Cornwall, in the southwestern extreme of Britain, was an important center of mining for several thousands of years because of rich deposits of tin, an essential ingredient for bronze. Surface work was always preferred because it represented less expense and danger than going underground, but the Cornish quickly developed subsurface excavations. During the industrial period, excavations ventured deeper underground, and miners discovered deposits of copper as well as tin, making Cornwall that much more valuable during a period when industry required all sorts of metals.