This is where I take a sideways look at different aspects of the geology and landscape in Northumberland and the Borders. At the moment all my new blog posts are being published on the Hadrian's Wall Community Archaeology website's blog page and are related (sometimes tenuously) to a mystery rock which appears with the WallCAP Newsletter. If you would like to receive the WallCAP newsletter do sign up as a volunteer on the WallCAP website, which doesn't commit you to anything but does mean you will be notified of all the latest WallCAP events both geological and archaeological.
A sharp eyed walk along the beach at Cocklawburn or on Lindisfarne and with a bit of luck you may find a small disc, shaped like a tiny petrified polo mint.
Before I answer that question, here is a little bit of background information from a manuscript fragment recently discovered in an obscure roman outpost at Ecclesia Novum-Oppidum near to the Fluvium Collegium (surprisingly close to where I live!) and published in the journal Falsus Nuntium.