INTRODUCTION:

General

Alum Bay in the western part of the Isle of Wight, near the Needles, has impressive cliff faces of vertical Tertiary strata, with conspicuously coloured sands. The Barton succession was studied in a student project by Rachel Helsby partly to help understand the occurrence of an unusual Barton limestone with Nemocardium and Xenophora that has been found offshore in Christchurch Bay by Dr Ken Collins. A previous project comparing the limestone with the Barton strata in the cliffs of the Hampshire coast has been undertaken by Sarah Snowdon. This webpage will be built-up progressively with addition of photographs, diagrams and text.

Alum Bay provides fine views of the Chalk Cliffs which extend out to the Needles. The Needles are isolated stacks of Chalk which is steeply dipping towards the north as part of the Brixton or Brighstone Monocline. This is the uppermost part of the Chalk in this area and is of the Campanian Stage of the Upper Cretaceous. More information on this will be given below.

INTRODUCTION:

Access to Alum Bay

It is easy to visit Alum Bay by car and you can drive directly to the Needles Pleasure Park and park on the cliff top. There are toilets, and in the summer, cafes, tourist shops and tourist facilities regarding coloured sands etc. In the winter the Pleasure Park and the chair-lift is not operational.

If you are coming from the mainland on a day-trip you may find, however, the ferry fare for cars is fairly expensive for a short visit. Should you wish to visit Alum Bay from the mainland at lower cost, you can drive to Lymington and park your car at the ferry terminal for a reasonable fee. You can then travel as a foot passenger on the Wight-Link Lymington ferry at a moderate price and this will take you to the interesting small town of Yarmouth. From here in the summer season you can easily catch a bus to Alum Bay, and (open-top) buses go in that direction about once an hour or even more frequently. In the winter the buses are less frequent, but it is not too difficult to get there. If you cannot find a bus to the bay soon after arriving you may be able to take a bus to Totland and walk a short distance to Alum Bay. You may also be able to travel by bus changing at Freshwater. In the winter, though, dress warmly and take waterproof clothes and be prepared for a little walking, some delay and some minor adventure. It is very worth-while to see the cliffs at this time of year when they are rain-washed and sea-washed and not crowded with tourists and not taped-off.

INTRODUCTION:

Safety

If studying geology at Alum Bay or visiting for any reason please follow the usual safety rules for study of cliffs. Generally the Tertiary sediments here are of soft sands and clays which slump or slide and there is generally a lower risk than at many other cliffs. The coast does retreat relatively rapidly, though, and the cliffs undergo active erosion, at least in winter. There are some high projecting ribs composed of iron-cemented sandstone which could in places present a hazard of falling debris. Any of the sandstones are prone to fall to some extent from time to time, although the falls may not be frequent and may take place during winter storms. There has been a recent fall of large sandstone blocks from the lower leaf of the Poole Formation, as shown in a photograph below. There are also some thin pebble beds in places so it is possible that a flint pebble could fall from certain places. Even blocks of friable clay, though, can be fatal when falling from a height. Examine the photographs below to consider the level of risk, especially if a party is involved. All cliffs anywhere can present some risk, but this can be reduced by avoiding certain high or unstable parts. Just walk down the beach towards the sea at any place where the cliffs appear unstable.

Accidents have happened from the digging out of sand so as to produce sand-caves. Geologists are unlikely to be involved in this, and it is more of a risk to visiting children. In the summer the cliffs of coloured sands, mostly Bracklesham, are taped off for this reason. Note, then, that much of the Eocene strata is inaccessible in summer (although part of the Barton Clay and most of the Barton Sand, London Clay and Reading Formation can be reached)

