OUGS East Anglian Branch Newsletter
Summer 2019
From the Branch Organiser
Dear All,
Welcome to another branch newsletter. I hope everyone has had a chance to read about our forthcoming Symposium in the main OUGS Newsletter. As you will have realised this is a ‘special’ at the instigation of the OU to celebrate their 50th Anniversary. Fewer field trips but more to explore at the OU itself, including lab tours, workshops and demonstrations, with OU staff speaking about their latest research. There is still time to book this - see the OUGS website for details and booking form.
Since the last newsletter I have attended both the AGM (including the OUGS Committee meeting) and the Branch Organisers’ meeting. At both, the future direction of the OUGS was discussed. Given ever falling membership numbers various ways forward have been proposed. Closer liaison with the OU is now on the cards, as exemplified by our forthcoming Symposium, which may help stabilize numbers. Should we consider smaller area groupings, with regional coordinators, perhaps based on area geology? Another area of discussion was the annual Symposium which is proving ever more expensive to run. Perhaps this ought to be a biannual event, with the AGM having a bigger profile. We discussed some of this at our last branch AGM and I would like to hear your further views on the subject.
More immediately, as a branch we need more suggestions of activities for our events co- ordinator to follow up. As I think I’ve pointed out before our branch covers a wide area and I’m sure there are geological gems yet to be explored. Don’t be shy of contacting any committee member with your wish list.
Phil Ridley
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On the beach at Walton-on-the-Naze, amongst the mountains of the Apennines and near the bank of the Yangtze River. (by Philip Findlay)
Fig.1 Pyritised twig with knot Fig.2 Pyritised twigs When I visit Walton-on-the-Naze, I always enjoy looking closely at pieces of the pyritised wood that can be found on the beach (Figs. 1 and 2). The recognisable, intricate details that remain intact on the surface of these fossils are both amazing and familiar, and, although I have heard it many times before, I am still surprised by the metallic clink produced when two of the fossils are gently tapped together. Erosion by the sea has set free the pieces of pyritised wood from the bed of blue-grey London Clay that is exposed in the cliff and along the beach. Geologists calculate that the London Clay and its fossils are between 57 and 52 million years old, dating from the Eocene epoch, although only the oldest strata now remain at the Naze. The pieces of wood, along with lots of sediment, were carried down by rivers to a sea where the waterlogged wood sank and the sediment settled, burying the wood and the process of fossilisation of the wood began.
Above the London Clay on the southern section of the Walton cliffs are the reddish-brown, coarse-grained, shelly sands of the Red Crag Formation. The Red Crag is much younger than the London Clay, just 2.4 million years old, from the early Pleistocene epoch. The boundary, the unconformity between the London Clay below and the Red Crag above, can be seen in the cliff, although in places it is obscured following collapses and slumping. (Fig.3).
Fig.3 Collapses of the cliff
Further to the north the Red Crag has been completely eroded and the London Clay is overlain instead by thick deposits of Loess (Brickearth), fine silt deposited as wind- blown dust during the last (Devensian) glaciation (Fig. 4)
Fig.4 Devensian Loess above, London Clay below The pyritised wood fossils used to be collected as an industrial ore from the beach at Walton and from other beaches in South-east England where the London Clay was similarly exposed to erosion by the sea. Their high iron sulphide (FeS2) content (Fig. 5), made the pyritised wood fossils the key raw material for a process that produced crystals of ferrous sulphate heptahydrate, FeSO4.7H2O. In the past, this compound was commonly known as green vitriol or copperas and so the pyritised wood fossils and other lumps of iron pyrites became known as copperas stones.
