GEOLOGY
Convenors Guy Moody micro.moody@gmail.com Jim Handley jim.s.handley@gmail.com
The Geology group meets at Bridges Community Centre on the 2nd Wednesday of the month at 2pm-3.30pm.
Click here for Simple Introduction to Chemistry for Geologists
The Geology group meets at Bridges Community Centre on the 2nd Wednesday of the month at 2pm-3.30pm.
Click here for Simple Introduction to Chemistry for Geologists
Planned Meetings and Field Trips 2019
Cribarth Geotrail visit July 10th
Our next field trip is to Cribarth Geotrail in Fforest Fawr Geopark on July 10th. Alan Bowring, Geopark Development Officer, has said that this is probably one of the most interesting parts of the western Brecon Beacons to visit. If the weather is good there are spectacular views along ice-cut valleys, evidence of the area's industrial past, signs of ancient geological movements and much more. You can even see evidence of a valuable mineral called 'rotten stone', but you can't see the stone itself. How can something be rotten and valuable at the same time? Intrigued? Why not come along?
The walk starts from the Craig-y-nos country park where a cafe and toilets are available (as well as all-day parking for a small fee). The first part of the walk involves a stiff climb of about 800 feet up the slopes of Cribarth. Both of us have both done it recently and we will have as many stops as people need for tired legs or lungs. The rest of the walk is reasonably flat although the ground is uneven and we do traverse some scree slopes at times. We would advise bringing at least one walking pole and wearing good stout boots or shoes. Otherwise just dress according to the weather forecast.
We are suggesting a 9:30 a.m. start from the free car park by the skate park in Monmouth. The driving time to the start is about an hour and a quarter so we will have time for a short stay at the country park before we set off up the mountain. All being well we will be back at the country park by about 3 pm. Do bring a packed lunch and something to drink and we will find a suitable spot for a picnic.
Please let us Guy know if you would like to come on this trip so that we can organise car-sharing, if necessary.
Extra Group meeting on Wednesday 21st August
In our email of 22nd May we suggested having an extra informal meeting at Bridges to share ideas on how we take our geology group forward. Do please have a look back at that earlier email. Having checked with Bridges we suggesting meeting at 2.00pm on Wednesday 21st August. Of course not everyone will be able to make that date but hopefully quite a lot of you can pop in for a cuppa and to bring your suggestions.
Cribarth Geotrail visit July 10th
Our next field trip is to Cribarth Geotrail in Fforest Fawr Geopark on July 10th. Alan Bowring, Geopark Development Officer, has said that this is probably one of the most interesting parts of the western Brecon Beacons to visit. If the weather is good there are spectacular views along ice-cut valleys, evidence of the area's industrial past, signs of ancient geological movements and much more. You can even see evidence of a valuable mineral called 'rotten stone', but you can't see the stone itself. How can something be rotten and valuable at the same time? Intrigued? Why not come along?
The walk starts from the Craig-y-nos country park where a cafe and toilets are available (as well as all-day parking for a small fee). The first part of the walk involves a stiff climb of about 800 feet up the slopes of Cribarth. Both of us have both done it recently and we will have as many stops as people need for tired legs or lungs. The rest of the walk is reasonably flat although the ground is uneven and we do traverse some scree slopes at times. We would advise bringing at least one walking pole and wearing good stout boots or shoes. Otherwise just dress according to the weather forecast.
We are suggesting a 9:30 a.m. start from the free car park by the skate park in Monmouth. The driving time to the start is about an hour and a quarter so we will have time for a short stay at the country park before we set off up the mountain. All being well we will be back at the country park by about 3 pm. Do bring a packed lunch and something to drink and we will find a suitable spot for a picnic.
Please let us Guy know if you would like to come on this trip so that we can organise car-sharing, if necessary.
Extra Group meeting on Wednesday 21st August
In our email of 22nd May we suggested having an extra informal meeting at Bridges to share ideas on how we take our geology group forward. Do please have a look back at that earlier email. Having checked with Bridges we suggesting meeting at 2.00pm on Wednesday 21st August. Of course not everyone will be able to make that date but hopefully quite a lot of you can pop in for a cuppa and to bring your suggestions.
Previous Meetings and Field Trips 2019
Aust Cliff Visit – 12. 06. 19.
16 members visited the Severn shoreline below the M48 bridge. The range of features seen and discussed included:
A great location to visit. Jim Handley
Aust Cliff Visit – 12. 06. 19.
16 members visited the Severn shoreline below the M48 bridge. The range of features seen and discussed included:
- The unconformity between the Black Rock carboniferous on which the bridge stands and the adjacent Mercia Mudstone of late Triassic age – perhaps 150m years apart.
- The well defined cliff line of red mudstone, then grey green Blue Anchor, followed by projecting light grey blocks of Penarth limestone. Above comes the famous Bone beds in the Westbury Formation, before the early Jurassic light brown limestone/mudstone Blue Lias. The cliff is part of a gentle anticline and near the bridge end was a clear normal fault with a down throw of about 4 feet.
- Evaporites seen were mainly of both horizontal and vertical aligned Gypsum. We did find some limestone with a display of small selenite crystals.
- Limestone beds with considerable shell fossils were easily seen on the beach. Two examples of apparent plant stem in limestone were also seen and we did find a small but beautifully lined black tooth.
- A deposit of actively growing tufa was spotted.
A great location to visit. Jim Handley
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At our meeting on 10th April, Alan Gray from Malvern U3A spoke on "The Canary Islands -- an example of oceanic hot spots.” Alan has recently led a group [including my wife and I] from Malvern on a week’s field work on Fuerteventura.
The earlier part of his talk explained:
March 13th Magma chambers and volcanoes, ancient and modern Richard Edwards
On Wednesday 13th March the geology group was lucky to have Richard Edwards one-time lecturer at Cambourne School of Mines and more latterly a founder member of the Malvern U3A geology group address us on the topic of “Magma chambers and volcanoes, ancient and modern”. Monmouth Geology Group was very please to welcome visitors from three surrounding U3As, Hereford, Ross-on-Wye and Usk.
The talk was one which he had previously used with particular reference to the geology of Malvern. Richard also admitted, that having been at a meeting that morning in which some very recent research on volcanoes had been presented, he was going to have to update his talk as he went along!
The talk started with an introduction into plate tectonics and the idea of island arcs as illustrated by the Japanese archipelago. We then dipped back in time to 542 – 635 when the ancient supercontinent of Gondwana existed. This allowed Richard to locate Malvern on the Avalonian Terrace where ancient faulting activity had brought Pre-Cambrian rocks to the surface.
