GEOLOGY
Jim Handley jim.s.handley@gmail.com
The Geology group meets at Bridges Community Centre from 2pm-3.30pm on the 2nd Wednesday of each month from September to May. During the summer months a monthly geological field trip or visit replaces the indoor talk. Talks and field trips are open to anyone with an interest in geology. No experience is required. You would be very welcome to pop along to meet us or to contact Jim for more information. You will find reports below of our activities over recent years.
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.
Our next indoor meeting will be in September. We shall have some activities outdoors during the summer. For further information please email Jim.
The Geology group meets at Bridges Community Centre from 2pm-3.30pm on the 2nd Wednesday of each month from September to May. During the summer months a monthly geological field trip or visit replaces the indoor talk. Talks and field trips are open to anyone with an interest in geology. No experience is required. You would be very welcome to pop along to meet us or to contact Jim for more information. You will find reports below of our activities over recent years.
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.
Our next indoor meeting will be in September. We shall have some activities outdoors during the summer. For further information please email Jim.
Geology Newsletters 2020
Previous Meetings and Field Trips
July 2022 Visit to Llangattock Escarpment
Guided Walk with Alan Bowring
On a beautiful warm afternoon 12 keen members drove across the new Gateway Bridge over the Clydach Gorge to the escarpment near Pant-y-Rhiw high above Llangattock and Crickhowell.
We were met by Alan Bowring (The Forest Fawr Geopark Development Officer) and his colleague Keira who proceeded to take us on an extended tour of the cliffs in the area.
The main site is known as Craig y Cilau. The obvious feature which can be seen from a great distance is a line of cliffs which have been extensively quarried in the nineteenth and early twentieth centuries. Access to the area for extraction of limestone wa provided by a tramway in the direction of Blaenavon and by an incline and tramway to the Mon. & Brecon canal at Llangattock. The stone was used to provide lime from kilns for construction and agriculture and as a flux in the iron industry.
The extensive quarrying has revealed the layer of rock which make up the hillside and Alan was able to explain the formation of the layers above overlying Old Red Sandstone at the base. The limestone is banded with layers of conglomerate and sandstone. From above the rock comprises Carboniferous Coal Measures, Trwch Limestone, Dowlais Limestone, Llanelly Formation and Abercrinan Oolite. it was noted that some of the horizontal bands have been Dolomitised which renders them useless for industry so that they were discarded as quarrying proceeded.
We visited old lime kilns and then walked along the base of the cliffs to view the remains of the working. Among the detritus there were fascinating boulders of banded rock with some interesting curved fossilised trails of worm like creatures in the mudstone. Lichens formed some strange and wonderful patterns on the fallen rocks. We also saw an impressive area of flowstone cascading down a cliff.
The entrance to the extensive caves which lie in the hillside was viewed.
The extent of the quarrying is most impressive and explains the large amount of spoil which hs been left behind.
Towards the west the escarpment has not been quarried and Alan led a group discussion about the origins of the formation of the giant cirque in the cliffs. The exact formative forces are not universally agreed. There was almost certainly glacial activity but an early meander of the River Usk could also have had a major impact on the existing shape of the land.
We were shown examples of rare whitebeam which is only found on these cliffs.
We returned to the carpark by the old tramway and were able to see the top of the incline and to see examples of the flat stones and shaped cast iron brackets which used to carry the iron tramlines. We passed the HQ of the Chelsea Caving Club which despite its name, is now the local club for speleologists.
Alan kept us enthralled for more than 3 hours by his knowledge of not only geology but also many wider aspects of the National Park and its flora and fauna.
Many thanks to him, his assistant and of course Jim Handley who arranged it all.
Martin
June 2022 Walk in Slade Valley near St Briavels
We have told you before about the app called Geoheritage of the Dean, which gives you a choice of 11 walks to explore in the Forest of Dean. Having now sampled one of these with our group walk in June we can confirm that the app is very user friendly, gives a lot of background info about the wider geology of the Forest and gives you all the guidance you need in a set of images to follow on each walk. Of course should you prefer you can still enjoy the walks from the comfort of that armchair!
Our walk called in the app 'St Briavels' explored the area to the north of that village.
We started on the relatively flat and open higher level on the western side of the Forest of Dean walking on Carboniferous limestone shales. The key feature was a series of swallow holes, or swallets, taking the drainage from some adjacent mudstones. Although rather hidden by summer foliage some of these swallow holes are quite sizeable, in one case having been used by a local farmer as his personal rubbish dump. Overall clear evidence of the impact of acidic rainwater on the limestone.
