ORIGIN OF VALLEYS. 385 
plaining the existence of any similar valleys in the Pacific. As in 
Tahiti, these valleys in general radiate from the centre, that is, take 
the direction of the former slopes; they often commence under the 
central summits, and terminate at the sea level, instead of continuing 
beneath it. 
The fluting of the walls of the Hanapepe Valley, a thousand feet 
or more in height, has been described on page 263. It cannot be 
doubted here that water was the agent; for the rills are still at work. 
The contrast between the same valley near the sea, and in the moun- 
tains, (the walls in the former case being nearly unworn vertically,) is 
explained on the same principle: for the mountains are a region of 
frequent rains and almost constant clouds, and therefore abound in 
streams and streamlets and threads of water; while below, there are 
grassy plains instead of forest declivities, and but little rain. ‘These 
furrowings vary from a few yards in width and depth to many 
furlongs. 
The precipice of Eastern Oahu, (page 236,) is an excellent place 
for studying farther this action. It is fluted in the same style as the 
Hanapepe Valley. In the distant view the vertical channels appear 
very narrow; but when closely examined they are found to be deep 
and often winding passages. ‘The precipice faces to the windward, 
and is directly under the whole line of peaks in the mountain range ; 
both of which facts account for an abundance of water. Going to the 
westward along the range, the precipice changes to a sloping declivity, 
and these passages become deeper and longer, and more winding, 
just in proportion to the increasing length of the slopes. Moreover, 
at the same time they decrease in number. Where there is no slope 
to collect the waters the rills act independently, and their furrowings 
like themselves are small, narrow, and numerous; but as the declivity 
becomes gradual, the rills flow on and collect into larger streams, and 
the furrowings become deeper and more distant. Over this region, 
no distinction can be drawn as regards origin between the flutings 
and gorges: and in respect to features, only this difference appears, 
that the size of the excavations is less and the number greater, 
the steeper the declivity. If a fissure be appealed to as the com- 
mencement of the longer valleys, it should also be admitted for each 
of the flutings. But this idea is wholly inadmissible. 
A brief review of the action and results of flowing waters will 
render the origin of these features intelligible. 
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