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Archive 2006

At each event we ask for a volunteer to record their experiences and impressions. These articles are published in our newsletter and eventually appear here as an archive of our activities. Note that these are only provided for reference, and are not endorsed by Event Leaders. Interpretations can change often and rapidly in Geology, any information stated should be verified from appropriate sources before being quoted.

The Art Bronze Foundry  Ardingly Sandstone and Tombstones at Fletching  Teaching the Dynamic Earth  NHM Earth Science Library  The Vale of Wardour, The SW Wiltshire Anticline  Shetland  Harwich and Wrabness, Essex

Visit to The Art Bronze Foundry (London) Limited

16 February 2006

Round by the gas works in Michael Road near Fulham Broadway is a restaurant ornately decorated with bronzes. The Art Bronze Foundry is next door. One or two people turned up and we waited, only to find that everybody else was inside in the warm. The shop was just big enough for our party.

Sculptures come in all sorts of material - from papier maché to ornately carved wood. This means that the first stage has to be quite gentle. So the lost wax method is eminently suitable. First a negative is made. Macwax, a releasing agent is sprayed on the model and then silicone rubber is applied with a spatula. This method gives good, accurate coverage. Three-dimensional models need a join. For example the join on heads passes vertically through the ears. Locating pegs help the two parts fit neatly together. Any errors here will give a wonky bronze. Silicone rubber is flexible, which helps separation, but its flexibility is also a disadvantage. It has to be supported by a plaster cast for the next stage to make an accurate representation. The cast is made of casting plaster possibly supported with scrim.

Now a positive is made. Molten wax is painted on to a thickness of 1/16th - 1/8th of an inch. This is an ideal thickness for bronze casting. Thicker bronze would distort too much as it shrinks on cooling and solid bronze could never be used. More wax is swilled in to join the pieces. The wax model is then separated from the silicone rubber mould. It is finely inspected and cleaned up to perfection. To help inspection the wax is coloured red colour and lighting is soft to prevent reflections. We only saw Paul use a blunt spatula and old green kitchen scourer. Obviously the finished casting cannot be better than the wax model so this stage is painstaking. Paul was working on a life-sized torso. The wax was sturdy and did not need support but there were peculiar ragged holes in the back walls.

One of the beauties of the lost wax method lies in the ease of connecting cut outs by wax sprues as well as attaching larger wax pathways which the molten bronze will follow during casting. The wax model looks like a peculiar insect with random appendages at this stage.

We went out to the casting room, which was delightfully warm on such a cold day. However on a hot day temperatures may reach well over 45°C.

Now a ceramic shell (investment) is made which completely surrounds the wax (inside and out). We were told that this involves at least eight dips whilst the model is spun. Now we could see the reason for the holes cut in the wax mould as they allow the ceramic core to form. Nails hold the inner and outer shells together. These shells are light and strong but, even so, vulnerable places are reinforced with chicken wire. There is a cup like structure at the top connected to several larger diameter wax sprues where molten bronze will be poured in and fed to all parts of the model. Normally the foundry only casts once a week but they did a special one for us.

First the inverted assembly is heated in a gas-fired kiln. During this time the wax mould and sprues melt and run out. The temperature is carefully controlled so that the molten wax can be collected for re-use rather than burn away. The hot assembly was put the right way up into a metal tank and propped up using stones ready to receive the molten alloy. The foundry prefers to use gun-metal (85% copper; 5% tin; 5% lead; 5% trace elements) but can make casting in other alloys (e.g. spelter, a lead/zinc alloy) if asked. Bronze ingots, which weigh about 20lb, are melted in a plumbago (graphite) crucible. Graphite is particularly suitable, as it gets stronger as it gets hotter. The temperature of the casting metal has to be between 1000°C and 1200°C. Although optical pyrometry could be used to measure the temperature a quick rough and ready cheap alternative is to stick a red-hot iron rod in and if the bronze does not stick the alloy is hot enough.

The process, once the crucible leaves the furnace, has to be quick. Two people controlled the crucible using handles at either end of an iron harness but an overhead gantry did the lifting controlled by a third who worked pulleys - somewhat akin to rubbing your tummy whilst patting your head. The bronze must not be allowed to cool too much as, if it becomes too sticky, it will not flow into all the cavities in the mould.

First slag was scraped from the top into a pit on the floor. Then each ceramic assembly was quickly filled. Finally the almost empty crucible was laid gently at an angle on the floor to cool. Cooling was quite rapid. Bits of ceramic seemed to pop around the tank. This is inevitable as bronze shrinks on cooling. After about half an hour cooling the ceramic shell was knocked away with hammer and chisel. We saw a flattish model (of a women's back) appearing. It turns out that flat shapes are difficult to cast, as the mould tends to be slightly flexible. Philip pointed out imperfections running across but was not concerned. Separating the casting from the investment is a good job for an apprentice as it is carried out in the yard whatever the weather. It might be unskilled but it is very important to remove every last bit of ceramic from the core as subsequent treatments include acid etching.

Back inside again we went to see the next stage in tidying up the casting called chasing. All sprues are removed and any traces of them obliterated. The pieces are welded together and the joins filled. Full advantage is taken of the excellent malleability of bronze to fill small holes simply by hammering with a steel tool to slide metal about. Sometimes the bronze is a little thin where the moulds have flexed so more can be welded in. The judgement of the craftsman is all-important at this stage. For instance we saw specific areas (knee and elbow of a prone body) being worked on to highlight them. At this stage the casting is a beautiful golden colour but it is vulnerable to corrosion. If left in London the casting would turn black and, indeed, some bronze statues have been painted black to avoid extra labour. At the seaside the copper content leads to green corrosion.

The idea of the patination process is to accelerate corrosion according to the sculptor's wishes. There are various treatments: potassium sulfate leads to a black finish, ammonium chloride with potash gives a green finish and iron III nitrate gives an attractive brown. Treatment with a bismuth salt leads to a rather curious white finish. However once again the craftsman's touch is all-important. For instance none of the finished artefacts we saw were a bland flat colour but all had highlighted areas.

Many famous sculptors brought their sculptures to the Art Bronze Foundry. If you have been to Kings Lynn you may have seen Vancouver's statue and in Westerham there is Winston Churchill. Epstein and Finck are two of the more famous sculptors who brought their models to the Foundry. There was a Bafta bronze on the table. It is quite heavy so it is likely that a less dense material has replaced the original bronze judging by the ease with which recipients wave their masks around at the awards ceremony.

The Art Bronze Foundry is eighty years old. The Foundry, whilst using traditional methods, readily uses modern materials. Silicon rubber moulds, which can be reused, have replaced gelatine negatives. The investment used to be made from bulky grog and plaster but, in the same way that plaster casts protecting broken bones have become thinner whilst retaining strength, these new shells are thin, light and strong. The turn round from original model to finished article is less than a week. This brings it own problems; the Foundry is dependent on a regular supply of customers to keep the plant operating.

Bill Hayter carefully explained legal aspects. The sculptor owns the original and may specify that the moulds can be used a certain number of times, say six. However it is unlikely that all six bronzes will be made at the same time. The foundry stores the moulds and when the sculptor has found a buyer he requests another casting. When the specified number has been made the mould is destroyed. Apparently this has not stopped a third party (an institution that should have known better) from requesting their own casting on the side but this is unacceptable.

When bronzes are sold the dimensions are carefully recorded. This cuts out the possibility of forgeries by making a new mould from a bronze. There are three stages at which shrinkage occurs so any forgeries made from that positive will be too small.

