We met, on a bitterly cold day, in Deans Yard. To our left the copingstone on the wall was Kentish Rag laid upside down
according to the cross bedding. This set the scene for the whole experience. Eric emphasised that the Abbey is a series
of unconformities and we saw them everywhere.
As a newcomer to geology I imagine that an experienced geologist can just look at a stone and know what it is but the delivery records have been kept and are not only invaluable for identification but also inform about hidden stones such as the fifty-five hundredweight of chalk used to pack the vaults.
Westminster Abbey stands on a gravel sand island strip in the Thames near one of the few crossing places. You might not think that it would be stable enough. The abbey does not have an under croft but under the raised Pavement it is perfectly dry. It is on the edge though as St Margaret’s Church, a stone’s throw to the north is off the eyot and has serious damp problems whilst under Parliament Square there are lenses of quick sand below the London Tertiary’s (which the test boreholes missed) that caused the new underground line builders to over run and nearly cost Hopkins, the architect of Portcullis House, his reputation quite undeservedly.
The wall, to the right of the entrance from Deans Yard, is of Reigate Stone. This stone from the Upper Greensand is easy to dress but, unfortunately, it is glauconitic so now the blocks are well rounded, particularly around the joints (we were told that the mortar might be one of the culprits). Down pipes around the cathedral cause particularly bad erosion and here galletting has been used possibly as an early remedy. Even the galletts are standing proud now though.
Inside the gatehouse there are bigger blocks of Reigate Stone. It was also used for the vaulting. The condition is much better although the odd piece has flaked away. But take care when you look. Often the walls have a preservative coat perhaps of lime wash). To the left a huge block of beautifully carved Carrara Marble standing on a breccia base celebrates a naval skirmish. The detail is crisp although one lizard has lost its head. We could appreciate why sculptors favour this marble.
The benching in the cloister, originally of Bath Stone, has had a fair amount of wear so has been repaired. But one repair has rudist bivalve shells in it so must have come from an older source, possibly France. The clois- ter itself is quite open and there is a marked difference in the condition of exposed and sheltered stones. We saw unconformities in abundance in the Chapter House wall from the Cloister. The yellowish stones at the base are magnesian limestone transported by sea from the Humber. There is white Bath Stone and Chilmark Stone above. We examined Chapter House wall in more detail from the east and Eric pointed out the characteristic blisters formed as the glauconitic Chilmark Stone erodes. Chilmark stone is the Wiltshire facies of Portland Stone and was chosen by Sir George Gilbert Scott. It was an unsuccessful choice though and has been systematically replaced by Portland Stone since 1900.
In the nave itself we looked at a selection of monuments to past geologists, Buckland and Lyell. The small Purbeck Marble columns attached to the main columns in the south transept are interesting. The seam is no more than about a meter thick and yet some are about double that height. The smaller columns are carved from vertical blocks and some clay-rich bands in the marble have worn into grooves and notches. The longer unbroken columns are actually length bedded. Look upwards in the Nave to see more Purbeck Marble pillars. The clerestory and vaulting are Reigate Stone.
After a brief prayer for peace we had our main treat. The shrine to Edward the Confessor, with royal tombs grouped in a horse shoe around, lies behind the altar screen. In front is the raised Great Pavement. Henry III visited the pope in 1259 and saw the Cosmati pave- ment being built there and returned home with a bag of bits and pieces to have his own built. This whole area would at one time have been patterned with small tesserae of coloured stone or ceramic. The Great Pavement itself is incised into a bed of Purbeck Marble. Although damaged this is the most complete Cosmati pavement known. Oliver Cromwell allowed his horses coronation. Perhaps most surprisingly the rubber underlay of the carpet, laid specifically to protect it, cut off its air supply causing even more damage and left black bits behind as well. Conservators are hard at work restoring it. Eric has recast his fingerprints using spit to clean it and even less appropriate human activities are said to work well but cleaning is difficult. Shoes off before stepping on it – see how privileged we were! We stood back to appreciate the geometric design of the Great Pavement, also known as the End of the World Pavement. It predicts the world to end in 19683 years time. I am not sure what the starting date is though.
After a hot soup in the very cold cloisters we passed modern monuments. There was still time for a final look outside. The top of the West Front looks as crisp as the architectural drawing Eric showed us, where it is faced by white Portland stone. At the bottom to the side are more Reigate Stone and Kentish Rag. Round the corner in the North Nave buttresses is the piéce de resistance of unconformities. A couple of courses at the bottom consist of older, reused masonry. Above this there is a wide course of Cornish Granite. Oolitic Chilmark stone sits unconformably on the granite followed by a yellow shelly oolite from Normandy and more oolite. At head height it is Bath Stone.
Our last view of the cathedral was the Henry VIIth Chapel tacked on to the east end. This is highly decorated Bath Stone. Eric not only gave us an idea of the fabric of Westminster Abbey and its contents but also passed on his enthusiasm by adding anecdotes a plenty which made us realise that this church is a gigantic living organism rather than just an historic building. We thoroughly enjoyed our tour and look forward to seeing the restored Great Pavement.
We are grateful to Eric for making the effort to get out of bed so early on such a bitterly cold winter’s day to come up from Frome to be with us.
Those of you who were lucky enough to attend the OUGS Symposium at Canford School this year might also have read that the architect Sir Charles Barry designed the wonderful Victorian buildings of the Tower, the Great Hall and the north front of the school. He was also the architect of the Houses of Parliament. For me this was a reminder that I had promised to write up the building stones walk that Eric Robinson led to Westminster, way back in February. So here, rather belatedly, are my memories of that visit.
Diana Wrench has already written about our visit to Westminster Abbey in the morning (See the April edition of the London Platform).
It was still bitterly cold after lunch when we met up with Eric again outside the front entrance to the Abbey and made our way
round to the Houses of Parlia- ment. There were other items of interest to see on the way.
First there was the Queen Elizabeth II 2002 Jubilee sundial made of concentric circles of varied stones lain flat in the pavement. The types of stone were, moving out from the inner ring around the central disc: Trevor microgranite from North Wales; Borrowdale tuff; red granite and Cornish granite. Two footprints have been placed where the observer should stand so that his or her shadow will fall on a scale that can be used to tell the time, but there was only dif- fused light on that grey and wintry day, with no sharp shadows.
Next we piled into a tiny shop in the Jewel Tower, where we bought cups of coffee to warm ourselves. The Jewel Tower was built by Edward III to store his clothes and jewels. It formed part of the original Palace of Westminster and survived the fire that destroyed almost all of the palace in 1834.
From there we went on to our main destination, the Palace of Westminster as it is today, otherwise known as the Houses of Parliament. It is built in dark yellow magnesian limestone. This choice of stone has been much criticised on aesthetic grounds, but it was actually rather a good one, because it is more resistant to weathering by London smog and acid rain than other limestones and has kept the detail of the carving crisp and undamaged.
Barry had been impressed by Southall Minster, which had previously been made in the same stone. It was quarried in Northern
England and transported by barge via the Humber. On the small scale there are tiny gaps in the fabric, which were formed during
diagenesis as a result of the transformation of CaO2 to MgO2.
Barry also made a sound choice of stone for the more rounded plinth, a Jurassic oolitic limestone from Lincolnshire. We could still see stone tool marks made by steel combs to remove any loose bits.
