AGE OF CORAL REEFS. 183 
filling up, by a process similar to that by which 
the islands themselves were formed. The gentle 
landward slope of the Reef and the channel be- 
tween it and the shore, are covered with a growth 
of the more branching lighter Corals, such as Sea- 
Fans, Corallines, etc., answering the same pur- 
pose as the intricate roots of the Mangrove-tree. 
All the débris of the Reef, as well as the sand 
and mud washed from the shore, collect in this 
net-work of Coral growth within the channel, 
and soon transform it into a continuous mass, 
with a certain degree of consistence and solidity. 
This forms the foundation of the mud-flats which 
are now rapidly filling the channel, and must 
eventually connect the Keys of Florida with the 
present shore of the peninsula. 
Outside the Keys, but not separated from them 
by so great a distance as that which intervenes 
between them and the main-land, there stretches 
beneath the water another Reef, abrupt, like the 
first, on its seaward side, but sloping gently to- 
ward the inner Reef, and divided from it by a 
channel. This outer Reef and channel are, how- 
ever, in a much less advanced state than the 
preceding ones. Only here and there a sand-flat 
large enough to afford a foundation for a bea- 
con, or a light-house, shows that this Reef also 
is gradually coming to the surface, and that a 
series of islands corresponding to the Keys must 
eventually be formed upon its summit. 
