CORAL FORMATIONS OF OAHU. 253 
stalagmites. Off Kaneohe, the islands of coral are six to eight feet 
above high tide. At the southwest corner of the island, the reef 
rock faces the sea in a bluff twenty to twenty-five feet high, and large 
masses, some of which are thirty feet in length, have been under- 
mined, and now lie at the foot of the bluff. On this point there are 
some places where its elevation is thirty feet above the sea. 
The height of the rock thus varies, much hke the surface of the 
submerged reefs. A large part of the bay of Kaneohe is now filled 
with reefs, which are rarely less than two feet below the surface, while, 
in many parts, they are ten to twenty feet. 
The reef rock contains many caverns, some of which are extensive. 
There are several of these caverns a short distance to the eastward of 
Diamond Hill, which are long winding horizontal chambers. Many 
of the subterranean streams between Koko Head and Honolulu make 
their appearance on the shores between the layers of this rock, or at 
the mouths of the caverns; and to the action of these running waters, 
and others trickling from above, we must attribute the origin of the 
limestone caves. The limestone plains are, in general, the most barren 
parts of the island. 
Coral Sand-rock.—In some parts of Oahu, the elevated reef is sur- 
mounted or backed by hills of coral sand-rock, formed of the beach- 
sands which were accumulated on the shores when this reef was 
beneath the water. ‘They occur, like the existing drift-heaps, on the 
windward sides of the island, from Diamond Hill, where there are 
some accumulations, around by the east point to the northeast as far 
as Kahuku Point. On the Kailua plains, and between Laiée and 
Kahuku, they form prominent bluffs, fifty to eighty feet above the sea 
and over three-fourths of a mile back from the coast, giving a singu- 
lar aspect to the scenery. One of these bluffs has been already men- 
tioned in our remarks on coral formations. The front has been broken 
down, (probably the result of degradations following its elevation,) so 
as to present a face of limestone, in most parts finely laminated. The 
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