A much higher risk is presented by the cliffs of Chalk with flint nodules, and some individuals and parties may wish to look at the Chalk only very briefly or just at a safe distance. This carbonate rock is dipping at a steep angle in high cliffs which are not stable. Large chunks have fallen as is shown by the various photographs in this webpage. Apart from occasional major collapses of chalk there is a significant risk that small pieces of flint or hard chalk may fall with high velocity at any time, but particularly in wet or frosty weather. Study of the Chalk cliffs should only take place with much care and with the wearing of safety helmets. If there any sign or sound of recent falls then persons should not approach and move away to the relative safety of the broad pebble beach. Climbing over the boulders westward along the foot of the Chalk cliff has the risk of injury from falling debris and of slipping and falling over the rocks. There is also risk of being trapped by the tide or being washed off by a wave. However, there is a fossil content in the Campanian Chalk here which is of interest. There is no reason to attempts to climb the Chalk cliffs here. Climbing on chalk is usually futile, very hazardous and should not be attempted. Risk of falling from the top of the cliffs exists at any part of the bay but it is the edge of the Chalk cliff from Alum Bay to the Needles which is particularly hazardous and should be avoided. While a fall from the Tertiary cliffs might cause injury, a fall from the Chalk would be fatal.

There are some other risks. There can be mudslides in the Barton Clay and the London Clay and it is possible, but not very likely, to become stuck in these. Headon Hill to the north of Alum Bay is not discussed in this particular webpage, but it should be noted that it is a hazardous place with regard to soft mud. Flint pebbles or flint nodules should not be hammered because of dangerous splinters.

These comments do not necessarily cover all potential hazards and it is the responsibily of the individual or group leader to assess risks by direct observation and proceed in a safe manner. No liability is accepted here, and this webpage is merely a description of the strata and outcrop, and is not advice to go to a particular piece of cliff or coastline.

INTRODUCTION:

Cliff-Section at Alum Bay

The various photographs and the cliff-section diagram given here indicate the main units visible in the cliffs of Alum Bay. It should be noted, though, that some of the succession here is not easily correlated with that elsewhere. The Reading Formation and the London Clay Formation do not present any major problems, although, of course, there can be argument about the exact position of the boundaries. The Boscombe Sands, Barton Clay, the Becton Sand are relatively straightforward. It is the Bracklesham Group which is more difficult to interpret. A number of coloured sand units alternate with heterolithic, laminated and lignitic sands and clays. Grey laminated beds like these occur elsewhere in the Bracklesham Group. They alternate elsewhere with greenish glauconitic sands that are quite fossiliferous. These green sands can be identified as specific formations by their fossil content. Alum Bay is unusual in that the sands are yellow or pink and are oxidised and generally without marine fossils. Correlations have been made and those of Insole, Daley and Gale (1998) are generally used here. There are complications, though, such as the upper and lower "leaf" of the Poole Formation and the Wittering Formation. Not every part is confidently tied in with the Whitecliff Bay section and some room for discussion exists. It should also be noted that older literature may use rather different correlations and that much of the Bracklesham Group may be listed as "Bagshot Sands". The Bracklesham Group will be discussed in more detail below.

STRATIGRAPHY;

Chalk - Introduction

Seen in the distance here from the steps are the Chalk cliffs. This chalk is of the Belemnitella mucronata Zone of the Campanian Upper Chalk (Upper Cretaceous). It consists of chalk with flints steeply dipping to the north. The Needles peninula extends east-west so the cliff line of Chalk here is along the strike and almost represents the Chalk/Tertiary boundary. With this steep dip towards the sea, large chunks of chalk separated by curved slip-planes fall from the cliff from time to time. The scars can be seen in these photographs (taken in different light and weather conditions).

The upper two photographs of the Chalk cliffs were taken 1995. They show the details of some cliffs falls at the time. Compare with photographs of the Chalk cliffs taken in September 2002, and others of 2002 elsewhere in this webpage. The cliffs appear too blue because of reflection of blue light from the sea. The strata are dipping steeply towards the sea, but it is not easy to make out the dip in the photograph. Notice the results of erosion of the old cliff-fall. The pile of debris orginally sloped fairly evenly as a fan towards the sea. Recent wave erosion has cut a small cliff in the debris cone, leaving only a part with the original top surface slope. There are other small seaward slopes with grass, here and there on the cliffs. It is not clear as what it is the origin of these. Comparison may provide some indication of the extent of coast erosion on the Chalk cliffs at this locality.

