At the last meeting Tony Thorp gave an illuminating talk on geological thin sections, the history and practicalities.
It was Henry Clifton Sorby (1826-1908) whose work laid the foundations of microscopical petrology which became the cornerstone of geology. A man of independent means, he took an interest in microscopy and following in the footsteps of William Nicol and sir William Brewster he learned to make transparent sections of specimens like teeth and bones for observation under a polarising microscope. Of greater importance was the fact that he made thin sections of rock and was the first person to appreciate it's value. His thin sections were 0.03mm (30μ) in thickness which is now the standard.
Tony went on to explain the use of the polarising microscope and the property of birefringence. In other words, as polarised light passes through a thin section the different minerals both refract and often re-polarise the light, so that light waves leaving a section are no longer aligned. By inserting a second polariser at 900 to the first all lightwaves that have not been re-polarised will be cut off and appear black. But any that were re-polarised will give a strong colour. Hence the patterning seen when observing a section.
Finally advice was give on how to make your own sections at home. I should add that Tony's ingenuity on achieving this was remarkable.
At the next meeting Michele Becker will give the ins and outs of bricks and brickmaking.
Thursday 31st August 2017
At the last meeting club secretary Bill Bagley gave a very informative talk on fossil wood. The talk commenced by a look at petrified forests throughout the world, from those in the UK at Glasgow, Brymbo and Lulworth Cove to those in the national park Arizona and on the Greek island of Lesvos. Bill then went on to describe the process of petrification which occurs in two stages of permineralisation followed by replacement and petrification. The original plant material may be replaced with silica, calcite or pyrite or another inorganic material like opal.
The talk ended with Bill showing the audience examples of fossil wood for sale on the internet and although fine specimens were a bit outside the pocket of most of us!
The next talk will be on Wednesday 20th September when Tony Thorp will give a talk entitled “Making and Using Thin Sections”
Saturday 22nd July 2017
GEOCONSERVATION AND THE SALTSCAPE PROJECT
Professor Cynthia Burek FGS from University of Chester gave the evening lecture on Wednesday 21 June 2017. Taking the title ‘Geoconservation and the Saltscape Project’, Cynthia introduced the concept of geoconservation and illustrated it with interesting references to a £1.5 million Lottery project which is protecting many aspects of the heritage of a huge salt industry which once existed in the Weaver Valley of Cheshire. The first Lottery application in 2012 failed, perhaps due to the Olympics, but a second application in 2014 was successful.
Geodiversity is part of the natural setting, an integral part of nature, and merits conservation in the same way that living species do. Geoconservation is action taken with intent to conserve and enhance geological and geomorphological (landform) features, processes, sites and species. Professor Burek, is the only professor of geoconservation anywhere, as far as she knows, and she emphasises the operative word, ‘action’. Mostly geoconservation applies to sites. There are exposure sites where there is usually more of the same behind the exposure; and integrity sites where a deposit or landform is an irreplaceable feature; and there are finite sites which, without conservation, would have a limited lifespan. There are also different strategies for conservation. Exposure sites merely need to be maintained but integrity and finite sites need to be conserved or preserved.
Unlike conservation practice in the biological and archaeological sciences, which is underpinned by public concern and legislation, geoconservation is a newcomer. Although geodiversity in a sense underpins biodiversity, its legislation is limited to a single reference in a paragraph of Planning Policy Guidance (PPG) 16 for England & Wales, which deals with archaeology and planning, though statutory protection of a geological site can be given in exceptional circumstances by designation as an SSSI (site of special scientific interest). Otherwise there is no legislation framing geoconservation. There are however, Geoparks, a UNESCO initiative, and there is the Geological Conservation Review (GCR), forty-five volumes of public record which documents important geological sites in the UK. These are all advisory regarding protection, as is the RIGS scheme, the designation of Regionally Important Geodiversity Sites (in Wales), or LGS, locally important geological sites (in England).
Cynthia outlined the nature of the salt industry around Winsford, Northwich and Middlewich (‘wych’ means salt). It lies in the Mercian Mudstone Group of the Triassic period. Iron Age peoples knew of it and the Roman 20th Legion exploited it. It is still used across the UK today. The underground caverns are so huge it can take half an hour to drive to the present salt face. Wet salt occurs in brine springs controlled by pumping, and dry salt is mined beneath an impermeable clay layer. A geological component of the Lottery project has included the identification of nine sites now reported to the LPA as requiring RIGS designation. Auditing is underway, with four already completed. Two conferences and six geological trails with leaflets are included in the work.
Clearly the Saltscape Project is one which it would be interesting for MWGC to visit. A lively discussion ensued, especially regarding the need to make RIGS information freely available on the internet wherever practicable, especially when it had been generated using public funds, a view with which Cynthia seemed in broad agreement.
Thursday 1st June 2017
From Heaven to Hell: a tale of two valleys
John Rodgers, President of the Cumbrian Geological Society guided Mid Wales Geology Club in the Lake District on a memorable weekend in 2016, and now has visited us at Plas Dolerw, Newtown to deliver a fascinating evening lecture in May 2017. John holidayed some years ago, driving through Death Valley in eastern California. This is a newly created landscape, with modern geomorphological features, one of the hottest places on the planet – average July daytime temperature 115ºF (46ºC), devoid of vegetation, a far cry one might think from the paradise which is the Vale of Eden in his home county of Cumbria. But you would be wrong to think that, as he amply demonstrated. He showed a strong similarity between the landscape features of Death Valley and those of Eden Valley, with one major difference: Death Valley is a new landscape still in formation, but the rocks of Eden Valley were created 250 million years ago when England was a hot, dry, unvegetated desert lying within the supercontinent of Pangaea. Since then Eden Valley has been covered and finally uplifted and eroded to reveal many aspects of its ancient depositional environment; it is an ‘exhumed landscape’.
John took us through many of the similarities between the two valleys: Death Valley as it is now, and Eden Valley revealed as it was long ago. Both valleys have mountains either side, with a faulted graben between, creating an arid valley floor, dry for long periods but with flash floods producing alluvial fans spreading from the mountainsides onto the valley floors. Imbrication (stacking alignment of the stones) reveals the flow directions. And even the differences brought about at a colder time by different snowfall on opposite valley sides can be discerned. On both valley floors magnificent wind-blown, crescent-shaped barchan sand dunes appeared, so characteristic of sandy deserts. As global sea levels began to rise, high evaporation from salt water lakes (playa lakes) led to salt deposits, and then to gypsum; dessication cracks can also be seen. The famous geological principle ‘the present is the key to the past’ enables us to interpret the relict structures of the beautiful Eden Valley in the context of those processes seen in action today, and in the geologically recent past, in the hell-hole which is Death Valley.
The next meeting will be on Wednesday 21st June when Prof. Cynthia Burek will give a talk entitled: Geoconservation and the Saltscape Project
Wednesday 10th May 2017
At the last meeting Sue Purcell gave a delightful talk on how, the structure, colour and form of rocks and minerals has influenced her work over the years. The works included acrylics, oils and pastels and in addition she had brought along a skirt which featured printed rocks and pebbles that she had produced many years previously.
The next meeting John Rodgers ( leader of our summer weekend 2016 in Cumbria)will give a talk entitled: “A Tale of Two Valleys” which will focus on the differing geologies of Death Valley California and the Eden Valley Cumbria.
Monday 17th April 2017
At the last meeting Prof. Paul Leonard took us through many of the projects he has been involved with in relation to his work as advisor to the government and to various industries. The work was wide ranging from the nuclear industry to dredging and the marine environment. It was a highly interesting talk and gave us insight into a world few of us know.
The next meeting will be on Wednesday 19th April when artist Sue Purcell will give us another of her popular talks linking art and geology. This year her talk is entitled: Rocks and Minerals in Art: an illustrated talk with drawings and paintings.
An example of her work can be seen below.
Friday 3rd March 2017
At the evening meeting on 18 February 2017 local historian Edward Parry gave a talk on the development of residential building style, mostly in and around Montgomeryshire. Titled ‘Building the Past’, the slide show presented numerous old buildings revealing the wide range of building materials seen in our urban and rural buildings over more than three hundred years, including a number of oddities. The talk produced a lively discussion.
The next meeting will be on March 15th when Professor Paul Leonard will give a talk entitled: Importance of Geology in Government Policy: a marine perspective.
Wednesday 8th February 2017
Following the club’s AGM on 18 January, member Nick Platt gave an entertaining short talk recalling his first job, as a junior site civil engineer at Clywedog dam during 1963-67. Work had hardly started when he arrived. Numerous old black & white photos showed a muddy Clywedog valley floor. Soon they were blasting out deep foundations for the dam and the buttresses which support it. Nick recalled how that was a time before surveying was supported by GPS and before calculations were done on a computer. Clywedog is the tallest concrete dam in Britain so everything was surveyed with great care and results laboriously calculated. An early task was to build a temporary bridge across the neck of the valley so work could be undertaken on both sides.
The river was supposed to flow around the workings through a 10 ft (3m) pipe specially laid for the purpose. Unfortunately, when it rained very hard one winter of construction , the laying of a single 10 ft diameter pipe, instead of a double pipe, proved to have been an inadvisable cost saving. The floods which Llanidloes town residents remember that year, are also remembered by workers on the washed out construction site! The dam is now one of the beauty spots of Mid Wales but in those days it caused offence to some minorities. Cranes provided just the target the Welsh Nationalists needed to try interrupt the work, but such was the hectic pace of activities that progress was only delayed a few weeks when one of the crane masts was blown up by activists.
After the talk, questions included the curious shape of the dam, bulging downstream from the reservoir instead of upstream into the reservoir. But Clywedog is a buttress dam, in which the water pressure is transferred to buttresses buried in the hard rock of the river downstream of the dam rather than outwards through the curvature to the softer valley sides.
The next meeting will be held on Wednesday 15th February when guest speaker Edward Parry will give a talk entitled: “ Building History:materials and style of buildings in Mid Wales”
Even if 2017 does not look good on the political front, for Mid Wales Geology Club it is a year in which to celebrate our 20th anniversary. Originally named the “Llanidloes and District Mineral Collectors Club”, it was founded by the present secretary, Bill Bagley and the late Jim Nicholls. The club has grown and changed over time expanding it’s interests to include other aspects of geology like sedimentology, stratigraphy, geochemistry, geophysics and geomorphology.
The anniversary will be celebrated by a day long series of talks and demonstrations in June.
Monday 14th November 2016
At the October meeting, member Tony Thorp gave a talk on “Diamonds”, in particular synthetic diamonds, but excluding gems. The contribution which diamond research and particularly that of Loring Coes made to geology is little acknowledged; but his synthesis of some forty metamorphic and other minerals enabled geologists for the first time to establish the P/T phase diagrams so essential in working out the provenance of metamorphic rocks.
