Grant Inst Lecture Theatre

Clough Medal Lecture 2023/24

Tony Prave presentation

Tony being presented with Clough Medal 2023-24

Our annual Clough Medal lecture took place on 28th February at the Grant Institute, Kings Buildings Campus, University of Edinburgh and also broadcast online. The audience for this years’ lecture was well over 100 (50+ in person and 54 on line).  Whether the fact that the lecture was preceded by a “pizza and pop” event, kindly supported by a donation from an EGS Fellow, or whether it was cohort of Tony Prave’s supporters from the University of St Andrews, it did make for a great atmosphere on the evening.

Graham Leslie, Chair of the Clough Committee had the honours of explaining that the Clough Medal was established in 1935 and is given each year to a person who has contributed to a geologist whose original work has materially increased the knowledge of the geology of Scotland and/or the north of England, or one working in Scotland or the north of England who has significantly advanced the knowledge of any aspect of geology.

The medallist for 2023/24 was Professor Antony (Tony) Prave (School of Earth and Environmental Sciences, University of St Andrews) who gave a lecture entitled “There is nothing left to learn about this scrap of NW Europe”.  He was presented with his medal by Mark Wilkinson, President of Edinburgh Geological Society.

Tony Prave started his academic career at The City University of New York in USA, before coming to the University of St Andrews in 1996 as a Senior Lecturer.  For the subsequent 27 years, he has carried a wide range of research; with two programmes having had particular scientific impact: that concerned with the Neoproterozoic, and that with the Palaeoproterozoic. In each case the modus operandi has been the same: (1) meticulous and painstaking fieldwork conducted from a base of deep theoretical knowledge and an open mind; (2) careful screening of samples through petrography and geochemistry; (3) advanced isotope geochemical analyses; and (4) imaginative interpretation of the data within the geological and field context. The impact of his published oeuvre has been substantial and paradigm changing.

Tony has brought new ideas, fresh thinking and novel approaches to study of the Dalradian sequences in both Scotland and Ireland. The complex geological – and especially metamorphic – history and the paucity of robust geochronology resulted in a wealth of opinion and speculation, sometimes dressed up as coherent theory. One grizzled veteran is known to have grouched about Prave’s “Olympian disregard of 40 years of research on the Dalradian”, but as his lecture demonstrated, it was merely that he pointed out that the evidence-base for previous thinking was weak.  Instead, Tony conceived fresh ideas from carefully selected samples of carbonate that might be suitable for carbon isotope chemostratigraphy – pace the adherents of metamorphic overprint – and in this he was spectacularly vindicated (Prave et al. 2009 J.Geol.Soc.Lond.). He has also had significant projects in Namibia and Death Valley, and was a central player with Simone Kasemann and others in applying novel isotopic approaches (including boron, calcium and magnesium isotope ratios) to some classic “Snowball Earth” sections in Namibia.

For the Palaeoproterozoic and the consequences of the Great Oxidation Event (oxygenation of the Earth’s surface) around 2.4Ga, Tony thorough work originated at the Loch Maree Group, became a key player in the multinational Fennoscandia Arctic Russia – Drilling Early Earth Project (FAR-DEEP). He was closely involved in successful funding initiatives to ICDP and NERC and was co-editor on three substantial volumes (each exceeding 500 pages) published by Springer in 2012/13. He followed this success with a similar-scale international drilling project on equivalent age sequences in Gabon.

The vote of thanks was given by Prof Tony Fallick FRSE, FRSA, FMinSoc (Clough Medal, 2013/14). He paid tribute to Tony’s perseverance in proving the doubters wrong on so many occasions and to ensuring that it’s the rocks that cannot lie.  It had been Tony’s ideas and drive that had brought success to the excellent teams both at University of St Andrews and also further afield, and in so doing he is a truly worthy recipient of the Clough Medal.  He asked for thank you from the audience present and online for the speaker and this was duly done by all.

If Fellows weren’t able to attend physically or virtually, a recording of the lecture is available here.

Fellows’ Night 2022 – No. 189!

On 14th December 2022, the Edinburgh Geological Society held its 189th Fellows’ Night at the Grant Institute, University of Edinburgh. This meeting takes place each year, close to the anniversary of the foundation of the Society (on 6th December). 
The pandemic has meant that a “normal” Fellows’ Night has not taken place for a few years now.

