Geology is the study of rocks, and Rathlin rocks! It all started with a big volcanic eruption 65 million years ago (that's about the time that dinosaurs went extinct). When the hot lava cooled down, it became basalt, which forms the rock of Rathlin Island. The strange shapes you can see at the Giant's Causeway on the Antrim Coast are also made from basalt.
Rathlin also has some chalk cliffs. Chalk is actually ground-down sea shells, which shows that at one time the island was completely covered by the sea.
