380 PACIFIC ISLANDS. 
rowed, as already described, the verdure is more varied and abundant, 
and cascades are numerous. 
This second kind of gorge, still farther towards the interior, changes 
in character, and becomes a gorge of the first kind, narrowing at 
bottom to a torrent’s course, along which are occasional precipices 
which only a torrent could descend. 
III. A wide valley leading towards the interior, with a very broad 
open area at bottom usually covered with vegetation, and enclosed by 
precipitous heights, exemplifies the ¢hard kind. They sometimes abut 
at head against vertical walls, but oftener terminate in a wide break in 
the mountains. 
The ridges of land which intervene between the valleys are flat 
table land, or only undulated where these valleys intersect the lower 
plains or slopes; but in the mountains, they are narrow at top, and 
sometimes scarcely passable along their knife-edge summits. Some 
of them extend inward, becoming narrower as we proceed, and termi- 
nate in a thin wall, which runs up to the central peaks. Others stop 
short of these central peaks, and the valleys either side consequently 
coalesce at their head, or are separated only by a low wall, into which 
the before lofty ridge had dwindled. The crest is often jagged, or 
rises in sharp serratures. 
The main valleys, which we have more particularly alluded to 
above, have their subordinate branches; and so the ridges, in neces- 
sary correspondence, have their subordinate spurs. 
Tahiti, with its ridges, peaks, and valleys, is a good illustration 
of the features here described; and a brief consideration of the fore- 
going remarks, (in connexion with the account on page 286 and 
beyond,) will enable the reader to conceive perfectly of this skeleton 
island. 
The causes operating in the Pacific, which have contributed to 
valley-making, are the following: 
1. Convulsions from internal forces, or volcanic action. 
2. Degradation from the action of the sea. 
3. Gradual wear from running water derived from the rains. 
4. Gradual decomposition through the agency of the elements and 
growing vegetation. 
The action of volcanic forces in the formation of valleys, is finely 
illustrated in the great rupture in the summit of Hale-a-kala (Kauai). 
The valleys formed by the eruption are as extensive as any in the 
Hawaiian Group, being two thousand feet deep at their highest part, 
and one to two miles wide. They extend from the interior outward 
