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• the fringe of the prograding deltaic complex. In some parts <br /> of the basin, thin and limited Lenses of carbonaceous silt- <br /> stone and coal occur in the upper 10150 ' of the Middle <br /> Sandstone. <br /> Directly above the Middle Sandstone is a <br /> coaly, black to gray , sandy siltstone of up to 13 ' thickness , <br /> which merges into the overlieing coal seam known as the <br /> Middle bed . <br /> Throughout most of the present workings , a <br /> honey coal/coaly siltstone parting of about 1 ' thickness , <br /> occurs approximately 3" to 18" above the base .of the coal . <br /> In the southeastern part of the basin the seam contains a <br /> second parting of boney coal to coaly gray siltstone , from <br /> 1. 5 ' - 4 ' in thickness , in the upper portion of the seam. <br /> The parting disappears in the northern portions of the <br /> present workings , on a roughly northeast-southwest trend. <br /> Above the seam, the main roof consists of a <br /> massive, dark gray carbonaceous siltstone. <br /> The sequence above the Middle bed , known as <br /> the Upper Bowie Shale Submember , is 40 ' -60 ' thick. It is <br /> considered a nonmarine sequence , although no specific <br /> boundary occurs between the nonmarine and marine rocks . <br /> Plane bedding and ripples are the only sedimentary structures <br /> observed in the interval . The- Upper Bowie is nearly identical <br /> to the Lower Bowie . <br /> 24 <br />