South of the Nida; the Olkusz hills, linked on to spurs of the Beskides, fill up the south-west corner of Poland, reaching 1620 ft., and containing the chief mineral wealth of the country; while a fourth range, 1000 to 1300 ft.
The zinc ores of the Olkusz district, more than 50 ft.
Thick, contain 8 to 14%, sometimes 25%, of zinc. The tin ores of Olkusz are still more important, and were extensively wrought as early as the 16th century.
Brown coal, or lignite, which appears in the Olkusz district in beds 3 to 7 ft.