Fig. 5 Fresh, broken surface of pyritised wood showing the metallic lustre of the iron sulphide
Green vitriol was used as a dye fixative, a mordant, in the dyeing of wool. It was also used to make inks and dyes, especially for dyeing leather. In Europe, by the middle of the sixteenth century, the use of copperas stones for producing green vitriol was well- established. George Bauer, a German mineralogist writing under the name Georgius Agricola, described several different processes used to produce green vitriol in De re metallica, published in 1556. The fourth of these different processes involved producing green vitriol from vitriolous earth or stones, “ex terris aut lapidibus atramento”. i Lou Henry Hoover and her husband Herbert Hoover completed the translation of the original De re metallica from Latin into English in 1912. In one of their footnotes they explain:
“The term for vitriol used by the Roman authors, followed by Agricola, is atromentum sutorium, literally shoemaker’s blacking, the term no doubt arising from its ancient (and modern) use for blackening leather”.ii
(Later, in 1929, Herbert Hoover became the 31st President of the United States.)
Fig. 6 shows a woodcut from De re metallica, illustrating some of the final stages described in the production of green vitriol from copperas stones.iii For more than a year, the copperas stones were first exposed to the weather and then immersed in water. The resulting liquid (a mixture of ferrous sulphate and sulphuric acid as well as water) was heated to remove excess water and then iron strips were added to produce even more green vitriol (the added iron reacting with the sulphuric acid). The woodcut shows: a lead cauldron (A) where excess water is removed, moulds (B), and on the ground by the pourer’s right foot, the “cakes” of green vitriol (C).
Fig. 6. Production of Green Vitriol in 1556
By the end of the sixteenth century, centres of the copperas industry were also active in England: Lambarde, for example, is reported to have noted in A Perambulation of Kent in 1579, that at Queensborough Castle on the Isle of Sheppey, there was the production of copperas - “out of a certein stone that is gathered in great plenty upon the shoare”. iv
The County of Essex, as well as supplying copperas stones for its own processing centres, also shipped the ore to other centres such as the one at Queensborough on the Isle of Sheppey and to centres nearer London, such as at Deptford. v
The first people paid to collect the copperas stones from the beaches would have recognised on the surface of the pyritised wood the same sort of intricate details as we can see today, and, similarly, this recognition may have prompted thoughts and ideas about the nature and the origin of these objects clearly displaying such familiar features. Unless the collectors were able to write down their reflections for circulation or had a public platform to share their thoughts with others, then their ideas fed only their own imaginations. This was over two centuries before James Hutton, in 1785, at a meeting of the Royal Society of Edinburgh, first publicly stated what the conclusions his own studies and observations had led him to and which he later summarised as: “….we may look for the transactions of time past, in the present state of things upon the surface of this earth, and read the operations of an ancient date in those which are daily transacted under our eye”.vi
Leonardo da Vinci (1452-1519) had observed and registered familiar details on the individual shells making up the shell beds he found embedded in rocks in the Apennine Mountains and he did write down his associated thoughts. The arguments that the shells had been left there after the Great Flood described in the Bible or that the shells had formed within the rock did not convince him.vii In a journal that he wrote between 1504 and 1510, now known as the Codex Leicester, he recorded what he saw as a past community of living shells: small and large shells, some with only a few and some with many growth rings. He wrote about the holes he saw in the shells, details that matched the borings suffered by living shells, and in doing so he set down perhaps some of the earliest records of trace fossils.viii His thoughts about the nature of those shells assumed their origin as living creatures that fed and grew in the sea, that were then buried in sediment at the bottom of the sea before the area later became land. He did not publish or circulate these writings during his lifetime so his explanations were not available to others until much later. His writings preceded the talk, mentioned above, given by Hutton at the University of Edinburgh, by more than two hundred and fifty years; however, similar ideas had already been written about and published more than four hundred years before da Vinci had written even the first word of his own journal.
