Welcome to the Geological Society of Glasgow

The Geological Society of Glasgow was founded in 1858 – the year in which Darwin and Wallace presented the idea of Natural Selection!

The website was upgraded in August 2019 to make it more readable on different sizes of display. We have tried to keep the same interesting and varied content that our original website had, while adding some new features. For new visitors, we would recommend the Local Rocks section, where we have assembled an introduction to the geology of the Glasgow area, with its diverse mixture of rocks and geological history. In this section, you will find the same geological map as you can see here, but  with additional ineractive features.

The society has a programme of monthly lectures, running from October to May, on topics by leading experts in their fields. We also run field excursions from April to September.

Please feel free to attend our meetings. You will be made most welcome and at the social session following the lecture you can talk to the lecturer and meet society members. Perhaps you will decide to join us in the society. We look forward to meeting you.

News
Events
Sunday 22 Sep

Anglesey

10:00 am

Anglesey’s rocks provide a detailed record of the events leading to the formation of southern Britain. Formed between 650 & 300 Ma, they include high grade gneisses, a granite pluton, metasediments, sandstones, mudstones and the famous Anglesey Blueschists. There are also Paleogene dykes, abundant glacial features, a number of NE–SW faults and large sandstones blocks possibly marking the location of an ancient subduction zone.

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                    [post_content] => The mountain of Arkle in west Sutherland consists of quartz arenites (quartz-cemented quartz sandstones) of Lower Cambrian age. The pale grey screes cover the planar unconformity with the underlying Lewisian gneisses, which have a shallow dip to the east-south-east (to the right in the photo).
                    [post_title] => Arkle: Lewisian-Cambrian unconformity
                    [post_excerpt] => The scenic site of an unconformity in the NW Highlands.
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                    [post_content] => The Arnaboll Thrust on the east side of Loch Eriboll is where the term mylonite was first used. Here the much older Lewisian gneisses lie structurally above the light-coloured quartz arenites of the Lower Cambrian Pipe Rock. The mylonites are derived from both units and form a narrow zone only a few metres thick.
                    [post_title] => Arnaboll Thrust
                    [post_excerpt] => The Arnaboll Thrust on the east side of Loch Eriboll is where the term mylonite was first used.
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                    [post_content] => Photo: Bill Gray

The Geological Society of Glasgow had a very successful weekend excursion to Antrim's Causeway Coast in September 2017. During the excursion we explored over 600 million years of geological history exposed on the northeast Irish coast of County Antrim, from Portrush to the Giant’s Causeway and Ballintoy Bay. The rocks are superb, with ages ranging through the Precambrian (basement), Dalradian Supergroup, Devonian (puddingstone conglomerate), Carboniferous, Triassic, Jurassic (ammonites, belemnites and bivalves), Cretaceous (chalk and metamorphosed chalk) and Palaeogene, including, of course, the spectacular North Atlantic Igneous Province with its lavas, sills and volcanic plugs.

One of the most spectacular of the formations that we saw was the Devonian puddingstone at Cushendun, which has been eroded to form the Cushendun Caves. These rocks were laid down by flash floods in a desert environment, and contain clasts with a huge range of sizes.

The caves feature, as do many other locations in Northern Island, in the television series Game of Thrones. (The caves appeared in season two as a cove in the Stormlands.) Game of Thrones tourist excursions are now a thriving industry in Northern Island and we saw several coaches devoted to these.

Bill Gray.
                    [post_title] => Cushendun Caves, County Antrim
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                    [post_content] => The Dob’s Linn area is where Charles Lapworth carried out his pioneering studies in the 1870s, in which he established the usefulness of graptolites for correlating different strata within the Ordovician and Silurian periods. It is also the location of the Global Boundary Stratotype Section and Point (GSSP) for the Ordovician-Silurian boundary, informally known as the ‘golden spike’.

In this area, the dominant rock type of the Southern Uplands, the Silurian Gala Greywackes, is underlain by the Upper Ordovician/Lower Silurian Moffat Shale Group. The Moffat Shale Group is exposed in a series of faulted inliers formed by imbricate thrusting, and Dob’s Linn is one such inlier. The Moffat Shale was deposited in the Iapetus Ocean over a period of 28 My, and it is composed of four main units; in chronological, and depositional, order, these are: the Glenkiln Shale, the Lower Hartfell Shale, the Upper Hartfell Shale and the Birkhill Shale. The first three of these were deposited in the Late Ordovician, while the Birkhill Shale was deposited partly in the Ordovician but mainly in the Llandovery epoch of the Silurian; the Ordovician-Silurian GSSP lies 1.6 m above its base.

