Tuesday Tutorials/Workshop Summaries
Tuesday Tutorials began as a way of introducing key geological concepts to people who may be new to geology or for those who would like to refresh their knowledge. Some tutorials are at a basic level, while others are quite challenging! However, the setting is fairly informal, with groups ranging in size from five to fifteen people or so. Questions are encouraged, & anyone may join us.
Tutorials are held in Abbot Hall Social Centre on the Tuesday following a lecture (usually in October, November, January, February, March), from 2.00-4.00pm. We each pay £3.00 to cover the cost of the session & bringing the correct change really helps. Contact Chris Anderson (chris.anderson.wgs@gmail.com) if you would like to join us.
2019 Tuesday Tutorials/Workshops
26th November 2019 – The Rock Cycle (Part 2)
Led by Audrey Brown
This session was something of a refresher for us, though Audrey included new material & tried to push our understanding of this explanation of how rocks are destroyed & formed which is so important to geology. Audrey started with the structure of the earth & what is at its core (molten rock which is believed to be mostly iron that is constantly circulating). She then went on to talk about mantle minerals & to divide them into two groups. Dark minerals, such as olivine, pyroxene, amphibole & biotite mica, are high in magnesium (Mg) & iron (Fe), & are referred to as Mafic. Light minerals, such as quartz, feldspars & muscovite mica, are high in silica (Si), Potassium (K) & sodium (Na), & are referred to as Felsic. Minerals remain in a fluid state at very high temperatures, & will begin to crystallize as temperatures drop (returning to fluid if temperatures rise again – which may be repeated & is known as fractional crystallization), with different crystals forming at different temperatures. This can be represented in a table, as can the make-up of igneous rocks with axes of volume percentage by mineral content & divided into: extrusive (appears on the surface) & intrusive (forms underground); & whether it is mafic, intermediate, or felsic. We then looked at how rocks are broken down when they reach the surface by weathering & erosion. Finally, we came to the rock cycle, with some rocks forming from deep underground while others are being worn down into constituent parts & reburied, with the liquid layer between the mantle & the crust playing an important role. This session helped to explain why geologists are so interested in chemical composition! C. Anderson
22nd October 2019 – The Stratigraphic Column
Led by Vic Parsons
Vic started this session by working through the geological time scale, with two columns on p1 of his handout. Column 1 showed eons & eras from the Hadean (4500 million years ago) to the Phanerozoic (up to present day), & column 2 showed the Phanerozoic eras & periods (from 500 ma Cambrian to present Quaternary period). On page 2, the Cenozoic (the last 65 million years or so) was broken down into eras, periods, & series/epochs. Vic then led us through some of the key people involved in the development of the column. From the 1600s through to the 1800s, men such as Nils Stensen, Giovanni Arduino, Abraham Gottlob Werner, John Phillips & J.D. Dana had noticed that rocks were stratified & that they contained fossils. Fossils came to be very important in starting to divide the time periods up, with certain fossils appearing in different strata. The stratigraphic column appears a rather odd arrangement because it was developed over several hundred years & added to as ideas about geology & the ability to date rocks developed. This was a fascinating session, with a lot of information to take in! C. Anderson
26th March 2019 – Maps: Next Steps
Led by Clive Boulter
Clive Boulter introduced us to the high-tech world of online maps & LIDAR images. Before this session, he had sent us detailed instructions of how to upload Google Earth Pro 7.3 (free) from https://www.google.co.uk/earth/download/gep/agree.html & asked that we bring along a laptop if we had one. Several of us shared, which was quite useful, given how challenging navigation around these digital maps could be! However, despite this, it soon became clear what an amazing resource such online maps are & what incredible things it is possible to do with them. As Clive explained, geological maps show what rocks are where & though these are vital data it is only at the surface. Extrapolating this information into the subsurface adds greatly to our appreciation of the information contained on a map & has many practical applications (ore deposits, petroleum, engineering, water resources, etc.). Clive’s aim was to encourage us to develop techniques that will allow mapping at the surface to be projected subsurface. To this end, we looked at air photos in 3D, visualising a range of geological settings on Google Earth in 3D, 3D models, & the application of these methodologies to understanding paper maps. Clive is clearly an enthusiast & his enthusiasm did rub off! C. Anderson & C. Boulter
26th February 2019 – An Introduction to Geological Maps
Led by Audrey Brown
Audrey started with a brief introduction to geological maps, then allowed us to wander freely to look at some of the maps she had brought with her (& try to address the questions she had set for each). Audrey explained that the BGS produce two types of geological map: A Solid Edition, which shows the first layer of bedrock; & a Solid & Drift Edition which includes glacial deposits & outcrops (areas where soil & vegetation is absent so can see all the rock), but otherwise not bedrock. The key to the maps is probably the hardest thing to come to grips with as they differ between maps, depending on the geology of the area covered. So, for instance, limestone would be identified by the same colour on all maps, but would not always appear on a map so would not be included in the key. As there are only so many colours that work well on a map, the colours are ‘named’ & patterns (known as ornament), are also used e.g. stripes, dots. One can visit the BGS website to look at geological maps, & manipulate them in various ways. This was a really helpful tutorial to those new to geology or who needed a bit of encouragement to look at a geological map. C. Anderson
