392 On the Geology of the Florida Keys. 
‘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 island 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 extrem- 
ity, 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 off, 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 pa- 
rent stem. Seaweeds and drift-wood become entangled among 
the stems, and very soon a permanent island is formed. Suc 
islands are generally found under the lee of the Keys. 
But the greater number, if not all, the Keys rest upon a foun- 
dation 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 founda- 
tion upon which they rest. At Key Vacca corals rise to a 
height of four feet above high water, and present not the slight- 
est evidence of disturbance, beyond the upward movement which 
otherwise worn into singularly rugged shapes, with sharp project- 
ing points. , 
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 shal- 
interspersed with living corals, are seen within six or eight inches 
i dark knobs of 