It is interesting to speculate when a bronze becomes a work of art. We all know that a painting by Claude Lorraine for instance is worth much more than a copy made by a pupil. But casting a bronze involves input by craftsmen as well as the designer and their work is an integral part of the finished article. The intellectual property holder has the original idea and produces the original, which is unlikely to have the nuances such as depth of colour of the finished bronze casting but they will have been consulted at each stage and signed the bronze. (Although it has been known for this to be done 'in house' when the sculptor has sufficient confidence in the foundry.)

I would like to record our thanks to the team at The Art Bronze Foundry for making us so welcome and going to such trouble to give us an insight into the history and development of casting bronzes.

Diana Wrench

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The Crags of Sussex: Ardingly Sandstone led by Gareth George,
followed by Identification of Tombstones at Fletching

1 April 2006

THIS, MY FIRST FIELD TRIP AS A BONA-FIDE MEMBER WAS A STRANGE EXPERIENCE. I ATTENDED SEVERAL TRIPS LAST YEAR AS A GUEST WHILST DOING S260, SO I RECOGNISED A FEW FACES AND WAS MADE TO FEEL WELCOME FROM THE START. THE SLIGHTLY SURREAL FEELING CAME FROM THE VENUE, NOT THE PEOPLE.

I first went to Harrison's when I was seventeen, which was a while ago, as I could be described as a mature student. Since then I have made dozens of trips to the vari- ous sandstone outcrops in Sussex and Kent, but have al- ways looked at them through the eyes of a climber. On this occasion, I saw them through the eyes of a geologist be- longing to Gareth George, an enthusiastic and knowledge- able chap, who clearly enjoyed what he was doing. I saw things in the rock which had never been there before, not- withstanding the fact that I have been interested in geology for some years now. We were introduced to planar and graded cross-bedding, hummocky cross-stratification, trun- cated waveforms and all manner of exotic structures.

After a pub lunch we visited Lake Park, where the most interesting geology had been exposed by tunnelling to create a walk around the lake. It had exposed the underside of the bed planes where one could see a bed come to an end in the roof but continue down the side of the tunnel at a shallow angle. Three dimensional geology - excellent!!

We finished our day in the graveyard of the church at Fletching, where the warden wanted us to try to identify the building stone and grave stones. A mixture of sandstone, limestone, marble and granite was found on the graves, some of the limestone probably attributable to Port- land and one slab of very weathered Large Paludina lime- stone (Sussex Marble). The church, which had undergone several periods of development and dated from the 11th century, was built mainly of sandstone, some of which was well weathered.

There was debate as to the provenance of the sandstone, but it was decided that it was probably the local, Lower Cretaceous, Tunbridge Wells Sands including some Ard- ingly Sandstone, which is what the day was all about.

I gained a lot from the day and enjoyed myself tremendously, my thanks to Gareth and Di for their efforts and to everyone else for making it such a pleasant day.

Doug Clements

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Teaching the Dynamic Earth

A demonstration of geomodels for teaching Earth Science.
Set up by Paul Grant and delivered by Nikki Edwards.

18 May 2006

Instead of our usual Thursday evening talk, we invited Paul Grant to come and give us a demonstration of the Earth Science Teaching models developed by ESTA (Earth Science Teachers' Association) and the Earth Science Education Unit at Keele University. Paul had whetted our appetite by showing us a video clip of his model of mountain-building processes when he talked to us about the Baetics last year.

In the event Paul was called away at short notice to accompany Imperial College students to the Baetics so he sent along Nikki Edwards to guide us through the models.

Paul had brought along the models a few days before - 6 big boxes and a gutter pipe. It was all very exciting and setting it up with my colleague Jill Darrell and Nikki was a bit like opening up a Christmas stocking. Nikki has her own models and unpacking Paul's produced a few surprises for her: Jill was despatched for some extra bits of kit.

And so the session began. As an ice-breaker we sat in groups and arranged rock specimens at appropriate positions in the rock cycle. Then in our groups we were launched to play with the activities on offer.

Laurie spent most of the time repeatedly applying heat to a small piece of granite and dunking it in cold water and managed to destroy it. Several of us had fun with the gutter. It was half-filled with sand then tilted up so that we could pour water from the top which overflowed into a bucket at the base. We each selected a monopoly house and placed it where we thought it would best withstand the 'melting glacier' from above. I can't remember who won but I know mine, strategically placed near the top at one side, was moved down slope almost immediately. I think the winner - about the only one not to move - was situated on a stable island within the braids. So our group moved on to the activity that had sparked off the session: alternating layers of flour and sand in a Ferrero Rocher box. An exact-fitting piece of wood acted as a 'slab-push' force and low and behold our 'mountain' acquired exotic folds and even a fault. I think it was Wilf we watched blow down a straw into a complicated arrangement of chemistry equipment to cause an oil-well blow-out, although Nikki was disappointed that no-one got completely soaked! Apparently this activity is very popular with kids. Finally Nikki brought out and demonstrated the piece de resistance: a wax volcano. It worked spectacularly! A layer of red wax was placed under a layer of sand in a glass beaker and then both were covered by water. The wax was gently heated from the base. Low and behold, the sand rose up and red 'lava' flowed down the sides at the top and also produced 'feeder tubes' to the 'ground surface' where it spread out evenly. It was even slightly explosive at one stage.

Unfortunately we were all having such a good time that no-one had the presence of mind to take photographs but details of the models are on their website: www.earthscienceeducation.com with moving images of the wax lava. The teachers amongst us were all enthusiastic about taking the ideas back to the classroom and newcomers to S260 will have gained insight into the basic principles of several geo-processes. For those who were unable to come but could also find the models useful in the classroom, an INSET sessions is offered to schools free of charge, except for travel and refreshment for the team member who facilitates the course, thanks to sponsorship of the UK Offshore Operators Associations. Details are on the website.

Many thanks to Paul Grand and Nikki Edwards for such an exciting evening which will additionally be very useful to quite a few of us. Also thanks to Jill Darrell for her muscle power enabling the models to be safely installed.

Diana Clements

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Visit to the Natural History Museum Earth Science Library

15 June 2006

The Earth Science library were kind enough to offer two London Branch members the opportunity to take a tour round the library facilities at the Natural History Museum in order to promote the wide range of material and services they have available to outside organisations and members of the public.

Jenny Parry and I were delighted to take them up on their offer to view some fantastic books, maps and works of art, both ancient and modern.

We started our tour in the main Earth Science Library. If you have visited the Natural History Museum you may have noticed its inconspicuous entrance opposite the Ordnance Survey Shop on the ground floor of the Earth Science building. The staff had displayed some of the fantastic material held in the library. This included twelve 3-dimensional wooden models of geological structures created by Thomas Sopwith (1803 - 1879), which were designed to help geologists and engineers to understand formations. The blocks are approximately ten centimetres square and individual strata are depicted using different colours/types of wood which produces a most fascinating and beautiful finished piece. They were often used in universities and colleges as teaching aids for map-work and structural geology, what a shame we do not have the opportunity to use such wonderful pieces of art as study materials today. We also viewed some unique books by George Cuvier (1769 - 1832), the Rev William Buckland (1784 - 1856), Thomas Burnett (1635 - 1715), and a beautiful illustrated work by John Fullwood (1854 - 1931) entitled 'Rocks and Minerals, chiefly from the South East Coast of England, an album of 122 pencil drawings and watercolours', these were just beautiful and unbelievably realistic.

