York: 2 billion years of Earth history: Cafe Scientifique York at the Guildhall
- 3 Aug 2022
- Start time
- 7:00 PM
- The Guildhall
- Dr Liam Herringshaw,
York: 2 billion years of Earth history
Dr Liam Herringshaw
Almost 2000 years having elapsed since the founding of Eboracum, York has plenty of history. Its streets, however, take us much further back in time, thanks to the variety of geological materials they contain. From Jurassic oysters to Precambrian ocean crust, via Cornish granite and Cumbrian volcanoes, they help us uncover more than 2 billion years of Earth history. Dr Liam Herringshaw will explain more in his Cafe Scientifique talk, and draw up a deep-time timeline of York in the process.
We are meeting in a new venue in the Council Chamber at the Guildhall. Tea/coffee available from 7pm. Talk and Q and A 7.15pm to 8.15pm
For Café Scientifique’s first meeting in the Guildhall, Liam Herringshaw took us on a journey through two billion years of earth history – his lock-down project. Constrained by Covid, Liam took to walking around York where he discovered many unusual geological stories and, with Simon Rogerson, presented walking tours on the themes of Air, Earth, Fire and Water. With the aid of a four and a half metre long time-line he explained how over two and a half million years there had been a number of ice ages and that in York we mostly see features from the most recent glaciation. While generally we think of the Vale of York as flat, the city is in fact built on one of the low ridges caused by ice-age deposit. It is easy to see why the Romans chose the slight prominence of York on which to build their military headquarters whilst the surrounding area was so marshy. Their problem was the lack of building materials which had to be imported and consisted mainly of dolomitic or magnesian limestone, dating from 255 million years ago and sandstone or millstone grit, even older at 320 million years. Evidence of sandstone can be seen in the various sarcophagi in Museum Gardens and the Multangular Tower.
York also has its fair share of exotic stones, mostly evident around Coney Street, for example, Impala black granite, a coarse grained igneous rock from South Africa, approximately two thousand and fifty-five years old. This can be seen on the current Mappin and Webb building at the corner of Market Street. The Guildhall, too, shows interesting features including a Jurassic limestone window sill and Lake District slate can be found in St Helen’s Square. Liam’s favourite discovery was the carboniferous Stigmaria cobble spied en route to the back of York Explore from the Fern Garden by Yorkshire Museum.
After the lecture some members were able to see the Jurassic oyster fossil as we exited the Guildhall and it provided the impetus to explore York’s geological past further.