Shen Kuo 沈括 (1031–1095) lived in China during the Song Dynasty. In 1088, when he retired to his home near the Yangtze River at Zhenjiang, he wrote Meng xi bitan, 梦溪笔谈 often referred to in English as Dream Pool Essays. One of the incidents he wrote about was a significant collapse of a river bank, not the Yangtze River, that had occurred a few years before much further north in Shaanxi Province, where he had been sent in 1080 to serve as the Commissioner for Prefectural Civil and Military Affairs.ix The river bank collapse exposed bamboo shoots and roots deep below the ground. They were all intact but completely transformed into stone, 悉化为石.x Shen Kuo noted that walnuts, the roots of reeds, and different kinds of snakes and crabs that had also changed into stone had been found in other places but these things were all still found at that time growing and living in those places. Bamboo did not grow and had never been known to grow in the region where the fossil bamboo had been exposed: bamboo could not survive there because the climate was too dry. To make sense of this, Shen Kuo speculated that at some time previously in that place, in ancient times, the climate must have been significantly different there: wet and suited to bamboo, 而宜竹, allowing it to grow.xi
Later in the same book, when Shen Kuo describes a mountain location, more than 300 miles from the coast at that time, where a band of spiral shells, clamshells and stones like bird eggs, 石子如鸟卵, ran horizontally across the cliff like a belt, 横亘石壁如带, he concludes: This is the seashore of the past, 此乃昔之海滨.xii
Science was not the only topic that Shen Kuo wrote about in his Dream Pool Essays: other topics he included were technology, mathematics, philosophy, art, linguistics and archaeology. The book was widely read and referred to and there were numerous reprints: it was first quoted in another book in 1095; a copy from the reprint in 1166 survives today in Japan.xiii
In 1905, Sir Archibald Geikie used what has now become a familiar expression when, in describing James Hutton’s approach towards geology, he stated: “The dominant idea in his philosophy is that the present is the key to the past”. xiv Shen Kuo and Leonardo da Vinci both showed that when making sense of observations they too shared that idea.
A report written in 1584, concerning the pay of collectors employed to gather the copperas stones from English beaches, suggested that an adult collector would typically gather 2000 lb (~900 kg) of copperas stones in a tide and children of 10 years in the same time would collect about 500 lb (~ 225 kg). xv Those collectors would have had little time to examine the copperas stones so it would have been on a much warmer day than the day of one of my recent visits in January to Walton-on-the-Naze, that those collectors might have been able to pause briefly to look more closely at a particular life-like detail that had caught their eye. If they speculated that the wood had grown in that region at some earlier time in the distant past then they were thinking similar thoughts to some of those already considered in the Apennine Mountains and alongside the Yangtze River.
Editor’s note: For anyone contemplating a visit to the cliffs at Walton there is now a trail guide available, called “Geowalk – The Naze, Essex’s premier geosite” written by yours truly for Essex Wildlife Trust, with help from GeoEssex and ERMS. It is available from the EWT visitor centre, where there are also geological displays, including characteristic fossils.
References.
1. Agricola, Georg, De re metallica (1556), p. 463,
Swanage and the Jurassic Coast by Ken Hubbard Introduction In September 2018 I had the good fortune to visit the Jurassic Coast for a holiday. Based at Swanage my friend and I enjoyed exceptionally mild weather for the time of year. We were only there for a short time, but I did manage to get some time to look at the geology of the area without annoying my friend too much. The area around Swanage includes Cretaceous and Jurassic period rocks. We did take the ferry to Poole Harbour one day which allowed me the opportunity to take the photos of the Chalk Cliffs and sea stacks including Old Harry (Figure 3). Our other outings were to the west of Swanage and included Durlston Country Park, Lulworth Cove (and Durdle Door) and Weymouth (stopping off at Osmington Mills to find Doggers). Both my friend and I are keen walkers, so we managed to clock up a total of 87km (54.4 miles in old money) in 4 days. I was a little disappointed that we didn’t get to visit Chesil Beach as I have never managed to get there in the past. Time was not on our side that day so once again I missed the chance. When we visited Lulworth Cove the intention was to also look at the Fossil Forest. Sadly, there had been a landslide and the footpath was closed. I now have two good reasons to return to Dorset one day in the future. It was good to see most of the classic coastal landforms whilst I was there; namely sea stacks, caves, arches, wave cut platforms (Figure 1), headlands and cliffs.
