NEWSLETTER, WINTER 2017

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WESTMINSTER ABBEY: SANCTUARY PAVEMENT SATURDAY 13th FEBRUARY

By Lesley Exton

Those able to secure a place on this over subscribed trip met up with Ruth Siddall, our leader for the afternoon outside Westminster Abbey (Fig 1). After negotiating around the tourists in front of the pavement, our party went round the rope barriers designed to keep the public out. We carefully walked along the edge of the pavement and found somewhere to sit so we could remove our shoes. Then in stocking feet we walked onto the Sanctuary Pavement for a more unusual building stone ‘walk’ examining a remarkable example of Italian Medieval decorative stonework.

The Sanctuary Pavement lies at the heart of the Abbey, designed to commemorate the new shrine for the bones of St Edward the Confessor (situated behind the High Altar). It is in the Cosmatesque style, which resembles a ‘patchwork quilt’ of stones of different shapes fitted together to make a pattern. The Cosmati were a family of decorative stone masons living in Rome in the 12th Century who established this method of paving, which typically involves a framework enclosing areas of polychromy stonework.

Fig 1. The group with Ruth outside Westminster Abbey. [Photo: Lesley Exton]

1 In this case it is a quincunx within a quincunx, surrounded by a border or roundels and tombs. However, it is not known if the paviours responsible for laying the Sanctuary Pavement were members of the family.

The design is supposed to represent the cosmos, so the earth is at the centre. The spirals around the roundels interconnect and so can be walked while completing the rosary. There is an inscription running round the centre originally done with inlaid brass letters but most have been lost over the centuries so it is difficult to read now. The majority of the stones (marbles and porphyries) were looted from Roman sites and re-cut to form the pieces we could see. The framework is Purbeck Marble (green), in Italy you would usually find Carrara marble used; however, it doesn’t survive very well in Britain’s much damper climate.

There were three phases of construction and/or repair. It was originally laid down in the 13th Century. The main stone varieties used are green and purple porphyry, the former Lapis Lacedaemonius comes from Greece while the latter Imperial Porphyry comes from Egypt’s eastern desert. Tadcaster limestone (yellow) a British limestone is used as a contrast. Both opaque and transparent coloured glass is also used and would have sparkled in candlelight. The first phase of restoration took place in the 17th/18th C and used stones that would be stock in trade at these times. They ignored the pattern using larger pieces and creating a more abstract pattern, so the repairs can be easily identified. The third phase occurred in the 19th C when Sir George Gilbert Scott replaced the eastern margin of the floor adjacent to the altar. He used both new and recycled stone in his designs.

Our time there went all too quickly as we looked at the different stones used, including many one- offs; e.g Africano (red and black marble breccia), Egyptian Gabbro and alabaster. Many thanks go to Ruth for a very interesting and unusual ‘building stone walk’. Unfortunately, photography of the pavement was not allowed, however, hopefully, Ruth will have plenty to show us when she comes to speak to us about the pavement in January 2018.

INDUSTRIAL GEOLOGY NEAR RIDGE, HERTFORDSHIRE SATURDAY THE 19th MARCH 2016

By Nick Pierpoint

After the HGS party had assembled at the South Mimms service station on the M25 we had a trip briefing and a Costa before setting out in tight convoy to Pinks Farm between Ridge and Ridge Hill which in turn is nestled in-between Potters Bar to the East and Shenley to the West in Southern Hertfordshire. The aim of the trip was to seek evidence for the geologically based industries around Pinks Farm.

Hertfordshire does not feature heavily in William Smith’s Memoirs with only six lines of text compared with the seven lines assigned to Rutland! To capture our attention Mike Howgate (trip leader) brought to our notice three blue dots on a William Smith map in the vicinity of Ridge. What were they recording? We were going to find out what these represented 200 years ago.

With a William Smith map and a map of the Shenley Chalk Mine produced by the Chelsea Speleological Society we established our bearings, as we examined an old ‘well’ and two shafts (Figs 2 & 3) which provided access to subterranean chalk workings. With the aid of a torch light tethered to a piece of string we were able to see the chalk, as it was lowered down a mine shaft. One of the shafts is home to a couple of hundred hibernating Daubenton bats which feed on damselfly

2 nymphs as they emerge from water. There was plenty of surface water around. We also heard stories of Mike’s adventure entering the caves down a free hanging caving ladder – not a trivial exercise.