This year we were determined to be “normal” again and so an in-person event was held at which a series of short talks were given by members and some refreshments enjoyed by all.
Four speakers were lined up for this event, but first Mike Browne (acting EGS President) gave a thank you to both Alison and Barry Tymon for their contribution to geoconservation in the Midlothian and Scottish Borders recently, and in Yorkshire previously. This work has added significantly to the total of number of local sites recognised for their geological interest across the Lothian and Borders region to 166.

The talks kicked off with Angus Millar (EGS Promotion Coordinator) (and his dog) taking up a challenge to visit 30 geoconservation sites in the month of November, and yes, he achieved this – 32 in fact and despite wet weather. Sites visited varied from Kilspindie beach erratics to the Eildon Hills, and Carlops glacial drainage channels to River Clyde oxbow lochs and active meanders. A fascinating demonstration of the breadth of geological sites on our doorsteps.

Second up was Bob Gatliff who updated Fellows on Siccar Point activities in 2022 – the embarking on the process of getting UNESCO heritage status for Hutton’s Unconformity, obtaining widespread support for the project and recognition by IUGS of Siccar Point being one of the first one hundred sites recognised for its geological heritage significance.

Thirdly, Mark Williamson (University of Edinburgh) described his geological reconnaissance of the Bilston Glen SSSI as a location for future undergraduate student visits. Its combination of mining heritage and exposures of the Lower Carboniferous (not always so clear) was described.

Finally, we heard from Prof James Floyd on his “Ships of stones” which described some fascinating collections of ornamental decoration using geologies from around the world. He explained how he discovered these treasures when engaged to give lectures on cruise ships. This had led to the discovery that not only was the best geology to be found at the islands they visited but that on board many of the ships was a wealth of geological interest as well (sadly not being recognised by many of the crew members and passengers).

In conclusion, I think everyone who attended came away with the feeling that geology surrounds us everywhere and that although not everywhere has that notice board just yet, there are a huge number of resources available through the EGS website (the Autumn Members’ Challenge is a good place to start).

We look forward to many more Fellows’ Nights in the future.

Merry Christmas and a Happy New Year,

Neil Mackenzie, EGS Secretary.

Clough Medal

Clough Medal Lecture 2021/22

On 2 March 2022 at 7pm, the annual Clough Medal lecture took place for the first time as combined physical and virtual event. The medallist for 2021/22 was Dr Tim Smithson who gave a lecture entitled the “A new beginning: recent discoveries in the early Carboniferous of northern Britain reveal rapid faunal replacement following the end-Devonian extinction”. He was presented with his medal by Dr Tom Challands, the President of the Edinburgh Geological Society.

Tim being presented with Clough Medal 2021

A brief outline of Tim’s career was described by Tom: Following his undergraduate studies at the University of Newcastle Upon Tyne (UNUT), 1972- 1975) Tim started his PhD under Alec Panchen at UNUT in 1976 but, being somewhat regarded as a genius in his field, he was offered a post-doctorate position in Montreal to work with Robert Carroll at McGill University before completing his PhD. By the time he had completed his PhD in 1983 Tim had already published four academic papers. Again, before completing his PhD, he was awarded a Sir Jamed Knott Fellowship at UNUT until 1984. Tim’s academic record is all the more impressive given that the major part of his career was spent in teaching and managerial roles in further education and not as a university academic.

During his time in further education (1985-2012), Tim was still actively engaged in fieldwork and research and published 18 research papers including perhaps his most notable work is his discovery and description in 1989 of Westlothiana lizziae (aka ‘Lizzie’) at first considered to be the earliest reptile but now considered to lie on the amniote stem. Besides ‘Lizzie’ Tim has described no less than ten new tetrapods and fourteen new fish taxa from Scotland.

Between 2012-17, he became involved in the highly successful TW:eed (Tetrapod World: early evolution and diversification) project, which was led by the late Prof. Jenny Clack at Cambridge University. He currently holds a position with Department of Zoology, University of Cambridge and continues to publish on all manner of things fossilferous.

Tim’s provided a well-crafted talk telling us about the history of the people involved and also the nature of discoveries. From Prof Alfred Romer (1894-1973), through Prof Stanley Westoll FRS (1912-1995), a previous holder of the Clough Medal in 1976-77, and on until the late Stan Wood (1939-2012); Tim explained how each had played their part in filling the fossil record of the late Devonian/ early Carboniferous period between 359 and 330 Ma.

