ORIGIN OF VALLEYS. 389 
when the rains swell the waters to a flood, all incredulity on this point 
must be removed. 
A few thousand feet in depth, even in the solid rocks, is no great 
affair for an agent of such ceaseless activity, during the periods which 
have elapsed since the lands became exposed to their influence. And 
when we take into view the lofty heights of the Pacific islands, their 
rapid declivities giving speed to the waters and transported stones 
and earth, we must admit that of all lands, these are especially fitted 
for denudation by torrents. 
The nature of the rocks also favours wear and removal. They 
are in successive layers, soft conglomerates or tufas frequently alter- 
nating with the harder basalt. Moreover, the rocks are commonly much 
fissured, owing to a tendency to a columnar structure; besides, they 
are often cellular. The waters thus find admission, promoting de- 
composition and also degradation. There are, also, frequent caverns 
between layers, which contribute to the same end. 
There is every thing favourable for degradation which can exist in 
a land of perpetual sunshine: and there is a full balance against the 
frosts of colder regions in the exuberance of vegetable life, since it oc- 
casions rapid decomposition of the surface, covering even the face of 
a precipice with a thick layer of altered rock, and with spots of soil 
wherever there is a chink or shelf for its lodgment. ‘The traveller 
ascending a valley on one of these islands on a summer day, when 
the streams are reduced to a mere creeping rill which half the time 
burrows out of sight, seeing the rich foliage around, vines and flowers 
in profusion covering the declivities and festooning the trees, and 
observing scarcely a bare rock or stone, excepting a few it may be 
along the bottom of the gorge, might naturally inquire with some 
degree of wonder, where are the mighty agents which have channeled 
the lofty mountains to their base? But though silent, the agents are 
still on every side at work: decomposition is in slow, but constant 
progress; the percolating waters are acting internally, if not at the 
surface. Moreover, at another season, he would find the scene 
changed to one of noisy waters, careering along over rocks and 
plunging down heights with frightful velocity ; and then the power 
of the stream would not be disputed.* 
* The rise of the streams is often so rapid, from the rains of the mountains, that in 
some instances, the native villages of the coast become flooded, before they have time even 
to remove their property.— Miss. Herald, xxiii. 207. 
Mr. Coan, who has often traversed the coast of Hawaii, north of Hilo, and during the 
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