Figs 2 & 3: Access points to the chalk workings – Drawholes. [Photos: Nick Pierpoint]

In this rural environment the chalk was mined using drawholes as open pits would destroy good arable land. Apparently mines were taxable assets whereas water wells were not, so mining also avoided prying eyes and perhaps helped reduce tax obligations! Could this be the reason mines do not feature in county records held in Hertford?

It has been suggested one of the larger water-filled depressions near Pinks Farm is due to cave roof collapse or a plugged mine shaft. If this were the case one would expect to see more water in the cave, but as the cave is dry they do not appear to be hydraulically connected.

Intriguingly there are several depressions in an adjacent field up to 25m across and 10m deep – are these collapse features or swallow holes? Several subtle concentric scar features suggest these are ‘active’ and getting deeper (Fig 4). Observational records suggest these are indeed swallow holes. The ponds represent a perched water table above the Chalk within the Lower Tertiary. The water table in this area lies deeper within the chalk below the base of the chalk workings.

Fig 4: Collapse features or swallow holes? [Photo: Nick Pierpoint]

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Nearby earth works on slightly elevated ground were chalk pits; some recent badger and mole activity has brought to the surface reddy brown clay material which is from either the Reading Beds or Upnor Formations. We were able to pick up several black coated, smooth, very well rounded to elongate pebbles most likely from the Upnor Formation, similar to those seen in Hertfordshire Puddingstone.

The speleological map showed the chalk has been worked in a series of galleries with approximately 20ft of head chalk. These man made caves have been tunnelled in excess of 1,132ft long, up to 40ft high and 32ft wide, with over 23,000 tonnes being extracted for agricultural purposes. Local records suggest these significant workings started prior to 1815 and continued to around 1912.

The penultimate site was in a flat field where London clay had clearly been worked for brick making. There was evidence of working faces and even remains of a drainage ditch which led to a series of drainage ponds. Why had these not drained? There was some discussion suggesting loess of Anglian origin (behaving as an impermeable layer) may have held a perched water table.

These sites are a complex series of industrial workings, with evidence of chalk and clay extraction commencing in the early 1800’s and lasting over a century. The clay is either from the Upnor Formation or Reading beds and used for brick making, although no evidence of the kilns remains visible. The many depressions across the location varied from swallow holes, dew ponds and potentially collapse structures with ponded water. One was located very proximal to a septic tank!

Our final stop was to a larger open Chalk pit which could well have represented one of the blue dots on the Smith Map (1815) near Ridge Hill. Smith used the blue dots to represent mines or mineral extraction as his maps were primarily for economic purposes.

A fine suggestion made by Mike was for HGS to celebrate William Smith in 2019, which coincides with the bi-centenary of geological sections he constructed between Cambridge and London part of which pass through Hertfordshire.

It was a truly fascinating few hours treading in the footsteps of William Smith and furthermore it was in Hertfordshire. The trip finished in the village of Ridge at the Old Guinea pub for an Italian lunch.

Thanks to Mike Howgate for leading this trip on a dry but cool March morning.

DENBIES WINE ESTATE AND DORKING’S MUSEUM CAVES SATURDAY 21st MAY

By Nikki Edwards

An overcast sky was an inauspicious start to what transpired to be a fascinating day in Surrey. HGS members gathered at Denbies winery, at 104 hectares, probably the largest vineyard in Europe, one mile north of Dorking, Surrey, with the aim of exploring the reasons for the siting of the vineyard, to sample its products, and visit Dorking Museum and South Street Caves.

Professor Dick Selley gave a lecture on The Geologic and Climatic Control on Two Millennia of English Viticulture. It was Dick Selley who applied the French concept of ‘terroir’ to the site, recognising the favourable combination of topography and geology coupled with the beneficial

4 effects of global warming, who suggested to his farmer friend that there was a good chance of establishing vines on his land.

Dick described evidence of Roman vineyards from the Isle of Wight to Lincolnshire and from Wrexham to Kent. It is estimated that Wollaston Roman vineyard, Northants, covered more than 12 acres and produced 11K litres of wine each year and in the first century CE, wine amphorae were buried with British Chieftains such as Verica, King of the Atrebates.

