E2BN Gallery

The layers of rocks give an indication of the ever-changing environmental conditions at the time of their formation. The early strata show a transition from marine to terrestrial. The cinder bed, for example, has the remains of echinoids (sea-urchins) in the rocks. These cannot survive in non-marine salinities and indicate that rock formed in marine conditions. They only occur in this layer at all other times the salinities were either above or below those of sea-water. Other layers such as the flint bed contain freshwater gastropods. Within the Purbeck formation is also layer called Great Dirt Bed, which represents an ancient soil in which conifer type tress grew. The many changes show that conditions fluctuated widely in this extensive shallow lagoon area over the time the rocks were being formed and possibly also seasonally (so that the lagoon became very salty in the dry summer but almost fresh water in the winter).