Fig. 1 Wave-cut platform (partially submerged) The Chalk of Ballard Down To the north of Swanage lies the Cretaceous chalk ridge of Ballard Down. This forms a sinuous ridge of steeply dipping Chalk which stretches from the sea at Ballard Point westwards through Corfe Castle and then on to Lulworth and further west. The Ballard Down Fault marks the position where the almost vertically dipping Chalk to the south meets the apparent near horizontal Chalk to the north (Figure 2 – taken from the ferry from Swanage to Poole). Seismic data reveals that a north-dipping reverse fault, which must have formed after the development of the Purbeck Monocline, is a later compressive event.
Figure 2—Ballard Down Fault (White arrow) photo looking westward
At Handfast Point there are many Chalk stacks including the Pinnacle and Old Harry. These are formed where the sea erodes a cave in the Chalk joints. Over time wave action widens the cave until it can no longer support the weight of the overlying rock and it collapses into the sea forming the stack. Figure 3 opposite shows the Chalk Stacks with a number of caves in existing stacks and the cliffs. Old Harry is on the right of the picture nearest to the yacht. The Chalk Group was laid down 99-65 Ma ago (Cretaceous) in a shallow sea thought to have been no deeper than 300m. It is classified into two subgroups the Grey Chalk and the White Chalk (Figure 9). The Portsdown Group Fig. 3 Chalk stacks at Handfast Point (Figures 2 & 3) is the youngest formation of the White Chalk Subgroup. It comprises soft to firm, white, flinty chalk and is typically 80-90m thick at this point. It formed in the Upper Cretaceous when global sea level was perhaps as much as 300m above present sea level. Vast numbers of planktonic algae bloomed in this shallow sea. The chalk contains bands of tabular or nodular flint. These can be seen as almost horizontal lines in the gently northward dipping beds. They formed by the dissolution of silica-rich organisms such as radiolarians and sponges. Durdle Door (Fig. 4) The Chalk ridge mentioned above at Ballard Down curves in an arc to outcrop at Swyre Head just to the west of Durdle Door. The view from Hambury Tout on the way to Durdle Door from Lulworth Cove is quite spectacular (Fig. 6). Solifluction deposits partially fill a dry valley at Scratchy Bottom just west of Durdle Door. The Portland Stone of which Durdle Door (Fig. 4) is made, is almost vertical at this point and forms a linear structure with the Blind Cow and the Bull rocks both further out to sea. These two rocks just protrude above the sea surface. Together these are relics of a reef barrier that once existed here.
Under the hand lens the Portland Limestone comprises of ooliths in a micritic matrix. It is a yellowish white in colour and can be found as a common building material for local village houses. The Portland Stone is near vertical at this point, but is almost horizontal at St Albans Head, 15km to the east, dipping at a very low angle to the south. It is part of an asymmetrical anticline associated with the Purbeck Monocline. The Portland Group was laid down 147.6-144.8 Ma ago (Jurassic). It comprises two subgroups, the Portland Stone Formation and the Portland Sand Formation (Figure 9). This marks the transition from marine to terrestrial conditions recorded in the rocks along this part of the coast and towards Swanage in the east. Stair Hole and Lulworth Cove Just to the west of Lulworth Cove is Stair Hole where a spectacular fold is visible which is called the Crumple (Fig. 5). This is the visible evidence of the Purbeck Monocline which formed approximately 30 Ma ago. It originated during the late Oligocene and early Miocene and is the northernmost ripple of the Alpine Orogeny. Looking west towards Hambury Tout the steeply inclined Purbeck Limestone Group is visible on the western wall of Stair Hole. On the right the pink coloured Wealden Group clays have slumped where the sea has breached the Portland Limestone and has eroded these soft sediments. As the sea removes these clays it erodes the base making them unstable and further slumping gradually excavates a larger hole.