We entered the building at the House of Lords end, furthest from Big Ben, and were shown into an entrance lobby where the elaborately decorative stonework included brocatelle, a Spanish marble from the Tertiary, Connemara marble from the Dalradian, black Valentian volcanic slate from the Silurian and red Monsal Dale limestone from Derbyshire. However, this was where the official guide took over from Eric. I won’t describe the rest of our visit in very great detail because I heard no more about the building stones and took no notes.
The famous architect Augustus Welby Pugin was only 28 years old when Barry enlisted his help to design the interiors of the building in1854, because of his knowledge of the Gothic style that had become extremely popular again in Victorian times. The next room we entered was a huge light and colourful hall used as a changing room by the Queen on her visits when opening Parliament. The decorative splendour was amazing, but was surpassed by the adjacent House of Lords with its elaborate golden throne and luxurious red leather seats. History oozed out of every nook and cranny of the place.
We walked on through the pivotal Central Lobby and the Members’ Lobby to the House of Commons, which was a lot more sober and subdued in its style and green colouration but still elegant and atmospheric. This chamber was destroyed in an air attack in 1941 and was redesigned by Sir Giles Gilbert Scott. It was fascinating to be able to walk past the front benches and take the same paths out past the counting points into the ‘ayes’ and the ‘nos’ corridors that Members of Parliament use when a debate ends in a division.
All the while the guide gave us delightful anecdotes and historical snippets such as how curtains used to be pulled around the Speaker’s chair so that he could obey the call of Nature without deserting his post, long before women were allowed to become MPs.
We left through the gloom of the mediaeval Westminster Hall, one of the few remaining buildings of the original Palace, with its vast hammerbeam roof. It had been a fascinating visit and I would highly recommend it to anyone who is interested in architecture, history or politics, although it has to be said that once inside, we had little opportunity to investigate the building stones. What an interesting day it had been – thank you Eric.
Chapter 1 in which we are introduced
“It rained and it rained and it rained”.
And it did. And the wind blew the rain across the car park where we met in the middle of Ashdown Forest for the start of our 15th Anniversary Geowalk. In fact the weather was so bad a few people decided that their health was more important than geology – strange people! Still, the remainder were not de- terred and, like Christopher Robin, put on their big boots and opened umbrellas and did not allow the weather to get them down.
So we repaired to the scant shelter of the nearby stand of trees to hear Brian introduce the walk and to remind us of the history of the Pooh Geowalks. Brian explained that he was there to show us the geology and topography and to tell us something of the history of the area and Sue was to talk about the more important topic of the Winnie-the-Pooh and the Enchanted Places of Ashdown Forest. After a while we could not put it off any longer and we had to brave the weather and set off on our Expodition.
Chapter 2 in which we find a heffalump trap
“Pooh’s first idea was that they should dig a Very Deep Pit and then the Heffalump would come along and fall into the Pit,
The particular part of the forest we started our walk towards was labeled on the map as “Five Hundred Acre Wood”, but we all knew it was really the “100 Aker Wood”. Soon we were walking on tracks through the lightly wooded areas with Brian ready and willing to describe the geology, topology and history of the area. The 6,400 acres of the Ashdown forest is the remains of the Lancaster Great Deer park, which was originally enclosed by a pale in 1296. Little of the original forest remains since the native trees were used in the smelting of iron derived from the Weald Clay, although Scots pines where introduced in the 1800’s. Complete reforestation has been prevented, until recent years, through the actions of the sheep formerly grazed in the forest by the Commoners.
Management of the forest is undertaken by the Board of Conservators who are changed with “preserving the forest as a quite &
natural area of outstanding beauty.” Ashdown Forest is located in the High Weald and most of the time we were walking on the
Hastings Beds, the lowest group in the Cretaceous sediments of the Weald, and in the main we stayed on one formation, the Ashdown
Beds. Unfortunately, as the weather was so foul Brian was unable to show us the exposures he would have liked as most of them were
on slippery slopes and it was also too cold to hang about.
As we walked, Sue drew our attention to an over- grown hollow beside the track. There was some speculation whether it might have been a saw pit or material may have been removed for building. How- ever, it was soon correctly identified as Pooh and Piglet’s heffalump trap and we wandered on.
Chapter 3 in which we discover the North Pole
“And we must all bring Provisions.”
As we walked, we kept our eyes open for any other Pooh related sites and sounds. Sue was able to assist with her encyclopaedic knowledge of the world of Winnie-the-Pooh, Christopher Robin and A.A.Milne. The identification of the various Pooh locations in the area comes from Christopher Robin Milne’s book “The Enchanted Places” and the popularity of the stories has ensured that a significant tourist trade has developed in the area, although this mainly centres round the gift shop and the Pooh Sticks bridge (the shop sells directions to the bridge in many languages).
Soon we entered a more thickly wooded area, and dropped down towards a stream flowing through it. The stream gave an opportunity
to view some exposed geology and soon after we realised that Christopher Robin, Pooh, Piglet, Rabbit, Wol, Eeyore, Tigger, Kanga,
Roo and Rabbit’s Friends and Relations had been there before us because there it was – the absolutely genuine North Pole! We knew
it was the North Pole because there was Pooh’s sign!
Luckily none of us emulated Roo by falling in and as the rain had stopped we decided to stop for lunch stream we munched our way through our Provisions.
Chapter 4 in which we play Pooh Sticks
“Come on stick! Stick, stick, stick!”
After lunch we made our way onwards towards the world famous Pooh Sticks Bridge. Our leaders had warned us to stock up on sticks before walking down to the bridge - other players had denuded the ground of every loose bit of wood that could be described as a stick long since. So, armed with a variety of playing sticks we arrived at the Pooh bridge, still looking very much like the E.H. Shepherd illustration. Of course, most of us were able to lean over the top rail to play - something not even Christopher Robin was able to do.
Soon we were all absorbed in the wonderful pastime of Pooh Sticks, with members rushing from one side of the bridge to the other like the children that all OUGS members are at heart.
Chapter 5 in which we say farewell
“But wherever they go, and whatever happens to them on the way, in that enchanted place on the top of the Forest a little boy
and his Bear will always be playing.”
All too soon we were on our way again, in increasingly better conditions and we started to rise again away from the water towards the top of forest. We started to get more distant views as we left the more wooded parts and came out on the more open heath like parts.
The final stretch of the walk (the traditional final push uphill) lead at last to Galleons Lap, the enchanted place of the final chapter of The House at Pooh Corner. Here we had also come to the final chapter of our geowalk. By the stone and plaque place there to commemorate the Bear and his creator, the immortal A.A. Milne, we said our thank you’s to our to leaders and made a small presentation. And then it was time to make our way back to our vehicles to change and to go home after a thoroughly enjoyable experience, despite the horrible start.
We are fortunate in having Paul Clasby as one of our members. Paul will be familiar to many of the London Branch who have attended the S236 or S260 revision days that the committee runs annually at Royal Holloway. Paul tutors on the fossils and always brings along his ‘favourite specimen’. This is a large gastropod Clavilithes macropspira that has an environmental tale to tell. He also brings along rare examples of Crassatella sulcata; rare, because they have survived with the two valves intact. These specimens come from Barton-on-Sea, near where Paul lives, and over the years he has built up a fabulous collection of his local fossils. Paul has been very generous with his time and has frequently led London Branch on collecting trips to Barton. Saturday 15 May was one such occasion: a glorious day which 16 of us spent pottering along the beach extracting fossils from the slumped clay. For those interested in molluscs this is a real haven with hun- dreds of species of bivalves and gastropods, usually with excellent preservation.