In his summary, Tim explained that:
• Vertebrates recovered quickly following the end-Devonian extinction;
• There is no evidence for either a fall in atmospheric oxygen or a post-extinction trough;
• Vertebrate diversity is much greater in the Early Carboniferous than previously recognised;
• For tetrapods this diversification probably began in the late Devonian; and
• Romer’s Gap is not a natural phenomenon but is an artefact of previous unsuccessful collecting.

The vote of thanks was given by Dr Dave Millward (ex-BGS) and who thanked Tim for an excellent talk which everyone had enjoyed. He was also thanked for a couple of things; i) being a Zoologist who was also interested in the rocks and ii) for Tim’s (and also the late Prof Jenny Clack’s) word-smithery around the naming of their fossils finds.

If Fellows weren’t able to attend physically or virtually, a recording can be found on our website.

Clough Medal Lecture 2020-21 – Dr Tony Spencer

Tony Spencer on The Garvellachs

On 17th February 2021 our annual Clough Medal lecture took place for the first time as totally virtual event. The medallist for 2020-21 was Dr Anthony M Spencer who gave a lecture entitled the “The Port Askaig Formation in Argyll: uncovering the evidence for repeated climatic change in a Crogenian glacial sequence”. He was presented with his medal (again virtually) by our Vice-President, Prof Emrys Phillips on behalf of the Edinburgh Geological Society.

A brief outline of Tony’s career was described by David Stephenson. Tony had first come across the Garvellach Islands during his Doctoral research at Liverpool University in 1963. He had been presented with the topic his supervisor, Prof Wally Pitcher, who with Prof Robert Shackelton had visited the islands in 1961. Tony completed his PhD in three years and then moved onto a Post-Doctoral research position. Their findings were noticed by the Geological Society of London and led to approval for a Special Publication “Late Pre-Cambrian Glaciation in Scotland” which was published in 1971.

Tony’s career turned in a different direction after this, to more off-shore geology with stints with both BP and Statoil, and in various parts of the globe. He retired in 2012, after which he turned his attentions back to the Garvellach Islands. He then explained how through collaboration with experts in a range of specialisms, they had been able to uncover together so much more, to build on what hade been done before.

The Garvellach Islands lie in the Forth of Lorne, off the west coast of Argyll. There are four main islands and many skerries around them. The islands expose around 550m of the Port Askaig Tillite Formation, around half of its total thickness. Contained with these exposed rocks are 47 diamictites (poorly sorted or non-sorted terrigenous non-calcareous sedimentary rocks). The sequence shows many examples of where grounded ice has scraped at the sediments when these were exposed on land, some marine drop-stones indicate the presence of intruding seas at other times and also periglacial features such a frost polygons and frost shattering of exposed surfaces. In total, they have identified 28 glacial periods, 25 inter-glacial periods and 23 periglacial periods, a total of 76 significant climatic episodes in this one sequence.

Clough Medal

The Clough Medal

We learnt from Tony about how many days had been spent by numerous geoscientists on the islands over the past eight years to gather this data. He also mentioned all the boat trips made to and from the islands by virtue of three generations of the MacLachlan family of Luing.
Finally, Tony touched on the Garvellach’s history of human occupation from AD 542 (1st Century) by monks from Ireland (?) through to just before the 2nd World War when the last residents on island left. Now only migratory geoscientists visit there, many of whom are longing to return for the delayed field season of 2020 (their 9th year!).

The audience for Tony’s talk was spread widely around the globe from the USA to Australia, via Stavanger in Norway where he was presented his lecture for this evening. The vote of thanks was given by Prof Tony Prave (University of St Andrews) who thanked him for a truly unique Clough Medal lecture delivered by virtual means. He also thanked Tony for the time he takes to support a wide range of students and his openness in sharing of ideas, and for explaining his material in such a compelling way.

Anyone who wasn’t able to attend, or would just like to listen again to Tony’s lecture, can find the recording on our YouTube channel, which can be accessed from the Lectures page.

‘Boring’ geology in Glasgow & EGS’ winter lecture programme

Not quite what it may seem, but BGS’ geologists would appear to be doing some interesting new work beneath Glasgow. We have heard directly about plans for this work as part of our previous lecture programme. This BBC news website article from its science section contains some beautiful images from the cores taken from beneath Glasgow. A link to this article is given here.

