How do rocks become folded?
The Earth’s surface consists of a number of ‘tectonic plates’ about 100 km thick. Plates move apart in some places, forming oceans by ‘sea-floor spreading’; elsewhere plates collide, forming mountain chains; or they can slide alongside each other (‘strike-slip’ motion). This constant movement is called ‘plate tectonics’, which includes the older theory of ‘continental drift’. The movement causes earthquakes on geological ‘faults’; the largest faults are the plate boundaries themselves (the 2010 Haiti earthquake was of strike-slip type, caused by the North America Plate sliding past the Caribbean Plate). Over millions of years, plates can move thousands of kilometres, at about the speed our fingernails grow! The Bude Formation became folded (literally squeezed) only 5-10 million years after it was deposited, when Africa and Europe, riding on separate plates, collided, near the very end of ‘Carboniferous time’. This collision folded and uplifted the sediments of the Cornubian Basin, form
