REVIEW OF VOLCANIC ACTION. 363 
must have gradually narrowed the vent to its present size. The ver- 
tical stratified walls, and the absence of scoria about them, might be 
considered decisive evidence that such cavities had never been craters 
with overflowing lavas, by those who had not seen a crater like 
Kilauea; but we have more than once remarked, and the importance 
of the truth will authorize the repetition, that both the upper and the 
lower pit of Lua Pele—the latter actually buried with lavas in 1840— 
have just such stratified walls wzthout any scoria about them. 
The principles here exemplified by Mount Loa are borne out by 
other parts of the Pacific, as will be gathered from the descriptions 
on the preceding pages of this volume. The different phases of vol- 
canic action, depending on the increasing height of the cone, the 
more or less perfect liquidity of the lavas, the continued or intermittent 
periods of activity, a gradual diminution of its action at later periods, 
the equiponderance of summit and fissure eruptions, or the prevalence 
of the former or latter, are the several modifying circumstances. 
‘There may be cases in which the fissurings of the mountains during 
a prolonged period of activity have taken place mostly from the centre, 
and have resulted in a constant increase of the angle of acclivity. 
But in Mount Loa they have in modern times occurred over all its 
sides, and we have no evidence that these rupturings have recently 
added to the rapidity of the slopes; while we have evidence that they 
have diminished the angle, and are still producing this result. 
gradually towards the sea. Mr. Darwin, (Vole. Islands, p. 30,) mentions a nearly 
similar area at Mauritius, one thousand feet deep, the shorter axis of which is thirteen 
geographical miles in length; and another at St. Jago, one of the Cape Verdes, (p. 17, 
20.) There is much resemblance in these areas to the circular craters of the lunar vol- 
canoes: yet some of them may have resulted from a subsidence of the interior of the 
island. Mr. Darwin speaks of the mountains of Mauritius as resembling “ the basal and 
disturbed remnants of a gigantic volcano,” and he quotes M. Bailly as suggesting that 
the enormous gulf was formed by the sinking in of the whole upper part of one great 
volcano. (Vole. Islands, p. 30, 31.) 
As another example of a similar area, we have alluded to the extensive plain on 
Tahiti, at the base of the lofty peak, forming the head of the Punaavia Valley. Eimeo 
also appears to be characterized by an extensive interior plain, surrounded by lofty walls, 
which are much broken into peaks. The resemblance of these circular areas to Kilauea 
and Mokua-weo-weo is too close in every feature to be passed by without consideration. 
Were Kilauea broken down at its southeast extremity by a gap like that of Hale-a-kala, 
we should have a Val-del-Bove of magnificent dimensions, ‘The resemblance of this 
famous valley to Kilauea or to the Maui crater, is distinctly brought out by the sketch by 
Mr. Lyell, in his Principles, volume ii., plate ix. 