BGS’ geologists drilling at UK Geo-energy Observatory in Glasgow

A reminder that this year’s winter lecture programme 2020/21, will contain a talk by the BGS’ Alison Monaghan on ‘Drilling into mines for heat: the UK Geo-energy Observatory in Glasgow’ on 3 February 2021. This will be joint meeting with the Mining Institute of Scotland.

Before then and to kicking-off our winter lecture programme on Wednesday 14th October will be a lecture on ‘The Falklands Plateau: its role in the break-up of Gondwana – and other geological controversies’ to be presented by Dave McCarthy (BGS) . This meeting will be held virtually and more details can be found at our lectures page.

Hopefully these lectures and others over the winter will indicate that the geology beneath Glasgow (and Edinburgh) is far from ‘boring’.

The Nigel Trewin Memorial Lecture 2020

Clough Medal Lecture – 19 February 2020

Prof K Whaler & Bob Gatliff – Clough Medal Award 2019

On Wednesday 19th February 2020, EGS Fellows gathered for the Clough Medal lecture held at the University of Edinburgh, Grant Institute.  The 2019-20 Clough Medal was awarded to Professor Kathy Whaler OBE, FRSE, FAGU (University of Edinburgh) for a distinguished career as an academic in the field of geophysics. Our current President, Bob Gatliff presented Kathy with the Clough Medal and was able to remind fellows that this year was notable on two counts. First that Kathy was only the third geophysicist to be awarded the medal and that it was over 40 years since Janet Watson received the medal. Kathy thanked the society for the recognition she had been given and was then able to explain some of the many facets of her research  in a lecture entitled “Adventures with Maxwell’s equations”.

Amongst the topics covered was her research in the field of geo-magnetism, involving the use of geophysics to large-scale earth processes, from the Earth’s core through the crust and even to interpreting the history of Mars geomagnetic record.  She also explained some recent research being undertaken in the Afar region of Ethiopia, called the RiftVolc project, which has drawn together a multidisciplinary group of researchers to understand crustal processes in the East African Rift. Finally, Prof Whaler touched on the future research topics including the important role played by the Earth’s magnetic field in protecting us from solar flares. She is also planning more research within the rift valley, where active volcanoes and the public are found close together.  At the end of the evening, Bob thanked Kathy for the wide ranging and fascinating lecture to celebrate the award of the 2019-20 Clough Medal.

CuningarLoopClydeGateway

Recycling the Past to Research for the Future: the Glasgow Geothermal Energy Research Field Site (GGERFS)

Contains public sector information licensed under the Open Government Licence v3.0.

On the 6th of February, a joint lecture of the Mining Institute of Scotland (MIS) and the Edinburgh Geological Society (EGS) was held at the Grant Institute of Geology , University of Edinburgh.
Dr Hugh Barron of the British Geological Survey (BGS, Scotland) gave us an overview of the Glasgow Geothermal Energy Research Field Site GGERFS, a research facility run by BGS Scotland and the Natural Environment Research Council (NERC), who also carry part of the funding.

Why geothermal energy?

Currently, only about 20% of Scotland’s total energy consumption is covered by renewable energies. It doesn’t sound impressive – and certainly we hope to do better in the future – still, compared with the rest of the UK, Scotland is remarkably successful in its implementation of renewable energies. And while our heat energy consumption is on average 3% higher than in the other parts of Britain (information accompanied by sympathetic laughter from the audience), compared with 2006 it has been reduced by impressive 30%.

New technologies may extend our exploitation of fossil fuels but they remain a finite resource. And considering the current rate of Global Warming it is even more important to find ways of generating energy which are low in CO2 and / or CH4 emissions. Geothermal energy clearly offers an interesting alternative.

Geothermal energy – for most people this conjures images of Iceland, where active volcanism provides subterranean heat, and hot springs are used in ingenious and spectacular ways. How could Scotland compare? For while our geology speaks of a rich volcanic past, by now our volcanoes are all extinct; eroded remnants of former explosive power.

However, geothermal energy is not just a question of how hot, but also of how much – relatively small differences in temperature over a large body of water still contain huge amounts of energy.
The tricky part is to extract this energy – and to make it widely available. As of now, it’s neither commercially nor technologically feasible to install a geothermal system for a single household property. For the most part, facilities are installed in large edifices or building complexes.

