The Green Cove Springs and Boulougne heavy-mineral sand deposits are in ridge areas on the Duval Upland of northern peninsular Florida. This upland is believed to be a regressional beach ridge plain. It is hypothesized that during development of the plain the regressing seas were characterized by periodic stillstands of relatively long durations and even by slight transgressions. During these intervals more prominent ridges formed and greater concentrations of heavy minerals accumulated. The hypothesis that the Green Cove Springs and Boulougne ore bodies formed in such ridge areas as a part of a beach ridge plain is consistent with field relationships and with sedimentary features of landforms in the region. The concept also is compatible with the hypothesis that Trail Ridge and the Trail Ridge heavy-mineral deposit west of the Duval Upland was built at the height of a marine transgression.