The clay here is very slumped. In the past we have walked to the beach from the Barton end of the section and then west down the section to Highcliffe, then back along the shoreline looking for sharks’ teeth. This time we did it in reverse as disastrous cliff falls at the Barton end have made access there very difficult. The advantage in doing it this way round is that from Highcliffe there is an excellent view of the cliffs, and despite the severe slumping, it is possible to make out the dip of the beds to the east. I was sorry to see that the explanatory board was no longer readable. It looked as if it was completely faded rather than vandalised. It would be good to see it replaced.
When we set off we could see the Needles over on the Isle of Wight in the distance but by lunch-time they had disappeared behind the haze. This did not deter the bikini-clad sunbathers along the beach. Several of them and their offspring were curious to see what we were up to with our rucksacks, big boots and trowels. And I am sorry to say that it was the non-OU students who found the best specimens. First prize goes to Pari Collis’ husband, Cliff, who found a spectacular specimen of Volutospina luctator, about 11 cm long and very spiny. As a bonus it was encrusted by a small oyster . Various children along the way also found good specimens of this genus of gastropod though none competed for size. Cliff, Pari and a couple of others had misunderstood the instructions and had started from the Barton end.
We met them mid-way looking very muddy but very excited by the prize gastro. The second best find was another big gastropod Clavilithes longaevus, similar to Paul’s favourite, but a different, rarer, species. This was found by one of the sunbather brigade that I had been showing our finds to only five minutes earlier! It came from a ledge (hardened, as it happens) beneath the in situ exposure of Bed C, bounded by septarian nodules. It was totally unsquashed and much coveted! I gave him a box and tissues so I hope he looks after it. One of our group, Ursula Scott, I think, found part of a squashed specimen of the more familiar Clavilithes macrospira in much the same place. Paul was impressed by the finding of a Sycostoma bulbus. This species of gastropod is rare, unlike the more common Sycostoma pyrus of which I saw several relatively small specimens.
Towards the end of the day Joanne Cassidy set the trend by sitting on the shingle and combing through it for sharks’ teeth.
Suddenly a joyous cry emanated from her as she jumped up and danced around clutching a whopper. It was even larger than the one
found by a sun-bather shortly before. Her patience was rewarded by several more teeth, a vertebra, an ear-bone of a fish (otolith)
and a piece of turtle shell, and surprisingly, several nice, unworn gastropods.
Dee Summers was also very excited about her very pointy sharks’ teeth. Dee had taken Paul’s advice and found them by walking down
the shore line. I am sure that there were other good finds that I didn’t set eyes on. Certainly many people found sharks’ teeth.
My own finds were very paltry in comparison, and none of the coveted teeth. More than one of the party commented to me that such
a day makes you glad to be alive and I would certainly go along with that!
Thank you Paul for leading us, and thanks to Iain Fletcher for making it happen.
PS for anyone wanting to learn more can I recommend two web-site addresses:
www.dmap.co.uk/fossils for excellent colour photos for fossil identification and
www.soton.ac.uk/~imw/barton.htm for detailed geology.
This is a classic locality for fossil collecting, and it is well worth a visit. It is on the south coast of England, 13 kilometres (8 miles) east of Bournemouth. The fossils are mostly marine shells, about 40 million years old. Over 600 species of fossils have been found, including over 200 species of gastropod (snails).
The collecting area is a section of coastal cliffs about 1½ km long and 30 metres high, above a sandy beach. The cliffs are made of clay, from which the fossils can be removed quite easily. They also show quite impressive landslips along the whole length, with a rate of retreat of about a metre a year. This creates a succession of terraces made of soft mud, easily trapping the unwary visitor. Along the top of the Barton cliffs are the much younger Pleistocene river gravels and brickearth.
Access to the beach is easiest from a public car park (grid reference SZ 216 933) on the cliff-top at Highcliffe, just west of Barton. To reach it, turn into Waterford Road (signposted “To the sea”) leading south off the main A337 road. The charge for parking (in 2004) was £3.80 for the day. From here a broad footpath leads down to the beach. Equipment needed for the trip includes wellies if going onto the clay (but if not, then walking boots are quite adequate), a hand trowel and collecting bags/pots. The sizes of most of the shells are between 1 cm and 4 cm. Once on the beach, a reasonable collection of fossils may be made simply by keeping on the sand and examining the adjacent low clay bluff. Venturing onto the clay terraces cannot be recommended.
These cliffs expose the dark grey marine clay deposits of the Barton Clay Formation, of Upper Eocene age. The Formation is 46 metres thick and dips to the east at a very gentle angle, 1 to 2 degrees. It has been divided into a series of beds, each given an identifying letter. The exposed section runs from A2 near the base in the west, to I (“eye”) on the western edge of Barton (beds G to I are in the overlying Becton Sand Formation — formerly the Barton Sand). The individual beds are not easy to tell apart on the first (or second) visit, with the variations being in sand content and glauconite (and fossils too).
The main marker in the sequence is formed by a pair of horizons, 1.8 metres apart, with light green concretions at least ½ metre long. These mark Bed C. Another concretionary horizon 7.5 metres higher up (by the Barton sea defences) marks the top of Bed E, 1½ m thick and notably rich in fossils: mostly the thin spiral shells of the genus Haustator (formerly called Turritella). The ‘conch’ shell Volutospina seems typical of the lower beds, with Haustator and the ‘smooth pointy snail’ Sycostoma in the upper beds. Shark teeth can best be found near the Highcliffe end of the beach, in the patches of gravel revealed when the tide is low, having been concentrated there by wave action.
The overall environment here 40 million years ago was like that of present-day Indonesia. There was a shallow shelf sea (with the coastline close to the north) and it had a sub-tropical climate, although at a latitude around 40 degrees north. Later, the shallow sea gradually silted up, becoming lagoons and then land.
1. “The Barton Beds” (two pages by Paul S. Clasby, unpublished?)
2. www.soton.ac.uk/~imw/barton.htm (for details of the geology)
3. www.dmap.co.uk/fossils (for excellent photographs of all? the Barton fossils, and others)
4. “British Cenozoic Fossils” fossil identification book by the Natural History Museum
5. “Field Guide to Barton on Sea” handout by Paul Jeffery for OUGS field trip 20 May 1990.
We gathered under the clock at Waterloo Station at 4.30 pm and heard Wilf's instructions in competition with the station tannoy.
The station tannoy won. We caught the train to Portsmouth Harbour and from there the ferry to Ryde Pier and then an ex- Northern
Line tube train which went from the end of Ryde Pier into Ryde and onto Shanklin. There Wilf led us on a 5-minute walk which
took 30 minutes round the sights of Shanklin, to the Hotel Aqua, our home for the next 3 nights. We had a meal and an evening
in the bar introducing us to our leader, Paul Grant, who addressed us as 'You Ogs' [UOGS], and gave us an outline and handouts
of the next few days' field trips.
Some of us had noticed that the Esplanade with the hotel on it had been cut out of a cliff of 25 metres of Lower Greensand.
May Day! The first of day of Summer, and it eased into it gently. A grey morning as we set off for Colwell Bay on the western side of the island, an hour’s drive from our excellent Aqua Hotel in Shanklin. Paul Grant, our leader, started off by explaining the geology of the island. After the compression of the Hercinian orogeny, post-Palaeozoic extension resulted in a series of half-grabens, allowing considerable deposition in the area. With the Alpine orogeny these faults were reactivated to form the Weald anticline onshore, and the monolistric anticline that runs west-east across the island.
