Presenter Caroline Nolan and Dr Patrick McKeever travel back to a time when Ireland straddled two continents on either side of a vast ocean.

When it closed over as a result of plate movement, it created a huge mountain range which stretched for over 1800 miles.

Sandstone which was formed on the ocean floor was transformed into quartzite by the extreme heat and pressure released by this event.

It is this metamorphic rock which makes up Mount Errigal.

At 2466 feet it is Donegal’s highest and best known mountain.

The fact that it is comprised of quartzite has made it more resistant to erosion as this is a denser and hardier rock than the sandstone from which it derives.