STRATIGRAPHY:

Chalk Stratigraphy

The Chalk in the southern part of Alum Bay is Campanian, of the zone of Belemnitella mucronata. At the end of the beach is the soft white chalk of the Studland Member. By walking about 50m along the base of the cliff from the Tertiary erosion surface there is a change to the harder chalk with thin marl bands which belongs to the Portsdown Member (Insole, Daley and Gale, 1998). There is no easy access to older parts of the Chalk succession here. To study older parts in the western part of the Isle of Wight go to Freshwater Bay and Compton Bay. (to be continued)

CHALK - THE NEEDLES

The Chalk Cliffs and Sea Stacks

Now see the Chalk cliffs at Harry Rocks across the bay to the West?

Go to:

Harry Rocks and The Foreland, near Swanage, Dorset.

STRATIGRAPHY:

Chalk-Tertiary Junction

The junction between the Upper Chalk and the Tertiary strata is seen at the southern end of Alum Bay. There is a well-defined corner where the cliff direction changes from roughly north-south to roughly east-west. The Chalk forms a high wall here and deeps steeply towards the north. The lowest Tertiary strata here is the Reading Formation of Palaeocene age and consists of reddish clays with a little sand and gravel. The Upper Cretaceous succession is not complete. The highest Chalk is of the Belemnitella mucronata Zone, of the Campanian, and the Maestrichtian strata has been eroded away. Thus the true K/T boundary, notable for the extinction of the dinosaurs, is not seen here. The Reading Formation lies on different parts of the Chalk succession in different places so that in broad terms there is an unconformity. However, within Alum Bay there is no obvious angular discordance between the Reading Formation and the Chalk.

The top of the Chalk is rather irregular and has oval pipes containing grey, argillaceous sand. The pipes seem to be of early Tertiary age and predate the folding. In other words they have in the past descended from the Tertiary surface downward into the Chalk, but since then folding has steeply inclined the top Chalk surface. You will notice the actual junction as a, steeply dipping, nearly vertical face from which the Reading strata is partly stripped away by erosion to reveal the details. It is rugged and deeply furrowed, and the solution pipes attain greater dimensions than at the equivalent position in Whitecliff Bay. Their sides are often undercut and, in many cases, open laterally into sand-filled fissures, some of which follow bedding planes. White (1921) considered this surface to have the general aspect of a foreshore with potholes worn in an approximately horizontal limestone. However, if the pipes are solution features, as they indeed appear to be, then what is visible is a surface affected by early karst rather than mechanical erosion and potholing. Solution pipes which are inclined like this and not simply vertical are rare and interesting features.

STRATIGRAPHY:

Reading Formation

The Reading Formation is easily recognisable. It consists for the most part of clays and marls that are mottled with a reddish iron oxide stain. These are palaeosols that were originally gley soils of swampy, flood plain environments. Less obvious is a pebble bed and some sand. Slumping and collapse of the cliff obscures some parts.

On the basal surface of the Tertiary is a thin conglomerate containing a mixture of well-rounded flints and grey pebbly sand, but it may be obscured by slumped debris. This lowest unit is the Reading Formation Bottom Bed (Insole et al.,1998). Apparently this bed does not seem, in the field, to contain glauconite grains but there is a greenish tint in the deeper pipes. There are scattered dark green flint pebbles in addition to unworn flint nodules, eroded from the underlying Chalk according to (White, 1921) .

