AbstractA survey involving 860 gravity measurements over the Fylde area of Lancashire is described. A line of movement in the pre‐Permian basement rocks is shown to cross the area from north north east to south south west forming the eastern edge of a deep sedimentary basin. Displacement of the Carboniferous along this line has reached 1000 m in places and was probably an important influence on Permo‐Triassic deposition in Northwest Lancash