Our walk then took us quite steeply downwards into the valley of the Slade Brook. On the walk down we had crossed the boundary with the older Devonian Tintern Sandstone. The valley is where the water flowing within the limestone new resurfaces. The fascinating feature is that this water now redeposits its calcium carbonate load, in so doing, creating the unusual series of pools each of which has a rim of calcium carbonate building up on the mosses to form tufa. The image below captures the result.
Our walk then climbed out of the valley to bring us to the eastern rim of the Wye valley. This is an excellent location to remind ourselves how the Wye has incised itself into the landscape regardless of whether it is crossing hard or soft rocks. During that process there are the remains fo several large meanders abandoned at various levels along the Wye. From our viewpoint, effectively on the top of an old river cliff line, we were looking down on one excellent example below us.
The weather was on our side too!
Jim
May 2022 Offshore Site Investigation - Prof. Brian Georgious
Brian, a member of our geology group, introduced us to his involvement in the practical side of researching and using structures in the exploration for and exploitation of gas and oil reserves, for example, in the North Sea.
His definition of geo engineering was:
An offshore investigation for engineering purposes is a study to determine the conditions, hazards and parameters for the safe engineering design of offshore structures.
We were first introduced to the key features of marine geology and the 2 main processes involved in their creation - namely endogenic producing large scale features fuelled by heat sources and exogenic involving the process of erosion and sedimentation.
Then came an explanation of the variety of fixed and floating offshore structures that are operating, together with a whole range of specialist subsea items of kit. One intriguing example was a suction caisson where a reduction of air pressure internally literally sucks the whole structure into the sea bed.
Brian, a member of our geology group, introduced us to his involvement in the practical side of researching and using structures in the exploration for and exploitation of gas and oil reserves, for example, in the North Sea.
His definition of geo engineering was:
An offshore investigation for engineering purposes is a study to determine the conditions, hazards and parameters for the safe engineering design of offshore structures.
We were first introduced to the key features of marine geology and the 2 main processes involved in their creation - namely endogenic producing large scale features fuelled by heat sources and exogenic involving the process of erosion and sedimentation.
Then came an explanation of the variety of fixed and floating offshore structures that are operating, together with a whole range of specialist subsea items of kit. One intriguing example was a suction caisson where a reduction of air pressure internally literally sucks the whole structure into the sea bed.
First offshore rig 1947 in 6m water off coast of Louisiana
Today 7000 platforms in excess of 2000m water
Today 7000 platforms in excess of 2000m water
We were introduced to an array of techniques used in site investigation offshore and to the range of geo hazards that might be encountered. Particularly impressive were 2 ships costing £140m + each used in this work and to hear about the dynamic positioning techniques employed to keep these ships in the exact same location. They are also designed to cope with up to a 3m swell whilst drilling. Other kit is designed to operate remotely on the seabed https://clearwellcaves.com/about-us/.
Brian told us about the hazard of landslides with particular reference to the Afen slide NW of the Shetlands which spreads 12 km in length from 830 km into the abyssal plain of the Norwegian Sea. It generated a tsunami affecting 600 km of Scotland's coastline and swept inland up to 29 km.
Moving on we learned about the issues associated with different forms of methane. This is 24 times more potent than Co2. The scale of possible world wide release of the eg: caused by the melting of ice sheets or of perma frost is quite mind blowing and may well have contributed to major past global warming and the Permian mass extinction.
Concluding Brian reminded us of some of the blow outs that have occurred, especially the BP Deep horizon incident in the Gulf of Mexico.
Brian told us about the hazard of landslides with particular reference to the Afen slide NW of the Shetlands which spreads 12 km in length from 830 km into the abyssal plain of the Norwegian Sea. It generated a tsunami affecting 600 km of Scotland's coastline and swept inland up to 29 km.
Moving on we learned about the issues associated with different forms of methane. This is 24 times more potent than Co2. The scale of possible world wide release of the eg: caused by the melting of ice sheets or of perma frost is quite mind blowing and may well have contributed to major past global warming and the Permian mass extinction.
Concluding Brian reminded us of some of the blow outs that have occurred, especially the BP Deep horizon incident in the Gulf of Mexico.
