An unconformity is a geological feature that represents a significant gap in the geological record. At Siccar Point, you can see nearly vertical Silurian greywacke rocks (formed about 425 million years ago) resting directly on top of gently dipping Devonian sandstone (formed about 370 million years ago). This dramatic juxtaposition highlights a long period of erosion and uplift that occurred between the formation of the two rock layers.

This specific unconformity is considered a classic example and is often used to illustrate the vast spans of time and the dynamic processes that have shaped the Earth's history.