This was followed by a discussion of the nature of lava and its components, a melt phase, a crystalline phase and a gas phase. New research has revealed that the magma chamber is not really in a liquid state as previously believed but a ‘mush’ of crystals with a relatively small proportion of melted material. It has become clear that the key processes in a magma chamber are partial melting and fractional crystallization which then determines the type of rock created.
Once the principles of volcanology were established Richard then went on to describe the detailed geology of the Malvern area and the different rock types and their constituent parts. He was also able to draw comparisons between the active volcanic geology in Japan with the deposits found in the Malvern Hills including examples of pyroclastic flows and pillow lava.
Finally, Richard drew our attention to the very active volcanic state of Japan and the distribution of nuclear power plants, which probably made most of us think moving to Japan was not a great idea. Guy Moody
January 9th 2019 Climate, past present and future. Keith Moseley
For its first meeting of 2019 the geology group welcomed one-time Head of Geology at Monmouth Boys School, Keith Moseley. His topic of climate, past, present and future was very wide ranging. Keith described the Earth from its foundation to the present day and the geological factors like plate tectonics and to the seeming impossible snowball earth that have shaped the World it. Over geological times the earth’s temperature has fluctuated greatly under the influence of events like long term vulcanism. Generally, the biosphere has been able to react to these changes because they have happened over such long timescales. The warning for the future is that human-led climate change is happening at a rate that is many times faster that has occurred naturally. It doesn’t mean life on Earth will disappear but it may change it very radically unless something can be done to reduce carbon emissions. Guy Moody
13th February 2019 Dating the Age of the Earth Cherry Lewis
In 1650 James Ussher, the Archbishop of Armagh, calculated using the ages of people mentioned in the Bible that God had created the world in 4004BC. For 2 centuries this was the perceived truth but then Charles Darwin [originally a geologist] and others argued that an age in millions of years must be involved both for geological processes and for the evolution of life.
Subsequently Lord Kelvin, working on the rate of cooling within the earth, suggested an age between 20 and 400 million years but then revised this to 100 m.
Only with the discovery of radioactive decay by Rutherford and work by others on the decay of one element into another e.g. from uranium to lead was a research tool available to give accurate calculations on what the age of the earth [and solar system] was. This was finally determined to be 4.5 billion years.
The remainder of Cherry’s talk focused on the lifetime work of Arthur Holmes both within this dating of the earth’s age and in establishing and publicising the principles of physical geography. His book on the latter was a key text for students for several decades.
For anyone wanting to know more about the substantial input of Holmes do track down a copy of Cherry’s book on him entitled ‘The Dating Game’ Jim Handley
The earlier part of his talk explained:
- The significance of the location of the Canary Islands on ocean crust just west of the African tectonic plate.
- The concept of mantle plumes, how these may originate in the mantle/outer core boundary area, and how the one beneath the Canaries not only fed successive island and sea mount growth, but also contributed to later activity such as cinder cones and fissure eruptions on various islands.
- The broad alignment of the islands from SW to NE, which also identifies the age range from El Hierro the youngest island at 1.2 m years in the west to Fuerteventura the oldest at 20m years in the east.
- How Fuerteventura and Lanzarote were linked when sea levels were lower.
- The physics within the plumes and associated magma chambers of various formats at different levels and how the range of minerals crystallize out at different temperatures. This produces a range of igneous rocks some extrusive i.e. erupted via volcanoes or cinder cones, or others intrusive i.e. cooled within the lithosphere into plutons. Whilst the chemistry can be similar, the resultant rock can be considerably different.
- The development of the original 3 shield volcanoes.
- The extensive key role erosion has played in reducing those volcanoes by 2/3 kilometres leaving a circular pattern of sharp- edged ridges [or cuchillos] gently dipping seaward from the centre of the volcano. Also spreading radially are the berrancas, or steep sided incised river valleys, now normally dry but evidence of wetter times in the past and flash floods now.
- How offshore winds from the Sahara have blown extensive silica grains and small calcium fragments to generate large beaches and sand dunes.
- The puzzle of how Sanctuary Mt. comprised of plutonic fine-grained trachyte with decorative leisegang rings has been lifted into its current position.
- The extensive dyke fields, possibly related to an extensional feature generated by major mass wastage into the sea. Other examples of major landslides probably generating tsunamis both here and on other islands.
- An impressive sea arch where the sides are formed from lava dykes but the top is a hard layer of calcium bonded sandstone.
- The existence on a lava beach of fossilised marine molluscs about 100,000 years old. They needed a mixture of sea and fresh water, which implies a different climate then.
- Examples of stripped ocean floor deposits now mixed with lava flows and dykes. How?
March 13th Magma chambers and volcanoes, ancient and modern Richard Edwards
On Wednesday 13th March the geology group was lucky to have Richard Edwards one-time lecturer at Cambourne School of Mines and more latterly a founder member of the Malvern U3A geology group address us on the topic of “Magma chambers and volcanoes, ancient and modern”. Monmouth Geology Group was very please to welcome visitors from three surrounding U3As, Hereford, Ross-on-Wye and Usk.
The talk was one which he had previously used with particular reference to the geology of Malvern. Richard also admitted, that having been at a meeting that morning in which some very recent research on volcanoes had been presented, he was going to have to update his talk as he went along!
The talk started with an introduction into plate tectonics and the idea of island arcs as illustrated by the Japanese archipelago. We then dipped back in time to 542 – 635 when the ancient supercontinent of Gondwana existed. This allowed Richard to locate Malvern on the Avalonian Terrace where ancient faulting activity had brought Pre-Cambrian rocks to the surface.
This was followed by a discussion of the nature of lava and its components, a melt phase, a crystalline phase and a gas phase. New research has revealed that the magma chamber is not really in a liquid state as previously believed but a ‘mush’ of crystals with a relatively small proportion of melted material. It has become clear that the key processes in a magma chamber are partial melting and fractional crystallization which then determines the type of rock created.
Once the principles of volcanology were established Richard then went on to describe the detailed geology of the Malvern area and the different rock types and their constituent parts. He was also able to draw comparisons between the active volcanic geology in Japan with the deposits found in the Malvern Hills including examples of pyroclastic flows and pillow lava.
Finally, Richard drew our attention to the very active volcanic state of Japan and the distribution of nuclear power plants, which probably made most of us think moving to Japan was not a great idea. Guy Moody
January 9th 2019 Climate, past present and future. Keith Moseley
For its first meeting of 2019 the geology group welcomed one-time Head of Geology at Monmouth Boys School, Keith Moseley. His topic of climate, past, present and future was very wide ranging. Keith described the Earth from its foundation to the present day and the geological factors like plate tectonics and to the seeming impossible snowball earth that have shaped the World it. Over geological times the earth’s temperature has fluctuated greatly under the influence of events like long term vulcanism. Generally, the biosphere has been able to react to these changes because they have happened over such long timescales. The warning for the future is that human-led climate change is happening at a rate that is many times faster that has occurred naturally. It doesn’t mean life on Earth will disappear but it may change it very radically unless something can be done to reduce carbon emissions. Guy Moody
13th February 2019 Dating the Age of the Earth Cherry Lewis
In 1650 James Ussher, the Archbishop of Armagh, calculated using the ages of people mentioned in the Bible that God had created the world in 4004BC. For 2 centuries this was the perceived truth but then Charles Darwin [originally a geologist] and others argued that an age in millions of years must be involved both for geological processes and for the evolution of life.
