102 
NEWER PLIOCENE PERIOD. 
[Ch. VIII. 
trees and herbage, which protect them from waste ; and in 
regard to the newer ones, such is the porosity of their compo- 
nent materials, that the rain which falls upon them is instantly 
absorbed, and, for the same reason that the rivers on Etna have 
a subterranean course, there are none descending the sides of 
the minor cones. 
No sensible alteration has been observed in the form of 
these cones since the earliest periods of which there are memo- 
rials ; and we see no reason for anticipating, that in the course 
of the next ten thousand or twenty thousand years they will 
undergo any great alteration in their appearance, unless they 
should be shattered by earthquakes, or covered by volcanic 
ejections. 
We shall afterwards point out, that, in other parts of Europe,, 
similar loose cones of scorise, which we believe to be of higher 
antiquity than the whole mass of Etna, stand uninjured at 
inferior elevations above the level of the sea. 
