The lower facies comprises the Peterborough Member, a fossiliferous organic-rich mudstone. Dolomite, limestone and chert with some fossiliferous units are particularly common. The limestones and dolomites of the Ellenburger Group are typically nonglauconitic and sparingly fossiliferous. These marine deposits have given rise to calcareous rocks which are often fossiliferous. The fossiliferous concretions are usually found within the thickest deposits of Francis Creek. Its sediments are approximately 400 feet thick, and its upper layers feature fossiliferous invertebrates. They are weakly metamorphosed and highly fossiliferous. The littoral zone contains the only fossiliferous strata. These sediments were found to be mainly shallow-water sediments, many of which are richly fossiliferous. It represents the only remaining known exposure of fossiliferous Pleistocene gravels along the River Avon. Fossils of these molluscs can be found in fossiliferous marine strata all over the world. Rock formations laid down in this time were frequently different types of fossiliferous limestone. The fossiliferous Barstow Formation (Miocene) is well exposed there. The parish lies on fossiliferous chalk and upper greensand. It is also the most fossiliferous (especially for ammonite fossils).