Numedalslågen, the third longest river in Norway, starting in Hordaland, ran through Buskerud unto Vestfold where it reached the sea, while river Begna sweeps into lake Sperillen. Buskerud was separated from Akershus as an amt of its own in 1685, but the amt was smaller than today. It then consisted of the present districts Eiker, Hallingdal, and Ringerike. The area of the present municipalities of Flesberg, Hurum, Kongsberg, Lier, Nore og Uvdal, Rollag and Røyken were transferred from Akershus amt to Buskerud amt in 1760. The name ' was changed to ' in 1919. The municipality of Skoger was transferred from Vestfold to Buskerud in 1964. The area Ringerike may once have been a small kingdom. During the 10th century, Norway's kings Olaf Tryggvason and Olaf Haraldsson grew up at Bønsnes in Ringerike. In the valley of Numedal, silver was mined in Kongsberg from the 17th century until discontinued in 1957. Weapons industry had been developed in Kongsberg from 1814, and various high tech industry companies now represent the town's major employers. At Modum there was also , a cobalt pigment production works (Blue Colour Works). Today, agriculture, lumber, wood-pulp mills and other related industries are the county's main economic activities; ample hydroelectric power is produced by the rivers Begna (') and Rands (') . Buskerud has also a large forested area. Substantial income is derived from high tech industries located in Kongsberg. Other significant income comes from the cabin areas in northern Buskerud. Buskerud's coat of arms were adopted in April 1966. It features a blue bear whose colours are symbolic of the blue colour works. The silver background of Buskerud's coat of arms represents the silver industry in Kongsberg.