VEGETABLE DEBRIH. 393 



whole cementt'd together by tlie infiltration of cnr- 

 bonate of lime. 



A coral reef, still inliabitorl by the animals, runs 

 parallel with the Keys, following the same curves, 

 and at a distance varyinir from 2000 to 6000 yards. 

 Between the reef and the Keys there is a navigable 

 channel (six or seven fatiioms in depth), which com- 

 municates with the open sea by a number of channels 

 traversing the coral reef. 



Generally speaking, the banks of coral forming 

 the reef do not reach to the surface of the sea ex- 

 cept at particular points, where the accumulation of 

 broken coral, &c. has initiated the formation of little 

 keys. 



The Gulf Stream flows beyond the reef of living 

 coral. 



i. Alga3 — Submarine Forests and Prairies — Flouting Senwec d of 

 thf Sargossa Seas — Extension of the Coasts l)y the Ilhizophora 

 Mangle. 



Marine vegetation, like marine animals, leaves its 

 debris to accumulate at the bottom of the sea ; but, 

 as we have before explained, their range is much 

 more limited than that of the animals, as they are 

 principally confined to the shallow parts of the sea 

 and to tlie neighbourhocxl of coasts. Their j)ro- 



