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The 300 feet width of the outcrop barrier pillar which <br />is assumed for the future minx appears to be conservative <br />if most of the pillar is located in sound coal. If, however, <br />most of the pillar width is formed by burnt-out coal or by <br />oxidized coal, the width may not he sufficient and <br />subsidence or sliding might occur as a result of the outcrop <br />barrier pillar failure. <br />we feel that additional data on geologic conditions in <br />the vicinity of the outcrop barrier pillar should be <br />collected so that reasonable interpretations could be made <br />on the proportions of butt-out coal, oxidized coal and sound <br />coal. The width of the outcrop barrier pillars should then <br />be re-evaluated so that potential crushing, sliding or other <br />failure of outcrop barrier pillars could be avoided. <br />• <br />41 <br />