Field investigations failed to confirm the presence of earlier (pre-Sangamon) Pleistocene or Citronelle (Pliocene) littoral ridges and marine deposits on the surface in coastal Mississippi, Alabama, and the Florida Panhandle. The contrast between the numerous marine surfaces on the Atlantic coastal plain and the single Sangamon interglacial barrier complex of the Gulf Coast may be explained by the different regional tectonic behavior of the 2 provinces.

Only 1 Pleistocene coastwise alluvial depositional surface was found in Mississippi and southwestern Alabama in addition to the Prairie (Pamlico, Beaumont) alluvial coastal plain. Its age could not be exactly determined. In addition to the known Pearl and Pascagoula River valley locations, intermediate valley terrace fragments ("Deweyville"?) were found near the mouth of the Biloxi and Tchoutacabouffa Rivers. These surfaces indicate the latest higher sea level stage which probably existed during the early Wisconsin stage.

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