62 J. D. Dana on Denudation in the Pacifie. 
in regions of a similar kind, no evidence that the valleys have 
depended for their origin on the mountain’s being a “crater of 
elevation,” as von Buch urges.* The regular stratification of the 
sides of these valleys; the ‘absence of all ‘tiltings ; their situation, 
as related to the rains; and the absence of fisstires ready for mak- 
ing valleys on the leeward declivities, are points which favor no 
such theory: and, moreover, it is an unnecessary hypothesis. 
We are thus led to conclude that between convulsions from 
subterranean forces, and degradation from waters supplied by the 
rains aud attending decomposition, a lofty volcanic dome ma 
be changed to a skeleton island like Tahiti e have referred 
to Mount Loa as still unfurrowed ; to Moiat Kea and Hale-a-kala 
as having only the lower slopes deeply channeled with narrow 
gorges; and to other islands, as exemplifying all gradations in these 
effects to these in which the original features are no longer to be 
traced: we have pointed out the difference in the windward and 
leeward slopes, aud have shown a on between the quantity 
of rain and the amount of degradation :—we have exhibited a 
model of the mountains, an RM deninble result of denudation, 
placed at their very base, as if for illustration :—and thus we have 
traced out and elucidated all the steps in the valley-making pro- 
cess, and have also ee them to be a necessary result from the 
action of rauning w 
Again, examples of soiluleidig from igneous forces have been 
pointed out in the great gorges of Hale-a-kala, and in Kilanea and 
other Hawaiian craters; in the mountain wall of Oahu, and simi- 
lar scenes on other islands; in the wide am phitheatre of central 
Tahiti: and the importance of this means of change has thus 
been exhibited. Yet few such changes are apparent on any one 
island, and these are marked by decided characters not often to be 
mistaken. It has also been shown that although fissures made 
by volcanic forces, may in some cases have given the direction 
to valleys, yet they are by no means necessary in order that val- 
leys should commence to form. 
With literal truth may we speak of the valleys of the Pacific 
Islands, as the furrowings of time, and read in them marks of age. 
Our former conclusion with regard to the different periods which 
have passed over the several Hawaiian Islands since the fires 
ceased aud wear begun, is fully substantiated. We also learn 
how completely the features of an island may be obliterated by 
this simple process, and even a cluster of ee like Orohena, Pito- 
hiti and Aorai of tere. be bere ved from a simple volcanic dome 
or cone. Mount Loa, alone, contains within itself the material 
from which an island like Tahiti might be modeled, that should 
have near twice its height and four times its geographical extent. 
* See eg Canaries, p. 285. 