Subsequently Lord Kelvin, working on the rate of cooling within the earth, suggested an age between 20 and 400 million years but then revised this to 100 m.
Only with the discovery of radioactive decay by Rutherford and work by others on the decay of one element into another e.g. from uranium to lead was a research tool available to give accurate calculations on what the age of the earth [and solar system] was. This was finally determined to be 4.5 billion years.
The remainder of Cherry’s talk focused on the lifetime work of Arthur Holmes both within this dating of the earth’s age and in establishing and publicising the principles of physical geography. His book on the latter was a key text for students for several decades.
For anyone wanting to know more about the substantial input of Holmes do track down a copy of Cherry’s book on him entitled ‘The Dating Game’ Jim Handley
2018
November 14th. Silver mining and mineralisation in Wales Tom Cotterell
A very large audience was present on November 14thwhen Tom Cotterell, the minerals curator at the National Museum of Wales, described the history of silver mining in Wales. Silver is only the 68thmost common element in the earth’s crust and rarely exists in elemental form. It is almost always a by-product of lead smelting. Silver is often found in a form of a tetrahedrite called freibergite which can contain up to 18% silver. Generally, however silver is found in very small quantities for example in Cardiganshire historically the yield was about 10 ounces per ton of mined material although Sir Hugh Middleton (see below) had a mine that yielded 100 oz per ton.
The major growth of silver mining in Wales occurred in Elizabethan times in Cardiganshire. Elizabeth 1st, seeking to encourage the exploration of silver to fill her coffers, invited German mining engineers to Wales and Cardiganshire in particular. She also formed the Society of Mines Royal to oversee the exploration. During and after her reign silver mining in Wales was very successful and indeed at one time there was a mint in Aberystwyth to prevent the silver being stolen on its way to the mint in London. The roads then being almost non-existent.
Silver certainly was for a time a very lucrative commodity. Sir Hugh Middleton at one time late in the 16thcentury had a clear profit of £2000 a month. He used his vast wealth to supply freshwater to London, an enterprise that bankrupted him, although the watercourse he created exists to this day.
Some of the mining approaches that Tom described were truly horrific. Horizontal adits were driven under silver bearing deposits with a view to draining them of water. How this was achieved without the drowning of the miners was a mystery. Many of the mines were complex and Tom was able to show us some very early documents that described the mines and their structures in quite a lot of detail. This was a very interesting talk about a subject many of us must have known little about.
October 10th. David Mushet – The Forest of Dean’s first geologist Speaker: Cherry Lewis
David Mushet is a name many of us may know in relation to his work as an industrialist in the iron and steel industry in the early 1800s. He made significant contributions to blast furnace technology and spent much of his life as an experimental metallurgist. What we may not know is his more general interest in geology particularly in the Forest of Dean and his contacts within the burgeoning field of geology in the early nineteenth century. This is the story that Chery Lewis set out to tell us at the October meeting of the geology group.
In the early nineteenth century one of the pioneer geologists was William Smith who through his work on land surveying realised that rocks were often laid down in strata and that fossils could be used to identify the same rocks in different localities. He was to publish, in 1815, the first geological map of England and Wales. He met up with the Duke of Bedford’s land agent John Farey and together they went on several geological excursions during which it seems likely Smith explained to Farey his analytical methods. Farey in turn became acquainted with John Mushet when Farey undertook a survey of the county of Derbyshire “in order to evaluate minutely its Stratification and Mineral Treasures”. John Mushet was a recommended mineral specialist and the two formed a close friendship.
It is clear by 1808 when Mushet moved to the Forest of Dean that he was considered both an expert in geology and industrial technology. His reason for moving to the Forest of Dean was to try and enhance the output of an iron mine (Whitecliff) owned by Thomas Halford.
Not long after Mushet moved to the Forest he was visited by John Farey and they spent time together investigating the geology of the forest and it was at this time that Mushet started to prepare geological sections of the rock sequences in the forest.
The sections that David Mushet went on to produce are some of the most remarkable creations you are likely to see. Cherry described how she was alerted to ‘something of interest’ in a local sale and decided to buy what her research eventually established to be an 11-foot vertical section produced about 1812. Cherry was able to display this section for us which is beautiful both in its overall construction but also in the impeccable hand writing that is used on it. Through her research Cherry was able to identify several other sections made by David Mushet using her gift of ‘serendipity’ a she called it but which I interpret as a synonym for a lot of hard work.
There is much more that can be told about David Mushet’s life, the business failures and troubles with his family and the mystery of how he came to be in Monmouth when he died but in spite of all those travails he has left a remarkable geological legacy.
November 14th. Silver mining and mineralisation in Wales Tom Cotterell
A very large audience was present on November 14thwhen Tom Cotterell, the minerals curator at the National Museum of Wales, described the history of silver mining in Wales. Silver is only the 68thmost common element in the earth’s crust and rarely exists in elemental form. It is almost always a by-product of lead smelting. Silver is often found in a form of a tetrahedrite called freibergite which can contain up to 18% silver. Generally, however silver is found in very small quantities for example in Cardiganshire historically the yield was about 10 ounces per ton of mined material although Sir Hugh Middleton (see below) had a mine that yielded 100 oz per ton.
The major growth of silver mining in Wales occurred in Elizabethan times in Cardiganshire. Elizabeth 1st, seeking to encourage the exploration of silver to fill her coffers, invited German mining engineers to Wales and Cardiganshire in particular. She also formed the Society of Mines Royal to oversee the exploration. During and after her reign silver mining in Wales was very successful and indeed at one time there was a mint in Aberystwyth to prevent the silver being stolen on its way to the mint in London. The roads then being almost non-existent.
Silver certainly was for a time a very lucrative commodity. Sir Hugh Middleton at one time late in the 16thcentury had a clear profit of £2000 a month. He used his vast wealth to supply freshwater to London, an enterprise that bankrupted him, although the watercourse he created exists to this day.
Some of the mining approaches that Tom described were truly horrific. Horizontal adits were driven under silver bearing deposits with a view to draining them of water. How this was achieved without the drowning of the miners was a mystery. Many of the mines were complex and Tom was able to show us some very early documents that described the mines and their structures in quite a lot of detail. This was a very interesting talk about a subject many of us must have known little about.
