Mesozoic sedimentary rocks are present throughout Florida and the Coastal Plain of Georgia, but chiefly in the subsurface in an area of approximately 93,500 square miles. The Mesozoic rocks in this area belong, for the most part, to the Gulf and Comanche series of the Cretaceous system. Rocks tentatively classified as part Jurassic and part Triassic underlie the Comanche series in parts of Florida and Georgia. In the northern part of the Georgia Coastal Plain, an irregular outcrop belt of sandstone and shale belonging to the early Upper Cretaceous Tuscaloosa formation borders on the south the crystalline rocks of the Piedmont. Southward from its outcrop in western Georgia, the Tuscaloosa formation dips under roughly parallel belts of the progressively younger Eutaw formation and formations equivalent to the Selma group of the Gulf series. In central and eastern Georgia, the Eutaw formation and formations equivalent to the Selma group are covered by overlaps of Tertiary formations. Conclusions in regard to the stratigraphy, structure, and thickness of the Mesozoic rocks are based largely on interpretations of the records of approximately 200 oil test wells. The total volume of the Mesozoic rocks in Florida and southern Georgia is estimated at 60,000 to 75,000 cubic miles.