The deep forereef, a rugged, near-vertical to overhanging cliff, extends from 55 m to approximately 122 m below sea level off Discovery Bay, on the north coast of Jamaica. This cliff is being constructed near its top by a complex, living reef-coral community which extends to approximately 70 m, where it merges with a community dominated by sponges. Active framework construction by sclerosponges, coupled with the lithification of unconsolidated sediment (largely coral and algal debris from above) which is retained by large debris and living sponge "dams," occurs to depths of approximately 105 m. Below this depth the deep forereef does not appear to be actively accreting seaward. The cliff face consists of a series of irregular, alternating promontories and reentrants. As i shallower reef zones, framework construction and organism diversity are maximized on the promontories, whereas the reentrants are regions of active downslope sediment movement and, near the base of the cliff, of active erosion.

The island slope which laps up against the base of the deep forereef either is covered with unlithified sediment and debris or consists of an unconformity surface of densely cemented debris (reef rock) undergoing intense biologic erosion. Nearly 50 m of densely lithified island slope deposits appears to have been exhumed in one area. Unlithified reef sediment, which is retained behind various kinds of reef-derived debris, rapidly decreases both in abundance and in grain size downward to 305 m, where pelagic sediment predominates. Below 200 m, rounded limestone blocks as tall as 30 m protrude upward through the island-slope sediment in the axis of a submarine canyon. These limestone blocks are also undergoing intense biologic erosion.