THE FLORIDA REEFS. 75 



frino'msr reef which skirts nearly the whole northern coast of 

 Cuba is in a less flourishing condition than the Florida Reef on 

 the opposite shore, which is reached not only by the main cur- 

 rent of the Gulf Stream, but also by the prevailing winds. The 

 circular outline of the main reef is readily explained by the action 

 of the Gulf Stream, which sweeping along the steep edge of the 

 southern extremity of the great Florida plateau carries with it a 

 superabundance of animal life, and gives the general direction 

 along which the conditions most favorable to the luxuriant growth 

 of corals exist when once the proper depth has been reached. 



For a similar reason, corals are found alive only on the edges 

 of the Great Bahama Bank, where they are subjected to the be- 

 neficent action either of currents or of winds, that drive the silt 

 clear of the growing corals, and bring an abundant supply of 

 food. The same causes which have formed the great mud banks 

 to the northward and westward of the Florida Reef have, in the 

 case of the Bahama Banks, formed the immense sand flats and 

 shallows which are fringed by living corals on the east and 

 west. They owe their existence, on the one side, to the wash 

 of the northerly trend of the great equatorial current, and to 

 the action of the trades ; on the other, to the clearing action of 

 the Gulf Stream. It must also be remembered that the Bahama 

 plateau was originally joined to Florida, as part of the great 

 fold which built up the framework of that peninsula, and that 

 it was also connected at one time with the island of Cuba. It 

 was also united with the reefs, now elevated to eleven hundred 

 feet, which joined the eastern and western islands in more recent 

 geological times, and formed, before the tertiary, the two ex- 

 tremities of Cuba. On the southern side the reefs are still in 

 full activity, while on parts of the northern coast, in the vicinity 

 of Havana, they have been elevated to a height of no less than 

 one thousand or eleven hundred feet, while the present barrier 

 reef of the north shore of Cuba forms an immense reef, extend- 

 ing with scarcely a break from Cape San Antonio to the eastern 

 edge of the old Bahama Channel. 



The Bahama plateau we may also fairly assume to have been 

 built up, little by little, from its original level, by the accumu- 

 lation of limestone formed in great part from the bodies of the 



