362 PACIFIC OCEAN. 
lengthening the sides of the mountain, and at the same time dimi- 
nishing the angle of acclivity about its flanks.* 
When Mount Loa changed its mode of action from a preponderance 
in its summit eruptions to fissure eruptions, cannot be known. There 
may have been a time when devastating floods swept a large part of 
the surface, and the structure at summit requires the supposition ; but 
at present the lavas break out through opened fissures whether the 
eruptions take place above or below, and the enlargement now in 
progress is only by this latter means.* 
We find evidence in Mount Kea and the other Hawaiian Islands, 
that they were formed mostly or wholly ata much lower than their 
present level. The elevation placing the summits at their existing 
height, may have been accompanied or followed by a series of 
changes throughout the group, and an extinguishing of some fires ; 
and with Mount Loa, the new phase in its mode of action, above 
alluded to, may have then taken place, and been accompanied by the 
opening of Kilauea. But this is conjecture; yet there is no doubt, we 
believe, as to the reality of the change. 
The history of Mount Loa, therefore, seems to be quite simple and 
intelligible. The cones of the Kilauea pit, show us a model of the 
mountain itself. They illustrate the germ-cone, proceeding from 
eruptions by overflowings, and through fissures: they illustrate the 
progress of the cone: and by becoming inactive, as they generally do, 
after reaching a certain size, and eruptions going on in the plain 
below, they exemplify nearly the existing condition of Mount Loa. 
The upper slopes of Mount Loa are not too steep to be coated with 
lavas, for this actually takes place in these recent times, though by 
fissure ejections. The lower slopes are more frequently flooded, and 
these are spreading out the base of the dome. ‘The fissure eruptions 
usually end in producing one or more small cones. 
The crater of the mountain may have been once much more exten- 
sive, and may have merited comparison with some of the large cir- 
cular areas inclosed by lofty walls, such as von Buch describes as 
occurring on Palma, one of the Canaries.t If so, diminishing action 
* All late eruptions of Vesuvius and Etna are of this kind. See Bischof, Amer, Jour. 
of Science, xxxvi. 251, 252. Humboldt says of Teneriffe—the interior of the peak 
shows it to be a volcano, which for thousands of years has thrown out fires only from its 
sides.—Reise, 1. 195. 
+ The Caldera of Palma is a nearly circular area, enclosed by lofty walls, and mea- 
suring six or eight square miles in diameter. From the top of the walls, the sides slope 
