Seismic refraction measurements of sand and clay strata in the vicinity of the Wilcox-Claiborne (Eocene) contact in Northern Lafayette County, Mississippi, have been used as a basis of delineation of the areal extent of a perched water table. Insitu velocities of relatively pure sand or pure clay strata have similar velocities; however, insitu velocities increased with moisture or water content and decreasing sorting coefficient. Velocities decreased with porosity and weathering. The perched water table was capped with a low velocity zone, between the overlying clay stratum and the underlying saturated sands. Upper and lower bounds of the velocities in the unsaturated upper zone of the water bearing sand allowed calculation of the thickness of the low velocity layer, and the surface of the perched water table was mapped. The maximum hydraulic head of the Lambert Springs site was seventy feet during the wettest season of the year. (Author)