Ch. IX.] 
SUBTERRANEAN LAVAS, 
the gradual elevation of a tract of land nearly as large as 
Iceland. We say nearly, because the lava which cooled down 
beneath the surface, and under considerable pressure, would 
be more compact than the same when poured out in the open 
air, or in a sea of moderate depths or shot up into the atmo- 
sphere by the explosive force of elastic vapours, and thus con- 
verted into sand and scorias. 
According to this theory, we must suppose the action of the 
upheaving power to be intermittent, and, like ordinary volcanic 
eruptions, to be reiterated again and again in the same region, 
at unequal intervals of time and with unequal degrees of force. 
If we follow this train of induction, which appears so easy 
and natural, to what important conclusions are we led ! The 
reader will bear in mind that the tertiary strata have attained 
in the central parts of Sicily, as at Castrogiovanni, for example, 
an elevation of about three thousand feet above the level 
of the sea, and a height of from fifty to two thousand feet in 
different parts of the Val di Noto. In this country, therefore, 
we must suppose a solid support of igneous rock to have been 
successively introduced into part of the earth's crust immedi- 
ately subjacent, equal in volume to the upraised tract, and this 
generation of subterranean rock must have taken place during 
the latter part of the newer Pliocene period. The dimensions 
of the Etnean cone shrink into insignificance, in comparison to 
the volume of this subterranean lava: and, however stao-P-er- 
ing the inference might at first appear, that the oldest founda- 
tions of Etna were laid subsequently to the period when the 
Mediterranean became inhabited by the living species of testacea 
and zoophytes, yet we may be reconciled to such conclusions, 
when we find incontestable proofs of still greater revolutions 
beneath the surface within the same modern period. 
Probable structure of the recent subterranean rocks of fusion. 
— Let us now inquire what form these unerupted newer Plio- 
cene lavas of Sicily have assumed ? For reasons already ex- 
plained, we may infer that they cannot have been converted 
