Observations and sampling to 350 m from a two-person submersible off Chub Cay, Berry Islands, Bahamas, suggest that accretion is occurring to varying degrees in all subdivisions of the platform margin profile. At the Chub Cay dive site, a nearly vertical wall extends to 140 m subsea; below, and extending to the limit of the dives, is a low-relief, fore-reef slope, ca. 50 degrees , of limestone veneered with sediment. This study supports the idea that the upper portion of the wall from 30 to 85 m, the brow or deep-reef, is a principal source of talus, now cemented, that foots the windward margins of Great Bahama Bank. We infer that the brow grows outward so rapidly that it calves periodically. The resulting debris largely bypasses the deeper wall, but some is perched on the steep fore-reef slope below, where it is soon incorporated into the slope by submarine cementation. This model further explains the observation that carbonate platform margins tend to steepen through time and shows how those steepened slopes can be maintained during their continued growth.