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 during the months September to April. During the summer months a monthly geological field trip replaces the indoor talk. Talks and field trips are open to anyone with an interest in geology. No experience is required. At the moment we have no restriction on membership numbers, our only limitation is finding a room big enough at Bridges.Note: U3A requests that you carry your 'In Case of Emergency (ICE)' card with details of who to inform in the event of an accident during a geological activity.
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 during the months September to April. During the summer months a monthly geological field trip replaces the indoor talk. Talks and field trips are open to anyone with an interest in geology. No experience is required. At the moment we have no restriction on membership numbers, our only limitation is finding a room big enough at Bridges.Note: U3A requests that you carry your 'In Case of Emergency (ICE)' card with details of who to inform in the event of an accident during a geological activity.
Click here for Simple Introduction to Chemistry for Geologists
Monmouth U3A Geology Newsletters
Date of Next zoom meeting September 8th 2.30pm:
River Usk: Source to sea. Part 1: Black Mountain to Abergavenny.
A presentation by Alan Bowring, Fforest Fawr Geopark Development Officer.
This meeting is a joint meeting with our Geology Group.
River Usk: Source to sea. Part 1: Black Mountain to Abergavenny.
A presentation by Alan Bowring, Fforest Fawr Geopark Development Officer.
This meeting is a joint meeting with our Geology Group.
Previous Meetings and Field Trips
Please see above for details of Zoom meetings and future trips
14th April 2020 ZOOM The Science of Scuba Diving Charles Emes ( Monmouth U3A)
`This was our first meeting using Zoom to bring together 31 'isolating' members to enjoy Charles' talk. The technology worked well with us being able to view the presentation slides in close up and Charles commentating even if out of our sight.
The main theme that came over was that one had to be aware of the risks involved so that appropriate measures could be put in place. Once this is done the rewards of diving in glorious settings to see fantastic sea life can be fully enjoyed.
Charles set the scene by describing the history, including the mistakes made, of diving.
This led him on to describe the work of various researchers and the relevant laws of physics involved e.g. the key role of Boyle’s Law describing the relationship between pressure and volume. This led up to J. S. Haldane's 1908 report on 'The Prevention of Compressed Air Illness' from which the first dive tables were derived. In essence these give the diver key information on how long they can safely stay at particular depths. This in turn has now been computerised into a readily readable format that the diver has with them. Divers now use Nitrox gas which is compressed air with 11% extra oxygen, the corresponding fall in nitrogen reducing the risk from nitrogen bubbles in the blood.
Charles then explained the factors that can get a diver into trouble. -- not monitoring depth and time properly, ascending too quickly, not observing the safety stop at 5m, and having residual nitrogen still in the blood from a previous dive. He then took us through a detailed look at the symptoms of, and any treatment, for a range of issues from decompression illness [think hyperbaric chamber], oxygen toxicity, hypercapnia, and ear barotrauma.
Safety involves being properly trained, diving within your limits, and always diving with a buddy.
At the end we were treated to a glorious set of images Charles has taken of life below the surface. Take your pick from dolphins, turtles, rays, fish, crabs and many others.
We zoomed in in every sense thanks to Charles. Jim Handley
11th March 2020 Archaeopteryx: The story of an iconic fossil
Cindy Howells, Curator of Palaeontology, National Museum of Wales, Cardiff.
Cindy has a long-term interest in Archaeopteryx and has visited the area of Germany between Stuttgart and Munich where most of the known fossils are found. She has intensively studied the specimens both at home and in the local museums.
She explained the unique nature of the Solenhofen lagoons where the fossils are found. Reef and basin deposits were laid down in late Jurassic time 150m years ago. The rock is “flaggy” limestone which is quarried extensively for use as roof and floor tiles. It dates from the Lower Tithonian period.
She explained the sequence of discovery of 13 Archaeopteryx specimens from 1861 when the first fossilised feather was found until 2019. There is one specimen which was found in rocks 500,000 years younger. This one has a wishbone and a fused wrist joint which implies that it was capable of stronger flight. It is not now classified as Archaeopteryx. Most of the other specimens are thought to belong to a single species.
