= 
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. 
is was no closet-theory,—because as respects the cone and 
crater 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 exter- 
nal accretions of ejected scoria and lava-currents. ese | 
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 
Ria! 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 
