A seismic data set was collected in northern Wisconsin in the summers of 1980--1981. The study area overlies a less heterogeneous portion of the Precambrian Puritan batholith, a body which has been intruded, and otherwise deformed since its emplacement. High-velocity bedrock lies beneath a thin glacial till layer. Other than a shallow penetration first arrival, there was no evidence of refractors or reflectors in the upper few kilometers. The data contain an abundance of energy, and our goal was to determine the source of that energy. A processing technique, based on the split array cross correlator (Jacobsen, 1957; Doll, 1983), was developed for locating diffractors with a sparse data set. The technique is similar to those used in underwater acoustics and radio astronomy for locating point sources. It assumes an acoustic medium with known veloctiy structure, in which inhomogeneities may be treated as point diffractors. The output is the windowed cross correlation of two stacks of delayed traces. The delays are determined by ray tracing for each source-to-grid point and grid point-to-receiver path. The cross correlations are calculated over a two-dimensional array of grid points. The method is useful when data are sparse and conventional linear methods fail to image subsurface structure. Our images show reflections and diffractions from a dipping interface at about 6--8 km depth, as well as other features associated with the Puritan batholith. ¿ American Geophysical Union 1988