West, Ian M. 2020. Geology of Colwell Bay Isle of Wight. Internet site: www.southampton.ac.uk/~imw/Colwell-Bay-Wight.htm. By Dr. Ian West, Romsey, Hampshire. Version: 2nd September 2020.
Geology of Colwell Bay, Isle of Wight

By Dr. Ian West,
Romsey, Hampshire
Visiting Scientist at:
Faculty of Natural and Environmental Sciences,
Southampton University,
Website hosted by iSolutions, Southampton University
Website archived at the British Library

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Isle of Wight Geology - Introduction and General
Alum Bay, near the Needles
The Needles, western Isle of Wight
Colwell Bay, northwestern Isle of Wight, Eocene
Whitecliff Bay, northeastern Isle of Wight, Eocene
Brighstone-Bay, Wealden, southwestern Isle of Wight
Isle of Wight Geological Bibliography

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Arriving at the Slipway, Colwell Bay, Isle of Wight, photograph September 2011

A general view of Colwell Bay looking northward from Colwell Chine, Isle of Wight, 2011


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Strata of the Isle of Wight in general

(The strata of Colwell Bay belong to the Headon Hill Formation, Solent Group, and are of late Eocene, Priabonian age)

- Holocene (Recent)
Blown Sand
Alluvium and Peat
- Pleistocene
Raised Beach
Valley Gravel
Plateau Gravel
Angular Flint Gravel
Solent Group
Barton Sand Formation
Barton Clay Formation

Bracklesham Group
"Bagshot Sands"  
Thames Group
Reading Formation
Bouldnor Formation (Bembr. Marls & Hamstead)
Bembridge Limestone Fmt.
Headon Hill Fmt. (Headon & Osborne)
Elmore Formation
Selsey Formation
Marsh Farm Formation
Earnley Formation
Wittering Formation
London Clay Formation
(Oldhaven Formation)
Cretaceous Upper Chalk
Middle Chalk
Lower Chalk  
Upper Greensand
Lower Greensand
Wealden Group
(Purbeck Fm. - in boreholes)
(Chalk with flints)
Ferruginous Sands
Atherfield Clay
Vectis Formation ("Wealden Shales")
Wessex Formation ("Wealden Marls")
(Jurassic underground only)  


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Viviparus, the lake snail, from the Headon Hill Formation near Sconce Point, Isle of Wight

The gastropod Viviparus is probably the most common fossil encountered in the Headon Hill Formation. It is a lake snail, very similar in appearance to modern pond-snails.

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(Headon Hill Formation, Tertiary strata, Northwestern Isle of Wight)

Totland Bay, Warden Ledge and Colwell Bay, as seen from Headon Hill, Isle of Wight, 28th September 2011

Cliff End and Fort Albert, Isle of Wight, seen across the Needles Passage from Hurst Castle, Hurst Spit, Hampshire, 2011

The Headon Hill Formation, exposed in the cliffs near Cliff End, Colwell Bay, Isle of Wight, 28th September 2011

Part of Colwell Bed, including Brambles Chine, northwestern Isle of Wight, as seen from Hurst Spit

An oblique view of Brambles Chine, Colwell Bay, Isle of Wight, with an eroding cliff exposing a lower part of the Headon Hill Formation, Priabonian, Upper Eocene, 28th September 2011

The cliffs of the northern part of Colwell Bay, Isle of Wight, including Linstone Chine, where there is a small anticlinal fold.

A small anticlinal fold at Linstone Chine is present, although not easily seen in the above photograph. This is of special interest because the Hatherwood Limestone Member reappears to the north. This limestone occurs under Headon Hill but is absent in most of Colwell Bay.

A northern part of Colwell Bay, north of Brambles Chine, Isle of Wight, as seen from Hurst Spit, 4th November 2013

Colwell Bay is a place to see the lower part of the Headon Hill Formation. It is easily reached by car or bus from Yarmouth and the ferry. There is a public car park at the seaward end of Colwell Chine Road. There is a holiday camp on the cliff top of the middle of the bay. There is easy walking on the beach. The cliffs are of only of medium height to fairly low.

