Technical paper . latteville formation and at the base of the overlying Galena forma-tion, the ores occurring in much greater abundance in the latter. Abetter idea can be obtained from the generalized sections of these twoformations, as given by Bain,c which are presented below: Generalized section of the Platteville limestone in the upper Mississippi Valley. Feet. 4. Thin beds of limestone and shale 10-15 3. Thin-bedded, brittle limestone, breaking with conchoidal fracture. 25-302. Buff to blue magnesian Limestone, heavy bedded, in many places a dolomite 15-25 1. Shale, blue, in some places s
Technical paper . latteville formation and at the base of the overlying Galena forma-tion, the ores occurring in much greater abundance in the latter. Abetter idea can be obtained from the generalized sections of these twoformations, as given by Bain,c which are presented below: Generalized section of the Platteville limestone in the upper Mississippi Valley. Feet. 4. Thin beds of limestone and shale 10-15 3. Thin-bedded, brittle limestone, breaking with conchoidal fracture. 25-302. Buff to blue magnesian Limestone, heavy bedded, in many places a dolomite 15-25 1. Shale, blue, in some places sandy 1-5 a See Grant, U. S., and Burchard, E. F., Lancaster-Mineral Point Folio Geol. Atlas 145, U. S. , 1907, p. 1. 6 See Grant, U. S., and Burchard, E. F., Op. cit., p. 14. c Bain, H. F., Zinc and lead deposits of the upper Mississippi Valley: U. S. Geol. Survey Bull. 294,1906,pp. 20 and 25. 67213°—15 2 10 MINING AND MILLING OF LEAD AND ZINC OEES. [Scale: 1 inch= 125 feet.] Sys-tem. Formation Thick-ness INFeet. Character of Rocks. Niagara limestone. 150+ Light-buff to gray dolomite. Basal beds massiveand rough weathering, succeeded by thinnerbeds, above which are layers containing moreor less chert. Fossiliferoiis. Top of formationeroded. Maquoketa shale Gray argillaceous and calcareous shale, locallyfossiliferous and magnesian at the top. Plastic blue and green shale and clay with indur-ated fossiliferous bands near the top. Drab and blue, thin, fissile shale and fossiliferous,thin, argillaceous limestone. Fine conglomer-ate locally near
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