Ch. VIII.J ANTIQUITY OF THE CONE OF ETNA. 
97 
tory of volcanos, we have some difficulty in deciding on the 
relative probability of these hypotheses ; but if we embrace the 
theory of explosions from below, the cavity would not con- 
stitute a crater in the ordinary acceptation of that term, still 
less would it accord with the notion of the so-called ' elevation 
craters.' 
ANTIQUITY OF THE CONE OF ETNA. 
We have stated in a former volume, that confined notions 
'n regard to the quantity of past time, have tended, more 
than any other prepossessions, to retard the progress of 
sound theoretical views in Geology ; the inadequacy of our 
conceptions of the earth's antiquity having cramped the free- 
dom of our speculations in this science, very much in the same 
way as a belief in the existence of a vaulted firmament once 
retarded the progress of astronomy. It was not until Descartes 
assumed the indefinite extent of the celestial spaces, and re- 
moved the supposed boundaries of the universe, that just 
opinions began to be entertained of the relative distances of 
the heavenly bodies ; and until we habituate ourselves to con- 
template the possibility of an indefinite lapse of ages having 
been comprised within each of the more modern periods of the 
arth's history, we shall be in danger of forming most erro- 
eous and partial views in Geology. 
Mode of computing the age of volcanos. —If history had be- 
queathed to us a faithful record of the eruptions of Etna, and 
a hundred other of the principal active volcanos of the globe, 
during the last three thousand years, — if we had an exact 
account of the volume of lava and matter ejected during that 
period, and the times of their production, — we might, perhaps, 
be able to form a correct estimate of the average rate of the 
growth of a volcanic cone. For we might obtain a mean result 
from the comparison of the eruptions of so great a number of 
vents, however irregular might be the development of the 
igneous action in any one of them, if contemplated singly 
during a brief period. 
Vol. III. H 
