A borehole drilled at Petrockstow (England) to investigate the thickness and lithologies of beds tentatively dated as Oligocene in a downwarp between two northwest-southeast wrench faults traversed 2167 feet of unconsolidated clays, sands, and quartz gravels overlying upper Carboniferous strata. Geophysical logs were recorded; the density and sonic velocities of the unconsolidated deposits differ markedly from those of the upper Carboniferous strata.