FLORIDA REEFS. 25 
island formed chiefly of broken shells and coral fragments thrown ujj on the 
edge of the reef, a new feature begins. The higher ledges approach each 
other again, and the depressions between them are shallower than those to 
the east. We have here in close succession from east to Avest the American 
Shoal under six feet of water, the Pelican Reef with about four feet of water, 
and East, Middle and West Sambos, three little keys of a few acres in ex- 
tent, consisting chiefly, like Looe Key, of broken shells and coral fragments, 
forming so light a crust upon the edge of the reef that storms occasionally 
wash away the whole accumulation. Between West Sambo and Sand Key, 
another depression on the reef, with a depth of water varying from four to 
five fathoms, forms the main channel leading into Key West. Toward Sand 
Key the reef widens considerably, but the corals are less crowded upon it. 
Large accumulations of coral sand intervene between the living heads, and 
detached masses and fragments of corals are thrown up in quantities upon 
the ridge, forming extensive shoals. To the east of Sand Key these shoals are 
known as the Eastern Dry Rocks and Rock Key ; to the west, as the Western 
Dry Rocks. Sand Key itself is a small island also consisting chiefly of coral 
fragments and coral sand heaped above the field of large coral boulders 
stretching almost uninterruptedly from Eastern Dry Rocks to Western Dry 
Rocks. This part of the reef contrasts remarkably with the Sambos, and, taken 
together, they explain the process by which a living reef is transformed into 
a dry key. At the Sambos as at Carysfort we have a field of Madrepora 
palmata mixed with a few stocks of Millepora alcicornis and bunches of Gor- 
gonia rising as a level ledge to the surface of the water at low tide. Upon 
the most prominent points of this ledge, coral boulders and sand are accumu- 
lated, every such accumulation forming the nucleus for a key. Comparing 
such incipient keys with Sand Key, we there find that the collection of 
coral boulders and sand has increased so much as to cover entirely the sum- 
mit of the once living reef, spreading also far down upon its slopes. Before 
the storm of 1846, vegetation was spreading over Sand Key, and a light- 
house was built upon it. In the hurricane of the 11th of October, the 
lighthouse was w^ashed away with the mass of coral boulders on which it 
stood. This mass of loose materials had in fact been mistaken for con- 
tinuous coral rock sufficiently solid to support the structure based upon it. 
This unfortunate event has shown that the loose cap resting upon the 
more solid reef should always be removed before laying the foundation 
of a lighthouse. The solid rock is not to be reached at the level of low- 
