Buckinghamshire is a ceremonial county in South East England southeast of London. The typical rock is white Cretaceous chalk which is not suitable for karstification, so there are no natural caves. But quarrying and mining has taken place for chalk, clay for brickmaking and gravel and sand in the river valleys. Flint, also extracted from the chalk quarries, was used to build local buildings. Several former quarries are now flooded, some have become nature reserves. Only one is open to the public.