Since reference ib made from time to time to examples of supposed subaqueous sliding on a large scale in the Silurian rocks (Salopian Series) of Denbighshire. Xorth Wales. for the purpose of supporting inferences about the mode of origin of certain intraformational disturbances, the stratigraphical evidence in Denbighshire is revieited. On the basis of zoning by means of p p t o l i t c s (or shelly faunas where available), the boundaries of the alleged sheets of slipped material prove to b" transgressive. In particular, the largest ' conteniporaneously-disturbed sheet includes parts of the undisturbed succession ranging in age from the nilssonz zone to the trrmcsccns zone. Its supposed base would have to cross its supposed surface, so that it would appear to have a negative thickness-of minus 1.000 feet or more. Acceptance of the hypothesis of large-scale sliding on the sea-floor in this area is thus incompatible with a belief in the value of graptolites as zonal indices in the Salopian roclts * The term ' slump ' IS 'ambiguous. being commonly applied to either subaerial landslips or subaqueous slides. The distinctive terminology is preferable, especially since subaerial slips sometimes continue as under-water slides.