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__________________________________________ Introduction _____________________________________ Purpose of the investigation____________________ Location and geographic setting__________________ Field work.____________________________________ Acknowledgments. ______________________________ Regional geology and stratigraphicrelations_____ ________ Structure ______________________________________ Regional stratigraphic summary __________________ Stratigraphic principles._________________________ Stratigraphic problems. _________________________ Platteville-Decorah boundary _ _______________ Beloit dolomite.____________________________ Unnamed limestone member, Decorah formation. _ Subdivisions of Galena dolomite ______________ Origin and application of the names.______________ Madison sandstone-________________________ Pecatonica dolomite member.________________ McGregor limestone member_________________ Quimbys Mill member _______________________ Stratigraphy of the mining district.___________________ Pre-Platteville rocks_ ___________________________ Pre-Cambrian rocks_________________________ Cambrian rocks_ ___________________________ Ordovician rocks____________________________ Prairie du Chien group __________________ St. Peter sandstone_ ____________________ Platteville formation____________________________ General features____________________________ Glenwood shale member.____________________ Lithologic description and stratigraphic relations _______________________________ Distribution.. __________________________ Fauna and correlation.__________________ Economic products______________________ Pecatonica dolomite member.________________ Lithologic description and stratigraphic re-lations_ ______________________________ Distribution, ___________________________ Fauna and correlation.__________________ Economic products______________________ McGregor limestone member.________________ Lithologic description and stratigraphic relations. ______________________________ Distribution. _ __________________________ Fauna and correlation.__________________ Economic products._____________________

The U. S. Geological Survey in cooperation with the Wisconsin Geological and Natural History Survey explored the Prairie du Chien group in the main productive area of the Wisconsin zinc-lead district during 1949-50. Eight properties-Crow Branch diggings, Leix, Harris, Spitzbarth, Kennedy, James, Raisbeck and Vinegar Hill Roaster were explored using both diamond and churn drills. Twenty holes were drilled that totaled 8,582 feet in depth. The objectives of the exploration were to determine if the Prairie du Chien and other formations below the principal ore-bearing strata (Galena, Decorah, and Platteville formations) of the district are favorable for ore deposits, and to determine the type of ore deposits, if present. Lean deposits of sphalerite, marcasite, and pyrite were found in the Prairie du Chien on five properties Crow Branch, Leix, Harris, Spitzbarth, and Vinegar Hill Roaster and also in the Franconia sandstone on the Leix property. In the drilled area the sulfides in the Prairie du Chien group occur in certain more brittle or soluble dolomite beds that contain cavities formed by brecciation or solution. Objectives of project The objectives of the exploratory program of diamond drilling and churn drilling, by the U. S. Geological Survey in cooperation with the Wisconsin Geological and Natural History Survey, were to

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