Fig. 5 Stair Hole looking at the Crumple One day this will form a new cove in a similar way to the formation of Lulworth Cove. The Purbeck Limestone is dark grey in colour; under the hand lens it is full of broken shell fragments orientated in many different directions. It was deposited in freshwater conditions; its densely packed shells are those of the freshwater snail Viviparis. This rock was laid down in lagoons and mudflats about 144.8-136.8 Ma ago (Cretaceous). It is the continuation of the transition from marine to terrestrial conditions mentioned earlier. Lulworth Cove is equally spectacular, especially viewed from Hambury Tout (Fig. 6). On a closer look from the wall of rock that separates Stair Hole from the cove the whole sequence of rocks from late Jurassic to Cretaceous age may be seen. From the seaward side moving inland, first is the Portland Stone (late Jurassic) then the Purbeck Beds (early Cretaceous). The profile drops in height where the Fig. 6 Lulworth Cove from Hambury Tout looking east soft rocks of the adjacent Wealden Clays and Greensand Formation occur. The height rises again where the Chalk wall forms the back wall of the cove. Doggers Rather strange looking spherical stones were found on the beach at Osmington Mills. The one shown in the photograph (Figure 7) is about 1m in diameter. They are from the Bencliff Grit Member, part of the Nothe Formation of the Corallian Group (Figure 9). These bizarre structures are very hard and remain intact when the unconsolidated sandy silt matrix is eroded. They are septarian nodules which are spherical masses of cemented sediment which formed during or after deposition. They are abundant on the Osmington Mills beach.
Fig. 7 Septarian nodule showing cross bedding
Swanage Bay
Fig. 8 Wealden Group clays of Swanage Bay I managed to find a little time the day we left to return home to walk along the beach at Swanage Bay towards Ballard Down. This is where the Wealden Group (Wessex Formation) can be found (Fig. 8). It is composed of varicoloured clays, silts and sands. Landslips are a very common occurrence and there is plenty of evidence for this. I found a complete shrub with the root-ball still attached on the beach. Looking up the cliff I could see the fresh marks of the position it grew in near the top of the cliff. Towards the top of the cliff there was a layer of sandstone approximately 0.5m thick. The colours of these clays are due to the presence of minerals. The red colour comes from ferric oxide, haematite, which develops after deposition. These soft sediments are easily eroded and form the Swanage Bay to the south of the Chalk Cliffs of Ballard Down. References Geology of the Jurassic Coast (P. Ensom, M. Turnbill) Geology of south Dorset and south-east Devon and its World Heritage Coast British Geological Survey 1:50 000 Series Sheets 342 (East) and 343 Swanage British Geological Survey 1:50 000 Series Sheet 341 and part 342 West Fleet and Weymouth Fig 9 Lithology
Events Diary
Important Notice re OUGS events – Insurance. Even though the OUGS has Public Liability Insurance cover for field and indoor meetings it is the responsibility of each individual to arrange their own Personal Accident and Personal Liability Cover. None of the information in any of the advertisements for field trips in this newsletter constitutes a brochure under the Package Travel Regulations (1992)
Date to be advised – Building stones of Cambridge Leader: Dr Steve Parry.
Date to be advised – The Jurassic/Cretaceous Boundary at Upware Leader: Dr Simon Kelly.
Spring 2020 – Crete We are exploring the possibility of a field trip to Crete in the spring of 2020, with Dr. Charalampos Fassoulas, from the University of Heraklion, as leader. Please contact Phil Ridley if interested. More details will follow in a future newsletter.
Branch Committee Members Branch Organiser – Philip Ridley. Tel. 01223 842922. Email: [email protected] Treasurer – Mike Sandison Longlea, Esplanade, Maylandsea, Essex, CM3 6AW Tel: 01621 741351 Email: [email protected] Secretary – Sue Brown Mill Cottage, Newbourne Road, Bucklesham, Ipswich, IP10 0BY Tel: 01473 736519 Email: [email protected]
Events Organiser – Sally Southall. Email:[email protected] Newsletter Editor – Mike Sandison – as above Branch Librarian – Ken Wightman. Tel. 07803 351029. Email: [email protected] Website Co-ordinator – Emma Emerton. Email: [email protected] Committee Members – Wendy Hamilton. Email: [email protected] Andrew Fleming. Email: [email protected]
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