We were then shown up to the fourth floor of the Palaeontological building where we were shown the special collections and the map room. There are three special collections rooms, palaeontology, mineralogy and the John Murray library (John Murray was the naturalist on the HMS Challenger expedition (1872 - 76), this collection was donated with the wishes that it was to be kept together).

Most of the material in these rooms pre-dates 1850 and is available for viewing by special request. Here we were privileged to view some unique pieces; the diaries and letters from the HMS Challenger expedition; A reference book by James Sowerby (1757 - 1822) containing some beautiful drawings of minerals, the staff had been kind enough to also retrieve the original specimen of Sulfur (kept at the museum) that Sowerby used as the source of his illustration; The series of twenty-one sets (355) photomicrographs of snowflakes by Wilson A. Bentley 'The Snowflake Man' (1865 - 1931). Bentley was the first person to photograph a single snowflake crystal in 1885 and was the first to make the discovery that no two snowflakes are alike. The pictures were taken during the winters 1885 - 1889 in Vermont, USA. He captured 5000 snowflakes in his life leading to him being affectionately known as 'Snowflake Bentley'.

On our return to the main library we were allowed more time to view some of the other works on display, this included the 'Geological evidences of the antiquity of man' (1873) by Sir Charles Lyell (1797 - 1875). Also some beautiful works of dinosaur art by Neave Parker (1910 - 1961), Henry de la Beche (1796 - 1855), and Thomas Hawkins (1810 - 1889), many of the specimens of reptiles that inspired his artwork were collected in Somerset and Dorset, and a beautiful watercolour by Sir William Hamilton (1730 - 1803) of an eruption at Campi Phlegraei (Naples, 1776).

We also had a chance to see the oldest book in the Earth Sciences library 'De Re Metallica' (1556) by Georgius Agrcola (1494 - 1555), the title translates as 'On the nature of metals', however this had a much wider meaning at the time and encompassed any mineral. Finally I have to mention 'The world's mineral masterpieces' (2002) by Eberhard Equit (1939 ®). Who is apparently widely regarded as being one of the finest contemporary mineral artists in the world, and you only have to look at this amazing volume to see why. I strongly recommend taking a look. A selection of his work can be viewed online at www.minrec.org follow the art museum link and select the artist from the list.

A big thank you to all the staff of the Earth Science Library who were most helpful and approachable, I hope this brief round-up of a wonderful visit will inspire some of you to take up the opportunity to view some of the wonderful archives available. You can access the library catalogue online at www.nhm.ac.uk or you can visit the library by appointment (48 hours notice required), contact the library staff.

Dee Summers

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Geology of the Vale of Wardour, The SW Wiltshire Anticline

17 June 2006

On a very hot Saturday morning we assembled in the village of Dinton with our guide Lesley Dunlop. Lesley introduced herself disarmingly, to those of us who did not already know her, as primarily a hard-rock geologist. However, we were very much in sedimentary territory and were going to perform a traverse of a section across the SW Wiltshire anticline, the axis of which ran by the river to the south of the village. We would start by walking to the north, and then walk back south (and a detour a little to the west) across the core of the anticline, and then follow the section in reverse order on the other side.

After appropriate warnings about the need to drink plenty of water in the hot weather, we set off through the picture-postcard village of Dinton, and then climbed a steep hill along a sunken lane, appropriately called "Steep Hollow". To the beginner in geology, a steep climb uphill away from the core of an anticline might seem counter-intuitive, but in fact "reverse topology" is commonly found. The upfolding of the rocks in an anticline causes a weakness, which results in more rapid erosion at the core of the anticline. That same weakness is exploited by rivers, as here, to create a valley.

We paused near the top and viewed the outcrop by Upper Greensand exposed on the sides of the sunken lane. This was characteristically green from the glauconite contained in it and there was also a lot of iron in the rock, which was not particularly well cemented and contained a lot of fine muddy grains. There was much cross-stratification in the lower part of the exposure near a springline. There was also a distinctive shell-bed, and there was some discussion as to the large number of rather broken-up fossils contained in it. Some thought that the fossils looked like Gryphaea because of their shape, but this could not be what they were, as Gryphaea is a Jurassic fossil, and here we were clearly in the Cretaceous. The consensus was that the fossils were terebratulid brachiopods.

However, subsequent research carried out by Di Clements in the Natural History Museum collections established that they were in fact bivalves, of the species Pycnodonte vesiculosus. They are also so identified, specifically in relation to this location, by Isobel Geddes in her book on Wiltshire Geology.

Lesley invited us to measure the dip of the rock (approximately 10° to the North, although the road itself was dipping to the south, following the reverse topology). We then walked up to the crossroads at the top of the ridge from which a chalk landscape was visible to the north. Here Lesley discussed what we had been seeing. The Upper Greensand was approximately 100 million years old. The glauconite and the fossils indicated a shallow marine environment, below the tidemark. Lesley also explained the broader context of the sequence of sedimentary rocks in the anticline, which had been folded and tilted after deposition, by the Alpine Orogeny, and then eroded.

While listening to this the writer was at this point bitten on the finger by a horsefly, which occasioned some discomfort in the following week. Future visitors to the location are advised to bring insect repellent. We then walked back downhill towards Dinton past a quarry at which we paused briefly. Here the rock was paler due to leaching, with iron nodules.

As we came back down towards the village, Lesley pointed out a change in slope as the road levelled off. At the point where the slope changed clay was seen to be exposed in a field by the side of the road. Lesley indicated that the flat level of the village indicated that it was lying on clay at this point. There was then a slight rise again. Re-entering the village and posing a wall on a building to one side we noticed a mixture of harder rocks from the locality, blocks of Greensand with shells, a greyer fossiliferous rock and some whiter carbonate rock. We passed a large new-style country house with an inscription proclaiming it to be "Wright's Manor", built in Chilmark Stone, a creamy variety of Portlandian stone used in Salisbury Cathedral, with a slate roof. It was noted that the stonemasons had inserted blocks of stone upside down into the wall. We then came to St Mary's church. This had some bits of Greensand in its construction, quite a lot of material from the Purbeck beds and a more blocky rock, like Chilmark, probably quarried very locally. Underlying us were now Jurassic beds of the Portland and Purbeck . Lesley said that there was a marked unconformity below the Lower Greensand. Some thirty to forty years of deposition were missing, having been probably eroded away early in the Cretaceous.

Leaving the village and turning a bit to the west, we crossed parkland, passing a lake. The parkland belonged to Philipps House, a National Trust Property built in 1817 on a Greensand ridge to the north- east which commanded a view down to the river Nadder. We crossed a road and then a field and passed through a spinney to a spot near the railway where we paused for lunch.

During lunch Lesley pointed that we were close to the core of the anticline. Here several fault lines ran. There were parallel fault systems running east-west, and the river utilised the weaknesses to lay its course. Lesley also pointed out that many of the anticline features were asymmetrical, the northern part (the side away from the direction of thrust) being steeper.

There was also some discussion over lunch about a fault running parallel to and on the south side of the anticline axis. This was thought to be a deep Mesozoic tension fault, one of a number in the area associated with the first opening of the Atlantic in the early Jurassic or earlier extension in the late Palaeozoic as an eastward extension of the Variscan Orogeny, now deeply buried. This may have controlled subsequent deposition and folding. Initially these faults were down-throwing to the south, and may have caused much thicker deposition of Jurassic sediments down a fault scarp to the south. The direction of movement or faults such as those would then have been reversed at the time of the compression due to the Alpine orogeny, so as to cause a down-throw to the north. Therefore although the impetus came from elsewhere, much of the movement in this area would have been on the ancient faults, which in this case may have contributed to the asymmetry of the anticline. The movement of the crust during the Alpine orogeny would also have caused a number of minor tension faults to open up which are found here trending in a NW/SE direction.

