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thin interval of what is thought to. be the Sunshine seam has <br /> • been encountered in the Paonia Shale . <br /> The B bed is the lowest coal seam mined . It <br /> occurs in the top 6 ' -3 ' of the Coal Basin interval , which <br /> consists of 20'-30 ' of coal seams and partings . <br /> Beneath the Coal Basin interval is the <br /> Rollins Sandstone, the upper member of the Iles Formation, <br /> which is the lower of the Cretaceous Mesaverde formation , <br /> and the lowest potential aquifer. <br /> Beneath the Rollins Sandstone lies impermeable <br /> Mancos Shale, which is some 3 , 000 ' thick and floors the <br /> basin. <br /> The upper coal seam mined is the Middle bed . <br /> The Middle bed ranges from 4' - 20' thickness , and occurs an <br /> average of 450' above the B bed . It rests on the Middle <br /> Sandstone. <br /> The B and Middle beds are separated by a <br /> thick layer of shale, siltstone , mudstone and sandstone , <br /> ranging from 370 ' -425 ' thickness , and by the Middle Sand- <br /> stone . <br /> Approximately 11 million tons of coal have <br /> been mined from the B bed since operations began in 1956 . <br /> The remaining reserves , though substantial , are found at <br /> depths between 2 ,.000 ' -3 , 000 ' . <br /> Coal qualities of the B bed average : <br /> 15 <br />