Sometimes the fossils are not complete but in a few specimens the creature is almost whole. Cindy communicated her great enthusiasm and deep knowledge this extraordinary link between dinosaurs and feathered birds.
12TH FEBRUARY 2020 DR. LUCY MCCOB, DEPT. OF NATURAL SCIENCES, NATIONAL MUSEUM OF WALES,
TALK ON TRILOBITES AND FOSSIL ARTHROPODS - LIFE ON LOTS OF LEGS, A PREHISTORY OF CREEPY CRAWLIES
This talk gave us a fascinating glimpse into the past, while linking it with creatures in our lives today, such as Wood Lice and Spiders. Indeed, humans are vastly outnumbered by insect species alone, many of which have existed for hundreds of millions of years. Arthropods have jointed legs and an exoskeleton but no internal backbone. The oldest trace fossils are dated from 550 mya, with actual Trilobite remains from 521 mya, Crustaceans 514 mya, and Chelicerates 500 mya. They, and others such as Hexapoda and Myriapoda, were described and illustrated.
Many fossils are usually partial skeletons so little is known of the interior organs, whether they had brains, what they ate, or how they reproduced. It is known that some shed their skeletons in order to grow, some had very complex eyes with many lenses, and some had no eyes at all. One of the first Trilobite fossils recorded was found near Llandeilo, and one of the biggest in Pembrokeshire. Currently, new ones have been found in St. Clears. Tribolites died out in the great Permean extinction event 251 mya.
Sea Scorpions, now extinct, existed between 460 - 251 mya, with some growing much larger than a human and Millipedes, one of the first land animals, have been dated around 414 mya.
"Arthur", found in the Joggins Fossil Cliffs, Nova Scotia, is about 2 metres wide, dating to 315 mya. Spider and insect fossils have been found dated 305 and 408 mya respectively. The Griffin Fly, the first animal to fly 300-320 mya, measured about half a metre wide. "Gold Bugs", so named because of their colour from iron pyrites, found in New York State, are so abundant that they are sold on the internet. "Water Bears" or Tardigrades which are not arthropods, can dry out completely and then re-hydrate themselves after surviving extreme conditions.
We should care about insects today, of course, as they are vital pollinators, while being aware that they can carry pests and parasites too. So, perhaps the motto should be "be nice to the Wood Lice"!
John Moseley – Fifty Years of Welsh Borderland Geology January 8th 2020
Having had some computer difficulties, John had kindly produced 9 pages of handouts to cover the range of his talk. Should anyone want a copy of these please get in touch with Jim at jim.s.handley@gmail.com
Having been inspired by his lecturers at Swansea University, John taught geology at a grammar school near Preston for 30 years, only moving to live at Longhope in the Forest of Dean on retirement. His knowledge and enthusiasm about the Welsh Marches stems from regularly leading his students on field trips to the area.
His talk focused in particular on 3 areas:
1. around Church Stretton with its classic fault lines and resultant landscape features
2. the Knighton area, where John has spent several recent years surveying around Prestigne, Kington and Shobden as part of a project to produce a geological map for the British Geological Society
3. as a volunteer warden for Gloucestershire Geology Trust at Huntley and Hobbs Quarry, near the A40 halfway between Ross and Gloucester, where the major East Malvern and Woolhope faultlines converge into the local Blaisdon fault. A whole range of features to be explored including drag folding , thrusting, slickensides and fault plane breccia.
Field trip to the Malvern Hills – 23rd October 2019
We met up with our leader Richard Edwards at a rather foggy North Hill Quarry car park.
