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Coal Measures and Coal Mining in Iowa, including paleontology and a discussion on the coal formation; also the methods of mining by Russell T. Hartman, 1898

Coal Measures and Coal Mining in Iowa by Russell T. Hartman, 1898, Page 21

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20. This has the axis large and strong, and about three volutions to the inch. Axis and base of volutions wrinkled. Volutions often greatly thickened near their bases and sometimes supported by oblique columns of calcareaus material. Frond expanding rapidly outward and rising with the expansion, marked on the upper side by fenestrules, which near the axis are polygonal, but which become elliptical or oval toward the circumference of the frond. Fronds on the underside; cells circular with vertical openings, and with margins usually thickened. Geological Position and localities.- Keokuk Iowa, Warsaw Illinois in the Saint Louis Limestone Reference: Hall's Geology of Iowa, Vol I, Pt 2.
 
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