and the Nature of the Liquidity of Lavas. 131 
“ Elevation,’ “ Denudation,” and “ Engulfment” Theories of 
Crater-formation.—It was, therefore, with no small surprise that 
I have since found this simple and natural mode of production 
denied to all cones and craters—including those of Vesuvius 
itself; and an hypothesis substituted of their originating in 
some sudden elevation of previously horizontal beds around a 
centre,—not (it would seem) of eruption, but of maximum ele- 
vation. I allude, of course, to the “ Elevation-crater theory” 
of MM. Von Buch and Elie de Beaumont. 
Sir Charles Lyell, M. Constant Prevost, and others, have 
amply refuted this unphilosophical theory; which, however, 
still appears to hold its ground to some extent on the Continent, 
through the prestige of the great names attached to it. It may, 
therefore, not be wholly useless to adduce some additional proofs 
of its unwarrantable character. But I must first be permitted 
to remark, that even Sir Charles Lyell, while supporting the 
view indicated above, of the generally eruptive origin of volcanic 
cones, has had recourse, in the case of some craters, to another 
agency, the influence of which I am induced to think he over- 
rates ;—I mean the excavating power of the sea in forming what 
he calls “craters of denudation.” This phrase, I think, he first 
employed in a paper on the subject read before this Society in 
December 1849. It is not repeated in the latest edition of his 
“Principles,” and I imagine, therefore, that he is no longer 
desirous of maintaining its propriety. 
I by no means doubt, that in the case of craters formed be- 
neath the sea, or in such close vicinity to it as to allow its waves 
and currents to enter and sweep round their interiors, these 
circumstances must have considerably modified the result. In 
the former case, that of subaqueous eruption, the resistance of 
the water above the vent would probably tend to throw off the 
ejected materials over a wider area. And thus, perhaps, we may 
account for the vast horizontal dimensions of the great crateri- 
form basins of Italy,—Bolsena, Bracciano, Albano, and others, 
evidently of submarine origin. In the latter case, that of sub- 
aérial craters to which the sea has had access through some 
lateral opening, no doubt great degradation of their internal 
slopes and cliffs, as well as of the outside, will have often taken 
place. Many, indeed, will have had their enclosure reduced to 
a mere skeleton, like Santorini. Some, like Graham’s Isle, have 
been entirely swept away. But the question being as to the 
origin of these crateriform hollows, not as to the cause of any 
subsequent alteration of figure, this, I believe, may in every 
instance, without exception, be most reasonably referred to vol- 
canic explosive eruptions. And, therefore, the employment of 
such a phrase as “craters of denudation,” in contradistinction 
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