Domesday Book records many vineyards, often newly-planted to cater for the tastes of the new rulers, but this attempt to establish a significant English wine industry was to prove short lived. English wine was of poor quality, and from the 1150s fine imported wines from Bordeaux and La Rochelle put the English vineyards out of business.

The most northerly place in which vineyards are recorded in the Domesday Book is Ely in Cambridgeshire. After the Norman Conquest, wine became increasingly popular: the Benedictine rule was 1 litre a day, but the monks of Battle Abbey were each allowed a gallon a day (!) and wine was used in medicine and for communion as well as just for drinking

The Little Ice Age of the 15th to 19th centuries was a major factor in the reduction of English wine- making, although some local estates with favourable sites managed to produce wine. For 75 years in the 17th century Deepdene Vineyard Dorking produced 6k litres a year from 7.5 acres (2.9 hectares), and Painshill Park, also in Surrey, planted their vineyard on ground leading down to a lake, so that the water at the base of slope reflected light onto the vines. Deepdene is now the Brockham Oil Field, producing oil since 1987.

Vines need a ‘modicum of moisture’, but do not like to have their roots waterlogged. The Chalk has a porosity of about 40% and thus can store large amounts of water, but the pores are extremely small, and as a result, permeability is low. The Chalk is extensively fractured, however, and the fractures give an extremely high permeability, allowing fluid to move in and out of the small pores. The fractures also ensure that the vines are always well-drained, but in the dry season the plants obtain moisture from the micro-porosity between the fractures - the inter-coccolithic shelter porosity - a dual system of water supply.

Fig 5: South to North cross-section through Northern Surrey showing the location of vineyards, ancient and modern. Note their positions on well-drained south-facing slopes. [©Richard Selley ‘The Winelands of Britain’]

5 Denbies Vineyard is on Chalk over Gault Clay, and faces South, ideal for vine growing.

After the lecture, we then embarked on the Classic Wine Tour beginning with a new film ‘featuring a notorious local geologist pontificating on how geology controls the location of Denbies, the deposition of the Chalk, updoming and erosion of the Weald, etc’. We then strolled through the winery before descending into the cellars for a tasting of three wines.

After lunch in the Conservatory Restaurant, we undertook the Vineyard Tour. Travelling in a series of trailer carriages, we climbed up through the vineyard (Fig 6) and along part of the North Downs Way, which afforded spectacular views of Box Hill, the North Downs, Mole Valley and the Weald.

Fig 6: Vines on the slope at Denbies. [Photo: Lesley Exton]

Professor Selley’s plan was for us to then depart convivially into the bucolic Surrey countryside, after purchasing relevant tasty souvenirs of our visit, but our day was not yet done. A short coach ride took us to Dorking High Street, where we divided into two groups, as space was limited in both places. Dorking Museum was a little gem of local information, with well-presented material, careful explanations and drawers of specimens to further illustrate key topics. (The calcite crystals on sale, however, looked rather like fluorite!)

Dorking is located at the boundary between soft Cretaceous Gault Clay and the Cretaceous Lower Greensand, of which the Folkestone Sands form the upper unit. These sands are soft enough to be dug by pick and shovel, do not collapse - very often – and so since the 17th century much of Dorking’s wine was stored in caves excavated in these sands, where the temperature at the bottom of the South Street caves is a steady 140C.

The gentle northerly dip of the Wealden was not obvious in the caves, but westerly trending cross- bedding was clearly seen, indicating that the currents in a shallow tidal sea flowed from the Redhill to Guildford areas. Dated at 120-110 ma, a ridge of land extended from Wales, through what is now the London Basin to Belgium, with a shallow sea to the south.

6 After the Lower Greensand was deposited and cemented it was uplifted. Naturally acidic rain water leached out the carbonate cement, which had previously corroded the rims of the quartz grains. After the removal of the cement, the irregular grains formed a jig-saw like fabric of interlocking sand particles – ‘locked sands’ and explains the unusual cohesiveness of the Folkestone Sand.

There is a suggestion that the River Mole may have flowed through the sands at the bottom of the excavations in the 16th century, but a century later the river flowed continuously between Dorking and Leatherhead, leaving the ‘Mystery Cave’ dry. Evidence of water in earlier times was given by the presence of three wells – one of them medieval – and Liesegang rings in the sands. These rusty markings formed by the diffusion of oxygen in subterranean water into pore space containing soluble ferrous iron. In places dark brown concretions of carstone had accumulated.

