50 Shades of Grey: Loughshinny’s Shady Past Revealed

Dr Patrick Roycroft
(Skerries Historical Society Meeting – 11th March 2014)

The March lecture of the Skerries Historical Society took us rather further back in time than we are used to – to 325 million years ago. Back then, Ireland was becoming part of a huge super-continent called Pangaea and was sitting over the equator and with a climate similar to the Bahamas today. That certainly sounded rather attractive though we were warned by geologist Patrick Roycroft that a tropical climate meant tropical storms as well, and, if you were in ‘Skerries’ 300 million years ago, you might find yourself face to face with some unpleasant looking insects, such as vast dragonflies with a two foot wingspan (that’s 65cm to younger readers).

Patrick’s talk was ’50 Shades of Grey: Loughshinny’s Shady Past Revealed’, but anyone hoping for an exposé of raunchy misbehaviour in that quiet village would have been surprised to find that the ‘shades’ referred to the bands of grey limestone which can be seen zigzagging up and down the cliffs from Loughshinny beach. The audience were gripped by the story of how Loughshinny got its famous folds.

It seems that way back in the Early Carboniferous period (325 million years ago), the earth was in a state of flux, tectonic plates were on the move and a vast basin, or rift, opened up right next to Skerries. Indeed, Patrick suggested that the edge of the rift must pass right through the heart of Skerries which, at that time, was starting to sink beneath the waves. Layers of sedimentary rock gradually formed, slowly filling up the Dublin Basin (so vast that it stretched to UCD in the south and inland as far as Westmeath).

The shallow tropical seas of ancient Skerries abounded in life. If you look carefully you can find fossils galore – of corals and crinoids – in the beach rocks between Skerries and Loughshinny.

And then those tectonic plates took another turn. At this point Patrick’s enthusiasm for his subject overtook him and he flung pointer and microphone aside so he could ‘become’ Spain and North Africa ramming poor old Ireland from below – and forming the Cork and Kerry mountains in the process. South Leinster, with its core of rigid granite, refused to bow to the force of this tectonic shunt; like a block of wood pushing plasticine, its effects rippled through the softer sedimentary rocks of the Dublin basin, especially at its former edges, which buckled into the beautiful folds we see today.

It’s not merely locals who admire these folds. Geologists come from all over the world to look at them, and Patrick told us we have a world class site on our doorstep of which we should be immensely proud. And now we understand it a bit better, maybe we can be!
Report by Oona Roycroft

Muttley Roycroft standing on a flying saucer / concretion – there’s another on the far left.

Loughshinny legend has it that this is a dragon’s tail – the rest of the mighty beast is buried under the cliff. But perhaps truth is even more wonderful than legend. This rock formation tells geologists that when Spain collided with the Southern Irish coast, it hit it a glancing blow which ‘bent’ the rocks in a clockwise direction.

1403folds2 — A closer look at the famous folds.

An example of Loughshinny’s amazing folds – evidence that Ireland was rammed by Spain and North Africa millions of years ago.