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 2018
November 14th Silver mining ans mineralisation in Wales
Tom Cotterell from the National Museum of Wales, Cardiff will give us a talk on minerals. Tom is a very experienced geologist and public speaker who introduced us to X-ray crystallography when we visited the Museum. Start 2 p.m. in the Wye room. Afternoon tea by arrangement.
December 12th
Christmas gathering. A table quiz and mini lectures, plus tea/coffee and seasonal eats.
November 14th Silver mining ans mineralisation in Wales
Tom Cotterell from the National Museum of Wales, Cardiff will give us a talk on minerals. Tom is a very experienced geologist and public speaker who introduced us to X-ray crystallography when we visited the Museum. Start 2 p.m. in the Wye room. Afternoon tea by arrangement.
December 12th
Christmas gathering. A table quiz and mini lectures, plus tea/coffee and seasonal eats.
Previous Meetings and Field Trips 2018
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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