Our day began with a close-up introduction to the East Malvern Faultline which is a key feature in the geological development of the area. We then spent some time in the adjacent Tank Quarry where the Malvern Hills Trust, in conjunction with Richard on behalf of the Earth Heritage Trust, have produced information displays and large exhibits including of diorite, dolerite and granite. Richard explained the current thinking of how the varying chemistry and pressures had created the range of igneous rock types within the earth crust and how these had been exposed at the surface as a result of the Variscan orogeny and subsequent major erosion of overlying deposits. We also looked at examples of granite and Quartz intrusions into existing rocks.
Moving south down the west side of the Hills we went into Dingle Quarry to appreciate again how different rocks had come to be in their existing relationships with each other. The weather now brightening allowed Richard to point out the landscape formed from Silurian marine deposits to the west.
A pleasant lunch was taken at The Kettle Sings with excellent and clearing views westwards.
Our final stop was on the top of the main ridge of the hills just north of the Malvern Hills Hotel. From here we focused on the Herefordshire Beacon to the south which is composed of igneous material thrust over the top of Silurian rocks [clearly shown on Richard’s handouts]. To the west we could again appreciate the ridge and vale landscape of Silurian rocks. In contrast to the east was the Worcester graben or rift valley filled with 10,000 feet of Permo – Triassic material giving a flattish plain for the River Severn. Just visible beyond was the top of the Jurassic age limestones of the Cotswolds.
A very good introduction to the variety of underlying rocks and the resultant different landscapes. Our thanks indeed to Richard. Jim Handley
9th October 2019
Convenor Guy Moody welcomed 25 members including several from Ross U3A who attended by invitation. He introduced our guest speaker: Geraint Owen, Honorary Senior Lecturer, University of Wales, Swansea to give a talk entitled “River Systems in the Geological Record”.
We were treated to a wide-ranging talk covering diverse but linked topics including: Characteristics of river deposits, Types of rivers and their deposits, Evolution of river systems and the Torridonian mountains of North West Scotland.
The audience were led at a great pace from Precambrian rivers and their deposits to more recent theories about the relationship between meanders and the evolution of vegetation in the Silurian and Devonian periods. While evidence of meanders can be found in the older rocks, only since 2014 has it been realised that they become more common as plants with roots provide stability to the surface of the land and the river bank.
The wild Torridon range in Scotland provides examples of cross bedding deposits with alternating sandstone and mudstone layers.
In conclusion Geraint Owen demonstrated that the geological record shows well preserved river systems and can distinguish between different styles of river system, in addition soft sediment deformation can provide information about non-channel environments.
The audience enjoyed a fascinating insight into the mysteries of geological time through the lens of river systems.
Guy Moody led enthusiastic applause for a very clear talk from a speaker who gave us a distillation of a lifetime’s work.
Martin Milling
11th September MANGANESE IN WALES Tom Cotterell
This was another very interesting and eloquent talk by Tom Cotterell from the National Museum of Wales, Cardiff, on 11th September. Together with beautiful pictures and graphs, he outlined the history of Manganese from its discovery in Britain in 1774, although it is known that the Romans were aware of it, to its importance in World Wars I & II. He showed us how beautiful it is when combined with other elements. It contributed to glass making in Bristol in the 1700's as impure oxides of Manganese, used for bleaching, were found in the Mendip Hills. Pure Manganese was discovered near Exeter but it ran out in 1820.
This led to North Wales being investigated, although there were small deposits in Mid and South Wales and the Forest of Dean. In 1883 it was realised that Manganese Silicates and Carbonates could be used in steel making and this took place between 1881-1946. In the counties of Caernarvon, Merioneth, Denbigh, Cardigan and Glamorgan various mines operated. In 1827, 50 men were employed mining Black Manganese near the small village of Rhiw on the Lleyn Peninsula. This mine eventually closed but re-opened again in 1902. The Nant, Benallt and Rhiw mines were worked between 1904-1946. This area is now a Site of Special Scientific Interest, (SSSI). The Llanaelhaearn mine operated pre-1833 and again in 1841 and 1872 but the workings were small scale.
