210 CORALS AND CORAL ISLANDS. 



most parallel to the main range of Keys from Cape Florida 

 to the western extremity of the Marquesas, where it is lost 

 in the deep. It follows, in its whole extent, the same curve as 

 the Keys encircling, to the seaward, the ship-channel already 

 mentioned. This is properly the region of living corals. 



"Throughout its whole range it does not reach the sur- 

 face of the sea, except in a few points where it comes almost 

 within the level of low-water mark, giving rise to heavy 

 breakers, such as Carysfort, Alligator Reef, Tennessee Reef, 

 and a few other shoals of less extent, but perhaps not less 

 dangerous. In a few localities, fragments of dead coral, and 

 coral sand begin to accumulate upon the edge of the reef, 

 forming small Keys, which vary in form and position accord- 

 ing to the influence of gales blowing from different direc- 

 tions — sometimes in the direction of the Gulf stream from 

 southwest to northeast, but more frequently in the opposite 

 direction, the prevailing winds blowing from the northeast. 

 Such are Sombrero Key, Love Key, the Sambos and Sand 

 Key. Here and there are isolated coral boulders, which pre- 

 sent projecting masses above water, such as the Dry Rocks 

 west of Sand Key, Pelican Reef, east of it, with many others 

 more isolated. Though continuous, the outer reef is, however, 

 not so uniform as not to present many broad passages over 

 its crest, dividing it, as it were, into many submarine elongated 

 hillocks, similar in form to the main Keys, but not rising above 

 water, and in which the depressions alluded to correspond 

 to the channels intersecting the Keys. The broad passages 

 leading into the ship-channel, which may be available as en- 

 trances into the safe anchorage within the reef, are chiefly the 

 inlet in front of Key Largo, and to the west of Carysfort 

 reef, with nine feet of water ; a passage between French reef 

 and Pickle reef, with ten feet ; another between Conch reef 



