Geological map

The ‘solid’ geology is the term used to describe bedrock, or consolidated rocks. In Cornwall these are predominantly sandstones, mudstones and some volcanic rocks of Devonian or Carboniferous age (400-300 million years old) and more recent Permian (290 million years old) granite intrusions and associated metamorphism. The bedrock map shows the distribution and composition of the solid rocks with the superficial cover removed. With its extensive rocky coast, Cornwall generally has good levels of exposure, which explains why the mines and quarries inland are so important in understanding the geology between the north and south coasts. The map is an interpretation of available data, which means that where the bedrock is not exposed at the surface the geology has been interpreted from boreholes, mine plans, geophysical surveys and interpolation from adjacent areas.

The ‘drift’ geology map shows superficial deposits, the youngest of the geological formations. These are unconsolidated deposits less than 2 million years old. River action since the Ice Age has led to silting up of the estuaries and has left deposits of alluvium and river terraces. Rising sea level since the last glaciation has also led to beach sand being gradually driven onshore, particularly on the north coast, forming belts of dunes. Peat deposits are found mainly on Bodmin Moor where they occur in wide marshy hollows.