File:The Quarterly journal of the Geological Society of London (12981371004).jpg

1858..
ABICH ^ETNA.
121
I found the same beds of lava laid open to the sight in the interior
of the neighbouring CistereUa. These beds rise in the vicinity of
the Montagnuola, and suddenly appear lifted up in order to form
the crater-like wall (fig. 5 a) which half surrounds the cone of the
Montagnuola, comparable (geologically) to Somma with regard to
Vesuvius, the central cone of eruption (c).
All those lava-currents which the subsidence of the CistereUa cut
through, following the same iaclination as the Piano del Lago in its
beginning from the Torre del Filosofo to the Montagnuola, show a
peculiar resemblance to the modem currents of Etna, partaking
of the magnetic property in a very high degree. By this quality all
those superior lavas of the Piano del Lago, as well as the upper beds
of the Cima della Yalle on the northern side, differ essentially from
the older beds, of more trachytic composition, which form the veri-
table central body of the mountain. I may remark that I made a
similar observation with regard to the very notable petrographical
difference between the older rocks of Ararat and the black doleritic
lavas covering the upper part of the burst mountain. I believe these
physical differences of the rocks belonging to one and the same
system to be in intimate dependence on a notable change in the
mode of formation governing the whole system.
Fig. 6. — Beds and DyTces on the slope between Giannicola atid
Musarra.
Direction of Dykes N.N.E.— S.S.W.
^^'yptti
'^^ylffy'r^'^
Fig. 6 gives an exact representation of what I saw higher up
than the great masses of the Giannicola or Musarra, illustrating the
almost horizontal position of the slightly curved beds, intersected by
dykes running in the above-mentioned direction of N.N.E.-S.S.W.
It must not be forgotten that this part of the slope corresponds to
the middle region of the interior body of the mountain (fig. 4 a, 6,
and fig. 1 CI), and that, in my opinion, both to the left and right of
those regions, the effect of original subsidence was still sensible
enough to prescribe the way that aU the future currents of doleritic
lava, poured out from the modem excentric volcano, should take down