After lunch, Lesley invited us to examine the loose material lying exposed on a bare patch of the field where we had stopped. This proved to be of varied origin, iron nodules from the Greensand, flints from the chalk, shelly limestones and laminated Purbeck material.

Moving across the railway (and crossing the core of the anticline) we came down to the river, passing an elegant hamlet with an old mill house. We followed along a path bordered by barbed wire and nettles, but then had to leave it passing under the barbed wire, the party losing some of its style and dignity for a moment in the process! We could see that the ground over which we were passing was partly alluvial , partly limestone. We were over the Jurassic. Crossing the river, we came up across a ploughed field containing laminated Purbeck stones, but on the upper and southern side there were numerous flints. Lesley observed that the River Nadder had probably cut down further after the deposition of the flints on the southern side of the field.

Passing along the top of the field there appeared to be significant amounts of clinker, thought to be from a limestone kiln , and then one of the party picked up a piece of what seemed to be carboniferous limestone, rather than the more recent Jurassic limestone we had been seeing. An animated discussion ensued about this, which was cut short when some one consulted the OS map and pointed out that we were walking along the course of a dismantled railway. What we had been looking at was in all probability remnants of the ballast!

Moving south, we skirted a fenced-off wooded area, and passed into a spinney through which ran a track. There we paused, to consider where we were in the succession. It was felt that we had now climbed up beyond the Purbeck and Lower Greensand beds and the ground was suggestive of Greensand, perhaps Upper Greensand. In that case where was the Gault? It was speculated that this was due to a fault. However, in retrospect, given that our passage through Dinton suggested that there was an extensive deposition of Gault in the area, it is probable that our initial assessment may have been mistaken. Passing along the track, we did in fact come upon Bog Pepper, just before a break of slope, which indicated a clay substrate. We reached Ford Lane, walked along it a short way and then most of us followed the steep track up to Fir Hill. A few of the less energetic of us stayed behind.

On the way up, we passed a second exposure of Upper Greensand, which contained a fossil bed very similar to that at the top of Steep Hollow above Dinton. We examined this more closely on the way down, but before proceeding took the dip of the Upper Greensand at that point. It was approximately 5° to the South. We continued up to the top of Fir Hill where there was a reservoir and from this point the Chalkland of Fovant Down was visible further to the south. On the Down, military units which had encamped there in the past had carved out their regimental badges into the Chalk. Some of us had seen those badges that morning on the drive over to Dinton.

It was felt that the structure of the anticline had been convincingly demonstrated. Summing up, Lesley said that the Vale of Wardour provided a good illustration of an Alpine anticline, like that found in the Weald, but in a much smaller area and with a more extensive series of rocks exposed, because the core went down into the Jurassic. It was well worth revisiting if some of us should be again in the area. We then walked back downhill and crossing the river returned to Dinton and the cars. Then, after a pause for appropriate refreshment at a local hostelry, we returned to London.

Richard Trounson

With thanks to Kim Vignitchouk for her photographs

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Shetland led by Allan Fraser

31 July - 7 August 2006

Day 1 (Monday 31st July)

Our comfortable overnight ferry trip from Aberdeen sea breaking to Lerwick was an excellent start to LOUGS visit to over rocks Shetland. It may have been misty as we all enjoyed a leisurely breakfast on board, but by the time we had disembarked, raided the Coop for lunch and had a dodgy tyre changed on the mini-bus (the Paddy Wagon), it was sunny.

Scalloway, on the west coast, where we were to stay at the North Atlantic Fisheries College was only a few miles drive from Lerwick. Shortly before reaching the town, was a viewpoint from where we could see all of Scalloway beneath us - the harbour with its old houses round it, new marina, ruined castle and the NAFC buildings nestling low on the shoreline. After leaving luggage behind at NAFC our convoy of 3 vehicles led by our guide Allen Fraser set off for Sumburgh Airport to pick up more arrivals. Several people had been delayed due to the earlier mist. Nearby Sumburgh Head Reserve made a wonderful spot for our picnic. Sunshine, lighthouse, cliffs, seat breaking over rocks made a wonderful backdrop for watching gannets, skuas, terns, puffins and even a basking shark.

It would need a small book to tell the story of the Broch and Iron Age Village we visited at Scatness where we spent a very interesting couple of hours. The onsite guides were very enthusiastic and were happy to answer our many questions about the set- tlement which has been occupied for 2000 years. The Broch, a double walled tower was probably for defence and the roundhouses and wheelhouses were built around it at later times. The dwellings were those of Iron Age people, followed by the Picts and later the Vikings. The whole area gradually fell into ruins and became covered in grass and buried from sight till a new road was being built for Sumburgh Airport. Excavation only began in 1995.

Back to our lodgings to unpack and freshen up be- fore dinner at Da Haaf the NAFC restaurant where the fish was delicious. The evening sun cast a warm light over the water and headlands creating a very attractive vista to end an enjoyable day.

Maggie Morley

Day 2 (Tuesday 1st August)

Location One - Scord Viewpoint

The view was stunning, if a little misty, with moun- tains and valleys and the surrounds of Scalloway before us. This was a stop to set the scene in geo- logical terms for the rest of the day and to some ex- tent the rest of the week. Allen introduced us to the names of major rock groups and types and the tec- tonic episodes which were the most significant events that shaped the current topography of the Shetland Islands.

The major rock group around the area is the Clift Hills Division including the Clift Hills Phyllite which, locally occurs in various colours due to the variation in the mineralogical content of the rocks, and has a dip which is near vertical. We could see this at a distance in the massive road stone quarry which dominates part of the skyline of Scalloway. The origin of the rocks is Pre-cambrian sediments which have been metamorphosed and folded during the Dalradian, some 400 to 600Ma. It is quite impressive to think that these rocks have been around so long and changed so much. The topography as seen from the view point has been shaped by the erosion of limestones in the valleys leaving harder and more resistant hills of the phyllite and of granite intruded around 500 Ma, such as the Hill of Berry.

The Tingwall Valley with Scalloway at its end marks the line of the Nesting fault which is thought to be part of the Walls boundary fault, part of the Great Glen Fault system. Up to now these had been words on the page but to see them for real was a treat and indications of what was to come.

Location Two - Black Gaet Junction

This stop was a road cutting approximately four metres high and a few hundred metres long. This was our first chance to look closely at the Clift Hills Phyllite and get our hands and our eyes on the rocks. The drivers of the traffic going past looked with surprise at us wearing our yellow hard hats, but they did not stop to ask what we were doing. The rocks were as interesting close too as they had looked from a distance. They were predominantly phyllites with darker bands of micaceous material, probably metamorphosed muds and some lighter layers which were probably metamorphosed sand and some bands of quartz. The original rocks de- rived from extensive weathering, transportation anddeposition of sediments as submarine fans or in deep basins. What was even more interesting was the evidence of the complicated life undergone during the metamorphic processes which produced the rocks that we were looking at today. Prompted by Allen we searched for and found strain bands cross- ing each other, fine scale crenellations and kink bands and, within the layers of quartz, boudinage structures. It was an excellent chance to see for ourselves some of the features of metamorphic rocks that we had only previously read about.

