STRUCTURE OF CORAL ISLANDS. 169 



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 entangled 

 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, and present not the 

 slightest evidence of disturbance, beyond the upward move- 

 ment which raised them to their present position. The rocky 

 mass of coral along the margin of the Key is undermined by 

 the waves, and otherwise worn into singularly rugged shapes, 

 with sharp projecting points. Even at some distance from the 

 water, bunches of coral project above the surface wherever the 

 overlying sand is washed away. 



"On Bahia-honda similar appearances are presented, where 

 the coral rocks extend seaward ; on the lee of the island a 

 long sand-bank is thrown up, and a lagoon of considerable 

 extent is formed, in which the mangrove-tree is seen striding 

 about in the soft mud. This island was washed in two by the 

 last hurricane, and the channel formed has three feet of water 

 at low tide. In the shallow water off many of the Keys, 

 very beautiful patches of Algae, interspersed with living corals, 

 are seen within six or eight inches of the surface. Off Indian 

 and Plantation Keys, dark knobs of coral are visible upon the 

 white mud of the bottom, which render the navigation amongst 

 these Keys dangerous. On lower Matacumba I traced the 

 rugged coral rocks for a mile in extent ; I also found them on 

 Conch Key, as I did indeed on nearly every island that I 

 examined, where a section could be found on the shore, from 

 which the overlying sands were washed." 



