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the three zones aze the Iles Formation, the Lower Williams Fork Formation, and the Upper Williams <br />Fork Formation. <br />Within the study azea,the strata beneath the principal coal zone display a greater abundance of coarser <br />grained sediments (i.e., sandstones) than does the overlying coal-bearing interval. They also contain <br />' few, if any, significantly thick or continuous coal seams. Therefore, this sequence of rocks is considered <br />the Iles Formation equivalent. Much of the upper Iles is exposed in the steep slope along the north <br />bank of the White River immediately west of where County Road 65 bridges the river. <br />' The B Horizon sandstone is the uppermost continuous sandstone in the Iles Formation equivalent. The <br />' top of B Horizon Sandstone shown on the accompanying stratigraphic column (see Figure 3-2) is <br />considered the contact between the Iles Formation and the Lower Williams Fork Formation. <br />Immediately above the B Horizon Sandstone, the lithology of the Mesaverde becomes notably finer <br />grained. Siltstones, mudstones, carbonaceous shales and coals predominate, with coarser grained <br />sediments filling a secondary role as sporadically occuring, laterally discontinuous sandstones. On the <br />' basis of this lithologic change, Mesaverde Group sediments lying above the top of the B Horizon aze <br />considered Lower Williams Fork Formation equivalents. The entire coal bearing portion of the Lower <br />Williams Fork is well exposed in the northeast wall of Scullion Gulch. The coal seams of the Lower <br />Williams Fork, as correlated by Westem Fuels, are also shown in Figure 3-2. <br />Data gathered during Westem Fuels exploration drilling progam indicates that the Upper Williams Fork <br />Fotmation equivalent can be sepazated from the Lower Williams Fork Formation on the basis of <br />' lithology and depositional environment. The contact between the finer grained lagoonal-paludal, <br />carbonaceous deposits of the Lower Williams Fork and the coazser grained terrestrial deposits of the <br />' Upper Williams Fork is marked by the thick cliff-forming sandstones that support the northeast rim of <br />Scullion Gulch. North and east of this rim aze the thick, massive lenticulaz sandstones of the Upper <br />Williams Fork Formation. <br />~rl <br />~I <br />1 <br /> <br /> <br />1 <br />10 <br /> <br />