district, administrative and historic county of Derbyshire, England, to the north of Derby. It takes its name from the River Amber, which joins the Derwent at Ambergate. The industrial eastern half of the district contrasts with the still rural western portion. Traditionally coal mining and ironworking were the staple industries, but from the late 1950s industrial diversification has taken place as mining declined in importance. Some of the derelict mining land has been reclaimed for new industrial estates, notably near Alfreton. Engineering is important at Ripley and Belper, which is also a centre of the cotton and hosiery industry. Jedediah Strutt, inventor of a stocking ribbing machine, built the town's first cotton mill in 1776. Among buildings of interest are the picturesque remains of Wingfield Manor House, begun in 1440 and dismantled in 1646. Area 102 square miles (264 square km). Pop. (2001) 116,475.