In the Merioneth Harlech Dome area, Manganese occurred as a bed and is now mostly mined away. Weather resistant Grits above the deposits gave clues to its existence. The Harlech Dome is now part of Snowdonia National Park and the Marine Basin has been geologically linked to Newfoundland. Black Manganese Oxides were mined from the 19th century and these were high grade but short-lived deposits.
In the Arenig District of Denbighshire, deposits were known about in the 1820's but access was limited until a railway was built in 1822. One of the area's biggest mines was Mynydd Nodol. The Royal Mines in the Central Wales Orefield also include Zinc. Eaglebrook and Frongoch came into operation as recently as 2006 and 2007 respectively. In Glamorgan, the Ty Coch Mine deposits were similar to those in the Forest of Dean but were never worked.
Manganese has been important to British Industry and mining was bank-rolled during World War II, as imports were banned, but it ceased after the war ended. Huge deposits of high-grade Manganese are mined in India today. One use is for railway tracks as Manganese steel is shock resistant, but that doesn't mean that it can withstand earthquakes! Kate Waldron
Geology Group Meeting on 21st August – OUR WAY AHEAD
14 of us got together to discuss ideas for the future of the group, using the earlier circulated note of first thoughts. This is a short note to highlight key things discussed.
Indoor meetings
Agreed to ask John Moseley [retired geology teacher] to talk on“Fifty Years of indulging in Welsh Borderland Geology” and to ask Alan Gray to return to talk about “Origins of Plate Tectonics”
Members agreed it is reasonable to sometimes pay extra to meet expenses of speakers.
Need to include time in meetings for members involvement in wider discussions, and in bringing in interesting images and samples to share. Flexible timing of tea breaks. Overall need to build up identification skills. Need to brief speakers on duration and level of talks.
Members to share writing up a short report of each meeting [or visit] for our website. Not to be a geological thesis just a few sentences of their impressions of ground covered. Possibly 3/4 to operate a rota system [as at science group]
Agreed to continue to invite Ross Group to some meetings.
Suggested topics included Glaciation, Formation and Extraction of Oil, Bedrock factors in civil engineering projects like the Channel, Crossrail or Severn tunnels, and how gold, silver and precious gemstones are formed. All ideas welcome especially identifying a speaker with the necessary knowledge.
Fieldtrips
Challenge to find range of places to visit that together meet range of mobilities of members.
Organisations like the South Wales Geological Association welcome
visitors to their field trips.
Hereford Resource Centre an option.
Dan yr Ogof, Wookey Hole or Clearwell caves preferably to include aspects not open to general public.
Special interests
Where e.g. a few members are interested in a particular aspect of geology like fossils, geology maps or landscape walking there is no reason why they cannot get together to pursue that interest further as an extra feature within the overall group.
Exchanging information
Agreed that passing information around the group is valuable with members dipping into whatever they like.
Agreed we will set up a monthly information newsletterby email into which links to items like the Earth Matters and EHT newsletter can be put. This could include members’ suggestions on books and articles they have found useful, plus seeking colleagues help or views on particular queries. Recognised that information about current TV programmes needs passing round more urgently. Tim and Wendy volunteered to get this newsletter under way.
Courses run by geologists
Some members have already been on day conferences and longer courses. Value of these recognised but appreciated these have to be undertaken outside of U3A programmes.
Guy and Jim to discuss options with Dave Green, a local geologist and teacher who has run courses and field trips in the area for many years. These are obviously run on a commercial basis.
Sharing the Workload
For the group to thrive everyone has a part to play. We already have help to set up the newsletter and to write up the September meeting. More of the same gratefully received!
Please see above for details of Zoom meetings and future trips
14th April 2020 ZOOM The Science of Scuba Diving Charles Emes ( Monmouth U3A)
`This was our first meeting using Zoom to bring together 31 'isolating' members to enjoy Charles' talk. The technology worked well with us being able to view the presentation slides in close up and Charles commentating even if out of our sight.
The main theme that came over was that one had to be aware of the risks involved so that appropriate measures could be put in place. Once this is done the rewards of diving in glorious settings to see fantastic sea life can be fully enjoyed.
