56 J. D. Dana on Denudation in the Pactfic. 
effect, and by its continuation to this time, the Retin have had 
scarcely a chance to make a beginning in denudat 
Mount Kea, which has beeu extinct for a ae ea has a 
succession of valleys on its windward or rainy side, which are 
several hundred feet deep at the coast and gradually diminish | 
bay extending in See about half or two-thirds of t 
way to the summit. But to the westward it has dry declivities, 
which are companiiincty even at base, with little running water. 
A direct connection is thus evinced between a windward exposure, 
and the existence of valleys: and we observe also that the time 
since volcanic action ceased is approximately or relatively indica- 
ted, for it has been long enough for the valleys to have advanced 
only part way to the summit. Degradation from running water 
would of course commence at the foot of the mountain, where 
the waters are necessarily more abundant and more powerful in 
denuding action, in consequence of their gradual accumulation on 
their descent. ‘Mount Kea, like Mount Loa, is nearly 14,000 
feet high, and the average slope i is 7 to 8 degrees. 
Hale-a-kala on Maui offers the same facts as Mount Kea, indi- 
cating the same relation between the features of the surface and 
the climate of the different sides of the island. On Eastern 
Oahu the valleys are still more extensive; yet the slopes of the 
original mountains may be in part distinguished. And thus we 
are gradually led to Kauai, the westernmost of the Hawaiian Isl- 
ands, where the valleys are very profound and the former slopes 
can hardly be made out. ‘The facts are so progressive in character, 
that we must attribute all equally to the running waters of the land. 
The valleys of Mount Kea alone, extending some thousands of 
feet up its sides, sustain us in saying, that time only is required 
or the formation of similar valleys elsewhere in the Pacific. 
As in Tahiti, so in other islands. these valleys take the direction 
of the former slopes ; and though they may be of great depth and 
cominence even under the central summits, they 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 a preceding page. It can- 
not be doubted here that water was the agent ; for the rills are seen 
at work. The contrast between the same valley near the sea, and 
in the mountains, (the walls in the former case being nearly un- 
worn vertically,) is explained on the same principle: for the 
mountains are a region of frequent rains and almost constant 
one, and therefore abound in streams and streamlets and threads 
water; while below, there are grassy plains instead of forest 
desir ities, and but little rain. These furrowings vary from a 
few yards in width and depth to many furlongs. 
The long and lofty precipice of Eastern Oahu, is an excellent 
place for studying farther this action. It is fluted in the same 
