250 Natural History of Volcanos and Earthquakes. 
small quantities of these only will be raised upwards, for the sur- 
face of the melted matters will soon sink below the opening of the 
rent at D, and steam will rise. Thus the elevation of a column 
of lava to a considerable height by a column of steam will take 
place. But if the lower opening of the rent CD descends more 
or less below the surface of the melted matters, considerable quan- 
tities of these will rise into it before this surface sinks below the 
opening. The same may take place if between the opening of 
the rent CD and the other rents, (those down which water flows 
from the surface,) ridges of solid rock reach downwards from the 
solid crust into the fluid mass. ) 
Such ridges may be viewed as occasioned by gradual solidifica- 
tion of the fluid mass from above downwards, for it is well known 
that melted matters, if they crystallize by cooling, exhibit on 
their under surface considerable inequalities ; and the consolida- 
tion of the melted matters in the interior of the earth is assuredly 
produced by crystallization. 
There is another circumstance which may cause a continuation 
of the rent CD into the melted matters. After the rising of the 
lava and steam in this rent, the walls of it are cooled by the for- 
mation of steam, and by the atmospheric air having a ready access 
to the empty channel. Therefore these walls may gradually in- 
crease by the solidifying of the melted matters; nay, the rent 
may be entirely solidified and obstructed, so that it can only now 
be re-opened by the force of ‘steam previous to a new eruption 
taking place. If even immense quantities of lava are ejected by 
the steam, yet the level of the melted matters in the interior may 
be but slightly changed, for in the same manner, as all seas on 
the surface of the earth communicate together, so the melted 
matter in the interior does the same. However, more or less time 
may elapse, before the melted matter which has sunk at one place 
in consequence of ejection, can regain its former level by the 
afflux of other melted matters from a distance. Therefore the 
repose and activity of a volcano, besides depending on the intel 
ruption and renewal of the supply of water to the volcanic focus, 
may also proceed from the alternate obstruction and re-opening of 
the lava channel by the melted matters. In the latter case m 
the state of rest, exhalations of steam will take place, inasmuch 
as water penetrates continually to the volcanic focus. 