At Colwell Bay there are good exposures of the lower part of the Headon Hill Formation. This is Upper Eocene, or in terms of stages it belongs to the Priabonian.

The Headon Hill Formation consists of the following Members:

(at the top)
Seagrove Bay Member
Osborne Marls Member
Fishbourne Member
Lacey's Farm Member
Cliff End Member (exposed at Colwell Bay)
Hatherwood Limestone Member (8m. at Headon Hill, but not present at Colwell Bay)
Linstone Chine Member (exposed at Colwell Bay)
Colwell Bay Mb. (includes Venus Bed; at Linstone Chine, Colwell Bay)
Totland Bay Member
(at the bottom)

The How Ledge Limestone is in the low cliff north of Colwell Chine and this is close to the top of the Totland Bay Member of the Headon Hill Formation (Insole et al., 1998. (The How Ledge Limestone is the lowest limestone of Headon Hill, where it is about 2m. thick. It should not be confused with the thicker (8m.) and more conspicuous Hatherwood Limestone Member in that cliff).

A notable feature of the middle of Colwell Bay is the Venus Bed (also seen at the northeast corner of Headon Hill). This consists of sandy muds with the bivalve Sinodia (Cordiopsis) suborbicularis (Goldfuss) (which was once known as "Venus incrassata, Cytherea incrassata, and Cordiopsis incrassata.

Sinodia suborbicularis, a bivalve from the late Eocene, Venus Bed of Colwell Bay and elsewhere on the Isle of Wight

An old faunal list for the Venus Bed, was given by Keeping and Tawney (1881).

The Colwell Bay Member is of importance on a broader scale. See the Colwell Bay Member paper by Chris King (2010). It is available online. The abstract is given below:

"Detailed logging of key outcrops and boreholes in mainly nearshore and marginal-marine sediments of the Colwell Bay Member has enabled regional correlations to be established. The Colwell Bay Member comprises a single depositional sequence, based by a combined sequence boundary and transgressive surface and terminated by a second sequence boundary. Regionally developed omission surfaces delimit five parasequence within the Colwell Bay Member. Environmentally controlled mollusc assemblages indicate progressive SW to NE progradation of marginally marine-marine environments within each parasequence. Previous interpretations of the Solent Group as deposited in a narrow embayment of the proto-English Channel are evaluated and rejected. It is interpreted as a remnant of wide area of coastal and near-coastal sediments deposited in a wide embayment of the southern North Sea Basin, now largely removed by mid-Tertiary uplift and erosion."


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Warden Point and Warden Ledge

Warden Ledge of sandstone of the Headon Hill Formation, between Totland Bay and Colwell Bay, Isle of Wight, September 2011, at low tide


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Copyright © 2020 Ian West, Tonya Loades and Joanna Bentley. All rights reserved. This is a private, academic website intended to be useful for research, reference and educational purposes. Images and text may not be copied for publication or for use on other websites such as online courses, without permission, or for any commercial activity. A reasonable number of images and some text may be used for non-commercial, non-charged, non-online and non-published academic purposes, including field trip handouts, student projects, dissertations etc, providing the source is acknowledged. All images so used must contain the original caption, including the copyright statement. Some images are not those of the author and the copyright is that of the original photographer and these are not for any use without specific permission from the source photographer. This particularly applies to aerial photographs, but also to some sets of field photographs.

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Dr Ian West, author of these webpages

Webpage - written and produced by:

Ian West, M.Sc. Ph.D. F.G.S.


at his private address, Romsey, Hampshire. It is kindly supported by Southampton University, and web-hosted by courtesy of iSolutions of Southampton University. The website is an unfunded, private activity, and does not represent the views of Southampton University. Any field activities shown are not necessarily those of any specific organisation and mostly represent private field work.

Written and produced by:

Ian West, M.Sc. Ph.D. F.G.S.

Romsey, Hampshire