Projects of this kind do exist: the town of Heerlen (Netherlands) has been running a minewater scheme since 2008. In Scotland, facilities were installed in Shettleston (Glasgow), and in Lumphinans (Fife). These two projects had to be stopped in the meantime, due to problems with clogging (Shettleston) and a lack of qualified personnel for maintenance (Lumphinans).
This shows why it is so important to run a research program to find solutions for those technical problems, and to create the base for reliable and easy to run systems.

An image from the public exhibition in Dalmarnock, Glasgow (September 2015), which presented the plans for the geothermal energy research field site. Staff from the BGS explained the research and answered the visitors’ questions:

Geothermal-Energy_getting-heat-from-the-ground

‘Reproduced with the permission of the British Geological Survey ©UKRI. All rights Reserved’

 The Past

Between the Highland Boundary Fault in the North and the Southern Uplands Fault in the South, we find five large coal mining areas:

  • The Fife Coalfield
  • The Central Coalfield
  • The Lothians Coalfield (which crosses the Southern Uplands Fault in an eastwards direction)
  • The Douglas Coalfield
  • The Ayrshire Coalfield
Geothermal-Energy_coal-fields-central-belt

https://www.gov.scot/crown-copyright/

Thousands of miners worked for centuries to extract the coal. What better way to honour their hard and dangerous work, than by re-using their constructions to improve our lives, protect our environment, and increase our knowledge?

Recycling

To use old coal mines offers a couple of advantages. The mines reach down to a depth of ~ 900 m, the shafts allow easy access to warm water with a maximum temperature of ca. 37° C. Records of these mines are still held by the BGS, and can offer information about promising future sites.

An interesting 3D view of the faulted and folded coal seams under the East End of Glasgow is provided by the Scottish Government:

Geothermal-Energy_coal-seams-under-Glasgow

‘Reproduced with the permission of the British Geological Survey ©UKRI. All rights Reserved’

From:
Potential for deep geothermal energy in Scotland: study volume 2

Research

The research is realised via the UK Geoenergy Observatories Project.
The project was commissioned by NERC, while BGS will carry out the research infrastructure and operate the facilities.
Two research sites have been created, with the aim to

  • Independently monitor underground energy technologies
  • Gather scientific evidence on new and established energy and storage technology to increase efficiency and sustainability
  • Gain a world-class understanding that could support management and regulation
  • Develop new, exportable technologies

The project’s timeline is set for 15 years, the duration of its last stage as a research facility will depend on the interest shown by the academic community.

There are many benefits to be gained from a dedicated research site.
First, as fracking has shown, we need to learn in advance what impact energy extraction might have on geology and environment. All the more, since effects cannot be directly observed, and intervention deep in the bedrock would be difficult or even impossible.
The people living close to these sites have a right to know what effects any project could have on their lives. As long as this information cannot be provided, the new technology isn’t likely to be accepted.

Secondly, this is an opportunity for gathering academics working in different fields. As astronomical missions are shared by many research teams, this could become a site where scientists can co-work in a professional environment, and share information across the borders of research interest or nationality.

Finally, besides technology, these days it’s mainly expertise that becomes a commodity. And more than money can be gained: to share knowledge is also an important way to connect people all over the world. Also, it’s in our own interest to help other countries to reduce their CO2 emissions, as the effects of Global Warming caused in one country won’t stop at the borders of the next.

The site itself is situated in the Cuningar Woodland Park, a community park which successfully managed to encourage usage by the local community. Its quite charming welcome sign at the entrance, a quote from Dr Seuss

“Welcome…’If you never did you should.
These things are fun and fun is good.'”

could apply to geology, as well as to all other sciences.

Soil and bedrock at the site are a mixture of both natural and man-made formations.

Geothermal-Energy_bedrock

‘Reproduced with the permission of the British Geological Survey ©UKRI. All rights Reserved’

Not all planned boreholes could be installed. The ‘surviving’ two include a weather station, gas probes, sensors for CO2 and CH4, and an active satellite based inSAR ground motion sensor. Seismometers are included as well ( in fact, they had been installed just the day before the talk). They are part of the UK seismic monitoring network.
The data acquisition in total includes environmental monitoring, soil chemistry, hydro-geochemistry, noise, and ecology.