Anyone interested in gems and the story of how De Beers operated the most successful cartel in marketing history for over a century, should consult “The Death of the Diamond” by Edward Jay Epstein. It is a good read, and one of the few books on diamonds unsullied by output from De Beers and Ayers publicity departments. It is now somewhat out of date, so supplement it by searching for ”Element Six”, or go to www.e6.com (De Beers have always been coy about using their own name!) Diamond possesses extraordinary mechanical, electrical;, optical, chemical and thermal properties which have made it a critical strategic material, particularly in times of war.
After Lavoisier and Smithson Tennant showed that diamond was indeed 100% carbon, like common graphite, researchers have endeavoured to convert the one into the other.
The discovery, in the 1870s, of primary diamonds at Kimberley in South Africa concentrated research into high temperatures and high pressures. James Hannay, Henri Moissan, Crookes, Parsons and others all failed, often in dangerous experiments ending in explosions, to produce diamond.
Before the turn of the century, the limit to achievable pressures in the laboratory was only some 2-3000 atmospheres. It was Percy Bridgman, regarded as the “Father of high pressure chemistry” and a Nobel laureate, who opened the way to higher pressures by inventing the “Bridgman Seal”, a simple device, based on the “de Bange” breach mechanism (invented in 1877 and still in use for the field pieces firing the salute on the queen’s birthday). With this device he defined the high pressure phases of dozens of materials, famously discovering ice VI, stable at 95 °C. However, although he squeezed carbon to over 100 000 atmospheres, he never produced diamond.
With World War 11, diamond became a critical strategic material and in 1941 GE, Norton Abrasives and Carborundum sponsored Bridgman in his efforts, however he was co-opted onto the Manhattan project and research was interrupted. (The behaviour of uranium and plutonium at high pressures was critically important at that time!)
With the breakup of the Bridgman team, Norton continued research on their own and their Loring Coes (of coesite fame) developed a simple pressure assembly comprising an Alundum (proprietary alumina-based ceramic) cylinder with a quarter inch bore and a steel reinforcing belt to keep it in compression. In the bore were top and bottom carbide pistons which could be used as electrodes and could apply pressure to a sample. If necessary, the sample could be surrounded by a carbon cylinder as a heating element.
With this device Coes proceeded to produce a whole series of minerals which were associated with diamond in kimberlites and eclogites, including garnets, pyroxenes, staurolite, kyanite, zircon, idocrase, tourmaline, beryl, sphene and topaz. He also squeezed quartz to 35000 atmospheres at 800 °C, producing coesite, which was unknown in nature at the time.Although Coes enabled the whole field of metamorphic mineralogy to be put on a quantitative basis, he never achieved diamond synthesis.
This was left to a team set up at GE as project “Superpressure”. The GE team included Francis Bundy, Herb Strong and Tracy Hall. The team worked very much as individuals and developed a series of different geometries of carbide anvils, retaining belts and gaskets. Some four years into the project, with no results from hundreds of experiments, most of which had a duration of a few hours, top management were considering whether to continue or not. This was a moment of truth and in a last ditch effort, Herb Strong set his apparatus up with a sample of “Steco” (a case hardening compound containing carbon and iron). He aimed at 50 000 atmospheres and 1250 °C and left it for 16 hours, overnight. Next day, he opened it up and there were apparently no diamonds, but he was interested in how much carbon was dissolved in the iron and sent a blob of fused material to metallurgy, for polishing and examination. A week later, metallurgy came back saying they could not polish the sample as it gauged up their polishing wheel! Eventually, two small diamonds were separated from the sample. It seemed they had succeeded. The next day, Dec 16th 1954, Tracy Hall set up his own apparatus in which the sample was contained between tantalum discs in the press and set to 100 000 atmospheres and 1600 °C and ran for 38 minutes. When opened, he saw dozens of diamonds stuck to the tantalum disc!
Strong’s result could not be repeated, but Hall’s was reproducible. Diamonds had been synthesised for the first time in a commercially reproducible procedure.
Meanwhile, out on a limb, in Sweden, the eccentric inventor, Balzar von Platen, working with the Swedish electrical firm ASEA developed a complex, expensive device comprising a cube packed with carbon, iron and a thermite mix, surrounded by carbide and steel wedges and miles of piano wire, in which he probably managed to produce the world’s first synthetic diamond in February 1953; but it was covered by a cloak of secrecy and the process was not revealed until after GE had announced their success. It is a mystery how this came about. It was either just commercial secrecy or possibly that they only discovered their small diamonds after the GE announcement.
So much is history, patents have run out and diamond presses are now commercially available for modest amounts. Diamonds are cheap and of higher quality than naturally occurring stones.
Even the amateur geologist can afford diamond hones, cutting and lapping discs for polishing specimens and making thin sections. The industry has moved on and synthetic diamonds are now produced by several processes, including crystallising from plasma (CVD) and explosive processes. A once rare material is in everyday use and we are all the better for it.
The Next Meeting will be on Wednesday 16th November. This is the member's evening with Bill Bagley and Colin Humphrey guiding us through their visit to Iceland in 2015.
Tuesday 11th October 2016
At the September meeting Dr Sara Metcalf gave a very interesting talk on Mesozoic mammals and mammalian evolution. Originally the finding of fossils of Mesozoic mammals and their immediate ancestors was fragmentary but since the 1990's many new fossils have been found, especially in China. The well-preserved fossils and the combined discipline of molecular phylogenetics have greatly enhanced the knowledge about mammalian evolution.
Using anatomical diagrams, cladograms and even a short YouTube video, Dr Metaclf took us through the evidence for evolution and the “family tree” of modern day mammals.
The next meeting will be on Wednesday 19th October when Tony Thorp will give a talk entitled “Diamonds from Peanuts...For Peanuts...And how Geologists can use them”
Wednesday 14th September 2016
At the August meeting David Pannett ( Shropshire Geological Society) explained how many of the landscape features observed in the Severn Valley are the result of glaciation. He explained how glaciations have occurred a number of times in the past 2-2.5 million years. The last of these being the Devensian from about 120,000 to 11,000 years BP.
The ice from these glaciations have given rise to many features to be found in the landscape, including moraines, kettle holes, outwash basins and river terraces. The origin of these features was explained. He took us on a trip up the Nant-y-Llyn valley to Pistyll Rhaeadr explaining the stepped profile of the valley, the corries and the classic hanging valley that is Pistyll Rhaeadr.
The talk was interesting and informative.
The next meeting will be on 21st September when Dr. Sara Metcalf will give a talk entitled: Mesozoic Mammals.
Monday 15th August 2016
Our next event will be on Wednesday the 17th of August, where guest speaker David Pannett from the Shropshire Geological Society will present his talk “Glacial Features in the Severn Basin”
Sunday 31st July 2016
At the last meeting Dr. Chris Simpson presented a snapshot of the geology to be found on the island of Cyprus. The main focus of the talk was the Troodos Ophiolite. Ophiolite is a fragment of oceanic crust and the underlying upper mantle that has been uplifted and emplaced onto continental crust.
The Troodos ophiolite was created during the complex process of sea-floor spreading and formation of oceanic crust and was emerged and placed in its present position through complicated tectonic processes related to the collision of the Eurasian plate to the north and the African plate to the south.( Geological Survey department cyprus) It is seen as the most complete, intact and studied ophiolite in the world.
With many good photographs Dr Simpson worked his way up through the stratigraphic column of the ophiolite commencing with the ultramafic rocks like harzburgite composed of olivine and orthopyroxene. Harzburgite along with dunite are interpreted as a “mantle sequence”, which represents residue from partial melting of the upper mantle. The next sequence was the layered gabbro with massive gabbro above. The gabbro is a residual of magma. During the slow cooling, the heaviest minerals lie in the depths, thereby creating the darker coloured gabbro, with light-coloured varieties in the higher layers. At higher levels and in small pockets, the products of this different crystallisation are to be found, known as plagiogranites or granophyre.
Above this is a sheeted dyke complex. They are pathways through which molten basaltic magma rose from the mantle to the seafloor where it solidified as a pillow lava. Some of the magma did not reach to the surface and solidified as dykes, consisting of dolerite. Above these are the volcanic rocks consisting of pillow lavas and lava flows. Basalts predominate in the pillow lavas and are characterised by large spherical to ellipsoid pillows. Their crust is glassy due to the rapid cooling but the insides of the pillows is honeycombed due to sudden expansion of gases in the lava.
The geology along with the wonderful weather makes Cyprus a lovely and interesting place to visit.
The next meeting will be held on 17th August when David Pannett will give a talk entitled: “Galcial Features in the Severn Basin.”
Wednesday 8th June 2016
Our next event will be on Wednesday the 15th of June where guest speaker Dr. Chris Simpson will give his talk “Cyprus Geology: a snapshot”
Monday 23rd May 2016
This month we had a talk by Jack Davies on “Reflections on Geomorphology”. It was much more than an investigation of the development Britain's geomorphology, more a geologist's life story. Starting with childhood freedoms exploring Britain by cycle, through student days, to theses typed in DS with multiple carbons, he had developed a deep understanding of the development of landforms and an appreciation of the uniquely diverse geology of the British Isles.
He described, from a personal perspective, the landforms resulting from the Cretaceous transgression of Wales, followed by Mid Tertiary uplift and the removal of the chalky deposits, with the initiation of drainage and erosion. Stripping back of the Mesozoic cover revealed a wave-trimmed peneplain, with superimposed radial drainage cutting down to the Palaeozoic rocks beneath.
Mid Tertiary uplift elevated the Welsh High Plateau and later negative changes in base level produced the Middle and Low Peneplains with consequent adaptation of drainage.
Later Pleistocene glaciations produced the 400ft, 300ft and 200ft platforms
It was a refreshing approach with no Powerpoint!
The next meeting will be on Wednesday 15th June when Dr Chris Simpson will give a talk entitled: Cyprus Geology: a snapshot
Thursday 12th May 2016
Our next meeting will be on Wednesday the 18th of May, where guest speaker Jack Davies will present his talk “Reflections on Geomorphology”
Tuesday 26th April 2016
Many people are under the impression that science and art are separate phenomena, but the illustrated talk by Sue Purcell showed this not to be the case. Geological landforms, rocks and fossils have inspired artists for generations from Leonardo da Vinci ( and probably before) to the present day.
Throughout the talk Sue took us on a journey from her early days in art to the present and explained how she uses pencil, acrylic and soft pastels to achieve the desired outcome. The art was as varied as the geology. From the micro fossil thecae of a graptolite to the frieze of a slate floor.
