An aeromagnetic survey was made in November, 1946, of a 1,785-square-mile area in central Pennsylvania, to gain information on the pre-Cambrian basement rocks and their relation to structure in the overlying Paleozoic sedimentary rocks. The area surveyed lies mainly in the Allegheny Plateau, but also includes a small part of the Valley and Ridge Province.

The major magnetic features are believed to reflect inhomogeneities in a geologically complex basement, rather than irregularities of the basement surface. Analysis of the magnetic results also indicates that the basement structural trends diverge somewhat from surface structure; and that the basement surface is not deformed concordantly with the highly folded Paleozoic rocks in the Valley and Ridge part of the area.

Depth estimates place the basement 19,000-22,000 feet beneath the surface in the west-central part of the area, which is in good agreement with estimates based on geologic considerations. Magnetic evidence, admittedly inconclusive, indicates that the basement may be deeper southeast of the Appalachian Front, rather than northwest, as is generally supposed.