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 Mudstone at Colin Glen Forest Park


 Find Triassic rocks at:




Geology Timeline:

Go BACK to geological foundations Go FORWARD to the Jurassic Period
Foundations Thumbnail Jurassic Period Thumbnail Ichthyosaur