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_16_ terrestrial interbedded shales, mudstones, sandstones, and coals which unconformably overlie the Upper Sandstone member of the Pierre Shale Formation. Three coal seams or zones exist within the Coalmont Formation in the general area of the mines. These are, in ascending order, the Sudduth seam, Hoyle seam and Capron seam. The Sudduth seam is the thickest and most widely mined seam in the region. This seam is located at the vase of the Coalmont Formation near the unconformable contact with the Pierre Shale. All three mines in the North Park Coal Field are mining the Sudduth coal seam. The coal in this seam is a subbituminus 8 coal with a low sulfur content (0.25%) and a heat output of about 10,800 BTU's per pound. The thickness of this seam varies between 10 and 7U feet. The Hoyle seam is locally discontinuous. This seam will only be mined at the Bourg Mine where the seam attains a minable thickness of 16 feet. This seam lies about 80 feet above the Sudduth seam. The Capron seam is stratigraphically located about 2,400 feet above the Sudduth coal and is commonly split into two beds. fhb Capron seam is not currently mined in the fvorth Park Coal Field. Previous glaciation and stream action have eroded the rock strata down to a broad alluvial plain. The Canadian kiver then deposited a 2.0 to 5.0 foot thick mantle of river alluvium over this erosional surface when the river was at an elevation of about 8,200 feet. These Upland Terrace desosits have since become eroded as the Canadian River and its tributaries have become incised. In the area of the Bourg Mine, these Upland Terrace deposits have been completely eroded away by Mann Draw. Remnant exposures of the Upland Nlluvial Terrace deposits still cap mesa tops in the area of the Marr Strip and Canadian Strip. The alluvium is present in the stream valleys of northeasterly-flowing tributaries of the Canadian River. These bogies of alluvium are usually poorly sorted and fine-grained. Coarse sands and gravels, when present, usually are contained in discontinuous lenticular pockets within the finer-grained alluvium. Mann Uraw and its tributary gulches contain up to 20 feet of fine-grained alluvial deposits. The alluvium consists of loam, silt and sand derived from the weathering of the Pierre Shale. The alluvial material of the streams traversing the Marr Strip, Sudduth, Williams, Bush and Bolton Draws, are composed on non-continuous, narrow lenses of clays, silts and poorly sorted sands and gravels. The sands and gravels are commonly isolated in pockets surroundetl by finer-grained alluvial sediments.