The area takes its name from the Dob's Linn waterfall, which is shown in the picture. The waterfall was named after the Scottish Covenanter Halbert Dobson, who successfully hid from his English pursuers in a cave near the waterfall for several weeks in the 1690s. The society has made several field trips to the area, the last of which was a joint excursion with the Edinburgh society in April 2010.

Bill Gray.
                    [post_title] => Dob's Linn
                    [post_excerpt] => This site in the Southern Uplands shows the Ordovician-Silurian boundary and is where Lapworth (1842 - 1920) recognised the importance of graptolites in understanding the stratigraphic sequences in the area.  
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                    [post_content] => Glasgow University's Centre for Open Studies organised an excursion tour to Gran Canaria in April-May 2016. One of the many spectacular views that the group had was this one into the caldera of the Tejeda volcano.

The rocks to the lower left of the brightly coloured rocks are shield basalts that belong to the lowest stratigraphic unit of Gran Canaria and are thus some of the oldest rocks on the island.They formed from lava that erupted from the volcano in the Miocene, between about 14.5 and 14 million years ago. Following the eruption of the basalts, a huge volume of ignimbrite (the P1 ignimbrite) was ejected, and this led to the collapse of the volcano's magma chamber to form the huge Tejeda Caldera, an elliptical structure with dimensions 20 km by 17 km. During the following 6 million years there were repeated cycles of pyroclastic eruptions from ring fractures at the caldera rim, and these produced extensive deposits of tuff both inside and outside the caldera.

The brightly coloured rocks to the right of the basalts are tuffs that were laid down inside the caldera during this prolonged phase of igneous activity. The bright colours are the result of low-temperature hydrothermal alteration caused by extensive flows of liquid in the faulted marginal areas of the caldera. Later erosional processes have removed the basalts that originally lay in front of the caldera and what we are seeing is a cross section through the rocks immediately adjacent to the caldera and into the caldera itself: the sloping junction between the shield basalts and the bright tuffs represents the margin of the caldera.

Bill Gray.
                    [post_title] => Gran Canaria: inside the caldera
                    [post_excerpt] => An exposure of part of an enormous caldera on the island of Gran Canaria.
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                    [post_content] => The Moeraki Boulders lie in Otago, on the east coast of South Island, New Zealand. While similar features are found around the world, these boulders are remarkable for their size, up to 2m diameter, and their almost spherical shape. Well-known on the tourist trail, they are fairly easy to access and seen as being of national importance. The boulders littering the beach emerged from the eroding cliffs of soft mudstone in which they formed. The boulders are septarian concretions with cracks occupied by mineral deposits. In some examples the internal pattern is exposed.

