The coal and iron ore deposits of the Black Country area provided a ready source of raw material. The area grew rapidly during the Industrial Revolution, and by the 20th century had grown into one large conurbation. However, the Black Country's coal mining industry was in decline by the early 20th century and the last coal pit in the area, Baggeridge Colliery at Sedgley, closed in 1968. Heavy industry began to decline in the 1970s and 1980s, with towns including Bilston, Darlaston, Wednesbury, Tipton and Brierley Hill being hit particularly hard by factory closures. However, new lighter industry began to develop in some of these areas, with a large retail park developing in the north of Wednesbury during the 1990s and a light industrial estate being built in the south of the town. Brierley Hill became home to the Merry Hill Shopping Centre, which developed between 1985 and 1990. Many of the former industrial sites in Tipton, however, have been mostly developed for new housing.