A shelly sandstone containing a modern microfauna, recovered from 43 fms, has been cemented by cryptocrystalline aragonite an clear fibrous aragonite. Numerous organic borings, some algal, penetrate both cement and shells. The rock resembles beachrock, and intertidal formation. On the basis of the radiocarbon-controlled sea-level curve and on the supposition that the age of the shells indicates time of cementation, we conclude that cementation occurred on the sea floor under a cover of 75 m of seawater. A widespread occurrence of aragonite-cemented sandstone along the east coast of the United States suggests that the submerged littoral sand may have been cemented on a large scale, and was controlled by methane originating in adjacent tidal marshes, now submerged.