FLORIDA REEFS. 5 



main range of keys from Cape Florida to the western extremity of the Mar- 

 quesas, 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 men- 

 tioned. 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 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 edges of the reef, forming small keys, which 

 vary in form and position according to the influence of gales blowing from 

 different directions, — 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, 

 Looe Key, the Sambos, and Sand Key. Here and there are isolated coral 

 boulders, which present 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 corre- 

 spond to the channels intersecting the keys. These broad passages leading 

 into the ship channel, which may be available as entrances 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's Reef, with ten feet ; another between Conch Reef 

 and Crocker's Reef, also with ten feet ; another between Crocker's Reef and 

 Alligator Reef, with two fathoms ; another between Alligator Reef and Ten- 

 nessee 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. 



The remark which has been made respecting the mud 'flats and their 

 gradual deepening from east to west applies equally to the general features 

 of the main reef, as well as to the intervening channel. To the eastward 

 the channel is shallower, the ground around the keys and reef becomes 

 shoaler, and there is a gradual dip towards the west, which makes the con- 

 nection less marked between the keys west of Key West, in the large groups 

 of the so-called Mangrove Islands, and the Marquesas, beyond which there is 



