206 CORALS AND CORAL ISLANDS. 



in its structure it shows the result of long-continued, steady 

 wave-work that cannot be referred to any other cause. 



" On Key West I found in the rocks, no beds of coral re- 

 taining their original position, although large fragments are 

 scattered through the mass. 



" Some of the small Keys, such as the Mangrove Keys, 

 are the result of gradual deposition of sedimentary matter, 

 and many of those interspersed among the larger islands have 

 not yet reached the level of high water, but are nevertheless 

 covered by a dense growth of this curious tree. It would be 

 difficult to imagine a plant better adapted to islaud-making 

 than the mangrove. Its long, pendulous seeds fall into the 

 shallow water, stick in the soft mud, and take root ; the bud 

 proceeding from the opposite extremity, soon shoots up above 

 water and sends down branches almost perpendicularly into 

 the mud, these take root and produce other trees, and so on. 

 Besides these, lateral shoots are given otf, and, at a distance of 

 three or four feet, enter the water and take root ; from the 

 part above water others proceed and take a similar stride, 

 and in this way they often travel twenty or thirty yards 

 from the parent stem. Seaweeds and drift-wood become en- 

 tangled among the stems, and very soon a permanent island 

 is formed. Such islands are generally found under the lee of 

 the Keys. 



"But the greater number, if not all the Keys, rest upon a 

 foundation of corals. At Sand Key, large rugged masses of 

 dead coral are seen bordering the Key on the windward side, 

 and rising above low water ; similar masses may be seen at 

 Sambo Key, and at other places along the outer reef. But 

 the Keys within this barrier present better opportunities for 

 studying the foundation upon which they rest. At Key 

 Vacca, corals rise to a height of four feet above high water, 



