130 Mr. G. P. Scrope on the Formation of Craters, 
I considered this law to be without exception; attributing 
the differences in figure and structure apparent among volcanic 
cones to the greater or less number and violence of the erup- 
tions to which they were owing,—some being the product of a 
single eruption, others of a vast number, often repeated through 
a series of ages,—to differences in the position of the orifices of 
discharge, whether from the summit of the cone, or its base, or 
any intermediate points,—and whether from under water, or in 
the air,—to the varying mineral character of the products,— 
and to the influences of subsequent degradation. 
At the same time I remarked that the earthquakes which 
always more or less accompany volcanic eruptions render pro- 
bable a certain amount of elevation in mass of the pre-existing 
superficial rocks ; and moreover that the rents they cause in the 
solid substance of the cone of a volcano in repeated eruption, 
into many of which rents liquid lava will be injected from the 
column rising in the central chimney, and cool down afterwards 
into more or less vertical dykes of solid rock, must have added 
considerably to the bulk and elevation of such a mountain, by a 
sort of inward distension. 
This was no closet-theory,—because, as respects the cone and 
erater of Vesuvius at least, I had the advantage, in the years 
1818, 1819, and 1820, of watching with my own eyes the out- 
ward growth of that cone, through a series of almost continual 
eruptions of a comparatively tranquil character, which during 
those years added considerably to its height and bulk by ex- 
ternal accretions of ejected scoria and lava-currents. These 
last, the lava-streams, issued from small cones and craters formed 
upon the solid platform which then composed the summit of the 
great cone, and dribbled slowly down its slopes, consolidating so 
rapidly there as in few instances to reach the base of the cone 
at all; although night after night they were to be seen flowing 
from the summit in streams of considerable breadth and bulk, 
and glowing with a bright light on its steep sides. 
Afterwards, in the latter part of the year 1822, I had seen 
the upper portion of this solid cone blown into the air (by which 
it lost a full third of its height), and a crater of vast dimensions 
drilled through its axis by continuous eruptive explosions of 
twenty days’ duration. 
I had previously made a close examination of the cones and 
craters of Etna, the Phlegrzan Fields, the Lipari Isles, Central 
France, and the Rhine district ; and their appearances accorded 
so completely with the supposition of an analogous mode of 
formation in their instances, that, upon the principle of ex- 
plaining the unknown by the known, it seemed impossible, or 
at least unnecessary, to imagine any other origin for them. 
