The Cape Romano-Ten Thousand Islands area of southwestern Florida is roughly at the southern end of quartz sand littoral drift. Shell hash is prominent offshore, and silt, clay, and peaty materials are important in the mangrove-barrier-and-lagoon strip. The area therefore appeared to offer an excellent opportunity for a study of changes in facies of modern sediments. The shoreline is one of low-to-moderate wave energy. Where wave energy is dominant (in the updrift direction), quartz sand beaches appear; where wave energy is very low and tidal energy is important, a mangrove swamp barrier separates the lagoon from the Gulf of Mexico. Wave energy seems to be decreasing toward the SE. The combination of decreasing energy and tidal current circulation produces a quartz sand island-and-shoal complex in the vicinity Cape Romano. Wave refraction appears to have given the shoal area its present form. The sediments of the area are essentially quartz sand and shell hash along the beaches and on the Gulf floor, and fine-grained sand, silt, clay, peaty material, and oyster bars in the mangrove-barrier-and-lagoon strip. Analysis of the microfauna (Foraminifera and ostracodes) permitted a separation of samples into 4 suites: marsh-river (mainland), lagoon, mangrove-island, and open Gulf. Organic and other fine-grained matter suspended in the water prevented a systematic study of sediment surface markings.