AGE OF CORAL REEFS. 183 



fil'ing 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 debris 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. 

 Tliis 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. 



