogHetto cent-i'e are inexpHcable by the " crater of elevation 
theory," but become plainly intelHgible on the principle of a double 
axis of eruption. Then, in the lower beds we perceive the lava 
streams flowing away from the old cone of eruption, and mingling in 
the intercoUine space with the ciir- 
i-ents ejected from the Mongibello 
crater, until, in the levelling pro- 
cess thus being efi'ected, the hori- 
zontality of the succeeding lavas of 
the middle portion occiirs, and after 
this the streams from the existing 
cone, flowing down in gi'eater force 
than those from Trifoglietto, gi'a- 
dually ovei'flowed and extinguished 
it — the lavas which thus flowed 
down presenting, of course, the oppo- 
site dip to those below, or towards 
the centi-e of Trifoglietto. 
The points of argument next 
brought forward are the want of 
continuity in the older and modern 
parts of Etna, and the truncation of 
its summit : these are followed by a 
discussion on the hypothesis of up- 
heaval by injection. Geologists who 
assume that lava cannot congeal into 
continuous stony layers on slopes 
exceeding five or six degrees, must 
unavoidably embrace the conclusion 
that nine-tenths of the lava-beds 
which constitute the nucleus of Etna, 
and not a few also which overlie that 
nucleus unconformably, were brought 
into their present position by me- 
chanical forces, after the materials 
of the mountain had accumulated 
on nearly level gi-ound. 
M. Elie de Beaumont has sug- 
gested that when new fissui-es are 
produced during an eruption, radi- 
ating from the centre, and traversing 
the nucleus of the mountain, the lava 
rising simultaneously to the rim of the highest crater would 
fill such fissures, causing a tumefaction and distension of the whole 
mass, and that thus a greater or less upheaval of the cone might 
result. There is no actual data, however, for deciding that the 
dyke-making process thus appealed to is usually attended by up- 
I Zoccalaro . 
Ziiffarana 