Location Three - Mail

We stopped on the road near the top of the cliff and went through the cemetery with many interesting head stones and monuments and fabulous views out to sea. We scrambled down onto the beach to look for pillow lavas. What we saw was a lot of grey rocks covered in slippery seaweed, according to the notes these are rocks in the Dunrossness Spilitic group. Spilite is formed when the plagioclase min- erals in basalt are altered by sea water to albite. So, the tectonic setting was right, but what of the pillow lavas to go with it? To find anything at all, we had to really get our noses on the rock. We were told that there were pillow lavas so we tried our best to find them. Scrabbling around on the beach in the rain is a real sign of dedication, but we did find what could, with the eye of faith, loosely be described as pillow lava like structures. I am not convinced about what we saw, but we did only have a short while on the beach and maybe with more time we would have found something that was more convincing. What this site did do, was to add to the story of volcanic and tectonic activity which shaped the landscape.

Location Four - Catpund Quarry and Catpund Burn

This locality, based in a quarry, was to us the chance to look at samples of steatite, talc and serpentinite of a very special type. We parked off the road to walk up a track which had been cut around 1987 with a view to the commercial extraction of talc. Once again in 1997 commercial interest was shown, but the quarry is not currently worked. As we walked up the track it was hard to know what to look at; where our feet were going so that we did not stumble, or at the amazing rocks shown in the cutting wall.

All the rocks within the Dunrossness spilite group that were mentioned in the notes were there - we were able to see the steatite with a thin black layer of metasediments of graphitic phyllite and the paler bands of steatite. To touch, the stea- tite was smooth and silky just like the implements that we had seen carved from it at the old Scatness site the day before. The quarry, when we reached it, was small and it was difficult to see how it could have been exploited in any commercial way but the rocks were very interesting. We could examine them close too and came to the conclusion they were an example of the very special rock that we had been looking for. We could see its brecciated nature, originating at the time of its formation, and the random spinifex texture of the serpentinite crys- tals without the aid of the 'eye of faith' and almost without hand lenses; we spent a long time looking and marvelling at these rocks. The observations are so special because, taken together they are indica- tions that the rock was originally laid down as a sequence of komatiite lavas. Allen's notes gave us a very succinct explanation of komatiite lavas - 'these represent ultra-basic, olivine rich lava flows that were erupted at very high temperatures (near 16000C) from deep within the mantle'. The extraor- dinary thing about this occurrence of the rocks and the cause of much discussion among us and the ex- perts too is the fact that they are extremely rare in rocks as young as Lower Ordovician. There is a very good explanation about why they might have oc- curred here in Allen's notes which I do not have the space to include. We were very interested in these rocks, but had to carry on up the track to go onto the next site.

The next visit involved quite a scramble up to the Burn of Catpund to see evidence of exploitation of the rock that had been successful rather earlier than the 20th century. This was a fascinating site in which we could see the old spoil heaps and over- grown quarry workings covering the whole area. On closer inspection we could see chisel marks on the exposed rocks and hollows in the ground where the steatite (also known as talc-magnesite, soap- stone or 'clebber' in Shetland) had been worked by the Norse people who lived in the islands after the Iron age. Norse people used the steatite to make cooking vessels, lamps and all manner of other useful and decorative objects. We had seen some of these objects during our visit to Old Scatness and it was very interesting to see the source rock for the objects that the Living History group were recreat- ing in the same way that the Norse people had done so long ago. It was another treat to visit this site and appreciate how the lives of the people were so closely linked to the geology. I would like to have spent more time exploring the landscape and look- ing at the rest of the settlement but it was lunch- time and we returned to the vans and went off to lunch and mull over all that we had seen so far.

Location Five - Maywick-Taing

This time we had some work to do with a beach section to study, discuss and then explain. It was still dull and drizzly as we walked down onto the beach, but this did not dampen our enthusiasm for the task in hand. The first rock to find was the 'hologram rock' so called because as you pick it up and move it around the pattern on its surface changes as the light highlights the differential folia- tion. This is caused by the multiphase deformation of the rock into phyllite, slightly more schistose than some we had previously seen. Handsome sam- ples were found, duly admired, photographed and picked up to be taken home as specimens. The next exposure was further along the beach across a stream which was flowing fast and looked more the colour of beer than water as it made its way from the peaty land across the beach to the sea. Where the stream went into the sea it too turned brown, this time, the colour of chocolate. But what of the rocks? The first part of the section was made up of layers of quartzite of various thicknesses and shapes directly associated with some discontinuous layers of shale. The discussion about the deposition of the original sediments suggested deltaic or maybe braided streams with some of the quartzite being altered channel fill with clay drapes. Closely associ- ated with these layers were many quartzite bands and brecciated layers indicative of episodes of tec- tonic activity. We looked for and found evidence of folding, compression, extension and faulting, further evidence for more than one phase of tectonic activ- ity. Taken together we were able to use these obser- vations as clues for interpretation of the next part of the section further along the beach. At first sight we saw a large orangey brown amorphous mass with no sign of any structure. Close to, the rock looked like iron rich sediment, but how could there be sediment in an area so obviously altered? It did not seem to fit with what we had seen already. The answer was suggested by the tectonic activity. We were looking at large blocks of quartzite which had been altered and dissolved by the action of hydrothermal fluids, hence its soft and crumbly texture and apparent sedimentary nature in an area dominated by metamorphic rocks from many phases of tectonic activity. It was a fascinating and stimulating site which generated lively discussion at many different levels.

Location Six - St Ninian's Isle Tombola

We stopped in a rubbly lay-by at the side of the road near Bigton towards the South end of the Is- land, not a very promising start. We then walked about 50 metres to the edge of the cliff and looked down on the tombola between the mainland and St Ninian's Isle. This was much more impressive - it is the largest active sand tombola in Britain with a beach length of 500 metres. What you see is a strip of sand curved symmetrically on both sides, looking in profile like a concave lens, which links the mainland with the Island. This particular tombola has been in existence since at least the dark ages and it is thought owes its stability to the sand overlying a cobble base. Even though the tombola remains the sand on its surface changes its profile over relatively short periods of time dependant on weather and tidal conditions. The time that we visited the weather had not been stormy so it was topped with sand with no sign of the cobble base. We caught glimpses of other tombolas during the week, but none as impressive as this one which was well worth the stop and, as stated in the notes, a fantastic photo opportunity.

Location Seven - Garths Ness

The last location of the day is hard to describe in words, but once again "spectacular" is a good start- ing point. We drove past Quendale and then up a rough track and parked near some derelict and scruffy MOD buildings - just left as they were when the last of the men went away - an even less promis- ing view than the last stop. We walked along the cliff top across the ness looking at the rocks as we went. The rocks, in the Clift Hills Division, are mainly striped hornblende schists containing epidote, plagioclase, quartz, chlorite and biotite. Allen explained that these rocks were most likely to be Dalradian in age originating from an Island arc envi- ronment. What we went to see was a massive zone of sulphide mineralisation approximately 32 metres long and 4.5 metres wide within the schists. This was exposed due to the entrepreneurial attempts to extract copper by Alexander Chrighton and Andrew Grierson, Laird of Quendale around 1800. What we saw was a large oblong, brownish body of rock with a curved surface bounded by straight lines delineat- ing the adits that had been dug to mine the copper. It must have been a backbreaking and time consum- ing job to shift so much rock to obtain copper in economically viable quantities. The men working this area seem to have been paid well for their trou- bles because, in order to improve the assay quality of the ore, they secreted copper pennies in the assay samples. Eventually they were found out when the ore that was sent for processing did not match the quality of that shown in the assay samples and the mine was closed down as being uneconomic. The following information from Allen's notes gives an- other indication of the tectonic activity that has gone into the building of Shetland. "This ore de- posit consists mainly of pyrrhotite with only very small amounts of pyrite and chalcopyrite. The ori- gin of the sulphide deposition is thought to be from a mixture of magmatic water, derived from a cooling volcanic dome and large volumes of sea water, con- ditions associated with young Island arcs. These deposits can often thicken and evolve to contain economic concentrations of copper, zinc, lead, barite and sometimes gold." This was a fascinating site, and like so many of the other locations covered in our first day and a half, it showed the close link be- tween geology and people's lives.

