Although some deep mining took place as early as the 1500s (in North East England, and along the Firth of Forth coast) deep shaft mining in the UK began to develop extensively in the late 18th century, with rapid expansion throughout the 19th century and early 20th century when the industry peaked. The location of the coalfields helped to make the prosperity of Lancashire, of Yorkshire, and of South Wales. The Yorkshire pits which supplied Sheffield were only about 300 feet deep. Northumberland and Durham were the leading coal producers and they were the sites of the first deep pits. In much of Britain coal was worked from drift mines, or scraped off when it outcropped on the surface. Small groups of part-time miners used shovels and primitive equipment.