Warm thanks to Clive and Adrian for their excellent planning of a great day out.

NB: The interplay of geology and climate is important. The geology of Denbies is the same as that of the Champagne region of France, but as the climate is warming, the summers are becoming too warm for the French vines. Two of the greatest French champagne houses have already bought land in Kent and Hampshire, indicating a sparkling future for English wine!!

NORTH NORFOLK 30th SEPTEMBER – 2nd OCTOBER 2016

By Mike Lambert

Nineteen of us took part in this 3-day field-trip led by our current President, Professor Charlie Bristow. Our aim was to increase our knowledge of North Norfolk's geological past, by visiting a variety of mostly coastal, Cretaceous and Quaternary sites between West Runton in the east and Sandringham in the west.

Our first stop was at Wiveton Downes, to look at the Blakeney Esker: a 3.5km ridge of mixed sand, gravel, pebbles and cobbles, which runs from Blakeney to Wiveton Downs and Glandford. This ridge's north-south orientation reflects the direction of flow of Anglian ice-sheets and glaciers, strongly suggesting that it has a glacial origin.

Charlie provided us with a range of possible explanations for the ridge, mostly involving the action of ice. For example, the ridge might represent debris that had fallen down a crevasse in the massive glacier that had once towered 500m above our heads. However, current thinking is that this ridge is an esker: i.e. the sediment deposited along a sub-glacial stream. This idea is supported by the discovery (made during recent, commercial extraction for aggregate) that the debris extends for 3- 4m below current ground level. Subsequent debris was stacked up along the walls of an ice tunnel running under the glacier, explaining why this stream bed now stands 30-40m above the surrounding country. It is the best example of an esker in England, although there are numerous, better examples in Wales and Ireland.

After lunch at Blakeney, we headed east to the beach at West Runton, where we were to examine a variety of strata and structures. First, we were met by local geologist, Russell Yeomans: there to tell us about his recent work on the large flint platform exposed on the beach. This flint bed extends under the sea, covering an estimated area of 10-15 square kilometres. The flint and underlying Chalk are from the Upper Campanian stage of the Cretaceous (78-73 ma). These strata are part of the Belemnitella Mucronata Formation (also exposed at Caister St Edmunds Quarry) and are characterised by the presence of large, tubular flint nodules known as paramoudra (Fig 7). Russell

7 pointed out these in-situ paramoudra, with their large, typically oval mouths protruding through the loose stones on the beach. One that we examined measured 1.5m by 4.5m and consisted of two joined, concentric rings of Flint.

Since publication of a paper by Bromley, Schulz and Peake in 1975, the accepted theory for paramoudra formation has been that they derive from burrows of an unidentified worm, silicified at the anoxic boundary, below the Chalk sea-floor. However, Russell presented evidence strongly suggesting that these paramoudra are the work of siliceous sponges as they developed and colonised the Cretaceous sea bed over millennia. He pointed out the many sponge fossils, sponge prints and rim marks that appear on the Flint. Recent photographs of deep sea sponge aggregations off the Canadian coast have led Russell to propose that this entire flint platform is part of a former Cretaceous Sponge Reef.

Fig 7: Paramoudra on the foreshore. [Photo: Lesley Exton]

Since publication of a paper by Bromley, Schulz and Peake in 1975, the accepted theory for paramoudra formation has been that they derive from burrows of an unidentified worm, silicified at the anoxic boundary, below the Chalk sea-floor. However, Russell presented evidence strongly suggesting that these paramoudra are the work of siliceous sponges as they developed and colonised the Cretaceous sea bed over millennia. He pointed out the many sponge fossils, sponge prints and rim marks that appear on the Flint. Recent photographs of deep sea sponge aggregations off the Canadian coast have led Russell to propose that this entire Flint platform is part of a former Cretaceous Sponge Reef.

The level of the beach at West Runton approximates to an unconformity between Cretaceous and Quaternary strata. Walking to the back of the beach, we found the West Runton Freshwater Bed projecting from the base of the low cliff. This bed is 1.6m thick, dark brown and rich in organic material. It was deposited during an inter-glacial, temperate environment in the Middle Pleistocene and has yielded mammalian fossils, including shrews, voles, beavers, lions, horses and deer. Between 1992 and 1995 the skeleton of a Steppe Mammoth (Mammuthus Trogontherii) was

8 recovered from this site. Based on evidence from the teeth of ancient voles and Marine Isotope Stages, Charlie dated this bed to 712 ka.

