THE FLORIDA REEFS. 75 
fringing 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 