Charles set the scene by describing the history, including the mistakes made, of diving.
This led him on to describe the work of various researchers and the relevant laws of physics involved e.g. the key role of Boyle’s Law describing the relationship between pressure and volume. This led up to J. S. Haldane's 1908 report on 'The Prevention of Compressed Air Illness' from which the first dive tables were derived. In essence these give the diver key information on how long they can safely stay at particular depths. This in turn has now been computerised into a readily readable format that the diver has with them. Divers now use Nitrox gas which is compressed air with 11% extra oxygen, the corresponding fall in nitrogen reducing the risk from nitrogen bubbles in the blood.
Charles then explained the factors that can get a diver into trouble. -- not monitoring depth and time properly, ascending too quickly, not observing the safety stop at 5m, and having residual nitrogen still in the blood from a previous dive. He then took us through a detailed look at the symptoms of, and any treatment, for a range of issues from decompression illness [think hyperbaric chamber], oxygen toxicity, hypercapnia, and ear barotrauma.
Safety involves being properly trained, diving within your limits, and always diving with a buddy.
At the end we were treated to a glorious set of images Charles has taken of life below the surface. Take your pick from dolphins, turtles, rays, fish, crabs and many others.
We zoomed in in every sense thanks to Charles. Jim Handley
11th March 2020 Archaeopteryx: The story of an iconic fossil
Cindy Howells, Curator of Palaeontology, National Museum of Wales, Cardiff.
Cindy has a long-term interest in Archaeopteryx and has visited the area of Germany between Stuttgart and Munich where most of the known fossils are found. She has intensively studied the specimens both at home and in the local museums.
She explained the unique nature of the Solenhofen lagoons where the fossils are found. Reef and basin deposits were laid down in late Jurassic time 150m years ago. The rock is “flaggy” limestone which is quarried extensively for use as roof and floor tiles. It dates from the Lower Tithonian period.
She explained the sequence of discovery of 13 Archaeopteryx specimens from 1861 when the first fossilised feather was found until 2019. There is one specimen which was found in rocks 500,000 years younger. This one has a wishbone and a fused wrist joint which implies that it was capable of stronger flight. It is not now classified as Archaeopteryx. Most of the other specimens are thought to belong to a single species.
Sometimes the fossils are not complete but in a few specimens the creature is almost whole. Cindy communicated her great enthusiasm and deep knowledge this extraordinary link between dinosaurs and feathered birds.
12TH FEBRUARY 2020 DR. LUCY MCCOB, DEPT. OF NATURAL SCIENCES, NATIONAL MUSEUM OF WALES,
TALK ON TRILOBITES AND FOSSIL ARTHROPODS - LIFE ON LOTS OF LEGS, A PREHISTORY OF CREEPY CRAWLIES
This talk gave us a fascinating glimpse into the past, while linking it with creatures in our lives today, such as Wood Lice and Spiders. Indeed, humans are vastly outnumbered by insect species alone, many of which have existed for hundreds of millions of years. Arthropods have jointed legs and an exoskeleton but no internal backbone. The oldest trace fossils are dated from 550 mya, with actual Trilobite remains from 521 mya, Crustaceans 514 mya, and Chelicerates 500 mya. They, and others such as Hexapoda and Myriapoda, were described and illustrated.
Many fossils are usually partial skeletons so little is known of the interior organs, whether they had brains, what they ate, or how they reproduced. It is known that some shed their skeletons in order to grow, some had very complex eyes with many lenses, and some had no eyes at all. One of the first Trilobite fossils recorded was found near Llandeilo, and one of the biggest in Pembrokeshire. Currently, new ones have been found in St. Clears. Tribolites died out in the great Permean extinction event 251 mya.
Sea Scorpions, now extinct, existed between 460 - 251 mya, with some growing much larger than a human and Millipedes, one of the first land animals, have been dated around 414 mya.