October 10th. David Mushet – The Forest of Dean’s first geologist Speaker: Cherry Lewis
David Mushet is a name many of us may know in relation to his work as an industrialist in the iron and steel industry in the early 1800s. He made significant contributions to blast furnace technology and spent much of his life as an experimental metallurgist. What we may not know is his more general interest in geology particularly in the Forest of Dean and his contacts within the burgeoning field of geology in the early nineteenth century. This is the story that Chery Lewis set out to tell us at the October meeting of the geology group.
In the early nineteenth century one of the pioneer geologists was William Smith who through his work on land surveying realised that rocks were often laid down in strata and that fossils could be used to identify the same rocks in different localities. He was to publish, in 1815, the first geological map of England and Wales. He met up with the Duke of Bedford’s land agent John Farey and together they went on several geological excursions during which it seems likely Smith explained to Farey his analytical methods. Farey in turn became acquainted with John Mushet when Farey undertook a survey of the county of Derbyshire “in order to evaluate minutely its Stratification and Mineral Treasures”. John Mushet was a recommended mineral specialist and the two formed a close friendship.
It is clear by 1808 when Mushet moved to the Forest of Dean that he was considered both an expert in geology and industrial technology. His reason for moving to the Forest of Dean was to try and enhance the output of an iron mine (Whitecliff) owned by Thomas Halford.
Not long after Mushet moved to the Forest he was visited by John Farey and they spent time together investigating the geology of the forest and it was at this time that Mushet started to prepare geological sections of the rock sequences in the forest.
The sections that David Mushet went on to produce are some of the most remarkable creations you are likely to see. Cherry described how she was alerted to ‘something of interest’ in a local sale and decided to buy what her research eventually established to be an 11-foot vertical section produced about 1812. Cherry was able to display this section for us which is beautiful both in its overall construction but also in the impeccable hand writing that is used on it. Through her research Cherry was able to identify several other sections made by David Mushet using her gift of ‘serendipity’ a she called it but which I interpret as a synonym for a lot of hard work.
There is much more that can be told about David Mushet’s life, the business failures and troubles with his family and the mystery of how he came to be in Monmouth when he died but in spite of all those travails he has left a remarkable geological legacy.
12thSeptember 2018
On a pleasant Autumn morning 14 members of the geology group met in Ross to follow parts of the ‘Explore Ross-on-Wye’ leaflet produced by the Herefordshire and Worcestershire Earth Heritage Trust. We were led by Pater Hancock from the Ross U3A who proved to have a great wealth of knowledge and expertise.
Our first stop was to examine (from a safe distance) the Brownstone (Lower Devonian c400 million years old) river cliffs adjacent to the road into Ross. Peter had us try and imagine what meteorological conditions had been present when the rocks were laid down. The reddish colour of the rocks implies a hot well oxygenated environment very different from what we are used to today. The layering and the cross-bedding told us that the rocks were probably laid down by vast water ways in a desert environment to account for the layers, the different slops of the cross-bedding and the different particle size. What we see are the remains of a huge area of ‘old red sandstone’ that stretched for thousands of miles of great thickness now largely eroded away.
A little further on into Ross we stopped in Eddie Cross Street and looked down towards the Rudhall Brook where Peter tried to get us to visualise the flow of a former meander of the River Wye as it stretched behind Penyard Hill. Also, at this spot we were able to look more closely at a wall faced with Brownstone which included examples of calcrete and a ‘dimpled’ rock face where softer pellets of mud, initially captured when the rock was laid down, have eroded away more quickly than the parent rock.
We then walked through the churchyard of St Mary’s Church to look at the church which is partly built from Tintern Sandstone, a rather drab rock compared with the Brownstone. Even so it still shows many of the same features as the Brownstone, but with many small gritty inclusions implying quite a rapid water flow rate.
After this we went into the public park over the cliffs we stood under previously, to get a wide view over the Wye, before walking down to the river to look at the ancient river terrace on which the castle stands before going back to our cars.
On a pleasant Autumn morning 14 members of the geology group met in Ross to follow parts of the ‘Explore Ross-on-Wye’ leaflet produced by the Herefordshire and Worcestershire Earth Heritage Trust. We were led by Pater Hancock from the Ross U3A who proved to have a great wealth of knowledge and expertise.
Our first stop was to examine (from a safe distance) the Brownstone (Lower Devonian c400 million years old) river cliffs adjacent to the road into Ross. Peter had us try and imagine what meteorological conditions had been present when the rocks were laid down. The reddish colour of the rocks implies a hot well oxygenated environment very different from what we are used to today. The layering and the cross-bedding told us that the rocks were probably laid down by vast water ways in a desert environment to account for the layers, the different slops of the cross-bedding and the different particle size. What we see are the remains of a huge area of ‘old red sandstone’ that stretched for thousands of miles of great thickness now largely eroded away.
A little further on into Ross we stopped in Eddie Cross Street and looked down towards the Rudhall Brook where Peter tried to get us to visualise the flow of a former meander of the River Wye as it stretched behind Penyard Hill. Also, at this spot we were able to look more closely at a wall faced with Brownstone which included examples of calcrete and a ‘dimpled’ rock face where softer pellets of mud, initially captured when the rock was laid down, have eroded away more quickly than the parent rock.
We then walked through the churchyard of St Mary’s Church to look at the church which is partly built from Tintern Sandstone, a rather drab rock compared with the Brownstone. Even so it still shows many of the same features as the Brownstone, but with many small gritty inclusions implying quite a rapid water flow rate.
After this we went into the public park over the cliffs we stood under previously, to get a wide view over the Wye, before walking down to the river to look at the ancient river terrace on which the castle stands before going back to our cars.
Fieldtrip to Craig Cerrig Gleisiad
5th August 2018
Leader Dilys Harlow
5th August 2018
Leader Dilys Harlow
11th July 2018 Forest of Dean Visit
Our trip was as much about mining history as geology. Fourteen of us started by taking the underground tour of Hopewell Colliery. With excellent guides, we had a remarkable insight into the working of a small Forest mine.
Access to the coal face is down a steep incline with a second way out along a half mile long adit cut through sandstone. We were able to see clearly the strata of coal, mudstone and sandstone. www.hopewellcolliery.com
We then went on a mile to Cannop Stone Works and walked up the historically significant Bixslade Valley. At first, walking along the route of the tramroad which served several quarries and coal mines. The tramway began working in 1812 and closed in 1950 with horse drawn trams for all of this time. Many of the sandstone blocks are still in place. Beyond the Stone Works, the minerals were loaded onto the Severn and Wye Railway, originally also horse drawn but converted to steam in 1868.
