Geology of Ayrshire Explained – 6 September 2022

Well-known local speaker Denis Rattenbury made a welcome return to our club last week, this time to explain to us how Ayrshire was shaped by geology, or as he put it “The Deep Time Story of Ayrshire”. Although referring to himself as an “amateur”, Denis had studied pure, or physical, geology at university many years ago. He began with an explanation of continental drift (nowadays known as plate tectonics) and rattled through 5,000M years of earth’s history in 30 minutes – quite a feat!

Denis cleverly wove the Ayrshire story into his expertly illustrated account of the collisions of continents and the journey of what is now Scotland from hemisphere to hemisphere through the various climatic zones to its current position on the globe. At some stage (around 400M years ago) Scotland (and Ayrshire) experienced a period (named the Old Red Sandstone) of arid conditions and associated seasonal torrents thus creating much of Ayrshire’s red rock formations still visible today. Volcanic activity around the same period resulted in the formation of massive rifts across what is now the Midland Valley of Scotland and includes resulting elevated ranges like the Carrick Hills. Some 50M years later, Scotland had moved into an equatorial part of the earth giving rise to the Carboniferous era of tropical forests and consequently the creation of vast peat bogs and coal-bearing deposits. More recently, (2M years ago), the cycle of ice-ages moulded the rocks into the landscapes we see around us today and since the ice melted there has been a slow (1mm/year) rebound (rise) of the land which is known as “isostasy”, manifested by the spectacular examples of raised beaches along much of the southern Ayrshire coastline.

And what of the future? Well Denis explained that mathematical models can predict with some certainty that the continents are once again coming together with, for example, the closing of both the Mediterranean Sea and the Atlantic Ocean. Whether human life will still exist then he couldn’t say.

Charles Gray congratulated Denis on his ability to convey such a complex picture to his appreciative audience.