256 J.D. Dana on the recent Eruption of Mauna Loa. 
The process of elevation in the liquid internal lavas has evidently 
en going on, as after previous eruptions, although out of sight, 
deep beneath the solid rock that forms the bottom of Kilauea ; 
and they have again reached a height that enables them to be 
distinguished. ‘The mode of progress and of eruption may there- 
fore correspond throughout with the views presented by the author 
in his Exploring Expedition Geological Report, and this Journal, 
vol. ix, 347. Yet it is also possible that the fires of Kilauea are 
dying out and that thus the change of condition is to be explained. 
Although the discharges at the summit of Mauna Loa produce 
no oscillations in the lavas of Kilauea, it may still be possible 
that the increased activity at the summit, and the diminished ac- 
tion of the flank crater, during the past few years, may be con- 
nected with the same changes below. These changes may can- 
Sist In some variations in the distribution of the heat, or, more 
probably, in a variation of size or direction in the openings or 
channels that serve to supply the water which feeds the fires. 
_ V. If Kilauea were to become extinct in its present condition, 
no evidence would exist of its former depth, or of the black ledge 
or shelf which has been so remarkable a feature in this crater. 
The present depth does not exceed 600 feet—400 feet less than 
after the eruption of 1840.* Moreover, as the precipitous rocky 
walls are wholly free from scoria and all other signs of recent fires: 
(looking much like bluffs of ordinary stratified rock), there is no 
evidence as to the great eruptions that have taken place, and only 
signs of a sort of Solfatara action with outflows of lava over the 
bottom of the confined area. ‘These facts bear on the conelu- 
sions that might be deduced from the existing features of extinct 
leanoes. oe 
VI. Mr. Coan speaks of the lavas as flowing from an orifice Ina 
broad stream down the mountain. It is probable that fissures 
opening to the fires below were continued at intervals along t 
course of the eruption, and that these afforded accessions to the 
fiery flood. Such was the case in 1840, and the three tufa hills 
at Nanawale, on the sea-coast, mark the positions where these 
opened fissures reached the sea. Any internal force sufficient to 
break through the sides of a mountain like Mauna Loa, mu 
necessarily produce a linear fissure or a series of fissures, and not 
a single tunnel-like opening. 2 
V e have yet received no definite facts as to the angle of 
slope down which the lavas descended. Yet we do know that 
in this and in a former eruption the stream continued over the de- 
clivities for thirty miles, and these declivities have an averag? 
angle of six or seven degrees, though made up of subordinate 
slopes varying probably between one and twenty degreees, 25 © 
® The central portions of the crater are much more raised than the lateral, and 
over them the depth cannot exceed 500 feet. 