After half a mile we reached Mine Train Quarry, currently worked by John Tainton and producing good quality pennant sandstone blocks at around 1000 tonnes per annum. In the Forest of Dean basin, the coal and sandstone are in the heart of the Forest with underlying iron ore and limestone outcropping around the boundary. Very unusually at Mine Train, there is a seam of iron ore (extending northwards) in the centre of the quarry and we were able to see the entrance. Inside the ore was worked by a series of jointed shafts and tunnels.
Across the track from the quarry is the overgrown entrance to the adit known as Lower Bixslade Level, accessing one of the many narrow coal seams. A little further up the track, a similar adit accesses the seam above. The Bixslade levels were worked by David Mushet who was such an important character in the mining history of the Dean and will be the subject of a future Group meeting.
Within such a short distance there is so much of interest. A few yards back down the valley is the shaft of Union Pit and its memorial to the four miners killed in 1902 by an inrush of water from the adjoining mine. It was in fact the largest single loss of life in the Dean Coalfield. There were a very large number of fatalities but in ones and twos. Unlike the South Wales coalfield and other in the UK, there is no methane gas in the workings and consequently it has been spared the terrible gas explosions such as at Senghenydd and Gresford.
A little further along is the small colliery Monument mine still producing house coal. This too has an adit access and tramway extending several hundred yards into the hill.
The Forest of Dean Local History Society have published a leaflet on a circular walk, including all the sites we visited in the Valley plus the remainder of the tramway and returning via Cannop Ponds which were constructed in the 1820’s to provide water power for the Parkend Ironworks 2 miles away. The water in the leat turned the largest water wheel on mainland Britain. Incidentally, all of the lakes in the Forest are man made. The link for the leaflet is www.forestofdeanhistory.org.uk and click on heritage and trails and walks.
The coal mines we looked at are of the type worked for centuries in the Dean. However they were constrained by the high water table. In the 20thcentury much larger mines with pumps were sunk to work the deeper seams. The main four were Northern United, Eastern, Princess Royal and Cannop, together employing over 5000 men. The last Northern closed in 1965.
We then finished a day of fine weather with a picnic at Wenchford. Richard Davies
Our trip was as much about mining history as geology. Fourteen of us started by taking the underground tour of Hopewell Colliery. With excellent guides, we had a remarkable insight into the working of a small Forest mine.
Access to the coal face is down a steep incline with a second way out along a half mile long adit cut through sandstone. We were able to see clearly the strata of coal, mudstone and sandstone. www.hopewellcolliery.com
We then went on a mile to Cannop Stone Works and walked up the historically significant Bixslade Valley. At first, walking along the route of the tramroad which served several quarries and coal mines. The tramway began working in 1812 and closed in 1950 with horse drawn trams for all of this time. Many of the sandstone blocks are still in place. Beyond the Stone Works, the minerals were loaded onto the Severn and Wye Railway, originally also horse drawn but converted to steam in 1868.
After half a mile we reached Mine Train Quarry, currently worked by John Tainton and producing good quality pennant sandstone blocks at around 1000 tonnes per annum. In the Forest of Dean basin, the coal and sandstone are in the heart of the Forest with underlying iron ore and limestone outcropping around the boundary. Very unusually at Mine Train, there is a seam of iron ore (extending northwards) in the centre of the quarry and we were able to see the entrance. Inside the ore was worked by a series of jointed shafts and tunnels.
Across the track from the quarry is the overgrown entrance to the adit known as Lower Bixslade Level, accessing one of the many narrow coal seams. A little further up the track, a similar adit accesses the seam above. The Bixslade levels were worked by David Mushet who was such an important character in the mining history of the Dean and will be the subject of a future Group meeting.
Within such a short distance there is so much of interest. A few yards back down the valley is the shaft of Union Pit and its memorial to the four miners killed in 1902 by an inrush of water from the adjoining mine. It was in fact the largest single loss of life in the Dean Coalfield. There were a very large number of fatalities but in ones and twos. Unlike the South Wales coalfield and other in the UK, there is no methane gas in the workings and consequently it has been spared the terrible gas explosions such as at Senghenydd and Gresford.
A little further along is the small colliery Monument mine still producing house coal. This too has an adit access and tramway extending several hundred yards into the hill.
The Forest of Dean Local History Society have published a leaflet on a circular walk, including all the sites we visited in the Valley plus the remainder of the tramway and returning via Cannop Ponds which were constructed in the 1820’s to provide water power for the Parkend Ironworks 2 miles away. The water in the leat turned the largest water wheel on mainland Britain. Incidentally, all of the lakes in the Forest are man made. The link for the leaflet is www.forestofdeanhistory.org.uk and click on heritage and trails and walks.
The coal mines we looked at are of the type worked for centuries in the Dean. However they were constrained by the high water table. In the 20thcentury much larger mines with pumps were sunk to work the deeper seams. The main four were Northern United, Eastern, Princess Royal and Cannop, together employing over 5000 men. The last Northern closed in 1965.
We then finished a day of fine weather with a picnic at Wenchford. Richard Davies
May 10th
On 10th May members of the Monmouth U3A Geology Group visited the Clydach Gorge roadworks on the A465 ‘Heads of the Valleys’ road. This was an unusual field trip for the group. Instead of studying rocks the visit gave a perspective of how the geology of the area affected this major road widening scheme.
The Public Liaison Officer for the project, Jeff Mapps, gave a fascinating presentation outlining the scope of the project. A simulated fly-through of the completed road was followed by descriptions of some of the major engineering challenges. Time lapse video of the assembly of bridges was particularly interesting, the 1300 ton crane making light work of moving prefabricated sections of bridge into precise locations.
The geological content of the presentation was astonishing. Over the first four years the construction team have shifted 1.3 million cubic meters of soil and rock, installed 8500 nails to anchor the rock in steep-sided cuttings, and covered over 4000 square meters of old mine workings at Brynmawr. Once removed, local rock and topsoil have been stored in a dedicated part of the site and re-used, reducing the carbon footprint of the works. At peak times the team is using up to 1000 tons of locally-sourced rock every week for road foundations.
The trip concluded with a minibus ride along the road. It was interesting to see that the concrete abutments had been faced with stone from the immediate locality, ensuring a good match to other rocks that were visible. Observant drivers will notice that the colour of the facing stone changes along the 8.1km of road.
The trip was both interesting and entertaining, giving a fascinating insight int the engineering, geological and logistical challenges of this important local project. Phil Charlesworth
On 10th May members of the Monmouth U3A Geology Group visited the Clydach Gorge roadworks on the A465 ‘Heads of the Valleys’ road. This was an unusual field trip for the group. Instead of studying rocks the visit gave a perspective of how the geology of the area affected this major road widening scheme.