Heading east along the cliff, we followed a band of Pleistocene Till to a point where it was overlain by around 5m of Chalk. This was the Wood Hill Block: a mass of chalk, the size of a village that was pushed up onto younger sediments by the southward flow of ice (Fig 8). Our plan had been to continue east towards Overstrand, to see further examples of Glaciotectonic Chalk Rafts, but this had to be abandoned due to the incoming tide.

Fig 8: Charlie pointing out a glaciotectonic chalk raft [Photo: Lesley Exton]

Day two began at Kings Lynn Museum to see their Seahenge exhibit. This Bronze Age structure was discovered at Holme-next-the-Sea in 1998. It consists of a ring of 55 wooden posts, with an overall diameter of 6-7m. At the centre of this enclosure was the large, upturned stump of an oak, its roots reaching into the air. Following its discovery, the timbers were conserved and treated with polyethylene glycol by the Mary Rose Trust. Carbon-14 dating combined with dendrochronology indicate that the central oak was felled in 2050 BC and the surrounding posts in 2049 BC.

Our next destination was the beach at Holme-next-the-Sea, where the Seahenge once stood. This involved a 2km walk along a coastal path that divided dunes, beach and sea on one side from salt- march on the other. Charlie described the exchange of sediments between these various environments. Currently, this part of the Norfolk coast is prograding. That is to say, it's accumulating sediment carried by dominant currents from the Lincolnshire coast and, to a lesser extent, from the Rhine. During storms, the sea may occasionally break into the dunes, which replenishes the beach. However, the dominant movement of sediment is inland: as windborn particles from the beach accumulate around marram grass growing on the dunes; and material from the dunes is trapped around vegetation in the salt-marsh.

Arriving on the beach, we saw evidence of the opposite process. Charlie led us to the large bed of

9 peat where Seahenge was discovered (Fig 9). Examining this peat, we found fragments from woody plants and small trees. Charlie passed round a 4,000-year-old but still identifiable leaf from the freshwater reed, Phragmites (Fig 10). This peat had formed during the Bronze Age, in a mixed freshwater-marsh and woodland environment.

Using his trowel, Charlie cut down through the peat to an underlying layer of clayey sediment, which he described as typical of salt-marsh. He explained about Walther's Law: whereby successive layers of beach, saltwater and freshwater sediment can be related to sequences of marine transgression and prograding. Evidently, this section of the Norfolk coast has a complicated history involving both processes.

Figs 9 & 10: Peat on the beach at Holme-next-the-Sea containing Phragmites leaves. [Photos: Lesley Exton]

Our final stop of the day was at Wells-next-the-Sea. Standing on the sea-wall, Charlie described the sometimes counter-productive nature of such sea-defences. Although the sea-wall appears to be protecting the town, over time it is actually preventing prograding. Along this section of coast, the 2mm annual rise in sea-level should be more than offset by a similar level of onshore accumulation of sediments. However, the sea-wall means that windborne and seaborne sediments are no longer being deposited inland. Furthermore, the sea-wall combined with 300 years of drainage schemes has led to the drying out, shrinkage and sinking of the peat that underlies the town. The net result is that the high-tide mark on the seaward side of the wall is now 3.5m above pavement level in the town. [Editor: Some of the party then retired to the cafe in the car park, while the rest of us explored the Lifeboat house sandbar. We were looking at the location of bedforms, which include ripples and dunes, noting their height, wavelength, crestline orientation and shape while the tide came in. It was also pouring with rain by this time so we didn’t attempt to try and do a sketch map of the bar. Thoroughly soaked we then retreated to the cafe to rejoin the others and a welcome hot drink to warm up.]

Day three began with a brief overview of the coast, just inland from Brancaster. Charlie described the system of barrier beaches and tidal channels that allow suspended sediments into the salt- marshes. We also heard about the rapid evolution of Scolt Head Island: a 6km long barrier island that is shifting from east to west. Over the past 90 years, sediment has been accreting at its western end at a rate of 6.28 metres per annum.

