360 PACIFIC OCEAN. 
alternating with the beds of lava; and their rarity over those moun- 
tains that are characterized by a crater of boiling lavas. Mount Loa, 
though so extensive, has no cinders over any part of its surface, ex- 
cepting small deposits in a few places: there are none at the very 
summit, where the action has now partially subsided. ‘The various 
eruptions through fissures, sometimes end, as the heat diminishes in 
these fissures, by making small cones of cinders; but these are not to 
be compared with those “showers of ashes” which proceed from a 
central crater, and sometimes cover the vicinity of volcanic regions for 
miles to a depth of many yards. 
A fourth consequence is the more convulsive character of the 
volcano of the Vesuvian stamp; for an ingress of waters below leads 
to more violent struggles between the escaping vapour and the semi- 
fluid lavas: yet this has its exceptions. Again, overflowings at sum- 
mit may be more frequent where the lavas are very liquid, and fissure 
eruptions where less so. But this, again, has many exceptions; for 
Mount Loa itself, at the present time, is ejecting its lavas through 
fissures. 
This leads us to speak of the influence of fissure eruptions on the 
forms of a volcanic cone. 
Influence of fissure eruptions.—It has been remarked that the more 
fluid boiling lavas, (of which those of Kilauea may be taken as a type, 
though the pools are but small compared with what the past may have 
witnessed,) may be so ejected, in extensive summit floods, uninter- 
ruptedly or with short intermissions for a period of time, as to flow 
down slopes of any angle of declivity. But there is a limit to the 
steepness of a cone of the kind supposed, in the weakness of the rocks 
which constitute it. ‘The elevation of the mountain increases the 
force required to raise the lavas to the summit. If, then, by any of 
the processes pointed out, the summit becomes raised beyond the 
ability of the mountain’s sides to sustain the consequent pressure, 
eruptions will break through the lower slopes instead of at summit; 
and the new layers, as well as the interlocking dike, (which some- 
times sends laterally interpolating layers,) will strengthen the cone 
again, and prepare it for other summit eruptions.* ‘The slope of a cone 
* See Scrope on Volcanoes, p. 156, Since writing the above, I have observed that he 
expresses the same opinion, as follows: ‘ Dikes being usually formed in a vertical direc- 
tion, and therefore transversely to the lateral beds or currents of lava, communicate a 
vast accession of strength to the structure of the mountain, acting as ties to the latter, 
which may be likened to the main beams of an edifice.” Lateral eruptions terd to for- 
