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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 181

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[page]180.[/page] of mining cannot be carried farther in that direction on account of percolating waters. I [?If?] however it is filled with clay and is not very wide it may be tunnelled and thus the work may be carried out beyond it. During the Carboniferous epoch the surface was subjected to oscillatory movements so there were periods of elevation and of subsidence. When the surface was above sea level it was subjected to the agents of denudation and water courses were formed, which often cut out part or all of the coal and sometimes cut deep into the underlying rocks. When the sea again encroached upon the land these channels were filled with clays or sands which subsequently hardened into shales or sandstones. When "cutouts", as these obstruct-
 
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