The Vincennes Magnetic Anomaly Lee County, lowa

Relative measurements of the vertical magnetic intensity in southern Lee County, Iowa, were made with a tripod-mounted, Askania Torsion Magnetometer, Type Gfz. The Vincennes magnetic anomaly is attributed to a body of magnetic rock in the Precambrian crystalline complex. From diamond drilling, the top of the body is known to be about 2900 feet below the surface. Although no unique interpretation is possible, a mathematical analysis of the magnetic data suggests that the body may be shaped something like a shallow dish approximately 1,000 feet thick through a diameter of 3 miles and tapering to a feather-edge at a diameter somewhat greater than 4 miles. The body may contain about 10 per cent of uniformly disseminated magnetite. The magnetic polarization of the body is assumed to be due entirely to the earth\u27s present magnetic field