AbstractThe geological section exposed in a deep boring for water in the Millstone Grit near Darwen, Lancashire, is described. Details are given of the lithology and palaeontology throughout a thickness of 700 ft. of rock, extending from the Holcombe Brook Grit well into the Fletcher Bank Grit. In discussion, the rhythmic character of sedimentation is emphasised, and attention is also particularly drawn to the importance of marine bands (withGastriocerasaff.sigma, Reticuloceras reticulatumearly mut. γ and late mut. β) and aLingulaband in determining the Grit