ORIGIN OF VALLEYS. 391 
part way to the summit, as on Mount Kea and Hale-a-kala, and evi- 
dently for the reason already explained. We can detect 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 fissures ready for making valleys on the leeward 
declivities, are points which favour no such theory : and, moreover, it 
is a wholly unnecessary hypothesis. 
Conclusion.—Between convulsions from subterranean forces, and 
degradation from waters supplied by the rains and attending decom- 
position, the lofty volcanic dome with its even surface may be 
changed to a skeleton island like Tahiti. We have referred to Mount 
Loa as still unfurrowed ; to Mount Kea and Hale-a-kala as having 
only the lower slopes deeply channelled with narrow gorges; and 
to other islands, as exemplifying all gradations in these effects, to 
those in which the original features are no longer to be traced: we 
have pointed out the difference in the windward and leeward slopes, 
and have shown a relation between the quantity of rain and the 
amount of degradation: we have exhibited a model of the moun- 
tains, an undeniable 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 process, and have also shown how they 
are a necessary result from the action of running water. At the 
same time we have explained the fact that although the sea levels a 
coast, it makes no valleys. 
Again, results of convulsions and igneous forces have been 
pointed to, in the great gorge of Hale-a-kala; in Kilauea and other 
Hawaiian craters; in the mountain wall of Oahu, and similar scenes 
on other islands; in the wide amphitheatre of central Tahiti: and the 
importance of this means of change has thus been exhibited. Yet it 
has been observed that few such changes are apparent on any one 
island, and these are marked by decided characters not often to be 
mistaken. Fissures made by the same cause, may in some cases 
have given the direction to valleys, though they are by no means 
necessary in order that valleys 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 conclusions with regard to the different periods which 
* See Iles Canaries, p. 285. 
