THE FLORIDA REEFS. 63 



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 orowth 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 owe 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 trachytic 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 livings in the West India seas. 



six to forty-seven per cent, of carbonate The most recent limestone contains, 

 of lime and from thirty to thirty-five per like the corals of which it is almost en- 

 cent, of phosphate of lime, with ten to tirely made up, ninety-six per cent, of oar- 

 twelve per cent, of carbonate of magne- bonate of lime and a little silica. In the 

 sia, and from ten to twelve per cent, of ooze the amount of carbonate of lime was 

 oxide of iron. This large amount of iron eighty-five per cent., there being also over 

 is probably brought down by the rivers, four per cent, of carbonate of magnesia, 

 and, coming in contact with the decompos- and eight per cent, of organic matter, with 

 ing organic matter, is deposited as a car- about one and one half per cent, cf silica, 

 bonate, and then slowly changed to a ses- and only a trace of phosphoric acid, which 

 quioxide. distinguishes this ooze from Atlantic ooze. 



