North Cornwall has a stretch of coastline that borders the Celtic Sea to the north. The Carboniferous sandstone cliffs that surround Bude (and stretch down as far south as Crackington Haven) were formed during the Carboniferous period, around 300 million years ago. They are part of what are known to geologists as the Culm Measures which continue eastwards across north Devon. The folded and contorted stratification of shale and sandstone is unique in southern England. During the Variscan Orogeny, which affected the entire Cornish coast, the cliffs were pushed up from underneath the sea, creating the overlapping strata. As the sands and cliffs around Bude contain calcium carbonate (a natural fertiliser), farmers used to take sand from the beach, for spreading on their fields. The cliffs around Bude are the only ones in Cornwall that are made of Carboniferous sandstone, as most of the Cornish coast is geologically formed of Devonian slate, granite and Precambrian metamorphic rocks). The stratified cliffs of Bude gave their name to a geological event called the Bude Formation. Many formations can be viewed from the South West Coast Path which passes through the town.