Long ago, the North American tectonic plate collided with and then moved away from the European and African plates, causing the land and seas in this region to rise and sink. Over time, layers of mud and sand built up and hardened into rocks such as limestone, shale, sandstone, and coal. These rocks formed in shallow seas, beaches, rivers, and swamps, eventually creating coal, oil, gas, salt, and limestone that have been important to West Virginians' lives and economies for centuries.