A brilliant day despite the rain showers, finished off with an excellent meal in the Herrislea Hotel just up the Tingwall valley.

Gillian Hetherington

Day 3 (Wednesday 2nd August)

Off to the far north. A day of ferry schedules and distances to cover, so a prompt start needed. No last-minute dashes for the loo, everyone was seated and strapped in at the appointed 08.45 departure time. First a dash for the wonderfully named Both of Taft for our first crossing, a grey day but the islands of Brigg to port and Samphrey to starboard to admire. Into Ulsta on Yell and a rush through a land- scape of wet grassland where, I suspect, the sheep have webbed feet.

The ferry between Gutcher and Belmont was to take only 15 minutes so I sat in the car and drank coffee. On to Unst, the most northerly of the Shetland isles, no need to hurry and the sun came out. To a beach location at The Wick of Skaw and the wonderfully photogenic Skaw granite. Bright red tabular pheno- chrysts of microcline feldspars up to 5cms. long, contrasted starkly with the grey banded xenoliths of metasediments that had been violently gathered as the granite was emplaced.

Next to The Tang of North Wick to see the ophiolite. Alan's wonderful field notes talk of metaharz- bergite in contact with Dalradian metasediments but to my eye such differentiation was impossible and I felt that the facilities of a good Earth Science lab would be needed to work out which was which. We did have the company of seals, eider, gannets, arctic terns and, a first for me, arctic skuas when the rocks became too confusing.

Our third location was to a talc quarry at Clibberswick which, unlike our visit in 2005, was not working which made the walk to the cliff top far less hazardous. A scramble down to the shore took us to a beach covered in serpentenite pebbles and an energetic time bouncing flat stones off the calm sea.

A lunch (and comfort) stop near the Boat Museum at Harroldswick was welcomed by all including the gulls who enjoyed the left-overs.

Location four was to a restored stone-built crushing mill where chromite had been extracted from a gaunge of dunite by crushing with a heavy rolled driven by a horse walking a circular path. Much debate ensued about who it all worked with may suggestions but no definitive conclusion.

The fifth site was to a group of chromite pits on a hillside above the mill and to a break-in-slope which marked the location of the MOHO after the obduction of the opholite. My hip was giving me jip so I sat out this trek and enjoyed the company of two other men-of-a-certain-age until it was time to make the trip back to the ferry and the discussion of "where shall we dine tonight?"

Peter Franklin

Day 4 (Thursday 3rd August)

Thor's Day, and the God with the hammer was to start to reveal some of the underlying qualities of Shetland gently masked from us until now - its Weather and the enigmaticity (should it be enig- maticness?) of its geology. But the day started straightforwardly enough - breakfast arrangements had settled down and ran like a well tuned machine, the weather was mild with just a touch of low cloud on the hills above the loch.

Physically and spiritually Shetland is as close to Norway as to Edinburgh. We paused at Scalloway's War Memorial to those who had died on the Shet- land Bus ferrying refugees and Special Forces be- tween Norway and Shetland in WW2; round the top is a field trip's worth of rocks collected by Nor- wegian schoolchildren, one stone from the home of each of those named.

Today was billed as a West to East traverse from Moine to Dalradian and back and across to the Dal- radian again. That low cloud was just enough to give a true Shetland atmosphere to our first stop, a view- point to appreciate the way glaciers had preferen- tially eroded softer metamorphosed limestones to create the long low valleys and sea arms called "voes". Lowering clouds meant we couldn't see a lot of it but Allen told us the tale of a church minister who prayed for timber to re-roof his church, and the captain of a timber ship who promised his cargo to God if he and his crew survived a furious storm.

On to the rocks; in a roadside quarry at Tumblin we saw dark pyroxene crystals lined up in monzanite indicating the effects of tectonic pressure - or per- haps some flow in the magma? There were certainly some pieces of serpentenite being digested. Sue found a lovely pistachio green sample of pyroxene turning to epidote - it must have sunk towards the bottom of the magma chamber.

At our next stop at a quarry at the edge of the Moine the Shetland Mist was getting wetter and colder but to compensate there was some stunning Valayre augen gneiss with huge oval crystals of microcline feldspar with regrowth shadows around them; I suspect a sample will appear at the GA rockfest in November, along with some rather fine Moine Schist from the same place.

Some much folded psammites at the next stop, some of the white lines fizzed with dilute acid, others didn't, so quartz veins there as well as metamor- phosed limestone. We walked down the hill through the long wet grass and were rewarded with a spectacularly boudinaged quartz dyke on the river bank - the best example in Shetland Allen said; on the far side you could see holes where the boudins had fallen out. Actually the strata was tilted vertical so the vein was concordant with it, so perhaps a sill rather than a dyke; and it was a vein so neither a sill nor a dyke. Ah well, that's field trip discussion for you.

After lunch, some in the pub others in the car park, we walked along the shore inspecting more spec- tacularly stretched and folded rocks. Some tried to work out their D1, D2, D3's etc and got very tired heads; some of the white bits fizzed with acid but others didn't so we had a mixture of minerals; there was a major vein standing proud which didn't fizz - quartzite; not so battered and bent - so more recent. But also some faulted psammites cross cut by simi- larly faulted quartzites - a bit enigmatic. Some fine examples of fault gauge too. There were red grano- diorite outcrops down on the beach and Allen told us that the next outcrop of these is 16 Km to the north - that's the throw of the Nesting Fault which had caused all the turmoil in the rocks we had just been looking at and also the arm of the sea where we were standing. He took out the geological map and showed us that if you (mentally) slide the two sides of this fault about 16 Km then all the differently col- oured patches on either side match up nicely.

By now the weather was turning distinctly chilly and some of us had put on all the layers we had, but our last stop was back with our good friend the Valayre gneiss. Large circular phenocrysts, some nicely rotated, pressure shadows, some tails like large fat tadpoles. Some parts were almost a melt I migmatite and there were some lineaments or shear zones. A variety of circumstances must have led to all this - very enigmatic; those who understood more were heard to remark that there were probably 3 PhD's to be earned in this quarry. However the hungry midges who guard the place eventually won and we withdrew to the vehicles and headed for home base, pausing on the way to visit the viewpoint we had hadn't been able to see in the morning; we still couldn't see it! But thanks Allen for another great day's field geology and for the handouts which explain so well how what we saw got there.

Bob Morley

Day 5 (Friday 4th August)

The first stop of the day was at Mavis Grind. Here the British Isles has its narrowest point. The Atlantic Ocean lies to the West of Mavis Grind with the North Sea to the east. It is possible to include both in one photograph. Here we heard stories of Viking longboats taking a "short cut". The BBC televised a re-enactment. This involved unloading the boat, carrying it over the Grind and re loading before con- tinuing the journey. What the television programme did not show, allegedly, was the boat breaking up and the debris being cleared by bulldozers.

