172 CORALS AXD CORAL LSLAXDS. 



Keys incircling, 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 surface 

 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 Car}-sfort, Alligator Reef, Tennessee Reef, 

 and a few other shoils 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 

 south-west to north-east, but more frequently in the opposite 

 direction, the prevailing winds blowing from the north-east. 

 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 wnthin 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 

 and Crocus reef, also with ten feet ; another between Crocus 

 reef and Alligator reef, with two fathoms ; another between 

 Alligator reef and Tennessee reef, with two fathoms and a 

 half; and a sixth to the west of Tennessee reef varying in 

 depth from two-and-a-half to three fathoms." 



Through the labours of Mr. de Pourtales, in connection 

 with the soundings by the Coast Survey, interesting facts 

 have been brought to light respecting the sea between the 



