The cause of this is unclear, but it James A. Musser, Arco Oil and Gas Co.; Yih Jeng and may be related to buried metasediments, subducted oceanic crust, J. C. Mareschal, Georgia Inst. of Tech.; and Transfer functions The survey line extends to the northwest from Savannah, Georgia in the Atlantic coastal plain, across the Piedmont plateau A laterally uniform geomagnetic variation, incident upon a and Blue Ridge provinces and into the Valley and Ridge province horizontally layered earth, will penetrate downward, and all electric of east-central Tennessee. These data were Fourier analyzed and and magnetic field variations will be horizontal. Thus the transfer functions relating the anomalous vertical magnetic field presence of a vertical component of the geomagnetic field varia-variations to variations in the horizontal field were computed for tions is an indication that either the incident variation is nonuniform various periods ranging from about 10 to about 4000 sec. The or the conductivity structure is not horizontally layered, or transfer functions define induction arrows (Parkinson vectors) both. In the middle latitudes, the magnetic field variations are seen which give an indication of the conductivity contrasts, depths, and to be very nearly uniform over large distances, so vertical field relative positions of anomalies.