Monday 28th March 2016
Our next meeting will be on the 20th of April, where Sue Percell will present her talk “Fossils in Art: an illustrated talk with drawings and paintings”
Saturday 26th March 2016
Chris Martin of CPAT (Clwyd Powys Archaeological Trust) gave a most enjoyable evening talk to Mid Wales Geology Club on 16 March 2016, entitled Remote Sensing in the Historic Environment. Chris is the Regional Archaeologist. He has been with CPAT for 35 years and is in charge of curatorial services, including a vast store of historical records. This was a follow up to the talk he gave last year on historic landscapes in our region. In recent years geophysics has provided new techniques of archaeological investigation but aerial photography has been the most common form of remote sensing over the years. The talk featured many stunning aerial photos, including many motte and bailey remains, which are more numerous in Powys than in any other part of Britain.
Sycharth motte & bailey, Llansilin, once the court of Owain Glyndwr (courtesy CPAT)
Recording of historic landscapes began in 1906 with aerial photography from a tethered balloon, and very soon after from aircraft. Archaeological aerial photography expanded greatly between the world wars. Later, the Cambridge University photographic collection of the 1960s and 70s became especially well known. In our own region Chris Musson took some thirty thousand aerial photos by the time he left CPAT in the late 1980s. These make up the largest part of CPAT’s aerial photo collection (delightful selections of these photos appear in three recently published books). CPAT has 40,000 to 50,000 aerial photos – and around 180,000 photos in all. Crop marks recorded in aerial photos have shown a great number of previously unnoticed subsurface structures/
Thornbury, near Montgomery: crop marks, possibly Roman temple and farmstead (courtesy CPAT)
3-D laser scanning is now used for recording surfaces in precise detail and is simple to do. The intricate detail of buildings and other structures can be recorded in just a few minutes. Lidar uses the same technique for aerial recording of landscape, usefully ‘seeing’ through surface vegetation and recording on a grid of down to a few centimetres. The great topographical accuracy of Lidar is now revealing surface features which do not show as crop marks. On-the-ground walkover geophysical techniques include those well known from programmes like Time Team, especially magnetometry, and electrical resistivity measurement, two easily used methods for determining archaeological anomalies. Short wavelength ground penetrating radar has also been successfully used but is limited to relatively shallow depths and needs specialist skills to interpret the readings.
In the discussion it was noted that Lidar is also much used in geology, but that the common geological technique of seismic analysis finds no use archaeology. Drones are being used in archaeology for small scale Lidar scanning, but it is worrying that dangerous use of drones by the general public might yet threaten their use by professionals. Chris Martin kindly offered to give club members a session on how to access and use the internet Lidar data derived from Natural Resources Wales and held by CPAT. This could be tried in Plas Dolerw or at CPAT’s offices in Welshpool.
Saturday 5th March 2016
Our next meeting will take place on Wednesday the 16th of March, where guest speaker Chris Martin of the Clwyd-Powys Archaeological Trust will present his talk "Remote Sensing in the Historic Environment"
Thursday 11th February 2016
Our next meeting will take place on Wednesday the 24th of February, where Professor Jerry Davies will present his talk “Sea level Change in the Geological Past: recognising the record in the rocks”
Thursday 28th January 2016
On 20 January 2016 the AGM was followed as usual by a short talk, this year by Roy McGurn: ‘The Anthropocene: a new epoch in the making’. An excellent turnout of members showed that he had chosen his subject well. The suggestion is that the Earth is being pushed into a new geological phase in which humans have themselves become a force of nature, exerting a significant effect on our ecosystems. In 2009 the Subcommission on Quaternary Stratigraphy formed a working group with 38 members to examine the case for making the Anthropocene a new epoch. This International Anthropocene Working Group will report in 2016 to the International Commission on Stratigraphy, though a formal ratification can only be made by the International Union of Geological Sciences. Meanwhile the term Anthropocene is already being widely used but without agreement on when this new epoch might have begun. Estimates vary from around 12000 years ago the end of the last Ice Age, when human influence begins to show in the fossil record, up to 16 July 1945, the first testing of a nuclear weapon, and the characteristic isotope marker which resulted. The biggest changes began to be apparent with the start of the industrial revolution, say late 18th cent.
Roy explained the present structure of geological time scales, with twelve geological periods from the Cambrian, and more before that, each divided into epochs and further subdivided into ages. The first attempt to subdivide the geological system came from Giovanni Arduino in the 18th cent, a mere four divisions, further developed by Abraham Werner at the turn of the 18th to 19th cent. Sedgwick, Murchison and then Lapworth developed a more detailed sequence in the 19th cent, on the basis of rock lithology and fossils, but without any idea of actual timescales. Dating had to await the discovery of radioactive isotopes in the 20th cent. The most recent epoch, the Holocene (the last 10,700 years), was finally endorsed in 1969. Changes continue to be made: The Pridoli epoch was a subdivision inserted into the Silurian period even more recently. Each ratified boundary is exemplified with a GSSP (Global Stratotype Section and Point), which is a precise location colloquially referred to as a golden spike. Often the beginning of an epoch is defined as the first appearance of a new fossil species. The beginning of the Holocene is defined as a particular climate change.
If there is to be an Anthropocene, then the term itself means that some aspect of human interference with ecosystems should define the boundary. The Anthropocene seems to be a basically different concept. Does is succeed the Holocene? Or is it a further age of the Holocene? Or maybe even a replacement of the Holocene? Geology has to take the long view; perhaps we will know for sure the Anthropocene was a new epoch only after it has ended! The talk stimulated a lively discussion. Members drew attention to the many ways in which clear and permanent signals of our human activity are already appearing in the geological record: metallic lead from Roman times, exotic materials, new elements, nitrogen from fertilisers, junk in ocean sediments, even new species from experimental breeding and direct genetic manipulation.
The next meeting will be held on February 24th ( note this is the fourth Wednesday) when Prof. Jerry Davies will give a talk entitled: “Sea Level Changes in the Geological Past: recognising the record in the rocks.”
Saturday 9th January 2016
The next indoor meeting will be on Wednesday 20th January. This will be the AGM followed by a talk by Roy McGurn entitled “The Anthropocene: a new epoch in the making”.
Wednesday 2nd December 2015
At the final meeting of the year, members heard a highly entertaining talk by Prof. Alex Maltman on wine, whisky and beer and the role of geology.
To begin, we were introduced to the incredible claims made by those whose job it is to market wines. For example, “You can taste the tectonic plates”; “The wine's secret is the grey-blue Devonian slate”; “Our Shiraz grows on soils 500 million years old”. The use of terms like earthy and stony also reflect the geological role. Yet the role of geology is more related to factors of slope, aspect, inclination, air flow patterns and drainage.
Similarly with whisky. Here the role of water (particularly if they are crystal waters tumbling from granite) is lauded by the advertising companies. Yet again their claims bare little resemblance to reality.
With beer it is slightly different. The very different mineral content of the water in places like Burton, Dublin and Pilsen, determines their very different types of beer. Or it did! Today the water composition is adjusted by the brewing specialists and you can make most types of beer anywhere. The meeting ended with a lively discussion followed by a finger buffet and mulled fruit juice. Professor Maltman was presented with a nice bottle of chianti. You can taste the soils of Tuscany in this wine!
Sunday 8th November 2015
The next meeting will take place on Wednesday 18th of November at Plas Dolerw, Newtown, where guest speaker Professor Alex Maltman will give his talk "Wine, Whiskey and Beer: The role of geology"
Sunday 11th October 2015
The next indoor meeting will be held on Wednesday 21st October when Michele Becker will give a talk entitled “ The Formation of Iron Pyrite” and Colin Humphrey will give a talk entitled “OT Jones: Wales' Greatest Geologist”
Volcanoes in the Classroom and Following in Darwin's Footsteps
At the last indoor meeting Tony Thorp and Michele Becker held a light-hearted evening of rocks. Tony's volcano had everyone holding their breath whilst awaiting the eruption. Michele then went on to explain fractional crystallisation in magma. This was followed by practical demonstrations of turbidity currents, normal and reverse grading. The latter actually being edible!
This evening was followed by a field trip in the steps of Darwin as detailed below.
Our September field trip, on the 20th, followed "In Darwin's footsteps" under the leadership of member Roy McGurn. Our meeting point was at the first location, Pen y Foel Lane, Llanymynech, where Roy explained the background to the dozen assembled members.
In August 1831, England's foremost geologist, Prof. Adam Sedgwick, set out on an expedition to map the "transition beds" of Wales, that had hitherto defied meaningful interpretation. The period was one of dramatic change in the understanding and concepts of geology. Although a biblical interpretation (according to Genesis) was not seriously regarded by many researchers by this time, the concept of some kind of creation was still strong.
For the previous 50 or so years, the theories of Abraham Gottleb Werner had held sway, that the rocks we see are the result of some sort of fluvial action, perhaps floods or deposits left by a retreating sea. The school of thought was broadly known as "Neptunism". Sedgwick himself had used his presidential address to the Geological Society to recant his belief in this theory that very spring.
The succeeding counter argument, perhaps broadly termed Plutonism, was the development of ideas presented by James Hutton in his two lectures to the Royal Society of Edinburgh as far back as 1788. Hutton had postulated the rock cycle, with rocks constantly being renewed from igneous rocks breaking through to the surface from great depth. Hutton could see no sign of a beginning , nor any sign of an end to this process, which finally challenged any concepts of a divine creation, which also postulated a day of judgement.
It could be said that Copernicus challenged the concept of the earth being at the centre of the Universe. (He was wise to publish his works when more or less on his death bed, as in his day such ideas would have amounted to Heresy.). Hutton challenged the idea of a biblical creation, again another heresy in an earlier time. In the summer of 1831, the third prophet who was to eventually challenge man's place at the centre of creation, began his journey here.
It is perhaps how fate works that the grandson of Hutton's friend, Erasmus Darwin, who invoked some ire himself with observations on the immutability of species was asked to accompany Prof. Sedgwick on his quest.
A few yards up the lane, they stopped and no doubt could see in the road cutting, steeply dipping shaley rocks on which Darwin could try out his newly acquired clinometer (a small plaque marks the spot). From this spot they could see the nearby limestone escarpment and quarries of Llanymynech Hill. These are almost flat and, if projected, would have been overhead at this point. These radically different dips would indicate an unconformity, as taken by Hutton to show a break in succession and maybe a period of erosion.
