I.YELL — ON CRATERS OF ELEVATION. 
.317 
cascaded into the Cava Grande. The lava there consolidated into 
a central stony mass on an inclination of 35 degrees. 
During the eruption of 1852, the lava cascaded more than once 
over the steep precipice of the Salto della Giumenta, more than 400 
feet high, which intervenes between the hills of Calanna and Zocco- 
laro, and at this spot measurements of inclined stony lava, at angles 
varying from 35 to 45 degrees, were taken with the clinometer, and 
in one case even 50 degrees were ascertained. 
The next remarkable instance given by Sir Charles is that of a 
steeply inclined continuous sheet of lava, 5,000 feet higher than the 
last mentioned, near the top of the great precipice of the Val del 
Bove, not far below the Cisterna. Thirty, thirty-five, and even 
thirty-eight degrees are there attained. 
Other similar instances are given, and quite enough is done even 
in this first part of the paper to prove the essential point, that lavas 
can be consolidated on slopes of considerable steepness. 
The second part of the paper enters into the subject of the struc- 
ture and position of the older volcanic rocks of Mount Etna, as seen 
in the Val del Bove, as also on the proofs of a double axis of elevation ; 
and by these means the " crater of elevation-h;)'pothesis" is again re- 
futed, and the opinions of M. Elie de Beaumont, both as to theory 
and many important matters of fact, are controverted. 
From a point in the Val del Bove called the Piano di Trifoglietto, 
midway between the Serra Giannicola and the hill of Zoccolaro, the 
beds of lava radiate in all directions (shown by the arrows in the 
map of the region of Etna and the Val del Bove at page 321) ; and 
from this quaquaversal dip Sir Charles assumes this point (T in the 
map referred to) to have been an ancient centre of ei'uption dis- 
tinct from the present cone of Etna, and that Etna had therefore at 
one pei'iod a double axis, or two points of permanent eruption, 
■with an intermediate valley, or intercolline space, between the two 
cones, which became gradually filled up by lavas and fragmentary 
matter. For the sake of distinguishing these, the extinct axis is 
termed the axis of Trifoglietto, and the present centre of activity 
the axis of Mongibello, — the modem Sicilian appellation of Mount 
Etna. 
The former existence of an old centre of eruption in the Piano del 
Trifoglietto had been inferred independently by S. Von Walters- 
hausen from the convergence towards a middle point in that area of 
thirteen or nioi'e dikes of greenstone, one of them of enormous 
dimensions, visible in the surrounding escarpments. The same 
geologist also observed in the gigantic buttresses of the cliffs, 2,000 
and 3,000 feet high, between the Giannicola and the Rocca del Corvo, 
that while in the lower part of the precipices the lava-beds dip at 
high angles inward towards the escarpment, or away from the Val 
del Bove, those in the middle portion become horizontal, and those 
nearer the summit dip towards the Val del Bove, as if they were 
sloping away fi-om some other point near the present great centre of 
Mongibello. 
VOL. n. B B 
