Geology of the Upper Mississippi Valley Base-Metal District Bedrock Geology Driftless Area Metallic Minerals Rocks and Minerals Data and Resources IC16-1978 Geology of the Upper Mississippi Valley Base-Metal District (3rd edition) Heyl, A.V.; Broughton, W.A.; West, W.S.; 1978 Report: 45 p. Download Related Collections Information Circular View Information Circular