From Mavis we walked to the first locality of the day. This was Virdins Quarry. The safety instruc- tions were to use the top level only as the bottom level was not safe. I think I also heard our leader mutter, "the top level isn't all that safe either" There were Ravens whirling around. Was this an omen? I asked myself. Here gabbro is intruded by granitic sills. The notes suggest that the granitic veins and sills "easily penetrated the gabbro-diorite" but evi- dence was found of the red granitic material digesting the darker gabbro-diorite. In this situation the magmas were mixed. The gabbro was probably still hot when it was intruded by the cooler granitic magma. Amphibole needles were seen to be ran- domly aligned indicating a lack of pressure. White scapolite veins had formed along faults and veins throughout the quarry. This altered feldspar was produced by hydrothermal fluids passing along the faults and cracks.

Locality two was a roadside cutting near the Brig. Our leader described this as a geological puzzle. At the Northern end of the cutting, the rock is said to be a granophyre with zenoliths of altered andersite. There is foliation in the incorporated material sug- gesting a folding of the country rock before assimilation. In some of the rocks there is onionskin weathering typical of dioritic rocks. Further along the cutting "the granophyre is in contact with a band of hornfelsed schist" (an indicator of contact metamor- phism). This in turn gives way to granite, and eventually to serpentenite. The answer to the puzzle is probably in the sequence: - 1) Country rock 2) Retrogressed to serpentonite 3) Granite intruded- hornsfelsed to baked serpentenite

Lunch stop was a rock field from where (according to the notice you can take a walk in the Arctic Circle.) It certainly felt like Arctic conditions. The views were fantastic. We were able to see the most northerly point of the British Isles - Muckle Flugger.

Locality 3: The Beorgs of Housetter. This locality was omitted because someone had dumped agricultural lime Our leader did not fancy wet lime from our boots collecting in his van.

Locality 4: Here we were to see the Great Glen Fault - Europe's largest tectonic feature. "The best exposure of the Great Glen Fault anywhere in the world" according to our leader. We followed the cliff top along the headland watched by the ever- present seals. At the appropriately named Otter Haad, an otter briefly surfaced before disappearing around the headland. We reached the line of the Great Glen Fault. A shallow depression which could have been a drainage ditch. Some photographers used people as markers others resorted to walking poles. I doubt if any one has convincing images. A walk along the fault involved bouncing on the springy sphagnum moss and kicking up cotton grass seeds. The fault is most impressive at the small bay of Back Sand. By scrambling down a gully we could make contact with the fault with its layer of fault gouge. This has been analysed and is said to be O.S metres thick and is composed of "a hematite-stained isotropic paste containing fragments of analcite and quartz" To the east of the fault the rocks are metamorphic rocks with folds ranging from tiny crenulations to huge structures. Interesting, dramatic and extremely photogenic and guess who hadn't got a camera! The most exciting find of the day, for me, was the discovery of otter footprints in the sand leading to a lair. Those members of the group who stayed on the cliff tops were watching the otter waiting in the bay for us to leave before coming ashore.

Our leader was most considerate and included a number of comfort stops throughout the day. At one locality there was also a shop. We were unable to resist the Shetland ice cream and almost the entire group were eating Bloo Coo outside the Loo (sorry).

Locality 5: Houd of Scatsta overlooking Sullom Voe. Here we saw evidence of a stunami generated by the Storegga slide off Normway about 8000 years ago. Marine sands can be found in the stream bank. The Tsunami is thought to have been 2Smetres high. The attention of some members of the group was di- verted by the take off of a plane from Tingwall air- port. Also overlooking Sullom Voe is a monument to the fighters of the RAF. Our leader informed us that the first bomb to be dropped on British soil landed on Sullom. It killed one rabbit and gave rise to the wartime song "Run Rabbit Run".

Locality 6: This was a viewpoint of The Ayres of Swinister This photogenic feature demonstrates local environmental change. For the evening meal we ate in the Da Haaf Restaurant. It was at its chaotic best. The meals got mixed up and I was left without a main course. An investigation revealed that Bob Morley had been given my meal in error. It was pointed out that we began the day with the Red Granitic Intrusion eating the Gabro-Diorite at Virdins Quarry and ended with the OUGS Executive Treasurer eating my Red Snapper.

Heather Rogers

Day 6 (Saturday 5th August)

Day 6's exercise was to examine some of the volcanics of the Eshaness peninsula. These volcanics are believed to have been caused by subduction of a small part of the Iapetus ocean crust beneath Scotland and Shetland around 36OMA ago.

We set off in good spirits, paused briefly at the local supermarket for provisions and interrupted a handsome cat intent on stalking seabirds. He didn't stand a chance anyway! Our first stop was the beach at Braewick on the south coast of Eshaness - a hard hat site because of divebombing terns. This site, we were told, would give us a chance for some investigative work so we set off with much enthusiasm despite the lack of any geochemical analysis to assist us. Well, what can be said about a place over which even the finest minds are divided. The rocks comprise rubbly basaltic lava flows overlain, we thought, by tuffaceous sandstone, some andesitic lava, bombs and not a whiff of a pillow lava. A bit of a dog's dinner really which left us a bit puzzled as to what it all meant and indeed in which order events had occured.

We then moved across to the NW coast where we walked in a northerly direction along a 2/3km traverse which crosses progressively older lava flows and represents a cross section through the flank of a volcano. The traverse started on an andesitic lava flow. This was soon covered by pyroclastic material displaying rhythmic layering which indicates different eruptions. We examined the very deep Kim O'Slettans blowhole which during exceptional storms has been seen to produce water as high as the nearby lighthouse. The blowhole, which appears to be crossed by intersecting dykes, is believed to be a collapsed lava conduit (or were we perhaps looking at eroded jointing partially filled with fine secondary material - the jury is still out). There is some conjecture as to whether this blowhole area was once part of a parasitic cone on the flank of the main volcano.

The coastline along this traverse is simply spectacular. The battering received from storm waves is phenomenal and rock debris has been lifted and strewn along certain 30-40m high cliff tops. Deep water at the base of these cliffs, the huge fetch across the Atlantic and fierce North Atlantic storms combine to produce storm waves capable of such action. Wave action has also contributed to a coastline deeply incised by geos as well as other spectacular features such as Moo Stack. Geos are deep inlets resulting from marine erosion of the cliff face along faults and joints. Incipient geos can be seen in the form of caves and tunnels. Compressed air and water within these openings leads to block loosening, further seawater penetration and eventual ceiling collapse. Glaciation can also play a part in geo formation.

For me the Grind of Navir (aptly translated as Gate of the Borer) was the most awe inspiring site of the day. Our notes described it as a large amphitheatre hewn out of ignimbrite. As it stands today there is a cliff wall with a gap in it measuring 1Om wide by 13m high some 12m above sealevel. Behind this cliff wall lies a quarry with a load of stone blocks waiting to be taken away. But it is the sea and not man that is responsible. Storm wave energy is further enhanced by the narrow cliff opening and produces a wave velocity sufficient to prise out large ignim- brite blocks up to 3m in length and move them 1OOm inland to form a storm "beach" about 3.Sm high The ferocity of North Atlantic storms is notorious but I had never imagined they could be quite so powerful or erosive.

We returned to our transport pretty wet and downcast but smiles were restored once we arrived at the Braewick restaurant for a warming evening meal and a glass or two of good cheer. As on previous exercises there were more questions than answers with one of our party feeling the necessity for a darkened room! More success was had on the animal front with sightings of an otter and several basking seals..

Ursula Scott

Day 7 (Sunday 6th August)

Allen suggested a revised itinerary, which meant our last day in the field. We left Scalloway, headed south stopping at Somerfield for our sandwich stop. (There was lot of scurrying about by some folk).