London Clay Formation

Bracklesham Group

The coloured sands, lignite beds and leaf beds are interesting features of the Bracklesham Group. Because the succession is so varied and is seen in vertical orientation in a short stretch of cliff-line it is not always easy to find your place within it. It is also complicated by the fact it does not have the normal Bracklesham sequence with glauconitic marine beds that are easily recognised units at Whitecliff Bay.

Certain marker horizons are shown in the photographs here. The base of the Boscombe Sand is marked by a crimson bed in a photograph above. In older literature (eg. White, 1921) this sand is placed within the Bracklesham sequence. In the recent guide by Insole, Daley and Gale (1998) it is classified as the basal formation of the Barton Group. It is of course, debatable as to whether this sand formation should be placed with the Barton Clay Formation, but, however, note that the Becton Sand Formation (Barton Sand) is also placed in the Barton Group.

The yellow soft sandy part of the Branksome Sand Formation is very conspicuous and, as can be seen in a photograph above, prone to collapse. The formation is about 65m thick and corresponds to Beds 25 to 27 of (Prestwich, 1846). It includes not just the obvious sand but the lignite beds (lower No. 27 of Prestwich) and some whitish marly clay above. The sands are well-sorted with low angle cross-bedding or flat lamination. Burrows of the trace fossil Ophiomorpha occur in some parts Insole, Daley and Gale (1998).

The unit of lignitic beds is conspicuously grey in colour. The 11 metres of laminated muds and lignites, here, resembles the Marsh Farm Formation (Bed 24) lower down (that is south) in the succession and should not be confused with that. Lignitic coals occur in definate beds within bed - 27, lower part, and are quite conspicuous. Each of the lignite beds in No. 27 has a thin underclay penetrated by rootlets similar to those seen at Whitecliff Bay , but they are thinner (White, 1921) . The original peat beds have been attributed to an origin on coastal, slightly saline marshes by Insole, Daley and Gale (1998). I have found a small piece of amber from tree remains in one of the lignite beds, many years ago. The lignite or brown coal development in the Isle of Wight might be connected with the proximity of an early structural high developing on the Tertiary axis to the south of Alum Bay. These peat accumulations might have developed on a protected accretionary shore just north of early rising land.

STRATIGRAPHY - BRACKLESHAM GROUP (Middle Eocene)

Poole Formation

The Poole Formation is the name for the lower part of the Bracklesham Group in the Poole, Dorset area. It consists of sands, grey clays with plant debris, lignite beds and pipe clay (ball clay) beds. The pipe clay is extensively worked in large pits in the Poole area. It is a kaolinite-illite clay, and more plastic than the kaolinite china clays of Devon and Cornwall. The Poole Formation is non-marine and has been deposited in the Poole Delta, the discharge area of a large river coming from the Dartmoor region. Although at a latitude of about 40 degrees north this was quite a hot delta, almost subtropical, because the Paleocene-Eocene was a time of greenhouse type, global warming. The almost tropical weathering beneath the dense forests led to much release of iron, and at times almost lateritic conditions. The abundance of iron in this relatively high latitude, but subtropical-type delta is ultimately responsible both the for bright colours of the ferruginous sands, and also for the pyrite from which Alum Bay (indirectly) takes its name. The source of the iron is not a controversial matter.

A major problem, does remain however. It is just when did reddish ferric hydroxide colouring originate. Was it due to penecontemporaneous oxidation or has it resulted from recent oxidation of contained pyrite (iron in reduced form as ferrous sulphide)? The matter is discussed with reference to Studland Bay, further below.

STRATIGRAPHY:

Eocene Inversion (Basin Inversion or Uplift)

Circumstantial evidence regarding the Eocene uplift in the southern part of the Isle of Wight comes from several sources since the idea was put forward in 1964 (West, 1964) , and opposed at the time by Denis Curry. A relevant recent publication is that of Gale et al. (1999) and this provides specific evidence for uplift and erosion in the south (more information regarding this work will be given later). Other evidence include the Palaeogene warping in the northern Isle of Wight (Daley and Edwards, 1971) , the Bartonian unconformity in Dorset (overstep by the Creechbarrow Beds), the tilted iron pipes of the Poole Formation of Studland, the 'Bagshot' overstep west of Broadmayne, Dorset(Arkell, 1947) , the gravels of Hardy's Monument, Blackdown, Dorset etc. This topic will be discussed more fully later.

