Geophysical and well data suggest that the Recent reef growth on the exposed northern Great Barrier Reefs forms only a thin veneer on earlier reef limestones. Reef framework growth up to sea level is principally from local prominences which supply sediment of unstable coral branches to neighbouring valleys. Once a large area of a reef reaches sea level, the SE winds play an important role in further development by causing the major lateral growth to be to leeward and characteristic intertidal deposits to accumulate. Leeward sand cays form during prevailing conditions on reefs across the shelf and may be eroded during storms but windward rampart deposits form during storms and are eroded during prevailing conditions on those reefs exposed to heavy surf. The ramparts on the inner-shelf reefs are stabilized by mangroves and cements resulting in a progressive elevation of the surfaces of reefs towards the mainland.