Cornish geology

The rocks of Cornwall have an amazing story to tell. They have been on a journey of 8,000 miles in just 400 million years. This journey has included tropical seas, deserts, volcanic eruptions and hot granites, mineral vapours rich in tin and copper and ever changing climate and sea levels.

Our Cornish journey starts in an ancient tropical ocean south of the equator where primitive fish swim in the warm waters and deserts stretch north across England and Europe. At this time you can walk to America.

 

On the horizon the African supercontinent slowly moves towards us as volcanoes erupt ash and lava. The ocean floor is squeezed away and the Lizard emerges. Further north, Coal Measure swamps and deltas form. Continents collide over a period of 80 million years, buckling the strata. If we could stretch the rocks out flat again Cornwall would be 300 miles long. Cornwall becomes part of Pangea.

Hot granites from inside the earth rise and cool to form the backbone of Cornwall. On their margins veins rich in tin and copper await the arrival of man 250 million years later. Warm seas lap our Cornubian Caribbean island while dinosaurs roam the landmass further east. The Altantic Ocean finally opens up as Cornwall continues its journey northwards. Chalk and flint are deposited in the clear waters and a mass extinction event wipes out the dinosaurs and many other species, just 60 million years before the present time.

Sea levels fluctuate again and West Penwith becomes an island. A beach forms at St Erth. Ice sheets then move southwards, they miss Cornwall but there are icebergs offshore. Sea level drops over 300 feet and it would be possible to walk to France. Man appears and is faced with tundra conditions including permafrost, cave dwellings, wolves and bears.

What has changed since?

The ice sheets have melted, river valleys have flooded and the English Channel has cut us off from Europe. Erosion and weathering have shaped the Cornish landscape and formed our magnificent coastline.

Man has discovered the mineral legacy in our rocks. They gave us mines, mineral wealth, building stones and china clay. Cornish inventors, such as Richard Trevithick, who pioneered high pressure steam locomotion, pushed back the frontiers of science and discovery. Poets, writers and artists are inspired.