The second location was on Trevor Rocks, above Llangollen, with a view of Castell Dinas Bran and up the Dee valley. Sedgwick had business in Llangollen, with Robert Dawson, a surveyor, who was to furnish him with notes on the limestone of the Vale of Clwyd.Sedgwick's mission was very vividly set out for him here. The prominent Mountain Limestone, as it was known is easily identified by its distinctive lithology. It was known elsewhere for the "Herefordshire Beds" to occur beneath the Mountain Limestone, again with a fairly distinctive lithology. Below the Herefordshire Beds, into deepest and darkest Wales, the lithology was a lot less distinctive and geologists at the time were having great difficulty making any sense of it. It was generally referred to as the transition beds..
Sedgwick needed to find a sequence of strata that took him down into the transition beds and from which he could derive fossil sequences to identify them. Ideally following the maps of the time, he needed to follow a sequence down from the Herefordshire Beds. (= Old Red Sandstone). Sedgwick was using a later version of Greenough's map that had partially corrected the Herefordshire Beds error. The red sandstone in the Vale of Clwyd had identified as New Red Sandstone, a rock common in England and known to be some way above the Mountain Limestone. However a small sliver of exposed rock was still indicated below the Mountain Limestone and was known as the Old Red Sandstone.
At this location the scree covers the base of the limestone. Tantalisingly traces of red soil may be found in places along here, a possible indicator of red sandstone (Old or New) beneath.
As Dinas Bran is significantly higher than the base of the limestone, even if the latter is "extrapolated" towards it, there seems to be something else happening between the two. A small fault is marked on the modern maps which must take the southern side up a little, so any base to the limestone will have been above the hilltop and hence long eroded away.
Sedgwick was not going to find much to help him here.
The third location was at Velvet Hill, next to the road up to Horseshoe Pass, at the entrance to Valle Crucis Abbey. Darwin's enthusiasm for his new clinometer is evident, he records:
"Saturday 6th August Vale of Crucis.
The bank above the abbey consists of Clay slate, which breaks at regular intervals, striking nw by n, d,25 to the ne by n. at different parts road observed beds of diluvium very Shrops only no sand:also boulders of trap."
The entrance to the abbey contains a small well. This is likely to have been the original road and the well may well have been a stop Sedgwick made to water his horse ahead of the long climb up Horseshoe Pass. Darwin busied himself with his notebook and clinometer.
Darwin went on to note.
"Beyond Vale of Crucis on the road to Rurhven the Limestone is seen having a grand escarpment to the west: The contrast between this and the more regular slope of the Clay Slatew gives more grandeur to the views. The Greywacke generally covered by gorse, Heath and Fern: the limestone either bare or the verdure very green." However Darwin's observation shows how they were using geomorphology to identify the outcrop of limestone. Beyond the pass the escarpment changes, with the rounded, heath covered greywackes he noted, seeming to break into the line of limestone hills, and the limestone outcropping into the greywacke area.
Next Step. Darwin notes "About 1/2 mile beyond Daforn, a black bituminous Limestone organic remains veined quartz in parts reddish in one part strata exactly arched. The line N by E."
This note refers to a disused quarry at Plas Newydd where, indeed we found limestone crags, reddish in parts. No arch, but much limestone may have been removed.
Darwin goes on "1/2 mile further a tortuous valley through Clay Slate generally dipping to the E. About a mile from the Ruthven beds of sandstone"
This is Nant y Garth, the faulting brings up the Silurian beds again and forms the end of the Vale of Clwyd. At its end, the road opens into a plain with hills either side, especially a clear line of them to the north. We are into Triassic New Red Sandstone, but outcrops are rare although the soil is red.
Appropriately, we ended our trip at the Castle Hotel, now a Wetherspoons, where Sedgwick and Darwin spent the night. Darwin notes:
"Ruthin: takes its name from the new Sandstone on which it is built. The soil is for some miles about the town and the plain may be considered of that formation. In most places covered up by diluvium. Mile to the west of the town a quarry of worked. The rock is spotted with brown the stone at Cardeston. Overlying Magn conglomerate. It is very irregular strat but the rock on which the castle is built nearly horizontal seams. petrifications this there are some beds of Old red Sand striking the same ways as the overlying stone but dipping at a greater angle. A further is more clearly visible in a water"
The elusive ORS has finally reappeared and Sedgwick may have thought he had an opening into the lower succession, the notes stress this rock is UNDER the limestone and does have all the appearance of the beds found in Herefordshire. However the boundaries into the lower beds are generally faulted here, in its simplest form the Vale of Clwyd is a rift valley, down faulted during the Upper Carboniferous-Triassic. Sedgwick was not to find a succession into the transition beds anywhere in North Wales, as the unconformity Darwin didn't observe way back in Llanymynech represented a break in deposition and a period of erosion that covered the entire Devonian period and the beginning of the Carboniferous.
Members had enjoyed a fascinating trip and Roy's research and leadership were really appreciated. Most members started to return home at this point, but noted that Ruthin contained a remarkable assortment of building stones, particularly evident in St. Peter's Church, where Sedgwick and Darwin attended Matins on Sunday 7th August 1831. They perhaps viewed the pot-pourri of stone used in its construction.
Ruthin seems worth a full day trip in its own right. Perhaps we could follow more footsteps at a future date.
Wednesday 9th September 2015
At the last indoor meeting 24 members enjoyed a talk by Graham Levins of the Welsh Mines Preservation Trust. Graham commenced by taking us to a variety of mines around Mid and West Wales. With some super photos, we were shown around the mines, above ground, and then descended into the mines themselves. He talked about his and the group’s involvement with the preservation of mining history in Wales.
Graham then went on to describe the celebrations surrounding the 400th anniversary of Sir Hugh Myddelton’s new river in London. In September 1613, the self-taught civil engineer brought clean drinking water to London through a new river to the heart of the city. The group visited the mines Sir Hugh was associated with in Mid Wales. Part of this included holding a short service at the site of the derelict chapel that Sir Hugh built for his miners C.1620. This was done in memory of his work, and the miners that worked there almost four hundred years ago.
The club would also like to express their thanks to Graham for the collection of minerals he has kindly donated.
The next indoor meeting will be on Wednesday 16th September when Tony and Michele will hold an evening on rocks. This will include how a volcano erupts , fractional crystallisation, the development of normal and reverse grading, tubidity currents and more.
Wednesday 5th August 2015
Our next meeting will be on Wednesday the 19th of August where guest speaker Graham Levins will give his talk on “The Mines of Central Wales: our industrial heritage”
Monday 20th July 2015
On Wednesday 15th of July 20 members and visitors attended the “Building Stones of Llanidloes” walk led by Michele Becker and Colin Humphrey. The group looked at the chapels, church, town hall, bank and short-bridge where a description of the type of building stone used, it’s geology and the history of the building was given. The talks focused on the inter-relationship between the use of stone and brick as building materials and the historical changes in the town.
Fossil Day with Joe Botting and Lucy Muir Sunday 26th July – Meet at the Commodore Hotel at 11am. The day will consist of talks on graptolites and the Llanfawr Lagerstatte. This will then be followed by a field trip to Llanfawr quarry (in Llandrindod) to find and identify graptolites to species level, in order to work out the age of the rocks.>
Joe and Lucy are also willing to identify any fossils you would like to bring with you. Don’t forget a packed lunch.
Sunday the 9th August. Andrew Jenkinson will take us round the Stiperstones, looking at "The making of a landscape"
Time & venue - 10.30 a.m. at the Auction Yard car park, Station Street, Bishop's Castle.
A circular itinerary, sharing cars, to look at sites illustrating the geological history of the area from the south end of the Long Mynd, across to the Stiperstones ridge, north to Snailbeach and return to Bishop's Castle for 4.30 to 5.00. Bring a packed lunch.
On the 19th August, Graham Levins, of the Welsh Mines Society, will talk on “The Mines of Central Wales: our industrial heritage”.
Sunday 31st May 2015
At the last indoor meeting Chris Martin ( Clwyd-Powys Archaeological Trust,CPAT) gave a very interesting talk on the evolution of CPAT from its inception in 1975 to the present day. CPAT is one of four Welsh archaeological trusts, with most of its work being in the Clwyd-Powys area.
CPAT commenced for the recording of archaeological information obtained from excavations which then evolved to include all other types of archaeological data. The data was, at first, kept on paper records but then became computerised and known as the “ Historical Environmental Record”. Information for the records was obtained from a wide range of sources, including old maps, OS records, aerial photography and much more. The record itself covers many areas, including,standing stones, iron-age enclosures, Medieval castles, agricultural buildings and defence and industrial remains. More recently, not only the sites are recorded but the environment in which they are located is also recorded. Therefore information about turnpikes, strip fields and canals now appear in the record.
Chris then went on to explain the methodology of record collecting. There are two different methods used:Firstly, The registry of landscapes of outstanding and special historic interest in Wales and historic landscape characterisation. This looks at the historic content of the landscape and gives purely a narrative story. Secondly, the historic landscape aspect known as LANDMAP. This looks at the surviving historical elements in the modern landscape. It looks at different aspects within the landscape and then produces a digital map. Both of these methods were developed by Cadw, CCW (Countryside Council for Wales) and the Welsh Archaeological Trust. All the information gathered can be used to provide advice to planning authorities, farmers, landowners, and environmental organisations.
All the above was brought together by looking at the report produced on the Historic Settlements in Flintshire.
The next indoor meeting will be on Wednesday 17th June when Tony Thorpe will give a talk entitled: “Concretions and How they Form.”
Sunday 10th May 2015
The next event will take place on Wednesday 20th of May where guest speaker Chris Martin (CPAT) will deliver his talk “Historic Landscapes in Wales: the work of Clwyd Powys Archaeological Trust”
Tuesday 7th April 2015
The next event will be on the 15th of April, where Roy McGurn will be giving his talk on The Geology of War
Wednesday 25th March 2015
A very informative talk was given by Kevin Voyce ( Hydrogeologist, Environment Agency) on the strategic water resource management of the River Severn catchment.
The upper River Severn catchment, here in Mid-Wales, is underlain by Ordovician and Silurian mudstones, shales and grits. These rocks have a low permeability and therefore do not store water, so that most of the water stored is above ground. The Clywedog dam was built in the 1960's to regulate the flow in the River Severn. If flow in the river is low, a release valve can be opened to release water from the reservoir and into the river to provide flow. The ground water storage in Mid-Wales contrasts sharply with that found across the border in Shropshire. Here the rocks consist of Permo-Triassic sediments of sandstones and mudstones. The sandstones have large pore spaces and therefore large storage capacity and high transmissivity. A scheme for supplementing the River Severn flow via use of the ground water has been set up. This required the drilling of a line of boreholes which draw water from the groundwater reserves and pump the water into the river to enhance flow.
