XIV 
AREA OF VOLCANIC ERUPTION 
The space, from under which volcanic matter on the 20th 
was actually erupted, is 720 miles in one line, and 400 miles 
in another line at right angles to the first; hence, in all proba¬ 
bility, a subterranean lake of lava is here stretched out, of 
nearly double the area of the Black Sea. From the intimate 
and complicated manner in which the elevatory and eruptive 
forces were shown to be connected during this train of phe¬ 
nomena, we may confidently come to the conclusion that the 
forces which slowly and by little starts uplift continents, and 
those which at successive periods pour forth volcanic matter 
from open orifices, are identical. From many reasons, I believe 
that the frequent quakings of the earth on this line of coast 
are caused by the rending of the strata, necessarily consequent 
on the tension of the land when upraised, and their injection 
by fluidified rock. This rending and injection would, if repeated 
often enough (and we know that earthquakes repeatedly affect 
the same areas in the same manner), form a chain of hills ;— 
and the linear island of St Mary, which was upraised thrice 
the height of the neighbouring country, seems to be undergoing 
this process. I believe that the solid axis of a mountain differs 
in its manner of formation from a volcanic hill, only in the 
molten stone having been repeatedly injected, instead of 
having been repeatedly ejected. Moreover, I believe that it 
is impossible to explain the structure of great mountain- 
chains, such as that of the Cordillera, where the strata, 
capping the injected axis of plutonic rock, have been thrown 
on their edges along several parallel and neighbouring lines 
of elevation, except on this view of the rock of the axis having 
been repeatedly injected, after intervals sufficiently long to 
allow the upper parts or wedges to cool and become solid ; 
—for if the strata had been thrown into their present highly- 
inclined, vertical, and even inverted positions, by a single blow, 
the very bowels of the earth would have gushed out ; and 
instead of beholding abrupt mountain-axes of rock solidified 
under great pressure, deluges of lava would have flowed out at 
innumerable points on every line of elevation. 1 
1 For a full account of the volcanic phenomena which accompanied the earth¬ 
quake of the 20th, and for the conclusions deducible from them, I must refer to 
Volume V. of the Geological Transactions. 