"Arthur", found in the Joggins Fossil Cliffs, Nova Scotia, is about 2 metres wide, dating to 315 mya. Spider and insect fossils have been found dated 305 and 408 mya respectively. The Griffin Fly, the first animal to fly 300-320 mya, measured about half a metre wide. "Gold Bugs", so named because of their colour from iron pyrites, found in New York State, are so abundant that they are sold on the internet. "Water Bears" or Tardigrades which are not arthropods, can dry out completely and then re-hydrate themselves after surviving extreme conditions.
We should care about insects today, of course, as they are vital pollinators, while being aware that they can carry pests and parasites too. So, perhaps the motto should be "be nice to the Wood Lice"!
John Moseley – Fifty Years of Welsh Borderland Geology January 8th 2020
Having had some computer difficulties, John had kindly produced 9 pages of handouts to cover the range of his talk. Should anyone want a copy of these please get in touch with Jim at jim.s.handley@gmail.com
Having been inspired by his lecturers at Swansea University, John taught geology at a grammar school near Preston for 30 years, only moving to live at Longhope in the Forest of Dean on retirement. His knowledge and enthusiasm about the Welsh Marches stems from regularly leading his students on field trips to the area.
His talk focused in particular on 3 areas:
1. around Church Stretton with its classic fault lines and resultant landscape features
2. the Knighton area, where John has spent several recent years surveying around Prestigne, Kington and Shobden as part of a project to produce a geological map for the British Geological Society
3. as a volunteer warden for Gloucestershire Geology Trust at Huntley and Hobbs Quarry, near the A40 halfway between Ross and Gloucester, where the major East Malvern and Woolhope faultlines converge into the local Blaisdon fault. A whole range of features to be explored including drag folding , thrusting, slickensides and fault plane breccia.
Field trip to the Malvern Hills – 23rd October 2019
We met up with our leader Richard Edwards at a rather foggy North Hill Quarry car park.
Our day began with a close-up introduction to the East Malvern Faultline which is a key feature in the geological development of the area. We then spent some time in the adjacent Tank Quarry where the Malvern Hills Trust, in conjunction with Richard on behalf of the Earth Heritage Trust, have produced information displays and large exhibits including of diorite, dolerite and granite. Richard explained the current thinking of how the varying chemistry and pressures had created the range of igneous rock types within the earth crust and how these had been exposed at the surface as a result of the Variscan orogeny and subsequent major erosion of overlying deposits. We also looked at examples of granite and Quartz intrusions into existing rocks.
Moving south down the west side of the Hills we went into Dingle Quarry to appreciate again how different rocks had come to be in their existing relationships with each other. The weather now brightening allowed Richard to point out the landscape formed from Silurian marine deposits to the west.
A pleasant lunch was taken at The Kettle Sings with excellent and clearing views westwards.
Our final stop was on the top of the main ridge of the hills just north of the Malvern Hills Hotel. From here we focused on the Herefordshire Beacon to the south which is composed of igneous material thrust over the top of Silurian rocks [clearly shown on Richard’s handouts]. To the west we could again appreciate the ridge and vale landscape of Silurian rocks. In contrast to the east was the Worcester graben or rift valley filled with 10,000 feet of Permo – Triassic material giving a flattish plain for the River Severn. Just visible beyond was the top of the Jurassic age limestones of the Cotswolds.
A very good introduction to the variety of underlying rocks and the resultant different landscapes. Our thanks indeed to Richard. Jim Handley
9th October 2019
Convenor Guy Moody welcomed 25 members including several from Ross U3A who attended by invitation. He introduced our guest speaker: Geraint Owen, Honorary Senior Lecturer, University of Wales, Swansea to give a talk entitled “River Systems in the Geological Record”.
We were treated to a wide-ranging talk covering diverse but linked topics including: Characteristics of river deposits, Types of rivers and their deposits, Evolution of river systems and the Torridonian mountains of North West Scotland.
