Nearly two thirds of the state of Georgia lies within the Coastal Plain province. A small area in the northwest corner of the state is occupied by highly folded and faulted Paleozoic rocks of the Valley-and-Ridge and the Blue Ridge provinces, and the remainder of the northern part of the state is covered by crystalline rocks of the Piedmont (Fig. no). In the Coastal Plain, the Cenozoic and Mesozoic strata range in thickness from a wedge edge at the northwest margin to more than 7,500 feet in the southwestern part of the state; in southeastern Georgia they range from 3,500 to 4,500 feet. Underlying the Cenozoic and Mesozoic deposits in southern Georgia, early Paleozoic clastic rocks were encountered in several wells, but their full thickness has not been penetrated. The volume of the sedimentary section in the Coastal Plain of Georgia is estimated to be 20,000 to 25,000 cubic miles.
The rocks underlying the Coastal Plain of Georgia range in age from pre-Cambrian to Recent, but the greater part of the sedimentary rocks are Cretaceous and Tertiary (Fig. 113). Schistose rocks and granite in the buried extension of the rocks of the Piedmont were encountered in shallow wells in the northeastern part of the Coastal Plain, and granite was encountered in two wells in Pierce County in the southeastern part of the state. Two wells in southeastern Georgia terminated in volcanic rocks that are considered to be of pre-Cambrian or early Paleozoic age. Seven wells in south-central Georgia and a