Paleocene and Eocene green cherty tuffs and pelagic sediments, in a generally volcanic rock sequence, crop out in Puerto Rico and the Dominican Republic. These rocks are here correlated by lithology and age with oceanic horizons found by reflection profiling and coring: Layer A in the Atlantic Ocean, and Layer A” and the Carib beds in the Caribbean Sea. The generally thin pelagic or airborne sediments in the ocean basins flank thicker clastic, pelagic, and volcanic deposits on the Antillean Ridge. Trenches north and south of the ridge apparently trapped most of the coarser volcanic material, preventing its reaching the ocean basins. Lithification (except that forming chert) and deformation of these sediments was also restricted to the Antillean Ridge. The zone of deformation is about 180 km wide, and the transition between deformed and undeformed rocks takes place over a distance in some places as short as 10 km.