22nd January 2019 – An Introduction to Minerals
Led by Bernard Skillerne de Bristowe
Bernard started us off with ‘What is a rock?’, & we answered ‘A collection of minerals!’. But what is a mineral? It appears there are a range of definitions but one Bernard seemed to like was ‘a naturally occurring solid with ordered atomic arrangement & definite though not fixed chemical arrangement’. He then went on to tell us how minerology is one of the oldest sciences e.g. lapis lazuli was traded 10,000 years ago. After a brief summary of the rock cycle, Bernard told us about some of the great names in the field. George Barrow (late 19th century), noted ‘zones’ with different minerals in different areas & in a particular order. Victor Goldschmidt (early 20th century) proposed contact metamorphism, & in the 1930s Peltier Scholan said that what was really important was the total composition of the rock & the different temperatures & pressures under which it was formed, which led others to produce pressure/temperature graphs. In the 1950s Stephen Richardson added a time curve to the graph to represent burial & exhumation of rocks. Around this period, theories of plate tectonics were being developed to explain movement of rock. Bernard then guided us through how minerals can be identified. Hardness is useful e.g. what can be scratched with a fingernail, or penknife, or resists scratching. Sometimes the structure & shape of mineral crystals can be seen with a hand lens. Colour is not very helpful as it can vary widely, nor is gravity as many minerals are within a narrow range. Some properties of minerals are important in industry e.g. optical/electromagnetic properties, & radioactivity. At the end we looked at some of Bernard’s extensive mineral collection. A challenging but enjoyable tutorial! C. Anderson
2018 Tutorials/Workshops
23rd October 2018 - Rocks in a Box
Led by Audrey Brown
Seated at tables of three or four people, each team worked its way through one of Audrey Brown’s boxes of rocks. Each rock was well-wrapped, creating a surprise element. Audrey’s selection was designed to challenge, puzzle & tease us, & I think most of us felt all three. There were some unusual rocks, some lovely fossils, & some rocks that were not rocks (beware of holiday purchases, though they might make lovely Christmas decorations). Our table recognised a fossil & a fake when we saw them & tended to be in the right rock group with most of our other specimens, but we would have won no prizes! It was an amusing & stimulating way to spend an afternoon. – C. Anderson
27th March 2018 - Why does Cumbria have so many different rock types?
Led by Audrey Brown
Audrey Brown began this workshop by giving us each a simplified version of a BGS map of Cumbria. She then described how hot, radioactive rocks solidify as they cool, & other rocks rise to the surface. Tectonic plates can be moving apart which enables new material to move to the surface & form ridges, or moving together, in which case one plate is forced down beneath the other - a process known as subduction. Subduction is associated with mountain building, earthquakes & volcanism. The oldest rocks in Cumbria are from the Ordovician period (480 million years ago), when what is now England was situated in the southern hemisphere on the edge of the Iapetus Ocean. Material washing over us from the Gondwana land mass formed the Skiddaw slates & mudstone. As we moved north, there was volcanic activity creating the Borrowdale Volcanic Group & Eycott Hill, with differing mineral combinations depending on the eruption, & whether ash fell on land or in water, & with melting due to hydration from the subducting slab. Eventually the Iapetus Ocean disappeared (was subducted), & erosion was followed by sea water coming in again, & new sedimentary deposits. Audrey took us through the Silurian, Devonian, Carboniferous, & Permian & Triassic periods, describing processes & location (which we then coloured in on our maps). Her final slide, a prediction of how the land masses might look in the future, showed the continents forming a single land mass, with the British Isles to the north of it in (blissful?) isolation. – C. Anderson & B. Kettle
27th February 2018 - Rocks of the Lake District
Led by Clive Boulter
The second workshop of 2018 on started with Clive Boulter explaining the differences between hand lenses (& how to use one), & why he always carries a pen-knife to check rock hardness (which we all had a go at doing). We then worked in small groups on some Shap granite, discussing what we observed & trying to identify what was in it. Clive told us how to estimate percentages of the different constituents of the rock, & when we were happy with this, we had a go at plotting it on an identification ‘pyramid’. We then examined various other rocks in our sample boxes, e.g. pumice which Clive had collected from the Cumbrian coast & probably came from the Caribbean. At the end, Clive let us look at part of his personal collection, which included some wonderful specimens. – C. Anderson
23rd January 2018 - Igneous Rocks
Led by Audrey Brown
Audrey Brown led the first WGS Tuesday Tutorial/Workshop on ‘Igneous Rocks’. She brought along different rock samples & after our first attempt at identifying the igneous examples, she helped us sort them into igneous, metamorphic & sedimentary. We then looked at the range of igneous rock samples & tried to describe their characteristics – crystals, mineral characteristics, colour. The Igneous rocks had no layers. The proportions of different minerals could be roughly gauged. Audrey then gave an overview of the different mineral compositions & Mafic & Felsic minerals/rocks, also an overview on extrusive & intrusive. We completed the volume:elements chart for granite to start with, comparing Shap Granite to a Granite from Peterhead & then wrote in the names of the other minerals & rocks, while looking at the rock samples. To end, we looked at some Peridotite. – A. Thompson