Bracklesham Group - Coloured Sands

Origin of the Coloured Sands

The coloured sands of Alum Bay are almost all within the Bracklesham Group. Some colours of sand are quite common. Yellow and brownish sands owe their colour to limonite (or goethite) which is the ferric hydroxide (effectively rust). This is usually produced by oxidation of dispersed pyrite or glauconite during recent or at least Quaternary weathering in wet, near surface conditions. Early oxidation similar produces the hydroxide in most cases but burial to significant temperatures often, but not always, converts the hydrated iron oxide progressively towards the anhydrous hematite. Red, as opposed to brown, colours often indicate early oxidation; this is a process which occurs in palaeosols, ancient soils. Regarding red palaeosols, particularly in the earlier Reading Formation of Alum Bay see the work of Buurman.

Thus the colours could be of palaeosol origin. However, there is some indirect evidence that the red and brown colours are the result of recent oxidation of pyrite. At Redend Point, Studland, on the opposite (western) side of Christchurch and Poole Bays, there are crimson-coloured sands like those of Alum Bay. These occur in the Redend Sandstones of the Poole Formation of the Bracklesham Group. They occur in sands beneath some steeply inclined ferruginous pipes which are not vertical but appear to be tilted in accordance with the 12° dip of the strata (Arkell, 1947). If the evidence of the dip of the pipes is correct then this suggests a penecontemporaneous origin. This is supported by the fact that they commence at and descend down from a lignite bed, probably once a peat deposit like the lignites of the Isle of Wight. The pipes have no relationship to present surface features or solution pipes. An example has been seen of a pipe at Studland Bay that is pyritic at low tide level. Pyritic pipes also occur in the Bracklesham Group offshore in Poole Bay. Thus the brown limonitic pipes there seem to be the result of oxidation of pyrite pipes. The associated red and brown colours in the sand at Redend Point are therefore also likely to be the result of oxidation of pyrite, particularly since colours occur where the pipes are abundantly developed. Just when this oxidation took place is an interesting problem, but if related to present tide-level then it is a relatively recent phenomenon.

There are, therefore, two alternative theories for the red and brown colours of the sands - a palaeosol origin or a recent origin by oxidation of pyrite. This clearly needs more investigation It should be noted, however, that Alum Bay has received its name because it was a place where pyrite was collected on the beach for the manufacture of alum. Not much pyrite is visible now (there is some) but perhaps pyrite is preserved, as at Studland, at and below low tide level. Perhaps the source of the pyrite of Alum Bay has been low-water exposures rather than the cliffs. We will leave the matter unresolved now for further study later.

A mention should also be made of other colours. Green is provided by glauconite, which is common in some more marine units such as the Barton Clay. It is usually, however, much contaminated with clay material. Pure quartz sands can give white. Lignitic material can provide a black colour. Bright yellow might be obtained from jarosite encrustations. It is difficult to think of a suitable source of blue.

In conclusion, it is the red-coloured sands of Alum Bay which make the place notable. There is much plant debris in the Bracklesham Group which would have caused local reducing conditions. In such circumstances iron can be trapped by sulphide ions (from sulphate-reducing bacteria) as pyrite. This was the source of alum from which the bay takes its name. It is probable that oxidation of pyrite either in the past or recently has produced the red and brown colours of iron oxides or hydroxides.

