They would not thus form a layer of flint keeping more or less to the same level in the chalk. At the periphery, where they entered the area, they would be lower in the chalk, and gradually rise.

"The flint is formed within the chalk rock that underlies Norwich and most of Norfolk," they explained. "This chalk is about 80 to 90 million years old and was formed at the bottom of the sea ...

the flint from there is black as charcoal when newly broken, but the outer patina is creamy white, probably from being in contact within the chalk it's usually embedded.

but the majority of flint mines were on the chalk hills of southern England, with underground galleries following the seams of flint reached by shafts up to 15m deep.

A fossil that was found on Mousehold Heath in Norwich could be 90 million years old, according to the Geological Society of Norfolk.