Our next stop, in Brancaster, was to visit a coastal reclamation project with which Charlie has been involved. Walking to the site, we passed reed-beds of Phragmites, their long-leaves identical to the 4,000-year-old specimen we'd seen at Holme-next-the-Sea. Charlie explained the purpose of this "managed alignment" project. The original intention had been to remove the sea-wall, enabling the re-establishment of 40Ha of salt-marsh. This salt-marsh would then have encouraged prograding and acted as a natural buffer against sea-level rise. However, the plan was thwarted by a number of

10 local interest groups and, in the end, only 3.7Ha have been returned to salt-marsh.

For our last two stops, we left the Holocene and returned to the Cretaceous. Before lunch, we visited the cliffs at St Edmund's Point, Hunstanton: much admired for their colourful banding (Fig 11). At the base, we saw the rusty-brown exposure of Carstone: a coarse, iron-rich sandstone deposited at the same time as the more southerly Greensands. Above this, we saw a narrower exposure of brick-Red, Red Chalk, its colouring thought to derive from higher sea temperatures and oxidation of its iron content. The uppermost portion of the cliff was white Chalk (actually part of the Grey Chalk sub-group), capped by a roughly 1m layer of slightly harder Totternhoe Stone. Haydon pointed out a heavily bioturbated section of chalk: where burrowing by crustaceans had led to preferential hardening and a swirling, nodular patterning of the face.

Fig 11: The group in front of Hunstanton cliffs. [Photo: Lesley Exton]

Our last stop was at Wolferton on the Sandringham Estate, to see an exposure of the Sandringham Sands (Fig 12). These loosely cemented sandstones date from the early-Cretaceous: above the Kimmeridge Clays and below the Carstone we'd just seen at Hunstanton. Charlie demonstrated how to compile a sedimentation-log based on the banding of the sandstone, relating this to Walther's law and to the patterns we'd observed on local dunes and beaches.

Thanks for this very successful trip go to: Professor Charlie Bristow for his knowledge and enthusiasm (even in the pouring rain); Adrian Champion for great planning; Percy, our driver, for getting us around safely; and to Haydon Bailey and Russell Yeomans for their specialist input.

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Fig 12: Exposure of the Sandringham Sands at Wolferton. [Photo: Lesley Exton]

PUBLIC AWARENESS OF OUR NATURAL HERITAGE IN SUBURBAN ENVIRONMENTS

By Nick Pierpoint

Each year a number of local geological groups visit a cluster of Hertfordshire Puddingstone and Sarcenstone blocks at Castle Hill Road in Berkhamsted, which is one of only twenty or so RIGS sites in our county. These blocks are described in detail in Hertfordshire Geology and Landscape (Ed J Catt 2010). Last year on a joint HGS/Reading Geological Society field trip including this site a discussion ensued which also included local resident (Professor Eric Brown and others) about why an information plaque had not been installed! Apparently there had been much discussion on the merits of a plaque over the last 20 years but not much progress. At the HGS committee meeting the following week I agreed to lead the action to see what could be achieved. I have a retired army friend who often said – someone who volunteers does not fully understand the challenge!

Hertfordshire Puddingstone is a conglomerate of typically well rounded flint pebbles, embedded fine pale coloured micro to crypto crystalline siliceous cement. The pebbles are considered to have been deposited during the Palaeogene as rafts or lenticular masses at the time of the Upnor and Reading Formations (51-55 million years ago). They were subsequently cemented with silcrete, which forms near the surface in high temperatures where groundwater with dissolved silica percolates through loose sediments and silica precipitates. There source of the silica is thought to be from the weathering of silicate minerals including clays.

At this site one of the blocks exhibits a sharp transition from Puddingstone to Sarcenstone which is a matrix of silicified quartzose sand with occasional floating flint pebbles. In this part of the county puddingstone is typically found as discreet blocks in younger sediments (Neogene and Quaternary) as consequence of erosion and disruption. It is possible these particular blocks had been transported

12 to Castle Hill by a process such as solifluction, before being moved to their current resting place by builders during nearby house construction.

In Berkhamsted there are a number of plaques at strategic historic sites detailing our human heritage. In the proposal to the Curry Fund of the GA the case for an opportunity to provide information about our natural heritage in a clear and concise manner was made. Following a successful application the next step involved simultaneous consultations with interested stakeholders which included the local residents association, Town Council and Dacorum Borough Council Highways Department who maintain the footpaths and grass verges on behalf of the County Council.

