Data from 31 seismic-refraction profiles are interpreted and presented in five structure sections. The subsurface structure east of Florida under the Blake Plateau is similar to that of the margin north of Cape Hatteras. Basement plunges seaward from Florida into a deep sedimentary trough under the Blake Plateau. A basement ridge parallels this north-south-trending trough on the seaward side, along the eastern edge of the plateau.

The basin under the Blake Plateau was separated from the South Florida-Andros Island basin, at least until the Early Cretaceous, by a southeastward extension of the Peninsular arch. This seaward extension trends from just east of Cape Kennedy to the western end of Little Bahama Bank.

The marked relief of the Florida shelf, the Florida Straits, and the Blake Plateau is evident only in the sedimentary layers and is the result of significant changes in thickness of the post-Paleocene section, especially the Eocene. The top of the Paleocene extends beneath the present physiographic irregularities with slight relief, whereas the Eocene thickness ranges from about 500 m. on Florida to about 70 m. on the Blake Plateau. Strong currents sweeping the Florida Straits and Blake Plateau probably are responsible for the absence of a thick post-Paleocene section The present orientation of the Florida Current may have existed as early as Paleocene time.

Besides the changes in relief within the sedimentary section, there are lateral facies changes and velocity variations. These variations are primarily dependent on the depth of burial. Nearly similar velocity-depth distributions are found for the Blake Plateau, the Florida Straits, the Bahama banks, and the Florida platform. The variations in thickness of the sediments in these areas result in variable velocities in the stratigraphic units, and correlation of the refraction data is difficult.