At Colwell Bay the beds relate the ‘listric’ side of the monocline with a gentle dip to the northeast. These are all within the Late Eocene Headon Hill Formation. We examined a small section of the Colwell Bay Member. First we came to an oyster bed near the back of the beach. This was packed with broken fragments of Striostrea velata in a channel cutting through the ‘Venus’ Beds. It was a while before I had a chance to examine the ‘Venus’ Beds for myself. As the group moved on, people kept bringing me their finds. I have had these identified in case other members want to compare their own fossils. Pictures of them can be found on www.dmap.co.uk/fossils. First I was brought examples of a small freshwater-brackish bivalve (Corbicula obovata) then the famous ‘Venus’ (currently named Pelecyora suborbicularis), a marine bivalve. Later on we saw these in life-position in the cliffs. I also have a fragment of Mytilus affinis.
This mix of marine and brackish-water species is also encountered in the gastropods, the most common of the marine ones being Editharus labiatus and Ancillus buccinoides. I was also handed Bonellitia pyrgota, Ampullella grossa and a Euspira. The most common brackish form is Ptychopotamides pseudocinctus, and Tympanatonus is also represented. I was instantly struck by the similarity with the older Abbey Wood fauna where there is a mix of marine and brackish fossils in the Early Eocene Harwich Formation, beneath the London Clay.
Luckily the rain held off so we could eat our lunch on the beach. Then it was back to the minibus and off to Alum Bay. We could just make out the Needles from the top of the cliff but the foghorn was hooting ominously. Some braved the chair lift but most of us walked down to the beach and then straight on past the famous candy-stripes to look at the Chalk to the extreme south of the beach.
The fog seemed to be worsening so I did take a few snaps as I hurried by. The Chalk here is caught up with the monocline and appears vertical, just like the Tertiary Beds. We clambered over the boulders looking for the zone fossil, the belemnite, Belemnitella mucronata that is characteristic of this part of the brilliant white Upper Chalk. We also found several echinoids, mostly in cross-section in the chalk boulders. One small pointed one was extracted, probably Echinocorys subconicula. Both these animals had calcite shells and were thus much more likely to be preserved than the aragonite shells of the ammonites and most of the other molluscs. Paul showed us a burrowed section which helped to explain the process of flint formation. The burrows were a pale grey in contrast to the Chalk and some ended in a section of hard flint. The grey colouration comes from spherules of silica that had not yet coagulated into flint.
Now the pretty bit, and it really was pretty. Whilst we had been peering at the Chalk the sun came out and the Alum Bay Sands were beautifully displayed. This meant a whole new set of photos … We started by examining the junction with the Chalk. Paul pointed out the karstic nature of the eroded Chalk surface before the deposition of the Lower Tertiary Lambeth Group. In this area the top of the Chalk has been completely eroded as elsewhere in England. There is no evidence around our shores of the earliest Tertiary Danian stage, and in the Isle of Wight, even the next group, the Thanet Beds, are also missing. Here the early Tertiary sea had re-excavated large holes which in some cases still contained sands which are probably from the Upnor Formation, the marine horizon that lies at the base of the Lambeth Group. Most of this section was severely landslipped but here and there it was possible to see the nature of the mottled clays which follow-on – mostly a deep red with green mottling, typical of the terrestrial ‘soils’ of the Reading Formation, still part of the Lambeth Group.
Next came the London Clay, which is my particular interest. We didn’t examine the intervening Harwich Formation, probably because it was also severely caught up in the slippage. As elsewhere in the London Clay there are horizons of septarian nodules where the clay has been cemented with calcium carbonate to form hard concretions. One such, half-weathered out from the clay, was over 1 metre long with wonderful trace fossils preserved around the outside, similar to those seen in Sheppey last June. Chris King has described 5 divisions of the London Clay but here only 3 are apparent. Paul described how movement on the extending faults allowed ‘basin accommodation’ which gradually filled up so that the resulting sediment showed a coarsening-up sequence. We were able to test this for ourselves at the junction of one of the divisions: the top of the underlying divisions was a sand, and the base of the overlying division a silty clay. Between the two was a distinct layer of small black pebbles deposited as the sea transgressed once more across the basin. The divisions in the London Basin are not nearly so clearly defined as deposition was further off-shore.
Now we came at last to the coloured sands of the Bracklesham Group. These are the source for the multi-striped bottles sold at the top of the chair lift. The cliff was cordoned off but Paul cleared it with the lift operators and brought us samples. So we examined pure white pipe clay and Paul showed us pictures of leaves that have been found within it. These were notable for their smooth outer edges, without serrations or pointed ‘drip’ ends, typical of equitorial conditions. We saw beds of lignite – differentiated from charcoal by the lack of blackened fingers when handling. Some horizons are very iron rich and water percolating down these had disappeared through the shingle ridge, reappearing further down the beach, staining the pebbles an amazing orange colour. There is apparently very little in the way of fossils in these sands. What struck me forcibly was the complete contrast with the sequence at Bracklesham and Selsey. What I have seen of the exposures on the mainland are richly glauconitic with certain horizons crammed with fossils. I was looking forward to seeing the section at Whitecliffe Bay, on the other side of the island, that lies between the two.
We looked briefly at the Barton Beds near the chair lift – superficially similar to the clay at Barton-on-Sea with the odd fossil poking out, but we did not have time to look closely, and by now the new shift on the chair lift was getting very agitated that Paul was behind the barrier. Maybe they are particularly sensitive about the area immediately beneath the chair lift with some good reason. I confess I really enjoyed my ride up while the stalwarts got their exercise for the day.
Last stop of the day was Freshwater Bay. The late afternoon sunshine gave a spectacular view of the cliffs to the east with
the Chalk stacks marching into the sea. Apparently this had been an arch not long since. We turned west but despite the shade,
the cliffs behind us were also a spectacle. The Chalk here was completely rubbly due to periglacial action and the flint rows had
become fractured and distorted, with their tops bending to the east. The Quaternary deposits above showed some structure but were
also partly disrupted. This was a ‘sunset’ finish to a really excellent day. The first day of summer had arrived after all!
Thank you Paul and thanks to Wilf for organising it and Paddy for driving us.
The day started dull, unlike the beautiful day before. As we headed towards Bembridge and Whitecliff Bay the rain set in. However, we were not daunted since we were going to see one of the best exposures in southern England for Tertiary strata. Running roughly west to east across the centre of the Isle of Wight is the nearly vertical chalk and Palaeogene strata (Reading Beds, London Clay, and Brackelsham to the Bembridge Limestone). They are exposed at the western end - Alum Bay and Needles that we saw on the first day - and at the eastern end at Whitecliff Bay and Culver Down where we were going on this day. So, we were to see a mirror image plus some other goodies.
Our first stop was at Sandhills holiday camp, where we took the zigzag path down to the beach of Whitecliff Bay. Here, we observed the Middle Chalk all the way through to the upper Eocene with its highly fossiliferous non-marine Bembridge Limestone. During the post-Cretaceous uplift, sea level rose and fell eleven times between the Reading and Bembridge. These transgressions and regressions are reflected in the many changes between pebbles, sand, marls and limestone that could be seen as we traversed along the beach. We observed the finer sediments of the deeper water and the sandy and pebbly deposits of shallower water at each movement in relative sea level.
