142 



CORALS AND CORAL LSLAMIXS. 



It is apparent that we are describing a second time an outer 

 reef. Without dwelHng further upon its characters, we may 

 pass to the features of the reef when raised 

 above the waters and covered with vege- 

 tation. 



Sections of coral islands and their lagoons 

 have been given by Captain Beechey and 

 Mr. Darwin. We add another, by way of 

 illustration, although little may be pre- 

 sented that is novel after the excellent 

 descriptions of these authors. Sketches of 

 several of these islands, showing the gene- 

 ral relation of the rim of land to the reef 

 and the lagoon within, are given in the 

 ^ maps of islands on pages 133, 135. The 



< accompanying sketch represents a section o 



< the rim of land from the sea on one side 

 ° (the left) to the lagoon on the other. In 

 i the view, the part ?n a represents the shallow 

 I sea bordering an island, and abruptly deep- 

 ir enin^ one to six hundred feet from the 

 § line of breakers. In these shallow waters 

 t are the growing corals ; yet, as before stated, 



a large part is often barren sand or coral 

 rock, especially where the depth is over 

 fifty feet. 



From ^ to ^ is the shore platform or 

 reef-rock, nearly at low-tide level, with the 

 margin {a) slightly elevated, and usually 

 much incrusted at top with Nullipores. 

 From the platform there is a rise, by a 

 steep beach {b c), of six or eight feet, to 

 g the wooded part of the coral belt repre- 

 sented between ^and d. From d to e there 

 is a gently sloping beach bordering the 

 lagoon. Beyond e, the waters of the lagoon at first deepen 

 gradually, and then fall off more or less abruptly. 