Thus the hydrogeologist needs to understand the properties of the rock, how much water it can store and its transmissivity. Also knowledge the presence of joints and faults in the rock is necessary as this can markedly affect storage and flow within the aquifer. Abstracting water from the aquifer may also lead to problems in nearby areas, for example with a wildlife reserve or a private borehole. Therefore safeguards must be put in place to protect other water users and monitoring must be undertaken. This includes checks on water levels, chemical analysis and monitoring of wildlife populations. The aim of the agency is to have a minimal environmental impact.
With growing population and therefore increasing requirements for water and the challenge of climate change the Environment Agency must work to be able to balance the growing needs with that of a dwindling resource. This will require water resource planning for the longer term and to secure the preservation of surface and ground water reserves.
The next meeting will be on Wednesday 15th April when club member Roy McGurn will give a talk entitled “ The Geology Of War”
On Sunday 26th April there will be a field trip to Hendre Quarry, near Ysbyty Ystwyth. Leader will be Prof. David James.
Tuesday 10th March 2015
The next event will be on the 18th of March where guest speaker Kevin Voyce of the Environment Agency will be giving a talk on "Strategic groundwater management"
Monday 23rd February 2015
Bill gave a really interesting talk on quartz and other forms of silica. The talk commenced with
a general description of the elements that go to make up the earth's crust. Bill then delved more
deeply into the chemical structure of silica and polymorphism and then into the different branches
of the quartz family. This consists of, firstly, basic quartz types, for example Rock crystal, Rose
Quartz and Citrine. Then there is amorphous quartz, including Opal and Obsidian. The Chalcedony
branch includes Chrysophrase, Onyx, Heliotrope and the Agates. Most of these are fairly well
known, but what are not quite so well known are some of the quartz/silica polymorphs. These are
varieties that have been altered by heat or pressure or by both heat and pressure. These include
minerals such as Keatite and Coesite. Silica also is present in many rock types, eg. Granite. These
groups were then looked at in much more detail, accompanied by photographs of each mineral.
Finally, the role of silica in technology was discussed from the use in quartz time-pieces to modern
uses in nanotechnology.
Alongside the talk Bill brought along a large number of superb specimens for all to view.
The next talk will be on Wednesday 18th March, when guest speaker Kevin Voyce (Environment Agency) will give a talk entitled: “Strategic Ground Water Management”
Tuesday 10th February 2015
Our next event will be on the 18th of February at 7:15 with Bill Bagley's talk "Quartz and other forms of silica"
Wednesday 4th February 2015
The AGM was held on 21st January, a cold evening with frequent snow flurries. The AGM was followed by one of Dr. Geoff Steel's very interesting talks. On this occasion his talk was entitled, “The Tyrone Ophiolite: ancient ocean floor on land in Northern Ireland”.
Geoff commenced the talk with an explanation of ophiolites in general. They are interpreted as fragments of ocean floor that have been sheared off from subducting crust, caught between colliding continents and then elevated to a continental location. A typical ophiolite suite can be defined as consisting of the following (from base up): unlayered serpentinised peridotite, layered gabbro, massive gabbro, sheeted dyke complex, pillow basalts, deep sea sediments. Although not all ophiolites contain all the layers. Ophiolites are important as they allow access to oceanic crust and upper mantle that otherwise would be unobtainable. The age of oceanic crust is dated to about 200my. Therefore, an ophiolite that is dated as much older allows study and understanding of much earlier events and provides evidence for the existence of old oceans and oceanic basins. The Tyrone ophiolite was obducted onto the continental margin of Laurentia during closure of the Iapetus Ocean during the Ordovician Period.
It was Geoff's intention to observe as many elements of the ophiolite as possible. On his tour he visited Beltonanean Mountain and Black Rock where he observed the gabbro. The gabbro here consisted of coarse to very coarse-grained varieties. The gabbros at Black rock are also cut by younger balsaltic and doleritic intrusions which are in the form of 1 to 2m wide dykes. These sheeted-dykes are also part of the ophiolite. They were also viewed at Carrickmore where they cut through Hornblende gabbro. Originally these dykes would have acted as feeders for the overlying sequence of pillow lavas. The latter were viewed at Creggan rock. The final location on the tour was the Carraghinault gold mine. This gold was formed as part of the orogenic phase of the closure of the Iapetus Ocean. As this is a working quarry it could only be viewed from a distance.
The talk ended with some of the members now thinking of a visit to Ireland!
The next meeting will be on Wednesday 18th February. Club Secretary, Bill Bagley will be giving a talk entitled: “Quartz and Other Forms of Silica.”
Thursday 18th December 2014
23 members attended and had an enjoyable evening at the November meeting. Members were entertained by a DVD ( Picnic in Siluria) produced by the geological section of the Woolhope Naturalists Field Club. The film was a re-enactment of an 1850’s field visit by Sir Roderick Murchison to a site near Aymestrey in Herefordshire. The scene was set by a short talk given by Robert Williams who was part of the re-enactment in the guise of Sir Charles Lyell.
The next indoor meeting will be held on Wednesday 21st January.This will be the AGM followed by a talk by Dr Geoff Steel entitled: “ The Tyrone Ophiolite; ancient ocean floor on land in Northern Ireland.”
Tuesday 28th October 2014
The next event will be a member's social evening on the 19th of November.
Sunday 19th October 2014
Mid Wales Geology Club’s evening meeting on 19 November will be more of a social event than usual. Billed as Mulled Wine, Mince Pies & Murchison, we will show the DVD produced several years ago by the Geology Section of the Woolhope Naturalists Field Club. The Woolhope arranged a re-enactment of the 1850s field visit by the eminent geologist Sir Roderick Murchison, to a site near Aymestrey in Herefordshire. Picnic in Siluria was complete with steam train and a large cast in Victorian costume. It concludes with a short modern footage of a geological visit to a nearby working quarry. Mid Wales Geology Club member Dr Geoff Steel is the current chairman of the Woolhope Geology Section. He says he played the part of a servant, and was not permitted to eat with the gentleman geologists!
Robert Williams, who attended the re-enactment in the guise of Sir Charles Lyell, will set the scene for us, and introduce the characters. Then we will enjoy mulled wine and mince pies (non-alcoholic for those who wish); and afterwards we will watch the DVD. Coffee and tea will be available before we close. We will be at the usual venue, Plas Dolerw, Milford Road, Newtown, commencing at 7.15 pm.
Wednesday 8th October 2014
At the last meeting we were treated to a super talk given by Chris Darmon. He commenced the talk by suggesting that the traditional view of how Iceland came to be where it is is now hotly debated. He would reveal more at the end of the talk!
Iceland is an island that spans the mid-ocean ridge along which the Eurasian and North American plates are moving apart. It also sits atop a mantle plume where magma upwells from from the earth's mantle ( it is this that is now in dispute). And the combination of the two are responsible for Iceland. Geologically Iceland is very young with the oldest rocks exposed at the surface between 14 and 16 million years old. It's surface is constantly changing due to rapid erosion and replenishment from volcanic action.
It is one of the most volcanic places on earth with hundreds of volcanoes many of which commence as fissure eruptions. One of the most deadly volcanoes was the eruption of Laki in 1783/4 which led to huge volumes of Sulphur dioxide being emitted into the upper atmosphere which in turn caused thousands of deaths both in Iceland an other areas of Northern Europe due to starvation and respiratory illness.
The main rock type on Iceland is volcanic and you will find pillow lavas and basalt columns. 90% of the igneous rock is basalt but there is also rhyolite, dacite and andesite present. One anomaly here is the presence of larger amounts of rhyolite compared to similar areas eg. Hawaii. Sedimentary rocks are also present and vary in type from volcanic in origin to lake, river and lagoonal. Thus there are tuffs, shales, mudstones, sandstones and conglomerates. There are even layers containing lignite and coal beds. This suggests that the environment on Iceland has been changing over time. Fossil plants are frequent and contain Angiosperms, Gymnosperms, Horsetails and many others. This suggests that the Miocene Period on Iceland was one of a humid, warm temperate climate. The decline of these species at the end of the Miocene suggests a cooling of the environment.
Most of the population of Iceland live around the coast and inland is deserted. They also make use of all the geothermal energy present for example to heat their homes. Iceland is now a very desirable destination for tourists and Chris has led tours there for the past twenty years.
At the end of the talk Chris presented some evidence to suggest that a mantle plume may not exist under Iceland.
The spreading rate at the ridges is to fast. This suggests that an expanse of older crust underlies Iceland submerged beneath younger lavas.
The dating of zircon from the Hvitserker ignimbrite dated to 126-242MYA. That is the Mesozoic. Therefore it was suggested that a continental crust must exist beneath at least part of Iceland.
The crust is too thick.
The crust above the mantle plume is not hot.
He went on to say that Gillian Foulger found that her seismic data showed that instead of a long narrow plume of magma coming from deep below Iceland there is actually a broad reservoir of molten rock less than 400km down. This suggests that remnants of crust left behind in the mantle at the fault line have a lower melting point than the surrounding mantle. Where this ancient crustal rock crosses the ridge it should melt more than the rock around it creating a shallow reservoir of magma that feeds Iceland's volcanoes. Thus there is no need for a mantle plume.
This idea of no plume links in with much other research suggesting that mantle plumes have no need to exist to explain other areas like Hawaii. A very controversial area of geology!
The next talk will be on Wednesday 15th October to be given by Tony Thorpe and entitled
“ A new look at metal extraction in the Bronze Age and the iron Age”
Also the members evening will be on Wednesday November 19th and will be a
“Mulled wine, Mince pies and Murchison” evening.
Sunday 7th September 2014
The next event will be on the 17th of September with Chris Darmon's talk “Iceland: Where geological processes happen in real time”
Tuesday 22nd July 2014
The next event will be on August 23rd
Thursday 10th July 2014
The last indoor meeting was a mineral evening led by Bill Bagley. The evening commenced with a talk by Bill about minerals and how to identify them. The talk was accompanied with some super photos of minerals. Bill had also brought in some lovely specimens from his collection. In the second half of the meeting members took part in a quiz in which they had to identify unknown minerals based on information provided. A most enjoyable evening was had by all.
The next meeting is the evening field trip which will be held at Gilfach nature reserve near Rhayader where we shall look at the geology. Meet in the car park at Gilfach at 6.30pm.
Friday 6th June 2014
The talk on “Fracking” given by Roy McGurn was both enjoyable and controversial. He commenced by talking about the “Spindletop” oilfield in Texas that was discovered on top of a salt dome in 1901. This marked the birth of the modern petroleum industry and had an enormous effect on world history and revolutionised industry and transport.
