THE FLORIDA REEFS. 6% 
but with a much steeper slope. These fringing limestones also 
formed the southern extremity of Florida at a time when the 
northern part of the Everglades had perhaps been built up to a 
level favorable for the growth of coral reefs. 
In the northern portion of the Everglades alone can we con- 
fidently speak of the first concentric reefs, which have little by 
little built up Florida toward the south. It seems highly 
probable that on the remainder of the peninsula north of the 
Everglades, both the newer and older limestones were built up 
by the same agencies now at work on the Florida Bank. There 
are to-day other submarine banks which undoubtedly owo their 
origin to similar agencies. "The great bank to the east of the 
Mosquito coast, which practically extends to Jamaica, has prob- 
ably been formed in the same way as the Yucatan and Florida 
banks; that is, by the gradual decay of the animals subsisting 
in great abundance upon its slope, and fed by the pelagic 
materials which the currents and the prevailing winds bring to 
the bank, and which have been pouring upon the top of the 
plateau for ages past. All the reefs on the south coast of 
Cuba between the Isle of Pines and the shore of the east and 
west may have had a similar origin. Among the West India 
Islands the barrier reefs of the windward side are built upon 
plateaux of a similar structure. The Grande Terre of Guade- 
loupe is a fine example of such a plateau, which has been ele- 
vated slightly above the level of the sea. At Barbados the 
whole shell of the island consists of a series of terraces, which 
have been successively lifted by the trachytie centre that forms 
the nucleus of the island. These terraces are entirely com- 
posed of limestone formed of the species of mollusks and radi- 
ates now living in the West India seas. 
six to forty-seven per cent. of carbonate 
of lime and from thirty to thirty-five per 
cent. of phosphate of lime, with ten to 
twelve per eent. of earbonate of magne- 
sia, and from ten to twelve per cent. of 
oxide of iron. This large amount of iron 
is probably brought down by the rivers, 
and, coming in contact with the deeompos- 
ing organic matter, is deposited as acar- 
bonate, and then slowly changed to a ses- 
quioxide. 
The most recent limestone contains, 
like the corals of which it is almost en- 
tirely made up, ninety-six per cent. of car- 
bonate of lime and a little silica, In the 
ooze the amount of carbonate of lime was 
eighty-five per cent., there being also over 
four per cent. of carbonate of magnesia, 
and cight per cent. of organie matter, with 
about one and one half per cent. cf silica, 
and only a trace of phosphoric acid, whieh 
distinguishes this voze from Atlantic ooze. 
