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


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.


[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.

2018 EGS Public Lecture – What the Ice Age ever do for us?

At this time of year, its good to reflect on our successes as a Geological Society. This year we held our 2018 Public Lecture event at Dynamic Earth, Holyrood Road, Edinburgh on 21st November 2018. The event attracted around 150 people of all ages. Our topic was the Ice Age and we heard from three excellent speakers – Prof Emrys Phillips and Dr Carol Cotterill (both BGS Scotland) and Dr Tom Bradwell (University of Stirling). This event was our 2nd major public lecture in recent years

Landscape and the human psyche – by Dr Carol Cotterill

During the interval at this event, a rolling slide show was presented giving an artistic interpretation of the landscape.  The work was put together by one of the speakers, Dr Carol Cotterill.  We thought that people may not have had a chance to view this in full and so a pdf download is now available.  Please note that the contents are copyrighted to Dr Cotterill, we would therefore encourage anyone who wants to make use of the material to contact Carol directly.

Thanks again to all who contributed to this year’s successful 2018 Public Lecture.

Evening Lecture Season Kicks-off

First EGS lecture in the newly refurbished Hutton Lecture Theatre, University of Edinburgh

The 2018-19 Evening Lecture Season started on Wednesday 10th October at the newly refurbished Hutton Lecture Theatre, Grant Institute of Geology at the University of Edinburgh.  A large audience came together to hear Professor Roy Thompson (University of Edinburgh) talking about Scotland’s Energy Trilemma.  The talk ranged across a range of energy sources, always with a neat geological/geophysical angle, climate change and the environment.  Prof Thompson richly entertained his audience with the latest news on the subject and ensured that we all went away better informed for the future. He has published a blog post about his lecture, including a downloadable pdf of his slides, at

The lecture set a high standard for forthcoming lectures, the next one of which will be held on the Wednesday 24th October (7.30pm) when Dr Graham Leslie (BGS) will speak on What place for world class geology in future Singapore.

Finally, a reminder of EGS’s Workshop on North West Highlands Geopark to be held at the Methodist Centre at 25 Nicholson Square, EH8 9BX on Saturday 27th October 2018 between 11am and 3pm.  Tickets to be purchased in advance, from


EGS Public Lecture: What did the Ice Age ever do for us?

Wednesday 21 November, 6.30pm at Dynamic Earth

Edinburgh Castle Rock, a volcanic plug an important defensive site, carved by ice moving from west to east. Photo: Barbara Clarke

Scotland’s scenery has been shaped by moving ice and meltwater over hundreds of thousands of years, but the Ice Age has also affected the sea bed around Scotland and it influences today’s society in surprising ways.

This public lecture, organised by the Edinburgh Geological Society and Dynamic Earth, gives the opportunity to hear first-hand about recent advances in our understanding of the Ice Age in Scotland.

The event will be chaired and introduced by Hermione Cockburn, the scientific director at Dynamic Earth. Presenters are Carol Cotterill, Emrys Phillips (both from the British Geological Survey) and Tom Bradwell (Stirling University). Each speaker will give a short presentation outlining different aspects of the Ice Age, followed by a panel discussion with questions from the audience.

Venue: Dynamic Earth, Holyrood Road, Edinburgh EH8 8AS. Parking is available in the Dynamic Earth underground car park (charges apply).

Tickets £5, free for students and under 18s. Advance ticket sales are now closed – some tickets available at the door, but get there early in case we sell out. Doors open 6pm, lecture starts at 6.30pm.


Public Lecture

Public Lecture: Scotland’s recent fossil finds
Wednesday 1 November 2017, 7 pm

In the last few years, very exciting new fossil finds have been made in several locations in Scotland, unlocking the secrets of key moments in evolution. In Skye and the Inner Hebrides, new reptile and mammal finds from the middle Jurassic add important knowledge about this time period which is sparsely represented elsewhere. In the Scottish Borders, new tetrapod fossils help fill ‘Romer’s Gap’ and demonstrate the migration of vertebrate life onto land and the evolution of our first five-fingered ancestors. And the pavements of Edinburgh and other urban areas are providing new Devonian fish fossils and furthering our understanding of life in Devonian lakes.

This public lecture gives the opportunity to hear first-hand about major advances in our understanding of Scotland’s geology and the evolution of life. Chaired by Mark Stephen from BBC Radio Scotland, the panel will include Nick Fraser (National Museums Scotland) and Steve Brusatte, Elsa Panciroli and Tom Challands (all from the University of Edinburgh). Venue: Appleton Tower, 11 Crichton Street, Edinburgh EH8 9LE.

Tickets £5, free for students and under 18s: Advance booking recommended – book now via Brown Paper Tickets

Reconstructions of past environments in Scotland. Left: Sauropods on a Jurassic plain (credit: Jon Hoad). Right: Carboniferous lake (credit: Mark Witton, ©NMS).