“Fracking” is a process that combines two technologies, hydraulic fracturing and direct drilling and is used to extract natural gas or oil from deep reserves below ground. The process allows energy companies to access previously unavailable energy sources. During the process water is mixed with sand and chemicals and the resultant mixture is injected, at high pressure, into a wellbore. This produces fractures in the deep rock formations along which the gas can migrate. The first experimental use of this method was in 1947 and commercially used in 1949 so it is not a new technology.
The method has huge potential benefits for energy but also has many environmental and health related consequences. It was these aspects that led to long debate at the end of his talk.
The next meeting will be on Tuesday 17th June when Bill Bagley will hold an evening looking at minerals.
Sunday 18th May 2014
The May 2014 fieldtrip was led by Tony Thorp on and around Gaer Fawr Hill near Guilsfield, on the western flank of the Guilsfield anticline. We were near the top of the Gaer Fawr Fm (Ordovician, Caradoc), a shallowing-up sandstone with abundant fossils, as seen in the small quarry at the nature reserve car park. This hard sandstone forms the hill. Above this in the steeply dipping sequence is the softer Dolhir Fm (Ashgill), which has now eroded to a valley. The Ordovician is then topped by the Nod Glas, a thin horizon of soft black shale, which we saw in the stream banks at the valley bottom. Above this in the sequence is the very hard Powis Castle Conglomerate, a beach deposit, now forming a ridge, along which we walked, looking across the eroded valley, at Gaer Fawr Hill. All these features were beautifully evident on a lovely dry day, with additional features to be seen in the stream bed (bentonites, evidence of faulting, and limestone). The day finished with a walk to the top of the iron age hill fort, through woods of stunning bluebell display.
Sunday 4th May 2014
The next indoor meeting is Wednesday 21st May when Roy McGurn will give a talk entitled: “Fracking: A hot topic but what’s it all about?”
This could turn out to be quite a lively talk!
Thursday 24th April 2014
Professor Mike Rosenbaum gave a very interesting talk as he took us back through time looking at some of the events that have led to the development of the Shropshire Landscape that we see today.
The talk commenced by looking at the effects of glaciation. The Anglian glaciation ( commenced 450,000 years ago) was the most extensive but in Shropshire and in Powys it’s effects were obliterated by the later Devensian glaciation (commenced 100,000 years ago). The Devensian ice moved Eastwards from Wales meeting the Irish sea ice from the North. During this period features eg. the Berwyns stuck up from the ice as Nunataks. This ice retreated about 20,000 years ago.
One noticeable effect of this ice is the Iron Gorge which was cut by a sub-glacial river and this has produced a gorge that has very steep sides. The steepness of the sides leads to instability and landslides have occurred and the land is still slipping.
One other very interesting idea that was discussed is one that arose from observations made by OT Jones in 1951. He observed that the river systems in Wales are radially centred on a high point in Anglesey. Later Brown in 1960 observed that that there is a wide elevated plateau covering central and southern Wales and the Marches. It has been suggested that the cause for these observations is due to the fact that the region was once over an ancient mantle plume. Luckily it is now inactive!
Keith Nicholls gave a very interesting talk based upon the research he is undertaking for his PhD. The focus of his research being the glaciation and subsequent extinction event during the Hirnantian Epoch of the Ordovician Period.
The late Ordovician extinction event is one of the five great extinctions in the geological record and is thought to have occurred in two phases 0.5-1 million years apart. The first phase at the beginning of the Hirnantian was closely correlated with the onset of glaciation due to the increase in the Gondwana ice cap which led to a fall in sea level whilst the second phase is correlated with a decrease in glaciation and subsequent rise in sea level.
His work focuses on paleoecology,sedimentology, sequence stratigraphy and stable isotope studies of the rocks in North wales. Using his research, and that from around the world, it has been shown that there was a large positive 13C excursion which suggests a global disturbance in carbon cycling. Also there was a parallel positive excursion in 18O suggesting evidence of cooling an/or ice sheet growth. Even so this area of research remains controversial.
The next indoor meeting will be held on Wednesday 16th April with a talk by Professor Mike Rosenbaum entitled: Shropshire’s Evolution: highlights of a journey through time.
At the last meeting we heard a superb talk by Dr Geoff Steele on the origins of life.
Even the oldest rocks on Earth have traces of life. They date from the early Archaen, about 3.8 billion years ago. Hence to search for life’s origins we are forced back into the Hadean. The name means “Hell” and it‘s a good description. Huge volcanic eruptions, burning ultraviolet radiation, noxious gases, enormous tides and constant bombardment by meteorites and comets do not sound like a good place to start.
No fossils survive from the Hadean. But the biochemistry of our own cells, and that of all other living organisms, preserves a remarkable record of our earliest times. It has given us a new kind of fossil hunting. In particular the DNA and RNA that store and manipulate our genes can be read like a book, complete with the copying errors and editing errors that tell so much about previous owners. They prove to us that all life on Earth is indeed related, as Charles Darwin proposed, and even allow a reasonable reconstruction of our common ancestor (a simple prokaryote). But where did that come from?
If our quest is the origin of life then we need to think carefully about what we’re looking for. What exactly is life? How is it defined? It seems that replication and metabolism are the minimum requirements, and if they are confined within an enclosed space such as a membrane then that object is perhaps “living”. Could such a thing have formed naturally in Hell? Research suggests that the conditions were right for RNA molecules to form. And they can act as both genes and enzymes giving both replication and metabolism. Hence the simplest life may have begun with just RNA, wrapped in the lipid membranes that form naturally when oil and water are shaken together. And it is astonishing to discover that one of our most basic enzymes, crucial to all modern life, appears to be a living fossil from that time.
The next meeting will be held on Wednesday 19th March when Keith Nicholls will give a talk entitled “The Late Ordovician Ice Age: a mass extinction”
Saturday 8th February 2014
The next indoor meeting will be on Wednesday 19th February where Dr Geoff Steel will give a talk entitled ‘The Origins of Life’.
Thursday 23rd January 2014
Our first meeting of the year was the AGM for which 21 people attended. The AGM was followed by one of Dr Sara Metcalf's super talks. This time on the “Grinshill Fossil”.
On a club field trip to Grinshill quarry in 2013 the owners donated, to Powysland Museum Welshpool, a slab of Tarporley Siltstone containing a series of 19 fossilised footprints and rain drop pits. The talk given by Sara elucidated the current thinking on what formed the prints. Fossils of the herbivorous reptile Rhyncosaurus have previously been found at Grinshill and footprints found have been attributed to that reptile. She went on to say that the slab of Tarporley siltstone was Lower Anisian ( Middle Triassic) in age and would have been laid down in low energy rivers in an arid landscape. Recent re-evaluation of the so-called Rhyncosauroides footprints of Owen and others by Geoff Tresise of Liverpool Museum has shown them to be not related to the actual Rhyncosaur beast that has been found at Grinshill, but probably from a small archosaur reptile called a Protorosaur.
On 20th November Prof. Bill Fitches gave a talk on gneissic rocks, especially in Greenland, in particular those on the western margin of this huge territory, recalling the 1970s working for the Greenland Geological Survey, landed by helicopter to lead isolated mapping teams under canvas for weeks at a time in this beautiful but harsh environment. Greenland is on a craton (ancient continental crust) which extends east beneath the Outer Hebrides and north-west Scotland.
The oldest rocks are 3.75 Ga; even the youngest are 2.3 Ga, but these old rocks are often overprinted by younger events. The gneisses result from extreme metamorphism of mudstones at 600°C after burial up to 30 km deep. The structures at field scale are stunning. The minerals have migrated to large-scale dark and pale bands visible from long distance. In places the gneisses are sheared into puzzling structures, and sometimes extensively cross-cut by igneous dyke swarms. Rocks derived from shale similar to our Silurian black shales, but ten times older, was so metamorphosed that the carbonaceous content has segregated as graphite. Perhaps the organic material came from extremely primitive life 3 Ga ago. We were introduced to a new range of features including en-bayonet dykes, tennis ball gabbros and football anorthosites!
The talk concluded with a look at the Swiss Alps where Bill Fitches, during his time on the academic staff at Aberystwyth University, took students to see similar TTG gneisses (tonalite-trondhjemite-granodiorite) a hundred times younger than those in Greenland, and derived from Permian granites. The Matterhorn, in the alpine pennine nappes, shows rock of the ancient African continent thrust north over the top of European basement gneiss; between the two a band of rock formed from the oceanic crust and sediments of the floor of the long-gone Tethys ocean.
The last indoor meeting was a talk given by James Cresswell of “GeoWorld Travel”. This was a highly informative and enjoyable talk.
Greenland has some of the oldest rocks on earth which are found in the Isua Greenstone Belt and have been aged at between 3.7 - 3.8 GA. Greenland forms part of the North American Plate whilst Svalbard forms part of the European plate. It is this relative difference in their positions which have produced the differences that can be seen in their geology. With this in mind, commencing at 4.6 GA James worked chronologically through geological time discussing plate movements, glaciation and rises and fall in sea level, sedimentation and orogenesis, the results of which can be seen in their geology. This detailed explanation along with superb photographs of spectacular rock formations made for a very pleasurable talk.
The next indoor meeting will be held on Wednesday November 20th where Professor Bill Fitches will give a talk entitled: “Greenland’s Ancient Gneissic Rocks”
22 September 2013 we enjoyed a splendid day walking up the Cat’s Back (Crib y Garth), Black Mountains, on the western edge of Brecon Beacons National Park. This spectacular ridge (arête) created in the Ice Age rises 240 metres from the parking below. Duncan Hawley’s usual ceaseless flow of information and careful tutoring revealed the evidence of the vast plains and meandering rivers of the early semi-arid Devonian period and drew us into discussion of several phenomena on which consensus has not yet been reached.
Monday 9th September 2013
Change to indoor meeting Wednesday 18th September
The talk due to be given by Professor Bill Fitches will now take place on Wednesday 20th November. Therefore the next meeting on 18th of September will be the Member’s evening. Talks will be given by Tony Thorpe and Colin Humphrey.
Sunday 1st September 2013
Indoor Meeting 21st August 2013
Talk given by member Dr Sara Metcalf on the fossil history of sharks and rays.
Sara gave an excellent talk in which she explained that there is a 400 million year fossil history of sharks. Thought to have arisen during the Devonian period there is some evidence that they could have evolved much earlier even into the Ordovician. There are about 1000 living species. She then went on to describe their morphology and how they differ from other fish. One major difference residing in the fact that they have a cartilaginous and not bony skeleton. This, of course leads to problems of fossilisation such that the main shark fossils are of teeth, dermal denticles,fin spines and calcified vertebrae. Trace fossils are rare but coprolites are frequent.