At the bottom of the path, we first turned north towards Black Rock to look at the Headon Hill Formation through to the Bembridge Limestone and Marl. Some of the harder sediments showed where organisms had burrowed, which were then filled with iron carbonate.
As sea level rose, the shoreline pushed forward with rias being formed. The energy of rivers was restricted, slowing inland and depositing their load with big rivers and big meander plains. This in turn deprived the sea basin of sediment.
North towards Howgate Bay there is a large exposure of Bembridge Marls at the top of the Eocene that contained bi-valves and gastropods.
So at Whitecliff Bay, we had seen the whole formation from the Upper Chalk to the top of the Eocene, through the Reading formation, London Clay, Bracklesham, Barton Headon and Osborne Beds to Bembridge Limestone and Marls. It displayed a mini Alum Bay with terrestrial deposits, lignite and sandstones that appear to be cyclic.
The last stop of the day was to include lunch at the Crab and Lobster Inn, Forelands at Bembridge overlooking Howlands Bay. To ensure that the pub did not object to our coach parking in their car park, those who were willing went into the pub, whilst the rest went down the short path to the beach to walk along to the raised beach. It forms part of the Bembridge raised beach at the top of the Eocene and displays large pebbles with cross-bedding and puzzling channels.
From Bembridge we all had to get back to the hotel so that we could collect our bags and be ferried to the station. In the hotel we thanked Paul for giving us all a very interesting and enjoyable weekend. We said our goodbye to those who were staying on the island or travelling home by car, and then those going by train went to the station to await the brightly coloured dinosaur decorated tube train to Ryde.
Essentially, the area of the Excursion is the along-strike equivalent of the Midland Valley of Scotland terrane with Dalradian rocks of North Mayo to the north separated by a major lineament (Highland Boundary Fault in Scotland) that bifurcates in Western Ireland about Clew Bay, to include the South Mayo terrane (SMT).
South of the SMT is the Connemara terrane that has similiarities with the Dalradian rocks to the North in County Mayo. These two terranes which were emplaced on to the Laurentian margin by strike-slip faults have the remains of a Volcanic Arc sandwiched between them. The Arc is named ajter Lough Nafooey in Connemara, where it outcrops.
To the South of the Connemara terrane is an area of highly metamorphosed rocks that include gneisses, layered gabbros and migmatites metamorphosed and altered by the intrusions of the layered gabbro and Galway granite plutons.
Day one started on the south side of Clew Bay near Westport where Sue showed us outcrops of the Deer Park schist complex of Cambrian-Ordovician age on the shore. After much group debate we thought that we could recognise a number of tight folds. The GSI guide (Ryan et al. 1983) indicate this area as a major shear zone and consider it to be a part of a fragmented ophiolite complex or a sheared serpentinite olistostrome.
We moved a short distance to the south and joined the Sunday morning pilgrims climbing the holy mountain of Croagh Patrick (764m). Fortunately our climb was not so high as the pilgrims, and we soon stopped to inspect a beautiful Melange deposit of Silurian age that contained large blocks of serpentinite with epidote inclusions. From the GSI geological map this melange deposit extends for 20km together with the Deer Park complex along the South of Clew Bay parallel with the Clew Bay thrust.
After lunch we travelled north to Pontoon on Lough Conn a few miles north of Castlebar where Sue showed us an outcrop containing really excellent examples of granitic magma mixing/mingling emplaced during the Grampian Orogeny. The chilled margins of the later more mafic magma could clearly be seen against the older granite. A memorial days geology.
Briefly, other days were:
Day two was a visit to the north of Clew Bay to look at Dalradian rocks and the Boundary Slide in Ashleam Bay.
Day three, Ordovician and Silurian rocks in the South Mayo Trough: post ice age scenery.
Day four, a visit down old lead mine and museum near Oughferard: Lough Nafooey Island Arc volcanics and pillow lavas: ancient lake Varves at Glassillaun Bay, stunning scenery in both areas.
Day five, The Burren Limestone Pavement, its famous flora and Cliffs of Moher (no show due to fog).
On our last day we visited the southern part of Conne- mara. One particular quarry Sue showed us along the road contained a migmatised paragneiss which contained patches of radiating needles of actinolite forming star patterns. I have since made a thin section of this gneiss and identified the main minerals: plagioclase feldspar 20%, quartz 20% and hornblende 60%.
A grey day. A day when we just knew why we had brought all that wet weather gear.
My turn to drive. Through Gallway, at sea level, very cloudy, past the coast-defending Dugguaire Castle, very cloudy and on to Ballyvaughan whose harbour provides whale watching trips, very cloudy with drizzle and then…
The coast road here is shown in the Michelin Guide to Ireland as a two-star Scenic Route, we saw… absolutely nothing. The road climbed in the clouds and visibility was reduced to 100m. At a crawl we went onwards and totally missed the entrance to the car park at the Cliffs of Moher, our first geological stop of the day. We descended the slope and found Ireland again, turned around and entered the grey world once again. All I can tell you about this renouned tourist stop is that the car park is large and it has a visitor’s centre and coffee shop with facilities.
The pathway to the view point is lined with slabs of the Clare shale which have the largest bioturbation tracks that I have
seen, 4-5cm across and up to half a metre in length, cross-cutting and interweaving like some Celtic tapestry.
Of the 700 foot high cliffs we saw nothing.
After leaving the Cliffs we drove down to the Lisconnor Rock Shop where many Euros changed hands, we even bought lunch.
Then onto the Burren, one of the largest Lower Carboniferous limestone pavements in Europe. Leaving the car, walking onto the pavement and knowing it covered nearly 1000 square kilometres, it was creepy to see that the world ended 100 metres in every direction. The pavement is truly superb, its clints and grikes home to a wondrous array of miniature plants hiding from the extremes of this environment. I’m not a botanist but I’m sure, if you were to ask, Heather Rogers has a full list of the plants seen.
And so, back to Oughterard, Sue Vernon driving. On the way we passed the Burren Interpretation Centre just outside Ballyvaughan,
our party decided not to stop, a mistake on two counts.
Firstly our journey time brought us to Gallway at rush hour which our Branch Organiser coped with in her usual calm and competent manner (but it took an age).
Secondly the two other cars had stopped at the centre and from conversations over pints of the black stuff it seems that this write-up could have been far more informative if we had stopped too.
1. GLENGOWLA MINES.
The morning was brighter than yesterday and the first stop of the day was a visit to Glengowla Mines. This is an old mine started in 1865 to work minerals, principally the lead ore galena with some ancillary fluorite and barite with very small amounts of silver. The mine had been closed for some time but now has been developed as a tourist attraction to show how it was worked by hand.
Old tools and wooden and steel buckets as well as primitive lifting tackle demonstrated the hardships for little rewards. A historic sample rescued from the deep mine showed how small and hard won were the ore fragments.
However, the underground geology was impressive. The mine is situated in the Connemara Dalradian metamorphic area and the country rock is of altered sediments, the very attractively banded Lakes Marble formation. This was shot through with a number of dolerite intrusions, notably in one section these appeared in echelon. Some baked edges were noted and mineral separation seen as odd bits of galena, fluorite, barite, scanty chalcopyrite and plenty of pyrite.
There is a reasonably stocked Rock Shop on site.
This was a very worthwhile visit.
2. THE GALWAY GRANITES.
The rest of the day was spent examining a number of exposures of differing Galway granites. These are all Devonian in age, about 400Ma and much younger than the rocks previously seen this week.
