However, by the 1930s, the coal mining industry began to diminish and, by the mid-twentieth century, the pits were closing at an increasing rate. In 1951, the Durham County Development Plan highlighted a number of colliery villages, such as Blackhouse, as 'Category D' settlements, in which future development would be prohibited, property would be acquired and demolished, and the population moved to new housing, such as that being built in Newton Aycliffe. Likewise, the railway industry also began to decline, and was significantly brought to a fraction of its former self by the Beeching cuts in the 1960s. Darlington Works closed in 1966 and Shildon Shops followed suit in 1984. The county's last deep mines, at Easington, Vane Tempest, Wearmouth and Westoe, closed in 1993.