What is chalk?

Chalk cliff and the sea

Ever since the days of early 19th-century interest in geology, the White Cliffs of Dover have offered one of the most accessible and complete records of the story of chalk formation.

How is chalk formed?

The cliffs are made from chalk, a soft white, very finely grained pure limestone, and are commonly 300-400m deep. The chalk layers built up gradually over millions of years.

They're formed from the skeletal remains of minute planktonic green algae that lived floating in the upper levels of the ocean. When the algae died, their remains sank to the bottom of the ocean and combined with the remains of other creatures to form the chalk that shapes the cliffs today.

Over millions of years, the seabed became exposed and is now above sea level. The resulting edge of chalk is the iconic White Cliffs of Dover.

Natural erosion

The cliffs only stay white because they're allowed to erode naturally. Where the cliffs are protected from erosion by man-made structures, like in the Port of Dover, plants will colonise the cliff-face making it appear green when viewed from the sea.

What’s in a name?

Chalk has many uses, but not all chalk is the same substance. For example, the chalk cliffs here are made of calcium carbonate. But the French chalk used to repair bicycle punctures is a natural magnesium silicate, and the chalk board chalk is actually gypsum or calcium sulphate.

Discover the history of the cliffs

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  • Men walking towards Langdon Prison

    Langdon Convict Prison 

    Langdon Convict Prison has left almost no traces, but in its heyday in the late 19th century it housed 102 prisoners on 20 acres of Dover’s cliffs. It was open only for 12 years, until 1896, although the work cost nearly £6 million in today’s money.

  • Men lined up at a prison

    The White Cliffs of Dover at War 

    The cliffs were on the frontline in both world wars and, with France just 21 miles away, the White Cliffs of Dover became a crucial part of the British defences.

  • A historic photograpgh of the cliffs railway

    The Tramway  

    The tramway cut was built in 1912 to connect the Dover tram system to the neighbouring village of St Margaret's. However, once the work was complete, the system was never built and thus the cut remains unused to this day.

  • A photograph of an aerial ropeway

    The aerial ropeway 

    The ropeway was designed to deliver coal to the port for export. Railway transport was expensive, so the aerial ropeway was built to take coal to Dover Harbour, an innovative solution to a logistical problem.