Thankfully the Highways Department records showed there were no utilities or cables beneath the verge where we proposed to dig and install the plaque. They had formally ‘licensed our proposal but the responsibility to conduct the work safely and without damaging any underground services rests with your organisation.’ Adding ‘Sounds heavy but, if you dig carefully, you should have no problems. Dig by hand and carefully!’ What is worse damaging a fibre optic cable belonging to Sky or breaking through into a water pipe?

Following an assessment of plaque styles and prices a contractor was selected. They are based in Rochester Kent, about 2 miles away from the coastal village of Upnor on the River Medway. How serendipitous that the sign describing the type Hertfordshire Puddingstone in Berkhamsted should be fabricated so close to the type section for the Upnor Formation, which is at Lower Upnor Pit, north of Chatham, Kent. (http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=UPR).

Fig 13: Nick by the newly installed plaque Castle Hill Road, Berkhamsted.

13 It has taken 8 months to get everything lined up to install the plaque, 2 hours to put in place and we hope it will provide a long legacy of making the wider public aware of our natural heritage.

Thanks to the Geological Association’s Curry Fund for providing financial support and my fellow diggers, including Clive and Liam from the HGS.

Catt.J (editor) Hertfordshire Geology and Landscape: Hertfordshire Natural History Society, 2010, p 110.

A LOOK BACK IN TIME (1) LITTLE HEATH, POTTEN END, HERTFORDSHIRE LEADERS: John Catt & Andrew Moffet 10th JULY 1979

The site consists of a number of disused pits in woodland which were presented to the National Trust for their geological interest and contain Plio/Pleistocene gravels and sands overlying Reading Beds (RB). One pit in particular has been re-excavated and a section cut, and this was the subject of the visit. John Catt gave a general description of the work recently carried out.

In 1920 Gilbert discovered flint pebbles from this pit which were unusually large for the Chilterns Plateau (CP) and not normally associated with the RB or the Chalk. The flints had the appearance of beach cobbles. The theory at the time was based on the discovery of Red Crag fossils at Rothamstead which matched similar assemblages at Netley Heath, Surrey & Lenham, Kent. The N. Downs deposits, which were earlier than those of CP were also inundated to a higher level. The theory was taken up by Wooldridge who developed a marine hypothesis of the sea cutting away the Tertiary beds and chalk beneath a sub-tertiary surface, thus leaving the CP lower than would be expected. Near the crest of the escarpment, the ground became steeper, giving an old cliff line at 230m OD. Wooldridge developed his theory of marine planation in his ‘Structure and Surface Geology of SE. England’. The Soil Survey (SS) was mapped by Avery on the Aylesbury Sheet (1964), who recognised with Loveday of Rothamstead, many soil characteristics on the CP showing weathered RB as well as Clay-with-flints. If the clay found was indeed from the RB, this negates the Wooldridge & Linton theory of marine planation removing RB and cutting into chalk. There must have been high level stages to explain Red Crag fossils, but none are now left. The SS developed the idea of sub-tertiary surface folding during Alpine earth movements.

Andrew Moffet then went on to develop the idea and to describe the findings in the exposure. Only this spot reveals the stratigraphy. The pit is 7m deep from the surface and by digging and auguring, the chalk was reached 3m further down. The chalk is overlain by gravels which are mainly angular and nodular flint, black and sometimes green coated, originally from the chalk. The gravel was lain down on chalk by the sea over a sub-tertiary surface. This is followed by grey sand similar in mineralogy to RB and then brown and red sand with gravel, well rounded, mainly flint, with some Quaternary pebbles 4-8mm in diameter. There are also some Hertfordshire Puddingstone (HPS) cobbles, well-rounded and some chert, but no quartzite or erratics. Sands follow: which are very well sorted, contrasting with and coarser than RB. Mineralogy is similar, plus andalusite and more anatase than would be expected from RB. Andalusite is claimed by Wooldridge to be a marine deposit. Finally, a small amount of brown/grey sand gravel, claimed by Gilbert to be glacial. It is very silty with organic matter, pebbles mainly flint but very little quartz and no HPS. Gilbert claimed the gravel to be of marine origin with beach-battered appearance, different from other CP stones and comparable with marine RB bottom bed. No fossils have been found but some fresh glauconite is present indicating a marine origin. The silt is of a particle size typical of loess deposit. The so called ‘glacial gravel’ contains no evidence of glacial origin with no erratics. The flints are

14 probably from RB with loess incorporated either by sub-aerial deposition or solifluxion. Mottling of the sand is due to oxidation/reduction of iron and silver sand by leaching out of iron deposits.

