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Issue 42 August '13

Wednesday 28th August 2013

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Rocks and Soils

The West Wight has outstanding geology and landforms. Rocks exposed along its coastline are amongst the most complete of their type in the world. It contains textbook examples of geographical features from the coloured sands of Alum Bay to the chalk stacks of the Needles and the fossil rich rocks of the north coast. Click on the links below to learn more.
Solid Geology of West Wight 

Cretaceous, 145 - 65 million years ago

Tertiary, 65 - 1.64 million years ago

Quaternary, 1.64 million years ago - 


Cretaceous, 145 - 65 million years ago - The oldest rocks in West Wight are the Wealden Group. The Wealden Mudstone lies on the south coast near Brook. Its soft clay has been eroded by the sea to form steep sided valleys known as chines. The clay soils here support a mix of arable and pasture.

Wealden Clays at Brook Bay

To the north of the Wealden Group lie bands of Lower Greensand, Gault and Upper Greensand. These were deposited in a shallow sea which covered much of what is now southern England. 
Lower Greensand is a soft, easily eroded sandstone which, where it meets the sea, forms the undulating soft cliffs of Compton Bay. Upper Greensand, which in West Wight is a narrow band sitting just to the south of the Chalk, is a harder rock and has been quarried for building stone. The loam soils arising from the sandstone support a mix of arable and pasture with woodland on the steep slopes.
In the late Cretaceous period rising sea levels progressively inundated the area and calcareous sediments, which eventually became chalk, were deposited. 60 million years ago the chalk was folded on an east west axis forming a hump. The high chalk downs visually dominate West Wight narrowing to the crags of the Needles. The chalk continues under the sea where it forms reefs and sea caves.

Chalk stacks, cliffs and downs at western tip of the Island


Tertiary, 65 - 1.64 million years ago - The folding of the chalk at the end of the Cretaceous period left lower areas of chalk. To the north of the downs these formed the south eastern section of the Hampshire Basin where the softer Tertiary rocks were deposited on top of the chalk during a period when the area was covered by shallow seas or deltas. This action resulted in the layers of clay, silt and sand, with occasional limestone of the Bracklesham Group, and Barton, Bembridge and Hamstead Formations. These layers are rich in fossils.


Quaternary, 1.64 million years ago to present - The West Wight landscape is also influenced by drift deposits. These overlay the solid geology. The eastern section of the chalk downs is capped with Quaternary deposits of clay and flint, flints set in sand, chalk rubble and reddish brown clay which has retained its woodland cover.

Mud flats of Newtown Harbour

Tidal flat deposits and river Alluvium dominate the floodplains of the Yar and Newtown estuaries. These give rise to rich wetland landscapes and pasture.
The southern section of the Yar is fringed by river terrace deposits of sand and gravel. These also appear in isolated areas for instance on Headon Hill and Cranmore. Beach deposits of sand and gravel are common around the coast.