IDRIA  , a

mining town in Carniola, Austria, 25 M . W. of Laibach . Pop . (Iwo) 5772 . It is situated in a narrow Alpine valley, on the river Idria, an affluent of the Isonzo, and owes its prosperity to the rich mines of quicksilver which were accidentally discovered in 1497 . Since 158o they have been under the management of the government . The mercurial ore lies in a bed of clay slate, and is found both mingled with schist and in the form of cinnabar . A special excellence of the ore is the greatness of the yield of pure metal compared with the amount of the refuse . As regards the quantity annually extracted, the mines of Idria rank second to those of Almaden in Spain, which are the richest in the world .