and the Nature of the Liquidity of Lavas. 135 
small] pit-craters occasionally met with in volcanic districts, such 
as the Gour de Tazana, and the lakes Pavin, Du Bouchet, and 
Serviéres in Central France. But even these show marks of 
explosive eruption in the scorie*sprinkled around their banks. 
And the occurrence of even a single bed of scoria is certain proof 
of some explosions having taken place from a body of liquid lava 
beneath; though, as I have said, this may have been accom- 
panied or followed by engulfment. Perhaps the singular cha- 
racter of the crater of Kilauea, in Owyhee, may be thought to 
claim for it an origin in subsidence rather than eruption. It is 
described as a vast sudden depression in what would otherwise 
be almost a level plain, on the side of the gently sloping vol- 
canic mountain of Mauna Loa. It has an irregularly oval form, 
from three to five miles in diameter, and is usually encircled by 
vertical cliffs some hundred feet high. Its bottom consists of a 
lake of lava, on some points (which occasionally change their 
situation) in continual ebullition, and at a white heat; but 
coated over for the most part by an indurated crust upon which 
it is often possible to walk. Sometimes, however, the incrusted 
portion is in the centre of the lake, forming a rough platform, 
surrounded by a circle of incandescent and seemingly fused lava, 
—sometimes the outer circle forms a solid shelf, within which 
an inner basin of lava boils at a greater or less depth below its 
edge. It is evident, from the account of this crater given by 
Professor Dana, in the American Journal of Science, as gathered 
from the relations of various observers during nearly a century 
past, that the surface of a vast boiling lake of subterranean lava 
existing here, rises and sinks at irregular intervals of several 
years in duration ; sometimes filling the entire cavity, and even 
pouring over its outer margin sheets of a very liquid lava,— 
sometimes sinking to a depth of a thousand feet or more,— 
especially when some outburst from a lower vent, or chain of 
vents, has ¢apped the internal reservoir. But, however interest- 
ing the characteristic features of this crater, both from the faci- 
lities it affords for observation, and the great scale on which they 
are developed, they do not seem to me to prove the origin of the 
cavity other than that of ordinary craters. The phenomena of 
Kilauea are not so exceptional as at first view might be sup- 
posed. Visitors who looked down into the great Vesuvian crater 
for a few years after its formation in 1822, saw pools of liquid 
and incandescent lava at its bottom, and small cones of scoria 
thrown up by an almost constant ebullition. The difference in 
the violence of the explosions, and in the amount of ejected 
scoria, arises, no doubt, as Professor Dana very justly observes, 
from the difference in the relative liquidity of the lavas,—those 
of Kilauea being very liquid, those of Vesuvius much more viscid 
