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• thickness, and identical to the under.lieing shale , occurs <br /> within the Rollins Member 25 to 75 feet above the base . The <br /> Rollins Sandstone varies in grain from very fine to coarse , <br /> but medium size predominates . <br /> Calcareous ironstone concretions , some as <br /> large as 20 ' or 30' long , occur mainly below the shale <br /> tongue. The sandstone varies from feldspathic to lithic , <br /> and is cemented by calcite and silica until the top 5 ' to <br /> 20' , where a silica-clay matrix predominates . The silica- <br /> clay matrix is common throughout the western Upper Cretaceous <br /> where coal directly overlies sandstone . <br /> Drill hole data indicate that , at times , the <br /> coal rests directly on the sandstone . Generally , however , <br /> • it is found interbedded with shales and siltstone up to 13 ' <br /> above the Rollins . <br /> The coal interval consists of coal seams and <br /> partings , which total 20 ' to 30 ' thickness , known as the <br /> Coal Basin Coal Interval. <br /> The partings , which occur erratically in the <br /> Coal Basin Interval, consists of sandstone and siltstone <br /> similar to the top of the Rollins . Coal intervals 25 ' to <br /> 30' thick occur where the partings are absent or very thin . <br /> With the exception of plant debris , they are devoid of <br /> macrofossils. <br /> The lower portion of the Coal Basin interval <br /> 10 <br />