The transect at Longboat Key is located across a relict tidal inlet that connected two islands in pre-historical time (FitzGerald, 1995; Barnard, 1998). The island is now a wave-dominated barrier although the southern portion was a drumstick barrier when it was separated from the northern portion. The stratigraphic cross-section across this area includes portions of both of the former barriers and Buttonwood Sound, the former tidal inlet.

None of the vibracores reached the Miocene carbonate strata. However, cores from the relict inlet and from Sarasota Bay did contain limestone clasts. A core taken by Knowles (1983) from just landward of the cross section shown here encountered limestone at 6.5 m below sea level. Cores from Sarasota Bay and Bowlees Creek (FitzGerald, 1995) penetrated Pleistocene sediments, which are muddy, well-sorted sands interpreted to have accumulated on an eolian strandplain.

The deepest strata penetrated in this cross section are shelly sands interpreted to represent channel deposits (FitzGerald, 1995; Yale, 1997), most likely associated with the relict inlet and its previous positions. Abundant washover deposits are present over the channel deposits and are also laterally equivalent to the same facies. The typical nearshore, beach, and dune deposits of sand and shelly sand comprise the present barrier facies.