 
Photos above: I McCallum
Some 60 million years ago, sediment was accumulating on the sea floor, with small fragments such as shells and plants within it. Calcite slowly built up around organic nuclei, forming spherical nodules with harder outer layers while the inner material dehydrated to give cracks which spread radially out to the rim. The cracks themselves filled with varying mineral deposits as groundwater conditions changed. The largest boulders are thought to have taken more than four million years to form. Following uplift onto the landmass of New Zealand in a period of mountain building, erosion was able to expose the Palaeocene mudstone beds that contain the boulders and from which they continue slowly to emerge. The effects of weathering have removed some of the outer layers, allowing the inner structure to be seen and breaking up some boulders. Although now protected by law, it is believed that many smaller boulders were removed from the beach prior to legislation. The newsletter item by Hayward (2014) considers the issue of geoconservation. The earthquake near Kaikoura in late 2016 has allowed similar boulders to be viewed following the uplift of the seafloor in that event. See this news item. To find out more:
  • The Moeraki Boulders, 1997. Miscellaneous series 9. Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand.  Website: at this location.
  • Boles, J.R., Landis, C.A. and Dale, P., 1985. The Moeraki Boulders--anatomy of some septarian concretions. Journal of Sedimentary Research55(3). (subscription required)
  • Thyne, G.D. and Boles, J.R., 1989. Isotopic evidence for origin of the Moeraki septarian concretions, New Zealand. Journal of Sedimentary Research59(2). (subscription required)
  • Hayward, B.W., 2014. Treasured spheres: protecting New Zealand’s heritage of spherical concretions. Newsletter no 12, Geoscience Society of New Zealand, pp 24-30. Available from: here  [Accessed 20 February 2018]
[post_title] => New Zealand's Moeraki Boulders [post_excerpt] => Remarkable concretions on the east coast of New Zealand's South Island. [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => new-zealands-moeraki-boulders-2 [to_ping] => [pinged] => [post_modified] => 2019-07-26 15:52:10 [post_modified_gmt] => 2019-07-26 15:52:10 [post_content_filtered] => [post_parent] => 0 [guid] => http://staging.gsocg.org/sites/new-zealands-moeraki-boulders/ [menu_order] => 0 [post_type] => iconic-sites [post_mime_type] => [comment_count] => 0 [filter] => raw ) [6] => WP_Post Object ( [ID] => 1673 [post_author] => 2 [post_date] => 2016-10-07 10:41:00 [post_date_gmt] => 2016-10-07 10:41:00 [post_content] => Siccar Point on the Berwickshire coast is one of the most famous geological sites in the world. It is the site of Hutton's Unconformity, where almost vertical beds of marine Lower Silurian greywackes are overlain by gently sloping beds of non-marine Upper Devonian conglomerates. The unconformity was discovered during a boat journey made in 1788 by the founder of modern geology James Hutton, the scientist and mathematician John Playfair and the geologist James Hall. The Silurian beds are approximately 435 million years old, while the overlying Devonian beds are aproximately 375 million years old. The unconformity therefore bridges a time gap of around 60 million years. The unconformity provided one of several pieces of evidence that Hutton produced in support of his theory that the Earth was much older than was widely believed in the eighteenth century. Although he did not know the ages of the Silurian and Devonian rocks at Siccar Point, he recognised that long periods of time would have been necessary for the Silurian rocks to have been tilted and eroded, and for the Devonian sediments to have been laid down on top of them. Bill Gray. [post_title] => Siccar Point [post_excerpt] => This famous site was an important source of evidence for 18th century scientists. [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => siccar-point [to_ping] => [pinged] => [post_modified] => 2019-07-25 20:30:14 [post_modified_gmt] => 2019-07-25 20:30:14 [post_content_filtered] => [post_parent] => 0 [guid] => http://staging.gsocg.org/sites/siccar-point/ [menu_order] => 0 [post_type] => iconic-sites [post_mime_type] => [comment_count] => 0 [filter] => raw ) [7] => WP_Post Object ( [ID] => 1675 [post_author] => 2 [post_date] => 2014-11-12 11:32:00 [post_date_gmt] => 2014-11-12 11:32:00 [post_content] => Glasgow University's Department of Continuing Education organised an excursion tour to the western Pyrenees in June 2012. One of the spectacular structures that the group saw was the Torla fold, which is on the left of the photograph. The picture was taken from the village of Torla, in northern Spain. The rocks in the Torla Fold belong to the Gallinera limestone formation, which was laid down in the Ypresian stage of the Eocene (around 50 Ma). The Gallinera Formation was distorted during the Pyrenean orogeny, which occurred later in the Eocene, at around 37 Ma, and resulted from the collision of the Iberian microplate with the Eurasian plate. The Torla fold looks like a recumbent fold, but is actually a slightly overturned drag fold caused by minor thrust faults associated with the Mont Perdu Thrust. This view is looking north, and the Mont Perdu Thrust is directed to the south, towards the camera. The plane of the thrust is roughly level with the top of the wedge-shaped bare slope that interrupts the tree cover on the mountain in the centre of the picture. Bill Gray. [post_title] => Torla Fold [post_excerpt] => The Torla Fold is a spectacular geological structure in the western Pyrenees, northern Spain. [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => torla-fold [to_ping] => [pinged] => [post_modified] => 2019-07-25 19:56:42 [post_modified_gmt] => 2019-07-25 19:56:42 [post_content_filtered] => [post_parent] => 0 [guid] => http://staging.gsocg.org/sites/torla-fold/ [menu_order] => 0 [post_type] => iconic-sites [post_mime_type] => [comment_count] => 0 [filter] => raw ) ) [post_count] => 8 [current_post] => -1 [in_the_loop] => [post] => WP_Post Object ( [ID] => 1667 [post_author] => 2 [post_date] => 2014-11-15 15:25:00 [post_date_gmt] => 2014-11-15 15:25:00 [post_content] => The mountain of Arkle in west Sutherland consists of quartz arenites (quartz-cemented quartz sandstones) of Lower Cambrian age. The pale grey screes cover the planar unconformity with the underlying Lewisian gneisses, which have a shallow dip to the east-south-east (to the right in the photo). [post_title] => Arkle: Lewisian-Cambrian unconformity [post_excerpt] => The scenic site of an unconformity in the NW Highlands. 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