The audience were led at a great pace from Precambrian rivers and their deposits to more recent theories about the relationship between meanders and the evolution of vegetation in the Silurian and Devonian periods. While evidence of meanders can be found in the older rocks, only since 2014 has it been realised that they become more common as plants with roots provide stability to the surface of the land and the river bank.
The wild Torridon range in Scotland provides examples of cross bedding deposits with alternating sandstone and mudstone layers.
In conclusion Geraint Owen demonstrated that the geological record shows well preserved river systems and can distinguish between different styles of river system, in addition soft sediment deformation can provide information about non-channel environments.
The audience enjoyed a fascinating insight into the mysteries of geological time through the lens of river systems.
Guy Moody led enthusiastic applause for a very clear talk from a speaker who gave us a distillation of a lifetime’s work.
Martin Milling
11th September MANGANESE IN WALES Tom Cotterell
This was another very interesting and eloquent talk by Tom Cotterell from the National Museum of Wales, Cardiff, on 11th September. Together with beautiful pictures and graphs, he outlined the history of Manganese from its discovery in Britain in 1774, although it is known that the Romans were aware of it, to its importance in World Wars I & II. He showed us how beautiful it is when combined with other elements. It contributed to glass making in Bristol in the 1700's as impure oxides of Manganese, used for bleaching, were found in the Mendip Hills. Pure Manganese was discovered near Exeter but it ran out in 1820.
This led to North Wales being investigated, although there were small deposits in Mid and South Wales and the Forest of Dean. In 1883 it was realised that Manganese Silicates and Carbonates could be used in steel making and this took place between 1881-1946. In the counties of Caernarvon, Merioneth, Denbigh, Cardigan and Glamorgan various mines operated. In 1827, 50 men were employed mining Black Manganese near the small village of Rhiw on the Lleyn Peninsula. This mine eventually closed but re-opened again in 1902. The Nant, Benallt and Rhiw mines were worked between 1904-1946. This area is now a Site of Special Scientific Interest, (SSSI). The Llanaelhaearn mine operated pre-1833 and again in 1841 and 1872 but the workings were small scale.
In the Merioneth Harlech Dome area, Manganese occurred as a bed and is now mostly mined away. Weather resistant Grits above the deposits gave clues to its existence. The Harlech Dome is now part of Snowdonia National Park and the Marine Basin has been geologically linked to Newfoundland. Black Manganese Oxides were mined from the 19th century and these were high grade but short-lived deposits.
In the Arenig District of Denbighshire, deposits were known about in the 1820's but access was limited until a railway was built in 1822. One of the area's biggest mines was Mynydd Nodol. The Royal Mines in the Central Wales Orefield also include Zinc. Eaglebrook and Frongoch came into operation as recently as 2006 and 2007 respectively. In Glamorgan, the Ty Coch Mine deposits were similar to those in the Forest of Dean but were never worked.
Manganese has been important to British Industry and mining was bank-rolled during World War II, as imports were banned, but it ceased after the war ended. Huge deposits of high-grade Manganese are mined in India today. One use is for railway tracks as Manganese steel is shock resistant, but that doesn't mean that it can withstand earthquakes! Kate Waldron
Geology Group Meeting on 21st August – OUR WAY AHEAD
14 of us got together to discuss ideas for the future of the group, using the earlier circulated note of first thoughts. This is a short note to highlight key things discussed.
Indoor meetings
Agreed to ask John Moseley [retired geology teacher] to talk on“Fifty Years of indulging in Welsh Borderland Geology” and to ask Alan Gray to return to talk about “Origins of Plate Tectonics”
Members agreed it is reasonable to sometimes pay extra to meet expenses of speakers.
Need to include time in meetings for members involvement in wider discussions, and in bringing in interesting images and samples to share. Flexible timing of tea breaks. Overall need to build up identification skills. Need to brief speakers on duration and level of talks.
Members to share writing up a short report of each meeting [or visit] for our website. Not to be a geological thesis just a few sentences of their impressions of ground covered. Possibly 3/4 to operate a rota system [as at science group]
Agreed to continue to invite Ross Group to some meetings.