Our first geo stop was by the side of the road near Dalsetter broch. It was a rounded stone unearthed in the 193O's when repairing the road. Being somewhat different to the surrounding geology it was identified as an erratic. It was evidence that ice from Norway had reached Shetland about 25,000 y BP. The rock is identified as Tonsbergite (southern Norway near Larvik) (Large rectangular to rhombic white feldspar crystals with over growths of reddish brown feldspar: of igneous origin around Tonsberg).

Back on the road an on to Shingley Geo at Broken Brough. Were we were able to see part of the Shetland Basin - well the shoreline - made up of lacustrine environments and Aeolian sandstones. This involved a walk down the hillside through peat type bog (on a hillside!) down to the shoreline and the example of Lake shoreline. I was not able to make it - the bog beat me. So I sat on a rock and looked on with binoculars. I was told one could see the three main lacustrine facies. There were sandstones and siltstones with low angle planar cross-stratification and ripple cross-lamination in each facies along with a layer of calcareous siltstone and mudstone typical examples of shallow seas, showing the effects on the facies by wind and currents on shallow sea deposition.

We moved on to lunch - back where we started Sumburgh head. The sun was shining like the first day! Then on to a high point (and very windy) Ward of Scousburgh, where there were spectacular views of St Ninian's Isle. And the long peninsular of the southern mainland.

We were on the move again and Eat Voe of Quarff. Here I could just stumble through the long grass to a small beach and look at the Basal Breccia. Here there was an example of course breccia- conglomerate and the unconformity with the underlying Quarff Nappe Metasediments. The composition of the breccia showed very course and angular clasts cutting into the Quarff Nappe. There was also mica and the rocks had a "high twinkle factor" (a technical term used by geophysicists including learned persons within our group)

We were approaching the end of last day and what better Allen thought, than to take us to the rubbish tip - ("was he trying to tell us something - I ask?"). He assured us there was a classic example of a conglomerate of alluvial fan and sand dykes just to the left of the scrap yard and along the shoreline. We tramped through the long grass to the shoreline (a mere 200 yards - be warned the Shetland yard is in fact A cubits long) So we had struggle all this way just to see this - a great example of a conglomerate with sand dykes, thought to have been emplaced by gas pressure along the faults and joints of the con- glomerate. So as we struggled by the scrap yard and the rubbish tip in the long grass back to the mini-bus we had a final memorable view of our week in Shetland.

And so our week in Shetland had finished. It had been a fascinating week and complex. So much had happened amongst these wonderful Islands. The geology had one stop and think - many times. The geological upheaval that had occurred over the past 700 + million years had left a puzzle that had seemed incredible to decipher.

Thanks Allen.

All was not finished, as Sue Hay and I were to find out. Sue and myself had celebrated our respective birthdays this past week and the group were not going to let us forget this ageing process. In the common room that evening, at our hall of residence, we had a surprise birthday cake - complete with candles (scurrying at the supermarket - all explained!). Thanks to all of you! Thanks to meeting old friends and new. Another great OUGS week.

Thanks Sue!

Ps. On the next day Gerry and I went for a ride around before catching the ferry. Looking for a place to eat our lunch we decided to drive down to the headland by the rubbish tip (wonderful place) anyway by the side of the road in a cutting there was a classic example of a conglomerate - without having to stomp across a field. I know now that part of this trip was Allen's way of keeping us fit. Shame I didn't take a photo of it!

Les Richmond

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A Novice Eye View of a Trip to Harwich and Wrabness, Essex

7 October 2006

My second field trip with the East Anglian and London Branches of OUGS was as informative and welcoming as was the first (Purfleet - September). We met at Wrabness rail station, Essex, on a glorious Saturday afternoon. There was quite a crowd - about twenty of us, including the leaders Bill George and Graham Ward.

We started by visiting All Saints Church - Wrabness; this church was built in Norman times out of Harwich Cement Stone, possibly collected from the local beach. The Church font is made out of two large septarian nodules - possibly from the Oxford Clay. Parkers Roman Cement was patented in 1796 - for more accurate details on this and the rest of the locale Bill George has written some comprehensive pamphlets (contact Di Clements for details).

Private Collection Peter Collins - Wrabness

We were then privy to look at private collections - to touch and see an exquisite gold coin - a 'cursing half noble' - beautiful galleon on one side and floral design on the reverse - found previously on the beach. Peter Collins, an OU member with a beach hut at Wrabness, showed us a reconstructed lower jaw and teeth from a 35 year old, juvenile Straight Tusked Elephant (Palaeoloxodon antiquus) that he had found. This impressed me as such a labour of love as tiny fragments of fossilised bone were found over the period of three years from Wrabness beach - the erosion here being immense - some 10m in the last twenty years.

This leads me to one of the main themes of the day - the appearance of 'foreign' erratic stones a number of examples were shown from collections and then others found subsequently on the beach; tourmaline quartz (Devon &: Cornwall), rhyolitic pyroclastic stone and schist probably from North Wales - Snowdonia most likely. The examples seen were well worn and most likely transported by the head waters of the River Severn and the 'ancient' Thames as they carved their ways through an old course of drainage from North Wales via St Albans, Chelmsford, Colchester and then to the current location of the River Stour - this was said to be pre-Anglian and pre-glacial. There was Hertfordshire pud- ding stone - like material from Hemel Hempstead - pebbles strongly cemented in a sand matrix - probably originally Woolwich and Reading beds formed into a silcrete hardpan under alternating wet/arid conditions; possibly monsoon- type rains - causing a migration of silica. Like sarsen but with pebbles in it. These large oddments were probably from the Kesgrave gravel beds - all a mystery and not only to me!

We continued our circular walk from the church to the beach at Wrabness, where we came to what was the highlight of the day, the cliff exposures. On the face of the 10/20 metre cliffs in the London clay there were a number of pale yellowish bands a few cm thick. These bands were remarkably regular, there are apparently 34 bands identified. Records show that these bands have been accurately drawn by ob- servers since 1708 - but they were only identified as volcanic ash bands in 1971. Shards of molten glass were found in the ash samples leading to this interpretation. Calculations have been made that each 30cm equates to approximately 5000 years between bands, the bands show that there were an- aerobic conditions in the sequence with no 'bioturbation'. This is one of the best areas to see such a sequence of massive volcanic action of this age in Britain. Some discussion ensued as to which volcanoes were responsible for these ash bands - possibly the tail end of the Scottish volcanoes, or French volcanoes but the interpretation I most liked was the possibility of it being the opening of the Atlantic Ocean - almost beyond my comprehension.

A number of small finds on the beach included a flint handaxe, found by John Jarvis, a pointed flake, found by Jan Blatchford, pieces of bone, sponge fossils and a part echinoid. The finds did not finish here as we moved from Wrabness towards the mouths of the Stour/Orwell rivers to the Low Light-house in Harwich. Here we were shown a lovely collection of pristine sharks teeth, fish vertebrae, decorated clay pipes and turtle bone fossils - all of which numbering a couple of hundred were found in the course of one year by Bill. Fossils have been collected here since 1690, a beautifully illustrated book was produced with excellent plates. Bill George (via Di) will be able to supply the name - a modern printing is available. Bill told us about Harwich cementstone lumps that we could see on the beach, these start to die out as you look towards the town and river - this has been accounted for possibly by there being a fault. There was a difference in stratigraphy found of a few metres some years ago in the town.

To finish the glorious afternoon, a beach comber's delight, as a number of sharks teeth were found, much to the delight of those lucky souls. This was a fascinating afternoon of sharing of knowledge from the two leaders especially and also from others in the group whose interests varied from geological to archaeological to nature.

Nicky Dunn

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