The most important genus during the Palaeozoic was that of Cladoselache, fossils of which can be found in the Cleveland Shales around Lake Erie in North America. By the start of the Carboniferous sharks had diversified and proliferated greatly and then remained relatively stable until the mass extinction at the end of the Permian. Two groups now emerged one moving into fresh water whilst the other remained marine. By the late Triassic the first modern sharks appear. These had a much more flexible jaw which increased their advantage when in competition for food.
By the Cenozoic Era all the modern sharks are present and also the biggest shark of all time Carcharodon Megalodon which is regarded as one of the largest and most powerful predators in vertebrate history.
Tuesday 20th August 2013
Next indoor meeting is 21st August when member Dr Sara Metcalf will give a talk on Fossil sharks entitled “Palaeontology with a bite: the fossil history of sharks & rays”
Evening field trip to Banc Dolhelfa landslide, near Llangurig
Wednesday 17 July 6.00 to 8.00pm
Leader: Colin Humphrey
Meet at 6.00 pm at the spacious roadside café car park, 3 miles south of the Llangurig roundabout on the A470 [SN 919 756] SY18 6RX. We will postpone the trip if the weather is unsafe, i.e. wet or very windy. If in doubt check on the day with Colin (01686 412397), Bill (413967) or Michele (411343).
Traditionally we do an evening field trip each year, this time to Banc Dolhelfa (small lay-by parking SN 922 748), a huge bedrock slide, one of the largest in Mid Wales, described in detail and interpreted for the first time last year. We will begin with a short drive to the opposite side of the river Wye to view and briefly discuss the whole site. Then we will drive back to a lay-by parking next to the slide and walk around it, a distance of 1 km, including a hill climb of 170 metres, to see the evidence close-up. Those who do not wish to climb to the top can easily pause and retrace their steps back to the road. The slide is fully explained, with photographs and diagrams, in Colin’s technical paper in OUGS Journal, vol 33 (2) 2012. A pre-publication version appears on our website and can be printed (6 pps). This can also be accessed directly by googling ‘banc dolhelfa’. Some copies from the journal will also be available on the evening. Following our work the site has been registered as a RIGS. Walking boots necessary; hard hat not needed; binoculars very useful.
Tuesday 11th June 2013
Indoor Meeting Wednesday 15th May
Member Kit Moorhouse gave a talk on The Geology of Salt in the Cheshire Basin
Although on our doorstep, this topic has been sadly neglected by our club. Kit's talk was therefore particularly welcome.
The halite deposits which underlie the Cheshire Basin originated in the Triassic Period when the area was part of the vast supercontinent of Pangea, at a latitude of 20-30 degrees north. i.e. about that of the Sahara or the Persian Gulf.
Sea water comprises three and a half percent salt, together with other dissolved salts such as Carnallite (potassium magnesium chloride) Polyhalite hydrated potassium magnesium chloride, Sylvite (potassium Chloride), Sylvinite (sodium chloride with potassium chloride) , Gypsum, and carbonates.
The evaporation of about 100 m of seawater is required to produce just 5cm of deposits so simple evaporation of sea water is insufficient to produce such massive deposits so some replenishment mechanism is necessary.
In Cheshire, halite is dominant, with no calcium sulphate or potassium salts.
The preferred model for their formation is that of a "Barred Basin" in which access to sea water is limited and evaporation leads to a gradient of salinity in which carbonates, sulphates and chlorides are crystallised out in that order progressively at increasing distance from the "bar". This could occur in a situation like the Mediterranian, fed from Gibralter, or more interestingly, the Gulf of Garabogazköl in Turkmenistan. This is fed from the Caspian Sea and in 1980, it was felt that it was drying out the Caspian Sea so the inlet was blocked up. Unfortunately it triggered a problem with wind blown salt contaminating surrounding land and in 1990 the inlet was opened up again. To produce thick deposits, space must be created and a subsiding basin is required.
In the case of the Cheshire Basin, like the Zechstein Sea in the north of England, the flooding is associated with the opening of the North Atlantic and the formation of half grabens. 2000m of Jurassic and Cretaceous deposits followed before erosion brought the deposits to the near surface.
The halite beds form part of the Mercia Mudstones Group (Once called Keuper Marl) and comprise salt with associated muds and silts which give them their characteristic yellow, red and blue colouration.
In Cheshire salt was recovered from briney springs by the Romans by evaporation from lead pans, This developed in medieval times to shallow pumping from the "Wet rock head" (brecciated mudstone where meteoric water had dissolved salt) Round Winsford salt was recovered fron wells and open pans. Subsidence led to craters, meres and lakes.
In 1850-1919 the industry grew, based on wells and pans. Subsidence became a problem, often at a distance and in 1890 a levy was imposed on the industry to provide compensation. In addition in the 19th and 20th centuries, it was mined, leaving pillars to support the roof. This led to subsidence when mines were flooded including the "Great Subsidence" in 1881.
The largest workings are at Winsford where it is mined leaving pillars to support the roof.
The beds are not structureless with bedding planes showing up as laminae of muddy layers and interesting polygons are visible on a 4-14 metre scale with dish-like forms corresponding to their edges.
Winsford produces about a third of the total UK salt, used for treating roads in winter and as a beet fertiliser in East Anglia. Brines are also produced by controlled pumping for table salt and process salt for sodium hydroxide and chlorine production.
Spherical cavities produced by controlled brine extraction can be used as storage facilities for natural gas and have been applied for that purpose in East Yorkshire.
This overview of the geological and industrial aspects of our salt industry was much appreciated by members who resolved to try to include a field trip to the area in the future.
Our next meeting is: "A guide to Astronomy & Space Science" by guest speaker - Danny Craig.
Monday 29th April 2013
EARLY GEOLOGICAL MAPS a talk by DUNCAN HAWLEY
There was unusual interest in the April evening meeting when Duncan Hawley, from Swansea Metropolitan University, spoke on Early Geological Maps. He also brought along a splendid selection from his own collection. ‘The geological map is the dynamic force in geology, and the history of its evolution and development is the history of the birth and growth of geology’, so said FJ North in 1928, when he was the first keeper of geology at the National Museum of Wales.
Packe, in 1743, used hatching to depict the topography of Kent, probably the first geomorphological map. Early maps were monochrome; some, like Wm Maton, in 1793, believing that colour would be a distraction. By early 1800s colour became widely used, as in Gimbernat’s map of the Tyrol. In 1809 Jamieson produced the first guide ‘on colouring geognostical maps’. The earliest maps merely noted spot descriptions of rock and correlation over long distances began with Guettard’s 1746 map of France and southern Britain, an early mineral map which picked out the chalk on both sides of the Channel, but depiction of continuous boundaries was common by mid 19th century. Guides on mapping geology were introduced in the 19th cent, for example Henry de la Beche’s Geological Manual (1831) and Ami Boué’s Guide du Geologue Voyageur.
Early geological cartographers frequently worked alone, a serious disadvantage, resulting in considerable inaccuracy. Wm Smith first attempted to delineate geological strata in 1801. His 1815 map is a magnificent one-man effort, with about 100 of the 400 printed copies still surviving. But the collaborative efforts of men like George Bellas Greenough achieved more, by compiling the work of local experts like Fitton, Buckland and Aikin. That effort, through the young Geological Society of London, was in fact already mostly completed by 1812, though not published until 1819. The earliest mappers even had to work without ordnance survey maps. Even with basic maps the geological contours were often inaccurate, changing markedly within a few years, as shown by comparing Murchison’s map of Wales and the borders in 1839 with that of the Geological Survey only six years later.
Colour posed a problem for early geological map publishers, first being added to individual copies by hand, often by young women, thought to be more skilled in that work; though hand colouring also sometimes led to inaccuracy, and darker colours could obscure the underlying information. Smith’s map used gradational colouring to show strata becoming younger, and Farey in the 1810s showed how structural features like faults can be interpreted using colour to show the outcrop patterns they produce. However, by the mid-1800s printed colour maps began to emerge and was cheaper but less accurate and more technically difficult to produce until the 1880s when printing became inevitable as more detail was added to maps. Today’s mapping is done with the geological equivalent of an iPad and the modern maps are things of beauty. What would the early workers have thought. The audience was much taken with Duncan’s evident enthusiasm for his subject, and a vote of thanks was proposed by Tony Thorp.
Next Indoor meeting: Wednesday 15th May
Two ½ hour talks:
Geology of Salt in the Cheshire Basin (Speaker - Kit Moorhouse)
Practical Geomorphology: How to Interpret the Landscape. (Speaker Julien Lovell)
Thursday 18th April 2013
Rocks of the Elan Valley Reservoirs
Sunday 28 April 2013 (leader: Colin Humphrey)
Next field trip will be Sunday 28 April. Gather at 10.30 am, car park at Visitor Centre, Elan Valley, Rhayader LD6 5HP (SN 928 647). Driving south on the A470 to Rhayader, turn right at the crossroads and stay on the B4518 for 3½ miles. Bring a packed lunch. Hard hat not essential but advisable if you wish to approach close to rock faces. We aim to return to the visitor centre by around 3 pm (toilets at visitor centre and lunchtime at Claerwen dam). The localities examined lie on or near a single five mile stretch of quiet reservoir road between Caban Coch and Claerwen dams, so we will move mostly by car; the walking is easy.
The roads which wind around the exceptionally beautiful and peaceful reservoirs of the Elan and Claerwen valleys reveal the Cerigwynion Grits which ended the Ordovician here, and the mudstones which began the Silurian. Rising and falling sea-level 440 million years ago produced a range of different types of deep-water sediment deposition. This sandstone and mudstone succession was deposited as a series of gently sloping lobes with slumps, debris flows and a wide range of turbidites. An unusual feature is the record of a very different depositional environment, the Caban Conglomerates, an erosive high energy submarine channel flow which cut through the sandstone/mudstone slope-apron and left its own story in the rock. Local folding (Rhiwnant Anticline) followed by natural erosion and man’s rock cutting and has left different rock facies conveniently juxtaposed.
Thursday 4th April 2013
“U.K. earthquakes and John Milne's contributions to the science” Dr Ian Stimpson, FGS
On Wednesday, the 20th March, Dr Ian Stimpson FGS, of the School of Physical & Geographical Sciences, Keele University. talked to an audience of 36 members and guests.
Ian last visited us two years ago, just after the disastrous earthquakes in Japan and New Zealand, when he gave us a splendid lecture on them in lieu of a talk on UK quakes. This talk is an updated version of the one we missed.
The first part of Ian’s talk focussed on John Milne, a geologist who could reasonably be described as “The Father of Seismology” because his legacy is so huge. In spite of this, he is comparatively unrecognised. This year is the centenary of his death.