February 2022 Finding Fossils and their Preparation - Mark Baggott
Mark does not claim to be a geologist but certainly is extremely knowledgeable and enthusiastic about Paleontology. His talk was very practically based relating to how his interests have developed and various locations where it has taken him. Having found his specimens he then skilfully prepares each one by using various air pressure driven tools to remove the surrounding rock and material to highlight the fine details of the particular fossils
Locations mentioned included the Aust cliffs and Garden cliffs on the Severn, the coastline near Whitby, and quarries in the Cotswolds, at Gilwern and at Whitman's Hill near Malvern.
Particular prepared fossils he had brought along included examples of trilobites, ammonites, nautilus and sea urchins. He mentioned his work with the National History Museum recently on an amazing collection of crinoids found in a Cotswold Quarry.
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November 2021 Wales Turbulant Geological Past -- Paul Bright
Paul gave us an interesting talk about the geology of Wales. His images highlighted, in different colours, the range of rocks and minerals and the areas in which they are present from SW to NE Wales.
Having shown us the overall geological setting of Wales, Paul then focused on two contrasting local areas of which he has personal knowledge. As he told us in an earlier newsletter they each come from strata of different periods, deposited in different environments and subjected to the effects of different organic episodes resulting from the interactions between different tectonic plates..
The first was in and around Snowdonia with its origins related to the tectonic forces of the Devonian period as two continents moved together. He particularly looked at the consequent landforms in the Dolwyddelan syncline and the formation of the metamorphic slate deposits, the latter now featuring as a Unesco World Heritage site.
Drawing on his coal mining expertise, Paul then focused on the South Wales coalfield and described how the deposits there were distorted and faulted by the much later Variscon orogeny in late Carboniferous time. He described his personal involvement in the development of the massive opencast site at Ffos Las.
The group were reminded that Charles Darwin & Alfred Wallace started their studies on the 'origins of species' in both the north & south of Wales by studying fossils which were uncovered by miners, quarry workers & the people.
Michael Benge.
October 2021 Geology and Scenery -- Dr Naylor Frith
It was lovely to be at 'Bridges' for a live meeting. Dr Naylor Firth, a retired geologist and local historian, discussed "Geology and Scenery", with many super images. It was an excellent overview of how the landscape has been developed and sculptured creating the myriad forms of scenery.
Consider starting way back in time with a flat monotonous landscape.
Construction: the volcanoes forming mountains, ejecting differing types of ash and lava, giving a variety of rock and land formations eg. sills and dykes.
Rearrangement: earthquakes altering the composition and position of the rocks at eg. ocean ridges, plate boundaries, faults, etc, with the tilting, bending and breaking of rocks, with some extreme conditions eg. pressure and temperature.
Demolition: Mainly by gravity, water and the atmosphere. Glaciers, influenced by gravity, gouging out U shaped valleys, moving and creating new debris. Water, from high speed to minimal movement, carrying, changing and depositing debris. Water dissolving minerals etc: Wind shifting materials, beautifully shown by sand dunes. Wind giving power to water, the sea waves changing the coastline.
Meanwhile the composition of the rocks can be influenced by differing physical and chemical reactions and the whole system keeps repeating the sequences. A never ending story of alteration.
Gillian Knowland.
It was lovely to be at 'Bridges' for a live meeting. Dr Naylor Firth, a retired geologist and local historian, discussed "Geology and Scenery", with many super images. It was an excellent overview of how the landscape has been developed and sculptured creating the myriad forms of scenery.
Consider starting way back in time with a flat monotonous landscape.
Construction: the volcanoes forming mountains, ejecting differing types of ash and lava, giving a variety of rock and land formations eg. sills and dykes.
Rearrangement: earthquakes altering the composition and position of the rocks at eg. ocean ridges, plate boundaries, faults, etc, with the tilting, bending and breaking of rocks, with some extreme conditions eg. pressure and temperature.
Demolition: Mainly by gravity, water and the atmosphere. Glaciers, influenced by gravity, gouging out U shaped valleys, moving and creating new debris. Water, from high speed to minimal movement, carrying, changing and depositing debris. Water dissolving minerals etc: Wind shifting materials, beautifully shown by sand dunes. Wind giving power to water, the sea waves changing the coastline.
Meanwhile the composition of the rocks can be influenced by differing physical and chemical reactions and the whole system keeps repeating the sequences. A never ending story of alteration.
Gillian Knowland.
Visits to Aust Cliff August 2021
The group made 2 visits to Aust Cliffs near the old Severn bridge. We were last there on 12th June 2019 – see that report for the main geological features we saw. An image from our recent visits of a rock embedded in the beach.
