Types of geographers known as geologists study what rocks are made of in order to help explain the world around us. Many rocks were formed millions of years ago. What's in them, and where they are, can tell us about the past. According to legend the Giant's Causeway in Ireland is what's left of a bridge that giants built between Ireland and Scotland. According to geographers, lava erupted through cracks here 50 million years ago and cooled to form hexagonal columns.