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indirectly controlled Bear Creek, all forks of Dutch Creek, <br /> both forks of Oilwell Creek, the south and north forks of <br /> Coal Creek, and Porcupine Creek. <br /> In common with other unroofed laccoliths of <br /> the area , the Coal Basin features , in addition to the dikes , <br /> a large area of baked shale near the center and numerous <br /> apparently hydrothermal calcite veins . <br /> C . Stratigraphy <br /> The strata of Coal Basin consist , principally , <br /> of Mancos Shale and the Mesaverde Group , although rocks <br /> varying in age from Pennsylvanian to Tertiary are present . <br /> Coal seams occur above the sandstone units of the Mesaverde <br /> Grouu . (See Table III-C-1) <br /> Mancos shale floors the vast majority of the <br /> basin. It is estimated to be 3 , 000 ' thick. Beneath the <br /> shale , bedrock units are the Cretaceous (Dakota) , Jurassic <br /> (Morrison and Entrada sandstones) , Permian (Weber sandstone) <br /> and Permo-Pennsylvania (Maroon) formations . The bedrock <br /> units outcrop on the Grand Hogback, then dip steeply beneath <br /> the overlying Coal Basin strata. They occur far beneath , <br /> and are unaffected by , raining activity . <br /> The Mancos Shale consists of drab gray , <br /> sparsely fossiliferous silty shale to shaley siltstone . <br /> Bedding is often difficult if not impossible zo detect , <br /> especially in the upper two-thirds of the formation . <br /> The overlieing Mesaverde formation consists , <br /> essentially , of shale beds interspersed with sandstone <br /> 7 <br />