THE WEST INDIAN WATERS 15 



with living organisms ; in the channels of the Windward 

 Islands, near Guadeloupe, and the Saintes, and about St. 

 Vincent and Barbados, dense forests of pentacrini undu- 

 late on the bottom like aquatic plants. 



The purely biologic aspect of the sea life is not more 

 wonderful than the architectural work that deep-sea ani- 

 mals and the millions of mollusks and coral polyps which 

 inhabit the shallower waters and banks perform. These 

 extract the lime carried in solution by the translucent sea- 

 water, and convert it into the shells and corals which are 

 so large a part of the beach sands, and the glaring white 

 limestones which are conspicuous features in the West 

 Indian Islands and the Florida and Yucatan peninsulas. 



The embryonic coral polyp is a free swimmer in the 

 sea, which in a second stage of its life-history becomes 

 permanently fixed on the banks, and devotes the remainder 

 of its life to extracting calcium carbonate from the sea and 

 assimilating it into its stony skeleton. It will thrive only 

 on shallow banks less than one hundred fathoms deep, and 

 where the temperature and clearness of the water are to its 

 liking. Once domiciled, it grows upward, and, dying, leaves 

 a huge skeleton of stone, upon which other polyps become 

 fixed and add their sum to the mass. Gradually the 

 growth reaches the surface of the waters, when the waves 

 and winds disintegrate it into calcareous sand and soil 

 upon which vegetation finds root. Thus the coral islands 

 are born. 



The coral-builders are at work over a vast range, which 

 is estimated at one fourth of the marine surface of the 

 region. To their incessant toil must be largely attributed 

 the formation of much of the calcareous plateaus by which 

 the Yucatan and Florida straits are contracted on both 

 sides, as well as of those rocky ledges which are washed 

 by high tides, and are revealed only by sandy dunes, such 

 as the Salt Key, or by their fringe of mangroves, like some 

 of the Florida Keys, and Anegada with its prolongation, 

 the dreaded Horseshoe Reef, connecting it with the Virgin 



