398 CORALS AND CORAL ISLANDS. 
In the raised coral rock of Oahu (p. 871) there are several 
long winding horizontal chambers, some of which are the 
sources of subterranean streams that open out on the shores 
between the layers of the rock, or from the mouths of caverns. 
These running waters, and others trickling from above, are 
obviously the eroding agents that have made the caves. 
As briefly remarked on page 194, caverns are still more re- 
markable on the island of Atiu, on which the coral reef-rock 
stands at about the same height above the sea as on Oahu, 
Rev. John Williams states that there are seven or eight of 
large extent on the island. Into one he entered by a descent 
of twenty feet, and wandered a mile in one only of its branches 
without finding an end ‘‘ to its interminable windings.” He says, 
“TInnumerable openings presented themselves on all sides as 
we passed along, many of which appeared to be equal in height, 
beauty and extent to the one we were following. The roof, a 
stratuin of coral rock fifteen feet thick, was supported by massy 
and superb stalactitic columns, besides being thickly hung with 
stalactites from an inch to many feet in length; some of these 
pendents were just ready to unite themselves to the floor, or to 
a stalagmitic column rising from it. Many chambers were 
passed through whose fretwork ceilings and columns of stalac- 
tites sparkled brilliantly, amid the darkness, with the reflected 
light of our torches. The effect was produced not so much by 
single objects, or groups of them, as by the amplitude, the 
depth, and the complications of this subterranean world.” 
Other similar caves exist on the neighboring island of 
Mauke. 
The Bermudas and Bahamas are also noted for their cay- 
erns. The great height of the easily eroded drift sand-rock 
gives these reef-regions a chance for caverns, large and small ; 
a notice of the Bermuda caverns will be found on page 224. 
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