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Flint nodules such as the one seen here are called paramoudras, also known as pot stones. These large nodules originally had a central core filled with chalk. Once exposed, the soft chalk is quickly washed out by wave action, leaving a large hole. One can occasionally spot pot stones in gardens where they serve as nature-made flower pots.

The chalk layer is only visible at low water. It is composed of calcium carbonate from the remains of microscopic marine organisms that once lived in a warm shallow sea which covered this area between 62 and 132 million years ago. Its upper few centimetres are composed of fragments of rocks.
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