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 sui-face of the sea 
except in a few points Avhere 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 submai'ine 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 fothoms. 
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 
