Sahara-desert

Triassic Period

Triassic Period

250 to 200 million years ago

Ancient Deserts

The story of the Belfast Hills begins during a time known to geologists as the Triassic period that took place from 250 to 200 million years ago. The island of Ireland as we now know it was just north of the equator (15 to 20oN), similar to where Sudan is today, and experienced hot, arid, desert conditions.

If you imagine the Belfast Hills being a bit like a giant birthday cake, the bottom horizontal layer of the ‘cake’ is made up of rocks from the Triassic period. These are mostly seen as red or orange mudstones that formed as layers of mud on the bottom of isolated bodies of water. These bodies of water were fed by water from a sea that existed much further to the south. As the water evaporated in the intense desert heat, the levels of salt increased making them an unpleasant place to live. The resulting mudstone is fossil free and its characteristic red or orange colour makes it easy to spot.

The start of the Triassic period was a desolate time, as it began just after a mass extinction that had wiped out over 90% of all life on Earth. But it was after this that planet Earth really began to change and by the time the Triassic period ended, a whole new range of creatures had evolved including the rodent-like mammals and the dinosaurs.

The best places to see Triassic rocks are Colin Glen Forest Park and at Belshaw’s Quarry.

Red-mudstones-at-Colin-Glen
Red mudstones at Colin Glen Forest Park

Geological Code of Conduct

Please help us to look after the geological heritage of the Belfast Hills and NEVER damage or remove any rocks or fossils from the outcrops. All of the rocks have been here for millions of years so please leave them for future generations to enjoy.