The first stop was a large roadside quarry not far on the road south of Maam Cross.
The gross view suggested that this was the edge of the Galway granite intrusions, as the dark country rock was intruded by a number of much lighter varying sized finger like veins. Closer examination showed the country rock consisted mostly of Dalradian sammites altered to steeply dipping banded paragneisses, some of which showed evidence of melting, leaving a schistose fabric (?phyllites). The veins of paler acidic rock with granite mineralogy tended to push upwards. A consistent set of minerals were found, plenty of biotite and “pods” of muscovite, some hornblende and garnets.
A dolerite sill was found, as well as some migmatites.
The second stop was farther south at a small riverbank exposure. This was within the Callowfinish granite, a pinkish granite with a fairly fine groundmass. Pink feldspars were abundant, some large and zoned and twinned. There was some suggestion of lineation.
The next stop near the coast after turning east was a much more substantial roadside outcrop with fresh surfaces. This was
quickly identified as a fine grained generally greyish granite, (Carla) but there was more to it!
On standing back, many diffuse, much darker patches and streaks of similar grain size to the light granite were evident. This was obviously some basic material appearing. However, margins were very diffused and there seemed to be no baking. This outcrop was indeed showing the well documented “magma mixing” area in the Galway granites. Close nose on revealed other features.
Some mineralisation was noted, pyrite, chalcopyrite and a patch of molybdenite, silvery blue-grey and greasy to the touch.
This mineral has been worked in the general area. A few pink feldspars were noted, some of which showed signs of degrading. Towards one end of the outcrop was a very pale, dirty cream, roughly half metre thick intrusion with different weathering patterns. This was a good example of an aplite vein, consisting almost entirely of microcrystalline quartz.
This stop was most interesting.
On the way to Spiddal, a stop was made to look at a very small outcrop of the extensive Murvey granite. This was quite pink overall in colour, fine grained with some larger pink feldspars. This is a slightly later intrusion and is thought to be related to final continental collision.
There was not time to see any other granites, especially the granodiorites but enough had been examined to give a good idea of the considerable variation in these Galway granites.
As a final treat, a quick call was made at the Connemara Marble Shop at Moycullen, to see the range of artefacts made and to note the characteristics and variation in the colours and banding of this exotic rock.
A great day again, so it was back to fine eating and of course the Black Stuff!
While not as hot as it had been earlier in the week, it was bright and breezy as we met at the car park opposite the Smuggler Pub at Pett Level. About 30 in all - some old hands, but it was nice to see new faces, we gathered round our leader, Ken Brooks of the Hastings and District Geological Society as he gave us an introduction to the geology of the stretch of coastline we were to look at and the fossils and trace fossils we might find, if we were lucky. The exposures we were to see dated from the Lower Cretaceous, when he envisaged a landscape of shallow lakes and meandering rivers. He showed and passed round for us to handle his own specimens, including casts of dinosaur (iguanodon) footprints and a verte- bra from the same creature, along with fish scales and teeth, conchostratans (shrimp-like crustaceans), burrows and gutter casts.
Ken shows his shark fin spine
The central part of Fairlight Cove is bounded by two reverse faults and consists of sandstone of the Ashdown Formation resting on a bed of silty Wadhurst Clay, subject to erosion by the sea when exposed as the base of the cliff by removal of the shingle. There was a very strong warning against going too near the cliff, which is very dangerous with huge chunks liable to break off without warning, and against which our hard hats would provide little protection.
The day was broken into two: the morning spent studying the rocks from the Cliff End sandstone close to our starting point, to the berm built in 1990 to protect the houses of Fairlight Cove from further erosion; the afternoon at Rock-a-Nore in Hastings itself.
As we walked along the sea front we were told of the sunken forest that had covered this part of the foreshore 5,000 years ago, invisible at present because the tide was still too high, and of caves made by groundwater at the end of the last Ice Age, where Mesolithic flints had been found. Here we saw a textbook example of a normal fault where the slip plane and downthrown strata are quite clear. In the fallen rocks we found the remains of gutter casts and trace fossils such as bivalve burrows.
Our first dinosaur footprint, iguanodon toe impressions, provoked lots of photographs, and from then on eager fossil-hunters brought bits of carbonised plant remains, the rounded teeth of lepidotes, scales and shark-teeth. We were intrigued by a chunk of the Cliff End Bone Bed, containing many fragments of shells, bones, teeth, plant material etc, which occurs as lenses in the Wadhurst Clay.
We looked also at sedimentary forms, finding evidence of point bar deposits from braided streams and erosion surfaces where the cross-stratification had been truncated. There were long reddish traces, showing as red dots in cross section, of horsetails (Equisitites lyelli) which had grown through the sediments, all helping to give a picture of the environment of the early Cretaceous.
Coming to the end of the morning walk, we saw a smaller dinosaur footprint partly embedded in a bigger one, a case of mother and baby? Finally as we rounded the corner, we saw the Haddock reverse fault, with the fault plane parallel to the beach, and the berm, made of huge blocks of Norwegian larvikite, already proving its value as the scree slopes are being grassed over.
After lunch, taken either at the pub or on the beach, we met up again at the car park at Rock-a-Nore and scrambled down on to the boulders of the fore shore. Here the cliffs are of the Ashdown Formation, beneath Cliff End sandstone and topped by the Wadhurst shaley clay, the origin of most of the fossils found on the beach.
The cliffs at Rock-a-Nore
Here we found sedimentary structures such as crossstratification, ripples, erosion features and bedding planes of bivalves. An interesting phenomenon is nodules of sandstone hardened with calcite, in one case resembling a prehistoric mother-goddess figure. In a hard sandstone block, ‘Hastings marble’, we saw part of a lepidotes with well-preserved scale impressions as well as our last dinosaur footprint.
The weather was worsening by about 4.00 so most of us make our way back to the car park, leaving a few hardy warriors still searching. The fresh fish to be had from the stalls in Old Hastings meant that we took something back with us, even if it wasn’t a bit of dinosaur!
Early on Saturday morning a combined group of enthusiasts from OUGS London Branch and the Kent Geologists Group met our leader Gareth George, an old friend of London Branch, for a day of study in the Cretaceous Lower Greensand of the Western Weald.
Our first location was in the Folkstone Formation at Charing Sandpit in Hook Lane (TQ 935 493). This visit had been arranged with the kind co-operation of the owners Brett Aggregates. Operations in the pit had been suspended for the day and the Deputy Manager Steve Murrell and some of the staff accompanied us throughout the visit.
The faces exposed in the pit exhibited well developed cross stratified sets up to 2m. high consisting of moderately well sorted fine to medium yellow quartz sand. Closer investigation revealed variations in the direction and form of the foresets, some being asymptotic with dip angles reducing with depth and some more wedge shaped. Some reactivation surfaces could be seen, and considerable secondary iron staining (Leisegang rings). Gareth explained that these features are typical of sands deposited below the wave base in shallow shelf seas under the influence of strong tidal currents with well defined spring and neap cycles. The direction of dip of the foresets is produced by the dominant current, with the subordi- nate current forming reactivation surfaces. Gareth demonstrated that sequences of 28 to 30 foresets (tidal bundle sequences) could be recognised, the spring bundles being thicker than the neap bundles which tend to be more asymptotic . Each sequence may be terminated with clay drapes and/or reactivation surfaces Measurements of the direction of dip of the foresets indicated a current direction from the north-east, and Gareth explained that this conforms to the paleogeography of the area with a connection to the proto North Sea to the east of the high ground of the London Platform to the north. In marked contrast current directions in the Folkstone Formation in the Eastern Weald trend towards the Bedfordshire Straights in the north-west.