Suggested topics included Glaciation, Formation and Extraction of Oil, Bedrock factors in civil engineering projects like the Channel, Crossrail or Severn tunnels, and how gold, silver and precious gemstones are formed. All ideas welcome especially identifying a speaker with the necessary knowledge.
Fieldtrips
Challenge to find range of places to visit that together meet range of mobilities of members.
Organisations like the South Wales Geological Association welcome
visitors to their field trips.
Hereford Resource Centre an option.
Dan yr Ogof, Wookey Hole or Clearwell caves preferably to include aspects not open to general public.
Special interests
Where e.g. a few members are interested in a particular aspect of geology like fossils, geology maps or landscape walking there is no reason why they cannot get together to pursue that interest further as an extra feature within the overall group.
Exchanging information
Agreed that passing information around the group is valuable with members dipping into whatever they like.
Agreed we will set up a monthly information newsletterby email into which links to items like the Earth Matters and EHT newsletter can be put. This could include members’ suggestions on books and articles they have found useful, plus seeking colleagues help or views on particular queries. Recognised that information about current TV programmes needs passing round more urgently. Tim and Wendy volunteered to get this newsletter under way.
Courses run by geologists
Some members have already been on day conferences and longer courses. Value of these recognised but appreciated these have to be undertaken outside of U3A programmes.
Guy and Jim to discuss options with Dave Green, a local geologist and teacher who has run courses and field trips in the area for many years. These are obviously run on a commercial basis.
Sharing the Workload
For the group to thrive everyone has a part to play. We already have help to set up the newsletter and to write up the September meeting. More of the same gratefully received!
Cribarth Geotrail -- Fieldtrip 10th July 2019
5 geology group plus 3 other U3A members made the 55 mile trip to visit the Cribarth Geotrail. They were led by Guy and Jim who had previously been on the same walk led by Alan Bowring from the Fforest Fawr Geopark.
The walk can be followed on the attached image taken from the trail guide. It starts from the Craig-y-nos country park which is very close to the famous Dan-yr-ogof show caves. Having gently ascended about 900 feet we spent several hours exploring the geology and the impact of quarrying on the landscape.
From the hilltop vantage points the landscape was laid before us in all directions. The 2 main rocks of Twrch Sandstone and Carboniferous Limestone dominate and give indications of the impact of the Variscon orogeny creating rocks dipping from the horizontal to the vertical. We could see the impact of local glaciers and the presence of many sink holes on the limestone. Scree slopes had us searching for fossils.
Extensive quarry remains with interconnecting tramways bear witness to work done here in often quite demanding conditions. The image references to rottenstone is to deposits of sand weathered from limestone shales which was in demand for use as an industrial polish. No trace of the sand can now be found only the hollows from where is was dug
We all agreed that the energy used was well rewarded.
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
5 geology group plus 3 other U3A members made the 55 mile trip to visit the Cribarth Geotrail. They were led by Guy and Jim who had previously been on the same walk led by Alan Bowring from the Fforest Fawr Geopark.
The walk can be followed on the attached image taken from the trail guide. It starts from the Craig-y-nos country park which is very close to the famous Dan-yr-ogof show caves. Having gently ascended about 900 feet we spent several hours exploring the geology and the impact of quarrying on the landscape.
From the hilltop vantage points the landscape was laid before us in all directions. The 2 main rocks of Twrch Sandstone and Carboniferous Limestone dominate and give indications of the impact of the Variscon orogeny creating rocks dipping from the horizontal to the vertical. We could see the impact of local glaciers and the presence of many sink holes on the limestone. Scree slopes had us searching for fossils.
Extensive quarry remains with interconnecting tramways bear witness to work done here in often quite demanding conditions. The image references to rottenstone is to deposits of sand weathered from limestone shales which was in demand for use as an industrial polish. No trace of the sand can now be found only the hollows from where is was dug
We all agreed that the energy used was well rewarded.
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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