The group made 2 visits to Aust Cliffs near the old Severn bridge. We were last there on 12th June 2019 – see that report for the main geological features we saw. An image from our recent visits of a rock embedded in the beach.
Ledbury visit on 11th August 2021
A group of us congregated in a Ledbury car park and Jim led us around various buildings where we looked at specific stones used to construct them, largely from local quarries. The understanding of the rocks’ formation to be gained by just looking at an individual stone was surprising.
The first two images above, (left and top centre) show fosilised tabulate coral and sea shells, both within Silurian aged Limestone. These were part of the Bye Street wall on the Barrett Brownling Institute.
The next (bottom centre) image shows ripple lamination from the beach that this Downton Castle Sandstone was formed from.
The next (right) image was spotted at the top of a door frame on the walk through to the Church. Leisegang bands and redox in this Old Red Sandstone are caused by fluids flowing through porous rock, changing the chemistry and colour of the rock, forming bands, rings or other shapes that do not align with the bedding.
The next (bottom centre) image shows ripple lamination from the beach that this Downton Castle Sandstone was formed from.
The next (right) image was spotted at the top of a door frame on the walk through to the Church. Leisegang bands and redox in this Old Red Sandstone are caused by fluids flowing through porous rock, changing the chemistry and colour of the rock, forming bands, rings or other shapes that do not align with the bedding.
The June Field Trip 2021
The u3a Geology group explored the Angidy Valley that wanders down to Tintern from the Trellech area. The Angidy Brook supplying the power for the iron works and wire works at Tintern from the early Elizabethan days to the late nineteenth century. Our field trip covered Industrial archaeology; the evidence of the control of the flow of the Brook to supply the power for the Works, and a created tidal dock where the Angidy Brook flows into the wider tidal River Wye, for boats transporting goods and people. Eg to bring in the ore, much of which came from Furness in Lancashire; the social history of that community including visiting the fire ruined St Mary’s Church on the Hill where Iron Masters and workers had been buried; their old pathways; the use of the furnace waste products converted into building blocks; the now stone slab covered leats used as pathways. Flora and fauna to be admired, especially at coffee break.
Then, of course, there was Geology. Rocks to be considered. Near Tintern Abbey, the River Wye flows through the Tintern Sandstone; it is part of the Old Red Sandstone Group. The Tintern sandstones are finer than the Old Red Sandstone. The Tintern Sandstone was used to construct Tintern Abbey, founded in1131. The main site for its working was at Barbadoes Quarry in part of the steep woods above Tintern known as Barbadoes Hill. However a large disused quarry in the Tintern Sandstone occurs on the Gloucestershire side of the river, just several hundred metres upstream of the Abbey. The village of Tintern is littered with Tintern Sandstone used as building blocks, much may have been reused from the Abbey building. There was Carboniferous Limestone, although it seemed like the sandstone, Jim’s little bottle of weak acid made it fizz. The other significant material found was a furnace waste product, blue tinted glass like lumps. The iron works supplied Bristol Glass works with a by-product for the colouration of their Blue Glass manufacture.
Then, of course, there was Geology. Rocks to be considered. Near Tintern Abbey, the River Wye flows through the Tintern Sandstone; it is part of the Old Red Sandstone Group. The Tintern sandstones are finer than the Old Red Sandstone. The Tintern Sandstone was used to construct Tintern Abbey, founded in1131. The main site for its working was at Barbadoes Quarry in part of the steep woods above Tintern known as Barbadoes Hill. However a large disused quarry in the Tintern Sandstone occurs on the Gloucestershire side of the river, just several hundred metres upstream of the Abbey. The village of Tintern is littered with Tintern Sandstone used as building blocks, much may have been reused from the Abbey building. There was Carboniferous Limestone, although it seemed like the sandstone, Jim’s little bottle of weak acid made it fizz. The other significant material found was a furnace waste product, blue tinted glass like lumps. The iron works supplied Bristol Glass works with a by-product for the colouration of their Blue Glass manufacture.
Thanks to Jim for all his time and effort in arranging interesting trips and talks.
Gillian Knowland
October 6th 2020 Walk around Craig-y-Dorth
It was Bill Bryson who wrote “It isn’t easy to become a fossil…. First you must die in the right place” [1]
My take on this is that it isn’t easy to become a Geologist either. First you must have a bloomin’ good imagination, an attribute that has obviously got lost in the coils of my DNA.
So thank goodness for Jim Handley’s explanations of how, what and where lay (and, in particular, no longer lies) in front of us as we surveyed the fantastic vistas on our circular walk on October 6th.
