AbstractA surface resistivity survey around and to the south of Garstang has indicated a predominance of boulder clay, with some sands and gravels, in an overburden of markedly variable thickness and lithology. The survey techniques, data processing and interpretation are discussed. The data suggest that the Lower Boulder Clay may be represented northeast of Garstang, with the Middle Sands present over a much wider area. The major subdivision, the Upper Boulder Clay, seems to be overlain by patches of presumed Upper Sands. Possible isopachytes of these four suggested subdivisions are presented, and certain hydrogeological implications briefly mentioned.