Further close investigation of the sands revealed that the dominant current sometimes changed direction, the two sets often separated by a highly bioturbated erosion surface. Many trace fossils could be identified, vertical Skolithos and Ophiomorpha burrows and large horizontal and sub-horizontal Thalassi- noides. Some small scale climbing cross ripple laminations could be seen superimposed on some of the foresets, thought to be caused by vortices set up in the lee of the dunes. In places the secondary iron forms hard concretions (carstone) which appear to be unrelated to bedding features or grain size, some even forming tubular structures. Similar features are seen in the Folkstone Formation throughout the Weald, and no simple explanation for their formation seems to be available.
At the end of our visit Steve Murrell took us on a tour of the production facilities in the works. The pit produces some ¼ million tons per year of mortar sand to the building industry and retail outlets, and at the present rate of production the pit has a remaining life of about 8 years. The sand is first dumped through a coarse 150mm. screen to remove concretionary iron, then taken by conveyor to the fine screening plant where it is put through a 5mm. screen of parallel piano wires. Throughout the process the moisture content is closely controlled to produce to final moisture content of about 7%.
Lunch was taken at the Chequers Inn in Loose village, an excellent hostelry which serves Harvey’s Bitter!
Our second location of the day was a short walk from the Chequers via Salts Lane and a public footpath to the abandoned Kentish Ragstone quarry in Quarry Wood. On the way to the quarry we could see large blocks of the stone in use in the viaduct built by Thomas Telford in 1830.
Although the quarry is somewhat overgrown some excellent exposures are accessible, and show the typical alternating bands of ’Rag and Hassock’ typical of the Hythe Formation in this area. The Ragstone bands consist of hard massive sandy limestone up to 1m. thick, highly bioturbated and with sharp erosional bases. The Hassock bands are generally thinner, and consist of loosely cemented glauconitic sands with occasional hard siliceous bands and low angle cross stratification. Some typical marine fossils were recovered. The fauna of the Hythe beds in this area is very varied, and includes ammonites, bivalves, belemnites, brachiopods and echinoids. The Hythe formation in this area is markedly different to that in the Western Weald, where it consists of heavily bioturbated glauconitic sandstones with lenticular chert beds and very rare fossils. There was some discussion regarding the cause of the alternating bands here, and the fashionable Milankovitch Cycles were invoked at one point. But why only in the Eastern Weald?
Some faulting and large in-filled open fissures were seen. The fissures are known as ’gulls’, and are a feature of valley cambering. The competent strata are moving down-slope into the adjoining valley, sliding taking place over the underlying Atherfield Clay.
So we came to the end of another excellent day. Many thanks must go to Gareth for his enthusiastic and informative leadership, to Brett Aggregates for their kind co-operation, to Diana Franks of Kent Geologist’s Group for her liaison with Brett Aggregates, and to our own Di Clements for organizing the trip.
Saturday 30th October : Minehead, Watchet and Blue Anchor
We all gathered on the Friday evening at the Beach Hotel, arriving by train to Taunton, bus and car. Those arriving at Taunton by train or bus were met by Eric and his son-in-law to be ferried onto Minehead in two cars because our minibus had broken down. However, the minibus was quickly repaired and ready for us at 9 a.m. on Saturday morning, never to break down again during the weekend.
We had all been wondering on the meaning of the name Minehead, thinking it had some relationship with a mine. However, Minehead Town Council’s website states that it was first mentioned in the Domesday Book of 1087, the name being Celtic, similar in origin to the Welsh mynydd (mountain), reflecting the prominence of North Hill just to the north west of the town.
Our hotel was opposite Minehead Station the terminus of the West Somerset Railway. We were greeted by the smell of coal smoke in the morning, so the first thing to do, after breakfast of course, was to go and look at the engine, which was in steam being polished for its first journey of the day. This engine was a 2-6-0 that had been “cannibalised” just recently. Its first outing had been in September (see photograph on www.lougs.org.uk). The railway was extended from Watchet to Minehead in 1874 and is now 22 miles long between Minehead and Bishops Lydeard although tracks do join with Taunton and, occasionally, Virgin Trains run a service called Somerset Venturer to Minehead. From 1860 onwards, under the auspices of the Luttrell family, new stone buildings were erected using local stone. For example, the Triassic red sandstone and Bath stone (windows) were observed in station buildings.
After leaving the station we stopped at the War Memorial on North Hill, which gave a good, although misty, view of the topography of the coastline and the link with South Devon was postulated. The Hercynian folding and faulting had forced Exmoor and the Quantock Hills apart, which formed the source of material forming in the valleys of Permian and Triassic periods. With the view of Palaeozoic wooded hills and rounded hills of the New Red Sand- stone we envisaged the Triassic monsoon drenching the landscape with the run-off eroding pebbles from the Palaeozoic beds, which tailed off into finer beds (Otter Sand- stones). Below us was the Pleistocene inlet that had been drained by the Luttrell family; previously the sea had extended inland.
Our second stop was in Watchet by the Eastern pier of the harbour. We observed geology in action since when the tide comes in silt is deposited, which has to be dredged by suction across the sea wall. We observed the seaward-dipping Mercia Mudstones, Rhaetian grey marls and black shales and the White and Blue Lias to the east of the harbour.
Coastal erosion was very marked at Watchet with its six metre tidal range. There has been an attempt to arrest this erosion with blocks of armour stone transported from the carboniferous limestone quarry at Frome. The Beach just east of Watchet harbour with seaward-dipping beds of mudstone, marl and shale and the armour can be seen in the third photograph on the LOUGS website.
The coast shows the passage from the warm climate with lacustrine and saline deposits of the Keuper Marls at the top of the Mercia Mudstone Group to chocolate and green layers of the Lias. Trace fossils were to be found here demonstrating the ecology of bivalves from freshwater to marine although evidence was hard to discern.
We walked back through the town, passing the Library, which had a number of interesting materials. These included sandstone pellets (nodules) in lime arid paler stone of Willaton. We also were impressed by the statue of the Ancient Mariner as we continued to walk across to Watchet West Beach. The first thing of note here were the cliffs, which had an inland dip compared to a seaward dip in the beds out to sea.
At the entrance to West Beach we observed the effects of the government ignoring the advice of the BGS. Sand had been extracted, which has led to ground being sucked away from elsewhere, demonstrating that you cannot isolate one part of the coast from another.
The Mudstone here had been deposited in water ponds during periods of semi-deserts that had been rich in salts. These evaporates had crystallised as lenticular deposits of gypsum (calcium sulphate) in the rocks. Later, when the rock was stressed and buckled during the Tertiary, fibrous gypsum formed that followed joints and bedding planes. Lenses of gypsum (alabaster) had gone into solution and filled up the cracks. Examples of gypsum in fallen blocks and mudstones can be seen in the website photographs. The cliffs had good examples of faulting; the photograph below being an example of a “trap door” slump.
There was considerable evidence of splintering in the cliffs west of Watchet Harbour with fractures at point of impact.
We now walked back to Watchet where we had our packed lunch.
