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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 194

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[page]194[/page] of the arrows, through the air entry until it meets the gate (a), when it is deflected into the side entry (b), thence it passes on until it comes to an open "break through" (c), where it crosses over to the entry (d), and from there again into the air entry through which it passes until the next pair of entries is reached when it passes through them as through the first pair, and so on through the mine, finally returning through the main entry and passing up the main shaft. "Break throughs" are openings from one entry of a pair to another entry of the same pair to another entry of teh same pair. They are placed twenty to twenty five yards apart; only one is open at a time, since they are for the purpose of keeping the air circulating near
 
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