The Future

The project is not meant to produce enough heat to cover all its costs, rather it is planned to finance itself through its use as a research site.
This research might include measuring the impact of the geothermal technology on the local environment, new technology, and even defining a base for legal and regulatory framework (as of now, there is no regulatory regime for geothermal technology in Scotland or the UK). In order to turn geothermal energy and heat into a profitable as well as beneficial industry, the extent of all related costs has to be established.

Research topics envisaged so far:

  • Faulting and subsurface flow partitioning
  • Chemical and heat tracer tests
  • Flow rates and sustainability of heat yields
  • Thermal breakthrough
  • Subsurface to surface impacts
  • Strategies to minimise clogging
  • Geo-microbiology
  • New technologies

An online data portal to make the results available for scientists and engineers world wide is planned.

Geothermal-Energy_collecting-and-sharing-data

‘Reproduced with the permission of the British Geological Survey ©UKRI. All rights Reserved’

The lecture offered an interesting view on a so far little-explored way of creating energy in Scotland. This project combines modern technology with the past – the constructions as well as the documentation held by the BGS – to add another piece to the mosaic of modern, decentralised energy production. The knowledge gained here can help to  facilitate the use of geothermal energy even on a modest scale. The smaller and simpler the technology, the wider the possible application world wide.

Thanks & Acknowledgement

Gratitude is owed to Dr Barron for holding this lecture. He gave a clear overview of the project, its background, goals, challenges and future. He also kindly answered many follow-up questions at the traditional after-talk-tea at the Cockburn Geological Museum.

 

Links

Contact Dr. Barron
hfb@bgs.ac.uk

British Geological Survey
https://www.bgs.ac.uk

NERC
http://www.nerc.ac.uk/

Grant Institute of Geology
https://www.ed.ac.uk/geosciences

University of Edinburgh
https://www.ed.ac.uk/

Glasgow Geothermal Energy Research Field Site GGERFS
https://www.bgs.ac.uk/research/energy/esios/glasgow/

Potential for deep geothermal energy in Scotland: study volume 2
https://www.gov.scot/publications/study-potential-deep-geothermal-energy-scotland-volume-2/pages/9/

Open Government Licence for public sector information
http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/

photo of the coast of Lewis with title "A Lewisian Perspective - the basement of the Earth"

A Lewisian Perspective: The basement of the Earth

Professor Frank Rennie of UHI

Professor Frank Rennie explains Lewisian geology

On March 6th Frank Rennie, Professor of Professional Rural Development at Lews Castle College, UHI, gave a fascinating lecture and comprehensive introductory tour of the geology of the Isle of Lewis.

The geology of the Lewisian gneisses is complicated, but is so much more than simply boring monotypic banded rocks, and this lecture highlighted features to look out for in the landscape.

Despite being a long-time member of the Edinburgh Geological Society, Prof. Rennie had never made it to one of our lectures so far. It was our pleasure finally to welcome him, even if it took him to be the presenter himself in order to make it here

Right at the start we’d like to invite our readers to have a look at the slides Professor Rennie provided for this talk and kindly shared online:

PowerPoint presentation – A Lewisian Perspective: The basement of the Earth

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Events at the Roots of the World

“Far, far below the deepest delving of the Dwarves, the world is gnawed by nameless things. Even Sauron knows them not. They are older than he. Now I have walked there, but I will bring no report to darken the light of day.” [1]

If there are such ‘nameless things’, and if they have been down at the roots of the mountains since the beginning of time,  at about 3.2 billion years ago they would have witnessed (and likely munched on) the earliest forms of what we now know as Lewisian gneisses.

These rocks formed in the root zone of a gigantic mountain range. What we see today are the worn-down roots of a once-mighty mountain belt. This is the end state of mountain building which, millions of years in the future, even the young Alps and the middle-aged Appalachians will approach.

The rocks formed 35 – 40 km deep in the crust in a highly metamorphic environment, at temperatures of ~ 900° C and a pressure of ~10 kbar. At the time of their formation, the rocks were buried in the Earth’s crust positioned at the South Pole.
But while their formation started at 3.2 billion years ago, the gneisses as a whole spanned a period of roughly 1.5 billion years, a detail often overlooked when the immense age of these rocks is mentioned.

