Seismic, gravity, aeromagnetic, and vertical and horizontal magnetic surveys in Indiana were interpreted collectively in a prescribed sequence that led to information ordinarily not obtained from the individual surveys. Prominent reflections and sharp, coincident magnetic and gravity anomalies in Pulaski County indicate a roughly circular body with its top at a depth of 1.4 km, 2.5 km in vertical thickness and 29 sq km in area, magnetic susceptibility contrast of 0.0088 cgs and density contrast of 0.21 g per cm 3 . This is interpreted as a basalt plug intruded into the granitic basement, possibly one of a series of vents along the Cincinnati arch that were the source for Precambrian basalt flows in Indiana.

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