UK Oil and Gas Future?

Is there a future for the UK oil and gas industry?

UK Oil and Gas Future?11 January 2017 at 7:00 pm
Lecture by: Dr Phil Richards, formerly BGS Scotland

Approximately 27 billion barrels of oil has been extracted from the UK North Sea. Some claim there are 14 billion barrels remaining to be exploited, but of those, nearly 6 billion barrels are classified as “Yet to Find”. Recently, we’ve been finding them in 10 to 15 million barrel increments, suggesting it might take some 38 years to find them all, by which time the North Sea’s infrastructure will be well and truly rusted away. How might we speed up the rate of new discoveries through the application of new technologies, and perhaps more importantly, by going back to basics and doing better geology?

Phil Richards worked as BGS Regional Hydrocarbons Manager, and has over 30 years of world-wide experience of oil exploration experience, specialising in creating the technical conditions necessary for inward investment in hydrocarbon exploration in developing basins. He has published over 50 papers on geology relating to oil and gas exploration.

Volcanoes and the making of Scotland

Volcanoes and the Making of Scotland

The next lecture of the Edinburgh Geological Society’s winter series will take place on Wednesday 23 November at 7:30pm in the Hutton Lecture Theatre at the Grant Institute of Geology, King’s Buildings, Edinburgh, when Professor Brian Upton, University of Edinburgh will talk about Volcanoes and the Making of Scotland.

Volcanoes have played a major role in the creation of Scotland’s geology. The most recent examples on the west coast are a mere 60 million years old, but rocks composing many of the famous Scottish landforms such as Glencoe are the direct result of earlier episodes of volcanism. Volcanoes and the Making of Scotland will explore back in time from the most recent examples to volcanoes of the obscure Precambrian times which left their signature in the ancient rocks of the far north-west.

Brian Upton is a Distinguished Fellow of the EGS and is Emeritus Professor of Petrology and Senior Honorary Professorial Fellow in the School of Geosciences of the University of Edinburgh.  The comprehensively-revised second edition of his highly-acclaimed book Volcanoes and the Making of Scotland has recently been published and has been enthusiastically reviewed.

The meeting will be followed by tea and biscuits in the Cockburn Museum of the Grant Institute, to which all are invited.
A link to a map of the campus can be found at .
Volcanic Hazards

Volcanic Hazards

The next lecture of the Edinburgh Geological Society’s winter series will take place on Wednesday 9 November at 7:30pm in the Hutton Lecture Theatre at the Grant Institute of Geology, King’s Buildings, Edinburgh, when Dr Charlotte Vye-Brown, BGS Scotland will talk about Volcanic Hazards. Of all the natural hazards, volcanic hazards are unique in the sense that there are many hazards associated with, and produced by, any single volcano that can have impacts hundreds or even thousands of kilometres away. Globally, an estimated 800 million people live within 100 km of a volcano that has the potential to erupt. There remain significant challenges to understand volcanic risk and assist with disaster mitigation. These challenges are pronounced in Africa due to significant knowledge gaps, lack of real-time monitoring, uncertainty, limited early warning capacity and pressure on resources. This talk will focus on recent research in Ethiopia on understanding the periodicity and character of past eruptions, identifying potential impacts, and evaluating future threat.

Charlotte Vye-Brown is a senior volcanologist with BGS in Edinburgh, working on projects on rift volcanism, particularly in East Africa; the volcanic history of the Ascension Islands; and emplacement and eruption styles of flood basalts.

The meeting will be followed by tea and biscuits in the Cockburn Museum of the Grant Institute, to which all are invited.

A link to a map of the campus can be found at .
Paleosols as evidence of terrestrial climate change.

Palaeosols and Climate Change

The next lecture of the Edinburgh Geological Society’s winter series will take place on Wednesday 26 October at 7:30pm in the Hutton Lecture Theatre at the Grant Institute of Geology, King’s Buildings, Edinburgh, when Dr Tim Kearsey, BGS Scotland will talk about Palaeosols as evidence of terrestrial climate change at major Palaeozoic vertebrate evolutionary events.
Climate change is a major driver of evolution. Palaeosols (fossil soils) are one of the few direct indicators of terrestrial climate and provide a record of climate changes and landscape architecture, and are critical in understanding the terrestrialization of vertebrates in the Carboniferous and the Earth’s largest mass extinction at the end of the Permian.

Tim Kearsey is a survey geologist and sedimentologist with BGS in Edinburgh. He has research interests in Palaeozoic stratigraphy and sedimentology; palaeosols and palaeo-environmental reconstruction; and geostatistics. In June 2015 he was joint leader (with David Millward) of the highly successful EGS excursion to Burnmouth.

The meeting will be followed by tea and biscuits in the Cockburn Museum of the Grant Institute, to which all are invited.

A link to a map of the campus can be found at .