The recent Climap investigations have indicated that during the glacial periods, Caribbean sea water temperatures were probably no more than 1-3^oC lower than present. Also, it has been found that major barrier reefs existed as far north as Florida during the early Holocene. Holocene reef buildups of 10-30 m in thickness are known to be widespread in the Caribbean and algal ridges, which occur sporadically throughout the region, are abundant in the eastern Lesser Antilles. The major reef framework building organisms present today, the Acro~ora corals, Millepora and the corallines Porolithon and Lithophyllum in shallow water, and the more massive corals, especially Montastraea, in deeper water, are quite capable of producing extensive frameworks at upward-building rates of over 6-10m/thousand years under the right sea level and antecedent platform conditions. The Caribbean-West Indies is geologically an active area. Much of the continental coast of South America, some of the coasts of the Greater Antillean islands as well as some of the young volcanic islands of the Lesser Antilles have unstable shorelines that are presently unsuitable for reef development. However, on more stable windward shores reef development is widespread. The extent of its occurrence on any stable shore is largely determined by pre-Holocene shoreline morphology and position relative to present sea level