LYELL ON CRATRRS OF ELEVATION. 
319 
heaval. On some occasions, as proved by the observations of 
Scacchi, Schmidt, and others, it indicates a collapse, or partial 
subsidence of the flank of the cone. That an uplifting of the 
incumbent mass must accompany the injection of liquid matter 
through fissures which are not perpendicular (Sir Charles notices 
some such fissures inclined at an angle of 75 degrees to the horizon), 
no one can deny ; and therefore, while rejecting the theory of a 
single terminal catastrophe, or any paroxysmal development of the 
elevating force, we may fairly ascribe no small influence to those dis- 
turbing operations, by which such innumerable dikes have been 
formed near the principal centres of eruption. But the great points 
to be kept in view are whether the quaquaversal arrangement of the 
beds in cones like Etna, and the high inclination of the lavas and 
scorite are not mainly, and in many cases exclusively, due to eruption ; 
and whether the upheaving power, granting its intervention, does not 
play a very subordinate part. Whether, in fact, it is more probable 
that, following the proposition of M. de Beaumont, a large portion of 
the lava-beds now dipping at an angle of 28 degi-ees had an original 
slope of only 5 or 6 degi'ees, the remaining 20 degrees being due to 
upheaval ; or whether the converse may not be more truly assumed, 
that the 23 degTees may have been the original average inclination, 
and that the additional 5 or 6 degrees may have been gained by sub- 
sequent elevatory movements — in other words, that a fifth part alone 
of the whole dip may be ascribable to elevation. 
The supposed ft-equent injection of lava in beds conformable to 
tufaceous strata, and to which Waltershausen attributes much of 
the upheaval of the mass of Etna, is then subjected to a similar 
sciTitiny and carefully considered. 
" Had the lavas," writes Sir Charles, " which slope away from the 
ancient centres of Trifoglietto and Mongibello been in great part in- 
jected between the tufl's, we should have fi'equently seen them pene- 
trating through the dikes. But though these last are of so many 
ditferent ages, and are continually seen to traverse the alternating 
lavas and tuflfs, I could discover no instance of such dikes being in 
their turn traversed by lavas. It may be asked, how in the escarp- 
ments of the Val del Bove can we distinguish a lava which has flowed 
originally at the sui'face from a tabular mass of rock which may have 
been forced, when in a melted state, into a fissure between two layers 
of tufi' ? I reply, that the lava has almost invariably its upper and 
lower scoria?, and sometimes immediately beneath the latter a layer 
of burnt tufi", such as I saw in the Balzo di Trifoglietto, at various 
heights in Monte Zoccalaro, and in the valley of St. Giacomo, where I 
traced a red tuff for a great distance, underlying the most powerful 
of the older lavas. Such red layers are never in direct contact vnth. 
the central and overlying crystalline stony layer, for there intervenes 
always a fundamental stratum of fragmentary and scoriaceous matter 
between the stony bed and the bui-nt tuff below. On the other hand, 
I looked in vain for an instance of some powerful sheet of lava which 
had one of these brick-red clays aboue as well as below it. Had the 
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