Barton Group (Middle Eocene)

The Barton Clay sequence in general resembles that at Barton-on-Sea and Highcliffe on the Hampshire Coast. It consists of grey clay with white aragonitic shells. It varies in content of quartz sand and of glauconite and has septarian nodules of argillaceous calcite (microspar) at certain horizons. The thickness at Alum Bay is greater than at Barton. The shells are more friable and because the strata are vertical there is only a limited exposure. As a result this section has been regarded as inferior to the Barton-on-Sea coast for fossil collecting. The mainland coast is not as good as in the past though because of sea-defences and accumulation of shingle. The Alum Bay section is interesting in the winter when it has to some extent been cleanly washed by storms. Only a limited part is obscured and that is near to the chair-lift, but even here more Barton Clay is becoming visible because of active coast erosion.

LOCATION:

Barton Clay Section - The Steps Pebble Bed

Description

Just north of the steps down to the beach is a remarkable pebble bed within the Barton Clay. To distinguish readily from the pebble bed at the base of the Barton Clay it is referred to here as the "Steps Pebble Bed". It is not known at other localities. The pebble bed is not like some other Eocene pebble beds, such as the one at the top of the Boscombe Sands) either in terms of sequence or pebble content.There is clay above and below the thin pebble bed and it has a matrix of clay, albeit sandy. Some pebbles occur in the clay above and below.

The bed is notable for being extremely poorly sorted and apparently bimodal in particle size. Rounded, blackened and battered pebbles show that much material is clearly of storm beach origin and of a type that is common in the Tertiary marine deposits. Very unusual at this stratigraphical level are the other pebbles which appear to be flint nodules that have come from directly from the Chalk with very little if any abrasion. They are fractured in many cases but this has mostly occurred after deposition. They seem to have the original white and thin cortex and probably not a weathering patina. Laboratory study is needed, though. With the pebbles, the clay and some sand dispersed through the clay are many aragonitic bivalve shells. In cross-section many of these appear to be Cardita -like bivalves. There may be some similarity to the occurrence of Cardium shells in modern pebble beaches, like those of the present Solent.

Preliminary Interpretation

Some initial ideas for discussion are put forward here. More information on the Barton Clay of Alum Bay will come from an undergraduate research project at present being undertaken by student Rachel Helsby. Reference needs to be made to the work of Plint (1982; 1983) and that of other authors and more information and literature references will be added in due course.

Thus the pebble bed is of small pebbles in sandy clay with more clay above and below. Application of Walther's Law suggests a shingle spit with soft sandy mud on either side and no major area of clean sand. The flint-pebble beach was to some extent starved of clastics and so sharks' teeth and fossil wood occur in the bed. Such accumulations would be expected at the low-water mark of the beach, and the teeth may have been derived in part from reworking of earlier deposited marine clay.

The relative deficiency of sand implies that the Barton Clay sea could be very shallow in parts but still with a predominantly clay type of sedimentation. Reduction in rainfall ( suggested because Upper Eocene has an evaporite facies in the Paris Basin) might have been responsible for the reduction in the deltaic input from the west that so affected the underlying parts of the Eocene in this area. The Barton Clay, though, does shoal upwards into the well-sorted Becton Sand (Barton Sand) before the lagoonal Headon Hill Formation was deposited. It is possible that the Becton Sand is reworked, well-sorted sand from the remains of the earlier delta.

Eocene Palaeogeography

(preliminary notes to be expanded)

The Bartonian, in the Middle Eocene, was the time when the Alpine Folding was just beginning. The folding of the Chalk and other strata in the Isle of Wight and Isle of Purbeck was not a sudden process after all the Tertiary sands and clays had accumulated. There was probably no mountain of soft Tertiary sands and clays on the southern part of the Isle of Wight (West, 1964) . It was a structural high relatively early in the Tertiary and a place of gradual uplift. At times it would have been a low-lying island or promonotry. It would have been a place of condensed sequences and erosion, and the Eocene sands and clays would have thinned towards it. Overstep southward would be expected. This is observed in an analogous situation further west at Creechbarrow Hill near Corfe Castle in the Isle of Purbeck, Dorset(Arkell, 1947) . At that locality there is an angular unconformity between the Creechbarrow Beds and the underlying strata. These beds overstep southward onto Chalk and contain large flint nodules derived from the Chalk. The Creechbarrow Limestone, a freshwater deposit at the top of the Creechbarrow Beds has been shown by Hooker (1977) to be of Bartonian age.