The Public Liaison Officer for the project, Jeff Mapps, gave a fascinating presentation outlining the scope of the project. A simulated fly-through of the completed road was followed by descriptions of some of the major engineering challenges. Time lapse video of the assembly of bridges was particularly interesting, the 1300 ton crane making light work of moving prefabricated sections of bridge into precise locations.
The geological content of the presentation was astonishing. Over the first four years the construction team have shifted 1.3 million cubic meters of soil and rock, installed 8500 nails to anchor the rock in steep-sided cuttings, and covered over 4000 square meters of old mine workings at Brynmawr. Once removed, local rock and topsoil have been stored in a dedicated part of the site and re-used, reducing the carbon footprint of the works. At peak times the team is using up to 1000 tons of locally-sourced rock every week for road foundations.
The trip concluded with a minibus ride along the road. It was interesting to see that the concrete abutments had been faced with stone from the immediate locality, ensuring a good match to other rocks that were visible. Observant drivers will notice that the colour of the facing stone changes along the 8.1km of road.
The trip was both interesting and entertaining, giving a fascinating insight int the engineering, geological and logistical challenges of this important local project. Phil Charlesworth
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April 16th
Jim led a small goup of members over a somewhat muddy course starting out at Redbrook and including some stiff climbs and wonderful views. Newland church, otherwise known as the Cathedral of the Forest offered some food for thought. Just how strong did the roof need to be to support the very heavy roof tiles? A building stone question if ever I heard one. Stowfield quarry gave us some spectacular views; looking down from the rim the works vehicles looked tiny (see picture). On the way back the Buckstone (picture) also offered both a great view and some tantalising questions; how did it end up being there and how could such a massive stone be moved? Thanks to Jim for leading us. I think we all felt we had had a good walk by the end of the day. |
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April 11th The Colorado Plateau
Alan Gray, from Malvern, gave the Geology Group a fascinating talk on 11th April. The Colorado Plateau, which is flat, is the size of the British Isles and famous for the Grand Canyon. The Grand Canyon is 277 miles long, up to 14 miles wide and 1 mile deep and no single theory explains how it was formed, as evidence is removed by erosion. Rising in the Rocky Mountains, the Colorado River runs through it, finishing its journey in Mexico, and causing half a millimetre of erosion per year. It is undoubtedly one of the natural wonders of the world and Alan showed beautiful photos of the Canyon, Monument Valley and Bryce Canyon illustrating the extraordinary colours, and breathtaking scale, of this part of the USA. For those who had visited it, many memories were stirred, and for those who have not, it is a very tempting holiday plan.
Alan Gray, from Malvern, gave the Geology Group a fascinating talk on 11th April. The Colorado Plateau, which is flat, is the size of the British Isles and famous for the Grand Canyon. The Grand Canyon is 277 miles long, up to 14 miles wide and 1 mile deep and no single theory explains how it was formed, as evidence is removed by erosion. Rising in the Rocky Mountains, the Colorado River runs through it, finishing its journey in Mexico, and causing half a millimetre of erosion per year. It is undoubtedly one of the natural wonders of the world and Alan showed beautiful photos of the Canyon, Monument Valley and Bryce Canyon illustrating the extraordinary colours, and breathtaking scale, of this part of the USA. For those who had visited it, many memories were stirred, and for those who have not, it is a very tempting holiday plan.
February the Geology Group speaker was Alan Bowring Fforest Fawr Geopark Development Officer. Alan described the origins of the Geopark which is based on the western half of the Brecon Beacons and then took us through the successive geological layers of the last 470 million years that underlie it. We may be able to arrange a walk later in the year otherwise there is the Geopark festival http://www.fforestfawrgeopark.org.uk/geofest-2018 at the end of May.
March Jana Horak the Head of Mineralogy and Petrology at the Natioanl Musueum in Cardiff described some of the major building stones to be found in Wales and more particularly locally. Monmouthshire is badly represented in terms of a building stone directory and it is hoped in the future the group may be able to take on some of this work.
March Jana Horak the Head of Mineralogy and Petrology at the Natioanl Musueum in Cardiff described some of the major building stones to be found in Wales and more particularly locally. Monmouthshire is badly represented in terms of a building stone directory and it is hoped in the future the group may be able to take on some of this work.
January 10th 2018 The Geology Group started off its 2018 season with a first! The Group held a joint meeting with the Ross U3A Geology Group in the Ball Room at the Bridges. Thirty one members from both groups enjoyed a presentation by geologist Dave Green on the geology of Monmouth and its surrounds. The group learned about the many local varieties of stone and geological faults as well as the complexities of the drainage patterns of the Monnow and the Wye rivers caused by the ice age and structural up lift. Dave proved to have an almost encyclopaedic knowledge of local geology and could probably have talked for several hours about our local area."
Previous Meetings and Field Trips 2017
November 8th 2017 was a double header occasioned by the unfortunate illness of the intended speaker. Jim Handley presented first on his exploration of Cornish geology followed by Guy Moody who reported on some museum and other visits he had recently made. Jim Handley gave a presentation on ‘Welcome to Cornwall’ This looked at the impact of the Variscan Orogeny on the rock strata of North Cornwall from Boscastle to Bude.
The impact of 2 continents crashing together over a long period, but centred around late Carboniferous times about 300mya in Britain, is displayed in the major folding of the sandstone and mudstones sedimentary deposits. Various types of folding are displayed in the cliffs eg from amazingly tight examples at Boscastle to chevron zig zags the full height of Millook cliffs [see below] to repeated folds along the cliffs near Bude including periclines.
Jim explained how many of the deposits were originally laid down on a continental shelf They then became unstable and collapsed down into deeper waters as a turbidity current – think underwater avalanches. The resultant turbidite deposits show a classical sequence feature displaying how larger grains were deposited first as coarser sandstones then fining upwards to mudstones. Many cliffs displayed repeated sequences from several turbidite episodes.
Guy Moody described his visits to various establishments under the title ‘A Dinosaur Summer’.
The first visit was to the National Show Caves Centre at Abercrave where the interest was twofold firstly the caves themselves and secondly the dinosaurs which are scattered around the grounds of the centre. The caves are in limestone and show a variety of stalactite formations and some underground waterfalls. The caves are generally accessible and will be considered for a field trip next summer. The dinosaurs are quite spectacular if not all the animals on display are actually dinosaurs, and add to the interest (see photo below). The 2nd visit was to the National Museum Cardiff where an exhibition of juvenile dinosaurs provided an insight into apparent nest building and maternal care by some dinosaur groups.
