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J. D. Dana on the Volcanoes of the Moon. 343, 
_ The etreular or slightly elliptical form of the moon’s craters 
is also exemplified to perfection. For the lakes of Kilauea have 
this shape ; and although the pit itself is oblong, owing to its sit- 
uation on a fissure, other large though extinct pit craters of Mount 
Loa are quite as regularly circular in form. Some are. twins ; 
that is, are made up of two or three coalescing circles. 
We have chosen Kilauea for these illustrations because it is now 
in action, and the features appealed to have been familiar to us, 
Since the first publications of Admiral Byron, and Rev. Charles 
8. Stewart. I may add that the facts are finely illustrated in the 
Narrative of the Exploring Expedition by Capt. Wilkes,* and 
they will be farther detailed in the Expedition Geological Report 
on the Hawaiian Islands, now in course of preparation. The 
exact application of these facts, as far as regards general features, 
to the. swmmit crater of Mt. Loa, will be found fully sustained 
by the plans and views accompanying the Narrative. - 
» Whence all this close resemblance to the lunar craters, while 
other volcanoes are so different? It arises from the fact that the 
action at Kilauea is simply boiling, owing to the extreme fluidi- 
ty of the lavas. The gases or vapors which produce this appear- 
ance of active ebullition, escape freely in small bubbles with lit- 
tle commotion, like the jets over boiling water; while at Vesu- 
Vius and other like cones they collect in immense bubbles before 
they accumulate force enough to make their way through ; and 
consequently the lavas in the latter case are ejected with so much 
Violence, that they rise to a height often of many thousand feet 
and fall around in cinders. This action builds up the pointed 
mountain, while the simple boiling of Kilauea makes no cinders 
and no cinder cones. Still, although the lavas of this crater are 
not thrown toa great height, they may make cones of any an- 
gle, even by overflowing alone ; especially by small or partial 
- Overflowings, which melt together, cooling at the same time rap- 
idly. They thus sometimes raise a steep rim around a pool. 
This point has been well presented by M. C. Prevost,f and in an- 
other place we shall mention many facts in illustration of it. 
If the fluidity of lavas, then, is sufficient for this active ebul- 
lition, we may have boiling going on over an area of an indefi- 
_ * See Narrative, Vol. iv, p. 125, and the map of part of Hawaii in Vol. vi. 
_ t Bulletin de la Soe. Geol. de France, xi, 1839 & 1840, p. 183. 
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