A Geology Practical in Chapeltown

An experiment in compaction, cementation and lithification

2019 commenced with the indoor meeting of the Sheffield U3A Geology Group at the Commercial Inn in Chapeltown. I particularly look forward to this event, because it increasingly provides me with the opportunity to plan my time for the coming year – as well as the continued social interaction with likeminded people, as I had discovered during the last meeting of 2018 in Totley. 

Listening to the introduction to the practical lesson

This year, Peter Kennett – who had led the group around the Porter Valley for the November 2018 field trip – was invited to give us a practical lesson in geology, using a wide variety of experiments that he had used when teaching geology to the students of High Storrs School. 

Learning about deformation

To start, we were split into small groups of 3-4 and given a tray of various rocks, together with a worksheet that introduced the Rock Cycle. This is a basic concept of geology that describes the transition between the three main rock types – igneous, sedimentary and metamorphic – over a period of time that is measured in millions of years. 

An introduction to the rock cycle

Having spent 3 years at Nottingham University to gain a modest BSc. 2:II (Hons) degree in geology, I don’t recall any practical lessons that made attempts to explain geological processes in the way that excited me, when learning chemistry at school - for example the combination of glycerol and potassium permanganate or dropping small pieces of lithium, sodium and potassium into water and seeing them whizz around at different speeds.

Learning about compaction and lithification

My group’s task was to demonstrate the processes of compaction and lithification of sediments – with or without the addition of clay or a natural cement that would bind the grains together – and those of others next to me were to demonstrate sedimentary deposition and the effects of compressive and tensile forces on rocks. 

An experiment to demonstrate sedimentary deposition

I particularly liked the experiment that showed how horizontal strata could be displaced as thrust faults – or overturned as nappes - as can be seen in mountains such as the Alps or Pyrenees. Using alternating layers of different coloured material, the effects of lateral compression could clearly be seen.

A squeeze box used to demonstrate deformation

This hive of activity took place before a good lunch, after which we resumed our learning with an explanation of geological maps and then discussed our field trip itinerary for the coming year. In the 12 years that the Group had been running, it has explored the Peak District National Park, as well as many interesting places further afield; however, to keep the members interested, it was felt that we needed to find some new field trip locations. 

Learning about the recrystallisation of minerals under pressure

Having previously led walks to Green Moor and around Sheffield city centre, and the Group now beginning to appreciate my experience as a geological conservation and building stone specialist, I was particularly pleased that – subject to works to its castle being finally completed – a day out to the historic market town of Pontefract was finally agreed.

Learning about physical and chemical weathering

In addition, somewhat to my surprise having only tentatively suggested it, “The Building Stones of Leeds” was immediately inked in for the first outdoor meeting of 2019 and I therefore had to get my act together and visit Leeds again very soon.

Various experiments in progress