Bluefish Channel, north of Key West is incised in a thick Recent carbonate bank on Pleistocene bedrock. The dominant sediments are Halimeda, foraminifera, mollusks, and fragments derived from the bedrock. The source area lies all along the channel; sediment mixing results in textural inversions and characteristically negatively-skewed channel sands. A sorting-grain size plot shows a sinusoidal trend similar to that of a beach environment. The best sorted sediment is mature medium calcarenite, a mixture of four constituents in almost equal proportions. Some calcarenites deposited at the tidal delta, adjacent to the channel, show the initial stages of penecontemporaneous, submarine cementation by chemically precipitated aragonite crystals. Hydrodynamically, the channel is in the upper-flow regime.