In the southeastern Coastal Plain, information is available on 60 widely scattered oil test wells that have been drilled through the Cenozoic and Mesozoic deposits into older rocks representing a wide variety of types.

In Florida and Georgia these buried pre-Mesozoic rocks fall in three general classifications which are:

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1. Dominantly marine sedimentary Paleozoic rocks that at present are known to range in age from late Cambrian or early Ordovician to Silurian.

2. Volcanic rocks which underlie sedimentary rocks considered to be of early Paleozoic age.

3. Crystalline rocks that are chiefly granitic and metamorphic. These rocks are possibly in part pre-Cambrian and in part Paleozoic in age.

In the Coastal Plain of Alabama, the buried pre-Mesozoic rocks are classified as:

1. Paleozoic sedimentary rocks that range in age from Cambrian and Ordovician to Pennsylvanian.

2. Metamorphic rocks that are possibly pre-Cambrian in age.

The volcanic rocks that underlie the early Paleozoic sedimentary rocks in Florida and Georgia have not been discovered in Alabama.

Most of the wells in the pre-Mesozoic rocks have been drilled within the past decade, and in Florida and southern Georgia the discovery of volcanic and crystalline rocks and Paleozoic strata is a comparatively recent addition to geologic knowledge. One map shows the location of the wells penetrating the pre-Mesozoic rocks and the types of rocks penetrated. Based on the study of cores and cuttings in connection with the geographic distribution of the wells, a diverse lithologic pattern is being revealed in the pre-Mesozoic rocks of the subsurface in the southeastern Coastal Plain. By means of contours drawn at 1,000-foot intervals on top of the pre-Mesozoic rocks, a second map shows the present configuration of the surface of these rocks. Two structural profiles drawn through series of wells in Georgia and Florida show an interpretation of the present structure of the pre-Mesozoic rocks and the relation of the overlying Mesozoic and Cenozoic deposits to the pre-Mesozoic surface.

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