The cliffs at Thorpeness © Tony Pick

Geology

In geological terms, the Suffolk Coast & Heaths Area of Outstanding Natural Beauty (AONB) is a young landscape - in fact it has the youngest rocks in Britain. Perhaps the most surprising thing about the geology of this area is that hidden beneath the surface is an ancient sea bed. Underlying everything is chalk, formed as part of a sea bed between 70 and 100 million years ago. In west Suffolk this chalk reaches right to the surface and has a pronounced effect on the kinds of wild plants that grow there. But in east Suffolk the chalk curves downwards and a wedge of younger deposits was formed on top of it. The oldest of these is London Clay deposited around 50 million years ago.

London Clay is visible mainly in the southern part of the AONB and stretches roughly as far north as Boyton. Many interesting finds have been made in the clay, including sharks' teeth and the remains of turtles - which show it was then part of a tropical sea - together with fossil driftwood and layers of volcanic ash, suggesting periods of volcanic activity. Within the clay are layers of ‘cementstone’, a harder material which has been used in local buildings, including Orford Castle, while the clay itself has been used to make bricks.

Further north, the London Clay is overlain by a much younger material, known as Crag. There are several types of Crag, aged between 1.5 and 3.75 million years old, including Red Crag, Norwich Crag and Coralline Crag. Of these, Coralline Crag is the oldest, and found exclusively in Suffolk. It is a creamy-golden, sandy limestone full of fossil shells. Red Crag contains Coprolite nodules, which a Cambridge professor named John Henslow decided to test after coming across them while on holiday at Felixstowe. He found they were rich in phosphate, a discovery that led to them being extracted from the Crag to make fertilizer. This became an important local industry, centred around the river Deben, and employed many hundreds of men in the 19th century.

Deposits within the Crag strata show clearly how the world was gradually cooling ahead of the ice-age, while the uppermost geology in the AONB, and indeed much of the landscape we see today, has been shaped directly by the ice-age itself. The great ice-sheet just reached the AONB area, diverting the course of an earlier river which had deposited the sands and gravels that make up so much of the soil along the coast. It is these infertile soils and the free-draining nature of these sands and the underlying Crag that has allowed the characteristic dry heathy landscape of coastal Suffolk to become established. Indeed without them it is unlikely that this unique and precious landscape would have been created.

What can be seen here...

Birds: sand martins often use the cliffs for nesting

Other features: The soft, crumbling local cliffs on the coast provide good views of the underlying rock strata.

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