The last stop of the day was at Blue Anchor. After parking the minibuses we passed by an old brick kiln by side of road, which
can be seen on the website. The beach between Blue Anchor and Watchet showed Liassic formation with inter-tidal bivalves in
liquefied sand. Again, we saw Mercia mudstone (Keuper Marl). There were examples of small stresses that triggered landslips.
The photograph below shows a fault with the Penarth Group to the left and in the background, consisting of dark shales and sandy limestones of the Westbury Formation, which contain bivalves and fragments of fish. At the base of the cliff is the Blue Anchor Formation of alternating grey and green mudstones. The foreground consisted of Mercia Mudstone of red marls and mudstones.
We observed the Septarian nodules (see photo on website) formed by shrinkage of clay minerals, a from of dewatering under water when ion exchange occurred. The cracks formed in the process were later filled with minerals precipitated.
We all had a marvellous day looking at the many features of this coastline, looking for and finding fossils of ammonites and bivalves that illustrated life in late Triassic and early Jurassic times. It is an area that is worth revisiting.
Sunday 31st October
Today was also rather overcast, and after a start made more leisurely by the change of clocks to GMT, we proceeded in convoy to the former Woolston Quarry, situated in a valley inland where New Red had infilled the Plaleozoic, and the terrain had subsequently been moulded by Pleistocene drainage.
The disused quarry had been billed in the notes as an accessible outcrop of the stone that underlies the valley. Some of the party were rather alarmed to discover that the “access” involved negotiating a particularly muddy lane serving a cow byre. Access was somewhat easier for the mini-van party whose parking arrangements enabled them to join the lane higher up the hill, but one or two members of this party got fairly well covered in deep mud. They had clung to the side of the lane only to discover to their chagrin that the centre was much firmer than it looked.
The party was, however, well rewarded after leaving the lane, crossing the
West Somerset railway line and walking up the meadow to the quarry exposures. The remains of the quarry well illustrate the varied
debris which had buried the original landscape - part of a fault graben between the Quantocks and Exmoor.
There were sequences of pebble-beds cemented into a hard matrix, fining up into flags of good red sandstone, followed by more pebbles. One of many railway quarries along the route to Watchett and Carhampton (most of which had been fully filled-in), this quarry had been worked for the finer-grained stones as material for drainage culverts, and the pebble beds as rubble for the base of the railway, as well as providing excellent stone for quays and harbour works.
Eric pointed out that the pebbles were not graded bedding (which would have
been expected in a typical river system), but rather they were unsorted and characteristic of a mud glacier supplemented by water.
This would be expected in a terrain surrounded by high ground, from which material was swept from time to time by flash floods,
like those that occurred in the wadis found in the Middle East and Morocco. Hollows found on the Quantocks today were once the
beginnings of the chutes for such episodic flows. In quieter times, siltstone was laid down.
The long-held model had been of a great drainage system, comparable to the Indus or Ganges, flowing north from what is now Brittany, but Eric pointed out a few problems with that interpretation, by drawing our attention to numerous pale, rounded pebbles, which could be found at some points along the quarry face. On examination, these proved to contain the fossil remains of crinoids and small brachiopods. As the pebbles were well-rounded, they would have travelled quite some distance prior to deposition.
Their presence was something of a mystery, since they were characteristic of the Carboniferous limestone facies found in the Mendips. However, it was difficult to explain how these had got across or through the Quantocks. The Carboniferous limestone material, which was abundant to the south, belonged to a culm facies, which was quite different.
Eric said that a solution to the mystery had emerged in January of this year at a meeting which had discussed earthquake records, and in particular, the links between the BGS records relating earthquakes in Somerset to those in South Wales, suggesting movements along ancient faults which linked both parts of the country.
From this discussion came a proposal that the limestone pebbles found at Woolston Quarry had been eroded off a ramp of Carboniferous material in what is now the Bristol Channel. The ramp had been thrust up in the Hercynian orogeny and was made of material which was a continuation of that found in the Mendips. Eric make the point that this was a convincing explanation of the presence at Woolston of material from that facies. The ramp had been eroded away and the whole area subsequently carved away to form the Bristol Channel in the Pleistocene, leaving only the islands of Steep Holm and Flat Holm, which displayed limestone of the same facies. The abundance of limestone material within the sandstone explains the presence of tufa-like material in joints in the quarry, which may have resulted from stresses subsequent upon deposition, in the Kimmeridgian or the Tertiary.
The presence of the limestone pebbles also explains the former abundance of lime-kilns in local villages within the valley, where the limestone pebbles had been burned.
Eric’s masterly exposition (drawing rapt attention from the party - interrupted only by the passing of two steam trains on the West Somerset line - the first drawn by a GWR tank engine and the second by the hybrid locomotive we had admired raising steam the previous day at Minehead station) mourned the passing of quarrying skills, and concluded in an attack on the Welsh Gorsedd for replacing the traditional stone circles with plastic pebbles.
After negotiating the muddy lane, the party went in convoy to St George’s (parish) church of the nearby Sampford Brett, a hamlet once dominated by two great landed estates, and reflecting the violent streak in the Somerset character, which had produced one of the team that had murdered Thomas a Beckett. The church, in large part covered by rendering, nonetheless demonstrated the versatility of the different materials from quarries, like Woolston, for use in church building.
Pointing to a window of Upper Lias limestone (weathered with characteristic “vents”) from Ham Hill - quite a distance from here - Eric said the stone was probably easily transported by river (via Sedgemoor) before being carted the final stretch.
He also gave us a disquisition on the various gravestone materials and the symbolism of the memorial carvings.
The convoy returned to the road and took an uphill route onto the Palaeozoic, through misty woods with yellow autumnal leaves, stopping at Raleighs Cross Inn for lunch, where we could sample Golden Hill Brewery Exmoor beer and other real ales.
After lunch, passing the Beulah Chapel which had been built by Welsh miners, we drove a short distance into the Brendon Hills to visit the remains of haematitic iron ore workings, near the Naked Boy Stone - a boundary stone at the junction of three parishes, which drew its name from the hallowed Anglican practice of beating choirboys along the parish boundaries so that they would remember them well.
Walking along the line of the disused West Somerset Mineral Railway - to where Metropolitan Line transport trains were “pensioned off” - we came to the remains of a Cornish engine house at Barrow Farm, built largely of Mort Slate (the local Devonian country rock through which the disused railway had run). The beam engine here had provided power both to pump the mine and raise the ore, which was then transported along the ‘Incline’ - Mineral Railway to Watchet - to go by sea to South Wales. In return, SouthWales provided steam coal for the engine, as will as miners to work the iron ore, in the latter part of the nineteenth century, because it had the right content in phosphorus for the Bessemer process then being developed in South Wales.
However, in contrast to the pocket deposits found in Llantrissant and Rubaina (and also at the Clearwell Caves in the Forest of Dean), the ore here, found in quartz veins, was very difficult to work. In the 1880s, due to the competition of cheaper ores from Spain and Sweden, the quarries closed (although an abortive attempt was made to revive them just before World War 1). We picked up samples of the ore and ore-veined quartz from the nearby spoil heap, which has been exposed by the activity of sheep.
As we returned to the road, Eric drew attention to a stile footrest, made out of a slab of the local Treborough slate, which was extensively used in the area for building and monumental purposes.
The party then disbanded, with the mini-bus hurrying back to Taunton for bus and rail connections. All in all, this was a most enjoyable weekend, for which the participants are greatly indebted both to Eric, and also to Marilyn Carter who worked so hard to organise it.