Chalk is a type of fine grained limestone which is porous, soft and mainly composed of the skeletal remains of microscopic, planktonic green algae

Chalk was formed when microscopic marine plants and animals died and their remains settled to the bottom of shallow to moderately deep, warm seas. They formed a mud that was compacted as more and more of these microscopic particles fell to the bottom. It would have taken billions upon billions of such particles to form a chalk bed such as is found in Berengrave nature reserve and it would have taken millions of years for such a bed to form

Many millions of years ago, the area which is now Berengrave nature reserve must have been under water, but falling sea levels, or rising land levels, have left the chalk exposed where it is today

Because chalk is porous it can hold a large volume of ground water, providing a natural reservoir that releases water slowly through dry seasons.

Chalk beds contain many fossils from larger creatures such as echinoids (sea urchins) and ammonites (sea snails)

They also contain flints , which are believed to be the crystallised remains of sea sponges . Flints can be worked to produce a cutting edge which is sharper than a surgeon's scalpel

Since prehistoric times, flints have been used for hand tools, including knives, axes and scrapers, and for weapons such as arrow heads and spear heads

In more modern times flints have been used for building, road making and in the production of pottery

' Flintlock ' firearms were in use for over 300 years and were so called because the firing mechanism, or 'lock', included a sliver of flint which, when struck against a steel plate, produced the spark to ignite the gunpowder and discharge the weapon