Finally, Wollaton Hall in Nottingham presented an exhibition of dinosaur fossils from China. This was a very impressive display of quite recent and quite rare feathered dinosaurs from north China and Mongolia. The detail in the feathered forms could leave no doubt that feathers were a common feature of dinosaurs and forces us to think of the evolution of dinosaurs in quite a different light. Guy Moody
November 8th 2017 was a double header occasioned by the unfortunate illness of the intended speaker. Jim Handley presented first on his exploration of Cornish geology followed by Guy Moody who reported on some museum and other visits he had recently made. Jim Handley gave a presentation on ‘Welcome to Cornwall’ This looked at the impact of the Variscan Orogeny on the rock strata of North Cornwall from Boscastle to Bude.
The impact of 2 continents crashing together over a long period, but centred around late Carboniferous times about 300mya in Britain, is displayed in the major folding of the sandstone and mudstones sedimentary deposits. Various types of folding are displayed in the cliffs eg from amazingly tight examples at Boscastle to chevron zig zags the full height of Millook cliffs [see below] to repeated folds along the cliffs near Bude including periclines.
Jim explained how many of the deposits were originally laid down on a continental shelf They then became unstable and collapsed down into deeper waters as a turbidity current – think underwater avalanches. The resultant turbidite deposits show a classical sequence feature displaying how larger grains were deposited first as coarser sandstones then fining upwards to mudstones. Many cliffs displayed repeated sequences from several turbidite episodes.
Guy Moody described his visits to various establishments under the title ‘A Dinosaur Summer’.
The first visit was to the National Show Caves Centre at Abercrave where the interest was twofold firstly the caves themselves and secondly the dinosaurs which are scattered around the grounds of the centre. The caves are in limestone and show a variety of stalactite formations and some underground waterfalls. The caves are generally accessible and will be considered for a field trip next summer. The dinosaurs are quite spectacular if not all the animals on display are actually dinosaurs, and add to the interest (see photo below). The 2nd visit was to the National Museum Cardiff where an exhibition of juvenile dinosaurs provided an insight into apparent nest building and maternal care by some dinosaur groups.
Finally, Wollaton Hall in Nottingham presented an exhibition of dinosaur fossils from China. This was a very impressive display of quite recent and quite rare feathered dinosaurs from north China and Mongolia. The detail in the feathered forms could leave no doubt that feathers were a common feature of dinosaurs and forces us to think of the evolution of dinosaurs in quite a different light. Guy Moody
Millook cliffs
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Gullfoss waterfall From Eurasian plate to American plate
Iceland 13 09 2017 Jim Handley
On the 13th September Jim opened the new season of the U3A geology group talks with a most lavishly illustrated talk about a trip he did to Iceland, that most geologically interesting of islands. It is fair to say he kept the group spellbound for an hour with his dramatic pictures and detailed knowledge.
Jim has kindly provided these notes on his talk.
Much of Iceland is less than 3 million years old. It has grown, and is still growing, as a result of plate tectonics and the effects of a mantle plume beneath it.
The former is where the Eurasian and American plates are moving apart with new lava being deposited between the two. Usually this happens at a mid-ocean ridge, but here it is happening in a dynamic belt across the island. The boundary of the 2 plates is particularly well seen near the site of the ancient Icelandic parliament at Pingvellir. Here stepped faulting occurs on either side of a large lake. Although not accepted by all geologists, most believe additional lava [or associated material] is also brought to the surface of the crust here by an upwelling plume originating in the mantle.
The impact of earthquakes [mainly small but very numerous], volcanoes [think of the impact of Eyjafjallajokull in 2010], and sustained lava flows from long fissures such as Laki in 1783 were illustrated. Iceland being so new geologically and having several large icefields is a classic place to see the impact of erosion whether by ice, water or wind. Thus glacial moraines, wind carved ash deposits and the impact of devastating floods are much in evidence.
Finally Jim used Heimey as a case study of the effects of living in such an active area. This is a small island in the Westmann group. It had 4000 residents when in 1973 a fissure opened up on the edge of town in the middle of the night. Everyone was safely evacuated by the resident fishing fleet. By the time the eruptions ceased after 6 months, the island was 2km larger, but 400 houses were buried under lava. The remainder had ash deposits to clear. The lava flow stopped [or was stopped by a massive use of water jets] just short of blocking the access to the harbour. A stunning place to visit with its lava flows and tunnel, the cone still with small fumaroles, and the new museum centred on the ruins of a house dug out of the ash.
Field Trips
31st May 2017 – led by Jim Handley
On our first fieldtrip of 2017 we walked on and studied the geomap created on the site of New fancy colliery south of Speech House. In natural stone this shows the outcropping rocks of the Forest of Dean and all the main past coal mines, quarries and iron mines. From it we could recognise the FoD syncline with the crumpling impact of the Variscon Orogeny.
We moved on to follow part of the Soudley Valley Geology Trail. In about half a mile we could identitify 6 rocks – the Devonian Brownstones, Conglomerates and Tintern sandstones and the newer Carboniferous Lower Limestone shales, Lower Dolomite and Crease Limestones. Lessons learnt included the cause of the steep dip of this eastern margin, unconformities between deposits and differences between terrestrial and marine deposits. Around us were remains of the extraction and usage of nature’s raw materials.
The geomap and trail leaflets were handed out, an extract of the local geology map, and a cross-section of the FoD geology.
June 28th 2017 led by Guy Moody
Geology trip to Hereford - Although the weather forecast was not very good we nevertheless set out for Hereford with hope for a dry day. We met first at the cathedral and followed the building stones trail produced by the Herefordshire and Worcestershire Earth Heritage Trust. The majority of the cathedral is built of old red stone with much of the internal structure originally covered in plaster. For the most part the plaster has now been removed but the mason’s marks on the columns remain. The trail covers a number of tombs and monuments which gave us an opportunity to see a variety of marbles and limestones. The recent monument to the SAS with its memorable blue syenite, a variety of granite that lacks quartz, provided a memorable end to the cathedral tour.
After lunch, with the weather still holding good, we set out to follow the Hereford City Centre walk again published by the Herefordshire and Worcestershire Earth Heritage Trust. Just across from the cathedral is the Hereford Museum and Art Gallery, a building with a wonderful selection of building stones including carboniferous limestone, oolitic limestone and some extraordinary coarse red columns of a mixed conglomerate and breccia from the Triassic. The Museum is topped by a selection of stone animals a reference to the Woolhope Naturalists Field Club for whom the building was originally created.
Further on we encountered some larvikite on the frontage of Boots and just opposite on the front of Marks and Spencer some nice granite column facings. Once we got our eye in we started seeing a variety of stones on shop fronts including a red granite next to the Butter Market, itself having some shelly limestone facings with very obvious shells.