In order to make this inconceivable time span more tangible, Professor Rennie used one year to represent the whole of Deep Time. In this comparison the Outer Hebrides formed between February and June, while the Lewisian gneisses appeared around May. Fortunately, we can be quite sure that no creature had them for elevenses, for on this time-scale even the first fish appeared only in November.

Lewisian Gneiss and Where to Find Them

Three types of Lewisian gneisses can be found: metasediments, granitic gneisses and undifferentiated gneiss which cannot be placed in either category, and is often referred to as ‘banded’ or ‘grey’ gneiss. This latter is a highly dense rock that doesn’t break or weather easily. The thin section (see presentation) shows crystals elongated by pressure on the matrix. Other tension-related phenomena, for example boudins, or pods, occur as well.

The gneiss may be the rock on which Lewis rests for the most part, but most of it is hidden under grass, peat and other surface covers. Outcrops are mostly found along rivers or at the coast.
At Ness, a flaggy and fractured metasedimentary assemblage can be seen, while at Scourie a dyke shows in the form of its absence – the intrusion building the dyke weathered easier than the grey gneiss, which is much less susceptible to erosion. In Dail Beag Precambrian granites cut through the gneiss.

The landscape of the Outer Hebrides both directed and was shaped by ice flow during the last Ice Age. Signs of this can be seen in Sough Galson or in the interesting raised beach over glacial till at Habost.

No More Mr Gneiss Guy

The geology of Lewis and its gneisses is much more complicated than many are aware of or care to learn about. On the other hand, there is demand for education – local people as well as visitors show their interest. Professor Rennie told of rocks brought to him for identification, and requests to lead geology tours around Lewis.
Maybe, with the help of the geological institutions in Scotland and the new Scottish Geology Trust, geological ‘wildlife safaris’ and / or rock identification events similar to those held for mushrooms (albeit with a less dangerous background) could be organised in the future.

It’s no use going back to yesterday, because I was a different rock then…

Many are aware that  Lewisian geology is more akin to that of Greenland than mainland Scotland. The question, however, why the Atlantic opened to the West of Lewis, instead of separating it from Scotland and keeping it nice and tidy with Greenland, could not be answered. This is a conundrum for future geologists to research and resolve.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Our heartfelt thanks go to Professor Rennie for investing time and effort in both this highly interesting lecture and his long-awaited visit to Edinburgh.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sources:
[1] J.R.R. Tolkien, The Lord of the Rings, The Two Towers, “The White Rider”

Clough Medal

Clough Medal Lecture – Sideways views of Scottish Garnets: Insights into Metamorphic Processes

The Clough Medal is presented annually to a geologist whose original work has materially increased the knowledge of the geology of Scotland and/or the North of England, alternatively someone who is Scottish and has significantly advanced the knowledge of any aspect of geology. Find out more about Charles T Clough.

This year’s recipient is Dr Tim Dempster from the University of Glasgow School of Geographical & Earth Sciences in recognition of the exceptional contributions he has made to advancing the understanding of the geology of Scotland, particularly the metamorphic geology of the Highlands, where he has employed a wide range of technologies to better understand the processes; and his work as a dedicated and popular teacher of undergraduate students, using the Highlands of Scotland as a ‘natural laboratory’.

In this joint lecture with the Geological Society of Glasgow Dr Dempster talked about garnets, the workhorse of metamorphic petrologists.

Being capable of recording original compositions during growth, garnets allow determination of pressure-temperature paths and durations of metamorphic events.

Concentrating on the contact zone between the garnet and its surrounding minerals, a 3D image of the garnet rather than a thin section – which would offer too small an area for clear analysis – was created. Then the team projected a ‘map’ of the adjacent minerals on the garnet’s surface and variations in its chemistry, e.g. the Calcium content, were recorded.

This way of analysing the garnet showed that the crystal’s growth itself can change the chemistry of the surrounding matrix and hence the reaction path during growth, leading to a ‘false’ temperature recording. Dr Dempster’s studies of garnets from the Scottish Highlands therefore question some key concepts of metamorphic equilibrium.

Background reading: Dempster, T. J., La Piazza, J., Taylor, A. G., Beaudoin, N. and Chung, P. (2017) Chemical and textural equilibration of garnet during amphibolitefacies metamorphism: The influence of coupled dissolution-reprecipitation. Journal of Metamorphic Geology, 35, 1111-1130.