The Highland Boundary Fault is a significant geological feature in Scotland, marking the boundary between the Scottish Highlands and the Lowlands. This fault is approximately 100 kilometers long and runs from the Isle of Arran in the west to Stonehaven in the east. It was formed millions of years ago due to tectonic activity, which caused the Earth's crust to fracture. The fault is characterized by a mix of rock types on either side, with ancient gneiss and schist in the Highlands and younger sedimentary rocks in the Lowlands. This geological divide influences the landscape, ecology, and climate of the regions it separates, making it an important feature in understanding Scotland's natural history.