Our gentle perambulation around the Craig-y-Dorth outcrop soon enabled us to pause near a pylon to see - touch, even - a fault line that had pierced the quartz conglomerate leaving small areas of slickenside with striations showing the scraping movement of the rocks.
Further round the circuit a dramatic 180° panorama opened up from our vantage point to enable Jim to point out what is effectively a blueprint of relative hardness that gives the ridges and valleys. Huge erosions have left those familiar peaks - the remains of erosion and glaciation - Hay Bluff to the north, the Blorenge in the west, the Skirrid and Sugar Loaf in front of us, plain to see, and the distant hills of the south Wales valleys towards the south.
The closer, sweeping lower ground is developed on the weaker Raglan mudstone which actually comes to the surface near Mitchel Troy and where the A40 enters the Gibraltar Tunnels.
The higher ground comprises the more resistant sandstones and calcretes in the St Maughans Formation above which lies the Brownstone Formation where those familiar peaks are often capped with resistant quartz conglomerate.
To the south we could just make out the upper hills of the south Wales valleys the coalfields of which were laid down in the Carboniferous, when Wales was sitting in shallow, warm waters around the Equatorial latitudes. And after seven months of Covid restrictions, I most certainly can’t imagine that.
Many thanks Jim, for such an instructive, absorbing and memorable walk.
[1] Bill Bryson ‘A Short History of Nearly Everything’
It was Bill Bryson who wrote “It isn’t easy to become a fossil…. First you must die in the right place” [1]
My take on this is that it isn’t easy to become a Geologist either. First you must have a bloomin’ good imagination, an attribute that has obviously got lost in the coils of my DNA.
So thank goodness for Jim Handley’s explanations of how, what and where lay (and, in particular, no longer lies) in front of us as we surveyed the fantastic vistas on our circular walk on October 6th.
Our gentle perambulation around the Craig-y-Dorth outcrop soon enabled us to pause near a pylon to see - touch, even - a fault line that had pierced the quartz conglomerate leaving small areas of slickenside with striations showing the scraping movement of the rocks.
Further round the circuit a dramatic 180° panorama opened up from our vantage point to enable Jim to point out what is effectively a blueprint of relative hardness that gives the ridges and valleys. Huge erosions have left those familiar peaks - the remains of erosion and glaciation - Hay Bluff to the north, the Blorenge in the west, the Skirrid and Sugar Loaf in front of us, plain to see, and the distant hills of the south Wales valleys towards the south.
The closer, sweeping lower ground is developed on the weaker Raglan mudstone which actually comes to the surface near Mitchel Troy and where the A40 enters the Gibraltar Tunnels.
The higher ground comprises the more resistant sandstones and calcretes in the St Maughans Formation above which lies the Brownstone Formation where those familiar peaks are often capped with resistant quartz conglomerate.
To the south we could just make out the upper hills of the south Wales valleys the coalfields of which were laid down in the Carboniferous, when Wales was sitting in shallow, warm waters around the Equatorial latitudes. And after seven months of Covid restrictions, I most certainly can’t imagine that.
Many thanks Jim, for such an instructive, absorbing and memorable walk.
[1] Bill Bryson ‘A Short History of Nearly Everything’
September 2020 Field Trips to Great Doward
Two field trips to Great Doward – September 2020
Due to Corvid 19 limitations we took 2 small groups on different dates. Both visits were led by Jim and took in the same three locations.
Lord’s Wood Quarry.
Here we made use of the extensive information prepared by the Earth Heritage Trust as a case study for interested students. Text, annotated diagrams, visual recreations of past conditions and even drone footage had been very effectively put together. These enabled us to appreciate the different depositional and weathering environments that had occurred over 350 million years ago and in locations within the southern hemisphere.
Severn Sisters viewpoint
A visually stunning situation overlooking the Wye gorge downstream from Biblin’s Bridge. The prefect place both for our coffee stop and to recap how the gorge was formed as an example of superimposed drainage triggered by a change in relative land and sea levels.
King Arthur’s Cave [and others nearby]
From the geological point of view we discussed its formation and how the external water flow involved may well have been part of an incised meander of the Wye flowing at this much higher level.
Using material gleaned from a current exhibition in Hereford, we talked about how archaeology had shown the cave had been used by both humans and a wide range of animals during the glacial and inter-glacial conditions of the last Devensian Ice Age.
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
Click here for Simple Introduction to Chemistry for Geologists
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
Click here for Simple Introduction to Chemistry for Geologists
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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