Geograph - photograph every grid square

An unconformity between the Cretaceous and the Palaeogene (early Tertiary) systems.

This site was originally a quarry - from 1830 - to provide chalk to lime the local acidic soil.

The upper level of chalk in the quarry was eroded before deposition of the overlying beds - this is the unconformity. The unconformity represents a missing time period of around 30 million years. After the period of erosion, the sea covered the site, depositing sands. Later, the site became estuarine, and clays were deposited. The lowest layers above the chalk contain pebbles coated by glauconite, which lends that layer a greenish hue. The sand and clay layers comprise the Reading Beds.