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Iles formations (Tweto, 1978) . References to both group <br /> and formation have been applied to the Mesaverde in the Coal <br />' Basin area (Collins, 1977; Full , 1974) . Regardless of the <br /> terminology used, several distinct units occur within the <br /> Mesaverde and are discussed below. Figure 783 .15-2 is a general- <br /> ized stratigraphic column showing the relationships and unit <br /> names given to the marker beds . Figure 783 . 15-3 is a more <br /> detailed stratigraphic column from Ray P. Full ' s report based I <br /> on work by Dr. Bruce Collins. The terminology used in Figure . <br /> 783 . 15-3 is used in this report . Reference to this and Figure <br /> 783 . 15-3 will aid in the following discussion. <br /> The upper 2 , 250 feet of the Mesaverde formation is an undiff- <br /> erentiated, non coal bearing unit of interbedded sandstones, <br /> • siltstone, and shales . Immediately beneath this undifferentiated <br /> 4 <br /> unit is a 500 foot sequence of shales , sandstones , and thin <br /> coal units , called the Paonia Shale member of the Mesaverde . <br /> The lower marker bed of the Paonia shale is the Placita coal <br /> seam. . This coal is variable in thickness , ranging from 0 to <br /> 10 feet thick and is not mined in the Coal Basin area (Collins, <br /> 1977) . <br /> The Placita seam forms the base of the Paonia Shale member. <br /> i <br /> Immediately below the Paonia Shale member is the Bowie Shale <br /> member, an interbedded sequence of sandstones, shales , and <br /> economic coal . The total -thickness of the Bowie .Shale member <br /> is approximately 675 feet . The upper most unit in the Bowie <br /> 7 <br />