48 J. D. Dana on Denudation in the Pacifie. 
Art. X.—On Denudation in the Pacific; by James D. Dana. 
Tue following pages are extracted from different chapters in 
the ere Report of the Exploring Expedition under Capt. 
Wilkes 
The valleys of the Pacific Islands have usually a course from 
the interior of the island towards the shores; or when the island 
consists of two or more distinct summits or ‘heights (like Mati) 
they extend nearly radiately from the centre of each division of 
the island. They are of three kinds: 
w gorge, with barely a pathway for a streamlet at 
bottom, the enclosing sides diverging upward at an angle of thirty 
to sixty degrees. Such valleys have a rapid descent, and are 
bounded by declivities Ha one hundred to two thousand feet or 
more in elevation, which are covered with ications though 
striped nearly horizontally by parallel lines of black roe. here 
are frequent cascades along their course ; and at head: they often 
abut against the sides of the central inaccessible heights of the 
island. The streamlet has frequently its source in one or more 
thready cascades that make an unbroken descent of one or two 
thousand feet down the precipitous yet verdant walls of the am- 
phitheatre around. 
narrow gorge, having the walls vertical or nearly so, and 
a flat strip of land at bottom more or less uneven, with a stream- 
let sporting along, first on this side, and then on that, now in rap- 
ids, and now with smoother and deeper waters. The walls may 
be from one hundred to one thousand feet or more in height ; they 
are richly overgrown, yet the rocks are often exposed, though 
every where more than half concealed by the green drapery. 
These gorges vary in character according to their position on 
the island. here they cut through the lower plains, (as the 
dividing plain of Oahu,) they are deep channels with a somewhat 
even character to the nearly vertical walls, and an open riband 0 
land at bottom. The depth is from one to three hundred feet, and 
the breadth as many yards. Farther towards the interior, where 
the mountain slopes and vegetation have begun, the walls are 
deeply fluted or furrowed, the verdure is more varied and abund- 
ant, and cascades are numerous. 
This second kiud of gorge, still farther towards the interior, 
changes in character, and becomes a gorge of the first kind, nat- 
rowing at bottom to a torrent’s course, oes which are occasional 
precipices rh only a torrent could descen 
™ 
* U.S. Exploring — during the years 1838- ey under the command 
of C. Wiixes, U. 8. N.—Geology by James D. Daya, A.M., Geologist of the Expedi 
tion. 750 pp. 4to, with a folio Atlas of 21 a of fi coat ° Shiladel phia: 1849. 