Sadly, some shops were not as the leaflet described with MacDonald’s having replaced its (natural) travertine frontage with some rather bland compound or plastic cladding. Around the corner from MacDonald’s we found St Peter’s church which has a very tradition old red sandstone structure which has been repaired with new red sandstone approximately 160 million years younger. After this there was just time to have a look at the Town Hall with its terracotta cladding – an example of geology once removed since terracotta is a fired clay product - before drizzle came and the afternoon bus to return to Monmouth.
12th July 2017 – led by Jim Handley
Our third trip was to Little Doward just up the A40 from Monmouth. Here we were able to compare and contrast similar rocks to those at Soudley, but outcropping at a much gentler dip on the west edge of a different syncline. The quartz conglomerate gives an insight into flash flooding within the arid terrestrial landmass lying to the south of the equator. The shales and limestones spoke of warmer shallow calcareous seas deposits with chemical changes then caused by magnesium rich fluids.
We also considered the major erosional impact in the superimposed Wye river valley triggered by relatively falling sea levels. This also explains the presence of the caves on Great Doward, now 100m above the river.
As well as geology the hill has an iron age fort, landscaping work done by local landowner and MP Richard Blakemore, and a range of fascinating wild life, including the plants of a limestone pavement.
Handouts used were Earth Heritage Leaflets of Little and Great Doward, a geological map extract, and an explanation of the Wye valley creation.
On the 13th September Jim opened the new season of the U3A geology group talks with a most lavishly illustrated talk about a trip he did to Iceland, that most geologically interesting of islands. It is fair to say he kept the group spellbound for an hour with his dramatic pictures and detailed knowledge.
Jim has kindly provided these notes on his talk.
Much of Iceland is less than 3 million years old. It has grown, and is still growing, as a result of plate tectonics and the effects of a mantle plume beneath it.
The former is where the Eurasian and American plates are moving apart with new lava being deposited between the two. Usually this happens at a mid-ocean ridge, but here it is happening in a dynamic belt across the island. The boundary of the 2 plates is particularly well seen near the site of the ancient Icelandic parliament at Pingvellir. Here stepped faulting occurs on either side of a large lake. Although not accepted by all geologists, most believe additional lava [or associated material] is also brought to the surface of the crust here by an upwelling plume originating in the mantle.
The impact of earthquakes [mainly small but very numerous], volcanoes [think of the impact of Eyjafjallajokull in 2010], and sustained lava flows from long fissures such as Laki in 1783 were illustrated. Iceland being so new geologically and having several large icefields is a classic place to see the impact of erosion whether by ice, water or wind. Thus glacial moraines, wind carved ash deposits and the impact of devastating floods are much in evidence.
Finally Jim used Heimey as a case study of the effects of living in such an active area. This is a small island in the Westmann group. It had 4000 residents when in 1973 a fissure opened up on the edge of town in the middle of the night. Everyone was safely evacuated by the resident fishing fleet. By the time the eruptions ceased after 6 months, the island was 2km larger, but 400 houses were buried under lava. The remainder had ash deposits to clear. The lava flow stopped [or was stopped by a massive use of water jets] just short of blocking the access to the harbour. A stunning place to visit with its lava flows and tunnel, the cone still with small fumaroles, and the new museum centred on the ruins of a house dug out of the ash.
Field Trips
31st May 2017 – led by Jim Handley
On our first fieldtrip of 2017 we walked on and studied the geomap created on the site of New fancy colliery south of Speech House. In natural stone this shows the outcropping rocks of the Forest of Dean and all the main past coal mines, quarries and iron mines. From it we could recognise the FoD syncline with the crumpling impact of the Variscon Orogeny.
We moved on to follow part of the Soudley Valley Geology Trail. In about half a mile we could identitify 6 rocks – the Devonian Brownstones, Conglomerates and Tintern sandstones and the newer Carboniferous Lower Limestone shales, Lower Dolomite and Crease Limestones. Lessons learnt included the cause of the steep dip of this eastern margin, unconformities between deposits and differences between terrestrial and marine deposits. Around us were remains of the extraction and usage of nature’s raw materials.
The geomap and trail leaflets were handed out, an extract of the local geology map, and a cross-section of the FoD geology.
June 28th 2017 led by Guy Moody
Geology trip to Hereford - Although the weather forecast was not very good we nevertheless set out for Hereford with hope for a dry day. We met first at the cathedral and followed the building stones trail produced by the Herefordshire and Worcestershire Earth Heritage Trust. The majority of the cathedral is built of old red stone with much of the internal structure originally covered in plaster. For the most part the plaster has now been removed but the mason’s marks on the columns remain. The trail covers a number of tombs and monuments which gave us an opportunity to see a variety of marbles and limestones. The recent monument to the SAS with its memorable blue syenite, a variety of granite that lacks quartz, provided a memorable end to the cathedral tour.
After lunch, with the weather still holding good, we set out to follow the Hereford City Centre walk again published by the Herefordshire and Worcestershire Earth Heritage Trust. Just across from the cathedral is the Hereford Museum and Art Gallery, a building with a wonderful selection of building stones including carboniferous limestone, oolitic limestone and some extraordinary coarse red columns of a mixed conglomerate and breccia from the Triassic. The Museum is topped by a selection of stone animals a reference to the Woolhope Naturalists Field Club for whom the building was originally created.
Further on we encountered some larvikite on the frontage of Boots and just opposite on the front of Marks and Spencer some nice granite column facings. Once we got our eye in we started seeing a variety of stones on shop fronts including a red granite next to the Butter Market, itself having some shelly limestone facings with very obvious shells.
Sadly, some shops were not as the leaflet described with MacDonald’s having replaced its (natural) travertine frontage with some rather bland compound or plastic cladding. Around the corner from MacDonald’s we found St Peter’s church which has a very tradition old red sandstone structure which has been repaired with new red sandstone approximately 160 million years younger. After this there was just time to have a look at the Town Hall with its terracotta cladding – an example of geology once removed since terracotta is a fired clay product - before drizzle came and the afternoon bus to return to Monmouth.
12th July 2017 – led by Jim Handley
Our third trip was to Little Doward just up the A40 from Monmouth. Here we were able to compare and contrast similar rocks to those at Soudley, but outcropping at a much gentler dip on the west edge of a different syncline. The quartz conglomerate gives an insight into flash flooding within the arid terrestrial landmass lying to the south of the equator. The shales and limestones spoke of warmer shallow calcareous seas deposits with chemical changes then caused by magnesium rich fluids.
We also considered the major erosional impact in the superimposed Wye river valley triggered by relatively falling sea levels. This also explains the presence of the caves on Great Doward, now 100m above the river.
As well as geology the hill has an iron age fort, landscaping work done by local landowner and MP Richard Blakemore, and a range of fascinating wild life, including the plants of a limestone pavement.
Handouts used were Earth Heritage Leaflets of Little and Great Doward, a geological map extract, and an explanation of the Wye valley creation.
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