Just how much southward overstep of the Eocene strata occurred in the vicinity of Alum Bay is an interesting point for discussion. A key publication with specific evidence for Eocene overstep and erosion is that of Gale et al. (1999) . Detritus at Whitecliff Bay reveals clear evidence of eroded strata to the south.

Further aspects will be discussed later, and there are some problems with the Tertiary succession. One of these is the greater thickness of Barton strata at Alum Bay than on the mainland. It is also of interest that in the Alum Bay area there is an unusual development of freshwater limestones in the Solent Group that is stratigraphically above the Barton strata.

STRATIGRAPHY:

Tertiary - Details

Clay Mineral Distribution

STRATIGRAPHY

Headon Hill Formation

Headon Hill

Headon Hill Formation (Solent Group)

(for text to be added)

PALAEONTOLOGY

Some Fossils of the Alum Bay Strata

Fossils of the Tertiary strata include the Eocene fossils of Alum Bay. The London Clay, the Bracklesham Group and the Barton Clay contain fossils (although Bracklesham fossils are rare at Alum Bay).

PALAEONTOLOGY:

Fossils of the Solent Group

A selection of just some of the many species of Solent Group (Upper Eocene to Oligocene) fossils are shown here. The left-hand diagram (coloured) is the more up-to-date. Most, but not all, of the common ones are included, together with a few rarer species. The centre and right-hand diagrams are very old with a few names updated. They may be useful supplements for identifying species not shown on the left-hand diagram. Treat the nomenclature on these with caution, though!

The molluscan fossils of the Solent Group are generally different from those of the marine Eocene strata beneath. They are most frequently found to be fairly small, white and thin-shelled and occur, often in abundance, in thin-bedded strata. They are preserved as aragonite, but usually without any preservation of shell colour. Most of them lived in lacustrine (lake) conditions or brackish, lagoonal water. Pondsnails such as Galba ( Lymnaea ) or Viviparusare common in freshwater strata such as the Bembridge Limestone. Planorbis - type gastropods are also typical of freshwater strata, and charophyte algae may be present with them. Brackish water molluscs include Corbicula and various cerithid (ornamented and turreted) gastropods. There are some truely marine horizons, usually fairly thin and particularly recognised by the presence of oyster shells or "Barton Clay - type" gastropods such as Athleta.

The Solent Group is very well exposed on the Isle of Wight and this is the best place in the country to see fossils of Upper Eocene to Oligocene age. The Group includes the Headon Hill Formation, particular well seen at Headon Hill, near Alum Bay in the west of the Isle of Wight.

ACKNOWLEDGEMENTS

Ian West is particularly grateful to the help of Dr. Rachel Helsby has investigated aspects of the Barton Clay at Alum Bay during an undergraduate project a few years ago. Dr Ken Collins, the discoverer of an offshore Barton outcrop, has helped initiate this work and has co-supervised the study by Rachel Helsby. We are very grateful to him. I much appreciate the arrangement of a geological field trip on a boat from Lymington to the Needles (Puffin boats) by the Probus organisation of Mudeford, and particularly the help of Peter Hollick. Dr. Yining Chen has very kindly assisted with recent field work on the Isle of Wight and elsewhere, and this help is much appreciated. iSolution, the computer services organisation at Southampton University has hosted this webpage, and aerial photographs have been provided courtesy of the Channel Coastal Observatory.

References and Bibliography

Please go to Isle of Wight Bibliography .