Stratification in solid rocks may be expressed by bedding planes or by any of a number of other layered features. Some features can be explained by, and parallels seen in, present-day sedimentary processes. Many lack any explanatory mechanism other than "environmental change" This phase, as normally used in geological literature, implies an external influence acting on the sediment, but an internal influence can also produce "environmental change" within the sediment. A sedimentary sequence from Galway Bay on the West Coast of Ireland is described and a mechanism is proposed to explain a change in sediment type which increases internal influences of in-fauna debris rather than a change in external environmental influences. It is suggested that a review of what constitutes an "environmental influence" is long overdue, especially in sediments which are produced in the main by the debris of an in-fauna.