The pit was then examined and a discussion ensued. Some small vein quartz pebbles were found and a few well worn HPS fragments.

CHAIRMAN’S CONCLUDING REMARKS

By Haydon Bailey

I look forward at this time of year to looking back, if you can follow my thought process. This is the chance I have to think back over the last year’s activities before we kick off our new programme. We’ve had some stunning and contrasting lectures, particularly when I remember Matthew Saker- Clark presenting his initial research on the Lower Jurassic palaeo-environmental conditions in Morocco, immediately followed by Emeritus professor Peter Friend looking at the status of new technology being used to map the geomorphology of Hertfordshire. Both were excellent presentations in their own way, but very different.

In April the Percy Evans lecture was given by Prof. Al Fraser of Imperial College reviewing the options for Shale Gas production from the Carboniferous of Northern England. Given the career that Percy Evans had in the hydrocarbon exploration industry this was extremely appropriate. Ironically, the next lecture was Dr. Colin Summerhayes looking at the changes in the Earth’s climate, from Greenhouse to Icehouse. We certainly tick the boxes when it comes to bringing in high quality speakers on extremely topical subjects.

June saw a visit from Dr. Bill McGuire who talked us through the giant volcanic eruption of Tambora some 200 years ago, which in itself caused dramatic deterioration in harvests across Europe in succeeding years. We took a step back in deep time during July when Susannah Maidment provided us with an insight into Dinosaur biodiversity. A subject we’ve rarely brought in but dinosaurs are ever popular and always a subject which will raise interest.

July also saw our “Summer event” which this year took the title “The Water table” with short presentations from Ilias Karapanos (Affinity Water), David Johnson (H & MWT) and myself, followed by an open discussion all carefully presided over by Rob Sage, now retired from Affinity Water. We welcomed the good weather for our picnic in the park and also for our stroll down the Ver Valley (Fig 14), ably led by members of the Ver Valley Society.

The range of lecture topics during the autumn has been eye opening with James Lawrence (Imperial) talking about Cliff line erosion on the south coast and, in total contrast, Dr. Doug Robinson (Bristol) providing us with a whistle stop tour of the origins of the Western Cordillera in the USA. Follow that – well we did with Steve Banham taking us to Mars in November. Finally to wrap up the year we had Dr. Chris Stringer of the Natural History Museum giving us One Million years of the Human story in Britain. I think we can reminisce on a stunning range of topics from some excellent speakers. We set the bar high and we now have to meet this threshold again over the next year – looking at the coming programme I think we have.

The year’s programme wouldn’t have been complete without our other activities, including field trips to Denbies Vineyard (thanks to Dick Selley), that amazing opportunity to crawl over the cosmati pavement in Westminster Abbey (thanks to Ruth Sidall) and the local trip around Ridge with Mike Howgate. Finally, we had the long weekend trip to North Norfolk under the guidance of our Honorary President Professor Charlie Bristow who managed to steer us carefully between the

15 showers (most of the time), through some fascinating coastal depositional processes only to cap off the event at the last location by showing us the same sedimentary structures but this time 115 million years old!

Fig14: Stroll down Ver Valley. [Photograph: Lesley Exton]

We had a great stand at the GA Festival of Geology focussing on our local hero the Hertfordshire Puddingstone (Fig 15). A really big thank you to everyone who contributed with their time and their lumps of puddingstone, particularly Jean Gardner for allowing me to raid her rockery, Chris Green for his very comprehensive posters and John Catt for providing that polished block from the front cover of the Hertfordshire Geology book.

This brings me to a quick glance over the forthcoming year. We’re going to be delving back as far as the Carboniferous and covering the globe from Antarctica to the U.K. via the Wallace line. Finally, we have Prof. Richard Fortey visiting us in December, so we have a great line up of speakers to come.

Fig 15: Hertfordshire Puddingstone display at the Festival of Geology [Photo: Haydon Bailey]

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