VOLCANIC ACTION, HAWAII 223 
the rising of the molten material, and the overflowings. The scoria 
is the froth of the surface still more inflated, like the scum on the sur- 
face of a boiling syrup. 
To compare Kilauea with other craters, we must keep in mind this 
important point, proved by the absence of cinders in the crater, and 
the free ebullition there, that the lavas are remarkably liquid, while 
those of other craters are comparatively viscid. The ejections of the 
great lake of Kilauea are 60 feet in height, while those of Vesuvius 
during an eruption may be 10,000 feet; and this, though not a direct 
measure of their relative liquidity, is a consequence of it. With this 
principle in view, we may translate the language of Kilauea into that 
of Vesuvius or Etna. The phases of their craters may be of the same 
general nature, and be due to a similar mode of action, varied only by 
‘the simple fact of the greater or less viscidity of the lavas. There 
may be the same succession of effects with the same results; and 
periods of quiet and violent action may have the same mutual relations 
and dependence. We need look to no extraordinary influx of waters 
to occasion an eruption, as the eruption is a result of a progressive 
state of things, perhaps long in action. I do not here deny that 
such a paroxysmal influx of waters may at times take place, and has 
produced results. 1 urge only that they are exceptions; and that 
phases of quiet and violent activity would necessarily succeed one 
another without such intervention. 
The same gradually acting cause will also produce occasional 
violent ruptures. For where the waters for a period find slow access 
to any centre of heat within the voleanic mountain beneath its cover 
of rocks, the vapours will gradually accumulate till the pressure breaks 
a way through the mountain, to give exit to the vapours, together 
with the compressed lavas. The starting of a cork from a bottle of 
soda-water and the escape of the liquid, as well as carbonic acid gas, 
though a familiar incident, depends on a general principle, with re- 
gard to pressure, to which even the lavas of a volcano must be obe- 
dient. The sudden outburst of lavas through fissures in the summit 
of the walls about Kilauea may be of this character. In many cases 
even violent earthquakes might attend this mode of action. 
VII. Kinds of Craters on Hawait.—The craters on Hawaii are of 
four kinds, according to their mode of formation; yet these kinds are 
not always distinct, owing to the combination of different effects in 
their origin. These kinds are as follows :—1l. Lava cones or domes ; 
2. Cinder or scoria cones; 3. Tufa cones; 4. Pit-craters. We omit 