John Milne was raised in Rochdale, read Natural Sciences at Kings College, London (Precursor of the Royal School of Mines) and then Mineralogy at the University of Freiberg in Germany, before surveying for coal in Newfoundland. He then took up a post as Professor of Geology and Mining at Imperial College, Tokyo. Typically, being of an adventurous nature, during 1875-76, he went there the difficult way, overland, making geological notes along the way! The earthquake which occurred on his first night in Japan triggered his lifelong interest in them. By 1889 he was a Fellow of the Royal Society, a considerable achievement for a geologist.
During this period in the 1880s there was a transition from a belief in the supernatural origins of earthquakes to a scientific one and in 1893 at the Koto convention, it was mooted for the first time that faults caused earthquakes rather than being the results of them.
In the late 1800s there was no accurate recorder of seismic vibration before Milne and Gray developed the Milne-Gray seismograph which measured the three components (north-south, east-west and up-down). His invention was not confined to geology, he developed a vibration detector for steam engines which facilitated the improvement of the track.
In 1895 when his home and laboratory burnt down he ended his 20 year stay in Japan, came back and set up home with his Japanese wife at Shide on the Isle of Wight. By 1908 the Milne-Shaw seismograph was the standard instrument for a worldwide network reporting back to him at his home, establishing the foundation of modern earthquake research, a remarkable achievement as he was in receipt of no government money.
His published log of recorded earthquakes clearly maps out what we came to understood as plate boundaries some 50 years later.
He died of Bright’s disease in 1913 at the young age of 62.
The scale of magnitude of earthquakes is based on the log of the size of the biggest displacement in the seismic trace, so from one step in magnitude to another is the equivalent of an increase of 32 times the amount of energy released. Shocks go from M 9.5 as the largest, recorded in Chile, to minus 5, when you break your pencil.
Most quakes are related to plate boundaries, but intraplate quakes occur, as in the UK. The risk is small here, but we are subject to magnitude 5 quakes and most of us remember one or two local “bumps”, including the Bishops Castle one in 1990, of magnitude 5.1. Strangely, we have more M 5 quakes than M 4 ones.
The UK is subject to compression leading to movement on ancient faults. Some small shallow quakes are related to coal extraction, when the stronger sandstones which separate the coal seams break; but larger quakes tend to be triggered at depth leading to only minor damage.
The distribution of earthquakes in the UK is problematic, being concentrated along the west coast, plus the Welsh borders, with the odd small patch round Dover. Very strangely, Ireland (North and South) has almost no quakes. We get on average one M 5-6 earthquake every 8 years. Fracking leads to shocks of about M -1 to M -2, of which we get about 23 every year.
Central within the UK there is a stable, roughly triangular, Midland Craton, within a complex patchwork of ancient terranes, all separated by faults along which movements can occur when intraplate pressure builds up. The overall distribution is however difficult to explain and some geologists invoke a “Hot Mantle Anomaly” to explain the larger deeper quakes which originate some 20 km down.
Colin Humphrey wound up the meeting by thanking Ian for a remarkably interesting talk and making the point that we should see our way to commemorating the life of John Milne, considering the huge legacy we have inherited from him.
At the indoor meeting, on the 17th April, Duncan Hawley will be giving a talk on “Early Geological Maps”.
Tuesday 12th March 2013
Next meeting will be on Wednesday 20th March. Dr Ian Stimpson will give a talk entitled ”Uk Earthquakes and the Centenary of John Milne“.
This is expected to be an excellent talk so please come along.
Sunday 24th February 2013
At this well attended meeting Colin Humphrey gave a very interesting talk on the age of the earth.
In an Age of Ignorance, until mid 17th cent, western thinking about the age of the earth was polarised. At first, eternalist philosophers like Aristotle thought the earth had always been here. Later, scriptural literalists like archbishop Ussher took the opposite view. In 1650 he declared in Annals of the Old Testament that creation began on the evening preceding Sunday 23 October 4004 BC. Many authors at the time were priests, constrained to think of the earth as around 6000 years old.
In the Age of Reasoning, philosophers and priests were replaced by polymaths, whose empirical thinking quickly departed from scriptural literalism. The mistaken concept of a cooling molten earth dominated thinking during the 18th and 19th centuries. Newton and Leclerc calculated cooling at 50,000 to 100,000 years. From 1860 Lord Kelvin led with an age of 98 million years, though by 1899 he had reduced this to 24 million years. Other scientists, from Hutton to Lyell and Darwin assumed gradual geological processes like sedimentation and erosion to take several hundred million years. Some thought periodic natural catastrophe to be more important in shaping the earth. All believed the earth to be millions of years old, and all were wrong, but oh how they argued!
The Age of Science began in the 20th century with an explosion of knowledge. In 1896 Becquerel discovered radioactivity. Within eleven years the Curies, Rutherford and others had explained and calibrated radioactivity, and ages up to 2 billion years were being determined for some earth minerals. Another advance came in the early 1950s with much improved mass spectrometry, and with the realisation that earth was the same age as the meteorites from the asteroid belt – 4.55 billion years. Now it only remained for geologists and palaeontologists to support this age with the explanation that earth's history has been alternations of vastly long periods with very little change, interrupted by sudden catastrophe, repeated again and again.
The talk finished with recent geological evidence for Noah’s Flood, an event which puzzled for centuries. 7600 years ago, in an unusually warm and wet period the Mediterranean overflowed into the low-lying Black Sea basin, in just a few months inundating a region nearly half the area of Britain.
The next meeting is on 20th March at 7.15pm when Dr Ian Stimpson will give a talk entitled "UK Earthquakes and the Centenary of John Milne."
If his last talk is anything to go by then expect a riveting talk on earthquakes and seismology.
Monday 4th February 2013
The next evening event will be a talk by Colin Humphrey, on Wednesday 20th February - 'The Age of the Earth: a history'. Philosophers, scientists and religious men argued for thousands of years without getting near the truth. Then the last century saw an explosion in understanding, which has continued even to the present day. There are many aspects to this interesting story, from Aristotle to Ussher, radioactivity and recent investigation of Noah’s Flood, with a lot of nonsense and controversy in between.
Tuesday 22nd January 2013
The AGM was held on 16th January 2013. As a few of the officers had come to the end of their period of service there have been a few changes to the committee. The committee is now as follows:
Chair - Michele Becker
Treasurer - Rheidol Davies
Secretary - Bill Bagley
Newsletter Editor - Tony Thorpe
New committee member - Janey Hasleden
Bill Bagley (outgoing Chair) commented on the very successful Welshpool Heritage Project undertaken in 2012 and a vote of thanks was given to Colin Humphrey for his work in coordinating the project. A vote of thanks was also given to Rheidol Davies for his work as Treasurer.
The AGM was followed by a talk given by Dr Sara Metcalf entitled "Fossils as Therapy". This intriguing talk highlighted how useful fossils can be in Outreach Educational work. Using two case studies:
a centre for adults with learning difficulties
a care home for the elderly
Sara went on to explain how the different groups could use the fossils as a learning experience and the great pleasure both groups gained from the sessions.
That both groups gained a sense of achievement whilst handling, making and discussing fossils. This form of therapy is now being widely undertaken by various establishments.
The next meeting will take place on 20th February - the talk will be given by Colin Humphrey entitled "The Age of the Earth - A History"
Tuesday 8th January 2013
The next meeting will be on the 16th of January. This will be the AGM, followed by a talk on 'Fossils as Therapy', given by Dr. Sara Metcalf.
In other news: The date for the Grinshill Quarry trip has been finalised to 6th of July, along with Shropshire Geological Society.
Tuesday 4th December 2012
Exhibition in Llanidloes
From 3 to 15 December 2012 Mid Wales Geology Club has an exhibition in the room behind the main gallery at Minerva Arts Centre, Llanidloes. For the first time this features all the club's four models (three of which made by Sue Cain), with interpretation boards, plus a display of some of Bill Bagley's splendid collection of minerals. A few volcanic rocks specimens and some fossils completes a display well worth a visit. This has been an opportunity to wheel out all the club's recently acquired kit, including the audio-slide display and the folding screens.
Tuesday 27th November 2012
The annual members evening was held on 21st November and consisted of three short talks by members and an auction of donated items.
Geoff Steele gave an account of Mica, its' chemistry, structure, occurrence in the UK and uses.
Michele Becker, talked about Shark dermal denticles, structure, function and how we, as humans, have copied their advantages for new technological innovations (biomimicry).
Peter McKenzie Dyer brought along two objects for identification: a badger skull from which the cause of death could be ascertained and a plate from the tooth of a mammoth.
A total of more than £100 was made on the auction.
The next meeting will be held on 16th January 2013. This will be the AGM after which Dr Sara Metcalfe will give a talk entitled "Fossils as Therapy".
We wish all the best to Tony Thorpe who is recovering after hip replacement surgery.
Friday 26th October 2012
The Annual Summer Weekend 2013
This event is the highlight of the club's year. The 2013 venue has just been confirmed for 7-10 June, and will concentrate on Devonian and Carboniferous coastal sections of south Pembrokeshire. Members will all stay at Orielton Field Centre near Pembroke, which is organising the weekend for the club. Sid Howells, a geologist with the Countryside Council for Wales will be the leader during Saturday and Sunday and will also give talks on the Friday and Saturday evenings. Those members who do not have to rush back to work will continue on their own during Monday. Around 20 members have already signed up. Any who still wish to do so should contact Michele Becker soon as vacancies are now very limited.
Thursday 4th October 2012
The next meeting is on the 17th October when Prof. Chris King will talk on:
'How to find a diamond mine - with eruptions'
Where do diamonds come from? How do you find diamonds? How can practical demonstrations get you thinking about Earth processes. 'All will be revealed' in this presentation.
Chris King is Professor of Earth Science Education at Keele and spent five years as a diamond prospector for De Beers.
This will interest everyone, so we are inviting guests.
Do let your friends and neighbours know, they will be welcome.
That is at the usual time and place, 7.15 for 7.30 p.m. at Plas Dolerw
Thursday 20th September 2012
With Dr Michele Becker's very enjoyable talk on the building stones of Welshpool (19 Sept) we have finished our recent Lottery project and the final report has just gone off. Welshpool's Geological Heritage Project was nearly two years in the preparation. Then it began in March with the exhibition at Powysland Museum. Since then has raced through many events (see the page and pictures on this site). Thanks to all the members who have helped, and also to our partners, the staff at Powysland Museum and at National Museum of Wales. Well done everyone. It has been fun.
Don't forget the next meeting: Wed 17 Oct, 7.15 pm, Plas Dolerw. Visitors welcome. Prof. Chris King will be talking about diamond prospecting, something he knows a thing or two about.